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A study of in-situ brightening of mechanical pulp via the electro-oxidation of sodium carbonate Kurniawan, Pogy 1998

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A STUDY OF IN-SITU BRIGHTENING OF MECHANICAL PULP VIA THE ELECTRO-OXIDATION OF SODIUM CARBONATE by Pogy Kurniawan B.A.Sc. (Chemical Engineering), University of British Columbia, Vancouver, British Columbia, Canada, 1993  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in THE FACULTY OF GRADUATE STUDIES DEPARTMENT OF CHEMICAL ENGINEERING  We accept this thesis as conforming to the required standard  THE UNIVERSITY OF BRITISH COLUMBIA September, 1998 © Pogy Kurniawan, 1998  In  presenting  this  thesis  in  degree at the University of  partial  fulfilment  of  the  requirements  for  an advanced  British Columbia, I agree that the Library shall make it  freely available for reference and study. I further agree that permission for extensive copying of  this thesis for  department  or  by  his  or  scholarly purposes may be granted by the head of her  representatives.  It  is  understood  that  copying  my or  publication of this thesis for financial gain shall not be allowed without my written permission.  Department of  £H£MfCAL  e*/G/Aiee/l/A/<$  The University of British Columbia Vancouver, Canada Date  DE-6 (2/88)  &f>TeMBdK  il,  tqtS  ABSTRACT This thesis project consists of investigative work on the in-situ electrochemical brightening of thermo-mechanical pulp (TMP) using sodium carbonate (Na C0 ) as the 2  3  source of brightening agents. The conditions for the electro-oxidation of Na2CC»3 to percarbonate (C2O6 ) and its eventual decomposition to hydrogen peroxide (H2O2) were 2  studied. Next, the factors that affected the in-situ electrochemical brightening of TMP were  investigated,  followed  by  the  sequential  simplex  optimization of the  electrochemical brightening process. To further study the role of Na2CC>3 and the active oxygen (C2O6" and/or H2O2) on the brightening process, several simulated brightening 2  experiments using merchant H2O2 were performed. Finally, a rough cost comparison between the conventional H2O2 and the electrochemical brightening method was performed. In most of the electro-brightening experiments, a platinized titanium hollow U tube anode and a tungsten rod cathode were used. The anode was water-cooled to raise the oxygen overvoltage at the anode and to suppress the hydrolysis of the oxidation product. The cathode area was approximately ten times smaller than the anode area to suppress the reduction of active oxygen on the cathode. Using a range of current densities (0.04 - 0.25 A/cm ), it was found that the 2  highest time-average current efficiency for the production of active oxygen over 30 minutes without pulp at 46°C was 41% at 0.14 A/cm and an anode voltage of 3.2 V vs 2  SHE. The maximum active oxygen concentration produced by electrolysis of sodium carbonate in the presence of pulp was about 50% higher than that without pulp. The investigation of the in-situ brightening of TMP using Na2CC»3 began with a full 2 factorial experiment with approximately 750 ml of pulp slurry in 1 M Na2CC>3 at 3  1% pulp consistency. The variables were temperature ( 46°C and 66°C), anode area (14.5 cm and 29 cm ), and current (5 A and 10 A). It was found that the combination 2  2  of temperature, current density and current concentration appears to have a positive effect on the active oxygen concentration, brightness gain and yellowness loss. However, this result may be unreliable due to the deterioration of the anode.  ii  Glassy carbon plate anode apparently gave 50% higher concentration of active oxygen than platinized titanium anode, but was not a good anode material for the in-situ electro-brightening reaction because its surface was eroded, introducing traces of carbon powder in the pulp suspension.  Furthermore, the loose carbon powder might  penetrate into the fiber network, giving an inaccurate brightness or yellowness reading on the spectrophotometer. The post-treatment of platinized titanium anode, by submersing it in warm « 1 M sodium hydroxide (NaOH) solution followed by reverse-polarizing of the electrodes in « 1 M of Na2CC>3 solution, was very important in suppressing the deterioration of the anode and ensuring the reproducibility of the brightening results. Experiments  on  platinized  titanium  anodes  with  different  electrode  configurations show that good current distribution improved brightness gain and lowered specific energy. A 10 %ISO brightness gain can be achieved by brightening pulp at 1% consistency at 46°C with a specific energy of 20,000 kWh/ton of pulp. The brightness increase & yellowness loss in a single-stage 3-hour run was about 14 %ISO & 7%, whereas a single-stage 6-hour run and a two-stage run at 3 hours/stage produced brightness gain & yellowness loss of 13 %ISO & 8% and 12 %ISO & 8% respectively. This means that brightening time longer than 3 hours may not be worthwhile. The presence of sodium carbonate in the brightening suspension actually decomposed hydrogen peroxide quite rapidly compared to the rate of decomposition in conventional peroxide brightening liquor.  This means that a continuous supply of  active oxygen has to be available for a brightness gain to occur in the presence of sodium carbonate. A  cost  comparison between  the  electrochemical and the  conventional  brightening method shows that the electrochemical method cost approximately 20% more in annual operating cost than the conventional brightening method. The capital cost of the electrochemical method is approximately 140% more than that of the conventional brightening method.  iii  TABLE OF CONTENTS ABSTRACT  ii  T A B L E OF CONTENTS  iv  LIST OF FIGURES  viii  LIST OF TABLES  x  NOMENCLATURE  xi  ACKNOWLEDGEMENTS  xiv  Chapter 1.  INTRODUCTION  1  Chapter 2.  THEORETICAL BACKGROUND  4  Principles of Pulp Bleaching and Brightening  4  2.1.1. The Composition of Wood Fiber  4  2.1.  2.2.  2.3.  !  2.1.1.1. The Structure of Wood Fiber  4  2.1.1.2. Chemical Composition of Wood Fiber  5  2.1.2. A Brief Comparison of Various Pulping Methods  6  2.1.3. Description and Objective of Pulp Bleaching and Brightening  8  2.1.4. Optical Properties of Mechanical Pulp  9  Mechanical Pulp Brightening by Hydrogen Peroxide  10  2.2.1. Structure of Lignin  10  2.2.2. Chemistry of Hydrogen Peroxide Brightening  12  2.2.3. Process Conditions of Peroxide Brightening  13  Factors Affecting Brightness Response in Mechanical Pulp Brightening  14  2.3.1. Effect of Pulp Consistency  14  2.3.2. Effect of Temperature, Retention Time and Alkalinity  14  2.3.3. Effect of the Stability of Brightening Liquor  15  2.3.4. Effect of Different Pulping Process  16  iv  2.4.  General Principles of Electrochemical Processes  16  2.4.1. Electrode Potential and Thermodynamics  17  2.4.2. Kinetics of an Electrode Process  18  2.4.3. General Polarization Curve of an Electrode Reaction  19  2.4.4. Electrochemical Cell Components  22  2.4.4.1. Electrode Materials and Electrolyte  22  2.4.4.2. Separators  22  2.4.4.3. The Electrical Double Layer  23  2.5.  The Electrosynthesis of Hydrogen Peroxide  23  2.6.  Percarbonates  24  2.6.1. Properties of "True" Percarbonates  25  2.6.2. Percarbonate by the Electro-oxidation of Sodium Carbonate  26  In-situ Electrochemical Brightening of Mechanical Pulp Using Sodium Percarbonate/Peroxide  29  2.7.1. Figures of Merit for the Production of Active Oxygen  30  2.7.2. Figures of Merit for the Brightening of TMP  32  Objective of this Project  33  2.7.  2.8.  Chapter 3. EXPERIMENTAL APPARATUS AND PROCEDURE  34  3.1.  Chemicals and Pulp  34  3.2.  Experimental Apparatus  35  3.3.  Experimental Procedures  39  3.3.1. Electrochemical Production of Active Oxygen  39  3.3.2. In-situ Brightening of Mechanical Pulp  41  3.3.3. Post Treatment of Electrodes after Electrochemical Run  42  3.3.4. Polarization Curve for the Electro-oxidation of Sodium Carbonate  43  Experimental Strategy  45  3.4.  v  Chapters RESULTS AND DISCUSSION 4.1.  4.2.  47  Electrochemical Production of Percarbonate and/or Hydrogen Peroxide  47  4.1.1. Polarization Curves for the Electro-oxidation of Sodium Carbonate  47  4.1.2. Current Efficiency at Different Current Densities  49  4.1.3. Comparison of Active Oxygen Concentration between In-situ Brightening Run and No-pulp Run  51  4.1.4. The Effect of Sodium Carbonate on the Decomposition of Hydrogen Peroxide  52  Factors Affecting the Electrochemical Brightening of Mechanical Pulp  54  4.2.1. A 2 Factorial Design Analysis (Effect of Temperature, Current Density and Current Concentration)  55  4.2.2. The Effect of Anode Material and Current Distribution  59  3  4.2.2.1. Glassy Carbon Anode  59  4.2.2.2. The Effect of Current Distribution  4.3.  4.4.  4.5.  (Different Electrode Configuration)  61  4.2.3. The Effect of Post Treatment for the Anode  66  4.2.4. Effect of Brightening Time  67  Optimization of the Electrochemical Brightening Process Using Sequential Simplex Optimization  74  Simulation of the Electrochemical Brightening of TMP Using Hydrogen Peroxide  77  Economics of In-situ Electrochemical Brightening Method  81  Chapter 5. CONCLUSIONS  83  Chapter 6. RECOMMENDATIONS AND FUTURE WORK  86  REFERENCES  87  vi  APPENDICES Appendix I.  Factorial Design Analysis  Appendix II.  Sample Calculations for the Factorial  Appendix III.  Design Analysis  93  Sequential Simplex Optimization  98  Appendix IV. Examples of Simplex Optimization Method (Project "FINAL 1" and "TRYOUT") Appendix V. Sampling and Analysis Procedures Appendix VI.  90  Cost Comparison between Electrochemical and Conventional Peroxide Brightening Process  Appendix VII. Raw Data  103 106  108 111  vii  LIST OF FIGURES 2.1  CIE L*a*b* Color Space  10  2.2  Lignin precursors  11  2.3  Interunit linkages in lignin  11  2.4  Proposed types of chromophores and leucochromophores in lignin  12  2.5  Oxidation of lignin with hydrogen peroxide  13  2.6  General polarization curve (or current density - potential plot)  20  2.7  Current density vs overpotential curve for a charge transfer controlled situation showing the different zones  21  2.8  Experimental condition and result from experiment before 1994  30  3.1  Combination of U-anode and tungsten cathode configuration (left) and glassy carbon anode (right)  36  3.2  Hollow plate electrode configuration  37  3.3  Different electrode configurations  38  3.4  Reactor and equipment setup for electrode design A  40  3.5  Reactor and equipment setup for electrode design B  40  3.6  Equipment setup for the measurement of polarization curve  44  4.1 4.2  Polarization curves for the electro-oxidation of sodium carbonate Average current efficiency and [ H 2 O 2 ] versus anode potential or current density at 46°C Plot of average current efficiency and [ H 2 O 2 ] vs time for anode potential  47  of 3.2 V vs SHE and temperature of 46°C  51  4.4  Concentration of active oxygen during brightening runs and no-pulp runs  52  4.5  Effect of carbonate on hydrogen peroxide  53  4.6  Cube plots for the responses of a full 2 factorial design  57  4.7  Effect of anode materials on the concentration of active oxygen  60  4.8  Comparison of the residual active oxygen concentration at 46°C for design A and design B Comparison of the residual active oxygen concentration at 66°C for design A and design B  4.3  4.9 4.10 4.11  3  50  64 64  Comparison of the residual active oxygen concentration between design A, design B and design D at 47°C  65  The effect of anode post treatment on the active oxygen concentration  67  viii  4.12  Residual active oxygen concentration profile for comparing 15-minute and 30-minute pre-generation time  70  4.13  Brightness gain and yellowness gain versus brightening time  71  4.14  Residual active oxygen profiles for runs with active oxygen generation at lower tempterature than the brightening temperature  73  4.15  Responses from simplex project " F I N A L 1"  76  4.16 4.17  Responses from simplex project " T R Y O U T " Hydrogen peroxide brightening of mechanical pulp in the presence of carbonate Hydrogen peroxide brightening in the presence of carbonate with variable additions of H 2 O 2 at different time intervals  76  4.18 4.19 4.20 III. 1  78 78  Comparison between an electrochemical and peroxide brightening run in the presence of carbonate  79  Effect of carbonate on the concentration of results ( 1M carbonate vs no carbonate)  80  H2O2  and the brightening  The simplex reflection move for (A) one-dimensional, (B) twodimensional, and (C) three-dimensional factor spaces  99  111.2  Possible moves in the variable-size simplex algorithm  100  111.3  Sample worksheet for a four-factor variable-size simplex algorithm  101  ix  LIST OF TABLES 2.1  Typical chemical composition of north american woods  5  2.2  Composition and properties of different spruce pulps  6  2.3  General classification of pulping processes  8  4.1  Variables and their levels in the 2 factorial design analysis 3  55  4.2  The design of full 2 factorial runs  55  4.3  Summary of responses from the factorial design  57  4.4  Main and interaction effects of the 2 factorial design  58  4.5  Brightening results from glassy carbon anode system at 46°C  61  4.6  Brightening results for different electrode configurations  62  4.7  Brightening results for the effect of anode treatment  66  4.8  Effect of brightening time at 46°C and 66°C  68  4.9  The effect of brightening time and longer active oxygen generation time  69  4.10  Results from two-stage brightening runs  72  4.11  Brightening results for runs where the temperature for active oxygen generation was lower than the brightening temperature  73  4.12  Initial vertexes and responses for project "FINAL 1" and " T R Y O U T "  75  4.13  Cost differences between conventional and electrochemical brightening process  82  II. 1  3  3  Current concentration and current density for corresponding current and anode area and the brightness results  95  II. 2  Summary of responses from the factorial design (without run 9)  96  II. 3  Summary of the main effects of temperature, current and anode area (without run 9)  97  IV. 1  Initial vertexes and responses for Projects " F I N A L 1" and " T R Y O U T "  103  IV.2  Simplex vertexes and responses for Project "FINAL 1"  103  IV.3  Simplex vertexes and responses for Project " T R Y O U T "  104  x  NOMENCLATURE (|)  current efficiency  (%)  <|)A  current efficiency of the primary anode reaction  (%)  r|  electrode overpotential (E - E )  (V)  OCA  anodic charge transfer coefficient  etc  cathodic charge transfer coefficient  AGceii  Gibbs free energy change of a cell reaction  (kJ)  AHceii  enthalpy change of a cell reaction  (kJ)  AS eii  entropy change of a cell reaction  (kJ K" )  A  electrode area  (m )  anode area  (m )  c  concentration  (kmol m" )  Co  concentration of the oxidized species  (kmol m" )  E  applied electrode potential  (V)  e"  electron  E  A  anode potential  (V vs SHE)  E  c  cathode potential  (V vs SHE)  E eii  total cell voltage  (V)  E  reversible or equilibrium electrode potential  (V vs SHE)  E ii  reversible potential of a cell reaction  (V vs SHE)  E  open circuit potential  (V)  Eohm  ohmic voltage drop across the cell  (V)  F  Faraday constant  i  current density  (kA m" )  I  current for a desired reaction  (kA)  iA  current density at the anode  (kA m" )  i  activation controlled current density  (kA m" )  in  current density for a desired reaction  (kA m" )  iL  mass transfer limiting current density  (kA m" )  1  C  A  A  C  r  r  ce  o c  a o  1  2  2  3  3  (96480 C equiv" ) 1  2  2  xi  2  2  2  io  exchange current density  (kA m" )  ilOT  total current density supplied to the system  (kA m" )  ITOT  total current supplied to the system  (kA)  k  first order reaction rate constant  km  mass transfer coefficient  (m s )  m  amount of material undergoing electrochemical change  (kmol)  MW  molecular weight  (kg kmol )  n  electron stoichiometry coefficient  (no unit)  0  oxidized species  Obulk  oxidized species in the bulk electrolyte  Oelectrode  oxidized species on the electrode surface  Q  amount of electrical charge  R  universal gas constant (8.314 kJ kmol" K" )  R  reduced species  R*  production rate of a desired product  Rbulk  reduced species in the bulk electrolyte  Relectrode  reduced species on the electrode surface  SE  specific energy  (kWh/kg)  STY  space time yield  (kgm'V)  T  temperature  (°C o r K )  t  time  (s)  volume of a batch reactor  (m )  V  2  1  1  (C) 1  R  2  1  (kmol s" ) 1  3  Abbreviations CIE  International Commission on Illumination  CTMP  chemi-thermo mechanical pulp  DP  degree of polymerization  DTPA  diethylene triamine pentaacetatic acid  ISO  International Standardization Organization  O.D.  oven dry  PGW  pressurized groundwood  xii  RMP  refiner mechanical pulp  SGW  stone groundwood  SHE  Standard Hydrogen Electrode  TMP  thermo-mechanical pulp  Xlll  ACKNOWLEDGEMENTS First of all, I would like to thank God for showing me that it is possible to go on after many disappointments. I thank God for giving me the most supportive supervisor, family, friends and teachers who never gave up on me. I would like to thank my supervisor, Colin Oloman, whose great mind inspired this thesis project. Thank you for your patience in correcting my "convoluted" and "long-winded" writing, for your constant encouragement and support, for listening to my problems, and for watching and guiding me to become an independent student.  I  also want to thank Mab for her quiet support, for recognizing my voice when I called and for delivering my message to Mr. Oloman. Next, I would like to thank the one person who patiently encouraged me to finish this thesis, who showed me that I could do better than I had done and who taught me the wisdom of life, Ata Saravi. Throughout my thesis writing years, I received tremendous support and encouragement from my friends and teachers whom I would like to thank, such as Elod and Cristina Gyenge, Jenny Been, J.J. and Jie-Ling Zhang, Saf and Nargis Kakar, Dr. Paul Watkinson, Dr. Bruce Bowen, Margaret Chen, Yu-Hong Tse, Dominggus Yawalata, Jinru Wang, Hong-Liang Hu, Rev. Gideon and Yohana Ang, Maliawan and Hetty Adam, and the congregation of the Indonesian Evangelical Church Vancouver. I would also thank the staff of Pulp and Paper Center and Chemical Engineering department for helping me when I needed a hand: Rita Penco, Helsa Leong, Tim Paterson, Peter Taylor, Horace Lam and Ken Wong. M y gratitude is extended to Dr. B.T. Yo, without whom I might not have studied in Canada and who continued to encourage me through my Dad. Most of all, I would like to thank my parents for their love, financial support and for not giving up on me. I also want to thank my sisters and brother whose loving support kept me going all these years. Finally, I would like to thank the Networks of Centres of Excellence (Mechanical and Chemimechanical Wood-Pulps Network) for the financial support through the research assistantship. xiv  Chapter 1 INTRODUCTION Environmental issues have compelled the pulp and paper industry to explore alternative production methods. One of the qualities sought for in paper is a high and stable brightness. Generally, this quality can be obtained from pulping and bleaching methods that lead to low pulp yields, dangerous effluents being introduced to the environment and a high production cost. Furthermore, tight environmental regulation of effluents forces the pulp and paper industry to move toward more chemical recovery and closed-cycle operations. To increase the pulp yield, high yield pulps (mechanical pulps) have become popular in the past decade. However, mechanical pulps have unstable brightness and are difficult to brighten to a high brightness level. Therefore, much research to produce high quality pulp at a reasonable cost has been done in the area of pulp brightening. The investigations include improvements on the current brightening technology and the search for alternative brightening agents and brightening methods. Presently, mechanical pulps such as thermomechanical pulps (TMP) are brightened using either sodium hydrosulfite (sodium dithionite, Na2S204) which has a reductive action, and hydrogen peroxide  (H2O2)  which has an oxidative action [1-6].  Hydrosulfite can be used where a brightness increase of 4 - 1 4 %ISO is required [5], while hydrogen peroxide can brighten high consistency (18% +) pulps up to 20 %ISO of brightness increase [4]. Unfortunately, the brightness gain is not stable on exposure to light, heat and air [1,9,10]. A brightness of over 80% ISO requires more than one brightening stage [7,10]. Lachenal et al. [8] were able to brighten groundwood pulp to 82 %ISO using a twostage hydrogen peroxide process. Others were able to reach 80%ISO using a two-stage peroxide (P)/ hydrosulfite (M) sequence [1]. At this brightness level, pulp could be used in long-life paper products such as copy papers, high-grade publication papers for books, business forms and writing papers, however, the instability of the brightness restricts the use of mechanical pulps to short-life papers such as newsprints. Although  1  Chapter 1. Introduction  the control of brightness reversion has been widely investigated in the field of pulp and paper research, there is still no known method that can permanently inhibit the yellowing of the pulp [21]. One way to improve the quality of mechanical pulps is to find alternative brightening agents that can perform better and are cheaper to manufacture than hydrogen peroxide. Among the oxidants, peroxysalts such as perborate [11], carbonateperoxyhydrate (a double salt of N a 2 C 0 and H 0 3  2  2  sometimes called "percarbonate")  [12-16], and peroxymonosulphate [17] have some brightening ability. Under special conditions, oxygen, although it usually causes pulp delignification, can also act as a brightening agent [10]. Most of the brightening agents mentioned above are produced using chemical methods and are usually generated outside of the brightening chamber before being used to brighten the pulp. Some potential brightening agents, once produced, are too unstable to be used effectively to brighten the pulp. This problem can be solved by generating the chemical inside the brightening reactor and using it directly to brighten the pulp. This process is called an "in-situ" brightening process. The production of unstable yet powerful brightening agents and immediate utilization of the product in an in-situ process can be done using electrochemical methods. Electrochemical technology has been long associated with the pulp and paper industry through the production of classic bleaching chemicals such as chlorine, sodium hypochlorite, sodium chlorate/chlorine dioxide and sodium hydroxide [10]. There are many other opportunities for the application of electrochemical technology in the pulp and paper industry, however, interest in the exploration of new electrochemical methods in pulp and paper related fields has just started to grow, along with stricter environmental regulations. One of the candidates percarbonate.  for an alternative  brightening agent is sodium  Currently, sodium percarbonates or sodium carbonate peroxyhydrate  (2Na2C03*3H202) is known as a safe bleaching agent in laundry applications. However, the chemical of interest in the present study is the "true" percarbonate (peroxocarbonate).  Percarbonate ion (C2O6 ") is believed to be a stronger oxidizing 2  2  Chapter 1. Introduction  agent than hydrogen peroxide  this can be seen from the standard reduction  (H2O2);  potential of both species in equation 1 and 2 below. T± 2C0 "  C 0 " + 2e" 2  2  E°ca. 2 V v s S H E  2  6  3  0 + 2H + 2e~ +  2  +± H 0 2  {Eqn. 1}  E°= 1.763 Vvs SHE {Eqn. 2}  2  However, percarbonate is readily hydrolyzed in solution to form hydrogen peroxide and bicarbonate ( H C O 3 ) according to equation 3 : C 0 ~ + 2H 0 -> 2HC0 " + H 0 . 2  2  6  2  3  2  2  {Eqn. 3}  The instability of solid true percarbonate prevents it from being widely used in the industry.  The available literatures on true percarbonates have been limited to the  investigation of the chemistry of percarbonates [12, 13] until Oloman's work in 1970. With the purpose to produce solutions containing active oxygen (percarbonate and/or peroxide), Oloman [14,15] was able to obtain good yields of active oxygen by electrochemical oxidation of sodium carbonate solutions at temperatures above 0°C. There is no fast and effective method to distinguish between percarbonate and hydrogen peroxide, however, a combination of the short lived percarbonate and hydrogen peroxide may be a stronger brightening agent than hydrogen peroxide alone. Furthermore, Oloman managed to brighten groundwood pulp with approximately 7 %ISO brightness gain by injecting the active oxygen into 10% consistency pulp [15]. The current study is a continuation of Oloman's work. The objective of this study is to investigate the conditions for producing active oxygen by electrochemical oxidation of sodium carbonate and to optimize the in-situ brightening of thermomechanical pulp (TMP) using the active oxygen. This process is worth looking into because sodium carbonate is a cheaper material than hydrogen peroxide and it is widely available in the pulp and paper industry. There is also a possibility to recover the sodium carbonate at the end of the brightening process, making this process environmentally and economically favorable. Furthermore, the continuous production of active oxygen can ensure a stable pH and the availability of active oxygen throughout the brightening process. This condition is useful in preventing alkali darkening of the pulp during the brightening process, and may result in a high and stable pulp brightness. The success of this electrochemical process may begin a new frontier in the pulp brightening sector of the industry. 3  Chapter 2 THEORETICAL BACKGROUND 2.1. Principles of Pulp Bleaching and Brightening In this chapter, the concepts of pulp bleaching and brightening are introduced, including the chemical components of wood fiber, pulping processes, the general objectives of brightening, and terminology in brightness measurement. 2.1.1. The Composition of Wood Fiber In order to understand the principles of pulp brightening process, it is essential to have some fundamental knowledge of wood fibers which constitute the building blocks of the pulp. 2.1.1.1. The Structure of Wood Fiber The main raw material for pulp and paper products is the wood fibers, among other non wood materials (bagasse, straws, bamboos, etc.). Wood fibers are basically hollow tapered tubes about 1 to 6 mm long with diameters approximately 10 to 60 microns  and wall thickness between 2 to 11 microns [1] depending on the wood  species. The fiber walls are made of mainly cellulose and hemicelluloses; the fibers are held together by lignin. The structure of these bundles of fiber differ among each wood species, especially between a softwood (evergreen) and a hardwood (deciduous) species. Despite their great abundance, hardwoods have not been used for pulping to a great extent. One of the reasons is that hardwoods have short and less uniform pulp fibers, leading to smoother paper with lower strength than softwood fibers [2]. The average length of a hardwood fiber is 0.9 to 2 mm, whereas that of a softwood fiber is 3 to 3.6 mm [19]. Another significant difference between hardwoods and softwoods is the chemical composition of the fibers. These two types of wood have different amount of cellulose, hemicelluloses and lignin (see Table 2.1).  4  Chapter 2. Background Literature  Table  2.1  Typical Chemical  Composition of North  American  W o o d s  Softwoods /o/\  Cellulose Hemicelluloses :  41-46  O-acetyl-4-O-methylglucuronoxylan O-acetylgalactoglucomannan Glucomannan 4-O-methylglucuronoarabinoxylan  Hardwoods (/o) 42-49  -  20-30  —  8-11  2-3 -  26-31 10-25  20-26 3-8  16-20  Lignin Extractives  [20]  -  2.1.1.2. Chemical Composition of Wood Fiber The principal components of wood fiber are cellulose, hemicelluloses and lignin. The properties of pulp are the result of the properties of those components. Cellulose, a carbohydrate, is a linear polymer of anhydroglucose (C6Hio05)  n  and constitutes 40-50% of most wood species. The strength of paper is due in part to the strength of hydrogen bondings among the cellulose fibers , within fibers and/or among fibers.  Since it is colorless, cellulose does not require bleaching or  brightening. However, the chemicals used to bleach or brighten the pulp may also degrade the cellulose by dissolving it. If the cellulose degradation is severe, pulp strength will decrease.  The extent of cellulose degradation in the pulp can be  measured by determining the average length of cellulose molecules (degree of polymerization). Most pulp fibers have a weight-averaged degree of polymerization (DP) in the 600 - 1500 range [1]. Like cellulose, hemicelluloses are also carbohydrate polymers that comprise 20-30% of the dry weight of wood. However, unlike cellulose which is derived from only glucose, hemicelluloses consist of several five-  and six-carbon sugars  nonuniformly linked. The DP of hemicelluloses is also smaller than that of cellulose. Softwoods and hardwoods have different dominant types of hemicelluloses (see Table 2.1). Hemicelluloses are colorless and need not be removed during a bleaching or brightening process. Furthermore, hemicelluloses are important for bonding in paper sheets and preserving pulp yield. Structurally different from cellulose and hemicelluloses, lignin comprises of 26-31%) of typical softwoods and 20-26% of typical hardwoods in North America. Lignin is the compound of utmost interest in a bleaching or brightening process 5  Chapter 2. Background Literature  because it contains chromophores that gives pulp its color. Lignin is a randomly linked, three-dimensional polymer consisting of phenylpropane units as building blocks. In order to obtain high brightness paper product, it is necessary to remove the color source in the pulp using either bleaching or brightening methods. In compliance with new environmental regulations, many pulp and paper industries are interested in pulp brightening methods. Another component of wood fiber that cannot be ignored is the extractives. Extractives are chemicals that can be removed with neutral solvents such as acetone, ethanol or benzene. They contain substances such as turpentines, wood resin and tall oil. The main functions of extractives in wood are as food reserves, protectants, and plant hormones [2].  Extractives impact color, odor, taste and occassionally decay  resistance to wood [19]. Most of the extractives are removed during the mechanical pulping process. The properties of different pulp types are shown in Table 2.2. The composition of cellulose, hemicelluloses and lignin in the groundwood pulp reflects that initially present in the wood without bleaching. The low tensile strength is the result of the fiber damage during the mechanical pulping process.  Other types of pulp give  significantly lower yield than groundwood pulp but with higher strength. T a b l e 2. 2.  C o m p o s i t i o n a n d properties of different s p r u c e  Pulp Groundwood Acid sulfite, unbleached Acid sulfite, bleached Kraft, unbleached Kraft, bleached  Unbleached Yield, % 95 55 50 50 47  Cellulose % 42 71 82 79 82  Hemi celluloses, % 31 17 18 17 18  pulps  [2]  Lignin %  Brightness, %  Tensile Strength,  27 6 0 4 0  62 63 90 20 90  2.5 9.5 10 11.5 11.5  km  2.1.2. A Brief Comparison of Various Pulping Methods Wood in its natural form needs to be defiberized before it is useful in the pulp and paper industry. The process of defibering the wood is called the pulping process. In general, pulping processes are divided into two groups, namely chemical pulping and mechanical pulping.  6  Chapter 2. Background Literature  The purpose of chemical pulping is to defiberize the wood into wood pulp using chemicals. Since wood fibers are held together by lignin, the function of the chemicals is to dissolve the lignin, leaving the length of the fibers relatively intact. Before the pulping process, the color of lignin is light brown, however, after the pulping process, the color of the residual lignin is much darker than the original lignin due to alkali darkening. Nevertheless, this dark color can be removed by treating the pulp with delignifying chemicals in the bleaching process, resulting in strong and high brightness pulp (e.g. Kraft pulp). The disadvantage of chemical pulping is the low pulp yield because during the process, lignin and maybe some cellulose and hemicelluloses are dissolved in the chemicals, leaving behind around 40 to 50% or sometimes less pulp yield. Mechanical pulping is a process of separating the fiber bundles in wood using mechanical methods, such as grinding. One of the oldest mechanical pulping methods is stone groundwood (SGW) pulping. This method of pulping preserves the pulp yield (also called high-yield pulping) by mechanically tearing the fibers apart from the wood matrix, retaining the lignin but resulting in short and broken fibers. The color of mechanical pulp is much lighter than chemical pulp, but it is difficult to brighten the mechanical pulp to a high brightness due to the presence of lignin in the pulp. To prevent damage on the wood fibers, current mechanical pulping methods include a thermal treatment to soften the wood chips before the mechanical grinding, such as thermomechanical pulp (TMP). There are also numerous pulping methods that combine chemical and mechanical pulping methods.  These are called the (chemi)mechanical pulps. The  purpose for these pulping methods is to obtain a relatively high yield pulp without necessarily losing the strength or properties of a chemical pulp. The summary of these three major classification of pulping methods are shown in Table 2.3.  7  Chapter 2. Background Literature  T a b l e 2.  3  General classification of pulping processes  [1]  Mechanical  (Chemi)mechanical  Chemical  Pulping by mechanical energy (small amount of chemicals and heat) High yield* (85-95%) Short, impure fibers • weak • unstable Good print quality Examples: • stone groundwood (SGW) • refiner mechanical pulp (RMP) • thermomechanical pulp (TMP)  Pulping with combinations of chemical and mechanical treatments. Intermediate yield (55-85%) "Intermediate" pulp properties (some unique properties)  Pulping with chemicals and heat (little or no mechanical energy)  * Yield =  Examples: • neutral sulfite semichemical • high-yield kraft • high-yield sulfite  Low yield (40-55%) Long, strong fibers • strong • stable Poor print quality Examples: • kraft • sulfite • soda  wt. of pulp produced (o.d.) wt. of original wood (o.d.)  2.1.3. Description and Objectives of Pulp Bleaching and Brightening Bleaching and brightening are chemical processes applied to cellulosic materials (such as wood fibers) to increase their brightness.  Brightness is the  reflectance of visible light from cellulosic materials formed into sheets [18]. The absorbance of visible light by wood pulp fibers is caused by the presence of lignin, one of the principal constituents of wood.  Native lignin in unprocessed wood is  colored slightly due to the chromophores in the lignin, and residual lignin remaining after a chemical {e.g., alkaline) pulping processes is highly colored.  Furthermore,  lignin darkens with age, heat and exposure to light. The common practice of increasing the pulp brightness is usually done by either lignin removal (bleaching process) or lignin discolorization (brightening process). In the manufacture of chemical pulps, most of the lignin is removed during pulping (a process of defibering the wood), and during the bleaching process, the lignin removal is continued.  This lignin removing process not only increases the  brightness, but the brightness stability of the product as well, and is accompanied by a low pulp yield.  In the manufacture of (chemi)mechanical pulps, wood is fiberized  mechanically with little or no lignin removal, and the brightness increase is obtained solely by the discolorization of lignin (i.e. the brightening process). The mechanical  8  Chapter 2. Background Literature  pulping and brightening process preserves most of the pulp yield, but has difficulty in reaching a high and stable brightness due to the presence of residual lignin in the pulp. Therefore, the principal objective of pulp brightening is to achieve a high brightness and a low yellowness with a secondary objective being high brightness stability. These objectives must be achieved without compromising the yield and the strength of the final product; cellulose degradation during brightening can lead to loss of strength in the product, in addition to increasing the production cost. 2.1.4. Optical Properties of Mechanical Pulp Optical property is an important quality sought for in most pulp and paper products. In printed paper applications for example, a bright and stable white color is an essential requirement. Whiteness, is a physiological phenomenon based on how the eyes perceive the interaction of visible light on the surface of a paper sheet. In the industry, there are other optical properties that do not depend on the perception of naked eyes, however, the measurement of these properties are essential in determining the overall quality of the paper product. Brightness is a term used to describe the whiteness of pulp or paper, on a scale from 0% (absolute black) to 100% (absolute white) relative to a magnesium oxide (MgO) standard, which has a brightness of about 96% by the reflectance of blue light (457 nm) from the pulp or paper [19]. Brightness is affected by how it is measured. The angle of incident light and the surface properties of the sheet have an effect on the brightness [18].  Therefore, several standard brightness measurements have been  developed, one of which is the ISO (International Standardization Organization) brightness.  Recent literature states that ISO brightness measured on a non-standard  machine might give a wrong brightness reading [23]. In this project, all brightness measurements were made on a Datacolor Elrepho spectrophotometer, which used to be a standard machine for ISO brightness measurement [23]. Along with the brightness, yellowness is also measured to determine the degree of yellow color on the pulp. Usually, a high brightness pulp or paper has a very low yellowness (sometimes even a negative value). However, it is also possible  9  Chapter 2. Background Literature  to have a bright yellow colored paper, which would result in a high brightness and yellowness values. Another optical measurement  is the CLE L*a*b* system.  This color  measurement system is developed by the International Commission on Illumination (CEE) to simplify the interpretation of the color of pulp or paper. The L * , a* and b* are color axes, where a* measures the red to green range, b* (at right angles to a*) measures the yellow to blue range, and L * measures the white to black range [24]. The CIE L*a*b* color space is shown in Figure 2.1. WHITE  BLACK  Figure 2.1  C I E L*a*b* C o l o r  Space  2.2. Mechanical Pulp Brightening by Hydrogen Peroxide The process of mechanical pulp brightening involves many aspects.  To  understand the mechanism of pulp brightening process in general, it is necessary to know the structure of lignin and its chromophores.  The mechanism of brightening  will be explained using hydrogen peroxide as the brightening chemical. Finally, the general problems in hydrogen peroxide brightening of mechanical pulps will be discussed. 2.2.1. Structure of Lignin Native lignin is a polymer comprised of coniferyl alcohol (softwood) or a mixture of coniferyl and sinapyl alcohol (hardwood) units [25].  Sometimes small  amounts of p-coumaryl alcohol units are also found in lignin (Fig.2.2).  The  polymerization of these alcohols causes the formation of a heterogeneous branched  10  Chapter 2. Background Literature  and cross-linked polymer where the phenylpropane units are linked by carbon-carbon and carbon-oxygen bonds.  Other reactions may also form cross-linking between  lignin and polysaccharide chains. The main linkages joining the phenylpropane units are depicted in Fig. 2.3.  The combination of these linkages will form a complex  structure of lignin.  CH OH I CH 2  HO  HO  p-Coumaryl Alcohol  Coniferyl Alcohol F i g u r e 2. 2  c  i  6 - 0  c  c  c  Lignin  c  c  c  C - O ^ C -  C  C  c  c  c  c  6  0  ^  P-(3  p-1  3  Precursors  CHGK/  c  OCH  Sinapyl Alcohol  c - c  0 0 0 0 (3-5  Chip T HO  P-O-4  F i g u r e 2. 3 I n t e r u n i t L i n k a g e s i n  5-5  c  C c - o ^ c -  O a-O-4  Lignin  During the brightening process, the structure of lignin is not changed significantly, however, the chromophores in the lignin will be modified. The basic chromophore units in lignin are carbonyl and ethylenic groups and aromatic rings. When present as non-conjugated groups, they do not impart color to the parent structure of lignin; however, when a sufficient number of these basic units linked conjugatively, they give rise to colored chromophores [26]. Some of the chromophore structures are shown in Figure 2.4. Among the most common chromophore types are  11  Chapter 2. Background Literature  the coniferaldehyde, quinone and stilbene. There are also some leucochromophores which are nominally colorless but readily converted to chromophores through dehydration or dehydrogenation reactions as illustrated in Figure 2.4.  VIB. Dihydroxystilbene (*max = 330nm)  Figure 2. 4 Proposed types of chromophores and leucochromophores in lignin [26]  2.2.2. Chemistry of Hydrogen Peroxide Brightening The principal reactive species in peroxide brightening system is the hydroperoxide or perhydroxyl ion (HOO~), a strong nucleophile, formed by the addition of alkali to hydrogen peroxide (see Eqn. 4). H 0 2  2  + HO" +± OOHT + H 0 2  {Eqn. 4}  The perhydroxyl ions usually eliminate the chromophores by changing them into some colorless compounds such as carboxylic acid fragments and other degradation products [26]. An example of a nucleophilic attack of a perhydroxyl anion on a lignin 12  Chapter 2. Background Literature  chromophore during peroxide brightening is shown in Figure 2.5. The phenolic units comprising lignin are not attacked directly by the perhydroxyl anion, so that the lignin is not modified to increase its solubility.  Hence, the brightening occurs without  significantly affecting the yield.  HC-O"  F i g u r e 2. 5  Oxidation of lignin with h y d r o g e n  peroxide  [26]  Under brightening conditions, hydrogen peroxide is partially decomposed to molecular oxygen according to Equation 5: 2H 0 2  The presence of 0  2  2  -> 0 + 2 H 0 2  2  {Eqn. 5}.  and radicals formed during the brightening process (HO) may  also cause the formation of new chromophores. Most of the chromophores found in the literature are the "proposed" chromophore types and there are certainly more chromophores whose structures are still unknown. This situation makes it difficult to achieve a stable brightness in mechanical pulps.  Despite the complexity of the  chromophore systems, much literature has been published concerning proposed chromophore elimination and formation reactions. Reasonably detailed information on pulp brightening can be found in "Pulp Bleaching: Principles and Practice" edited by Dence and Reeve [44]. 2.2.3. Process Conditions of Peroxide Brightening Peroxide brightening of mechanical pulps is usually carried out by mixing an alkaline peroxide solution (commonly referred to as brightening liquor) with the pulp for an amount of time. The brightening liquor consists of hydrogen peroxide, caustic soda, sodium silicate, water and (sometimes) some additives such as magnesium 13  Chapter 2. Background Literature  sulfate.  Caustic soda is an alkali source to maintain a p H of around 10.5 to 11.5,  where the equilibrium in Eqn. 4 will shift to the right, producing the desired perhydroxyl anion. The mixture of pulp and liquor is held in a bleaching tower for 0.5 to 4 or more hours at a temperature that commonly ranges from 60 to 77°C [4]. At the end of a brightening process, the pulp pH is lowered to prevent alkali darkening before being sent to the paper machine. Usually sulfur dioxide is used for the pH adjustment. 2.3. Factors Affecting Brightness Response in Mechanical Pulp Brightening There are several factors that influence the brightness response of mechanical pulp during the brightening process, namely consistency, retention time, temperature, alkalinity, stability of brightening liquor, and even the preceding pulping process. Some factors alone may have a significant impact on the brightness response; sometimes many of these factors are interrelated in affecting the brightness response on the pulp. 2.3.1. Effect of Pulp Consistency Hydrogen peroxide brightening has been carried out over a wide range of consistency, from 4% to 35%. Commonly, at low consistency (< 15%), mechanical pulp requires more peroxide to achieve the same brightness than it does at medium (15-25%) or high (25-35%) consistency. A l i et al. [27] reported that increasing the pulp consistency from 4% to 20% will increase the peroxide concentration by a factor of 6. However, further increase in pulp consistency may not improve the brightness level, usually because of equipment constraints. 2.3.2. Effect of Temperature, Retention Time and Alkalinity Among the variables affecting brightness response of mechanical pulp, time and temperature are two factors that are most closely related. At high consistency, time and temperature can be interchanged. Generally, a certain brightness level can be obtained by brightening the pulp either at a very high temperature for a short time or at a low temperature for a longer time. Nevertheless, there is a limitation to the amount of retention time needed to achieve a certain brightness level. 14  At high  Chapter 2. Background Literature  temperatures (90-95°C), brightness increase is very rapid, reaching a maximum in 30 minutes or less, however, the final brightness is less than that achieved at a lower temperature (35-75°C).  The reason for this is because the peroxide decomposes  rapidly at high temperature, exposing the pulp to a possible alkali darkening process. The reaction rates of both the brightening and peroxide decomposition are increased at high temperatures. For any given peroxide application, an optimum alkali charge is required to achieve a maximum brightness gain. If the initial pH is too high (> 11), the reaction of the pulp with the hydroxyl ions (OH") will cause alkali darkening. On the other hand, if the initial pH is too low, the low perhydroxyl anion concentration may hinder the brightness increase. To compensate the problems from alkalinity, the retention time and temperature has to be manipulated to achieve the desired brightness level. The rule of thumb on the relationship between temperature, retention time and alkalinity is as follows [4]: • Low temperature (35-44°C), medium-high alkali —> Long retention time (4-6 hrs) • Medium temperature (60-79°C), medium alkali —> Medium retention time (2-3 hrs) • High temperature (93-98°C), low alkali —> Short retention time (5-20 min). 2.3.3. Effect of the Stability of Brightening Liquor During the brightening process, hydrogen peroxide partly decomposes into molecular oxygen and water according to Eqn. 5.  The decomposition reaction is  catalyzed by metal impurities (iron, manganese, copper, nickel and chromium) present in the pulp and/or in the brightening liquor.  In order to reduce the rate of  decomposition, additives and chelating agents are added to the brightening liquor and the pulp is pretreated with some chelating agents. Some of the common additives and chelating agents are sodium silicate, magnesium sulfate and diethylene triamine pentaacetic acid (DTPA). The pre-treatment of pulp with D T P A has been proven by A l i et al. [27] to enhance the effect of sodium silicate in stabilizing the brightening liquor. The roles of silicate in aiding peroxide brightening include absorption of metal ions, metal surface passivator and penetrant, buffer, coating agent and detergent [22, 27]. Pre-chelated pulp also brightens to higher levels than unchelated pulp no matter 15  Chapter 2. Background Literature  what the silicate dosage is [27]. Silicate application in modern mechanical pulp brightening process is around 3% or less on pulp, while the pulp pretreatment usually adds DTP A in the range of 1 to 6 kg/tonne of pulp [26]. 2.3.4. Effect of Different Pulping Process (Chemi)mechanical pulping refers to different methods of pulping, most of which involves grinding and refining to separate the wood fibers. Pulps obtained from grinding, such as stone groundwood (SGW) and pressurized groundwood (PGW) pulps, contain high amounts of debris and are easier to brighten. On the other hand, refiner pulping processes produce pulps with lower brightness and are less bleachable than groundwood because of the heat generated during the pulping processes. of  the  examples  of refiner  pulps  are  refiner  mechanical  pulp  Some (RMP),  thermomechanical pulp (TMP) and chemithermo-mechanical pulp (CTMP). The relative bleachability of (chemi)mechanical pulps made from the same wood species tends to be as follows [4]: SGW > P G W > C T M P > T M P > R M P  2.4. General Principles of Electrochemical Processes Most conventional processes are thermochemical processes, however, there are some important processes that cannot proceed spontaneously due to unfavorable thermodynamics conditions. These processes can be taken to a high conversion by an application of some electrical energy.  This interchange of electrical and chemical  energy is the basis of electrochemical technology.  Currently, electrochemical  technology is not limited to the production of "exotic" materials alone, but it has become a "green" alternative to some conventional processes.  A n electrochemical  process uses a "clean" reagent with negligible mass, the electron, to initiate chemical reactions and the side products are often benign to the environment. What actually happens in an electrochemical reaction is a transfer of electrons between chemical species or ions and an electrolyte through a reduction and oxidation (redox) reaction. The redox reaction occurs on the electrodes: reduction occurs on the cathode and oxidation occurs on the anode. 16  The electrodes are in contact with an  Chapter 2. Background Literature  electrolyte that allows the movement of charged species to and from the electrodes to maintain charge balance on the electrodes. A simple reversible redox reaction can be written as follows: O  +  ne  ^  R  {Eqn. 6},  where O is the oxidized species which gains n moles of electrons and R is the reduced species which looses n moles of electrons. 2.4.1. Electrode Potential and Thermodynamics The driving force for an electrochemical reaction is the potential difference between the electrode and the electrolyte.  The potential difference between the  electrode and the electrolyte for a specific reaction at equilibrium is called the reversible electrode potential (E ) of that reaction. The difference between the applied 1  electrode potential (E) and the reversible electrode potential (E ) is called the r  overpotential (r\). Therefore, when an applied electrode potential (E) is higher than E  r  (r\ is positive), the reaction in Eqn. 6 will tend to go from right to left in an electrooxidation of R. On the other hand, if E is less than E (r| is negative), the reaction will r  tend to go from left to right in an electro-reduction of O. The  spontaneity  of  an  electrochemical  reaction  depends  on  the  thermodynamics of the reaction. When the electrodes are connected externally, some reactions may proceed spontaneously (e.g. battery or galvanic cells) while some other reactions require an external power supply to drive the reaction. The driving force for a spontaneous cell reaction is a negative value of Gibbs free energy change, A G i i , ce  which is defined by the following expression: AGceii  = AHceii  - T ASceii  {Eqn.  7}  where AHceii and A S i i are the enthalpy change and entropy change of the cell reaction ce  and T is the temperature. For spontaneous cell reactions, TAS ii > AHceii and A G i i is ce  ce  negative. The Gibbs free energy for an electrochemical cell reaction is related to the reversible equilibrium potential, E u, by the following expression: r  ce  AGceii  = - n F E ii  {Eqn. 8}  r  ce  where F is the Faraday constant (=96480 C mol" ). By convention, the cell potential, 1  E eii C  is the difference between the cathode and anode potentials 17  Chapter 2. Background Literature  Eceii =  E  - E  c  {Eqn.  A  9}  A spontaneous cell will have a negative AG ii value, and therefore, a positive E i i r  ce  ce  value. 2.4.2. Kinetics of an Electrode Process A n electrochemical reaction may proceed slowly or quickly depending on its kinetics.  A n electrode reaction is a sequence of several basic steps. The rate of a  reaction depends on the speed of the basic steps. To maintain a current, it is essential to supply reactant to and remove the product from the electrode surface, as well as to allow electron transfer reaction to occur on the electrode surface [29]. The overall (cathodic) process: O + ne" —» R must occur in at least three steps [32], all of which take place at the interface between an electrode and the electrolyte: (i)  reactant supply (mass transport from bulk electrolyte to the electrode surface) Obulk  *  Oelectrode  (ii) electron transfer (electron transport at the electrode surface) Oelectrode  "t" He  *  Relectrode  (iii) product removal (mass transport away from the electrode surface) Relectrode  *  Rbulk  The rate of the overall process will be determined by the slowest of the three steps. Usually, other fundamental steps may accompany the above three steps. These fundamental steps include [29,32]: (i)  Chemical reactions Pure chemical reactions may precede electron transfer, accompany it, or follow it.  (ii) Phase formation at the electrode surface Many electrode reactions involve the formation of a new phase on the electrode surface, the removal of one or the transformation from one phase to another. (iii) Adsorption on the electrode surface A n adsorbate may bond itself on the surface via a variety of interactions including electrostatic forces, covalent bonding, ion-dipole effects and metallic bonding. The adsorbed species may be a reactant, a product or an intermediate. An 18  Chapter 2. Background Literature  adsorbate may change the rate of the electrode reaction, its pathway and/or its products. The rate of the overall sequence is constrained by the slowest step, which could be electron transfer or mass transfer. 2.4.3. General Polarization Curve of an Electrode Reaction The overall rate of a single electrochemical reaction O + ne' ->  R  {Eqn. 10}  can be expressed by the Faraday's law of electrolysis (Equation 11) [32]: m =-% n-F  =i ^ n-F  (mol)  {Eqn. 11}  where: m is the amount of material undergoing electrochemical change; Q is the amount of electrical charge involved, and in a constant current situation, Q is the product of current, I, and time, t; F is the Faraday's constant, equivalent to the charge of one mol of electrons; n is the number of moles of electrons transferred in the reaction. When more than one reaction occurs on the surface, it is necessary to define current efficiency,  as the fraction of electrical charge used for the primary (desired)  reaction. In the case of a constant current [32]. (J) = I / ITOT  {Eqn.  12}  where I is the partial current for the desired reaction and ITOT is the total current supplied to the system. In a constant volume (VR) batch system, the concentration is given by c = ITI/VR. Differentiating equation 11 with respect to time and incorporating the current efficiency in equation 1 2 yields an overall rate expression which can be written in term of current density, iTOT,as follows [32]: d c dt  =  ^ i j O T n • F • VR  ( m o l m  -i -i) s  {Eqn. 13}.  The rate expression in equation 13 depends on the operating current density (ITOT), the current efficiency ((()) and the working electrode area (A). The kinetics of an electrochemical reaction can be summarized in a general polarization curve as plotted in Figure 2.6.  19  Chapter 2. Background Literature  Potential  Figure Curve a  -  2. 6 G e n e r a l  p o l a r i z a t i o n c u r v e (or c u r r e n t d e n s i t y - p o t e n t i a l plot)  s h o w s a pure activation controlled current, iac; curve b c u r r e n t h a v i n g a m a s s t r a n s f e r l i m i t e d v a l u e , i L , at h i g h  the  actual  [41] measured  potentials.  Until a certain equilibrium potential is reached, an electrochemical reaction will undergo an infinite resistance. When the applied electrode potential exceeds the equilibrium potential, the reaction will be controlled by electron transfer (activation controlled) until the activation controlled current density (i ) is reached. ac  With an  increasing electrode potential, the reaction will proceed into the mixed control zone until it reaches a mass-transfer limiting current density  the maximum current  density which can be supported by the reactant (for this particular electrode reaction). Once the mass transfer limiting current density is reached, no matter how much potential is applied, the amount of chemical change for that specific reaction will be the same.  Usually, when the applied potential continues to increase, a secondary  electrochemical reaction will proceed. Under electron transfer control, the current density is related to overpotential according to the Butler-Volmer Equation [32]: 1  exp  a  A  nF?7 R T  exp  R T  20  (kA nT)  {Eqn. 14}  Chapter 2. Background Literature  where i is the exchange current density (equilibrium current density), OCA and etc are 0  the transfer coefficients for the anodic and cathodic processes, and r\ is the overpotential (E - E ). A general curve of current density vs overpotential is shown in 1  Figure 2.7.  The dashed curves show the partial anodic and cathodic current densities.  i/kAm" A 2  Anodic (oxidation) process  '(Hi)  >T|/V  Cathodic (reduction) process V  Figure  2. 7 C u r r e n t d e n s i t y v s  The solid curve shows the net current density predicted by the Butler-Volmer equation.  overpotential curve for a charge transfer  situation s h o w i n g the  different z o n e s  controlled  [32]  Under mass transport control, the limiting current density ( i ^ can be expressed as [32]: where k  i = k nF Ac L  m  m  {Eqn. 15}  is the mass transfer coefficient which depends on electrolyte composition,  temperature and flow conditions; n is the stoichiometry number of moles of electron; A is the working electrode area and c is the concentration of the reactant. The desired strategy for a general electrochemical system is to minimize the overpotential for the desired reaction in order to minimize energy costs and encourage a high current efficiency and selectivity, while maximizing the overpotential for the side reactions in order to minimize their occurrence [32]. 2.4.4. Electrochemical Cell Components Electrochemical processes are carried out in an electrochemical cell. A simple electrochemical cell consists of electrodes (cathode and anode), an electrolyte, and an external electrical connection.  Sometimes a separator is used to separate the  electrolyte into anolyte and catholyte. Electrochemical reactions are heterogeneous 21  Chapter 2. Background Literature  reactions that take place in the electric double layer at the boundary between the electrode phase (often solid metal or carbon) and the electrolyte phase (often a solution of a salt in water) [32]. 2.4.4.1. Electrode Materials and Electrolyte The kinetics of an electrode process relies heavily on the choice of electrode material. In general, a good electrode material should have the following properties: high physical and chemical stability, high electrical conductivity, ease of fabrication into a suitable physical form, suitable electrocatalytic properties, long lifetime, nonpolluting and non-contaminating, low cost, safe and readily available and repairable. In some cases where more than one reaction occurs at an electrode, the electrode material should have a high exchange current density for the desired product but a low one for the unwanted product. The electrolyte is a medium for ion transport via migration, consists of at least three essential components: a solvent, a high concentration of supporting electrolyte and the electroactive species [32]. Electrolyte movement may be used to enhance mass transport of species towards (or away from) the electrode. 2.4.4.2. Separators Sometimes, an ion permeable separator which serves as a divider for the anode and the cathode is used in an electrochemical cell. Several main reasons for using a separator are as follows: (i)  To prevent the mixing of anode and cathode products in order to maintain a chemical stability or safety.  (ii) To avoid an unwanted side reactions to happen on the other electrode, hence encouraging a high current efficiency for the desired reaction. (iii) To maintain electrolyte purity. (iv) To avoid physical contact between an anode and a cathode if the electrodes are closely spaced. There are three classes of separators: porous spacers, microporous separators and ion exchange membranes. Porous spacers are very open structures that provide a  22  Chapter 2. Background Literature  physical barrier between electrodes, but little or no resistance to the mixing of anolyte and catholyte. Microporous separators or "diaphragms" act as both convection and diffusion barriers by slowing the transport of solvent, solute and ions. Diaphragms are also physical separators which do not distinguish between species. On the other hand, ion  exchange  membranes  divide the  cell  into two  hydraulically separated  compartments which function as barriers to convection and diffusion while permitting selective migration of ions [32]. The decision to use a separator depends on the economics and the nature of the electrode reactions. In addition to increasing the cost and the complexity of the cell construction, a separator increases the cell resistance and the required cell voltage for a given current density. 2.4.4.3. The Electrical Double Layer The electrical double layer is the discontinuous interphase region of molecular dimensions between the electrode phase (often a solid metal or carbon) and the electrolyte phase (often a solution of a salt in water). The properties of solutions and species in this region are very different from the ones in the bulk electrolyte. Electrochemical reactions take place in this region. The potential difference between the electrode and the electrolyte provides the driving force for an electron transfer reaction across the interface. 2.5. The Electrosynthesis of Hydrogen Peroxide The conventional source of  H2O2  is a thermochemical process based on the  autooxidation of anthraquinols. However, peroxide can also be obtained by several electrosynthetic routes. The capital and energy costs for electrochemical methods are high but these methods allow on-site generation of dilute hydrogen peroxide (about 3%  H2O2  in electrolyte solution), which is the adequate amount needed for pulp  bleaching or brightening. One electrochemical method in the pulping industry is the electrosynthesis of alkaline peroxide by the cathodic reduction of oxygen. The electro-reduction of O2 at  23  Chapter 2. Background Literature  an appropriate cathode gives peroxide in the form of perhydroxyl ion ( H 0 ). The 2  reaction is as follows: 0  + H 0 + 2e" -» OH" + H 0 "  2  2  E° - - 0.08 V vs SHE {Eqn. 16}  2  The desired product can be reduced further : H 0 " + H 0 + 2e" -» 3 0 H 2  E° = + 0.87 V vs SHE {Eqn. 17}  2  or oxidized at the anode: 0  2  + H 0 + 2e" « - OH" + H 0 " 2  E° = + 0.08 V vs SHE {Eqn. 18}  2  in competition to the desired anode reaction, oxygen evolution. In this system, the reduction of HO2  to O H is thermodynamically favored over the reduction of O2 to  HO2 . Therefore, the choice of cathode materials with properties that will promote the desired reaction plays a substantial role in obtaining a satisfactory current efficiency for HO2 . A separator (membrane or diaphragm) is also needed to suppress the loss of H0  2  by anodic oxidation. A n old commercial way to produce H2O2 electrochemically is by the electro-  oxidation of sulfuric acid (H2SO4) to peroxydisulphuric acid, followed by its hydrolysis and distillation to produce up to 50 wt% H2O2 [10]: S 0 " + 2e" 2  8  <- 2S0 "  E ° = +2.1 V v s SHE  2  4  e  H2S2O8 + 2 H 0 -> 2 H S 0 2  2  4  + H2O2 (distill)  {Eqn. 19} {Eqn. 20}  2.6. Percarbonates Percarbonates  are strong oxidizing and bleaching agents. Most of the  percarbonates known at the present time can be roughly divided into three groups. The first one is the peroxocarbonate or the "true" percarbonate, for example, the electrolytic potassium percarbonate  (K2C2O6),  obtained by anodic oxidation of  concentrated solutions of potassium carbonate ( K C 0 ) at -10 to -15°C [13, 16]. The 2  3  solid potassium percarbonate was readily hydrolyzed into bicarbonate and hydrogen peroxide at room temperature, and hence found no commercial application. However, in  1970, Oloman proposed that the active oxygen produced by the "true"  percarbonates could be used to bleach the pulp. The present project continues the  24  Chapter 2. Background Literature  work of Oloman in utilizing the active oxygen produced by the electro-oxidation of sodium carbonate (NaCOs) to brighten thermomechanical pulp (TMP). The second known "percarbonates" are the peroxyhydrates of carbonates (e.g. 2Na2C03'3H202) obtained from the addition reaction of Na2C03 and H2O2. This type  of percarbonates has been used extensively in the detergent industry as a powerful cleaning and bleaching agent.  Much research has been performed in the process of  manufacturing of this type of percarbonate [30,31]. Prokopchik et al. [13] have used polarography to differentiate between the true percarbonates and peroxyhydrates in solution. The difference between the potentials of a peroxocarbonate and H2O2 amounts to 300 - 400 mV.  The third group of percarbonates are the "chemical" peroxocarbonates (e.g. K2C2O6)  which are obtained by the action of CO2 and peroxide compounds (peroxides  of alkali metals) [13]. 2.6.1. Properties of "True" Percarbonates The first "true" percarbonates were made by E.J. Constam and A . von Hansen in 1897 by the electrolysis of a saturated solution of the carbonates of the alkali metals and of ammonium on a Pt anode at a temperature of -10°C or lower [16]. The percarbonates were formed at the anode and the hydroxyls of the alkali metals or of ammonium were formed at the cathode. Solid percarbonates  can only be obtained in the form of potassium  percarbonate with a K2C2O6 content of 50-79%. Khomutov et al. found that it was not possible to separate lithium, sodium and rubidium percarbonate from the anolyte because of the low solubility of the carbonates of these alkali metals at low temperatures [12]. Furthermore, the yield of potassium percarbonate (K2C2O6) per current is affected by the current concentration and increases with a decrease in the quantity of electricity applied, with an increase in the current density, with an increase in the potassium carbonate (K2CO3) concentration, and with a decrease in the temperature [12].  25  Chapter 2. Background Literature  Percarbonate is readily hydrolyzed in water according to the following reaction: C 0 " + 2 H 0 -> 2HCCV + H 0 2  2  6  2  2  2  {Eqn. 3}  and the hydrogen peroxide subsequently decomposes according to: 2H 0 2  2  -> 2 H 0 + 0 2  {Eqn. 5}.  2  Well dried solid K2C2O6 can be stored for a long time, but in a moist state, it rapidly decomposes and in 3 to 5 days loses up to 90% of its active oxygen. Prokopchik et al. have produced some data which show that the hydrolysis of percarbonate in water is first order with respect to percarbonate with a rate constant which increases with decreasing pH and increasing temperature [13,15]. For example, at a pH of 8 and a temperature of-10°C, the half-life of percarbonate is 2.3 minutes. At 10°C and pH 8, the percarbonate half-life is 0.36 minute. Because of its instability and high cost, solid potassium percarbonate finds no worthwhile commercial application. 2.6.2. Percarbonate by the Electro-oxidation of Sodium Carbonate Of all the alkali metal carbonate salts, sodium carbonate is the cheapest. It is also found quite abundantly in the pulp mill as the inorganic smelt from the recovery furnace [1,2]. Although it is not possible to produce solid sodium percarbonate [12], it is possible to obtain solution with active oxygen by the electrolysis of sodium carbonate solution. The electrochemical production of  percarbonate is very similar to the  production of some inorganic peracid salts such as peroxydisulphate, perborate and perchlorate. These per-salts are generated at relatively high current density and low temperature on high oxygen overvoltage anodes such as Pt, Pt/Ir and Pb02 [10]. Just as percarbonate, these per-salts will eventually be hydrolyzed to hydrogen peroxide [10, 11]. The production of peroxydisulphates (S2O8 ") typically uses water cooled Pt 2  anodes at 5 - 10 k A m at « 5 V per cell to give S2O8 " at about 80% current efficiency 2  2  [10]. The water cooled anode is used to raise the oxygen overvoltage at the anode and suppress the hydrolysis of the product. Recently, glassy carbon (a cheaper alternative to platinum) in the presence of 0.02 M fluoride ion has been shown to be an effective anode for S 0 " generation at 25°C, pH<5 [10]. 2  2  8  26  Chapter 2. Background Literature  In 1970 Oloman found that the electro-oxidation of sodium carbonate solution can give useful yields of active oxygen (mainly hydrogen peroxide), although the best yield obtained was not high enough to allow this process to compete with the conventional method of hydrogen peroxide production. The principal reactions that occur in the electrolyte are as follows [15]: Anode reactions: Primary:  C 0 " + 2e"«- 2 C 0 " 2  2  E° = ca.2 VvsSHE {Eqn. 21}  2  6  3  Secondary: 2 H 0 + 0 + 4e' <- 40H" 2  E° = 0.4 VvsSHE  2  {Eqn. 22}  0 + 2 H 0 + 2e•<- H 0 + 20H" E° = 0.15 VvsSHE {Eqn. 23} 2  0  2  2  2  + H 0 + 2e" « - OH" + H 0 " E° = 0.08 VvsSHE {Eqn. 24}  2  2  2  Cathode reactions: Primary:  2 H 0 + 2e" 2  H + 20H 2  Secondary: H 0 " + H 0 + 2e" -»• 3 0 H 2  2  -  E° = - 0.8 VvsSHE {Eqn. 25} E° = 0.87 VvsSHE {Eqn. 17}  Thermodynamically, the primary anode reaction (Eqn. 21) is less favorable than the secondary anode reactions (Eqn. 22 - 24). Eqn. 22 can be slowed by using high oxygen overvoltage material (such as Pt) as the anode.  Eqn. 23 and 24 are  probably fast, but they are mass-transport limited. Eqn. 21 is further promoted by cooling the anode to increase the oxygen overvoltage of the anode. Kinetically, the oxidation of carbonate as well as the stability of hydrogen peroxide is favorable at room or lower temperature, while brightening is a slow process which is effective at high temperature (60°C or higher). At room or higher temperatures, the percarbonate hydrolyzes to form bicarbonate and hydrogen peroxide which finally decomposes into water and oxygen, according to Eqns. 3 and 5. The cooling of the anode also helps prolong the life of the percarbonate and/or peroxide around the anode. The rate of percarbonate hydrolysis and peroxide decomposition is a function of temperature and solution pH, especially in the presence of decomposition catalysts such as the transition metal ions. When the electrochemical generation of percarbonate is performed in an undivided cell, the percarbonate and peroxide can be easily reduced on the cathode. In  27  Chapter 2. Background Literature  order to reduce the mass transfer of active oxygen species to the cathode (to suppress Eqn. 17), a cell with differential electrode area i.e. with a high ratio of anode/cathode area may be used.  Since both electrodes operated at the same current, the small  cathode area would suppress the electro-reduction of H2O2 at the cathode surface, which occurs under mass transfer control. The destruction of H2O2 at the cathode may also be suppressed by putting a diaphragm around the cathode. Oloman found the basic conditions necessary for the production of active oxygen from sodium carbonate solution in a divided cell as follows [14]: - the initial Na2CC»3 concentration is about 0.5 to about 4 molar. - the anode current density is about 0.05 to about 1.0 A/cm . 2  - the ratio of active anode area to anode chamber volume is above 1 cm /cm . 2  3  - the anode material is any material with a high oxygen overpotential and high dissolution potential, such as platinum, gold, and graphite. - the anolyte temperature is from 0 to 40°C. - the anolyte pH during the electrolysis is between 12 and 9. To reduce the rate of decomposition of the active oxygen in the pulp slurry, it is necessary to remove the decomposition catalysts by adding some stabilizers such as sodium silicate and magnesium sulfate and chelating agents such as D T P A into the solution.  The addition of these particular additives and chelating agent is reasonable  because most of the active oxygen produced would eventually become H2O2 (Eqn. 3) and these additives are effective for a H2O2 pulp brightening system [36-39]. The yield of active oxygen is measured using the permanganometric method, the same method used to measure the amount of hydrogen peroxide.  It is very  difficult to differentiate the percarbonate from the hydrogen peroxide, hence the presence of both or either one of them is called the "active oxygen". Several methods of distinguishing the "true" percarbonates from the peroxyhydrates of carbonates and from the hydrogen peroxide have been proposed, including the polarography and the Riesenfeld test [13], however, these methods are not efficient for a fast determination of the components of active oxygen.  28  Chapter 2. Background Literature  2.7. In-situ Electrochemical Brightening of Mechanical Pulp Using Sodium Percarbonate/Peroxide The active oxygen produced by the electro-oxidation of sodium carbonate should have the same oxidizing strength if not stronger than hydrogen peroxide alone. Even though the yield of active oxygen obtained from this process is not enough to make the process viable as a commercial method for producing hydrogen peroxide, this yield is enough to be used in the pulp brightening process. Oloman found that the product solutions from the experimental cell brighten groundwood pulp in a similar manner as does the hydrogen peroxide [15]. To maximize the use of the active oxygen  (C2O6 " 2  and/or  H2O2)  for the  brightening of mechanical pulp, an in-situ brightening method is proposed. The short life of percarbonate and peroxide prompts an immediate application of these species on the pulp before they decompose.  By producing the active oxygen in the same  reactor where the brightening takes place, the active oxygen produced can be used immediately before it hydrolyses or decomposes. In the brightening process, it is imperative to maintain some residual active oxygen in the brightening liquor to prevent alkali darkening on the pulp. To prevent alkali darkening in the experiments, the active oxygen was produced for at least fifteen minutes before the pulp was introduced into the brightening liquor. The active oxygen also needs to be stabilized by the addition of additives and chelating agent, such as sodium silicate, magnesium sulfate and DTP A. Oloman et al. [33, 34] investigated the working conditions for the in-situ generation of active oxygen and brightening of mechanical pulp. In summer 1992, P. Kurniawan and J. Been [33, 34] were successful in bleaching chemical softwood pulp in-situ using this method, however, the result was not as satisfactory as the conventional chemical bleaching methods.  The high current density used in this  process actually destroyed the cellulose as well as  delignified the chemical pulp.  When used in preliminary experiments to brighten thermomechanical pulp in-situ, this process gave up to 12 points increase in brightness [33, 34]. conditions and result are shown in Figure 2.8.  29  The experimental  Chapter 2. Background Literature  The success in brightening the T M P pulp to a brightness gain of 12 %ISO at only 1% pulp consistency initiated further investigation into this process. There is a possibility that this brightening process might be able to compete with the conventional peroxide brightening process. process should be studied.  The role of different variables in the  Optimization of the process was desirable. The  performance of each process (the production of active oxygen and the brightening of TMP) was determined by the figures of merit. The Best Result from Experiments before 1994 Operating Conditions:  Chemicals:  Na C0 : 1.0 M; NaHC0 : 0.13 M; Na Si0 : 0.034 M; M g S 0 : 0.04 g ; DTPA: 0.6 g. Current: 7 Amperes; Voltage: 14 V pH: =10.7 Temperature: 60°C Cathode: Stainless steel rod (20 cm long, 2 mm diameter) Anode: Water cooled platinizedtitaniumU-tube. Anode area: 14.5 cm . Reaction time: 180 minutes. Total volume: 700 ml. Pulp: TMP (Original Brightness: 51 %ISO; Yellowness: 31 %). Pulp Consistency: 1%. 2  3  3  2  3  4  2  Result:  Maximum [H 0 ] : 0.027 M. Final Brightness: 63 %ISO (Brightness gain: 12 %ISO). Final Yellowness: 25 % (Yellowness gain: -6%). 2  Figure  2. 8  2  Experimental Condition  and  Result from  Experiment before  1994  2.7.1. Figures of Merit for the Production of Active Oxygen The performance of the production of active oxygen can be quantified by several figures of merit. These figures of merit are useful for determining the capital, operating and energy cost for the process. The net rate of production of hydrogen peroxide is the rate of peroxide generation from the primary anode reaction minus the rate of decomposition of hydrogen peroxide in the bulk solution for a batch reactor, by the secondary anode and by cathode reactions, as shown below : . k\H 0 ]  =  dt  2  2  -  rate of destruction of  H ^  at the anode and cathode  2-F-V  R  where: 30  {Eqn. 26}  Chapter 2. Background Literature  [H2O2]:  concentration of hydrogen peroxide (kmol/m )  t  time (seconds)  AA  anode area (m )  iA  current density at the anode (kA/m )  k  rate constant of the decomposition of H 2 O 2  <J)A  current efficiency of the primary anode reaction (%)  F  Faraday constant (96487 Coulombs/ kmol)  VR  volume of electrolyte in the reactor (m )  3  2  2  (s") 1  3  During steady state, the net rate of peroxide production is zero, hence the concentration of hydrogen peroxide becomes: [H O ]= 2-F-k-V A A 1 A  2  1  2  A  2  2 J  In order to maximize  D  -k  [H2O2],  rate of destruction of F ^ C ^  {Eqn. 27}  at the anode and cathode  the first term at the right hand side of Equation 26 has  to be maximized while the second term has to be minimized. The economic viability of the production of hydrogen peroxide by the electrooxidation of sodium carbonate can be estimated using the following figures of merit: i,,  Current Efficiency  n F R*  or  ITOT  'TOT  nF E cell  Specific Energy  SE =  Space Time Yield  STY: <t>-I "MW n•F•V  3600 <f> MW  (x 100 %)  {Eqn. 28}  (kWh/kg)  {Eqn. 29}  (kg i n Y )  {Eqn. 30}  1  D  D  where  Vc  'cell  {Eqn. 31}  - rj - E ohm A  n  stoichiometry number of moles of electron per mole of C2O6" produced  F  Faraday constant (96487 Coulomb/equivalent)  R*  production rate of desired product, H 2 O 2 (kmol/s)  ID  current density for the specific process (kA/m )  ID  current for the specific process (kA)  i-roT  total current density applied to the cell (kA/m )  E ell  cell voltage  C  2  2  2  (Volt)  Note: E  31  ce;;  is negative by Eqn. 29.  Chapter 2. Background Literature  M W : molecular weight of the product, E  o c  (gram/mol) or (kg/kmol)  H2O2  : open circuit potential (Volt)  Eohm  : ohmic voltage drop across the cell (Volt)  T|  : cathodic overpotential (Volt)  C  TJA  : anodic overpotential  (Volt)  VR  : volume of electrolyte in the reactor (m ) 3  For a constant current electrolysis, the current efficiency is ratio of the amount of charge used to manufacture the desired product compared to the total charge supplied [32]. It is desirable to achieve a current efficiency of 100%. The specific energy determines the amount of energy required to produce one kilogram of H C»2, 2  hence this figure of merit can estimate the energy cost for the process. Finally, the space time yield expresses the mass of H 2 O 2 produced per unit time which can be obtained in a unit reactor volume. Ideally, this process should be operated at high current density with high current efficiency, low specific energy and high space time yield. 2.7.2. Figures of Merit for the Brightening of TMP The performance of the brightening of TMP can be expressed using several figures of merit that are similar to the ones for the production of H 2 O 2 , but because of the different nature of reactions involved, the figures of merit are defined differently. The figures of merit for the brightening process are as follows: \E \-1 • time u  Specific Energy  SE =  (kWh/tonne)  Space Time Yield  STY = f P P— (tonne m" s" ) Reactor volume x time  !  tonne of pulp T o n n e s o  ul  3  1  {Eqn. 32} {Eqn. 33}  An ideal brightening process should also have a low specific energy and high space time yield.  32  Chapter 2. Background Literature  2.8. Objective of this Project The objective of this project is to investigate the conditions for the electrochemical brightening of thermomechanical pulp using sodium carbonate as the raw material to produce active oxygen. Several variables (such as the temperature, current density, current concentration, electrode design and brightening time) will be examined to determine their role on the active oxygen production and the brightening process.  Optimization experiments will be performed using the sequential simplex  optimization method to find how much brightness increase can be obtained with this process.  The commercial viability of the process will also be studied.  From the  investigation, hopefully the electro-brightening mechanism can be explained and a new and effective reactor design can be proposed.  33  Chapter 3 EXPERIMENTAL APPARATUS AND PROCEDURE The experiments performed in this study consist of electrochemical brightening of thermomechanical pulp (TMP) at different temperatures, current densities, pH and electrode configurations. Some of the experiments were performed without the use of pulp, and in several cases, a saturated calomel electrode was used as a reference electrode for the anode potential. 3.1. Chemicals and Pulp A l l or some of the following chemicals were used in the experiments without further purification: - sodium carbonate (Na2COs), certified grade, from Fisher Scientific, - sodium bicarbonate (NaHCOs), certified grade, from Fisher Scientific, - sodium silicate (Na2Si03.5H20), technical grade, from Fisher Scientific, - magnesium sulfate (MgS0 .7H 0), certified grade, from Fisher Scientific, 4  2  - hydrogen peroxide (H2O2), 30% in water, from Fisher Scientific, - sodium hydroxide (NaOFT), certified grade, from Fisher Scientific, - sulfuric acid (H2SO4), reagent grade, 96%, from Fisher Scientific, - diethylenetriaminepentaacetic acid (DTPA), as sodium salt, 40% in water, from Acros Organics, - potassium permanganate (KMnC^), 1 N , from Fisher Scientific. -  1,10 phenantroline (ferrous sulfate or ferroin indicator), 0.025 M solution.  The water for each experiment was distilled water and was used without further distillation. The T M P that was used consists of approximately 55% SPF (spruce, pine and fir) and 45% hembal (hemlock and balsam). The pulp had been treated in the mill with 2 kg/tonne of DTP A. The pulp used in Run P - l to P-29A was further treated in the lab with approximately 0.4% DTP A at 70°C for V2 hour at 2 - 3% consistency. It  34  Chapter 3. Experimental  was then reconcentrated in the centrifuge to approximately 20 - 28%, bagged and frozen. 3.2. Experimental Apparatus A l l of the experiments were carried out in a 1000 ml Pyrex beaker, except for the experiments involving the use of a hollow plate electrode where a 2000 ml Pyrex beaker was used. Different types of anode were used, some of which required water cooling. The water for cooling the anode was recirculated in a refrigerated cooling bath "Endocal" model RTE-9 by Naslab. The power source for electrolysis was a DC power supply capable of producing a maximum of 25 Amperes of current. Measurements of pH and temperature of the system were carried out using a digital bench-top p H meter and temperature by Cole-Parmer model 05669-20. Stirring of the pulp suspension or brightening solution was done with a Teflon coated stirrer powered by a 40-Watt electric motor. Several electrode configurations were used in the experiments, but usually the material for the cathode was tungsten and for the anode was platinized titanium. In some experiments, a glassy carbon plate was used as the anode. In most experiments, the cathode was a 4 mm diameter tungsten rod with a length of 15 cm, and the anode was a 6-mm diameter platinized titanium tube shaped like a " U " with water flowing in and out of the tube to cool the anode. The purpose of cooling the anode is to decrease the exchange current density for oxygen evolution (i.e., to increase oxygen overpotential). The distance between the anode and cathode and the design of the electrodes are very important in reducing the energy cost for this process.  A small distance  would reduce the resistance between the electrodes while a good design of electrodes could improve the current distribution on the electrode surface.  The sketches of  different anodes and electrode configurations are shown in Figure 3.1 and Figure 3.2. The different electrode configurations were used in different experiments that study the effects of electrode configuration on the brightening reaction or the production of active oxygen.  35  Chapter 3. Experimental  Cooling Watet Out  4 mm  Cooling Water In  1  y  Titanium tube  2 cm 1 cmi i i  i i I  2 cm J  Solid Fiberglass_ Clamp  Insulator  -Stainless Steel Bolt  11 cm  insulator  Glassy Carbon  Tungsten Cathode  Platinized Titanium Anode  Anode Area: 29 cm 2  R2.2 cm  Glassy Carbon Anode (2 m m thickness) Modified Electrode Design  F i g u r e 3.1  C o m b i n a t i o n o f U - A n o d e a n d T u n g s t e n C a t h o d e c o n f i g u r a t i o n (Left) a n d Glassy Carbon Anode  36  (Right)  Chapter 3. Experimental  Cooling \ waten lnlet/\ Outlet  /Hollow insulated titanium box  'Thin Tungsten Cathode  5.8 cm  /Platinized Titanium Anode (Plate) Anode Area: 43.5 cm  2  A  Thin Tungsten cathode  ^Platinized Titanium Anode F i g u r e 3. 2  Hollow Plate Electrode Configuration  To prevent unwanted reactions from happening on the surface of the anode, the area other than the desired platinized surface area was insulated.  Three types of  insulator were used, namely silicone glue, white Teflon tape, and molding PVC tube. In most experiments, the insulator was silicone glue, but after a while, there were noticable black pits around the platinized surface that were covered by the silicone glue. There was a possibility that some corrosion occurred due to an electrochemical reaction between the silicone glue and the platinized surface or between the silicone glue and exposed titanium surface that were not completely platinized. The corrosion could have been triggered by the high current density near the insulated area. Therefore, the Teflon tape was used as the alternative insulator. The Teflon tape was removed after every experiment, and a new layer of insulator was used at the  37  Chapter 3. Experimental  beginning of each experiment.  The molding tube was used to insulate the un-  platinized titanium surface to prevent electrochemical reaction on the titanium surface when it was immersed into the electrolyte. Throughout this project, four electrode configurations were used, namely Design A, B , C and D. The sketch of these configuration is shown in Figure 3.3. A l l configurations use a thin (4 mm diameter) tungsten rod as the cathode. The reason for using a thin rod is to reduce the mass transfer of hydrogen peroxide (active oxygen) to the cathode. Design A and B both have a U-tube platinized titanium anode.  The  difference between design A and B is that design B allows a better current distribution around the anode area than design A. Design B also reduces the resistance due to distance between the electrodes. In Design C, a glassy carbon plate was used as the anode. This material was used because it was claimed to be a cheaper alternative to platinum. The electrode of Design D (Figure 3.2) is a hollow titanium plate where the anode is the platinized area and the cathode consists of very thin (0.5 mm diameter) tungsten rods spaced equally across the platinized area, located at a very small distance (< 0.5 mm) from the surface. The purpose of this design is to improve the current distribution across the anode area and to reduce losses due to the distance between the electrodes.  o b Design A  Design B  o o Design C  Design D F i g u r e 3.  3  Different Electrode  38  Configurations  Chapter 3. Experimental  3.3. Experimental Procedures The experimental procedure for the electrochemical brightening o f T M P using sodium carbonate can be divided into: (i). the electrochemical production o f active oxygen, (ii). the in-situ brightening o f T M P , (iii). the measurement o f active oxygen concentration using the permanganometric method and (iv). the post-treatment o f pulp and the electrode. The procedure for measuring the polarization curve o f the electrooxidation o f carbonate is also presented.  3.3.1. Electrochemical Production of Active Oxygen The required amount o f chemical species, such as Na2C03, N a H C 0 3 , Na2Si03, MgS04  7H2O, and D T P A , was put into a 1 liter glass beaker and dissolved using  distilled water, making up a total volume o f 700 ml. The reactor (glass beaker) was then immersed partly in a water bath whose temperature was set to the required value. Before immersing the anode into the electrolyte, the area o f the anode other than the desired surface area was insulated. The electrodes and the stirrer are then immersed into the electrolyte. It was necessary that all exposed platinized anode area was completely immersed and only about 2 cm o f the cathode was immersed in the electrolyte to maximize the utilization o f the anode surface for the desired reaction and at the same time to minimize the destruction o f active oxygen on the cathode.  The anode was connected to a  recirculating cold water bath by plastic tubes. When all the equipment was in place, the electrodes were connected to the power supply (see Figure 3.4 and 3.5). The electrochemical production o f active oxygen was started when the temperature o f water bath B was about 3 to 5°C higher than the desired brightening temperature.  The cooling water circulation (from bath C ) was turned on. The power  supply was turned on to the desired current immediately following the circulation o f the cooling water. The flowrate o f the cooling water was adjusted manually until the desired brightening temperature was reached.  The temperature o f the cooling water  bath C was maintained at 4°C. Throughout the reaction time, several 5 ml samples o f solution were taken to be tested for the content o f hydrogen peroxide. The reported hydrogen peroxide concentration corresponds to the concentration accumulated from  39  Chapter 3. Experimental  time 0 to the time of sampling. At the end of reaction time, the power supply was turned off and the equipment was disassembled and cleaned for the next experiment.  Legends : A . Electrolyte or pulp suspension. B. Water Bath to control reaction temperature C . C o o l i n g water bath to supplysooling water for the a n o d e .  F i g u r e 3. 4.  Reactor and  Legends : A. Electrolyte or pulp suspension. B. Water Bath to control reaction temperature C. Cooling water bath to supplycooling water for the anode.  Figure 3.5  Reactor and  D. P l a s t i c t u b i n g E . 1. A n o d e : P l a t i n i z e d T i t a n i u r E . 2. C a t h o d e : T u n g s t e n R o d F. P l a s t i c Stirrer a n d m o t o r G. Power Supply  E q u i p m e n t Setup for Electrode Design  A  D. Plastic tubing E. Modified electrode design: Anode: Platinized Titanium Cathode: Tungsten Rod F. Plastic Stirrer and motor G. Power Supply  E q u i p m e n t S e t u p for Electrode D e s i g n  40  B  Chapter 3. Experimental  3.3.2. In-Situ Brightening of Mechanical Pulp The preparation for the in-situ brightening of mechanical pulp is essentially the same as the electrochemical production of active oxygen. Since the alkali darkening is a fast reaction, it is necessary to have some active oxygen in the brightening liquor before the introduction of pulp to the system. Usually, active oxygen was produced for about 15 to 30 minutes before the pulp was put into the solution. If the active oxygen concentration before the introduction of pulp is high, it would be easier for the pulp to attain a high brightness gain. The total brightening time was measured from the time the power supply was turned on until the time the power supply was turned off. The involvement of pulp in the system requires good mixing to ensure a thorough mixing of the chemicals and the pulp. With the constraint of stirrer size, and reactor (beaker) size, the best pulp consistency for most of the experiments was from 1 to 1.5%.  A higher consistency would create some unmixed volume in the pulp  suspension and might cause a fire hazard near the cathode due to a high temperature and high concentration of hydrogen gas in that area. When the brightening reaction was over, the pulp suspension was washed with approximately 300 ml 4 N sulfuric acid in a 4-liter glass beaker. After all the pulp suspension was poured into the sulfuric acid solution, the suspension was stirred with a glass stirrer and the pH was adjusted to the acidic range by adding sulfuric acid. The reason for this washing and pH adjustment is to prevent alkali darkening of the pulp. The acidic pulp suspension was then poured into a handsheet maker machine. Again, the p H of the suspension was measured and adjusted to about pH 6 to 7 (by the addition of sulfuric acid). Then the solution was drained from the pulp suspension, leaving just the pulp in the form of a circular handsheet. This handsheet was removed and dried in the constant humidity room (23°C and 50% relative humidity) for at least 24 hours. The electrodes were treated according to the procedure in section 3.3.3 and the other equipment was cleaned and dried for the next experiment.  41  Chapter 3. Experimental  3.3.3. Post Treatment of Electrodes After Electrochemical Run At the end of the experiment, electrodes were cleaned and treated depending on the type of the electrodes. After washing the anode, all insulator was removed from the anode. For the glassy carbon plate anode, there was no need to treat the anode with chemicals. It was just washed, dried and stored for the next experiment. The platinized titanium anode, on the other hand, needed soaking in warm NaOH solution for 2 or more hours. After the soaking, the electrodes were treated using reverse polarization in Na2CC>3 solution, where the tungsten became an anode and the platinized titanium became a cathode. This process was aimed at removing chemical buildup due to the oxidation on the platinized titanium that could not be removed by soaking in the N a O H solution. The reverse polarization procedure is done as follows. The electrolyte used for this process was approximately 1 M of Na2C03. This electrolyte was a reasonable choice because it was the base solution for all the electrochemical runs, hence there was hardly any possibility that some unwanted or unknown chemical could be formed on the electrode surface. Firstly, the tungsten rod was connected to the positive side of the power supply and the platinized titanium to the negative side. The power supply was turned on to give a current of approximately 25 amperes (the maximum current output on the power supply) for about 3 to 5 seconds. Then the current was turned off and the polarity of each electrode was reversed (tungsten became negative and platinized titanium became positive). The current was then increased to the maximum value for another 3 to 5 seconds.  Finally, the polarity was reversed again and  maximum current was supplied for 3 to 5 seconds. At this point, the surface of the tungsten would look shiny and the platinized titanium was clean and silvery white. The electrodes can then be washed with distilled water, dried and stored for the next experiment. Without the treatment with warm NaOH and reverse polarization, the performance of the anode decreased significantly as can be seen in the next chapter, giving unrepeatable results.  The presence of Si03 " in the brightening suspension 2  might have caused some of the Si03 ~ to react on the anode, which had a pH less than 2  10, according to the following reaction:  42  Chapter 3. Experimental  Si0 " + 2H -> Si0 4 + H 0 2  +  3  2  2  The solid silicon dioxide (Si0 ) would dissolve in warm NaOH solution as follows: 2  2NaOH + Si0 -» Na Si0 + H 0 2  2  3  2  The NaOH treatment and reverse polarization, however, did not completely stop the deterioration of the anode; it only slowed the process. The anode used in this project had been damaged before the reverse-polarization treatment was performed on it. The damage caused some pits on the anode surface, and even after the surface was replated, the pits were not covered completely.  Therefore, the anode continued to  deteriorate even after reverse polarization treatment. If this treatment was performed on a brand new anode, the anode might have a long lifetime and its performance might be more consistent. 3.3.4. Polarization Curve for the Electro-oxidation of Sodium Carbonate The purpose of measuring the i-E (Current density-Potential or polarization) curve of the electro-oxidation of sodium carbonate is to investigate the optimum condition or the condition for the highest current efficiency for the production of active oxygen. For this measurement, a reference electrode is needed. The equipment was set up according to Figure 3.6. After the equipment was set up, the power supply was set up in such a way that it became current controlled, i.e., by turning the voltage control knob to the maximum value and the current knob to zero. The power supply was then turned on and the current was increased from 0 to about 11 Amperes and the anode potential at each current was recorded. The voltage and current values were plotted on a polarization (i-E) curve. From the polarization curve, one should be able to determine the approximate range of operating current density which favors the desired reaction. Using these operating current densities, one can perform several experiments to measure the current efficiency of each condition.  43  Chapter 3. Experimental  6  6 A  Legends : A.  Voltmeter  B.  Reference  E . electrode  (Saturated Calomel  Electrode)  C.  Platinized Titanium  A n o d e  D.  T u n g s t e n  Figure  3.  6  Plastic  stirrer  F.  A m p e r e m e t e r  G -  P o w e r  S u p p l y  A n o d e  E q u i p m e n t S e t u p for the  M e a s u r e m e n t of Polarization  Curve  The current efficiency measurement was performed by electrochemically producing active oxygen for 30 minutes at a range current densities. A 30-minute time was chosen was because it was the amount of time needed to produce a reasonable amount of active oxygen (about 0.03 M ) to begin the pulp brightening process. At times longer than 30 minutes, there could still be about 0.01 M increase in the concentration of residual active oxygen, but it also meant less time for the actual brightening process since the total brightening time includes the time to produce active oxygen without the presence of pulp. The amount of residual active oxygen at 30 minutes was measured and the result was used to determine the current efficiency for that particular current density. A graph of current efficiency versus current density was plotted. From this graph, one can determine the best operating current density which would give the highest current efficiency for active oxygen (not necessarily the best brightening current density).  44  Chapter 3. Experimental  3.4. Experimental Strategy This thesis project began with a full 2 factorial design where the variables 3  were reaction temperature, current and anode area.  Investigation on these three  variables would show the effects of reaction temperature, current density and current concentration on the brightening of mechanical pulp using sodium carbonate. However, several problems related to the physical condition of the anode caused inconsistency and irreproducibility of some results, thus prompted a change of investigative strategy for this project. The next part of the thesis project consists of a more fundamental investigation of the electrochemical system.  Some experiments were performed to find the  optimum working current density which included the measurement of the current efficiency of the electrochemical production of active oxygen in sodium carbonate solution. During these experiments, many post-experiment treatments were performed on the platinized titanium anode in order to maintain a consistent and reproducible experimental condition throughout all experiments. When the best anode treatment was found, several brightening experiments were performed to measure the effect of different anodes and electrode designs. Problems encountered with the U-tube platinized titanium anode also started some investigation on the effect of different anode material and different electrode configurations. Glassy carbon plate was used as an alternative anode material and a hollow plate electrode design (Design D in Figure 3.3 and Figure 3.2) was tested and compared with the hollow U-tube configuration (see Design B in Figure 3.3). After determining the best way to clean the electrodes after every use, optimization experiments were attempted using Design B. The Simplex optimization software was used to design the experiments. This method was chosen because it was a faster method to find the optimum condition without doing as many experiments as the factorial design.  The software designed experiments using information from  previous experiments, hence it could eliminate some runs that would obviously give a weak response. If a factorial design was used to approach the optimum, a fixed set of experiments had to be performed before a conclusion could be made, and this procedure would consume a lot of time i f a lot of variables (more than 4) were  45  Chapter 3. Experimental  involved. For the Simplex method, four factors, i.e., current, anode area, temperature and pH, were varied to achieve an optimum condition for generating active oxygen and brightening mechanical pulp. The responses measured were pulp brightness and yellowness gain. The final part of the thesis project was to investigate why the results from the Simplex method differed little from each other (i.e., the brightness gain for each experiment was about the same). The expectation from a Simplex method is that the results should get better as more experiments were performed. indication was not observed even after five runs.  However, this  Therefore, several brightening  experiments using hydrogen peroxide were performed to see if this inability to achieve higher brightness gain was because a maximum brightness gain for one 3-hour stage brightening had been reached. To see if a higher brightness gain could be reached, two stage brightening and six hour brightening runs were also performed. Cooling water temperature, pulp yield and the L*, a*, b* measurements were recorded. These variables are not discussed in this thesis because the data were not complete. The cooling water for the first 34 experiments (P-l to P-34) came from the tap water with an average temperature of around 10°C. Starting from experiment P35, the cooling water came from an ice bath and its temperature was maintained around 4°C.  The flowrate of the cooling water which varied with each experiment,  was not recorded.  This variable might be affecting the brightening results.  The  average pulp yield for the electro-brightening of TMP using sodium carbonate was approximately 95%. L * , a* and b* values were recorded along with the brightness and yellowness measurements, however, the changes in L * and b* was similar to the change in brightness and yellowness, hence discussion of L * and b* results were omitted from this thesis.  46  Chapter 4 RESULTS AND DISCUSSION The experimental strategy described in section 3.4 suggests a set of chronological experiments based on "trial and error" investigation strategy. In this chapter, however, the results will not be presented chronologically. Instead, they will be divided into three main sections, namely: the electrochemical production of active oxygen (without the presence of pulp), factors  affecting the electrochemical  brightening of mechanical pulp, and finally, the optimization of the electrochemical brightening method.  To preserve the chronological part of the experiments, all  brightening results shown in the tables in Chapter 4 will have a true experiment number (shown as "P-number"), and all non-pulp runs will be shown as "NP-number". 4.1. Electrochemical Production of Percarbonate and/or Hydrogen Peroxide In this section, the optimum operating current density for the highest current efficiency for the production of active oxygen was investigated. Polarization curves (current density versus potential plots) for the electro-oxidation of sodium carbonate were generated to find the range of current density which would produce percarbonate at 46°C and 56°C . From this range of current density, a curve of current efficiency versus current density was produced. Since most of the brightening experiments were performed at certain current densities (such as 0.35 and 0.17 A/cm ), 2  the current  efficiency was measured against time at those current densities. Finally, a comparison of the concentration of residual active oxygen between a brightening run and a no-pulp run is also presented in this section. 4.1.1. Polarization Curves for the Electro-oxidation of Sodium Carbonate The purpose for obtaining the polarization curve for the electro-oxidation of carbonate to percarbonate is to determine the mass transport limiting current density for this reaction. From this information, a "reasonable" working current density could be found. The polarization (i-E) curves for the electro-oxidation of sodium carbonate (Eqn. 26) on a water-cooled, platinized titanium U-tube anode with bulk electrolyte at 46 and 56 °C were generated and are shown in Figure 4.1.  47  Chapter 4. Results and Discussion  Polarization Curves of the Electro-oxidation of Sodium Carbonate at Different Temperatures 0.6 T—  0  1  2  3  4  5  6  Anode Potential (VvsSHE)  Figure 4.1. Experimental 0.6  g; M g S 0  Platinized  Polarization  C u r v e s for the  conditions: N a 4  . 7 H  2  0  = 0.04  g.  Titanium U-tube;  2  C 0  3  = 1.0  Electro-oxidation  M ; N a H C 0  = 0.13  3  Anode: Water-cooled Cathode: Calomel  Tungsten Electrode  of S o d i u m  M ; Na Si0 2  Carbonate  = 0.034 M ; D T P A  3  =  (cooling water temperature ~ 4°C)  rod; Reference electrode:  Saturated  (SCE).  The estimated limiting current density for the primary reaction can be calculated using Eqn. 15: i =nFk c L  m  {Eqn. 15}  0  where: n = 2, F = 96500 Coulomb mol" , k 1  « 1.0 x 10" m s" , and c = 1 M of 5  m  1  0  Na2CC>3. Using the above information, the estimated limiting current density for the primary reaction is 1.9 kA/m or 0.19 A/cm . 2  2  From Figure 4.1, there is no clear  indication about this limiting current density. The polarization curves look like a pure activation control curve. The reason for the difficulty to determine the limiting current density for the primary reaction is that there is interference from side reactions and gas evolution in the polarization curve. The method used to measure the polarization curve in this project was a crude method without taking into account the effect of current distribution, electrode material, temperature, pH and side reactions. The interfering  48  Chapter 4. Results and Discussion  reactions had to be isolated by performing polarization curves on the interfering reactions alone and the results be compared with the polarization curves from the electro-oxidation of carbonate.  A more detailed investigation was performed by  Zhang et al. [43] who examined the kinetics of electro-oxidation of carbonate on platinum in aqueous solution using a rotating ring (platinum) - disk (platinum) electrode at 24°C and pH 10.75. The polarization curve plotted in Figure 4.1 did not give useful information regarding the kinetics of the electro-oxidation of carbonate on platinized titanium anode in aqueous solution due to the crudeness of the measurement  method.  However, an estimated mass transfer limiting current density of 0.19 A/cm will be 2  used as a basis to set a range for measuring the average current efficiency of the electro-oxidation of carbonate over 30 minutes of reaction time.  4.1.2. Current Efficiency at Different Current Densities Using 0.19 A/cm as a basis, the measurement of the average current efficiency 2  was performed on a range of current density from 0.04 to 0.25 A/cm , the production 2  of active oxygen was performed for 30 minutes and the concentration of active oxygen (as hydrogen peroxide) was measured at the end of the 30 minutes.  The average  current efficiency for each 30-minute run was calculated and plotted against the respective current  density (see  Figure 4.2). The plot of hydrogen peroxide  concentration and current efficiency versus anode potential is also shown in Figure 4.2. Figure 4.2 shows that the highest average current efficiency (41%), with 0.022 M H2O2, was achieved at an anode potential of 3.2 V vs SHE and a current density of 0.14 A/cm . Even though the concentration of active oxygen produced at the higher 2  anode potential was higher, the current efficiency was decreasing.  This means  operating the process at a high anode potential (higher than 3.2 V vs SHE) might not be economical because of the low current efficiency.  49  Chapter 4. Results and Discussion  Current Density (A/cm ) 0.05  0.10  _J  45  0.15  I  0.25  0.20  I  L_  0.035  40  0.03  35 +  0.025  30 0.02  20  H  +  a  0.015  1 c  15  0.01  10 0.005  5  0 2.5  3  3.5  4.5  Anode Potential (V vs SHE) F i g u r e 4. 2  Average Current Efficiency  and  Density Data source was Anode: 1.0  f r o m T a b l e 4.1.  Water-cooled Platinized M ; [NaHC0 ]= 3  0.13  [HfeOJ v e r s u s A n o d e  Experiment  time for e a c h point was  Titanium U-tube, Cathode:  30  minutes.  Tungsten rod.  [Na C0 ]  M ; [ N a S i 0 ] = 0 . 0 3 4 M ; [ D T P A ] = 0.6 2  P o t e n t i a l or. C u r r e n t  a t 4 6 ° C  3  2  g; [ M g S 0 ] = 0.04 4  3  =  g.  To investigate the production of active oxygen at an anode potential which gave 41% average current efficiency after thirty minutes, a plot of average current efficiency and [H2O2] versus time at the anode potential of 3.2 V vs SHE was produced (see Figure 4.3).  This plot is useful in observing the active oxygen  concentration profile throughout the electro-oxidation time. Figure 4.3 shows that at thirty minutes, the average current efficiency of the production of active oxygen was approximately 25%, instead of the expected 41%. Such a big difference in current efficiency could be the result of anode deterioration. At the end of an electrochemical run, usually the anode was washed with distilled water until no trace of carbonate could be seen on the platinized surface. Apparently, this kind of post treatment was not adequate and the deterioration of anode had begun, proven by the decrease in current efficiency. A routine anodic post treatment, which consisted of soaking the anode in warm NaOH solution for at least 2 hours, followed by the reverse polarization of the anode and cathode in Na2C03 solution, was initiated after some yellowish color and small black pits were visible on the platinized titanium surface. When the polarization curve and current density experiments reported above  50  Chapter 4. Results and Discussion  were performed (the results were shown in Figures 4.1 to 4.3), the damage on the platinized titanium was not yet visible to naked eyes.  Current Efficiency and [ H 0 ] versus Time 2  o -|  ,  0  50  ,  ,  100  150  2  |_ o  , 200  250  Time (minutes) Figure  3.2  V vs  Experimental Conditions: N a 0.6  g;  [H2O2]  4. 3 P l o t o f A v e r a g e C u r r e n t E f f i c i e n c y a n d  M g S 0  4  . 7 H  2  0  = 0.04  g.  2  C 0  S H E and 3  = 1.0  M; N a H C 0  p H « 10.4.  vs  Temperature of  Anode:  3  = 0.13  Time for A n o d e  Potential  of  46°C M; N a S i 0 2  3  = 0.034 M ; D T P A  Water-cooled Platinized Titanium  t u b e ; C a t h o d e : T u n g s t e n rod; Total v o l u m e : 700  =  U-  ml.  4.1.3. Comparison of Active Oxygen Concentration Between In-Situ Brightening Run and No-Pulp Run During the electro-brightening of mechanical pulp using the active oxygen generated in-situ, the concentration of active oxygen was different from that measured with no pulp present in the solution. The difference can be seen in Figure 4.4 which shows two sets of brightening runs (P-50 and P-51) performed at 47°C with a current density of 0.33 ± 0.08 Amp/cm . 2  Each brightening run was compared with the  corresponding no-pulp run (for example: P-50 was compared with NP-50). Figure 4.4 shows that the concentration of active oxygen in the brightening runs (P-50 and P-51) was higher than that in the corresponding no-pulp runs (NP-50 and NP-51). One would expect that when the pulp was present, the concentration of active oxygen would be reduced by the brightening action. However, this is not the case with the electrochemical brightening runs in this thesis. This difference may be due to: (a), reaction of the permanganate titre with trace organics or pulp fibers in the 51  Chapter 4. Results and Discussion  filtered liquor sample from the brightening runs, and/or (b). stabilization of the active oxygen by the pulp through the mechanism suggested by Liden and Ohman [45] in the conventional peroxide brightening. In this mechanism, the presence of pulp and excess magnesium precipitates stabilizes the redox cycle of iron and manganese.  Comparison of [H 0 ] Between Brightening Runs and No-Pulp Runs 2  0.060  2  -i  o . o o o -I  1  0  1  20  40  ,  ,  ,  ,  ,  ,  60  80  100  120  140  160  —j 180  T im e (m inutes)  F i g u r e 4. 4  Concentration  of Active O x y g e n  During Brightening  Runs and  No-Pulp  Runs Experimental Conditions: 0.6  g;  M g S 0  4  . 7 H  tube; Cathode: Temperature:  2  0  =  0.04  Tungsten  47.2°C.  N a g.  C 0  3  = 1.0  p H «  M; N a H C 0  10.7.  3  Anode:  rod; Total volume:  700  = 0.13  M ; Na Si0  current was  2  Water-cooled  3  = 0.034 M ; D T P A  Platinized  m l ; C u r r e n t d e n s i t y : 0.33  N o t e : In a l l t h o s e f o u r r u n s , t h e r e w a s  t h e first 15 m i n u t e s after the  4.1.4.  2  no  pulp  Titanium ± 0.08  in the  = U -  A/cm ;  solution  2  for  supplied.  The Effect of Sodium Carbonate on the Decomposition of Hydrogen Peroxide In the next sections, most experimental results show that the electrochemical  sodium carbonate system could not brighten the pulp to the same extent as the conventional hydrogen peroxide brightening system. The pulp could be brightened electrochemically to more than 12 points brightness gain in 1% pulp consistency, but the yellowness of the pulp did not decrease significantly.  In other words, the  brightened pulp would look bright yellow, whereas the pulp brightened with hydrogen peroxide would have low yellowness.  52  Chapter 4. Results and Discussion  Throughout the electro-brightening experiments, it was found that the brightening reaction was most effective when the initial concentration of active oxygen at the time of pulp addition, was high (usually higher than 0.020 M for a 10point brightness gain).  Several attempts to produce a high initial concentration of  active oxygen were successful (as will be explained in section 4.2.4), however, the resulting brightness gain was not satisfactory. Therefore, it was necessary to look into the chemicals in the brightening solution and how they affected the active oxygen. Since there were no "true" percarbonates available in the market and the electrochemically generated active oxygen would eventually become hydrogen peroxide, the investigation used hydrogen peroxide to represent the active oxygen. The effect of carbonate on H2O2 is shown in Figure 4.5. Figure 4.5 shows that the presence of carbonate in the solution (in the form of Na C0 and NaHC0 ) decomposed H 0 quite quickly (between 20 to 35% loss in the 2  3  3  first 15 minutes).  2  2  This means that the active oxygen which was produced  electrochemically, could have been decomposed immediately by the carbonate in the brightening solution. In order to increase the amount of residual active oxygen, it is necessary to find a method that would produce active oxygen at a rate higher than the decomposition rate by carbonate and/or to stabilize the active oxygen in carbonate solution. Effect of Sodium Carbonate on Hydrogen Peroxide 0.045 T  0  -|  ,  ,  ,  ,  1  0  50  100  150  200  250  Time (minutes) F i g u r e 4. 5  Effect of Carbonate on  Note: T h e presence of carbonate minutes,  H y d r o g e n Peroxide (from NX-1, NX-5 a n d  c a u s e d a 36%  H  2  0  2  while the a b s e n c e of carbonate  53  decomposition preserved  H  2  0  NX-6)  in t h e first 2  .  15  Chapter 4. Results and Discussion  4.2. Factors Affecting the Electrochemical Brightening of Mechanical Pulp The in-situ electrochemical brightening of mechanical pulp is never used in the pulp and paper industry, however, it is a method worth looking into in this age where environmental safety is an important concern. The simplest approach in the investigation was to assume that the brightening process was similar to hydrogen peroxide brightening process. This assumption was chosen because the resulting brightening chemical from the electro-oxidation of sodium carbonate would eventually decompose into hydrogen peroxide. It is therefore reasonable to begin the investigation of the factors affecting the in-situ electrobrightening process by looking into the factors that affect a hydrogen peroxide brightening process, such as the temperature, consistency, pH, time and additives. In this thesis project, the effect of pH and additives were not investigated in order to reduce the number of variables. The pH was maintained to be between 10.2 to 10.7 (a good pH range for alkaline brightening). This was easily done because there was a constant supply of brightening chemical throughout the electro-brightening process (a feature that the ordinary peroxide brightening does not possess) and there was a buffer (sodium bicarbonate) in the brightening suspension. To control the effect of the additives, a large amount of additives was used to help preserve hydrogen peroxide. The effect of temperature was investigated along with current density and current concentration because these two latter effects dictate the specific energy and the space time yield of the electrochemical process.  A full 2 factorial design was 3  performed with temperature, current and anode area as the factors.  The main and  interaction effects of these three factors were analyzed. Other factors examined were the effect of different electrode materials, different electrode configurations, and the effect of post treatment of the anode. The effect of brightening time and two-stage brightening on brightness gain were also investigated.  Finally, the electro-brightening runs were compared to conventional  peroxide brightening runs to find similarities and differences between the two brightening methods.  54  Chapter 4. Results and Discussion  4.2.1. A 2 Factorial Design Analysis (Effect of Temperature, Current Density and Current Concentration) 3  The objective of this investigation was to determine the main and interaction effects of three process variables, i.e., temperature, current and anode area (or temperature, current concentration and current density). The pH, brightening time and consistency was held constant at 10.8, 3 hours and 1% respectively. The responses measured were the concentration of active oxygen at 30 minutes after the current was started, the brightness gain and the yellowness gain*. Centerpoint replication was performed three times to provide a variance and an overall curvature effect estimate. The levels of the variables are shown in Table 4.1. A total of eleven runs were performed randomly, eight of which were the factorial runs and three were centerpoint replications (see Table 4.2). Some of the runs were replicated two or three times to estimate the experimental error for each response. Table 4.1  Variables  and  T h e i r L e v e l s in the  Variables  2  3  Low(-)  Factorial  Design Analysis  Level High (+)  I  I Centerpoint (O)  Temperature (°C)  {T}  46  66  56  Current (Ampere)  {I}  5  10  7.5  Anode Area (cm )  {A}  15  29  22  2  T a b l e 4. 2  Run  The  D e s i g n of Full 2  Reference Run  3  Factorial  Runs  Temperature  Current  1  P-4;P-18  +  2  P-5;P-21  +  3  P-6;P-22  4  P-7; P-12; P-14  5  P-8;P-15  +  6  P - l l ; P-20; P-23  O  7  P-16  8  P-17  -  -  9  P-19  +  +  Anode Area  Replication (r) 2  -  +  2  +  2  +  +  3  +  +  2  O  O  3 1  +  -  A negative value in yellowness gain means a decrease in yellowness, which is a desirable effect sought for in the brightening of mechanical pulp. 55  1 1  Chapter 4. Results and Discussion  A summary of the average response from each run is shown in Table 4.3 and the cube plots of each response as a function of temperature, current and anode area (without the centerpoints) are shown in Figure 4.6. From the replicated runs, the response error (standard deviation) for [H2O2] was SH = ± 0.004 M, for brightness gain was SAB = ± 1.4 %ISO and for yellowness gain was SAY = + 2 % (see calculation in Appendix II). Figure 4.6 shows that there were some anomalies in the factorial design results. On all three cube plots, the responses for a high temperature, high current and low anode area run were different from the average of the seven other responses on each cube by more than 65%.  This is evidence that there was a problem in with the  equipment (anode deterioration). The anomaly in Figure 4.6 is emphasized in Table 4.3 where the 95% confidence intervals of each response was more than 30% of the average value. The high confidence interval values for all these effects showed a strong possibility of experimental errors due to anode deterioration. A quantitative analysis of the factorial design can be done by calculating the main and interaction effects of all the factors. The main and interaction effects for the factorial design are presented in Table 4.4. The significance of the effects depends on the 95% confidence interval of the effects as calculated in Appendix II. If the absolute value of the effect is smaller than the 95% confidence interval, it can be concluded that the effect has no significance on the response. Table 4.4 shows that anode area has a significant effect on brightness gain and yellowness gain. Table 4.4 shows that temperature has a negative effect on brightness gain, whereas in the conventional brightening practice, brightening process is promoted by high temperature. This contradiction happens because of the anomalous run (Run 9) in the factorial design. In Figure 4.6 the brightness gain for run 9 (high temperature, high current and low anode area) is 2.0 %ISO, whereas the brightness gains for other runs range from 8.0 to 11 %ISO.  This low value from run 9 must have distorted the  main effect calculation, giving a negative effect of temperature on brightness gain and a high 95% confidence level. The calculation of the curvature effect (see Appendix II) also show that the curvature effects were not significant at 95% confidence level.  56  Chapter 4. Results and Discussion  0.010  0.012  T E M P  0.012 0.005  + AREA  0.015  0.016  CURRENT +  0.011  0.016  9.5  11 8.5  +4  2.0  Yellowness Gain  Brightness Gain 9.5 10  8.0 F i g u r e 4. 6 T a b l e 4. 3  Run  T  Summary  I  Cube  Z  r  -5  -3  Plots for the R e s p o n s e s  of Responses  A  10  of a Full 2  from the Factorial  Factorial  Design  Design  [H 0 ]  Brightness Gain  Yellowness Gain  (M)  (%ISO)  (%)  2  2  1  +  -  -  2  0.012  8.5  -3  2  +  -  +  2  0.010  11  -5  3  -  +  2  0.015  9.5  -5  4  -  +  +  3  0.016  10  -7  5  +  +  +  2  0.012  9.5  -5  6  O  O  O  3  0.015  10  -4  7  -  +  -  1  0.016  10  -5  8  -  -  -  1  0.011  8.0  -3  9  +  +  -  1  0.005  2.0  +4  0.012 ±0.007  8.4 + 2.5  -3.5 + 3.6  Average Values"  Average values were calculated without including the centerpoints (Run 7) and the error was the 95% confidence interval for the main and interaction effects.  57  Chapter 4. Results and Discussion  T a b l e 4. 4  Main a n d Interaction Effects of the 2  EFFECTS  FACTORS  3  Factorial  [H 0 ] 2  2  (M)  -0.005  Design  BRIGHTNESS GAIN  (% I S O )  YELLOWNESS GAIN  -1.7  3.2  0.0004  -1.3  0.5  0.002  2.7  -0.003  -2.4  MAIN  TEMPERATURE (XI)  MAIN  C U R R E N T (X2)  MAIN  A N O D E A R E A (X3)  INTERACTION  X1X2  INTERACTION  X1X3  0.0003  2.1  -1.5  INTERACTION  X2X3  0.0014  0.9  -1.7  INTERACTION  X1X2X3  0.003  1.8  -1.5  ± 0.007  ±2.5  95% C O N F I D E N C E INTERVAL  (%)  -3.7  2.7  + 3.6  A calculation of main effects of temperature, current and anode area without the anomalous run 9 is presented in Appendix II section D (see Table 11.2 and 11.3). Table 11.3 shows that neither temperature, current, nor anode area has any significant effect on the active oxygen concentration, brightness gain and yellowness gain. Discounting run 9, the temperature appears to have a negative effect on active oxygen concentration and positive effects on brightness gain and yellowness gain, although these effects are not statistically significant.  This is in agreement with the  conventional brightening practice. Table 11.3 also shows that current and anode area have a positive effect on the concentration of active oxygen and brightness gain, and a negative effect on yellowness gain. Since current and anode area can be interpreted as current concentration and current density, it can be said that high current concentration and current density are favorable in an electrochemical brightening of mechanical pulp. Table 4.4 (including run 9) shows that the combination of temperature, current and anode area has a positive effect on active oxygen concentration, brightness gain and yellowness loss. From the factorial design results, it was concluded that treatment should be done on the anode to prevent further deterioration in the subsequent runs. The U-tube anode was replated with platinum of approximately 0.03 mm in thickness and the anode was treated with warm NaOH and reverse polarization after each experiment starting from Run P-49.  58  Chapter 4. Results and Discussion  4.2.2. The Effect of Anode Material and Current Distribution While the U-tube anode was re-plated, a new anode (a glassy carbon plate) was used in the in-situ brightening of TMP. The behavior of the glassy carbon anode in the brightening conditions was investigated.  Following the return of the restored  platinized U-tube anode, the effect of different electrode configuration (current distribution) was investigated. 4.2.2.1. Glassy Carbon Anode A glassy carbon plate anode with an exposed area of 29 cm was used to repeat 2  Run 2, 3 and 4 from the factorial design experiment (see Table 4.2). The reason for an anode area of 29 cm was that the factorial design results showed a high anode area 2  was favorable for the production of active oxygen, brightening gain and yellowness reduction. The performance of the glassy carbon anode was compared with the results from the U-tube factorial experiment. For the glassy carbon anode experiments, two temperatures, 46°C and 66°C, were tested, but the attempt at 66°C resulted in a visible deterioration of the anode in the brightening suspension.  At a temperature of 46°C, the concentration of the  residual active oxygen throughout the brightening time was recorded for different currents (5 and 10 A) and hence different current densities (0.17 and 0.34 A/cm ). 2  The result was compared with the one from the factorial design (P-22 and P-12) and plotted in Figure 4.7. Figure 4.7 shows that at 5 Amperes, the concentration of residual active oxygen in the system using glassy carbon anode was lower or the same as in the system using platinized titanium anode.  However, at 10 Amperes, the concentration  of residual active oxygen in the system using glassy carbon anode was approximately twice thatfromthe platinized titanium anode. The reason for the high concentration in the glassy carbon system may be that at the high current, the glassy carbon disintegrated and the presence of carbon particles caused a higher reading of active oxygen concentration. The erosion of the glassy carbon surface could be seen from the physical condition of the anode at the end of each experiment. For all experiments  59  Chapter 4. Results and Discussion  with 10 Amperes, the "glassy-looking" surface of the anode became a "dull grey" surface.  It was as if a layer of the surface was removed during the experiment.  Furthermore, on the edges of the anode, black pits containing fine carbon powder were found. The first speculation on the reason for the dull surface was the presence of sodium silicate and/or magnesium sulfate in the brightening suspension.  Three  brightening experiments (P-27A, P-28A and P-29A) without either or both additives still resulted in the erosion of the glassy carbon surface. Therefore, it was concluded that the high current density (0.34 A/cm ) caused the erosion of the glassy carbon 2  anode. Despite the erosion of the anode and a possibly "mistakenly" high reading of active oxygen concentration in the glassy carbon system, the brightening results (brightness gain and yellowness gain) from this system were comparable to the platinized titanium system (see Table 4.5).  Effect of Different Anode Materials on [Active Oxygen] (Glassy Carbon Plate vs Platinized Titanium U-Tube) 0.035 T  0.000 -I 0  , 20  , 40  , 60  , 80  , 100  , 120  , 140  , 160  1 180  Time (minutes)  F i g u r e 4. 7 E f f e c t o f A n o d e M a t e r i a l s o n t h e C o n c e n t r a t i o n o f A c t i v e O x y g e n The  chemicals used were  and  0.023 M M g S 0  4  1.0  M N a C 0 , 2  3  0.13  M N a H C 0  - 7 H 0 ; the total v o l u m e w a s 2  and  the brightening time w a s  60  3  , 0 . 0 3 4 M N a S i 0 , 0.6 g D T P A , 2  3  700 m l ; the p u l p c o n s i s t e n c y 3 hours.  was  1%  Chapter 4. Results and Discussion  T a b l e 4. 5  Run  Brightening Results from  G l a s s y C a r b o n A n o d e S y s t e m at  Current (Amp)  Anode type  Additives  P-22  5  Platinized Titanium  P-24A  5  P-12  46°C  All present  AB (% ISO) 11  AY (%) -6  Glassy Carbon  All present  8  -7  10  Platinized Titanium  All present  9  -4  P-26A  10  Glassy Carbon  All present  9  -10  P-27A  10  Glassy Carbon  No silicate  8  -10  P-28A  10  Glassy Carbon  8  -9  P-29A  10  Glassy Carbon  No silicate & No MgS0 No MgS0  10  -10  4 4  The most significant difference in the brightening results between the system using glassy carbon (GC) and platinized titanium (PtTi) anode was the yellowness loss.  The pulp brightened in the PtTi system had a relatively small reduction in  yellowness compared to the pulp in the GC system. When seen with naked eyes, the pulp brightened with the GC system was less bright than the pulp with the PtTi system of the same brightness level, probably because of the presence of some carbon in the pulp fiber from the GC system. The high reading of yellowness loss was again caused by the presence of carbon in the pulp fiber, which gave rise to an overall less yellow color reading to the spectrophotometer.  The presence of fine carbon powder in the  pulp fiber could also give an erroneous brightness reading. Although it was possible to electrochemically brighten T M P with glassy carbon as an anode, erosion of the anode would result in a high operating cost because it was not possible to reuse the same anode surface for a subsequent brightening. Furthermore, the pulp brightened with this method would contain carbon powder in the fiber. 4.2.2.2. The Effect of Current Distribution (Different Electrode Configuration) A good current distribution is an important factor in minimizing the specific energy for a process. The first electrode configuration that was used in this thesis project was design A in Figure 3.3. The distance between the cathode and the closest "leg" of the anode was approximately 5 cm. There was also a stirrer between the electrodes. Such an electrode configuration resulted in a relatively high E n because ce  61  Chapter 4. Results and Discussion  of the resistance mainly due to the distance between the electrodes. A better current distribution was obtained by implementing design B (Figure 3.3). In this design, the distance between the electrodes was reduced to 2.2 cm, and both "legs" of the anode was exposed to the cathode directly. A n even better electrode configuration was design D (Figure 3.2 and Figure 3.3). In this hollow plate configuration, the distance between the cathode and the anode surface was less than 1 mm. Furthermore, the cathode was spread out across the anode surface to distribute the current more evenly. Design D , however, was tested only once to see if any brightening could be done with this configuration. The brightening results from the different electrode configurations (except the one from design D) are presented in Table 4.6. T a b l e 4.  Run  6.  Brightening R e s u l t s for Different Electrode Configurations ( D e s i g n A & B)  Experimental  Cell Voltage (V)  AB  AY  T(°C)  1(A)  Design A  Design B  (%ISO)  (%)  46 46 66 66 66 66 46 46  10 10 5 5 10 10 5 5  20  _ 13  9 9 3 5 6 11 10 6  -5 -5 2 -4 -2 -5 -5 -3  SE  SE/AB  (kWh/ton)  (k\Vh/ton/%ISO)  8.0 *10 8.9 * 10 — P-37 5.2 *10 5.8 * 10 — P-40 9 1.8*10" 6.0 * 10 — P-32 8 1.6 *10 3.2 * 10 P-44 15 6.0 *10 1.0 * 10 11 P-42 4.4 *10 4.0 * 10 10 _ P-22* 2.0 *10 2.0 * 10 P-30 8 1.6 *10 2.7 * 10 *Note: The original brightness and yellowness of all pulp except P-22 was 51 %ISO and 32 % respectively, while the brightness for P-22 was 45 %ISO and the yellowness was 33 %. The brightening time was 3 hours. Weight of pulp = 7.5 gr O.D. P-38  4  3  4  3  3  4  3  4  4  4  3  4  3  4  3  Table 4.6 shows that cell voltage decreased when the design was changed from design A to design B. In most cases, design B resulted in higher brightness gain than design A. The yellowness loss tend to be higher in design B than in design A, except for P-22 due to a different pulp. The specific energy decreased by between 11% and 35% when the distance between the electrodes was reduced. In terms of the specific energy per brightness gain, design B generally required less specific energy for each point of brightness gain than design A. Low temperature (46°C) runs also resulted in less specific energy per brightness gain than high temperature (66°C) runs.  ** SE (Specific Energy) was calculated using Equation 37.  62  Chapter 4. Results and Discussion  To further show that the distance between anode and cathode decreased the specific energy of the system, an experiment using the electrode design D was performed (Run P-52). The concentration of chemicals for Run P-52 was the same as that for all the runs in Table 4.6 but the total volume was 1400 ml and the brightening time was 3 hours. The brightening temperature was 47°C.  The anode area was 44  cm and the weight of the pulp was 15 g O.D. The current was 23 Amperes and the 2  cell voltage was 8.5 Volts. The specific energy for this system was 3.9 * 10 kWh/ton 4  of pulp. The brightening result was + 7 %ISO for the brightness gain and - 4% for the yellowness gain***.  This brightness gain was reasonable because the original  brightness of the pulp was higher than that in all the runs in Table 4.6. Usually pulp with higher original brightness is more difficult to brighten than one with lower original brightness.  Furthermore, the pulp at the back-side of the electrode (the  insulated part) might not be adequately exposed to the active oxygen.  This might  cause an uneven brightening on the pulp, resulted in an overall low pulp brightness. The  performance  of  two  electrode-configurations  over the residual  concentration of active oxygen at 46°C and 66°C is presented in Figure 4.8 and Figure 4.9 respectively. Figure 4.8 shows that at 46°C, Design B had more residual active oxygen in the brightening suspension than Design A.  Design B (with a better current  distribution) produced and/or protected more active oxygen than Design A. At 66°C, Figure 4.9 shows that Design B had more residual active oxygen than Design A at the first 60 minutes, but after 60 to 80 minutes, the residual active oxygen in Design A was more than in Design B. A possible reason for this is that after 60 minutes of brightening time, the rate of decomposition of active oxygen at the cathode might be more dominant than the production of active oxygen.  Since the distance between  anode and cathode for design B was shorter than for design A, the active oxygen was decomposed faster on the cathode of design B. For both Design A and B, the amount of active oxygen at 46°C, as expected, was higher than the one at 66°C at the respective current densities.  *** The pulp was differentfromthe all the pulp in Table 4 - 7 . Original brightness: 53 %ISO and original yellowness: 31%.  63  Chapter 4. Results and Discussion  Comparison of the Residual Active Oxygen Concentration at 46°C Design A vs Design B 0.050 -[ 0.045 -  Design B, I=10A (P-37) Design A, I=10A (P-38) j  (M)  0.040 0.035 -  "5" 0.030 S o 0.025 >. H o 0.020 ••g  <  0.015 -  Design A, 1=5 A (P-22)  0.010 0.005 0.000 20  40  60  80  100  120  140  160  180  Time (minutes) F i g u r e 4. 8  C o m p a r i s o n o f t h e R e s i d u a l A c t i v e O x y g e n C o n c e n t r a t i o n at 4 6 ° C f o r Design A a n d Design  B  C o m p a r i s o n of R e s i d u a l A c t i v e O x y g e n C o n c e n t r a t i o n at 66 ° C D e s i g n A vs D e s i g n B 0.030 Design B , I = 10 A (P-42)  Design A , I = 10 A (P-44)  0.020  o 5  0.015  o.oio Design B , I = 5A (P-32)  0.005  0.000 20  40  60  80  100  120  140  160  180  Time (minutes) F i g u r e 4. 9  C o m p a r i s o n o f R e s i d u a l A c t i v e O x y g e n C o n c e n t r a t i o n at 6 6 ° C f o r D e s i g n and  Design  B.  Note: Pulp was present in the brightening suspension throughout all the runs in Figure 4.8 and 4.9.  64  A  Chapter 4. Results and Discussion  The effect of specific energy for brightening on the residual active oxygen concentration is plotted in Figure 4.10.  Figure 4.10 compares the residual active  oxygen concentration from Run P-46 (Design A), Run P-47 (Design B) and Run P-52 (Design D).  Comparison of Residual Active Oxygen Concentration (Design A, Design B & Design D) 0.030 Design B, SE= 7.1 *10 kWh/ton Brightness gain : 10 %ISO Yellowness gain : - 4 % 4  0.025  0.020  C v en ^  0.015  I u  Design A , SE=8.8*10 kWh/ton, Brightness gain: 7 %ISO Yellowness gain: -2 % 4  0.010 0.005  Design D , SE=3.9*10*kWh/ton, Brightness gain: 7 %ISO Yellowness gain: -4 %.  0.000 20  40  80  100  120  140  160  180  200  Time (minutes) Figure 4.10  C o m p a r i s o n of Residual Active O x y g e n Concentration between D e s i g n B a n d D e s i g n D at  Design A,  47°C.  Figure 4.10 shows that the residual active oxygen concentration and the brightening result of Run P-47 (Design B) were the highest of the three runs. Run P52 (Design D), with the lowest specific energy, had the second highest residual active oxygen concentration but its brightening result did not differ muchfromthe result of run P-46 (Design A) which had the lowest residual active oxygen concentration throughout the. brightening process.  The reason for such a small difference in the  brightening result for Design A and Design D was that the pulp for run P-46 had a lower original brightness (51%ISO) than that of run P-52 (53%ISO). Furthermore, there might be some uneven brightening on the pulp in Design D. Eventually, a reactor configuration that gives a low specific energy per brightness gain, is able to operate at a high current density and has a good mixing (to handle high pulp consistency), will be the choice reactor for the in-situ brightening of mechanical pulp. 65  Chapter 4. Results and Discussion  4.2.3. The Effect of Post Treatment for the Anode Most, i f not all, of the experimental results presented previously were not replicable because of the anode deterioration. Even after the replating of the anode, the high current (10 Amp) seemed to accelerate the deterioration. In order to optimize the brightening process, it is necessary to be able to replicate the results. Treating the anode by soaking it in warm NaOH for at least 2 hours followed by reverse polarization of the electrodes could restore the anode surface after each experiment and enable a reasonable replication of results. For the investigation of the effect of post treatment on the anode, Run P-47 was repeated several times, with and without the post treatment. The brightening results are given in Table 4.7, and the residual active oxygen concentration is plotted in Figure 4.11. Table 4.7 shows that there was a significant improvement in the brightening results after the post-treatment of the anode. The cell voltage was reduced from 17 V to an average of 13.3 V ; the brightness gain improved from 8 %ISO to an average of 10.8 %ISO and the yellowness gain was reduced from - 2% to - 4.8%. The response error of the runs with anode post treatment was also shown in Table 4.7. T a b l e 4. 7.  Brightening  Results for the  Run  Anode Treatment  P-48 P-49 P-50 P-51 P-56  No Yes Yes Yes Yes  Effect  of A n o d e  Treatment  V || (V) 17 13 12 13 15 ce  AB  AY  (%ISO) 8 10 12 10 11  (%)  -2 -3 -5 -5 -6 Average values* 13.3 ± 1.3 11 ± 1 -5 ± 1 Note: The experimental condition was as follows: [Na C0 ] = 1.0 M, [NaHC0 ] = 0.13 M, [Na Si0 ] = 0.034 M, [DTPA] = 0.6 gr, [MgS0 .7H 0] = 0.023 M, total volume = 700 ml, anode area = 28 cm , temperature = 47°C, current = 11.5 A and brightening time = 3 hours. 2  2  3  4  2  * The average values did not include Run P-48.  66  2  3  3  Chapter 4. Results and Discussion  With anode post-treatment, the cell voltage and the brightness gain were replicated with less than 10% error, whereas the yellowness gain was replicated with about 25% error. The reproducibility of these runs was much better than the one in the factorial design experiments (section 4.2.1.) where the runs were replicated with at least 30% error due to the anode deterioration.  In the residual active oxygen  concentration profile (Figure 4.11), the runs with anode post-treatment had more residual active oxygen than the run without any anode post-treatment. The above results (Table 4.7 and Figure 4.11) proved that the anode post treatment was necessary step to improve the reproducibility of an experiment.  0.050  T  o.ooo -I  ,  ,  ,  ,  ,  ,  ,  ,  ,  i  0  20  40  60  80  100  120  140  160  180  200  Time (minutes) Figure  4.11.  T h e Effect of A n o d e  Post Treatment o n the Active O x y g e n  Concentration  4.2.4. Effect of Brightening Time The role of brightening time in an electrochemical brightening process is to produce enough active oxygen for brightening the pulp and to allow time for the slow brightening reactions to occur. Before the introduction of pulp into the brightening solution, the electro-oxidation of sodium carbonate to generate active oxygen was done for 15 to 30 minutes. The amount of active oxygen produced during this period would be adequate to initiate pulp brightening and to prevent the pulp from  67  Chapter 4. Results and Discussion  undergoing alkaline darkening. The rest of the brightening time would allow more production of active oxygen and brightening of the pulp. The brightening time has some effect on the brightening result of the pulp. The results of TMP brightened at 46 and 66°C for different brightening times (1.5, 2 and 3 hours) are presented in Table 4.8. The current density for all runs was 0.35 A/cm and the pulp consistency was 1 % (total volume was approximately 700 ml). 2  T a b l e 4. 8  Run  E f f e c t o f B r i g h t e n i n g T i m e at 4 6 ° C a n d 6 6 ° C  Temperature  Brightening Time  AB  AY  CQ  (minutes)  (% ISO)  (%)  P-35  46  90  6  -2  P-37  46  180  9  -5  P-41  46  120  7  -4  P-36  66  90  7  -3  P-42  66  180  11  -5  Table 4.8 shows that increasing the brightening time improved the brightness gain and the yellowness loss. There was a 6%ISO brightness increase when the pulp was brightened for 90 minutes, but the brightness gain was only 3%ISO when the brightening time was extended to 180 minutes. This means that a major part of the brightness gain happened early in the process. Therefore, it is necessary to have a large concentration of active oxygen when the pulp is introduced into the brightening solution. One way to have a large concentration of active oxygen at the time of pulp addition is by increasing the active oxygen pre-generation time (before the addition of pulp). The maximum concentration of active oxygen was usually found around 30 minutes after the current was started.  Previously (before Run P-77), all electro-  brightening runs had a pre-generation time of 15 minutes. If the same brightening results could be obtained by increasing the pre-generation time (to 30 minutes) without increasing the brightening time, the pulp would have less exposure to the electric current, hence reducing thefiberloss. The effect of 30-minute pre-generation time was investigated by repeating Run P-62 (the best Simplex run from section 4.3). The brightening results can be seen in Table 4.8. The residual active oxygen concentration profile is plotted in Figure 4.12.  68  Chapter 4. Results and Discussion  T a b l e 4. 9  T h e Effect of Brightening T i m e a n d L o n g e r Active O x y g e n Generation Time  ( B r i g h t e n i n g R e s u l t s f o r the Repetition of R u n P-62) R u n  Active Oxygen Generation  Time  Brightening Time  A Brightness  (minutes)  A  Yellowness  (%ISO)  <%)  P-62  15 minutes  180  12  -7  P-63  15 minutes  180  11  -7  P-70  15 minutes  180  10  -5  P-85  32 minutes  90  1  1  P-88  30 minutes  120  11  -6  P-80  31 minutes  180  11  -6  P-77  39 minutes  210  11  -6  P-78  30 minutes  210  12  -7  P-92  30 minutes  360  13  -8  P-89 30 minutes 390 15 -10 Note: Experimental Condition for above runs: Na C0 = 1.0 M; NaHC0 = 0.11 M; Na Si0 = 0.034 M; DTPA= 0.6 g; MgS0 .7H 0= 0.023 M; Electrode Design C; Anode Area= 27.5 cm ; Temperature= 54°C; Current= 11.2 Amp; Pulp Consistency 1 %; Original Pulp Brightness= 53 %ISO; Original Pulp Yellowness= 31 %. All brightening time includes the active oxygen generation time. 2  3  3  2  3  2  4  2  When the 180-minute runs were compared,  it could be seen that the  brightening results were more or less the same. The average brightening results of the runs with 15-minute pre-generation time (Runs P-62, P-63 and P-70) were the same as the brightening results for the run with 30-minute pre-generation time (Run P-80). Figure 4.12 shows that the residual active oxygen concentration (after 2 hours of brightening time) for all the runs were about 0.030 M.  The concentrations in the  earlier part of the brightening time were different for each run, but the brightness gain for all runs were either 11 or 12 %ISO. A similar trend is also seen in Figure 4.12. This means that a certain active oxygen concentration after 2 hours of brightening time should be maintained in order to achieve a certain brightness gain (depending on the temperature).  69  Chapter 4. Results and Discussion  Residual Active Oxygen Concentration Profile (15-minute vs 30-minute Pre-generation Time) 0.040 0.035 0.030 0.025 0.020 0.015 0.010  —•—Run P-62  0.005  - * - R u n P-78  "•IB"-'Run P-63 - » - R u n P-80 0.000 20  40  60  80  100  120  140  160  180  200  Time (minutes) Figure 4.12  R e s i d u a l Active O x y g e n C o n c e n t r a t i o n Profile for C o m p a r i n g and  15-minute  30-minute Pre-generation Time.  Run P-62 was also repeated with about 30 minutes of active oxygen generation to investigate the effect of brightening time. The results are presented in Table 4.9. Table 4.9 shows that there was a minimum time before a reasonable brightness gain could be achieved (compare Runs P-85 and P-88). Furthermore, doubling this time only improved the brightness by 2 %ISO (compare Run P-80 and P-92) and lowered the yellowness by 2%. A plot of brightness gain and yellowness gain versus brightening time is shown in Figure 4.13. Figure 4.13 shows that the biggest brightness increase and yellowness decrease happen around 100 to 120 minutes of brightening time. A longer brightening time only improved the brightening results by a small increment. In the conventional peroxide brightening process, the brightness increases with increasing brightening time until the maximum brightness gain (around 20 %ISO) is achieved. After that, longer brightening time will not increase the brightness of pulp, unless multiple stages of brightening are performed. In this electrochemical process, the brightness gain levels off between 120 to 300 minutes of brightening time but the brightness increases again after 300 minutes of brightening time.  The possible explanation for this  phenomenon is the role of cooling water temperature.  70  Chapter 4. Results and Discussion  In all brightening runs longer than 300 minutes, the cooling water temperature was not maintained at 4°C between 150 to 240 minutes of the runs (the temperature increased to around 10°C or higher). At around the 240 minute of the brightening th  time, the cooling water temperature was brought down to 4°C again. The lowering of the cooling water temperature increased the overpotential of oxygen evolution on the PtTi anode and improved the production of active oxygen, which in turn increased the brightness of the pulp. Brightness Gain & Yellowness Gain vs Brightening Time  Brightening Time  Figure  4.13.  (minutes)  Brightness Gain & Yellowness Gain versus Brightening  Time  Figure 4.13 shows that there is hardly any brightness gain under 100 minutes of brightening time, even though the concentration of active oxygen in an electrochemical run is the highest at around the first 60 minutes (see Figure 4.12). In a conventional peroxide brightening process, some brightness gain is achieved as soon as the peroxide is mixed to the pulp. The main difference between the electrochemical and the conventional brightening runs is the initial active oxygen concentration. In order to maintain some residual peroxide at the end of a conventional brightening process, the initial concentration of peroxide has to be very high (about 0.1 M), whereas in the electrochemical run, the initial concentration of active oxygen at the point of pulp addition was very low (about 0.02 M ) .  In most electrochemical  brightening runs, the concentration of active oxygen increased to a maximum at  71  Chapter 4. Results and Discussion  around 60 minutes, then it decreased until about 120 minutes andfinallyit increased again gradually. The low initial concentration of active oxygen and the uneven pulp mixing at the beginning of pulp addition, slow the brightening process in the first 100 minutes of the brightening time. To obtain a more definite result, the brightness of pulp at different brightening times (under 100 minutes) has to be measured. Since an 11 %ISO brightness gain could be obtained with a brightening time of as low as 2 hours (see Run P - 88 in Table 4.9), instead of performing a straight 6hour run, it might be possible to achieve the same or better result if the brightening was performed in two 3-hour stages. Two 2-stage brightening runs with the same experimental conditions as the runs in Table 4.9 were attempted (Run P-86 and P-90) and the results are shown in Table 4.10. Table 4.10.  Results from Two-Stage Brightening Runs  Run  Stage  Active Oxygen Generation Time  Brightening Time  A Brite (% ISO)  A Yellow (%)  P-86  1 2  40 min. 35 min.  190 min. 280 min.  14  -9  P-90  1 2  30 min. 30 min.  180 min. 180 min.  12  -8  Note: In each stage, a new batch of brightening chemical was used and between stages, the pulp was washed with sulfuric acid to remove the chemicals from the previous stage.  Table 4.10 shows that a two-3-hour run produced a similar result as a straight 6-hour electrochemical run (compare Run P-90 with P-92). However, the longer twostage brightening run (total time of 7.8 hours) did not give results as good as a straight 6.5 hour brightening run (compare P-86 with P-89). It was possible that after each stage of brightening, the fresh brightening chemicals could not attack more chromophores to further improve the brightening results. Another way to increase the concentration of active oxygen at the time of pulp addition into the brightening solution was to produce the active oxygen at room temperature or around 30°C and after about 30 minutes, the temperature was increased to 54°C for the purpose of brightening the pulp.  At room temperature, the  concentration of active oxygen produced was higher than at 54°C, hence the pulp would be exposed to a high concentration of active oxygen when it was introduced to the brightening solution. The residual active oxygen profile of this type of run (Run  72  Chapter 4. Results and Discussion  P-82, P-83 and P-84) is plotted in Figure 4.14 and compared to the resultfromRun P88 where the active oxygen was produced for 30 minutes at 54°C before the addition of pulp. Figure 4.14 shows that indeed the concentration of active oxygen generated at 32 to 37°C was higher than that generated at 54°C. The total brightening time of Runs P-82, P-83 and P-84 was adjusted to 3.2 hours, adding an extra 12 minutes to compensate for the time to increase the solution temperature from the thirties to fifties. The brightening results of these runs are presented in Table 4.11.  Comparison of Residual Active Oxygen Profile Among Runs with Active Oxygen Generation at Room Temperature and at Brightening Temperature 0.040 -r 0.035 0.030  •5-  P-82 83 P-84 P-88  0 0 2 5  Generation of Active Oxygen for Runs P-82, P-83 and P-84 was done at 32 to 37°C and pulp was introduced after 43 minutes, while for Run P-88, generation of active oxygen was at 54°C and pulp was introduced after 30 minutes.  > 0.015 -G  <  — 0.010 0.005 0.000  20  40  60  80  100  120  140  160  180  T i m e (minutes) Figure 4.14.  Residual Active Oxygen  at L o w e r T e m p e r a t u r e s  Table 4.11  Run  P-82 P-83 P-84 P-88  Profiles for R u n s with Active O x y g e n  (32 t o 3 7 ° C ) t h a n t h e B r i g h t e n i n g T e m p e r a t u r e  Brightening Results for Runs where the Temperature for Active  Time for Generation of Active Oxygen  43 minutes 43 minutes 45 minutes 30 minutes  Generation (54°C).  Oxygen  Brightening Time  AB  AY  (% ISO)  (%)  192 minutes 192 minutes 192 minutes 180 minutes  11 10 12 11  -7 -7 -7 -6  With a higher concentration of active oxygen before pulp addition, one would expect better brightening results for Run P-82 to P-84 than Run P-88. Indeed the 73  Chapter 4. Results and Discussion  average brightness gain and yellowness gain for the first 3 runs were better than for Run P-88, however, the difference was only 1%IS0 for brightness gain and -1% for yellowness gain. These differences are not statistically significant. Furthermore, the extra 12 minutes in increasing the temperature would certainly increase the operating cost.  4.3.  Optimization of the Electrochemical Brightening Process Using Sequential Simplex Optimization A factorial design experiment only shows the effects of design factors at  certain values supplied by the researcher. For example, the current was limited to 5, 7.5 and 10 Amperes; the anode area was limited to 14.5, 21.75 and 29 cm , and the 2  temperature was limited to 46, 56 and 66°C. The optimum operating conditions might lie outside the combination of these values, however, identifying them would require an extensive number of experiments. The sequential simplex optimization offers an effective method to reach an optimum set of operating conditions. This method is based on the evolutionary operation (EVOP) which discards the bad operating conditions and uses the good operating conditions to find a better operating conditions. The explanation on the sequential simplex optimization and its comparison with the factorial design experiment are presented in Appendix III. In this thesis project, two sets of sequential simplex experiments were performed using SEVLPLEX-V to find an optimum brightening condition. The two simplex projects were called "FINAL 1" whose purpose was to maximize the multiplication of brightness gain and the absolute value of yellowness gain* (A Brite x I A Yellow | ), and "TRYOUT" whose purpose was to maximize the brightness gain (A Brite) alone.  Both simplex projects were a variable-size simplex with 4 factors  (current, anode area, temperature and pH) and used the same initial yertexes supplied from previous experiments. The upper and lower limits for the factors and responses are as follows:  The reason for using the absolute value of yellowness gain was to simplify the multiplication of the responses.  74  Chapter 4. Results and Discussion  Factor Name  Unit  Current Area Temperature PH  Amp cm °C 2  Lower Limit 0 5 25 9  Upper Limit 20 29 70 11.8  Response Name  Unit  ABrite  %ISO  I A Yellow |  Lower Limit 0 0  %  Upper Limit 20 30  For both projects, the pulp consistency was 1%, the electrode configuration was Design B and the anode was treated with NaOH and reverse polarization after each run. The initial vertexes and responses for both projects are shown in Table 4.12 Table 4.12  Vertex 1 2 3 4 5  Initial v e r t e x e s a n d  Run# P-47 P-31 P-50 P-23 P-16  r e s p o n s e s f o r P r o j e c t " F I N A L 1" a n d  Current (Amp)  Area (cm )  Temp  11.5 10.0 11.5 7.5 5.0  28 29 29 21.75 14.5  47 46 48 56 46  pH  CO  2  10.68 10.62 10.64 10.68 10.69  " T R Y O U T "  A Brite (% ISO) 10.1 8.7 12.2 13.3 9.5  A Yellow (%) -4.3 -4.8 -4.9 -7.0 -5.1  The purpose for performing two simultaneous simplex projects was to investigate the effect of maximizing a different number of responses.  In the  brightening of mechanical pulp, usually a high brightness gain was the main target, however, in this thesis project, a low yellowness gain also have an important role in ensuring a high brightness gain.  Therefore, it would be interesting to see the  responses from the different vertexes given by the two simplex projects. The responses from the vertexes suggested by S I M P L E X - V for project " F I N A L 1" and " T R Y O U T " are shown in Figure 4.15 and 4.16 respectively. The interpretation of the direction of the simplex is presented in Appendix IV. Figures 4.15 and 4.16 show that the responses fell within the range of responses from the initial vertexes. The reason for this was that the range of the initial vertexes was not wide enough for the simplex to move around.  For the simplex  method to work well, it should be started with extreme ranges of initial vertexes. Another reason for the small ranges of responses could be the system itself. When the brightness gain and yellowness gain stayed within the same range regardless of the change in the experimental conditions, a question should be asked about the role of carbonate in the brightening of mechanical pulp. 75  Chapter 4. Results and Discussion  It was assumed that sodium carbonate was oxidized to form percarbonate, which was hydrolyzed to form hydrogen peroxide.  Until now, the brightening  "behavior" of the sodium carbonate electrochemical system was assumed to be similar to the "behavior" of hydrogen peroxide in the common alkaline brightening process (without carbonate).  The responses from the electrochemical brightening system  raised the question if this "similar behavior" was true. Therefore, an investigation to compare alkaline peroxide brightening process in the presence of sodium carbonate with the electrochemical percarbonate/peroxide brightening process was performed and the results are presented in section 4.4. Brightness Gain vs Absolute Yellowness Cain Simplex Project " FIN A L 1"  7 H  |  5  U  S  4  £  I >  H  3  The number above each point is the vertex number. The "I" indicates an initial vertex.  2  1 9  0  10  11  Brightness G a i n (% ISO) Figure 4.15  R e s p o n s e s from Simplex Project "FINAL  1" ( m a x i m i z i n g A B r i t e x A Y e l l o w )  Note: All the above AYellow values were negative.  Brightness Gain vs Absolute Yellowness Gain for Simplex Project " T R Y O U T "  1-4  7 6 5  H  1-2 •  T10 * > IS  T6 • T9 • 1-1  •  4  T7 • 1-3 •  T8 •  3 2 1 •  10  11  12  Brightness G a i n (% I S O )  Figure 4.16  R e s p o n s e s f r o m S i m p l e x Project " T R Y O U T " ( m a x i m i z i n g A Brite  76  only)  Chapter 4. Results and Discussion  4.4. Simulation of the Electrochemical Brightening of TMP using Hydrogen Peroxide The purpose of simulating the electrochemical brightening process was to investigate the difference between the brightening chemicals produced by the electrooxidation of sodium carbonate and the merchant hydrogen peroxide and to show the effect of the presence of carbonate on the performance of hydrogen peroxide in brightening the pulp. Hydrogen peroxide (H2O2) solution (30% w/w) was added (at certain time intervals) to the carbonate solution (a combination of Na2C03, NaHCC>3, Na2SiC>3, MgS04.7H 0, and DTP A) matching the amount of active oxygen measured 2  in an electrochemical process. A brightening experiment without any carbonate (i.e. chemicals involved were NaOH, Na2Si03, MgS04.7H 0, DTP A and H2O2) was also 2  performed as a comparison to the simulated process. Several brightening experiments using straight peroxide in the presence of carbonate were performed*; each one was an attempt to simulate an electrochemical brightening process. The brightening results are shown in Figures 4.17 and 4.18. Figure 4.17 shows that in the presence of carbonate, the hydrogen peroxide decomposed very rapidly. The H2O2 profile of Run P-75 shows that in less than 30 minutes, the concentration of H2O2 was decreased to about 5 % of its initial concentration. Furthermore, the brightness gain was only 6 %ISO and the yellowness gain was -3 %. On the other hand, with the same total amount of H2O2 as added in Run P-75 but with different method of adding H2O2, Run P-76 could achieve a much higher brightness gain (15 % ISO) and lower yellowness gain (-10%). The main difference between Run P-75 and P-76 was that Run P-76 had several high concentrations of H2O2 (> 0.070 M ) throughout the 3-hour brightening time, whereas the high H2O2 concentration for Run P-75 was found in the first 10 or 20 minutes.  This means that in the presence of carbonate, in order to obtain a  reasonable brightening result, there should always be a constant supply of active oxygen throughout the brightening time. In the conventional industrial brightening of mechanical pulp (without carbonate present), H2O2 is supplied to the pulp only initially and the brightening process goes on without additional supply of H2O2.  * All runs were performed at 60°C for 3 hours without current. Pulp consistency was 1 %.  77  Chapter 4. Results and Discussion  Peroxide Brightening of Mechanical Pulp in the Presence of Carbonate (Total H 0 added = 35 ml) 2  2  0.400 -| 0.350 -  (M)  0.300 -  O  0.250 0.200 0.150 0.100 0.050 0.000 60  80  100  T i m e (minutes) Figure 4.17  H y d r o g e n P e r o x i d e B r i g h t e n i n g o f M e c h a n i c a l P u l p in the  P r e s e n c e of  Carbonate  Hydrogen Peroxide Brightening in the Presence of Carbonate (Variable Additions of H 0 ) 2  2  0.25 -P-71  P-71  A Brightness = 14 %ISO; A Yellowness = -8 % Total H 0 added = 17 ml.  P-72  A Brightness = 12 %ISO; A Yellowness = -8 %. Total H 0 added = 17 ml.  P-74  A Brightness = 17 %ISO; A Yellowness = -12 •/.. Total H 0 added = 50 ml.  P-76  A Brightness = 15 %ISO; A Yellowness = -10%. Total H 0 added = 35 ml.  -P-72  2  •P-74  0.2 A  -P-76  2  2  2  20  40  60  80  2  2  2  2  100  120  140  160  180  Time (minutes) Figure 4.18  H y d r o g e n Peroxide Brightening in the Presence Additions of H  2  0  2  at Different T i m e  of Carbonate with  Variable  Intervals.  Comparing the brightening results of runs with different total amount of H2O2 added, Figure 4.18 shows that even with double amount of H 2 0 added, the brightness 2  gain or yellowness gain was not doubled. In the presence of carbonate, the brightness gain that could be achieved in one stage of brightening would level off regardless of  78  Chapter 4. Results and Discussion  how much more H 2 O 2 was added. The same situation also applies to the conventional alkaline hydrogen peroxide brightening. In order to investigate the difference between the action of the active oxygen produced electrochemically and the merchant H 2 O 2 , two experiments were performed (Run P-87 and P-88). The results are shown in Figure 4.19. Comparison Between Electrochemical Brightening Run and No Current Peroxide Brightening Run in the Presence of Carbonate 0.035 T •  P-87 (no current)  ~W~P-88 (Electrochemical run)|  "3 0.025  a u  0.020  c  "5" 6X >.  0.015  P-87 : Total amount of H 0 2  M  o  added = 4.5 ml.  A Yellowness = -5 %.  £ 0.010 H  "  2  A Brightness = 9 %ISO;  0.005  P-88 : Electrochemical Run at 5 4 ° C . A Brightness = 11 %ISO; A Yellowness = -6 %.  0.000 20  60  80  100  120  140  160  Time (minutes) F i g u r e 4.19  Comparison Between in t h e  A n Electrochemical and Peroxide Brightening Run Presence  of Carbonate  Figure 4.19 shows that the electrochemical brightening run gave a better result than the no current run. However, these two runs could not confirm the difference between the active oxygen produced electrochemically and hydrogen peroxide because the "manual" run did not simulate a constant supply of hydrogen peroxide like the electrochemical run. One way to simulate the electrochemical brightening process is to use an automated method which measures the residual continuously and supplies fresh  H2O2  H2O2  concentration  as needed to match the concentration of active  oxygen measured in the electrochemical run..  Another way to investigate the  difference between the active oxygen and hydrogen peroxide was to brighten the pulp using sodium percarbonate (almost impossible to obtain at non freezing temperature) and compare the brightening results with the ones from peroxide brightening.  79  Chapter 4. Results and Discussion  The effect of the presence of carbonate in the brightening solution was investigated by performing a brightening experiment without electricity using only NaOH, the additives and H2O2 (Run P-93) and comparing the brightening results with Run P-87. The H2O2 concentration profile of Run P-87 was the closest to the one of Run P-93. The results are presented in Figure 4.20.  Effect of Carbonate on Hydrogen Peroxide 0.035 •  P-87 (with carbonate)  -W-P-93 (without carbonate)  0.030  0.025  P - 87: Total amount of H 0 added = 4.5 ml (added 2  2  4 times). A Brightness = 9 % ISO; 0.010  A Yellowness = -5 %. P-93:  Total amount of H 0 added = 2.5 ml (added 2  2  2 times). A Brightness = 13 %ISO;  0.005  A Yellowness = -5 %. 0.000 20  40  60  80  100  120  140  160  Time (minutes) F i g u r e 4. 2 0 Effect o f C a r b o n a t e o n t h e C o n c e n t r a t i o n o f H  2  0  2  and the Brightening  R e s u l t s (~ 1 M c a r b o n a t e v s n o c a r b o n a t e )  The presence of carbonate in the brightening solution decomposed the hydrogen peroxide at such a rate that with a higher amount of total H2O2 added, the brightening result was not as good as the one without carbonate. This result was in agreement with the finding by Rudie et al. [46] who substituted dilute Na2C03 for NaOH in peroxide bleaching of spruce CTMP. Rudie et al found that substituting 50% of the caustic charge decreased the brightness gain by 1 point in TAPPI brightness, whereas substituting 80% of the caustic charge decreased the brightness gain by 1.5 points. The yellowness gain, however, was the same for Run P-87 and P-93 despite the big difference in the brightness gain.  If Run P-93 had been repeated with the  same amount of H2O2 added as Run P-87, the brightness and yellowness gain would certainly have surpassed that of Run P-87.  80  Chapter 4. Results and Discussion  4.5. Economics of In-situ Electrochemical Brightening Method One of the most important considerations in using a new process is the economic consideration. The in-situ electrochemical brightening method presented in this thesis is a new process. The main differences between this method and the usual mechanical pulp brightening method are: • Equipment The use of electrochemistry requires an electrochemical reactor and electrodes. The material used for the reactor and the electrodes would affect the maintenance cost. The size and design of the reactor would dictate the operating cost. This insitu brightening method could reduce the chemical transportation cost (increase the safety of chemical handling). • Electrical Power Consumption An electrochemical reactor requires electricity. The amount of energy needed for the brightening process might be immense, depending on the reactor design. • Brightening Chemical The in-situ electrochemical brightening process used sodium carbonate (Na2C0 ) 3  as the raw chemical to produce active oxygen, such as percarbonate and H2O2. In the ordinary brightening process, H2O2 was supplied externally as the brightening chemical. The price of N a C 0 (about $0.107kg) is much lower than H 0 (about 2  3  2  $l/kg) or NaOH (about $ 0.30/kg). The price of N a C 0 2  3  2  could be lower if the  Na2C03 is a recycle product, for example: in a closed-cycle pulp mill where Na2C0  3  is a product of the chemical recovery process.  brightening process  could achieve  If the electrochemical  a reasonable result (compared to the  conventional brightening process), it could be used in a closed-cycle pulp mill. The reactor used in this thesis project was very rudimentary, however, the amount of power consumption could be estimated from the experimental results. The calculation for the cost comparison for an electrochemical brightening process and a conventional H2O2 brightening process is presented in Appendix VI. The cost differences are presented in Table 4.13.  81  Chapter 4. Results and Discussion  Table 4.13  C o s t differences process  between conventional  (Basis: 500 t o n s of O . D . pulp  and electrochemical  brightening  /day)  Conventional Brightening  Electrochemical Brightening  Capital Cost = $ 5,000,000 Operating Cost = $ 13,000,000 Operating cost per ton of pulp = $ 80/ton of pulp  Capital Cost = $ 12,000,000. Operating cost = $ 16,000,000 Operating cost per ton of pulp = $90 /ton of pulp  Table 4.13 shows that the electrochemical brightening process costs more than the conventional peroxide brightening process. The capital cost of the electrochemical process is about 140% more than the cost of the conventional process, whereas the operating cost of the electrochemical process is about 20% more than that of the conventional process. About 50% of the operating cost of the electrochemical process is the cost of electricity. In order to make the electrochemical process a competitive process, the electricity cost has to be reduced by designing a good reactor and electrode configuration that would minimize the specific energy of the brightening process.  82  Chapter 5. CONCLUSIONS The polarization curve of the electro-oxidation of carbonate into percarbonate did not show a clear mass transport limiting current density for the primary reaction. The reason was that many reactions occurred on the electrodes and the method used to measure the polarization curve was not a precise method to separate the output from different reactions.  The measurement of current efficiency of active oxygen  generation (for V hour) at different current densities showed that at 46°C, the highest 2  current efficiency (41 %) could be achieved at a current density of 0.14 Amp/cm and 2  anode voltage of 2.98 V vs SCE. A subsequent experiment performed at an anode potential of 2.9 V vs SCE resulted in a 25 % average current efficiency over 30 minutes instead of the expected 41 %.  The cause of this difference was the  deterioration of the platinized surface of the anode. The concentration of residual active oxygen for a no-pulp run was lower than that of an in-situ brightening run. The probable reason for this difference was that the pulp might have reacted with potassium permanganate during the titration for active oxygen and/or the pulp might have protected the active oxygen. A full 2 factorial experiment of the in-situ brightening of mechanical pulp 3  using sodium carbonate showed that the three factors tested (temperature, current and anode area) had no significant effect on the concentration of active oxygen in the first 30 minutes of the run. However, the anode area (current density) had a significant positive effect on the brightness gain and yellowness loss. Although the effect has no statistical significance, it appears that a combination of high temperature, current density and current concentration is favorable for the electrochemical brightening of mechanical pulp.  The high response errors (for active oxygen concentration,  brightness gain and yellowness gain) indicated anode deterioration, which was confirmed by visual observation. The rate of anode deterioration could be reduced by post-treatment of the anode by soaking it in warm NaOH solution ( > 1 M) for at least 2 hours, followed by the reverse polarization of the electrodes in 1 M Na2C03 solution.  83  Chapter 5. Conclusions  When a different anode material was used (glassy carbon vs platinized titanium), it was found that glassy carbon underwent erosion in each experiment. The amount of erosion increased with increasing current density. This erosion required that a fresh glassy carbon surface be used in each run making it impractical to use glassy carbon as an anode. Despite the erosion problem, the brightness gain from glassy carbon runs was comparable to the one from the platinized titanium runs. The glassy carbon seemed to reduce the yellowness gain of the pulp, however, the carbon particles in the pulp might have "deceived" the spectrophotometer to read a low yellowness value. Using platinized titanium as the anode material, experiments with different electrode configurations showed that good current distribution on the electrodes reduced the specific energy.  Generally, design B had a lower specific energy/  brightness gain compared to Design A. A minimum of 15 minutes of active oxygen pre-generation time (before pulp addition) was important in providing active oxygen in the brightening solution hence preventing alkali darkening on the incoming pulp.  For the same total brightening  time, a 30-minute pre-generation time gave the same brightening results as a 15minute pre-generation time, but less pulp exposure to electric current. The highest brightness increase during a brightening reaction usually happened between 100 to 120 minutes of brightening time. A longer brightening time did not improve the brightening results by much. The final brightness of a pulp depended on the concentration of the active oxygen after 120 minutes. Two-stage brightening was attempted but the results were similar to or worse than a one-stage brightening with the same total time. The brightness gain in the second stage of brightening was very low, indicating that afreshbatch of brightening chemicals could not perform effectively. Producing active oxygen at 30°C for about 30 minutes followed by the brightening of pulp at 54°C for a total of 192 minutes gave a similar brightening result as the runs where the temperature of active oxygen production and pulp brightening was equal. Therefore it was not considered a good brightening option.  84  Chapter 5.  Conclusions  The simplex method to optimize the brightness gain and yellowness gain was only able to achieve a brightness gain of 12 %ISO and yellowness gain of -7 %. The rest of the optimization results did not differ significantly from each other. The initial vertexes might not be spread out enough. A comparison of pulp brightening in conventional NaOH liquor versus Na2C03 liquor showed that the presence of Na2C03 worsened the brightening results. Added H2O2 decomposed more rapidly in the Na2C03 liquor than in NaOH liquor even in the presence of additives. Pulp brightening in concentrated Na2C03 liquor is only effective with constant electrochemical generation of active oxygen - to compensate for the decomposition of peroxide. A cost comparison analysis between the electrochemical and the conventional brightening process showed that the electrochemical process costs more to operate than the conventional brightening process. The operating cost for the electrochemical process is about $ 90/ton of pulp, whereas the one for the conventional brightening process is about $ 80/ ton of pulp.  85  Chapter 6 RECOMMENDATIONS AND FUTURE WORK 1. A new freshly platinized titanium U-tube should have been used in the simplex optimization and factorial design experiments. After each experiment, the anode should be treated with warm NaOH and reverse-polarized in 1 M Na2C03.  2. The initial vertexes for the simplex optimization method should be more spread out. It might be a good idea to initialize the optimization on the lower and upper limits of the factors.  3. More experiments should be performed on Design D. A new reactor with good mixing ability should be made to accommodate the shape of electrode design D.  4. A comparative study between the industrial brightening method and the electrochemical brightening method should be performed. The same kind of pulp should be used.  5. More study on the effect of carbonate on the brightening of mechanical pulp should be performed. There should be an investigation on the kind of chemicals produced by the electro-oxidation of sodium carbonate and the role of these chemicals in brightening the pulp.  86  References  REFERENCES [I] . Smook, G. A., Handbook of Pulp and Paper Technologists. 2 edition, Angus Wilde Publications, Vancouver (1992). [2]. Rydholm, S. A., Pulping Processes. John Wiley and Sons, Inc., New York (1965). [3]. Sjostrom, E., Wood Chemistry: Fundamentals and Applications. Academic Press, Inc., San Diego, California (1981). [4]. Presley, J. R , and Hill, R. T., "Peroxide Bleaching of (Chemi)Mechanical Pulps" in Pulp Bleaching: Principles and Practice, edited by Carlton W. Dence and Douglas W. Reeve, TAPPI Press, Atlanta, U.S.A., pp. 457 - 473 (1996). [5]. Ellis, M. E., "Hydrosulfite (Dithionite) Bleaching" in Pulp Bleaching: Principles and Practice, edited by Carlton W. Dence and Douglas W. Reeve, TAPPI Press, Atlanta, U.S.A., pp. 491 - 501 (1996). [6].  Been, J., "Mechanical Pulp Bleaching", unpublished paper (May 24, 1991).  [7]. Joachimides, T., "High Brightness Mechanical Pulps", TAPPI Pulping Conference Proceedings, pp. 131 - 139 (1989). [8]. Lachenal, D.; Bourson, L., and Lachapelle, R., "Bleaching of High Yield Pulp to Very High Levels", presented in the Conference on paper: High yield pulp and the valuation of recycledfiber,Montreal, 12-14* October (1989). [9]. Heitner, C , "Chemistry of Brightness Reversion and Its Control" in "Pulp Bleaching: Principles and Practice", edited by Carlton W. Dence and Douglas W. Reeve, TAPPI Press, Atlanta, U.S.A., pp. 185 (1996). [10]. Oloman, C , Electrochemical Processing for the Pulp & Paper Industry. The Electrochemical Consultancy, England (1996). [II] . Varennes, S.; Daneault, C , and Parenteau M., "Bleaching of Thermomechanical Pulp with Sodium Perborate", TAPPI Journal, 79, 245-250 (March 1996). [12]. Khomutov, N. Ye., "Electrolytical Synthesis of Percarbonates" in Chemistry of Peroxide Compounds, edited by Chernyayev I.I., Publishing House of the Academy of Science of the U.S.S.R, Moscow, pp. 221 - 225 (1963).  87  References  [13]. Prokopchik, A. Yu and Vashykyalis, A.I., "Electrochemical Properties of Peroxycarbonates" in Chemistry of Peroxide Compounds, edited by Chernyayev I.I., Publishing House of the Academy of Science of the U.S.S.R., Moscow, pp. 228 - 236 (1963). [14]. Oloman, C , "Proposed Patent Application Process for Electro-chemical Oxidation of Carbonate Solutions". B.C. Research, Vancouver, Canada (January 13, 1970). [15]. Oloman, C , "In-House Project - Project 2022 - Electrochemical Preparation of Oxidizing Bleaching Agents" (March 20, 1970). [16]. Constam, E. J., and Hansen, A., U.S. Patent No. 579.317 "Process of Manufacturing Percarbonates", (March 13, 1897). [17], Springer, E. L., and Sweeney, J. D., "Bleaching Groundwood and Kraft Pulps with Potassium Peroxymonosulphate - Comparison with Hydrogen Peroxide", TAPPI Pulping Conference Proceedings, Toronto, Canada (Oct. 1986). [18]. Reeve, D. W., "Introduction to the Principles and Practice of Pulp Bleaching" in "Pulp Bleaching: Principles and Practice", edited by Carlton W. Dence and Douglas W. Reeve, TAPPI Press, Atlanta, U.S.A., pp. 1-23 (1996). [19] Biermann, C. J., "Essentials of Pulping and Papermaking". 2 Academic Press Inc., San Diego, California (1996).  nd  edition,  [20] Minor, J. L., "Production of Unbleached Pulp" in "Pulp Bleaching: Principles and Practice", edited by Carlton W. Dence and Douglas W. Reeve, TAPPI Press, Atlanta, U.S.A., pp. 25 - 57 (1996). [21]. Heitner, C , "Chemistry of Brightness Reversion and Its Control" in "Pulp Bleaching: Principles and Practice", edited by Carlton W. Dence and Douglas W. Reeve, TAPPI Press, Atlanta, U.S.A., pp. 185 - 212 (1996). [22]. Ali, T.; Evans, T. D.; Fairbank, M.; McArthur, D.; and Whiting, P., "The Role of Silicate in Peroxide Brightening of Mechanical Pulp. Part VI: Interactions of Silicate and Papermaking Polymers", Journal of Pulp and Paper Science, 6, 16, pp.J169 - J172 (November 1990). [23]. Bristow, J. A., "What is ISO brightness ?", TAPPI Journal, 77, pp.174 - 178 (May 1994). [24]. Jordan, B. and O'Neill, M., "The Case for Switching to CLE L*a*b* Color Description for Paper", Pulp and Paper Canada, 88:10, pp.T382 - T386 (1987).  88  References  [25]. Gellerstedt, G., "Chemical Structure of Pulp Components" in "Pulp Bleaching: Principles and Practice", edited by Carlton W. Dence and Douglas W. Reeve, TAPPI Press, Atlanta, U.S.A. (1996), pp. 91-111. [26]. Dence, C. W., "Chemistry of Mechanical Pulp Bleaching" in "Pulp Bleaching: Principles and Practice", edited by Carlton W. Dence and Douglas W. Reeve, TAPPI Press, Atlanta, U.S.A., pp. 161 - 181 (1996). [27]. Ali, T.; McArthur, D.; Stott, D.; Fairbank, M.; and Whiting, P., "The Role of Silicate in Peroxide Brightening of Mechanical Pulp. 1. The Effects of Alkalinity, pH, Pre-Treatment with Chelating Agent and Consistency", Journal of Pulp and Paper Science, 6, 12, pp.J166 - J172 (November 1986). [28]. Oloman, C. W., "Lecture Notes in Electrochemical Engineering", CHML 477, U B C , (1994). [29]. Pletcher, D. and Walsh, F. C , "Industrial Electrochemistry". 2 Chapman and Hall, New York (1990).  nd  edition,  [30]. Yue, L.; Cai, J., "Synthesis of Stabilized Sodium Percarbonate", Huaxue Fanying Gongcheng Yu Gongyi (Chemical Reaction Engineering and Technology). 12. 2. pp.208 - 213 (June 1996). [31]. Cui, J.; Guo,Y.; Gao, J.; Xiai, Q., "Synthesis of Sodium Percarbonate at Normal Ordinary Temperature", Hua Shueh Shih Chieh (Chemical World), 37, 5, pp.243 - 247 (1996). [32]: Walsh, F., "A First Course in Electrochemical Electrochemical Consultancy, New York (1993).  Engineering", The  [33]. Kurniawan, P., "A Study of In-situ Electrochemical Brightening of Mechanical Pulp in Sodium Carbonate Solution", 4 year undergraduate thesis, Department of Chemical Engineering, University of British Columbia, Vancouver (April 1993). th  [34]. Kurniawan, P. "A Study of the Electrochemical Brightening of Thermomechanical Pulp in the Concentrated Sodium Carbonate Solution", Summer Report, Department of Chemical Engineering, University of British Columbia, Vancouver (November 1992). [35]. Osminin, E.N.; Zuikov, A.A.; Ivanova, L.M.; and Trefilova, L.S., "Effect of An Alkaline Medium on Peroxide Bleaching of Thermomechanical Pulp at High Temperatures", Bumazh. Prom.. No. 2: pp. 7 - 8 (Feb. 1987). [36]. Ali, T.; Fairbank, M.; McArthur, D.; Evans, T. and Whiting, P., "The Role of Silicate in Peroxide Brightening of Mechanical Pulp. Part n. The Effects of Retention  89  References  Time and Temperature", Journal of Pulp and Paper Science, 2, 14, pp.J23 - J28 (March 1988). [37]. Colodette, J. L.; Rothenberg, S.; and Dence, C. W., "Factors Affecting Hydrogen Peroxide Stability in the Brightening of Mechanical and Chemimechanical Pulps. Part I: Hydrogen Peroxide Stability in the Absence of Stabilizing Systems", Journal of Pulp and Paper Science, 6, 14, pp. J126 - J132 (November 1988). [38]. Colodette, J. L.; Rothenberg, S.; and Dence, C. W., "Factors Affecting Hydrogen Peroxide Stability in the Brightening of Mechanical and Chemimechanical Pulps. Part II: Hydrogen Peroxide Stability in the Presence of Sodium Silicate", Journal of Pulp and Paper Science, 1, 15, pp. J3 - J9 (January 1989). [39]. Colodette, J. L.; Rothenberg, S.; and Dence, C. W., "Factors Affecting Hydrogen Peroxide Stability in the Brightening of Mechanical and Chemimechanical Pulps. Part III: Hydrogen Peroxide Stability in the Presence of Magnesium and Combination of Stabilizers", Journal of Pulp and Paper Science, 2, 15, pp.J45 - J51 (March 1989). [40]. Murphy, T. D., "Design and Analysis of Industrial Experiments", Chemical Engineering, pp.168 - 182, (June 1977). [41]. Gileadi, E., "Electrode Kinetics for Chemists. Chemical Engineers and Material Scientists". VCH Pub. Inc., New York (1993). [42]. Walters, F. H.; Parker, Jr., Llyod R ; Morgan, S. L.; and Deming, S. N., "Sequential Simplex Optimization: A Technique for Improving Quality and Productivity in Research. Development, and Manufacturing". CRC Press, Inc., Boca Raton, Florida (1991). [43]. Zhang, J. J. and Oloman, C. W., "Kinetics of Electro-oxidation of Carbonate on Platinum in Aqueous Solution", Feb. 10, 1997 (to be published). [44]. Dence, C. W., and Reeve, D. W. (editors)."Pulp Bleaching: Principles and Practice". TAPPI Press, Atlanta, U.S.A. (1996). [45]. Liden, J. and Ohman, L. O , "Redox Stabilization of Iron and Manganese in the +11 Oxidation State by Magnesium Precipitates and Some Anionic Polymers. Implications for the Use of Oxygen-Based Bleaching Chemicals", Journal of Pulp and Paper Science, 23, 5, p.J193 (May 1997). [46] Rudie, A. W., McDonough, T.J., Rauh, F., Klein, R.J., Parker, J.L., and Heimburger, S.A., "An Evaluation of Sodium Carbonate as a Replacement for Sodium Hydroxide in Hydrogen Peroxide Bleaching of CTMP", 78 Annual Meeting of Canadian Pulp and Paper Association, Montreal, Jan 30-31, pp. B201 - B208 (1992). th  90  APPENDIX I Factorial Design Analysis (based on the paper by Thomas D. Murphy, Jr. [40]) One of the purpose for performing an experimental design was to investigate the interaction among a number of variables in an organized manner. One of the most common experimental design class is the two-level factorial design. In this design, if there are n factors to be investigated, a full two-level factorial design for each factor would require 2" experimental runs. For n > 2, centerpoints may be added to confirm a non-linear behavior of the system. The factorial design analysis allows the calculation of main, interaction and curvature effects of all the factors. A. Estimation of the Main Effects Consider n variables (Xi, X ,  X ) at two levels, i.e., "high" (+) and "low" (-). The  2  n  main effect is calculated as the difference between the average "high" and "low" factor level responses: Main effect of X = ^ {  ( responses at high X; ) - V ( responses at low X;) — ' ^ — , - {Eqn. Al} ( half the number of factorial runs) V  (  B. Estimation of the Interaction Effects The interaction effect is calculated as the average response difference between one half of the factorial runs and the other half. An interaction column is formed from the two factor columns that interact by multiplying the entries in the factor columns. As an example, a 2 factorial design is given below. 2  Run  Xi  X  2  XiX  2  (Interaction Column) +  Response  1  +  +  2  +  -  3  -  +  -  Y  3  4  -  -  +  Y  4  91  Y, Y " 2  Appendix I.  Interaction Effect = [( i + 4 ) - (^2 + Y )] Y  Y  3  { E q n >  A  2  }  C. Curvature Effects The curvature effect is the difference between the average of the centerpoint responses and the average of the factorial points. When all the effects are calculated, the significance of these values depends on the confidence interval (W) of the effects. If the calculated "effect" value is smaller than the confidence interval, it can be concluded that this effect is insignificant to the design. The confidence interval for the main and interaction effects is given by the following equation : W(effect) =  {Eqn. A3}  VN/4  whereas, the confidence interval for the curvature effect is given by the following equation : W (curvature effect) = t s  +^  {Eqn. A4}  where: t = student's Y statistics with v degrees of freedom s = response error (or pooled response error) with v degrees of freedom. N = the number of factorial runs in the design. C = the number of centerpoints. The response error can be calculated using the following equation :  {Eqn. A5}  (r-1) And the pooled response error can be calculated as 2  7  ?fe"l)s?  s =\,  {Eqn.A6}  2  A  i  Sample calculations for the factorial design analysis are given in Appendix II.  92  Appendix II Sample Calculations for the Factorial Design Analysis  A. Sample Calculation for the Response Errors for [H2O2], Brightness Gain and Yellowness Gain The following replicated runs and their responses were performed (see Table 4.2 and 4.3 for the complete experimental details):  Run  r  [H 0 ] (M)  Average [H 0 ]  AB (% ISO)  Average AB  (%)  Average AY  2  2  2  2  AY  1  2  0.014; 0.010  0.012  10; 7.0  8.5  -4; -1  -3  2  2  0.009; 0.010  0.010  10; 11  11  -4;-5  -5  3  2  0.013; 0.016  0.015  9.0; 10  9.5  -5; -5  -5  4  3  0.010; 0.016;  0.016  11; 9.0; 9.0  10  -8; -4; -10  -7  0.021 5  2  0.015; 0.009  0.012  11; 8.0  9.5  -5; -4  -5  6  3  0.007; 0.020;  0.015  5.0; 11; 14  10  1; -6; -7  -4  0.019 Note: "r" = the number of replicated runs; "AB" = brightness gain; "AY"= yellowness gain.  The response error or the standard deviation of each run was calculated using Equation A 5 from Appendix I, and the results are shown below:  (H)  g(AB)  2  0.003  2  2  2  2  0.001  1  1  3  2  0.002  0.7  0  4  3  0.005  1  3  5  2  0.004  2  1  6  3  0.007  5  4  Run  r  1  S  Note: "S" = standard deviation or response error for each run; "H" = [H2O2]  93  S  (AY)  Appendix II.  The pooled variance* for k= 5 separate estimates of error s;, each with n replicates, was calculated using Equation A6 from Appendix I. Hence : (1)  The pooled estimate of the response error for [H2O2] is : (0.003) +(0.00T) +(0.002) +2(0.005) +(0.004) 2  c 2  2  2  2  2  Su =  _ 1x10 1 A  —  5  1+1+1+2+1 S = + 0.004 M. H  (2)  The pooled estimate of the response error for Brightness Gain is : 2  (2.0) + (1,0) + (0.7) + 2 • (1.0) + (2.0) 2  JAR =  2  ***  2  2  1 +1 +1 +2 +1  2  — 1y  SAB= ± 1.4%ISO.  (3)  The pooled estimate of the response error for Yellowness Gain is. 2  (2) +(l) +(0) +2(3) +(l) 2  a AY  2  2  2  2 A  1+1+1+2+1  SAY = ± 2 %.  B. Calculation of the Confidence Interval for Each Effect The confidence interval for the main and interaction effect is calculated according to Equation A3 and for the curvature effect according to Equation A4 from Appendix I. (1)  The 95% confidence interval for the Main Effects The total degrees of freedom for the main effects are v = 5, two degrees of  freedom from the three centerpoints, and three degrees offreedomfromthe three variables. The student's f value for 95% confidence interval and v = 5 is 2.571. l  Therefore, the 95% confidence interval for the main effects on: (i) [H 0 ] is  W([H 0 ], effect) = ± 0.007 M.  (ii) Brightness gain is  W(AB, effect) = + 2.5 % I S O .  2  2  2  2  (iii) Yellowness gain is W(AY, effect) = ± 3.6 %.  In the calculation of pooled variance, only Run 1 to 5 were accounted for because Run 6 consists of centerpoint replicates.  94  Appendix 11.  (2)  The 95% confidence interval for the Curvature Effects If all effects werefirstorder and interactive, the expected response value at the  centroid of the design should be the average of the responses of the factorial runs: Average of [H 0 ] = 0.012 M; Average of brightness gain = 8.4 %ISO; 2  2  Average of yellowness gain = -3.5%. On the other hand, the actual centerpoint responses were 0.015 M, 10 % ISO and - 4 % for [H 0 ], brightness gain and yellowness gain respectively. 2  2  The difference between the average of the actual centerpoint responses and the factorial responses gave an estimate of a curvature effect of -0.002 M for [H 0 ], +1.6 2  2  %ISO for brightness gain and +0.5 % for yellowness gain. The total degrees of freedom for the curvature effects are v = 5. The student's value for 95% confidence interval and v = 5 is 2.571.  Therefore, the 95%  confidence interval for the curvature effects on: (i) [H 0 ] is  W([H 0 ], curvature) = +0.007 M.  (ii) Brightness gain is  W(AB, curvature) = ± 2.4 %ISO.  2  2  2  2  (iii) Yellowness gain is W(AY, curvature) = + 3.5 %.  C. Effect of Current Density and Current Concentration T a b l e 11.1 C u r r e n t C o n c e n t r a t i o n a n d C u r r e n t D e n s i t y f o r C o r r e s p o n d i n g C u r r e n t a n d A n o d e A r e a a n d the  Run  Temperature  CO  Current (A)  Brightness  Results  Anode Area (cm )  Current Concentration (A/dm )  Current Density (A/cm )  Brightness Gain (%ISO)  Yellowness Gain  2  3  2  (%)  1  66  5  15  7  0.34  8.5  -3  2  66  5  29  7  0.17  11  -5  3  46  5  29  7  0.17  9.5  -5  4  46  10  29  13  0.34  10  -7  5  66  10  29  13  0.34  9.5  -5  6  56  7.5  22  10  0.35  10  -4  7  46  10  15  13  0.69  10  -5  8  46  5  15  7  0.34  8  -3  9  66  10  15  13  0.69  2  4  95  Appendix II.  D. Estimates of the Main Effects of Temperature, Current and Anode Area (Discounting the result from Run 9) The main and interaction effects shown in Table 4.4 included the result from the anomalous Run 9. By discounting the result from Run 9, the main effects of temperature, current and anode area can be estimated as follows: Main Effect of X; = E(responses at high X;)/( the number of high Xi runs) £ (responses at low X;)/( the number of low Xj runs) T a b l e II. 2  S u m m a r y o f r e s p o n s e s f r o m t h e f a c t o r i a l d e s i g n ( w i t h o u t R u n 9)  Run  T  I  A  [Active oxygen] (M)  Brightness Gain (%ISO)  1  +  -  -  Yellowness Gain (%)  0.012  8.5  -3  2  +  -  +  0.010  11  -5  3  -  +  0.015  9.5  -5  4  +  +  0.016  10  -7  +  +  0.012  9.5  -5  7  +  -  0.016  10  -5  8  -  -  0.011  8.0  -3  Average Values  0.013  9.5  -5  Response Error  ± 0.004  ±1.4  ±2  5  +  For active oxygen concentration . the main effects of : a) . Temperature: [(0.012+0.01+0.012)/3]- [(0.015+0.016+0.016+0.011)/4] =-3.17E-3 b) . Current: [(0.016+0.012+0.016)/3] - [(0.012+0.010+0.015+0.011)/4] = 2.67E-3 c) . Anode Area: [(0.010+0.015+0.016+0.012)/4] - [(0.012+0.016+0.011)/3]= 2.5E-4  For brightness gain . the main effects of : a) . Temperature: [(8.5+11+9.5)/3] - [(9.5+10+10+8)/4] = 0.295 b) . Current: [(10+9.5+10)/3] - [(8.5+11+9.5+8.0)/4] = 0.583 c) . Anode Area: [(ll+9.5+10+9.5)/4] - [(8.5+10+8.0)/3] = 1.167  For yellowness gain . the main effects of : a). Temperature: [(-3-5-5)/3] - [(-5-7-5-3)/4] = 0.667  96  Appendix II.  b) . Current: [(-7-5-3)/3] - [(-3-5-5-3)/4] = -1 c) . Anode Area: [(-5-5-7-5)/4] - [(-3-5-3)/3] - -1.833  T a b l e II. 3  S u m m a r y of the Main Effects of Temperature, Current a n d A n o d e (without  Run  Area  9)  Factor  [active oxygen] (M) -0.003  Brightness Gain (%ISO) 0.3  Yellowness Gain  Current  0.003  0.6  -1  Anode Area  0.0003  1.2  -2  95% Confidence Interval  ± 0.007  ±2.5  ±4  Temperature  (%) 0.7  Table II. 3 shows that temperature, current and anode area do not have significant effects on the concentration of active oxygen, brightness gain and yellowness gain.  Although these effects are insignificant, the table shows that  temperature appears to have a negative effect on active oxygen concentration and positive effects on brightness gain and yellowness gain. The current and the anode area also appear to have a negative effect on yellowness gain and positive effect on active oxygen concentration and brightness gain. This situation is consistent with the conventional peroxide brightening practice.  97  Appendix III Sequential Simplex Optimization (taken from Walters et.al. [42])  In investigating a new process, the researchers would usually speculate the experimental conditions or the results of the process. They can either estimate the experimental conditions using a general theory or randomly perform experiments covering a wide range of experimental conditions. With some luck, the researchers might find a "good" experimental condition to focus their work on. More often than not, the "good" experimental condition turned out to be "not good enough" and the worst case was that the researchers wasted their time and effort shooting in the dark. Researchers also tend to be reluctant in investigating areas where they felt was "theoretically impossible to produce a good result" and they also tend to stay at the "comfortable" zone.  Most of the above experimental techniques were ineffective.  Sequential simplex optimization method offers a simple, effective and sequential way to find an optimum experimental condition. The simplicity of a sequential simplex optimization method lies in its ease in computation. There is no need for solving complicated equations. "A simplex is a geometric figure that has a number of vertexes (corners) equal to one more than the number of dimensions in the factor space" [42]. In other words, a k factor simplex is defined by k+1 points in that factor space. Each vertex in a simplex represents a set of experimental conditions. The lines drawn between the vertexes are used to visualize the simplex; they have no other function. Therefore, a one-factor (dimension) simplex is represented by a line, a two-factor simplex is represented by a triangle and a threefactor simplex is represented by a tetrahedron. Simplexes of higher dimensions are represented by "hypertetrahedra" that cannot be drawn, but their properties are analogous to the visualized simplexes.  The simplex moves by rejecting one vertex  (usually the one that gives the worst response) and projecting it through the average of the remaining vertexes to create one new reflection vertex on the opposite side of the simplex. This new vertex correponds to a new set of experimental conditions to be evaluated (see illustration in Figure 111.1). 98  Appendix III.  A  •  Old  New  New B  it-  T  c  New  \  1 \  \  \  old  °  HP  *-•;' \ A  i Old  F i g u r e III. 1  T h e s i m p l e x reflection m o v e f o r (A) o n e - d i m e n s i o n a l , (B) a n d (C) t h r e e - d i m e n s i o n a l factor  Dashed  lines represent the old simplex.  two-dimen-sional,  spaces.  Dark circles represent the vertexes.  circles s h o w the average of the remaining vertexes  Open  [42].  W. Spendley, et.al. published a paper in 1925 [42] which introduced the Simple Evolutionary Operation (EVOP) as a fast procedure for a simplex to reach optimum conditions. In the Simple EVOP, the worst vertex (W) would be rejected and the next-to-the-worst vertex (N) would automatically become the worst vertex (W) in the next simplex run regardless of the response from the new reflection vertex (R). This kind of simplex is also called the Fixed-Size Simplex Algorithm. In 1965, Nelder and Mead [42] introduced a Variable-Size Simplex Algorithm which allows the simplex "to expand in directions that are favorable and to contract in directions that are unfavorable" [42]. The possible moves in the variable-size simplex algorithm are shown in Figure III.2. 99  Appendix III.  1  F i g u r e III. 2  2  3  Possible moves  4 5 6 Value of XI  7  8  9  in the variable-size s i m p l e x  algorithm.  P = centroid of the remaining vertexes; B = best vertex; N = next-to-the-worst vertex; W = worst (wastebasket) vertex; R = reflection vertex; C = contraction vertex on the R side; C = contraction vertex on the W side. R  w  The procedures for the Variable-Size Simplex are as follows [42]: 1. Rank the vertexes of the first simplex on a worksheet in decreasing order of response from best to worst. Put the worst vertex into the row labeled W . 2. Calculate and evaluate the reflection vertex R: A. If N < R < B , use simplex B . . . N R , and go to 3. B . If R > B , calculate and evaluate the expansion vertex E: i. If E > B , use simplex B...NE, and go to 3. ii. If E < B , use simplex B . . . N R , and go to 3. C. If R < N, calculate the contraction vertex (CR or Cw): i. If R > W , calculate and evaluate CR, use simplex B...NCR, and go to 3. ii. If R < W , calculate and evaluate Cw, use simplex B . . . N C , and go to 3. W  100  Appendix III.  3. Always transfer the current row labeled N to the row labeled W on the next worksheet. Rank the remaining retained vertexes in order of decreasing response on the new worksheet, and go to 2.  A sample of a variable-size simplex, four factor worksheet is shown in Figure III - 3.  Simplex No.  Factor  -> Xi  x  X4  2  Response  Rank  Vertex  Times  Number  Retained  B Coordinates of retained vertexes N  P =l/k W  W  (P-W) R = P + (P-W)  R  0  Cw = P-(P-W)/2  Cw  0  CR = P + (P-W)/2  CR  0  E = R + (P-W)  E  0  (P-W)/2  F i g u r e III. 3  S a m p l e Worksheet for a four-factor Variable-Size Simplex Algorithm  [42]  A sequential simplex software called SIMPLEX-V can adjust up to 12 continuous factors using either a fixed-size or variable-size sequential simplex algorithm. SIMPLEX-V is an interactive menu-driven computer program for guiding a sequential simplex optimization. Initially, the program asks the user for various experimental parameters such as the number of factors, their names and boundaries, and whether the response is to be maximized or minimized.  SIMPLEX-V can  calculate a corner or tilted initial simplex, or accept a user-defined starting simplex from existing experimental information. After the responses at the initial vertexes have been evaluated, SIMPLEX-V automatically carries out the logic of the chosen 101  Appendix III.  simplex (fixed- or variable-size) algorithm and calculates the coordinates of the future vertex. The user then performs an experiment using this new vertex and the result or response is supplied to the program and SIMPLEX-V will evaluate and give another vertex. This procedure can be continued indefinitely, but usually the user can stop once the responses stay at the approximately the same level. At this stage, another optimization method, such as a factorial design analysis can be used to find the optimum conditions.  102  APPENDIX IV Examples of Simplex Optimization Method (Project "FINAL 1" and "TRYOUT") Two simplex optimization were performed to investigate the effect of maximizing a different number of responses on the direction of the simplex. Project " F I N A L 1" had a purpose to maximize the product of brightness gain and absolute value of yellowness gain ( A Brite x | A Yellow |), whereas project " T R Y O U T " only maximized the brightness gain (A Brite). The upper and lower limits for the factors and responses are as follows: Factor  N a m e  Current Area Temperature PH  Unit  Lower  Upper  Limit  Limit  Amp cm °C  0 5 25 9  2  Response  Unit  Name  20 29 70 11.8  %ISO  A Brite  %  I A Yellow |  Lower  Upper  Limit  Limit  0 0  20 30  The initial vertexes and responses for projects "FINAL 1" and " T R Y O U T " are shown in Table IV. 1. T a b l e IV. 1  Initial v e r t e x e s a n d  Vertex  R u n #  1 2 3 4 5  P-47 P-31 P-50 P-23 P-16  r e s p o n s e s for  Projects "FINAL 1" and  Current  Area  T e m p  (Amp)  (cm )  (°C)  2  11.5 10.0 11.5 7.5 5.0  28 29 29 21.75 14.5  p H  A  Brite  (%  47 46 48 56 46  10.68 10.62 10.64 10.68 10.69  " T R Y O U T " A  ISO)  Yellow (%)  10.1 8.7 12.2 13.3 9.5  -4.3 -4.8 -4.9 -7.0 -5.1  The simplex vertexes and responses for both projects are shown in Table IV.2 and Table IV.3. T a b l e IV. 2 Vertex  6 7 8 9 10  Simplex vertexes and R u n #  P-54 P-55 P-59 P-62 P-64  r e s p o n s e s f o r P r o j e c t " F I N A L 1"  Current  A r e a  T e m p  (Amp)  (cm )  (°C)  7.8 4.4 9.7 11.2 9.2  2  17.6 13.4 24.4 27.5 23.6  52.5 54.3 48.8 54 56.4 103  p H  A Brite (%  10.72 10.69 10.68 10.68 10.68  ISO)  11.1 7.6 10 12 10.6  A  Yellow (%)  -6.1 -3.1 -4.8 -7.0 -6.0  Appendix IV  T a b l e IV. 3 Vertex  T6 T7 T8 T9 T10  Simplex Vertexes and Responses R u n #  P-54 P-58 P-61 P-65 P-68  for Project  Current  Area  T e m p  (Amp)  (cm )  (°C)  7.8 11.8 7.8 8.7 11  17.6 28.9 20.6 22.5 29  52.5 53.3 57.9 55.2 53.4  2  P H  " T R Y O U T " A (%  10.72 10.68 10.68 10.68 10.64  Brite  A  ISO)  11.1 11.7 10.4 9.8 9.5  Yellow (%)  -6.1 -6.0 -4.6 -5.1 -5.3  Interpretation of the Simplex Direction It was interesting to note that the first vertex suggested by SIMPLEX-V for both projects (Vertex 6 and T6) was the same regardless of the different number of responses to maximize. The reason for this was that when the initial vertexes were ranked according to their responses, both projects had the same worst vertex, i.e. vertex 2. Therefore, the projection of the next vertex, which was the average of the remaining vertexes, was the same for both projects. After vertex 6 and T6, the simplex went on different directions for both projects. For project "FINAL 1", program SIMPLEX-V moved the direction of the vertexes back and forth to explore the best combination of factors and the best vertex (other than the initial vertex 1-4) was obtained at vertex 9 (A Brite = 12.0 and A Yellow = -7.0). After vertex 9, the response was not as good as the one from vertex 9, but the brightness gain was maintained at a minimum of 10 %ISO and yellowness gain at -5%. On the other hand, project "TRYOUT" seemed to be moving towards a lower brightness gain direction.  Vertex T7 gave a better response than T6, but the  subsequent vertexes (from T8 to T10) had worse responses. The responses from the suggested vertexes was worse than the response from the initial vertex 1-4. The direction of the vertexes for both projects showed that program SIMPLEX-V was more effective in finding the optimum conditions when two responses were involved. By trying to maximize both the brightness gain and the yellowness gain, the simplex in project "FINAL-1" moved more effectively toward the optimum condition than the simplex in project "TRYOUT". It might take a lot more experiments for project "TRYOUT" to reach a vertex with good brightness gain. The simplex experiments were stopped because after 5 experiments, the 104  Appendix IV  responses were still within the responses of the initial vertexes.  Furthermore, the  brightness gain from each vertex was within 9 to 13 %ISO and the yellowness gain was within -3 to -7%; this range of values were also obtained in the previous experiments before the simplex optimization experiments. A possible reason for the responses to fall within this range was that the initial vertexes did not cover a large range of experimental conditions. For example, the pH values were approximately 10.67 ± 0.05.  This range was very small for a simplex to move in a significant  direction. A similar situation also occurred for the anode area and the temperature. Because the initial ranges of each factor were so small, the simplex were "reluctant" and slow to move into another area. If the simplex experiments were continued, a better vertex than vertex 1-4 might have been found, however, the number of experiments to be performed in order to reach this vertex could be enormous. It would have been wiser to initialize the simplex with extreme ranges of experimental conditions, however, this also meant more experiments and time.  105  APPENDIX V Sampling and Analysis Procedures A. Measurement of the Concentration of Active Oxygen The concentration of active oxygen in the electrolyte or pulp suspension was measured using the permanganometric method. This method is actually a method for measuring the concentration of hydrogen peroxide in solution.  Since the active  oxygen produced by the electro-oxidation of sodium carbonate would eventually become hydrogen peroxide, it is reasonable to assume that all active oxygen present is hydrogen peroxide. The measurement was taken every 15 or 30 minutes depending on the length of the run or as needed. At the sampling time, one sample of 5 ml electrolyte solution was pipetted from the system. The sample was added to approximately 40 ml (not critical) of icecold 0.5 M H 2 S O 4 (concentration also not critical) in 150 ml Erlenmeyer flask. Into the flask, 2 drops of ferroin indicator (1,10 Phenantroline) was added, which would help detect the endpoint of the titration.  This mixture was titrated with 0.1 N  potassium permanganate (KMn04). The relationship between the volume of KMn04 and the concentration of active oxygen is as follows: 1 ml 0.1 N KMn0  4  =  0.001701 g H 0 2  2  0.00602 g C 0 " 2  2  =  6  0.00005 mol of active oxygen.  If pulp was present in the sample, before the addition of ferroin indicator, the acidified sample was filtered using suction filter. indicator.  The filtrate was then treated with ferroin  If the pulp was not filtered out, the permanganate titre could be  unreasonably high because the pulp also reacted with the potassium permanganate.  106  Appendix V  B. Measurement of the Optical Properties of Mechanical Pulp  The optical properties of mechanical pulp, such as brightness, yellowness, L*, a* and b*, was measured using an Elrepho spectrophotometer. A standard handsheet for the brightness measurement was formed according to the TAPPI Official Method T 272 om-92. When the handsheet was dried, it was folded twice, dividing the circular sheet into 4 equal division and measurement was taken at each fold on both surfaces, hence eight measurements were taken.  The final value was the average of the eight  measurements.  107  APPENDIX VI Cost Comparison between Electrochemical Brightening Process and Conventional Peroxide Brightening Process Basis : 500 tons of OD pulp per day  Conventional Peroxide Brightening Process Cost per day : •  3% H 0 per weight of pulp = 15,000 kg H 0 . Cost of H 0 = 15,000 kg x $ 1/kg = $ 15,000 2% NaOH per weight of pulp = 10,000 kg NaOH. Cost of NaOH = 10,000 kg x $ 0.30/kg = $ 3,000 3% Na Si0 per weight of pulp = 15,000 kg Na Si0 . Cost of Na Si0 = 15,000 kg x $ 0.70/kg = $ 10,500 0.3 % MgS0 per weight of pulp = 1,500 kg MgS0 . Cost of MgS0 = 1,500 kg x $ 0.15/kg = $ 2,250 0.3% DTPA per weight of pulp = 1,500 kg DTPA. Cost of DTPA = 1,500 kg x $2.50/kg = $ 3,750 Heating with steam @ $ 0.02/kWh steam. Heat Balance: Heat from steam = heat to increase pulp temperature from 30 - 70°C Assumptions: 1. The steam is saturated steam at P = 1 arm. 2. The consistency of the pulp for brightening is 20%. 3. The heat capacity of the pulp is the same as that of water. Calculation for the amount of steam needed per day: Qsteam = mol of water x heat capacity of water x temperature increase where: mol of water =(80%/20%) x 500 tons/18 g m o l ^ l l . l x 10 mol H 0 . heat capacity of water = 75.4 J mol" °C"\ temperature increase = 70°C - 30°C = 40°C. ••• Qsteam = 3.4 X 10 J = 93 X lfj kWTl. The cost of steam per day = 93,000 kWhx $0.02 /kWh = $ 1,860 2  2  2  2  • •  2  3  2  2  •  2  2  3  3  4  4  4  • •  7  2  1  ?  •  3  The estimated capital cost:  Cost per year : Assumptions : 1. One year = 350 operating days 2. Maintenance cost = 10% of capital cost/year • Estimated chemical cost (H 0 + NaOH + additives) • Heating cost • Maintenance cost 2  2  T O T A L COST PER YEAR APPROX.  108  $  5,000,000  $ $ $  12,075,000 651,000 500,000  $  13,000,000  Appendix VI  Basis : 500 tons of OD pulp per day  Electrochemical Brightening with Na2CC>3  :  Cost per day : Assumptions: 1. The consistency of pulp for electro-brightening process = 20%. 2. The electrochemical process was able to brighten 20% consistency pulp. 3. 98% chemical recovery of Na C0 and NaHC0 in the recycle. 4. The amount of additives used (Na Si0 , MgS0 , and DTP A) is the same as in the conventional peroxide brightening (no recycle of additives). 2  3  3  2  4  4  • CostofNa C0 (MW= 105.99) Amount of Na C0 needed for 20% pulp consistency = 0.106 kg Na C0 /kg liquor. Initial Na C0 charge = (0.8 kg liquor/0.2 kg pulp)(0.106 kg Na C0 /kg liquor) = 0.42 kg Na C0 / kg pulp. For 500 tons of pulp, the cost of initial charge of Na C0 is: 500,000 kg pulp x 0.42 kg Na C0 /kg pulp x $ 0.1/kg Na C0 = $ 21,000 Assuming 2% losses per charge, then the amount of losses per day is: 2% x 0.42 kg Na C0 /kg pulp x 500 ton pulp/day = 4.2 ton Na C0 /day The cost of additional Na C0 needed per day is: $0.1/kg Na C0 x 4,200 kg Na C0 = $ 420 2  3  2  2  3  2  3  2  2  3  2  2  2  2  3  3  2  3  3  2  3  3  2  3  3  3  2  3  • CostofNaHC0 (MW = 84.01) Amount of NaHC0 needed : 0.13 x 0.084 = 0.011 kg NaHC0 /kg liquor Initial NaHC0 charge = (0.8/0.2) (0.011) = 0.044 kg NaHC0 /kg pulp. For 500 tons of pulp, the cost of initial charge of NaHC0 is: 500,000 kg pulp x 0.044 kg NaHC0 /kg pulp x $0.1/kg NaHC0 = $ 2,200 Assuming 2% losses per charge, then the amount of losses per day is: 2% x 0.044 x 500,000 = 440 kg NaHC0 / day The cost of additional NaHC0 needed per day is : $0.1/kgNaHCO x440kgNaHCO = $ 44 3  3  3  3  3  3  3  3  3  3  3  3  • Cost of Na Si0 per day • Cost ofMgS0 per day • Cost of DTPA per day 2  $ 10,500 $ 2,250 $ 3,750  3  4  • Electricity cost: The power consumption of this process can be estimated from the specific energy. The lowest specific energy (for 1% pulp consistency) which gave at least 10 %ISO brightness gain was 20,000 kWh/ton of pulp (Run P-22). For 20% pulp consistency, the specific energy should decrease to 1,000 kWh/ton of pulp. For 500 tons of pulp, the amount of energy needed is 500 x 1,000 kWh = 500,000 kWh. .'. The cost of electricity = 500,000 kWh x $ 0.05 /kWh = $ 25,000 • Anode area required : To brighten 20% pulp for 3 hours, anode area needed was 29 cm . The amount of pulp brightened = (20% / 1%) x 7.5 g = 150 g. In 1 day (24 hrs), the amount of pulp brightened is (24 hr / 3 hr) x 150 g = 1.2 kg of pulp. To brighten 500 tons of pulp per day, the anode area required is (500 tons / 1.2 kg) x 29 x 10^* m = 1,200 m anode area. 2  2  109  2  Appendix VI  The estimated capital cost would be 1,200 m x $ 10,000/m = Total initial chemical cost (Na C0 + NaHC0 ) = Cost per year : Assumptions : 1. One year = 350 operating days 2. Maintenance cost = 10% of capital cost/year • Additional Na C0 + NaHC0 = 350 days x $ 464.00/day = • Cost of additives = 350 days x $ 16,500 /day = • Electricity cost: 350 days x $25,000/day = • Maintenance cost 2  2  2  3  3  2  3  3  TOTAL COST PER YEAR APPROXIMATELY  $ $  12,000,000 23,200  $ $ $ $  162,400 5,775,000 8,750,000 1,200,000  $  16,000,000  COST DIFFERENCES BETWEEN THE CONVENTIONAL PEROXIDE AND T H E E L E C T R O C H E M I C A L BRIGHTENING PROCESS  Conventional Brightening Capital Cost = Operating Cost =  $ 5,000,000 $ 13,000,000  Electrochemical Brightening Capital Cost = Operating cost =  110  $ 12,000,000 $ 16,000,000  Appendix VII. Raw Data  APPENDIX VII RAW DATA Sample # P-l to P-23 are Factorial Design Experiments Sample #  P-l  Conditions:  Anode type:  Platinized Titanium  Anode area:  14.5 cm  Water-cooled U-tube  Temperature:  60°C  Cathode type:  Tungsten Rod  Total Volume:  [Na C0 ]  1.0 M  Current:  700 ml 7 Amp  [NaHC0 ]  0.13 M  Time:  3 hours  [Na Si0 ]  0.034 M  Weight of pulp:  7.5 gOD  [DTPA]  0.6 g 0.04 g  Original Brightness: Original Yellowness:  44 %ISO 34%  2  3  3  2  3  [MgS0 ] 4  2  Original L * : 81 ; a * :2.6;b*: 15.7 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 ~ and/or H 0 ) during brightening process pH Time Temperature Voltage [H 0 ] 2  2  6  2  2  2  (min) 8 31 74 120 148  10.8 10.8 10.8 10.8 10.8  2  (°C)  (V)  (M)  67 68 66 67 69  19 20 20 20 21  0.011 0.013 0.009 0.008 0.006  Brightness: L * : 86 (+5)  54%ISO (+ 10) Yellowness: a * : 0 (-2.6) b*: 15.2 (-0.5)  Sample # Conditions:  P-2  29% (-5)  Platinized Titanium  Anode area:  14.5 cm  Water-cooled U-tube  Temperature:  46°C  Cathode type:  Tungsten Rod  Total Volume:  700 ml  [Na C0 ]  1.0 M  Current:  7 Amp  [NaHC0 ]  0.13 M  Time:  3 hours  [Na Si0 ]  0.034 M  Weight of pulp:  7.5 g OD  [DTPA]  0.6 g  Original Brightness:  44 %ISO  [MgS0 ]  0.04 g  Original Yellowness:  34%  Anode type:  2  3  3  2  3  4  2  Original L * : 81 ; a * :2.6;b*: 15.7 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 " and/or H 0 ) during brightening process 2  2  Time  pH  (min)  6  2  2  Temperature  Voltage  [H 0 ]  (°C)  (V)  (M)  2  2  26  10.8  47  17  0.01  60 92  10.8 10.8 10.8  46 46 46  17 17  0.009 0.008 0.008  10.8  46  123 151 Pulp yield: Brightness: L * : 84 (+3)  49%ISO (+ 5) a * : 1.1 (-1.5)  Yellowness: b*: 16.4 (+0.7)  18 18 33% (-1)  111  0.009  Appendix VII. Raw  Sample # Conditions:  P-3 Anode type:  Platinized Titanium  Anode area:  14.5 cm  Water-cooled U-tube  Temperature:  66°C  Cathode type: [Na C0 ]  Tungsten Rod 1.0 M  Total Volume: Current:  700 ml 7 Amp  [NaHCOj]  0.13 M  Time:  3 hours  [Na Si0 ]  0.034 M  Weight of pulp:  7.5 g OD  [DTPA]  0.6 g  Original Brightness:  44 %ISO  [MgS0 ]  0.04 g  Original Yellowness:  34%  2  3  2  3  4  2  Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 " and/or H 0 ) during brightening process 2  2  Time  pH  6  2  2  Temperature  Voltage  [H 0 ] (M)  2  2  CO  (V)  9  10.8  67  13  0.014  (min)  30  10.6  68  14  0.017  60  10.5  66  14  0.014  92  10.5  65  125 151  10.5 10.5  65 65  14 15 15  0.009 0.006 0.005  Pulp yield: Brightness: L * : 88 (+7) Sample # Conditions:  56%ISO (+ 12) Yellowness: a * : -0.6 (-3.2) b*: 16.1 (+0.4)  30% (-4)  P-4 Anode type:  Platinized Titanium  Anode area:  14.5 cm  Water-cooled U-tube  Temperature:  66°C  Cathode type:  Tungsten Rod  Total Volume:  700 ml  [Na C0 ]  1.0 M  Current:  5 Amp  [NaHCOj]  0.13 M  Time:  3 hours  [Na Si0 ]  0.034 M  Weight of pulp:  7.5 g OD  [DTPA]  0.6 g  Original Brightness:  44 %ISO  [MgS0 ]  0.04 g  Original Yellowness:  34%  2  3  2  3  4  2  Original L * : 81 ; a * :2.6;b*: 15.7 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 " and/or H 0 ) during brightening process 2  2  Time  pH  (min)  6  2  2  Temperature  Voltage  [H 0 ]  (°C)  (V)  (M)  2  2  31  10.7  66  12  0.014  61  10.7  65  14  0.015  91 115 161  10.7 10.7 10.5  66 67 65  13 12  0.011 0.009 0.008  13  Pulp yield: Brightness: L * : 87 (+6)  54%ISO (+ 10) Yellowness: a * : -0.6 (-3.2) b*: 16.0 (+0.3)  30% (-4)  112  Appendix VII. Raw Data  Sample # Conditions:  P-5 Anode type:  Platinized Titanium  Anode area:  29 cm  Water-cooled U-tube  Temperature:  66°C  Cathode type: [Na C0 ]  Tungsten Rod 1.0 M  Total Volume: Current:  700 ml 5 Amp  [NaHC0 ]  0.13 M  Time:  3 hours  [Na Si0 ]  0.034 M  Weight of pulp:  7.5 g OD  [DTPA]  0.6 g 0.04 g  Original Brightness: Original Yellowness:  44 %ISO 34%  2  3  3  2  3  [MgS0 ] 4  2  Original L * : 81 ; a * :2.6;b*: 15.7 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 ~ and/or H 0 ) during brightening process 2  2  6  pH  Time  2  2  Temperature  Voltage  [H 0 ]  (°C)  (V)  (M)  (min)  2  2  5 31  10.6 10.6  65 63  10 10  0.002 0.009  59  10.6  62  10  0.013  116  10.6  64  10  0.013  152 162  10.5 10.5  63 63  10 10  0.011 0.011  Pulp yield: Brightness: L * : 88 (+7) Sample # Conditions:  54%ISO (+ 10) Yellowness: a * : -0.4 (-3.0) b*: 16.1 (+0.4) P-6 Platinized Titanium Anode type:  30% (-4)  Anode area:  29 cm  Water-cooled U-tube  Temperature:  46°C  Cathode type:  Tungsten Rod  Total Volume:  700 ml  [Na C0 ]  1.0 M  Current:  5 Amp  [NaHC0 ]  0.13M  Time:  3 hours  [Na Si0 ]  0.034 M  Weight of pulp:  7.5 g OD  [DTPA]  0.6 g  Original Brightness:  44 %ISO  [MgS0 ]  0.04 g  Original Yellowness:  34%  2  3  3  2  3  4  2  Original L * : 81 ; a * :2.6;b*: 15.7 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 ~ and/or H 0 ) during brightening process 2  2  Time  pH  (min)  6  2  2  Temperature  Voltage  [H 0 ]  (°C)  (V)  (M)  2  2  12 31  10.9 10.9  46 42  11 13  0.012 0.013  63  10.9  46  12  0.016  91  10.8  45  12  0.017  125  10.8  47  13  0.018  164  10.9  45  13  0.023  Pulp yield: Brightness: L * : 86 (+5)  53%ISO (+ 9) Yellowness: a * : 0.6 (-2.0) b*: 14.7 (-1.0)  29% (-5)  113  Appendix VII. Raw  Sample # Conditions:  P-7 Anode type:  Platinized Titanium  Anode area:  29 cm  Water-cooled U-tube  Temperature:  46°C  Cathode type: [Na CO ] [NaHCOj]  Tungsten Rod 1.0 M 0.13 M  Total Volume: Current:  700 ml 10 Amp  Time:  [Na SiOj] [DTPA]  0.034 M  Weight of pulp:  3 hours 7.5 gOD  0.6 g 0.04 g  Original Brightness: Original Yellowness:  44 %ISO 34%  2  s  2  [MgS0 ] 4  2  Original L * : 81 ;a*:2.6;b*: 15.7 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen (C 0 ' and/or H 0 ) during brightening process 2  2  Time (min)  pH  4 30 74 133 150  10.9 10.8 10.8 10.8 10.8  6  2  2  Temperature  Voltage  [H 0 ]  (°C)  (V)  (M)  46 48 48 46 44  23 21 21 22 21  0.009 0.010 0.029 0.030 0.030  2  2  Pulp yield: Brightness: L * : 86 (+5)  55%ISO(+ 11) Yellowness: a*: 0.3 (-2.3) b*: 13.3 (-2.4)  Sample # Conditions:  P-8 Anode type:  26% (-8)  Platinized Titanium  Anode area:  29 cm  Water-cooled U-tube  Temperature:  66°C  Total Volume: Current:  700 ml 10 Amp  [NaHCOj]  Tungsten Rod 1.0M 0.13 M  Time:  3 hours  [Na Si0 ]  0.034 M  Weight of pulp:  7.5 g OD  [DTPA]  0.6 g 0.04 g  Original Brightness: Original Yellowness:  44 %ISO 34%  Cathode type:  [Na C0 ] 2  3  2  3  [MgS0 ] 4  2  Original L * : 81 ;a*:2.6;b*: 15.7 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen (C 0 " and/or H 0 ) during brightening process 2  2  Time  pH  (min)  6  2  2  Voltage  [H 0 ]  (°C)  Temperature  2  2  (V)  (M)  4 31  10.5 10.6  67 61  14 17  0.001 0.015  80 92 133  10.7 10.7 10.5  63 62 64  16 17 16  0.011 0.009 0.007  164  10.7  64  17  0.005  Pulp yield: Brightness: L * : 87 (+6)  55%ISO(+ll) Yellowness: a*: -0.2 (-2.8) b*: 15.4 (-0.3)  29% (-5)  114  Appendix VII. Raw Data  Sample # Conditions:  P-9  Mid-Point #1 Platinized Titanium  Anode area:  21.75 cm  Water-cooled U-tube  Temperature:  56°C  [Na C0 ]  Tungsten Rod 1.0 M  Total Volume: Current:  700 ml 7.5 Amp  [NaHC0 ]  0.13 M  Time:  3 hours  [Na SK> ]  0.034 M  Weight of pulp:  7.5 gOD  [DTPA]  0.6 g  Original Brightness:  44 %ISO  [MgS0 ]  0.04 g  Original Yellowness:  34%  Anode type:  Cathode type: 2  3  3  2  3  4  2  Original L * : 81 ; a * :2.6;b*: 15.7 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 " and/or H 0 ) during brightening process 2  2  pH  Time  6  2  2  Temperature  Voltage  [H 0 ]  (°C)  (V)  (M)  (min)  2  2  4  10.8  58  14  0.006  31 66 97  10.8 10.8 10.8  57 56 57  17 18 18  0.008 0.006 0.006  125  10.8  56  18  0.005  Pulp yield: Brightness: L * : 83 (+2) Sample # Conditions:  45%ISO (+ 1) Yellowness: a * : 1.3 (-1.3) b*: 18.6 (+2.9) P-10  37% (+3)  Mid Point #2 Platinized Titanium  Anode area:  21.75 cm  Water-cooled U-tube  Temperature:  56°C  Cathode type: [Na C0 ]  Tungsten Rod 1.0 M  Total Volume: Current:  700 ml 7.5 Amp  [NaHC0 ]  0.13 M  Time:  3 hours  [Na Si0 ]  0.034 M  Weight of pulp:  7.5 g OD  [DTPA]  0.6 g 0.04 g  Original Brightness: Original Yellowness:  45 %ISO 33%  Anode type:  2  3  3  2  3  [MgS0 ] 4  2  Original L * : 82 ;a*: 1.9; b*: 15.9 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 ~ and/or H 0 ) during brightening process 2  2  Time  pH  (min)  6  2  2  Temperature  Voltage  [H 0 ]  (°C)  (V)  (M)  2  2  4 36  10.8 10.8  57 57  15 14  0.004 0.005  65 97 121  10.8 10.8 10.8  56 56 56  14 15 15  0.006 0.007 0.007  155  10.8  56  16  0.007  Pulp yield: Brightness: L * : 83 (+1)  47%ISO (+2) a * : 0.9 (-1.0)  Yellowness: b*: 17.4 (+1.5)  35 % (+2)  115  Appendix VII. Raw Data  Sample #  P-ll  Mid Point #3  Conditions:  Anode type:  Platinized Titanium  Anode area:  21.75 cm  Water-cooled U-tube  Temperature:  56°C  Cathode type:  Tungsten Rod  Total Volume:  700 ml  [Na C0 ]  1.0 M  Current:  7.5 Amp  [NaHC0 ]  0.13 M  Time:  3 hours  [Na Si0 ]  0.034 M  Weight of pulp:  7.5 gOD  [DTPA]  0.6 g  Original Brightness:  [MgSOJ  0.04 g  Original Yellowness:  45 %ISO 33%  2  3  3  2  3  2  Original L * : 82 ; a * :1.9; b*: 15.9 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 ~ and/or H 0 ) during brightening process 2  2  Time  pH  6  2  2  Temperature  Voltage  [H 0 ]  (°C)  (V)  (M)  (min)  2  2  4  10.8  55  16  31  10.7  56  15  0.001 0.007  71  10.7  56  15  0.008  93  57 55  15 15  0.008  148  10.7 10.7  158  10.8  55  15  0.008  Pulp yield: Brightness: L * : 85 (+3) Sample # Conditions:  0.008  50%ISO (+5) a * : 0.2 (-1.7)  Yellowness: b*: 17.6 (+1.7)  P-12  Repeat Sample P-7 Platinized Titanium  Anode area:  29 cm  Water-cooled U-tube  Temperature:  46°C  Cathode type: [Na C0 ]  Tungsten Rod  Total Volume: Current:  700 ml  1.0 M  [NaHCOj]  0.13 M  Time:  3 hours  [Na Si0 ]  0.034 M  Weight of pulp:  7.5 g OD  [DTPA]  0.6 g  Original Brightness:  45 %ISO  [MgS0 ]  0.04 g  Original Yellowness:  33%  Anode type:  2  3  2  3  4  34 % (+1)  2  10 Amp  Original L * : 82 ;a*: 1.9; b*: 15.9 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 " and/or H 0 ) during brightening process 2  2  Time  pH  (min)  6  2  2  Temperature  Voltage  [H 0 ]  (°C)  (V)  (M)  2  2  4  11.0  46  20  0.011  30  10.9  46  20  0.016  71  10.8  45  21  0.017  102  10.9  46  19  0.016  141  10.8  46  20  0.014  155  10.8  46  20  0.014  Pulp yield: Brightness: L * : 87 (+5)  54%ISO (+9) a * : -0.4 (-2.3)  Yellowness: b*: 15.5 (-0.4)  29 % (-4)  116  Appendix VII. Raw Data  Sample #  P-14  Repeat Sample P-7 after treating the anode with N a O H  Conditions:  Anode type:  Platinized Titanium  Anode area:  29 cm  Water-cooled U-tube  Temperature:  46°C  Cathode type:  Tungsten Rod  Total Volume:  700 ml  [Na C0 ]  1.0M  Current:  10 Amp  [NaHCOj]  0.13M  Time:  3 hours  [Na Si0 ]  0.034 M  Weight of pulp:  7.5 gOD  [DTPA]  0.6 g  Original Brightness:  45 %ISO  [MgS0 ]  0.04 g  Original Yellowness:  33%  2  3  2  3  4  2  Original L * : 82 ;a*: 1.9; b*: 15.9 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 ~ and/or H 0 ) during brightening process 2  2  Time  6  pH  2  2  Temperature  Voltage  [H 0 ] 2  2  CO  (V)  (M)  5  11.0  45  22  0.015  33 64  10.9 10.9 10.9 10.9 10.9  21 22 22  0.021 0.021  112 131 162  46 46 47 46 45  20 21  (min)  Pulp yield: Brightness:  54%IS0 (+9)  L * : 85 (+3)  a * : -0.4 (-2.3)  Sample #  P-15  Conditions:  Anode type:  Yellowness:  0.017 0.017 0.015  23% (-10)  b*: 11.9 (-4.0)  Platinized Titanium  Anode area:  29 cm  Water-cooled U-tube  Temperature:  66°C  Tungsten Rod  Total Volume:  700 ml  [Na C0 ]  1.0 M  Current:  10 Amp  [NaHC0 ]  0.13 M  Time:  3 hours  [Na Si0 ]  0.034 M  Weight of pulp:  7.5 g OD  [DTPA]  0.6 g  Original Brightness:  45 %ISO  [MgS0 ]  0.04 g  Original Yellowness:  33%  Cathode type: 2  3  3  2  3  4  2  Original L * : 82 ; a * :1.9; b*: 15.9 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 ~ and/or H 0 ) during brightening process 2  2  Time  pH  6  2  2  Temperature  Voltage  [H 0 ] (M)  2  2  CO  (V)  3  10.5  63  15  0.005  32  10.6  66  0.009  60  10.6  63  15 15  93  10.5  63  16  0.008  159  10.6  63  16  0.008  (min)  Brightness: L * : 86 (+4)  53%ISO (+8) a * : 0.4 (-1.5)  Yellowness: b*: 14.7 (-1.2)  29 % (-4)  117  0.009  Appendix VII. Raw Data  Sample #  P-16  Conditions:  Anode type:  Platinized Titanium  Anode area:  14.5 cm  Water-cooled U-tube  Temperature:  46°C  Cathode type:  Tungsten Rod  Total Volume:  700 ml  [Na C0 ]  1.0 M  Current:  10 Amp  [NaHCOj]  0.13 M  Time:  3 hours  [Na Si0 ]  0.034 M  Weight of pulp:  7.5 gOD  [DTPA]  0.6 g 0.04 g  Original Brightness: Original Yellowness:  45 %ISO 33%  2  3  2  3  [MgS0 ] 4  2  Original L * : 82 ;a*: 1.9; b*: 15.9 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 " and/or H 0 ) during brightening process 2  2  Time  pH  6  2  Temperature  Voltage  38 63 120 147 161 Pulp yield: Brightness:  [H 0 ] 2  2  CO  (V)  (M)  10.7 10.7  51 48  21  10.7  46  0.010 0.016 0.017  10.7 10.7 10.7  46 46 46  (min) 4  2  22 23 23 23  a * : 0.7 (-1.2)  Sample #  P-17  Conditions:  Anode type:  0.015 0.015  23  55%ISO (+10) Yellowness:  L * : 86 (+4)  0.017  28 % (-5)  b*: 14.4 (-1.5)  Platinized Titanium  Anode area:  14.5 cm  Water-cooled U-tube  Temperature:  46°C  Cathode type: [Na C0 ]  Tungsten Rod  Total Volume:  700 ml  1.0 M  Current:  5 Amp  [NaHCOj]  0.13 M  Time:  3 hours  [Na Si0 ]  0.034 M  Weight of pulp:  7.5 gOD  [DTPA]  0.6 g  Original Brightness:  45 %ISO  [MgS0 ]  0.04 g  Original Yellowness:  33%  2  3  2  3  4  2  Original L*: 82 ;a*: 1.9; b*: 15.9 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 " and/or H 0 ) during brightening process 2  2  Time  pH  (min)  6  2  2  Temperature  Voltage  [H 0 ]  CO  (V)  (M)  2  2  4  10.8  48  16  0.009  33 63  10.8  46  15  10.8  46  15  0.011 0.013  96  10.8  46  15  0.011  121  10.8  46  16  0.011  154  10.8  45  15  0.011  Brightness: L * : 86 (+4)  53%ISO (+8) a * : 1.0 (-0.9)  Yellowness:  30 % (-3)  b*: 15.0 (-0.9)  118  Appendix VII. Raw Data  Sample #  P-18  Conditions:  Anode type:  Platinized Titanium  Anode area:  14.5 cm  Water-cooled U-tube  Temperature:  66°C  Tungsten Rod 1.0 M  Total Volume:  [Na C0 ]  700 ml 5 Amp  [NaHC0 ]  0.13 M  Time:  3 hours  [Na SiO ]  0.034 M  Weight of pulp:  7.5 gOD  [DTPA]  0.6 g  Original Brightness:  [MgS0 ]  0.04 g  Original Yellowness:  45 %ISO 33%  Cathode type: 2  3  3  2  s  4  Current:  2  Original L * : 82 ; a * :1.9; b*: 15.9 Note: Pulp was introduced after the initial 15 minutes.. Concentration of Active Oxygen ( C O ~ and/or H 0 ) during brightening process 2  2  Time  pH  s  2  2  Temperature  Voltage  [H 0 ]  (°C)  (V)  (M) 0.007 0.010  (min)  2  2  6 35 71  10.5 10.5 10.5  65 66 64  11 11 11  95  10.6  64  12  0.008  12  0.007  172 Brightness:  10.6 52%ISO (+7)  L * : 85 (+3)  a * : 1.3 (-0.6)  Sample # Conditions:  P-19 Anode type:  63  0.009  32 % (-1)  Yellowness: b*: 16.2 (+0.3)  Platinized Titanium  Anode area:  14.5 cm  Water-cooled U-tube  Temperature:  66°C  Cathode type:  Tungsten Rod  Total Volume:  700 ml  [Na C0 ]  1.0 M  Current:  10 Amp  [NaHC0 ]  0.13 M  Time:  3 hours  [Na Si0 ]  0.034 M  Weight of pulp:  7.5 g OD  [DTPA]  0.6 g 0.04 g  Original Brightness:  45 %ISO 33%  2  3  3  2  3  [MgS0 ] 4  Original Yellowness: Original L * : 82 ; a * : 1.9; b*: 15.9  Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 ~ and/or H 0 ) during brightening process 2  2  Time  pH  (min)  6  2  2  Temperature  Voltage  [H 0 ]  (°Q  (V)  (M)  2  2  5  10.2  70  19  0.002  31  10.3  66  19  0.005  66  10.4  67  18  0.005  92  10.4  65  19  0.003  120  10.4  66  20  0.003  153  10.4  66  20  0.003  Brightness: L * : 84 (+2)  47%IS0 (+2) a * : 1.9 (0)  Yellowness: b*: 18.3 (+2.4)  37 % (+4)  119  2  Appendix VII. Raw Data  Sample #  P-20  Midpoint  Conditions:  Anode type:  Platinized Titanium  Anode area:  21.75 cm  Water-cooled U-tube  Temperature:  56°C  Cathode type:  Tungsten Rod  Total Volume:  700 ml  [Na C0 ]  1.0 M  Current:  7.5 Amp  [NaHCOj]  0.13 M  Time:  3 hours  [Na Si0 ]  0.034 M  Weight of pulp:  7.5 g OD  [DTPA]  0.6 g  Original Brightness:  [MgS0 ]  0.04 g  Original Yellowness:  45 %ISO 33%  2  3  2  3  4  2  Original L * : 82 ;a*: 1.9; b*: 15.9 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 " and/or H 0 ) during brightening process 2  2  Time  6  pH  2  2  Temperature  Voltage  (min)  [H 0 ] 2  2  (°C)  (V)  (M)  6  10.6  56  15  0.010  62  10.5  53  18  0.025  98  10.5  54  19  0.021  134 155  10.5  52 55  17 17  0.020 0.018  Pulp yield: Brightness:  10.5  56%ISO(+ll) Yellowness:  L * : 87 (+5)  a * : 0.6 (-1.3)  Sample # Conditions:  P-21  27 % (-6)  b*: 13.6 (-2.3)  Platinized Titanium  Anode area:  29 cm  Water-cooled U-tube  Temperature:  66°C  Cathode type: [Na C0 ]  Tungsten Rod 1.0M  Total Volume: Current:  700 ml 5 Amp  [NaHC0 ]  0.13 M  Time:  3 hours  [Na Si0 ]  0.034 M  Weight of pulp:  7.5 g OD  [DTPA]  0.6 g  Original Brightness:  45 %ISO  [MgS0 ]  0.04 g  Original Yellowness:  33%  Anode type:  2  3  3  2  3  4  2  Original L * : 82 ; a * :1.9; b*: 15.9 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 ~ and/or H 0 ) during brightening process 2  2  Time  pH  (min)  6  2  2  Temperature  Voltage  [H 0 ]  (°C)  (V)  (M)  2  2  5  10.7  67  9  0.002  34  10.6  65  10  0.010  65  10.6  64  10  0.013  101  10.6  64  10  0.011  135  10.6  65  9  0.007  161  10.7  66  10  0.008  Pulp yield: Brightness: L * : 87 (+5)  56%ISO(+ll) Yellowness: a * : 0(-1.9)  28 % (-5)  b*: 14.5 (-1.4)  120  Appendix VII. Raw Data  Sample #  P-22  Conditions:  Anode type:  Platinized Titanium  Anode area:  29 cm  Water-cooled U-tube  Temperature:  46°C  Tungsten Rod 1.0 M  Total Volume:  700 ml  [Na C0 ]  Current:  5 Amp  [NaHC0 ]  0.13 M  Time:  3 hours  [Na Si0 ]  0.034 M  Weight of pulp:  7.5 g OD  [DTPA]  0.6 g  Original Brightness:  [MgS0 ]  0.04 g  Original Yellowness:  45 %ISO 33%  Cathode type: 2  3  3  2  3  4  2  Original L * : 82 ;a*: 1.9; b*: 15.9 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 ~ and/or H 0 ) during brightening process 2  2  Time  pH  6  2  2  Temperature  (min)  Voltage  [H 0 ]  CQ  2  2  (V)  (M)  6 40  10.7 10.7  46 45  11 11  0.009 0.016  70  10.7 10.7  47 45  10  0.018  10.6  46  10 11  0.019 0.019  10.6  47  11  0.018  91 125 157 Pulp yield: Brightness: L * : 86 (+4)  55%ISO (+10) Yellowness: a * : 0.9 (-1.0) b*: 14.3 (-1.6)  Sample #  P-23  MidPoint  Conditions:  Anode type:  Platinized Titanium  Anode area:  21.75 cm  Water-cooled U-tube  Temperature:  56°C  Cathode type:  Tungsten Rod  Total Volume:  700 ml  [Na C0 ]  1.0 M  Current:  7.5 Amp  [NaHC0 ]  0.13 M  Time:  3 hours  [Na Si0 ]  0.034 M  Weight of pulp:  7.5 g OD  [DTPA]  0.6 g  Original Brightness:  45 %ISO  [MgS0 ]  0.04 g  Original Yellowness:  33%  2  3  3  2  3  4  28 % (-5)  2  Original L * : 82 ; a * :1.9; b*: 15.9 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 " and/or H 0 ) during brightening process 2  2  Time  pH  (min)  6  2  2  Temperature  Voltage  [H 0 ]  (°Q  (V)  (M)  2  2  4  10.7  56  14  0.002  31  10.7  56  14  0.019  63  10.7  55  14  0.020  104  10.6  54  14  0.019  138  10.6  55  14  0.018  151  10.6  56  14  0.018  Pulp yield: Brightness: L * : 88 (+6)  59%IS0 (+14) Yellowness: b*: 13.9 (-2.0)  26 % (-7)  a * : 0.1 (-1.8)  121  Appendix VII. Raw Data  Sample #  P-24A  Using Glassy Carbon Anode (A)  Conditions:  Anode type:  Glassy Carbon  Anode area:  29 cm  Temperature:  46°C  2  Cathode type:  Tungsten Rod  Total Volume:  700 ml  [Na C0 ]  1.0 M  Current:  5 Amp  [NaHCOj]  0.13 M  Time:  3 hours  [Na Si0 ]  0.034 M  Weight of pulp:  7.5 g OD  [DTPA]  0.6 g  [MgS0 ]  0.04 g  Original Brightness: 45 %ISO Original 33% Yellowness: Original L * : 82 ;a*: 1.9; b*: 15.9  2  3  2  3  4  Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 ~ and/or H 0 ) during brightening process 2  2  Time  pH  6  2  2  Temperature  Voltage  [H 0 ]  (°C)  (V)  (M)  11.0 11.0  46 46  0.002 0.011  45  92  11.0 11.0  14 14 14  10.9  46  14 14  0.020  130 159  10.9  46  13  0.019  (min) 4 30 71  45  Brightness: L * : 84 (+2)  53%ISO (+8) a * : 0.7 (-1.2)  Yellowness: b*: 12.9 (-3.0)  Sample #  P-25A  Using Glassy Carbon Anode (A)  Conditions:  Anode type:  Glassy Carbon  2  2  0.018 0.019  26% (-7)  Anode area:  29 cm  Temperature:  66°C  Tungsten Rod  Total Volume:  700 ml  [Na C0 ]  1.0 M  Current:  5 Amp  [NaHC0 ]  0.13 M  Time:  3 hours  [Na Si0 ]  0.034 M  Weight of pulp:  7.5 g OD  [DTPA]  0.6 g  Original Brightness:  45 %ISO  [MgS0 ]  0.04 g  Original Yellowness:  33%  Cathode type: 2  3  3  2  3  4  2  Original L * : 82 ;a*: 1.9; b*: 15.9 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 " and/or H 0 ) during brightening process 2  2  Time  pH  (min)  6  2  2  Temperature  Voltage  [H 0 ]  CO  (V)  (M)  2  2  4  10.8  66  9  0.001  26  10.7  67  9  0.006  75  10.6  65  8  0.007  89  10.5  65  9  0.005  125  10.4  65  8  0.006  153  10.4  65  9  0.005  Brightness: L * : 77 (-5)  42%ISO (-3) a * : -0.2 (-2.1)  Yellowness: b*: 11.2 (-4.7)  24% (-9)  Observation: The anode started to desintegrate, resulting in greenish brown color in the suspension.  122  Appendix VII. Raw Data  Sample # Conditions:  P-26A Anode type:  Using Glassy Carbon Anode (A) Glassy Carbon Anode area:  29 cm  2  Temperature:  46°C 700 ml  Cathode type:  Tungsten Rod  Total Volume:  [Na C0 ] [NaHCOj]  1.0 M 0.13 M  Current: Time:  [Na Si0 ] [DTPA] [MgS0 ]  0.034 M  Weight of pulp:  3 hours 7.5 g OD  0.6 g 0.04 g  Original Brightness: Original Yellowness:  45 %ISO 33%  2  3  2  3  4  10 Amp  Original L * : 82 ;a*: 1.9; b*: 15.9 Need to use new/fresh anode surface.  Note: Pulp was introduced after the initial 15 minutes.  Concentration of Active Oxygen (C 0 " and/or H 0 ) during brightening process 2  2  Time  pH  6  2  2  Temperature  Voltage  [H 0 ]  (°C)  (V)  (M)  51 46 48 53 46  18 18 18 18 19  0.011 0.021 0.032 0.025 0.027  (min)  2  2  6 32 66 133 152 Pulp yield: Brightness: L * : 84 (-3)  54%IS0 (+9) a*: 0.4 (-1.5)  Yellowness: b*: 11.3 (-4.6)  Sample #  P-27A  Using Glassy Carbon Anode (A) without Silicate  Conditions:  Anode type:  Glassy Carbon  Anode area:  29 cm  Cathode type:  Tungsten Rod  [Na C0 ] [NaHC0 ]  1.0 M 0.13 M  Temperature: Total Volume: Current:  46°C 700 ml 10 Amp  Time:  [Na Si0 ] [DTPA] [MgS0 ]  0  Weight of pulp:  3 hours 7.5 g OD  0.6 g 0.04 g  45 %ISO Original Brightness: 33% Original Yellowness: Original L * : 82 ;a*: 1.9; b*: 15.9  10.7 10.6 10.6 10.4 10.5  2  3  3  2  3  4  23% (-10)  Note: Pulp was introduced after the initial 15 minutes Concentration of Active Oxygen (C 0 " and/or H 0 ) during brightening process 2  2  Time  pH  (min) 5 35 61 100 123 157 Pulp yield: Brightness: L * : 84 (+2)  10.5 10.3 10.4 10.4 10.3 10.4 53%IS0 (+8) a*: 0.4 (-1.5)  6  2  2  Temperature  Voltage  [H 0 ]  (°C)  (V)  (M)  47 49 46 48 46 43  20 20 20 20 20 19  0.011 0.020 0.027 0.025 0.025 0.019  Yellowness: b*: 11.2 (-4.7)  2  2  23% (-10)  Observation: The surface of the anode is still eroded even with the absence of silicate.  123  2  Appendix VII. Raw Data  Sample #  P-28A  Using Glassy Carbon Anode (A) without Silicate & M g S 0 .  Conditions:  Anode type:  Glassy Carbon  Anode area:  29 cm  Cathode type:  Tungsten Rod  Temperature: Total Volume:  46°C 700 ml  [Na COj]  1.0 M  Current:  10 Amp  [NaHCOj]  0.13 M  Time:  3 hours  [Na SiOj]  0  Weight of pulp:  7.5 g OD  [DTPA]  0.6 g  Original Brightness:  45 %ISO  [MgS0 ]  0  Original Yellowness:  33%  4  2  2  4  2  Original L * : 82 ; a * :1.9; b*: 15.9 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 " and/or H 0 ) during brightening process 2  2  Time  pH  6  2  2  Temperature  Voltage  [H 0 ]  CO  (V)  (M)  24 22  0.012 0.031  (min)  2  2  7 32  10.5 10.4  46 47  83  10.4  48  22  0.028  115 146 161  10.6 10.5  49 46  21 21  10.4  47  22  0.028 0.026 0.024  Pulp yield: Brightness: L * : 84 (+2)  53%IS0 (+8) a * : 0.5 (-1.4)  24% (-9)  Yellowness: b*: 11.6 (-4.3)  Observation: The surface of the anode is still eroded even with the absence of silicate and MgS0 . 4  Sample #  P-29A  Using Glassy Carbon Anode (A) without M g S 0 .  Conditions:  Anode type:  Glassy Carbon  Anode area:  29 cm  Cathode type:  Tungsten Rod  Temperature: Total Volume:  46°C 700 ml  [Na COj]  1.0 M  Current:  10 Amp  [NaHCOj]  0.13 M  Time:  3 hours  [Na SiOj]  0.034 M  Weight of pulp:  7.5 g OD  [DTPA]  0.6 g  Original Brightness:  45 %ISO  Original Yellowness:  33%  4  2  2  0  [MgS0 ] 4  Original L * : 82 ;a*: 1.9; b*: 15.9 Note: Pulp was introduced after the initial 15 minutes Concentration of Active Oxygen ( C 0 ~ and/or H 0 ) during brightening process 2  2  Time  pH  6  2  Temperature  2  Voltage  [H 0 ] 2  2  CO  (V)  (M)  5  10.8  43  17  0.015  30  10.7  46  17  0.029  61  10.6  49  17  0.025  104  10.6 10.5  50 52  17  0.022  17  0.022  (min)  177 Pulp yield: Brightness: L * : 85 (+3)  55%IS0 (-10) a * : 0.5 (-1.4)  Yellowness:  23% (-10)  b*: 11.4 (-4.5)  124  2  Appendix VII. Raw Data  From Sample P-30 onward, a modified U-tube with clamp was used as the anode to decrease resistance between the electrodes (bring them closer). Sample # Conditions:  P-30  Using the Modified U-tube Platinized Titanium  Anode area:  29 cm  Modified U-tube  Temperature:  46°C  Cathode type:  Tungsten Rod  Total Volume:  [Na C0 ]  1.0 M  Current:  700 ml 5 Amp  [NaHC0 ]  0.13 M  Time:  3 hours  [Na Si0 ]  0.034 M  Weight of pulp:  7.5 gOD  [DTPA]  0.6 g 0.04 g  Original Brightness: Original Yellowness:  51 %ISO 32%  Anode type:  2  3  3  2  3  [MgSOJ  2  Original L * : 84 ;a*: 2.9;b*: 15.0 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 ~ and/or H 0 ) during brightening process 2  2  Time  pH  6  2  2  Temperature  Voltage  [H 0 ]  (°Q  (V)  (M)  (min)  2  2  4  10.7  40  8  0.008  31 60 91 126  10.7 10.6 10.6 10.6  43 45 45 45  8 7 8 8  0.021 0.024 0.020 0.021  Pulp yield: Brightness:  57%ISO (+6)  29% (-3)  Yellowness:  L * : 88 (+4)  a * : 1.1 (-1.8)  b*: 14.6 (-0.4)  Sample # Conditions:  P-31  Using the Modified U-tube Platinized Titanium  Anode area:  29 cm  Modified U-tube  Temperature:  46°C  Cathode type: [Na C0 ] [NaHCOj]  Tungsten Rod 1.0 M 0.13 M  Total Volume: Current:  700 ml 10 Amp  Time:  2.6 hours  [Na Si0 ]  0.034 M  Weight of pulp:  7.5 gOD  [DTPA]  0.6 g 0.04 g  Original Brightness: Original Yellowness:  51%ISO 32%  Anode type:  2  3  2  3  [MgS0 ] 4  Original L * : 84 ;a*: 2.9;b*: 15.0 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 ~ and/or H 0 ) during brightening process 2  2  Time  pH  (min)  6  2  Temperature  Voltage  [H 0 ]  CO  (V)  (M)  12 13  0.010 0.033  13  0.035  14 13  0.026 0.022  4 33  10.7  47  10.6  46  61  10.5  92 142  10.5 10.6  46 46  Pulp yield: Brightness: L * : 89 (+5)  59%ISO (+8) a * : 0.8 (-2.1)  2  46 Yellowness: b*: 13.9 (-1.1)  27% (-5)  125  2  2  2  Appendix VII. Raw Data  Sample #  P-32  Using the Modified U-tube  Conditions:  Anode type:  Platinized Titanium  Anode area:  29 cm'  Modified U-tube  Temperature:  66°C  Cathode type:  Tungsten Rod  Total Volume:  700 ml  [Na C0 ]  1.0 M  Current:  5 Amp  [NaHC0 ]  0.13 M  Time:  3 hours  [Na Si0 ]  0.034 M  Weight of pulp:  7.5 gOD  [DTPA]  0.6 g  Original Brightness:  51 %ISO  [MgS0 ]  0.04 g  Original Yellowness:  32%  2  3  3  2  3  4  Original L * : 84 ;a*: 2.9; b*: 15.0 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 2  Time  pH  10.6 10.6 10.5  96 126 155  10.5 10.5 10.5  Pulp yield: Brightness:  56%ISO (+5)  2  2  Temperature  Voltage  [H 0 ]  CO  (V)  (M)  60 65 64 64  7 7 8  0.006 0.011 0.010 0.008  (min) 5 34 64  and/or H 0 ) during brightening process  2 6  2  9 9  64 63  2  0.010 0.013  9 28% (-4)  Yellowness:  L * : 88 (+4)  a * : 0.4 (-2.5)  b*: 15.0 (0)  Sample #  P-33  Conditions:  Anode type:  With Cathode less immersed in the suspension Platinized Titanium Anode area:  29 cm  Modified U-tube  Temperature:  66°C  Cathode type:  Tungsten Rod  Total Volume:  700 ml  [Na C0 ]  1.0M  Current:  5 Amp  [NaHC0 ]  0.13 M  Time:  3 hours  [Na Si0 ]  0.034 M  Weight of pulp:  7.5 g OD  [DTPA]  0.6 g  Original Brightness:  51%ISO  [MgS0 ]  0.04 g  Original Yellowness:  32%  2  3  3  2  3  4  Original L * : 84 ;a*: 2.9; b*: 15.0 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 ~ and/or H 0 ) during brightening process 2  2  Time  pH  6  2  2  Temperature  Voltage  [H 0 ] (M)  2  2  CO  (V)  61 62  7 7  0.006  33  10.6 10.6  57  10.5  63  7  0.012  91  10.5  64  8  0.012  124  10.5 10.5  63 62  8 9  0.011  (min) 5  152 Pulp yield: Brightness: L * : 88 (+4)  57%IS0 (+6) a * : 0.1 (-2.8)  Yellowness:  29% (-3)  b*: 15.2 (+0.2)  126  0.011  0.011  2  Appendix VII. Raw Data  Sample #  P-34 Anode type:  Platinized Titanium  Anode area:  29 cm  2  Modified U-tube  Temperature:  66°C  Cathode type: [Na COj]  Tungsten Rod 1.0 M  Total Volume:  700 ml 10 Amp  [NaHCOj]  0.13 M  Time:  3 hours  [Na SiOj]  0.034 M  Weight of pulp:  7.5 g OD  [DTPA]  0.6 g 0.04 g  Original Brightness: Original Yellowness:  51 %ISO 32%  2  2  [MgS0 ] 4  Current:  Original L * : 84 ; a * : 2.9;b*: 15.0 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 " and/or H 0 ) during brightening process 2  2  Time  pH  6  2  Temperature  (min) 4 31 145  2  Voltage  [H 0 ]  (°Q  (V)  (M)  74 68 66  10 10 10  0.007 0.024 0.024  10.7 10.8 10.7  2  2  Brightness: L * : 88 (+4)  58%ISO (+7) a * : 0.3(-2.6)  Yellowness: b*: 14.3 (-0.7)  Sample #  P-35  Using Ice Bath as Cold Water Supply for the Anode  Anode type:  Platinized Titanium  Anode area:  29 cm  Cathode type:  Modified U-tube Tungsten Rod  Temperature: Total Volume:  46°C 700 ml  [Na C0 ]  1.0 M  Current:  10 Amp  [NaHCOj]  0.13 M  Time:  1.5 hours  [Na Si0 ]  0.034 M  Weight of pulp:  7.5 g OD  [DTPA]  0.6 g 0.04 g  Original Brightness: Original Yellowness:  51 %ISO 32%  2  3  2  3  [MgSQ ] 4  27% (-5)  Original L * : 84 ; a * : 2.9;b*: 15.0 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 " and/or H 0 ) during brightening process 2  2  Time  pH  (min)  6  2  Temperature  2  Voltage  [H 0 ] 2  2  (°Q  (V)  (M)  4  11  48  13  0.012  33 68  11 11  48 47  13 13  0.021 0.022  Brightness: L * : 88 (+4)  57%IS0 (+6) a * : 0.8(-2.1)  Yellowness: b*: 15.6 (+0.6)  30% (-2)  127  2  Appendix VII. Raw Data  Sample # Conditions:  P-36  Using Ice Bath as Cold Water Supply for the Anode  Anode type:  Platinized Titanium Modified U-tube -  Anode area:  29 cm  Temperature:  66°C  Total Volume:  700 ml  Current:  10 Amp  2  Cathode type:  Tungsten Rod  [Na C0 ]  1.0 M  [NaHCOj]  0.13 M  Time:  1.5 hours  [Na Si0 ]  0.034 M  Weight of pulp:  7.5 g OD  [DTPA]  0.6 g  Original Brightness:  51 %ISO  [MgS0 ]  0.04 g  Original Yellowness:  32%  2  3  2  3  4  Original L * : 84 ;a*: 2.9; b*: 15.0 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 ~ and/or H 0 ) during brightening process 2  2  Time  pH  6  2  2  Temperature  Voltage  (°C)  (min)  [H 0 ] 2  2  (V)  (M)  6  10.7  66  10  0.008  25  10.7  67  10  0.019  49  10.7  67  65  10.6  66  11 11  0.016 0.016  Brightness: L * : 86 (+2) Sample # Conditions:  58%IS0 (+7) a * : 0(-2.9) P-37  29% (-3)  Yellowness: b*: 15.5 (+0.5)  [Na C0 ]  Using Ice Bath as Cold Water Supply for the Anode Platinized Titanium Anode area: Modified U-tube Temperature: Tungsten Rod Total Volume: 1.0 M Current:  29 cm 46°C 700 ml 10 Amp  [NaHC0 ]  0.13 M  Time:  3 hours  [Na Si0 ]  0.034 M  Weight of pulp:  7.5 g OD  [DTPA]  0.6 g  Original Brightness:  [MgS0 ]  0.04 g  Original Yellowness:  51 %ISO 32%  Anode type: Cathode type: 2  3  3  2  3  4  2  Original L * : 84 ;a*: 2.9; b*: 15.0 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 " and/or H 0 ) during brightening process 2  2  Time  pH  (min) 6  10.8  6  2  2  Temperature  Voltage  [H 0 ]  (°C)  (V)  (M)  44  13  0.012  13  0.031  31  2  2  66  36  16  0.046  93  46  14  0.038  135  46  14  0.031  Brightness: L * : 88 (+4)  60%ISO (+9) a * : 1.3 (-1.6)  Yellowness: b*: 14.3 (-0.7)  27% (-5)  128  Appendix VII. Raw Data  Investigating the Effect of Different Electrode Location Sample # Conditions:  P-38  Using Design A Platinized Titanium  Anode area:  29 cm  [Na C0 ]  Modified U-tube Tungsten Rod 1.0 M  Temperature: Total Volume: Current:  46°C 700 ml 10 Amp  [NaHCOj]  0.13 M  Time:  3 hours  [Na Si0 ]  0.034 M  Weight of pulp:  7.5 g OD  [DTPA]  0.6 g  Original Brightness:  51 %ISO  [MgS0 ]  0.04 g  Original Yellowness:  32%  Anode type: Cathode type: 2  3  2  3  4  2  Original L * : 84 ;a*: 2.9;b*: 15.0 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 " and/or H 0 ) during brightening process 2  2  Time  pH  6  2  2  Temperature  Voltage  [H 0 ]  CO  (V)  (M)  (min)  2  2  6  10.7  50  21  0.008  30  10.7  45  21  0.027  62  10.6  47  20  0.036  98 122 163  10.6 10.6 10.6  46 46 45  21 21 21  0.034 0.031 0.034  Brightness: L * : 89 (+5)  60%ISO (+9) a * : 0.9 (-2.0)  Yellowness: b*: 14.0 (-1.0)  Sample # Conditions:  P-39 Anode type:  Using Design A Platinized Titanium Modified U-tube  (Repeat P-38) Anode area: Temperature:  Cathode type:  Tungsten Rod 1.0 M  Total Volume: Current:  700 ml  [Na C0 ] [NaHC0 ] [Na Si0 ]  0.13 M 0.034 M  Time: Weight of pulp:  3 hours 7.5 gOD  [DTPA]  0.6 g 0.04 g  Original Brightness: Original Yellowness:  51 %ISO 32%  2  3  3  2  3  [MgS0 ] 4  27% (-5)  29 cm 46°C  10 Amp  Original L * : 84 ;a*: 2.9;b*: 15.0 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 " and/or H 0 ) during brightening process 2  2  Time  pH  (min)  6  2  2  Temperature  Voltage  [H 0 ]  (°C)  (V)  (M)  2  2  5 44  10.8 10.7  42 42  21 21  0.012 0.029  67  10.7  42  21  0.036  135  10.7  44  21  0.036  Brightness: L * : 90 (+6)  61%ISO(+10) a * : 0.5 (-2.4)  Yellowness: b*: 14.2 (-0.8)  27% (-5)  129  2  Appendix VII. Raw Data  Sample #  P-40  Conditions:  Anode type:  Using Design A Platinized Titanium  Anode area:  29 cm  Modified U-tube  Temperature:  66°C  Tungsten Rod 1.0M  Total Volume:  700 ml  [Na C0 ]  Current:  5 Amp  [NaHC0 ]  0.13 M  Time:  3 hours  [Na Si0 ]  0.034 M  Weight of pulp:  7.5 gOD  [DTPA]  0.6 g  Original Brightness:  51 %ISO  [MgS0 ]  0.04 g  Original Yellowness:  32%  Cathode type: 2  3  3  2  3  4  (Repeat P-21) 2  Original L * : 84 ;a*: 2.9;b*: 15.0 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 " and/or H 0 ) during brightening process 2  2  Time  pH  6  2  Temperature  Voltage  [H 0 ]  (°C)  (V)  (M)  10.7  49  10 9  0.006 0.009  10.4 10.5  60  9 10  0.004 0.018  (min) 5  2  30 79 142 Brightness:  54%IS0 (+3)  54  2  2  34% (+2)  Yellowness:  L * : 88 (+4)  a * : 0.8 (-2.1)  Sample #  P-41  Using Design C  Conditions:  Anode type:  Platinized Titanium  Anode area:  29 cm  Modified U-tube  Temperature:  46°C  Cathode type:  Tungsten Rod 1.0 M  Total Volume: Current:  700 ml  [Na C0 ] [NaHC0 ]  0.13 M  Time:  2 hours  [Na Si0 ]  0.034 M  Weight of pulp:  7.5 gOD  [DTPA]  0.6 g  Original Brightness:  51 %ISO  [MgS0 ]  0.04 g  Original Yellowness:  32%  2  3  3  2  3  4  b*: 17.8 (+2.8)  10 Amp  Original L * : 84 ;a*: 2.9; b*: 15.0 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 ~ and/or H 0 ) during brightening process 2  2  Time  pH  (min)  6  2  2  Temperature  Voltage  [H 0 ]  (°C)  (V)  (M)  2  2  6  10.9  44  12  0.011  32  10.7  45  12  0.030  62  10.7  44  11  0.033  Brightness: L * : 89 (+5)  58%IS0 (+7) a * : 1.1 (-1.8)  Yellowness: b*: 14.5 (-0.5)  28% (-4)  130  z  Appendix VII. Raw Data  Sample #  P-42  Using Design C  Conditions:  Anode type:  Platinized Titanium  Anode area:  29 cm  [Na C0 ]  Modified U-tube Tungsten Rod 1.0 M  Temperature:  Cathode type:  66°C 700 ml 10 Amp  [NaHC0 ]  0.13 M  Time:  3 hours  [Na Si0 ]  0.034 M  Weight of pulp:  7.5 g OD  [DTPA]  0.6 g 0.04 g  Original Brightness:  51 %ISO 32%  2  3  3  2  3  [MgS0 ] 4  Total Volume: Current:  Original Yellowness:  2  Original L * : 84 ;a*: 2.9;b*: 15.0 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 " and/or H 0 ) during brightening process 2  2  pH  Time  6  2  2  Temperature  Voltage  [H 0 ]  (°C)  (V)  (M)  (min)  2  2  8  10.5  64  13  0.010  31  10.4  64  12  0.021  68 96  10.2 10.3  79 64  12 12  0.009 0.013  12  0.014  121  10.3  66  Brightness: L * : 90 (+6)  62%IS0(+11) a * : 0.3 (-2.6)  Yellowness: b*: 14 (-1.0)  Sample # Conditions:  P-44 Anode type:  Using Design A Platinized Titanium Modified U-tube  27% (-5)  Anode area:  29 cm  Temperature:  66°C  Cathode type:  Tungsten Rod  Total Volume:  700 ml  [Na C0 ]  1.0 M  Current:  10 Amp  [NaHC0 ]  0.13 M  Time:  3 hours  [Na Si0 ]  0.034 M  Weight of pulp:  7.5 g OD  [DTPA]  0.6 g 0.04 g  Original Brightness: Original Yellowness:  51 %ISO 32%  2  3  3  2  3  [MgS0 ] 4  Original L * : 84 ;a*: 2.9;b*: 15.0 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 " and/or H 0 ) during brightening process 2  2  Time  pH  (min)  6  2  2  Temperature  Voltage  [H 0 ]  (°C)  (V)  (M)  2  2  5  10.7  54  16  0.008  30  10.5  65  15  0.019  61  10.5  65  16  0.014  93 171  10.5  64  10.6  47  16 17  0.016 0.024  Brightness: L * : 88 (+4)  2  57%ISO (+6) a * : 1.3 (-1.6)  Yellowness:  30% (-2)  b*: 15.6 (+0.6)  131  Appendix VII. Raw Data  Sample # Conditions:  P-45  Using Design C Platinized Titanium  Anode area:  29 cm  Modified U-tube  Temperature:  46°C  Cathode type:  Tungsten Rod  Total Volume:  700 ml  [Na C0 ]  1.0M  Current:  10 Amp  [NaHC0 ]  0.13 M  Time:  3 hours  [Na Si0 ]  0.034 M  Weight of pulp:  7.5 g OD  [DTPA]  0.6 g 0.04 g  Original Brightness: Original Yellowness:  51%ISO 32%  Anode type:  2  3  3  2  3  [MgS0 ] 4  2  Original L * : 84 ;a*: 2.9;b*: 15.0 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 ~ and/or H 0 ) during brightening process 2  2  Time  pH  6  2  2  Temperature  (min)  Voltage  [H 0 ] 2  2  (°C)  (V)  (M)  4 32 62 108  10.7 10.7 10.7 10.7  46 48 44 44  13 13 13 13  0.007 0.018 0.020 0.018  151  10.7  45  13  0.015  Brightness:  Yellowness:  L*:  a*:  b*:  Sample # Conditions:  P-46 Anode type:  Using Design A Platinized Titanium  Anode area:  28.09 cm  Modified U-tube  Temperature:  47.25 °C  Cathode type: [Na C0 ]  Tungsten Rod 1.0 M  Total Volume: Current:  700 ml 11.56 Amp  [NaHC0 ]  0.13 M  Time:  3 hours  [Na Si0 ]  0.034 M  Weight of pulp:  7.5 g OD  [DTPA]  0.6 g 0.04 g  Original Brightness: Original Yellowness:  51 %ISO 32%  2  3  3  2  3  [MgS0 ] 4  Original L * : 84 ;a*: 2.9;b*: 15.0 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 " and/or H 0 ) during brightening process 2  2  Time  pH  (min) 6 35 60 100 131 177  Pulp yield: Brightness: L * : 89 (+5)  11.0 10.8 10.8 10.8 10.8 10.7  6  2  2  Temperature  Voltage  [H 0 ]  (°C)  (V)  (M)  45 51 45  21 21  0.010 0.012 0.013  45 46  23 22  47  22  22  95% 58%IS0 (+7) a * : 1.1 (-1.8)  Yellowness:  30% (-2)  b*: 15.4 (-0.4)  132  2  2  0.013 0.013 0.013  2  Appendix VII. Raw Data  Sample #  P-47  Using Design C (same condition as P-46)  Anode type:  Platinized Titanium  Anode area:  28.09 cm  Modified U-tube  Temperature:  47.25 °C  Cathode type:  Tungsten Rod  Total Volume:  700 ml  [Na C0 ]  1.0 M  Current:  11.56 Amp  [NaHCOj]  0.13 M  Time:  3 hours  [Na SiOj]  0.034 M  Weight of pulp:  7.5 g OD  [DTPA]  0.6 g  Original Brightness:  [MgS0 ]  0.04 g  Original Yellowness:  51 %ISO 32%  2  3  2  4  2  Original L * : 84 ;a*: 2.9;b*: 15.0 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 " and/or H 0 ) during brightening process 2  2  Time  pH  6  2  2  Temperature  Voltage  [H 0 ]  CO  (V)  (M)  (min)  2  2  4  10.7  47  19  0.010  33  10.7 10.7  47 48  0.028  10.7 10.6  46 47  17 17 17 18  0.021  10.6  45  18  0.018  63 91 123 153  95%  Pulp yield: Brightness: L * : 90 (+6) Sample # Conditions:  0.027 0.021  61%ISO (+10) a * : 1.0 (-1.9) P-52  28% (-4)  Yellowness: b*: 14.3 (-0.7)  (New Electrode Design) Platinized Titanium  Anode area:  43.5 cm  Plate Design  Temperature:  47.2 °C  Total Volume:  [Na C0 ]  Thin tungsten rods 1.0M  Current:  1400 ml 23 Amp  [NaHCOj]  0.13 M  Time:  3 hours  [Na SiOj]  0.034 M  Weight of pulp:  15gOD  Original Brightness:  53 %ISO 31%  Anode type: Cathode type: 2  3  2  [DTPA] [MgS0 ] 4  1-2 g 0.08 g  Original Yellowness:  Original L * : 86 ;a*: 2.7;b*: 14.8 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 " and/or H 0 ) during brightening process 2  2  Time  pH  (min)  6  2  2  Temperature  Voltage  [H 0 ]  (°C)  (V)  (M)  2  2  6  10.8  0.010  10.7  45 47  8  32  9  0.020  63  10.6  48  9  0.022  90  10.6  48  10  0.022  124  10.5  50  10  0.015  161  10.5  49  10  0.012  Pulp yield: Brightness: L * : 89 (+3)  95% 60%ISO (+7) a * : 1.0 (-1.7)  Yellowness:  27% (-4)  b*: 14.3 (-0.5)  133  2  Appendix VII. Raw  Simplex Optimization Method  Gathering data for the initial vertex for the optimization methods  Sample #  P-48  Repeat Sample P-47 without anode depolarization  Conditions:  Anode type:  Platinized Titanium  Anode area:  28.09 cm  Modified U-tube  Temperature:  47.25 °C  Tungsten Rod  Total Volume:  700 ml  [Na C0 ]  1.0 M  Current:  11.56 Amp  [NaHCOj] [Na Si0 ]  0.13 M 0.034 M  Time: Weight of pulp:  3 hours 7.5 g OD  [DTPA]  0.6 g  Original Brightness:  51 %ISO  [MgS0 ]  0.04 g  Original Yellowness:  32%  Cathode type: 2  3  2  3  4  2  Original L * : 84 ;a*: 2.9;b*: 15.0 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 ~ and/or H 0 ) during brightening process 2  2  pH  Time  6  2  2  Temperature  Voltage  [H 0 ]  (°C)  (V)  (M)  (min)  2  2  6  10.8  49  19  0.008  34  10.7  46  18  0.015  68  10.7  47  17  0.018  145  10.7  48  18  0.016  Pulp yield:  94%  Brightness:  59%ISO (+8)  30% (-2)  Yellowness:  L * : 89 (+5)  a * : 1.6 (-1.3)  Sample #  P-49  Repeat Sample P-47 with anode depolarization  Conditions:  Anode type:  Platinized Titanium Modified U-tube  Anode area: Temperature:  28.09 cm  Cathode type:  Tungsten Rod  Total Volume:  700 ml  [Na C0 ]  1.0 M  Current:  11.56 Amp  [NaHCOj]  0.13 M  Time:  3 hours  [Na Si0 ]  0.034 M  Weight of pulp:  7.5 g OD  [DTPA]  0.6 g  Original Brightness:  51 %ISO  [MgS0 ]  0.04 g  Original Yellowness:  32%  2  3  2  3  4  b*: 15.3 (-0.3)  47.25 °C  Original L * : 84 ;a*: 2.9;b*: 15.0 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C O ~ and/or H 0 ) during brightening process 2  2  Time  pH  (min)  s  2  2  Temperature  Voltage  [H 0 ]  (°C)  (V)  (M)  2  2  4  10.8  47  13  0.011  32  10.6  53  13  0.028  79  10.7  46  14  0.030  98  10.7  45  14  0.036  123  10.6  46  15  0.040  178  10.6  46  14  0.038  Pulp yield:  97%  Brightness:  61%ISO (+10)  L * : 90 (+6)  a * : 2.3 (-0.6)  Yellowness:  29% (-3)  b*: 14.3 (-0.7)  134  2  Appendix VII. Raw Data  Sample #  P-50  Conditions:  Anode type:  Platinized Titanium  Anode area:  29 cm  Cathode type:  Modified U-tube Tungsten Rod  Temperature: Total Volume:  47.25 °C 700 ml  [Na COj]  1.0 M  Current:  11.56 Amp  [NaHCOj]  0.13 M  Time:  3 hours  [Na Si0 ]  0.034 M  Weight of pulp:  7.5 g OD  [DTPA]  0.6 g  Original Brightness:  51 %ISO  [MgSQ ]  0.04 g  Original Yellowness:  32%  2  2  3  4  2  Original L * : 84 ; a * :2.9; b*: 15.0 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 ~ and/or H 0 ) during brightening process 2  2  Time  pH  6  2  2  Temperature  Voltage  [H 0 ]  (°C)  (V)  (M)  (min)  2  2  5  10.8  44  13  0.010  32  10.6  50  12  0.040  60  10.6  50  12  0.040  90  10.6  46  13  0.050  124  10.6  50  13  0.050  157  10.6  44  13  0.050  Pulp yield:  96%  Brightness:  63%ISO (+12)  L * : 91 (+7)  a * : 1.7 (-1.2)  27% (-5)  Yellowness: b*: 13.7 (-1.3)  Sample #  NP-50  (No Pulp Run of Sample P-50)  Conditions:  Anode type:  Platinized Titanium  Anode area:  29 cm  Modified U-tube  Temperature:  47.25 °C  Tungsten Rod  Total Volume:  700 ml  [Na COj]  1.0 M  Current:  11.56 Amp  [NaHCOj]  0.13 M  Time:  3 hours  [Na Si0 ]  0.034 M  Weight of pulp:  0  [DTPA]  0.6 g  [MgS0 ]  0.04 g  Cathode type: 2  2  3  4  2  Concentration of Active Oxygen ( C 0 " and/or H 0 ) during brightening process 2  2  Time  pH  (min)  Temperature (°C)  6  2  2  Voltage  [H 0 ]  Theoretical  Actual  Current Efficiency  (V)  (M)  (mol)  (mol)  (%)  2  2  5  10.7  49  13  0.010  0.02  0.007  16  10.7  49  13  0.020  0.06  0.014  24  30  10.7  48  13  0.025  0.11  0.018  16  63  10.7  50  13  0.024  0.23  0.017  7  88  10.7  45  17  0.017  0.32  0.012  4  111  10.7  44  16  0.012  0.40  0.008  2  0.46  0.008  2  128  10.7  47  17  0.011  135  Appendix VII. Raw Data  Sample # P-51 Conditions: Anode type: Cathode type: [Na C0 ] [NaHCOj] [Na SiO] [DTPA] [MgS0 ] 2  3  2  s  4  29 cm Anode area: 47.2 °C Temperature: 700 ml Total Volume: 11.56 Amp Current: 3 hours Time: 7.5 g OD Weight of pulp: 53 %ISO Original Brightness: 31% Original Yellowness: Original L*: 86 ;a*: 2.7;b*: 14.8  Platinized Titanium  2  Modified U-tube Tungsten Rod 1.0 M 0.11M 0.034 M 0.6 g 0.04 g  Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen (C 0 " and/or H 0 ) during brightening process 2  2  Time (min) 4 30 63 94 123 155  Pulp yield: Brightness: L*: 91 (+5)  pH 10.8 10.6 10.6 10.6 10.6 10.6 97% 63%ISO (+10) a*: 0.7 (-1.0)  P-56 Sample # Conditions: Anode type:  6  2  2  Temperature (°C)  Voltage (V)  [H 0 ] (M)  43 50 46 47 47 47  14 13 13 13 14 14  0.010 0.029 0.041 0.039 0.033 0.040  Yellowness:  2  3  2  3  4  2  26% (-5)  b*: 13.9 (-0.9)  (Repeat Sample P-51) Anode area: Temperature:  Platinized Titanium Modified U-tube  Cathode type: [Na C0 ] [NaHCOj] [Na Si0 ] [DTPA] [MgS0 ]  2  29 cm  47.25 °C  700 ml Total Volume: 11.56 Amp Current: 3 hours Time: 8.0 g OD Weight of pulp: 53 %ISO Original Brightness: 31% Original Yellowness: Original L*: 86 ;a*: 2.7; b*: 14.8  Tungsten Rod 1.0 M 0.11M 0.034 M 0.6 g 0.04 g  Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen (C 0 ~ and/or H 0 ) during brightening process 2  2  Time (min)  pH  4  10.8  31 61 91 121  6  2  Temperature  2  CO  Voltage (V)  [H 0 ] (M)  43  17  0.011  10.7 10.6  47 48  17 16  0.046 0.044  10.6 10.6  47 47  16 16  0.043 0.041  91% Pulp yield: 64%IS0(+11) Brightness: L*: 91 (+5) a*: 0.2 (2.5)  Yellowness:  2  25% (-6)  b*: 13.2 (-1.6)  136  2  2  Appendix VII. Raw Data  Sample #  NP-51  (No Pulp Run of Sample P-51)  Conditions:  Anode type:  Platinized Titanium  Anode area:  29 cm  2  Modified U-tube  Temperature:  47.25 °C  Cathode type:  Tungsten Rod  Total Volume:  700 ml  [Na C0 ]  10 M  Current:  11.56 Amp  2  3  [NaHC0 ]  0.13 M  Time:  3 hours  [Na Si0 ]  0.034 M  Weight of pulp:  0  3  2  3  [DTPA]  0.6 g  [MgS0 ]  0.04 g  4  Concentration of Active Oxygen ( C 0 " and/or H 0 ) during brightening process 2  2  6  2  2  Time  pH  Temperature  Voltage  [H 0 ]  Theoretical  Actual  Current Efficiency  (min) 5  10.8  (°C) 46  (V) 15  (M) 0.010  (mol) 0.02  (mol) 0.007  (%) 39  2  2  31  10.7  48  16  0.023  0.11  0.016  14  63  10.7  48  16  0.020  0.23  0.014  6.2  92  10.7  49  17  0.015  0.33  0.011  3.2  123  10.7  49  17  0.009  0.44  0.006  1.4  135  10.7  49  17  0.009  0.49  0.006  1.3  P-53  (2% Pulp Consistency)  Anode type:  Platinized Titanium  Anode area:  29 cm  Cathode type:  Modified U-tube Tungsten Rod  Temperature: Total Volume:  47.2 °C 868 ml  [Na C0 ]  1.0 M  Current:  11.56 Amp  [NaHC0 ]  0.13 M  Time:  3 hours  [Na Si0 ]  0.034 M  Weight of pulp:  20gOD  [DTPA]  0.86 g  Original Brightness:  53 %ISO  [MgS0 ]  0.06 g  Original Yellowness:  31%  2  3  3  2  3  4  2  Original L * : 86 ;a*: 2.7; b*: 14.8 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 ~ and/or H 0 ) during brightening process 2  2  Time  pH  (min)  6  2  2  Temperature  Voltage  [H 0 ]  (°C)  (V)  (M)  2  2  7  10.7  48  15  0.012  105  10.3  62  15  0.018  127  10.5  46  16  0.025  147  10.5 .  45  16  0.036  Pulp yield: Brightness: L * : 90(+4)  62%ISO (+9) a * : 0 (-2.7)  Yellowness:  26% (-5)  b*: 14.0 (-0.8)  137  Appendix VII. Raw Data  Simplex Optimization Method (Project Final 1) Factors:  Current, Area, Temperature, and pH.  Responses:  A Brightness x AYellowness  Vertices:  Sample P-47, P-31, P-50, P-23, P-16  Vertices:  Sample P-47, P-31, P-50, P-23, P-16  Simplex Optimization Method (Project Tryouf) Factors:  Current, Area, Temperature, and pH.  Responses:  A Brightness  Sample #  P-54  (Simplex F I N A L 1 & Tryout Run 1)  Conditions:  Anode type: Cathode type:  Platinized Titanium Modified U-tube Tungsten Rod  Anode area: Temperature: Total Volume:  17.62 cm 52.5 °C 700 ml  [Na C0 ] [NaHCOj] [Na SiOj]  1.0M 0.07 M 0.034 M  Current: Time: Weight of pulp:  7.75 Amp 3 hours 7.5 g OD  [DTPA]  0.6 g  Original Brightness:  53 %ISO  [MgS0 ]  0.04 g  Original Yellowness:  31%  2  3  2  4  2  Note: Pulp was introduced after the initial 15 minutes. Original L * : 86 ;a*: 2.7;b*: 14.8 Concentration of Active Oxygen ( C 0 " and/or H 0 ) during brightening process 2  2  Time (min) 7 31 62 94  pH  6  2  2  10.8  Temperature (°C) 48  Voltage (V) 15  [H 0 ] (M) 0.009  11.3  50  14  0.030  11.2 10.8  52 51  14 14  0.041 0.039  131  10.7  51  14  0.033  154  10.7  53  14  0.038  Pulp yield: Brightness:  97% 64%ISO(+ll)  2  2  25% (-6)  Yellowness:  L * : 91 (+5)  a * : -0.1 (-2.8)  b*: 13.4 (-1.4)  Sample #  P-55  (Simplex F I N A L 1 Run 2)  Conditions:  Anode type: Cathode type: [Na COj] [NaHCOj]  Platinized Titanium Modified U-tube Tungsten Rod 1.0 M 0.07 M  Anode area: Temperature: Total Volume: Current: Time:  13.44 cm 54.25 °C 700 ml 4.38 Amp 3 hours  [Na Si0 ]  0.034 M  Weight of pulp:  8.0 g OD  [DTPA]  0.6 g  Original Brightness:  53 %ISO  2  2  3  2  0.04 g 31% Original Yellowness: [MgS0 ] Note: Pulp was introduced after the initial 15 minutes. Original L * : 86 ;a*: 2.7;b*: 14.8 Concentration of Active Oxygen ( C 0 " and/or H 0 ) during brightening process 4  2  Time  pH  (min) 5 32 62 91 121 165  11.0 10.7 10.7 10.7 10.7 10.6  Pulp yield:  90%  L * : 90 (+4)  a * : 0.1 (2.6)  6  2  2  Temperature  Voltage  (°C)  (V)  (M)  59 56 47  8 8 9 9 9 9  0.004 0.014 0.026  50 50 50 Brightness:  [H 0 ] 2  0.030 0.029 0.030  61%IS0(+8) Yellowness:  b*: 14.9 (+0.1)  138  2  28% (-3)  Appendix VII. Raw Data  Sample #  P-S7  (Simplex Tryout Run 2 ) - > 1.5 hour run  Anode type: Cathode type:  Platinized Titanium Modified U-tube Tungsten Rod  Anode area: Temperature: Total Volume:  28.89 cm 53.31 °C 700 ml  [Na C0 ]  1.0 M  Current:  11.84 Amp  [NaHCOj]  0.06 M  Time:  1.5 hours  [Na Si0 ]  0.034 M  Weight of pulp:  8.0 g OD  [DTPA]  0.6 g  Original Brightness:  53 %ISO  [MgS0 ]  0.04 g  Original Yellowness:  31%  2  3  2  3  4  2  Original L * : 86 ;a*: 2.7;b*: 14.8 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen (C O ~ and/or H 0 ) during brightening process 2  2  Time  pH  fi  2  2  Temperature  Voltage  [H 0 ]  (°C)  (V)  (M)  (min)  2  2  8  10.8  51  14  0.015  31  10.7  57  13  0.033  61  10.7  53  14  0.030  Pulp yield:  92%  Brightness:  60 %ISO (+7)  L * : 89 (+3)  a * : 1.3 (-1.4)  29 % (-2)  Yellowness: b*: 14.9 (+0.1)  P-58  (Simplex Tryout Run 2) —> 3 hour run  Anode type:  Platinized Titanium  Anode area:  28.89 cm  Modified U-tube  Temperature:  53.31 °C  Cathode type:  Tungsten Rod  Total Volume:  700 ml  [Na C0 ]  1.0 M  Current:  11.84 Amp  [NaHC0 ]  0.06 M  Time:  3 hours  [Na Si0 ]  0.034 M  Weight of pulp:  8.0 g OD  [DTPA]  0.6 g  Original Brightness:  53 %ISO  [MgS0 ]  0.04 g  Original Yellowness:  31%  2  3  3  2  3  4  Original L * : 86 ;a*: 2.7;b*: 14.8 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 " and/or H 0 ) during brightening process 2  2  Time  pH  (min)  6  2  2  Temperature  Voltage  [H 0 ]  (°C)  (V)  (M)  2  2  5  11.0  49  15  0.009  31  10.8  56  15  0.029  60  10.8  52  15  0.031  91  10.7  53  14  0.031  135  10.7  52  14  0.035  152  10.7  52  14  0.038  Pulp yield: Brightness: L * : 91 (+5)  90% 65 %ISO (+12) a*:-0.5 (-3.2)  Yellowness:  25% (-6)  b*: 13.7 (-1.1)  139  2  Appendix VII. Raw Data  Sample #  P-59  (Simplex Final 1 Run 3)  Conditions:  Anode type:  Platinized Titanium  Anode area:  24.36 cm  Cathode type:  Modified U-tube Tungsten Rod  Temperature: Total Volume:  48.81 °C 700 ml  [Na C0 ]  1.0 M  Current:  9.72 Amp  [NaHCOj]  0.10 M  Time:  3 hours  [Na Si0 ]  0.034 M  Weight of pulp:  8.0 g OD  [DTPA]  0.6 g  Original Brightness:  53 %ISO  [MgSOJ  0.04 g  Original Yellowness:  31%  2  3  2  3  Original L * : 86 ;a*: 2.7; b*: 14.8 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 " and/or H 0 ) during brightening process 2  2  pH  Time  6  2  2  Temperature  Voltage  [H 0 ]  CC)  (V)  (M)  (min)  2  2  8  10.7  48  17  0.014  31  10.6  51  16  0.036  62  10.6  48  15  0.040  92  10.6  48  14  0.040  127  10.6  47  14  0.041  10.6  49  14  0.039  150  90%  Pulp yield: Brightness:  63 %ISO (+10)  26 % (-5)  Yellowness:  L * : 90 (+4)  a * : 0.7 (-2.0)  Sample #  P-60  (Peroxide Brightening —> No Current)  Conditions:  Anode type:  Platinized Titanium  Anode area:  0  Cathode type:  Modified U-tube Tungsten Rod  Temperature: Total Volume:  52.5°C 700 ml  [Na C0 ]  1.0 M  Current:  0  [NaHCOj] [Na SiOj] [DTPA]  0.10 M 0.034 M 0.6 g  Time: Weight of pulp: Original Brightness:  3 hours 8.0 g OD 53 %ISO  [MgS0 ]  0.04 g  Original Yellowness:  31%  2  3  2  4  b*: 13.7 (-1.1)  Original L * : 86 ;a*: 2.7;b*: 14.8 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 " and/or H 0 ) during brightening process 2  2  Time  pH  (min) 2  10.7  29  10.6  6  2  2  Temperature  Voltage  [H 0 ]  CQ 53  (V) 0  (M) 0.027  54  0  0.052  2  2  79  10.6  53  0  0.018  105  10.6  53  0  0.028  123  10.6  53  0  0.048  10.6  53  0  0.023  158 Pulp yield:  93%  Brightness:  64%IS0(+11)  L * : 91 (+5)  a * : 0.3 (-2.4)  Yellowness:  26 % (-5)  b*: 14.0 (-0.8)  140  2  Appendix VII. Raw Data  Sample #  P-61  (Simplex Tryout Run 3)  Conditions:  Anode type: Cathode type:  Platinized Titanium Modified U-tube Tungsten Rod  Anode area: Temperature: Total Volume:  20.63 cm 57.91 °C 700 ml  [Na C0 ]  1.0 M  Current:  7.80 Amp  [NaHC0 ]  0.08 M  Time:  3 hours  [Na Si0 ]  0.034 M  Weight of pulp:  8.0 g OD  [DTPA]  0.6 g  Original Brightness:  53 %ISO  [MgS0 ]  0.04 g  Original Yellowness:  31%  2  3  3  2  3  4  2  Original L * : 86 ;a*: 2.7;b*: 14.8 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 ~ and/or H 0 ) during brightening process 2  2  Time  pH  6  2  2  Temperature  Voltage  [H 0 ]  (°C)  (V)  (M)  (min)  2  2  5  11.0  52  11  0.009  31  10.8  57  11  0.029  66  10.8  58  11  0.024  103  10.7  57  11  0.024  131  10.7  56  11  0.026  159  10.7  57  11  0.026  Pulp yield:  92%  Brightness:  63 %ISO (+10)  26 % (-5)  Yellowness:  L * : 91 (+5)  a * : 0.4 (-2.3)  Sample #  P-62  (Simplex F I N A L l Run 4)  Conditions:  Anode type: Cathode type: [Na C0 ]  Platinized Titanium Modified U-tube Tungsten Rod 1.0 M  Anode area: Temperature: Total Volume: Current:  27.53 cm 53.99 °C 700 ml 11.18 Amp  [NaHC0 ]  0.11M  Time:  3 hours  [Na Si0 ]  0.034 M  Weight of pulp:  8.0 g OD  [DTPA]  0.6 g •  Original Brightness:  53 %ISO  [MgS0 ]  0.04 g  Original Yellowness:  31%  2  3  3  2  3  4  b*: 14.0 (-0.8)  2  Original L * : 86 ;a*: 2.7;b*: 14.8 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 " and/or H 0 ) during brightening process 2  2  Time  pH  (min)  6  2  2  Temperature  Voltage  [H 0 ]  (°C)  (V)  (M)  2  2  6  10.8  51  14  0.013  31  10.7  56  14  0.038  75  10.6  56  14  0.029  106  10.6  53  14  0.030  124  10.6  54  14  0.031  153  10.6  54  14  0.031  Pulp yield:  93%  Brightness:  65 %ISO (+12)  L * : 91 (+5)  a * : -0.6 (-3.3)  Yellowness:  24 % (-7)  b*: 13.1 (-1.7)  141  Appendix VII. Raw Data  Sample #  P-63  (Repeat Sample P-62)  Conditions:  Anode type:  Platinized Titanium  Anode area:  27.53 cm  Modified U-tube  Temperature:  53.99 °C  Tungsten Rod  Total Volume:  700 ml  Cathode type:  2  [Na C0 ]  1.0 M  Current:  11.18 Amp  [NaHC0 ]  0.11M  Time:  3 hours  [Na Si0 ]  0.034 M  Weight of pulp:  8.0 g OD  [DTPA]  0.6 g  Original Brightness:  53 %ISO  [MgS0 ]  0.04 g  Original Yellowness:  31%  2  3  3  2  3  4  Original L * : 86 ;a*: 2.7;b*: 14.8 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 " and/or H 0 ) during brightening process 2  2  Time  pH  6  2  2  Temperature  Voltage  [H 0 ]  (°Q  (V)  (M)  (min)  2  2  6  10.8  52  15  0.013  33  10.6  58  15  0.031  63  10.6  58  15  0.026  90  10.6  52  16  0.033  121  10.6  53  15  0.033  172  10.6  51  15  0.036  Pulp yield: Brightness:  64%ISO(+ll)  24 % (-7)  Yellowness:  L * : 91 (+5)  a * : -0.7 (-3.4)  b*: 12.5 (-2.3)  Sample # Conditions:  P-70 Anode type:  (Repeat Sample P-62) Platinized Titanium Modified U-tube  Anode area: Temperature:  27.53 cm 53.99 °C  Cathode type:  Tungsten Rod  Total Volume:  700 ml  [Na C0 ]  1.0 M  Current:  11.18 Amp  [NaHC0 ] [Na Si0 ] [DTPA]  0.11M 0.034 M  Time: Weight of pulp:  3 hours 8.0 g OD  0.6 g  Original Brightness:  53 %ISO  [MgS0 ]  0.04 g  Original Yellowness:  31%  2  3  3  2  3  4  Note: Pulp was introduced after the initial 15 minutes.  Original L * : 86 ;a*: 2.7;b*: 14.8  Concentration of Active Oxygen ( C 0 ~ and/or H 0 ) during brightening process 2  2  Time  pH*  6  2  2  Temperature  Voltage  [H 0 ]  (°C)  (V)  (M)  (min)  2  2  5  11.1  54  15  0.006  36  10.9  57  15  0.025  70  10.9  55  15  0.026  105  11.1  51  15  0.028  125  11.0  54  14  0.025  173  10.9  56  15  0.024  *Note: The pH meter might be in error. Pulp yield:  90%  Brightness:  63 %ISO (+10)  L * : 90 (+4)  a * : -0.1 (-2.8)  Yellowness:  26 % (-5)  b*: 13.8 (-1.0)  142  2  Appendix VII. Raw Data  Sample #  P-64  (Simplex F I N A L 1 Run 5)  Conditions:  Anode type:  Platinized Titanium Modified U-tube  Anode area: Temperature:  23.59 cm 56.43 °C  Cathode type:  Tungsten Rod  Total Volume:  700 ml  [Na C0 ]  1.0 M  Current:  9.24 Amp  [NaHC0 ]  0.09 M  Time:  3 hours  [Na Si0 ]  0.034 M  Weight of pulp:  8.0 g OD  [DTPA]  0.6 g  Original Brightness:  53 %ISO  [MgS0 ]  0.04 g  Original Yellowness:  31%  2  3  3  2  3  4  2  Original L * : 86 ;a*: 2.7;b*: 14.8 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 " and/or H 0 ) during brightening process 2  2  Time  pH  6  2  2  Temperature  Voltage  [H 0 ]  (°C)  (V)  (M)  (min)  2  2  6  10.8  51  13  0.012  32  10.7  55  12  0.034  61  10.6  56  12  0.026  91  10.6  57  12  0.026  121  10.6  57  12  0.028  154  10.5  57  12  0.029  Pulp yield: Brightness:  64%ISO(+ll)  25 % (-6)  Yellowness:  L * : 91 (+5)  a * : -0.1 (-2.8)  b*: 13.4 (-1.4)  Sample #  P-65  (Simplex Tryout Run 4)  Conditions:  Anode type: Cathode type:  Platinized Titanium Modified U-tube Tungsten Rod  Anode area: Temperature: Total Volume:  22.47 cm 55.18 °C 700 ml  [Na C0 ]  1.0M  Current:  8.72 Amp  [NaHC0 ]  0.09 M  Time:  3 hours  [Na Si0 ]  0.034 M  Weight of pulp:  8.0 g OD  [DTPA]  0.6 g  Original Brightness:  53 %ISO  [MgS0 ]  0.04 g  Original Yellowness:  31%  2  3  3  2  3  4  Original L * : 86 ;a*: 2.7;b*: 14.8 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen (C O ~ and/or H 0 ) during brightening process pH Time Temperature Voltage [H 0 ] (min) (M) rc) (V) 5 10.8 54 14 0.010 33 10.6 57 13 0.023 2  2  fi  2  2  2  2  61  10.6  57  12  0.023  96  10.5  57  12  0.020  124  10.6  56  12  0.021  154  10.6  57  13  0.024  Pulp yield: Brightness: L * : 91 (+5)  63 %ISO (+10) a * : -0.2 (-2.9)  Yellowness:  26 % (-5)  b*: 14.0 (-0.8)  143  2  Appendix VII. Raw Data  Sample #  P-66  (Peroxide Brightening —> No Current)  Conditions:  Anode type:  Platinized Titanium  Anode area:  0  Modified U-tube Tungsten Rod (added manually)  Temperature: Total Volume: Current:  56 °C 700 ml 0  Time:  3 hours  [Na SiOj]  0.034 M  Weight of pulp:  8.0 g OD  [DTPA]  0.6 g  Original Brightness:  53 %ISO  [MgS0 ]  0.04 g  Original Yellowness:  31%  Cathode type: [Na C0 ] - > [H 0 ] 2  3  2  2  [NaHCOj] - > [NaOH] 2  4  Original L * : 86 ;a*: 2.7;b*: 14.8 Note: Pulp was introduced after the initial 15 minutes. Concentration of H 0 2  2  during brightening process  pH  Time  Temperature  Voltage  [H 0 ]  CC)  (V)  (M)  (min)  2  2  5  11.5  55  0  0.032  31  11.0  58  0  0.061  61  10.9  56  0  0.059  107  10.8  56  0  0.063  125  10.7  56  0  0.059  180  10.7  50  0  0.056  Pulp yield: Brightness:  64% —> Delignification ? 63 %ISO (+10)  Yellowness:  22 % (-9)  L * : 90 (+4)  a * : 0.8 (-1.9)  Sample #  P-67  (High p H and current)  Conditions:  Anode type:  Platinized Titanium Modified U-tube Tungsten Rod  Anode area: Temperature: Total Volume:  [Na COj]  1.0 M  Current:  12 Amp  [NaHCOj] [Na SiOj]  0.02 M 0.034 M  Time: Weight of pulp:  3 hours 8.0 g OD  [DTPA]  0.6 g  Original Brightness:  53 %ISO  [MgS0 ]  0.04 g  Original Yellowness:  31%  Cathode type: 2  2  4  b*: 12.5 (-2.3)  29 cm 62 °C 700 ml  2  Original L * : 86 ; a * : 2.7;b*: 14.8 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 " and/or H 0 ) during brightening process 2  2  Time  pH  (min)  6  2  Temperature  2  Voltage  [H 0 ] 2  2  (°C)  (V)  (M)  4 34  11.6 11.2  59 65  12 12  0.008 0.028  66  11.0  64  13  0.024  105  10.9  62  13  0.023  131  10.8  64  14  0.024  169  10.7  65  13  0.024  Pulp yield:  87%  Brightness:  63 %ISO (+10)  L * : 91 (+5)  a * : -1.0 (-3.7)  Yellowness:  25 % (-6)  b*: 14.0 (-0.8)  144  Appendix VII. Raw Data  Sample #  P-68  (Simplex Tryout Run #5)  Conditions:  Anode type:  Platinized Titanium  Anode area:  29 cm  Cathode type:  Modified U-tube Tungsten Rod  Temperature: Total Volume:  53.4 °C 700 ml  [Na C0 ]  1.0 M  Current:  10.96 Amp  [NaHC0 ]  0.11M  Time:  3 hours  [Na Si0 ]  0.034 M  Weight of pulp:  8.0 g OD  [DTPA]  0.6 g  Original Brightness:  53 %ISO  [MgS0 ]  0.04 g  Original Yellowness:  31%  2  3  3  2  3  4  2  Original L * : 86 ;a*: 2.7;b*: 14.8 Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 " and/or H 0 ) during brightening process 2  2  Time  pH  6  2  2  Temperature  CQ  (min)  Voltage  [H 0 ] (M)  2  2  5  10.7  54  (V) 13  0.008  33  10.5  60  15  0.025  65  10.5  59  14  0.021  95  10.5  54  14  0.021  121  10.5  53  15  0.023  151  10.5  54  15  0.024  Pulp yield:  89%  Brightness:  62 %ISO (+9)  26 % (-5)  Yellowness:  L * : 90 (+4)  a * : -0.3 (-3.0)  Sample #  P-69  (Simplex F I N A L 1 Run # 6)  Conditions:  Anode type:  Platinized Titanium  Anode area:  22.78 cm  Modified U-tube  Temperature:  54.5 °C  Cathode type:  Tungsten Rod  Total Volume:  700 ml  [Na C0 ]  1.0 M  Current:  9.36 Amp  [NaHC0 ]  0.08 M  Time:  3 hours  [Na Si0 ]  0.034 M  Weight of pulp:  8.0 g OD  [DTPA]  0.6 g  Original Brightness:  53 %ISO  [MgS0 ]  0.04 g  Original Yellowness:  31%  2  3  3  2  3  4  b*: 13.8 (-1.0)  Original L * : 86 ;a*: 2.7; b Note: Pulp was introduced after the initial 15 minutes. Concentration of Active Oxygen ( C 0 ~ and/or H 0 ) during brightening process 2  2  Time  pH  (min)  6  2  2  Temperature  Voltage  [H 0 ]  CQ  (V)  (M)  2  2  4  11.0  53  13  0.009  31  10.8  55  14  0.026  65  10.8  55  14  0.021  104  10.7  56  14  0.020  132  10.7  53  14  0.021  10.7  54  13  0.020  150 Pulp yield:  87%  Brightness:  60 %ISO (+7)  L * : 89 (+3)  a * : 1.0 (-1.7)  Yellowness:  28 % (-3)  b*: 14.2 (-0.6)  145  2  Appendix VII. Raw Data  Sample #  P-71  Purpose:  To see what caused the yellow colour in the solution/suspension.  Conditions:  Anode type:  (Using Straight Peroxide for Brightening) Platinized Titanium  Anode area:  29 cm  Modified U-tube  Temperature:  60 °C  [Na C0 ]  1.0M  Total Volume:  700 ml  [NaHCOj]  0.10M  Current:  0  [Na Si0 ]  0.034 M  Time:  3 hours  [DTPA]  0.6 g  Weight of pulp:  8.0 g OD  [MgS0 ]  0.04 g  Original Brightness:  53 %ISO  added in interval  Original Yellowness:  31%  2  3  2  3  4  H 0  2  Time (min) H 0  2  2  30%  2  Original L * : 86 ;a*: 2.7; b*: 14.8 2  Addition :  0  Initially, add 5.0 ml of H 0  23  At 23 min. add 3 ml of H 0  133  At 133 min. add 5 ml of H 0  143  At 143 min. ->  149  At 149 min. add 2 ml of H 0  2  0.028 M  169  At 169 min. add 2 ml of H 0  2  0.025 M  2  ->  2  2  2  96%  Brightness:  67%ISO (+14)  2  0.06 M 0.038 M  2  Pulp yield:  0.035 M  2  2  0.06 M  Yellowness:  23% (-8)  L * : 92 (+6)  a * : -1.9 (-4.6)  b*: 12.9 (-1.9) (Using Straight Peroxide for Brightening)  Sample #  P-72  Purpose:  To see what caused the yellow colour in the solution/suspension.  Conditions:  [Na CO ]  1.0 M  Temperature:  60 °C  [NaHCOj]  0.10 M  Total Volume:  700 ml  [Na Si0 ]  0.034 M  Current:  0  [DTPA]  0.6 g  Time:  3 hours  [MgS0 ]  0.04 g  Weight of pulp:  8.0 g OD  H 0 30%  added in interval  Original Brightness: 53 %ISO  2  s  2  3  4  2  2  No Anode  Original Yellowness: 31% Original L * : 86 ; a * : 2.7; b*: 14.8  Time (min) H 0 2  2  Addition :  19 28  add5mlofH202 add 3 mlofH202  138  add5mlofH202  0.06 M  153  add2mlofH202  0.035 M  163 171  0.029 M add2mlofH202  Pulp yield:  97%  Brightness:  65%ISO (+12)  L * : 91 (+5)  0.028 M at 19 minutes. 0.035 M  a * : -1.8 (-4.5)  0.023 M  Yellowness:  23% (-8)  b*: 13.2 (-1.6)  146  Appendix VII. Raw Data  Sample #  P-73  Conditions:  [Na C0 ]  1.0 M  Temperature:  [NaHCOj]  0.10M  Total Volume:  700 ml  [Na SiOj]  0.034 M  Current:  0  [DTPA]  0.6 g  Time:  3 hours  [MgS0 ]  0.04 g  Weight of pulp:  8.0 g OD  H 0 30%  27.60 ml at t=0  Original Brightness:  53 %ISO  Original Yellowness:  31%  (Peroxide Brightening of Mechanical Pulp) 2  3  2  4  2  2  No electrodes  60 °C  Original L * : 86 ;a*: 2.7; b 14.8 Concentration of Active Oxygen ( H 0 ) during brightening process 2  Time  pH  2  Temperature  Voltage  [H 0 ]  CQ  (V)  (M)  (min)  2  2  2  10.5  60  0  0.367  30  10.7  60  0  0.023  59  10.7  60  0  0.013  95  10.7  60  0  0.008  126  10.7  60  0  0.006  150  10.7  60  0  0.009  Observation: There was lots of foam during the first 15 to 20 minutes of the experiment. After that, no foam was detected for the rest of the run (3 hour run). Pulp yield: 92% Brightness: 91 (+5) Sample # Conditions:  65%ISO (+12) a * : -1.5 (-4.2) P-74  Yellowness:  23% (-8)  b*: 13.2 (-1.6) (Peroxide Brightening of Mechanical Pulp)  [Na COj] [NaHCOj]  1.0 M 0.10M  Temperature: Total Volume:  60 °C 700 ml  [Na SiOj] [DTPA] [MgS0 ] H 0 30%  0.034 M 0.6 g 0.04 g Use 15 ml initially, then add more during the run  Current: Time: Weight of pulp: Original Brightness:  0 3 hours 8.0 g OD 53 %ISO  2  2  4  2  2  31% Original Yellowness: 2.7; b*: 14.8 Original L * : 86 ; a * : Concentration of Active Oxygen ( H 0 ) during brightening process 2  Time  pH  2  Voltage  [H 0 ]  60  (V) 0  (M) 0.191  Temperature  Pulp was added after 5 min.  10.5  60  0  0.020  At 38 min. add 7 ml H202  59  10.5  60  0  0.021  At 68 min. add 7 ml H202  70  10.4  61  0  0.086  At 99 min. add 7 ml H202  91  10.5  59  0  0.021  At 129 min, add 7 ml H202  121  10.5  61  0  0.021  At 150 min. add 7 ml H202  CQ  (min) 2  10.4  31  2  . Comment  2  Observation: There was lots of foam upon the addition of hydrogen peroxide. Pulp yield:  93%  Brightness:  70%ISO (+17)  L * : 92 (+6)  a*:-2.3 (-5.0)  Yellowness:  19% (-12)  b*: 11.2 (-3.6)  147  Appendix VII. Raw Data  Sample #  P-75 P-75  Conditions:  [Na [ N a COsl C0 ]  (Peroxide Brightening of Mechanical Pulp) 1.0 M  Temperature:  60 °C  [NaHCOj] [Na Si0 ]  0.10 M 0.034 M  Total Volume: Current:  700 ml 0  [DTPA] [MgS0 ] H 0 30%  0.6 g 0.04 g 35mlatt=0  Time: 3 hours Weight of pulp: 8.0 gOD Original Brightness: 53 %ISO  22  3  2  3  4  2  2  No electrodes  Original Yellowness: 31% Original L * : 86 ;a*: 2.7; b*: 14.8  Concentration of Active Oxygen ( H 0 ) during brightening process 2  Time (min) 3 30  pH  59  10.6 10.7 10.7  90  10.7  122 148  10.7 10.7  2  Temperature  Voltage  [H 0 ]  (°C) 65 59  (M) 0.343 0.017  59  (V) 0 0 0  59  0  0.006  2  2  Pulp was added 5 minutes after initial H 0 addition 2  2  0.009  60 0 0.005 60 0 0.005 Observation: There was lots of foam during the first 15 to 20 minutes of the experiment. After that, no foam was detected for the rest of the run (3 hour run). Pulp yield: 91% Brightness: 59%ISO (+6) Yellowness: 28% (-3) L * : 89 (+3) Sample # Conditions:  a * : 0.4 (-2.3)  b*: 14.8 (0)  P-76  (Peroxide Brightening of Mechanical Pulp)  [Na C0 ]  1.0M  Temperature:  60 °C  [NaHC0 ]  0.10M  Total Volume:  700 ml  [Na Si0 ] [DTPA] [MgS0 ] H 0 30%  0.034 M 0.6 g 0.04 g  0 Current: Time: 3 hours Weight of pulp: 8.0 g OD Original Brightness: 53 %ISO Original Yellowness: 31% Original L * : 86 ;a*: 2.7; b*: 14.8  2  3  3  2  3  4  2  2  Use 10 ml initially, then add more during the run  Concentration of Active Oxygen ( H 0 ) during brightening process 2  Time (min) 3 23  pH  2  Voltage  10.5  Temperature (°C) 61  (V) 0  [H 0 ] (M) 0.145  Pulp was added after 5 min.  10.6  59  0  0.026  At 30 min. add 5 ml H 0  2  32  10.5  61  0  0.084  50  10.5  60  0  0.020  At 60 min. add 5 ml H 0  2  61  10.5  60  0  0.081  80  10.5  60  0  0.020  At 90 min. add 5 ml H 0  2  91  10.5  60  0  0.083  112  10.5  60  0  0.019  122  10.4  60  0  0.070  142  10.5  60  0  0.019  152  10.5  60  0  0.071  2  2  Comment  2  2  2  At 120 min. add 5 ml H 0  2  At 150 min. add 5 ml H 0  2  2  2  Observation: Pulp looked brighter after the addition of 5 ml of H202, but looked less bright 20 minutes after the addition of peroxide. Pulp yield: 88% Brightness: 68%IS0 (+15) Yellowness: 21% (-10) L * : 92 (+6)  a * : -2.0 (-4.7)  b*: 12.4 (-2.4)  148  Appendix VII. Raw Data  Sample #  P-77  (Repeat P-62, P-70, P-63 with more active 0  Conditions:  Anode type:  Platinized Titanium Modified U-tube Tungsten Rod 1.0 M  Cathode type: [Na C0 ] 2  3  2  generation)  Anode area: Temperature: Total Volume: Current:  27.53 cm 53.99 °C 700 ml 11.18 Amp 2  [NaHCOj]  0.11 M  Time:  3.5 hours  [Na SiOj]  0.034 M  Weight of pulp:  8.0 g O D  [DTPA]  0.6 g  Original Brightness:  [MgS0 ]  0.04 g  Original Yellowness:  2  4  53 %ISO 31%  Original L * : 86 ;a*: 2.7; b*: 14.8 Note: Pulp was introduced after the initial 39 minutes. Concentration of Active Oxygen ( C 0 " and/or H 0 ) during brightening process 2  2  6  2  2  Time (min)  pH  Temperature CC)  Voltage (V)  [H 0 ] (M)  37  10.7  51  16  0.030  60  10.7  55  15  0.030  94  10.7  54  15  0.023  173  10.7  55  15  0.023  10.7  53  15  0.021  184  L * : 91 (+5) Sample # Conditions:  2  95%  Pulp yield: Brightness:  2  64%IS0(+11) a * : -1.2 (-3.9) P-78  25% (-6)  Yellowness: b*: 13.9 (-0.9)  (Repeat Sample P-77)  Anode type:  Platinized Titanium  Anode area:  27.53 cm  Modified U-tube  Temperature:  53.99 °C  Cathode type:  Tungsten Rod  Total Volume:  700 ml  [Na COj]  1.0 M  Current:  11.18 Amp  [NaHCOj]  0.11M  Time:  3.5 hours  [Na SiOj]  0.034 M  Weight of pulp:  8.0 g OD  [DTPA]  0.6 g  Original Brightness: 53 %ISO  [MgS0 ]  0.04 g  Original Yellowness: 31%  2  2  4  2  Original L * : 86 ;a*: 2.7; b*: 14.8 Note: Pulp was introduced after the initial 35 minutes. Concentration of Active Oxygen ( C 0 " and/or H 0 ) during brightening process 2  2  Time  pH  (min)  6  2  2  Temperature  Voltage  [H 0 ] 2  2  CC)  (V)  (M)  25  10.8  52  15  0.024  63  10.8  54  14  0.033  99  10.7  54  15  0.028  162  10.7  54  15  0.030  174  10.7  53  15  0.030  10.7  53  16  0.029  185 Pulp yield: Brightness: L * : 91 (+5)  95% 65%IS0 (+12) a * : -1.4 (-4.1)  Yellowness:  24% (-7)  b*: 13.4 (-1.4)  149  Appendix VII. Raw Data  Sample #  P-79  (Repeat Sample P-23 with more initial H 2 0 2 generation)  Conditions:  Anode type:  Platinized Titanium  Anode area:  21.75 cm  Modified U-tube  Temperature:  56. °C  Cathode type:  Tungsten Rod  Total Volume:  700 ml  [Na COj]  1.0 M  Current:  7.5 Amp  [NaHCOj]  0.09 M  Time:  3 hours  [Na SiOj]  0.034 M  Weight of pulp:  8.0 g OD  [DTPA]  0.6 g  Original Brightness:  53 %ISO  [MgS0 ]  0.04 g  Original Yellowness:  31%  2  2  4  2  Original L * : 86 ; a * : 2.7; b*: 14.8 Note: Pulp was introduced after the initial 30 minutes. Concentration of Active Oxygen (C2062- and/or H202) during brightening process Time  pH  Temperature  Voltage  [H 0 ]  (°Q  (V)  (M)  (min)  2  2  - 26  11.0  52  10  0.019  60  10.9  58  10  0.021  109  10.8  57  10  0.018  121  10.8  57  10  0.018  139  10.8  55  10  0.020  161  10.8  55  10  0.020  Pulp yield: Brightness:  62%ISO (+9)  26% (-5)  Yellowness:  L * : 90 (+4)  a * : -1.1 (-3.8)  Sample #  P-80  (Repeat Sample P-78)  Conditions:  Anode type:  Platinized Titanium  Anode area:  27.53 cm  Modified U-tube  Temperature:  53.99 °C  Cathode type:  Tungsten Rod  Total Volume:  700 ml  [Na COj]  1.0 M  Current:  11.18 Amp  [NaHCOj]  0.11M  Time:  3 hours  [Na SiOj]  0.034 M  Weight of pulp:  7.6 g OD  [DTPA]  0.6 g  Original Brightness:  50 %ISO  [MgS0 ]  0.04 g  32% Original Yellowness: Original L * : 84 ; a * : 2.9;b*: 15.2  2  2  4  b*: 14.4 (-0.4)  Note: Pulp was introduced after the initial 31 minutes. Concentration of Active Oxygen ( C 0 2  Time  pH  (min)  2 6  and/or H 0 ) during brightening process 2  2  Temperature  Voltage  [H 0 ]  CQ  (V)  (M)  2  2  29  10.9  53  15  0.024  62  10.8  57  14  0.024  90  10.8  56  15  0.018  168  10.7  54  15  0.025  Pulp yield: Brightness: L * : 90 (+6)  61%ISO(+ll) a*:-1.1 (-4.0)  Yellowness:  26% (-6)  b*: 14.3 (-0.9)  150  2  Appendix VII. Raw Data  Sample # Conditions:  P-81  (Repeat Sample P-79) Platinized Titanium  Anode area:  21.75 cm  Modified U-tube  Temperature:  56. °C  Cathode type:  Tungsten Rod  Total Volume:  700 ml  [Na C0 ]  1.0 M  Current:  7.5 Amp  [NaHCOj]  0.09 M  Time:  3 hours  [Na SiOj]  0.034 M  Weight of pulp:  7.6 g OD  [DTPA]  0.6 g  Original Brightness:  50 %ISO  [MgSOd  0.04 g  Original Yellowness:  32%  Anode type:  2  3  2  Original L * : 84 ;a*: 2.9; b*: 15.2 Note: Pulp was introduced after the initial 31 minutes. Concentration of Active Oxygen ( C 0 ~ and/or H 0 ) during brightening process 2  2  6  2  2  Time (min)  pH  Temperature (°C)  Voltage (V)  [H 0 ] (M)  27  11.0  53  11  0.018  60  10.9  56  11  0.026  94  10.9  55  11  0.023  133  10.9  55  11  0.019  146  10.9  56  11  0.020  157  10.9  56  11  0.019  2  2  Pulp yield: Brightness:  63%ISO (+13)  25% (-7)  Yellowness:  L * : 91 (+7)  a * : -1.3 (-4.2)  b*: 14.2 (-1.0)  Sample #  P-82  Conditions:  Anode type:  (Produce H 0 at 30°C, then increase temperature to 54°C) 27.53 cm Platinized Titanium Anode area: Modified U-tube 53.99 °C Temperature: Tungsten Rod 700 ml Total Volume: 2  Cathode type:  2  2  [Na C0 ]  1.0 M  Current:  11.18 Amp  [NaHCOj] [Na SiOj]  0.11 M 0.034 M  Time: Weight of pulp:  3.2 hours 8.0 g OD  [DTPA]  0.6 g  Original Brightness:  53 %ISO  [MgS0 ]  0.04 g  Original Yellowness:  31%  2  3  2  4  Original L * : 86 ;a*: 2.7; b*: 14.8 Note: Pulp was introduced after the initial 43 minutes. Concentration of Active Oxygen ( C 0 " and/or H 0 ) during brightening process 2  2  Time  PH  (min)  6  2  2  Temperature  Voltage  [H 0 ]  (°C)  (V)  (M)  2  2  19  11.2  32  17  0.024  42  10.9  50  15  0.033  62  10.8  55  14  0.033  95  10.9  54  14  0.025  124  10.8  56  14  0.025  154  10.8  56  14  0.025  Pulp yield: Brightness:  64%IS0(+11)  L * : 91 (+5) a * : -0.9 (-3.6)  Yellowness:  24% (-7)  b*: 13.3 (-1.5)  151  2  Appendix VII. Raw Data  Sample #  P-83  (Repeat Sample P-82)  Anode type:  Platinized Titanium Modified U-tube  Anode area: Temperature:  27.53 cm 53.99 °C  Cathode type:  Tungsten Rod  Total Volume:  700 ml  [Na C0 ]  1.0 M  Current:  11.18 Amp  [NaHC0 ]  0.11M  Time:  3.2 hours  [Na Si0 ]  0.034 M  Weight of pulp:  8.0 g OD  [DTPA]  0.6 g  Original Brightness:  53 %ISO  [MgS0 ]  0.04 g  Original Yellowness:  31%  2  3  3  2  3  4  Original L * : 86 ;a*: 2.7; b*: 14.8 Note: Pulp was introduced after the initial 43 minutes. Concentration of Active Oxygen ( C 0 " and/or H 0 ) during brightening process 2  2  pH  Time  6  2  2  Temperature  Voltage  [H 0 ]  (°C)  (V)  (M)  (min)  2  2  21  10.9  36  18  0.031  38  10.6  49  15  0.034  76  10.6  53  15  0.034  113  10.5  52  15  0.030  137  10.5  51  15  0.030  170  10.5  54  15  0.030  Pulp yield:  96%  Brightness:  63%ISO (+10)  L * : 90 (+4) Sample # Conditions:  a * : -0.9 (-3.6) P-84  24% (-7)  Yellowness: b*: 13.4(-1.4)  (Repeat Sample P-83 using different pulp)  Anode type:  Platinized Titanium  Anode area:  27.53 cm  Cathode type:  Modified U-tube Tungsten Rod  Temperature: Total Volume:  2  [Na C0 ]  1.0 M  Current:  [NaHC0 ] [Na Si0 ]  0.11 M 0.034 M  Time: Weight of pulp:  53.99 °C 700 ml 11.18 Amp 3.2 hours 7.5 g OD  [DTPA] [MgS0 ]  0.6 g 0.04 g  Original Brightness: Original Yellowness:  50 %ISO 32%  2  3  3  2  3  4  Original L * : 84 ; a * :2.9; b*: 15.2 Note: Pulp was introduced after the initial 45 minutes. Concentration of Active Oxygen ( C 0 " and/or H 0 ) during brightening process 2  2  Time  pH  (min)  6  2  2  Temperature  Voltage  [H 0 ]  (°C)  (V)  (M)  2  2  20  10.7  37  17  0.028  47  10.5  48  15  0.033  62  10.4  53  14  0.031  91  10.4  54  14  0.028  125  10.4  55  15  0.020  162  10.4  52  15  0.029  Pulp yield: Brightness: L * : 90 (+6)  86% 62%IS0 (+12) a * : -0.6 (-3.5)  Yellowness:  25% (-7)  b*: 13.6(-1.6)  152  2  Appendix VII. Raw Data  Sample #  P-85  (Short time run: 1.5 hours)  Conditions:  Anode type:  Platinized Titanium  Anode area:  27.53 cm  Modified U-tube  Temperature:  53.99 °C  Cathode type:  Tungsten Rod  Total Volume:  700 ml  [Na C0 ]  1.0 M  Current:  11.18 Amp  [NaHCOj]  0.11M  Time:  1.5 hours  [Na Si0 ]  0.034 M  Weight of pulp:  8.0 g OD  [DTPA]  0.6 g  Original Brightness:  53 %ISO  [MgS0 ]  0.04 g  Original Yellowness:  31%  2  3  2  3  4  2  Original L * : 86 ;a*: 2.7; b*: 14.8 Note: Pulp was introduced after the initial 32 minutes. Concentration of Active Oxygen ( C 0 ~ and/or H 0 ) during brightening process 2  2  Time (min)  pH  21  10.4  29  10.3  60  10.2  75  10.2  Pulp yield:  94%  Brightness:  54%IS0 (+1)  6  2  2  Temperature  Voltage  CQ 46  (V) 15  [H O ] (M) 0.026  50  14  0.030  56  14  0.026  53  14  0.019  2  z  32% (+1)  Yellowness:  L * : 86 (+0)  a * : 3.5 (+0.8)  b*: 15.7(+0.9)  Sample #  P-86  (Two Stage Brightening)  Conditions:  Anode type:  Platinized Titanium  Anode area:  27.53 cm  Cathode type:  Modified U-tube Tungsten Rod  Temperature: Total Volume:  53.99 °C 700 ml  [Na C0 ]  1.0 M  Current:  11.18 Amp  [NaHC0 ]  0.11M  Time:  2 x 3hr runs  [Na Si0 ]  0.034 M  Weight of pulp:  8.0 g OD  [DTPA]  0.6 g  Original Brightness: 53 %ISO  [MgS0 ]  0.04 g  Original Yellowness: 31%  2  3  3  2  3  4  2  Original L * : 86 ;a*: 2.7; b*: 14.8 Note: Pulp was introduced after the initial 40 minutes in Stage 1 and 35 minutes in Stage 2. Concentration of Active Oxygen ( C 0 ~ and/or H 0 ) during brightening process 2  2  Time (min)  pH  36  10.3  65  10.2  6  2  Temperature  2  Voltage  [H 0 ]  50  (V) 13  (M) 0.030  53  13  0.033  CD.  2  2  Stage 1 was stopped at 3 hour and 10 minutes, pulp was washed with sulfuric acid, electrodes were reverse polarized. 32  10.2  55  17  0.031  64  10.2  57  15  0.024  Stage 2 was stopped at 4 hours and 37 minutes. Pulp yield:  92%  Brightness:  67%ISO(+14)  L * : 92 (+6)  a * : -1.0 (-3.7)  Yellowness:  22% (-9)  b*: 12.5(-2.3)  153  Appendix VII. Raw Data  Sample #  P-87  (Brightening with straight peroxide for comparison with P-88)  Conditions:  Anode type:  Platinized Titanium  Anode area:  27.53 cm  Modified U-tube  Temperature:  53.99 °C  Cathode type:  Tungsten Rod  Total Volume:  700 ml  [Na C0 ]  1.0 M  Current:  0 Amp  [NaHCOj]  0.11M  Time:  2.5 hours  [Na SiOj]  0.034 M  Weight of pulp:  8.0 gOD  [DTPA]  0.6 g  Original Brightness:  53 %ISO  [MgS0 ]  0.04 g  Original Yellowness: 31%  H 0  add 1.4 ml initially.  Original L * : 85 ; a * : 2.6; b*: 14.8  2  3  2  4  2  30%  2  2  Concentration of H 0 during brightening process 2  2  Time (min)  pH  2  10.5  31  Temperature  Voltage  CC) 54  (V) 0  10.5  54  0  0.031  56  10.4  54  0  0.024  At 62 min. add 0.3 ml of H 0 .  109  10.5  53  0  0.016  At 115 min. add 0.8 ml of H 0  141  10.5  54  0  0.026  Pulp yield:  96%  Brightness:  62%ISO (+9)  L * : 90 (+5) Sample #  a * : -0.7 (-3.3)  [H 0 ] (M) 2  Comment  2  0.029  At 6 min. add 2 ml of H 0 . 2  2  b*: 14.1(-0.7)  P-88  (Electrochemical run comparing with P-87).  Anode type:  Platinized Titanium  Anode area:  27.53 cm  Modified U-tube  Temperature:  53.99 °C  Cathode type:  Tungsten Rod  Total Volume:  700 ml  [Na COj]  1.0 M  Current:  11.18 Amp.  [NaHCOj]  0.11M  Time:  3 hours  [Na SiOj]  0.034 M  Weight of pulp:  8.0 g OD  [DTPA]  0.6 g  Original Brightness:  53 %ISO  [MgS0 ]  0.04 g  Original Yellowness:  31%  2  2  4  2  Original L * : 85 ; a * :2.6; b*: 14.8 Note: Pulp was added after the initial 30 minutes. Concentration of Active Oxygen ( C 0 ~ and/or H 0 ) during brightening process 2  2  Time  pH  (min)  6  2  2  Temperature  Voltage  [H 0 ]  CC)  (V)  (M)  2  2  21  10.5  48  18  0.020  34  10.5  54  16  0.026  55  10.4  52  16  0.028  113  10.4  51  16  0.025  143  10.3  51  16  0.025  Pulp yield:  98%  Brightness:  64%IS0(+11)  L * : 91 (+6)  a * : -0.6 (-3.2)  Yellowness:  25% (-6)  b*: 13.8 (-1.0)  154  2  2  26% (-5)  Yellowness:  2  Appendix VII. Raw Data  Sample #  P-89  (6 hour electrochemical run)  Conditions:  Anode type: Cathode type:  Platinized Titanium Modified U-tube Tungsten Rod  [Na C0 ] [NaHCOj] [Na SiOj] [DTPA] [MgS0 ]  1.0 M 0.11 M 0.034 M 0.6 g 0.04 g  2  3  2  4  Anode area: Temperature: Total Volume:  27.53 cm 53.99 °C 700 ml 11.18 Amp. Current: 6.5 hours Time: 8.0 g OD Weight of pulp: 53 %ISO Original Brightness: 31% Original Yellowness: Original L * : 85 ; a * :2.6 b*: 14.8 2  Note: Pulp was added after the initial 30 minutes. Concentration of Active Oxygen ( C 0 " and/or H 0 ) during brightening process 2  2  Time  6  2  2  pH  Temperature  Voltage  [H 0 ]  (min) 20 60  10.5 10.4  CC) 51 55  (V) 16 15  (M) 0.025 0.034  2  2  101  10.4  54  15  0.029  326  10.2  55  16  0.040  356  10.2  55  16  0.037  370  10.2  55  16  0.034  Pulp yield:  95%  Brightness:  68 %ISO (+15)  21 %(-10)  Yellowness:  L * : 92 (+7)  a * : -1.8 (-4.4)  Sample #  P-90  (Two Stage Electrochemical Brightening)  Conditions:  Anode type: Cathode type:  Platinized Titanium Modified U-tube Tungsten Rod  Anode area: Temperature: Total Volume:  27.53 cm 53.99 °C 700 ml  [Na C0 ] [NaHCOj] [Na SiOj] [DTPA]  1.0 M 0.11M 0.034 M 0.6 g  Current: Time: Weight of pulp: Original Brightness:  11.18 Amp 2 x 3hr runs 8.0 g OD 53 %ISO  2  3  2  b*: 11.9 (-2.9)  2  0.04 g  Original Yellowness: 31% Original L * : 85 ; a * :2.6; b*: 14.8 Note: Pulp was introduced after the initial 30 minutes in Stage 1 and 30 minutes in Stage 2. [MgS0 ] 4  Concentration of Active Oxygen ( C 0 " and/or H 0 ) during brightening process 2  2  Time (min)  pH  19  6  2  2  Temperature (°C)  Voltage (V)  [H 0 ] (M)  10.5  49  16  0.020  51  10.4  57  15  0.023  94  10.4  56  17  0.019  2  2  Stage 1 was stopped at 3 hours, pulp was washed with sulfuric acid, electrodes were reverse polarized. 20  10.5  51  19  0.026  82  10.4  54  17  0.025  91  10.5  54  16  0.024  113  10.5  52  16  0.025  145  10.4  52  16  0.028  Stage 2 was stopped at 3 hours, and pulp was washed with sulfuric acid. Pulp yield: Brightness: L * : 91 (+6)  92% 65 %ISO (+12) a * : -1.4 (-4.0)  Yellowness:  23% (-8)  b*: 13.0(-1.8)  155  Appendix VII. Raw  Sample # Conditions:  P-91  (Brightening with straight peroxide like Sample P-87)  Anode type:  Platinized Titanium  Anode area:  27.53 cm  Modified U-tube  Temperature:  53.99 °C  Tungsten Rod  Total Volume:  700 ml  [Na C0 ]  1.0 M  Current:  0 Amp  [NaHCOj]  0.11M  Time:  2.5 hours  [Na SiOj]  0.034 M  Weight of pulp:  8.0 g OD  [DTPA]  0.6 g  Original Brightness:  53 %ISO  [MgS0 ]  0.04 g  Original Yellowness:  31%  add 1.5 ml initially.  Original L * : 85 ; a * :2.6; b*: 14.8  Cathode type: 2  3  2  4  H 0 30% 2  2  Concentration of H 0 2  Time  2  2  during brightening process  pH  Temperature  Voltage  [H 0 ] 2  Comment  2  CQ  (V)  (M)  1  10.6  54  0  0.031  Pulp added at 5 min.  34  10.5  53  0  0.024  At 45 min. add 0.5 ml of H 0 .  62  10.5  54  0  0.025  At 155 min. add 0.5 ml of H 0  158  10.5  55  0  0.020  (min)  Pulp yield:  95%  Brightness:  63%ISO (+10)  2  2  26% (-5)  Yellowness:  L * : 91 (+6)  a * : -1.0 (-3.6)  b*: 14.3(-0.5)  Sample #  P-92  (6 hour electrochemical run)  Conditions:  Anode type:  Platinized Titanium  Anode area:  27.53 cm  Cathode type:  Modified U-tube Tungsten Rod  Temperature: Total Volume:  53.99 °C 700 ml  [Na C0 ]  1.0 M  Current:  11.18 Amp.  [NaHCOj]  0.11 M  Time:  [Na Si0 ]  0.034 M  Weight of pulp:  6 hours 8.0 g OD  [DTPA]  0.6 g  Original Brightness:  53 %ISO  [MgSOJ  0.04 g  Original Yellowness:  31%  2  3  2  3  Original L * : 85 ; a * : 2.6; b*: 14.8 Note: Pulp was added after the initial 30 minutes. Concentration of Active Oxygen ( C 0 " and/or H 0 ) during brightening 2  2  Time  pH  6  2  2  Temperature  Voltage  [H 0 ]  CQ 51  (V) 16  (M) 0.023  10.4  56  15  0.022  10.4  54  15  0.021  159  10.3  52  15  0.031  304  10.3  54  15  0.031  321  10.3  55  15  0.025  334  10.3  53  15  0.025  347  10.3  53  15  0.019  (min) 21  10.5  56 86  Pulp yield: Brightness: L * : 92 (+7)  92% 66 %ISO (+13) a * : -1.3 (-3.9)  Yellowness:  23 % (-8)  b*: 12.8 (-2.0)  156  2  2  2  2  Appendix VII Raw Data  Sample #  P-93  (Brightening with straight peroxide and N a O H )  Conditions:  Anode type:  Platinized Titanium  Anode area:  27.53 cm  Cathode type:  Modified U-tube Tungsten Rod  Temperature: Total Volume:  54 °C 700 ml  [Na C0 ]  0M  Current:  0 Amp  [NaHCOj]  0M  Time:  2.5 hours  [Na SiOj]  0.034 M  Weight of pulp:  8.0 g OD  [DTPA]  0.6 g  Original Brightness:  53 %ISO  [MgS0 ]  0.04 g  Original Yellowness:  31%  H 0  add 1.5 ml initially.  Original L * : 85 ; a * :2.6; b*: 14.8  2  3  2  4  2  2  30%  2  N a O H was added to adjust p H . Concentration of Active Oxygen ( C 0 " and/or H 0 ) during brightening process 2  2  Time (min) 1  pH  6  2  2  10.4  Temperature (°C) 54  Voltage (V) 0  [H 0 ] (M) 0.030  Pulp added at 7 min.  33  10.0  53  0  0.020  At 40 min. add 1.0 ml of H  59  10.1  54  0  0.033  102  10.3  54  0  0.027  122  10.3  54  0  0.027  137  10.2  54  0  0.026  Pulp yield: Brightness: L * : 93 (+8)  94% 66%ISO (+13) a * : -1.7 (-4.3)  Yellowness:  26% (-5)  b*: 15.2(+0.4)  157  2  2  Comment  2  Appendix VII. Raw Data  No-Pulp Runs (For Measuring Current Efficiency and Polarization Curve) Current Efficiency Measurement for the Modified TJ-tube Sample # NP-3 (no pulp) Conditions: Anode type:  Platinized Titanium  Anode area:  29 cm  Modified U-tube  Temperature:  46°C  Cathode type:  Tungsten Rod  Total Volume:  700 ml  [Na C0 ]  1.0M  Current:  10 Amp  [NaHCOj]  0.13 M  Time:  3 hours  [Na SiOj]  0.034 M  [DTPA]  0.6 g  [MgS0 ]  0.04 g  2  3  2  4  2  Concentration of Active Oxygen ( C 0 ~ and/or H 0 ) during brightening process 2  2  Time  pH  6  2  2  Temperature  Voltage  [H 0 ]  Theoretical mol  (°C)  (V)  (M)  (mol)  (mol)  (%)  (min)  2  2  Actual mol Current Efficiency  5  10.7  47  13  0.008  0.02  0.006  36  16  10.7  48  13  0.022  0.05  0.015  31  30  10.7  46  14  0.029  0.09  0.020  22  74  10.7  46  14  0.032  0.23  0.022  10  99  10.7  46  14  0.028  0.31  0.020  6  120  10.6  47  14  0.024  0.37  0.017  5  152  10.7  47  15  0.013  0.47  0.009  2  Sample #  NP-4  (no pulp)  Conditions:  Anode type:  Platinized Titanium  Anode area:  29 cm  Modified U-tube  Temperature:  46°C  Cathode type:  2  Tungsten Rod  Total Volume:  700 ml  [Na COj]  1.0M  Current:  5 Amp  [NaHCOj]  0.13 M  Time:  3 hours  [Na Si0 ]  0.034 M  [DTPA]  0.6 g  [MgS0 ]  0.04 g  2  2  3  4  Concentration of Active Oxygen ( C 0 " and/or H 0 ) during brightening process 2  2  Time  pH  (min)  Temperature  6  2  2  Voltage  [H 0 ]  Theoretical mol  Actual mol  Current Efficiency  (°C)  (mol)  (mol)  (%)  2  2  (V)  (M)  4  10.7  50  8  0.005  0.01  0.004  56  16  10.7  47  7  0.008  0.02  0.006  23  30  10.7  46  7  0.011  0.05  0.008  17  59  10.7  46  8  0.015  0.09  0.011  11  94  10.7  46  8  0.015  0.15  0.011  7  119  10.7  46  9  0.012  0.18  0.008  5  151  10.7  46  10  0.001  0.23  0.001  0.3  158  Appendix VII. Raw Data  Sample #  NP-5  (no pulp)  Conditions:  Anode type:  Platinized Titanium  Anode area:  29 cm  Modified U-tube  Temperature:  66°C  Tungsten Rod  Total Volume:  700 ml  [Na C0 ]  1.0M  Current:  10 Amp  [NaHCOj]  0.13 M  Time:  3 hours  [Na Si0 ]  0.034 M  [DTPA]  0.6 g  [MgS0 ]  0.04 g  Cathode type: 2  3  2  3  4  2  Concentration of Active Oxygen ( C O " and/or H 0 ) during brightening process 2  2  Time  pH  s  2  2  Temperature  Voltage  [H 0 ] (M)  (mol)  (mol)  (%)  2  2  Theoretical mol Actual mol  Current Efficiency  CC)  (V)  5  10.7  67  10  0.012  0.02  0.008  54  15  10.7  66  10  0.016  0.05  0.011  24  30  10.7  67  10  0.018  0.09  0.013  14  61  10.8  64  11  0.015  0.19  0.011  6  (min)  Current Efficiency at Different Current Density at 46°C Conditions: Anode type:  Platinized Titanium  Anode area:  29 cm  Modified U-tube  Temperature:  46°C  Cathode type:  Tungsten Rod  Total Volume:  700 ml  [Na C0 ]  1.0 M  Current:  [NaHC0 ]  0.13 M  Time:  [Na Si0 ]  0.034 M  [DTPA]  0.6 g  [MgS0 ]  0.04 g  2  3  3  2  3  4  2  30 minutes  Current  Current Density  Anode Voltage  [H202]  Theoretical mol  Actual mol  Current Efficiency  (Amp)  (Amp/cm )  (V vs S C E )  (M)  (mol)  (mol)  (%)  1.2  0.04  2.01  0.005  0.011  0.004  31  2.4  0.08  2.37  0.01  0.022  0.007  32  2.8  0.10  2.53  0.014  0.026  0.010  38  3.5  0.12  2.73  0.018  0.032  0.013  39  4.1  0.14  2.98  0.022  0.038  0.015  41  5.7  0.20  3.51  0.026  0.053  0.018  34  7.4  0.25  3.98  0.032  0.069  0.022  33  2  159  Appendix VII. Raw Data  Current Efficiency vs Time at Certain Anode Potential (2.91 V vs S C E ) Conditions:  Anode type:  Platinized Titanium  Anode area:  29 cm  Modified U-tube  Temperature:  46°C  Cathode type: Tungsten Rod  Total Volume:  700 ml  [Na COj]  1.0 M  Current:  [NaHCOj]  0.13 M  2  [Na Si0 ]  0.034 M 0.6 g  [MgS0 ]  0.04 g  3  4  Time  6.68 +/- 0.02 A  [DTPA]  2  pH  Anode Potential: 2.91 Vvs SCE  Temperature  (min)  2  Voltage  [H 0 ]  Theoretical  Actual  Current Efficiency  CQ  (V)  (M)  (mol)  (mol)  (%)  2  2  4  10.5  46  10  0.007  0.008  0.0049  59  15  10.5  46  10  0.014  0.031  0.0098  31  31  10.4  46  10  0.021  0.064  0.0147  23  46  10.4  47  10  0.027  0.096  0.0189  20  60  10.4  47  10  0.031  0.125  0.0217  17  91  10.4  47  10  0.034  0.189  0.0238  13  122  10.4  47  10  0.034  0.253  0.0238  9  0.037  0.422  0.0259  6  203 Sample #  NX-1  Measuring the decomposition of hydrogen peroxide in sodium carbonate solution  Conditions:  Anode type:  Platinized Titanium  Anode area:  29 cm  Modified U-tube  Temperature:  54°C  Cathode type: Tungsten Rod  Total Volume: 700 ml  [Na COj]  1.0 M  Current:  [NaHCOj]  0.11 M  No Pulp  [Na SiOj]  0.034 M  H 2 0 2 30%  3 ml (added only once in the beginning)  [DTPA]  0.6 g  Time  3 hours  [MgS0 ]  0.04 g  2  2  4  0 Amp  Concentration of Active Oxygen ( C 0 " and/or H 0 ) during brightening process 2  2  Time  2  pH  (min)  6  2  2  Temperature  Voltage  [H 0 ]  % Decomposition  CQ  (V)  (M)  (%)  2  2  2  10.3  54  0  0.039  15  10.3  54  0  0.033  15  34  10.3  54  0  0.025  24  48  10.3  54  0  0.022  12  61  10.3  54  0  0.019  14  75  10.3  54  0  0.016  16  90  10.3  54  0  0.016  0  128  10.3  54  0  0.013  19  183  10.3  54  0  0.010  23  160  Appendix VII. Raw Data  Sample #  NX-2  Measuring the decomposition of hydrogen peroxide in sodium carbonate solution  Conditions: Anode type:  Platinized Titanium  Anode area:  29 cm  Modified U-tube  Temperature:  54°C  Cathode type: Tungsten Rod  2  Total Volume:  700 ml  [Na COj]  1.0 M  Current:  0 Amp  [NaHCOj]  0.11M  No Pulp  [Na SiOj]  0.034 M  H 2 0 2 30%  [DTPA]  0.6 g  [MgS0 ]  0.04 g  2  2  4  2 ml added At 34 min., 3 hours  Time  Concentration of Active Oxygen ( C 0 " and/or H 0 ) during brightening process 2  2  Time  pH  6  2  2  Temperature  Voltage  [H 0 ]  % Decomposition  (°C)  (V)  (M)  (%)  (min)  2  2  2  10.4  54  0  0.038  15  10.4  54  0  0.032  16  32  10.4  54  0  0.026  19  36  10.4  54  0  0.057  50  10.4  54  0  0.043  25  62  10.4  54  0  0.034  21  77  10.4  54  0  0.027  21  90  10.4  54  0  0.022  19  141  10.4  54  0  0.015  32  184  10.4  54  0  0.012  20  Sample #  NX-5  Measuring the decomposition of hydrogen peroxide in sodium carbonate solution  Conditions: Anode type:  Platinized Titanium  Anode area:  29 cm  Modified U-tube  Temperature:  54°C  Cathode type:  Tungsten Rod  Total Volume:  700 ml  [Na COj]  1.0 M  Current:  0 Amp  [NaHCOj]  0.11M  No Pulp  [Na SiOj]  0.034 M  H 2 0 2 30%  added 2.5 ml initially  [DTPA]  0.6 g  [MgS0 ]  0.04 g  Time  3 hours  2  2  4  Concentration of Active Oxygen ( C 0 " and/or H 0 ) during brightening process 2  2  Time  pH  (min)  6  2  2  Temperature  Voltage  [H 0 ]  % Decomposition  (°C)  (V)  (M)  (%)  2  2  1  10.5  54  0  0.039  15  10.5  54  0  0.025  36  31  10.5  54  0  0.018  28  46  10.5  54  0  0.014  22  60  10.5  54  0  0.011  21  97  10.5  54  0  0.012  -9  122  10.5  54  0  0.007  42  202  10.5  54  0  0.007  0  161  2  Appendix VII. Raw Data  Sample #  NX-6  Measuring the decomposition of hydrogen peroxide without carbonate  Conditions: Anode type:  Platinized Titanium  Anode area:  29 cm  Modified U-tube  Temperature:  54°C  Cathode type:  Tungsten Rod  Total Volume:  700 ml  [Na C0 ]  0M  Current:  0 Amp  [NaHCOj]  0M  No Pulp  [Na Si0 ]  0.034 M  H 2 0 2 30%  added 2.5 ml initially  [DTPA]  0.6 g  [MgS0 ]  0.04 g  Time  3 hours  2  3  2  3  4  2  Concentration of Active Oxygen (C 06 " and/or H 0 ) during brightening process 2  2  Time  pH  (min)  2  2  Temperature  Voltage  [H 0 ]  CQ  (V)  (M)  2  2  1  10.6  54  0  0.039  15  10.5  54  0  0.039  30  10.5  54  0  0.039  45  10.5  54  0  0.039  59  10.5  54  0  0.039  65  10.5  54  0  0.039  121  10.4  54  0  0.039  199  10.4  54  0  0.039  162  

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