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Electro-brightening of mechanical pulp Jung, Joey Chung-Yen 2000

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ELECTRO-BRIGHTENING OF MECHANICAL PULP  by Joey Chung-Yen Jung  B . S c , Chinese Culture University, Taipei, Taiwan, 1994  A THESIS SUBMITTED IN P A R T I A L F U L F I L L M E N T OF T H E REQUIREMENTS FOR T H E D E G R E E OF M A S T E R OF APPLIED SCIENCE  T H E F A C U L T Y OF G R A D U A T E STUDIES D E P A R T M E N T OF C H E M I C A L A N D BIOLOGICAL E N G I N E E R I N G  We accept this thesis as conforming to the required standard  THE UNIVERSITY OF BRITISH C O L U M B I A  September 2000 © Joey Chung-Yen Jung  3.000  In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of the r e q u i r e m e n t s f o r an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g of t h i s t h e s i s f o r s c h o l a r l y purposes may be g r a n t e d by the head of my department or by h i s or her r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g or p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n .  Department of C h e m i c a l and B i o l o g i c a l E n g i n e e r i n g The U n i v e r s i t y of B r i t i s h Columbia Vancouver, Canada Date  Oct.  10  th  2000  Abstract  Abstract The electro-oxidation of sodium carbonate (Na2C03) to percarbonate (C2O6 "), with its 2  subsequent hydrolysis was investigated as a means to produce peroxide and to drive the in-situ electrochemical brightening of thermo-mechanical pulp. The conditions for the electrochemical production of peroxide and factors that affected the in-situ electrochemical brightening of TMP were studied by conducting variable level experiments.  The investigations were performed  using a 2-liter batch electrochemical reactor, fabricated of titanium, with a platinum anode. To promote peroxide generation, different types of cathode material and diaphragms were evaluated; and major modifications to the reactor comprising the anode, cooling system, mixer, and position of thermocouple were performed. The important quantitative findings are as follows: •  Experiments with uncovered zirconium cathode generated the highest peroxide concentration than other cathode materials with or without a diaphragm.  •  The pH of the electrolyte dominated the process of peroxide accumulation through its effect on the concentration of  CO3 ". 2  High pH (>11) resulted in high peroxide concentration.  While brightening, alkali darkening will not negate the brightening responses in high pH («11.5).  •  Temperature had a significant effect on peroxide generation and on brightening. Low anode coolant temperature (1°C) resulted in higher peroxide concentration in the early stage of the process; and high electrolyte temperature promoted the production of peroxide and raised the brightening responses.  •  The investigation of peroxide production (without pulp) indicated that under equipment limitations, the maximum peroxide concentration for 180 minutes was around 0.08M. The experimental conditions were as follows: • • • • •  Electrolyte: 2 M N a C 0 , 400ppm M g S 0 , 0.002M DTP A (pH = 11.6) Electrolyte temperature: 60°C Current set point: 30A (float voltage) Mixing speed: 200rpm Anode coolant: 1°C at 6 liter per minute 2  3  4  Abstract •  Electro-brightening of 2.5 % consistency TMP achieved a 17.4 % ISO of brightness gain and a 19.2 % of yellowness loss with pulp (initial brightness: 41.6 % ISO; initial yellowness: 36.8 %) and experimental conditions mentioned above. The specific brightening energy for kWh this brightened T M P was 17 x 10  , which corresponded to an operation cost of ton%ISO approx. $ 1,020 per ton of OD pulp for 20 % ISO brightness gain. The economic reactor 5  • • , • , • •u ,*r ton%ISO sizing factor, brightening space-time yield, was 0.145 m hr n  . , . . . A brightness reversion  test showed that electro-brightened pulp has the same brightness stability as conventional peroxide brightened pulp. •  The 2 factorial experiment indicated that the combination of high current, high electrolyte 3  temperature, and high sodium carbonate concentration has positive effects on electrobrightening responses. •  Long brightening retention time (240 minutes) resulted in less brightness gain and yellowness loss, which means brightening time longer than 180 minutes is not worthwhile. Also, cycling current on/off with a 30-minute interval gave less brightness gain and yellowness loss than that of a comparable standard electro-brightening run. This indicates that the 30-minute interval was too long or there was not enough peroxide available to brighten the pulp.  •  High pulp consistency (4.5%) had higher brightening responses than low pulp consistency (2.5%), which demonstrates the electro-brightening process is similar to the conventional peroxide brightening process, with respect to pulp consistency.  The in-situ electrochemical brightening process could not be optimized in this thesis study, due to limitations of the laboratory reactor.  The Teflon coating and non-conductive glue in the  reactor were deteriorated under the experimental conditions to the extent that the reactor was unsuitable for further experiments. However, in-situ electrochemical brightening of TMP using sodium carbonate as the source of brightening agent does produce a brightened pulp that is comparable to that obtained using merchant peroxide.  - iii -  Table of Contents  Table of Contents Abstract Table of Contents List of Figures List of Tables Nomenclature Acknowledgement  ii iv vii x xi xiv  Chapter 1 Introduction  1  Chapter 2 Theoretical Background  3  2.1  Elements of Wood Chemistry 2.1.1 Cellulose 2.1.2 Hemicellulo ses 2.1.3 Lignin  3 4 5 5  2.2  Elements of Mechanical Pulping and Principles of Brightening 2.2.1 Elements of mechanical pulping 2.2.2 Principle of brightening 2.2.3 Brightness, yellowness, and color reversion 2.2.4 Alkali darkening  7 7 7 9 11  2.3  Mechanical Pulp Brightening by Hydrogen Peroxide 2.3.1 The chemistry of peroxide brightening 2.3.2 The conditions of conventional peroxide brightening process 2.3.3 Factors affecting brightening response in peroxide brightening process (A) Effect of consistency of pulp (B) Effect of pH (C) Effect of temperature (D) Effect of additives or stabilizers (E) Effect of residual peroxide and retention time  11 11 15 16 16 16 17 17 18  2.4  Principles of Related Electrochemical Processes 2.4.1 Thermodynamics of the electrochemical system 2.4.2 Electrode kinetics and mass transfer 2.4.3 Elements of electrochemical cell (A) Electrolyte (B) Voltage balance (cell voltage) (C) Electrode materials (D) Product rate of peroxide  19 20 20 23 23 23 23 23  2.5  Production of Hydrogen Peroxide  24  - iv -  Table of Contents 2.5.1 2.5.2  2.5.3 2.6  The chemical process of hydrogen peroxide production The electrolytic process of hydrogen peroxide production (A) Anodic oxidation of sulfuric acid (B) Electroreduction of oxygen (C) Electro-oxidation of sodium carbonate Figures of merit for the electro-oxidation of sodium carbonate  In-Situ Electro-Brightening of Mechanical Pulp by Electro-Oxidation of Sodium Carbonate 2.6.1 Figures of merit for the electro-brightening of mechanical pulp  25 25 25 25 26 28  29 31  Chapter 3 Proposed Research Objectives  32  Chapter 4 Experimental Apparatus and Procedure  33  4.1  Experimental Apparatus 4.1.1 Original experiment apparatus 4.1.2 Modification of the cooling system of the electrochemical reactor 4.1.3 Modifications of the anode, cathode, and setup of the thermocouple of the electrochemical reactor (A) Deterioration of the anode surface (B) Modification of anodes (C) Difficulty of reliable temperature measurements of the electrolyte (D) Modification of the set-up of the thermocouple, ribbon mixer, and cathode 4.1.4 Modification of the cover of the electrochemical reactor  41 41 44 45 47 49  4.2  Experimental Procedures 4.2.1 Electroplating of platinum on the anode 4.2.2 Electrochemical production of peroxide 4.2.3 In-situ brightening of mechanical pulp  50 50 51 51  4.3  Picture of Electrochemical Brightening System  52  Chapter 5 Experimental Results and Discussion 5.1  Factors Affecting Electrochemical Production of Peroxide 5.1.1 Anode coolant temperature 5.1.2 Cathode material and diaphragm 5.1.3 Current distribution (Different electrode configuration) 5.1.4 Anode current density 5.1.5 Bulk electrolyte temperature 5.1.6 Stabilizers and chelating agents (A) Magnesium (B) DTPA (Diethylenetriaminepentaacetic acid - penta sodium salt) 5.1.7 pH 5.1.8 Heating pattern  33 34 39  55 55 56 57 62 64 65 67 67 68 70 75  Table of Contents 5.2  Factors Affecting Electro-Brightening of Mechanical Pulp 5.2.1 A 2 factorial experiment (effect of temperature, current, and electrolyte concentration) (A) Main and interaction effects on brightness gain (B) Main and interaction effects on yellowness loss (C) Main and interaction effects on concentration of peroxide (D) The specific brightening energy and brightening space time yield (E) Summary of the results from changing temperature, current and concentration of sodium carbonate 5.2.2 pH 5.2.3 Pulp consistency 5.2.4 Brightening time 5.2.5 Pre-generating peroxide 5.2.6 Energy saving 5.2.7 Current efficiency  77  3  5.3  Performance of the Electro-Brightening Reactor 5.3.1 Temperature limitation 5.3.2 Current limitation  5.4  Pictures of Teflon Deterioration and Pulp Samples  77 80 81 82 83 84 85 86 88 91 93 96 98 98 99 100  Chapter 6 General Discussion and Conclusions  103  Chapter 7 Recommendations and Future W o r k  107  References  108  Appendix I Design and Analysis of Factorial Experiments  113  Appendix II Factorial Design Analysis Calculation  116  Appendix III The Calculation of Electroplating of Platinum  120  Appendix I V The Calculation of Peroxide Current Efficiency  121  Appendix V Chemicals and Pulp  123  Appendix V I The Calculation of Coolant Heat Transfer  124  Appendix VII Sampling and Analysis Procedures  125  Appendix VIII Raw Data  132  Appendix I X Brightness Reversion Experiment  200  Appendix X Ideas for Designing New Reactor  202  - vi -  List of Figures  List of Figures Figure 2.1  A mature Softwood Fiber  3  Figure 2.2  Structure of Cellulo se  4  Figure 2.3  Lignin Precursors for Plants  5  Figure 2.4  A Hypothetical Depiction of a Portion of a Softwood Lignin Molecule  6  Figure 2.5  Examples of Chromophores and Leuco-Chromophores in Lignin  8  Figure 2.6  Relative Spectral Distribution for Evaluating Brightness and Opacity  9  Figure 2.7  Reflectance of Visible Light for Different Pulps  10  Figure 2.8  Possible Reaction Mechanism in Peroxide Brightening of Mechanical Pulp  12  Figure 2.9  Oxidation of Lignin with Hydrogen Peroxide  12  Figure 2.10  Potential-pH Equilibrium Diaphragm of H 0 - H 0 system  13  Figure 2.11  Formation of H 0 by the oxidation of water  14  Figure 2.12  Formation of H 0 by the reduction of oxygen  14  Figure 2.13  Decomposition of Hydrogen Peroxide to Water and Oxygen  15  Figure 2.14  General Polarization Curve  22  Figure 2.15  Tafel Plots for H Evolution in 1M Yt and for 0 Evolution in 1M OH"  27  Figure 4.1  Original Experimental Set-up Developed by Dr. Zhang and Prof. Oloman  34  Figure 4.2  Original Electrochemical Reactor  36  Figure 4.3  Original Anode Design  37  Figure 4.4  Theoretical domains of corrosion, immunity and passivation of titanium,  2  2  2  2  2  2  2  2  2  at 25°C  38  Figure 4.5  Original Anode Design  39  Figure 4.6  Experimental Set-Up with the New Cooling System  40  Figure 4.7  Aging of the Platinized Anode  42  Figure 4.8  Potential-pH equilibrium diagram for the system titanium-water, at 25°C  43  Figure 4.9  Modification of Anode  45  Figure 4.10  Measure Error of the Temperature using the New Cooling System  46  Figure 4.11  Detail Information of the Electrochemical Reactor  48  Figure 4.12  Detail Information of the Cover of the Electrochemical Reactor  50  - vii -  List of Figures Figure 4.13  Electrochemical Brightening System  53  Figure 4.14  Electrochemical Brightening Reactor (1) with Zirconium Cathode  53  Figure 4.15  Electrochemical Brightening Reactor (2)  54  Figure 4.16  Handsheet Maker used in this Study  54  Figure 5.1  Effect of Coolant Temperature on Peroxide Generation  56  Figure 5.2  Effect of Diaphragm on Stainless Steel Cathode on Peroxide Generation  58  Figure 5.3  Effect of Cathode Materials with Diaphragm on Peroxide Generation  59  Figure 5.4  Effect of Diaphragm on Zirconium Cathode on Peroxide Generation  60  Figure 5.5  Pourbaix Diagrams for Zirconium  61  Figure 5.6  Cathode Configurations  62  Figure 5.7  Effect of Current Distribution on Peroxide Generation  63  Figure 5.8  Effect of Current Density and Concentration of N a C 0 on Peroxide 2  3  Generation  64  Figure 5.9  Effect of Temperature on Peroxide Generation  66  Figure 5.10  Effect of Stabilizer on Peroxide Generation  68  Figure 5.11  Effect of Chelating Agent on Peroxide Generation  69  Figure 5.12  Effect of pH on Peroxide Generation (2) (V3.10; V3.12; V3.13)  71  Figure 5.13  Effect of pH & DTP A on Peroxide Generation (D) (V3.17; V3.18)  72  Figure 5.14  Relative Concentration vs pH [36]  73  Figure 5.15  Pourbaix Diagrams of Carbon-Water System [33]  74  Figure 5.16  Effect of Heating Pattern on Peroxide Generation  75  Figure 5.17  Cube Plots for the Responses of a Full 2 Factorial Design  79  Figure 5.18  Interaction Plots on Concentration of Peroxide & Probability vs Effects  83  Figure 5.19  Effect of pH on Brightness Gain and Yellowness Loss  86  Figure 5.20  Effect of Pulp Consistency on Brightness Gain and Yellowness Loss  87  Figure 5.21  Effect of Brightening Time  Figure 5.22  Effect of Brightening Time versus Peroxide Concentration  90  Figure 5.23  Profile of the Residual Peroxide Concentration  92  Figure 5.24  Effect of Energy Saving on Peroxide Generation  94  Figure 5.25  Effect of Saving Energy on Brightness Gain and Yellowness Loss  95  3  - viii -  .89  List of Figures Figure 5.26  Peroxide Current Efficiency versus Current and Concentration of Sodium Carbonate  96  Figure 5.27  Current Limitation of Electro-Brightening Reactor  99  Figure 5.28  Teflon Deterioration (1)  100  Figure 5.29  Handsheet of Unbrightened Pulp  101  Figure 5.30  Handsheet of Brightened Pulp (20A, 60°C; 2 M N a C 0 )  101  Figure 5.31  Teflon Deterioration (2)  102  Figure IX. 1  Brightness Loss of Pulp Pads Under 8 Fluorescent Lamps  200  Figure IX.2  Yellowness gain of Pulp Pads Under 8 Fluorescent Lamps  201  Figure X. 1  Rough Draft of the New Reactor Design  202  Figure X.2  Detail Design of the Reactor Body  203  Figure X.3  Elevation and Plan of the reactor  204  2  - ix -  3  List of Tables  List of Tables Table 2.1  Typical Compositions of North American Woods  Table 2.2  Relationship of Temperature, Alkali of Brightening Liquor, and Retention Time. 19  Table 2.3  Principal Reactions for Electro-Oxidation of Sodium Carbonate  26  Table 2.4  Experimental Conditions by Kurniawan and Oloman  30  Table 2.5  Best Brightening Results by Kurniawan and Oloman  31  Table 4.1  Overall Layout of the Experimental Apparatus and Procedure  33  Table 5.1  Organization of Chapter 5  55  Table 5.2  Effect of Diaphragm and Cathode Material on Peroxide Generation  57  Table 5.3  Effect of Electrode Configuration on Peroxide Generation  63  Table 5.4  Effect of Stabilizer and Chelating Agent on Peroxide Generation  67  Table 5.5  pH Effect at Four Different Experimental Conditions  70  Table 5.6  Variables, Levels and the Design of the 2 Factorial Experiments  78  Table 5.7  Effect on Brightness Gain  80  Table 5.8  Effect on Yellowness Loss  81  Table 5.9  Effect on Concentration of Peroxide  82  Table 5.10  Comparison of SBE and B S T Y of Factorial Experimental Results  83  Table 5.11  Effect of Pre-Generating Peroxide  92  Table 5.12  Data of Gas Analysis and Current Efficiency  97  Table A2.1  Summary of Responses from the Factorial Design  3  -x-  4  116  Nomenclature  Nomenclature electrode overpotential  (V)  anodic overpotential  (V)  Tic  cathodic overpotential  (V)  a  anodic charge transfer coefficient  AB  brightness gain  (%I  Gibbs free energy change of a cell reaction  (kJ)  enthalpy change of a cell reaction  (kJ)  entropy change of a cell reaction  (kJ)  AY  yellowness loss  (%)  A.Area  electrode area  (m )  AAnode  anode area  (m )  a  Q  activity of oxidized species  a  R  activity of reduced species  c  concentration  (M)  bulk concentration  (M)  current efficiency  (%)  current efficiency of primary anode reaction  (%)  E  applied electrode potential  (V),  e"  electron  E  A  anode potential  (V)  E  c  cathode potential  (V)  total cell voltage  (V)  thermodynamic cell poential  (V)  standard electrode potential  (V)  a  equilibrium potential of anode  (V)  C  equilibrium potential of cathode  (V)  ohmic voltage drop across the cell  (V)  ^  c  b  CE CE  P  Ecell  E° E  e  E  e  Eohm  2  2  - xi -  Nomenclature E  equilibrium electrode potential  r  (V)  F  Faraday constant (98480)  (C mol" )  i  current density  (kA m~ )  I  applied current  j  i  A  2  (kA)  anode current density  ' 'Anode  l  1  J  (kAm" ) 2  '  v  ic  cathode current density  (kA m" )  iL  mass transfer limiting current density  (kA m" )  i  exchange current density  (kA m" )  i  anodic mass transfer limiting current density  (kA m" )  i  cathodic mass transfer limiting current density  (kA m" )  0  La  Lc  i  partial current density  IparUai  partial current  i  total current density  Iiotai  total current  Partjal  Total  k K  first  2  2  2  2  2  (kA m" ) 2  (kA) (kA m" ) 2  (kA)  order reaction rate constant  (s" ) 1  total mass transfer coefficient  (m s" )  MW  molecular weight  (kg kmoi" )  m  amount difference of material  (kmoi)  n  electron stoichiometry coefficient  O  oxidized species  Q  amount of electrical charge  R  universal gas constant (8.314)  R'  reduced species  R*  production rate of the desired product  (kmoi s" )  SE  specific energy  (kWh/kg)  STY  space time yield  (kg m" s" )  t  time  T  temperature  Vsatch  volume of a batch reactor  (m )  VReactor  volume of electrolyte  (m )  m  1  1  (C) (kJ kmoi" K" ) 1  1  3  1  (s) (K or ° C )  - xii -  3  3  1  Nomenclature SBE  Specific Brightening Energy  BSTY  Brightening Space Time Yield  (kWh/ton/%ISO) ltonx%ISO/ \  Abbreviations CIE  International Commission on Illuminatin  DTPA  diethylene triamine pentaacetic acid  EDTA  Ethylenediaminetetraethanoic acid  ISO  International Standardization Organization  O.D.  over dry  SHE  Standard Hydrogen Electrode  TMP  thermo-mechanical pulp  - xiii -  /m  ) 3  x hr'  A cknowledgment  Acknowledgment I would like to thank God for guiding me through the final stage of my thesis and for giving me the strength to finish it. I thank my thesis supervisor, Professor Colin Oloman, for giving me the opportunity to perform this research. His guidance, passion, encouragement and inspiration are the motivations for me to keep on going and to finish. Next, I thank Mr. Elod Gyenge for his suggestions and input during the past several years. I also appreciate the advice and assistance from Dr. Jiujun Zhang in the initial phases of this work. Throughout my master, the friendship of the members of the Electrochemical Engineering Group at U B C is acknowledged, particularly Jielin Song and Lixin Gao. The help of the staff of the Pulp and Paper Centre and Chemical Engineering Department was essential to the successful completion of the present study: Peter Taylor, Tim Paterson, Ken Wong, Horace Lam, Chi Chen, Peter, and Chris. I also thank Rita Penco and Judy Mackenzie for librarianship; Tomas Hu for tested the brightness reversion. Thanks to Dr. Yuan-Shing Perng for introducing me to U B C and Professor Oloman while I searched in Taiwan for a school for advanced study. Without his introduction, I might not have studied in Canada. I would like to thank Pamela for her understanding, patience, and encouragement. Most of all, I would like to thank my parents for their love, caring and financial support. Without them, I could not have made it. Finally, I would like to thank the Networks of Centres of Excellence for financing this project.  - xiv -  Chapter 1  Chapter 1 Introduction The demand for brighter paper has not ceased even though people are aware that effluents of the bleaching process cause pollution of the environment.  Moreover, chemical pulping and  bleaching processes produce low pulp yield at high cost.  Thus, market trends and strict  environmental regulation of effluents have driven the pulp and paper industry to explore alternative bleaching methods, to improve the bleaching process for more chemical recovery and closed-cycle operation, and to make more use of mechanical pulp. Mechanical pulps became important in the past several decades. So far, mechanical pulps have been used extensively in short-life paper like newsprints. Notwithstanding, mechanical pulps face problems in achieving high brightness and unpredictable brightness reversion.  In  mechanical pulp brightening, the commercial brightening agents are sodium dithionite and hydrogen peroxide. Generally, brightening by sodium dithionite alone can achieve 4 ~ 14 % ISO brightness gain, and up to 20 % ISO gain by hydrogen peroxide in one stage brightening. [1] However, brightness over 80 % ISO requires multiple brightening stages. [2] Therefore, recent research has focused on improving brightening technology and searching for alternative brightening agents to aim at the long-life paper market such as copy papers and writing papers. Researchers  have  examined  oxidants  like perborate [3], percarbonate [4 ~ 6], and  peroxymonosulphate [7] as alternative brightening agents in the past few years. However, they found that these chemicals and technologies are not ready to be introduced to the brightening industry. Hence, the search for economic, environmentally friendly brightening agents capable of achieving about 20 % ISO brightness gain remains unfulfilled.  It is the objective of the  present study to investigate such new brightening agents or processes.  One candidate worth looking into is sodium percarbonate. (Na C 06). The percarbonate ion is a 2  2  strong oxidizing agent that hydrolyzes to form hydrogen peroxide according to the following equation: C 0 " + 2 H 0 -> 2HC0 " + H 0 2  2  6  2  3  2  2  [1.1]  Chapter 1 Introduction Both percarbonate and hydrogen peroxide have the potential to be used to brighten mechanical pulp. Solid percarbonate (e.g. N a 2 C 0 e ) is an unstable compound, which has been produced in 2  the laboratory [4] but never used in industry. In 1970, Oloman produced solutions contained both percarbonate and hydrogen peroxide by electrochemical oxidation of sodium carbonate solution. [8] He managed to use this solution to brighten groundwood pulp to obtain 7 % ISO brightness gain at 10 % pulp consistency. Since sodium carbonate is a cheap material that is widely available in pulp and paper mills, Oloman's work has opened a window for the use of percarbonate as an alternative brightening agent for mechanical pulp. From 1993 to 1998, Been, Kurniawan and Oloman further researched this process.  They  investigated the conditions for producing percarbonate solution by electrochemical oxidation of sodium carbonate and tried to optimize the process of in-situ electrochemical brightening of softwood thermomechanical pulp. [9] Their work on this system achieved a brightness gain of 12 % ISO in a crude beaker batch reactor at 1 % pulp consistency. Further work by Zhang and Oloman in 1995 improved the system to operate up to 5% consistency. The present study is a continuation of Been, Kurniawan, Zhang and Oloman's work.  The  objective of this study is to further explore the potential of the in-situ electro-generation of peroxy species process by using a scaled-up and improved 2-liter batch reactor. A long-term objective is to improve this process and make it become environmentally and economically favorable by recovering the unused sodium carbonate to make it a closed-cycle operation. Hopefully, this electrochemical process can set a marker for the pulp brightening industry.  Chapter 2  Chapter 2 Theoretical Background The concepts introduced in this chapter are the elements of wood and mechanical pulping chemistry, the fundamental of electrochemistry, the electrosynthesis of hydrogen peroxide, and the in-situ electro-brightening of mechanical pulp using sodium carbonate.  2.1 Elements of Wood Chemistry Wood is a heterogeneous material chemically as well as anatomically, which can be divided into two categories: softwood and hardwood. Woods from gymnosperms are called softwoods, and woods from angiosperms are known as hardwoods. Wood of common trees of North America is composed of tubular cells, which are the "fiber" in paper technology.  A l l wood fibers have  similar structural and chemical features. Figure 2.1 shows a typical softwood fiber. [10]  Lumen S3, secondary wall, 0.07-0.1 /tin thick S2, secondary wall, 05-8 f<m thick SI, secondary wall, 0.1-02 pin thick Primary ceil wall, 0.03-1 J) urn thick Middle lamella • lignin & pectin cement adjacent fibers together  Figure 2.1 A mature Softwood Fiber [10] (From U.S. For. Ser. Res. Paper FPL-5,1963) These fibers are basically hollow tapered tubes about 1 to 6mm long with diameters 10 to 60 microns, which are mainly composed of cellulose and hemicelluloses bound together by lignin. Other components of the wood that commonly called extractives are small amounts of pectin,  Chapter 2 Theoretical Background starch, proteins, and metals.  The composition of hardwoods and softwoods by the class of  compounds is displayed in Table 2.1.  Component  Hardwoods (%)  Softwoods (%)  40-50  45-50  2-5  20-25  15-30  5-10  18-25  25-35  1-5  3-8  0.4-0.8  0.2-0.5  Cellulose Hemicelluloses (Galacto) Glucomannans Xylans Lignin Extractives Ash Table 2.1  Typical Compositions of North American Woods [10]  2.1.1 Cellulose Cellulose is the principal components of wood fiber. It determines the characteristics of the fiber, thereby influencing the functional use of fiber in papermaking. condensed formula of cellulose is (C6H12O6-  C6H10O5.  Cellulose is a linear polymer of anhydro-D-glucose,  H 0 - » C6H10O5), connected by P-(1^4)-linkages. 2  On the molecular level, the  The structure of cellulose is  shown in Figure 2.2 [10]  Figure 2.2  Structure of Cellulose [10]  Physically, cellulose is a white solid material. This fibrous substance is insoluble in water and organic solvents.  Cellulose in wood is about 50-70% crystalline and forms the backbone  structure of a wood fiber. The crystalline form of cellulose is particularly resistant to chemical attack and degradation. The hydrogen bonding between cellulose molecules results in the high  Chapter 2 Theoretical Background strength of cellulose fibers. These properties make it especially desirable as a component of paper.  2.1.2 Hemicelluloses Hemicelluloses are white solid materials that are rarely crystalline or fibrous in nature.  The  presence of hemicelluloses increases the tensile strength of paper and the pulp yield. Hemicelluloses are short chain sugar polymers that including the six-carbon sugars: mannose, galactose, glucose, and 4-O-methyl-D-glucuronic acid and the five-carbon sugars: xylose and arabinose. Hemicelluloses are much more soluble and susceptible to chemical degradation.  2.1.3 Lignin Lignin is the second main constituent of wood and it is the mechanical reinforcement agent for the tree. Lignin makes up approximately 28% of coniferous woods and 24% in hardwoods. [11] Lignin is the adhesive or binder in wood that holds the fibers together. It is highly concentrated in the middle lamella. There are three basic lignin monomers in lignin. Figure 2.3 shows these basic elements. [10]  grasses  hardwoods & softwoods  CH-OH Hi II,  CH  hardwoods  CH,OH I 2  HC  II CH  OH  p-coumaryl alcohol Figure 2.3  conlferyl alcohol  sinapyl alcohol  Lignin Precursors for Plants [10]  Chapter 2 Theoretical Background Different types of plants contain different lignin precursors. Grasses and straws contain all three lignin monomers, hardwoods contain both coniferyl alcohol (50-75%) and sinapyl alcohol (25-50%), and softwoods contain only coniferyl alcohol. [10]  Contact between phenolic lignin precursors and dehydrogenating enzymes leads to the initial abstraction of a hydrogen atom from the phenolic precursor. polymerization process. [12]  This sets in motion the entire  The involvement of enzymes during lignification is limited to  generating phenoxy radicals at the locale of lignification. The complexity of chemical structure of lignin results from the existence of several mesomeric forms of one phenoxy radical, and the polymerization occurs by random coupling of phenoxy radicals in several mesomeric forms. The polymerization of these alcohols causes the formation of a heterogeneous branched and cross-linked polymer, where the phenylpropane units are linked by C-C and C - 0 bonds. A wide variety of linkages are possible between the phenylpropane units.  The linkages between  phenylpropane units polymerized the lignin to a complex polymer consisting amorphous, 3-D structure. Figure 2.4 illustrates a softwood lignin molecule. CH.OH  I  2  HC-CWV -WO—CH  Figure 2.4  A Hypothetical Depiction of a Portion of a Softwood Lignin Molecule [10]  Chapter 2 Theoretical Background 2.2  Elements of Mechanical Pulping and Principles of Brightening  2.2.1 Elements of Mechanical Pulping Mechanical pulping is a process of separating the fiber bundles in wood using mechanical methods. Refiner mechanical pulping involves the mechanical reduction of wood chips in a precision built attrition disk mill, a refiner. [12] During the mechanical pulping process, the lignin is retained in the pulp thus results a total yield of pulp about 90-98%. Thus, mechanical pulp is pulp produced by using only mechanical attrition to pulp lignocellulosic materials. The fiber sources of mechanical pulp are often from light colored, non-resinous softwoods.  The  characteristics of mechanical pulps are high yields, high bulk, high stiffness, and low cost. However, paper from mechanical pulp has low strength because the lignin reduces the strength of hydrogen bonding between fibers. The lignin in mechanical pulp also causes color reversion with exposure to air and light. [10]  Mechanical pulping preserves the pulp yield but results in short and broken fiber. To prevent damage to the wood fibers, a thermal treatment is used to soften the wood chips before the mechanical grinding process.  The process is called thermomechanical pulping. This process  steams (165~185°C) the raw wood chips for a short period at relatively low pressure (6~10kg/cm ) and refining after the lignin has softened. The step of preheating makes the wood 2  chips less brittle so that they are reduced in size at the breaker bar section of the refiner, thereby allowing easier fiber separation without fiber breakage or splintering, creating more long fibers, less debris, and fewer shives. The pretreated, mechanical pulp is called thermomechanical pulp. (TMP)  2.2.2 Principle of Brightening The objectives of mechanical pulp brightening are (1) to decolorize lignin and other components; (2) to preserve high pulp yield; (3) to avoid mechanical damage to the fibers; and (4) to inhibit the formation of coloured carbonyl groups.  The carbohydrate components of wood, cellulose  and hemicellulose, are almost colorless and their contribution to the color of wood is negligible.  Chapter 2 Theoretical Background Thus, the main contributor to color in wood is lignin. Brightening mechanical pulp is achieved by chemically altering the portions of the lignin molecule that absorb the light, while preserving the lignin. The action of brightening is to change the chemical structure of chromophores to relatively colorless substances, eliminate auxochromes, and to break the chemical bonds between chromophores and auxochromes without dissolving the major components of wood.  Chromophores are most often-conjugated double bond systems arising in the lignin of pulps. One group of chromophores contributing to the color of lignin is the coniferylaldehyde end group; [12] the other groups are the aromatic aldehydes, ketones, and o- and p-quinones. Other chromophores such as sap-stain induced by microorganisms, dirt, and metal ions that complex with lignin may also colorize the pulp. [10] Furthermore, there are some leuco-chromophores which will convert to chromophores through dehydration or dehydrogenation reactions. Figure 2.5 illustrates some examples of chromophores and leuco-chromophores in lignin. [13]  I. Coniferaldehyde (A.„„^=340nnO  Figure 2.5  II A. p-Quinone fA. ,v=373nm) m  III A. o-Quinone (X.„„„=420rim)  IV A. p-Quinone methide (A, =310nm) m<v  V A. o-Quinone methide fX ,«=400nm') m  VI A. p. p'-Stilbene quinone (X „=478nm) m  Examples of Chromophores and Leuco-Chromophores in Lignin [13]  Chapter 2 Theoretical Background 2.2.3 Brightness, Yellowness, and Color Reversion Brightness is defined as the reflectance of blue light (457nm) from an opaque surface of pulp sheets compared to a specified reflecting, diffusion standard surface. [14] Figure 2.6 [12] shows the section of the visible spectrum used for the determination of brightness and the curve for spectral sensitivity to light for a normal observer according to the CIE system. (International Commission on Illumination).  Wavelength nm  Figure 2.6  Relative Spectral Distribution for Evaluating Brightness and Opacity [12] (a: brightness; b: opacity)  The brightening of pulp can be considered as a removal of light-absorbing substances for the pulp. The color of unbrightened pulp is yellow or brown, which means that the absorption of light is greatest in the complementary colors of yellow and brown of the visible spectrum, which is the blue part of the spectrum. Therefore, the reflectance of blue light will be lower than that of light in the other parts of the visible spectrum as shown in Figure 2.7. [12] As the purpose of brightening is to remove color; the brightness difference is the change of the reflectance of light. [12]  Chapter 2 Theoretical Background  100  I  i  400  500  Wavelength  ;  l  600  (  700  nm  Figure 2.7 Reflectance of Visible Light for Different Pulps [12] (a: bleached chemical pulp; b: peroxide-bleached mechanical pulp; c: unbrightened mechanical pulp; d: unbleached sulfite pulp; e: unbleached sulfate pulp)  Brightness is affected by the measuring method. The angle of incident light and the surface properties of the sheet have an effect on the brightness. General Electric (Tappi Standard T452, U.S.A.) and Zeiss Elrepho (official standard worldwide, except the U.S.A.) are two widely accepted methods of measuring brightness. This thesis project used the Zeiss Elrepho (CPPA method). Zeiss Elrepho specifies the sample being diffusely illuminated with a highly reflecting integrating sphere.  Reflected light is measured 90° to the sample, and the reflectance is  compared to absolute reflectance from an imaginary perfectly reflecting, diffusing surface, for example, opal glass. Brightness is the ratio of the reflectance to absolute reflectance expressed as % ISO. For general commercial uses, MgO powder is used as brightness standard with 96% of absolute reflectance. [10]  Yellowness is the degree of yellow color on the pulp or paper. Yellowness loss in brightening is a fast change due to exposure to brightening agent. Yellowness increase is a gradual change  - 10-  Chapter 2 Theoretical Background from the original appearance of a pulp or a paper as a result of aging or exposure to air, light, heat, certain metallic ions, and fungi.  Color reversion is loss of brightness plus increase of  yellowness. Color reversion is due to modification of residual lignin forming chromophores, which are particularly susceptible in mechanical pulps. Chemical pulps may also experience color reversion when exposed to high temperature. [10]  2.2.4 Alkali Darkening Alkali darkening is attributed to some brightening-resistant chromophores and new-formed chromophores in the alkaline condition of the brightening process. Final brightness obtained in alkaline brightening of mechanical pulps is a compromise between opposing darkening and brightening reactions.  During alkaline brightening, coniferaldehydes and simple o- and p-  quinones are efficiently removed by brightening agents. However, other chromophores like stilbenes [15], hydroxy-quinones [16-18], and quinone condensation products [18-19] are formed.  2.3 Mechanical Pulp Brightening by Hydrogen Peroxide  2.3.1 The Chemistry of Peroxide Brightening The active component in alkaline brightening with peroxide is the perhydroxyl ion, H O 2 " [13], which is formed by the addition of alkali to hydrogen peroxide as follows: H 0 + HO" o H 0 " + H 0 2  2  2  2  kPa = 11.6 at 25°C  [2.1]  The brightening of mechanical pulp with perhydroxyl ions is probably a decoloration of p- and o-quinones and coniferylaldehyde structure. [12] It changes the chromophores to colorless compounds such as carboxylic acid fragments and other degradation products. The conjugated system is destroyed in the reaction and the aldehyde groups formed are subsequently oxidized to carboxyl groups in the alkaline medium.  During peroxide brightening, OH" and H 0 " ions 2  compete in nucleophilic attack on the quinones. [20] For coniferylaldehyde a possible reaction mechanism is shown in Figure 2.8. [12]  Chapter 2 Theoretical Background  C =CH-  ^  OH  CHO HOP" OH"  A~\- HO V,,,/  C  +  ? ° H  CHO  -CHO  +  H,0 3  Figure 2.8 Possible Reaction Mechanism in Peroxide Brightening of Mechanical Pulp [12] Another example of a nucleophilic attack of a perhydroxyl anion on lignin chromophores during peroxide brightening is shown in Figure 2.9. [13]  OCH-:  Figure 2.9  Oxidation of Lignin with Hydrogen Peroxide [13]  The phenolic unit comprising lignin is attacked indirectly by H O 2 " , thus the lignin is not modified and the solubility does not increase. Hence, brightening by H O 2 " results in high yield pulp. Furthermore, new p- and o-quinones can be formed under peroxide brightening conditions as a result of side reactions, e.g. alkaline darkening. The competing reactions that occur in the peroxide bleaching process - decoloration on the one hand and the formation of new chromophoric groups on the other hand - requires the brightening process to be stopped before all the peroxide is consumed.  - 12 -  Chapter 2 Theoretical Background Peroxide is unstable at the pH used for pulp bleaching and some of the peroxide decomposes in the bleaching process.  Catalytic decomposition of hydrogen peroxide produces oxygen and  water as follows: 2 H 0 -> 0 + H 0 2  2  2  [2.2]  2  Figure 2.10 shows the potential-pH equilibrium diagram of the system hydrogen peroxide-water at 25°C.  -2  -1  0  1  2  3  4  5  6  7  8  3  10  11  12  13  14  15 J 6 pH  Figure 2.10 Potential-pH Equilibrium Diaphragm of H 0 - H 0 system (From Marcel Pourbaix, Atlas of Electrochemical Equilibria in Aqueous Solutions) 2  - 13 -  2  2  Chapter 2 Theoretical Background In the first case, the hydrogen peroxide is reduced to water according to the reaction H 0 + 2if + 2e" -> 2 H 0 2  2  [2.3]  2  at electrode potentials corresponding to the portion of Figure 2.10 below the family of lines (2-3). In the second case, it is oxidized to oxygen in the solution, according to the reaction 0 + 2H+ +2e" <- H 0 2  2  [2.4]  2  at electrode potentials corresponding to the portion of Figure 2.10 above the family of lines (4-5).  As shown in Figure 2.11 and Figure 2.12, these two families of lines represent the domains in which hydrogen peroxide could be reduced to water (Figure 2.11) or oxidized to oxygen (Figure 2.12). -2  0  Z-  "T~ T  4  "1  6 1  8 1  10 12 1  14  r  T 1 of formation of hydroge -  ^peroxide by oxidation of water  16 -2 2  0,8  0,8  0,4  region of reduction of 0,4 hydrogen peroxide in water (oxidizing action of hydrogen peroxide)'  4  6  8 "i  10  12  1  1  14 r  -1,6-  12  ^ region of the oxidization of hydrogen peroxide in oxygen (reducing action of hydrogen peroxide)-^  0,8 0,4 0 -0,4  -1-0,8  -0,8  -1,2  -1,2 -1*  -1-1,6 0  2  4  6  Figure 2.11  JL  8  10  12  14  2  16 .  ^region of formation of hydrogen peroxide by 0,4 reduction of oxygen^  -1,2,  16 i  0  -0,4  -2  2  16| 1/2  1,2  0  0  T — r  16 -2  0  2  6  8  10  JL  12  14  16 pH  Formation of H 0 by Figure 2.12 Formation of H 0 by the the oxidation of water reduction of oxygen (From Marcel Pourbaix, Atlas of Electrochemical Equilibria in Aqueous Solutions) 2  2  2  2  Below the family of lines (2-3) (Figure 2.11) hydrogen peroxide could act as an oxidizing agent with the formation of water.  Above the family of lines (4-5) (Figure 2.12) hydrogen peroxide  could act as a reducing agent with the formation of oxygen. Hydrogen peroxide thus is unstable and reducible to water below the family of lines (2-3) (Figure 2.11); and unstable and oxidizable  - 14-  Chapter 2 Theoretical Background to oxygen above the family of lines (4-5) (Figure 2.12). Figure 2.13 is a simple diagram that plotted these two families of lines together. -2 ? I  I  -2  0  2  4  1  1  1  6 1  6  10  12  1  1  1  i  t  «  '  »  i  t  0  2  4  6  8  10 12  14 16 1  1  t  I  14 16  Figure 2.13 Decomposition of Hydrogen Peroxide to Water and Oxygen (From Marcel Pourbaix, Atlas of Electrochemical Equilibria in Aqueous Solutions) It is found that these two domains of instability have a common area, in which hydrogen peroxide is doubly unstable.  Consequently, i f a solution of hydrogen peroxide was in contact  with a metallic surface whose electrode potential is situated in this domain of double instability, the hydrogen peroxide could decompose spontaneously into water and oxygen.  2.3.2 The Conditions of Conventional Peroxide Brightening Process Conventional peroxide brightening of mechanical pulp is carried out in alkaline medium. The charges on over-dry pulp are 0.5-3% peroxide, 0.05% magnesium ion and some additives such as E D T A and sodium silicate. Other brightening conditions are temperature of 40~60°C, pH of 10.5-11, pulp consistency of 10-20%, and 1-3 hour retention time. The alkali is supplied by the caustic soda and the source of magnesium ion is magnesium sulfate.  At the end of two or  multiple stages of brightening process, pulp pH is lowered to prevent alkali darkening by adding sulfur dioxide before the papermaking process. The conventional peroxide brightening process  - 15 -  Chapter 2 Theoretical Background is usually done continuously in a tower that maybe downflow or a combination of upflow and downflow. The most common type is downflow in order to achieve a good utilization of the bleaching agent. The peroxide brightening process was a single-stage process traditionally. In recent years, multiple stage brightening is introduced to satisfy the demand for higher-quality, brighter mechanical pulps.  2.3.3 Factors Affecting Brightening Response in Peroxide Brightening Process Optimum brightening results are dependent upon consistency, pH, temperature, additives or stabilizers, and retention time. These factors have significant impact on brightening responses both alone and by their interaction.  (A)  Consistency of Pulp  Brightness gain will increase with increasing pulp consistency. The increase of pulp consistency reduced the volume of aqueous phase, and raises the concentration of brightening chemicals. Therefore, the brightening response is promoted.  Manufacture often brighten mechanical pulps in medium consistency, 10% ~ 15%, or low consistency, 3% ~ 6%, although peroxide brightening can be carried out over from a range 4% to 35%.  A brightening gain up to 12 % ISO can be obtained by peroxide brightening mechanical  pulp with medium consistency. For brightness gain above 12 % ISO, high consistency pulp is generally required. However, mechanical pulp with brightness gain higher than 20% ISO is difficult to obtain in one stage peroxide brightening even at high consistency. [9]  (B)  pH  An optimum pH is required to achieve a maximum brightness gain. High pH will lead to the formation of new chromophores, which cause alkali darkening.  It will also accelerate the  decomposition of peroxide to oxygen and water via reaction [2-2]. However, if the pH is too low, it will hinder the brightness increase.  - 16-  Chapter 2 Theoretical Background (C)  Temperature  The peroxide brightening process usually proceeds between 40°C to 60°C industrially. This brightening temperature is 20°C lower than with chemical pulps since lignin removal is not the goal. [10] The brightening reaction is accelerated at higher temperature. However, conventional brightening of mechanical pulp with temperature higher than 70°C will promote the decomposition of hydrogen peroxide and decrease the brightening efficiency.  (D)  Additives or Stabilizers  Metal ions such as Fe , M n , and C u 3+  the pulp.  2+  2+  catalytically decompose hydrogen peroxide and color  The source of these metals may be impurities of process water, corrosion of the  equipment, and extractives of the pulp. The most important metal ions responsible for catalytic decomposition of H 2 O 2 in decreasing order of catalytic capacity are: M n > Fe > Cu. [21] M n and C u  2+  2 +  will catalyze auto-oxidative reactions and accelerate brightness reversion, which form  new colored structures in lignin. On the other hand, the F e will form colored complexes with 3+  lignin. [22] Other research also suggests that excess alkali in bleach liquor enhances catalytic decomposition of peroxide. [23] Metal ions such as aluminum and calcium have a lesser effect on peroxide decomposition, but high concentrations of calcium and aluminum may provoke color reversion. [24] To manage the metal effect in order to improves the peroxide brightening of TMP, chemicals are added to deactivate these ions.  1) Magnesium Sulfate (Stabilizer) Magnesium sulfate acts as a stabilizer when the process water is not sufficiently hard.  One  function of magnesium ion is to mitigate carbohydrate degradation by oxygen under alkaline conditions. Magnesium ion will form insoluble floes by adsorbing or co-precipitating heavy metal ions. Magnesium can also stabilize alkaline hydrogen peroxide solution by scavenging superoxide anion radicals, Of" by interrupting free radical chain decomposition reactions. [25] The reaction is as follows: 202- + M g - > M g ( 0 ) 2 +  2  2  The dosage is about 0.05% weight percent magnesium sulfate on OD pulp.  - 17-  [2.5]  Chapter 2 Theoretical Background  2) Diethylenetriaminepentaacetic acid (Chelate) Diethylenetriaminepentaacetic acid (DTPA) removes metal ions from pulp by chelating. D T P A forms a ring structure with the metal ion, which inhibits the metal ion catalytic effect. [26] The electrons of D T P A from the five oxygen atoms and the free electron doublet from the three nitrogen atoms form the eight ligands of this chelating agent. [27] These ligands participate in the formation of the chelate with the metal ions. Otherwise, metal ions will form a colored complex with the phenolic lignin structure. Approximately 0.25% of D T P A as the sodium salt by weight is added on OD pulp before the addition of hydrogen peroxide.  3) Sodium Silicate (Buffer) A buffering agent such as sodium silicate, 5% on OD pulp, is also added to keep the pH high even as organic acids are produced as a result of some carbohydrate degradation.  Sodium  silicate also stabilizes hydrogen peroxide in the presence of heavy metals as it forms insoluble heavy metal silicates or adsorbs these metals in calcium and magnesium silicate floes. [10] [28]  (£)  Residual Peroxide and Retention Time  Residual peroxide concentration and retention time are important factors in the peroxide brightening process. As a rule of thumb, about one-tenth of the added peroxide should be left when the brightening process is terminated. [12]  During peroxide brightening and refining,  quinones are intermediate products in the Dakin reaction of peroxide with p-hydroxy carbonyl compounds. Thus, there is a risk of colored hydroxy p-quinone formation whenever mechanical pulps are treated with alkaline peroxide. [20]  Optimum retention time depends on the dosage of peroxide but is usually between 1 and 3 hours. Excessive retention periods will result in alkali darkening and reversion of brightness due to insufficient peroxide. Optimum retention time is also dependent on temperature and pH of the brightening liquor. The relationship between these factors is shown in Table 2.2.  - 18-  Chapter 2 Theoretical Background Temperature ( C)  pH of the Brightening Liquor  Retention Time (Minutes)  35 - 4 4 (Low)  Medium alkali ( 1 0 - 12)  240 - 360  60 - 79 (Medium)  Medium alkali ( 1 0 - 1 2 )  120- 180  93 - 98 (High)  Low alkali ( 8 - 10)  U  Table 2.2  .5-20  Relationship of Temperature, Alkali of Brightening Liquor, and Retention Time  2.4 Principles of Related Electrochemical Processes Electrochemical engineering has associated with pulp and paper industry for many years. The present electrochemical processes include the supply of bleaching chemicals such as chlorine, sodium chlorate, chlorate dioxide and sodium hydroxide. This section provides some elements and fundamental equations of thermodynamics, electrode kinetics, and mass transfer in electrochemical system in order to explore new applications.  Electrochemical engineering involves the interconversion of chemical and electrical energy. It requires integrated treatment of electrochemistry and engineering concepts.  Generally, an  electrochemical system is a transfer of electrons between electrodes and electrolyte.  The  participation of the electrons is represented in the reversible redox reaction as follows: O + ne" <=> R'  [2.6]  where O is the oxidized species, R ' is the reduced specie, and n is the electron stoichiometry coefficient.  Two kinds of reactions will occur on the surface of the electrodes in an  electrochemical system: reduction reaction and oxidation reaction.  The oxidation reaction  occurs on the anode and reduction reaction occurs on the cathode.  The difference between the applied electrode potential (E) and the reversible electrode potential (E ) is called the overpotential (r|). When r\ is positive, E > E , equation 2.6 will tend to go from e  e  right to left and the reaction is an oxidation reaction.  On the other hand, i f r| is negative,  equation 2.6 will tend to go from left to right and the reaction is a reduction reaction.  - 19-  Chapter 2 Theoretical Background 2.4.1  Thermodynamics of the Electrochemical System  Electrochemical processes are driven by both thermal and electrical energy. Thermodynamically, the driving force for a spontaneous cell reaction is a negative value of Gibbs free energy,  AG . Cell  Electrochemically, the driving force for an electrochemical reaction is the potential difference between the electrode and the electrolyte. The Gibbs free energy for the overall chemical change in an electrochemical system can be related to the equilibrium cell potential E  by the  CM  expression: AG =-nFE Cell  [2.7]  Cell  where F is the Faraday constant, 96480 C/mol. For spontaneous cell reactions, T AS  Cell  thus AG  Cell  is negative and E  > AH ; Ce!l  is positive.  Cell  Conventionally, the thermodynamic cell potential, E , is the difference between the cathode T  Cen  and the anode potentials. ELII = E c - E  [2.8]  A  where Ec is the equilibrium electrode potential for the cathode and E A is the equilibrium electrode potential for the anode. Each electrode potential, E , can be calculated from the Nernst e  equation as follows: E =E° +^ln^ nF e  e  [2.9]  a  R  where E° is the standard electrode potential (Volt), R is the gas constant (kJ/kmol/K), a  Q  is the  activity of the oxidized species, and a is the activity of the reduced species. R  2.4.2  Electrode Kinetics and Mass Transfer  Consider a single electrode reaction in the cathodic direction. 0 + ne"->R'  -20-  [2.10]  Chapter 2 Theoretical Background The relationship between its reaction rate, R , and the electric current is expressed by the Faraday's law as follows: [2] I=-FR*  [2.11]  v  where I is the current applied to the system and v is the reactant stoichiometric coefficient. In a batch process, equation 2.9 can be written as follows: [29] » = i U i i (mol) nF nF  [2.12]  where m is the amount material converted, Q is the amount of electrical charge involved, and t is time. If more than one reaction occurs on the electrode surface, current efficiency, CE, becomes an important concern in the electrochemical process. The current efficiency is the fraction of electrical charge used for the desired reaction. For a constant supplied current: [29] [2.13]  C E = ^ ? L I Total  where I partial is the partial current for the desired reaction and I Total is the total current supplied to the system. Consider a batch system with constant volume, VBatch; the reactant concentration, c,  m can be expressed as c=  .  ^Batch  By differentiating equation 2.12 with respect to time and  combining with equation 2.13, the overall rate expression can be written as follows: dc d  where i  Total  t  =  CE-A -i Area  Total  ^kmol^  n-FVBaton  is the operating current density and the AArea is the working electrode area.  The overall rate of an electrochemical reaction is strongly influenced by the electrode potential. The current density dependence of electrode potential can be described by recording the polarization curve as shown in Figure 2.14.  -21 -  Chapter 2 Theoretical Background  Figure 2.14  General Polarization Curve [30]  Figure 2.14 is a general polarization curve obtained by plotting the current density versus the potential. In Figure 2.14, curve (a) shows a pure activation controlled current, i ; and curve (b) ac  shows the actual measured current having a mass transfer limited value, i , at high potentials. L  While the applied electrode potential is between equilibrium potential and the potential supplied by activation controlled current density, the reaction is under kinetic control (activation control). Once the mass transfer limiting current density is reached, the reaction is under mass transfer control and the rate of reaction will remain fixed at the mass transport limit.  For a reaction under mass transport control, the limiting current density, i , can be expressed by L  the equation as follows:  i =nFK C L  m  b  [2.15]  where K is the mass transfer coefficient which depends on electrolyte composition, temperature, m  and flow conditions; n is the stoichiometry number of moles of electron, and Q, is the bulk concentration of reactant. In Figure 2.15, if the overpotential exceeds + 0.1V, the equilibrium of the reaction is considered in anodic direction. Thus, current density can be expressed as Tafel equation, connected for mass transfer, as follows: [2]  -22-  Chapter 2 Theoretical Background  j/  n = a+b\n{i)-b\n{\-  t  a  where a=  RT  m  anF  (0>  ^  =  RT  [2.16]  j  > & "Ha is the anodic overpotential.  In summary, the  m  anF  overpotential for the desired reaction should be minimized for an ideal electrochemical system in order to increase the current efficiency and reduce the energy costs. 2.4.3  Elements of Electrochemical Cell  Most electrochemical processes are carried out in an electrochemical cell. A n electrochemical cell basically comprises the electrolyte, a cathode, an anode, and sometimes a separator. (A)  Electrolyte  The electrolyte needs to provide a medium for ion transport in the electrochemical system. Generally, the electrolyte provides a relatively low resistance medium between the electrodes and stabilizes the electrical double layer structure and its influence on electrode kinetics. The electrolyte must at least contain the essential components as follows: a solvent, reactant species and sometimes supporting electrolyte. [29] (B)  Voltage Balance (Cell Voltage)  The overall performance of an electrochemical cell with current flow requires a calculation of the voltage balance. When electric current flows through the cell, the electrode potentials are displaced from the equilibrium values by the over-potentials and a voltage drop occurs across the electrolyte. The total cell voltage is related to the current by the voltage balance of equation as follows: [2] iCell  Where  *la  E  :  C e  - E  a e  + T| - T| c  a  - ZH,ohm  [2.17]  Anodic overpotential (V)  Ecell  Total cell voltage (V)  Equilibrium potential of  "Ho  Cathodic overpotential  cathode (V HE)  (V)  S  Eohm  (V)  Ohmic voltage drop across the cell  E/  Equilibrium potential of anode (V HE)  (S){ / ) is  S  k  (s: length of current path (m); k: electrical conductivity of electrolyte (mho m" ) 1  -23 -  Chapter 2 Theoretical Background (C)  Electrode Materials  Electrodes should have adequate mechanical strength and resistance to erosion and other types of physical attack by electrolyte, reactants, and the products. The resistance to chemical attack and the ability to avoid corrosion also are important. In general, adequate electrode materials should have high electrical conductivity, ease of fabrication into suitable form, and long lifetime. The ideal electrode material for most processes should be totally stable in the electrolysis medium and promote the desired reaction with a high current efficiency at low overpotential and suppress the undesired reactions. (D)  Rate of Peroxide Accumulation  The rate of accumulation of H 2 O 2 in a batch electrochemical reactor can be expressed as: d[H 0 ] 2  2  dt where n  Consum  =  A i CE Anode Anode  _* y  P  2-FK  k  HO  Consum  [2.18]  (kmol/s)  Re actor  = [rate of destruction of H 0 at cathode and anodes] 2  2  rate of [h0 \ destruct 2  rate of \h0 \destruct  by equation 2.28 (p.26)  by equation 2.30 (p.26)  2  where:  [H2O2]  Concentration of H 2 O 2 (kmol/m )  t  Time (seconds)  AAnode  Anode area (m )  lAnode  Current density at anode (kA/m )  k  Rate constant of H 2 O 2 homogeneous decomposition (s" )  CE  Current efficiency of primary anode reaction (%)  Faraday constant (96487 C/kmol)  VR, eactor  3  2  2  D  1  Volume of electrolyte (m ) 3  During steady state, the net rate of peroxide production is zero, hence [ H 2 O 2 ] becomes: [H 0 ] 2  2  AAnode ' Anode ' CE 1  2kFK Re actor  consum  n p  k  [2.18a]  2.5 Production of Hydrogen Peroxide Hydrogen peroxide has been used in industry as a chemical compound since 1818.  Its  commercial manufacturing process can be divided into two major types: chemical and  -24-  Chapter 2 Theoretical Background electrolytic.  The major chemical process is the anthraquinone process, and the obsolete  electrochemical, commercial process is electro-oxidation of sulfuric acid. 2.5.1  The Chemical Process of Hydrogen Peroxide Production  The conventional, thermochemical process production of hydrogen peroxide is based on autooxidation of anthraquinols. The cyclic anthraquinone process for producing hydrogen peroxide, involves two main steps. In first step, the alkylanthraquinone is dissolved in a water-immiscible organic solvent. It is hydrogenated in the presence of a particulate hydrogenation catalyst, to yield a solution of the corresponding alkylanthrahydroquinone in the solvent. The first step is oxygenation of this solution by oxygen to regenerate the solution of the alkylanthraquinone and hydrogen peroxide. The following equation shows the process mechanism. [31]  [2.19] 2.5.2  The Electrolytic Process of Hydrogen Peroxide Production  Hydrogen peroxide can be obtained by several electrolytic methods. The commercial methods are anodic oxidation of sulfuric acid and cathodic reduction of oxygen.  Other method in  progress is anodic oxidation of sodium carbonate. [31] (A)  Anodic Oxidation of Sulfuric Acid  Hydrogen peroxide can be generated from electro-oxidation of sulfuric acid to peroxydisulphuric acid, followed by hydrolysis and distillation to produced peroxide up to 50 wt%. [2] S 0 + 2e" <- 2S0 "  Ee° = 2.1VsHE  2  2  8  4  H S 0 + 2 H 0 -> 2 H S 0 + H 0 2  2  8  2  -25 -  2  4  2  2  [2.20] [2.21 ]  Chapter 2 Theoretical Background (B)  Electroreduction of Oxygen  Peroxide can be obtained by cathodic reduction of oxygen. The electroreduction of oxygen to hydrogen peroxide can be carried out in both alkaline and acidic conditions.  The  electroreduction of oxygen at appropriate cathode generates the peroxide in the form of perhydroxyl ion, H O 2 " . The reactions under alkaline conditions are: 0 + H 0 +2e" -> H 0 " + OH"  E° =  H 0 " + H 0 + 2 e ->30H"  E° = 0.87V E  [2.23]  E° =  0.67 V E  [2.24]  E° = 0.87V E  [2.25]  2  2  2  2  2  -0.08 V E S H  SH  [2.22]  The reactions under acidic conditions are: 0 + 2 l T +2e" - » H 0 " 2  2  2  H 0 " + 2H+ +2e" -> 2 H 0 2  2  2  S H  SH  In this process, the reduction of perhydroxyl ion to hydroxyl ion is thermodynamically favored over the reduction of oxygen to perhydroxyl ion. Thus, cathode materials need to be chosen carefully to promote the desired reaction at a reasonable current efficiency. So far, the cost for this electrochemical method is high but it does allow on-site generation of dilute hydrogen peroxide, which can be used for pulp brightening or bleaching. (C)  Electro-oxidation of Sodium Carbonate  In 1970, Oloman revealed that hydrogen peroxide could be generated in a solution by electrooxidation of sodium carbonate on platinum. [32] In this the process, the principal reactions that occur in the electrolyte are shown in Table 2.3. [9] Anode Reactions  E°  Primary Secondary  C 0 " + 2e" <— 2 C 0 ' 40H"  0.4  [2.27]  HO~ + OH"  0.08  [2.28]  H + 20H"  -0.8  [2.29]  3 OH"  0.87  [2.30]  3  2  2  0 + H 0 +2e" 2  2  <r-  )  [2.26]  2  6  2 H 0 + 0 + 4e" <-  S H E  «2  2  2  at 298°C ( V  Cathode Reactions Primary Secondary Table 2.3  2 H 0 + 2e" - » 2  H 0 " + H 0 + 2e" -> 2  2  2  Principal Reactions for Electro-Oxidation of Sodium Carbonate  -26-  Chapter 2 Theoretical Background The hydrogen peroxide is formed as percarbonate from the primary anode reaction is hydrolyzed to byproduct bicarbonate as follows: C 0 " + 2 H 0 -> 2HC0 " + H 0  [2.31]  2  2  6  2  3  2  2  However, depending on the pH, the peroxide may exist as H 0 2  or H 0 " according to the  2  2  equation as follows: H 0 + OH" <=> H 0 + H 0 " 2  2  2  [2.32]  2  The standard electrode potential data shown in Table 2.3 indicates that secondary anode reactions [2.27-2.28] are thermodynamically more favorable than primary anode reaction [2.26]. Moreover, reaction 2.28 is even faster than reaction 2.27 but limited by mass transport constraint. To slow reaction 2.27, the anode can be cooled to increase the over-voltage. Furthermore, higher over-voltage for reaction 2.27 can be obtained by choosing the anode material. The appropriate choice of anode material should accelerate the primary anode reaction and be poor for oxygen evolution to make equation 2.27 and 2.28 less favorable. A n ideal anode material for the electrooxidation of sodium carbonate to percarbonate  is platinum.  Platinum provides high  overpotential and is a poor catalyst for oxygen evolution as shown in Figure 2.15. [2] Also, platinum is relatively stable in Na C03 at high potential. 2  (pH = 0) 2H+ +2e" -> H  .2  Figure 2.15  <«g < J )  2  -1  0  Tafel Plots for H Evolution in 1M 2  -27-  0 + 2 H 0 +4e" <- 40H" (pH=14) 2  2  -1  O  and for 0 Evolution in 1M O H [2] 2  Chapter 2 Theoretical Background Research done by Kurniawan and Oloman in 1998 showed a series of conditions for the production of hydrogen peroxide in an undivided cell as follow: [9] 1.  the initial concentration of sodium carbonate is around 1M  2.  magnesium compounds or other stabilizers are needed to suppress peroxide decomposition  3.  anode current density is around 0.05 ~ 1.OA/cm  4.  the anode material should have high oxygen overpotential and survive under high  2  alkaline condition (pH>l 1) 5.  the anode operating temperature should be held around 0°C  6.  differential electrode area should be employed to reduce the mass transfer of peroxide to cathode  2.5.3  7.  diaphragm could be used on the cathode to suppress the destruction of H 2 O 2  8.  the pH of the electrolyte should be from 9 - 1 2  Figures of Merit for the Electro-Oxidation of Sodium Carbonate  The figures of merit listed below can be used to determine the efficiency for the production of peroxide by electro-oxidation of sodium carbonate.  These figures of merit can characterize the  design of the reactor and reflect the performance of the reactor. A)  Current Efficiency  (%) CE =  =  n  hotal  B)  F  [2.33]  R  ^Total  Specific Energy  (kWh/kg) SE=  — \E \ 3600 MW-CE " 1  C)  [2.34]  Cell Ce 1  Space-Time Yield  (kg m" s" ) 3  S  T  y  =  VroductionRate  =  Re actorVolume  -28-  CE-I  Partial  MW  -F-V  n  Keactor  1  ^  Chapter 2 Theoretical Background where: Ipartial VReaotor  n  Current of equation 2.22 : Volume of Electrolyte (m ) 3  Electro stoichiometry coefficient  R*  Production rate of H 2 O 2 (kmol/s)  Eceii  Total cell voltage (V)  MW  Molecular weight of H 2 O 2 (kg/kmol)  ofC 0 " 2  2  iTotai  6  Total current density applied to the  ipartial  cell (kA/m ) F  Current density of equation 2.25 (kA/m )  2  2  Faraday constant  iTotai  Total current applied to the cell (kA)  (96487 kC/kmol)  The ideal process should achieve 100% current efficiency for reaction 2.22 with high space-time yield and low specific energy.  The specific energy estimates the required electrochemical  energy for this process but not includes the energy consuming by the temperature control or other energy cost (e.g. mixing). The space-time yield measures the productivity of H 2 O 2 relative to the size of the reactor. 2.6 In-Situ Electro-Brightening of Mechanical Pulp by Electro-Oxidation of Sodium Carbonate Peroxide produced by the electro-oxidation of sodium carbonate can be used as an oxidative brightening species in a pulp slurry. This process has great potential due to the price of sodium carbonate being low. Also, sodium carbonate is recycled and abundant in the pulp mill in the inorganic smelt from the recovery furnace [33].  In-situ brightening is proposed due to the  following potential advantages: (1) The brightening agent is formed in the electrolytic cell and reacts immediately with the pulp, which reduces the efficiency losses due to the quick decomposition of peroxide species. (2) In-situ brightening simplifies the process into only one stage and saves the cost for transporting and storing the conventional brightening agent such as hydrogen peroxide. (3) In-situ brightening reduces the dependence of pulp mills on brightening agent producers. (4) In-situ brightening can maintain and control the level of peroxide on the pulp throughout the brightening process. The potential disadvantages of the in-situ brightening  -29-  Chapter 2 Theoretical Background process are: (1) Optimum conditions for production of hydrogen peroxide and for brightening of mechanical pulp are not the same. (2) Pulp would decrease the effective electric conductivity of the electrolyte. (3) Mixing is difficult in the electrochemical reactor with high pulp consistency.  In conventional brightening, to maintain residual peroxide in the brightening liquor to prevent alkali darkening is imperative. Due to the nature of the electro-brightening process, this demand can be fulfilled.  The supply of the oxidative species by electro-oxidation sodium carbonate to  produce peroxide is continuous till the end of the brightening process.  Research done by  Kurniawan and Oloman in 1993 indicated that adding stabilizers or chelating agents has the same effect as in the conventional process [34]. In 1995, Oloman and Zhang designed a batch electro-brightening reactor which brightened the pulp up to 5% consistency to have 13.9% ISO brightness gain and 6.5% yellowness loss.  In 1998, Kurniawan and Oloman reported the operating conditions for the in-situ generation of peroxide for brightening the mechanical pulp. They examined the factors affecting the electrobrightening of mechanical pulp. Table 2.4 and 2.5 show the experimental conditions and the best brightening results for one stage brightening.  Operating Conditions: Chemicals  1M N a C 0 ; 0.11M N a H C 0 ; 0.034M N a S i 0 ; 0.6g DTP A; 0.04g M g S 0 2  3  3  2  3  4  Current & Voltage  11 A & 15 V  PH  « 10.7  Temperature  *54°C  Cathode Material  Tungsten rod; area: 19 cm  Anode Material & Area  Platinized titanium modified water cooled U-tube; area: 28 cm  Reaction Time  210 minutes (pulp was introduced after the initial 35 minutes)  Total Volume  700 ml  Pulp & Pulp Consistency  Softwood TMP & 1 %  Table 2.4  Experimental Conditions by Kurniawan and Oloman [9]  -30-  2  Chapter 2 Theoretical Background Results: Maximum [ H 2 O 2 ]  0.033 M  Brightness Gain  12% ISO  Yellowness Loss  7%  Pulp Yield  95 %  Table 2.5  2.6.1  Best Brightening Results by Kurniawan and Oloman [9]  Figures of Merit for the Electro-Brightening of Mechanical Pulp in a Batch Reactor  The following set of figures of merit can be used to characterize the performance of the electrochemical reactor for commercial purposes. The specific brightening energy estimates the electrochemical energy consumed per ton of OD pulp for each %ISO increase. The brightening space-time yield has economic implications in determining the size and thus the capital cost of the reactor. [2] A)  (kWh/ ^ /{ton  Specific Brightening Energy  x  % ISO)  ceii • I time  E  SBE  B)  (ton%ISO)/ /(m hr\  Brightening Space-Time Yield  T> C T V Lib  [2.36]  Tonnes of Pulp • Brightness Gain  3  Tonnes of Pulp • Brightness Gain  1Y  [2.37]  Reactor Volume • time Practical application of pulp brightening requires low specific brightening energy and high brightening space-time yield.  -31 -  Chapter 3  Chapter 3 Proposed Research Objectives The proposed work includes the production of hydrogen peroxide and the in-situ electrobrightening of mechanical pulp by electrolysis of sodium carbonate liquor. The production of hydrogen peroxide is an in-situ process according to the reactions 2.26 to 2.30.  Previous work by Dr. Jiujun Zhang on this system was carried out in a 2-liter batch system with pH range from 10.5 to 11.8. The objective of this thesis project is to improve the design of Zhang's batch in-situ electro-brightening reactor, to establish the effects and interactions of variables such as temperature, pH, and current density, and finally to manipulate these variables to optimize the process.  The experimental plan embraced modifying the electro-brightening  reactor and examining the basic electrochemical behavior of the batch system, the rate of hydrogen peroxide generation, and the brightening of softwood TMP.  Other variables to be  investigated include the electrolyte composition, effect of additives, cathode material and configuration, pulp consistency, brightening retention time, and periodic application of the electric current.  A further objective of this thesis project is to investigate the advantage and disadvantage of the existing reactor and collect data for designing a new reactor to produce hydrogen peroxide up to 0.1M for in-situ brightening, since the objective of optimization was not reached due to reactor deterioration.  -32-  Chapter 4  Chapter 4 Experimental Apparatus and Procedure The equipment used in this study included an electrochemical-brightening reactor, standard peroxide analysis glassware, and mechanical pulp testing apparatus. The experiments included generation of peroxide and electro-brightening of mechanical pulp. A flow sheet of the overall organization of this chapter is summarized in Table 4.1. No  Overall layout  4.1  Experimental apparatus  1.  Original electrochemical reactor setup  2.  Modification  of the  cooling system  of the  electrochemical reactor 3.  Modification of the anode, cathode, and position of the thermocouple of the electrochemical reactor  4.  Modification of the cover of the electrochemical reactor for gas sample collection  4.2  4.3  Experimental procedure  1.  Electroplating of platinum on the anode  2.  Electrochemical production of peroxide  3.  In-situ electro-brightening of mechanical pulp  Pictures of Electrochemical Brightening System Table 4.1  Overall Layout of the Experimental Apparatus and Procedure  4.1 Experimental Apparatus The electrochemical reactor was modified several times throughout the project.  These  modifications included the cooling system and configuration of both the electrodes and the mixer.  -33 -  Chapter 4: Experimental Apparatus and Procedures 4.1.1  Original Experiment Apparatus  Dr. Jiujun Zhang and Professor Colin Oloman developed the original experimental set-up shown in Figure 4.1 in 1995. The set-up included a D C power supply, a motor set, a temperature control unit, and an electrochemical reactor.  A B C D E F G I J  Figure 4.1  DC motor control DC power supply Temperature control Thermocouple Heater Mixer motor Electrochemical reactor Cooling water inlet Cooling water outlet  Original Experimental Set-up Developed by Dr. Zhang and Prof. Oloman  -34-  Chapter 4: Experimental Apparatus and Procedures The D C motor control and mixer control powered and controlled the mixer. Both of these components were made by Glas-Col. The D C motor control had 0.5 horsepower and 293ounceinch torque. The ratio of electricity to speed and torque of the mixer motor were l m V per rpm and l m V per ounce-inch. The D C power supply, X H R 20-50, was capable of producing a maximum 50 Amperes of current at 20 volts. The positive of the D C power supply connected to the vessel directly and the negative connected to the rotating cathode through a brush.  The electrolyte temperature control included a control box, a heater, and a thermocouple. The heater and the thermocouple were made by O M E G A , and the control box was composed by Mr. Alex Lee at the chemical engineering shop of U B C . The control box included a microprocessorbased temperature controller, CN76000. The CN76000 was a first-order sensor functioning with a reverse control action made by O M E G A . The output of the control box was connected to the heater clamped on the bottom of the electrochemical reactor. The heater was a 200 W electric pail heater. The input of the control box was connected to J type thermocouple located on the outside wall of the electrochemical reactor through a supported rubber. The thermocouple was quarter inch OD with a layer of Teflon coating on the surface.  The electrochemical reactor used tap water as anode coolant, connected to the reactor by quarter inch ID P V C tubing. The temperature of the cooling water was around 15°C in summer and 10°C in winter with a flow rate of approximate 1.5 liters per minute.  The cooling water  discharged to a sink directly, without recycle.  The electrochemical reactor shown, in Figure 4.2, was a 2.1-liter, titanium vessel. The reactor inside wall was covered by a layer of Teflon, except four platinized anode surfaces with a total area of 64 cm . Four cooling chambers were attached behind the anode areas with individual 2  water inlet and outlet on the outside wall of the reactor. The ribbon mixer was located on the cathode by three clamps. The distance between the mixer and the reactor wall was made to approximate 3 mm to provide better mixing and prevent pulp sticking on the wall while electrobrightening the pulp.  -35 -  Chapter 4: Experimental Apparatus and Procedures  Platinized Anode Surface Mixer Ribbon Support  Cooling Chamber Ribbon Mixer  Supported Rubber  Titanium Cathode covered with diaphragm  Thermocouple  0.64 cm (1/4 inch) N P T Connector 22.75 cm  Supported Rubber  (7.5 inch) J  Figure 4.2  Original Electrochemical Reactor  -36-  Chapter 4: Experimental Apparatus and Procedures Cooling Water Outlet Teflon Coating  Platinized Anode Surface (8 cm x 2 cm x approx 10 fim) 0.64 cm (1/4 inch) N F T Connector  Cooling Water Inlet ^ ' , Cooling Chamber Figure 4.3  ^Titanium Vessel  Original Anode Design  Figure 4.3 shows the details of the original anode design. The cooling chambers were also made of titanium, fitted with 2, A inch NPT connectors. These connectors connected to the cooling l  source with A inch polyethylene tube. These connectors and tubes were purchased from Colel  Parmer Instrument Company.  The platinum layer was electroplated onto the titanium wall, and each platinized anode area was 16cm (8cm x 2cm) in area by a few microns thick. The rest of the area was covered with a layer 2  of Teflon to prevent titanium exposure to the electrolyte.  The reason to prevent titanium  exposure to the electrolyte is because titanium is not a noble metal.  Its domain of  thermodynamic stability does not have any portion in common with the domain of thermodynamic stability of water. Titanium will be corroded in the presence of very oxidizing solutions, such as hydrogen peroxide solutions, especially i f one attempts to use it as an electrolytic anode. complexes T i 0 2  2+  The exposed titanium would react with peroxide and form the orange that accelerates the decomposition of peroxide. Titanium would no longer  corrode i f it were covered with a non-conducting material, such as Teflon. Figure 4.4 represents the theoretical conditions for corrosion, immunity and passivation of titanium at 25°C  -37-  Chapter 4: Experimental Apparatus and Procedures  ;2 -i 0 1  i  M  corrosion  a e 7 i  )  a ii i; n m i  ii  z  w  ?  ? corrosion t.*  it i 06.  0,6  08  06  a* a.z o  OA  at  0 •<u OK -as -a». -i  passivation  Icorrosion  -0.2  -a* -0,6  -a* corrosion  -l  -1.2  -1,2  -M  -u  -1.8  -2 -t2.  -1,6  -IB  M  Figure 4.4  2 1-2.2  immunity 4  «  t  M  1  II  II  li  I) H  I)  1-2.4  «  pH  Theoretical domains of corrosion, immunity and passivation of titanium, at  25°C (Form Marcel Pourbaix, Atlas Of Electrochemical Equilibria in Aqueous Solutions) [35]  Figure 4.5 displays the detailed information of the original cathode design. The cathode was a Vi inch O.D. titanium tube covered with a layer diaphragm, which made the total OD of the cathode to be A inch. The titanium tube was drilled with holes for releasing the gas generating from the 3  cathode reaction.  The gas, mainly hydrogen, went through the holes and discharged to  atmosphere from the top of the titanium tube.  The ribbon mixer was made of stainless steel and wrapped by Teflon tape to prevent corrosion. Furthermore, The diaphragm on the titanium tube cathode was a layer of microporous polypropylene. It was used to suppress the reduction of peroxide by the cathode.  -38-  Chapter 4: Experimental Apparatus and Procedures Connector to Motor  Figure 4.5 Original Cathode Design 4.1.2  Modification of the Cooling System of the Electrochemical Reactor  It was evident from the previous research that electro-oxidation of carbonate ions to percarbonate ions was favored when the working temperature of anode was under 10°C. The peroxide produced using the original experimental set-up mention in the previous paragraph was about 0.008M and not able to brighten the pulp to a brightness gain higher than 13 %ISO. For the present work, a new cooling system was set up to provide a better cooling to the anode in order to promote the production of peroxide. Also, a J-type, surface thermocouple purchased from Cole-Parmer replaced the original thermocouple in order to obtain a more reliable temperature reading of the electrolyte. Figure 4.6 shows the new experimental set-up.  -39-  Chapter 4: Experimental Apparatus and Procedures  A B C D E F G H I J K  Figure 4.6  DC control DC power supply Temperature controller Surface thermocouple Heater Mixer motor Electro-brightening reactor pH meter Centrifugal pump Ice water tank Laboratory stirrer  Experimental Set-Up with the New Cooling System  The new cooling system was designed to provide cooling water with lower temperature and higher flow rate. The new cooling system consisted an ice water tank, a centrifugal pump, a laboratory stirrer, and about 12 feet 3/8 inch P V C tubing.  The centrifugal pump had 1/8  horsepower and was made by Eastern. The laboratory stirred was made by TalBoys Engineering Corp. Its rpm range was 500 to 7500. Test runs showed that the temperature of the cooling  -40-  Chapter 4: Experimental Apparatus and Procedures water output was around 5°C. Since this temperature was below the temperature of the tap water; the cooling water was recycled in order to reduce the cost of ice.  Together with the centrifugal pump and the 3/8-inch tubing, the flow rate of the cooling water could reach 6 liters per minute. With continuing supply of fresh ice cube to the system, and continuously mixing the recycle water and ice, the temperature of the cooling water was around 1°C. These changes enhanced the cooling efficiency and allowed the anode to be cooled to the desired level.  4.1.3  Modifications of the Anode, Cathode, and Setup of the Thermocouple of the Electrochemical Reactor  The difficulty of getting reliable temperature reading of the electrolyte, deterioration of the anode surface, and uneven mixing of the brightened pulp were observed from the experiments using the new cooling system. The electrochemical reactor was subject to major modifications in the attempt to overcome these problems and thereby improve the brightening process.  (A)  Deterioration of the Anode Surface  The performance of the platinized anode surface decreased significantly from run to run. This was caused by the deterioration of the platinized anode. The platinum layer electroplated on the anode surface was consumed, and the remnant platinum was not enough to function as the electrocatalyst. Figure 4.7 shows the aging of the platinized anode. The experimental data in Figure 4.7 indicate that the anode deteriorated significantly after each run. These four runs were done under the same experimental conditions. The first run was performed  after  re-electroplating the platinum on the anode surface using hydrogen  hexachloroplatinate hydrate solution. The third run was performed on the third day after the first run, and the fourth and the fifth run were performed on the fourth and fifth day. A second run was performed but with different experimental conditions so it is not listed here.  -41 -  Chapter 4: Experimental Apparatus and Procedures  200  Brightening Time (Minutes) •  FIRST RUN  —  THIRD R U N  •  —  A •  Figure 4.7  —  FOURTH RUN  —  FIFTH R U N  Aging of the Platinized Anode  The four runs used to plot Figure 4.7 were with the experimental conditions as follows: The electrolyte contained 1M N a C 0 , 0.13M N a H C 0 , 0.03M NaSi0 , 0.007% M g S 0 « 7 H 0 , and 2  3  3  3  4  2  0.01%) DTPA. The experiments were run for 180 minutes with 20A from the D C power supply. The temperature of the electrolyte was controlled at 60°C.  -42-  Chapter 4: Experimental Apparatus and Procedures Figure 4.7 shows that the highest peroxide concentration of the first run was 0.036M. However, the highest peroxide concentration of the third run dropped 47 %. The concentration of peroxide further decreased another 33% for the fourth and fifth run. Further experiments produced even lower concentration of peroxide.  This proved the deterioration of the anode and showed there was not enough platinum on the anode surface to produce peroxide. Therefore, the titanium was exposed to the electrolyte and the platinum needed to be re-electroplating on the anode surface. However, the chemicals for electroplating of platinum were hydrogen hexachloroplatinate hydrate, phosphoric acid, and ammonium phosphate dibasic. This would cause corrosion on titanium based on the acidic conditions of the electrolyte.  Figure 4.8 shows that corrosion of titanium would be initiated while re-electroplating the platinum onto the anode. [35]  -43 -  Chapter 4: Experimental Apparatus and Procedures Figure 4.8 considers the oxides Ti203 and T I O 2 in the hydrated state. It shows the conditions of thermodynamic stability of titanium and those derivatives of it, which can exist in the presence of water and aqueous solution free from substances with which titanium can form soluble complexes or insoluble salts.  From Figure 4.8, one can observe that once the pH was lower than 8 and the electrode potential was higher than -1.8, Ti would be oxidized to T i , which means titanium would go from 2+  immunity zone into corrosion zone. According to Figure 4.8, the titanium would be corroded due to the process of the electroplating under acidic condition. Observation of the titanium surface confirmed the corrosion of titanium.  (B)  Modification of Anodes  The anodes were modified to solve the loss of platinum during the electro-brightening experiments. To eliminate the need of electroplating the anodes and to prevent titanium getting corroded during the electroplating process, platinum foil was used as a substitution. Figure 4.9 shows the detailed design of the modified anode.  The platinum foils were glued onto four recessed areas that were milled into the inside wall of the titanium vessel. Each recess area was about 1mm deep and was filled with conductive glue. Each platinum foil was 0.1mm thick, 8cm long, and 2cm wide. The conductive glue was silverbased, conductive epoxy, made by R B C industries. The edges between platinum foil and Teflon coating were covered by non-conductive epoxy made by Industrial Formulators of Canada Ltd. The titanium-based reactor was sent to recoat a layer of Teflon before gluing the platinum foil onto the reactor. A Teflon pre-coat is needed because the Teflon coating process was run at a temperature of 540°C and would destroy both the conductive and non-conductive glue.  -44-  Chapter 4: Experimental Apparatus and Procedures  Elevation  Plan  Cooling Water Inlet  Figure 4.9  (C)  Modification of Anode  Difficulty of Reliable Temperature Measurements of the Electrolyte  The surface thermocouple attached to the electrochemical reactor could not longer monitor the temperature of the electrolyte reliably, due to the improved cooling efficiency.  Figure 4.10  shows the temperature profile of an experiment using the new cooling system. It displays three temperature profiles. These profiles were recorded from the outside wall of the reactor, the inside wall of the reactor, and the electrolyte. The temperature of the outside wall was the reading from the surface thermocouple attached on the reactor surface. The temperature of the inside wall was measured by contacting the thermocouple to the Teflon surface beside the anode surfaces. The electrolyte was measured by sticking the thermometer inside the reactor. When recording these readings, the mixing was turned off while the DC power supply remained turning on.  -45 -  Chapter 4: Experimental Apparatus and Procedures  50  100  150  200  Experimental Time (Minutes)  Figure 4.10  •  Electrolyte Temperature  •  Inside-wall Reactor Temperature  *  Outside-wall Reactor Temperature  Measure Error of the Temperature using the New Cooling System  These profiles show that there was an 8 to 12°C difference between the real electrolyte temperature and the temperature recorded by the thermocouple. The error of the temperature made the temperature of the electrolyte an uncontrolled variable.  Even though the real  electrolyte temperature had reached the set point, the heater would continuously provided the energy to the reactor because the temperature reading received by the temperature control was much lower than reality. This caused the temperature of the electrolyte to run over the set-point temperature, and the experimental results could not represent the effects of the factors specified.  -46-  Chapter 4: Experimental Apparatus and Procedures (D)  Modification of the Set-Up of the Thermocouple, Ribbon Mixer, and Cathode  The thermocouple was relocated to monitor the temperature of the electrolyte continuously and reliably. The new design placed the thermocouple into the middle of the reactor. This allowed the thermocouple reading directly from the electrolyte so the temperature control could respond simultaneously. Figure 4.11 shows the new design of the thermocouple and the detail of the electrochemical reactor.  As shown in Figure 4.11, a hole about 3/8-inch OD was drilled on the reactor wall, which allow the quarter inch thermocouple to be positioned near the centre of the reactor. A quarter inch titanium NPT coupling was welded outside the 3/8-inch hole, and sent out for Teflon coating to prevent corrosion. The thermocouple was fixed into the electrochemical reactor by a quarter inch S.S. compression fitting. Another Teflon fitting plugged the hole from inside the reactor to prevent hold-up of pulp.  As shown in Figure 4.11, the ribbon mixer was cut into half to allow insertion of the thermocouple. All the parts including ribbon mixer, clamps, screws, and screw caps were sent out for Teflon coating instead of wrapping by Teflon tape. Also, a new design of mixer was tried out to correct the uneven mixing of pulp found during the test run with the original experimental set-up. This new design of ribbon mixer consisted two types of stirrer, a clockwise stirrer and an anticlockwise stirrer. As the mixer started spinning, the upper stirrer moved the pulp downward and the lower stirrer moved the pulp upward. By putting these two stirrers onto the same mixer, it provided a better mixing and prevented pulp sticking on the bottom of the electrochemical reactor.  -47-  Chapter 4: Experimental Apparatus and Procedures Recess Areas (4 of them) about 1 mm to fit glued Platinum sheet  Thermocouple  Figure 4.11  1 / 4  "  S S  - Compression Fitting  Detail Information of the Electrochemical Reactor -48-  Chapter 4: Experimental Apparatus and Procedures Some experiments were done with a diaphragm wrapped around the cathode.  Several  diaphragms were tried out including microporous polypropylene, polypropylene felt, and polypropylene string. In all cases, the diaphragm was tied on the cathode using Nylon fishing line.  In this project, three different materials were used as cathode: titanium, stainless steel, and zirconium. A l l these types of cathodes were half inch O.D. tube. The test runs showed that when zirconium was the cathode material without a diaphragm, the electrochemical process produced the highest concentration of peroxide. Subsequently, the study of the electrochemical process of generating peroxide and brightening mechanical pulp was focussed on using zirconium as cathode without a diaphragm.  4.1.4  The Modification of the Cover of the Electrochemical Reactor  Figure 4.12 displays two covers that were used in this study. The ordinary cover was used while performed the process of electrochemical generation of peroxide and the process of electrobrightening of mechanical pulp. The modified cover was used for collecting the gas sample generating from the process. Both these covers were made of Plexiglas.  For the ordinary cover, the male pipe connector on the small hole connected with 3/8-inch tubing that directed the gas to the sink. Besides collecting samples for peroxide analysis, the large hole was used for adding the un-brightened pulp into the brightening solution for the electrobrightening process.  The modified cover for collecting the gas sample was drilled with only one hole. The purpose was to prevent any gas leaking to the atmosphere. While running the experiments, the connector was joined to a gas sample bag by A inch tube. X  -49-  Chapter 4: Experimental Apparatus and Procedures  Hole for Collecting  Hole for Gas  Ordinary Cover Figure 4.12  Hole for Collecting  Cover for Gas Collection  Detail Information of the Cover of the Electrochemical Reactor  4.2 Experimental Procedures The experimental procedure can be divided into: 1.  Electroplating of platinum on the anode  2.  Electrochemical production of peroxide  3.  In-situ brightening of mechanical pulp  4.2.1  Electroplating of Platinum on the Anode  When electroplating the surface, the cathode was the titanium vessel and the anode was a graphite rod. The electrolyte consisted of 15 g/1 of H P t C l , 45 g/1 of H P 0 , and 240 g/1 of 2  6  3  4  (NH4)2HP04. The system was preheated and controlled at 70°C before starting the procedure. Each 16 cm of plated area was electroplated at 16 mA for 12 minutes. The calculation of this 2  procedure is seen in Appendix III. -50-  Chapter 4: Experimental Apparatus and Procedures 4.2.2  Electrochemical Production of Peroxide  The desired amount of sodium carbonate was put into a 2-liter glass beaker and dissolved using 1-liter distilled water. Another 500-ml glass beaker was used to dissolve the required amount of magnesium sulfate by adding 250 ml distilled water. In some experiments, certain amount of sodium bicarbonate was added to control the pH. Stabilizer such as sodium silicate and/or D T P A was also added in some experiments. After these chemicals dissolved, the two solutions was combined and made up to a total volume of 1.5 liter before pouring into the reactor.  The cathode and the stirrer were immersed into the electrolyte and fixed on the top of the reactor. The electro-brightening reactor then was connected with mixer motor, heater, and temperature control as shown in Figure 4.5. The four anode panels were connected to a re-circulating ice water tank by P V C tubes. When all equipment was in place, the power supply was connected to the electrodes through the titanium vessel and the conductive brush.  The electrochemical production of peroxide was started by turning on the power supply, cooling water circulation, and heater. The power supply was turned on to the desired current such as 20 Amps and the flow rate of the cooling water was adjusted manually to match the desired brightening temperature.  For the first stage of experiments, original setup, the cooling water  temperature was around 15°C.  The second stage of experiments, the cooling water was  maintained at 1°C. At the end of each experiment, the power supply, the heater, the cooling system, and the motor were shut off and disconnected.  The reactor was disassembled and  cleaned for the next run.  Throughout the experiment, several 5 ml samples of solution were taken from the reactor for measurement of peroxide concentration. (Corresponding to the concentration accumulated from time 0 to the time of sampling.)  4.2.3  In-Situ Brightening of Mechanical Pulp  The procedure for preparing electrolyte for in-situ brightening of mechanical pulp was the same as the electrochemical production of peroxide. The required amount of wet pulp with known  -51 -  Chapter 4: Experimental Apparatus and Procedures moisture content was then mixed with the electrolyte before starting.  Different pulp  consistencies, from 2.5 weight % to 8.6 weight %, were investigated in this study. At p H higher than 11, the alkali-darkening effect needed to be considered. To see i f higher initial peroxide concentration had a significant effect on the brightness gain, some experiments were conducted by adding the pulp to the solution after generating peroxide for 30 minutes.  The pulp slurry was removed from the reactor and transferred to a 10-liter tank after each run. Several 5 to 8 gram samples were taken and added with sulfuric acid and distilled water to adjust pH to the acidic range. The samples then were made into handsheets by a handsheet maker with pH adjusted to 6. The handsheets were air-dried overnight in a constant humidity room. (23°C and 50% relative humidity) The rest of the pulp was dewatered and disposed. The pH of the all the waste solution was adjusted to above 5.5 before draining according to Greater Vancouver Sewerage & Drainage District Sewer Bylaws. The following day, the air-dried handsheets were further dispersed and standard pressed handsheets were made according to TAPPI standard practice, T272 sp-97. [36] Brightness and yellowness of the handsheets were measured using an Elrepho spectrophotometer.  For each  handsheet, several measurements were taken on both surfaces. The brightness and yellowness reported in this thesis were the average of these measurements. When making the handsheets, the filtrate from all pulp samples (including the unbrightened original pulp) was not recycled, which could cause a systematic error in the brightness and yellowness value due to the loss of high lignin content fines to the filtrate.  However, since this is a comparative study, the  conclusions on brightness gain and yellowness loss should not be effected by the lack of recycle in the handsheet preparation.  4.3 Pictures of Electrochemical Brightening System The following pictures illustrate the electrochemical brightening system, the electrochemical reactor, and the handsheet maker.  -52-  Chapter 4: Experimental Apparatus and Procedures  Chapter 4: Experimental Apparatus and Procedures  Chapter 5  Chapter 5 Experimental Results and Discussion The fundamental electrochemical behavior of the batch system was scrutinized and major factors affecting the generation of peroxide and the brightening of TMP were investigated. (pH, current density, reaction temperature,  electrolyte concentration) The results gained from these  experiments are analyzed and discussed here. Table 5.1 summarizes the overall organization of this chapter. Chapter contents 5.1  Factors affecting electrochemical production of peroxide  5.2  Factors affecting electro-brightening of mechanical pulp  5.3  Performance of the electro-brightening reactor  5.4  Pictures of Teflon deterioration and pulp samples Table 5.1  Organization of Chapter 5  The results in this chapter are divided into four different sections ( V I , V2, V 3 , V4), which are defined as follows: •  V I : Experiments performed with original experimental set-up developed by Dr. Jiujun Zhang and Professor Colin Oloman (Figure 4.1, Figure 4.2)  •  V2: Experiments accomplished using the new cooling system and surface thermocouple. (Figure 4.6)  •  V 3 : Experiments carried out with final modifications on uncovered zirconium cathode, platinum sheet anode, mixer, and location of thermocouple. (Figure 4.9, Figure 4.11)  • 5.1  V4: Brightening experiments performed with final modifications mentioned above. Factors Affecting Electrochemical Production of Peroxide  Results from experiments designed to examine the generation of peroxide using the electrochemical batch reactor in the absence of pulp are presented. Factors like pH, temperature,  -55-  Chapter 5: Experimental Results and Discussion and electrolyte concentration were studied. Variables like cathode material, diaphragm material, electrode configuration, and effect of chelating agents were also investigated. 5.1.1  Anode Coolant Temperature  Cooling the anode could increase the oxygen overvoltage. This would promote the oxidation of carbonate ions to percarbonate ions. Two different cooling sources, ice water and tap water, were used to investigate this effect. Normally, tap water was supplied at an average of 15°C while cooling water was at 1°C.  Two runs with the same experimental conditions but different  cooling source are shown in Figure 5.1  200  Experimental Time (Minutes) COOLING T E M P E R A T U R E S 6 D E G R E E CELSIUS COOLING T E M P E R A T U R E S D E G R E E CELSIUS  Figure 5.1  Effect of Coolant Temperature on Peroxide Generation  -56-  Chapter 5: Experimental Results and Discussion The two runs shown in Figure 5.1 are run V.3-8 and V.3-10. The experimental conditions for these two runs are as follows: the electrolyte consisted of 1 M sodium carbonate and 400 ppm M g ; the current set point was at 20 A (anode current density: 3.1 kA/m ); the electrolyte 2 +  2  temperature was 60°C; the retention time was 180 minutes; and the cathode material in these two runs was zirconium without diaphragm. The results showed that the run using ice water cooling produced higher peroxide concentration in the early stage of the experiment.  The ice-water  cooling run also demonstrated a more rapid rise in peroxide concentration during the time period of 30 to 110 minutes. However, both runs generated roughly the same amount of peroxide at the end of the experiment. These results confirmed that lower cooling temperatures had a positive effect in the generation of peroxide. 5.1.2  Cathode Material and Diaphragm  Peroxide generated in an undivided electrochemical cell could be easily reduced on the cathode. Different diaphragm and cathode materials were tried to suppress the undesirable electroreduction of peroxide. Three kinds of diaphragms were tested by wrapping them around the cathode. These diaphragms were microporous radiation grafted polypropylene, polypropylene felt and polypropylene string. Also, three different materials were chosen to be the cathode. These were titanium, stainless steel, and zirconium. The experiments whose results are shown in Table 5.2 were done to find the effect of different diaphragm and cathode materials.  Run No. V2.05  Stainless Steel  Polypropylene Felt  Platinized  Maximum [ H 0 ] (M) 0.010  V2.06  Stainless Steel  Microporous Polypropylene  Platinized  0.006  V2.07  Stainless Steel  Polypropylene String  Platinized  0.003  V3.01  Zirconium  Polypropylene String  Platinum Sheet  0.013  V3.02  Zirconium  Polypropylene String  Platinum Sheet  0.040  V3.03  Zirconium  Polypropylene String  Platinum Sheet  0.031  V3.04  Zirconium  Without Diaphragm  Platinum Sheet  0.035  Cathode  Diaphragm  Anode  2  ([H 0 ]: Concentration of Peroxide) Effect of Diaphragm and Cathode Material on Peroxide Generation 2  Table 5.2  2  I  -57-  2  Chapter 5: Experimental Results and Discussion Results from Run V2.05 and Run V2.06 are shown in Figure 5.2.  These two runs were  performed with the experimental conditions as follows: the electrolyte consisted of 1 M sodium carbonate and 400 ppm M g ; the current was controlled at 20 A (anode current density: 3.1 2 +  kA/m ); and the electrolyte temperature was controlled at 20 degree. 2  20  40  60  80  100  Experimental Time (Minutes)  Figure 5.2  •  POLYPROPYLENE FELT  •  MICROPOROUS POLYPROPYLENE  Effect of Diaphragm on Stainless Steel Cathode on Peroxide Generation  The amount of peroxide generated in these runs was stable and neither declined nor increased. However, Run V2.05 with a Polypropylene Felt diaphragm produced 75% more peroxide than  -58-  Chapter 5: Experimental Results and Discussion V2.06 with microporous polypropylene.  This might be due to polypropylene felt being  hydrophobic and microporous polypropylene being hydrophilic. Results in Figure 5.3 were performed under similar experimental conditions as experiments shown in Figure 5.2, except the electrolyte was pure 1 M sodium carbonate. Figure 5.3 shows two runs carried out using the same diaphragm but different cathode and anode material. Figure 5.3 illustrated the change of peroxide concentration in these two runs. Run V3.01 resulted in an increase of peroxide concentration but Run V2.07 resulted in a decreasing of peroxide concentration. This difference showed that platinum sheet and zirconium were better material to be used as anode and cathode in this reactor.  0  25  50  75  Experimental Time (Minutes)  Figure 5.3  m  Zirconium Cathode, Platinum Sheet A n o d e  «  Stainless Steel Cathode, Platinized A n o d e  Effect of Cathode Materials with Diaphragm on Peroxide Generation  -59-  100  Chapter 5: Experimental Results and Discussion Figure 5.4 plots the results of Run V3.02, V3.03 and V3.04. The experimental conditions of these runs are as follows: the electrolyte was 1M N a C 0 plus 400ppm M g ; the electrolyte 2 +  2  3  temperature was controlled at 40°C; and the current was controlled at 20 A . The cathode material for these three runs was zirconium and the anode coolant temperature was 1°C. Run V3.02 and V3.03 were run with using polypropylene string as diaphragm. Run V3.04 was run without using diaphragm.  0  50  100  150  200  Experimental Time (Minutes)  Figure 5.4  •  WITH P O L Y P R O P Y L E N E STRING  DIAPHRAGM  •——  WITH P O L Y P R O P Y L E N E STRING  DIAPHRAGM  A  WITHOUT DIAPHRAGM  Effect of Diaphragm on Zirconium Cathode on Peroxide Generation  -60-  Chapter 5: Experimental Results and Discussion Result in Figure 5.4 show that even with the same experimental conditions, RunV3.03 only produced 78% of the peroxide Run V3.02 did. This might due to the corrosion of zirconium cathode observed at the end of Run V3.03 after tearing off the diaphragm. The corrosion might be caused by high over-potential and pH between the diaphragm and the zirconium cathode. Figure 5.5 shows the Pourbaix diaphragm of zirconium, where areas II indicate corrosion susceptibility. Due to the alkaline conditions under the diaphragm, (pH>13) Zr would be oxidized to HzrCV at potential higher than -2.2  In order to remove the corrosion products,  VSHE-  the zirconium tube was mechanically polished before use in other runs. However, the corroded stains could not be taken off. -1 0 ~i—r  1.6 E  1  2  M1.4  3 ~i  4 i  5 i  6 i  7 i  8 i  9 l  10 11 l i  Zr 0 ? 2  1.2  II  7  ZrOa?  1  12 13 14 15 16 1.6 i—I—i—r 1.4  1  Zr O ? 2  1.2  s  0.8  0.8  0.6  0.6  -2  0.4  ZrO  0.2  0.4 + +  0.2  Zr0 • 2H 0 2  0  2  0  -0.2  HZr03"  -0.2  -0.4  -0.4  -0.6  -0.6  -0.8  -0.8  -1  -1  -1.2  -1.2  -1.4  II  -1.6 -1.8  -1.4 -1.6  _  -1.8  -2  -  -2  -2.2  -  -2.2  -2.4  -  -2.4  -2.6 -2  -1  0  1  2  J 3  1 1 1 4 5 6  1 I 7 8  I 9  I I 10 11  I I L -2.6 12 13 14 15 16 PH  Figure 5.5 Pourbaix Diagrams for Zirconium (From Principles and Prevention of Corrosion by Denny A. Jones) [37]  The zirconium tube did not further corroded with experiments performed without diaphragm. Thus, subsequent experiments from Run V3.04 were done without a diaphragm.  -61 -  Chapter 5: Experimental Results and Discussion 5.1.3  Current Distribution (Different Electrode Configuration)  A good current distribution is another important factor. A differential electrode area i.e. with a increased ratio of anode/cathode area was tested by using Teflon tape to isolate the cathode surface. Three kinds of electrode configurations were used as shown in Figure 5.6.  (A)  03)  (C)  - Active Cathode Area  Figure 5.6  Cathode Configurations  The cathode area in design A was 16 cm with an anode/cathode ratio at 4 by using Teflon Tape 2  to cover up the rest of the zirconium tube. In design B, a Teflon coated mixer was attached to the zirconium tube. The cathode area was reduced to 13 cm with the ratio at 4.9. To further test 2  the effect of electrode configuration, the Teflon tape tied on the zirconium tube was taken off in design C while the mixer was locked on the cathode. The total cathode area was 24 cm , and the 2  ratio was 2.7. Table 5.3 illustrates the results from these electrode configurations. Table 5.3 showed that cell voltage decreased when the design changed from design A to design C. In these cases, design C resulted in higher peroxide concentration than the other two designs. -62-  Chapter 5: Experimental Results and Discussion Experiment conditions: electrolyte: 1M Na2C03 + 400ppm M g ; current: 20A; 2 +  electrolyte temperature set point: 60°C; experiment time: 180 minutes; anode coolant temperature: 1°C Run No.  Electrode Configuration  Voltage (V)  Peroxide Concentration (M)  V3.09  (A)  16.6  0.044  V3.22  (B)  15.6  0.055  V3.34  (Q  13.4  0.058  Table 5.3  Effect of Electrode Configuration on Peroxide Generation  Figure 5.7 shows the results from these runs.  0  50  100  150  Experimental Time (Minutes)  Figure 5.7  • •  DESIGN A  A  DESIGN C  DESIGN B  Effect of Current Distribution on Peroxide Generation  -63 -  200  Chapter 5: Experimental Results and Discussion In Figure 5.7, design B and design C had similar peroxide profiles under the same current condition, but Design C resulted in lower cell voltage. Design C was used in the subsequent experiments because it reduced the energy cost. 5.1.4  Anode Current Density  Different current densities were tried to see the effect on generating hydrogen peroxide. Two runs with the same experimental conditions but different current densities were conducted, 3.13 and 6.25 kA/m . 2  The experimental conditions were as follows: electrolyte temperature was  60°C; initial electrolyte pH was 11.7; cathode material was zirconium tube without diaphragm; anode coolant temperature was 1°C; and cathode configuration was design C. The production of peroxide was performed for 180 minutes and the concentration of peroxide was measured at 15minute intervals beginning 15 minutes after the experiment started.  200 Experimental Time (Minutes) m  9  A  Figure 5.8  CURRENT DENSITY: 3.13 kA/m 2 (Current: 20A) A  CURRENT DENSITY: 6.25 kA/m 2 (Current: 40A) A  CURRENT DENSITY: 4.7 IWm 2 (Current: 30A) A  Effect of Current Density and Concentration of N a 2 C C > 3 on Peroxide Generation -64-  Chapter 5: Experimental Results and Discussion Results shown in Figure 5.8 confirm the importance of current density.  With the same  electrolyte composition (1M Na2C03), the higher current density (6.25 kA/m ) produced 33% 2  more peroxide than the lower current density (3.13 kA/m ) in the first 120 minutes. However, 2  the final concentration of peroxide was not significantly higher with higher current density. Moreover, the other run with 2 M N a 2 C C > 3 and current density at 4.70 kA/m produced higher 2  concentration of peroxide at the end of the experiment, which indicated sodium carbonate concentration has significant effect on peroxide generation.  It can be observed from Figure 5.8, the peroxide in the reactor became stable after a period of time and remained stable till the end of the experiment. This might be due to the rate of peroxide reduction at the cathode and oxidation at the anode matching the rate of peroxide generating from the anode, (eg. Equation 2.24 ~ 2.28) Therefore, a compromise must be made between the production rate and the current efficiency of peroxide generation when choosing an optimal current density. 5.1.5  Bulk Electrolyte Temperature  The oxidation of carbonate as well as the stability of hydrogen peroxide was favored at room or lower temperature. Lower temperature (0-10°C) should increase the anode oxygen over-voltage and suppress oxygen evolution. However, experiments with reactor V3 showed that higher peroxide concentration was produced at a higher bulk electrolyte temperature. The experimental conditions for these experiments are as follows: electrolyte consisted of 1M Na C03 and 2  400ppm M g ; current was 20A for 180 minutes; cathode material was zirconium tube without 2 +  diaphragm; and the anode coolant was around 2°C at 6 liter per minute. Figure 5.9 presents the results  from  the  two  runs  with  different  bulk  temperature.  (30°C  and  60°C)  The results indicate that the residual peroxide concentration was higher with high bulk temperature.  Even though the peroxide produced electrochemically would decompose more  rapidly in high temperature,  high temperature still increased the net rate of peroxide  accumulation. With an efficient cooling system to maintain the working temperature for anode around 0°C to 5°C, peroxide could survive in an environment with a high electrolyte temperature.  -65 -  Chapter 5: Experimental Results and Discussion  0.06  I  I  I  I RunV3.06  CO  g  0.04  H  C  o O  0  •g  H  H  Run V3.05  0.03  x o  -  -  o.oi "D  -  5^  0.00 50  100  150  Experimental Time (Minutes)  Figure 5.9  -j  R E A C T O R T E M P E R A T U R E : 30 D E G R E E C E L S I U S  _#  R E A C T O R T E M P E R A T U R E : 60 D E G R E E C E L S I U S  Effect of Bulk Temperature on Peroxide Generation  -66-  200  Chapter 5: Experimental Results and Discussion  5.1.6  Stabilizers and Chelating Agents  Stabilizers and chelating agents were added to the solution to prevent peroxide decomposition. Peroxide would decompose due to the presence of heavy metal compounds from process water and equipment. Stabilizers such as sodium silicate and magnesium sulfate were used to suppress peroxide decomposition by removing the heavy metal ions from solution. [25] Chelating agent such as D T P A were chosen in this project to prevent the metal compounds from functioning as catalysts in the decomposition of peroxide. [26 ~ 27] However, sodium silicate was abandoned because it caused Si02 deposition on the anode and affected the performance of the anode. Table 5.4 presents the experiments performed to investigate the effect of additives.  Experimental conditions: electrolyte: 1 M Na2C03 + additives; electrolyte temperature set point: 20°C; current: 20 A ; anode coolant temperature: 1°C No.  Run No.  Cathode  Additives  1  V3.01  Zirconium tube with polypropylene string diaphragm  -  V3.02  400ppm M g  2 +  Experimental conditions: electrolyte: 1 M Na C03 + additives; electrolyte temperature set 2  point: 60°C; current: 20 A ; anode coolant temperature: 1°C 2  V3.10  Zirconium tube  400ppm M g  V3.15  without diaphragm  400ppm M g ; N a H C 0  400ppm M g  V3.18 Table 5.4  (A)  2 +  400ppm M g  V3.17  2 +  2 +  2 +  3  + 0.002 M D T P A  + 0.002 M DTPA; N a H C 0  3  E Tect of Stabilizer and Chelating Agent on Peroxide Generation  Magnesium  Run V3.01 and Run V3.02 were carried out to investigate the effect of the stabilizer, magnesium sulfate. Results of Figure 5.10 indicate that Run V3.02 produced 3 times more peroxide than V3.01.  -67-  Chapter 5: Experimental Results and Discussion  Experimental Time (Minutes)  Figure 5.10  -A  1 M N a 2 C 0 3 pH=1l.6  -9  1M N a 2 C 0 3 + 400ppm Mg2+; pH=11.6  Effect of Stabilizer on Peroxide Generation  Results shown in Figure 5.10 clearly demonstrate the effect of the M g . With the stabilizer, the 2+  electrochemical process produced three times more peroxide. The action of magnesium in N a 2 C C > 3 liquor has been shown by others working in this department. [38].  (B)  DTPA (Diethylenetriaminepentaacetic acid - Penta Sodium Salt)  The experiments were performed under two region of pH, 10.5 and 11.8, fixed by adding sodium bicarbonate. Run V3.15 and Run V3.18 were started at pH= 10.5, and Run V3.10 and Run  -68-  V3.17  Chapter 5: Experimental Results and Discussion were started at pH around 11.8. Approximately 0.05 weight % of D T P A was added to Run V3.17 and Run V3.18. Results from these runs are plotted in Figure 5.11.  0.06 c  •B 0.05-| CO  "c 0  0.04 ^  .g  0.03 -I  1  0.02  2  o.oi  c o O x o  C (D  H  "D X  0.00  100  150  Experimental Time (Minutes)  200  pH=10.5 without DTPA pH=10.5 with 0.002M DTPA pH=11.6 with 0.002M DTPA pH=11.6 without DTPA Figure 5.11  Effect of Chelating Agent on Peroxide Generation  The results show that no matter under which region of pH, the present of D T P A promoted the accumulation of peroxide.  This might be due to D T P A chelating the metal compounds,  preventing them from functioning as catalysts in the decomposition of peroxide.  -69-  Chapter 5: Experimental Results and Discussion 5.1.7  pH  In the previous research by Colin W. Oloman, Junjun Zhang and Pogy Kurniawan, the pH of the aqueous sodium carbonate solutions was controlled around 10.75 using sodium bicarbonate according to the equation: HCOaoCOa^+Ff  Ka = 4 . 8 x l 0 '  n  Result from section 5.1.6 indicated that pH might be a significant factor affecting the peroxide production.  Thus, experiments  with 1M sodium carbonate concentration  (electrolyte  concentration) were performed to explore this effect, among variables like stabilizer and electrolyte temperature. These experiments are divided into four groups due to the different experimental conditions. The experimental conditions and results are shown in Table 5.5 Final  Experimental Conditions: (Electrolyte: 1M N a2C03 + additives; Current: 20A; Coolant: 1°C at 6 liter per minute) Electrolyte Temperature Additives Initial Final Voltage <°C) pH pH (V) Actual Set Point  [H 0 ]  Cat.  Run  No.  No.  1  V3.14  16.1  20  33  11.60  -  0.0570  V3.16  16.3  20  33  10.50  -  0.0160  V3.10  12.5  60  56  11.60  -  2  3  4  2  (M)  400ppm Mg  2  0.0425  2 +  0.0600  V3.12  12.6  60  56  11.85  11.10  V3.13  12.2  60  56  10.50  10.20  V3.19  16.3  20  33  11.85  11.36  V3.20  16.2  20  33  10.50  10.62  V3.17  12.8  60  56  11.94  11.27  + 0.002  0.0570  V3.18  12.3  60  56  10.50  10.30  MDTPA  0.0160  0.0090 0.0530  400ppm Mg  2 +  0.0200  ([H 0 ]: Maximum Peroxide Concentration) 2  Table 5.5  2  pH Effect at Four Different Experimental Conditions  The investigated pH range was from 10.5 to 11.9. The initial pH was fixed by adding sodium bicarbonate to the electrolyte. Results in Table 5.5 show that pH in most of the runs went down during the experimental process. This meant one of the secondary reactions (e.g. H 0 -> 0 + 2  -70-  2  2  Chapter 5: Experimental Results and Discussion 2H  +  +2e") was favored. Moreover, the temperature set point for runs V3.14, V3.16, V3.19, and  V3.20 was 20°C but rose to 33°C, due to the Joule heating at high cell voltage (16 V).  Figure 5.12 plots the experimental results at category 2 in Table 5.5. It clearly demonstrates that the higher the pH, the higher the peroxide produced. Moreover, unlike the other two runs which resulted in increasing peroxide concentration, the peroxide concentration decreased after 20 minutes for the run with initial pH at 10.5.  0  50  100  150  Experimental Time (Minutes)  • • •  Figure 5.12  Initial pH at 11.6 Initial pH at 11.9 Initial pH at 10.5  Effect of pH on Peroxide Generation (2) (V3.10; V3.12; V3.13)  -71 -  200  Chapter 5: Experimental Results and Discussion Figure 5.13 shows pH effect on experiments with DTP A (category 4).  0  50  100  150  200  Experimental Time (Minutes) — • —  •  Figure 5.13  Initial pH at 10.5 Initial pH at 11.94  pH Effect on Experiments with DTPA (V3.17; V3.18)  Figure 5.13 demonstrates that pH is still the dominating factor. The initial pH at 10.5 seems to be the factor that limited the peroxide generation. It also can be observed from Table 5.5, p H still restricts the peroxide production at higher bulk electrolyte temperature.  Generally,  experiments started with pH at 10.5 produced roughly 0.016M ~ 0.020M of peroxide; and runs started with higher pH produced at least 3 times more peroxide. Results from these experiments show that a higher pH helped produce higher concentrations of peroxide.  -72-  Chapter 5: Experimental Results and Discussion The reason that pH had such a strong effect on peroxide generation is that it affects the concentration of C 0 " ions in the electrolyte. The relative concentrations of H C 0 " and C 0 " in 2  2  3  3  3  water solution were determined by the concentration of H . [39] As shown in Figure 5.14, both +  of these species are pH-dependent. Near the middle of the pH range, the H C 0 " ion dominates, 3  with a maximum concentration close to pH 8. At high pH (>12) the principal species is C 0 " . 2  3  Figure 5.14 Relative Concentration vs pH [39] (Chemical Principles with Qualitative Analysis, sixth edition)  The limit of the domains of relative predominance of the dissolved substances for H C 0 " and 3  C 0 " is p H 10.34. [35] Figure 5.15 is the Pourbaix diaphragm for carbon-water system at 25°C. 2  3  The portion of the diagram above the line logC=0 refers to solutions containing 1 gram of dissolved carbon per liter in the form of H C 0 + H C 0 " + C 0 ' . The portion of the diagram 2  2  3  3  3  bellow this line refers to solutions thermodynamically saturated with solid carbon.  -73 -  Chapter 5: Experimental Results and Discussion -2  -2  -1  -1  0  0  i  2  1  2  3  3  4  4  5  6  5  7  6  7  8  9  8  9  10  10  II  II  12  12  13  13  14  14  15  16  15  pH  J6  Figure 5.15 Pourbaix Diagrams of Carbon-Water System [35] (Atlas of Electrochemical Equilibria in Aqueous Solutions, by Marcel Pourbaix)  From Figure 5.15, due to the potential supplied to the electro-system being higher than - 0 . 4 V and the pH for pure 1M sodium carbonate solutions being around 11.7, primary ion in this system. Since the  CO3 " 2  CO3 " 2  ion was the  ion was dominant, the rate of peroxide generation  was high. However, if the pH was set around 10.5, near the region that HCO3" ion was dominant, there will be not enough  CO3 " 2  ion for generating peroxide by reaction  22 .7.  Thus the peroxide  concentration was low. Thus, experiments start with pH as low as 10.5 will limit the primary anodic reaction,  C2O6 " 2  + 2e" <- 2 C 0 " , of 2  3  peroxide production.  -74-  the electro-oxidation process and result in poor  Chapter 5: Experimental Results and Discussion 5.1.8  Heating Pattern  Run V3.07 and Run V3.10 were performed at different initial electrolyte temperature to see the effect on peroxide generation. Run V3.07 was carried out by pre-cooling the electrolyte to 5°C without applied current, and Run V3.10 was done without pre-cooling the electrolyte. The initial electrolyte temperature for Run V3.10 was around 20°C. The experimental conditions for these two runs are as follows: electrolyte consisted of 1M N a 2 C C < 3 and 400ppm M g ; electrolyte 2 +  temperature set point was 60°C; current was 20A, and the anode coolant temperature was around 2°C. Figure 5.16 shows the peroxide produced in these two runs.  60  I  i  i  i  i  0  |  i  i  i  i  50  |  100  i  i  i  150  200  Experimental Time (Minutes) 1  Initial Temperature: 5 Degree Celsius (Run V3.07)  %  Initial Temperature: 20 Degree Celsius (Run V3.10)  Figure 5.16  Effect of Heating Pattern on Peroxide Generation  -75 -  Chapter 5: Experimental Results and Discussion Figure 5.16 shows that experiment performed with lower initial electrolyte temperature produced higher concentration of peroxide. This might be due to the initial temperature being much closer to the temperature required to promote the primary reaction at the anode. (0°C) Also, the experiment with lower initial electrolyte temperature had a more rapid increase of peroxide concentration during the whole process, which provides the residual peroxide required at the end of brightening process.  Figure 5.16 also presents the temperature curves recorded from these two runs. What can be observed from this figure is that the two temperature curves are mostly identical after 50 minutes. This information shows that cooling beforehand did not preclude maintaining the electrolyte at  -76-  Chapter 5: Experimental Results and Discussion  5.2  Factors Affecting Electro-Brightening of Mechanical Pulp  The in-situ electrochemical brightening of mechanical pulp has not been used in the pulp and paper industry. However, it is a method worth looking into since environmental safety is an important concern in the 21 century. st  For electro-brightening to be used commercially, the  brightened pulp needs to have a brightness above 60 % ISO. The electro-brightening process investigated here uses sodium carbonate as mediator. Since the generated percarbonate ions would hydrolyze into hydrogen peroxide, the assumption that the electro-brightening process was similar to commercial hydrogen peroxide brightening was made. Therefore, similar factors that affect a commercial hydrogen peroxide brightening process were chosen as the factors affecting the in-situ electro-brightening process.  These factors were  temperature, consistency, pH, brightening time, and additives. The Na2C03 concentration, an additional factor, specific to electro-brightening, was also investigated. In this thesis project, a 2 factorial design was performed with factors (factorial factors) as 3  follows: bulk temperature, current, and sodium carbonate concentration, while holding other variables constant. The main and interaction effects of the three factorial factors were analyzed. However, the held constant variables such as pulp consistency, additives, time, and coolant flow might also interact with the effects of the factorial factors. Thus, the effects obtained from the factorial experiments could only apply at the fixed levels of the other variables. Besides factorial experiments, investigations were performed on variables such as the effect of electro-brightening time, pulp consistency, two-stage brightening, and periodic application of the current. The range of initial pH (between 10.5 to 11.8) was also investigated to explore the alkaline darkening effect. The effect of additives was not investigated in order to reduce the number of variables. However, a fixed amount of additives were used to help preserve hydrogen peroxide. 5.2.1  A 2 Factorial Experiment (Effect of Temperature, Current, and Electrolyte Concentration)  This thesis used software, Jass, to design and analyze two-level factorial experiments.  Full  factorial design is the basis of most classical statistical experimental designs. In a full factorial design, the factors are set to all possible combinations of the low and high values. Factorial  -77-  Chapter 5: Experimental Results and Discussion designs are valuable, because they can be used to detect "factor interaction," that is, where the effect of one factor on the response depends upon the level of another factor. [40] The initial pH of all these factorial design experiments was around 11.6. The pulp consistency and electrobrightening time were held constant at 2.5% and 3 hours respectively. 400ppm M g  2 +  The additives were  and 0.002 M DTP A. The responses measured were the concentration of peroxide,  the brightness gain, and yellowness loss of the pulp. measured 30-minute intervals throughout the process.  The concentration of peroxide was A total of twelve runs was performed  randomly, ten of which were the factorial runs and two were centerpoint runs. Table 5.6 shows the levels of the variables and the design of full 2 factorial runs. 3  Experimental conditions: cathode material was zirconium tube with diaphragm; anode coolant was 1°C at 5.5 liter per minute; and cathode configuration was design C. Variables  Region I (-)  Center Point (0)  Region II (+)  [Na C0 ] (M)  1  1.5  2  Temperature (°C)  40  50  60  Current (A)  10  20  30  1.6  3.1  4.7  2  3  Anode Current Density (kA/m ) 2  No 1  Run No. V4.02; V4.03  [Na C0 ]  Current  Temperature  -  -  -  2  V4.04  +  -  -  3  V4.05; V4.22  0  0  0  4  V4.06; V4.07  -  +  +  5  V4.08  -  -  +  6  V4.09  +  +  -  7  V4.10  -  +  -  8  V4.ll  +  +  +  9  V4.12  +  -  +  2  3  ([Na C0 ]: Concentration of sodium carbonate) 2  Table 5.6  3  Variables, Levels and the Design of the 2 Factorial Experiments 3  -78-  Chapter 5: Experimental Results and Discussion The factorial experiments were performed randomly to discount the reliability of the reactor. Replicated runs on centerpoint and two factorial points were performed.  The replication of  centerpoint provides an estimate of response error and a greater precision for the overall curvature estimate.  The replication of factorial points estimates the precision of main and  interaction effects.  o U <L> t-H  I  !  30  H  o  1 Na C0 Conc. (M) 2  3  (A)  Brightness Gain (% ISO) -BFigure 5.17  Yellowness Loss  Cube Plots for the Responses of a Full 2 Factorial Design 3  The cube plots of each response as a function of temperature, current, and concentration of sodium carbonate are shown in Figure 5.17. From the replicated runs, the pooled response error (standard deviation) for brightness gain was 0.4 % ISO, for yellowness loss it was 0.6 %, and for concentration of peroxide it was 3 mM. (See calculation in Appendix II) These pooled response errors indicated that brightening responses were significant and deterioration of the reactor did  -79-  Chapter 5: Experimental Results and Discussion not affect the brightening responses while factorial experiments performed. Further analysis of interactions was examined using the Jass software. (A)  Main and Interaction Effects on Brightness Gain  Figure 5.17 (B) indicates that the highest brightness gain, 17.4 % ISO, was obtained at the highest level of all three factors. Table 5.7 presents the calculated effects supplied from Jass software. The effects column showed the relative values of the significant effects. Effect  Factors  Main Effect (% ISO)  t-Ratio  13  580  Average Main  Concentration (C)  4.3  85  Main  Current (I)  1.0  19  Main  Temperature (T)  2.6  51  Interaction  Cxi  -0.4  -8  Interaction  CxT  1.0  20  Interaction  Txl  -0.6  -12  Interaction  CxIxT  2.2  43  t-ratio test for curvature = -48.3; S =0.07 with 1 d.f; Confidence Level: 95 %  Table 5.7  Effects |.C 4+  1 1 1  3+ 1  1  |.T 2 +| . C I T  1 1 1  1 + ..  r i i  0+  1 1  1"  Effect on Brightness Gain  The calculation shows that the concentration of sodium carbonate caused the most significant effect. Comparably, the increase of temperature was also an important factor within main and interaction effects. However, current showed little effect on brightness gain. On the contrary, the interaction effect among concentration of sodium carbonate, current, and temperature was significant as well. The effect diagram shown in Table 5.7 indicated that the concentration of sodium carbonate showed a 93% probability of affecting the brightness gains, while temperature showed 70% probability and the interaction among the three factors showed 63% probability at the 95% level of confidence.  -80-  Chapter 5: Experimental Results and Discussion Furthermore, calculation from Jass software showed that apart from the effect of temperature depending on the level of current on brightness gain, other interactions were not significant. (B)  Main and Interaction Effects on Yellowness Loss  The cube plot in Figure 5.17 (C) shows that 19.2% of yellowness loss was acquired at the highest level of all three factors. The 19.2% yellowness loss was the best result obtained in all the factorial design experiments.  The calculation demonstrated that all the main effects  presented in Table 5.8 are statistically significant for this result. Effect  Factors Average  Main Effect (%)  t-Ratio  14.3  643.0  Main  Concentration (C)  2.3  46.5  Main  Current (I)  2.5  49.5  Main  Temperature (T)  3.9  78.5  Interaction  Cxi  -0.3  -5.5  Interaction  CxT  0.2  3.5  Interaction  Txl  0.0  0.5  Interaction  CxIxT  21.5  1.1  Effects 4 + .T i i l l 3+  1  l-I |.C 2+  1 1 1  1 +. CIT I i  1  |.CT O + .IT |.CI  t-ratio test for curvature = -3.8; S = 0.07 with 1 d.f; Confidence Interval: 95 % Table 5.8  Effect on Yellowness Loss  As could be seen in Table 5.8, the effect of temperature was found to be the most critical variable. It was interesting to note that the other two main effects, current and concentration of sodium carbonate, were calculated to have similar main effect indicating these two factors were equally important. Similar results were observed for the interaction effects. The temperature / current / concentration of sodium carbonate was determined to be the most prominent interaction effect as shown in the effect diagram at Table 5.9.  The interaction effects between  temperature/current and temperature / concentration of sodium carbonate were insignificant.  Chapter 5: Experimental Results and Discussion  (C)  Main and Interaction Effects on Concentration of Peroxide  As illustrated in Figure 5.17 (A), the highest residual concentration of peroxide, 0.059 M , was recorded during the electro-brightening experiment under the highest level of all three factors. The factorial analysis data are shown in Table 5.9.  Effect  Factors  Main Effect (mM)  t-Ratio  34.8  105  Average Main  Concentration (C)  13.3  26.5  Main  Current (I)  7.5  15.5  Main  Temperature (T)  7.3  14.5  Interaction  Cxi  4.3  8.5  Interaction  CxT  1.8  3.5  Interaction  Txl  14.3  28.5  Interaction  CxIxT  3.8  7.5  t-ratio test for curvature = -17; S =7E-4 with 1 d.f.; Con]idence Interval: 95 %  Table 5.9  Effects | . IT  1 |.C .0125 +  1 1 1  .0100 +  1 1 1  .0075 +..  1 1 1  .0050 + |.CI |.CIT  1 .0025 + |.CT  Effect on Concentration of Peroxide  For the concentration of peroxide, the main effect of a concentration of sodium carbonate together with two factors interactions of temperature and current were most significant. The other two main factors, current and temperature, have similar effect to the concentration of peroxide. However, these two factors showed less influence on increasing the concentration of peroxide. Other interaction effects were insignificant to the concentration of peroxide Figure 5.18 plots the probability versus effects.  Result in Figure 5.18 shows that the interaction effect between current and temperature has the highest probability to generate this result. Concentration of sodium carbonate also shows a 79% probability of influence.  -82-  Chapter 5: Experimental Results and Discussion  p R O B A B I L I T Y %  93 90 87 84 79 74 69 63 56 50 44 37 31 26 21 16 13 10 7  + .0000  .0025  .0050  .0075  .0100  .0125  E F F E C T S (M)  Figure 5.18 (D)  Interaction Plots on Concentration of Peroxide & Probability vs Effects  The Specific Brightening Energy and Brightening Space-Time Yield  The specific brightening energy and brightening space-time yield of the factorial experimental results are presented in Table 5.10. Run No. V4.02  Current (A) 10  Cell Voltage (V) 11.5  AY (%) 9.4  AB (%ISO) 7.5  SBE (kWh/ton/%ISO) 11 x 10  BSTY [(ton*%ISO)/m /hrl 0.062  V4.04  10  8.2  12.9  13.3  4 x 10  0.111  V4.05  20  11.3  14.5  15.2  10 x 10  V4.06  30  20.0  15.9  10.4  40 x 10  V4.08  10  9.9  14.2  11.8  6 x 10  2  0.099  V4.09  30  16.7  14.0  12.3  28 x 10  2  0.103  V4.10  30  20.0  13.2  11.6  36 x 10  2  0.097  V4.ll  30  13.9  19.2  17.4  17 x 10  2  0.145  V4.12  10  7.5  15.9  15.3  3 x 10  Table 5.10  2  2  2  2  2  3  0.127 0.088  0.129  (AB: Brightness gain; AY : Yellowness loss) (SBE: specific brightening energy; BSTY: brightening space-time yield) Comparison of SBE and BSTY of Factorial Experimental Results  -83 -  Chapter 5: Experimental Results and Discussion Comparing the results of Run V 4 . l l (with the highest brightness gain) and Run V4.12 (with the lowest specific brightening energy), the low current run (Run V4.12) required 82.4% less specific brightening energy (specific energy for each point of brightness gain). On the other hand, the high temperature run (Run V 4 . l l ) resulted in 64.7% less specific brightening energy than low temperature run (Run V4.09).  Generally, experimental conditions that give a low  specific brightening energy, are able to operate at a high current density and handle high pulp consistency, should be the choice conditions for the in-situ electro-brightening of mechanical pulp. In terms of brightening space-time yield (space time yield for each point of brightness gain), where high brightening space-time yield was required, Run V4.11 resulted in the highest B S T Y (17.2% higher than Run V4.12). Also, Run V4.11 resulted in 17% higher yellowness loss than Run V4.12. Consider both the brightening figures of merit and brightening responses; the experimental conditions of Run V 4 . l l were determined as the better for in-situ electrobrightening of mechanical pulp.  (E)  Summary of the Results from Changing Temperature, Current and Concentration of Sodium Carbonate  The best result obtained by previous investigator using sodium carbonate as the electrochemical mediator to generate peroxide and brighten pulp was 12 % ISO of brightness gain and 7 % of yellowness loss. [9] Previous work also indicated that temperature had a negative effect on brightness gain. However, the electro-brightness process studied in this thesis using the 2-liter, titanium reactor was promoted by high temperature, as in conventional brightening practice. This further improved the potential of brightening pulp by using the electrochemical method.  The variables of current and concentration of sodium carbonate also played important roles in increasing the brightness gain and yellowness loss. The factorial experiments indicated that using higher temperature, higher current, and higher concentration of sodium carbonate will brighten the pulp close to industrial level. The experiment was able to achieve a brightness gain of 17.4 % ISO and yellowness loss of 19.2 %, with a steady state peroxide concentration corresponding to approximately 9.3 wt % of peroxide charge on OD pulp.  -84-  Although the  Chapter 5: Experimental Results and Discussion brightness gain did not increase as much as expected, the large improvement of yellowness loss was impressive compared to the results obtained by the previous researchers. Some anomalies were observed in the factorial results.  The peroxide concentration in run  number 1 and run number 7 responded differently than expected. Unlike peroxide concentration in other runs that increased along with brightness gain and yellowness loss, their peroxide concentration was lower as brightness gain and yellowness loss increased. This reflected the phenomenon observed during running these experiments, lots of gas bubbles generated from the anodes. More oxygen bubbles implied that the current efficiency for generating peroxide was decreased. Since the current efficiency of primary anode reaction decreased (Reaction 2.26), the first term at the right hand side of equation 2.18a was decreased thus resulted in low peroxide concentration. Moreover, the safety of the process became problematic because the increase of oxygen gas along with the hydrogen gas produced on the cathode aggravated the potential of gas explosion.  5.2.2  pH  Brightening with initial high pH (>11) would lead to the formation of new chromophores and cause alkali darkening. High pH would also rapidly decompose peroxide into water and oxygen. These two limiting factors mean that conventional peroxide brightening liquor must be sufficiently alkaline to maintain an adequate concentration of perhydroxyl ions, but not so alkaline as to cause excessive peroxide decomposition and pulp darkening. To prevent the two incidents mentioned above, the initial pH of the system was held at 10.5 in the beginning of the study to reduce the number of variables. However, subsequent research indicated that higher pH, corresponding to higher carbonate concentration, would promote the production of peroxide. (Section 5.1.7)  Thus, further investigations were done with a pH range of 10.0-11.5.  The  results are shown in Figure 5.19 The experimental conditions for these runs were as follows: electrolyte consisted of 1M sodium carbonate and 400ppm of M g ; the current was 20A; the temperature set point was 60°C; anode 2 +  coolant was 1°C at 5.5 liter per minute; and the cathode material for these runs was titanium tube  -85-  Chapter 5: Experimental Results and Discussion with polypropylene felt tied on it. Experiment with initial pH at 10.30 was fixed by adding sodium bicarbonate. 15  I  I I  ,  ,  ,  |  •  ,  i  |  i  i  i  i  i  J  Initial pH= 11 .50 (Run VI. 14)  12 -  •  _  -  <  liitialpH= 11.23 (Run VI. 13) . 6 -+I 3  ~ m  +  0  1  1  9.0  i  1  9.5  1 1  \  !  -  TnitfaTpH = ID". 3D" (Run V i :  —i  10.0  1  1  j  1  10.5  1  1  1 11.0  1  1  2  1  )  1  "  1  •  11.5  •  •  12.0  Final p H B R I G H T N E S S GAIN YELLOWNESS LOSS  Figure 5.19  Effect of pH on Brightness Gain and Yellowness Loss  The final pH values of these experiments decreased from the initial values. Experiment results display that both brightness gain and yellowness loss increased with the initial pH. This means the peroxide generating by electro-brightening not only could overcome the damage caused by alkali darkening effect, but also can improve the whitening of the pulp.  5.2.3  Pulp Consistency  The study in this thesis mainly brightened pulps with 2.5% consistency due to practical reasons such as ease of mixing and electric conductivity. However, different consistency was tried to see if consistency has the same effect on the electro-brightening process as in the conventional brightening process.  -86-  Chapter 5: Experimental Results and Discussion Results shown in Figure 5.20 confirm that high pulp consistency improved the brightening efficiency.  These experiments were performed using an uncovered zirconium tube as cathode.  Results in Figure 5.20 (A) were performed with experimental conditions as follows: electrolyte consisted of 1M sodium carbonate, 400ppm M g , and 0.002M DTP A ; temperature set point was 2 +  60°C; current was 20A; and anode coolant was 1°C at 5.5 liter per minute.  Experimental  conditions in Figure 5.20 (B) were the same as in Figure 5.20 (A), except the current was 3OA and the electrolyte consisted of 2M N a 2 C C > 3 instead of 1M N a 2 C C > 3 .  VI Vl  o -J  VI VI  o>  d  o % >*  o 0  (A) 19.5  ~i  19.0  -  18.5  -_•  18.0  -  1  1  1 1  r~  -i—i—|—i—i—i—i—|—i—i—i—i—|—i—i—i-  s  o  Vi Vi  & -a  •c CQ  [NaiCOj]: 2M Current: 30A  RunV4.11  RunV3.32  17.5  17.0  -A—r 2 . 0  -i  1  1  1  2 . 5  1  1  1-  3 . 0  -i  1 1  3 . 5  4 . 0  Pulp Consistency {%) BRIGHTNESS Y E L L O W N E S S  Figure 5.20  r  4 . 5 (B)  GAIN LOSS  Effect of Pulp Consistency on Brightness Gain and Yellowness Loss  -87-  Chapter 5: Experimental Results and Discussion Figure 5.20 (A) illustrates that as pulp consistency rose from 4.6 % to 6.6 % in 1M Na C03, the 2  brightness gain increased 4.7 % ISO. On the other hand, yellowness loss also increased 1.4 %. However, Figure 5.20 (B) shows that brightness gain and yellowness loss in 2 M Na2C03 only increased slightly with the increasing pulp consistency. (0.1 % ISO for brightness; 0.15 % for the yellowness) The result of brighter pulp might be due to the hydroxyl radical concentration per gram of OD pulp decreasing with increasing pulp consistency, since hydroxyl radical would participate in pulp darkening reactions. [41 ~ 42] Although the results in Figure 5.20 (B) are not expected, they are worth further research since brightness increased more than 17 % ISO and yellowness decreased more than 19 %.  In  comparison, medium (10%) and high (20%) consistency pulp are generally required for brightness gains up and above 12 % ISO in the conventional commercial brightening process. Theoretically, brightening pulp using 2 M Na2C03 and pulp consistency above 7 % should result in higher brightness gain and yellowness loss but was not examined in this study due to the experimental equipment limitations.  5.2.4  Brightening Retention Time  The role of brightening time in electro-brightening was to produce enough active oxygen for brightening the pulp and to allow time for the slow brightening reactions to occur.  The  brightening time for the electro-brightening process of the 2 factorial design experiments was 3  180 minutes with the electrolyte temperature at 60°C and pH>l 1.0. However, to further explore the effect of brightening time on brightness gain and yellowness loss, experiments with different brightening time (30, 60, 90, 120, 180, and 240 minutes) were performed; and the results were plotted in Figure 5.21. The experimental conditions are as follows: electrolyte consisted of 2 M N a C 0 , 400ppm M g , and 0.002 M DTPA; temperature set point was 60°C; current was 30A; 2 +  2  3  anode coolant was 1°C at 6 liter per minute; cathode was uncovered zirconium tube; and the pulp consistency was 2.5%. Results in Figure 5.21 show that brightness gain and yellowness loss increased with brightening time. Figure 5.21 demonstrates that a major part of brightness gain was achieved early in the  -88-  Chapter 5: Experimental Results and Discussion process. Therefore, having a large concentration of active oxygen when the pulp was introduced into the brightening solution is necessary.  M  0  50  100  150  200  250  Brightening Time (Min)  • • Figure 5.21  BRIGHTNESS GAIN YELLOWNESS LOSS  Effect of Brightening Time  Figure 5.21 also indicates that the brightness gain leveled off between 90 to 120 minutes of brightening time but increased again after 120 minutes. This might be because the peroxide producing in the reactor reached high enough and attacked the chromophores again as observed in Figure 5.22. However, the brightness went down when extended to 240 minute. The possible explanation for this phenomenon is that after 180 minutes, the peroxide producing in-situ was not enough to resist the alkaline darkening effect.  -89-  Chapter 5: Experimental Results and Discussion  Brightening Time (Minutes) —•— • —*— •-— —*— 1  Figure 5.22  30 Minutes (Run V4.15) 60 Minutes (Run V4.13) 90 Minutes (Run V4.16) 120 Minutes (V4 14) 180 Minutes (Run V4.11) 240 Minutes ( R u n V 4 . 1 7 )  Brightening Time versus Peroxide Concentration  The same pattern could be also observed on yellowness loss. The total yellowness loss in 180 minutes was 19.2 %, which was an impressive improvement compared to the research done by previous investigators. The yellowness went down 2 % as the brightening time increased to 240  -90-  Chapter 5: Experimental Results and Discussion minutes. The decreased yellowness indicated that the peroxide in the reactor was not enough to overcome the effect of alkaline darkening.  Thus, the generation of higher concentration of  peroxide (e.g. higher consistency) might be the key factor for larger brightness gain and yellowness loss.  One other phenomenon observed during the runs was the longer the brightening time, the lower the final pH. For example, the final pH for the 180 minutes run was 10.6, and the final pH for the 240 minutes run was 10.5. Since lower pH was not favorable for HCO3'  CO3 " 2  ions but favorable for  ions; and would suppress peroxide generation, this could be the main reason for loss of  brightness with longer brightening time. (>180 minutes)  5.2.5  Pre-Generating Peroxide  As shown in Figure 5.22, the concentration of peroxide generating during electro-brightening increased to a maximum at around 120 minutes, then it decreased until about 150 minutes and finally it increased again gradually.  The low initial concentration of peroxide slows the  brightening process in the early stage. Comparably, in the conventional brightening process, the initial concentration of peroxide is around 0.1 M in order to maintain enough residual peroxide at the end of the process; whereas in the electro-brightening process, the initial concentration of peroxide was 0 M . One way to have a large concentration of peroxide at the time of pulp addition is by pregenerating the peroxide.  Before the introduction of pulp into the brightening solution, the  electro-oxidation of sodium carbonate to generate peroxide was done for 30 minutes. By pregenerating the peroxide, one could hope that the amount of peroxide produced during this period would be adequate to initiate pulp brightening and to prevent the pulp from undergoing alkaline darkening. The conditions for these experiments are as follows: electrolyte additives consisted of 400ppm M g  2 +  and 0.002 M DTP A; anode coolant was 1°C at 6 liter per minute; and cathode  was uncovered zirconium tube.  -91 -  Chapter 5: Experimental Results and Discussion  Run No.  [Na C0 ]  Units V4.05  M 1.5  2  Current  3  | 1  V4.19  Initial [H 0 ] M 0  AB  AY  A 20  Electrolyte Temperature °C 50  % ISO 15.2  %  14.5  Final [H 0 ] M 0.051  20  50  0.050  14.9  15.4  0.050  2  2  2  2  V4.12  2  10  60  0  15.3  15.9  0.032  V4.20  2  10  60  0.021  15.0  15.4  0.026  ([Na C0 ]: Concentration of Sodium Carbonate; [H 0 ]: Concentration of Peroxide; AB : Brightness Gain; AY 2  3  2  Table 5.11  2  : Yellowness Loss)  Effect of Pre-Generating Peroxide  Table 5.11 shows two comparisons between the standard electro-brightening process and pregenerating peroxide electro-brightening processes. The peroxide concentration profile is plotted in Figure 5.23. The pre-generating peroxide data (first 30 minutes) for Run V4.19 and V4.20 is not plotted in this figure.  1 0 0  5 0  1 5 0  Brightening T i m e (Minutes) Initial Peroxide Concentration: 0.050M (RUN V4.19) Initial Peroxide Concentration: OM (RUN V4.12) Initial Peroxide Concentration: 0.021 M (RUN V4.20) Initial Peroxide Concentration: OM (RUN V4.05)  Figure 5.23  Profile of the Peroxide Concentration  -92-  2 0 0  Chapter 5: Experimental Results and Discussion Figure 5.23 shows that both runs pre-generating peroxide for 30 minutes had similar pattern. Both curves decreased from the point that pulp was added till 60 minutes. After 60 minutes, both peroxide concentrations increased. The overall results from the pre-generating peroxide runs and standard runs, gave a difference of only 0.3 % ISO for brightness gain and 0.5 % for yellowness loss.  These differences were not statistically significant. Hence the effect of the extra 30  minutes of pre-generating time appears to be insignificant. Results in Figure 5.23 show the differences of the peroxide concentration after 100 minutes were not significant for Run 4.05 and Run 4.19. From Figure 5.23, although the peroxide concentration of pre-generating peroxide run (Run V4.19) ended slightly higher than standard run (Run V4.05), the differences were only 0.001M. However, the brightness results from the pre-generating peroxide run were decreased compared to the standard run. One could assume that the pre-generating peroxide could not attack the non-brightening pulp initially at the time pulp was added to the solution.  5.2.6  Energy Saving  Electrical energy consumption is an important concern in an electrochemical process. For the electro-brightening process, a big portion of the operating cost is the electric energy cost.  The  amount of energy needed for the electro-brightening process depended on the electro-reactor design and the operating procedures. Thus, it was essential to see how to reduce the electricity cost and maintain brightness gain and yellowness loss.  Experiments for reducing the electric energy consumption were investigated. Both Run V4.18 and Run V4.21 were using 2 M N a C 0 , 400ppm M g , and 0.002 M DTP A as brightening 2 +  2  3  solution. The anode coolant was 1°C at 5.5 liter per minute. The reactor was charged at 30A and the temperature of brightening solution was 60°C. To obtain higher initial concentration of peroxide, the electro-oxidation of sodium carbonate to generate peroxide was run for 30 minutes before the introduction of pulp to the brightening solution.  -93 -  Chapter 5: Experimental Results and Discussion Run V4.18 and Run V4.21 were run under different experimental condition. Run V4.18 was run with 3 OA for a straight 3 hours after the pulp was added to the brightening solution. Instead of driving the reactor for a straight 3 hours, the power of Run V4.21  was shut off 30 minutes after  the pulp was introduced into the brightening solution. The mixing of the pulp slurry, the cooling of the anode, and the temperature control of the brightening solution were continuing during this period. After the pulp brightening for 30 minutes without current passing through the reactor, the power was then turned back on to 30A for another 30 minutes. The experiment was run for a total 180 minutes by repeating turning on and off the power by 30 minutes intervals. By doing this, the total minutes of the brightening time with consuming electric power was 120 minutes. Hence the energy consumption of Run V4.21 was only 57% of Run V4.18. Figure 5.24 shows the peroxide concentration profile of these two runs. 0.08 - i  c <u 0.02 +'O T3 5*  Standard F^un (V4.18) E n e r g y Saying Run (V4.21)  X  0.00 A 100  50  0  150  Brightening Time (Minutes) Figure 5.24  Effect of Energy Saving on Peroxide Generation  -94-  200  Chapter 5: Experimental Results and Discussion Results in Figure 5.24 indicate that energy saving run can generate the same peroxide concentration as standard run during the period that power supply was on. Figure 5.25 displays the results of brightness gain and yellowness loss from these two runs.  Yellowness Loss  Brightness Gain  Energy Saving Run  Experimental Condition Standard Run  AB (%ISO) 16.2  Energy Save Run  11.8  Standard Run  17.0  SBE (kWh/ton/%ISO) 16 x 10'  BSTY (ton*%ISO/m /hr/) 0.123  15.6  11 x 10'  0.181  AY SO/  3  (AB : Brightness gain; AY : Yellowness loss) (SBE: specific brightening energy; B S T Y : brightening space time yield) Figure 5.25 Effect of Energy Saving The results show that cutting down the charging time to 120 minutes from 210 minutes decreased the specific brightening energy and increased the brightening space time yield. However, both the brightness gain and yellowness loss reduced for the energy saving run. Also, the peroxide concentration was down to 25mM during the time that power was off comparing to 58mM of peroxide while the power was on. The lower concentration of peroxide indicates that there was not enough residual peroxide in the brightening solution to brighten the pulp during the period of power off.  -95 -  Chapter 5: Experimental Results and Discussion 5.2.7  Current Efficiency  The estimation of current efficiency for peroxide was performed using gas chromatography to analyze the gas samples collected from the electro-brightening experiments. Gas collection bags from B C Research Inc. were for this purpose. Gas samples were sealed in the gasbags and sent to B C Research Inc. for gas analysis.  The current efficiency was gauged on a range of current density from 1.6 kA/m to 4.7 kA/m . 2  2  The general experimental conditions for these runs are as follows: electrolyte additives consisted of 400ppm M g  2 +  and 0.002 M DTPA; electrolyte temperature set point was 60°C; anode coolant  was 1°C at 5.5 liter per minute; and the cathode material was uncovered zirconium tube. The production of peroxide was performed for 45 minutes and the gas sample was collected at the end of the 45 minutes. By assuming that only two reactions, C20 " + 2e" <- 2CO3 " and 2H2O + 2  2  6  0  2  + 4e~ <— 40H", happened on the anodes, and only one reaction, 2H2O + 2e" —» H2 + 20H",  happened on the cathode, the peroxide current efficiency for each 45-minutes run was calculated and plotted against the respective current and the concentration of sodium carbonate in Figure 5.26.  19.8 %  13.5 % 16.3 %  / • IM  Figure 5.26  Concentration of Sodium Carbonate 2 M  /  Current  ' 10A  Peroxide Current Efficiency versus Current and Concentration of Sodium Carbonate  -96-  Chapter 5: Experimental Results and Discussion The detailed information of Figure 5.26 displays in Table 5.12.  ([Na C0 ]: Concentration of Sodium Carbonate; [H ]: Concentration of Hydrogen Gas) ([0 ]: Concentration of Oxygen Gas; [N ]: Concentration of Nitrogen Gas) 2  2  3  2  2  Table 5.12 Figure 5.26  Data of Gas Analysis and Current Efficiency  shows that the highest peroxide current efficiency 2 (25 .  %), with 1 M sodium  carbonate, was achieved at a current density of 16 . kA/m . (The detailed calculations are shown 2  in Appendix IV.)  Another phenomena which can be observed was that although better  conductivity was provided by a higher concentration of sodium carbonate 2 (M,)  the peroxide  current efficiency was lower, which is an opposite of expected. Data from these experiments also indicated that even though higher peroxide concentration was generated using higher current density, the peroxide current efficiency was decreased.  This is supported by a higher rate of  oxygen gas generation on the surface of anode, which was observed during the experiment. The low current efficiency implies that operating the process at a high current density might not be economical because of the low current efficiency and higher voltage.  The current efficiency data shown above might be incorrect because more reactions may occur  2 H 2 O+O 2 and reaction like 2 H + H0 + 2e" -» 2 H 0  on the anodes and the cathode than assumed in the previous paragraph. Reaction like  + 4e' <- 2 H 0might happen at the 2 2  happen on the cathode.  anodes,  +  2  2  However, it does give a rough idea of how the peroxide current  efficiency was distributed in this study.  -97-  2  Chapter 5: Experimental Results and Discussion  5.3  Performance of the Electro-Brightening Reactor  The limitations of the electro-brightening reactor on temperature and current density were recorded during performing experiments at variable conditions. The results gathered from these experiments show the barrier of the experimental conditions for both peroxide generation and pulp brightening in this study.  5.3.1  Temperature Limitation  Experiments performed on the electro-brightening reactor recorded the temperature limitations. The original proposal was set to investigate the brightening results with temperature range from 30°C to 60°C or even higher. Notwithstanding, both 30°C and 60°C could not be reached without violating other operating conditions in this study.  For the purpose of brightening pulp, the temperature of the brightening solution should be around 60°C. However, with the improved cooling system, temperature control became a major concern. The capacity of the heater, 200 Watts, was too small to provide the required heat for holding the temperature with heat transferred to the coolant, as shown in Appendix VI. Hence, the temperature of the brightening solution could not rise to the required 60°C without lowering the cooling flow rate, while operating at 10A (current density: 1.6 kA/m ). In order to raise the 2  temperature to the required value, the cooling flow rate was lowered from 6 liter per minute to 0.5 liter per minute. However, the anode surface temperature was thus raised. High temperature around the anode might damage the conductive glue between the titanium wall and the platinum foil, and the non-conductive glue that covered the edge of the platinum anode since this glue could not survive under the high temperature, high current and high alkaline conditions. This was confirmed from the deterioration of the glue observed during the experiments. The color of the non-conductive glue started to change from transparent to yellow after 10 runs. As other experiments were performed, the glue fell off the surface.  This exposed the layer of silver-  conductive glue to the brightening solution, which probably enhanced decomposition and affected the brightening results.  -98-  the peroxide  Chapter 5: Experimental Results and Discussion It was also difficult to hold the temperature at 30°C. Joule heating with 30A (current density: 4.7 kA/m ) would simply heat the brightening solution over 30°C. Even turning off the heater, the 2  temperature of the brightening solution was around 33°C due to the Joule heating. Thus, the temperature boundary of the brightening solution was set between 40°C and 60°C with adjusted coolant flow in the 2 factorial experiment. 3  5.3.2  Current Limitation  Results indicate that the higher the current density, the higher the brightness gain and yellowness loss was obtained. Experiments performed at 40A were investigated using the modified reactor. However, the current could not be maintained at 40A and dropped to 12.3 A. The experimental conditions were as follows: electrolyte consisted of 2 M sodium carbonate, 400ppm M g , and 2+  0.002 M DTPA; temperature was 60°C; and anode coolant was 1°C at 6 liter per minute. Figure 5.27 displays the profile of the current plotted against the voltage and experimental time. The small variations in voltage were caused by the D C power supply operating at the limit of its voltage capacity.  Figure 5.27  Current Limitation of Electro-Brightening Reactor  -99-  Chapter 5: Experimental Results and Discussion Results in Figure 5.27 show that this experiment was under voltage control all the time (Maximum 20.1V), and indicate that something happened in the reactor.  Thus, the reactor was  disassembled and found that Teflon coating on the mixer and the inside wall o f the reactor were peeled off.  This phenomenon showed that the Teflon could not sustain high current and high  alkaline conditions.  The exposed titanium caused voltage drop, which increasing the electric  cost. Moreover, the exposed stainless steel mixer caused corrosion and emitted metal ions to the pulp slurry. The exposed titanium and the metal ions will increase the decomposition rate of peroxide, and affect the brightening result. (Section 5.1.6)  5.4 Pictures of Teflon Deterioration and Pulp Samples The following pictures illustrate the Teflon deterioration and pulp samples.  Figure 5.28  Teflon Deterioration (1)  - 100 -  Chapter 5: Experimental Results and Discussion  - 102 -  Chapter 6  Chapter 6 General Discussion and Conclusions General Discussion The electro-oxidation, peroxide generation process was investigated using sodium carbonate as the mediator and was introduced to brighten thermo-mechanical pulp in-situ.  The following  observations and conclusions are obtained. Peroxide Generation 1. Experiments performed with uncovered zirconium cathode generated at least six times more peroxide than other cathode material with or without diaphragm.  Zirconium is a good  candidate material for new reactor body and cathode. 2. Temperature had a significant effect on peroxide generation.  Lower anode coolant  temperature (1°C) resulted in higher peroxide concentration in the early stage of the process. Pre-cooling the electrolyte to around 5°C before driving current on the system also helped to produce higher peroxide concentration in the early stage of process. Further, experiments concluded that later in the electro-generation process, high electrolyte temperature promoted the production of peroxide. 3. Anode current density has considerable effect on peroxide concentration but was less significant than temperature.  High anode current density produced high peroxide  concentration, but decreased the peroxide current efficiency and increased the energy consumption. 4. The pH of the electrolyte dominates the generation of peroxide, probably through its effect on concentration of CO3 " species in the electrochemical process. 2  CO3 " 2  At pH higher than 11,  was the primary ion in the electrolyte, thus the peroxide concentration was high.  When pH was 10.5, the H C O 3 ' was the primary ion, which resulted in low peroxide concentration. Generally, electrolyte at high pH (>11) produced 3.5 times more peroxide than low pH (10.5).  - 103 -  Chapter 6 General Discussions and Conclusions 5. High electrolyte concentration (2M N a 2 C C < 3 ) increased the conductivity and decreased the total cell voltage  (E hm 0  decreased) and energy input. High  CO3 " 2  concentration also promoted  the percarbonate generation as well as peroxide accumulation. 6. Additives such as magnesium sulphate and D T P A demonstrate positive effect on preserving peroxide species (suppressed the secondary reactions) in the electrochemical peroxide process. Electro-Brightening of Mechanical Pulp 7. The full 2 factorial design experiment of the in-situ brightening of mechanical pulp showed 3  that the three factors (temperature, current, and concentration of sodium carbonate) had positive significant effect on the brightening response. carbonate presented the most dominant effect.  The concentration of sodium  A combination of high temperature, high  current, and high sodium carbonate concentration (unbuffered by sodium bicarbonate) is favorable for the electrochemical brightening of mechanical pulp. 8. Results indicate that alkali darkening will not negate the brightening responses in high p H electro-brightening («11.5).  Brightness gain and yellowness loss of the brightened pulp  increased along with the increased pH in the pH range of 10.5 to 11.8. On the other hand, the pH of the electro-brightening experiments decreased during the process to below 11 in most runs, which helped prevent alkali darkening at the end of the process, while probably reducing the efficiency of peroxide generation. 9. High pulp consistency (4.5%) had higher brightening responses than low pulp consistency (2.5%) in this study, which demonstrates the electro-brightening process has the same character as the conventional peroxide brightening process. 10. The 30 minutes of peroxide pre-generation time (before pulp addition) showed no significant effect on brightness gain and yellowness loss, hence indicating the electro-brightening process can overcome the initial alkali-darkening effect. 11. The highest yellowness decrease during a brightening process usually happened between 30 to 90 minutes of brightening time.  However, the highest brightness increase usually  - 104-  Chapter 6 General Discussions and Conclusions happened from 90 to 180 minutes. The final brightness of pulp depended on the peroxide concentration after 120 minutes.  If peroxide concentration at 120 minutes is high (e.g.  >0.065 M), it will spur another increase of brightness.  On the other hand, a longer  brightening time (240 minutes) saw a decrease in peroxide concentration and did not improve the brightening results. 12. Saving energy in the electro-brightening process with 30 minutes power off intervals gave a reduced brightness gain and yellowness loss. The results indicated that there was not enough peroxide left in the pulp slurry to brighten during the power off periods. Performance of the Electro-Brightening Reactor 13. Teflon coating deterioration occurred while operating under high temperature and high current conditions. Also, erosion of the non-conductive glue was observed after number of runs. Furthermore, the equipment (e.g. heater) does not have enough capacity to provide the required experimental range of temperature.  These phenomena limit the experimental  boundary conditions to 60°C and 3 OA, and make results at more extreme conditions unreliable. Conclusions The carbonate electro-oxidation process of generating peroxide in a batch electro-brightening reactor without pulp can achieve up to 0.08 M peroxide. The experimental conditions were as follows: electrolyte: 2 M sodium carbonate, 400ppm M g , and 0.002M D T P A ; electrolyte 2 +  temperature: 60°C; anode coolant: 1°C with flow at 6 liter per minute; and current: 30A, while using a platinum sheet anode and zirconium cathode in an undivided cell. In-situ electro-brightening of softwood TMP (initial brightness: 41.6 % ISO; initial yellowness: 36.8 %) at 2.5% consistency in sodium carbonate liquor achieved a brightness gain of 17.4% ISO and a yellowness loss of 19.2%. These results correspond to a specific brightening energy of 17 x 10 — — ton%ISO 2  and a brightening space-time yield of 0.145  t 0 n  m  / /  ° ^ ^ Xhe high value hr  of specific brightening energy represents an operation cost of approximately $ 1,020 per ton of OD pulp for 20 % ISO brightness gain, (cost of A C energy: 0.03 $/kWh [43]) The low value of the brightening space-time yield indicates that a large reactor is required, with consequent high  - 105 -  Chapter 6 General Discussions and Conclusions capital cost. Moreover, brightness reversion test (Appendix IX) showed that electro-brightened pulp has the same brightness stability as conventional peroxide brightened pulp. Based on such figures of merit, the use of this process would not be practical in comparison to conventional pulp brightening methods due to the high energy and equipment cost. However, the process does offer the potential to recycle sodium carbonate in a closed-cycle T M P mill and may be worth further investigation on this basis.  - 106-  Chapter 7  Chapter 7 Recommendations and Future Work 1. Further investigation is required on the effect of factors such as higher pulp consistency (up to 10%), higher mixing speed (up to 500rpm), higher concentration of sodium carbonate (up to 2.5M), and different level of pH (from 10.8 to 11.5) by using the existing electrochemical batch system. 2.  Further investigation is required on the effect of energy saving by cycling the current at various intervals.  3.  Optimize the electro-brightening process by using the existing electrochemical reactor with the fixed cooling water temperature (« 1°C) and within the boundary conditions of the factors as follows: current: 30A, Temperature: 60°C.  4. Implement an on-line monitoring and measuring device so the detailed current, voltage, pH, and electrolyte temperature of the reactor can be recorded continuously.  5. More study on the effect of additives should be performed in order to find out a more effective peroxide stabilizing system for the sodium carbonate brightening process.  6. Design a new reactor with the potential of performing experiments under higher current (up to 50A), and higher temperature (up to 80°C) conditions. Some ideas for designing the new reactor are presented in Appendix IX.  - 107-  Reference  References [1]  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)  [2]  Colin Oloman, Electrochemical Processing for the Pulp and Paper Industry. The Electrochemical Consultancy, Hampshire, England (1996)  [3]  Varennes, S.; Daneault, C , and Parenteau M . , "Bleaching of Thermomechanical Pulp with Sodium Perborate", TAPPI Journal. 79: 245 ~ 250 (March 1996)  [4]  Khomutov, N . Ye., "Electrolytical Synthesis of Percarbonates" in Chemistry of Peroxide Compounds, edited by Chernyayev 1.1., Publishing House of the Academy of Science of the U.S.S.R., Moscow, pp. 221 ~ 225 (1963)  [5]  Prokopchik,  A.  Yu  and  Vashykyalis,  A.T., "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) [6]  Constam, E. J., and Hansen, A . , U.S. Patent No. 579.317 "Process of Manufacturing Percarbonates", (March 13, 1897)  [7]  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)  [8]  Oloman C , "Proposed Patent Application Process for Electro-chemical Oxidation of Carbonate Solutions". B C Research, Vancouver, Canada (January 13, 1970)  [9]  Pogy Kurniawan, A Study of In-Situ Brightening of Mechanical Pulp via the ElectroOxidation of Sodium Carbonate. M.A.Sc. Thesis, U B C , Vancouver, Canada (1998)  - 108-  Reference [10]  Christopher J. Biermann, Essentials of Pulping and Papermaking. Academic Press, Inc., San Diego, CA, U.S.A. (1993)  [11]  J. Newell Stephenson, Preparation & Treatment of Wood Pulp, Volume 1, M c G R A W Hill Book Company, Inc. New York, U.S.A. (1950)  [12]  James P. Casey, Pulp and Paper Chemistry and Chemical Technology. Third Edition, Volume 1, Tryon, N.C. (1979)  [13]  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. (1996), pp 161-181  [14]  Clifford A . et al, "Electrosynthesis of Alkaline Peroxide Solutions", Electrochem. Soc. Spring Meeting, Montreal, Canada (May 1990)  [15]  Gellerstedt, G. and Agnemo, R , "The Reactions of Lignin with Alkaline Hydrogen Peroxide. Part V. The Formation of Stilbenes", Acta Chem. Scand.. B34(6): 461-462 (1980)  [16]  Gellerstedt, G , Hardell, H.-L and Lindfors, E,-L, "The Reactions of Lignin with Alkaline Hydrogen Peroxide. Part IV. Products from the Oxidation of Quinone Model Compounds". Acta Chem. Scand. B34: 669-673 (1980)  [17]  Clare, S.I. and Steelink, C , "Free Radical Intermediates in the Formation of Chromophores from Alkaline Solutions of Hardwood Model Compounds", TAPPI Journal. 56(5): 119-123 (1973)  [18]  Simpson, B . , Ayers, J., Schwab, G., Galley, M . and Dence, C , "Relations of oBenzoquinones in Aqueous Media. Implications in Pulping and Bleaching", TAPPI Journal, 61(7)41-46(1978)  - 109-  Reference [19]  Hosoya, S., Seike, K . and Nakano, J., "Bleaching of High-Yield Pulp. Reactions of Quinones and Quinone Polymers with some Reducing Reagents", Mokuzai Gakkaishi. 22(5): 314-319(1976)  [20]  G. Leary and D. Giampaolo, "The Darkening Reactions of T M P and B T M P During Alkaline Peroxide Bleaching", Journal of Pulp and Paper Science. 25(4): 141-147, (1999)  [21]  Basciano, C. R., "Importance of Hydrogen Peroxide Brightening of Mechanical Pulps", Proceedings of the 76 Annual Meeting. Technical Section. Canadian Pulp and Paper th  Association, Montreal, (1990) pp. 47 [22]  Williams, M . D . , and Garland, C P . , "Brightness and Bleaching of Thermomechanical Pulps from Different Radiata Pine", Appita Journal. 41(2): 138 ~ 139 (1988)  [23]  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. 14(6): J126 ~ J132 (1988)  [24]  Gupta, V . N . , "Effect of Metal Ion on Brightness, Bleachability and Colour Reversion of Groundwood", Pulp and Paper Magazine of Canada. 71(18): 69-77 (1970)  [25]  Colodette J.L., Rothengberg S., Dence C. W., "Factors Affecting Hydrogen Peroxide Stability in the Brightening of Mechanical Pulp, Part III: Hydrogen Peroxide Stability in the Presence of Magnesium and Combination of Stabilizers", Journal of Pulp and Paper Science. 15: J45 (March, 1989)  [26]  Hart, J. R., "Chelating Agents in the Pulp and Paper Industry", TAPPI Journal. 64(3): 43 - 4 4 (1981)  [27]  Bambrick, D.R., "The Effect of DTP A on Reducing Peroxide Decomposition", TAPPI Journal. 68(6): 96 - 100 (1985)  - 110-  Reference [28]  Strunk, W.G., "Factors Affecting Hydrogen Peroxide Bleaching for High-Brightness TMP", Pulp & Paper. 54(6): 156 ~ 160 (1980)  [29]  Frank Walsh, A First Course in Electrochemical Engineering. The Electrochemical Consultancy, Hampshire, England (1993)  [30]  Gileadi, E., Electrode Kinetics for Chemists. Chemical Engineers and Material Scientists. V C H Pub. Inc., New York, U.S.A. (1993)  [31]  Robert Powell, Hydrogen Peroxide Manufacture. Noyes Development Corporation, New Jersey, U.S.A. (1968)  [32]  Oloman, C , "In-House Project - Project 2022 - Electrochemical Preparation of Oxidizing Bleaching Agents" B C Research (March 20, 1970)  [33]  Rydholm, S. A., Pulping Processes, John Wiley and Sons, Inc., New York, U.S.A. (1965)  [34]  Pogy Kurniawan, A Study of In-Situ Electrochemical Brightening of Mechanical Pulp in Sodium Carbonate. C H N L 492 Thesis, U B C , Vancouver, Canada (1993)  [35]  Marcel Pourbaix, Atlas of Electrochemical Equilibria in Aqueous Solutions. Translated from the French by James A . Franklin, National Association of Corrosion Engineers, Huston, Texas, U.S.A. (1974)  [36]  "Foaming Handsheets for Reflectance Testing of Pulp (Sheet Machine Procedure)", TAPPI Method. T 272 sp-97  [37]  Denny A . Jones, Principles and Prevention of Corrosion 2 . Prentice hall, Upper Saddle nd  River, NJ 07458 (1996) [38]  Lee, H . , Park, and Oloman, C , "Stability of Hydrogen Peroxide in Sodium Carbonate Solution", TAPPI Journal (Published in August 2000)  - Ill -  Reference [39]  William L . Masterton, Emil J. Slowinski, Conrad L . Stanitski, Chemical Principles with Qualitative Analysis 6 . Saunders Golden sunburst Series, CBS College Publishing, New th  York U.S.A. (1986) [40]  Tomas G. Oberg, Stanley N . Deming, "Find Optimum Operating Conditions Fast", Chemical Engineering Progress. AICHE, Vol.96 (4): 53 ~ 59 (2000)  [41]  Hobbs, G. C. and Abbot, J., "The Role of Radical Species in Peroxide Bleaching Processes", APPITA. 45(5): 344 ~ 348 (1992)  [42]  Been, J., " A Novel Approach to Kinetic Modeling of the Hydrogen Peroxide Brightening of Mechanical Pulp", TAPPI Journal. 78 (8): 144 ~ 152 (1995)  [43]  Mathur, I. and Dawe, R., "Using On-Site Produced Alkaline Peroxide for Pulp Bleaching", TAPPI Journal. 82: 157 ~ 164 (1999)  [44]  Murphy, T. D., "Design and Analysis of Industrial Experiments", Chemical Engineering, pp. 1 6 8 - 182 (June 1977)  [45]  Jordan, B. and O'Neill, M . , "The Case for Switching to CIE L*a*b* Color Description for Paper", Pulp and Paper Canada. 88:10, pp. T382-T386 (1987)  - 112-  Appendix I  Appendix I Design and Analysis of Factorial Experiments (Based on Thomas D. Murphy, Jr. [44]) The benefit of performing the two-level factorial design experiments is that it can give more information per experiment than unplanned approaches.  Factorial design is a mathematical  method that will determine the experimental response surface. In the design, considering there are n factors to be investigated, a full design would require 2 experimental runs. Two-level n  experimental design can filter out the individual and interaction effects between a large numbers of variables that might influence the experimental responses. By using this organized approach, the conclusions from a statistically designed experiment are often evident without extensive statistical analysis. The results obtaining from this technique also exhibit more reliability in the light of experimental and analytical variation.  The main, interaction, and curvature effects are calculated during the factorial design analysis.  A.  Main Effects  Consider n variables (Xi, X , X „ ) at two levels, i.e. "+" and 2  The main effect is calculated  as the difference between the average "+" and "-" factor level responses.  Main effect o f * = Response at^  X-response  at^  X,)  ( 1 )  (half the number of factorial runs)  B.  Interaction Effects  The interaction effect is the average response difference between one half of the factorial runs and the other half. A n interaction column shown below is a two-factor factorial design example. It is formed from the columns that comprise the interaction, by multiplying the entries in the factor column.  - 113 -  Appendix I  Run No.  Xi  x  X1X2  2  Response  (Interaction Column)  1  +  +  +  Y,  2  +  -  -  Y  2  3  -  +  -  Y  3  4  -  -  +  Y  4  Interaction effect of Xy = C.  +  ^  4  )  ^  2  (  2  )  Curvature Effects  The curvature effect is the difference between the average of the center point responses and the average of the factorial points. D.  Confidence Interval  The effects calculated from factorial design are point estimates. reliability or precision of these estimates.  They do not indicate the  The significance of these values depends on the  confidence interval (W), i.e., the interval that includes the "true" effect at the stated confidence level. The commonly used confidence levels are 90, 95, 99%. The confidence-interval width is a function of the response error estimate for a main effect. The confidence interval is given by the following equation:  W (Effect) = (Main Effect Estimate) ± - J L  (3)  A confidence interval for the curvature effect is calculated as: W (Effect) = (Curvature Effect) ± ts^  +^  where C = number of center points N = the number of factorial points in the design  - 114-  (4)  Appendix I t = student's 'f statistics with v degrees of freedom s = response error (or pooled response error) with v degrees of freedom The response error of each run is calculated using the following equation:  (5)  The pooled response error, for k=3 separate estimates of error s;, each with n replicates, is calculated by:  (6)  This thesis used Jass software to design and analysis the data.  Jass would design the  experiments in a random order including needed replicating runs. The software provides several different approaches to explore and interpret the data from the experiments, such as plotting the variables, calculating the main and response error effects, and plotting the interaction. Plotting the variables could show the variable versus the observation order that the data was collected. The purpose of this diagram was to detect a pattern in the response variable with respect to the order that the data was collected. Calculating the effects could find out how much, on the average, the response changed when a factor went from a low to a high level. By using Jass to calculate the effect, it also gave standard errors for the effects, t-Ratios and a dot plot of the effects with the proper reference distribution placed over it. To further examine the interactions, the averaged response was plotted on the vertical axis. The combinations with the same levels of the factor were connected with a line. If there were no interaction, the lines drawn would be parallel.  Nonparallel lines meant that the effect of the factor depended on the level of the  interacting factor.  - 115 -  Appendix II  Appendix II Factorial Design Analysis Calculation A . Calculation for the Response Error for Brightness Gain, Yellowness Loss, and Concentration of Peroxide The following replicated runs were performed during the factorial design experiments.  The  details are as follows:  No  C (M)  I (A)  T (°C)  n  Brightness Gain (% ISO)  Yellowness Loss (%)  [H 0 ] (M)  1  1.0  30  40  1  11.6  13.2  0.020  2  1.0  10  40  2  7.5  9.4  0.027  3  1.0  30  60  2  10.4  15.9  0.036  4  2.0  10  60  1  15.3  15.9  0.029  5  2.0  30  40  1  12.3  14.0  0.032  6  1.5  20  50  2  15.2  14.5  0.043  7  1.0  10  60  1  11.8  14.2  0.022  8  2.0  30  60  1  17.4  19.2  0.059  9  2.0  10  40  1  13.3  12.9  0.038  No  n  AB (% ISO)  Ave. A B (% ISO)  2  2  7.3; 7.7  7.5  6  2  15.1; 15.2  15.2  3  2  10.0; 10.8  10.4  1 Ave. A Y  AY  [H 0 ] (M)  II (%) 0.026; 0.028 9.4 | 9.1; 9.7 j J 14.6; 14.5 j 14.5 0.042; 0.043 j 15.3; 16.5 j 15.9 0.033; 0.039 (%)  2  2  2  2  Ave. [ H 0 ] (M) 2  2  0.027 0.043 0.036  (n = number of runs; A B = brightness gain; A Y = yellowness loss; [ H 0 ] = Cone. Of Peroxide) (C: Na C03 Concentration; I: Current; T: Temperature) 2  2  2  Table A2.1  Summary of Responses from the Factorial Design  - 116-  Appendix II  Using the equation: Si =  , the response error of each run was calculated and  shown below: No  r  1  2  0.2828  0.4243  0.001414  2  2  0.0707  0.0707  0.000707  3  2  0.5657  0.8485  0.004243  5  AB  S  Ar  B. Calculation for the Pooled Response Error  The pooled variance for k=3 separate estimates of error si, each with r; replicates, is calculated by equation: s = 2  Z(i-i)  1.  The pooled response error for brightness gain  S  2  =(°  2 8 2 8  )  +(00707) +(0.5657)  2  2  AB  2  _  3  = ± 0.37 % ISO  2.  The pooled response for yellowness loss (0.4243) +(0.0707) +(0.8485) 2  S  tY  3.  2  2  _ = 0.302  =±0.55 %  The pooled response for concentration of peroxide  117  Appendix II (0.001414) +(0.000707) +(0.004243) 2  2  2  3 [ff,0 ]  = 6.83E-6  = ± 2.6E-3 M  2  C. Calculation for the Confidence Interval  By using a 95% confidence level, at v = 5, t is equal to 2.571 [38], the confidence interval can be calculated by equation: W (Effect) = (Main Effect Estimate) ±  ts  Two degrees of freedom  were come from the center points, and three degrees of freedom from the three variables.  1. The confidence interval for brightness gain main effect (Effect) = (Main Effect Estimate) ± 0.667 % ISO  2. The confidence interval for yellowness loss main effect W  Ar  (Effect) - (Main Effect Estimate) + 0.998 %  3. The confidence interval for concentration of peroxide main effect W  [HM  (Effect) = (Main Effect Estimate) ± 4.726E-3 M  D. Calculation for Curvature Effects at 95% Confidence Interval Assuming all the effects was first order and interactive, the average of the responses of the factorial runs should be the expected responses value at the centroid of the design. These values were: average of brightness gain = 13.0 % ISO, average of yellowness loss = 14.4 %, and average concentration of peroxide = 0.035 M . However, the actual center points responses were brightness gain = 15.2 % ISO, yellowness loss = 14.5 %, and concentration of peroxide = 0.043 M . The difference between the estimate value and the factorial responses presented an estimate  -118-  Appendix II of curvature effect of-2.21 % ISO for the brightness gain, -0.12 % of yellowness loss, and 8.2E-3 for concentration of peroxide.  The 95% confidence interval for the curvature effects can be calculated using equation: W (Effect) = (Curvature Effect) ± 1.  t  s  ^ +  ^  Curvature effect for 95% confidence interval of brightness gain  (Effect) = (Curvature Effect) ± 1.4 % ISO  2.  Curvature effect for 95% confidence interval of yellowness loss  W  AY  3.  (Effect) = (Curvature Effect) ± 2.0 %  Curvature effect for 95% confidence interval of concentration of peroxide  W  [HA]  (Effect) = (Curvature Effect) ± 9.6E-3 M  - 119-  Appendix III  Appendix III The Calculation of Electroplating of Platinum Each 16 cm platinized anode area was electroplated one by one with the 200 ml solution consisted of 15 g/1 H P t C l , 45 g/1 H P 0 , and 240 g/1 ( N H ^ H P C v The current density was set 2  6  3  4  at 1 mA/cm . Assuming 100% current efficiency, the current was set at 16 mA for 12 minutes to 2  obtain an approximate 10 urn platinum thickness. The cathodic reaction and detail calculation was as follows:  PtCl " (aq) + 4e"  Pt (s) + 6C1" (aq)  2  6  Density of platinum = 21.45 g/cm  3  21.45 x 16 x 1 x 10' = 0.343 g « 0.00176 mol Pt 3  /  * \  Electrode area (cm ) 2  10 urn thickness  ,. IxTime 0.0\6xTime Thus, according to m = ; 0.0176 = nxF 4x96487 Time = 11.79 minutes  The process was controlled at 70°C with continuing stirring.  - 120-  E ° = 0.744 V  (III. 1)  Appendix IV  Appendix IV The Calculation of Peroxide Current Efficiency Assume that only two reactions happened on the anodes; i.e.: C 0 " + 2e <- 2 C 0 "  E° = 2 V  2 H 0 + 0 + 4e" <- 40H"  E ° = 0.4 V  2  2  2  6  3  2  2  S H E  S H E  the reaction on the cathode is 2 H 0 + 2e -> H + 20FT 2  E ° = -0.8 V E  2  S H  For generating 0.5 mol of 0 —» 2F; for generating 1 mol of H - » 2F 2  2  .'. At anodes  At cathode  0.5 mol 0 - » 2F  1 mol H - » 2F  nmol0 ->Ixtx(l-CE)  nmolH ->IxT  2  2  2  2  0.5x/x/x(l-CE)  n  ^  :  n  Ixt  L  N  2F where C E is peroxide current efficiency  2  Or  (1)  Generating peroxide for 45 minutes with 2 M Na C03 at 30A 2  (from head gas analysis)  0.5x1 n  Ql  n„  xtx(\-CE) 2£ Ixt IF  l-CE =>  => 0.6905  29.86% ~ 69.05%  0.2986 =  2 ^>  IF  , „ „ 0.2986 l-CE = 2 x 0.6905  C E = 0.135* 13.5%  - 121 -  Appendix IV (2)  Generating peroxide for 45 minutes with 1 M N a 2 C C > 3 at 10A (from head gas analysis) 0.5x1 "o  2  ~  H2  ^ 27.62%  2F  =  n  xtx(\-CE) ~ 71.26%  Ixt_  IF 0.2762  l-CE  =>  , „  = 2  => 0.7126  _  l-CE = 2 x  0.2762 0.7126  =>  C E = 0.225 « 22.5 %  (3)  Generating peroxide for 45 minutes with 1 M Na C03 at 3 0 A 2  (from head gas analysis) 0.5x1 "o  ~  Hi  28.29%  2F  2  n  xtx(\-CE) ~ 70.58%  Ixt_  IF 0.2829  l-CE  =>  , _  = 2  => 0.7058  n  l-CE = 2 x  0.2829 0.7058  =>  CE = 0.198* 1 9 . 8 %  (4)  Generating peroxide for 45 minutes with 2 M N a C 0 at 3 0 A 2  (from head gas analysis) 0.5x1 n  xtx(l-CE) 28.96%  2F  Qi  n  ~  Hi  ~ 69.18%  Ix1_  IF 0.2896  l-CE  =>  = 2  =>  , ^  => 0.6918  „  l-CE = 2 x  CE = 0.163 * 16.3 %  - 122-  0.2896 0.6918  3  Appendix V  Appendix V Chemicals and Pulp The chemicals and pulp used in this thesis study are as follows:  •  Sodium carbonate ( N a 2 C C > 3 ) , certificate A.C.S., form Fisher Scientific Co Ltd,  •  Sodium bicarbonate (NaHCOa), certificate A.C.S., form Fisher Scientific Co Ltd,  •  Sodium silicate (Na2Si03»5H20), certificate A.C.S., form Fisher Scientific Co Ltd,  •  Magnesium sulfate ( M g S 0 » 7 H 0 ) , certificate A.C.S., form Fisher Scientific Co Ltd,  •  Sulfuric acid (H2SO4), reagent A C S . , from Fisher Scientific Co Ltd,  •  Diethylenetriaminepentaacetic acid (DTPA, Ci4Hi N Na50io), as pentasodium salt, 40%  4  2  8  3  in water, from Acros Organics, •  Potassium iodide (KI), reagent A.C.S., from Fisher Scientific Co Ltd,  •  Ammonium Molybdate ((NH4)6Mo 024*4H 0), certified A.C.S., from Fisher Scientific 7  2  Co Ltd, •  Sodium  thiosulfate  Solution  N/10  (24.819mg  Na S20 «5H 0 2  3  2  /ml),  certified  0.1005-0.0995N), from Fisher Scientific Co Ltd, •  Ammonium phosphate ( ( N H ^ H P C ^ ) , certified A.C.S., from Fisher Scientific Co Ltd,  •  Non-conductive epoxy, from Industrial Formulators of Canada Ltd.  •  Conductive epoxy (resin: RBC-6100; hardener: B-130), from R B C Industries Inc.  •  Hydrogen hexachloroplatinate (IV) hydrate  (HPtCl6), 2  reagent A.C.S., from Aldrich  Chem. Co.  The water used for all experiments was distilled water and was used without further distillation.  The Thermo Mechanical Pulp (TMP) used for brightening consisted of approximately 55% SPF (spruce, pine, and fir) and 45% hembal (hemlock and balsam). The pulp was treated in the mill with 2 kg/tonne of DTPA. The initial brightness and yellowness of the T M P were 41.6 % ISO and 36.8 %.  - 123 -  Appendix VI  Appendix VI The Calculation of Coolant Heat Transfer With the new anode coolant system and the modified electro-brightening reactor, the heat transfer can be calculated as follows:  The coolant flow rate is 6 liter per minute. The inlet coolant temperature is 1°C and the outlet temperature is around 6°C. Thus, the heat loss to the coolant is: H = Q x C x AT= U x A x AT p  where H :  Heat loss (kJ/s)  Q:  Coolant flow rate (kg/s)  Cp:  Heat capacity component (^/(frg  AT:  Temperature change of coolant (K)  A:  Anode surface areas (m )  U:  Heat transfer coefficient (0.5 ^/,o  ^ )i C  -  Plll0  4-22  2  r  2 J - estimate  for coolant flow rate: ^ // / . /mm  6  „/ ^  x  1 0 0 0  lmin  ,  kg „ , £ e V y * /s  n  x 1000-^- = o.l  6 0 s e c  K  m  kJ  = 0 . 1 ^ - x 4.2176—— x(279K-214K)*2.U—=2110W s kg-K s  Hiost=  Or  x  bJ  Ira  iost  H  \m /  3  =6  0.S-  kW x(4xl6xlO-)wx(60-l)°C= 189xl0" kW «\90QkW C-m 4  2  3  r  The capacity of the heater is 200 W . Thus, since heat generated from the heater (200 W ) < heat loss (2110 W ) , the required reactor temperature cannot be reached i f the heat generated from Joule heating 5  to  0.5  (I  x V hm) 0  < 1910 W .  This situation required that the coolant flow be reduced from  liter per minute to maintain reactor temperature up to  - 124-  60°C.  Appendix VII  Appendix VII Sampling and Analysis Procedures 1.  Measurement of Peroxide Concentration  The measurement was taken every 30 minutes. Each time, 5 ml of electrolyte was pipetted from the reactor. The pipette is of special design with a mesh on the pipette entrance to filter out the pulp. The sample was added to 5 ml of 20%  H2SO4  and 10 ml distilled water to make up to a  volume of 20 ml in a 125 ml Erlenmeyer flask. After mixing, 5 drops of saturated ammonium Molybdate solution, 5 ml of 1M potassium iodide solution, and 3 drops of 0.5% starch indicator were added before titration with 0.1N Na2S2U3.  The reactions and detailed calculations are  shown as follows: H 0 + 2KI + H 2 S O 4 2  2  -> K 2 S O 4  + 2H 0 + I 2  2  1 mole H 2 O 2 = 2 moles of S 0 " 2  2  3  H -VH =^M -V  M  A  l0l  S20l  Si0t  so>-  M  V  Hfii  = 5.00ml (±0.003 ml); M S 0}  s n }  . = 0.1000M±0.005M  2  M  =  Hn  n  2  U ,  0.1000 ±0.005 . rxV 2 x (5.00 ±0.003)' T  „  (  r  n  n  ,  „  nss^,\  2  _ =0.01-^  S.O}~  2^3  S,0  H o =0.0l-V (±0.0lml)  M  2  2.  2  SiOr  Measurement of the Optical Properties of Mechanical Pulp  The optical properties of mechanical pulp, brightness and yellowness, was measured using an Elrepho spectrophotometer. A standard handsheet for the brightness measurement was formed according to the TAPPI standard practice T272 sp-97.  - 125 -  Appendix VII  T 272 sp-97 OFFICIAL METHOD - 1 9 9 2 S T A N D A R D P R A C T I C E - 1997 © 1 9 9 7 TAPPI The information and data contained in this document were prepared by a technical committee of the Association. The committee and the Association assume no liability or responsibility in connection with the use of such information or data, including but not limited to any liability or responsibility under patent, copyright, or trade secret laws. The user is responsible for determining that this document is the most recent edition published.  Forming handsheets for reflectance testing of pulp (sheet machine procedure) 1.  Scope  1.1 This practice describes the procedure using the TAPPI sheet machine for preparing reflectance-testing specimen sheets of bleached or unbleached pulp whose fibers are readily dispersed in water. This practice permits the preparation of sheets having a smooth and reproducible surface for reflectance measurements with a minimum of washing or contamination of the sample. 1.2 The pulp sample slurry is adjusted to a pH of 6.5 ± 0.5. 1.3 TAPPI Standard Practice T 218 describes a procedure for using the Biichner funnel for making handsheets for the same application. The purpose for having two practices is discussed in sections 4.3 and 4.4. 1.4 See Appendix for consideration of recycled pulps. 2.  Applicable documents  2.1 TAPPI Official Test Methods referred to for parts of this procedure include: T 400 "Sampling and Accepting a Single Lot of Paper, Paperboard, Containerboard, or Related Product;" T 205 "Forming Handsheets for Physical Tests of Pulp;" and T 402 "Standard Conditioning and Testing Atmospheres for Paper, Board, Pulp Handsheets, and Related Products." 2.2 Reflectance testing on handsheets prepared by this practice can be performed using TAPPI Official Test Methods T 442 "Spectral Reflectance Factor, Transmittance, and Color of Paper and Pulp (Polychromatic Illumination)," T 452 "Brightness of Pulp, Paper, and Paperboard (Directional Reflectance at 457 nm)," or T 525 "Diffuse Blue Reflectance Factor of Pulp (Diffuse Brightness)." 2.3 TAPPI Standard Practice T 218 "Forming Handsheets for Reflectance Testing of Pulp (Biichner Funnel Procedure)" differs from this practice in the manner in which the sheets are made. 3.  Summary  3.1 A properly selected specimen of the pulp to be evaluated is dispersed in a small volume of water, the pH of the slurry and the water in the sheet machine is adjusted to a pH of 6.5 ± 0.5 and formed into a sheet on a sheet machine. The sheet is pressed and dried under controlled conditions to produce a reproducible surface for reflectance testing. 4.  Significance  4.1 The reflectance of a sheet composed of fibers is dependent on the structure of the surface and orientation of the fibers. Industrially made pulp sheets have a variety of structures and surface textures and may contain impurities  Approved by the Optical Properties Committee of the Process and Product Quality Division TAPPI  - 126-  Appendix VII T272 sp-97  Forming handsheets for reflectance testing 12 of pulp (sheet machine procedure)  removable in water. The dispersion of the pulp and the forming of a uniform sheet in a repeatable manner are therefore necessary for accurate testing (1). 4.2 It is well established that the reflectance of pulps, particularly unbleached, is affected by pH (2). Accordingly, this practice establishes a pH which will be an optimum for most pulps. If however, reflectance must be measured at a specific pH, all water used in preparation of the sheets shall be appropriately adjusted and the actual pH reported. 4.3 The procedure described in this practice for forming the sheets and the Biichner funnel procedure described in Practice T 218 may not produce equivalent results. The 150 mesh stainless steel wire screen of the sheet machine may result in the loss of fines which are frequently defined as being able to pass a 200 mesh screen. Stone groundwood, which contains a large percentage of fines, would be particularly affected by the sheet machine. Dilution factors between the two procedures are different, and opposite sides of the sheets are tested (2). 4.4 In selecting which of the practices to use (T 218 or T 272), consideration should be given to the drainage characteristics of the pulp. For example, recycled or low freeness pulps may require an unreasonable time to remove the excess water from the funnel (T 218) and the fibers may not be distributed evenly. In that case the sheet machine practice (T 272) would be preferred. 4.4.1 Two of the advantages of the Biichner funnel practice (T 218) are that less water is involved so pH control is more convenient and the equipment is less expensive. 4.5 This practice includes precautions to prevent contamination of the pulp with color-causing materials during preparation of the sheets. 4.6 The reflectance of a sheet prepared according to this procedure may not be the same as that of a sheet made from the same pulp under industrial papermaking conditions since pulp fines retention will probably be different and no heat is used to dry the sheet.  5.  Apparatus and reagents  5.1 Disintegrator', as described in TAPPI T 205, or a high-speed mixer with two fixed ripple-edge stainless steel mixing blades on a stainless steel shaft and fitted with a square-shaped 1000-mL stainless steel canister . 1  1  NOTE 1:  A disintegrator with a stainless steel paddle and shaft and canister made of stainless steel or plastic is preferred. It is essential, if an old model bronze disintegrator is used, that the interior of the canister, the paddle, and the shaft be chromium-plated or plasticcoated to prevent discoloration of the pulp.  NOTE 2:  The high-speed mixer recommended is of the "malted-milk" type, not the "blender" type. For ease of cleaning, it should have fixed, ripple-edged blades rather than hinged blades. The canister is specially made to fit the mixer but is square because this shape is more efficient than the common round "malted-milk" can (Fig. 1).  5.2 Balance, capable of weighing to the nearest 0.2 g. 5.3 Graduated vessels, two calibrated 2000-mL glass cylinders or stainless steel cups. 5.4 Filter paper, sheets of smooth, 185-mm white filter paper, free from water soluble impurities. 5.5 Sheet machine, the TAPPI 159-mm (6.25-in.) sheet machine (see T 205) provided that the sheet mold must meet the following conditions. 5.5.1 For bleached pulp the entire inner surface of the mold, grid plate, and water leg must be chromium- or nickel-plated. The forming surface should be of 150-mesh stainless steel wire backed by a 20-mesh stainless steel screen. Purified water must be piped in, using plastic or aluminum pipes, and special care must be taken so that it does not become contaminated. 5.6 Water, distilled or deionized, preferably at pH 6.0-7.0. The water should be tested for purity as follows:  Names of suppliers of testing equipment and materials for this method may be found on the Test Equipment Suppliers list in the bound set of TAPPI Test Methods, or may be available from the TAPPI Technical Services Department.  - 127-  Appendix 31 Forming handsheets of pulp (sheet machine  Fig. 1  for reflectance procedure)  testing  T 272 sp-97  H i g h - s p e e d m i x e r ( s a m e as T 2 1 8 ) ( a l t e r n a t i v e t o disintegrator) s h o w i n g special canister fitted to the mixer.  5.6.1 Adjust 2000 mL o f the water to p H 4.5 with alum and allow it to stand for 10 min. 5.6.2 Dip one piece of 150-mm filter paper into the water and remove it at once. Lay it on a blotter in the press referred to in 5.8 5.6.3 Using the Biichner funnel, filter the 2000 mL of water through another piece of the filter paper. Transfer this paper to another blotter. 5.6.4 Press and dry both filter papers as described in 8.3 and 8.4. 5.6.5 Determine brightness of both filter papers. The paper used to filter the water should not be more than 0.2% lower in brightness than the one merely dipped in the water. 5.6.6 Since colloidal particles may pass through a deionizing bed, deionized water should be filtered through a high-quality filter just before use. A vessel 100-150 mm in diameter packed to a depth of 50-80 mm with slurried highbrightness pulp meets this requirement. If the vessel is transparent, the need for pulp replacement can be checked visually. 5.7 Couch roll and plate (see T 205) for transferring sheet from wire to blotter. 5.8 Pump and press with pressure gage (see T 205). 5.9 Press template (see T 205), for centering the sheets in the press. 5.10 Drying rings (see T 205), with rubber searings for holding the sheets during drying. 5.11 Drying plates (see T 205), highly-polished chromium-plated sheet metal disks, 159 mm (6.25-in.) diameter, and about 0.5 mm (0.020-in.) thick. 5.12 Blotting paper (see T 205), sheets o f standard white non-fluorescent blotting paper. For pulp brighter than the blotters, sheets o f similar pulp are useable as insurance against color transfer.  - 128-  Appendix VII T272 sp-97  NOTE 3:  5.13  6.  Forming handsheets for reflectance testing / 4 of pulp (sheet machine procedure) Some blotters contain fluorescent material. The blotters used should be checked with an ultraviolet lamp to ascertain that such material either is absent or is not transferred to the test sheets. Acetic acid 10%.  5.14  Sodium hydroxide (NaOH) approximately 0.1M.  5.15  pH meter.  5.16  Silicone-treated wiping cloth, prepared by applying silicone oil to a lint free cotton cloth.  Sampling  6.1 Select a sample of the pulp in accordance with a previously determined sampling procedure. If the pulp is in dry sheet form, T 400 is applicable and recommended. 6.2  Since the optical properties of many pulps change significantly during the first few hours after  manufacture, optical readings for control purposes should be taken at some definite interval after processing, which should be stated in the report. In any event, store pulp samples so that they are not subject to contamination, a marked change in moisture content, or a significant influence o f heat or light.  7.  Test specimens 7.1  If the pulp is so dry that it will not readily disperse using the procedure given below, tear about 25 g into  small pieces, soak in prepared water (distilled or deionized, preferably at p H o f 6.0 - 7.0) for at least 4 h, dilute to 2000 mL, and stir in the disintegrator until the fibers are well separated, as judged by examining a small quantity diluted with water in a beaker or graduated cylinder. Then handle the pulp as though it had been received as a slurry. NOTE 4:  Before adding pulp to the disintegrator, make sure the entire inside surface of the disintegrator and the propeller shaft are clean.  7.2 weighing 4 g.  T o provide the number of test pieces needed for reflectance measurements, prepare two handsheets, each  7.2.1 Weigh out two separate portions of pulp equivalent to 4 ± 0.2 g of moisture-free fiber, or measure the corresponding volume of premixed slurry.  8.  Procedure 8.1  Dispersing  8.1.1  The water used in pulp disintegration and dispersing and handsheet forming shall be as described in 5.6.  8.1.2  If the disintegrator is used, dilute the pulp portion (7.2.1) to 1000 m L with water at room temperature  and disintegrate for 15,000 revolutions (5 min) (see Note 4). 8.1.3  If the high speed mixer is used, add the pulp portion (7.2.1) to 500 m L of water and disintegrate at 13,000  rpm for 2 min. Transfer to a graduated cylinder and dilute to 1,000 m L using the dilution water to rinse out the mixer. 8.1.4 NOTE 5:  8.2 8.2.1  Using the p H meter, adjust the p H to 6.5 ± 0.5 with acetic acid or sodium hydroxide (5.13 and 5.14). Additives including EDTA shall not be used unless stated. If a pH other than that specified is used, the control shah be ± 0.5 of the intended value. The deviation from the standard shall be reported. Forming Disperse the test portions as directed in 8.1, but dilute each disintegrated sample portion to 2000 m L in  a graduated cylinder of that size. Close the drain valve of the sheet machine and fill it with water to about 150 mm above the wire. M i x the diluted sample portion by pouring it back and forth between two containers three times, then pour it into the sheet machine. A d d distilled or deionized water until the depth is about 350 mm above the wire. Stir the pulp slurry with a stainless steel or plexiglass rod (do not use the standard mixing paddle), moving it back and forth across the deckle until the fibers are distributed uniformly. D O N O T STIR IN A C I R C L E .  A figure 8 stirring motion is  recommended for best distribution. After 3 s open the drain valve and drain off the water. NOTE 6:  The combined water and pulp slurry should be within the 6.5 ± 0.5 pH range. It may not be necessary to adjust the water in the sheet machine if the adjusted pulp stock results in the finished pH being within the specified range.  - 129-  Appendix VII 51 Forming handsheets for reflectance testing of pulp (sheet machine procedure)  T 272 sp-97  8.2.2 Couch the sheet from the wire using blotters of suitable quality, using the couch roll or air couching as described in T 205. Lay the sheet, on the attached blotter, in the press on an initial pad of two blotters, center a polished drying plate over the sheet and add two more blotters. Repeat procedure for second sheet. NOTE 7:  If experience shows that finished sheets tend to stick to the plates, the plate surface may be wiped occasionally with a clean siliconetreated cloth. Check carefully that this has no effect on the brightness of the pulps being tested by making measurements with and without the oil.  8.2.3 The stack from top to bottom will then consist of two blotters, drying plate, test sheet, and two blotters. 8.2.4 Continue to assemble blotters, plates, and test sheets in the press until up to four sets have been accumulated. Cover the top sheet with two blotters. 8.3 Pressing 8.3.1 Put on the cover of the press and hand-tighten two of the diagonally opposite, or all four, wing nuts. Raise the pressure as indicated by the gage to 50 psig, equivalent to approximately 350 kPa on the sheet in 30 s from the time the needle begins to move, and maintain this pressure for 90 s. At the end of that time, release the pressure and remove the press cover. NOTE 8:  The pressing procedure is similar to the second cycle of pressing in T 205. With a thick stack of blotters, take care that the press piston does not travel to the end of its stroke and give a false pressure reading.  8.4 Drying 8.4.1 Remove the stack of blotters, plates, and sheets from the press. 8.4.2 Lay a sheet of 185-mm filter paper on the test sheet with light hand pressure and fit the assembled plate, test sheet, and filter into a set of drying rings. When the pile of rings is filled, place a heavy weight on top or clamp the pile together. 8.4.3 Dry the test sheets with the attached filter papers in the drying rings in an atmosphere in accordance with T 402. The drying operation may be accelerated by circulating air through the drying rings by means of a fan, but do not use hot air. 8.4.4 After the sheets have been dried, remove them from the drying rings with the plates and filter papers attached and store in the conditioned room until tested. Do not remove the plates and attached filter papers until the test sheets are to be cut into specimen tabs for the reflectance readings. Then remove the filter papers without bending the test sheets. Cut the specimen tabs with the test surface, the smooth surface pressed next to the polished plate, uppermost. Be sure the surface of the cutter is clean. 8.4.5 Make the reflectance tests, using method selected per 2.2, at least 2 but no more than 24 h after forming the test sheets, as their optical properties may change with time. 9.  Precision  The purpose of this Standard Practice is to make sheets with constant and reproducible surface characteristics. A statement of precision is not applicable. 10.  Keywords  Handsheets, Pulps, Reflectance, Handsheet formers, Brightness, Formation 11.  Additional information  11.1 Effective date of issue: May 22, 1997. 11.2 T 272 has been reclassified from an Official Method to a Standard Practice. Studies at the Pulp and Paper Research Institute of Canada (PAPRICAN) and the Finnish Pulp and Paper Institute (KCL) (2) indicate that the pH of the slurry can have a significant effect on sheet brightness. The pH of the water is specified at 6.5 ± 0.5 unless otherwise indicated. 11.3 Related Methods: Scandinavian Scan C-l 1; Canadian CPPA C-5; ISO 3688.  - 130-  Appendix VII T272 sp-97  Forming handsheets for reflectance testing 16 of pulp (sheet machine procedure)  Appendix A. 1  Sheet pressing and drying procedure.  A. 1.1 This TAPPI practice differs from other test methods used in world trade including SCAN, CPPA, and ISO in the manner in which the sheets are pressed and dried. In the TAPPI procedural method, the sheets are pressed in direct contact with the polished drying plate and dried in that condition. In the other methods, a filter paper is placed between the sheet and the plate before pressing and drying. Concern has been expressed that the difference in surface texture which may result from the different procedures may have an effect on the measured optical properties. A. 1.2 In the event that observed differences are suspected to be due to that difference in procedures, the user of the method may want to make an additional set of sheets with a filter paper inserted between the sheet and the plate prior to pressing and drying. Optical properties measured on the sheets produced by the two procedures will resolve those questions. A.2  Recycled pulps  A.2.1 With recycled pulp, the dispersion and the subsequent sheet formation may result in rinsing that does not occur as effectively in the papermaking process. As a result,, the brightness observed in actual use may be different from that determined by this handsheet procedure. In the event brightness-robbing contaminants are rinsed out, the sheet brightness could be higher than the brightness experienced in actual use. Conversely, components that enhance brightness could be washed out resulting in a handsheet lower in brightness than experienced in actual use. Caution should be exercised in relating brightness values from laboratory tests to what might be experienced in the paper making process. Alternate procedures such as determination of brightness on the pulp sheets as received could be considered. However, these should not be considered as conforming with this TAPPI Standard Practice. References 1.  Koon, C. M . , and Niemeyer, D. E., "The Influence of Certain Variables in Forming Brightness Handsheets," 114(5):30 (1942). Jousimaa, T., " K C L Y256-1, The Effect of Sheet Forming Conditions on Brightness," ISO/TC6/SC5 N 749.  Paper Trade J.  2.  Your comments and suggestions on this procedure are earnestly requested and should be sent to the TAPPI Divisions Administrator.  - 131 -  Technical B  Appendix VIII  Appendix VIII Raw Data The results in this appendix are divided into four different sections, V I , V2, V3, V4, as follow: •  VI:  Original experimental setup (Figure 4.1, 4.2, 4.3, and"4.5)  •  V2:  New cooling system and surface thermocouple (Figure 4.6)  •  V3:  New modifications of cathode, anode, mixer, and location of thermocouple (Figure 4.9 and 4.11)  •  V4:  Brightening experiments with modifications of the electro-brightening system mentioned in V2 and V3.  1.  Original Experiment No.: VI (Titanium cathode with polypropylene felt)  1. Initial experiment Experimental conditions: • Electrolyte: 1.5 Liter Solution (1.0M N a C 0 , 0.13M N a H C 0 , 0.03M NaSi0 , 0.007% M g S 0 7 H 0 , 0.01% DTP A) • Experimental time: 180 minutes • Mixing speed: 200rpm 2  3  3  4  Reactor Outside Wall Temperature (°Q V1.01 V1.02 V1.03  46 48 47  3  2  Voltage  Current  (V) 10.9±1.0 10.0±1.0 9.7±1.0  • • . • • •  Current set point: 20A Weight of pulp: 300g wet pulp Anode coolant inlet temperature: 12.9°C Anode coolant outlet temperature: 20.5°C Anode coolant flow rate: 0.2 1/min Pulp consistency: 4.2%  (A)  Brightness Gain (% ISO)  Yellowness Loss  20.0 20.0 20.0  10.2 13.0 11.7  8.5 9.2 8.6  - 132-  (%)  Hydrogen Peroxide Concentration (M) 0.006 0.008 0.007  Appendix VIII Raw Data 2. Experiment No.: V I . 1 - Temperature configuration Experimental conditions: • Electrolyte: 1.5 liter solution (1.0M N a C 0 , 0.13MNaHCO , 0.03M NaSi0 , 0.007% M g S 0 7 H 0 , 0.01% DTPA) • Final [ H 0 ] : 0.012 M • Anode coolant inlet temperature: 15°C 2  3  3  4  2  3  2  2  Experimental time: 180 minutes Mixing speed: 200 rpm Current set point: 20A No pulp Anode coolant flow rate: 0.2 1/min  Reactor Inner Reactor Outside Sidewall Wall Temperature Temperature (°C) (°C)  (Min)  Solution Temperature (°C)  15  36  48  30  2.0  30  38  51  31  9.0  45  42  53  34  16.0  60  48  64  38  20.0  75  48  61  40  19.0  90  48  60  41  19.0  105  48  60  41  17.0  120  48  60  41  16.0  135  49  60  42  16.0  150  49  60  42  16.0  165  51  60  43  16.0  180  51  60  43  16.0  Time  Coolant Outlet Temperature (°C)  3. Experiment No.: V I .2 - Temperature configuration Experimental conditions: • Electrolyte: 1.5 liter solution (1.0M N a C 0 , 0.13M N a H C 0 , 0.03M NaSi0 , 0.007% M g S 0 7 H 0 , 0.01% DTPA) • Anode coolant inlet temperature: 15°C 2  3  3  4  2  • Experimental time: 60 minutes • Mixing speed: 200 rpm • Current set point: 20A • No pulp • Anode coolant flow rate: 0.2 1/min Reactor Outside Coolant Outlet Hydrogen Peroxide Wall Temperature Temperature Concentration (M) (°Q (°C) 3  Experimental Time (Min)  Bulk Solution Temperature (°C)  0  25  19  16  0.002  15  42  29  19  0.002  30  45  34  17  0.002  45  45  37  16  0.002  60  48  38  15  0.003  - 133 -  Appendix VIII Raw Data 4. Experiment No.: VI.3 - Temperature configuration Experimental conditions: • Electrolyte: 1.5 liter solution (1.0M N a C 0 , 0.13M N a H C 0 , 0.03M NaSi0 , 0.007% M g S 0 7 H 0 , 0.01% DTP A) • Anode coolant inlet temperature: 13.5°C 2  3  3  4  Time  Solution Temperature  (Min)  <°c>  Experimental time: 90minutes Mixing speed: 200 rpm Current set point: 20A No pulp Anode coolant flow rate: 0.2 1/min  Reactor Outside Coolant Outlet Wall Temperature Temperature (°Q  <°o  28  0  3  2  • • . e •  18  15  Hydrogen Peroxide Concentration (M)  30  35  27  16  0.001  60  37  29  16  0.002  90  39  31  17  0.002  5. Experiment No.: V I . 4 - Temperature configuration Experimental conditions: • Electrolyte: 1.5 liter solution (1.0M N a C 0 , 0.13M N a H C 0 , 0.03M NaSi0 , 0.007% M g S 0 7 H 0 , 0.01% DTP A) • Anode coolant inlet temperature: 14.5°C 2  3  3  4  Time  3  2  • • • • •  Experimental time: 180 minutes Mixing speed: 200 rpm Current set point: 20A No pulp Anode coolant flow rate: 0.2 1/min  (Min)  Solution Temperature (°C)  0  25  18  17  30  35  27  17.5  0.001  60  37  29  18  0.002  90  39  31  19  0.003  120  43  34  19  0.003  150  49  38  18  0.003  180  55  45  32  0.003  Reactor Outside Coolant Outlet Wall Temperature Temperature C°C) (°C)  - 134-  Hydrogen Peroxide Concentration (M)  Appendix VIII Raw Data 6. Experiment No.: V I .5 - Temperature configuration Experimental conditions: • Electrolyte: 1.5 liter solution (1.0M N a C 0 , 0.13M N a H C 0 , 0.03M NaSi0 , 0.007% M g S 0 7 H 0 , 0.01% DTPA) • Anode coolant inlet temperature: 13.5°C 2  3  3  4  Time  Experimental time: 180 minutes Mixing speed: 200 rpm Current set point: 20A No pulp Anode coolant flow rate: 0.2 1/min  3  2  (Min)  Solution Temperature (°C)  0  23  7  30  41  60  Reactor Outside Coolant Outlet Wall Temperature Temperature (°C) (°C) .  Hydrogen Peroxide Concentration (M)  37  16 17  0.001  45  40  16  0.002  90  49  43  17  0.002  120  51  45  16  0.003  150  67  50  20  0.003  180  65  57  32  0.003  7. Experiment No.: V I .6 - Temperature configuration (re-electroplating of platinum: first time) Experimental conditions: • Electrolyte: 1.5 liter solution (1.0M N a C 0 , 0.13MNaHCO , 0.03MNaSiO , 0.007% M g S 0 7 H 0 , 0.01% DTPA) • Anode coolant inlet temperature: 13°C 2  3  3  4  Time  3  2  • • • • •  July 03, 98  Experimental time: 180 minutes Mixing speed: 200 rpm Current set point: 20A No pulp Anode coolant flow rate: 0.2 1/min  (Min)  Solution Temperature (°C)  0  23  17  17  30  37  26  16  0.028  60  37  27  18  0.036  90  38  28  20  0.033  120  39  29  17  0.029  150  40  30  19  0.025  180  41  30  20  0.023  Reactor Outside Coolant Outlet Wall Temperature Temperature (°C) (°C)  - 135 -  Hydrogen Peroxide Concentration (M)  Appendix VIII Raw Data 8. Experiment No.: V I .7 - Temperature configuration (re-electroplating of platinum: first time) Experimental conditions: • Electrolyte: 1.5 liter solution (1.0M N a C 0 , 0.13MNaHCO , 0.03MNaSiO , 0.007% M g S 0 7 H 0 , 0.01% DTP A) • New Pt coating (second run) • Anode coolant inlet temperature: 13.5°C 2  3  3  4  3  2  July 14, 98  Experimental time: 120 minutes Mixing speed: 200 rpm Current set point: 20A No pulp Anode coolant flow rate: 0.2 1/min  Time  Solution Temperature  (Min)  (°C)  0  27  25  18  30  38  31  16  0.003  60  39  31  17  0.005  90  39  32  18.5  0.008  120  39  32  18  0.008  Reactor Outside Coolant Outlet Wall Temperature Temperature (°C) (°C)  9. Experiment No.: VI.8 - Temperature configuration (re-electroplating of -platinum first time) Experimental conditions: • Electrolyte. 1.5 liter solution (1.0M N a C 0 , 0.13MNaHCO , 0.03MNaSiO , 0.007% M g S 0 7 H 0 , 0.01% DTP A) • New Pt coating (third run) • Anode coolant inlet temperature: 13.5°C 2  3  3  4  Time  3  2  Solution Temperature  Hydrogen Peroxide Concentration (M)  July 17, 98  Experimental time: 180 minutes Mixing speed: 200 rpm Current set point: 20A No pulp Anode coolant flow rate: 0.2 1/min  Reactor Outside Coolant Outlet Wall Temperature Temperature (°C) (°Q  Hydrogen Peroxide Concentration (M)  (Min)  <°o  0  26  18  17  30  35  24  19  0.007  60  35  26  17  0.010  90  37  27  18  0.012  120  38  27  18  0.018  150  46  32  19  0.005  180  47  36  18.5  0.005  - 136-  Appendix VIII Raw Data 10. Experiment No.: V I . 9 - Temperature configuration (re-electroplating of -platinum first time) Experimental conditions: • Electrolyte: 1.5 liter solution (1.0M N a C 0 , 0.13MNaHCO , 0.03M NaSi0 , 0.007% M g S 0 7 H 0 , 0.01% DTPA) • New Pt coating (fourth run) • Anode coolant inlet temperature: 15°C 2  3  3  4  Time  3  2  July 23, 98  Experimental time: 90 minutes Mixing speed: 200 rpm Current set point: 20A No pulp Anode coolant flow rate: 0.21 1/min  (Min)  Solution Temperature (°C)  0  29  21  17  30  38  29  19  0.005  60  39  32  18  0.007  90  41  33  20  0.008  Reactor Outside Coolant Outlet Wall Temperature Temperature (°Q (°C)  11. Experiment No.: V1.10 - Temperature configuration (re-electroplating of -platinum first time) Experimental conditions: • Electrolyte: 1.5 liter solution (1.0M N a C 0 , 0.13M N a H C 0 , 0.03M NaSi0 , 0.007% M g S 0 7 H 0 , 0.01% DTPA) • New Pt coating (fifth run) • Anode coolant inlet temperature: 1°C 2  3  3  4  Time  3  2  Hydrogen Peroxide Concentration (M)  July 24, 98  Experimental time: 60 minutes Mixing speed: 200 rpm Current set point: 20A No pulp Anode coolant flow rate: 0.2 1/min  (Min)  Solution Temperature (°Q  0  25  19  4  30  35  25  4  0.007  60  37  27  4  0.007  Reactor Outside Coolant Outlet Wall Temperature Temperature (°C) (°Q  - 137-  Hydrogen Peroxide Concentration (M)  Appendix VIII Raw Data 12. Experiment No.: V I . 11 - Temperature configuration Experimental conditions: • Electrolyte: 1.5 liter solution (1.0M N a C 0 , 0.13MNaHCO , 0.03M NaSi0 , 0.007% M g S 0 7 H 0 , 0.01% DTP A) • [ H 0 ] : 0.008M • Initial p H = 10.63 • Anode coolant inlet temperature: 13.5°C 2  3  3  4  2  13  3  2  2  Dec. 10, 98  Experimental time: 180 minutes Mixing speed: 200 rpm Current set point: 20A 1 % pulp consistency, 300g wet pulp Temperature control: 50°C Anode coolant flow rate: 0.2 1/min  Time  Current  Voltage  Reactor Outside Wall Temperature  (Min)  (A)  (V)  0  20  15.4  (°o  60  20  120 180  Coolant Outlet Temperature  C°C)  Mixing Speed (RPM)  18  17  200  10.5  24  18  200  20  11.8  26  16  400  20  12.6  28  18  400  Experiment No.: V I . 12 - Temperature Configuration  Experimental conditions: • Electrolyte: 1.5 liter solution (1.0M N a C 0 , 400ppm M g ) • [ H 0 ] : 0.0095M Initial p H = 10.0 Temperature control: 50°C Anode coolant inlet temperature: 15°C 2+  2  2  3  2  Time  Current  Voltage  (Min)  (A)  0  Jan. 25, 99  Experimental time: 180 minutes Mixing speed: 200 rpm Current set point: 20A 1 % pulp consistency Weight of wet pulp: 300g Anode coolant flow rate: 0.2 1/min  (V)  Reactor Outside Wall Temperature (°C)  Coolant Outlet Temperature (°C)  Mixing Speed (RPM)  20  15.4  14  18  200  60  20  11.3  24  19  400  120  20  10". 9  26  17  400  180  20  11.7  24  18  400  Brightness gain: Yellowness loss:  5.2 (46.8) 8.1 (28.7)  - 138 -  Appendix VIII Raw Data 14  Experiment No.: V I . 13 - Temperature configuration  Experimental conditions: • Electrolyte: 1.5 liter solution (1.0M N a C 0 , 400ppm M g ) [ H 0 ] : 0.006M Initial pH = 10.94 Temperature control: 50°C Anode coolant inlet temperature: 15°C 2+  2  3  2  2  Time  Current  Voltage  (Min)  (A)  0  Jan. 26, 99  Experimental time: 180 minutes Mixing speed: 200 rpm Current set point: 20A 1 % pulp consistency Weight of wet pulp: 300g Anode coolant flow rate: 0.2 1/min  (V)  Reactor Outside Wall Temperature (°C)  Coolant Outlet Temperature (°C)  Mixing Speed (RPM)  20  15.4  14  18  200  60  20  11.8  24  17  400  120  20  12.2  23  18  400  180  20  11.9  23  18  400  Brightness gain: Yellowness loss:  15  10.1 9  (51.8) (27.5).  Experiment No.: V I . 14 - Temperature configuration  Jan. 27, 99  Experimental conditions: • Electrolyte: 1.5 liter solution (1.0M N a C 0 , 400ppm M g ) [ H 0 ] : 0.005M Initial p H = 11.01 Temperature control: 40°C Anode coolant inlet temperature: 15°C 2+  2  2  3  2  Experimental time: 180 minutes Mixing speed: 200 rpm Current set point: 40A 1 % pulp consistency Weight of wet pulp: 300g Anode coolant flow rate: 0.2 1/min Reactor Outside Wall Coolant Outlet Temperature Temperature (°C) (°C)  Time  Current  Voltage  (Min)  (A)  (V)  0  40.0  17.5  33  19  200  60  37.0  20.1  39  20  400  120  33.2  20.1  40  20  400  180  30.6  20.1  39  20  400  Brightness gain: Yellowness loss  13.0(54.1) 12.3 (24.4)  - 139-  Mixing Speed (RPM)  Appendix VIII Raw Data 16  Experiment No.: V I . 15 - Temperature configuration (re-electroplating of -platinum second time)  Experimental conditions: • Electrolyte: 1.5 liter solution (1.0M N a C 0 , 400ppm M g ) • [ H 0 ] : 0.025M • Initial p H = 10.0 • Temperature control: 40°C • Anode coolant inlet temperature: 15°C 2+  2  3  2  2  Time  Current  Voltage  (Min)  (A)  0  • • • • • •  Feb. 1, 99  Experimental time: 180 minutes Mixing speed: 200 rpm Current set point: 40A 1 % pulp consistency Weight of wet pulp: 300g Anode coolant flow rate: 0.2 1/min  (V)  Reactor Outside Wall Temperature (°C)  Coolant Outlet Temperature (°C)  Mixing Speed (RPM)  40.0  19.7  24  20  200  60  40.0  18.8  28  19  400  120  39.8  20.1  28  19  400  180  12.3  20.1  32  19  400  17  Experiment No.: V. 1.16 - Temperature configuration  Experimental conditions: • Electrolyte: 1.5 liter solution (1.0M N a C 0 , 400ppm M g ) • [ H 0 ] : 0.025M • Initial pH = 10.58 • Temperature control: 40°C • Anode coolant inlet temperature: 15°C 2+  2  2  3  2  Time  Current  Voltage  (Min)  (A)  0  • • • • • •  Feb. 3, 99  Experimental time: 58 minutes Mixing speed: 200 rpm Current set point: 40A 1 % pulp consistency Weight of wet pulp: 300g Anode coolant flow rate: 0.21/min  (V)  Reactor Outside Wall Temperature (°C)  Coolant Outlet Temperature (°C)  Mixing Speed (RPM)  40.0  20.1  24  18  200  9  35.5  20.1  24  19  200  29  27.7  20.1  26  19  200  58 17.7 20.1 Observation: huge voltage drop  28  18  400  - 140-  Appendix VIII Raw Data  2. 18  Experiment No.: V2 Experiment No.: V2.01 - Stainless steel cathode with polypropylene felt  Experimental conditions: • Electrolyte: 1.5 Liter Solution (1.0M Na C0 ) • Experimental time: 73 minutes • Mixing speed: 200rpm • Initial p H = 11.60 2  3  • • • • •  Apr. 21, 99  Current set point: 40A No pulp Anode coolant inlet temperature: 1°C Anode coolant outlet temperature: 5°C Anode coolant flow rate: 6 1/min  Time  Current  Voltage  (Min)  (A)  (V)  Reactor Outside Wall Temperature (°C)  0  29.5  20.1  23  10  . 29.5  20.1  42  20  39.6  20.1  49  23  40  19.5  53  28  39.9  20  60  30  38.3  20.1  62  37  39.4  20.1  67  50  40  19.5  69  60  39.2  20.1  68  0.007  70  37.9  20.1  68  0.008  73  37  20.1  67  0.007  - 141 -  Hydrogen Peroxide Concentration (M)  Appendix VIII Raw Data 19  Experiment No.: V2.2 - Stainless steel cathode with polypropylene felt  Apr. 26, 99  Experimental conditions: • Electrolyte: 1.5 Liter Solution (1.0M Na C0 ) • Experimental time: 147 minutes • Mixing speed: 200rpm • Initial pH = 11.66 2  20  3  • • • • •  Current set point: 40A No pulp Anode coolant inlet temperature: 1°C Anode coolant outlet temperature: 5°C Anode coolant flow rate: 6 1/min  Time  Current  Voltage  (Min)  (A)  (V)  Reactor Outside Wall Temperature (°C)  0  22.6  20.1  27  10  31.9  20.1  32  20  39.2  20.1  45  30  40  17.5  59  40  40  17.2  62  50  40  17.3  62  60  40  17.5  63  0.010  80  40  17.7  64  0.010  85  40  17.8  64  0.011  95  40  18  64  0.011  107  40  18.5  64  113  40  18.7  65  145  40  20.1  65  147  39.7  20.1  65  Hydrogen Peroxide Concentration (M)  0.075  Experiment No.: V2.3 - Stainless steel cathode with polypropylene felt  • Electrolyte: 1.5 Liter Solution (1.0M Na C0 ) • Experimental time: 10 minutes • Electrolyte temperature control: 20°C • Initial p H = 11.66 2  3  Time  Current  (Min)  (A)  0  Apr. 28, 99  Current set point: 40A No pulp; Mixing speed: 200rpm Anode coolant inlet temperature: 1°C Anode coolant flow rate: 6 1/min Anode resistance: 0.08f2  Voltage (V)  Reactor Outside Wall Temperature (°C)  Hydrogen Peroxide Concentration (M)  27.9  20.1  24  0.003  5  35.3  20.1  39  0.003  10  35.7  20.1  41  0.003  - 142-  Appendix VIII Raw Data 21  Experiment No.: V2.4 - Stainless steel cathode with polypropylene felt  • Electrolyte: 1.5 Liter Solution (1.0M Na2CC>3) • Experimental time: 90 minutes • Mixing speed: 200rpm • No pulp • Initial p H = 11.6  • • • • •  Current set point: 20A Anode coolant inlet temperature: 1°C Anode coolant outlet temperature: 5°C Anode coolant flow rate: 6 1/min Anode resistance: 0.08Q (cool); 0.11Q (hot)  Time  Current  Voltage  (Min)  (A)  (V)  Reactor Outside Wall Temperature £Cj  0  20  173  19  5  20  17  21  10  20  16J?  22  15  20  16A  22  20  20  16T  23  25  20  16.5  24  30  20  16_6  24  35  20  16/7  24  40  20  167  24  45  20  16J5  24  50  20  16J*  24  55  20  16j?  24  60  20  16_6  26  70  20  16J)  26  80  20  16J5  25  90  20  16.8  25  - 143 -  Apr. 28, 99  Hydrogen Peroxide Concentration (M)  _  0.007 0.007  0.008 0.008 0.008  Appendix VIII Raw Data 22  Experiment No.: V2.5 - Stainless steel cathode with polypropylene felt  • Electrolyte: 1.5 Liter Solution (1.0M N a C 0 , 400ppm M g ) • Experimental time: 80 minutes • Mixing speed: 200rpm • No pulp • Initial p H = 11.6 2+  2  3  May 13, 99  Current set point: 20A Anode coolant inlet temperature: 1°C Anode coolant outlet temperature: 5°C • Anode coolant flow rate: 6 1/min • Anode resistance: 0.08Q (cool); 0 . H Q (hot)  Time  Current  Voltage  (Min)  (A)  (V)  Reactor Outside Wall Temperature (°C)  0  20  16.6  18  5  20  16  21  10  20  16.1  21  15  20  16.1  22  20  20  16  23  25  20  16.1  23  30  20  16.1  23  35  20  16.2  23  40  20  16.1  23  45  20  16.1  23  50  20  16.2  23  55  20  16.2  24  0.011  60  20  16.2  24  0.011  66  20  16.3  24  70  20  16.3  24  0.011  80  20  16.4  24  0.011  - 144-  Hydrogen Peroxide Concentration (M)  0.011 0.011  Appendix VIII Raw Data 23 •  Experiment No.: V2.6 - Stainless steel cathode with microporous polypropylene May 17, 99 Electrolyte: 1.5 Liter Solution (1.0M Current set point: 20A N a C 0 , 400ppm M g ) Anode coolant inlet temperature: 1°C Experimental time: 90 minutes Anode coolant outlet temperature: 5°C Mixing speed: 200rpm Anode coolant flow rate: 6 1/min No pulp Anode resistance: 0.08Q (cool); Initial p H = 11.6 0 . H Q (hot) 2+  2  • • • •  24  3  Time  Current  Voltage  (Min)  (A)  0  20  (V) 16.5  30  20  16.3  23  40  20  16.2  23  50  20  16.3  24  0.006  60  20  16.2  24  0.006  70  20  16.3  24  0.006  80  20  16.4  24  0.006  90  20  16.5  24  0.006  Reactor Outside Wall Temperature (°C)  Hydrogen Peroxide Concentration (M)  20  Experiment No.: V2.7 - Stainless steel cathode with polypropylene string  • Electrolyte 1.5 Liter Solution (1.0M Na C0 ) • Experimental time: 90 minutes • Mixing speed: 200rpm • No pulp; initial pH = 11.6 Time Current Voltage 2  3  0.007  May 19, 99  • Current set point: 20A • Anode coolant inlet temperature: 1°C • Anode coolant outlet temperature: 5°C • Anode coolant flow rate: 6 1/min • Total resistance: 80.23Q (hot); Reactor Outside Wall Hydrogen Peroxide Temperature Concentration (°C) (M)  (Min)  (A)  (V)  0  20  17.1  19  10  20  16.6  21  20  20  16.2  22  30  20  16.2  23  0.004  40  20  16.2  23  0.004  50  20  16.2  23  0.004  60  20  16.3  24  0.004  70  20  16.4  24  0.004  80  20  16.4  25  0.004  90  20  16.4  24  0.004  - 145 -  Appendix VIII Raw Data  3. 25  Experiment No.: V3 Raw Data Experiment No.: V3.1 - Zirconium cathode with polypropylene string  • Electrolyte: 1.5 Liter Solution (1.0M  • Current set point: 20A  Na2CC>3) • Experimental time: 90 minutes • Mixing speed: 200rpm • No pulp; initial pH = 11.6  e • • •  Jun. 8, 99  Anode coolant inlet temperature: 1°C Anode coolant outlet temperature: 5°C Anode coolant flow rate: 6 1/min No mixer  Time  Current  Voltage  (Min)  (A)  (V)  Reactor Temperature (°C)  0  20  19.9  18  1  20  18.6  19  5  20  17.2  23  7.5  20  16.9  25  10  20  16.6  27  13  20  16.5  28  15  20  16.4  29  22.4  20  16.2  30  25  20  16.1  31  30  20  16.1  31  35  20  16.1  32  0.010  40  20  16  32  0.011  50  20  16.1  32  0.013  60  20  16.2  32  0.013  70  20  16.2  32  0.013  80  20  16.3  32  0.013  90  20  16.3  33  0.013  - 146 -  Hydrogen Peroxide Concentration (M)  Appendix VIII Raw Data ,6 Experiment No.: V3.2 - Zirconium cathode with diaphragm • Electrolyte: 1.5 Liter Solution (1.0M N a C 0 , 400ppm M g ) • Experimental time: 140 minutes • Mixing speed: 200rpm • No pulp; initial p H = 11.6 2+  2  3  • • • • •  June 9, 99  Current set point: 20A Anode coolant inlet temperature: 1°C Anode coolant outlet temperature: 5°C Anode coolant flow rate: 6 1/min No mixer  Time  Current  Voltage  (Min)  (A}  £V}  Reactor Temperature £CJ  0  20  19J  20  2  20  18,2  21  3.5  20  T7_6  22  5.5  20  T7_3  24  7.5  20  17  _26  10  20  16_9  27  13  20  16/7  29  15  20  16/7  29  18  20_  16_5  29  20  20  16_4  30  22.5  20  31  25  20  16A 163  30  20  16_2  32  35  20  163  32  40  20  \_62  32  0.028  50  20  16.3  32  0.031  60  20  163  33_  0.034  70  20  16_4  33  0.036  80  20  16A  33  0.037  90  20  16A  33  0.037  100  20  16.5  33  0.038  HQ  20  16.6  33  0.039  120  20  16_6  33  0.039  130  20  16/7  33  0.040  140  20  16.9  34  0.040  - 147-  Hydrogen Peroxide Concentration (M)  3J  0.024  Appendix VIII Raw Data 27  Experiment No.: V3.3 - Zirconium cathode with diaphragm Electrolyte: 1.5 Liter Solution (1.0M N a C 0 , 400ppm M g ) Experimental time: 60 minutes Mixing speed: 200rpm No pulp Initial p H = 11.6  • • • • • •  2+  2  3  June 10, 99  Current set point: 20A Electrolyte temperature set point: 40°C Anode coolant inlet temperature: 1°C Anode coolant outlet temperature: 5°C Anode coolant flow rate: 6 1/min No mixer  Time  Current  Voltage  (Min)  (A)  (V)  Reactor Temperature (°C)  0  14  20  7  1  14.7  20  9  2  15.8  20  11  3  16.5  20  13  4  17.3  20  13  5  18.3  20  16  6  18.9  20  17  7  19.8  20  7.3  20  20  19  7.5  20  19.9  19  8  20  19.7  20  9  20  19.1  22  10  20  18.8  23  12  20  18.3  24  13  20  18.1  26  15  20  17.7  27  20  20  17.2  29  30  20  16.7  31  0.019  40  20  16.7  32  0.026  50  20  17  33  0.029  55  19.9  20  57  17.3  20  58  16.5  20  60  20  20  34  0.031  .  Hydrogen Peroxide Concentration (M)  19  0.009  65 14.1 20 34 0.031 Some kind of oxidation or chemicals form on the zirconium tube, it was observed after tearing out the diaphragm  - 148 -  Appendix VIII Raw Data 28  Experiment No.: V3.4 - Zirconium cathode without diaphragm Electrolyte: 1.5 Liter Solution (1.0M N a C 0 , 400ppm M g ) Experimental time: 180 minutes Mixing speed: 200rpm No pulp Initial p H = 11.6 2+  2  3  June 22, 99  Current set point: 20A Electrolyte temperature set point: 20°C Anode coolant inlet temperature: 1°C Anode coolant outlet temperature: 5°C Anode coolant flow rate: 6 1/min No mixer  Time  Current  Voltage  (Min)  (A)  (V)  Reactor Temperature (°C)  0  19.3  20  13  0.5  20  20  13  1  20  19.3  15  Hydrogen Peroxide Concentration (M)  2  -  20  18.3  17  4  • 20  17.5  18  5  20  17.2  19  6  20  16.9  20  10  20  16.4  23  15  20  16.2  26  20  20  16  27  30  20  15.7  29  0.019  40  20  15.7  29  0.023  50  20  15.6  30  0.027  60  20  15.7  31  0.028  70  20  15.7  31  0.030  80  20  15.7  31  0.030  90  20  15.7  31  0.032  100  20  15.8  31  0.032  no  20  15.8  31  0.033  120  20  15.9  31  0.034  130  20  15.9  . 31  0.034  140  20  16  31  0.034  150  20  16  31  0.034  160  20  16.1  32  0.034  170  20  16.1  32  0.035  16.1  32  0.035  180 20 Zirconium cathode was corroded  - 149-  0.011  Appendix VIII Raw Data '.9 Experiment No.: V3.5 - Uncovered zirconium cathode • Electrolyte: 1.5 Liter Solution (1.0M N a C 0 , 400ppm M g ) • Experimental time: 180 minutes • Mixing speed: 200rpm • No pulp • Initial p H = 11.6 2+  2  3  Time  Current  (Min)  (A)  0  • • • • • •  June 24, 99  Current set point: 20A Electrolyte temperature set point: 20°C Anode coolant inlet temperature: 1°C Anode coolant outlet temperature: 5°C Anode coolant flow rate: 6 1/min Cathode configuration: (A)  Voltage  Reactor Temperature £Cj  176  20  14  1  18/7  20  14  3  20  18j>  17  5  20  VIS  17  7  20  17J  19  9  20  16J5  21  10  20  16_6  21  12  20  16J  22  15  20  16_4  22  20  20  16_2  24  30  20  16J  25  0.020  40  20  16  27  0.025  50  20  16_  28  0.029  60  20  16  29_  0.031  70  20  119  29  0.034  80  20  119  29  0.035  90  20  1_5_9  30  0.037  100  20  16  29  0.037  110  20  16  30  0.038  120  20  16J  30  0.039  130  20  16  30  0.039  140  20  16J  31  0.040  150  20  16_2  31  0.040  160  20  163  31  0.040  170  20  16A  3J  0.040  180  20  16.5  31  0.040  - 150-  Hydrogen Peroxide Concentration (M)  0.013  Appendix VIII Raw Data 30  Experiment No.: V3.6 - Uncovered zirconium cathode  • Electrolyte: 1.5 Liter Solution (1.0M N a C 0 , 400ppm M g ) • Experimental time: 180 minutes • Mixing speed: 200rpm • No pulp • Initial pH = 11.6 2+  2  3  • • • • • •  June 25, 99  Current set point: 20A Electrolyte temperature set point: 60°C Anode coolant inlet temperature: 2°C Anode coolant outlet temperature: 5°C Anode coolant flow rate: 6 1/min Cathode configuration: (A)  Time  Current  Voltage  (Min)  (A)  (V)  Reactor Temperature (°C)  0  16.5  20  11  1  17.7  20  12  3  20  18.8  19  5  20  17.1  27  7  20  16.1  33  9  20  15  35  10  20  13.9  38  15  20  13.4  44  25  20  12.9  51  30  20  12.7  52  0.025  40  20  12.7  54  0.030  45  20  12.7  54  50  20  12.8  54  0.034  60  20  12.8  55  0.039  70  20  12.8  56  0.042  80  20  12.9  56  0.044  90  20  12.9  56  0.046  100  20  12.9  57  0.047  110  20  12.9  57  0.048  120  20  13  57  0.049  130  20  13  57  0.048  140  20  13.1  57  0.049  150  20  13.2  57  0.051  160  20  13.2  58  0.050  170  20  13.2  58  0.051  180  20  13.3  58  0.050  - 151 -  Hydrogen Peroxide Concentration (M)  0.015  Appendix VIII Raw Data <' 1 Experiment No.: V3.7 - Zirconium tube cathode • Electrolyte: 1.5 Liter Solution (1.0M N a C 0 , 400ppm M g ) • Experimental time: 180 minutes • Mixing speed: 200rpm • No pulp • Initial p H = 11.6 2+  2  3  • • • • • •  June 26, 99  Current set point: 20A Electrolyte temperature set point: 60°C Anode coolant inlet temperature: 2°C Anode coolant outlet temperature: 5°C Anode coolant flow rate: 6 1/min Cathode configuration: (A)  Time  Current  Voltage  (Min)  (Aj  QQ  Reactor Temperature (°Q  0  133  19S  5  1  15/7  19_9  7_  3  193  193  14  5  20  18  23  7  20  16_5  29  9  20  15J5  32  10  20  ISA  34  15  20  13J5  36  20  20  13_3  43  30  20  123  52  0.025  40  20  123  53  0.031  50  20  123  55  0.036  60  20  123  56  0.039  70  20  123  56  0.041  80  20  12,6  56  0.043  90  20  127  56  0.045  100  20  12/7  56  0.046  HQ  20  118  56  0.046  120  20  12j?  56  0.047  130  20  12_9  57  0.047  140  20  12_9  57_  0.047  150  20  119  57  0.047  160  20  13  57  0.047  170  20  13J  57  0.047  180  20  13.2  58  0.047  - 152-  Hydrogen Peroxide Concentration (M)  .  0.014  Appendix VJII Raw Data 2  Experiment No.: V.3 8  June 26, 99  • Electrolyte: 1.5 Liter Solution (1.0M N a C 0 , 400ppm M g ) • Experimental time: 180 minutes • Mixing speed: 200rpm • No pulp • Initial p H = 11.6 2+  2  3  Time  Current  (Min)  Voltage  • • • • • •  Current set point: 20A Electrolyte temperature set point: 60°C Anode coolant inlet temperature: 16°C Anode coolant outlet temperature: 19°C Anode coolant flow rate: 61/min Cathode configuration: (A) Reactor Temperature  Hydrogen Peroxide Concentration  LYJ  £9  (M)  0  19^9  19_9  2J  1  20  VL5  22  3  20  15.5  31  5  20  14_4  38  7  20  13_5  43  9  20  119  47  10  20  12/7  49  15  20  1_1_9  56  20  20  1_L5  59  30  20  1_1_3  62  0.018  40  20  1L3  63  0.022  50  20  11J  62  0.026  60  20  11/7  6J  0.029  70  20  1_1_8  6J  0.032  80  20  1_L9  61  0.035  90  20  12  6J  0.037  100  20  12  61  0.038  110  20  Y2A  6J  0.041  120  20  111  61  0.042  130  20  122  6J  0.042  140  20  12_2  6J  0.043  150  20  123  6J  0.043  160  20  123  62  0.043  170 180  20 20  12A 12.4  62 62  0.044 0.044  - 153 -  0.010  Appendix VIII Raw Data 3  Experiment No.: V.3 9  June 26, 99  • Electrolyte: 1.5 Liter Solution (1.0M N a C 0 , 400ppm M g ) • Experimental time: 180 minutes • Mixing speed: 200rpm • No pulp • Initial pH = 11.6 2+  2  3  • • • • • •  Current set point: 20A Electrolyte temperature set point: 20°C Anode coolant inlet temperature: 1°C Anode coolant outlet temperature: 5°C Anode coolant flow rate: 6 1/min Cathode configuration: (A)  Time  Current  Voltage  (Min)  (A)  (YJ  Reactor Temperature ^CJ  0  \%3  19_9  17  1  197  19_9  17  3  20  18J  19  5  20  YL9  23  7  20  175  24  9  20  Y73  26  10  20  17J  27  15  20  167  28  20  20  1^6  30  30  20  163  3J  0.025  40  20  16_2  32  0.030  50  20  16_2  32  0.034  60  20  16_2  33  0.035  70  20  16_2  33  0.038  80  20  16_2  33  0.039  90  20  163  33  0.040  100  20  16_4  33  0.040  110  20  33  0.041  120  20  16A 16A  33  0.041  130  20  16J5  33  0.042  140  20  I(y6  33  0.042  150  20  167  34  0.043  160  20  16.9  33  0.044  170  20  16^9  33  0.044  180  20  17  34  0.044  - 154-  Hydrogen Peroxide Concentration (M)  0.013  Appendix VIII Raw Data 4 Experiment No.: V.3 10  June 27, 99  • Electrolyte: 1.5 Liter Solution (1.0M Na2C03, 400ppm M g ) • Experimental time: 180 minutes • Mixing speed: 200rpm • No pulp • Initial pH = 11.6  • • • • • •  2+  Current set point: 20A Electrolyte temperature set point: 60°C Anode coolant inlet temperature: 1°C Anode coolant outlet temperature: 5°C Anode coolant flow rate: 6 1/min Cathode configuration: (A)  Time  Current  Voltage  (Min)  (A)  (V)  Reactor Temperature £Cj  0  20  19J>  20  1  20  18J8  21  3  20  17J  24  5  20  16_  31  7  20  ISA  36  9  20  14J  39  10  20  41  15  20  142 132  47  20  20  12J5  5J  30  20  12A  53  0.023  40  20  12A  54  0.028  50  20  123  56  0.032  60  20  12A  56  0.036  70  20  12_4  56  0.038  80  20  12J5  56  0.039  90  20  12_5  56  0.040  100  20  1Z6  57  0.041  110  20  12/7  56  0.041  120  20  12_8  57  0.041  130  20  1Z9  57  0.042  140  20  1Z9  57  0.042  150  20  13  57  0.042  160  20  13A  57  0.042  170  20  13J  57  0.043  180  20  13.1  57  0.043  - 155 -  Hydrogen Peroxide Concentration (M)  0.013  Appendix VIII Raw Data 35  June 30, 99  Experiment No.: V . 3 11  • Electrolyte: 1.5 Liter Solution (1.0M N a C 0 , 400ppm M g ) • Experimental time: 80 minutes • Mixing speed: 200rpm • No pulp • Initial pH = 10.5 (controlled by N a H C 0 ) 2+  2  3  3  Current set point: 20A Electrolyte temperature set point: 60°C Anode coolant inlet temperature: 0°C Anode coolant outlet temperature: 5°C Anode coolant flow rate: 6 1/min Cathode configuration: (A)  Time  Current  Voltage  (Min)  (A)  (V)  Reactor Temperature (°Q  0  17.2  20  12  1  18.4  20  13  2  19.8  20  14  3  20  19.2  16  4  20  18.4  17  5  20  17.8  21  6  20  17.2  24  7  20  16.6  28  8  20  16  31  9  20  15.6  33  10  20  14.9  37  15  20  13.8  43  20  20  13  49  30  20  12.3  53  0.008  40  20  12.2  56  0.006  50  20  12.2  56  0.007  60  20  12.2  57  0.007  70  20  12.2  57  0.007  80  20  12.3  57  0.008  - 156-  Hydrogen Peroxide Concentration (M)  0.009  Appendix VIII Raw Data 6  Experiment No.: V.3 12  July 1, 99  • Electrolyte: 1.5 Liter Solution (1.0M N a C 0 , 400ppm M g ) • Experimental time: 180 minutes • Mixing speed: 200rpm • No pulp • Initial pH = 11.85; final pH = 11.0 2+  2  3  • • • o • •  Current set point: 20A Electrolyte temperature set point: 60°C Anode coolant inlet temperature: 1°C Anode coolant outlet temperature: 5°C Anode coolant flow rate: 6 1/min Cathode configuration: (A)  Time  Current  Voltage  (Min)  (A)  (V)  Reactor Temperature £Cj  0  16J5  20  10  1  VL9  20  11  3  20  1^6  19  5  20  16j?  26  7  20  15.7  32  9  20  14_8  36  10  20  14j>  37  15  20  114  44  20  20  12j?  48  30  20  \2A  52  0.028  40  20  123  53  0.034  50  20  12.3  53  0.040  60  20  123  54  0.044  70  20  12_4  54  0.049  80  20  12A  54  0.050  90  20  12_5  54  0.052  100  20  12_5  54  0.055  110  20  12_6  54  0.056  120  20  127  54  0.057  130  20  127  54  0.058  140  20  12J  55  0.059  150  20  12J  56  0.059  160  20  12j)  56  0.060  170  20  ]Z9  56^  0.060  180  20  12.9  56  0.061  - 157-  Hydrogen Peroxide Concentration (M)  0.015  Appendix VIII Raw Data 37  July 1, 99  Experiment No.: V.3 13  • Electrolyte: 1.5 Liter Solution (1.0M N a C 0 , 400ppm M g ) • Experimental time: 90 minutes • Mixing speed: 200rpm • No pulp • Initial pH = 10.5; final pH = 10.2 (controlled by NaHCQ ) Time Current Voltage 2+  2  3  • • • • • •  Current set point: 20A Electrolyte temperature set point: 60°C Anode coolant inlet temperature: 1°C Anode coolant outlet temperature: 5°C Anode coolant flow rate: 6 1/min Cathode configuration: (A)  3  (Min)  (A)  (V)  Reactor Temperature (°Q  0  17.8  20  12  1  19.1  20  13  2  20  19.5  14  3  20  18.9  16  4  20  18.4  18  5  20  18  19  6  20  17.8  21  7  20  17.1  24  8  20  16.7  27  9  20  15.9  29  10  20  15.4  33  15  20  13.8  42  0.012  20  20  13  48  0.012  30  20  12.3  53  0.011  40  20  12.2  54  0.010  50  20  12.1  55  0.009  60  20  12.2  56  0.009  70  20  12  56  0.009  80  20  12.1  56  0.009  90  20  12.2  56  0.009  - 158 -  Hydrogen Peroxide Concentration (M)  Appendix VIII Raw Data 8  Experiment No.: V.3 14  July 7, 99  • Electrolyte: 1.5 Liter Solution (1.0M N a C 0 , 400ppm M g ) • Experimental time: 180 minutes • Mixing speed: 200rpm • No pulp • Initial pH = 11.6 2+  2  3  • • • • • •  Current set point: 20A Electrolyte temperature set point: 20°C Anode coolant inlet temperature: 1°C Anode coolant outlet temperature: 5°C Anode coolant flow rate: 6 1/min Cathode configuration: (A)  Time  Current  Voltage  (Min)  (A)  (V)  Reactor Temperature £ Q  0  153  20  8  1  16_6  20  9  2  172  20  11  3  18T  20  13  4  19T  20  14  5  19J?  20  16  6  20  19A  18  7  20  18_9  20  8  20  ISA  22  9  20  18_2  22  10  20  173  23  15  20  16.8  27  20  20  16_5  29  30  20  16  3J  40  20  15_9  31  50  20  L5_9  32  0.039  60  20  15_9  32  0.045  70  20  16  32  0.048  80  20  16J  32  0.050  120  20  16_1  33  0.055  130  20_  16_1  33  0.055  140  20  16_2  33  0.055  150  20  163  33  0.055  160  20  163  33  0.056  170  20  163  33  0.057  180  20  16.4  33  0.057  - 159-  Hydrogen Peroxide Concentration (M)  0.012 0.025  Appendix VIII Raw Data 39  July 8, 99  Experiment No.: V . 3 15  • Electrolyte: 1.5 Liter Solution (1.0M N a C 0 , 400ppm M g ) • Experimental time: 200 minutes • Mixing speed: 200rpm • No pulp • Initial pH = 10.5; final pH = 10.76 (controlled by NaHCQ ) Current Voltage Time 2+  2  3  • • • • • •  Current set point: 20A Electrolyte temperature set point: 20°C Anode coolant inlet temperature: 1°C Anode coolant outlet temperature: 5°C Anode coolant flow rate: 6 1/min Cathode configuration: (A)  3  (Min)  (A)  (V)  Reactor Temperature (°Q  0  19.3  20  12  1  20  19.2  16  3  20  17.6  21  5  20  16  27  7  20  15  32  10  20  13.9  38  0.009  15  20  13  45  0.010  20  20  12.5  49  0.011  30  20  12.1  52  0.009  40  20  12  53  0.008  50  20  12  54  0.009  60  20  12.1  54  0.009  70  20  12.1  54  0.010  80  20  12.1  54  0.010  90  20  12.2  54  0.011  100  20  12.2  54  0.011  110  20  12.3  54  0.010  120  20  12.3  54  0.012  130  20  12.4  54  0.012  140  20  12.4  55  0.012  150  20  12.5  55  0.012  160  20  12.5  56  0.012  170  20  12.5  56  0.013  180  20  12.6  56  0.013  190  20  12.6  56  0.013  200  20  12.6  57  0.013  - 160-  Hydrogen Peroxide Concentration (M)  Appendix VIII Raw Data •0 Experiment No.: V.3 16  July 8, 99  • Electrolyte: 1.5 Liter Solution (1.0M N a C 0 , 400ppm M g ) • Experimental time: 180 minutes • Mixing speed: 200rpm • No pulp • Initial pH = 10.5 (controlled by N a H C 0 ) 2+  2  3  • • • • • •  Current set point: 20A Electrolyte temperature set point: 20°C Anode coolant inlet temperature: 1°C Anode coolant outlet temperature: 5°C Anode coolant flow rate: 61/min Cathode configuration: (A)  3  Time  Current  Voltage  (Min)  (A)  (V)  0  19J5  20  15  1  20  193  16  3  20  18^4  19  20  177  22  7  20  173  24  9  20  17  26  10  20  16_8  26  0.010  15  20  16A  28  0.012  20  20  16_2  31  0.014  30  20  16  32  0.016  40  20  16  33  0.017  50  20  16  33  0.017  60  20  16  33  0.017  70  20  16T  33  0.017  80  20  16T  0.017  90  20  0.017  100  20  33  0.016  110  20 20  0.017  130  20  33 34 34  0.017  120 140  20  34  0.016  150  20  34  0.017  160  20  35_  0.017  170  20  162 162 163 16A 16A 163 163 166 163  33 33  35  0.016  180  20  16.7  36  0.016  5  •  - 161 -  Reactor Temperature CQ  Hydrogen Peroxide Concentration (M)  0.016  Appendix VIII Raw Data \\ Experiment No.: V.3 17  July 09, 99  • Electrolyte: 1.5 Liter Solution (1.0M N a C 0 , 400ppm M g , 1.3g DTP A ) • Experimental time: 180 minutes • Mixing speed: 200rpm • No pulp • Initial pH = 11.94; final pH = 11.27 2 +  2  3  • • • • • •  Current set point: 20A Electrolyte temperature set point: 60°C Anode coolant inlet temperature: 1°C Anode coolant outlet temperature: 5°C Anode coolant flow rate: 6 1/min Cathode configuration: (A)  Time  Current  Voltage  (Min)  (A)  (V)  Reactor Temperature (°C)  0  16.6  20  12  1  17_9  20  14  3  20  19  21  5  20  16.9  28  7  20  15_6  33  10  20  JA4  39  15  20  133  47  20  20  127  50  30  20  115  53  0.037  40  20  114  53  0.045  50  20  1_15  53  0.045  60  20  116  53  0.052  70  20  118  53  0.055  80  20  119  53  0.056  90  20  118  54  0.058  100  20  13  54  0.057  110  20  119  54  0.058  120  20  119  55  0.058  130  20  112  54  0.058  140  20  13_2  54  0.057  150  20  112  54  0.057  160  20  132  54  0.058  170  20  13^2  54  0.057  180  20  13.3  54  0.057  - 162-  Hydrogen Peroxide Concentration (M)  0.020  Appendix VIII Raw Data 42  Experiment No.: V.3 18  July 10, 99  • Electrolyte: 1.5 Liter Solution (1.0M N a C 0 , 400ppm M g , l,3g D T P A ) • Experimental time: 180 minutes • Mixing speed: 200rpm • No pulp • Initial pH = 10.5; final pH = 10.3 (controlled by N a H C 0 ) 2 +  2  3  Current set point: 20A Electrolyte temperature set point: 60°C Anode coolant inlet temperature: 1°C Anode coolant outlet temperature: 5°C Anode coolant flow rate: 61/min Cathode configuration: (A)  3  Time  Current  Voltage  (Min)  (A)  (V)  Reactor Temperature (°C)  0  19.1  20  16  1  20  19.7  17  3  20  17.4  24  5  20  15.9  31  7  20  14.9  35  9  20  14.2  39  10  20  13.9  41  15  20  12.8  48  20  20  12.4  52  30  20  12  55  0.011  40  20  12  56  0.011  50  20  12.1  56  0.012  60  20  12  56  0.012  70  20  11.9  57  0.012  80  20  12  56  0.012  90  20  12.1  56  0.013  100  20  12.1  56  0.013  110  20  12.1  57  0.014  120  20  12.1  57  0.014  130  20  12.3  56  0.016  140  20  12.3  56  0.016  150  20  12.4  56  0.016  160  20  12.4  57  0.016  170  20  12.5  57  0.016  180  20  12.6  57  0.017  - 163 -  Hydrogen Peroxide Concentration (M)  0.012  •  Appendix VIII Raw Data •3 Experiment No.: V.3 19  July 10, 99  • Electrolyte: 1.5 Liter Solution (1.0M N a C 0 , 400ppm M g , 1.3g DTP A ) • Experimental time: 180 minutes • Mixing speed: 200rpm • No pulp • Initial p H = 11.6 • Final pH = 11.36 at 34.8°C 2 +  2  3  • • • • • •  Current set point: 20A Electrolyte temperature set point: 20°C Anode coolant inlet temperature: 1°C Anode coolant outlet temperature: 5°C Anode coolant flow rate: 6 1/min Cathode configuration: (A)  Time  Current  Voltage  Reactor Temperature  (Min)  (Al  LYJ  (!Q  0  20  19.8  19  1  20  18j?  21  3  20  17J5  23  5  20  17J  26  7  20  16j)  27  9  20  16J  28  10  20  16_5  28  15  20  16_1  31  20  20  16  32  30  20  118  32  0.033  40  20  119  33  0.041  50  20  118  33  0.046  60  20  16  33  0.048  70  20  16J  33  0.050  80  20  16J  33  0.050  90  20  162  33  0.052  100  20  \62  33  0.052  110  20  162  33  0.052  120  20  16J  33  0.0S2  130  20  163  34  0.053  140  20  16A  34  0.053  150  20  16_4  35  0.053  160  20  16.6  34  0.053  170  20  16J3  34  0.052  180  20  16.7  34  0.051  - 164-  Hydrogen Peroxide Concentration ; (M)  0.020  Appendix VIII Raw Data 44  Experiment No.: V.3 20  July 11, 99  • Electrolyte: 1.5 Liter Solution (1.0M N a C 0 , 400ppm M g , 1.3g D T P A ) • Experimental time: 180 minutes • Mixing speed: 200rpm • No pulp • Initial pH = 10.5; final pH = 10.62 (controlled by adding 15.62g N a H C 0 ) 2 +  2  3  Current set point: 20A Electrolyte temperature set point: 20°C Anode coolant inlet temperature: 1°C Anode coolant outlet temperature: 5°C • Anode coolant flow rate: 6 1/min • Cathode configuration: (A)  3  Time  Current  Voltage  (Min)  (A)  (V)  Reactor Temperature (°Q  0  19  20  14  1  20  19.8  16  3  20  18.7  19  5  20  17.9  22  7  20  17.4  24  9  20  17  26  10  20  16.8  26  15  20  16.3  28  20  20  16.1  30  30  20  15.8  32  0.019  40  20  15.7  32  0.019  50  20  15.7  32  0.020  60  20  15.8  32  0.019  70  20  15.9  32  0.021  80  20  15.9  33  0.022  90  20  16  33  0.021  100  20  16.1  33  0.020  110  20  16.2  33  0.021  120  20  16.2  33  0.021  130  20  16.2  33  0.020  140  20  16.3  34  0.020  150  20  16.4  34  0.020  160  20  16.4  34  0.021  170  20  16.4  34  0.020  180  20  16.4  34  0.020  - 165 -  Hydrogen Peroxide Concentration (M)  0.017  Appendix VIII Raw Data •5 Experiment No.: V . 3 21  July 11, 98  • Electrolyte: 1.5 Liter Solution (1.0M N a C 0 , 400ppm M g ) • Experimental time: 180 minutes • Mixing speed: 200rpm • No pulp • Initial pH = 11.59; final pH = 11.2 2+  2  3  • • • • • •  Current set point: 20A Electrolyte temperature set point: 20°C Anode coolant inlet temperature: 1°C Anode coolant outlet temperature: 5°C Anode coolant flow rate: 6 1/min Cathode configuration: (B)  Time  Current  Voltage  (Min}  (A)  (V)  Reactor Temperature £C)  0  19  14  13  1  20  14/7  14  3  20  15/7  16  5  20  162  17  7  20  16/7  19  9  20  VTA  20  10  20  17_3  20  15  20  182  22  20  20  18/7  24  30  20  19_8  27  0.028  40  19_9  20  28  0.032  50  19_8  20  28  0.036  60  19_8  20  29  0.036  70  193  20  29  0.038  80  20  20  29  0.039  90  20  19_8  29  0.038  100  20  19J>  29  0.039  110  20  193  28  0.038  120  20  18j>  28  0.036  130  20  18.8  28  0.035  140  20  18_3  28  0.035  150  20  18J  27  0.034  160  20  177  27  0.033  170  20  17.3  27  0.031  180  20  16.9  26  0.030  - 166-  Hydrogen Peroxide Concentration (M)  0.016  Appendix VIIIRaw Data 46  Experiment No.: V . 3 22  July 12, 99  Electrolyte: 1.5 Liter Solution (1.0M N a C 0 , 400ppm M g ) Experimental time: 180 minutes Mixing speed: 200rpm No pulp Initial pH = 10.59; final pH = 10.77 (controlled by adding NaHCOa) 2+  2  3  Current set point: 20A Electrolyte temperature set point: 60°C Anode coolant inlet temperature: 1°C • Anode coolant outlet temperature: 5°C • Anode coolant flow rate: 61/min • Cathode configuration: (B)  Time  Current  Voltage  (Min)  (A)  (V)  Reactor Temperature (°C)  0  16.7  20  14  1  17.3  20  16  2  18.4  20  19  3  19.6  20  22  4  20  19.4  25  5  20  18.6  28  6  20  18.4  29  7  20  18  31  8  .20  17.7  32  9  20  16.9  35  10  20  16.4  37  15  20  15.7  41  20  20  15.4  42  30  20  15.3  43  0.030  40  20  15.4  43  0.036  50  20  15.4  44  0.043  60  20  15.7  43  0.048  70  20  15.6  44  0.050  80  20  15.6  44  0.052  140  20  15.6  46  0.055  150  20  15.7  45  0.056  160  20  15.8  45  0.055  170  20  16  46  0.055  180  20  16.1  46  0.055  - 167-  Hydrogen Peroxide Concentration (M)  0.018  Appendix VIII Raw Data \1 Experiment No.: V.3 23  July 12, 99  • Electrolyte: 1.5 Liter Solution (1.0M N a C 0 , 400ppm M g ) • Experimental time: 180 minutes • Mixing speed: 200rpm • No pulp • Initial pH = 11.31; final pH = 10.68 2+  2  3  • • • • • •  Current set point: 20A Electrolyte temperature set point: 60°C Anode coolant inlet temperature: 1°C Anode coolant outlet temperature: 5°C Anode coolant flow rate: 61/mih Cathode configuration: (C)  Time  Current  Voltage  (Min)  (A)  (V}  Reactor Temperature £Cj  0  20T  18J  16  1  20  179  17  2  20  174  19  3  20  166  22  4  20  16_2  24  5  20  15__8  26  6  20  153  28  7  20  15  29  8  20  14JS  3J  9  20  145  32  10  20  14_3  33  15  20  137  36  20  20  114  38  40  20  13_1  41  0.039  50  20  13T  41  0.044  60  _20  13J  42  0.047  70  20  13_1  42  0.049  120  20  111  49  0.052  140  20  112  48  0.056  170  20  113  48  0.054  180  20  12.3  48  0.054  - 168-  Hydrogen Peroxide Concentration (M)  0.019  Appendix VIII Raw Data 48  July 12, 99  Experiment No.: V.3 24 Electrolyte: 1.5 Liter Solution (1.0M N a C 0 , 400ppm M g ) Experimental time: 180 minutes Mixing speed: 200rpm No pulp Initial p H = 11.59 at 18.4°C Final p H = 10.82 at 44.8°C 2+  2  3  • • • • • •  Current set point: 20A Electrolyte temperature set point: 20°C Anode coolant inlet temperature: 1°C Anode coolant outlet temperature: 5°C Anode coolant flow rate: 61/min Cathode configuration: (C)  Time  Current  Voltage  (Min)  (A)  (V)  Reactor Temperature (°C)  0  20  20  14  1  20  19.2  16  3  20  17.3  21  4  20  16.6  24  5  20  15.9  26  6  20  15.5  28  9  20  14.6  32  10  20  14.4  33  15  20  13.7  37  20  20  13.3  39  30  20  13.1  40  0.030  40  20  13.1  41  0.037  50  20  13  42  0.043  60  20  13.1  42  0.048  70  20  13.2  42  0.050  80  20  13.2  42  0.053  90  20  13.2  42  0.054  100  20  13.2  42  0.054  110  20  13.2  43  0.056  120  20  13.3  43  0.057  130  20  13.4  43  0.057  140  20  13.4  43  0.058  150  20  13.4  44  0.058  160  20  13.6  43  0.058  170  20  13.6  43  0.058  180  20  13.6  43  0.058  - 169-  Hydrogen Peroxide Concentration (M)  0.016  Appendix VIII Raw Data 49  Experiment No.: V.3 25  July 13, 99  • Electrolyte: 1.5 Liter Solution (1.0M N a C 0 , 400ppm M g ) • Experimental time: 120 minutes • Mixing speed: 200rpm • No pulp • Initial p H = 10.5 (controlled by adding 6.6g NaHCOs) 2+  2  3  Current set point: 20A Electrolyte temperature set point: 20°C Anode coolant inlet temperature: 1°C Anode coolant outlet temperature: 5°C Anode coolant flow rate: 6 1/min Cathode configuration: (C)  Time  Current  Voltage  (Min)  (A)  (V)  Reactor Temperature (°C)  0  20  17.2  19  1  20  17.1  20  2  20  17.1  20  3  20  17.1  21  4  20  17.1  21  5  20  17.1  21  6  20  17  22  7  20  17  22  8  20  17  22  9  20  17  23  10  20  17  23  15  20  16.9  24  0.010  30  20  16.8  24  0.012  40  20  16.9  24  0.010  50  20  17  25  0.010  60  20  17.1  25  0.010  70  20  17.2  25  0.010  80  20  17.3  25  0.010  90  20  17.4  25  0.009  100  20  17.5  25  110  20  17.5  25  0.008  120  20  17.5  25  0.009  - 170-  Hydrogen Peroxide Concentration (M)  Appendix VIII Raw Data 0  Experiment No.: V.3 26  July 14, 99  • Electrolyte: 1.5 Liter Solution (1.0M N a C 0 , 400ppm M g , 1.3g DTPA) • Experimental time: 180 minutes • Mixing speed: 200rpm • No pulp • Initial pH = 11.6 2 +  2  3  • • • • • •  Current set point: 20A Electrolyte temperature set point: 60°C Anode coolant inlet temperature: 1°C Anode coolant outlet temperature: 5°C Anode coolant flow rate: 5.5 1/min Cathode configuration: (C)  Time  Current  Voltage  Reactor Temperature  (Min)  (A)  (V)  (V)  0  20  ]93  12  1  20  19J  14  2  20  18J)  15  3  20  18.3  17  4  20  18  18  5  20  177  19  6  20  VTA  21  7  20  164  23  8  20  L5_9  26  9  20  15J  27  10  20  15T  29  15  20  13_9  34  0.020  30  20  13  40  0.036  20  12_9  42  0.047  60  20  13  42  0.054  75  20  12J  44  0.056  90  20  13  43  0.057  120  20  133  43  0.054  135  20  13L3  42  0.054  150  20  134  43  0.055  165  20  13_5  42  0.054  180  20  13.7  43  0.055  45  •  - 171 -  Hydrogen Peroxide Concentration (M)  Appendix VIII Raw Data 51  Experiment No.: V . 3 27  July 18, 99  Electrolyte: 1.5 Liter Solution (1.0M N a C 0 , 400ppmMg , 1.3gDTPA) Experimental time: 180 minutes Mixing speed: 200rpm Weight of wet pulp: 300g Initial p H = 11.54 at 26.9°C Final p H = 10.23 at51.3°C 2+  2  3  • • • •  Current set point: 20A Electrolyte temperature set point: 60°C Anode coolant inlet temperature: 1°C Anode coolant outlet temperature: 5°C Anode coolant flow rate: 5.5 1/min Cathode configuration: (C) Pulp consistency: 4.6%  Time  Current  Voltage  (Min)  (A)  (V)  Reactor Temperature (°C)  0  17.3  20  13.0  1  17.8  20  14.0  2  18.3  20  17.0  3  19  20  21.0  4  19.8  20  23.0  5  20  19.2  26.0  6  20  18.5  28.0  7  2.0  18.2  29.0  8  20  17.9  31.0  9  20  17.3  33.0  10  20  17.1  34.0  15  20  15.9  41.0  30  20  14.9  50.0  45  20  14.9  51.0  60  20  14.8  52.0  75  20  14.9  52.0  90  20  14.7  52.0  105  20  14.3  54.0  120  20  14.4  53.0  135  20  14.3  52.0  150  20  14.2  54.0  165  20  14.2  52.0  180  20  14.3  52.0  Brightness gain: 7.3 Yellowness decrease: 12.2  - 172 -  Appendix VIII Raw Data 12 Experiment No.: V.3 28  July 15, 99  • Electrolyte: 1.5 Liter Solution (1.0M N a C 0 , 400ppm M g , 1.3g DTP A) • Experimental time: 180 minutes • Mixing speed: 200rpm • No pulp • Final pH = 10.74 at 41.2°C 2 +  2  3  • • • • • •  Current set point: 20A Electrolyte temperature set point: 60°C Anode coolant inlet temperature: 0°C Anode coolant outlet temperature: 10°C Anode coolant flow rate: 5.5 1/min Cathode configuration: (C)  Time  Current  Voltage  (Min)  (A)  (V)  £Q  0  20  182  18  1  20  18  19  2  20  17_2  2J  3  20  167  23  4  20  163  24  5  20  157  27  6  20  153  29  7  20  149  3J  8  20  147  32  9  20  144  33  10  20  1_4_2  34  15  20  13J5  37  0.021  30  20  107  57  0.032  45  20  104  61  0.035  60  20  103  62  0.038  75  20  10  62  0.042  90  20  106  60  0.047  105  20  108  60  0.042  120  20  107  60  0.042  135  20  108  60  0.041  150  20  10.9  60  0.040  165  20  109  _6J  0.040  180  20  11  60  0.040  - 173 -  Reactor Temperature  Hydrogen Peroxide Concentration (M)  .  Appendix VIII Raw Data 53  Experiment No.: V.3 29  July 16, 99  • Electrolyte: 1.5 Liter Solution (1.0M N a C 0 , 400ppm M g , 1.3g DTPA) • Experimental time: 180 minutes • Mixing speed: 200rpm • Weight of wet pulp: 300g • Initial p H = 11.57 at 25.9°C • Final p H = 10.74 at 41.2°C 2 +  2  3  Current set point: 20A Electrolyte temperature set point: 60°C Anode coolant inlet temperature: 0°C Anode coolant outlet temperature: 5°C Anode coolant flow rate: 5.5 1/min Cathode configuration: (C) Pulp consistency: 6.6%  Time  Current  Voltage  (Min)  (A)  (V)  Reactor Temperature (°Q  0  20  20  24  3  19.1  20  31  7  20  19  30  9  20  18.2  42  11  20  16.5  46  15  20  14  59  30  20  14.3  61  45  20  14.5  60  60  20  14.2  62  75  20  14.4  62  90  20  14.4  61  105  20  15.1  59  120  20  13.9  63  135  20  14.5  60  150  20  14.7  61  165  20  14.8  60  180  20  15  59  Brightness gain: 12.0 (55.4) Yellowness decrease: 13.6(19.9)  - 174-  Hydrogen Peroxide Concentration (M)  0.020  Appendix VIII Raw Data 4  Experiment No.: V.3 30  July 17, 99  • Electrolyte: 1.5 Liter Solution (1.0M N a C 0 , 400ppm M g ) • Experimental time: 180 minutes • Mixing speed: 200rpm • No pulp • Final p H = 10.80 at 49.5°C 2+  2  3  • • • • • •  Current set point: 40A Electrolyte temperature set point: 60°C Anode coolant inlet temperature: 0°C Anode coolant outlet temperature: 3°C Anode coolant flow rate: 5.5 1/min Cathode configuration: (C)  Time  Current  Voltage  (Min)  (A)  (V)  Reactor Temperature £C)  0  194  20  9  1  20.8  20  12  2  2 2 J >  20  16  3  247  20  21  4  26_7  20  24  5  28j*  20  28  6  3L5  20  33  7  33J  20  36  8  348  20  39  9  363  20  42  10  38_2  20  45  15  40  18.6  56  0.028  30  40  173  63  0.049  45  40  174  63  0.055  60  40  174  64  0.057  75  40  174  64  0.057  90  40  175  65  0.058  105  40  1X6  65  0.057  120  40  177  65  0.057  135  40  17_9  66  0.057  150  40  18  66  0.057  165  40  18T_  66  0.057  180  40  18.1  67  0.056  - 175 -  Hydrogen Peroxide Concentration (M)  Appendix VIII Raw Data 55  Experiment No.: V.3 31  July 25, 99  Electrolyte: 1.5 Liter Solution (1.0M N a C 0 , 400ppmMg , 1.3g DTP A) Experimental time: 180 minutes Mixing speed: 200rpm No pulp Initial p H = 11.76 at 28.8°C Final pH = 10.78 at 58.9°C 2+  2  3  • • • • • •  Current set point: 30A Electrolyte temperature set point: 60°C Anode coolant inlet temperature: 0°C Anode coolant outlet temperature: 3°C Anode coolant flow rate: 5.5 1/min Cathode configuration: (C)  Time  Current  Voltage  (Min)  (A)  (V)  Reactor Temperature (°C)  0  29.7  20  20  1  30  16.9  30  2  30  15.8  34  3  30  15.3  36  4  30  14.8  38  5  30  14.1  41  8  30  13.3  46  9  30  13.3  46  10  30  13.1  47  15  30  12.6  51  0.038  30  30  12  54  0.058  45  30  11.8  57  0.067  60  30  11  63  0.070  75  30  11.7  59  0.078  90  30  11.7  60  0.082  105  30  11.9  59  0.081  120  30  11.9  59  0.080  135  30  11.9  61  0.080  150  30  11.8  61  0.079  165  30  12.1  59  0.080  180  30  12  61  0.079  - 176-  Hydrogen Peroxide Concentration (M)  Appendix VIII Raw Data 56  Experiment No.: V.3 32  July 25, 99  • Electrolyte: 1.5 Liter Solution (1.0M N a C 0 , 400ppm M g , 1.3gDTPA) • Experimental time: 180 minutes • Mixing speed: 200rpm • Weight of wet pulp: 300g • Final p H = 10.32 at 58.8°C 2 +  2  3  • • • • • • •  Current set point: 30A Electrolyte temperature set point: 60°C Anode coolant inlet temperature: 0°C Anode coolant outlet temperature: 5°C Anode coolant flow rate: 5.5 1/min Cathode configuration: (C) Pulp consistency: 4.2%  Time  Current  Voltage  (Min)  (A)  (V)  Reactor Temperature (°C)  0  30  19.6  24  3  30  17.8  31  6  30  16.9  35  7  30  16.6  37  8  30  16.3  38  9  30  16  40  10  30  15.6  41  15  30  14.7  47  30  30  13.6  62  45  30  13.3  60  60  30  13.6  62  75  30  13.6  58  90  30  13.2  59  105  30  13.1  62  120  30  12.8  62  135  30  12.7  62  150  30  12.8  62  165  30  12.8  62  180  30  12.8  62  Brightness gain: Yellowness loss:  17.5 (59.0) 19.3(17.4)  - 177-  Hydrogen Peroxide Concentration (M)  0.035  Appendix VIII Raw Data  Experiment No.: V4 Raw Data  4. 57  Experiment No.: V4.01  July 27, 99  Electrolyte: 1.5 Liter Solution (1.0M N a C 0 , 400ppm M g , 1.3g DTP A) Experimental time: 180 minutes Mixing speed: 200rpm Weight of wet pulp: 320g Final p H = 10.72 at35.1°C 2 +  2  3  Current set point: 30A Electrolyte temperature set point: 20°C Anode coolant inlet temperature: 0°C Anode coolant outlet temperature: 5°C Anode coolant flow rate: 5.5 1/min Cathode configuration: (C) Pulp consistency: 4.37%  Time (Min)  Control (A)  Voltage (V)  Reactor Temperature (°C)  0  29.2  20  18  1  30  20  20  2  30  19.2  23  3  30  18.9  24  4  30  18.6  26  5  30  18.5  27  6  30  18.2  28  7  30  18.1  29  8  30  18.1  29  9  30  17.9  31  10  30  17.7  31  15  30  17.5  34  30  30  17.3  37  45  30  17.2  38  60  30  17.2  39  75  30  17  39  90  30  17.1  39  105  30  17.1  39  120  30  17.2  38  135  30  17.2  39  150  30  17.2  39  165  30  17.2  40  180  30  17.2  40  - 178-  Appendix VIII Raw Data 58  Experiment No.: V4.02  Aug. 2, 99  • Electrolyte: 1.25 Liter Solution (1.0M N a C 0 , 400ppm M g , 1.3g DTPA) • Experimental time: 180 minutes • Mixing speed: 200rpm • Weight of wet pulp: 150g • Initial p H = 11.55 • Final p H = 10.45 at42.5°C 2 +  2  3  • • • • • • •  Current set point: 10A Electrolyte temperature set point: 40°C Anode coolant inlet temperature: 0°C Anode coolant outlet temperature: 5°C Anode coolant flow rate: 5.5 1/min Cathode configuration: (C) Pulp consistency: 2.5%  Time (Min)  Current (A)  Voltage (V)  Reactor Temperature (°C)  0  10  12.8  21  1  10  12.5  23  3  10  12.2  26  5  10  12  29  7  10  11.9  31  9  10  11.6  34  11  10  11.5  36  15  10  11.1  38  30  10  10.6  43  60  10  11.1  39  90  10  11.7  40  120  10  11.7  40  150  10  11  40  180  10  10.6  43  Brightness gain: Yellowness loss:  7.5 (49.1) 9.4 (27.4)  - 179-  Appendix VIII Raw Data 59  Experiment No.: V4.03  Aug. 3, 99  • Electrolyte: 1.25 Liter Solution (1.0M N a C 0 , 400ppm M g , 1.3g DTP A) • Experimental time: 180 minutes • Mixing speed: 200rpm • Weight of wet pulp: 150g • Initial p H = 11.47 at 18.6°C • Final p H = 10.45 at 43°C 2 +  2  3  Current set point: 10A Electrolyte temperature set point: 40°C Anode coolant inlet temperature: 0°C Anode coolant outlet temperature: 5°C Anode coolant flow rate: 5.5 1/min Cathode configuration. (C) Pulp consistency: 2.5%  Time  Current  Voltage  (Min)  (A)  (V)  Reactor Temperature (°C)  0  10  11.6  14  1  10  11.8  14  3  10  11.7  16  5  10  11.2  20  7  10  10.8  23  9  10  10.6  26  11  10  10.5  28  15  10  10.2  31  0.014  30  10  9.4  38  0.027  60  10  9.2  40  0.026  90  10  9  42  0.027  180  10  8.7  41  0.022  Brightness gain: Yellowness loss:  7.5 (49.1) 9.4 (27.4)  - 180-  Hydrogen Peroxide Concentration (M)  Appendix VIII Raw Data 60  Experiment No.: V4.04  Aug. 5, 99  • Electrolyte: 1.5 Liter Solution (2.OM N a C 0 , 400ppmMg , 1.3gDTPA) • Experimental time: 180 minutes • Mixing speed: 200rpm • Weight of wet pulp: 150g • Initial p H = 11.68 at 19.3°C • Final pH = 10.87 at 35.7°C 2+  2  3  • • • • • • •  Current set point: 1 OA Electrolyte temperature set point: 40°C Anode coolant inlet temperature: 0°C Anode coolant outlet temperature: 5°C Anode coolant flow rate: 5.5 1/min Cathode configuration: (C) Pulp consistency: 2.5%  Time  Current  Voltage  (Min)  (A)  (V)  Reactor Temperature (°C)  0  10  8.6  22  1  10  8.6  23  3  10  8.6  24  5  10  8.5  26  7  10  8.4  28  9  10  8.3  29  11  10  8.3  30  15  10  8.2  32  0.017  30  10  8  37  0.024  60  10  7.9  40  0.038  90  10  7.8  39  0.033  120  10  7.8  39  150  10  7.7  39  0.071  180  10  7.6  39  0.038  Brightness gain: Yellowness loss:  13.3 (54.9) 12.9 (23.9)  - 181 -  Hydrogen Peroxide Concentration (M)  Appendix VIII Raw Data 61  Experiment No.: V4.05  Aug 5, 99  Electrolyte: 1.5 Liter Solution (1.5M N a C 0 , 400ppm M g , 1.3g DTP A) Experimental time: 180 minutes Mixing speed: 200rpm Weight of wet pulp: 150g Initial pH = 11.39 at 29 C Final pH = 10.56at51.8°C 2 +  2  3  U  Current set point: 20A Electrolyte temperature set point: 50°C Anode coolant inlet temperature: 0°C Anode coolant outlet temperature: 5°C Anode coolant flow rate: 5.5 1/min Cathode configuration: (C) Pulp consistency: 2.5%  Time  Current  Voltage  (Min)  (A)  (V)  Reactor Temperature (°C)  0  20  14.7  23  1  20  14.4  24  60  20  11  54  90  20  11.6  49  0.043  120  20  10.9  55  0.042  150  20  11.5  51  0.043  180  20  11.6  51  0.051  Brightness gain: Yellowness loss:  15.2(56.8) 14.5 (22.3)  - 182-  Hydrogen Peroxide Concentration (M)  Appendix VIII Raw Data 62  Experiment No.: V4.06  Aug 5, 99  • Electrolyte: 1.5 Liter Solution (1.0M N a C 0 , 400ppmMg , 1.3g DTPA) • Experimental time: 120 minutes • Mixing speed: 200rpm • No pulp 2+  2  3  • • • • • •  Current set point: 30A Electrolyte temperature set point: 60°C Anode coolant inlet temperature: 0°C Anode coolant outlet temperature: 5°C Anode coolant flow rate: 5.5 1/min Cathode configuration: (C)  Time  Current  Voltage  (Min)  (A)  (V)  Reactor Temperature (°C)  0  19.2  20  12  1  20.4  20  15  3  21.5  20  17  5  22.7  20  20  7  24.4  20  26  9  27  20  32  11  28.9  20  38  15  30  18.2  57  0.025  30  30  17.9  62  0.024  60  30  18  62  0.020  90  30  18.6  70  0.023  120  30  18.7  76  0.022  - 183 -  Hydrogen Peroxide Concentration (M)  Appendix VIII Raw Data 63  Experiment No.: V4.07  Sept 9, 99  • Electrolyte: 1.5 Liter Solution (1.0M N a C 0 , 400ppm M g , 1.3g DTP A) • Experimental time: 180 minutes • Mixing speed: 200rpm • Weight of wet pulp: 150.3 6g • Final p H = 10.51 2 +  2  3  • • • • • • •  Current set point: 30A Electrolyte temperature set point: 60°C Anode coolant inlet temperature: 0°C Anode coolant outlet temperature: 5°C Anode coolant flow rate: 5.5 1/min Cathode configuration: (C) Pulp consistency: 2.5%  Time  Current  Voltage  (Min)  (A)  (V)  Reactor Temperature (°C)  Hydrogen Peroxide Concentration (M)  0  19.7  20  13  1  21.4  20  19  3  23.1  20  23  5  25  20  28  7  27.8  20  34  9  30  19.6  40  11  30  18.9  46  15  30  17.8  51  0.024  30  30  17.6  63  0.028  60  29.6  20  63  0.025  90  26.2  20  61  0.036  120  26.8  20  65  0.040  150  27.8  20  70  0.036  27.8 20 62 180 Lots of forming comes out, which increased the gas hold-up and the voltage Brightness gain: Yellowness loss:  10.4 (52.1) 15.9 (20.9)  - 184-  0.033  Appendix VIII Raw Data 64  Experiment No.: V4.08  Sept 13, 99  Electrolyte: 1.5 Liter Solution (1M N a C 0 , 400ppm M g , 1.3gDTPA) Experimental time: 180 minutes Mixing speed: 200rpm Weight of wet pulp: 150g Final p H = 10.49 at 42.1 °C  Current set point: 10A Electrolyte temperature set point: 60°C Anode coolant inlet temperature: 0°C Anode coolant outlet temperature: 5°C Anode coolant flow rate: 5.5 1/min Cathode configuration: (C) Pulp consistency: 2.5%  2 +  2  3  Time  Current  Voltage  (Min)  (A)  0  10  (V) 10.6  1  10  10.6  22  3  10  10.4  24  5  10  10.2  27  7  10  10  29  9  10  10  31  11  10  9.9  33  15  10  9.9  37  0.012  30  10  9.4  41  0.019  60  10  7.6  58  0.019  90  10  7.7  59  0.0185  120  10  7.8  59  0.020  150  10  7.8  59  0.022  180  10  7.9  60  0.022  Brightness gain: Yellowness loss:  11.8 (53.4) 15.7 (57.3) 14.2 (22.6) 18.7 (18.1) -  September September September September  Reactor Temperature (°C)  Hydrogen Peroxide Concentration (M)  21  17, 20, 17, 20,  1999 1999 1999 1999  Un-neutralized, brightened pulp was stored in a beaker for two days before making the second set of handsheets.  - 185 -  Appendix VIII Raw Data 65  Experiment No.: V4.09  Sept 15, 99  • Electrolyte: 1.5 Liter Solution (2M N a C 0 , 400ppm M g , 1.3g DTP A) • Experimental time: 180 minutes • Mixing speed: 200rpm • Weight of wet pulp: 150g • Final p H = 10.77 at 45.9°C 2 +  2  3  Current set point: 30A Electrolyte temperature set point: 40°C Anode coolant inlet temperature: 0°C Anode coolant outlet temperature: 5°C • Anode coolant flow rate: 5.5 1/min • Cathode configuration: (C) • Pulp consistency: 2.5%  Time  Current  Voltage  (Min)  (A)  (V)  Reactor Temperature (°C)  0  26.3  19.9  13  1  29.3  19.9  19  3  30  18.4  23  5  30  16.7  28  7  30  15.8  34  9  30  15.7  40  11  30  15.8  46  15  30  15.1  51  0.033  30  30  16.6  63  0.039  60  30  16.7  63  0.034  90  30  17.1  61  0.032  120  30  17.1  65  0.031  150  30  17.3  70  0.032  180  30  17.2  62  Brightness gain: Yellowness loss:  12.3 (53.9) 14.0 (22.8)  - 186-  Hydrogen Peroxide Concentration (M)  Appendix VIII Raw Data 66  Experiment No.: V4.10  Sept 16, 99  Electrolyte: 1.5 Liter Solution (1M N a C 0 , 400ppm M g , 1.3g DTP A) Experimental time: 180 minutes Mixing speed: 200rpm Weight of wet pulp: 150g Initial p H = 11.62 at 22.8°C Final p H = 10.49 at 40.8°C 2 +  2  3  Current set point: 3OA Electrolyte temperature set point: 40°C Anode coolant inlet temperature: 0°C Anode coolant outlet temperature: 5°C Anode coolant flow rate: 5.5 1/min Cathode configuration: (C) Pulp consistency: 2.5%  Time  Current  Voltage  (Min)  (A)  (V)  Reactor Temperature (°C)  0  20.8  19.9  14  1  21.5  20  17  3  22.5  20  19  5  23.3  20  21  7  25.9  20  30  9  27.6  20  34  11  29.1  20  42  15  29.5  20  43  0.028  30  29.3  20  44  0.035  60  27.3  20  46  0.026  90  26.5  20  46  0.034  120  23.1  20  41  0.021  150  22.8  20  42  0.020  180  23  20  43  0.019  Brightness gain: Yellowness loss:  11.6(53.2) 13.2(23.5)  - 187-  Hydrogen Peroxide Concentration (M)  Appendix VIII Raw Data 67  Sept 20, 99  Experiment No.: V4.11  • Electrolyte: 1.5 Liter Solution (2M N a C 0 , 400ppm M g , 1.3g DTPA) • Experimental time: 180 minutes • Mixing speed: 200rpm • Weight of wet pulp: 150g • Initial p H = 11.78 at 24.1°C • Final p H = 10.62 at 56.2°C 2 +  2  3  Current set point: 30A Electrolyte temperature set point: 60°C Anode coolant inlet temperature: 0°C Anode coolant outlet temperature: 5°C Anode coolant flow rate: 5.5 1/min Cathode configuration. (C) Pulp consistency: 2.5%  Time  Current  Voltage  (Min)  (A)  (V)  Reactor Temperature (°C)  0  30  19.4  21  1  30  18.7  24  3  30  16.5  34  5  30  16  37  7  30  15.3  42  9  30  14.9  46  11  30  14.5  49  15  30  14.2  55  0.033  30  30  13.7  62  0.038  60  30  13.6  60  0.038  90  30  13.9  58  0.059  120  30  13.4  57  0.069  150  30  13.8  63  0.059  180  30  15.7  54  0.063  Brightness gain: Yellowness loss:  17.4 (59.0) 19.2(17.6)  - 188-  Hydrogen Peroxide Concentration (M)  Appendix VIII Raw Data 68  Experiment No.: V4.12  Sept 22, 99  Electrolyte: 1.5 Liter Solution (2M N a C 0 , 400ppm M g , 1.3g DTP A) Experimental time: 180 minutes Mixing speed: 200rpm Weight of wet pulp: 150g • Pulp consistency: 2.5% 2 +  2  3  Current set point: 10A Electrolyte temperature set point: 60°C Anode coolant inlet temperature: 0°C Anode coolant outlet temperature: 5°C Anode coolant flow rate: 5.5 1/min Cathode configuration: (C)  Time  Current  Voltage  (Min)  (A)  (V)  Reactor Temperature (°Q  0  10  9.7  13  1  10  9.7  15  3  10  9.5  18  5  10  9.1  22  7  10  8.7  25  9  10  8.5  27  11  10  8.3  28  15  10  8  32  0.014  30  10  7.1  45  0.020  60  10  6.3  58  0.022  90  10  6  62  0.021  120  10  6.3  59  0.027  150  10  6.3  60  0.029  180  10  6.5  58  0.032  Brightness gain: Yellowness loss:  15.3 (56.9) 15.9(20.8)  - 189-  Hydrogen Peroxide Concentration (M)  Appendix VIII Raw Data 69  Experiment No.: V4.13  Sept 16, 99  • Electrolyte: 1.5 Liter Solution (2M N a C 0 , 400ppm M g , 1.3g DTPA) • Experimental time: 60 minutes • Mixing speed: 200rpm • Weight of wet pulp: 150g • Initial p H = 11.78 at 24.1°C • Final pH = 10.69 at 61.5°C 2 +  2  3  Current set point: 3OA Electrolyte temperature set point: 60°C Anode coolant inlet temperature: 0°C Anode coolant outlet temperature: 5°C Anode coolant flow rate: 5.5 1/min Cathode configuration: (C) Pulp consistency: 2.5%  Time  Current  Voltage  (Min)  (A)  (V)  Reactor Temperature (°C)  0  30  18.3  24  1  30  17.5  29  3  30  16  34  5  30  15.2  38  7  30  14.7  42  9  30  14.4  45  11  30  14.1  48  15  30  13.9  52  0.032  30  30  13.3  61  0.037  60  30  13.3  57  0.042  Brightness gain: Yellowness loss:  12.1 (55.7) 14.1 (22.7)  - 190-  Hydrogen Peroxide Concentration (M)  Appendix VIII Raw Data 70  Experiment No.: V4.14  Oct 1, 99  • Electrolyte: 1.5 Liter Solution (2M N a C 0 , 400ppm M g , 1.3g DTP A) • Experimental time: 120 minutes • Mixing speed: 200rpm • Weight of wet pulp: 150g • Final p H = 10.72 at 62.9°C 2 +  2  3  Current set point: 3OA Electrolyte temperature set point: 60°C Anode coolant inlet temperature: 0°C Anode coolant outlet temperature: 5°C Anode coolant flow rate: 5.5 1/min Cathode configuration: (C) Pulp consistency: 2.5%  Time  Current  Voltage  (Min)  (A)  (V)  Reactor Temperature (°C)  0  30  18.5  23  1  30  17.7  25  3  30  16.9  28  5  30  16.2  32  7  30  15.6  37  9  30  14.9  42  11  30  14.4  45  15  30  13.9  51  0.030  30  30  13.5  62  0.034  60  30  13.7  62  0.040  90  30  14.2  61  0.059  120  30  14.2  60  0.060  Brightness gain: Yellowness loss:  13.1 (54.7) 15.6(22.2)  - 191 -  Hydrogen Peroxide Concentration (M)  Appendix VIII Raw Data 71  Experiment No.: V4.15  Oct 18, 99  Electrolyte: 1.5 Liter Solution (2M N a C 0 , 400ppmMg , 1.3gDTPA) Experimental time: 30 minutes Mixing speed: 200rpm Weight of wet pulp: 150g Pulp consistency: 2.5% 2+  2  3  Current set point: 30A Electrolyte temperature set point: 60°C Anode coolant inlet temperature: 0°C Anode coolant outlet temperature: 5°C Anode coolant flow rate: 5.5 1/min Cathode configuration: (C)  Time  Current  Voltage  Reactor Temperature  (Min)  (A)  (V)  0  25.1  20  (°o  1  27.7  20  18  3  30  17.8  29  5  30  16.8  33  7  30  15.3  41  9  30  15  44  11  30  14.6  47  15  30  14  52  30  30  15.2  61  Brightness gain: Yellowness loss:  9.5 (51.1) 9.4 (27.4)  - 192-  Hydrogen Peroxide Concentration (M)  14  0.036  Appendix VIII Raw Data 72  Experiment No.: V4.16  Oct 18, 99  Electrolyte: 1.5 Liter Solution (2M N a C 0 , 400ppm M g , 1.3g DTP A) Experimental time: 90 minutes Mixing speed: 200rpm Weight of wet pulp: 150g Pulp consistency: 2.5% 2 +  2  3  Current set point: 3OA Electrolyte temperature set point: 60°C Anode coolant inlet temperature: 0°C Anode coolant outlet temperature: 5°C Anode coolant flow rate: 5.5 1/min Cathode configuration: (C)  Time  Current  Voltage  (Min)  (A)  (V)  Reactor Temperature (°C)  0  30  16.2  32  1  30  15.4  37  3  30  14.8  41  5  30  14.3  45  7  30  13.9  49  9  30  13.9  50  11  30  13.7  52  15  30  13.6  57  0.033  30  30  13.4  63  0.036  60  30  14.4  59  0.052  90  30  13.5  63  0.062  Brightness gain: Yellowness loss:  13.5 (55.1) 14.3 (22.5)  - 193 -  Hydrogen Peroxide Concentration (M)  Appendix VIII Raw Data 73  Experiment No.: V4.17  Oct 19, 99  • Electrolyte: 1.5 Liter Solution (2M N a C 0 , 400ppm M g , 1.3gDTPA) • Experimental time: 240 minutes Mixing speed: 200rpm Weight of wet pulp: 150g Final p H = 10.46 at 50.9°C 2 +  2  3  Current set point: 3OA Electrolyte temperature set point: 60°C Anode coolant inlet temperature: 0°C Anode coolant outlet temperature: 5°C Anode coolant flow rate: 5.5 1/min Cathode configuration: (C) Pulp consistency: 2.5%  Time  Current  Voltage  (Min)  (A)  (V)  Reactor Temperature (°C)  0  28.7  20  21  1  30  17.7  30  3  30  16.4  37  5  30  16  40  7  30  15.5  45  9  30  15  48  11  30  14.8  51  15  30  14.6  56  0.036  30  30  14.5  62  0.037  60  30  14.6  64  0.045  90  26.5  14.9  62  0.056  120  23.1  15.3  60  0.065  150  22.8  15  60  0.058  180  23  14.9  63  0.058  210  30  14.9  62  0.056  240  30  14.9  62  0.057  Brightness gain: Yellowness loss:  15.8 (57.4) 17.2(19.5)  - 194-  Hydrogen Peroxide Concentration (M)  Appendix VIII Raw Data 74  Oct 20, 99  Experiment No.: V4.18  • Electrolyte: 1.5 Liter Solution (2M N a C 0 , 400ppm M g , 1.3g DTP A) • Brightening time: 210 minutes • Mixing speed: 200rpm Weight of wet pulp: 150g Final p H = 10.65 at 55.5°C Pre-generated H 2 O 2 time: 30 minutes 2 +  2  3  Current set point: 3OA Electrolyte temperature set point. 60°C Anode coolant inlet temperature: 0°C Anode coolant outlet temperature: 5°C Anode coolant flow rate: 5.5 1/min Cathode configuration: (C) Pulp consistency: 2.5%  (V)  Reactor Temperature (°C)  Hydrogen Peroxide Concentration (M)  30  12.5  55  0.067  1  30  12.9  56  3  30  13  57  5  30  13.1  7  30  13.3  59  9  30  13.4  60  11  30  13.4  60  15  30  13.5  62  0.039  30  30  13.5  60  0.037  60  30  14.3  62  0.055  90  30  13.8  62  0.060  120  30  14.7  58  0.067  150  30  14.6  58  0.060  180  30  14.4  61  0.060  Time  Current  Voltage  (Min)  (A)  0  Brightness gain: Yellowness loss:  16.2 (57.8) 17.0(19.7)  - 195 -  •  59  Appendix VIII Raw Data 75  Oct 26, 99  Experiment No.: V4.19  • Electrolyte: 1.5 Liter Solution (1.5M N a C 0 , 400ppmMg , 1.3gDTPA) • Experimental time: 180 minutes • Mixing speed: 200rpm • Weight of wet pulp: 150.27g • Final p H = 10.61 at 54.4°C • Pre-generated H 2 O 2 time: 30 minutes 2+  2  3  Time  Current  Voltage  (Min)  (A)  0  Current set point: 20A Electrolyte temperature set point: 50°C Anode coolant inlet temperature: 0°C Anode coolant outlet temperature: 5°C Anode coolant flow rate: 5.5 1/min Cathode configuration: (C) Pulp consistency: 2.5%  (V)  Reactor Temperature (°C)  Hydrogen Peroxide Concentration (M)  20  10.7  47  0.054  1  20  10.9  49  3  20  11.1  50  5  20  11.3  52  7  20  11.5  52  9  20  11.9  52  11  20  12.3  52  15  20  12.5  52  0.040  30  20  12.8  48  0.035  60  20  12.8  51  0.032  90  20  14  43  0.034  120  20  13.1  53  0.040  150  20  12.6  53  0.047  180  20  13.2  53  0.056  Brightness gain: Yellowness loss:  14.1 (55.7) 15.4 (21.3)  - 196-  Appendix VIII Raw Data 76  Experiment No.: V4.20  Oct 25, 99  • Electrolyte: 1.5 Liter Solution (2M N a C 0 , 400ppm M g , 1.3g DTP A) • Experimental time: 180 minutes • Mixing speed: 200rpm • Weight of wet pulp: 150.27g • Final pH = 10.26 at 62.26°C • Pre-generated H 2 O 2 time: 30 minutes 2 +  2  3  Time  Current  Voltage  (Min)  (A)  0  Current set point: 10A Electrolyte temperature set point: 60°C Anode coolant inlet temperature: 0°C Anode coolant outlet temperature: 5°C Anode coolant flow rate: 5.5 1/min Cathode configuration: (C) Pulp consistency: 2.5%  (V)  Reactor Temperature (°C)  Hydrogen Peroxide Concentration (M)  10  8.6  36  0.026  1  10  8.7  39  3  10  8.5  43  5  10  8.4  44  7  10  8.3  48  9  10  8.2  50  11  10  8.1  51  15  10  8.1  54  30  10  7.8  59  0.022  60  10  7.9  59  0.021  90  10  7.7  61  120  10  8  58  0.021  150  10  7.6  62  0.019  180  10  7.9  61  0.021  Brightness gain: Yellowness loss:  15.0 (56.6) 14.4 (22.4)  - 197-  Appendix VIII Raw Data 11  Experiment No.: V4.21  Nov 17, 99  Electrolyte: 1.5 Liter Solution (2M Current set point: 3OA N a C 0 , 400ppm M g , 1.3g DTPA) Electrolyte temperature set point: 60°C Experimental time: 210 minutes Anode coolant inlet temperature: 0°C Mixing speed: 200rpm Anode coolant outlet temperature: 5°C Weight of wet pulp: 150g Anode coolant flow rate: 5.5 1/min Final p H = 10.54 at 51 °C Cathode configuration: (C) Pre-generated H 2 O 2 time: 30 minutes Pulp consistency: 2.5% Total brightening time was 180 minutes with stopping power at a 30 minutes interval. 2 +  2  3  Time  Current  Voltage  (Min)  (A)  0  (V)  Reactor Temperature (°C)  Hydrogen Peroxide Concentration (M)  30  11.8  55  0.072  1  30  12.1  55  3  30  12.3  56  5  30  12.6  58  7  30  12.7  60  9  30  12.8  60  11  30  13.1  61  15  30  13.5  61  0.043  30  0  0  56  0.035  60  30  13.5  59  0.025  90  0  0  60  0.057  120  30  14.3  60  0.038  150  0  0  60  0.058  Brightness gain: Yellowness loss:  11.8 (53.5) 15.6(21.2)  - 198-  Appendix VIII Raw Data 78  Experiment No.: V4.22 ~ V4.25 (Gas analysis for calculating current efficiency)  Nov 17, 99  2  3  Hydrogen Content 71.26 mol%  2  3  70.58 mol%  28.29 mol%  1.13 mol%  19.84%  No.  Experiment Conditions  V4.22  lMNa CO +400ppm Mg +1.3gDTPA; Current set point: 10A; Temperature: 60°C lMNa CO +400ppm Mg +1.3gDTPA; Current set point: 30A; Temperature: 60°C 2 M Na CO +400ppm Mg +1.3gDTPA; Current set point: 10A; Temperature: 60°C 2 M Na CO +400ppm Mg +1.3gDTPA; Current set point: 30A; Temperature: 60°C  Oxygen Content 27.62 mol%  Nitrogen Content 1.12 mol%  Current Efficiency 22.5%  2+  V4.23  2+  V4.24  2  3  69.18 mol%  28.96 mol%  1.86 mol%  16.3%  2  3  69.05 mol%  29.86 mol%  1.09 mol%  13.5%  2+  V4.25  2+  - 199 -  Appendix IX  Appendix IX Brightness Reversion Experiment A n electro-brightened pulp sample (Run V 4 . l l ) was sent to Paprican Vancouver Lab for brightness reversion test. The test was performed placing the sample under 8 fluorescent lamps. A conventional peroxide brightened pulp sample with brightness of 57.38 % ISO and yellowness of 17.44 % was used as a control sample.  The control sample was prepared with the  experimental conditions as follows: brightening liquor consisted of 0.001M NaOH, 0.034M N a S i 0 , 0.01M H 0 (6% H 0 on dry pulp), 400ppm M g , and 0.002M D T P A (penta sodium 2 +  2  3  2  2  2  2  salt); pulp consistency was 0.5%; temperature was 60°C, and cooking time was 2 hours. Results indicate that electro-brightened pulp has the same brightness stability as conventional peroxide brightened pulp. Figure IX. 1 shows the profile of brightness loss of these two samples.  0  50  100  150  200  Exposure Time (Hours) • • Figure IX. 1  Conventional Peroxide Brightening  Electro-brightening  Brightness Loss of Pulp Pads Under 8 Fluorescent Lamps  -200-  250  Appendix IX Figure IX. 2 shows the profile of yellowness gain of these two samples.  16  6  —I—i—i—i—i—|—i—i—i—i—|—i—i—i—i—|—i—i—i—i—|—i—i—i—r  — | — i — n — i — i — | — i — i — i — i — | — i — i — i — i — | — i — i — i — i — | — i — H — i — i — |  0  50  100  150  200  250  Exposure Time (Hours)  Figure IX.2  •—  Conventional Peroxide Brightening  •—  Electro-brightening  Yellowness gain of Pulp Pads Under 8 Fluorescent Lamps  The Yellowness gain was measurement by the CIE L*a*b* system. This color measurement system is developed by the International Commission on Illumination (CIE) 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. [45]  -201 -  Appendix X  Appendix X Ideas for Designing New Batch Reactor The new reactor should have the allowance to operate at extreme experimental conditions, (i.e. 50Aand90°C) The ideas are as follows: •  The reactor is divided to three parts. (Upper part, middle part, and lower part)  •  A surrounding coolant chamber is installed to provide a uniform coolant temperature.  •  Zirconium is the candidate material for the reactor body, cathode and mixer.  •  The anode is platinum mesh, which is locked on the middle part of the reactor body.  •  Two thermocouples will be employed to monitor the upper and lower part of the electrolyte temperature.  Figure X . 1 presents the rough draft.  Figure X.1  Rough Draft of the New Batch Reactor Design  -202-  Appendix Figure X.2 shows the details of the reactor design. Bolt  HP —HP Zirconium based reactor body  gj  3/8" Coolant outlet  Platinum mesh -  Coolant chamber ~  -Weld  Thermocouple  •—IFlange  Figure X.2  Detail Design of the Reactor Body  203  Appendix X  Figure X . 3 shows the elevation and plan of the whole reactor. Cooling chamber Platinum mesh  Lower thermocouple.  Ribbon mixer support \  Coolant Outlet  Coolant inlet  1/4" NPT Coupling  Ribbon mixer Upper mixer  Upper thermocouple  1 / 4  "  S S  " Compression Fitting Connected to (-)  Coolant outlet Cooling chamber  |p  Zr reactor body  Thermocouple  Flange Approx. 15cm Figure X.3  Elevation and Plan of the reactor  -204-  

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