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

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ELECTRO-BRIGHTENING OF M E C H A N I C A L PULP by Joey Chung-Yen Jung B.Sc , Chinese Culture University, Taipei, Taiwan, 1994 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF M A S T E R OF APPLIED SCIENCE THE F A C U L T Y OF G R A D U A T E STUDIES DEPARTMENT OF C H E M I C A L A N D BIOLOGICAL ENGINEERING 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 presenting 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 requirements 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 that 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 reference and study. I f u r t h e r agree that permission f o r extensive copying 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 granted 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 understood that copying 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 gain s h a l l not be allowed without my w r i t t e n permission. Department of Chemical and B i o l o g i c a l Engineering 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 t h 2000 Abstract Abstract The electro-oxidation of sodium carbonate (Na2C03) to percarbonate (C2O62"), with its 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 C O 3 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 2 C 0 3 , 400ppm MgS0 4 , 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 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 TMP was 17 x 10 , which corresponded to an operation cost of 5 ton%ISO approx. $ 1,020 per ton of OD pulp for 20 % ISO brightness gain. The economic reactor • • , • , • • u n,*r ton%ISO . , . . sizing factor, brightening space-time yield, was 0.145 . A brightness reversion m hr test showed that electro-brightened pulp has the same brightness stability as conventional peroxide brightened pulp. • The 2 3 factorial experiment indicated that the combination of high current, high electrolyte temperature, and high sodium carbonate concentration has positive effects on electro-brightening 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 i i Table of Contents iv List of Figures v i i List of Tables x Nomenclature xi Acknowledgement xiv Chapter 1 Introduction 1 Chapter 2 Theoretical Background 3 2.1 Elements of Wood Chemistry 3 2.1.1 Cellulose 4 2.1.2 Hemicellulo ses 5 2.1.3 Lignin 5 2.2 Elements of Mechanical Pulping and Principles of Brightening 7 2.2.1 Elements of mechanical pulping 7 2.2.2 Principle of brightening 7 2.2.3 Brightness, yellowness, and color reversion 9 2.2.4 Alkali darkening 11 2.3 Mechanical Pulp Brightening by Hydrogen Peroxide 11 2.3.1 The chemistry of peroxide brightening 11 2.3.2 The conditions of conventional peroxide brightening process 15 2.3.3 Factors affecting brightening response in peroxide brightening process 16 (A) Effect of consistency of pulp 16 (B) Effect of pH 16 (C) Effect of temperature 17 (D) Effect of additives or stabilizers 17 (E) Effect of residual peroxide and retention time 18 2.4 Principles of Related Electrochemical Processes 19 2.4.1 Thermodynamics of the electrochemical system 20 2.4.2 Electrode kinetics and mass transfer 20 2.4.3 Elements of electrochemical cell 23 (A) Electrolyte 23 (B) Voltage balance (cell voltage) 23 (C) Electrode materials 23 (D) Product rate of peroxide 23 2.5 Production of Hydrogen Peroxide 24 - iv -Table of Contents 2.5.1 The chemical process of hydrogen peroxide production 25 2.5.2 The electrolytic process of hydrogen peroxide production 25 (A) Anodic oxidation of sulfuric acid 25 (B) Electroreduction of oxygen 25 (C) Electro-oxidation of sodium carbonate 26 2.5.3 Figures of merit for the electro-oxidation of sodium carbonate 28 2.6 In-Situ Electro-Brightening of Mechanical Pulp by Electro-Oxidation of Sodium Carbonate 29 2.6.1 Figures of merit for the electro-brightening of mechanical pulp 31 Chapter 3 Proposed Research Objectives 32 Chapter 4 Experimental Apparatus and Procedure 33 4.1 Experimental Apparatus 33 4.1.1 Original experiment apparatus 34 4.1.2 Modification of the cooling system of the electrochemical reactor 39 4.1.3 Modifications of the anode, cathode, and setup of the thermocouple of the electrochemical reactor 41 (A) Deterioration of the anode surface 41 (B) Modification of anodes 44 (C) Difficulty of reliable temperature measurements of the electrolyte 45 (D) Modification of the set-up of the thermocouple, ribbon mixer, and cathode 47 4.1.4 Modification of the cover of the electrochemical reactor 49 4.2 Experimental Procedures 50 4.2.1 Electroplating of platinum on the anode 50 4.2.2 Electrochemical production of peroxide 51 4.2.3 In-situ brightening of mechanical pulp 51 4.3 Picture of Electrochemical Brightening System 52 Chapter 5 Experimental Results and Discussion 55 5.1 Factors Affecting Electrochemical Production of Peroxide 55 5.1.1 Anode coolant temperature 56 5.1.2 Cathode material and diaphragm 57 5.1.3 Current distribution (Different electrode configuration) 62 5.1.4 Anode current density 64 5.1.5 Bulk electrolyte temperature 65 5.1.6 Stabilizers and chelating agents 67 (A) Magnesium 67 (B) DTPA (Diethylenetriaminepentaacetic acid - penta sodium salt) 68 5.1.7 pH 70 5.1.8 Heating pattern 75 Table of Contents 5.2 Factors Affecting Electro-Brightening of Mechanical Pulp 77 5.2.1 A 23 factorial experiment (effect of temperature, current, and electrolyte concentration) 77 (A) Main and interaction effects on brightness gain 80 (B) Main and interaction effects on yellowness loss 81 (C) Main and interaction effects on concentration of peroxide 82 (D) The specific brightening energy and brightening space time yield 83 (E) Summary of the results from changing temperature, current and concentration of sodium carbonate 84 5.2.2 pH 85 5.2.3 Pulp consistency 86 5.2.4 Brightening time 88 5.2.5 Pre-generating peroxide 91 5.2.6 Energy saving 93 5.2.7 Current efficiency 96 5.3 Performance of the Electro-Brightening Reactor 98 5.3.1 Temperature limitation 98 5.3.2 Current limitation 99 5.4 Pictures of Teflon Deterioration and Pulp Samples 100 Chapter 6 General Discussion and Conclusions 103 Chapter 7 Recommendations and Future Work 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 IV 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 2 0 2 - H 2 0 system 13 Figure 2.11 Formation of H 2 0 2 by the oxidation of water 14 Figure 2.12 Formation of H 2 0 2 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 2 Evolution in 1M Yt and for 0 2 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, 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 2 C 0 3 on Peroxide 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 3 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 .89 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 - viii -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; 2M Na 2 C0 3 ) 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 - ix -List of Tables List of Tables Table 2.1 Typical Compositions of North American Woods 4 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 3 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 116 - x -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 (m2) AAnode anode area (m2) aQ activity of oxidized species aR activity of reduced species c concentration (M) c b bulk concentration (M) CE current efficiency (%) C E P current efficiency of primary anode reaction (%) E applied electrode potential (V) , e" electron E A anode potential (V) E c cathode potential (V) Ecell total cell voltage (V) thermodynamic cell poential (V) E ° standard electrode potential (V) E e a equilibrium potential of anode (V) E e C equilibrium potential of cathode (V) Eohm ohmic voltage drop across the cell (V) - xi -Nomenclature E r equilibrium electrode potential (V) F Faraday constant (98480) (C mol"1) i current density (kA m~2) I applied current (kA) j i anode current density (kAm" 2) lA ' 'Anode J v ' ic cathode current density (kA m"2) iL mass transfer limiting current density (kA m"2) i 0 exchange current density (kA m"2) iL a anodic mass transfer limiting current density (kA m"2) iL c cathodic mass transfer limiting current density (kA m"2) iPartjal partial current density (kA m"2) IparUai partial current (kA) iTotal total current density (kA m"2) Iiotai total current (kA) k first order reaction rate constant (s"1) K m total mass transfer coefficient (m s"1) M W molecular weight (kg kmoi"1) m amount difference of material (kmoi) n electron stoichiometry coefficient O oxidized species Q amount of electrical charge (C) R universal gas constant (8.314) (kJ kmoi"1 K" 1) R' reduced species R* production rate of the desired product (kmoi s"1) SE specific energy (kWh/kg) STY space time yield (kg m"3 s"1) t time (s) T temperature (K or ° C ) Vsatch volume of a batch reactor (m3) VReactor volume of electrolyte (m3) - xii -Nomenclature SBE Specific Brightening Energy (kWh/ton/%ISO) B S T Y Brightening Space Time Yield ltonx%ISO/ ) \ /m3 x hr' Abbreviations CIE International Commission on Illuminatin DTPA diethylene triamine pentaacetic acid E D T A Ethylenediaminetetraethanoic acid ISO International Standardization Organization O.D. over dry SHE Standard Hydrogen Electrode TMP thermo-mechanical pulp - xiii -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 2C 206). The percarbonate ion is a strong oxidizing agent that hydrolyzes to form hydrogen peroxide according to the following equation: C 2 0 6 2 " + 2 H 2 0 -> 2HC0 3 " + H 2 0 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 2 0 e ) is an unstable compound, which has been produced in 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 (%) Cellulose 40-50 45-50 Hemicelluloses (Galacto) Glucomannans Xylans 2-5 15-30 20-25 5-10 Lignin 18-25 25-35 Extractives 1-5 3-8 Ash 0.4-0.8 0.2-0.5 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. On the molecular level, the condensed formula of cellulose is C6H10O5. Cellulose is a linear polymer of anhydro-D-glucose, (C6H12O6- H 2 0 -» C6H10O5), connected by P-(1^4)-linkages. 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] g r a s s e s h a r d w o o d s & s o f t w o o d s h a r d w o o d s Hi II, CH-OH CH,OH I 2 H C II CH CH OH c o n l f e r y l a l c o h o l p - c o u m a r y l a l c o h o l s i n a p y l a l c o h o l Figure 2.3 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. This sets in motion the entire polymerization process. [12] 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/cm2) and refining after the lignin has softened. The step of preheating makes the wood 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 II A. p-Quinone III A. o-Quinone IV A. p-Quinone methide V A. o-Quinone methide VI A. p. p'-Stilbene (A.„„^=340nnO fA.m,v=373nm) (X.„„„=420rim) (A,m<v=310nm) fXm,«=400nm') quinone (X m „=478nm) Figure 2.5 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 ; l ( 400 500 600 700 Wavelength 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 2 0 2 + HO" o H0 2 " + H 2 0 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 H0 2 " ions 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 = C H - CHO HOP" OH" -CHO ^ A ~ \ - C H O + ? H ° + H,0 OH V,,,/ CHO 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 2 0 2 -> 0 2 + H 2 0 [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 J6 pH Figure 2.10 Potential-pH Equilibrium Diaphragm of H 2 0 2 - H 2 0 system (From Marcel Pourbaix, Atlas of Electrochemical Equilibria in Aqueous Solutions) - 13 -Chapter 2 Theoretical Background In the first case, the hydrogen peroxide is reduced to water according to the reaction H 2 0 2 + 2if + 2e" -> 2 H 2 0 [2.3] 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 2 + 2H+ +2e" <- H 2 0 2 [2.4] 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 1,2 0,8 0,4 0 -0,4 -1,2, -1,6-0 "T~ Z- 4 T 6 8 10 12 14 T -"1 1 1 1 r 1 of formation of hydroge ^peroxide by oxidation of water 16 -2 2 0 2 4 6 8 10 12 14 16 region of reduction of hydrogen peroxide in water (oxidizing action of hydrogen peroxide)' JL -2 0 2 4 6 8 10 12 14 16 -2 0 2 16| 1/2 0,8 0,4 0 0,4 -1-0,8 -1,2 -1-1,6 T — r ^ region of the oxidization of hydrogen peroxide in oxygen (reducing action of hydrogen peroxide)-^ ^region of formation of hydrogen peroxide by reduction of oxygen^ " i 1 1 r i 2 1.6 12 0,8 0,4 0 -0,4 -0,8 -1,2 -1* 6 8 10 12 14 16 pH JL Figure 2.11 Formation of H 2 0 2 by Figure 2.12 Formation of H 2 0 2 by the the oxidation of water reduction of oxygen (From Marcel Pourbaix, Atlas of Electrochemical Equilibria in Aqueous Solutions) 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 0 2 4 6 6 10 12 14 16 ? I 1 1 1 1 1 1 1 1 1 I « ' » i t i t t I -2 0 2 4 6 8 10 12 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, i f 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 wil l promote the decomposition of hydrogen peroxide and decrease the brightening efficiency. (D) Additives or Stabilizers Metal ions such as Fe 3 + , M n 2 + , and C u 2 + catalytically decompose hydrogen peroxide and color the pulp. 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 2 + and C u 2 + will catalyze auto-oxidative reactions and accelerate brightness reversion, which form new colored structures in lignin. On the other hand, the Fe 3 + will form colored complexes with 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 2 + - > M g ( 0 2 ) 2 [2.5] The dosage is about 0.05% weight percent magnesium sulfate on OD pulp. - 17-Chapter 2 Theoretical Background 2) Diethylenetriaminepentaacetic acid (Chelate) Diethylenetriaminepentaacetic acid (DTPA) removes metal ions from pulp by chelating. DTPA forms a ring structure with the metal ion, which inhibits the metal ion catalytic effect. [26] The electrons of DTPA 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 DTPA 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 ( UC) pH of the Brightening Liquor Retention Time (Minutes) 35 - 4 4 (Low) Medium alkali ( 1 0 - 12) 240 - 360 60 - 79 (Medium) Medium alkali (10-12) 120- 180 93 - 98 (High) Low alkali ( 8 - 10) . 5 - 2 0 Table 2.2 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 e) is called the overpotential (r|). When r\ is positive, E > E e , equation 2.6 will tend to go from 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, AGCell. 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 ECM by the expression: AGCell=-nFECell [2.7] where F is the Faraday constant, 96480 C/mol. For spontaneous cell reactions, T ASCell > AHCe!l; thus AGCell is negative and ECell is positive. Conventionally, the thermodynamic cell potential, ETCen, is the difference between the cathode and the anode potentials. ELII = E c - E A [2.8] 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 e , can be calculated from the Nernst equation as follows: Ee=E°e+^ln^ [2.9] nF aR where E° is the standard electrode potential (Volt), R is the gas constant (kJ/kmol/K), aQ is the activity of the oxidized species, and aR is the activity of the reduced species. 2.4.2 Electrode Kinetics and Mass Transfer Consider a single electrode reaction in the cathodic direction. 0 + ne"->R' [2.10] - 2 0 -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 = - F R * [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) [2.12] nF nF 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] C E = ^ ? L [2.13] 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= . By differentiating equation 2.12 with respect to time and ^Batch combining with equation 2.13, the overall rate expression can be written as follows: dc = CE-AArea-iTotal ^kmol^ d t n-FVBaton where iTotal 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, iac; and curve (b) shows the actual measured current having a mass transfer limited value, iL, at high potentials. 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, iL, can be expressed by the equation as follows: iL=nFKmCb [2.15] where K m is the mass transfer coefficient which depends on electrolyte composition, temperature, and flow conditions; n is the stoichiometry number of moles of electron, and Q, is the bulk concentration of reactant. In Figure 2.15, i f 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] - 2 2 -Chapter 2 Theoretical Background na = a+b\n{i)-b\n{\- j/t j [2.16] R T RT where a= m ( 0 > ^ = > m& "Ha is the anodic overpotential. In summary, the anF 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. An 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] i C e l l : E e C - E e a + T | c - T | a - ZH, ohm Where *la Eohm Anodic overpotential (V) Equilibrium potential of cathode (V SHE) Ecell "Ho E / (V) [2.17] Total cell voltage (V) Cathodic overpotential (V) Equilibrium potential of anode (V SHE) Ohmic voltage drop across the cell (S){is/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[H202] = AAnodeiAnodeCEP _k*HOy dt 2-FK Consum (kmol/s) [2.18] Re actor where nConsum = [rate of destruction of H 2 0 2 at cathode and anodes] where: [ H 2 O 2 ] AAnode k rate of [h02 \ destruct rate of \h02 \destruct by equation 2.28 (p.26) by equation 2.30 (p.26) Concentration of H 2 O 2 (kmol/m3) Anode area (m2) Rate constant of H 2 O 2 homogeneous decomposition (s"1) Faraday constant (96487 C/kmol) t lAnode C E D VR, eactor Time (seconds) Current density at anode (kA/m2) Current efficiency of primary anode reaction (%) Volume of electrolyte (m3) During steady state, the net rate of peroxide production is zero, hence [ H 2 O 2 ] becomes: [H202] AAnode '1Anode ' CEp nconsum 2kFK Re actor 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 - 2 4 -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 auto-oxidation 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 2 0 8 + 2e" <- 2S0 4 2 " Ee° = 2.1VsHE [2.20] H 2 S 2 0 8 + 2 H 2 0 -> 2 H 2 S 0 4 + H 2 0 2 [2.21 ] -25 -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 2 + H 2 0 +2e" -> H0 2 " + OH" E ° = -0.08 V S H E [2.22] H0 2 " + H 2 0+2e ->30H" E ° = 0 . 8 7 V S H E [2.23] The reactions under acidic conditions are: 0 2 + 2 lT +2e" -» H 2 0 2 " E ° = 0.67 V S H E [2.24] H 2 0 2 " + 2H+ +2e" -> 2 H 2 0 E ° = 0 . 8 7 V S H E [2.25] 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 electro-oxidation 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 ° at 298°C ( V S H E ) Primary C 2 0 6 2 " + 2e" <— 2 C 0 3 2 ' «2 [2.26] Secondary 2 H 2 0 + 0 2 + 4e" <- 40H" 0.4 [2.27] 0 2 + H 2 0 +2e" <r- HO~ + OH" 0.08 [2.28] Cathode Reactions Primary 2 H 2 0 + 2e" - » H 2 + 20H" -0.8 [2.29] Secondary H0 2 " + H 2 0 + 2e" -> 3 OH" 0.87 [2.30] Table 2.3 Principal Reactions for Electro-Oxidation of Sodium Carbonate - 2 6 -Chapter 2 Theoretical Background The hydrogen peroxide is formed as percarbonate from the primary anode reaction is hydrolyzed to byproduct bicarbonate as follows: C 2 0 6 2 " + 2 H 2 0 -> 2HC0 3 " + H 2 0 2 [2.31] However, depending on the pH, the peroxide may exist as H 2 0 2 or H0 2 " according to the equation as follows: H 2 0 2 + OH" <=> H 2 0 + H0 2 " [2.32] 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. An ideal anode material for the electro-oxidation 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 2C03 at high potential. (pH = 0) 2H+ +2e" -> H 2 <«g < J ) 0 2 + 2 H 2 0 +4e" <- 40H" (pH=14) .2 -1 0 -1 O Figure 2.15 Tafel Plots for H 2 Evolution in 1M and for 0 2 Evolution in 1M OH [2] - 2 7 -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/cm2 4. the anode material should have high oxygen overpotential and survive under high 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 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 2.5.3 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 F R [2.33] hotal ^Total B) Specific Energy (kWh/kg) SE= — \ECell\ [2.34] 3600 MW-CE1 Ce"1 C) Space-Time Yield (kg m"3 s"1) S T y = VroductionRate = CE-IPartial MW ^ Re actorVolume n-F-VKeactor - 2 8 -Chapter 2 Theoretical Background where: Ipartial Current of equation 2.22 VReaotor : Volume of Electrolyte (m3) n Electro stoichiometry coefficient o f C 2 0 6 2 " iTotai Total current density applied to the cell (kA/m2) F Faraday constant (96487 kC/kmol) R* Production rate of H 2 O 2 (kmol/s) Eceii Total cell voltage (V) M W Molecular weight of H 2 O 2 (kg/kmol) ipartial Current density of equation 2.25 (kA/m2) iTotai Total current applied to the cell (kA) 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 - 2 9 -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 electro-brightening 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 2 C 0 3 ; 0.11M NaHC0 3 ; 0.034M Na 2 Si0 3 ; 0.6g DTP A; 0.04g M g S 0 4 Current & Voltage 11 A & 15 V PH « 10.7 Temperature * 5 4 ° C Cathode Material Tungsten rod; area: 19 cm Anode Material & Area Platinized titanium modified water cooled U-tube; area: 28 cm 2 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-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 Best Brightening Results by Kurniawan and Oloman [9] 2.6.1 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) Specific Brightening Energy (kWh/ x ^ /{ton % ISO) SBE Eceii • I time Tonnes of Pulp • Brightness Gain [2.36] B) Brightening Space-Time Yield (ton%ISO)/ /(m3hr\ T> C T V Tonnes of Pulp • Brightness Gain Lib 1Y Reactor Volume • time [2.37] 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 electro-brightening 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. - 3 2 -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 Experimental procedure 1. Electroplating of platinum on the anode 2. Electrochemical production of peroxide 3. In-situ electro-brightening of mechanical pulp 4.3 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 DC power supply, a motor set, a temperature control unit, and an electrochemical reactor. A DC motor control B DC power supply C Temperature control D Thermocouple E Heater F Mixer motor G Electrochemical reactor I Cooling water inlet J Cooling water outlet Figure 4.1 Original Experimental Set-up Developed by Dr. Zhang and Prof. Oloman - 3 4 -Chapter 4: Experimental Apparatus and Procedures The DC 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 293ounce-inch 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 DC power supply, X H R 20-50, was capable of producing a maximum 50 Amperes of current at 20 volts. The positive of the DC 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 OMEGA, and the control box was composed by Mr. Alex Lee at the chemical engineering shop of UBC. The control box included a microprocessor-based temperature controller, CN76000. The CN76000 was a first-order sensor functioning with a reverse control action made by OMEGA. 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 cm2. Four cooling chambers were attached behind the anode areas with individual 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 electro-brightening the pulp. -35 -Chapter 4: Experimental Apparatus and Procedures Platinized Anode Surface Mixer Ribbon Support Cooling Chamber Supported Rubber Ribbon Mixer Thermocouple Titanium Cathode covered with diaphragm 0.64 cm (1/4 inch) N P T Connector Supported Rubber 22.75 cm (7.5 inch) J Figure 4.2 Original Electrochemical Reactor -36-Chapter 4: Experimental Apparatus and Procedures Cooling Water Outlet 0.64 cm (1/4 inch) NFT Connector Teflon Coating Platinized Anode Surface (8 cm x 2 cm x approx 10 fim) Cooling Water Inlet ^ ' , ^Titanium Vessel Cooling Chamber Figure 4.3 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, lA inch NPT connectors. These connectors connected to the cooling source with lA inch polyethylene tube. These connectors and tubes were purchased from Cole-Parmer Instrument Company. The platinum layer was electroplated onto the titanium wall, and each platinized anode area was 16cm2 (8cm x 2cm) in area by a few microns thick. The rest of the area was covered with a layer 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. The exposed titanium would react with peroxide and form the orange complexes Ti02 2 + 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 - 3 7 -Chapter 4: Experimental Apparatus and Procedures ;2 -i 0 1 M i a e 7 i ) a ii i; n m i ii 06. 08 OA at 0 •<u OK -as -a». -i -1.2 -M -1.8 -2 -t2. c o r r o s i o n ? ? c o r r o s i o n c o r r o s i o n passivation Icorrosion immunity M 4 « t M 1 II II l i I) H I) « pH z w t.* it i 0,6 06 a* a.z o -0.2 -a* -0,6 -a* - l -1,2 -u -1,6 -IB 2 1-2.2 1-2.4 Figure 4.4 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 3A inch. The titanium tube was drilled with holes for releasing the gas generating from the 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. - 3 9 -Chapter 4: Experimental Apparatus and Procedures A DC control B DC power supply C Temperature controller D Surface thermocouple E Heater F Mixer motor G Electro-brightening reactor H pH meter I Centrifugal pump J Ice water tank K Laboratory stirrer Figure 4.6 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 - 4 0 -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 RUN — A — FOURTH RUN • — FIFTH RUN Figure 4.7 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 2 C 0 3 , 0.13M NaHC0 3 , 0.03M NaSi0 3 , 0.007% MgS0 4 «7H 2 0 , and 0.01%) DTPA. The experiments were run for 180 minutes with 20A from the DC power supply. The temperature of the electrolyte was controlled at 60°C. - 4 2 -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 2 + , which means titanium would go from 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 silver-based, 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. - 4 4 -Chapter 4: Experimental Apparatus and Procedures Elevat ion P lan Cooling Water Inlet Figure 4.9 Modification of Anode (C) 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) • Electrolyte Temperature • Inside-wall Reactor Temperature * Outside-wall Reactor Temperature Figure 4.10 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. - 4 6 -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. A l l 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. - 4 7 -Chapter 4: Experimental Apparatus and Procedures Recess Areas (4 of them) about 1 mm to fit glued Platinum sheet Thermocouple 1 / 4 " S S - Compression Fitting Figure 4.11 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 electro-brightening 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 electro-brightening 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 XA inch tube. - 4 9 -Chapter 4: Experimental Apparatus and Procedures Hole for Collecting Hole for Gas Hole for Collecting Ordinary Cover Cover for Gas Collection Figure 4.12 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 2 PtCl 6 , 45 g/1 of H 3 P 0 4 , and 240 g/1 of (NH4)2HP04. The system was preheated and controlled at 70°C before starting the procedure. Each 16 cm 2 of plated area was electroplated at 16 mA for 12 minutes. The calculation of this procedure is seen in Appendix III. - 5 0 -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 DTPA 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 pH 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. - 5 2 -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 Factors affecting electro-brightening of mechanical pulp Performance of the electro-brightening reactor Pictures of Teflon deterioration and pulp samples 5.2 5.3 5.4 Table 5.1 Organization of Chapter 5 The results in this chapter are divided into four different sections (VI, V2, V3, 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) • V3: Experiments carried out with final modifications on uncovered zirconium cathode, platinum sheet anode, mixer, and location of thermocouple. (Figure 4.9, Figure 4.11) • V4: Brightening experiments performed with final modifications mentioned above. 5.1 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, - 5 5 -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) C O O L I N G T E M P E R A T U R E S 6 D E G R E E C E L S I U S C O O L I N G T E M P E R A T U R E S D E G R E E C E L S I U S Figure 5.1 Effect of Coolant Temperature on Peroxide Generation - 5 6 -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 2 + ; the current set point was at 20 A (anode current density: 3.1 kA/m 2); the electrolyte 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 electro-reduction 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. Cathode Diaphragm Anode Maximum [H 2 0 2 ] I (M) V2.05 Stainless Steel Polypropylene Felt Platinized 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 ([H 2 0 2 ] : Concentration of Peroxide) Table 5.2 Effect of Diaphragm and Cathode Material on Peroxide Generation - 5 7 -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 2 + ; the current was controlled at 20 A (anode current density: 3.1 kA/m 2); and the electrolyte temperature was controlled at 20 degree. 20 40 60 80 100 Experimental Time (Minutes) • POLYPROPYLENE FELT • MICROPOROUS POLYPROPYLENE Figure 5.2 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 - 5 8 -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 75 100 Experimental Time (Minutes) m Zirconium Cathode, Platinum Sheet Anode « Stainless Steel Cathode, Platinized Anode Figure 5.3 Effect of Cathode Materials with Diaphragm on Peroxide Generation - 5 9 -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 2 C 0 3 plus 400ppm M g 2 + ; the electrolyte 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) • WITH P O L Y P R O P Y L E N E STRING D I A P H R A G M • — — WITH P O L Y P R O P Y L E N E STRING D I A P H R A G M A WITHOUT D I A P H R A G M Figure 5.4 Effect of Diaphragm on Zirconium Cathode on Peroxide Generation - 6 0 -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 V S H E - In order to remove the corrosion products, the zirconium tube was mechanically polished before use in other runs. However, the corroded stains could not be taken off. 1.6 E M 1 . 4 1.2 1 0.8 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1 -1.2 -1.4 -1.6 -1.8 _ -2 --2.2 --2.4 --2.6 -1 0 ~ i — r 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 ~ i i i i i i l l i i — I — i — r -2 Z r O + + Z r 2 0 7 ? ZrOa? Z r 2 O s ? Z r 0 2 • 2 H 2 0 II HZr03" II J 1 1 1 1 I I I I I I L 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1 -1.2 -1.4 -1.6 -1.8 -2 -2.2 -2.4 -2.6 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11 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 2 with an anode/cathode ratio at 4 by using Teflon Tape 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 2 with the ratio at 4.9. To further test 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 2, and the 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. - 6 2 -Chapter 5: Experimental Results and Discussion Experiment conditions: electrolyte: 1M Na2C03 + 400ppm M g 2 + ; current: 20A; 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 50 100 150 200 Experimental Time (Minutes) • DESIGN A • DESIGN B A DESIGN C Figure 5.7 Effect of Current Distribution on Peroxide Generation -63 -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 15-minute intervals beginning 15 minutes after the experiment started. 200 E x p e r i m e n t a l T i m e ( M i n u t e s ) m CURRENT DENSITY: 3.13 kA/mA2 (Current: 20A) 9 CURRENT DENSITY: 6.25 kA/mA2 (Current: 40A) A CURRENT DENSITY: 4.7 IWmA2 (Current: 30A) Figure 5.8 Effect of Current Density and Concentration of N a 2 C C > 3 on Peroxide Generation - 6 4 -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 2) produced 33% more peroxide than the lower current density (3.13 kA/m 2) in the first 120 minutes. However, 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 2 produced higher 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 2C03 and 400ppm M g 2 + ; current was 20A for 180 minutes; cathode material was zirconium tube without 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 CO g 0.04 C o O 0 0.03 •g x o o . o i "D 5^ 0.00 I I I I RunV3.06 H H H Run V3.05 ---50 100 150 Experimental Time (Minutes) 200 - 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 Figure 5.9 Effect of Bulk Temperature on Peroxide Generation -66-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 DTPA 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 2C03 + additives; electrolyte temperature set point: 60°C; current: 20 A; anode coolant temperature: 1°C 2 V3.10 Zirconium tube without diaphragm 400ppm M g 2 + V3.15 400ppm M g 2 + ; N a H C 0 3 V3.17 400ppm M g 2 + + 0.002 M DTPA V3.18 400ppm M g 2 + + 0.002 M DTPA; N a H C 0 3 Table 5.4 E Tect of Stabilizer and Chelating Agent on Peroxide Generation (A) 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. - 6 7 -Chapter 5: Experimental Results and Discussion Experimental Time (Minutes) -A 1 M N a 2 C 0 3 pH=1l.6 -9 1M Na2C03 + 400ppm Mg2+; pH=11.6 Figure 5.10 Effect of Stabilizer on Peroxide Generation Results shown in Figure 5.10 clearly demonstrate the effect of the M g 2 + . With the stabilizer, the 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 V3.17 - 6 8 -Chapter 5: Experimental Results and Discussion were started at pH around 11.8. Approximately 0.05 weight % of DTPA 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 ^  c o O .g 0.03 -I x o 1 0.02 H C (D 2 o . o i "D X 0.00 100 150 Experimental Time (Minutes) pH=10.5 without DTPA pH=10.5 with 0.002M DTPA pH=11.6 with 0.002M DTPA pH=11.6 without DTPA 200 Figure 5.11 Effect of Chelating Agent on Peroxide Generation The results show that no matter under which region of pH, the present of DTPA promoted the accumulation of peroxide. This might be due to DTPA 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 p H 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: H C O a o C O a ^ + F f 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 Cat. No. Run No. Experimental Conditions: (Electrolyte: 1M N Current: 20A; Coolant: 1°C at 6 liter a2C03 + additives; per minute) Final [H 2 0 2 ] (M) Voltage Electrolyte Temperature <°C) Initial pH Final pH Additives (V) Set Point Actual 1 V3.14 16.1 20 33 11.60 -400ppm M g 2 + 0.0570 V3.16 16.3 20 33 10.50 - 0.0160 2 V3.10 12.5 60 56 11.60 - 0.0425 V3.12 12.6 60 56 11.85 11.10 0.0600 V3.13 12.2 60 56 10.50 10.20 0.0090 3 V3.19 16.3 20 33 11.85 11.36 400ppm M g 2 + + 0.002 M D T P A 0.0530 V3.20 16.2 20 33 10.50 10.62 0.0200 4 V3.17 12.8 60 56 11.94 11.27 0.0570 V3.18 12.3 60 56 10.50 10.30 0.0160 ([H 2 0 2 ]: Maximum Peroxide Concentration) Table 5.5 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 2 0 2 -> 0 2 + - 7 0 -Chapter 5: Experimental Results and Discussion 2 H + +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 50 100 150 200 Experimental Time (Minutes) • Initial pH at 11.6 • Initial pH at 11.9 • Initial pH at 10.5 Figure 5.12 Effect of pH on Peroxide Generation (2) (V3.10; V3.12; V3.13) -71 -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) — • — Initial pH at 10.5 • Initial pH at 11.94 Figure 5.13 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, pH 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. - 7 2 -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 3 2 " ions in the electrolyte. The relative concentrations of H C 0 3 " and C 0 3 2 " in 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 3 " ion dominates, with a maximum concentration close to pH 8. At high pH (>12) the principal species is C0 3 2 " . 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 HC0 3 " and C 0 3 2 " is pH 10.34. [35] Figure 5.15 is the Pourbaix diaphragm for carbon-water system at 25°C. 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 2 C 0 3 + HC0 3 " + C 0 3 2 ' . The portion of the diagram bellow this line refers to solutions thermodynamically saturated with solid carbon. -73 -Chapter 5: Experimental Results and Discussion -2 -1 0 i 2 3 4 5 6 7 8 9 10 II 12 13 14 15 16 -2 -1 0 1 2 3 4 5 6 7 8 9 10 II 12 13 14 15 J6 pH 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 -0.4V and the pH for pure 1M sodium carbonate solutions being around 11.7, C O 3 2 " ion was the primary ion in this system. Since the C O 3 2 " ion was dominant, the rate of peroxide generation was high. However, i f the pH was set around 10.5, near the region that HCO3" ion was dominant, there will be not enough C O 3 2 " ion for generating peroxide by reaction 2.7. 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" <- 2C032", of the electro-oxidation process and result in poor peroxide production. - 7 4 -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 2 + ; electrolyte 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. 6 0 I i i i i | i i i i | i i i 0 5 0 1 0 0 1 5 0 2 0 0 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 - 7 6 -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 s t century. 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 3 factorial design was performed with factors (factorial factors) as 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 - 7 7 -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 electro-brightening time were held constant at 2.5% and 3 hours respectively. The additives were 400ppm M g 2 + and 0.002 M DTP A. The responses measured were the concentration of peroxide, the brightness gain, and yellowness loss of the pulp. The concentration of peroxide was measured 30-minute intervals throughout the process. 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 3 factorial runs. 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 2 C0 3 ] (M) 1 1.5 2 Temperature (°C) 40 50 60 Current (A) 10 20 30 Anode Current Density (kA/m2) 1.6 3.1 4.7 No Run No. [Na 2 C0 3 ] Current Temperature 1 V4.02; V4.03 - - -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 V 4 . l l + + + 9 V4.12 + - + ([Na 2C0 3]: Concentration of sodium carbonate) Table 5.6 Variables, Levels and the Design of the 2 3 Factorial Experiments - 7 8 -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 ! H o 1 Na 2 C0 3 Conc . (M) 30 (A) Brightness Gain (% ISO) -B-Yellowness Loss Figure 5.17 Cube Plots for the Responses of a Full 2 3 Factorial Design 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 - 7 9 -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 Effects Average 13 580 | . C 4 + 1 1 Main Concentration (C) 4.3 85 Main Current (I) 1.0 19 1 3 + 1 Main Temperature (T) 2.6 51 1 | . T | . C I T Interaction C x i -0.4 -8 2 + 1 Interaction C x T 1.0 20 1 1 1 + .. r i Interaction T x l -0.6 -12 Interaction C x I x T 2.2 43 i 0 + 1 t-ratio test for curvature = -48.3; S =0.07 with 1 d.f; Confidence Level: 95 % 1 1" Table 5.7 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. - 8 0 -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 Main Effect (%) t-Ratio Effects Average 14.3 643.0 4 + . T i Main Concentration (C) 2.3 46.5 i l l Main Current (I) 2.5 49.5 3 + 1 l-I | . C 2 + Main Temperature (T) 3.9 78.5 Interaction C x i -0.3 -5.5 1 1 Interaction C x T 0.2 3.5 1 1 +. CIT I Interaction T x l 0.0 0.5 i 1 | . C T Interaction C x I x T 1.1 21.5 O + . IT | . C I 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 Effects | . IT 1 | . C .0125 + 1 1 1 .0100 + 1 1 1 .0075 +.. 1 1 1 .0050 + | . C I | . C I T 1 .0025 + | . C T Average 34.8 105 Main Concentration (C) 13.3 7.5 7.3 4.3 1.8 14.3 3.8 26.5 15.5 14.5 8.5 3.5 28.5 7.5 Main Current (I) Main Temperature (T) Interaction C x i Interaction C x T Interaction T x l Interaction C x I x T t-ratio test for curvature = -17; S =7E-4 with 1 d.f.; Con] idence Interval: 95 % Table 5.9 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. - 8 2 -Chapter 5: Experimental Results and Discussion 93 90 87 p 84 R 79 O 74 B 69 A 63 B 56 I 50 L 44 I 37 T 31 Y 26 21 % 16 13 10 7 + .0000 .0025 .0050 .0075 .0100 .0125 EFFECTS (M) Figure 5.18 Interaction Plots on Concentration of Peroxide & Probability vs Effects (D) 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. Current (A) Cell Voltage (V) AY (%) AB (%ISO) SBE (kWh/ton/%ISO) B S T Y [(ton*%ISO)/m3/hrl V4.02 10 11.5 9.4 7.5 11 x 102 0.062 V4.04 10 8.2 12.9 13.3 4 x 102 0.111 V4.05 20 11.3 14.5 15.2 10 x 102 0.127 V4.06 30 20.0 15.9 10.4 40 x 102 0.088 V4.08 10 9.9 14.2 11.8 6 x 102 0.099 V4.09 30 16.7 14.0 12.3 28 x 102 0.103 V4.10 30 20.0 13.2 11.6 36 x 102 0.097 V 4 . l l 30 13.9 19.2 17.4 17 x 102 0.145 V4.12 10 7.5 15.9 15.3 3 x 102 0.129 (AB: Brightness gain; AY : Yellowness loss) (SBE: specific brightening energy; BSTY: brightening space-time yield) Table 5.10 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 electro-brightening 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. Although the - 8 4 -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 p H 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 2 + ; the current was 20A; the temperature set point was 60°C; anode coolant was 1°C at 5.5 liter per minute; and the cathode material for these runs was titanium tube - 8 5 -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 12 m 6 -+-3 + ~ 0 I I I Initial pH= 11 , , , | • , i | i i i .50 (Run VI. 14) i i J _ • -- < liitialpH= 11.23 (Run VI. 13) . -I \ ! -1 1 1 i 1 1 TnitfaTpH = ID". 3D" (Run Vi : 1 2 ) " — i 1 1 j 1 1 1 1 1 1 1 1 • • • 9.0 9.5 10.0 10.5 11.0 F i n a l p H 11.5 12.0 B R I G H T N E S S G A I N Y E L L O W N E S S L O S S 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 i f 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 2 + , and 0.002M DTP A ; temperature set point was 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 s o Vi Vi & - a •c CQ 1 9 . 5 1 9 . 0 -1 8 . 5 -_• 1 8 . 0 -1 7 . 5 1 7 . 0 -A—r ~i 1 1 1 1 r~ [NaiCOj]: 2M Current: 30A RunV4.11 (A) -i—i—|—i—i—i—i—|—i—i—i—i—|—i—i—i-RunV3.32 -i 1 1 1 1 1 1- -i 1 1 r 2 . 0 2 . 5 3 . 0 3 . 5 4 . 0 Pulp Consistency {%) 4 . 5 ( B ) B R I G H T N E S S G A I N Y E L L O W N E S S L O S S Figure 5.20 Effect of Pulp Consistency on Brightness Gain and Yellowness Loss - 8 7 -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 2C03, the 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 2M 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 3 factorial design experiments was 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 2 C 0 3 , 400ppm M g 2 + , and 0.002 M DTPA; temperature set point was 60°C; current was 30A; 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 - 8 8 -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) • B R I G H T N E S S GAIN • Y E L L O W N E S S L O S S Figure 5.21 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. - 8 9 -Chapter 5: Experimental Results and Discussion Brightening Time (Minutes) — • — 30 Minutes (Run V4.15) • 60 Minutes (Run V4.13) — * — 90 Minutes (Run V4.16) •-— 120 Minutes (V4 14) — * — 180 Minutes (Run V4.11) 1 240 Minutes (RunV4.17 ) Figure 5.22 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 - 9 0 -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 C O 3 2 " ions but favorable for HCO3' 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 pre-generating 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 pre-generating 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 2 C0 3 ] Current Electrolyte Temperature Initial [H 2 0 2 ] AB AY Final [H 2 0 2 ] Units M | A °C M % ISO % M V4.05 1.5 1 20 50 0 15.2 14.5 0.051 V4.19 20 50 0.050 14.9 15.4 0.050 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 ([Na2C03]: Concentration of Sodium Carbonate; [H202]: Concentration of Peroxide; AB : Brightness Gain; AY : Yellowness Loss) Table 5.11 Effect of Pre-Generating Peroxide Table 5.11 shows two comparisons between the standard electro-brightening process and pre-generating 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. 5 0 1 0 0 1 5 0 Brightening Time (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) 2 0 0 Figure 5.23 Profile of the Peroxide Concentration - 9 2 -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 2 C 0 3 , 400ppm M g 2 + , and 0.002 M DTP A as brightening 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 O 0.02 +'-Standard F^un (V4.18) T3 5* Energy Saying Run (V4.21) X 0.00 A 0 50 100 150 200 Brightening Time (Minutes) Figure 5.24 Effect of Energy Saving on Peroxide Generation - 9 4 -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 Standard Run Experimental Condition Standard Run Energy Save Run AB (%ISO) AY SO/ 16.2 17.0 11.8 15.6 SBE (kWh/ton/%ISO) 16 x 10' 11 x 10' B S T Y (ton*%ISO/m3/hr/) 0.123 0.181 (AB : Brightness gain; AY : Yellowness loss) (SBE: specific brightening energy; BSTY: 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 BC Research Inc. for gas analysis. The current efficiency was gauged on a range of current density from 1.6 kA/m 2 to 4.7 kA/m 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 6 2" + 2e" <- 2CO32" and 2H2O + 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 % / / Current • ' 10A I M Concentration of Sodium Carbonate 2 M Figure 5.26 Peroxide Current Efficiency versus Current and Concentration of Sodium Carbonate - 9 6 -Chapter 5: Experimental Results and Discussion The detailed information of Figure 5.26 displays in Table 5.12. ([Na2C03]: Concentration of Sodium Carbonate; [H2]: Concentration of Hydrogen Gas) ([02]: Concentration of Oxygen Gas; [N2]: Concentration of Nitrogen Gas) Table 5.12 Data of Gas Analysis and Current Efficiency Figure 5.26 shows that the highest peroxide current efficiency (22.5 %), with 1M sodium carbonate, was achieved at a current density of 1.6 kA/m 2 . (The detailed calculations are shown in Appendix IV.) Another phenomena which can be observed was that although better conductivity was provided by a higher concentration of sodium carbonate (2M), 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 on the anodes and the cathode than assumed in the previous paragraph. Reaction like 2H2O + O2 + 4e' <- 2H202 might happen at the anodes, and reaction like 2H+ + H202 + 2e" -» 2H20 might happen on the cathode. However, it does give a rough idea of how the peroxide current efficiency was distributed in this study. - 9 7 -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 2). In order to raise the 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 the peroxide decomposition and affected the brightening results. -98-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 2) would simply heat the brightening solution over 30°C. Even turning off the heater, the 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 3 factorial experiment. 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 2M sodium carbonate, 400ppm M g 2 + , and 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 DC 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 of 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 wil l 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 2" species in the electrochemical process. At pH higher than 11, C O 3 2 " was the primary ion in the electrolyte, thus the peroxide concentration was high. When pH was 10.5, the HCO3' 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 (E0hm decreased) and energy input. High C O 3 2 " concentration also promoted the percarbonate generation as well as peroxide accumulation. 6. Additives such as magnesium sulphate and DTPA 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 3 factorial design experiment of the in-situ brightening of mechanical pulp showed that the three factors (temperature, current, and concentration of sodium carbonate) had positive significant effect on the brightening response. The concentration of sodium carbonate presented the most dominant effect. 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 pH 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 2 + , and 0.002M DTPA; electrolyte 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 102 — — and a brightening space-time yield of 0.145 t 0 n / / ° ^ ^ Xhe high value ton%ISO m 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 TMP 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 Hil l , 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. Y u 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". BC Research, Vancouver, Canada (January 13, 1970) [9] Pogy Kurniawan, A Study of In-Situ Brightening of Mechanical Pulp via the Electro-Oxidation of Sodium Carbonate. M.A.Sc. Thesis, UBC, 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, McGRAW-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 o-Benzoquinones 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 TMP 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 t h Annual Meeting. Technical Section. Canadian Pulp and Paper 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" BC 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. CHNL 492 Thesis, UBC, 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 n d . Prentice hall, Upper Saddle 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) - I l l -Reference [39] William L. Masterton, Emil J. Slowinski, Conrad L. Stanitski, Chemical Principles with Qualitative Analysis 6 t h. Saunders Golden sunburst Series, CBS College Publishing, New 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. 168- 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 n experimental runs. Two-level 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 2 , X „ ) at two levels, i.e. "+" and 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. An 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. X i x 2 X 1 X 2 (Interaction Column) Response 1 + + + Y , 2 + - - Y 2 3 - + - Y 3 4 - - + Y 4 Interaction effect of Xy = + ^ 4 ) ^ 2 ( 2 ) C. 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. They do not indicate the reliability or precision of these estimates. 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^ + ^  (4) where C = number of center points N = the number of factorial points in the design - 114-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: 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. (6) - 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 2 0 2 ] (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 A B (% ISO) Ave. A B (% ISO) A Y 1 Ave. A Y (%) II (%) [H 2 0 2 ] (M) Ave. [H 2 0 2 ] (M) 2 2 7.3; 7.7 7.5 | 9.1; 9.7 j 9.4 0.026; 0.028 0.027 6 2 15.1; 15.2 15.2 J 14.6; 14.5 j 14.5 0.042; 0.043 0.043 3 2 10.0; 10.8 10.4 j 15.3; 16.5 j 15.9 0.033; 0.039 0.036 (n = number of runs; A B = brightness gain; A Y = yellowness loss; [H 2 0 2 ] = Cone. Of Peroxide) (C: Na 2C03 Concentration; I: Current; T: Temperature) Table A2.1 Summary of Responses from the Factorial Design - 116-Appendix II Using the equation: Si = shown below: , the response error of each run was calculated and No r SAB 5 A 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 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: s2 = Z ( i - i ) 1. The pooled response error for brightness gain S2 = ( ° 2 8 2 8 ) 2 +(00707)2 +(0.5657)2 _ AB 3 = ± 0.37 % ISO 2. The pooled response for yellowness loss (0.4243)2 +(0.0707)2 +(0.8485)2 _ = 0.302 StY = ± 0 . 5 5 % 3. The pooled response for concentration of peroxide 117 Appendix II (0.001414)2 +(0.000707)2 +(0.004243)2 3 = 6.83E-6 [ff,02] = ± 2.6E-3 M 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 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 WAr (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 calculated by equation: W (Effect) = (Main Effect Estimate) ± ts Two degrees of freedom -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) ± t s ^ + ^ 1. 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 WAY (Effect) = (Curvature Effect) ± 2.0 % 3. 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 2 PtCl 6 , 45 g/1 H 3 P 0 4 , and 240 g/1 ( N H ^ H P C v The current density was set at 1 mA/cm 2. Assuming 100% current efficiency, the current was set at 16 mA for 12 minutes to obtain an approximate 10 urn platinum thickness. The cathodic reaction and detail calculation was as follows: PtCl 6 2 " (aq) + 4e" Pt (s) + 6C1" (aq) E° = 0.744 V (III. 1) Density of platinum = 21.45 g/cm3 21.45 x 16 x 1 x 10'3 = 0.343 g « 0.00176 mol Pt / * \ Electrode area 10 urn (cm2) 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-Appendix IV Appendix IV The Calculation of Peroxide Current Efficiency Assume that only two reactions happened on the anodes; i.e.: C 2 0 6 2 " + 2e <- 2C0 3 2 " E° = 2 V S H E 2 H 2 0 + 0 2 + 4e" <- 40H" E° = 0.4 V S H E the reaction on the cathode is 2 H 2 0 + 2e -> H 2 + 20FT E° = -0.8 V S H E For generating 0.5 mol of 0 2 —» 2F; for generating 1 mol of H 2 -» 2F .'. At anodes At cathode 0.5 mol 0 2 -» 2F 1 mol H 2 -» 2F n m o l 0 2 - > I x t x ( l - C E ) n m o l H 2 - > I x T 0 . 5 x / x / x ( l - C E ) Ixt nn : ^ L N Or 2F 2 IF where CE is peroxide current efficiency (1) Generating peroxide for 45 minutes with 2M Na 2C03 at 30A (from head gas analysis) 0.5x1 xtx(\-CE) nQl 2 £ 29.86% n„ Ixt ~ 69.05% IF l-CE 0.2986 , „ „ 0.2986 => = => l - C E = 2 x 2 0.6905 0.6905 ^> CE = 0.135* 13.5% - 121 -Appendix IV (2) Generating peroxide for 45 minutes with 1M N a 2 C C > 3 at 10A (from head gas analysis) 0.5x1 xtx(\-CE) "o2 = 2F ^ 27.62% nH2 ~ Ixt_ ~ 71.26% IF l-CE 0.2762 , „ _ 0.2762 => = => l -CE = 2 x 2 0.7126 0.7126 => CE = 0.225 « 22.5 % (3) Generating peroxide for 45 minutes with 1M Na 2C03 at 30A (from head gas analysis) 0.5x1 xtx(\-CE) " o 2 2F 28.29% nHi ~ Ixt_ ~ 70.58% IF l-CE 0.2829 , _ n 0.2829 => = => l - C E = 2 x 2 0.7058 0.7058 => CE = 0 .198* 1 9 . 8 % (4) Generating peroxide for 45 minutes with 2 M N a 2 C 0 3 at 30A (from head gas analysis) 0.5x1 xtx(l-CE) nQi 2F 28.96% nHi ~ Ix1_ ~ 69.18% IF l-CE 0.2896 , ^ „ 0.2896 => = => l - C E = 2 x 2 0.6918 0.6918 => CE = 0.163 * 16.3 % - 122-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 (MgS0 4 »7H 2 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 8N 3Na50io), as pentasodium salt, 40% in water, from Acros Organics, • Potassium iodide (KI), reagent A.C.S., from Fisher Scientific Co Ltd, • Ammonium Molybdate ((NH4)6Mo7024*4H20), certified A.C.S., from Fisher Scientific Co Ltd, • Sodium thiosulfate Solution N/10 (24.819mg Na 2 S20 3 «5H 2 0 /ml), certified 0.1005-0.0995N), from Fisher Scientific Co Ltd, • Ammonium phosphate ( (NH^HPC^) , 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 RBC Industries Inc. • Hydrogen hexachloroplatinate (IV) hydrate (H2PtCl6), 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 TMP 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 p x AT= U x A x AT where H: Heat loss (kJ/s) Q: Coolant flow rate (kg/s) Cp: Heat capacity component (^ /(frg ^ )i CPlll0 - 4-22 AT: Temperature change of coolant (K) A: Anode surface areas (m2) U: Heat transfer coefficient (0.5 ^ /,or 2 J - estimate for coolant flow rate: ^ // „ / \m3 lmin , nkg „ , £eV 6 / . = 6 x x x 1000-^- = o . l Ky / m m ^ 1 0 0 0 / 6 0 s e c m* /s Ira bJ kJ Hiost =0.1^-x 4.2176—— x(279K-214K)*2.U—=2110W s kg-K s kW Or Hiost= 0.S- rx(4xl6xlO-4)w2x(60-l)°C= 189xl0" 3 kW «\90QkW C-m 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 if the heat generated from Joule heating (I x V 0hm) < 1910 W . This situation required that the coolant flow be reduced from 5 to 0.5 liter per minute to maintain reactor temperature up to 6 0 ° C . - 124-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 2 0 2 + 2KI + H2SO4 -> K 2 S O 4 + 2 H 2 0 + I 2 1 mole H 2 O 2 = 2 moles of S 2 0 3 2 " MHA-VHl0l=^MS20l-VSi0t Mso>-S20} 0.1000 ±0.005 T . _ MHn = rxV 2 =0.01-^ n 2 U , „ (r n n , „ nss^,\ S.O}~ S,0 2^3 VHfii = 5.00ml (±0.003 ml); M s n } . = 0.1000M±0.005M  2 x (5.00 ±0.003) ' MH2o2=0.0l-VSiOr(±0.0lml) 2. 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 STANDARD PRACTICE - 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 mixer1 with two fixed ripple-edge stainless steel mixing blades on a stainless steel shaft and fitted with a square-shaped 1000-mL stainless steel canister1. 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 plastic-coated 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 for reflectance testing T 272 sp-97 of pulp (sheet machine procedure) F i g . 1 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 rna t i ve to d i s i n t e g r a t o r ) s h o w i n g spec ia l can is te r f i t t e d to t h e m i x e r . 5.6.1 Adjust 2000 mL of the water to pH 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 high-brightness 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 of standard white non-fluorescent blotting paper. For pulp brighter than the blotters, sheets of similar pulp are useable as insurance against color transfer. - 128-Appendix VII T272 sp-97 Forming handsheets for reflectance testing / 4 of pulp (sheet machine procedure) NOTE 3: 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. 5.13 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. 6. 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 of 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 of 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 To provide the number of test pieces needed for reflectance measurements, prepare two handsheets, each weighing 4 g. 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 mL 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 mL of water and disintegrate at 13,000 rpm for 2 min. Transfer to a graduated cylinder and dilute to 1,000 mL using the dilution water to rinse out the mixer. 8.1.4 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). NOTE 5: 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. 8.2 Forming 8.2.1 Disperse the test portions as directed in 8.1, but dilute each disintegrated sample portion to 2000 mL 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. Mix the diluted sample portion by pouring it back and forth between two containers three times, then pour it into the sheet machine. Add 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 T 272 sp-97 of pulp (sheet machine procedure) 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 silicone-treated 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," Paper Trade J. 114(5):30 (1942). 2. Jousimaa, T., " K C L Y256-1, The Effect of Sheet Forming Conditions on Brightness," ISO/TC6/SC5 N 749. Your comments and suggestions on this procedure are earnestly requested and should be sent to the TAPPI Technical Divisions Administrator. B - 131 -Appendix VIII Appendix VIII Raw Data The results in this appendix are divided into four different sections, V I , V2, V3, V4, as follow: • V I : 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 • Current set point: 20A Na 2 C0 3 , 0.13M NaHC0 3 , 0.03M NaSi0 3 , • Weight of pulp: 300g wet pulp 0.007% M g S 0 4 7 H 2 0 , 0.01% DTP A) . Anode coolant inlet temperature: 12.9°C • Experimental time: 180 minutes • Anode coolant outlet temperature: 20.5°C • Mixing speed: 200rpm • Anode coolant flow rate: 0.2 1/min • Pulp consistency: 4.2% Reactor Outside Wall Temperature ( ° Q Voltage (V) Current (A) Brightness Gain (% ISO) Yellowness Loss (%) Hydrogen Peroxide Concentration (M) V1.01 46 48 47 10.9±1.0 10.0±1.0 9.7±1.0 20.0 20.0 20.0 10.2 13.0 11.7 8.5 9.2 8.6 0.006 0.008 0.007 V1.02 V1.03 - 132-Appendix VIII Raw Data 2. Experiment No.: V I . 1 - Temperature configuration Experimental conditions: • Electrolyte: 1.5 liter solution (1.0M N a 2 C 0 3 , 0.13MNaHCO 3 , 0.03M NaSi0 3 , 0.007% M g S 0 4 7 H 2 0 , 0.01% DTPA) • Final [H 2 0 2 ] : 0.012 M • Anode coolant inlet temperature: 15°C Experimental time: 180 minutes Mixing speed: 200 rpm Current set point: 20A No pulp Anode coolant flow rate: 0.2 1/min Time (Min) Solution Temperature (°C) Reactor Inner Sidewall Temperature (°C) Reactor Outside Wall Temperature (°C) Coolant Outlet 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 3. Experiment No.: V I .2 - Temperature configuration Experimental conditions: • Electrolyte: 1.5 liter solution (1.0M • Experimental time: 60 minutes N a 2 C 0 3 , 0.13M NaHC0 3 , 0.03M NaSi0 3 , • Mixing speed: 200 rpm 0.007% M g S 0 4 7 H 2 0 , 0.01% DTPA) • Current set point: 20A • Anode coolant inlet temperature: 15°C • No pulp • Anode coolant flow rate: 0.2 1/min Experimental Time (Min) Bulk Solution Temperature (°C) Reactor Outside Wall Temperature ( ° Q Coolant Outlet Temperature (°C) Hydrogen Peroxide Concentration (M) 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 • Experimental time: 90minutes N a 2 C 0 3 , 0.13M NaHC0 3 , 0.03M NaSi0 3 , • Mixing speed: 200 rpm 0.007% M g S 0 4 7 H 2 0 , 0.01% DTP A) . Current set point: 20A • Anode coolant inlet temperature: 13.5°C e No pulp • Anode coolant flow rate: 0.2 1/min Time (Min) Solution Temperature <°c> Reactor Outside Wall Temperature <°o Coolant Outlet Temperature ( ° Q Hydrogen Peroxide Concentration (M) 0 28 18 15 30 35 27 16 0.001 60 37 29 16 0.002 90 39 31 17 0.002 5. Experiment No.: VI.4 - Temperature configuration Experimental conditions: • Electrolyte: 1.5 liter solution (1.0M • Experimental time: 180 minutes N a 2 C 0 3 , 0.13M NaHC0 3 , 0.03M NaSi0 3 , • Mixing speed: 200 rpm 0.007% M g S 0 4 7 H 2 0 , 0.01% DTP A) • Current set point: 20A • Anode coolant inlet temperature: 14.5°C • No pulp • Anode coolant flow rate: 0.2 1/min Time (Min) Solution Temperature (°C) Reactor Outside Coolant Outlet Wall Temperature Temperature C°C) (°C) Hydrogen Peroxide Concentration (M) 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 - 134-Appendix VIII Raw Data 6. Experiment No.: V I .5 - Temperature configuration Experimental conditions: • Electrolyte: 1.5 liter solution (1.0M N a 2 C 0 3 , 0.13M NaHC0 3 , 0.03M NaSi0 3 , 0.007% M g S 0 4 7 H 2 0 , 0.01% DTPA) • Anode coolant inlet temperature: 13.5°C Experimental time: 180 minutes Mixing speed: 200 rpm Current set point: 20A No pulp Anode coolant flow rate: 0.2 1/min Time (Min) Solution Temperature (°C) Reactor Outside Wall Temperature (°C) Coolant Outlet Temperature (°C) Hydrogen Peroxide Concentration (M) 0 23 7 . 16 30 41 37 17 0.001 60 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) July 03, 98 Experimental conditions: • Electrolyte: 1.5 liter solution (1.0M N a 2 C 0 3 , 0.13MNaHCO 3 , 0.03MNaSiO 3, 0.007% M g S 0 4 7 H 2 0 , 0.01% DTPA) • Anode coolant inlet temperature: 13°C • Experimental time: 180 minutes • Mixing speed: 200 rpm • Current set point: 20A • No pulp • Anode coolant flow rate: 0.2 1/min Time (Min) Solution Temperature (°C) Reactor Outside Wall Temperature (°C) Coolant Outlet Temperature (°C) Hydrogen Peroxide Concentration (M) 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 - 135 -Appendix VIII Raw Data 8. Experiment No.: V I .7 - Temperature configuration (re-electroplating of platinum: first time) July 14, 98 Experimental conditions: • Electrolyte: 1.5 liter solution (1.0M N a 2 C 0 3 , 0.13MNaHCO 3 , 0.03MNaSiO 3 , 0.007% M g S 0 4 7 H 2 0 , 0.01% DTP A) • New Pt coating (second run) • Anode coolant inlet temperature: 13.5°C Experimental time: 120 minutes Mixing speed: 200 rpm Current set point: 20A No pulp Anode coolant flow rate: 0.2 1/min Time (Min) Solution Temperature (°C) Reactor Outside Wall Temperature (°C) Coolant Outlet Temperature (°C) Hydrogen Peroxide Concentration (M) 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 9. Experiment No.: VI.8 - Temperature configuration (re-electroplating of -platinum first time) July 17, 98 Experimental conditions: • Electrolyte. 1.5 liter solution (1.0M N a 2 C 0 3 , 0.13MNaHCO 3 , 0.03MNaSiO 3, 0.007% M g S 0 4 7 H 2 0 , 0.01% DTP A) • New Pt coating (third run) • Anode coolant inlet temperature: 13.5°C Experimental time: 180 minutes Mixing speed: 200 rpm Current set point: 20A No pulp Anode coolant flow rate: 0.2 1/min Time (Min) Solution Temperature <°o Reactor Outside Wall Temperature ( ° Q Coolant Outlet Temperature (°C) Hydrogen Peroxide Concentration (M) 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.: VI .9 - Temperature configuration (re-electroplating of -platinum first time) July 23, 98 Experimental conditions: • Electrolyte: 1.5 liter solution (1.0M N a 2 C 0 3 , 0.13MNaHCO 3 , 0.03M NaSi0 3 , 0.007% M g S 0 4 7 H 2 0 , 0.01% DTPA) • New Pt coating (fourth run) • Anode coolant inlet temperature: 15°C Experimental time: 90 minutes Mixing speed: 200 rpm Current set point: 20A No pulp Anode coolant flow rate: 0.21 1/min Time (Min) Solution Temperature (°C) Reactor Outside Wall Temperature ( ° Q Coolant Outlet Temperature (°C) Hydrogen Peroxide Concentration (M) 0 29 21 17 30 38 29 19 0.005 60 39 32 18 0.007 90 41 33 20 0.008 11. Experiment No.: V1.10 - Temperature configuration (re-electroplating of -platinum first time) July 24, 98 Experimental conditions: • Electrolyte: 1.5 liter solution (1.0M N a 2 C 0 3 , 0.13M NaHC0 3 , 0.03M NaSi0 3 , 0.007% M g S 0 4 7 H 2 0 , 0.01% DTPA) • New Pt coating (fifth run) • Anode coolant inlet temperature: 1°C Experimental time: 60 minutes Mixing speed: 200 rpm Current set point: 20A No pulp Anode coolant flow rate: 0.2 1/min Time (Min) Solution Temperature ( ° Q Reactor Outside Wall Temperature (°C) Coolant Outlet Temperature ( ° Q Hydrogen Peroxide Concentration (M) 0 25 19 4 30 35 25 4 0.007 60 37 27 4 0.007 - 137-Appendix VIII Raw Data 12. Experiment No.: VI . 11 - Temperature configuration Dec. 10, 98 Experimental conditions: • Electrolyte: 1.5 liter solution (1.0M N a 2 C 0 3 , 0.13MNaHCO 3 , 0.03M NaSi0 3 , 0.007% M g S 0 4 7 H 2 0 , 0.01% DTP A) • [H 2 0 2 ] : 0.008M • Initial pH= 10.63 • Anode coolant inlet temperature: 13.5°C 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 (Min) Current (A) Voltage (V) Reactor Outside Wall Temperature (°o Coolant Outlet Temperature C°C) Mixing Speed (RPM) 0 20 15.4 18 17 200 60 20 10.5 24 18 200 120 20 11.8 26 16 400 180 20 12.6 28 18 400 13 Experiment No.: VI . 12 - Temperature Configuration Jan. 25, 99 Experimental conditions: • Electrolyte: 1.5 liter solution (1.0M Na 2 C0 3 , 400ppm Mg 2 + ) • [H 2 0 2 ] : 0.0095M Initial pH= 10.0 Temperature control: 50°C Anode coolant inlet temperature: 15°C 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 Time (Min) Current (A) Voltage (V) Reactor Outside Wall Temperature (°C) Coolant Outlet Temperature (°C) Mixing Speed (RPM) 0 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.: VI . 13 - Temperature configuration Jan. 26, 99 Experimental conditions: • Electrolyte: 1.5 liter solution (1.0M N a 2 C 0 3 , 400ppm Mg 2 + ) [H 2 0 2 ] : 0.006M Initial pH = 10.94 Temperature control: 50°C Anode coolant inlet temperature: 15°C 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 Time Current (Min) (A) Voltage (V) Reactor Outside Wall Temperature (°C) Coolant Outlet Temperature (°C) Mixing Speed (RPM) 0 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: 10.1 9 (51.8) (27.5). 15 Experiment No.: VI . 14 - Temperature configuration Jan. 27, 99 Experimental conditions: • Electrolyte: 1.5 liter solution (1.0M N a 2 C 0 3 , 400ppm M g 2 + ) [H 2 0 2 ] : 0.005M Initial pH= 11.01 Temperature control: 40°C Anode coolant inlet temperature: 15°C 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 Time (Min) Current (A) Voltage (V) Reactor Outside Wall Temperature (°C) Coolant Outlet Temperature (°C) Mixing Speed (RPM) 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-Appendix VIII Raw Data 16 Experiment No.: V I . 15 - Temperature configuration Feb. 1, 99 (re-electroplating of -platinum second time) Experimental conditions: • Electrolyte: 1.5 liter solution (1.0M • Experimental time: 180 minutes N a 2 C 0 3 , 400ppm M g 2 + ) • Mixing speed: 200 rpm • • • • [H 2 0 2 ] : 0.025M Initial pH= 10.0 Temperature control: 40°C Anode coolant inlet temperature: 15°C • Current set point: 40A • 1 % pulp consistency • Weight of wet pulp: 300g • Anode coolant flow rate: 0.2 1/min Time (Min) Current Voltage Reactor Outside Wall Temperature (A) (V) (°C) Coolant Outlet Temperature (°C) Mixing Speed (RPM) 0 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 Feb. 3, 99 Experimental conditions: • Electrolyte: 1.5 liter solution (1.0M N a 2 C 0 3 , 400ppm Mg 2 + ) • [H 2 0 2 ] : 0.025M • Initial pH = 10.58 • Temperature control: 40°C • Anode coolant inlet temperature: 15°C • 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 Time (Min) Current Voltage Reactor Outside Wall Temperature (A) (V) (°C) Coolant Outlet Temperature (°C) Mixing Speed (RPM) 0 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 28 18 400 Observation: huge voltage drop - 140-Appendix VIII Raw Data 2. Experiment No.: V2 18 Experiment No.: V2.01 - Stainless steel cathode with polypropylene felt Experimental conditions: Apr. 21, 99 • Electrolyte: 1.5 Liter Solution (1.0M Na 2 C0 3 ) • Experimental time: 73 minutes • Mixing speed: 200rpm • Initial pH= 11.60 • 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 (Min) Current (A) Voltage (V) Reactor Outside Wall Temperature (°C) Hydrogen Peroxide Concentration (M) 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 -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 2 C0 3 ) • Experimental time: 147 minutes • Mixing speed: 200rpm • Initial pH = 11.66 • 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 (Min) Current (A) Voltage (V) Reactor Outside Wall Temperature (°C) Hydrogen Peroxide Concentration (M) 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 0.075 20 Experiment No.: V2.3 - Stainless steel cathode with polypropylene felt Apr. 28, 99 • Electrolyte: 1.5 Liter Solution (1.0M Na 2 C0 3 ) • Experimental time: 10 minutes • Electrolyte temperature control: 20°C • Initial pH= 11.66 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 Time Current Voltage Reactor Outside Hydrogen Peroxide (V) Wall Temperature Concentration (Min) (A) (°C) (M) 0 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 Apr. 28, 99 • Electrolyte: 1.5 Liter Solution (1.0M • Current set point: 20A N a 2 C C > 3 ) • 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 pH = 11.6 0.11Q (hot) Time Current Voltage Reactor Outside Wall Hydrogen Peroxide Temperature Concentration (Min) (A) (V) £ C j (M) 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 0.007 35 20 16/7 24 40 20 167 24 0.007 45 20 16J5 24 50 20 16J* 24 55 20 16j? 24 0.008 60 20 16_6 26 70 20 16J) 26 0.008 80 20 16J5 25 90 20 16.8 25 0.008 - 143 -Appendix VIII Raw Data 22 Experiment No.: V2.5 - Stainless steel cathode with polypropylene felt May 13, 99 • Electrolyte: 1.5 Liter Solution (1.0M N a 2 C 0 3 , 400ppm Mg 2 + ) • Experimental time: 80 minutes • Mixing speed: 200rpm • No pulp • Initial pH= 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 . H Q (hot) Time (Min) Current (A) Voltage (V) Reactor Outside Wall Temperature (°C) Hydrogen Peroxide Concentration (M) 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 0.011 35 20 16.2 23 40 20 16.1 23 0.011 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-Appendix VIII Raw Data 23 Experiment No.: V2.6 - Stainless steel cathode with microporous polypropylene • Electrolyte: 1.5 Liter Solution (1.0M N a 2 C 0 3 , 400ppm M g 2 + ) • Experimental time: 90 minutes • Mixing speed: 200rpm • No pulp • Initial pH= 11.6 May 17, 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 Reactor Outside Wall Hydrogen Peroxide Temperature Concentration (Min) (A) (V) (°C) (M) 0 20 16.5 20 30 20 16.3 23 0.007 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 24 Experiment No.: V2.7 - Stainless steel cathode with polypropylene string May 19, 99 • Electrolyte 1.5 Liter Solution (1.0M • Current set point: 20A Na 2 C0 3 ) • 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; initial pH = 11.6 • Total resistance: 80.23Q (hot); Time Current Voltage Reactor Outside Wall Hydrogen Peroxide Temperature Concentration (Min) (A) (V) (°C) (M) 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. Experiment No.: V3 Raw Data 25 Experiment No.: V3.1 - Zirconium cathode with polypropylene string Jun. 8, 99 • Electrolyte: 1.5 Liter Solution (1.0M • Current set point: 20A N a 2 C C > 3 ) e 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; initial pH = 11.6 • No mixer Time (Min) Current (A) Voltage (V) Reactor Temperature (°C) Hydrogen Peroxide Concentration (M) 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 -Appendix VIII Raw Data ,6 Experiment No.: V3.2 - Zirconium cathode with diaphragm June 9, 99 • Electrolyte: 1.5 Liter Solution (1.0M • Current set point: 20A N a 2 C 0 3 , 400ppm Mg 2 + ) • Anode coolant inlet temperature: 1°C • Experimental time: 140 minutes • Anode coolant outlet temperature: 5°C • Mixing speed: 200rpm • Anode coolant flow rate: 6 1/min • No pulp; initial pH = 11.6 • No mixer Time Current Voltage Reactor Hydrogen Peroxide Temperature Concentration (Min) (A} £V} £CJ (M) 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 16A 31 25 20 163 3 J 30 20 16_2 32 0.024 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-Appendix VIII Raw Data 27 Experiment No.: V3.3 - Zirconium cathode with diaphragm June 10, 99 Electrolyte: 1.5 Liter Solution (1.0M N a 2 C 0 3 , 400ppm Mg 2 + ) Experimental time: 60 minutes Mixing speed: 200rpm No pulp Initial pH= 11.6 • 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 Reactor Hydrogen Peroxide Temperature Concentration (Min) (A) (V) (°C) (M) 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 . 19 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 0.009 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 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 June 22, 99 Electrolyte: 1.5 Liter Solution (1.0M N a 2 C 0 3 , 400ppm Mg 2 + ) Experimental time: 180 minutes Mixing speed: 200rpm No pulp Initial pH= 11.6 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 (Min) Current (A) Voltage (V) Reactor Temperature (°C) Hydrogen Peroxide Concentration (M) 0 19.3 20 13 0.5 20 20 13 1 20 19.3 15 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 0.011 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 n o 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 0.035 180 20 16.1 32 0.035 Zirconium cathode was corroded - 149-Appendix VIII Raw Data '.9 Experiment No.: V3.5 - Uncovered zirconium cathode June 24, 99 • Electrolyte: 1.5 Liter Solution (1.0M • Current set point: 20A N a 2 C 0 3 , 400ppm Mg 2 + ) • Electrolyte temperature set point: 20°C • Experimental time: 180 minutes • Anode coolant inlet temperature: 1°C • Mixing speed: 200rpm • Anode coolant outlet temperature: 5°C • No pulp • Anode coolant flow rate: 6 1/min • Initial pH= 11.6 • Cathode configuration: (A) Time Current Voltage Reactor Hydrogen Peroxide Temperature Concentration (Min) (A) £ C j (M) 0 1 7 6 20 14 1 18/7 20 14 3 20 18j> 17 5 20 VIS 17 7 20 1 7 J 19 9 20 16J5 21 10 20 16_6 21 12 20 1 6 J 22 15 20 16_4 22 0.013 20 20 16_2 24 30 20 1 6 J 25 0.020 40 20 16 27 0.025 50 20 16_ 28 0.029 60 20 16 2 9 _ 0.031 70 20 1 1 9 29 0.034 80 20 1 1 9 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 1 6 J 30 0.039 130 20 16 30 0.039 140 20 1 6 J 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-Appendix VIII Raw Data 30 Experiment No.: V3.6 - Uncovered zirconium cathode June 25, 99 • Electrolyte: 1.5 Liter Solution (1.0M • Current set point: 20A N a 2 C 0 3 , 400ppm M g 2 + ) • Electrolyte temperature set point: 60°C • Experimental time: 180 minutes • Anode coolant inlet temperature: 2°C • Mixing speed: 200rpm • Anode coolant outlet temperature: 5°C • No pulp • Anode coolant flow rate: 6 1/min • Initial pH = 11.6 • Cathode configuration: (A) Time Current Voltage Reactor Hydrogen Peroxide Temperature Concentration (Min) (A) (V) (°C) (M) 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 0.015 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 -Appendix VIII Raw Data '< 1 Experiment No.: V3.7 - Zirconium tube cathode June 26, 99 • Electrolyte: 1.5 Liter Solution (1.0M • Current set point: 20A N a 2 C 0 3 , 400ppm Mg 2 + ) • Electrolyte temperature set point: 60°C • Experimental time: 180 minutes • Anode coolant inlet temperature: 2°C • Mixing speed: 200rpm • Anode coolant outlet temperature: 5°C • No pulp • Anode coolant flow rate: 6 1/min • Initial pH= 11.6 • Cathode configuration: (A) Time Current Voltage Reactor Hydrogen Peroxide Temperature Concentration (Min) (Aj QQ ( ° Q (M) 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 0.014 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 5 7 _ 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-Appendix VJII Raw Data 2 Experiment No.: V.3 8 June 26, 99 • Electrolyte: 1.5 Liter Solution (1.0M • Current set point: 20A N a 2 C 0 3 , 400ppm Mg 2 + ) • Electrolyte temperature set point: 60°C • Experimental time: 180 minutes • Anode coolant inlet temperature: 16°C • Mixing speed: 200rpm • Anode coolant outlet temperature: 19°C • No pulp • Anode coolant flow rate: 61/min • Initial pH= 11.6 • Cathode configuration: (A) Time Current Voltage Reactor Hydrogen Peroxide Temperature Concentration (Min) 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 0.010 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 20 12A 62 0.044 180 20 12.4 62 0.044 - 153 -Appendix VIII Raw Data 3 Experiment No.: V.3 9 June 26, 99 • Electrolyte: 1.5 Liter Solution (1.0M • Current set point: 20A N a 2 C 0 3 , 400ppm M g 2 + ) • Electrolyte temperature set point: 20°C • Experimental time: 180 minutes • Anode coolant inlet temperature: 1°C • Mixing speed: 200rpm • Anode coolant outlet temperature: 5°C • No pulp • Anode coolant flow rate: 6 1/min • Initial pH = 11.6 • Cathode configuration: (A) Time Current Voltage Reactor Hydrogen Peroxide Temperature Concentration (Min) (A) (YJ ^ C J (M) 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 0.013 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 16A 33 0.041 120 20 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-Appendix VIII Raw Data 4 Experiment No.: V .3 10 June 27, 99 • Electrolyte: 1.5 Liter Solution (1.0M • Current set point: 20A Na2C03, 400ppm Mg 2 + ) • Electrolyte temperature set point: 60°C • Experimental time: 180 minutes • Anode coolant inlet temperature: 1°C • Mixing speed: 200rpm • Anode coolant outlet temperature: 5°C • No pulp • Anode coolant flow rate: 6 1/min • Initial pH = 11.6 • Cathode configuration: (A) Time Current Voltage Reactor Hydrogen Peroxide Temperature Concentration (Min) (A) (V) £ C j (M) 0 20 19J> 20 1 20 18J8 21 3 20 17J 24 5 20 1 6 _ 31 7 20 ISA 36 9 20 1 4 J 39 10 20 142 41 15 20 132 47 0.013 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 1 3 J 57 0.043 180 20 13.1 57 0.043 - 155 -Appendix VIII Raw Data 3 5 Experiment No.: V . 3 11 June 30, 99 • Electrolyte: 1.5 Liter Solution (1.0M N a 2 C 0 3 , 400ppm M g 2 + ) • Experimental time: 80 minutes • Mixing speed: 200rpm • No pulp • Initial pH = 10.5 (controlled by NaHC0 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 (Min) Current (A) Voltage (V) Reactor Temperature ( ° Q Hydrogen Peroxide Concentration (M) 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 0.009 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-Appendix VIII Raw Data 6 Experiment No.: V.3 12 July 1, 99 • Electrolyte: 1.5 Liter Solution (1.0M • Current set point: 20A N a 2 C 0 3 , 400ppm Mg 2 + ) • Electrolyte temperature set point: 60°C • Experimental time: 180 minutes • Anode coolant inlet temperature: 1°C • Mixing speed: 200rpm o Anode coolant outlet temperature: 5°C • No pulp • Anode coolant flow rate: 6 1/min • Initial pH = 11.85; final pH = 11.0 • Cathode configuration: (A) Time Current Voltage Reactor Hydrogen Peroxide Temperature Concentration (Min) (A) (V) £ C j (M) 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 0.015 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-Appendix VIII Raw Data 37 Experiment No.: V.3 13 July 1, 99 • Electrolyte: 1.5 Liter Solution (1.0M N a 2 C 0 3 , 400ppm Mg 2 + ) • Experimental time: 90 minutes • Mixing speed: 200rpm • No pulp • Initial pH = 10.5; final pH = 10.2 (controlled by NaHCQ 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 (Min) Current (A) Voltage (V) Reactor Temperature ( ° Q Hydrogen Peroxide Concentration (M) 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 -Appendix VIII Raw Data 8 Experiment No.: V.3 14 July 7, 99 • Electrolyte: 1.5 Liter Solution (1.0M • Current set point: 20A N a 2 C 0 3 , 400ppm Mg 2 + ) • Electrolyte temperature set point: 20°C • Experimental time: 180 minutes • Anode coolant inlet temperature: 1°C • Mixing speed: 200rpm • Anode coolant outlet temperature: 5°C • No pulp • Anode coolant flow rate: 6 1/min • Initial pH = 11.6 • Cathode configuration: (A) Time Current Voltage Reactor Hydrogen Peroxide Temperature Concentration (Min) (A) (V) £ Q (M) 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 0.012 20 20 16_5 29 30 20 16 3J 0.025 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-Appendix VIII Raw Data 3 9 Experiment No.: V . 3 15 July 8, 99 • Electrolyte: 1.5 Liter Solution (1.0M N a 2 C 0 3 , 400ppm Mg 2 + ) • Experimental time: 200 minutes • Mixing speed: 200rpm • No pulp • Initial pH = 10.5; final pH = 10.76 (controlled by NaHCQ 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 (Min) Current (A) Voltage (V) Reactor Temperature ( ° Q Hydrogen Peroxide Concentration (M) 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-Appendix VIII Raw Data •0 Experiment No.: V.3 16 July 8, 99 • Electrolyte: 1.5 Liter Solution (1.0M • Current set point: 20A N a 2 C 0 3 , 400ppm M g 2 + ) • Electrolyte temperature set point: 20°C • Experimental time: 180 minutes • Anode coolant inlet temperature: 1°C • Mixing speed: 200rpm • Anode coolant outlet temperature: 5°C • No pulp • Anode coolant flow rate: 61/min • Initial pH = 10.5 • Cathode configuration: (A) (controlled by NaHC0 3 ) Time Current Voltage Reactor Hydrogen Peroxide Temperature Concentration (Min) (A) (V) CQ (M) 0 19J5 20 15 1 20 193 16 3 20 18^ 4 19 5 • 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 33 0.017 90 20 162 33 0.017 100 20 162 33 0.016 110 20 163 33 0.017 120 20 16A 34 0.017 130 20 16A 34 0.016 140 20 163 34 0.016 150 20 163 34 0.017 160 20 166 35_ 0.017 170 20 163 35 0.016 180 20 16.7 36 0.016 - 161 -Appendix VIII Raw Data \\ Experiment No.: V.3 17 July 09, 99 • Electrolyte: 1.5 Liter Solution (1.0M • Current set point: 20A N a 2 C 0 3 , 400ppm M g 2 + , 1.3g DTP A ) • Electrolyte temperature set point: 60°C • Experimental time: 180 minutes • Anode coolant inlet temperature: 1°C • Mixing speed: 200rpm • Anode coolant outlet temperature: 5°C • No pulp • Anode coolant flow rate: 6 1/min • Initial pH = 11.94; final pH = 11.27 • Cathode configuration: (A) Time Current Voltage Reactor Hydrogen Peroxide Temperature Concentration (Min) (A) (V) (°C) (M) 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 0.020 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-Appendix VIII Raw Data 42 Experiment No.: V.3 18 July 10, 99 • Electrolyte: 1.5 Liter Solution (1.0M N a 2 C 0 3 , 400ppm M g 2 + , l,3g DTPA ) • Experimental time: 180 minutes • Mixing speed: 200rpm • No pulp • Initial pH = 10.5; final pH = 10.3 (controlled by NaHC0 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) Time Current Voltage Reactor Hydrogen Peroxide Temperature Concentration (Min) (A) (V) (°C) (M) 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 0.012 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 -Appendix VIII Raw Data •3 Experiment No.: V.3 19 July 10, 99 • Electrolyte: 1.5 Liter Solution (1.0M • Current set point: 20A N a 2 C 0 3 , 400ppm M g 2 + , 1.3g DTP A ) • Electrolyte temperature set point: 20°C • Experimental time: 180 minutes • Anode coolant inlet temperature: 1°C • Mixing speed: 200rpm • Anode coolant outlet temperature: 5°C • No pulp • Anode coolant flow rate: 6 1/min • Initial pH = 11.6 • Cathode configuration: (A) • Final pH = 11.36 at 34.8°C Time Current Voltage Reactor Hydrogen Peroxide Temperature Concentration (Min) (Al LYJ (!Q ; (M) 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 0.020 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-Appendix VIII Raw Data 44 Experiment No.: V.3 20 July 11, 99 • Electrolyte: 1.5 Liter Solution (1.0M N a 2 C 0 3 , 400ppm M g 2 + , 1.3g DTPA ) • Experimental time: 180 minutes • Mixing speed: 200rpm • No pulp • Initial pH = 10.5; final pH = 10.62 (controlled by adding 15.62g NaHC0 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 (Min) Current (A) Voltage (V) Reactor Temperature ( ° Q Hydrogen Peroxide Concentration (M) 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 0.017 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 -Appendix VIII Raw Data •5 Experiment No.: V . 3 21 July 11, 98 • Electrolyte: 1.5 Liter Solution (1.0M • Current set point: 20A N a 2 C 0 3 , 400ppm Mg 2 + ) • Electrolyte temperature set point: 20°C • Experimental time: 180 minutes • Anode coolant inlet temperature: 1°C • Mixing speed: 200rpm • Anode coolant outlet temperature: 5°C • No pulp • Anode coolant flow rate: 6 1/min • Initial pH = 11.59; final pH = 11.2 • Cathode configuration: (B) Time Current Voltage Reactor Hydrogen Peroxide Temperature Concentration (Min} (A) (V) £ C ) (M) 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 0.016 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-Appendix VIIIRaw Data 46 Experiment No.: V . 3 22 July 12, 99 Electrolyte: 1.5 Liter Solution (1.0M N a 2 C 0 3 , 400ppm Mg 2 + ) Experimental time: 180 minutes Mixing speed: 200rpm No pulp Initial pH = 10.59; final pH = 10.77 (controlled by adding NaHCOa) 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 (Min) Current (A) Voltage (V) Reactor Temperature (°C) Hydrogen Peroxide Concentration (M) 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 0.018 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-Appendix VIII Raw Data \1 Experiment No.: V.3 23 July 12, 99 • Electrolyte: 1.5 Liter Solution (1.0M • Current set point: 20A N a 2 C 0 3 , 400ppm M g 2 + ) • Electrolyte temperature set point: 60°C • Experimental time: 180 minutes • Anode coolant inlet temperature: 1°C • Mixing speed: 200rpm • Anode coolant outlet temperature: 5°C • No pulp • Anode coolant flow rate: 61/mih • Initial pH = 11.31; final pH = 10.68 • Cathode configuration: (C) Time Current Voltage Reactor Hydrogen Peroxide Temperature Concentration (Min) (A) (V} £ C j (M) 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 1 3 7 36 0.019 20 20 114 38 40 20 13_1 41 0.039 50 20 13T 41 0.044 60 _20 1 3 J 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-Appendix VIII Raw Data 48 Experiment No.: V.3 24 July 12, 99 Electrolyte: 1.5 Liter Solution (1.0M N a 2 C 0 3 , 400ppm Mg 2 + ) Experimental time: 180 minutes Mixing speed: 200rpm No pulp Initial pH= 11.59 at 18.4°C Final pH= 10.82 at 44.8°C • 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 (Min) Current (A) Voltage (V) Reactor Temperature (°C) Hydrogen Peroxide Concentration (M) 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 0.016 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-Appendix VIII Raw Data 49 Experiment No.: V.3 25 July 13, 99 • Electrolyte: 1.5 Liter Solution (1.0M N a 2 C 0 3 , 400ppm M g 2 + ) • Experimental time: 120 minutes • Mixing speed: 200rpm • No pulp • Initial pH= 10.5 (controlled by adding 6.6g NaHCOs) 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 (Min) Current (A) Voltage (V) Reactor Temperature (°C) Hydrogen Peroxide Concentration (M) 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-Appendix VIII Raw Data 0 Experiment No.: V.3 26 July 14, 99 • Electrolyte: 1.5 Liter Solution (1.0M • Current set point: 20A N a 2 C 0 3 , 400ppm M g 2 + , 1.3g DTPA) • Electrolyte temperature set point: 60°C • Experimental time: 180 minutes • Anode coolant inlet temperature: 1°C • Mixing speed: 200rpm • Anode coolant outlet temperature: 5°C • No pulp • Anode coolant flow rate: 5.5 1/min • Initial pH = 11.6 • Cathode configuration: (C) Time Current Voltage Reactor Hydrogen Peroxide Temperature Concentration (Min) (A) (V) (V) (M) 0 20 ]93 12 1 20 1 9 J 14 2 20 18J) 15 3 20 18.3 17 4 20 18 18 5 20 1 7 7 19 6 20 VTA 21 7 20 1 6 4 23 8 20 L5_9 26 9 20 1 5 J 27 10 20 15T 29 15 20 13_9 34 0.020 30 20 13 40 0.036 45 • 20 12_9 42 0.047 60 20 13 42 0.054 75 20 1 2 J 44 0.056 90 20 13 43 0.057 120 20 133 43 0.054 135 20 13L3 42 0.054 150 20 1 3 4 43 0.055 165 20 13_5 42 0.054 180 20 13.7 43 0.055 - 171 -Appendix VIII Raw Data 51 Experiment No.: V . 3 27 July 18, 99 Electrolyte: 1.5 Liter Solution (1.0M N a 2 C 0 3 , 400ppmMg 2 + , 1.3gDTPA) Experimental time: 180 minutes Mixing speed: 200rpm Weight of wet pulp: 300g Initial pH= 11.54 at 26.9°C Final pH= 10.23 at51.3°C 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 (Min) Current (A) Voltage (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 • Current set point: 20A N a 2 C 0 3 , 400ppm M g 2 + , 1.3g DTP A) • Electrolyte temperature set point: 60°C • Experimental time: 180 minutes • Anode coolant inlet temperature: 0°C • Mixing speed: 200rpm • Anode coolant outlet temperature: 10°C • No pulp • Anode coolant flow rate: 5.5 1/min • Final pH = 10.74 at 41.2°C • Cathode configuration: (C) Time Current Voltage Reactor Hydrogen Peroxide Temperature Concentration (Min) (A) (V) £Q (M) 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 -Appendix VIII Raw Data 53 Experiment No.: V.3 29 July 16, 99 • Electrolyte: 1.5 Liter Solution (1.0M N a 2 C 0 3 , 400ppm M g 2 + , 1.3g DTPA) • Experimental time: 180 minutes • Mixing speed: 200rpm • Weight of wet pulp: 300g • Initial pH= 11.57 at 25.9°C • Final pH= 10.74 at 41.2°C 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 (Min) Current (A) Voltage (V) Reactor Temperature ( ° Q Hydrogen Peroxide Concentration (M) 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 0.020 Brightness gain: 12.0 (55.4) Yellowness decrease: 13.6(19.9) - 174-Appendix VIII Raw Data 4 Experiment No.: V.3 30 July 17, 99 • Electrolyte: 1.5 Liter Solution (1.0M • Current set point: 40A N a 2 C 0 3 , 400ppm Mg 2 + ) • Electrolyte temperature set point: 60°C • Experimental time: 180 minutes • Anode coolant inlet temperature: 0°C • Mixing speed: 200rpm • Anode coolant outlet temperature: 3°C • No pulp • Anode coolant flow rate: 5.5 1/min • Final pH = 10.80 at 49.5°C • Cathode configuration: (C) Time Current Voltage Reactor Hydrogen Peroxide Temperature Concentration (Min) (A) (V) £ C ) (M) 0 194 20 9 1 20.8 20 12 2 2J> 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 -Appendix VIII Raw Data 55 Experiment No.: V.3 31 July 25, 99 Electrolyte: 1.5 Liter Solution (1.0M N a 2 C 0 3 , 400ppmMg 2 + , 1.3g DTP A) Experimental time: 180 minutes Mixing speed: 200rpm No pulp Initial pH= 11.76 at 28.8°C Final pH = 10.78 at 58.9°C • 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 (Min) Current (A) Voltage (V) Reactor Temperature (°C) Hydrogen Peroxide Concentration (M) 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-Appendix VIII Raw Data 56 Experiment No.: V.3 32 July 25, 99 • Electrolyte: 1.5 Liter Solution (1.0M N a 2 C 0 3 , 400ppm M g 2 + , 1.3gDTPA) • Experimental time: 180 minutes • Mixing speed: 200rpm • Weight of wet pulp: 300g • Final pH= 10.32 at 58.8°C • 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 (Min) Current (A) Voltage (V) Reactor Temperature (°C) Hydrogen Peroxide Concentration (M) 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 0.035 Brightness gain: 17.5 (59.0) Yellowness loss: 19.3(17.4) - 177-Appendix VIII Raw Data 4. Experiment No.: V4 Raw Data 57 Experiment No.: V4.01 Electrolyte: 1.5 Liter Solution (1.0M N a 2 C 0 3 , 400ppm M g 2 + , 1.3g DTP A) Experimental time: 180 minutes Mixing speed: 200rpm Weight of wet pulp: 320g Final pH= 10.72 at35.1°C July 27, 99 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 • Electrolyte: 1.25 Liter Solution (1.0M N a 2 C 0 3 , 400ppm M g 2 + , 1.3g DTPA) • Experimental time: 180 minutes • Mixing speed: 200rpm • Weight of wet pulp: 150g • Initial pH= 11.55 • Final pH= 10.45 at42.5°C Aug. 2, 99 • 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: 7.5 (49.1) Yellowness loss: 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 2 C 0 3 , 400ppm M g 2 + , 1.3g DTP A) • Experimental time: 180 minutes • Mixing speed: 200rpm • Weight of wet pulp: 150g • Initial pH= 11.47 at 18.6°C • Final pH= 10.45 at 43°C 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) Hydrogen Peroxide Concentration (M) 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-Appendix VIII Raw Data 60 Experiment No.: V4.04 Aug. 5, 99 • Electrolyte: 1.5 Liter Solution (2.OM N a 2 C 0 3 , 400ppmMg 2 + , 1.3gDTPA) • Experimental time: 180 minutes • Mixing speed: 200rpm • Weight of wet pulp: 150g • Initial pH= 11.68 at 19.3°C • Final pH = 10.87 at 35.7°C • 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 (Min) Current (A) Voltage (V) Reactor Temperature (°C) Hydrogen Peroxide Concentration (M) 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: 13.3 (54.9) Yellowness loss: 12.9 (23.9) - 181 -Appendix VIII Raw Data 61 Experiment No.: V4.05 Aug 5, 99 Electrolyte: 1.5 Liter Solution (1.5M N a 2 C 0 3 , 400ppm M g 2 + , 1.3g DTP A) Experimental time: 180 minutes Mixing speed: 200rpm Weight of wet pulp: 150g Initial pH Final pH = = 11.39 at 29 UC 10.56at51.8°C 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 (Min) Current (A) Voltage (V) Reactor Temperature (°C) Hydrogen Peroxide Concentration (M) 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-Appendix VIII Raw Data 62 Experiment No.: V4.06 • Electrolyte: 1.5 Liter Solution (1.0M N a 2 C 0 3 , 400ppmMg 2 + , 1.3g DTPA) • Experimental time: 120 minutes • Mixing speed: 200rpm • No pulp Aug 5, 99 • 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 (Min) Current (A) Voltage (V) Reactor Temperature (°C) Hydrogen Peroxide Concentration (M) 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 -Appendix VIII Raw Data 63 Experiment No.: V4.07 Sept 9, 99 • Electrolyte: 1.5 Liter Solution (1.0M N a 2 C 0 3 , 400ppm M g 2 + , 1.3g DTP A) • Experimental time: 180 minutes • Mixing speed: 200rpm • Weight of wet pulp: 150.3 6g • Final pH= 10.51 • 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 (Min) Current (A) Voltage (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 0.036 180 27.8 20 62 0.033 Lots of forming comes out, which increased the gas hold-up and the voltage Brightness gain: 10.4 (52.1) Yellowness loss: 15.9 (20.9) - 184-Appendix VIII Raw Data 64 Experiment No.: V4.08 Sept 13, 99 Electrolyte: 1.5 Liter Solution (1M N a 2 C 0 3 , 400ppm M g 2 + , 1.3gDTPA) Experimental time: 180 minutes Mixing speed: 200rpm Weight of wet pulp: 150g Final pH= 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% Time (Min) Current (A) Voltage (V) Reactor Temperature (°C) Hydrogen Peroxide Concentration (M) 0 10 10.6 21 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) - September 17, 1999 15.7 (57.3) - September 20, 1999 14.2 (22.6) - September 17, 1999 18.7 (18.1) - September 20, 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 2 C 0 3 , 400ppm M g 2 + , 1.3g DTP A) • Experimental time: 180 minutes • Mixing speed: 200rpm • Weight of wet pulp: 150g • Final pH= 10.77 at 45.9°C 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 (Min) Current (A) Voltage (V) Reactor Temperature (°C) Hydrogen Peroxide Concentration (M) 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-Appendix VIII Raw Data 66 Experiment No.: V4.10 Sept 16, 99 Electrolyte: 1.5 Liter Solution (1M N a 2 C 0 3 , 400ppm M g 2 + , 1.3g DTP A) Experimental time: 180 minutes Mixing speed: 200rpm Weight of wet pulp: 150g Initial pH= 11.62 at 22.8°C Final pH= 10.49 at 40.8°C 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 (Min) Current (A) Voltage (V) Reactor Temperature (°C) Hydrogen Peroxide Concentration (M) 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-Appendix VIII Raw Data 67 Experiment No.: V4.11 Sept 20, 99 • Electrolyte: 1.5 Liter Solution (2M N a 2 C 0 3 , 400ppm M g 2 + , 1.3g DTPA) • Experimental time: 180 minutes • Mixing speed: 200rpm • Weight of wet pulp: 150g • Initial pH= 11.78 at 24.1°C • Final pH= 10.62 at 56.2°C 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 (Min) Current (A) Voltage (V) Reactor Temperature (°C) Hydrogen Peroxide Concentration (M) 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-Appendix VIII Raw Data 68 Experiment No.: V4.12 Sept 22, 99 Electrolyte: 1.5 Liter Solution (2M N a 2 C 0 3 , 400ppm M g 2 + , 1.3g DTP A) Experimental time: 180 minutes Mixing speed: 200rpm Weight of wet pulp: 150g • Pulp consistency: 2.5% 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 (Min) Current (A) Voltage (V) Reactor Temperature ( ° Q Hydrogen Peroxide Concentration (M) 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-Appendix VIII Raw Data 69 Experiment No.: V4.13 Sept 16, 99 • Electrolyte: 1.5 Liter Solution (2M N a 2 C 0 3 , 400ppm M g 2 + , 1.3g DTPA) • Experimental time: 60 minutes • Mixing speed: 200rpm • Weight of wet pulp: 150g • Initial pH= 11.78 at 24.1°C • Final pH = 10.69 at 61.5°C 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 (Min) Current (A) Voltage (V) Reactor Temperature (°C) Hydrogen Peroxide Concentration (M) 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-Appendix VIII Raw Data 70 Experiment No.: V4.14 Oct 1, 99 • Electrolyte: 1.5 Liter Solution (2M N a 2 C 0 3 , 400ppm M g 2 + , 1.3g DTP A) • Experimental time: 120 minutes • Mixing speed: 200rpm • Weight of wet pulp: 150g • Final pH= 10.72 at 62.9°C 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 Hydrogen Peroxide Reactor Concentration (Min) (A) (V) Temperature (°C) (M) 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 -Appendix VIII Raw Data 71 Experiment No.: V4.15 Oct 18, 99 Electrolyte: 1.5 Liter Solution (2M N a 2 C 0 3 , 400ppmMg 2 + , 1.3gDTPA) Experimental time: 30 minutes Mixing speed: 200rpm Weight of wet pulp: 150g Pulp consistency: 2.5% 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 (Min) Current (A) Voltage (V) Reactor Temperature (°o Hydrogen Peroxide Concentration (M) 0 25.1 20 14 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 0.036 Brightness gain: Yellowness loss: 9.5 (51.1) 9.4 (27.4) - 192-Appendix VIII Raw Data 72 Experiment No.: V4.16 Oct 18, 99 Electrolyte: 1.5 Liter Solution (2M N a 2 C 0 3 , 400ppm M g 2 + , 1.3g DTP A) Experimental time: 90 minutes Mixing speed: 200rpm Weight of wet pulp: 150g Pulp consistency: 2.5% 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 (Min) Current (A) Voltage (V) Reactor Temperature (°C) Hydrogen Peroxide Concentration (M) 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 -Appendix VIII Raw Data 73 Experiment No.: V4.17 Oct 19, 99 • Electrolyte: 1.5 Liter Solution (2M N a 2 C 0 3 , 400ppm M g 2 + , 1.3gDTPA) • Experimental time: 240 minutes Mixing speed: 200rpm Weight of wet pulp: 150g Final pH= 10.46 at 50.9°C 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 (Min) Current (A) Voltage (V) Reactor Temperature (°C) Hydrogen Peroxide Concentration (M) 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-Appendix VIII Raw Data 74 Experiment No.: V4.18 Oct 20, 99 • Electrolyte: 1.5 Liter Solution (2M N a 2 C 0 3 , 400ppm M g 2 + , 1.3g DTP A) • Brightening time: 210 minutes • Mixing speed: 200rpm Weight of wet pulp: 150g Final pH= 10.65 at 55.5°C Pre-generated H 2 O 2 time: 30 minutes 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 (Min) Current (A) Voltage (V) Reactor Temperature (°C) Hydrogen Peroxide Concentration (M) 0 30 12.5 55 0.067 1 30 12.9 56 3 30 13 57 5 30 13.1 • 59 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 Brightness gain: Yellowness loss: 16.2 (57.8) 17.0(19.7) - 195 -Appendix VIII Raw Data 75 Experiment No.: V4.19 Oct 26, 99 • Electrolyte: 1.5 Liter Solution (1.5M N a 2 C 0 3 , 400ppmMg 2 + , 1.3gDTPA) • Experimental time: 180 minutes • Mixing speed: 200rpm • Weight of wet pulp: 150.27g • Final pH= 10.61 at 54.4°C • Pre-generated H 2 O 2 time: 30 minutes 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 (Min) Current (A) Voltage (V) Reactor Temperature (°C) Hydrogen Peroxide Concentration (M) 0 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 2 C 0 3 , 400ppm M g 2 + , 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 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% Time (Min) Current (A) Voltage (V) Reactor Temperature (°C) Hydrogen Peroxide Concentration (M) 0 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 N a 2 C 0 3 , 400ppm M g 2 + , 1.3g DTPA) Experimental time: 210 minutes Mixing speed: 200rpm Weight of wet pulp: 150g Final pH= 10.54 at 51 °C Pre-generated H 2 O 2 time: 30 minutes Total brightening time was 180 minutes with 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% stopping power at a 30 minutes interval. Time (Min) Current (A) Voltage (V) Reactor Temperature (°C) Hydrogen Peroxide Concentration (M) 0 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 Nov 17, 99 (Gas analysis for calculating current efficiency) No. Experiment Conditions Hydrogen Content Oxygen Content Nitrogen Content Current Efficiency V4.22 lMNa 2CO 3+400ppm Mg 2 + +1.3gDTPA; Current set point: 10A; Temperature: 60°C 71.26 mol% 27.62 mol% 1.12 mol% 22.5% V4.23 lMNa 2CO 3+400ppm Mg 2 + +1.3gDTPA; Current set point: 30A; Temperature: 60°C 70.58 mol% 28.29 mol% 1.13 mol% 19.84% V4.24 2M Na2CO3+400ppm Mg 2 + +1.3gDTPA; Current set point: 10A; Temperature: 60°C 69.18 mol% 28.96 mol% 1.86 mol% 16.3% V4.25 2M Na2CO3+400ppm Mg 2 + +1.3gDTPA; Current set point: 30A; Temperature: 60°C 69.05 mol% 29.86 mol% 1.09 mol% 13.5% - 199 -Appendix IX Appendix IX Brightness Reversion Experiment An 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 Na 2 Si0 3 , 0.01M H 2 0 2 (6% H 2 0 2 on dry pulp), 400ppm M g 2 + , and 0.002M DTPA (penta sodium 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 50 100 150 200 250 Exposure Time (Hours) • Conventional Peroxide Brightening • Electro-brightening Figure IX. 1 Brightness Loss of Pulp Pads Under 8 Fluorescent Lamps -200-Appendix IX Figure IX. 2 shows the profile of yellowness gain of these two samples. 16 — I — i — i — i — i — | — i — i — i — i — | — i — i — i — i — | — i — i — i — i — | — i — i — i — r 6 — | — 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) • — Conventional Peroxide Brightening • — Electro-brightening Figure IX.2 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 Thermocouple Platinum mesh -Coolant chamber ~ •—I-HP — H P Zirconium based reactor body gj 3/8" Coolant outlet Flange -Weld 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 Ribbon mixer support \ Coolant inlet Lower thermocouple. Coolant Outlet 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 Flange Thermocouple Approx. 15cm Figure X.3 Elevation and Plan of the reactor -204-

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