Study of Trisodium Borate Formation and Its Reaction with Green Liquor in Partial Autocausticizing
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Western Michigan University ScholarWorks at WMU Master's Theses Graduate College 12-2003 Study of Trisodium Borate Formation and Its Reaction with Green Liquor in Partial Autocausticizing Pasupathy Rajan Subbaiyan Follow this and additional works at: https://scholarworks.wmich.edu/masters_theses Part of the Wood Science and Pulp, Paper Technology Commons Recommended Citation Subbaiyan, Pasupathy Rajan, "Study of Trisodium Borate Formation and Its Reaction with Green Liquor in Partial Autocausticizing" (2003). Master's Theses. 4957. https://scholarworks.wmich.edu/masters_theses/4957 This Masters Thesis-Open Access is brought to you for free and open access by the Graduate College at ScholarWorks at WMU. It has been accepted for inclusion in Master's Theses by an authorized administrator of ScholarWorks at WMU. For more information, please contact [email protected]. STUDY OF TRISODIUM BORA TE FORMATION AND ITS REACTION WITH GREEN LIQUOR IN PARTIAL AUTOCAUSTICIZING by Pasupathy Rajan Subbaiyan A Thesis Submitted to the Faculty of The Graduate College in partial fulfillment of the requirements forthe Degree of Master of Science Department of Paper Engineering, Chemical Engineering and Imaging WesternMichigan University Kalamazoo, Michigan December 2003 Copyright by Pasupathy Rajan Subbaiyan 2003 ACKNOWLEDGMENTS I would like to thank my Thesis Advisor Dr. John Cameron for his valuable advice and ideas, which brought some cohesiveness to this topic. His help in coalescing my ideas into something substantive has been invaluable. Secondly, I would like to thank Murugavel Anbalagan and Biljana Bujanovic, who took time to discuss with me their ideas in the experimental set-up and for helping me to carry out some experiments. I also thank the members of my thesis committee, Dr David Peterson and Dr Said AbuBakr for taking time to review my work. Lastly, I would like to thank the U.S. Borax Inc. and the Department of Energy forproviding necessary financialsupport to complete this project. Pasupathy Rajan Subbaiyan ii STUDY OF TRISODIUM BORA TE FORMATION AND ITS REACTION WITH GREEN LIQUOR IN PARTIAL AUTOCAUSTICIZING Pasupathy Rajan Subbaiyan,_M.S. WesternMichigan University, 2003 This thesis investigates a new development of autocausticizing the green liquor with trisodium borate. Sodium metaborate (NaBO2) reacts with the sodium ° carbonate (Na2CO3) in the char bed at 850 C in the recovery furnace to form trisodium borate (Na3BO3) which in tum, when dissolved in water produces sodium hydroxide (NaOH) regenerating sodium metaborate (NaBO2). The main objective of this research is to study the formation of trisodium borate from the reaction of sodium metaborate with sodium carbonate at different molar ratios of carbonate to borate and to determine the effect of the process parameters such as products concentration and temperature on the reaction of trisodium borate with green liquor producing sodium hydroxide. The results show evidence of trisodium borate formation due to decarbonization of sodium carbonate by sodium metaborate and with increase in sodium carbonate to sodium metaborate molar ratios, the decarbonization of sodium carbonate lowers, where more carbon dioxide (CO2) is released, which needs to be effectively purged out to improve decarbonization. The reaction of trisodium borate with green liquor (Na2S, H2O and Na2CO3) was fast and about 85% of trisodium borate formed reacts with water to form sodium hydroxide. TABLE OF CONTENTS ACKNOWLEDGMENTS...................................................................... n LIST OF TABLES.............................................................................. V LIST OF FIGURES .........................................·......................... ........... Vl CHAPTER 1. INTRODUCTION Overview of Original Kraft Chemical Recovery Process. .. .. .. .. .. .. .. 1 Recovery Boiler....... .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 3 Recausticizing Process.. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 4 Slaking and Causticizing..................... .. .. .. .. .. .. ... .. ... ... .. .. .. 5 Calcining. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 6 Overall Chemistry.. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 8 2. AUTOCAUSTICIZING OF SMELT WITH SODIUM BORATES Autocausticizing................................................................... 9 Decarbonization of Sodium Carbonate with Sodium Metaborate......... 11 Conventional Causticizing AfterPartial Borate Autocausticizing......... 12 Chemistry of Autocausticizing Reactions..................................... 12 3. OBJECTIVES AND EXPERIMENTAL .............................................. 15 4. METHODOLOGY Experimental Reagents.. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 1 7 Preparation of Trisodium Borate................................................ 17 Determination of Reaction Rate and Equilibrium............................. 18 Causticizing........................................................................ 19 iii Table of Contents - Continued CHAPTER 5. RESULTS AND DISCUSSION Decarbonization of Sodium Carbonate with Sodium Metaborate........... 20 Reaction ofNa3BO3 with Green Liquor....................................... 26 Causticizing Efficiency Results....... .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 29 Cost Savings... .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 31 CONCLUSIONS................................................................................. 32 FINANCIAL SUPPORT AND FACILITIES................................................ 33 REFFERENCES................................................................................. 34 APPENDICES A. Decarbonization and Weight Loss Details...... .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 36 B. Amount ofNaOH Produced after the Reaction ofNa3BO3 with H2O............ 37 C. Split up of Decarbonization Results.................................................... 38 D. Effectof Temperature on Hydrolysis ofTrisodium Borate......................... 39 E. Effectof Concentration on Hydrolysis of Trisodium Borate....................... 42 F. Partial Autocausticizing and Causticizing Details.......... .. .. .. .. .. .. .. .. .. .. .. 44 iv LIST OF TABLES 1. Different Carbonate to Borate Molar Ratio and CO2 Evolved forEach Condition................................................................................ 20 2. Percentage ofNaOH Produced at DifferentInitial Na3B03 Concentration...... 28 3. Conditions for Causticizing Experiments.............................................. 30 V LIST OF FIGURES 1. Typical KraftRecovery Cycle. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 7 2. Percentage ofDecarbonization ofNa2CO3 by NaBO2 .. .... ...... .. ...... .. .. ....... 21 3. Theoretical and Actual Weight Loss Due to Decarbonization...... .. ... .. .... 23 4. Percentage of Trisodium Borate Reacted with Water to Form NaOH............. 24 5. Summary of Autocausticizing Results......... .-....................................... 25 6. Reaction Rate ofNa3BO3 with Water at DifferentTemperatures .................. 27 7. Effectof Concentration on the Rate and Equilibrium for the Reaction of Trisodium Borate with Water.......................................................... 29 8. Effect of Time on Causticizing Efficiency at 35% Autocausticizing Level...... 30 vi CHAPTER! INTRODUCTION Overview of Original Kraft Chemical RecoveryProcess Kraft pulping is a modification of the soda process, which employs the use of sodium hydroxide (NaOH). Originally, the soda process could not compete with the sulfiteprocess due to the cost associated with sodium hydroxide (NaOH) and the need for chemical recovery. Around 1879, 111 C.F. Dhal in Germany was looking for alternativesto reduce costs associated with the soda process. The makeup chemical used in the soda process was sodium carbonate (Na2CO3), and he replaced it with the cheaper sodium sulfate (Na2SO4). Upon heating sodium sulfate with carbon at high temperature, one forms sodium sulfide (Na2S) (Reaction 1). Mixing sodium sulfide with water provides a mixture of sodium hydroxide (NaOH) and sodium hydrosulfide (NaSH) (Reaction 2). With this innovation, the Kraft process was born.The first mill was in Sweden in 1890 and the first mill in the United States was up and running in Roanoke Rapids, NC (Champion) in 1909. Na2SO4 � Na2S (sodium sulfide).......................................... ...... (1) Na2S + H2O NaOH + NaSH ..................................................(2) 1 Kraft pulps initially had two distinct disadvantages121, a dark pulp and chemical recovery was required. However, the pulp is stronger and has better dimensional stability. Chemical recovery systems rapidly became quite advanced and most advanced mills are now shooting for98-99% chemical recovery. The Kraft recovery cycle is a closed cycle process designed to destroy toxic waste from pulping, to co-generate steam and power and more importantly to recycle pulping chemicals. A series of process and different types of equipment are used to convert the weak black liquor into re-generated pulping liquor and in the process generates steam and power. The Kraft recovery cycle is a series process beginning with application of pulping liquor, (white liquor) to wood chips. Pulping results in the dissolution of 40 to 60 % of the weight of the wood. The liquor containing the spent pulping chemicals and the dissolved organic matter