Study of decarbonization reaction of sodium carbonate by sodium borates

Today, the chemical process industries are facing many challenges in the wake of skyrocketing energy price. Paper industry as a whole is also not only looking into improving the process efficiency of its chemical recovery process but also is exploring to meet these challenges with gasification based energy/chemical recovery process. Borate based autocausticizing technology appears promising, provided it could be effectively integrated into both types of chemical recovery processes based on the principles of chemistry and chemical engineering.; My research was focused on the decarbonization reactions of sodium carbonate by sodium metaborate (NaBO2) and sodium diborate (Na4B 2O5) and drew a parallel between organo-borate complexes and sodium metaborate occurring in the recovery boilers. The primary objectives of this study is to provide information on the stoichiometry and the effect of the rate controlling parameters on the decarbonization reaction between sodium borates and sodium carbonate both above and below the melting points of the reactants. Another objective of the study was to verify the melting/freezing point of trisodium borate (Na3BO3), which is the reaction product of the decarbonization reactions. The final objective of the study was to critically examine the stoichiometry of the causticization reaction of Na3BO3 in the aqueous phase since its reaction behavior would provide clue for its viability in various pulping processes.; Efforts were also undertaken to obtain the phenomenological rate parameters from the reaction data. The heat of reaction of metaborate-based decarbonization was also estimated at various temperatures. A major finding of the study is that reaction occurs below the melting points of the reactants. However, the reactions are rapid above the pooled meting point of the system. The decarbonization reactions are reversible in nature and carbon dioxide removal is necessary for a high-degree of conversion. Trisodium borate shows incongruent melting/freezing point characteristics. The causticization reaction of Na3BO 3 is reversible in nature. Finally, it is recommended that a superheated steam line (with substantial degree of superheat) should be integrated inside the molten bed to periodically sweep out the CO2 released from the decarbonization reaction to attain quick, efficient and complete conversion of the decarbonization reactions inside the smelt bed or gasification bed.