The leaching of NaOH from 4 : 5-sodium-titanate produced in an autocausticization process: Kinetics and equilibrium

Black liquor gasification, including autocausticization with titanates, is one of very few alternatives to the conventional recovery process in the Kr aft pulp process. Autocausticization with titanates can be divided into two subprocesses: one where the reaction between the titanate and the black li quor occurs and one with the reaction between water and the titanate. The a im of this paper was to investigate the second sub-process, i.e. the leachi ng of sodium hydroxide from 4:5 sodium titanate. A laboratory batch reactor was used in the experimental part and a computer programme was written to calculate the parameters in the overall reaction rate expression. It was fo und that the overall reaction rate was dependent on both the bulk concentra tion of sodium hydroxide and the temperature. A low bulk concentration of s odium hydroxide gave a faster overall reaction rate than a high concentrati on. Temperature had the opposite influence: a high temperature gave a high overall reaction rate. Furthermore, the reaction was found to be a slightly endothermic reaction with a heat of reaction of 7.6 kJ/mol of produced sod ium hydroxide. The equilibrium concentration was found to increase with inc reasing temperature.