Antisolvent Precipitation of Potassium Bicarbonate from KHCO3 + H2O + Ethanol/2-Propanol Systems in the CO2 Capture Process

Abstract

For the energy-saving hot carbonate process, which contains a crystallization step, the antisolvent precipitation of potassium bicarbonate was investigated by adding ethanol and 2-propanol in a simulated effluent solution of CO2 absorption column. The feasibility of using the antisolvent was verified with the equilibrium data of ternary systems and a KHCO3 recovery. The ternary systems of KHCO3 + H2O + ethanol/2-propanol were equilibrated with varying amounts of alcohols at a preset temperature, and the equilibrium concentrations were determined using the cloud point method. In the ethanol system, a homogeneous and a solid liquid phase were observed, whereas in the 2-propanol system, a liquid liquid phase as well as the homogeneous and solid liquid phases were observed. The equilibrium data were correlated with a local concentration parameter in the range of the antisolvent. From the correlation, the amount of antisolvent that has an effect equivalent to a cooling-only method and the optimum concentration of the antisolvent were evaluated. An addition of 17 wt % of ethanol and 57 wt % of 2-propanol had an effect equivalent to cooling the solution from 333 K to 303 K. The optimum concentrations of the ethanol system and the 2-propanol system were found to range from 32.93 wt % to 60.07 wt % and from 6.24 wt % to 17.88 wt %, respectively, and the bicarbonate recovery yield was almost doubled when the optimum concentration of the antisolvent was applied. Considering the antisolvent concentration that has an effect equivalent to cooling crystallization and the optimum concentration of the antisolvent, ethanol was found to be a more feasible antisolvent than 2-propanol.