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 CO 2 absorption column. The feasibility of using the antisolvent was verified with the equilibrium data of ternary systems and a KHCO 3 recovery. The ternary systems of KHCO 3 + H 2 O + 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 2propanol 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.

Energy-Efficient Ethanol Concentration Method for Scalable CO2 Electrolysis

“…We measured the amount of ethanol in the gas phase over solutions of 3 wt% ethanol in different liquidspure deionized water, KOH in water, carbonate salts in water (Figure S1, Table S2)deploying every time the same controlled conditions. We were not able to quantify the ethanol concentration in the gas phase for the 7 M KHCO 3 solution due to immediate crystallization upon addition of ethanol; however, for KOH and K 2 CO 3 solution samples, the effect of salting-out is surprisingly highthe concentration of ethanol in the vapor phase above 7 M KOH is 6 times higher than that above watersuggesting that a vapor–liquid equilibrium-driven approach (distillation) can yield an efficient separation method.…”