Conceptual Design of a Novel CO2 Capture Process Based on Precipitating Amino Acid Solvents

Amino acid salt based solvents can be used for CO2 removal from flue gas in a conventional absorption–thermal desorption process. Recently, new process concepts have been developed based on the precipitation of the amino acid zwitterion species during the absorption of CO2. In this work, a new concept is introduced which requires the precipitation of the pure amino acid species and the partial recycle of the remaining supernatant to the absorption column. This induces a shift in the pH of the rich solution treated in the stripper column that has substantial energy benefits during CO2 desorption. To describe and evaluate this concept, this work provides the conceptual design of a new process (DECAB Plus) based on a 4 M aqueous solution of potassium taurate. The design is supported by experimental data such as amino acid speciation, vapor–liquid equilibria of CO2 on potassium taurate solutions, and solid–liquid partition. The same conceptual design method has been used to evaluate a baseline case based on 5 M MEA. After thorough evaluation of the significant variables, the new DECAB Plus process can lower the specific reboiler energy for solvent regeneration by 35% compared to the MEA baseline. The specific reboiler energy is reduced from 3.7 GJ/tCO2, which corresponds to the MEA baseline, to 2.4 GJ/tCO2, which corresponds to the DECAB Plus process described in this work, excluding the low-grade energy required to redissolve the precipitates formed during absorption. Although this low-grade energy will eventually reduce the overall energy savings, the evaluation of DECAB Plus has indicated the potential of this concept for postcombustion CO2 capture.