Carbon dioxide absorption characteristics of aqueous amino acid salt solutions

Abstract

In the present study, the aqueous potassium salts of 16 common amino acids and some blends with piperazine (PZ) were experimentally screened. Critical solution concentration and surface tension were measured to assess the aqueous solutions as CO2 absorbents for membrane-gas absorption (MGA). Cyclic CO2 absorption and desorption were conducted on the prepared absorbent solution, at 40°C with a continuous feed of 15kPa CO2 (N2 balance) and at 80°C with a N2 feed, respectively. The cyclic CO2 absorption performances were evaluated by computing and comparing net cyclic capacity as well as initial rates of absorption and desorption. From the experimental results, it was found that (i) longer distance between amino group-CO2-binding site-and other functional group and (ii) bulkier functional group of amino acid, would result in higher net cyclic capacity as well as faster CO2 desorption. Of the 16 amino acids, the alanine (ALA), serine (SER), and α-aminobutyric acid (AABA) salts had relatively fast initial rates of absorption and desorption, resulting in high net cyclic capacity. A small amount of PZ added as a rate promoter to the ALA, SER, and AABA salts increased net cyclic capacity by more than 25%. This result indicates that such salts could be energy-efficient alternates for monoethanolamine (MEA). Due to their high surface tension values, thus lower membrane pore wettability, ALA and SER salt solutions with PZ addition could be utilized as CO2 absorbing liquids in membrane contactors.