New absorbents for hydrogen sulfide: Deep eutectic solvents of tetrabutylammonium bromide/carboxylic acids and choline chloride/carboxylic acids

Abstract

Solubility of hydrogen sulfide (H2S) in a new class of solvents, i.e., deep eutectic solvents (DESs) namely, tetrabutylammonium bromide (TBAB)/carboxylic acid and Choline chloride (ChCl)/carboxylic acid, was determined at 298–318 K and 0.10–0.60 MPa. The molar ratio of hydrogen bond acceptor (HBA) to hydrogen bond donor (HBD) was taken in the range from 1:1 to 1:4. Some important operating parameters affecting the H2S absorption were investigated, such as, concentration of carboxylic acid, temperature and pressure. It was observed that the solubility of H2S in the DESs increased with decreasing concentration of carboxylic acid, Moreover, it increased almost linearly with the increasing pressure (0.10–0.60 MPa) and decreased with the increasing temperature. The solubility of H2S in the DESs TBAB/Pro with the molar ratio of 1:1 was as high as 3.81 mol of H2S/ kg of DES at 298 K and 0.50 MPa. Compared with other solvents (e.g., ionic liquids), presently used DESs exhibited almost the same capacity for H2S, moreover, after their regeneration and recycling, no any remarkable change in H2S absorption capacity was found. Desirably, such DESs present high absorption selectivity for H2S over other gases such as CH4, CO and H2, which indicates them as potential absorption solvents for removing H2S selectively from natural gas as well as gas streams originating from coal gasification process.