Selection of suitable aqueous potassium amino acid salts: CH₄ recovery in coal bed methane via CO₂ removal

In this study, we identified suitable potassium amino acid salt absorbents for CO₂ removal for purposes of recovering CH₄ from coal bed methane (CBM). We checked critical concentrations of each blended solvent that did not produce any precipitate during CO₂ absorption. From among these, we selected 8 solvents that gave no precipitate. The selected absorbents were assessed in terms of their CO₂ loading capacity and absorption/desorption rate in comparison with monoethanolamine (MEA) through a screening test. We regulated a 10% CO₂ balance in CH₄, because the feed gas was assumed to approximate the CBM. From the results obtained, it seems that 4 M SAR, 1.5 M ALA + 1 M PZ, and 1.5 M SER + 1 M PZ are good CO₂ absorbents, because their cyclic CO₂ loading (0.223, 0.208, and 0.18 mol, respectively, of CO₂/mol of absorbent) is higher than those of other selected solvents (e.g:, 4 M GLY + 1 M PZ, which has the lowest cyclic CO₂ loading). In addition, we checked that the high concentration of amino acid salts interrupted CO₂ absorption, decreasing the solubility. These solvents also have a relatively high surface tension at 25 C (70.6; 73.3; 68.6 mN/m), when compared with pure water it (72.0 mN/m). We therefore conclude that the suggested absorbent is adequate for use in the CO₂ removal process.