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.