Study on the micro-macro kinetic and amino acid-enhanced separation of CO2-CH4 via sII hydrate

Hydrate method can achieve the safe capture of higher concentrations of CO2 in biogas and improve the utilization efficiency of CH4 gas. In this study, the separation performance of CO2–CH4 gas mixture via the hydrate method was studied at a lower pressure with 5.56 mol% tetrahydrofuran (THF). Based on the experimental results, the enhanced competition for CH4 gas within a small hydrate cage formed at higher temperatures results in a hydrate growth pattern similar to that of the pure CH4-THF hydrate system, this led to a maximum gas capture of 43.59 ± 0.48 mmol/mol, a CO2 recovery of 81.6%, and the best separation factor of 2.31 ± 0.38 at 282.95 K. Furthermore, different concentrations (500–3000 ppm) of l-phenylalanine and l-leucine enhanced the separation efficiency at 282.95 K, and the CO2 recovery increased to nearly 84%. Moreover, the separation factor under the amino acid system was highest with 1000 ppm l-phenylalanine at 0.97 ± 0.16, lower than that of the pure THF system, and indicated that the capture ability of hydrate to CH4 gas was greatly enhanced by amino acids. Thus, higher concentrations of CO2-enriched gas could be attained in future studies of multistage separation of CO2–CH4 mixtures due to enhancement of the CO2 capture separation efficiency.