Effect of a Combination of Amino Acids on the Kinetics and Separation of a Biogas Mixture through Gas Hydrate Technology

Hydrate-based gas separation has the potential to capture and separate CO2 in biogas in order to enrich its calorific value. Authors' previous work examined the individual effects of hydrophobic and hydrophilic amino acids on the hydrate formation kinetics by employing biogas. The present study examines the kinetics of hydrate formation by employing a CH4(50%)/CO2(50%) gas mixture using the combination of two categories of amino acids at varying concentration ratios. Such a combination effect of different amino acids on the hydrate formation kinetics has not been examined before. In this article, kinetic parameters such as CO2 recovery, separation factor, gas uptake, t90, residual, and hydrate gas composition have been calculated and presented along with morphological observations during hydrate formation. Different combinations of hydrophobic (l-methionine, l-tryptophan) and hydrophilic amino acids (l-arginine, l-histidine) have been used at the experimental conditions of 274.2 K and 6.0 MPa in different concentration ratios. The highest recovery of CO2 of 42% was achieved using 0.1 wt % l-tryptophan and 0.1 wt % l-histidine in 1:1 concentration ratio, while the highest gas uptake of 133 ± 1.6 mmol/mol was achieved using 0.1 wt % l-tryptophan and 0.3 wt % l-histidine (1:3 concentration ratio). The hydrate dissociation kinetics was also examined along with morphological observations in the study.