Kinetic and Morphological Investigations on the Effect\nof Hydrophobic and Hydrophilic Amino Acids during Hydrate Based Gas\nSeparation of CH<sub>4</sub>CO<sub>2</sub> (Biogas)

Biogas\nhas been playing a pivotal role in energy transition, and\n its production has been increasing globally. Upgradation of biogas\nis essential for enriching the calorific value of biogas. For the\npurpose of separating out CO<sub>2</sub> from biogas and producing\npurified CH<sub>4</sub>, hydrate based technology has been proposed.\nIn the present study, we examine for the first time the kinetics of\nhydrate formation employing a 50–50 mol % mixture of CH<sub>4</sub>–CO<sub>2</sub> in the presence of amino acid additives\nat selected concentrations and operating conditions (<i>T</i> and <i>P</i>). Kinetic parameters of gas separation like\nrecovery of CO<sub>2</sub>, separation factor, gas uptake, <i>t</i><sub>90</sub>, and residual and hydrate gas composition\nhave been studied. Concentrations of amino acids and driving force\nwere varied to study their effect on the kinetics of hydrate formation,\nenabling the identification of optimal process conditions to achieve\na higher separation factor alongside improved gas uptake. Three hydrophobic\n(l-methionine, L-tryptophan, and l-phenylalanine)\nand two hydrophilic amino acids (arginine and histidine) at concentrations\nof 0.1 and 0.5 wt % were chosen to see their effect on separation\nof the biogas mixture along with kinetics under comparable temperature\nand pressure conditions. It was seen that hydrophobic amino acids\nact as efficient additives in enhancing the hydrate formation rate\nyet result in poor separation efficiency. On the other hand, hydrophilic\namino acids showcase a higher separation efficiency but with reduced\ngas uptake/gas recovery at 274.2 K and 6.9 MPa/4.9 MPa. The highest\nseparation factor of 8.24 ± 0.37 was achieved using 0.1 wt % l-arginine at 3 MPa driving force. Further, morphological observations\nduring hydrate formation using different amino acids at performed\nexperimental conditions have been presented.