Biogas separation employing sII and sH promoters coupled with kinetic additives: Investigation of hydrate formation/dissociation kinetics

Biogas separation is essential for producing high purity CH 4 as a clean fuel while enabling CO 2 capture within carbon capture, utilization and storage (CCUS). However, insufficient separation can result in methane losses and incomplete CO 2 capture, undermining climate benefits by high impact CH 4 emissions with continued CO 2 release. Hydrate based gas separation (HBGS) can be a potential solution for this purpose. The successful application of hydrate-based biogas storage depends on resolving the challenge of slow formation kinetics by developing methods that can effectively accelerate hydrate onset and growth. Thermodynamic additives (Tetrahydrofuran (THF), Cyclopentane (CP), 1,3 Dioxolane (DIOX) [forming sII structure] and Tetrabutyl methyl ether(TBME) [forming sH structure] at their stoichiometric concentrations alongside combinations with kinetic additives were employed to separate 24.8 mol% CO 2 / 74.2 mol% CH 4 (biogas) mixture at 4.7 MPa and 283.2 K. Dimethyl sulfoxide (DMSO) and piperazine were also tested in combination for their effect on formation kinetics and separation efficiency. Highest gas uptake of 102.72 ± 5.12 mmol/mol was obtained using 2.86 mol% TBME with 0.1 wt% l-leucine. Selective separation ability of TBME forming sH hydrate was found to be higher compared to THF, CP and DIOX (structure sII hydrates) as it demonstrated highest separation factor of 2.45 ± 0.1, employing 2.86 mol% TBME with 5 wt% piperazine. DIOX sII mixed hydrate showed better performance compared to THF and CP in terms of gas uptake and rate of hydrate formation specifically in combination with l-methionine. Dissociation study of mixed hydrates with morphological observations show case higher thermodynamic stability of CP compared to THF and DIOX, other sII promoters. Overall, this work provides the systematic comprehensive evaluation of sII and sH promoters integrated with different bio-additives, advancing HBGS as a viable strategy for simultaneous methane enrichment and CO 2 capture with reduced environmental impact aligning with United Nations sustainable development goals (SDGs) of 7 and 13.