Enhancing CO2 Capture and H2 Enrichment by Coupling THF with Kinetic Promoters for Hydrate-Based CO2/H2 Separation: Experimental Investigation & Chemical Potential Driven Kinetic Model

Hydrate-based CO2/H2 separation provides an attractive route for pre-combustion CO2 capture with simultaneous H2 enrichment; however, its practical application remains constrained by sluggish hydrate formation and the limited understanding of environmentally benign kinetic promoters under CO2-rich fuel-gas conditions. In this study, we first examine the effect of the thermodynamic promoter tetrahydrofuran (THF) on hydrate formation from a CO2/H2 (60:40) mixture at 3.0 MPa and establish 5.56 mol % as the optimum concentration under the investigated experimental conditions. Increasing the THF concentration from 3.0 to 5.56 mol % increases gas uptake from 15.98 to 20.93 mmol/mol H2O and reduces T90 from 74.5 to 18.5 min over 280.2–283.2 K. The optimized THF system is subsequently coupled with three hydrophobic amino acids (0.5 wt % l-Methionine, l-Leucine, and l-Tryptophan) to promote hydrate growth. Their effects are evaluated experimentally and further interpreted using a chemical-potential-driven kinetic model for structure II (sII) hydrate formation. The amino acids influence hydrate growth in a molecule-dependent manner, with l-Leucine and l-Methionine exhibiting the most favourable kinetic and hydrate-yield characteristics. Despite the enhanced formation behaviour, the preferential separation of CO2 is retained: gas chromatographic analysis shows 92.7–94.7% CO2 in the hydrate phase, while the residual vapour is enriched to as much as 59.3% H2. By combining THF and amino-acid-assisted promotion, and chemical-potential-based kinetic modelling, this study links molecular-level promotion with macroscopic hydrate growth and phase selectivity in a CO2-rich CO2/H2 system. The findings provide a basis for developing hydrate-based separation processes that couple CO2 capture with H2 enrichment.