Hydrates-Based Separation of CH₄/N₂ Gas Using Copper Foam and Chemical Promoters

Hydrate-based gas separation (HBGS) offers a safe and promising route for capturing low-concentration coalbed methane (CH₄). Herein, the formation behavior of CH₄ hydrates promoted by 1,3-dioxolane (1,3-DIOX) and porous copper foam (CF) was systematically investigated. Experimental results demonstrated that the combined use of CF (60 PPI) and 5.56 mol % 1,3-DIOX under a coupled spraying-stirring mode markedly accelerates hydrate formation, yielding a maximum gas storage capacity of 0.1733 mol CH₄ per mole H₂O at 3.0 MPa, which is 10.1 times higher than that of the static pure water system. At 4.0 MPa, the maximum capacity is 0.1244 mol CH₄/mol H₂O, which is 3.7 times higher than that of the static pure water system. Furthermore, due to the higher thermodynamic driving force, the induction time for the 10% CH₄ system is shorter than that of the 5% system. Specifically, the induction time with 0.3 wt % l-leucine was 21.31%-40.38% shorter than that of the combined CF and 1,3-DIOX system. After single-stage separation, the CH₄ content was effectively enriched from 5% to 8.0%-10.25% and from 10% to 17.9%-21.7%. Compared to l-leucine, the system containing sodium lignosulfonate demonstrated a higher CH₄ concentration in the hydrate phase, indicating superior selectivity. The CH₄ recovery rates for the feeding gas systems with 10% and 5% CH₄ were approximately 40% and 50%, respectively. Comparing to the reported results in smaller reactors of 58-1000 mL, the comparable CH₄ recovery here is realized in a much larger scale reactor of 3927 mL, which is really a great improvement. These findings confirm that the proposed CF/1,3-DIOX system is an effective strategy for the enrichment of low-concentration CBM, providing a viable technical route for multistage industrial separation processes.