Experimental investigation on the synergistic influence of tetra-n-butyl ammonium bromide(TBAB) and cyclopentane(CP) in hydrate-based gas separation

To enhance the CO2 separation efficiency of hydrate-based gas separation (HBGS) technology, the kinetic process of hydrate formation from synthesized CH4/CO2/N2 gas mixtures in the presence of cyclopentane (CP) and tetra -n-butyl ammonium bromide (TBAB) and gas separation efficiency were studied at an initial pressure of 7.0 MPa and temperatures ranging from 275.1 to 290.1 K. The crystallographic properties of the mixed hydrates were also evaluated by Raman, powder X-ray diffraction(XRD) and cryo-scanning electron microscop(cryo-SEM). Results showed that the combination of CP and TBAB tended to inhibit the separation efficiency compared with pure CP. The maximum CH4 recovery was 1.37 and the CO2 split ratio was 0.791 when using CP and TBAB solution. The order of CO2 split ratio in the different systems followed the order SDS > CP > TBAB/CP > CP/SDS > TBAB. Meanwhile, the adsorption capacity and gas consumption also decreased with an increase in TBAB concentration. Raman and XRD tests revealed that sI, sII, and semi-clathrate hydrates were found to coexist after hydrate formation and no other types of hydrates was formed. CH4 could only enter the small cages (512) of the hydrate. SEM images showed that the hydrate crystals were ellipsoid-shaped with different sizes and stacked together to form a globular structure, suggesting that the specific surface area of the hydrate crystals enhanced with the increasing of TBAB concentration. These findings can be used to evaluate the feasibility of applying TBAB and CP in HBGS technology.

Automated summary

The kinetic process of hydrate formation from CH4/CO2/N2 gas mixtures in the presence of CP and TBAB and its effect on gas separation efficiency were studied. The combination of CP and TBAB was found to inhibit the separation efficiency compared to pure CP. The CO2 split ratio followed the order SDS > CP > TBAB/CP > CP/SDS > TBAB, and both the adsorption capacity and gas consumption decreased with increasing TBAB concentration. Raman and XRD tests confirmed the presence of sI, sII, and semi-clathrate hydrates, and SEM images showed ellipsoid-shaped hydrate crystals with increasing specific surface area at higher TBAB concentration. These findings are important for evaluating the feasibility of using TBAB and CP in HBGS technology.