Hydrate-based gas separation is a promising method for CO2 capture from CO2/CH4 gas mixtures, and with improved gas separation efficiency, rate of hydrate formation, and gas uptake, this process has the potential to be taken from the lab scale to industry. In this regard, a significant body of work has been conducted in recent years with the aim to enhance the kinetics of the hydrate-based CO2 capture process. The present study presents a review of the kinetic studies performed on the enhancement of hydrate-based CO2 capture from CO2/CH4 in terms of using additives, porous media, nanofluids, etc. Future research directions are also discussed. The present review aims to aid understanding of the mechanism of the hydrate-based CO2 capture process and to provide references for the development of hydrate-based CO2 capture technology toward industrial applications in the near future.

Surfactants can be used to improve the coal surface wettability and reduce the CH 4 adsorption capacity of coals, so they are usually added to fracturing fluids to promote coalbed methane (CBM) production. In this work, the impacts of a surfactant cocamidopropyl betaine (CAB) on coal structures and CH 4 adsorption characteristics were investigated. The CAB solutions with five CAB concentrations (0, 0.002, 0.006, 0.008, and 0.01 mol/L) were prepared and used to treat coal samples. The treated coal samples were dried and tested for infrared spectroscopy experiments, liquid nitrogen adsorption experiments, and CH 4 adsorption experiments. The results indicate that the hydrophilicity of the coal samples was enhanced after being treated with CAB solutions; the number of hydroxyl functional groups increased; and some aliphatic, aromatic, and oxygen-containing structures disappeared, which promoted the replacement of CH 4 by H 2 O and reduced the amount of adsorbed CH 4 . Meanwhile, the pore volume of the coal samples increased and the CBM migration rate was improved. Among the five CAB concentrations, 0.008 mol/L CAB was determined to be an optimal concentration to increase the CBM extraction efficiency. Compared to the untreated coal, the amount of adsorbed CH 4 decreased by 13.18% and the CBM migration channel volume increased by 16.74% at 0.008 mol/L CAB. The results reported in this work will offer new insights into the improvement of CBM extraction efficiency using CAB.

This work presents data on the phase behavior of tetra-n-butyl phosphonium bromide (TBPB) semiclathrate hydrate formed in the presence of CO 2 at a stoichiometric concentration (2.57 mol % TBPB). A high pressure microdifferential scanning calorimeter (HP μ-DSC) was employed to measure the phase equilibrium data and identify the dissociation behaviors of TBPB + CO 2 semiclathrate hydrate. It was found that the phase equilibrium conditions for TBPB + CO 2 semiclathrate hydrate formed at 2.57 mol % TBPB were lower than CO 2 hydrate formed in pure water and TBPB + CO 2 semiclathrate hydrate formed at 0.5 mol % TBPB. The coexistence of CO 2 hydrate (sI) and TBPB + CO 2 semiclathrate were identified in the 2.57 mol % TBPB solution. When adding 500 ppm sodium dodecyl sulfate (SDS) into the 2.57 mol % TBPB solution, CO 2 hydrate disappeared and more TBPB + CO 2 semiclathrate hydrate was formed. However, under the same temperature and pressure conditions, CO 2 consumption during the formation of TBPB + CO 2 semiclathrate hydrate was reduced when 500 ppm of SDS was added to the 2.57 mol % TBPB solution. Therefore, future work should aim to increase the CO 2 storage capacity of TBPB semiclathrate hydrate.