This work reports an experimental investigation on the morphology and kinetics of CO2 hydrate formation in the presence of sodium dodecyl sulfate (SDS). The experiments were conducted at 277.15 K and 3.5 MPa, and the quantity of SDS varies from 0 to 3000 ppm. The “wall climbing” phenomenon of CO2 hydrate formation in the presence of SDS was observed, and the growth of CO2 hydrate above the gas–liquid interface was found to become stronger as the SDS concentration was increased from 300 to 3000 ppm. This indicates that the promoting effect of SDS on CO2 hydrate formation was enhanced with the increase of SDS concentration. The largest gas consumption for CO2 hydrate formation in SDS solutions was obtained at 1500 ppm of SDS among the four SDS concentrations tested in this work, which increased by 85% compared to that obtained in pure water under the same temperature and pressure conditions. When CO2 hydrate formation was conducted for a considerably long period, two rapid jumps in the gas consumption could be observed as the SDS concentration increased above 300 ppm, and the plateau between the two jumps was shortened with the increase of SDS concentration. As a result, a high efficiency for CO2 hydrate formation was obtained at 1500 and 3000 ppm of SDS. This will provide an implication to the improvement of the hydrate-based CO2 capture technology in the future.

The consumption of natural gas is of great importance to optimize China's energy structure toward reduced CO 2 emissions and is projected to increase in the next 10 years. Coalbed methane (CBM) is a primary unconventional natural gas and has been recognized as a significant energy resource to supplement conventional fossil fuels (oil and coal) as a result of its huge potential. It has been established that the hydrate-based gas separation is a promising method for the purification of lowconcentration coalbed methane (LCCBM). In this work, the research on hydrate-based CH 4 separation from LCCBM conducted by Chinese researchers over the past 10 years has been reviewed. It is found that significant progress has been made to understand the hydrate-based CH 4 separation technology. On the other hand, the challenges related to achieving milder pressure operating conditions and enhancing the rate of hydrate formation should be overcome. Hence, further work is required to bridge the gap between the gas separation science and the technology. In this regard, future research directions are proposed in this work to help advance the research of hydrate-based CH 4 separation from LCCBM.

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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.