Evaluation of CO2 removal from a CO2+CH4 gas mixture using gas hydrate formation in liquid water and THF solutions

In this work, the performance of hydrate formation for CO2 removal from a simulated recovered shale gas (40mol% CO2 and 60mol% CH4) was evaluated in liquid water, and THF and THF/SDS solutions. Experiments were carried out at a fixed temperature of 277.15K and in the pressure range of (2.8–6.7) MPa. The impact of driving force (overpressure) on hydrate growth and CO2 selectivity was studied both in liquid water and in THF solutions. It was found that higher driving force resulted in a reduction of the final gas uptake as well as a significant decrease of the CO2 recovery and separation factor. The results indicated that mass transfer for hydrate growth was greatly hindered at high driving force, and the competition between CH4 and CO2 molecules for the occupancy of hydrate cavities became stronger with the increase of driving force. Although the kinetics of hydrate formation with the CO2/CH4 gas mixture was improved by adding THF and SDS into liquid water, the selectivity for CO2 removal from the CO2/CH4 gas mixture was compromised as compared to that in liquid water. The highest CO2 recovery (52%) and separation factor (8.8) were obtained at a low driving force (2.5MPa) in liquid water, which were much higher than those obtained in THF and THF/SDS solutions. As a result, enhancing the kinetics of hydrate formation without reducing CO2 selectivity is the key factor to improve the hydrate based gas separation process for CO2 removal from the CO2/CH4 gas mixture.