Experimental Study on the Influence of the Temperature and Gas-Liquid Ratio on Hydrate-Based CO2 Separation from the CH4-CO2 Gas Mixture under Static Conditions

The purification of bionatural gas is the premise and basis for the efficient utilization of biological gas. The separation of mixed gas by the hydrate-based method can realize the efficient separation of CO2 gas from bionatural gas. The formation features of mixed gas hydrates were studied under static conditions through experiments in this work, and the quantitative effects of the temperature, gas-liquid ratio, and other factors on the formation process of the CH4/CO2 mixed gas hydrate and the selective formation properties of the mixed gas hydrate were deeply analyzed. During the hydrate generation process, fluctuations in system pressure, gas component concentration, gas consumption, CH4 recovery, and separation factors were discovered. According to the results, the temperature and gas-liquid ratio have obvious effects on the formation characteristics and selective formation of the CH4/CO2 mixed hydrate. When the temperature is fixed at 277 and 278 K, the separation effect of CH4/CO2 gas is greatly influenced by the gas-liquid ratio, and there is an optimal gas-liquid ratio for separation. A large or small gas-liquid ratio is not favorable to hydrate formation and mixed gas separation. The three gas-liquid ratio conditions all show a good separation effect, and the concentration of CH4 in the residual gas phase can be increased from 60% to 71.12%, at 279 K. Furthermore, the CO2 capture rate is as high as 45%, but the CH4 recovery rate is low, only 90.13%; and the lower the gas-liquid ratio, the higher the CH4 concentration in the remaining gas phase and the CO2 capture rate, as well as the better the separation effect. Additionally, adsorption between the hydrate cage and methane molecules has a substantial impact on the efficient separation of CH4/CO2 gas during the mixed hydrate formation process. The relevant results give essential theoretical guidance and a reference for mixed gas separation by a hydrate-based method.