Research Progress of Selective Formation and Enhancement Mechanism of CH4/CO2Mixed Gas Hydrates: A Review

Abstract

Efficient purification and separation of biogas are the prerequisites and foundations for realizing the efficient utilization of biogas on a large scale. Unpurified biogas as well as the gas produced by the overall gasification combined cycle containing CO₂, SO₂, and other gas impurities, which will reduce the calorific value of biogas and aggravate environmental pollution. Biogas purification is possible using the hydrate technique of mixed gas separation technology. The formation–decomposition dynamics of mixed gas hydrates and the advancement of research on the mixed gas separation technology of their hydrate technique are thoroughly reviewed in this study, especially the selective hydrate formation of CH₄containing gas mixtures and their gas separation properties. Highlighted are the quantitative impacts of various variables on the gas mixture hydrate formation process and its kinetic principles. On this basis, the influences of different driving forces, gas–liquid ratios, and gas components on the formation of gas mixture hydrates and their gas separation effects are detailed. Various factors’ regulatory mechanisms and ways of enhancing their effects on the formation of gas mixture hydrate and its gas separation process are described. Finally, the mechanism of the influence of hydrate selective formation on the separation characteristics of gas mixtures is analyzed in depth. Additionally, the challenges and future directions for the large-scale application of hydrate-based mixed gas separation technology were explored. It is noted that the key to achieving an effective purification and separation process of gas mixtures is the directional regulation of the selective hydrate formation process and the synergistic coupling of various reinforcing techniques. More in-depth research is required in this field.