Experimental Study on Hydrate Formation with Synthesized CH4/CO2/N2 Ternary Mixtures

The variations in the equilibrium conditions of the hydrate phase between different gas components can be employed for gas separation. The use of hydrate-based gas separation technologies for CH4 recovery from biogas has gained prominence. In this study, the formation of a ternary mixture gas hydrate with CH4, CO2, and N2 was studied. The amount of gas consumed and the hydrate formation rate were calculated using pressure and temperature variations during the reaction. Gas composition changes, the CH4 recovery factor, and CO2 split ratio were the key parameters considered to evaluate the technical feasibility of HBGS. Results indicated that the formation of the mixture gas hydrate depends on the driving force between the hydrate equilibrium conditions and operating conditions. The process of hydrate formation can be divided into two stages: Most of the CO2 formed the hydrate in the first stage, and both CH4 and N2 may have entered the hydrate structure in the second stage. For a given gas, the CO2 separation and CH4 recovery could not be optimized for one specific P–T condition. The powder X-ray diffraction measurements indicated that the ternary mixture gas hydrate was an structure I. The experimental results herein can provide data and theoretical support for CH4 purification and CO2 separation from biogas.