Combining gas hydrate crystallization and membrane technology: A synergistic approach to natural gas separation

Abstract

This study aims to extend the investigation of natural gas separation using gas hydrates. This work presents a mathematical modeling and experimental study on gas separation using gas hydrate-membrane crystallization. A membrane module was added to the gas hydrate 4 l crystallization reactor, which was used to provide an additional driving force for separation. Inlet mixture separated to the three flows enriched by different gas components. A mixture is approximating natural gas with the following composition was used: CH4 (75.68 mol.%) - С2H6 (7.41 mol.%) - C3H8 (4.53 mol.%) - n-C4H10 (2.47 mol.%) - CO2 (5.40 mol.%) - H2S (1.39 mol.%) - N2 (3.01 mol.%) - Xe (0.11 mol.%). The process was carried out in a single mass transfer apparatus. The obtained data was compared to mathematical calculation and to results of continuous gas hydrate crystallization without a membrane, presented in our previous work. Experimentally it was found that the combined method allows for 20% more efficient concentration of xenon in the gas hydrate phase compared to the method without a membrane module. Its content in gas mixture increased from 0.440 mol.% to 0.609 mol.% at stage cut θ=0.65. H₂S and CO₂ are the primary components permeable through the membrane. So, CO2 content in gas hydrate phase decreased by 55%. The methane content in the gas phase reached 88% purity in a single cycle of gas hydrate-membrane crystallization at the same stage cut value. As a result of the addition of the membrane module to the system, hydrogen sulfide recovery decreased by 19–36% and xenon recovery increased by 25%.