Natural gas purification by asymmetric membranes: An overview

Natural gas, as a very important source of energy and chemical feedstock, can be used in place of coal to lower net carbon dioxide emissions. Membrane separation technology is an attractive alternative for natural gas purification where the impurities represented by acid gases (CO₂ and H₂S) as well as inert gases (N₂) must be removed to meet the transportation and usage specifications. From the economic benefits viewpoint, asymmetric membranes are required for industrial manufacture and applications. This paper aims to review the latest development of various kinds of asymmetric membranes for natural gas purification, mainly focusing on CO₂ removal from CH₄, including H₂S and N₂ separation from CH₄ as well. According to material types, polymeric, inorganic, mixed-matrix and carbon molecular sieve membranes are introduced. The associated fabrication approaches and transport properties are discussed for each kinds of asymmetric membranes. Towards the practical implementation, an emphasis is placed on hollow fiber asymmetric structure for these polymeric, mixed-matrix and carbon molecular sieve membranes.