| Summary: | 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.
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