Research progress in separation technology of methane and nitrogen from coalbed methane
The exploration and utilization of unconventional natural gas such as coalbed methane can effectively alle-viate the problem of natural gas shortage and reduce the resource waste and greenhouse effect caused by its direct e-missions,among them,the separation of methane(CH4)and nitrogen(N2)has become the key point in the con-centration enhancement of low concentration coalbed methane.Summarizing and analyzing the research progress of methane and nitrogen separation technology in coalbed methane can lay a foundation for the practical application of separation technology and help promote the industrialization process of large-scale concentration of low concentration methane gas.The current research status of CH4 and N2 separation technologies in recent years were summarized,characteristics of the main separation technologies for CH4 and N2were demonstrated,the research progress of technol-ogies such as cryogenic separation,pressure swing adsorption separation,membrane separation,and solvent absorp-tion separation for the separation of CH4 and N2 both domestically and internationally were discussed.The cryogenic separation technology is mature and the product gas CH4 has high purity and recovery rate,but it is only suitable for separating large-scale coalbed methane in large coal mines;pressure swing adsorption technology has the characteris-tics of low energy consumption and good separation effect,at present,it has become the most promising CH4 and N2 separation technology for industrial applications.The development of low-cost and high-performance adsorbents such as activated carbon,carbon molecular sieves,zeolite molecular sieves,and metal organic framework materials(MOF)is the core of pressure swing adsorption,in the future,it is necessary to regulate the pore structure of adsor-bents and optimize their surface properties;membrane separation technology for CH4 and N2 separation has the advan-tages of small land occupation,low energy consumption,and low pollution,which can improve the separation effi-ciency,economy,and service life of polymer membranes,inorganic membranes,MOF gas separation membranes,etc.Emphasizing the improvement of membrane separation performance to enhance the adaptability of membrane ma-terials to complex oil and gas environments is important,that is,designing and screening bottom membrane materials with excellent performance has become an important direction for the industrial application of membrane separation of CH4/N2.The solvent absorption separation technology is limited in practical industrial applications of CH4/N2 due to the low solubility of CH4 and N2 in solvents,difficulty in regeneration desorption,and high usage of absorbents.
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