Study On The Preparation And Regulation Of Hybrid Carbon Membranes With Excellent Gas Separation Selectivity

The separation of gas mixtures is frequently needed in many areas of production and life.It includes not only the production of raw materials and daily necessities,but also the issues of environmental protection and resource recovery.At present,most of traditional gas separation technologies are subjected to the disadvantages of complex equipment,large investment and high energy consumption.Differetently,the newly devoloped membrane separation technology has shown great potential in the fields of CO₂ removal,H₂ recovery,air separation,and natural gas purification,etc.,due to the outstanding advantages of simple operation,low cost,low energy consumption and strong adaptability.Nevertheless,the disadvantages of commonly used organic membranes,such as poor heat resistance,low mechanical strength and low permeability,and so on,have strictly limited their wide applications.Therefore,it is imperative to develop new membrane materials with high performance.Carbon membranes,a new type of membrane material,are usually fabricated by the pyrolysis of organic membranes,featuring with the merits of excellent temperature resistance,high pressure tolerance,thermal stability and separation performance.However,carbon membranes are more expensive than organic membranes.It is necessary to further greatly improve the separation performance,so as to improve the cost-performance ratio and market competitiveness of carbon membranes.In this regarding,here three kinds of additives,with prominent adsorption function towards specific gases,were selected to prepare high-performance hybrid carbon membranes.It is believed that the present work would not only enrich the preparation theory of carbon membrane,but also lay an important fundation for their practical application in the future.In this work,hybrid precursor membranes were prepared by a certain number of times of spin-coating and drying on plate supports by using polyimide as precursor and sepiolite（SEP）,or acid modified sepiolite（H-SEP）or cerium oxide（Ce O₂）as dopants.Subsequently,supported hybrid carbon membranes were obtained after pyrolysis of high temperature.The thermal stability,surface functional groups,microstructure,morphology and particle size distribution of the membranes and dopants were analyzed by thermogravimetric analyzer,Fourier transform infrared spectrometer,X-ray diffraction,scanning electron microscope and laser particle size distribution analyzer,respectively.The gas separation performance of hybrid carbon membrane was tested by one-component and two-component gases.The effects of the amount of dopant,permeation temperature and permeation pressure on the microstructure and gas separation performance of hybrid carbon membrane were investigated,and the optimal process conditions were determined.The results showed that:（1）The thermal stability of precursor membrane was improved by the incorpoartion of three additives;With the increase of additive amount,the microstructure of carbon membrane tends to be compact;As the permeation temperature increases,the gas permeability of the carbon membrane increases.（2）The hybridization of sepiolite significantly improves the gas separation performance of carbon membrane;At 30°C and 0.01MPa,when the amount of SEP accounts for 0.2%of the raw material,the permeability of the carbon membrane to CO₂ and O₂ is 6711.5 Barrer and 6062.1 Barrer,the selectivity of CO₂/N₂ and O₂/N₂ reached 30.4 and 27.4,respectively.（3）Acid treatment can effectively remove the carbonate impurity in natural sepiolite and reduce the average particle size obviously.At 30℃and 0.01MPa,when the amount of dopant H-SEP accounts for 0.2%of the raw material,the permeability to H₂,CO₂ and O₂ is 2423.3 Barrer,855.1 Barrer and670.0 Barrer,the selectivity to H₂/N₂,CO₂/N₂ and O₂/N₂ were 40.1,14.1 and 11.1,respectively.（4）The addition of Ce O₂ reduces the degree of imidization of the precursor membrane,which has a great impact on the pyrolysis process of the membrane.The permeability of the hybrid carbon membrane is significantly lower than that of the pure membrane.At 30°C and 0.02MPa,when the carbon membrane is prepared with 0.2%Ce O₂,the permeability to O₂ is 240.3 Barrer,and the selectivity of O₂/N₂ is 16.3.（5）Compared with the single-component gas test,the permeability of the mixed gas test gas is reduced and the selectivity is increased.