Research On The Optimization Of Microstructure And Gas Separation Of Mixed Matrix Carbon Membranes Based On Ion Regulation

With the development of society,people have higher and higher requirements for the technology of efficient separation of gas mixtures,and it has become one of the hotspots of academic research.Most of the traditional gas separation technologies have some disadvantages,such as high production cost,large equipment volume,tedious process,high energy consumption and so on.Membrane gas separation technology has been widely concerned by researchers because of its low production cost,small equipment size,easy to operate and environment-friendly,and shows a broad commercial prospect in the fields of CO₂recovery,air separation and natural gas purification.However,the organic membrane separation materials on the market not only have poor acid-alkali resistance and heat resistance,but also have low gas permeability and selectivity,so it is difficult to meet the demand.Therefore,it is necessary to develop new high performance membrane materials.Carbon molecular sieve membrane（carbon membrane for short）developed in recent years has the advantages of excellent acid and alkali resistance,high temperature resistance,gas separation,mechanical strength,low production cost and so on.However,carbon membrane is also restricted by the trade-off relationship between gas permeability and selectivity,which limits its industrial application.Therefore,in this paper,the microstructure and properties of carbon membranes were optimized by zeolite and its loaded ions to enhance gas separation.This study is not only helpful to enrich the preparation theory of carbon membrane,but also provide an important basis for the industrial application of carbon membrane in the future.Firstly,using polyimide as precursor and zeolite containing Ag⁺,Zn²⁺and Ni²⁺as dopant,mixed matrix carbon membranes（MMCMs）were prepared on flat support by coating,drying and carbonization.The microstructure and properties of carbon membranes were analyzed by scanning electron microscope（SEM）,Fourier transform infrared spectrometer（FT-IR）,X-ray diffraction（XRD）,thermogravimetric analyzer（TGA）and X-ray photoelectron spectroscopy（XPS）.The effects of zeolite carrier type,amount,ion type and content on the microstructure and gas separation of MMCMs were investigated,and the effects of operating conditions such as osmotic temperature and osmotic pressure on the gas separation of carbon membrane were also investigated.The results showed that:（1）Ag⁺ was exchanged with many kinds of zeolite materials（NaY,ZSM-5 and SAPO-23）,and zeolite（AgY,Ag ZSM-5 and Ag SAPO-23）composite MMCMs were successfully prepared.Among them,AgY zeolite has the most significant effect on improving the gas separation of MMCMs.With the increase of the content of AgY zeolite,the thermal stability of the precursor membrane increased,and the internal structure of the obtained MMCMs became denser.The gas permeability of MMCMs increases with the increase of permeability temperature,while the selectivity increases with the increase of permeability pressure.When the content of AgY is 0.8%,at 30℃and 0.05MPa,the permeability of H₂,CO₂,O₂ and N₂ were 1178.03 Barrer,319.98 Barrer,141.8 Barrer and10.12 Barrer,respectively,and the selectivity of H₂/N₂,CO₂/N₂ and O₂/N₂ were 116.4,31.6and 14,respectively.（2）The ion exchange of Zn²⁺or Ni²⁺with NaY zeolite was used to prepare Zn Y and Ni Y zeolites,and carbon membranes were prepared with them as dopants.It was found that the introduction of zeolite improves the thermal stability of the precursor membrane,makes the microstructure of the obtained MMCMs more compact,and effectively improves the gas selectivity;when the content of Zn Y zeolite is 0.8%,at 30℃,0.05MPa,the permeability of the carbon membrane to H₂,O₂ and N₂ is 93.58 Barrer,49.73 Barrer and 1.64Barrer,respectively,while the selectivity to H₂/N₂ and O₂/N₂ were 57.84 and 30.32,respectively.（3）Ag Zn Y zeolite was prepared by exchanging Ag⁺with Zn²⁺at the same time for NaY zeolite,and carbon membranes were prepared with it as dopant.The introduction of zeolite can improve the thermal stability of the precursor membrane and effectively regulate the gas separation performance of MMCMs.Under the condition of 30℃and 0.05MPa,the permeability of H₂,CO₂,O₂ and N₂ were 719.51 Barrer,221.39 Barrer,133.86 Barrer and 5.56Barrer,respectively,while the selectivity of H₂/N₂,CO₂/N₂ and O₂/N₂ were 129.41,39.82 and24.08,respectively,when Ag⁺:Zn²⁺=6 was used.（4）Compared with the pure component,the permeability and selectivity of the prepared carbon membrane to mixed gas are lower.