Preparation And Separation Properties Of Molecular Sieves Mixed Matrix Membranes

Membrane separation technology is widely regarded as the most promising separation technology due to its inherent advantages such as low energy consumption,high separation efficiency,simple operation,low investment,strong adaptability,and environmental friendliness.Generally,thin membranes have homogeneous and heterogeneous structures.Mixed matrix membranes?MMMs?,as a representative of heterogeneous membranes,are widely concerned by researchers because of their comprehensive utilization of the advantages of matrix and filler.The most widely used matrix materials are polymers,Ordered microporous materials?zeolite molecular sieves,metal organic frameworks and porous organic frameworks?are one of the main filler types for the preparation of such membranes.Mixed matrix membranes have been extensively studied in the fields of liquid separation and gas separation.In the field of gas separation,the capture and separation of carbon dioxide is one of the hot issues in the world today.Carbon dioxide?CO₂?,as the main component of greenhouse gases,is also one of the most common pollutants in the world.It has greatly changed the global climate,and from the current development trend,the concentration of CO₂in the atmosphere will continue to rise.This will bring a series of ecological and environmental problems,such as greenhouse effect,sea level rise,etc.,threatening the life on the planet.Therefore,reducing CO₂ emissions,capturing and storing CO₂ gas after combustion,and achieving sustainable development of human society have become one of the main problems facing the world today.To overcome this serious environmental problem,advanced carbon dioxide capture and separation technologies are urgently needed.To this end,researchers have developed different CO₂ separation technologies such as low-temperature distillation,chemical cycling,solvent absorption,pressure swing adsorption,and membrane methods.Among them,membrane separation is widely regarded as the most promising technology due to its many advantages.In the field of liquid separation,the dehydration technology of alcohol-water azeotrope has always been a difficulty in the alcohol production process.High-quality alcohols needed in production and life,especially anhydrous ethanol?Et OH?and isopropyl alcohol?IPA?are very important chemical raw materials and alternative biofuels.A key challenge in the production of high-purity alcohols is how to remove residual moisture from them.Since most alcohols can form azeotropic mixtures with water,for example,5 wt%EtOH-H₂O or 12.3wt%IPA-H₂O can form an azeotropic mixture,but the separation by traditional refining/distillation methods is very difficult.Fortunately,the pervaporation membrane separation technology provides a feasible way for separating alcohol-water azeotropes,and it is possible to prepare high-quality anhydrous alcohols.In this paper,molecular sieve AlPO₄-18 was synthesized by hydrothermal and microwave-assisted methods,and the synthesized materials were characterized by powder X-ray diffraction?XRD?,scanning electron microscopy?SEM?,and particle size distribution statistics.The effects of the two synthesis methods on materials properties were compared.We chose nano-sized molecular sieve AlPO₄-18 synthesized by microwave-assisted method as the filler material.Considering the ease of processing and the relatively high porosity of the polymer matrix,we selected PIM-1 as the polymer matrix and prepared a series of AlPO₄-18/PIM-1 mixed matrix membranes with different loadings.They were characterized by thermogravimetric analysis,XRD,SEM,and gas adsorption;and subsequently used in separation of CO₂/N₂ and alcohol-water azeotropes.The effects of different AlPO₄-18loadings on morphology and separation of the membrane were systematically investigated.The experimental results showed that with more addition of AlPO₄-18,the selectivity and flux?permeation?of the membrane were improved,and the best separation performance was achieved with the optimal loading of 15 wt%.In CO₂/N₂ separation,the ideal separation factor for CO₂ over N₂ was 30.9,the separation factor for the mixture gas of CO₂ and N₂ was33.1,the permeability of CO₂ was 4500 Barrer.In pervaporation the separation factor of ethanol/water azeotrope?95%ethanol?was 224,and total?water?flux was 1.1 kg m^-22 h^-1.The separation factor of isopropanol/water azeotrope?87.7%isopropanol?was 249,and total?water?was 2.07 kg m^-22 h^-1.The above results reflected not only the high selectivity brought by the microporous filler,but also the advantages of the high permeability of the microporous PIM-1 polymer matrix,showing its great promise as advanced materials in membrane separation.