Preparation Of Mixed Matrix Membrane Based On Nano-Metal-Organic Framework For Hydrogen Separation

Energy is the material basis for human survival and development.For a long time,people have used non-renewable fossil fuels,which have a negative impact on the environment and energy structure.Now,people are committed to find clean energy that can replace fossil fuels to meet the requirements of sustainable development.Hydrogen is considered to be a good clean energy because of its high combustion calories and the product is clean and recyclable water.The main sources of H₂ come from natural gas,ammonia and syngas,and the reactions produce gas mixtures containing N₂,CH₄,H₂O,CO impurites.These impurities not only affect H₂ purity which alters the combustion efficiency and also the product cleanness undesirable in environment.Thus,so it is especially important to separate and purify H2 from the mixed gases.There are many methods for separating H₂,such as adsorption,distillation,membrane technology.Membrane separation is favorable technology because of its advantages of resource saving,environmental friendliness,simple operation,and no phase transition.Membrane material is the core of membrane separation technology.Polymer membranes are widely used in hydrogen separation due to their economic and easy membrane formation.However,there is a trade-off effect between the selectivity and the permeability of polymer membranes.Mixed Matrix Membranes（MMM）based on metal organic frameworks（MOFs）have the characteristics of high specific surface area,adjustable structure and high porosity of MOFs,and easy processing of polymers,which are expected to break the Robeson upper limit.Two classic MOF materials（ZIF-8 and UIO-66-NH₂）are selected as fillers of mixed matrix membranes.The above crystals of different sizes were synthesized.Nanoscale ZIF-8 can be effectively incorporated in the polymer.ZIF-8 nanocrystals were blended with PAN matrix to yield continuous ZIF-8@PAN MMMs.Dopamine and urea were used to modify the Ui O-66-NH₂ nanocrystals.Polydopamine were coated on the outer surface of Ui O-66-NH₂ acting as an intermediate layer between Ui O-66-NH₂ and PAN.During heating the membrane,the urea was decomposed to gas,forming extra pores providing additional path for gas transport;which is expected to improve the selectivity and permeability in gas separation.The synthesized crystals and MMMs were characterized by powder X-ray diffraction（XRD）,scanning electron microscope（SEM）,thermogravimetric analysis（TGA）,N₂ adsorption,etc.The prepared crystals had uniform shape,suitable size（50 nm-200 nm）,and excellent thermal stability.At the same time,the mixed matrix membranes with different doping amounts was performed in H₂/N₂ single gas permeation tests.For ZIF-8@PAN MMMs,the optimum test pressure was 0.26 MPa,and the optimum doping amount was 10%.Ideal selectivity of ZIF-8@PAN is about 3.5 times higher than the pure PAN membrene,reaching 5.23.For Ui O-66-NH₂/urea/PD@PAN MMMs,the optimum test pressure was 0.30MPa,and the optimum doing amount was 30%.Compared with PAN,the ideal selectivity was approximately 4 times higher and the permeability reached around 6500 Barrer.The above results showed that mixed matrix membranes of ZIF-8 or Ui O-66-NH₂ were successfully prepared with good separation property owing to the high permeability of the polymer matrix and the high selectivity of the MOF filler.These membrane are expected to be applied to practical application in gas separation.