Preparation And Optimization Of U-shaped Hollow Fiber Alcohol Permselectivity Pervaporation Membrane And Membrane Module

Biobutanol is a kind of bio-liquid fuel with high energy density and high gasoline mixing degree,which has very broad application prospect.The production of acetone-butanol-ethanol（ABE）by biomass fermentation is the main way to prepare biobutanol.The fermentation product butanol is highly toxic to microorganisms,and the yield of butanol is low in the conventional batch fermentation process.Therefore,in the fermentation process,it is necessary to adopt the in situ separation technology to separate butanol in time,so as to reduce the inhibitory effect of butanol on microorganisms in the fermentation process.As a membrane separation technology,pervaporation（PV）has the advantages of energy conservation and environmental protection,mild operating conditions,which can be use in the separation of liquid mixtures.Therefore,it can be used to in situ extract biobutanol from fermentation broth,which is of great significance in the field of biofuel purification and concentration.Membrane module has an important influence on the development of pervaporation membrane separation technology.At present,preferred pervaporation membrane module mostly adopts plate and frame membrane module,which has high cost and heavy equipment in practical application.In constrast,hollow fiber membrane module has the advantages of high packing density,small footprint and low component cost.Therefore,it is of great significance to develop hollow fiber pervaporation membrane modules.In this study,polyvinylidene fluoride（PVDF）hollow fiber ultrafiltration membrane was used as the substrate to construct a hollow fiber membrane module with U-shape structure.The polyether block amide（PEBA）was assembled on the surface of PVDF substrate by dip-coating method.The U-shape PEBA/PVDF hollow fiber pervaporation composite membrane with alcohol permselectivity performance was obtained.The U-shaped hollow fiber membrane in the component oscillates continuously under the action of fluid erosion,which increases the relative motion between fluid and membrane,thus effectively reducing concentration polarization.The computational fluid dynamics（CFD）software was used to simulate the fluid flow in the component form.The U-shape hollow fiber membrane module CFD model was established.The packing density and feed flow rate conditions,which affect the performance of the U-shape hollow fiber membrane module were investigated.The simulation results were used to optimize the membrane module.Firstly,the polyether block amide（PEBA）was assembled on the surface of polyvinylidene fluoride（PVDF）substrate by dip-coating method.The U-shaped PEBA/PVDF hollow fiber pervaporation composite membrane was obtained.PEBA is a thermoplastic elastomer composed of flexible polyether（PE）segment and rigid polyamide（PA）segment,which has a high affinity for butanol.The morphology and chemical properties of PVDF membrane surface before and after assembly were analyzed and characterized.The effects of preparation conditions such as PEBA concentration,drying temperature,drying time and lifting speed on the properties of composite membrane were studied.The effects of operating conditions such as feed temperature and feed flow rate on the properties of composite membrane were also investigated.In addition,the stability of PEBA/PVDF hollow fiber pervaporation composite membrane with U-shaped structure and the separation performance of ABE fermentation broth simulation system were investigated.The results showed that when PEBA/PVDF hollow fiber composite membrane was used to separate 1 wt.%n-butanol/water mixture at 60℃,the permeation flux was 2720 g·m^-2·h^-1,with the separation factor of 17.38,showing a good butanol permselectivity separation performance.Secondly,the influence of the structure of U-shaped hollow fiber pervaporation membrane module on its separation performance was studied by experimental and computational fluid dynamics（CFD）software.The flow field distribution of hollow fiber membrane modules with different structures was simulated.The U-shaped hollow fiber membrane module model was drawn by 3D drawing software,and then imported into computational fluid dynamics software for simulation.The effects of packing density,inlet and outlet position and baffle style on the flow field of hollow fiber membrane module were systematically studied to optimize the module.The results show that by optimizing the flow structure of hollow fiber membrane module,the concentration polarization of the separation membrane surface is reduced,and the mass transfer efficiency of hollow fiber membrane is improved.The separation performance of U-shaped hollow fiber membrane modules can be improved by appropriate packing density and increasing feed velocity.In this study,the U-shaped PEBA/PVDF hollow fiber pervaporation compositemembrane with preferential pervaporation performance impregnation-lift method was prepared successfully by the dip-coating method.Through the design of composite membrane structure and membrane components,pervaporation membrane with excellent performance was obtained.Computational fluid dynamics software was used to optimize the component design.It provides a new idea for the large-scale preparation of priority pervaporation membrane components.