Study On Distillation Performance Of Using Hollow Fiber Membrane Contactor To Separate The Ethanol-Water Solution

Hollow fiber membrane contactor is developed pretty rapid in the decades because of its excellent separation and mass transfer performance. Among various separation technologies using hollow fiber membrane, membrane distillation has been focused on as a new chemical separation operation by lots of researchers. However, the influences of distillation separation efficiency and gas-liquid mass transfer performance are complicated and needed to be improved in both theoretical and experimental ways. They all limit the distillation applications of hollow fiber membrane contactor.Hollow fiber membrane modules were used in the separation of ethanol-water solution distillation to delve the distillation separation efficiency and gas-liquid mass transfer performance in this research. The optimal membrane materials and the best packing density were used to fabricate the hollow fiber membrane modules with better spatial structure to enhance the distillation process.The effects of different kinds of membrane materials on separation efficiency and mass transfer performance were estimated. Three kinds of the most general membrane materials are respectively used to fabricate the modules with same packing density:Polyvinylidene fluoride (PVDF), polypropylene (PP) and polysulfone (PS). The results show that the separation efficiency of PVDF and PP membrane is approximate and2-3times higher than PS membrane; PVDF membrane has a better mass transfer performance than others; after comprehensively comparing three different membrane materials which are all far more superior to conventional distillation packing, PVDF membrane is more suitable to be chosen as the packing material for this ethanol-water solution distillation research.The effects of membrane swelling were evaluated. The variation of PVDF, PP, and PS membrane materials on morphology and dimension were chewed over to discuss their applicabilities to this experimental system furthermore. The results show that these membrane all have a certain degree of deformation on inner pore canal and outer&inner surface which would have some influences on mass transfer and operational stability; PVDF membrane has more advantages in membrane thickness and porosity; PS and PVDF membrane have a little higher swelling gradient than PP membrane; after comprehensively comparing these materials, PVDF membrane gets slighter influences from swelling and has better performances on operational stability.The effects of different packing density of PVDF hollow fiber membrane contactor on separation efficiency and mass transfer performance were analyzed as well as the different contribution to total mass transfer resistance. The results show that when the packing density decreases, the membrane distribution is more uniform on the shell-side which as a result decreases the transfer resistance and improves the mass transfer performance; ethanol-water distillation is liquid control and the overall mass transfer effects could be improved by controlling it; when the packing density is constant, the overall mass transfer coefficient is larger and the mass transfer performance is enhanced as the gas speed increasing, and the experimental value differs from the theoretical one.The effects of different coiled angles on separation efficiency and mass transfer performance were investigated and compared with straight membrane modules by using the coiled PVDF hollow fiber membrane contactor. The results show that coiled membrane modules fabricated with same membrane area and different coiled angles have better performances on separation efficiency and mass transfer than conventional straight membrane modules; the separation efficiency increases as the coiled angles decrease; the membrane module gets the best mass transfer performance when the coiled angle is45°by the synergistic effect of coiled angle and packing density; when the coiled angle below45°, the membrane module would get better mass transfer performance than that with coiled angle larger than45°.