Dehydration Of Aqueous Ethanol Solution Using Zeolite Filled Chitosan Pervaporation Membranes

Ethanol is a good alternative for non-renewable energy resource such as fossil oil. In the process of ethanol fermentation production, ethanol dehydration has been proved to be a difficult task due to formation of ethanol/water azeotrope. Pervaporation, as a novel liquid mixture separation technology, has outstanding technical advantages and favourable promising application prospects in the dehydration of organic aqueous solutions, due to its low energy cost, environment-benign and unrestraint of vapor-liquid equilibrium.In our work, chitosan (CS) and HZSM5 was chosen out as the membrane material and inorganic material respectively. Unmodified HZSM5 filled chitosan (CS) membranes were prepared by incorporating HZSM5 into chitosan. Meanwhile, 3-mercaptopropyltrimethoxysilane (MPTMS) modified HZSM5 filled chitosan membranes were prepared in the same procedure. The structure morphology, the physical and chemical properties of the membranes were characterized and analysed by FTIR, SEM, XRD, DMA, TGA and XPS. The relationships among membrane material, membrane structure and separation performance were tentatively discussed.The separation performance of HZSM5 filled chitosan membranes for dehydration of aqueous ethanol solution was investigated. Due to the weak hydrogen-bonding interaction between organic-inorganic phases and high rigidity of chitosan chains, nanometer-scale voids occurred at the interface leading to the decrease of selectivity. Enhancement of hydrogen-bonding interaction by decreasing Si/Al in HZSM5 improved the interface morphology and reduced nanometer-scale voids. The effects of HZSM5 content and perating conditions on the swelling and pervaporation performance were discussed. From the results, HZSM5(25)-CS-08 membrane with Si/Al 25 and HZSM5 content 8% exhibited the separation performance with a permeation flux of 117.45g/(m2h) and a separation factor of 177.03 at 80oC for 90wt% aqueous ethanol solution, keeping feed flow rate 60L/h, downstream pressure under 0.1kPa.The separation performance of MPTMS modified HZSM5 filled chitosan membranes for dehydration of aqueous ethanol solution was investigated.–SO3H group was grafted on the surface of HZSM5 after MPTMS modification, and a much stronger ionic-bonding interaction had replaced the weak hydrogen-bonding interaction between HZSM5 and chitosan, which essentially eliminated the nano-meter scale voids at the interface. The effects of reaction time, modified HZSM5 content and operating conditions on the swelling and pervaporation performance were discussed. From the results, HZSM5(25)/MPTMS(24)-CS-08 membrane with Si/Al 25, reaction time 24h and modified HZSM5 content 8% exhibited the separation performance with a permeation flux of 278.54g/(m2h) and a separation factor of 274.46 at 80oC for 90wt% aqueous ethanol solution, keeping feed flow rate 60L/h, downstream pressure under 0.1kPa.