| As an advanced bio-fuel, butanol has many advantages over ethanol. Butanol is regarded as a good gasoline additive and even a promise substitute for gasoline. Acetone-butanol-ethanol (ABE) fermentation is one of the largest biotechnological processes to product butanol. However, the fermentation process suffers from severe inhibition due to the high toxicity of butanol to microorganisms, thus the yield and productivity of ABE fermentation process are low. As a rapidly developing membrane technology, pervaporation has the greatest potential to be incorporated with the fermentation process because it has not only higher selectivity for butanol and lower energy consumption but also less effect on microorganisms. The development of the membrane materials with high flux and selectivity is the key to the pervaporation technology and its industrial application. Based on the solution-diffusion theory, polyoxyethylene containing polymers are promising membrane materials for butanol/H2O separation. In this work, the poly(ethylene-b-ethylene oxide) block copolymer (PE-b-PEO) were synthesized and then blended with the PEG or PEO additives to prepare blend membranes, which were used for pervaporation separation of butanol/H2O mixtures.The PB-b-PEO was synthesized via the method of monomer-activated sequential anionic polymerization. The polymerization kinetics of EO was studied herein. It was found that EO polymerization rate strongly increased with the amount of i-Bu3Al added and the [Al]/[Li] ratio. A curvature of the conversion vs time plots, corresponding to an induction period, were observed in particular at lower amount of organoaluminum added ([Al]/[Li]=6). At higher amounts of activator ([Al]/[Li]=10and14) the induction period was limited. The PB-b-PEO was successfully hydrogenated by p-toluenesulfonyl hydrazide (TSH) under atmospheric pressure to prepare the PE-b-PEO. The copolymers were characterized with GPC,’H-NMR and FTIR.The blend membranes were prepared by using PE-b-PEO as membrane material and PEG1500or PEO4,000,000as additives. It was found that both the permeation flux and separation factor increased with the increasing additive content, and the pervaporation performance of PEPEO/PEO blend membranes were better than the PEPEO/PEG blend membranes. Moreover, the effects of feed concentration and operating temperature on the pervaporation performance were also investigated by using PEPEO/PEO-30blend membrane. It was found that with the increase of butanol concentration in the feed, the permeation flux increased linearly, while the separation factor decreased. Both the permeation flux and separation factor increased with increasing operating temperature, and the relationships between the permeation flux and the temperature were in accordance with the Arrhenius equation.The flux of butanol is more sensitive to temperature.Also, the mass transfer mechanism of alcohol/water was investigated. It was found that with the increase of carbon number in the alcohols, the affinity to the ether oxygen group increased. As a result, the swelling degree of the PE-b-PEO homogeneous membrane increased. By comparing the solubility selectivity and separation factor of PEPEO/PEO-30blend membrane, it was demonstrated that the pervaporation separation of butanol/water mixtures by the oxyethylene group containing polymer membranres was dominated by the solubility selectivity. |
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