| Pervaporation (PV) has become one of the most promising separation process for low concentration ethanol aqueous solution due to low-cost and achieve continuous product coupled with fermentation. However the materials with good ethanol-permselective properties are few and restrict industrialization process. In addition, inorganic-organic matrix mixed membranes show excellent separation performance for ethanol dehydration. However, inorganic materials are hard to well disperse and incompatibility with polymer matrix. This study focuses on the membrane material selection based on different principles. Alcohol-soluble and hydrophobic materials were chosen to separation low concentration ethanol solution and investigated the pervaporation performance. Moreover, transport model was built to analyze the membrane separation properties. For mixed matrix dehydration membrane, the zeolite was modified using 3-aminopropyl-triethoxysilane to improve the dispersibility and compatibility. And the effect of ultrasonic treatment on membrane structure and performance were investigated.1. Base on solubility parameter principle, the feasibility of concentrated ethanol by alcohol-soluble materials was first investigated. This study focused on PVB membrane performance due to the poor film-forming of other material. However, the pervaporation results showed the PVB membranes were more perm-selective to water than to ethanol. Sum frequency generation (SFG) was employed to analyze property of membrane surface in different environment. It was found that the hydrophobicity of PVB membrane decreased due to the change of surface states. The water contact angel of PVB membrane confirmed this result. The contact angel decreased from 83.4° to 70.4°。Therefore, the preferential adsorption selectivity to ethanol of PVB membrane will decrease according to solution-diffusion mechanism.2. Adopted UNIFAC-FV model and Fujita free volume theory to study the solubility and diffusivity of ethanol and water in the PVB membranes. It was found that the sorption selectivity was more than 1 in certain range due to the affinity of PVB and ethanol is greater than the water. However, the diffusion selectivity was far less thanl due to the membrane swelling and free volume increase caused by ethanol concentration and temperature increase. Finally, the combination of sorption and diffusion induced PVB membrane was water perm-selective. Moreover, the comparison between theoretical and experimental results and error analysis showed the model can accurately reflect the sorption and diffusion behavior of water and ethanol in the PVB membranes.3. Selection and preparation of PVDF asymmetric membranes base on similar polarity principle. The effects of molecular weight, thickness of casting blade, evaporation temperature, dissolve temperature, composition and temperature of coagulation bath on the morphology and separation performance of membranes were first investigated. From the sing-factor experiment results, the optimum condition was the material was 6020, evaporation, dissolve temperature and coagulation bath temperature,60℃,40℃,25℃ respectively and composition of coagulation bath was water (separation factor and flux was 7.20 and 2.95 Kg·m-2-h-1).4. In view of the hydrophobic surface membrane has good ethanol-permselective performance. More hydrophobic PVDF asymmetric membranes were prepared by adding ammonia in casting solution in order to improve the selectivity. And the effect of ammonia on the membrane surface properties and performance were investigated. The result of water contact angel demonstrated the hydrophobicity of PVDF asymmetric membranes increased after adding ammonia. As a result, the pervaporation performance was improved that the separation factor increased to 9.23 when the concentration of ammonia was 5.88mM compared to 7.20 without ammonia.Second, try to modified PDMS membranes by super-hydrophobic PVDF and found that although the hydrophoicity of membranes increased, the results of pervaporation showed the performance of PVDF/PDMS was not improved. The separation factor just increased from 5.03 to 5.80. The results were due to porous PVDF surface membrane failed to reduce the chance of water in contact with the PDMS membrane.5. The study on mixed matrix membranes pervaporation dehydration of ethanol. Polyacrylic acid sodium (PAAs) was chosen as the bulk polymer and NaA zeolite was employed as the inorganic filler due to its hydrophilic nature. To improve the dispersion and compatibility of NaA zeolite with PAAs membranes, NaA zeolite surface was modified with amino functional silane-coupling agents. Compared to unmodified zeolite, the dispersibility and compatibility of modified zeolite was improved obviously and non-selective voids eliminated due to the electrostatic repulsion effect and ion-ion interaction between-NH3+group on surface-modified NaA and COO- group on PAAs. Furthermore, the effect of ultrasonic dispersion on the membrane structure and performance were investigated. With increasing ultrasonication time, the viscosity of the casting solution decreased as the chain entanglements decreased and crystallization occurred. When the ultrasonic time exceeded 2.5 h, the relative separation factor decreased due to the appearand & of a lamellar structure.In summary, the study on performance of ethanol perm-selective membrane choose by different selection principles and process mechanism which provides a new idea for ethanol perm-selective membranes development. Silane coupling agent proved to be a good method to improve the compatibility and dispersion of mixed matrix membranes through electrostatic repulsion effect and ion-ion interaction. The high performance mixed matrix membranes can be prepared by this method. |
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