Study On PVDF Hollow Fiber Composite Membrane And Pervaporation Dehydration Of Isopropanol

As an emerging technology, membrane technology is increasingly expanding and the number of people dealing with membranes is growing rapidly because of its intrinsic properties of energy saving and clean. Membrane technology is believed to be one of the innovative and high technologies at 21 century.Since the successful commercialization of pervaporation for ethanol dehydration launched by GFT in 1980s, the development of this process is restricted by the the low flux. Membranes and modules with high flux is desirable, and more over, lower cost is also one of the goal of this process. In order to solve the problem mentioned above, pervaporation dehydration with hollow fiber membrane and module were studied in this paper.Firstly, the fabrication of hollow fiber membrane was studied. Factors that could influence the membrane structure were investigated, including polymer molecule weight, polymer concentration, additives and surfactants etc. It was found that fabrication was unstable and nascent membrane was un-circular when using "weak coagulation". Dope solution with high viscosity can improve the stability, while the microstructure of the resulting membrane was uneven. After investigate the influence of the solvents, we found that the instability of the fabrication was caused by the fast formation of the skin layer. When PEG concentration in the dope solution is high (>8wt%), the resulting membrane has regular fingerlike structure due to the different exchange speed of the solvent and non-solvent, while the mechanical strength of such membrane is poor. The finger like structure can originate from beneath the sponge like structure, which improve that during the fabrication, the "weak coagulation"has diffused into the nascent membrane. The PVDF hollow fiber membrane single skin layer and finger like structure in the cross section was fabricated successfully, and the pervaporation performance was improved by using such membranes.The structure stability of hollow fiber composite membrane made by routine method is poor, and the factors that affected it are investigated. The main factor that leads to the breakage of composite membrane structure is thermal shrinkage of the support membrane. The thermal shrinkage of hollow fiber membrane is due to the special manufacturing process, which leads to the orinentation of the polymer chains. While flat sheet membranes have no thermal shrinkage due to the support of non-woven fabric. And more over, pretreatment of alkali will also damage the membrane structure, which should be pay more attention. Effect of temperature, feed concentration, hollow fiber module length and packing density on the composite membrane performance were studied.Inorganic nano-particals were filled to the PVA solution to improve the membrane performance. PAM/MMT nano-composite was synthesized by in situ polymerization and characterized by XRD and TEM. The effect of MMT on the hybrid membrane was investigated. The hydrophobic silicalite nano-particals were synthesized, and the influence was also discussed.Based on solution-diffusion model and Flory-Huggins theory, the transport model of isopropanol-water system in PVA membrane was established at 333 K. The calculated values of the model were in good agreement with experimental values.