Synthesis Of MFI Zeolite Membranes

Applications of MFI zeolite membranes are based on the regular channel structure and excellent sorption characteristics of MFI zeolite. The previous research works have indicated that MFI zeolite membranes have good separation performances. The membrane can be expected to realize the separation in molecular level. It has wide potential applications in fields of pervaporation, gas separation and membrane reactor. With the gradual decreasing of petroleum resources, it is more and more essential and urgent to develop an energy-conserving and high-efficient production technology of fuel ethanol. High silicon MFI zeolite membrane (silicalite-1) has a good separation performance for ethanol/water mixtures, and it can be expected to apply in membrane bioreactor coupled with fermentation and pervaporation process. Synthesis technique is the key part of MFI zeolite membrane's research work. Hydrothermal crystallization is the most common synthesis technique for preparation of MFI zeolite membrane, including in situ growth and seeded growth methods, respectively. It was also adopted in this study. In the course of this study, first, MFI zeolite membranes were prepared by in situ growth method reported in the literature. XRD, SEM, EDX and pervaporation testing were used for characterizing these membranes. The heat and weight change of MFI zeolite powders during its calcination process was investigated by DSC and TGA,respectively,in order to optimize the calcination procedure of MFI zeolite membrane. Based on the above results, this thesis was focused on study of the influence of different factors on the morphology and property of MFI zeolite membranes prepared by in situ growth. According to the membrane characterization results, the suitable conditions for synthesis of MFI membrane are following as: mullite tube with average pore size of 1μm; synthesis time of 48 hours; synthesis temperature of 185℃; gel composition of n(TEOS):n(TPAOH):n(H₂O)=1:0.17:120; gel stirring time of 30 minutes. The membrane prepared under this optimized condition showed a better separation performance. Presently, the best membrane prepared by in situ growth method had a separation factor of 61 with a flux of 1.18 kg/m2·h (ethanol feed concentration of 5wt%; pervaporation temperature of 60°C), and the ethanol concentration in the permeate side was condensed to 76.5wt%. Whereafter, the seeded growth method was applied to synthesize MFI zeolite membrane. Three seeding methods were adopted. The morphology and separation performance of these membranes were discussed, and the results showed that the method B got the best achievement. The synthesis time was also optimized. Compared with in situ growth,the seeds greatly affected crystal growth onto the porous tube. In addition, under our present synthesis conditions, the better membranes was prepared by the seeded growth method. The best membrane prepared by the seeded growth method had a separation factor of 69 with a flux of 0.85 kg/m2·h at 60°C for 5wt% ethanol solution. Although the membranes prepared in this work had a good performance, the synthesis technology needs to be further optimized in order to prepare better membrane.