Preparation Of Multi-functional Ti-containing Zeolite Membrane For Synthesis Of Propylene Oxide

Titanium silicate (TS-1) zeolite membranes have drawn much attention in recent years dueto their good catalytic properties. TS-1zeolite membrane has been applied in a wide range ofmany oxidation reactions, such as epoxidation of propylene to propylene oxide (PO) andhydroxylation of benzene to phenol. Specially, TS-1zeolite membrane not only has theexcellent catalytic performance, but also can be integrated with the membrane separationtechnology. Therefore, the TS-1membrane has become research hot issue.In this paper, TS-1zeolite membranes were prepared on porous alumina tubes by usingthe hydrothermal technique. Then they were assembled to membrane reactors for applicationsin epoxidation of propylene to PO.The morphology and permeation properties of the as-prepared TS-1membranes werecharacterized by means of SEM, XRD, FT-IR and permeation tests. The effects ofcrystallization time and ratio of Ti/Si on membrane structure, membrane thickness, membranegrowth rate, deposition amount of TS-1membrane and gas permeation performance wereinvestigated. Moreover, the effects of reaction temperature, reaction time, propylene feedpressure, feed rate of H2O2, H2O2concentration on the results of propylene epoxidation werestudied in detail. The experimental results are illustrated as follows:1. It indiated that the deposition amount of TS-1zeolite membrane increased withincreasing crystallization time during30~96hours. However, the gas permeation fluxdecreased with the increase of the membrane thickness and deposition amount of TS-1zeoliteon the support. In addition, when the crystallization time was48h, TS-1zeolite has thehighest growth rate of the TS-1zeolite membrane was obtained, that is0.087μm/h, while noobvious defects could be observed in the TS-1membrane with thickness of4μm.2. The changes of the molar ratio of Ti/Si in the synthesis solution not only affected thecontent of Ti element in TS-1zeolite framework, but also influnced the membranemorphology and permeation performance. When the Ti/Si molar ratio<0.02, Ti elementmainly existed in the form of framework titanium; however, when the Ti/Si molar ratio>0.02framework and non framework titanium coexisted. Moreover, increasing Ti/Si molar ratio willresult in the decrease of cross linking degree of TS-1zeolite. Correspondingly, the depositionamount of the TS-1zeolite membrane will decrease,and the defects in the membrane willincrease, which resulted in the increase of propylene permeation flux.3. In order to evaluate the catalytic properties of the as-prepared TS-1zeolite membrane,the reaction of propylene epoxidation was carried out, It found that PO selectivity of90%andH2O2conversion of20%were gained under a suitable reaction conditions, which werereaction time of12h, reaction temperature of333K, the propylene feed pressure of0.4MPa,H2O2feed rate of40ml/min, H2O2concentration of1.11mol/L and the Ti/Si molar ratio of0.02. Although the results of propylene epoxidation on TS-1zeolite membrane were not as good as the TS-1zeolite powders, TS-1zeolite membrane had high reaction efficiency.Moreover, The as-prepared TS-1zeolite membrane has better regeneration performance, hichprovides the theoretical basis for application of the TS-1zeolite membrane used inepoxidation of propylene.