Preparation And Application Of Ti-Containing Zeolite Films And Titanium Silicalite-Palladium Composite Membranes

Ti-contianing zeolite is an excellent catalytic material and Ti-containing zeolite films supported on various substrates have shown potential applications. Pd membrane has exceptional hydrogen permeation and exhibits unique property for direct hydroxylation of benzene to phenol. The purpose of this work is to design bifunctional titanium silicalite-Pd (TS-Pd) composite membrane based on the advantages of Ti-containing zeolite and Pd membrane for solving the problems existed in one-step oxidation benzene to phenol using sole Pd membrane reactor. It is promising to open a novel catalytic-oxidation process.This paper investigated the preparation of highly catalytic Ti-containing zeolite and films using silicalite-1 (Sil-1) as seeds and optimized the synthesis parameters. Different TS-Pd composite membranes were prepared and applied in one-step benzene hydroxylation, and the influences of titanium silicalite layer on reaction were investigated. At last, Pd membrane reactor with'microchannel'characteristic was constructed and further optimized the reaction conditions of benzene hydroxylation. The main contents and results are as follows:1. TS-1 films with similar physical and reaction behaviors were prepared on ceramic tubes using submicron Sil-1 particles instead of titanium silicalite-1 (TS-1) as seeds. Some factors on influencing TS-1 films formation and catalytic properties were investigated. Film thickness, morphology and orientation could be effectively controlled by adjusting crystallization time and times. The best molar composition of Ti/Si, H2O/Si and TPAOH/Si in mother liquid was 0.02,250 and 0.35. A uniform TS-1 layer was grown on the surface of stainless steel packing rings and SiO2 pellets by covalently seeding method and modified seeding-rotation method, which provided some effective methods to deposit high quality film on the surfaces with complex geometries. Compared with TS-1 film supported on tube and powder, the catalytic activity of TS-1 films supported on stainless steel rings and SiO2 pellets were dramatically increased due to provide a large interfacial contact area and improve the mass transfer processes. The reuse and regeneration of film were increased compared with powder catalyst.2. Pd-TS-1 composite membrane with excellent behevior was prepared. H2 flux and H2/N2 ideal selectivity of Pd-TS-1 membrane at 673 K were 8.1×10-4 mol·m-2-s-1·Pa-0.5 and 1030. Pd-TS-1 membrane was stable over a period of 340 h,19-H2-N2gas exchanging cycles at 673 K,18 temperature cycles between 473?523 K and 20 pressure cycles between 50?150 KPa at 473 K. The reactor configuration, H2/O2 feed ratio, pressure and temperature had important influences on benzene reaction. The best benzene conversion of 5.4% was obtained when H2/O2 feed ratio was 4.7 and pressure was 100 KPa. The degree of benzene hydrogenation increased and benzene conversion decreased with increasing temperature at 423?573 K. The water was mainly formed by reacting H2 with O2 on the surface of Pd membrane. Pd-TS-1 composite membrane had stable benzene conversion and phenol yield after reaction 80 h.3. TS-1 films with more inter-particle pores and hollow structure were prepared by adding TEA on the mother liquid and post-treated with TPAOH solution, which increased the flux and catalytic activity. Ti-containing mesoporous zeolite with pure mesoporous phase and zeolitic secondary building units as well as TS-1-like environment has been successfully assembled from submiron Sil-1 particles, which showed excellent hydrothermal stability and catalytic activity. A new TOF-SIMS method was used to detect the zeolite fragments existed in mesoporous catalyst. A mesoporous membrane was deposited on the surface of ceramic tubes by hydrothermal growth method using Sil-1 as seed, which possessed higher H2 and N2 flux with 3.68 and 1.02×10-6 mol·m-2·s-1·Pa-1 and H2/N2 selectivity of 3.62. The catalytic activity was improved compared with conventional Ti-containing mesoporous membrane.4. Different TS-Pd composite membranes were prepared and applied in one-step hydroxylation of benzene to phenol, a novel catalytic route was put forward and the catalytic mechanism of composite membrane was analyzed. The results showed that the configuration of titanium silicalite layer and feed model had important impact on the reaction. Benzene conversion increased with increasing the pore size of titanium silicalite. Pd-TS-1p composite membrane exhibited the highest benzene conversion (6.0%) and phenol selectivity (94.5%) and the lowest water generation rate (24 mg/min), which indicated increasing the material efficiency. Composite membrane displayed the bifunctional effect of catalytic oxidation for Ti-contaning zeolite and H2 permeation for Pd membrane.5. A novel Pd-TS-1p membrane reactor with similar'microchannel'characteristic was designed for benzene hydroxylation. Benzene conversion increased from 6.4% to 7.5% due to increase the contact area of reactants. A layer of Pd membrane was deposited on hollow fiber ceramic tube and similar'microchannel'reactor was constructed, which exhibited higher catalytic activity than conventional membrane reactor:benzene conversion increased from 5-7 % to 15-20%. The effects of feed model, H2/O2 ratio and temperature were investigated. The hydrogenation increased with increasing temperature at 423-523K. Pd membrane reactor had stable benzene conversion and phenol yield after reaction 46h.