Preparation And Properties Of Sandwich-like TS-1-Pd Composite Membrane

Hydrogen as a clean energy is widely used in the field of petroleum processing and fuel cell. Due to increasing demand of pure hydrogen, hydrogen purification and separation technology has attracted much attention. Palladium membrane has a unique selective permeability to hydrogen, it is a good material for hydrogen permeation. Furthermore,applications of palladium membrane in the catalytic reactions show great potential. Therefore,the preparation of palladium membrane with high hydrogen permeability and good stability has become hot topic.In this paper, high stable palladium membrane was obtained on the Pd/Sil-1 zeolite nanoparticles modified macroporous alumina tube. Furthermore, in order to obtained palladium composite membrane with the function of selective oxidation, TS-1 catalytic layer was introduced on the surface of palladium layer with self-assembly technique and hydrothermal synthesis method to form a sandwich-like TS-1-Pd composite. The membrane morphology and structure were determined by SEM, EDX, XRD. In addition, the gas permeability and membrane stability in long-term operation were tested. TS-1-Pd composite membrane was assembled to membrane reactor, it was applied in the catalytic epoxidation of propylene to propylene oxide. The main results are described as follows:Pd/Sil-1 zeolite nanoparticles could not only effectively improved the surface of porous alumina carrier, but also the palladium nucleus were successfully introduced in the modified layer. After electroless plating, dense palladium membrane with high hydrogen permeability,and excellent stability was obtained. The membrane thickness is about 6 μm. The results of gas permeation test and membrane stability test indicates that the resistance of support and the modified layer to the gas permeation could be neglected, and the controlling step of hydrogen permeating through palladium membrane was the surface process. The hydrogen permeance is up to 1.95×10-6 mol·m-2·Pa-1 and H2/N2 ideal selectivity can reach 1165 at 775 K. The membrane permeability was stable for continuous operation of 15 days at 673 K.The silicalite-1 zeolite seed was successfully introduced onto the surface of palladium membrane by self assembly method, then TS-1 catalytic layer was formed on the surface of palladium membrane by hydrothermal method. The sandwich-like TS-1-Pd composite membrane was consititued by TS-1 zeolite layer, palladium layer and porous support. The permeation behavior of the TS-1-Pd composite membrane was the same as that of pure palladium membrane. Due to the existence of TS-1 zeolite layer on the surface of palladium membrane, the the hydrogen permeation flux was not very high. Fortunately, the TS-1-Pd composite membrane was stable after continuous operation for 10 days at the temperature of423 K.TS-1-Pd composite membrane was assembled to membrane reactor for gas phase epoxidation of propylene. To determine the optimal reaction conditions, the effects of totalfeed rate under ideal H2/O2/C3H6 feed ratio, H2/O2 feed ratio, propylene feed rate and reaction temperature on the reaction properties were investigated. Experimental results show that the highest yield of PO could be obtained under the conditions which were described as follows:oxygen feed rate of 20 ml/min, hydrogen feed rate of 20 ml/min, propylene feed rate of 10ml/min, reaction temperature of 180 ℃. Therefore, further studies are required in the future.