(683g) Oriented ZSM-5 Membranes in Stainless Steel Tube for Catalytic Cracking of n-Dodecane

MFI zeolite membranes with preferred orientation have attracted much attention in various areas including separation, chemical sensor, optics, and antisepsis. The application of oriented zeolite membranes in catalytic process is also recognized as of high potential in both industry and academia. Synthesis of oriented zeolite membrane in a reactor, however, remains a challenge and the application of oriented MFI zeolite membranes in catalytic membrane reactors (CMR) has not been reported. Here we would like to present our recent work on the preparation of oriented ZSM-5 membrane as a CMR and study of the effect of zeolite orientation on catalytic properties. A TiO2 modified procedure was reported, which allowed us to prepare highly b-oriented ZSM-5 monolayers on inner wall of stainless steel tube (SST) (Meiling ji et al., Microporous and Mesoporous Materials, 2012,155, 117). The procedure consists of depositing a smooth TiO2 layer on the rough inner surface of SST and growing a b-oriented ZSM-5 monolayer on it. The method is extended to demonstrate the synthesis of b-oriented ZSM-5 double-layer on inner surface of SST by depositing another thin TiO2 layer between the two zeolite layers. Without the TiO2 interlayer, ZSM-5 double-layer with a&b-oriented is obtained. To better understand the effect of membrane orientation on the catalytic activity, the catalysis properties of the as-prepared three types of membranes, i.e., b-, a&b-, and b&b-oriented ZSM-5 membrane, were investigated by catalytic cracking of n-dodecane under the supercritical conditions (550 ºC,4 MPa). A blank SST was also tested under the same condition as reference and a nearly constant low conversion of n-dodecane was observed over this material. It was found that conversion of supercritical n-dodecane effectively increased by the introduction of a single layer of b-oriented ZSM-5 membrane and further increased by the addition of another ZSM-5 layer. Particularly, the addition of the second b-orineted layer significantly increased the catalytic conversion of n-dodecane and maintains a good stability. Comparatively, catalytic activity of the a&b-oriented ZSM-5 membrane decreased dramatically after 20 min, and the conversion of n-dodecane dropped to a level comparable with that of the blank SST. In despite of the heavier amount of carbon deposition were detected after reaction, the deactivation rate were much slower over the b-oriented ZSM-5 CMRs (both single layer and double layer). We proposed that the straight channels in b-axis and sinusoidal channels in a-axis, which may cause different diffuse rate of both reactant and products, are responsible for this phenomenon.