Study On Some Key Preparation Factors Of ZSM-5 Zeolitic Catalyst Modified By Silica

Para-xylene (PX) is the main raw material for the manufacture of polyester. The increasing demand of para-xylene appears along with the fast increase of the polyester industry. Toluene disproportionation over highly shape-selective catalysts to para-xylene can enlarge its supply and turns out to be very competitive compared with the existing industrial process.Using HZSM-5 as the main active component in extrudate catalysts with tow different binders, the effect of molding conditions, such as binder content, peptizer on chemical liquid deposition (CLD) with silicone, and the effect of hydrothermal treatment for catalysts on the conversion of toluene and selectivity of para-xylene in toluene disproportionation were studied. The influence of reaction conditions on the catalytic performance of the typical modified catalyst was investigated. The main results are as follows.Influences of binder content on the preparation of CLD modified HZSM-5 catalysts was studied. It was revealed that Yanggan clay was a satisfying binder and when the catalyst contained 20wt% binder, it exhibited the high shape-selectivity for para-isomer with a high toluene conversion. It was also found that the multi-cycle CLD procedure improved the para-selectivity. Hydrothermal treatment could influence the performance of the modified catalyst. After 100% steam treatment of the catalyst at 300～350℃ for 2 h under atmospheric pressure, the conversion of toluene and selectivity of PX reached 23.1% and 96.5%, respectively. The study of reaction conditions indicated that high pressure, relatively low reaction temperature and low WHSV favored the increase of the yield of para-xylene. The conversion, selectivity and yield of para-xylene reached 25.8%. 94.1% and 10.5%, respectively, under the optimal reaction conditions of 420 ℃, 2.5 MPa, 1.5 h^-1, 2～3 of molar ratio of H₂/toluene.When colloidal silica was used as the catalyst binder, HNO₃ solution as peptizer...