Molding Of ZSM-5 Catalysts And Their Catalytic Performances In Toluene Disproportionation

Para-xylene (PX) is the raw material of the polyester industry for manufacturing terephthalic. Converting toluene into PX and benzene by selective disproportionation of toluene has attracted great research interest.This thesis reviewed the state of the art of technology for PX production by toluene disproportionation over catalysts with ZSM-5 as active phase. The effect of Si/Al ratio of HZSM-5, pre-hydrothermal and post-hydrothermal treatment of ZSM-5, and the molding promoter on the conversion of toluene and selectivity of para-xylene in toluene disproportionation were investigated. The influence of reaction conditions on the catalytic performances of modified catalyst, as well as its catalytic stability was tested. The main results are summarized as follows.When the Si/Al ratio of the HZSM-5 raw material increased, the conversion of toluene declined, and the produced xylene isomers approached to a distribution of the thermodynamic equilibrium. After modifying the HZSM-5 with the Si/Al ratio of 38 by the chemical liquid desposition (CLD), the catalyst exhibited the para-xylene selectivity of 74.0%, toluene conversion of 24.4%, and the para-xylene yield of 8.9%. The catalyst with a second CLD modification could still retain a high activity. After a 100% steam treatment for HZSM-5 raw material at 300~500℃(pre-hydrothermal treatment), the activity of HZSM-5 in powder increased obviously. Treated at 320℃, the activity increased by 10%. Treated at 320℃followed by a CLD modification, the catalyst exhibited the para-xylene selectivity of 94.9%, toluene conversion of 27.1%, and the para-xylene yield of 11.0%.After the CLD modification for HZSM-5 followed by the post-hydrothermal treatment at 320℃, the resulting catalyst exhibited the para-xylene selectivity of 90.1%, the toluene conversion of 25.7% and the para-xylene yield of 9.4%. The activity of the catalyst decreased with the increase of temperature of post-hydrothermal treatment, while the selectivity of PX rose firstly, and then...