Shape-selective Disproportionation Of Toluene Over Modified Medium-pore Zeolite With 10-Membered Ring Openings

Para-xylene (PX) is the main raw material for the manufacture of pureterephthalic acid. The increasing demand of para-xylene appears along with the fastincrease of the polyester industry. Toluene disproportionation over highlyshape-selective catalysts to para-xylene can enlarge its supply and turns out to bevery competitive compared with the existing industrial process. This thesis reviewsthe state of the art of the technology for para-xylene production and points out thatthe development of toluene shape-selective technology plays an important role interm of industry and fundamental research. Moreover, the recent advance in processtechnology of toluene disproportionation and its catalysts is summarized. In detail,the review focuses on the previous modifying methods for HZSM-5 zeolite aimingto improve the para-isomer selectivity. The modification by chemical liquiddeposition (CLD) with organic silicon has been considered to the most valuablemethod both in laboratory and industry, which leads to the passivation of unselectiveacid sites on the external surface and reduction of the pore opening size of the parentZSM-5 zeolite catalyst.Using HZSM-5 as the main active component in extrudate catalysts, the effectsof the binder type, binder content, source of organic silicones, CLD solvent type,CLD time, quantity and cycles, acid treatment and hydrothermal treatment on theconversion of toluene and selectivity of para-xylene in toluene disproportionationwere investigated. The catalytic stability of the modified catalyst was tested, as wellas the influence of reaction conditions on the catalytic performance of modifiedcatalyst. The optimum reaction conditions were obtained.The performance of unmodified MCM-22 zeolite with 10-member ring poreopenings in disproportionation of toluene was also studied, and the effect of CLDwith silicone on the activity and selectivity of the MCM-22 catalyst wereinvestigated. ii南京工业大学硕士学位论文The main results are summarized as flows.1. Modification of HZSM-5 catalyst by CLD.Influences of various binders such as Al2O3, silica sol, Yanggan clay, and etc, inthe preparation of CLD modified HZSM-5 catalysts were studied. It was revealed thatYanggan clay was the optimum binder and in this case the catalyst containing 20wt%binder exhibited the high shape-selectivity of para-isomer with good tolueneconversion. Studies on various silylation agents during the CLD modification ofHZSM-5 showed that the silicone with low molecular weight (SA) was a satisfyingsilylation agent. Non-polar solvents, especially cyclohexane, were found to be helpfulfor CLD. The Para-selectivity was influenced slightly by the deposition time in CLD,and 7-10 h was found to be the best deposition time. It was also found that theincrease of the amount of CLD agent and the multi-cycle CLD procedure improvedthe para-selectivity. The optimal deposition amount of the silylation agent was 0.3-0.4ml/gcat. Treatments for the compacted catalyst by acids, such as oxalic acid and citricacid, could improve the toluene conversion, with enhancement of the para-xyleneselectivity. Disproportionation of toluene over the catalyst, which was modified byoxalic acid treating and twice CLD (once with 0.4ml/gcat SA), exhibited thepara-xylene selectivity of 91.2% with toluene conversion of 26.5%. Hydrothermaltreatment influenced the performance of the modified catalyst. After 100% steamtreatment at 300-350 ℃ for 2 h under atmospheric pressure,the conversion of tolueneand selectivity of PX reached 23.5% and 96.5%, respectively.2. Effect of reaction conditions on toluene disproportionationThe catalytic stability test over the obtained catalyst with the time on stream of200 h showed that the catalyst maintained the stable conversion of toluene of around23% with 96.5% selectivity. The study of reaction conditions indicated that highpressure, relatively low reaction temperature and low WHSV favored the increasingof the yield of para-xyl...