Preparation And Xylene Isomerization Of Meso-ZSM-22Composite

In recent years, with the rapid development of economics, the demand for PTA or otherintermediates for organics has been increasing continuously, which leads to the short supplyof PX. So far, China has become the biggest consumer of PX. So it becomes more and moreimportant to improve the productivity of PX. Besides increasing the isomerization unit,improving the catalytic performance of xylene isomerization for para isomer selectivity is oneof the best choice.The textural properties especially pore distribution and acidic properties of zeolite usedas the active component can play an important role in catalytic efficiency and productdistribution. Micro-Mesoporous composite molecular sieves with suitable pore structure,suitable acidity and high hydrothermal stablility share potential applications in xyleneisomerization.In this paper, Meso-ZSM-22was synthesized through three different methods: onlyalkali treatment, self-assembly with or without additional Si sources. All the products werecharacterized by XRD, SEM, TEM, FT-IR, TPD, N2adsorption/desorption. Meta xyleneisomerization was studied over catalyst made by the three different methods.The development of porosity in ZSM-22zeolite by desilication in alkali medium hadbeen studied. Investigation of the infuence of concentration of NaOH, temperature and timeduring this treatment on the porous and acidity properties of the Meso-ZSM-22showed thatspecific surface area of Mesoporous, Mesoporous pore volume and total amount of acidincreased, while the ratio of Si/Al and amounts of B type acid decreased, because ofdesilication. And the main influence factors order is alkali concentration> alkali treatmenttemperature> alkali treatment time. The Mesoporosity created slightly affected the relativecrystallinity of ZSM-22zeolite. A novel micro-Mesoporous core-shell Meso-ZSM-22was synthesized by self-assemblymethod with or without additional Si sources, and the commercial microporous zeolite treatedby NaOH was the nuclear. As for the method without additional Si, Mesoporous structure canbe synthesized with good crystallinity by addition10wt%CTAB. And for the method with Sisources, the optimum experimental condition are: SiO2:CTAB:H2O=1:0.15:100and the massratio ZSM-22to SiO2was3and the crystallization time was24h. Materials prepared by thetwo methods lost some B acidic sites, especially with additional Si, but compared with pureMCM-41, the hydrothermal stability and acidity of the composite had been improvedobviously.The study of catalytic performance of Meso-ZSM-22prepared in the paper for metaxylene found that the conversion of MX increased with rising temperature, but the paraselectivity just the other way. Experiments showed that the parent material was the mostactive for MX with the same temperature, but the core-shell material by method without Sisource had the best para selectivity under the same temperature.