Low-temperature hydrothermal modification of HZSM-5 and its aromatization performance for hexene
In order to prepare catalysts of T 70-HZ-5,T 100-HZ-5,and T 150-HZ-5,low-tem-perature hydrothermal modification was carried out on HZSM-5 at 70,100 and 150℃,respectively.These catalysts were characterized by X-ray diffrac-tion,X-ray fluorescence spectroscopy,physical ad-sorption,chemical adsorption,and infrared spec-troscopy,and their catalytic performance for hexene aromatization was evaluated.The results showed that low-temperature hydrothermal modification main-tained the complete crystal structure of HZSM-5 and increased its silicon aluminum mole ratio[n(Si)/n(Al)],the ratio of B acid to L acid(B/L),and the average pore size.The decrease in acidity and the increase in pore size were beneficial for prolonging the lifespan of HZSM-5,while the increase in B/L value was beneficial for improving selectivity.Under the conditions of reaction temperature of 405 ℃,re-action pressure of 0.2 MPa,and mass space velocity of 2 h-1,the catalytic lifespan of T 100-HZ-5 could reach 44 h,which was 36 h longer than the catalyst without modification.After 8 h of reaction,the se-lectivity of the mixture of benzene,toluene,and xy-lene(BTX)in HZSM-5 had rapidly decreased to about 35％,while T 100-HZ-5 was still close to 55％.
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