Thiophene Sulfur Cracking Law And Modified Zeolite Desulfurization Performance

It is well known that the main sulfur-containing compounds in FCC gasoline is thiophene and its derivatives with short alkyl chains. In this paper, the cracking rule of thiophene and short chain alkylthiophenes in decane solution on modified zeolite was studied, under FCC conditions. The results show that the sequence of sulfur-containing compounds cracking from difficulty to ease is thiophene, 2-methylthiophene, 2,5-dimethylthiophene. And the reaction net of cracking on modified Y has been built up as well. Firstly carbenium forms on acid sites, and then the reaction of trans alkylation and alkylation takes place quickly, at the same time, C-S bond breaks through hydrogen transfer or hydrogenation of active hydrogen.The influence of different modification methods of zeolite Y on its desulfuration ability was investigated. The results show that AF~ exchanging makes the amount of acid sites and L acid increase, and the activity of hydrogen transfer is also enhanced, which increases the cracking-desulfuration ability of the zeolite. The effect of the crackingdesulfuration on zeolite is not obvious by means of exchanging, impregnation and mixture of Zn as the cracking activity of the zeolites decreases. Modification of zeolite surface by Zn-Al gel can increase not only the ratio of L/B, but also the selectivity of hydrogen, and then increase the ability of the cracking-desulfi.iration.The adsorption and desorption of thiophene on modified zeolite Y and oxide compounds was also investigated. It shows that thiophene can adsorpt on NaY, but no reaction. The reaction of thiophene can take place under 403K on the modified zeolite Y, and produce H2S and sulfur in solid. The addition of Zn can not increase the adsorption ability of thiophene on alumia, the same to modification of zeolite surface by Zn-Al gel. According to above results, it is suggested_that the acid sites are the adsorption sites of thiophene on zeolite. The reason for the increase of desulfuration effect of modification by Zn-Al gel may be that the zeolite by modification enhances the supply ability of active hydrogen, which promotes saturation and cracking of thiophene.