Study On Alkylation Process For Thiophenic Sulfur Removal Over Zeolite Catalyst

Olefinic Alkylation of Thiophenic Sulfur (OATS) is a kind of non-hydrodesulfurization process. Sulfur species present in cracked naphthas are converted and removed by passing the naphtha over acid catalyst to alkylate the thiophenic compounds in the naphtha using the olefins present in the naphtha. Alkylated thiophenes are concentrated in the heavy portion by distillation and then removed by hydrodesulfurization.The advantage of USY zeolite easily modulated property was applied to prepare catalyst by steaming. The effects of different conditions of reaction temperature and USY steaming treatment on alkylation performance were investigated. The alkylation reactions performance of different fractions in the FCC gasoline was also studied. The deactivation of USY was the main factor to limit its industrialization. The modern analyses such as SEM, TG, XRD, IR were taken to study the reasons of deactivation. Considering the disadvantage of USY, MgY and Hβwere used to carry on subsequent studies.The results showed that the desulfurization performances of USY zeolites were optimum under the conditions as follows: the steaming temperature as 350℃, the steaming time as 5 h, reaction temperature as 120℃. The pyridine adsorption infrared spectrogram suggested that USY zeolite with larger acid sites, especially strong Bronsted acid sites, performed better function on the alkylation reactions. It was suggested that the decrease in alkylation capability of thiophene derivatives enhanced other two parallel competitive reactions: the aromatics alkylation and hexene alkylation(or called hexene oligomerlzation). The USY zeolite was deactivated after three times reactions. It was indicated that the USY was instability. The fresh,the deactivated and the regenerated were characterized by a lot of techniques such as SEM, TG, XRD, IR. On the basis of the characterization, the mechanism of the deactivation was proposed. The deactivation of USY can be attributed to the deposition of slowly diffusing organic by products inside USY framework.Hβ-1 zeolite prepared by calcining had better alkylation performance, but the olefin of C4 and C5 fractions were decreased more. The Hβzeolite was deactivated after three times reactions. It was the same as the USY zeolite on stability. The alkylation performance of MgY zeolite was investigated under different conditions. The results indicated that the catalytic performance was lower and it should be studied further to obtain the optimum preparation condition.