Study On The Reaction Of Olefin With Hydrogen Sulfide Over Gasoline Hydrofining Catalyst NiMoS/γ-Al₂O₃

One of the problems for gasoline hydrotreating in our country was appeared gradually, which was in the process of gasoline hydrofining, the content of weight mercaptans was increasing after hydrodesulfurization process, and the weight mercaptans were not removed effectively. Other weight sulfides were formed which accompanied with the formation of weight mercaptans. In the process of gasoline hydrotreating, recombination mercaptans and other sulfides(for example thioether) were formed by the reaction of H2S and olefin, H2S was produced by the sulfides hydrodesulfurization and olefin was mainly from the feedstock of gasoline. With more and more severe standard for the sulfur in gasoline, the formation of weight mercaptan and other sulfides will be a big obstacle for producing clean gasoline. In this work, basic research on the formation of weight mercaptans and other sulfides was conducted systemically, which has important theoretical and practical meaning.The reaction of 1-hexene and H2S was studied, which were included no catalyst without hydrogen,γ-Al₂O₃ as catalyst without hydrogen, NiMoS/γ-Al₂O₃ as catalyst without hydrogen and NiMoS/γ-Al₂O₃ catalyst with hydrogen. The formation laws under different reaction conditions were obtained, and the reaction mechanisms were obtained though the analysis of thermodynamic data and GS-MS analysis. When the reaction condition was no catalyst and without hydrogen, the reaction mechanism obey free radical reaction pathway, product was mainly included hexanethiol, dihexyl sulfide and dihexyl disulfide. Whenγ-Al₂O₃ as catalyst without hydrogen, the mechanism was carbonium ion mechanism, sulfide compounds in product were mainly hexanethiol and dihexyl sulfide. When the condition was NiMoS/γ-Al₂O₃ without hydrogen, the mechanism was also carbonium ion mechanism, hexanethiol and thiophene derivatives were major sulfide compounds in product. When NiMoS/γ-Al₂O₃ as catalyst with hydrogen, the mechanism was also carbonium ion mechanism, sulfide compounds in product were mainly hexanethiol and dihexyl sulfide.Effects of NiMoS/γ-Al₂O₃ modified by HF or H3PO4 on the reaction of 1-hexene and hydrogen sulfide were detected. With the concentration of acid in the dipping solvent increasing, the content of mercaptan and other sulfide compounds was increasing, which proved that the reaction mechanism of 1-hexene and hydrogen sulfide over NiMoS/γ-Al₂O₃ with hydrogen was obey carbonium ion reaction pathway.The reaction of cyclohexene, 1,3-dipentene, 1-octene with hydrogen sulfide over NiMoS/γ-Al₂O₃ under hydrogen were detected, through the thermodynamic data and sulfur compounds in product, the mechanisms of reaction of cyclohexene, 1,3-dipentene, 1-octene with hydrogen sulfide were proposed.Take thiophene and 1-hexene as model compounds, the formation law and mechanism for the reaction of 1-hexene and hydrogen sulfide was detected for the thiophene-olefin reaction system over NiMoS/γ-Al₂O₃ under hydrogen. In this process, hydrogen sulfide was produced in situ by thiophene hydrodesulfurization. This work was closed to industry practicality, provided evidence for the formation of weight mercaptan and other sulfides, provided evidence for the formation of weight mercaptan and other sulfides, provided theoretical advices for controlling the formation of weight mercaptans. From the GC-MS analysis, the sulfur compounds in product were mainly tetrahydrothiophene, 2-hexanethiol, 1-hexanethiol, alkylthiophene, alkyltetrahydrothiophene, dihexyl sulfide and bisulfide, through the analysis of product and thermodynamic data, the mechanism was obtained and which was also obey carbonium ion pathway.