Study On The Thiols Structure And Composition And Sweetening In Hydrorefining Gasoline

Application of FCC gasoline selective hydrodesulfurization process became more and more widely. One of the problems for gasoline hydrotreating was that the content of the higher molecular weight mercaptan (more than C6) increased after hydrodesulfurization, and few researches for structure of thiols in hydrorefining gasoline were did at home and abroad. So the higher molecular weight mercaptan couldn't be removed effectively by existing sweetening process. In this work, structure and composition of thoils in hydrorefining gasoline were analyzed, and sweetening catalysts for higher molecular weight mercaptan were explored to improve solubility, instability and activity of catalyst, which has important thearitical and practical meaning for industry.Chemical extraction combined with GC/DFPD technology was applied to structure composition and content analysis of thiols in the heavy fraction of hydrorefining gasoline. It was found that thiols in the heavy fraction of gasoline before hydrogenation were mainly C6 mercaptan and more isomeric thiols, which almost account for 60% of the total mercaptan sulfur, while that in the heavy fraction of hydrorefining gasoline accounted for over 88% of the total mercaptan sulfur. Relative content of higher molecular weight mercaptans in the heavy fraction of hydrorefining gasoline increased significantly than that in gasoline before hydrogenation. Effects of caustic wash, different sweetening process and sweetening degree on structure composition of thiols in the heavy fraction of hydrorefining gasoline were investigated. The results showed that types of thiols in gasoline before and afte caustic wash were almost similar, but the relative content of each thiol had changed. Relative content of the higher molecular weight mercaptan decreased after caustic wash, while the content of C6SH and mercaptans with higher molecular than C6 increased. Mercaptans in gasoline treated by different sweetening processes and depth were mainly C7 mercaptan and more isomeric thiols, and the amount was 60%~85%.To improve dispersion of catalyst in the alkali solution and select activator with good performance, then highly dispersed catalyst system was obtained. Influence factors on sweetening activity of catalyst system for weight mercaptans in simulated gasoline and hydrogasoline were investigated. Under similar conditions, highly dispersed catalyst was more active than conventional catalyst; When the alkali concentration was 10wt%, conversion of mercaptans increased with reaction temperature. The catalytic activity can be increased by rising the concentration of catalyst. The higher molecular weight mercaptans and i-thiols couldn't be easily oxidated. Stability of catalyst was characterized by UV-Vis and DLS, and found that compared with catalyst without activator, highly dispersed catalyst had good stability and high activity in a period of time.Cobalt phthalocyanine multisulphonamide catalyst was synthesized by reacting cobalt phthalocynine with chlorosulphonic acid, and the optimum reaction conditions were explored, then highly soluble liquid catalyst with 23.8% active component was obtained. Structure of Cobalt phthalocyanine multisulphonamide was characterized by UV-Vis, IR, and sulfur content analysis, and found that the sulphonic group number of CoSPc is 3.4. The size distribution and stability of catalyst were investigated by DLS. The results showed that highly soluble liquid catalyst had better dispersity and solubility in alkali solution, and particle size changed smaller with the extension of placement time, so catalyst had weaker aggregation degree and high stability. Liquid catalyst we prepared and catalyst from MERICHEM Co. had equivalent catalytic activity. When the volume ratio of catalyst to oil was 1:5 and the reaction time was 15min, conversion of mercaptans in gasoline could be up to 100%.