Olefin Alkylation Of Thiophenic Sulfur Of Gasoline Over MCM-22Zeolite

An olefin alkylation thiophenic sulfur （OATS） process was investigated in a modelgasoline over modified MCM-22zeolite catalysts, owing to the more and more interesting tothe deep sulfur removal from gasoline.In model gasoline[thiophenic（4000ppm）∶xylene∶hexane∶methylcyclohexane=1∶3∶8∶313（v/v）], the HMCM-22zeolite possesses good thiophenes alkylation ability, wherethe alkylation reactivity of thiophenes is much higher than that of the xylene alkylation andhexane oligomerization. Reaction temperature benefits the xylene alkylation and hexeneoligomerization in contrast to the space velocity. In addition, coherent agent Al₂O₃onlyenhances the catalyst strength with a little affect on the thiophene conversion.The potassium modification notably decreases the strong acid sites of the HMCM-22,while less influences its weak acid sites. The strong acid sites of MCM-22zeolite benefit theOATS activity. With the K loading increasing, the OATS catalytic activity of thex%K/HMCM-22is obviously decreased in contrast to the stability. In addition, the MCM-22zeolite modified by the proper K exhibits maximum OATS selectivity.Alkali-treatment of MCM-22results in a preferential removal of silicon speciesaccompanying that of aluminum, besides the incensement of the external surface andmesopore volume. The alkali-treated MCM-22catalyst shows a higher stability in the OATSprocess than the none-treated sample. The improvement of the reaction stability is ascribed tothe increases of mesopore volume and acidity of HMCM-22, besides the decrease of cokedeposition velocity over the alkali-treated HMCM-22. This alkali-treatment method can leadto the increase of mesopore volume, modifying the pore channel block and enhancing thediffusion of reactants and products. The optimum MCM-22zeolite catalyst, prepared in0.1MNaOH solution,2h at temperature of70℃, shows good reaction stability. Under the reactionconditions of120℃,1.5MPa, WHSV1.0h^-1， the thiophene conversion, hexaneoligomerization and xylene conversion can reach>99%,<10%and <5%, respectively, duringthe160h time-on-stream.