Effect of Olefins on Formation of Sulfur Compounds in FCC Gasoline

The effect of olefins on formation of sulfur compounds in FCC gasoline was studied in a small-scale fixed fluidized bed (FFB) unit at temperatures ranging from 400℃ to 500℃, a weight hourly space velocity (WHSV) of 10 h-1, and a catalyst/oil ratio of 6. The results showed that C4-C6 olefins contained in the FCC gasoline could react with H2S to form predominantly thiophenes, alkyl-thiophenes as well as a fractional amount of thiols, while large molecular olefins such as heptene could react with hydrogen sulfide to form benzothiophenes. The amount of sulfur compounds formed at different tem-peratures over different catalysts were in proportion to the mass fractions of olefins in the feedstock,with the amount of sulfur compounds formed over REUSY catalyst exceeding those formed over the shape selective zeolite catalyst owing to the effect of catalyst performance and the impact of catalyst on the degree of olefin conversion. The amount of sulfur compounds generated and their increase reached a maximum at 450℃ and a minimum at 400℃ because of the influence of temperature on the thermody-namic and kinetic constants for formation of sulfur compound as well as on the olefin conversion degree.Based on the above-mentioned study, a reaction network and a model for prediction of sulfur com-pounds generated upon reaction of olefins in FCC gasoline with H2S were established.