AM-92-15 Catalytic Effects on the Sulfur Distribution in FCC Fuels

Description:

This article examines the effect of catalyst properties on the sulfur distribution in FCC-derived gasolines. Experiments were carried out using both the Davison Circulating Riser (DCR) pilot unit and pure compound small fixed bed. The ,range of catalysts examined in this study include a gasoline yield catalyst, an octane catalyst, an octane-barrel catalyst, and a maximum bottoms cracking catalyst, which also span the range of typical equilibrium unit cell sizes. The gasoline samples were analyzed using gas chromatography equipped with an atomic emission detector selective to only those compounds in the gasoline which contain sulfur. The results show that the sulfur compounds found in FCC gasoline include CI - C4 mercaptans, thiophene, methylthiophenes, tetrahydrothiophene, ethylthiophenes, propylthiophenes, butylthiophenes, and benzothiophene. For full range gasolines, small differences are observed between catalysts which exhibit high hydrogen transfer activity and those with low hydrogen transfer activity, with the latter producing higher levels of high boiling alkylthiophenes. When the gasoline is undercut to a T90 = 300°F, the catalyst differences disappear. These results are also supported by pure compound studies of thiophene cracking. This study shows that the cracking chemistry of sulfur-containing species is very different from that of typical hydrocarbons.