Cracking behavior of organic sulfur compounds under realistic FCC conditions in a microriser reactor Original Research Article

A laboratory-scale once-through microriser reactor was used in a qualitative study on the distribution of aromatic sulfur in the catalytic cracking products of an extra heavy gas oil (EHGO) under a broad range of conditions overlapping with realistic fluid catalytic cracking (FCC) conditions. Fifteen to twenty percent of the feed was uncrackable, corresponding to the amount of polycyclic aromatics in the feed. Gasoline was not overcracked to gas. The selectivity to gasoline was found to be independent of process parameters, in contrast to the selectivity to light cycle oil (LCO) and gas. Higher temperature and catalyst-to-oil (CTO) ratio led to an increased overall cracking rate. Initially, the amount of gasoline sulfur increased with residence time due to the formation of aliphatic sulfur compounds. Subsequently, these aliphatic species were cracked to hydrocarbons and H2S. The gasoline sulfur concentration decreased as function of conversion due to the dilution of sulfur compounds by the additional formed sulfur-free gasoline hydrocarbons. Stable LCO sulfur species were predominantly formed by dealkylation of alkylated benzothiophenes from the heavy cycle oil (HCO) fraction. The LCO sulfur concentration was found to be temperature dependent. Aromatics without side chains, such as thiophene, benzothiophene and dibenzothiophene, were found to be uncrackable under the applied conditions. It is discussed if optimization of the conditions can contribute to significant lower sulfur levels in gasoline.