Effect of operating conditions on HDS of CGO blended middle distillate

Abstract

Abstract The utilization of heavier stream of petroleum hydrocarbon such as coker gas oil (CGO) via diluting with straight run gas oil (SRGO) (blended feed: SRGO and CGO; 30/70) in order to enhance the middle distillate pool of fuel (heating oil, diesel fuel, jet fuel, and kerosene). Usually, CGO fraction has a propensity to retain refractory sulfur, nitrogen and aromatics compounds. The former two elements are mainly associated with the aromatic sulfur and nitrogen compounds (i.e., refractory). Hence, a systematic study was conducted with the variation of hydrotreating operating conditions to convert sulfur, nitrogen, and aromatic compounds. The performance was carried out in a fixed bed bench-scale reactor unit, using a commercial CoMo/Al2O3 (catalyst X) catalyst after sulfidation. The CGO has a significantly higher amount of nitrogen, aromatic, and refractory sulfur compounds than that of SRGO, which makes this blend more challenging. Hence, the operating conditions have been investigated to remove sulfur and nitrogen compounds and improve the cetane index during the hydroprocessing. The variation in operating conditions is to achieve 450 ppmS in the hydrotreated product using CGO and SRGO blend as a feedstock. The conversion of sulfur and nitrogen compounds indicated that hydrodesulfurization (HDS) is selectively higher than hydrodenitrogenation (HDN) where hydrogenation played a crucial role in their selectivities at high conversion. The hydrogenation function also relates to the cetane index that decreases with increasing aromatic content. The degree of inhibition (HDS and cetane index) depends on the feed composition (nitrogen and aromatics) that consumes a large amount of hydrogen. Conclusively, beyond 90% of HDS conversion, most of the sulfur compounds are refractory, which requires a stronger hydrogenation function to remove steric-hindrance from the refractory molecule.