Hydrotreating of light cycle oil over NiMo and CoMo catalysts with different supports

Abstract

To overcome the inhibition of aromatic compounds in low nitrogen light cycle oil (LCO) on its deep hydrodesulfurization (HDS), CoMo and NiMo sulfide catalysts supported on γ-alumina, alumina coated zeolite (ACZ) and TiO2 were investigated with the objective of achieving ultra-low sulfur through direct desulfurization route at relatively high temperature of 360°C. Higher temperature certainly accelerated the HDS probably through direct desulfurization route over all the catalysts studied. It also resulted in reduction of total aromatics by about 50% leading to a significant cetane number improvement. Conventional Al2O3-supported CoMo and NiMo catalysts were quite active for HDS, hydrogenation and hydrogenolysis, but they could not meet the demand of deep HDS to achieve 10–15ppm sulfur in hydrotreated products, even at higher reaction temperatures of 340–360°C. Higher acidity alumina coated zeolite (ACZ)-supported catalysts exhibited higher HDS activity compared to Al2O3-supported catalysts. However, they also exhibited highest cracking activity and coke formation, which make them unsuitable for deep HDS at high temperatures. Low-acidic, non-polar (TiO2 and powdered activated carbon (PAC)) supported catalysts could achieve the deep HDS of LCO at 350–360°C. The HDS activity of TiO2-based catalysts was better than Al2O3-supported catalysts and their cracking activity was significantly lower than Al2O3- and ACZ-supported catalysts. When the LCO was hydrotreated over CoMo/PAC at 350°C, the product contains only 12ppm sulfur. Hence, it is concluded that low-acidic, non-polar supports (such as TiO2 and PAC) are more suitable for CoMo and NiMo catalysts to achieve deep HDS of aromatic-rich feedstock such as LCO.