COMPARISON BETWEEN THE PERFORMANCE OF CONVENTIONAL AND HIGH-METAL CO-MO AND NI-MO CATALYSTS IN DEEP DESULFURIZATION OF KUWAIT ATMOSPHERIC GAS OIL

Due to environmental constraints, sulfur content of diesel fuel has been restricted to very low levels (500 ppm maximum) in many countries. As a result, a greater emphasis has been placed in recent years on the development of catalysts and processes for deep desulfurization of diesel blending streams to produce low sulfur diesel fuel. In the present work we have compared the performance of a conventional Go-Mo catalyst with that of high metal loading Go-Mo and Ni-Mo catalysts in deep desulfurization of Kuwait atmospheric gas oil. The tests were carried out in a fixed bed reactor unit using 75 mi of catalyst under the conditions: P=32 bar; LHSV = 4h(-1); H-2/oil ratio = 100 ml/ml; temperature range = 330 - 390 degrees C. HDS activity of the high molybdenum Go-Mo catalyst was superior to that of the conventional Go-Mo hydrotreating catalyst. High metal loading Co-Mo/Al2O3 catalyst also showed a substantially higher HDS activity than the Ni-Mo/Al2O3 catalyst containing a similar high metal loading. The unreacted sulfur compounds remaining in the product after high severity hydrotreating were identified as dibenzothiophenes with alkyl substituents next to the sulfur atom. The desulfurization of such low reactive alkyl dibenzothiophenes was found to occur at a substantially lower temperature over the high metal loading Go-Mo catalyst compared with the conventional Go-Mo catalyst. The results have been explained on the basis of the slacking and dispersion of MoS2 slabs as well as in terms of the nature of the sulfur vacancies in the MoS2 layers in these catalyst systems.