Hydrocracking in the Deep-desulfurization of Heavy-oil

Abstract

In the deep-hydrodesulfurization of Khafji atomospheric residue over a cobalt-molybdenumalumina catalyst in the fixed-bed cocurrent up-flow reactor, hydrocracking of the residue occurring simultaneously with the desulfurization was studied under the following experimental conditions; total pressure: 50-200 kg/cm², temperature: 400-460°C, LHSV=1-6, and hydrogen-oil ratio: 500-3000.
The relation between hydrocracking and hydrodesulfurization, the reaction order of hydrocracking, its dependence upon the reaction pressure and temperature, and the hydrogen consumption in it are examined here.
The value indicating the extent of hydrocracking, such as the amount of produced gaseous C_1-4 saturated hydrocarbons, density and viscosity, fractional ratio of 300°C cut distillate and residue, and asphaltene content in the product oil, changed markedly near the point of desuclfurization of 85-90% except for the viscosity. This observation suggests that rapid hydrocraking reaction occurred in the region of desulfurization above 85-90%. The reaction order of hydrocracking appears to be the 2nd order in the region of comperatively low desulfurization, which agrees well with that of the hydrodesulfurization reaction reported in our previous paper. But, in the region of higher desulfurization, where the effect of desulfurization reaction on hydrocracking can be eliminated, the reaction order was found to be the 1 st which is considered to be proper as the reaction order of hydrocracking of the heavy oil. The reaction rate of hydrocracking appears to have a maximum value at the pressure around 150 kg/cm². It seems to be most probable that the hydrogen consumption have a linear corelation with the fractional ratio of hydrocracking as follows: z11-12=17 z+4.