Kinetics and Selectivity in Thermal Hydrocracking and Catalytic Hydrocracking of Asphaltenes

A pentane-insoluble mixture of asphaltenes was processed by thermal hydrocracking and catalytic hydrocracking over Ni-Mo/gamma-Al2O3 catalyst in a microbatch reactor at 430 degrees C. The experimental data of asphaltene conversion adequately fit second-order kinetics to give the apparent rate constants of 2.435x10(-2) and 9.360x10(-2) (wt frac)(-1) min(-1) for the two processes, respectively. A three-lump kinetic model is proposed to evaluate the rate constants for parallel reactions of asphaltenes producing liquid oil (k(1)) and gas+coke (k(3)), and consecutive reaction producing gas+coke (k(2)) from this liquid oil. The evaluated constants for asphaltenes hydrocracking, in the presence and absence of the catalyst, respectively, show that k(1) is 2.430x10(-2) and 9.355x10(-2) (wt frac)(-1) min(-1), k(2) is 2.426x10(-2) and 6.347x10(-3) min(-1), and k(3) is 5.416x10(-5) and 4.803x10(-5) (wt frac)(-1) min(-1). As compared with the thermal hydrocracking of asphaltenes, the catalytic hydrocracking of asphaltenes promotes liquid production and inhibits coke formation effectively.