Hydrothermal hydrodenitrogenation and hydrodesulfurization over nickel-based catalysts in sub/supercritical water

Abstract

As an inherent by-product of the petroleum industry, oily sludge has substantial potential as energy resource due to its high oil content and calorific value. The hydrodenitrogenation/hydrodesulfurization of nitrogen/sulfur compounds quinoline and thiophene in oily sludge at sub/supercritical hydrothermal conditions was studied, along with its catalytic properties and reaction mechanism. The effects of nickel-based catalysts, hydrogen sources, and reaction conditions on hydrodenitrogenation (HDN) of quinoline were examined. A reaction kinetic model for quinoline in supercritical water was developed. An experimental investigation on hydrodesulfurization (HDS) of sulfur-containing thiophene was conducted, and the catalytic properties of nickel-based catalysts for simultaneous HDN and HDS of quinoline and thiophene were evaluated. Within 400–440 °C, ethanol was superior to formic acid as hydrogen source. Ni-Co/γ-Al₂O₃ had the most effective catalytic impact on denitrogenation of quinoline. The conversion efficiency of 5 wt% quinoline reached 94.67 %, while denitrogenation efficiency was 57.08 % at 24 MPa, 440 °C, and 60 min. The hydrogenation and ring-opening steps had significant effects on the overall denitrogenation process. The hydrodesulfurization catalysis from Ni-Mo/γ-Al₂O₃ was the most prominent for thiophene. At 24 MPa, 440 °C, and 60 min, the desulfurization efficiency of thiophene reached 57.34 %. Desulfurization of thiophene mainly followed the hydrogenation route, with thiophene rings being saturated before desulfurization occurred.