Effects of the operating variables on hydrotreating of heavy gas oil: Experimental, modeling, and kinetic studies

The effects of H2 purity, pressure, gas/oil ratio, temperature, and LHSV on hydrotreating activities were investigated in a micro-trickle bed reactor using a commercial NiMo/γ-Al2O3 catalyst. Heavy gas oil (HGO) from Athabasca bitumen was used as feed. Due to their significant effects on H2 partial pressure, H2 purity, pressure, and gas/oil ratio were chosen and used in a central composite design (CCD) method. Experimental conditions used were H2 purity, pressure, and gas/oil ratio were: 75–100 vol.% (with the rest methane), 7–11 MPa, and 400–1200 mL/mL, respectively. The effect of LHSV (0.65–2 h−1) and temperature (360–400 °C) were studied in a separate set of experiments. Vapor/liquid equilibrium (VLE) calculations were performed to determine the inlet and outlet H2 partial pressures. It was observed that the enhancing effects of H2 purity on hydrodenitrogenation (HDN) and hydrodearomatization (HDA) activities were greater than that of gas/oil ratio; however, it was comparable to pressure. Hydrodesulphurization (HDS) activity was not considerably affected by H2 purity, pressure, or gas/oil ratio. Increasing LHSV led to a decrease in HDS, HDN, and HDA activities while increasing temperature resulted in an increase in HDS and HDN; HDA had maximum activity at about 385 °C. Kinetic fitting of the data to a pseudo-first-order power law model suggested that conclusions on hydrotreating activities’ responses to a changing H2 pressure could be equally drawn from either inlet or outlet H2 partial pressure. However, from the catalyst deactivation standpoint, it is recommended that such conclusions are drawn from the outlet H2 partial pressure.