Catalytic removal of naphthenic acids over Co-Mo/γ-Al2O3 catalyst to reduce total acid number (TAN) of highly acidic crude oil

Abstract We demonstrated catalytic removal of naphthenic acids in highly acidic crude oil over catalyst prepared by impregnating CoO-MoO3 on mesoporous γ-Al2O3, and its sulfidate-form treated via post-synthetic sulfidation treatment to increase activity at lower temperature. We used almost real highly acidic crude prepared mixing heavy Castilla crude oil and naphthenic acids; total-acid-number (TAN) of this feedstock was 2.192 mgKOH/g. Our target TAN of product was 0.5 mgKOH/g (requirement of conventional refinery industry). For optimizing reaction conditions, temperature, hydrogen-pressure, hydrogen-to-oil (H2/oil) ratio and liquid-hourly-space-velocity (LHSV) of feed were screened. The oxide-form catalyst reduced TAN to lower than 0.5 mgKOH/g for 82 h, under optimized condition (T = 350 °C, PH2 = 0.5 MPa, H2/oil = 25 Nm3/m3, and LHSVfeed = 10 h-1). After sulfidation, this catalyst achieved target TAN at lower temperature (250℃) for 72 h (PH2 = 4.0 MPa, H2/oil = 50 Nm3/m3, and LHSVfeed = 3 h-1). Mechanism study shows that the removal of naphthenic acids occurred mainly through decarboxylation, decarbonylation and hydrodeoxygenation.