Selective Deoxygenation of Waste Cooking Oil to Diesel-Like Hydrocarbons Using Supported and Unsupported NiMoS 2 Catalysts.

This work aimed to study the deoxygenation of two different waste cooking oils (WCOs; palm oil and soybean oil) using alumina (γ-Al 2 O 3 )-supported and unsupported NiMoS 2 catalysts prepared by the hydrothermal method. The variables evaluated in this study were the reactant concentration, reaction time, and nickel (Ni)/[Ni + molybdenum (Mo)] atomic ratio (0.2 and 0.3) affecting the yield and selectivity of alkane products. The supported NiMo sulfide (NiMoS 2 )/γ-Al 2 O 3 catalyst prepared by impregnation had the drawback of a lack of layers and stacks, so combining the γ-Al 2 O 3 with unsupported NiMoS 2 catalysts using a hydrothermal method was evaluated. The main products obtained from the deoxygenation of the two WCOs were normal (n-)alkane compounds (C 15 , C 16 , C 17 , and C 18 ). The catalyst efficiency was ranked as 0.2-NiMoS 2 /γ-Al 2 O 3 ≈ 0.2-NiMoS 2 > 0.3-NiMoS 2 /γ-Al 2 O 3 ≈ 0.3-NiMoS 2 . The catalyst that gave the high n-C 15 -C 18 yield was 0.2-NiMoS 2 /γ-Al 2 O 3 under a reaction condition of 300 °C, 40 bar initial H 2 pressure, and oil concentration of 5 wt %. For the hydrodeoxygenation (HDO) of waste palm oil, the n-C 14 -C 18 yield was 56.4% (C 14 , C 15 , C 16 , C 17 , and C 18 at 1.3, 6.7, 14.5, 11.8, and 22.1%, respectively), while that for the waste soybean oil was 58% (C 14 , C 15 , C 16 , C 17 , and C 18 at 1.1, 3.8, 6.7, 17.2, and 29.2%, respectively). The n -C 18 /n-C 17 and n -C 16 /n-C 15 ratios were both greater than 1 for both types of WCO, revealing that the deoxygenation mainly proceeded via HDO rather than decarbonylation and decarboxylation. The 5-10% lower n -C 14 -C 18 yield from the waste oil compared with the fresh oil was acceptable, implying the effective oil treatment and some impurity removal.