Selective Deoxygenation of Waste Cooking Oil to Diesel-Like Hydrocarbons Using Supported and Unsupported NiMoS2 Catalysts

Abstract

This work aimed to study the deoxygenation of two different waste cooking oils (WCOs; palm oil and soybean oil) using alumina (?-Al2O3)-supported and unsupported NiMoS2 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 (NiMoS2)/?-Al2O3 catalyst prepared by impregnation had the drawback of a lack of layers and stacks so combining the ?-Al2O3 with unsupported NiMoS2 catalysts using a hydrothermal method was evaluated. The main products obtained from the deoxygenation of the two WCOs were normal (n-)alkane compounds (C15 C16 C17 and C18). The catalyst efficiency was ranked as 0.2-NiMoS2/?-Al2O3 ? 0.2-NiMoS2 > 0.3-NiMoS2/?-Al2O3 ? 0.3-NiMoS2. The catalyst that gave the high n-C15-C18 yield was 0.2-NiMoS2/?-Al2O3 under a reaction condition of 300 ?C 40 bar initial H2 pressure and oil concentration of 5 wt %. For the hydrodeoxygenation (HDO) of waste palm oil the n-C14-C18 yield was 56.4% (C14 C15 C16 C17 and C18 at 1.3 6.7 14.5 11.8 and 22.1% respectively) while that for the waste soybean oil was 58% (C14 C15 C16 C17 and C18 at 1.1 3.8 6.7 17.2 and 29.2% respectively). The n-C18/n-C17 and n-C16/n-C15 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-C14-C18 yield from the waste oil compared with the fresh oil was acceptable implying the effective oil treatment and some impurity removal. ? 2023 The Authors. Published by American Chemical Society.