Synthesis of bimetallic catalysts supported silane-sba-15 for green diesel production

Abstract

Green diesel as the renewable energy fuel substitution shows a promising and potentially contributing to the development of green and sustainable energy. Green diesel consisting of hydrocarbon (C12-C20) that is structurally similar to the fossil-based diesel fuel. Recent technology used in producing green diesel was by deoxygenation reaction, in which hydrocarbons are generated from the removal of oxygen in the triglycerides of oil. In deoxygenation reaction, the presence of catalyst is crucial to ensure a more efficient reaction to produce green diesel. Due to its 2D hexagonal structure, large surface area and pore volume, highly ordered mesopore channel, and thick pore walls, SBA-15, offers good characteristics as a mesoporous silica support. Since SBA-15 contain low acidic strength and active sites, modifications such as surface functionalization and addition of metal promoters could be done to enhance the properties of SBA-15. Hence, the addition of metal promoters such as nickel (Ni) and cobalt (Co) in this study is to provide more catalytic active sites for deoxygenation reaction. Indeed, the use of bimetallic 5wt.% of Ni-Co catalyst supported with SBA-15 has increased the efficiency of deoxygenation reaction due to their excellent synergistic effect. The surface functionalization of SBA-15 was done by the addition of silane, 3-mercaptosilane (MPTMS) via co-condensation method with various concentrations of silane loading. The result revealed that the acidity of the synthesized catalyst was increasing due to the presence of sulfonic acid (from oxidation of MPTMS) and homogeneous distribution of Ni and Co were observed due to the interaction between the metal species and support. Our effort for the functionalization of silane-SBA-15 support was continued by introduced three types of functional group from mercaptosilane (-SH), aminosilane (-NH2) and phenylsilane (-Ph). It was revealed that each silane gave varies impact to the support and the synthesized bimetallic Ni-Co catalyst. Among the synthesized bimetallic catalyst, the NiCo/SBA-15-NH2 catalyst appeared as the most efficient catalyst, as it possessed highest acidity strength (5038.91 μmol/g) than the NiCo/SBA-15-SH (2019.08 μmol/g) and NiCo/SBA-15-Ph (2430.05 μmol/g). Indeed, the presence of amino group in NiCo/SBA-15-NH2 has increased the electrostatic attraction between the silane-SBA-15 support and metal species, resulting in the increased of the dispersion of the metal species. The performance of the synthesized catalysts: NiCo/SBA-15-SH, NiCo/SBA-15-NH2, and NiCo/SBA-15-Ph were evaluated in a deoxygenation reaction (350°C, 2 hours, 5 wt.% of catalyst loading) of waste cooking oil (WCO) to produce low-cost green diesel. The result revealed that the hydrocarbon yield produced for NiCo/SBA-15-NH2, NiCo/SBA-15-Ph, NiCo/SBA-15-SH was 86%, 83% and 77%, respectively. Additionally, the optimized condition for deoxygenation of WCO by NiCo/SBA-15-NH2 was at 300°C for 1.5hours of reaction. It was determined that the activation energy of NiCo/SBA-15-NH2 was 22.2 KJ/mol, which proved that low reaction temperature and time was needed to activate the reaction. The reusability of synthesized NiCo/SBA-15-NH2 catalyst was proven to be reused until 4th reaction cycle and the total production cost for green diesel was estimated. Lastly, the green diesel produced by NiCo/SBA-15-NH2 catalyst was used to prepare blended diesel fuel (G2.5 and G5), which shows the improvement of the kinematic viscosity, cetane number and pour point properties.