Synthesis of mesoporous calcium titanate catalyst for transesterification of used cooking oil

Abstract

Biodiesel is a promising alternative for conventional diesel fuel due to the unsustainable feature of the resources and unstable price of the fuels. However, the production cost is higher compared to the conventional ones and is significantly contributed from the feedstock. Realizing that a large portion of used cooking oil (UCO) is generated daily, this research aims to investigate and explore the production of biodiesel from UCO. In the production reaction process, undoubtedly, catalyst plays an important role. It has been shown that calcium oxide (CaO) is one of the best heterogeneous basic catalysts in transesterification reaction for biodiesel production. However, the catalyst has low surface area which restricts the active basic sites to disperse on the catalyst surface. Moreover, CaO catalyst faces leaching problem, poor stability and porosity which hinder its catalytic activity and reusability. Therefore, in this study, it is aimed to modify CaO supported titanium with a mesoporous structure by a sol-gel-hydrothermal method to overcome the limitations of CaO catalyst. The property of the mesoporous calcium titanate (MCT) catalyst was characterized via x-ray diffraction, x-ray photoelectron spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, nitrogen physisorption, Fourier transform infrared spectroscopy, Fourier transform Raman spectroscopy, thermal gravimetric analysis, hydrogen thermal programmed-reduction and carbon dioxide thermal programmed-desorption. The catalytic activity of the MCT catalyst towards biodiesel production from UCO was evaluated by varying the transesterification reaction parameters. From the catalytic activity results, the highest biodiesel yield of 80 % was achieved under reaction conditions of 3:1 of methanol to UCO molar ratio, 0.2 wt. % catalyst loading at 65 °C for 1 h. Reusability study suggested that this catalyst can be recycled for five successive times. The kinetic studies revealed that the reaction follows a pseudo first order model. The activation energy of the transesterification reaction of UCO over MCT catalyst obtained was 21.25 kJ mol-1 that indicates the rate of reaction was diffusion limited or mass transfer limited. Meanwhile the thermodynamic parameters show results of enthalpy<0, entropy<0 and Gibbs free energy>0. The tested fuel properties of the product were also in agreement with ASTM D6751 and EN 14214 standards. Additionally, it can be concluded that the synthesized MCT catalyst was found to achieve improvement in the catalyst characteristics as well as the catalytic activity compared to commercial CaO catalyst in transesterification reaction for biodiesel production from UCO.