Optimization of Heterogeneous Transesterification of Non-Food Sources To Produce Biodiesel

Abstract The paper is focused on the optimization of reaction conditions to produce biodiesel by heterogeneous transesterification over Ni-Mg/Al mixed oxide. Preparation of biodiesel by the commonly used homogeneous transesterification produces a large amount of wastewater and other disadvantages like soap formation, difficult separation, polluted glycerin, and limitation of the catalyst used due to the content of free fatty acids. Heterogeneous transesterification offers easier separation and the possibility of reusing catalysts. As an oil source of vegetable oil, non-food plant Camelina sativa was used. Ni-Mg/Al mixed oxide was obtained from hydrotalcite, prepared by co-precipitation. The catalyst was characterized by different techniques to measure basicity, acidity, crystalline structure, and textural properties. The novelty lies in the complex optimization of reaction conditions (ratio of methanol to oil, amount of catalyst to oil, reaction temperature, reaction pressure, reaction time) to obtain a high content of FAME in biodiesel due to the European standard and in the introduction of two-step transesterification from an unconventional source. Transesterification was carried out in a batch reactor. Optimal reaction conditions to obtain the content of FAME in biodiesel higher than 96.4 wt% were the reaction temperature of 140 °C, for 7 h with a molar ratio of methanol to oil of 18/1, an amount of catalyst 3 wt%, and a pressure before reaction of 0.5 MPa(g) for one-step transesterification. For two-step transesterification, two reactions for 3 h at 140 °C, a molar ratio of 18/1, and 3 wt% of catalyst reached FAME content more than 97%. Graphical Abstract