Biodiesel is a green diesel fuel that is synthesized via the transesterification reaction of plant oils or animal fats with light alcohols, mainly methanol, in the presence of commonly homogeneous alkaline catalysts. One way to make the biodiesel synthesis process more eco-friendly is the use of heterogeneous catalysts as they are reusable. But with these catalysts, the transesterification reaction mixture will be a three-phase mixture containing methanol, oil and catalyst that leads to long reaction times and high process costs. In this study, the ultrasound waves were used to synthesis of the biodiesel from the Jatropha oil in the presence of CaO as a heterogeneous catalyst. The effect of two different co-solvents (acetone & hexane) on improving the homogeneity of the reaction mixture and therefore to enhance the conversion yield of the oil to biodiesel was considered. Experiments were carried out by a probe type ultrasonic instrument at an output power of 200 W and frequency of 20 kHz. The results showed that both of the considered co-solvents had positive effect on developing the conversion yield and the acetone was the more efficient one due to its moderate polarity, which could improve the miscibility of the oil with the methanol. A biodiesel sample with a conversion yield of 90.33% was synthesized under optimal operating conditions including 25% v/v acetone to methanol, 12:1 methanol to oil molar ratio, 4% w/w catalyst to oil, 55°C reaction temperature and 60 min reaction time. Hnmr and densitometry were used to determine the percentage of the synthesized biodiesel samples. Also, some of the physicochemical properties of the synthesized biodiesel were analyzed, which were in accordance with the ASTM and EN standards.
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