Intensified synthesis of biodiesel using low-cost feedstock and catalyst via conventional as well as ultrasonic irradiation based approach

In the present work, the synthesis of biodiesel has been investigated using low-cost feedstock and a catalyst using conventional and ultrasonic irradiation based approach. The novelty of the present work is used of calcium oxide (CaO) as a catalyst for the synthesis of biodiesel using frying oil as a feedstock via esterification followed by transesterification process. Reaction parameters such as concentration of catalyst, operating temperature, and a molar ratio of oil to methanol (MROM) have been optimized for esterification and transesterification. Reduced free fatty acid value (FFA) helps in the production of pure biodiesel of utmost quality through the transesterification reaction. Decreasing trends of FFA of oil with the increasing temperature, MROM, and catalyst concentration up to the optimized conditions has been obtained during esterification reaction. The maximum reduction in the FFA of oil up to 0.51 mg KOH/g of oil was obtained in 20 min only at an optimal temperature 55°C, MROM of 1:3 and 1 wt. % of H2SO4 during the esterification reaction. The energy required for the conventional based approach was found to be 37.3 kJ/mg. In case of transesterification reaction, it has been observed that the effect of MROM, catalyst concentration, and temperature on yield of biodiesel strongly affects the yield of biodiesel. Decreasing trends of biodiesel yield with increasing range of reaction parameters such as MROM and reaction temperature has been observed for conventional as well as the US irradiation based approach. Furthermore, with increasing heterogeneous CaO catalyst concentration from 0.1 to 0.2 wt. %, yield of biodiesel increases from 72.1 wt. % to 85.7 wt. % and 64.3 wt. % to 68.5 wt. % using a convention-based approach and US-based approach, respectively. The maximum yield of biodiesel as 85.7 wt.% (energy required was 1.8 × 10−4 g/J) was obtained using a conventional based approach and 68.57% (energy required 5.1 × 10−4 g/J) US irradiation based approach at an optimal MROM of 1:8, 0.2 wt. % of CaO and 55°C temperature. Hence, the present study clearly established that significant intensified synthesis of biodiesel can be obtained using optimum MROM, temperature and catalyst concentration via a conventional based approach than the US irradiation based approach.