Optimization of the Synthesis of Biodiesel via Ultrasound-Enhanced Base-Catalyzed Transesterification of Soybean Oil Using a Multifrequency Ultrasonic Reactor

Biodiesel has become one of the premier forms of alternative energy sources. However, its growth is hindered by the cost of production, which makes it uncompetitive compared to petrodiesel. Hence, research efforts are ongoing to reduce the cost of production of biodiesel using various emerging approaches. Ultrasound has been reported to aid biodiesel formation at relatively lower energy costs. However, not many reports are available that give in-depth analysis of the effects of ultrasound on biodiesel formation. This paper reports the result of a study to evaluate the effect of high-frequency ultrasound on the synthesis of biodiesel from soybean oil using methanol and potassium hydroxide as catalysts. The effects of various parameters, such as ultrasonic power, ultrasonic frequency, oil/methanol molar ratio, catalyst loading, and temperature, on biodiesel formation were studied to optimize the process. It is shown that high-frequency ultrasound can achieve >90% conversions within 30 min with relatively low-energy inputs. A specially designed multifrequency ultrasonic reactor, which has the potential to reduce the energy losses because of scattering, reflection, and absorption, was used for this study.