*Article* **Microwave-Assisted Noncatalytic Esterification of Fatty Acid for Biodiesel Production: A Kinetic Study**

**Hoang Chinh Nguyen 1, Fu-Ming Wang 2, Kim Khue Dinh 1, Thanh Truc Pham 3, Horng-Yi Juan 3, Nguyen Phuong Nguyen 1, Hwai Chyuan Ong 4,\* and Chia-Hung Su 3,\***


Received: 22 March 2020; Accepted: 26 April 2020; Published: 1 May 2020

**Abstract:** This study developed a microwave-mediated noncatalytic esterification of oleic acid for producing ethyl biodiesel. The microwave irradiation process outperformed conventional heating methods for the reaction. A highest reaction conversion, 97.62%, was achieved by performing esterification with microwave irradiation at a microwave power of 150 W, 2:1 ethanol:oleic acid molar ratio, reaction time of 6 h, and temperature of 473 K. A second-order reaction model (R<sup>2</sup> of up to 0.997) was established to describe esterification. The reaction rate constants were promoted with increasing microwave power and temperature. A strong linear relation of microwave power to pre-exponential factors was also established, and microwave power greatly influenced the reaction due to nonthermal effects. This study suggested that microwave-assisted noncatalytic esterification is an efficient approach for biodiesel synthesis.

**Keywords:** esterification; biodiesel; noncatalytic reaction; kinetic; microwave irradiation; bioenergy
