Optimization of a novel liquid-phase plasma discharge process for continuous production of biodiesel

The conventional transesterification process employed in biodiesel production from vegetable oils is not only a time-consuming process but operated under raised temperatures. A novel liquid-phase plasma discharge process was developed and evaluated in this study. The process could continuously convert soybean oil to biodiesel under room temperature at a much faster rate than the conventional method. Two feeding flowrates (2.7 ml s⁻¹ and 4.1 ml s⁻¹) were used in the experiments. Methanol to oil molar ratio, R_momr, and NaOH to oil weight ratio, R_NaOWR, were each examined at five levels (3, 4, 5, 6, and 7 for R_momr, and 0.4, 0.6, 0.8, 1.0, and 1.2 wt% for R_NaOWR). Central Composite Design and Response Surface Methodology to optimize the conversion rate and applied voltage was conducted. At the flowrate of 2.7 ml s⁻¹, the optimal values of R_momr, R_NaOWR, conversion rate, and applied voltage were 5.08, 0.79 wt%, 97.2%, and 1.17 kV, respectively. While at 4.1 ml s⁻¹, these values became 5.18, 0.70 wt%, 99.74%, and 1.27 kV. All regression models generated by the Central Composite Design and Response Surface Methodology fitted the experimental data well. The biodiesel produced by the novel liquid-phase plasma discharge process met the industrial quality standards (ASTM Standards).