Application of Response Surface Method for Optimization of Biodiesel Production Directly from Wet Microalgae Assisted by Radio Frequency Heating

The procedure for biodiesel production directly from wet microalgae ( Chlorella vulgaris ) assisted by radio frequency (RF) heating was optimized in this study using response surface methodology (RSM). A three-variable, five-level central composite design (CCD) was employed to evaluate the effects of three key parameters, i.e., HCl to MeOH ratio (v/v), MeOH volume and RF heating time. An optimized point was successfully found. The best predicted FAME yield of 93.1% was obtained at HCl to MeOH ratio of 4.27 (v/v), MeOH volume of 28.5 mL and RF heating time of 19.2 min. Experiments carried out at the optimized point resulted in 92.7 ± 0.1% yield, which validated the reliability of the prediction model. All processing steps, including cell destruction, esterification and transesterification, were carried out under temperatures below 100 °C and atmospheric pressure. Therefore, no pressure-proof nor high-temperature apparatus was required. The procedure shows great potential for industrial application because of its high FAME yield, simple operation, low chemical consumption and short processing time. The principles of the procedure can also be applied to other microalgae with high lipid contents