Production of biodiesel from microalgae oil (Chlorella protothecoides) by non-catalytic transesterification in supercritical methanol and ethanol: Process optimization

• Non-catalytic transesterification of microalgae oil was conducted with supercritical methanol and ethanol.
• Response surface methodology was used for the optimization study.
• Quadratic models were developed to predict the FAMEs and FAEEs yield.
• Optimal conditions were predicted and high experimental yields were achieved.

Production of biodiesel through non-catalytic transesterification of microalgae oil in supercritical methanol and ethanol was studied. The response surface methodology (RSM) combined with a five-parameter-five-level central composite design (CCD) was employed to optimize the (270–350 °C), pressure (80–200 bar), alcohol-to-oil molar ratio (10:1–42:1), residence time (10–50 min) and water content (0–10 wt%). Thirty-two experiments were designed and conducted for each alcohol species. Quadratic models were built based on the yields of fatty acid methyl esters (FAMEs) and fatty acid ethyl esters (FAEEs). Optimal conditions and yields for FAMEs and FAEEs were predicted with the models, and model predictions were verified by additional independent experiments conducted under predicted optimal conditions. Optimal biodiesel yields obtained in this work were 90.8% and 87.8% with methanol and ethanol, respectively. The significance of the parameters was evaluated by the analysis of variance (ANOVA). The effects of single parameters and the interacted parameters on the biodiesel yield were also discussed.

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