Continuous production of fatty acid methyl esters from corn oil in a supercritical carbon dioxide bioreactor

Continuous production of fatty acid methyl esters (FAMEs) from corn oil was studied in a supercritical carbon dioxide (SC-CO2) bioreactor using immobilized lipase (Novozym 435) as catalyst. Response surface methodology (RSM) based on central composite rotatable design (CCRD) was employed to investigate and optimize the reaction conditions: pressure (11–35 MPa), temperature (35–63 °C), substrate mole ratio (methanol:corn oil 1–9) and CO2 flow rate (0.4–3.6 L/min, measured at ambient conditions). Increasing the substrate mole ratio increased the FAME content, whereas increasing pressure decreased the FAME content. Higher conversions were obtained at higher and lower temperatures and CO2 flow rates compared to moderate temperatures and CO2 flow rates. The optimal reaction conditions generated from the predictive model for the maximum FAME content were 19.4 MPa, 62.9 °C, 7.03 substrate mole ratio and 0.72 L/min CO2 flow rate. The optimum predicted FAME content was 98.9% compared to an actual value of 93.3 ± 1.1% (w/w). The SC-CO2 bioreactor packed with immobilized lipase shows great potential for biodiesel production.

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► Corn oil was successfully converted to fatty acid methyl esters in a SC-CO2 bioreactor.
► Response Surface Methodology (RSM) was adequate for optimizing reaction conditions.
► Low pressures and CO2 flow rates, and high substrate mole ratios and temperatures yielded higher conversions.
► Expanded reaction medium resulted in high yields due to good mass transfer.
► Compared to the conventional biodiesel process, this process is a green technology which eliminates use of organic solvents, chemical catalysts, and wastewater.