Continuous production of biodiesel from microalgae by extraction coupling with transesterification under supercritical conditions

•Two kinds of microalgae Chrysophyta and Chlorella sp. were selected as feedstock.•A continuous process of transesterification coupling scCO2 extraction was conducted.•No catalyst loaded and residue after extraction can be reused for health products.

Raw material for biodiesel has been expanded from edible oil to non-edible oil. In this study, biodiesel continuous production for two kinds of microalgae Chrysophyta and Chlorella sp. was conducted. Coupling with the supercritical carbon dioxide extraction, the oil of microalgae was extracted firstly, and then sent to the downstream production of biodiesel. The residue after decompression can be reused as the material for pharmaceuticals and nutraceuticals. Results showed that the particle size of microalgae, temperature, pressure, molar ration of methanol to oil, flow of CO2 and n-hexane all have effects on the yield of biodiesel. With the optimal operation conditions: 40 mesh algae, extraction temperature 60 °C, flow of n-hexane 0.4 ml/min, reaction temperature: 340 °C, pressure: 18-20 MPa, CO2 flow of 0.5 L/min, molar ration of methanol to oil 84:1, a yield of 56.31% was obtained for Chrysophyta, and 63.78% for Chlorella sp. due to the higher lipid content.

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