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

•Biodiesel was prepared directly from soybean flakes using a coupling process.•Extraction and transesterification under supercritical conditions were combined.•Extraction was found to be the crucial step in the coupling process.•Mobile biodiesel processor could be easily moved and biodiesel would be produced locally.•Promising routes were proposed to improve the production efficiency and capacity.

A continuous process of supercritical extraction coupling with supercritical methanol transesterification was put forward to prepare biodiesel directly from full-fat soybean flakes. This method is meaningful to the industrialized production of biodiesel. It can lower the high cost of the refined vegetable oil as feedstock. Furthermore, it gives a possibility that a mobile biodiesel processor could be easily moved to various locations where raw materials are available and produce biodiesel in situ. The experimental results indicated that a residence time of more than 2.5 h was required to obtain a stable fatty acid methyl ester yield. The maximum biodiesel yield of 86% was obtained at 350 °C, 20 MPa and 3 h, with the molar ratio of methanol-to-oil of about 42:1. In addition, based on the investigation of the process optimization, oil extraction was found to be the crucial step for the coupling process and other promising routes were proposed to improve both the production efficiency and the capacity.

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