Continuous biocatalytic conversion of the oil of corn distiller's dried grains with solubles to fatty acid methyl esters in supercritical carbon dioxide

Abstract

A ‘green’ process based on supercritical fluid technology to extract and convert the oil of corn distiller's dried grains with solubles (DDGS) to fatty acid methyl esters (FAME) was developed. Supercritical carbon dioxide (SC-CO2)-extracted corn DDGS oil was converted into FAME in a continuous SC-CO2 bioreactor using immobilized lipase. The highest mass yield of 95.0% FAME was obtained at 19.4 MPa, 63 °C, at methanol mole fraction of 0.875 mol mol−1 of corn oil and methanol mixture. The CO2 flow rate at standard conditions of temperature and pressure (25 °C K, 101.3 kPa) was 720 cm3 min−1, with the substrate mixture flow of 27 mg min−1 at an enzyme loading of 2 g. The product with the highest FAME mass fraction contained 6.0% MAG, 0.61% DAG, 0.06% TAG and 0.01% glycerol. Performance of the bioreactor was also investigated over time. The FAME mass fraction of the product obtained over two days was 89.0%, whereas it decreased to 72.5%, 76.5% and 43.8% after 3, 4 and 5 days, respectively. FAME mass fraction of the product increased to 80.2% after treating the enzyme bed using pure SC-CO2 to remove residual components.