Phosphorus-free oil extraction from rice bran using CO2-expanded hexane

CO2-expanded hexane is used to extract phosphorus-free bio-oil from rice bran, which constitutes the main byproduct of the rice milling process, containing approximately 20-25 wt% oil. Optimal extraction conditions, namely 25 degrees C temperature, 5.1 MPa pressure, 0.87 CO(2 )mole fraction, and 0.2 mol CO2-expanded hexane per gram of rice bran, provide an approximate oil yield of 25%, with less than 5 ppm phosphorus. This yield exceeds the one obtained using hexane (20%), and the phosphorus concentration is 50 times lower compared to that present in the oil extracted using hexane. The extractant performances of CO2-expanded hexane with a CO2 mole fraction of 0.87 at 25 degrees C and 5.1 MPa, supercritical CO2 at 40 degrees C and 20 MPa, and liquid CO2 at 25 degrees C and 7 MPa were compared. The oil yield decreased in the order CO2-expanded hexane (24.6%) > supercritical CO2 (7.0%) > liquid CO2 (3.2%), at 0.2 mol of solvent per gram of rice bran. Furthermore, phosphorus concentrations in the extracted oil decreased in the order CO2-expanded hexane (3.4 ppm) > supercritical CO2 (almost zero) = liquid CO2 (almost zero). In summary, CO2-expanded hexane yields a well-balanced extractant that isolates high-yield oil with a low phosphorus concentration.