Enhanced selective extraction of hexane from hexane/soybean oil mixture using binary gas mixtures of carbon dioxide

Carbon dioxide (CO2) can effectively separate hexane from a mixture of soybean oil (SBO) and hexane with a slight coextraction of SBO. Previous research demonstrated that CO2 entrained with helium significantly reduced SBO solubility in CO2. In this study, CO2 was mixed with three gases (He, N2, or Ar) (0.5-30 vol %) to decrease SBO solubility while attempting to maintain hexane solubility. The binary gas mixtures (at 25 degrees C and 9.31 MPa) were passed through a 25 wt % hexane/SBO mixture inside a 2.5 m fractionation column. Coextracted SBO was inversely proportional to binary gas concentration, whereas residual hexane in the raffinate was proportional to binary gas concentration. The 10% binary mixture of N2 or Ar was the best compromise to obtain both low residual hexane levels (i.e., 26 ppm) and low SBO coextraction (i.e., only 40 mg). This carry-over of SBO represents a 95% reduction in SBO carry-over compared to neat CO2.