USE OF LIQUID CARBON DIOXIDE TO REMOVE HEXANE FROM SOYBEAN OIL

Authors: Eller, Fred; Taylor, Scott; CURREN, MEREDITH - CANADA

Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/25/2004
Publication Date: 10/1/2004
Citation: Eller, F.J., Taylor, S.L., Curren, M.S. 2004. Use of liquid carbon dioxide to remove hexane from soybean oil. Journal of the American Oil Chemists' Society. 81(10):989-992.

Interpretive Summary: Soybean oil is generally extracted from soybeans using the solvent hexane which is flammable, toxic and hazardous to the environment. To separate the hexane from the soybean oil, a great deal of energy as heat is required to distill the solvent. Researchers at the National Center for Agricultural Utilization Research, Peoria, Illinois, studied the use of liquid carbon dioxide as an alternative to current energy intensive methods employing heat to separate hexane from soybean oil. Passing liquid carbon dioxide at 25 C and 1350 psi through a mixture of hexane and soybean oil was found to be very effective at separating the hexane from the soybean oil. The amount of hexane remaining in the soybean oil depended on how much carbon dioxide was passed through the mixture, the more carbon dioxide, the less residual hexane. Liquid carbon dioxide decreased the concentration of hexane to less than 20 ppm, which is well below what current distillation methods achieve. Carbon dioxide is inexpensive, non-toxic, non-flammable, and the liquid carbon dioxide method to separate hexane from soybean oil/hexane mixtures is effective, environmentally-friendly and is less energy intensive than standard distillation methods.

Technical Abstract: The use of liquid carbon dioxide (L-CO2) was investigated as a means to remove the solvent hexane from the mixture of soybean oil (SBO) and hexane resulting from the hexane extraction of soybeans. Two concentrations of hexane in soybean oil were investigated, representing the concentration after the first stage stripper (i.e., 10% hexane) as well as 25% hexane. Using a fractionation tower, L-CO2 at 25oC and 1350 psi was passed through 50 mL of the hexane/SBO mixture at a rate of 3-4 L/min (expanded gas). Five different volumes of CO2 (i.e., 100, 200, 300, 500 and 1000 liters expanded gas) were tested to determine the amount of L-CO2 required to effectively remove the hexane from the mixture. After passing through the hexane/SBO mixture, the expanded CO2 was passed through a chilled collection vial to capture hexane as well as any SBO extracted with the hexane. The SBO was subsequently removed from the fractionation column and analyzed for residual hexane using ISO Method 9832:2002. There was no clear relationship between the amount of hexane collected and liters of CO2, however, there was significantly more hexane collected from the 25% sample than from the 10% sample. It is hypothesized that the collection efficiency for hexane was low. The amount of SBO extracted with the L-CO2 increased with liters of CO2 used and significantly more SBO was collected from the 25% sample. The hexane may be acting as a co-solvent to increase the solubility of the SBO in the L-CO2. Residual hexane decreased as the amount of L-CO2 used increased and the residual hexane was less than 20 ppm with 200 liters CO2. This research demonstrates the effectiveness of using L-CO2 to remove hexane from mixtures of hexane and SBO at both low pressures and temperatures thus saving energy costs.