A Novel Method for the Production of Biodiesel from the Whole Stillage-Extracted Corn Oil

The extraction of corn oil from whole stillage and condensed distillers' solubles (CDS) with hexane and its conversion to biodiesel were investigated. The analysis of the extracted oil showed 6-8 wt.% free fatty acid (FFA) in this oil. Acid, base, acid-base, and acid-base catalyzed transesterifications with intermediate neutralization with anion exchange resin were investigated. Experiments were performed with model corn oil substrates which contained 1.0-6.0 wt.% FFA. The effect of catalyst at 0.50-1.25 wt.% was studied at a 1:8 oil/methanol molar ratio. At 6.0 wt.% FFA concentration, the acid-catalyzed scheme was slow and resulted in less than 20% yield after 4 h, while the base-catalyzed was mostly consumed by the FFA and very little conversion was achieved. The acid-base catalyzed scheme succeeded in reducing the FFA content of the oil through the acid-catalyzed stage, and yields in excess of 85% were achieved after the second stage of the reaction with a base catalyst. However, formation of water and soap prevented the separation of product phases. An alternative acid-base catalyzed scheme was examined which made use of a strong anion exchange resin to neutralize the substrate after the initial acid-catalyzed stage. This scheme resulted in the effective removal of the acid catalyst as well as the residual FFA prior to the base-catalyzed stage. The subsequent base-catalyzed stage resulted in yields in excess of 98% for a 7.0 wt.% FFA corn oil and for the corn oil extracted from CDS.