Improved ethanol–water separation using fatty acids

As a means to reduce the processing costs for separating ethanol from fermentation broth, several fatty acids have been tested as liquid solvents for extracting ethanol from water. Valeric acid, the lowest molecular weight fatty acid used in this study, extracted the most ethanol but was not an ideal solvent since it also extracted water and was quite soluble in water. Oleic acid, the highest molecular weight fatty acid used in this study, was not soluble in water but was not a good solvent because it extracted low amounts of ethanol. Nonanoic acid was found to be the best extracting solvent, providing a reasonable ethanol distribution coefficient (0.354) and a 69.5% vapour rich ethanol stream using flash separation. Nonanoic acid extraction combined with the flash process is shown to require 38% less thermal energy to separate an equivalent amount of ethanol from fermentation broth compared to the traditional distillation process.