Extraction of Vegetable Oils with Furfural

As discussed in chapter 14.1, furfural is an outstanding extractant for separating compounds with double bonds from compounds without double bonds, the reason being that the double bonds of furfural attract double bonds of other molecules, due to the fact that energy is liberated when a double bond system is enlarged. 

One such application of furfural is the extraction of vegetable oils such as soybean oil to get an extract rich in double bonds, and a raffinate depleted of double bonds. The extract rich in double bonds can be used as a drying oil for paints and varnishes, where the double bonds react with oxygen of the ambient air to form cross-linked polymers. On the other hand, the raffinate depleted of double bonds is a more desirable product for the food industry than the nonextracted soybean oil. Thus, two advantages are obtained in a single operation. 

The furfural input is very much greater than the oil input, a typical ratio being 6 parts of furfural for each part of feed oil. 

Contrary to customary extraction, in such a column the dispersed phase and the continuous phase change roles. In the upper portion, furfural droplets fall through a continuous oil phase, whereas in the lower portion oil droplets rise through a continuous furfural phase, with an interface between these two regions. 

The product of condenser 10, collected in decanter 14, forms two liquid phases, a heavy furfural phase and a light aqueous phase. The heavy furfural phase, consisting of approximately 92 % furfural and 8 % water, by weight, enters a dehydration column 15 energized by a steam coil in the bottom. The sump fraction, representing pure furfural freed of water, is withdrawn by pump 16 and fed into tank 7. The head fraction of column 15, having a composition close to the furfural/water azeotrope, joins the vapor stream of column 9 in condenser 10. 

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