6.5.Є.2 Supercritical Extraction

In addition to water, carbon dioxide and alcohols have been used for super­critical extraction. The use of supercritical carbon dioxide to extract oil from coal, tar, and various crops or crop waste has been extensively studied [101­105]. These studies have shown that supercritical carbon dioxide can be very effective in extracting certain types of chemicals from various carbohydrates, lignin, and organic materials. More work is, however, needed.

Xiu et al [106] reported an interesting study of supercritical extraction of swine manure by ethanol in the temperature range of 240°C to 360°C and at a pressure of 6.37 MPa under noncatalytic conditions. The maximum yield of oil at 26.7% was obtained at 340°C. At the same temperature, the highest lique­faction yield of 62.77% was obtained. The study concluded that the supercriti­cal ethanol liquefaction was an effective way to remove oxygen and utilize carbon and hydrogen in swine manure to produce energy-condensed biofuel.