Continuous extraction of glycerol acetates from their mixture using supercritical carbon dioxide

Supercritical carbon dioxide was used for partially selective extraction of triacetin from a mixture of triacetin, diacetin, and monoacetin with a molar ratio of 1:2:1. The extraction was carried out in two stages. In the first stage, a central composite design was used to optimize the four variables of pressure, temperature, liquid CO2 flow rate, and extraction time at three levels using a semi-continuous, supercritical carbon dioxide extraction setup. The composition of the extract under the predicted optimum conditions (i.e., 109 bar, 56 °C, 0.86 mL min−1, and 61 min) was about 69% triacetin accompanied by only 30% diacetin and no detectable monoacetin. In the second stage, the effect of the two factors, pressure (100, 109, and 140 bar) and liquid CO2 flow rates of 0.86 and 1.5 mL min−1 measured at average laboratory temperature (27 °C) and pressure (0.89 bar), were studied using a continuous, supercritical carbon dioxide fractionation setup equipped with a glass-bead packed column kept under a thermal gradient of 56–70 °C. The experimental design was organized as a 3 × 2 general factorial design. Under the best conditions (i.e., 140 bar and 1.5 mL min−1), the extraction yield of triacetin and diacetin were 41.8 and 3.0%, respectively, without any detectable monoacetin as verified by GC-FID.