Recovery of triglycerides from used frying oil by extraction with liquid and supercritical ethane

The extraction of triglycerides from used frying oil with liquid and supercritical ethane has been studied in a semibatch system at different temperatures (25–80 °C) and pressures (150–250 kg/cm2). It has been found that isobaric decreases of temperature and isothermal increases of pressure lead to both increasing extraction yields and decreasing separation efficiencies. Lipid fractions recovered in the high density region had acceptable concentrations of polar compounds.Results with ethane have been compared to those reported for CO2 in earlier works. At similar reduced densities of the solvents, oil solubility in ethane was higher than in CO2, being the separation efficiency of polar fractions slightly better when using ethane.The extraction process was further analyzed in a packed countercurrent column. At optimum conditions (250 kg/cm2, 25 °C, and solvent-to-oil ratio 45 g:g) about 85% of the triglycerides were recovered, being 11.2% the polar content of the triglyceride fraction recovered.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights▶ Triglycerides separated from used frying oil by extraction with dense ethane. ▶ Optimum extraction conditions corresponded to the high density region. ▶ At such conditions, about 85% of triglycerides recovered and polar content reduced to one-third. ▶ Ethane was better than CO2 for the selective extraction of triglycerides from oil.