Mono- and Di-tert-butyl ethers of glycerol are potential oxygenate additives of diesel fuel. Their synthesis and the solubility measurement of the isomers in scCO 2 has been our main interest. Addition of these ethers to diesel fuel increases its quality and decreases the particulate matter emissions, carbon oxide, and carbonyl compounds in exhaust gases. Di tert–butyl ether of glycerol (DTBG) is usable as potential oxygenate additive to diesel fuel because it blends good enough with diesel fuel. Mono-tert-butyl ether of glycerol (MTBG) has a low solubility in diesel fuel and therefore the separation of MTBG from DTBG is important and useful. Using a continuous flow apparatus, ternary solubility of MTBG and DTBG in supercritical carbon dioxide (scCO 2 ) were measured at temperatures of 313.15, 333.15, and 348.15 K in the pressure range of (80-200) bar and the expanded gas flow rate of 180 ±10 mL.min -1 . At 333.15 and 348.15 K the ternary solubility increased with pressure up to 152 bar where it reaches a plateau. While, the ternary solubility of MTBG and DTBG in scCO 2 at 313.15 K increased with pressure almost linearly until 200 bar and no plateau is observed. The experimental data for ternary solubility of MTBG and DTBG were correlated by Bratle equation. At 348.15 K and pressure of 80 bar MTBG was found insoluble in scCO 2 . Moreover, the extraction selectivity of MTBG and DTBG of ? = (y m /y d ) = 2.43 at 348.15K and pressure of 200 bar. The flow rate of 0.3 mL.min -1 of liquid CO 2 was found as optimum flow rate for extraction of more than 93% MTBG and DTBG by scCO 2 . For extraction of DTBG, the % recovery of 38.04 and 61.85 was obtained at 2h and 4h extraction time, respectively, at pressure of 80 bar, temperature of 348.15 K and flow rate of 180 ± 10 mL.min -1 . After 2h of extraction time at pressure of 80 bar, temperature of 348.15 K, and flow rate of 180 ±10 mL.min -1 DTBG were obtained with 96% purity. By increasing the pressure up to 200 bar and after 1h of extraction time, MTBG were extracted with 93% purity. For extraction of MTBG, the % recovery of 28.9 and 41.75 were obtained at 1h and 3h after extraction at pressure of 200 bar and temperature of 348.15 K with flow rate of 180 ±10 mL.min -1 , respectively. Higher recovery of MTBG and DTBG was achieved using a counter current column with packing height of 50 cm. The highest recovery was reached at 348.15 K and 80 bar with flow rate of 0.3 mL.min -1 of liquid CO 2 and 0.1 mL.min -1 of sample with 88% and 95% for MTBG and DTBG at 5h of extraction time, respectively.
