Continuous synthesis of d,l-α-tocopherol catalyzed by sulfonic acid-functionalized ionic liquid in supercritical carbon dioxide

Continuous synthesis of d,l-α-tocopherol catalyzed by a sulfonic acid-functionalized ionic liquid was conducted in supercritical carbon dioxide (SC-CO₂). The product was continuously separated from the reaction mixture by SC-CO₂ extraction during the course of reaction. Decompression of the supercritical fluid mixture downstream gave the product free of ionic liquid. The yield of d,l-α-tocopherol was improved with non-polar SC-CO₂ and polar propylene carbonate as solvents. The selectivity of d,l-α-tocopherol to trimethylhydroquinone (TMHQ) between CO₂-rich and ionic liquid-rich phase increased with the increase of pressure, and decreased with the increase of temperature at temperatures from 70 to 115 °C and pressures from 15 to 25 MPa. Effect of temperature, pressure and flow rate on the continuous synthesis of d,l-α-tocopherol was studied. The conversion of isophytol (IP) and the yield of d,l-α-tocopherol increased with decreasing pressure. The extraction rate of d,l-α-tocopherol increased with increasing pressure and decreased with increasing temperature. d,l-α-Tocopherol yield of 90.4% was obtained at 100 °C, 20 MPa and a CO₂ residence time of 12.6 min.