Phase equilibria for separation of high boiling point organics from ionic liquids by supercritical CO2 or C3H8

Abstract

Application of room temperature ionic liquids (RTILs) as reaction media, catalysts and solvents, will encounter a problem of organics separation from RTILs systems. The utilization of supercritical fluids (SCFs) to separate high boiling point organics needs quantitative phase equibliria data and modeling. The phase equilibria and modeling for separating high boiling point organics from RTILs by supercritical (SC) CO 2 and C 3 H 8 have been studied thereof to take their advantage of low critical temperature. The long-term stability of 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF 6 ]) and 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([bmim][CF 3 SO 3 ]) has been observed in SC CO 2 and C 3 H 8 , which for [bmim][PF 6 ] is below 120 °C while [bmim][CF 3 SO 3 ] can stay stable at 120 °C over 72 h. The solubility of CO 2 and volume expansivity in [bmim][CF 3 SO 3 ] at 40, 50 and 60 °C and pressure of 1–20 MPa were measured, as well the solving behavior has been determined for C 3 H 8 –[bmim][CF 3 SO 3 ] system under conditions of 100, 110 and 120 °C, 1–9 MPa. C 3 H 8 give a much lower dissolving molarity in [bmim][CF 3 SO 3 ] than CO 2 under the same pressure and reduced temperature. The ternary phase equilibria of CO 2 –[bmim][CF 3 SO 3 ]–DBT, C 3 H 8 –[bmim][CF 3 SO 3 ]–DBT, CO 2 –[bmim][CF 3 SO 3 ]–naphthalene and C 3 H 8 –[bmim][CF 3 SO 3 ]–naphthalene are determined in a wide pressure and molality of solute in this ionic liquid (IL) at given temperature 323 and 393 K, respectively. Modified Chrastil's association model was extended to ternary system with the equation c A / m A = d k exp(( a / T ) + b ) giving a good correlation. The error between experimental data and the calculated concentration of solute in SCF phase for CO 2 –[bmim][CF 3 SO 3 ]–DBT, C 3 H 8 –[bmim][CF 3 SO 3 ]–DBT, CO 2 –[bmim][CF 3 SO 3 ]–naphthalene and C 3 H 8 –[bmim][CF 3 SO 3 ]–naphthalene are 5.0, 6.0, 7.9 and 9.4%, respectively. Extraction of naphthalene from [bmim][CF 3 SO 3 ] is calculated in continuous and batch processes. Batch SCF extraction may be applied to separate high boiling point organics from ILs. As long time and recycle solvent to feed ratio are necessary for using SC CO 2 , C 3 H 8 could be a good alternative since it shows nearly a magnitude higher solving power than SC CO 2 .