Equilibrium Behavior of Binary- and Ternary Systems of Supercritical Fluid/Organic/Ionic Liquid

摘要

The volume change of an ionic liquid and the phase separation behavior of room temperature ionic liquid (RTIL)/organic compound mixture in supercritical carbon dioxide were measured in a high pressure view cell. 1-Butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF{sub}6]) and 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF{sub}4]) were used as ionic liquid(IL). Methanol and dimethyl carbonate were selected as organic compounds of interest. For a fixed amount of [bmim][PF{sub}6] the lower critical endpoint (LCEP) pressure, where the liquid phase is split, decreased as increasing the amount of organic compound. The LCEP pressure became higher as the water content of ionic liquid was higher. However, for water contents above a certain value, no LCEP was formed. LCEP appeared 1.0 MPa higher for a mixture with [bmim][BF{sub}4] than with [bmim][PF{sub}6]. There was almost no difference in the K-point pressures for different types of ionic liquid and for different amounts of organic liquid. When the concentration of ionic liquid ([bmim][PF{sub}6]) (IL/(IL+MeOH)) in the initial liquid mixture was larger than 5.9 mol% at the LCEP of the mixture, the volume of L{sub}1 became larger than the volume of L{sub}2. When it was smaller, however, the volume became smaller, too. The volume change of ionic liquid in the presence of carbon dioxide decreased as increasing the temperature, while it increased as increasing the pressure. For temperatures between 313.15 to 343.15 K at 300 bar, the volume was about 123 ～ 125% of the original.