Sub/supercritical carbon dioxide induced phase switching for the reaction and separation in ILs/methanol

Separation of products from ionic liquid (IL) solvents is one of the main challenges that hinder their utilizations. In this study, the production of γ-valerolactone (GVL) by selective hydrogenation of α-angelica lactone (AL) and separation of the products from the IL solvent were carried out by using subcritical CO2 as a “switch” at room temperature. After the mixture was separated into two phases by subcritical CO2, AL and nano Pd/C catalyst were only found in the lower IL-rich phase, GVL was produced with quantitative yield and enriched in the upper methanol-rich phase. Pure GVL can be obtained by depressurizing to release CO2 and evaporation to remove methanol of the upper phase, the lower phase containing IL, catalyst and methanol can be recycled for the next reaction. The strategy may provide a new approach to produce and separate products from IL solvents at mild conditions.