Solubility of high-value compounds in environmentally friendly solvents–liquid poly(ethylene glycol) and ionic liquids: Experimental study and thermodynamic analysis

• Liquid poly(ethylene glycol) (PEG) and ionic liquids were tested as solvents for five high-value compounds.
• Solubility of thymol, ferulic acid, vanillic acid, caffeic acid and caffeine, in liquid PEG and ionic liquids is studied.
• Liquid PEG200 and PEG400 and ionic liquid [C4mim][OTf] showed as good solvents for the high value compounds.

In this work the (solid + liquid) equilibria (SLE) of the solution of sustainable solvents with five high-value compounds, thymol, ferulic acid, vanillic acid, caffeic acid and caffeine, was investigated. The sustainable solvents studied were liquid poly(ethylene glycol) of average molecular mass 200 and 400 – (PEG200 and PEG400), respectively as well as imidazolium ionic liquids with bistriflamide and triflate anions ([C4mim][NTf2] and [C4mim][OTf]). The obtained SLE data were correlated using the semi-empirical equation proposed by Grant. The activity coefficients of the studied solutes were calculated. Based on these correlations and calculations as well as on the thermo-physical properties of the pure constituents, the SLE behavior of the studied solutions was analyzed and discussed.