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 ([C(4)mim][NTf2] and [C(4)mim][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. (C) 2013 Elsevier Ltd. All rights reserved.