Solvent Screening for Separation of Lignin-Derived Molecules Using the NIST-UNIFAC Model

Separationand purification technologies as one of the 12principles of green chemistry are discussed. Liquid-liquid phase equilibria were calculatedto investigatethe potential separations of value-added components from productsobtained by lignin depolymerization. In this study, the ability ofthe group-contribution model was evaluated in the prediction of mutualsolubility and liquid-liquid phase equilibria of phenolic compounds.The phase equilibria behaviors of quaternary systems were evaluatedby the NIST-UNIFAC model so that the predicted results were in goodagreement with the available experimental data. In sequence, the partitioncoefficients of 29 lignin-derived molecules with complex and polarfunctional groups were predicted by the model with good accuracy (RMSE= 0.7424). The abilities of binary, ternary, and quaternary solventsystems were evaluated in the counter-current chromatography (CCC)separations of the products reported in the literature that are obtainedthrough lignin depolymerization processes. Based on the empiricalsolvent selection criteria for CCC measurements, promising solventsystems were found for some of the lignin products. The difficultseparations of some products in other cases can be attributed to thevery similar chemical structures of the monomers. Finally, it wasfound that the NIST-UNIFAC model could qualitatively predict the solventsystems from the Arizona series, suitable for the separation of 4-hydroxybenzoicacid, vanillin, acetovanillone, syringaldehyde, acetosyringone, vanillicacid, and syringic acid.