Solubility of glucose, xylose, fructose and galactose in ionic liquids: Experimental and theoretical studies using a continuum solvation model

A molecular screening of 64 ionic liquids (IL’s) for the solubility of monosaccharides such as d-(+)-Glucose, d-(+)-Xylose, d-(−)-Fructose and d-(+)-Galactose were performed by continuum solvation model (COSMO-RS) over the temperature range of 303.15–373.15 K. The IL data set consisted of 31 cations and 23 anions comprising of cations such as imidazolium, ammonium, pyridinium, pyrrolidinium, phosphonium, sulfonium and piperidinium. The imidazolium and ammonium based IL’s gave the highest solubility for cations possessing lesser number of carbon side chains. Based on the screening studies, the following two IL’s were chosen: 1-ethyl-3-methylimidazolium thiocyanate ([EMIM][SCN]) and Tris(2-hydroxyethyl)methyl ammonium methylsulfate [TMA][MeSO4] to experimentally study the solubility of monosaccharides in the two IL’s. The experimentally obtained solid–liquid equilibria (SLE) values were then compared with COSMO-RS predicted values. The root mean square error (RMSE) values of monosaccharides such as d-(+)-Glucose, d-(+)-Xylose, d-(−)-Fructose and d-(+)-Galactose in [EMIM][SCN] were 3.11%, 3.12%, 2.32% and 1.83% respectively while the corresponding figures in [TMA][MeSO4] is 1.47%, 1.20%, 2.94% and 0.70%. The overall solubility ranking in two IL’s was: d-(−)-Fructose > d-(+)-Xylose > d-(+)-Glucose > d-(+)-Galactose.