Solubility of monosaccharides in ionic liquids - Experimental data and modeling

Abstract

Biomass represents nowadays one of the more sustainable alternatives as a source of fuels and chemicals. The capability of ionic liquids to act as selective solvents and catalysts for biomass processing has already been proven. Thus they are a serious alternative to conventional solvents, provided that phase equilibria with biomass derived compounds is studied. To overcome the lack of experimental data on phase equilibria of biomass carbohydrates in ionic liquids, the solubilities of monosaccharides such as D-(+)-Glucose, D-(-)-Fructose, D-(+)-Xylose and D-(+)-Galactose in two ILs were measured in a temperature range from 288 K to 328 K. The ionic liquids selected for this work were the 1-etyhl-3-methylimidazolium ethylsulfate, [emim][EtSO4], and the Aliquat (R) 336. The experimental technique used a combination of an isothermal method to attain the solid-liquid equilibrium, and quantitative analysis by HPLC with refractive index detector. For the two ionic liquids, the ranking of solubility follows the series: D-(-)-Fructose > D-(+)-Xylose > D-(+)-Glucose > D-(+)-Galactose. The correlation of the solubility data was achieved through local composition thermodynamic models NRTL and UNIQUAC. For both models the average relative deviations are almost all below 4%, which is a satisfactory result. The apparent standard thermodynamic functions of dissolution were also determined from the experimental data using an approach based on a modified Van't Hoff equation. The results show good accuracy.