Experimental and theoretical studies on thermodynamic properties of three ionic liquids based on dicyanamide anion (namely, 1-butyl-3-methylimidazolium dicyanamide, 1-butyl-1-methylpyrrolidinium dicyanamide, and 1-butyl-1-methylpiperidinium dicyanamide) and their binary mixtures with sugar alcohols (D-sorbitol and xylitol) were conducted in order to assess the applicability of the salts ionic liquids for dissolution of those biomass-related materials. Density and dynamic viscosity (at ambient pressure) of pure ionic liquids are reported in the temperature range from T = 293.15 to 363.15 K. Solid-liquid equilibrium phase diagrams in binary systems {sugar alcohol + ionic liquid} were measured with dynamic method up to the fusion temperature of sugar alcohol. The impact of the chemical structure of both the ionic liquid and sugar alcohol were established and discussed. For the very first time, the experimental solubility data were reproduced and analyzed in terms of equation of state rooted in statistical mechanics. For this purpose, perturbed-chain statistical associating fluid theory (PC-SAFT) was employed. In particular, new molecular schemes for the ionic liquids, D-sorbitol, and xylitol were proposed, and then the pure chemicals were parametrized by using available density and vapor pressure data. The model allowed accurate correlation of pure fluid properties for both ionic liquids and sugar alcohols, when the association term is taken into account. The results of solid-liquid equilibria modeling were also satisfactory. However, one or two adjustable binary corrections to the adopted combining rules were required to be adjusted in order to accurately capture the phase behavior. It was shown that a consistent thermodynamic description of extremely complex systems can be achieved by using relatively simple (but physically grounded) theoretical tools and molecular schemes.
Ionic liquids have been considered as "green" replacements for volatile organic compounds in modern and clean industrial processes since the beginning of the 1990s. It has been shown recently that when combined with renewable feedstocks derived from biomass (like carbohydrates) they form systems attractive for sustainable chemical engineering and technology. Promising features of such systems have induced research activity in various areas of pure and applied chemistry. In particular, new experimental data on different thermodynamic properties of biomaterials dissolved in ionic liquids are required. In this paper we present both experimental and theoretical thermodynamic studies of binary mixtures composed of sugars and two low-viscous ionic liquids based on 1-butyl-3-methylimidazolium cation and dicyanamide or trifluoroacetate anion. Solubility of D-(+)-glucose, D-(−)-fructose, and sucrose in the ionic liquids was determined as a function of temperature. The results indicate that both ionic liquids under consideration can be successfully applied as alternative solvents for sugars. Additionally, thermal characterization of pure sugars was performed with differential scanning calorimetry. The obtained solid−liquid equilibrium phase diagrams were analyzed in terms of perturbed-chain statistical associating fluid theory (PC-SAFT). It was shown that the PC-SAFT model is capable of representing phase behavior of the studied systems quantitatively.
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