Apparent Molar Properties and Viscosity Studies of Ternary Systems Composed of Model Lignin and Xylose in DBU Based Ionic Liquid–DMSO Solutions

Abstract

As the world aims for sustainable energy production, biomass dissolution and conversion to value-added products using ionic liquids (ILs), with or without cosolvents, are hot topics in the current scenario. This study focuses on the analysis of volumetric, acoustic, and viscosity properties of ternary systems comprising an IL, [DBU][OTf], an aprotic solvent, namely dimethyl sulfoxide (DMSO), and model biomolecules lignin or xylose in the temperature range of 293.15−333.15 K. Here we compare the properties of the model compounds lignin and xylose, a complex polymer responsible for the rigidity of the plants and the monomer unit of hemicellulose, respectively. Ternary systems of lignin or xylose (0.005, 0.010, 0.015, 0.020, 0.025, 0.030, and 0.035 m) were prepared using the binary solutions of IL in DMSO (0.1−0.4 m) which contributes to a sum of four ternary systems with lignin (I-D-L) and another four with xylose (I-D-X) as the solute. Apparent molar properties (V ϕ and K Sϕ ) were determined with density and speed of sound measurements, and the partial molar properties were evaluated with the help of the Redlich-Mayer equation. Solute−solute, solute−solvent, and solvent−solvent interactions were explained with the empirical parameters S V and S K obtained from the fitting equation. Dynamic and kinematic viscosities were also measured to understand the flow properties of the system. Intermolecular free length (L f ), relaxation time (τ), and acoustic impedance (Z) were also determined to elucidate the intermolecular interactions prevailing in these ternary systems. The experimental values of the dynamic viscosity were fitted well with the VTF model, and the Arrhenius plots were used for the calculation of the energy requirement (E η ) for the particles to move across each other in the ternary systems. This study enhances the ternary system database containing ionic liquids and biomolecules, benefiting biomass processing design, separation processes, and theoretical modeling of complex systems.