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

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 (Vϕ and KSϕ) 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 SV and SK obtained from the fitting equation. Dynamic and kinematic viscosities were also measured to understand the flow properties of the system. Intermolecular free length (Lf), 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 (Eη) 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

Thermophysical Properties and Carbon Dioxide Absorption Studies of Guanidinium-Based Carboxylate Ionic Liquids

In this work, five 1,1,3,3-tetramethylguanidine (TMG)-based ionic liquids (ILs) with [TMG] cations as well as monocarboxylic acid anions {[CH3-(CH2)n–COOH], where n = 2, 3, 4, 5, and 6} were synthesized and characterized by 1H NMR and 13C NMR. CO2 absorption capacity was studied for even number carboxylic acid anions [TMG]­[But], [TMG]­[Hex], and [TMG]­[Oct]. The maximum absorption capacity of CO2 was observed for [TMG]­[Oct], which clearly indicated that the increase in chain length increases the absorption capacity. The physicochemical properties such as density (ρ), speed of sound (u), viscosity (η) and refractive index (nD) were measured as a function of temperature over the range from 293.15 to 343.15 K at atmospheric pressure (0.1 MPa). The experimental density values were fitted with a second-order polynomial equation and correlated with the expected density proposed by the Gardas–Coutinho model. The thermodynamic properties, such as thermal expansion coefficient (α), isentropic compressibility (βs), and free length theory (Lf) were calculated. The strength of ionic interaction between the ions was estimated by calculating lattice potential energy (UPOT) and standard entropy (S°) from experimental data. The experimental viscosity values were fitted by applying the Vogel–Fulcher–Tammann equation and correlated with an Arrhenius-type equation. Thermal decomposition temperatures (Td) were investigated using TG analysis. The intermolecular interactions of the ILs have been analyzed with the experimental refractive index data at various temperatures, and the effects of carboxylate anion chain length and temperature on physicochemical properties were also investigated

Structural Arrangements of Guanidinium-Based Dicarboxylic Acid Ionic Liquids and Insights into Carbon Dioxide Uptake through Structural Voids

Crystallization of ionic liquids (ILs) is essential for determining the crystal structure and molecular interactions between cations and anions; however, studies on crystallization of viscous ILs are scarce. This study investigates the network formation and intermolecular interactions present in the ILs to understand and enhance their CO2 absorption capability. In this context, five 1,1,3,3-tetramethylguanidine [TMG]-based ILs, with odd and even anionic dicarboxylic acids such as, succinate [Suc], glutarate [Glu], adipate [Adp], pimelate [Pim], and suberate [Sub], were synthesized. The in-situ cryo-crystallization technique was used to determine the structure of two viscous ILs, [TMG]­[Glu] and [TMG]­[Pim], at low temperatures (173 K). The dominance of intermolecular atomic contacts in studied ILs was visualized by performing a Hirshfeld surface analysis. The CIF obtained from the crystal data was used to optimize the ILs, and the highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) energies were calculated using the DFT at the B3LYP/6-311G++ (d, p) level. Among the several interesting properties of [TMG]-based ILs, the CO2 absorption capacity of [TMG]­[Glu] and [TMG]­[Pim] has been investigated through structural voids to establish the increase in CO2 absorption with the addition of −CH2 group on the anion

Influence of Cation Size on the Ionicity, Fluidity, and Physiochemical Properties of 1,2,4-Triazolium Based Ionic Liquids

Interpreting the physiochemical properties and structure–property correlations of ionic liquids (ILs) is a key to the enlargement of their optimized structures for specific applications. In this work, a series of ILs based on 1-alkyl-1,2,4-triazolium cation with trifluoromethanesulfonate anion were synthesized and the effect of cation and temperature on physiochemical properties such as density, viscosity, speed of sound, conductivity, and rheology was studied. Temperature dependence densities were correlated with the densities estimated by the Gardas and Coutinho model, whereas viscosity and molar conductivity have been found to satisfy the Vogel–Tammann–Fulcher (VTF) equation over the studied temperature range 293.15–343.15 K. Further, to explore the wide range of applications, ionicity has been tested by correlating the fluidity with molar conductivity and it was found that synthesized ILs can be referred to as “good ILs”. Furthermore, the fluidity behavior describing the interactions between the cation and anion of ILs was investigated through their rheological properties, and the Newtonian behavior of ILs has been examined by varying the effect of shear rate on viscosity. Finally, the impact of structure variants in terms of the N-1 functionalized 1,2,4-triazole ring has been analyzed over the studied properties

Effect of Nitro Groups on Desulfurization Efficiency of Benzyl-Substituted Imidiazolium-Based Ionic Liquids: Experimental and Computational Approach

In the maneuver to achieve desulfurization, we have explored various nitro-substituted positional isomeric imidazolium-based aprotic ionic liquids (ILs). Ortho-, meta-, and para-substituted nitro benzyl group-aided imidazolium-based ILs were synthesized and used to understand the extractive desulfurization (EDS) efficiency of fuels. ILs chosen for the experiment were optimized using the B3LYP method and 6-311­(++)­g­(d,p) of Gaussian 09, and their interactions with thiophene derivatives were analyzed using the integrated electric field polar continuum model solvation. Free energy of solvation provided qualitative information about the ability of ILs to achieve desulfurization. Parameters affecting the efficiency of synthesized ILs were perused, such as the effect of IL volume, concentration, duration of rotation, and other such parameters. Lewis acidity, availability of the Lewis acidic site and π–π interaction influenced the EDS efficiency of ILs

Structural Dependence of Protic Ionic Liquids on Surface, Optical, and Transport Properties

We report a systematic study to understand the structural dependence of protic ionic liquids, having ammonium or hydroxylammonium as cation and carboxylate as anion, on surface, optical, and transport properties. Experimental measurements of surface tension, refractive index, and electrical conductivity were investigated in the temperature range from (293.15 to 333.15) K at atmospheric pressure to understand the effect of the hydroxyl group on the cationic part and alky chain length and inclusion of highly electronegative fluorine atoms on the anionic part of studied protic ionic liquids. Further, surface entropy, surface energy, critical temperature, parachor, molar refraction, electronic polarizability, thermo-optic coefficient, and free volume were estimated from experimental values. Experimental electrical conductivity data were correlated using the Vogel–Tammann–Fulcher equation. The ionicity was assessed on the basis of the fractional Walden rule, and it was found that the studied protic ionic liquids fall below the ideal line. Upon hydroxyl group functionalization on the cationic chain length, the surface tension and refractive index of ionic liquids increase significantly, whereas the electrical conductivity decreases over the nonfunctionalized ionic liquid counterpart. Moreover, experimental and calculated results were explained to understand the effect of temperature and moiety of ionic liquid on studied thermophysical properties

Infinite dilution partial molar volumes, <i>V</i>₂ºof ascorbic acid in water and in aqueous solutions of [DEEA][Pro]at <i>T</i> = (293.15 to 328.15) K.

<p>^a<i>m</i>_B, molality of [DEEA][Pro] in water.</p><p>^bstandard deviation.</p><p>^cS_v /m³·kg·mol⁻².</p><p>^dRef [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0126091#pone.0126091.ref032" target="_blank">32</a>].</p><p>^eRef [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0126091#pone.0126091.ref033" target="_blank">33</a>].</p><p>^fRef [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0126091#pone.0126091.ref049" target="_blank">49</a>].</p><p>^gRef [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0126091#pone.0126091.ref050" target="_blank">50</a>].</p><p>^hRef [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0126091#pone.0126091.ref052" target="_blank">52</a>].</p><p>ⁱRef [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0126091#pone.0126091.ref029" target="_blank">29</a>].</p><p>Infinite dilution partial molar volumes, <i>V</i>₂ºof ascorbic acid in water and in aqueous solutions of [DEEA][Pro]at <i>T</i> = (293.15 to 328.15) K.</p

Effect of DBU (1,8-Diazobicyclo[5.4.0]undec-7-ene) Based Protic Ionic Liquid on the Volumetric and Ultrasonic Properties of Ascorbic Acid in Aqueous Solution

In order to understand the strength and type of interactions involved in ternary solutions, the effect of solute or cosolute concentration and temperature is needed, as an understanding of these interactions is helpful in biochemical and biophysical chemistry. In this regard, we have studied the volumetric and ultrasonic properties of one of the most important vitamins, i.e., ascorbic acid, in water and in the presence of newly synthesized protic ionic liquid (1,8-diazabicyclo[5.4.0]­undec-7-en-8-ium trifluoroacetate) at temperatures of 293.15–328.15 K and at atmospheric pressure. The experimentally measured density and speed of sound data were used to calculate apparent molar volume and isentropic compressibility, infinite dilution partial molar volume, and partial molar isentropic compressibility. Volume of transfer (Δ_t<i>V</i>₂° and Δ_t<i>K</i>°_s,2), expansion coefficients, pair and triplet volumetric interaction coefficients were also evaluated and discussed in terms of various interactions occurring between ascorbic acid and PIL on the basis of the structural interaction model

Infinite dilutionpartial molar isentropic compression, <i>K</i> °_s,2 of ascorbic acid in water and in aqueous solutions of [DEEA][Pro]at <i>T</i> = (293.15 to 328.15) K.

<p>^a<i>m</i>_B, molality of [DEEA][Pro] in water.</p><p>^bstandard deviation.</p><p>^cS_v /m³·kg·mol⁻²·Pa^-1.</p><p>^dRef [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0126091#pone.0126091.ref032" target="_blank">32</a>].</p><p>^eRef [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0126091#pone.0126091.ref052" target="_blank">52</a>].</p><p>^fRef [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0126091#pone.0126091.ref029" target="_blank">29</a>].</p><p>Infinite dilutionpartial molar isentropic compression, <i>K</i> °_s,2 of ascorbic acid in water and in aqueous solutions of [DEEA][Pro]at <i>T</i> = (293.15 to 328.15) K.</p

The densities, <i>ρ</i>, apparent molar volumes, <i>V</i>_{2, ϕ}, speeds of sound, <i>u</i> and apparent molar isentropic compression, K_{s,2, ϕ°} of ascorbic acid in water and in aqueous [DEEA][Pro] solutions at temperatures, <i>T</i> = (293.15 to 328.15) K and at ambient pressure.

<p>^a<i>m</i>_B is the molality of [DEEA][Pro] in water.</p><p>^b<i>m</i> is the molality of ascorbic acid in water or water + [DEEA][Pro] solutions.</p><p>^c<i>ρ</i>_o is the density of [DEEA][Pro] in water.</p><p>^d<i>u</i>_o is the speed of sound of [DEEA][Pro] in water.</p><p>The standard uncertainties are <i>u</i> (<i>T</i>) = 0.01 K, <i>u</i>(<i>m</i>) = 1.03·10⁻⁵ mol·kg⁻¹, <i>u</i>(<i>ρ</i>) = 7.0·10⁻³ kg·m⁻³, <i>u</i> (<i>u</i>) = 0.5 m·s⁻¹, <i>u</i> (<i>P</i>) = 0.05 kPa. The combined uncertainties, <i>U</i> are <i>U</i> (<i>V</i>_ϕ) = (0.20 to 0.04)·10⁶ m³·mol^-1 and <i>U</i> (<i>K</i>_<i>s2</i>,ϕ) = (0.60 to 0.12)·10⁻¹⁵ m³·mol^-1·Pa^-1 for low and high concentration range of ascorbic acid, respectively (level of confidence, <i>k</i> = 0.95). The experiment was conducted under atmospheric pressure.</p><p>The densities, <i>ρ</i>, apparent molar volumes, <i>V</i>_{2, ϕ}, speeds of sound, <i>u</i> and apparent molar isentropic compression, K_{s,2, ϕ°} of ascorbic acid in water and in aqueous [DEEA][Pro] solutions at temperatures, <i>T</i> = (293.15 to 328.15) K and at ambient pressure.</p