Infinite dilution activity coefficients of apple juice aroma compounds

<p>Molecular simulations see widespread use in calculating various physical properties of interest, with a key goal being predictive molecular design. These simulations, including molecular dynamics (MD) simulations, begin with a underlying energy model or force field and then, based on this model, use simulations to compute properties of interest. However, one of the most significant challenges in molecular dynamics and modeling studies is ensuring that the force field is a good enough approximation of the underlying physics that computed quantities can be used to reproduce experimental properties with the desired level of accuracy. Parameterization of force fields depend on various experimental properties including as much of the chemistry of interest as possible. Physicochemical properties measurable in a relatively straightforward manner are particularly interesting for developers. Such properties can be measured for a relatively diverse chemical set and used to expand the parameterization dataset as needed. Here, we examine infinite dilution activity coefficients (IDACs) which are experimental quantities that can play this role. We retrieved 237 empirical IDACs from NIST's ThermoML, a database of measured thermodynamic properties, and we estimated the corresponding values using solvation free energy calculations. We found that calculated IDAC values correlate strongly with experiment. Specifically, the natural logarithm of calculated and experimental IDAC values shows a Pearson correlation coefficient of 0.85+/-0.02. The calculated IDAC values allow us to identify strengths and potential weaknesses of force field parameters for specific functional groups in solutes and solvents, suggesting these may be a valuable source of data for force field parameterization, capturing some of the same type of information as hydration and solvation free energies and thus potentially providing a useful new source of experimental data.</p>

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Infinite dilution activity coefficient measurements of organic solutes in selected deep eutectic solvents by gas-liquid chromatography

10.51415/10321/3058 ◽

2018 ◽

Author(s):

◽

Nkululeko Nkosi

Keyword(s):

Liquid Chromatography ◽

Activity Coefficients ◽

Infinite Dilution ◽

Deep Eutectic Solvents ◽

Gas Liquid Chromatography ◽

Organic Solutes ◽

Separation Processes ◽

Infinite Dilution Activity Coefficients ◽

Tetramethylammonium Chloride ◽

Selectivity And Capacity

Many separation processes in the chemical and petrochemical industries are energy intensive, and unfortunately, involve a range of solvents that are environmentally harmful and destructive. Alternative, sustainable separation techniques are desired to replace these conventional methods used in the separation of azeotropic as well as close-boiling mixtures, with the intention of reducing energy costs and adverse impact on the environment. In the present study, a new class of solvents called deep eutectic solvents (DESs) of Type III were investigated as alternatives to conventional solvents currently employed in separation processes. DESs are classified as ‘green’ solvents because of a range of favourable properties including lower cost, desirable solubility properties and reduced environmental impact (Abbott et al., 2003b; Smith et al., 2014). The infinite dilution activity coefficients (IDACs) values of 24 solutes – including alk-1-anes, alk-1-enes, alk-1-ynes, cycloalkanes, alkanols, alkylbenzenes, heterocyclics, esters, and ketones – were measured at 313.15, 323.15, 333.15 and 343.15 K by gas-liquid chromatography (GLC) in DESs. The four investigated DESs were as follows: 1) Tetramethylammonium chloride + Glycerol (DES1); 2) Tetramethylammonium chloride + Ethylene Glycerol (DES2); 3) Tetramethylammonium chloride + 1,6 Hexanediol (DES3); and 4) Tetrapropylammonium bromide + 1,6 Hexanediol (DES4). This work focused on the performance of DESs as extractive solvents for selected azeotropic and close-boiling binary mixtures. The two key performance criteria for these extractive solvents – selectivity and capacity – were determined from experimental infinite dilution activity coefficients (IDACs) of various solutes. The effect of solute molecular structure on IDAC values was investigated. Moreover, the effect of varying the hydrogen bond donors (HBDs) in DESs on IDAC values was examined. Partial excess molar enthalpies at infinite dilution were determined from the experimental IDAC data. Moreover, common industrial separation problems were selected to investigate DES potential to separate various mixtures by determining selectivity and capacity at infinite dilution. The results obtained in this study indicate that the use of a long carbon chain HBDs greatly decreases miscibility of DESs with organic solutes. For systems such as n-heptane - toluene, acetone - ethanol, cyclohexane - benzene and n-hexane - benzene systems, DES4 was the best solvent regarding the separation performance index. However, further investigation for DES4 by measurements of vapour-liquid equilibria (VLE) and liquid-liquid equilibria (LLE) data is suggested, as these data would provide additional pertinent information regarding the separation of such mixtures using DES4. The data produced from this study can be used to extend the applicability range of predictive models such as Universal Quasi- Chemical Functional Group Activity Coefficients (UNIFAC) and modified UNIFAC (Do) which are already incorporated in some chemical engineering process simulators.

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