Extremely low vapor‐pressure data as access to PC‐SAFT parameter estimation for ionic liquids and modeling of precursor solubility in ionic liquids

Precursor solubility is a crucial factor in industrial applications, dominating the outcome of reactions and purification steps. The outcome and success of thermodynamic modelling of this industrially important property with equations of states, such as Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT), vastly depends on the quality of the pure-component parameters. The pure-component parameters for low-volatile compounds such as ionic liquids (ILs) have been commonly estimated using mixture properties, e. g. the osmotic pressure of aqueous solutions. This leads to parameters that depend on the solvent, and transferability to other mixtures often causes poor modeling results. Mixture-independent experimental properties would be a more suitable basis for the parameter estimation offering a way to universal parameter sets. Model parameters for ILs are available in the literature [10.1016/j.fluid.2012.05.029], but they were estimated using pure-IL density data. The present work focuses on a step towards a more universal estimation strategy that includes new experimental vapor-pressure data of the pure IL. ILs exhibit an almost negligible vapor pressure in magnitude of usually 10−5 Pa even at elevated temperatures. In this work, such vapor-pressure data of a series of 1-ethyl-3-methyl-imidazolium-based [C2mim]-ILs with various IL-anions (e. g. tetrafluoroborate [BF4]−, hexafluorophosphate [PF6]−, bis(trifluoromethylsulfonyl)imide [NTf2]−) were experimentally determined and subsequently used for PC-SAFT parameter estimation. The so-determined parameters were used to predict experimental molecular precursor solubility in ILs and infinitely diluted activity coefficients of various solvents in ILs. The parameters were further compared to modeling results using classical parametrization methods (use of liquid-density data only for the molecular PC-SAFT and the ion-based electrolyte PC-SAFT). As a result, the modeled precursor solubilities using the new approach are much more precise than using the classical parametrization methods, and required binary parameters were found to be much smaller (if needed). In sum, including the pure-component vapor-pressure data of ILs opens the door towards parameter estimation that is not biased by mixture data. This procedure might be suitable also for polymers and for all kind of ionic species but needs extension to ion-specific parametrization in the long term

Thermochemical Properties of Xanthine and Hypoxanthine Revisited

© 2017 American Chemical Society. The standard molar enthalpies of formation of xanthine and hypoxanthine were measured by using high-precision combustion calorimetry. The standard molar enthalpies of sublimation of these compounds at 298.15 K were derived by the quartz-crystal microbalance technique. Limited thermodynamic data available in the literature are compared with our new experimental data. In addition, we use the G4 method to calculate the molar enthalpies of formation of xanthine and hypoxanthine in the gas phase. There is good agreement between the evaluated experimental data and the quantum-chemical calculations. (Chemical Equation Presented)

Vapor pressures and vaporization enthalpies of 5-nonanone, linalool and 6-methyl-5-hepten-2-one. Data evaluation

© 2014 Elsevier B.V.. Vapor pressures and vaporization enthalpies for 5-nonanone, linalool and 6-methyl-5-hepten-2-one seem to be in disarray. Temperature dependences of vapor pressures for these pure compounds were measured by using the static and the transpiration techniques. Molar standard enthalpies of vaporization at the reference temperature were derived. Available literature data on vapor pressures and vaporization enthalpies were collected and analyzed. The consistent data set for each compound was evaluated. Reliable thermodynamic parameters of vaporization were derived and used to test some commonly used predicting procedures

The melting properties of D-α-glucose, D-β-fructose, D-sucrose, D-α-galactose, and D-α-xylose and their solubility in water: a revision

Saccharides are still commonly isolated from biological feedstock by crystallization from aqueous solutions. Precise thermodynamic data on solubility are essential to optimize the downstream crystallization process. Solubility modeling, in turn, requires knowledge of melting properties. In the first part of this work, following our previous work on amino acids and peptides, D-α-glucose, D-β-fructose, D-sucrose, D-α-galactose, and D-α-xylose were investigated with Fast Scanning Calorimetry (FSC) in a wide scanning rate range (2000 K·s−1 to 10000 K·s−1). Using the experimental melting properties of saccharides from FSC allowed successfully modeling aqueous solubility for D-sucrose and D-α-galactose with the equation of state PC-SAFT. This provides cross-validation of the measurement methods to determine accurate experimental melting properties with FSC. Unexpectedly, the experimental FSC melting temperatures, extrapolated to zero scanning rates for thermal lag correction, were higher than results determined with DSC and available literature data. To clarify this inconsistency, FSC measurements towards low scanning rates from 10000 K·s−1 to 1 K·s−1 (D-α-glucose, D-β-fructose, D-sucrose) overlapping with the scanning rates of DSC and literature data were combined. At scanning rates below 1000 K·s−1, the melting properties followed a consistent non-linear trend, observed in both the FSC and the literature data. In order to understand the non-linear decrease of apparent melting temperatures with decreasing heating rate, the endothermic peaks were investigated in terms of isoconversional kinetics. The activation energies in the non-linear dependency region are in the range of 300<EA<600kJ∙mol−1. These values are higher than the enthalpy of sublimation for D-α-glucose, indicating that the non-linear behavior does not have a physical nature but attributes to chemical processes corresponding to the decomposition of molecular compounds within the crystal lattice before melting. The melting properties reported in the literature, commonly determined with conventional methods such as DSC, lead to inaccurate results due to the decomposition of these biomolecules at low heating rates. In addition, the FSC results at lower scanning rates coincide with results from DSC and literature in the overlapping scanning rate range, further validating the accuracy of FSC measurements to determine reliable melting properties of thermally labile biomolecules. The experimental FSC melting properties determined at higher scanning rates are considered as the correct equilibrium melting properties, which are not influenced by any chemical processes. The combination of FSC and PC-SAFT opens the door to model solubility of solid compounds that commonly decompose before melting

Alkyl-imidazolium tetrafluoroborates: Vapor pressure, thermodynamics of vaporization, and enthalpies of formation

© 2017 Elsevier B.V. The absolute vapor pressures for the series of [C n mim][BF 4 ] ionic liquids with (n = 2, 4, 6, 8, and 10) were measured over the temperature range 404–457 K by using the quartz-crystal microbalance. An absence of possible thermal decomposition was monitored by the ATR-IR spectroscopy. The molar enthalpies of vaporization of ionic liquids under study were derived from vapor pressure temperature dependences and adjusted to the reference temperature 298.15 K. The liquid phase molar enthalpy of formation of [C 2 mim][BF 4 ] was derived from the solution calorimetry and combined with its molar vaporization enthalpy to get the first experimental gas-phase molar enthalpy of formation of the [BF 4 ] − containing ionic liquid. A computational approach based on the DLPNO-CCSD(T) method was used to calculate the theoretical gas-phase molar enthalpy of formation of [C 2 mim][BF 4 ]. The theoretical and experimental results were found to be in agreement within the combined uncertainties, providing the mutual validation of experimental and computational procedures used in the current study

Thermodynamic properties of glycerol: Experimental and theoretical study

© 2015 Elsevier B.V. Vapor pressures of highly pure glycerol were measured by the static and the transpiration methods in a broad temperature range. The standard molar enthalpy of vaporization of glycerol was derived from the vapor pressure temperature dependencies. Thermodynamic data on glycerol available in the literature were collected, evaluated, and combined with own experimental results. We recommend the set of vaporization and formation enthalpies for glycerol at 298.15K (in kJmol-1): δfHm° (g)=-(578.8±0.6), δfHm° (l)=-(669.3±0.5), and δlgHm° =(90.5±0.3) as the reliable benchmark properties for further thermochemical calculations. Quantum-chemical calculations of the gas phase molar enthalpy of formation of glycerol have been performed using the G4 method and results were in agreement with the recommended experimental data. The standard molar entropy of formation and the standard molar Gibbs function of formation of glycerol were estimated

Thermochemistry of ammonium based ionic liquids: Thiocyanates - Experiments and computations

© Springer Science+Business Media New York 2015. Abstract Molar enthalpies of solution of tetra-n-butylammonium thiocyanate [N(Bu)4][SCN] and tetra-n-pentylammonium thiocyanate [N(Pe)4][SCN] in water were measured by using solution calorimetry. The enthalpy of combustion of [N(Bu)4][SCN] was measured by using rotation bomb combustion calorimetry and the enthalpy of formation of this ionic liquids was derived. The thermal behavior of [N(Bu)4][SCN] was studied using differential scanning calorimetry. Quantum-chemical calculations of the molar enthalpy of formation in the gaseous phase have been performed for the series [N(R)4][SCN] with RA =(Me, Et, n-Bu, and n-Pe) using the G3MP2 level of theory. Experimental and calculated values of the enthalpies of formation are in agreement within the boundaries of the experimental uncertainties

Prediction of the enthalpies of vaporization for roomerature ionic liquids: Correlations and a substitution-based additive scheme

© 2015 Elsevier B.V. All rights reserved. The literature data on the enthalpies of vaporization for aprotic ionic liquids (ILs) published by the end of May 2014 were analyzed and the most reliable ΔlgHm values were derived for 68 ILs. The selected enthalpies of vaporization were correlated with density and surface tension using symbolic regression and a number of effective correlation equations were proposed. The substitution-based incremental scheme for prediction of the enthalpies of vaporization of imidazolium, pyridinium and pyrrolidinium ILs was developed. The standard error of the regression for the developed scheme is significantly lower than that for the atom-based group-contribution schemes proposed earlier

Structure-property relationships in ionic liquids: Chain length dependence of the vaporization enthalpies of imidazolium-based ionic liquids with fluorinated substituents

© 2015 Elsevier B.V. Molar vaporization enthalpies of fluoroalkyl-substituted imidazolium-based ionic liquids were derived from two concurring quartz crystal microbalance (QCM) and thermogravimetry (TGA) methods. For comparison, enthalpies of vaporization measured at elevated temperatures have been adjusted to the reference temperature 298K and tested for consistency. It was found that vaporization enthalpies of fluorine substituted families are significantly higher compared to the analogous ILs with the alkyl-substituted cation. This is in agreement to molecular solvents, where fluorination typically increases vaporization enthalpy relative to hydrocarbon analogues. A useful group contribution for the incremental CF2 fragment in the alkyl chain was recommended for the quick estimation of vaporization enthalpies of various substituted IL cations (e.g., imidazolium, ammonium, pyridinium, etc.)

Hydrogen Bonding Between Ions of Like Charge in Ionic Liquids Characterized by NMR Deuteron Quadrupole Coupling Constants—Comparison with Salt Bridges and Molecular Systems

We present deuteron quadrupole coupling constants (DQCC) for hydroxyl-functionalized ionic liquids (ILs) in the crystalline or glassy states characterizing two types of hydrogen bonding: The regular Coulomb-enhanced hydrogen bonds between cation and anion (c–a), and the unusual hydrogen bonds between cation and cation (c–c), which are present despite repulsive Coulomb forces. We measure these sensitive probes of hydrogen bonding by means of solid-state NMR spectroscopy. The DQCCs of (c–a) ion pairs and (c–c) H-bonds are compared to those of salt bridges in supramolecular complexes and those present in molecular liquids. At low temperatures, the (c–c) species successfully compete with the (c–a) ion pairs and dominate the cluster populations. Equilibrium constants obtained from molecular-dynamics (MD) simulations show van't Hoff behavior with small transition enthalpies between the differently H-bonded species. We show that cationic-cluster formation prevents these ILs from crystallizing. With cooling, the (c–c) hydrogen bonds persist, resulting in supercooling and glass formation. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA