Morpholinium and piperidinium based ionic liquids: Vaporization thermodynamics

Ionic liquids (ILs) have gained increasing attention in a wide range of material synthesis related applications. For the first time, vapor pressures and vaporization enthalpies of four morpholinim based ILs with a common bis(trifluoromethylsulfonyl)imide ([NTf2]−) or trifluorotris(perfluoroethyl)phosphate ([FAP]−) anions were measured using a Quartz Crystal Microbalance (QCM). The enthalpies of vaporization measured at elevated temperatures have been adjusted to the reference temperature 298 K. The experimental vaporization enthalpies were compared with theoretical values available in the literature, as well as with empirical values derived from a gas-liquid-chromatographic method based on activity coefficients at infinite dilution. New experimental vaporization enthalpies were tested for consistency with help of structure property-relationships

Vaporization Thermodynamics of Morpholinium Based Ionic Liquids

Ionic liquids (ILs) have gained increasing attention in a wide range of material synthesis related applications. For the first time, vapor pressures and vaporization enthalpies of four morpholinim based ILs with a common bis(trifluoromethylsulfonyl)imide ([NTf2]) anion were measured using Langmuir-Quartz Crystal Microbalance (QCM). The enthalpies of vaporization measured at elevated temperatures have been adjusted to the reference temperature 298 K. The experimental vaporization enthalpies were compared with theoretical values available in the literature, as well as with empirical values derived from a gas-chromatographic method based on activity coefficients at infinite dilution. New experimental vaporization enthalpies were tested for consistency with help of structure property-relationships

Ionic liquids alkyl-imidazolium thiocyanates: Comprehensive thermochemical study

Ionic liquids containing imidazolium cation and thiocyanate anion are attracting considerable attention for industrial applications due to low viscosities, low melting points and good conductivity. A comprehensive thermodynamic study of [Cnmim][SCN] series with (n = 2, 4, and 6) was performed in this paper. Vapor pressures were measured by using the quartz-crystal microbalance (QCM). Vaporization enthalpies have been derived by using thermogravimetry and QCM and adjusted to the reference temperature 298.15 K. An absence of possible thermal decomposition during vapor pressure measurements was monitored by the ATR-IR spectroscopy. The liquid phase standard molar enthalpy of formation of [C4mim][SCN] was measured by using combustion calorimetry, combined with the evaluated vaporization enthalpy to get gas-phase standard molar enthalpy of formation. The latter experimental value was in close agreement with theoretical gas-phase molar enthalpy of formation of [C4mim][SCN], calculated by the high-level quantum chemical method G3MP2. These experimental and theoretical results were applied for estimation of aqueous standard molar enthalpies of formation of [Cnmim] cations, as well as for calculation of solubilities of practically relevant solutes in of [Cnmim][SCN] series of ionic liquids

Heat capacities of ionic liquids based on tetrahydrothiophenium cation and NTf<inf>2</inf> anion

© 2020 Elsevier B.V. The isobaric heat capacities of seven ionic liquids (ILs) based on the S-alkyl-tetrahydrothiophenium cation [CnTHT] with alkyl chain lengths of Cn = 4,5,6,7,8,9,10 and the bis[(trifluoromethyl)sulfonyl]imide, [NTf2] anion were measured in a differential scanning calorimeter in the temperature range 310−376 K. Measurements have been performed for the first time. Experimental results were extrapolated to the reference temperature of 298 K. A linear trend of the Cp,mo(liq, 298 K) -values for [CnTHT][NTf2] with the growing alkyl chain length was observed and compared with trends available for the other ILs with 5-membered (imidazolium and pyrrolidinium) and 6-membered (pyridinium) ring cations as [NTf2] salts. The new Cp,mo(liq, 298 K) -values for for [CnTHT][NTf2] were used for mutual validation of experimental and theoretical results by a group-additivity method available in the literature. The agreement observed between experimental and additive calculations, together with the reasonable chain-length dependence demonstrated for the [CnTHT][NTf2] series was considered as evidence of internal consistency of the heat capacities measured in this work

Volatility of molten salts [Ph<inf>4</inf>P][NTf<inf>2</inf>] and Cs[NTf<inf>2</inf>]

© 2020 The Authors. Published by Wiley-VCH GmbH The two ionic compounds [Ph4P][NTf2] and Cs[NTf2] were qualified to be suitable liquid materials for different high temperature applications. Development and optimization of these application techniques require knowledge of the thermodynamic properties of vaporization. Vapor pressures and vaporization enthalpies have been measured by using quartz-crystal microbalance. Solubility parameters and miscibility of ionic liquids in practically relevant solvents were assessed

Thermochemical properties of pyrazine derivatives as seminal liquid organic hydrogen carriers for hydrogen storage

This work contributes to our primary interest in applications of experimental and computational thermochemistry methods for providing the basic data required in chemical-process design. Pyrazine derivatives are considered as a seminal liquid organic hydrogen carriers. The standard molar enthalpies of vaporisation/sublimation of pyrazine derivatives were derived from the vapour pressure temperature dependences measured by the static and transpiration method. Enthalpies of fusion of the solid compounds were measured using DSC. Thermodynamic data on solid–gas, liquid–gas, and solid–liquid phase transitions available in the literature were collected and combined with own experimental results. We have evaluated and recommended the set of vaporisation and formation enthalpies of pyrazine derivatives at 298.15 K as the reliable benchmark properties for further thermochemical calculations. Gas phase molar enthalpies of formation of pyrazine derivatives calculated by the high-level quantum-chemical method G4 were in agreement with the recommended experimental data. Compilation of experimental and theoretical results derived in this work is useful for optimisation of hydrogenation/dehydrogenation reactions involved in the hydrogen storage technologies

Sublimation thermodynamics of nucleobases derived from fast scanning calorimetry

© 2020 the Owner Societies. The five fundamental units of the genetic code: Uracil (U), thymine (T), cytosine (C), adenine (A) and guanine (G) are known for extremely low vapor pressure and low thermal stability at elevated temperatures. Therefore, application of conventional techniques for the determination of sublimation enthalpies and vapor pressures fails to provide accurate results. Recently, a Fast Scanning Calorimetry method (FSC) for vapor pressure determination was developed for investigation of extremely low volatile, as well as for thermally unstable molecular and ionic molecules. This success has encouraged application of the FSC method for determination of vapor pressures and sublimation enthalpies of the five nucleobases, where available literature data are in disarray. The thermodynamic data of the nucleobases available in the literature were collected, evaluated, and combined with our experimental results to reconcile available experimental data. The set of evaluated thermochemical data on the five nucleobases was recommended as the benchmark properties for these thermally labile compounds

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

In the footsteps of August Michaelis: Syntheses and Thermodynamics of Extremely Low-Volatile Ionic Liquids

© 2020 The Authors. Published by Wiley-VCH GmbH A series of nine different known ionic liquids or low melting salts was synthesised and purified. They are composed of the [NTf2]– (bis(trifluoromethane)sulfonimide), [OTf]– (trifluoro-methane-sulfonate), or [B(CN)4]– (tetracyanidoborate) anion and [Ph4P]+ (tetraphenylphosphonium), [Ph3BzP]+ (triphenylbenzyl phosphonium), [nBu4P]+ (tetra-nbutylphosphonium), [nBuPh3P]+ (tri-phenyl-nbutylphosphonium), [nBu4N]+ (tetra-nbutylammonium), or the [PPN]+ (bis(triphenylphosphine)iminium) cation. Precise vapour pressure data and enthalpies of vaporisation were measured using the Quartz Crystal Microbalance (QCM) method and evaluated. Structure-property relations are established using the obtained data as well as literature known data of ILs with alkyl-substituted imidazolium cations. It turns out that ILs with the tetracyanidoborate anion have even higher values of the enthalpy of vaporisation than those with the common [NTf2]− or [OTf]− anion and therefore are even less volatile

Application of the Flash DSC 1 and 2+ for vapor pressure determination above solids and liquids

In this work, we adapted a procedure for vapor pressures determination utilizing a fast scanning chip calorimeter to the case of a stagnant gas phase. The validity of the developed procedure was checked by comparing the vapor pressures determined in this work for several polyaromatic, heteroaromatic, and long-chain compounds with reliable vapor pressure data available in the literature. The results of the comparison show that the commercial Flash DSC 1 and the Flash DSC 2+ (Mettler Toledo, Switzerland) can be used for a reliable appraisal of the vapor pressures in a wide temperature range, which allows using these devices without additional technical changes as a source of comprehensive and internally consistent information about the energy of phase transitions