Standard Molar Enthalpies Of Vaporization Research Articles

Experimental Determination of the Standard Enthalpy of Formation of Trimellitic Acid and Its Prediction by Supervised Learning.

The standard molar enthalpy of formation for trimellitic acid (TMAc) in the crystalline phase at 298.15 K, ΔfHm°(cr), was calculated experimentally from the enthalpy of combustion through combustion calorimetry experiments. Likewise, the standard molar enthalpy of sublimation was determined from the standard molar enthalpy of fusion and from the standard molar enthalpy of vaporization from differential scanning calorimetry and thermogravimetry, respectively. Subsequently, the standard molar enthalpies of formation in the gas-phase at 298.15 K, ΔfHm°(g), were calculated. The enthalpies of formation for TMAc, hemimellitic, and trimesic acids were predicted using multiple linear regression (MLR) with a nonreplacement evaluation technique. MLR was applied to the data set that allowed estimating these thermochemical properties with an R2 greater than 0.99. This model was used to compare the predicted and experimental results for benzene carboxylic acids.

7-Methoxy-4-methylcoumarin: Standard Molar Enthalpy of Formation Prediction in the Gas Phase Using Machine Learning and Its Comparison to the Experimental Data.

Experimentally, the standard molar enthalpy of formation in the crystalline phase at 298.15 K, ΔfHm°(cr) for 7-methoxy-4-methylcoumarin (7M4MC) was calculated by traditional linear regression, which was obtained by combustion calorimetry. Similarly, the standard molar enthalpy of sublimation was determined through the standard molar enthalpy of fusion and by the standard molar enthalpy of vaporization, from differential scanning calorimetry and thermogravimetry, respectively; lately using these results, the standard molar enthalpy of formation in the gas phase was calculated at 298.15 K, ΔfHm°(g). In addition ML was used to predict the standard molar enthalpy of formation in the gas phase for the 7M4MC, constructing an experimental data set containing three kinds of functional groups: esters, coumarins, and aromatic compounds. The procedure was performed by using multiple linear regression algorithms and stochastic gradient descent with a R2 of 0.99. The obtained models were used to compare those predicted values versus experimental for coumarins, resulting in an average error rate of 9.0%. Likewise, four homodesmic reactions were proposed and predicted with the multiple linear regression algorithm of ML obtaining good results.

Reversible storage and release of hydrogen with LOHC: Evaluation of thermochemical data for methyl-quinolines with complementary experimental and computational methods

The liquid organic hydrogen carriers (LOHC) are aromatic molecules, which can be considered as an attractive option for the storage and transport of hydrogen. A considerable amount of hydrogen can be loaded and unloaded with a reversible chemical reaction. Methyl-substituted quinolines are available from petroleum, coal processing, wood preservation or they can be synthesized from aniline. Quinolines can be considered as potential LOHC systems, provided they have favorable thermodynamic properties, which were the focus of this current study. The absolute vapor pressures of methyl-quinolines were measured using the transpiration method. The standard molar enthalpies of vaporization of methyl-quinolines were derived from the vapor pressure temperature dependences. Thermodynamic data on vaporization and formation enthalpies available in the literature were collected, evaluated, and combined with own experimental results. The theoretical standard molar gas-phase enthalpies of formation of methyl-quinolines, calculated using the quantum chemical G3MP2 and G4 methods, agreed well with the evaluated experimental data. The hydrogenation/dehydrogenation reaction enthalpies of methyl-quinolines were calculated and compared with the data for other potential liquid organic hydrogen carriers. The comparatively low enthalpies of reaction make these heteroaromatics a seminal LOHC systems.

Molecular versus ionic liquids: Development of a thermodynamic framework for predicting vaporization thermodynamics

Ionic liquids based on the pyridinium and quinolinium cations show good result in desulfurization of fuels. The knowledge of their vaporisation thermodynamics is of practical importance. The standard molar enthalpies of vaporization of pyridinium based ionic liquids were derived from the vapor pressure temperature dependences measured by the quartz-crystal microbalance method. We have collected available primary experimental results on vapour pressures, and enthalpies of phase transitions (solid-solid, crystal-gas, and liquid-gas) of analogous molecular species – substituted pyridines and quinolines. These data were evaluated using the structure-property correlations. The consistent sets of evaluated thermodynamic data on the molecular and ionic liquids were used to develop the “centerpiece” based group-additivity method for predicting enthalpies of vaporization of molecular and ionic compounds. The general transferability of the contributions to the enthalpy of vaporization from the molecular liquids to the ionic liquid has been established.

Prediction of thermodynamic properties: centerpiece approach—how do we avoid confusion and get reliable results?

The absolute vapor pressures of three amino-alcohols were measured using the transpiration method. The consistent set of standard molar enthalpies of vaporization for eighteen amino-alcohols was evaluated using empirical and structure–property correlations. The averaged values of vaporization enthalpies were recommended as reliable benchmark properties for the heat management of CO2 capture technologies. Centerpiece approach based on the group-additivity principles was developed toward amino-alcohols.Graphic abstract

Hydrogen Storage: Thermodynamic Analysis of Alkyl-Quinolines and Alkyl-Pyridines as Potential Liquid Organic Hydrogen Carriers (LOHC)

The liquid organic hydrogen carriers (LOHC) are aromatic molecules, which can be considered as an attractive option for the storage and transport of hydrogen. A considerable amount of hydrogen up to 7–8% wt. can be loaded and unloaded with a reversible chemical reaction. Substituted quinolines and pyridines are available from petroleum, coal processing, and wood preservation, or they can be synthesized from aniline. Quinolines and pyridines can be considered as potential LOHC systems, provided they have favorable thermodynamic properties, which were the focus of this current study. The absolute vapor pressures of methyl-quinolines were measured using the transpiration method. The standard molar enthalpies of vaporization of alkyl-substituted quinolines and pyridines were derived from the vapor pressure temperature dependencies. Thermodynamic data on vaporization and formation enthalpies available in the literature were collected, evaluated, and combined with our own experimental results. The theoretical standard molar gas-phase enthalpies of formation of quinolines and pyridines, calculated using the quantum-chemical G4 methods, agreed well with the evaluated experimental data. Reliable standard molar enthalpies of formation in the liquid phase were derived by combining high-level quantum chemistry values of gas-phase enthalpies of formation with experimentally determined enthalpies of vaporization. The liquid-phase hydrogenation/dehydrogenation reaction enthalpies of alkyl-substituted pyridines and quinolines were calculated and compared with the data for other potential liquid organic hydrogen carriers. The comparatively low enthalpies of reaction make these heteroaromatics a seminal LOHC system.

Paving the way to the sustainable hydrogen storage: Thermochemistry of amino-alcohols as precursors for liquid organic hydrogen carriers

The absolute vapour pressures of four amino-alcohols were measured using the transpiration method. A consistent set of standard molar enthalpies of vaporization for eighteen amino-alcohols was evaluated using empirical and structure–property correlations. The averaged values of vaporization enthalpies are recommended as reliable benchmark properties for thermochemical calculations of the energetics of chemical reactions including synthesis of alkyl-substituted pyrazines, compounds considered as seminal liquid organic hydrogen carriers (LOHC)

Sustainable hydrogen storage: Thermochemistry of amino-alcohols as seminal liquid organic hydrogen carriers

Amino-alcohols are considered for sustainable hydrogen storage systems based on catalytic peptide formation. Experimental and theoretical thermochemical studies of amino-alcohols have been performed, including vapour pressure measurements, combustion calorimetry, and quantum-chemical calculations. The standard molar enthalpies of vaporization of amino-alcohols were calculated from the temperature dependence of the vapour pressures measured by the transpiration method. Energies of combustion for six amino-alcohols were measured using the high-precision combustion calorimetry. The available in the literature primary data on vapour pressures, enthalpies of vaporization, and enthalpies of formation of amino-alcohols were collected and evaluated. The experimental standard molar gas-phase enthalpies of formation of amino-alcohols were derived from the evaluated results. The high-level G3B3, G3MP2, and G4 quantum-chemical methods were used to establish consistency of the experimental and theoretical results. The surprisingly low enthalpy of reaction of the reversible dehydrogenation of 2-amino-ethanol, calculated from the experimental data, makes this liquid organic hydrogen carrier system (LOHC) promising for further optimization and development.

Evaluation of vaporization thermodynamics of pure amino-alcohols

The absolute vapour pressures of three amino-alcohols were measured using the transpiration method. The consistent set of standard molar enthalpies of vaporization for eighteen amino-alcohols was evaluated using empirical and structure–property correlations. Correlation of vaporization enthalpies with normal boiling temperatures was established. Vaporization enthalpies of amino-alcohols obey the group-additivity rules. The averaged values of vaporization enthalpies were recommended as reliable benchmark properties for the heat management of CO2 capture technologies.

Calculation of Abraham model L-descriptor and standard molar enthalpies of vaporization for linear C7-C14 alkynes from gas chromatographic retention index data

Abraham model L solute descriptors have been determined for an additional 33 linear C 7 -C 14 alkynes based on published gas chromatographic retention indices for solutes eluted from capillary columns coated with squalane and apiezon L stationary phases. Standard molar enthalpies of vaporization and sublimation at 298 K are calculated for the 33 linear alkynes using the reported solute descriptors and our recently published Abraham model correlations. Calculated vaporization enthalpies derived from the Abraham model compare very favourably with values based on a popular atom-group additivity model.

Calculation of Abraham model L-descriptor and standard molar enthalpies of vaporization and sublimation for C9 - C26 mono-alkyl alkanes and polymethyl alkanes

Abraham model L solute descriptors have been determined for 127 additional mono-alkyl alkanes and polymethyl alkanes based on published gas chromatographic retention indices for solutes eluted from a fused-silica capillary column coated with a cross-lined methyl silicone stationary phase. Standard molar enthalpies of vaporization and sublimation at 298 K are calculated for the 127 mono-alkyl alkanes and polymethyl alkanes using the reported solute descriptors and our recently published Abraham model correlations. Calculated vaporization and sublimation enthalpies derived from the Abraham model compare very favourably with values based on a popular atom-group additivity model.

Abraham Solvation Parameter Model: Prediction of Enthalpies of Vaporization and Sublimation of Mono-methyl Branched Alkanes Using Measured Gas Chromatographic Data

Abraham model L solute descriptors have been determined for 174 additional mono-methyl branched alkanes based on published linear-programmed gas chromatographic retention indices. Standard molar enthalpies of vaporization and sublimation at 298 K are calculated for the 174 mono-methylated alkanes using the reported solute descriptors and our recently published Abraham model correlations. Calculated vaporization and sublimation enthalpies derived from the Abraham model compare very favorable with values based on a popular atom-group additivity model. Unlike the additivity model the Abraham model gives different predicted values for each mono-methyl alkane having a given C n H 2n+2 molecular formula

Thermochemistry of organometallic compounds: Structure-property relationships in alkylferrocenes

The standard molar enthalpies of vaporization of ethylferrocene n-butylferrocene, and 1,1‘-dimethylferrocene have been determined from the temperature dependence of vapor pressures measured by the transpiration method. Vapor pressures and vaporization enthalpy of the n-butylferrocene were also measured by the static method. The internal consistency of thermodynamic data on vaporization and formation enthalpies of alkyl-substituted ferrocenes has been proved by using structure-property analysis and quantum-chemical calculations. The simple procedures were developed for calculation enthalpies of vaporization and enthalpies of formation of alkyl substituted ferrocenes based on the reliable data for alkylsubstituted benzenes. Parameters of these procedures are expected to be transferable for prediction of thermodynamic properties of organometallic compounds.

Development of Abraham model expressions for predicting the standard molar enthalpies of vaporization of organic compounds at 298.15 K

Published experimental standard molar enthalpies of vaporization data at 298.15 K have been compiled from the chemical and engineering literature for 703 liquid organic and organometallic compounds. The compiled experimental data are used to develop predictive expressions based on the Abraham model. The derived correlations provide reasonably accurate mathematical descriptions of the observed molar enthalpies of vaporization. Standard deviations between the experimental and back-calculated molar enthalpies of vaporization are on the order of 2.2 kJ mol−1, which is comparable to (if not better than) many of the existing predictive methods. The derived mathematical expressions can be used to estimate molar enthalpies of vaporization of additional compounds at 298.15 K, provided that the Abraham model compound descriptors are known.

Vaporization thermodynamics of compounds modeling lignin structural units

Vapour pressures and standard molar enthalpies of vaporization of trans-anethole, estragole, eugenol, and trans-isoeugenol were derived by the transpiration method. A large number of the primary experimental results on temperature dependences of vapour pressures have been collected from the literature and have been treated uniformly in order to derive vaporization enthalpies at the reference temperature 298.15 K. The available data were evaluated and validated with help of empirical methods based on gas-chromatographic measurements and structure-property relationships.

Thermal and structural properties of ethyl 2- and 3-aminobenzoates: Experimental and computational approaches

Calorimetric experiments performed for ethyl 2-aminobenzoate and ethyl 3-aminobenzoate allowed the determination of their standard (p° = 0.1 MPa) molar enthalpies of formation, in the gaseous phase, at T = 298.15 K. The techniques used were static bomb combustion calorimetry and high temperature Calvet microcalorimetry, which enabled the determination of the standard molar enthalpies of formation in the liquid phase, and the standard molar enthalpies of vaporization, at T = 298.15 K, of the above aminobenzoates.In addition, computational calculations, through the G4 composite method, were performed to estimate the enthalpies of formation in the gas phase of the title compounds. Boltzmann weighted averages were performed over sets of stable conformers of each compound, using Gibbs energy to compute population weights. The ethyl 2-aminobenzoate presents an intramolecular hydrogen bond, which was confirmed through topological analyses of the electron density.Furthermore, the energetic effect caused from exchanging the position of the amino substituent was evaluated, and was also compared with similar compounds.

Energetic vs structural study of two biomass degradation derivatives: 2-Cyclopentenone and 3-methyl-2-cyclopentenone

The standard molar enthalpies of formation in the gaseous state, at T = 298.15 K, of the 2-cyclopentenone and 3-methyl-2-cyclopentenone were derived from their standard molar energies of combustion and from their standard molar enthalpies of vaporization, obtained from static-bomb combustion calorimetry measurements and high-temperature Calvet microcalorimetry, respectively. The enthalpies of hydrogenation of the two cyclopentenones were derived from their gas-phase enthalpies of formation and the gas-phase enthalpies of formation of the corresponding cycloalkanones. The gas-phase standard molar enthalpy of formation of the compounds studied were also obtained using high level ab initio calculations and are in very good agreement with the experimental ones. In addition, thermochemical parameters associated to 2-cyclopentenone and 3-methyl-2-cyclopentenone transformations were investigated using the G3(MP2)//B3LYP level of theory. The conversions of both compounds to longer chain alkanes were found to be thermodynamically favourable.

How much different are thermochemical properties of enantiomers and their racemates? Thermochemical properties of enantiopure and racemate of methyl- and butyl lactates.

This work is a contribution to the molecular understanding of the thermodynamic properties of the chiral compounds. A comprehensive thermochemical study of the liquid enantiopure and racemate pairs of optically active alkyl lactates has been performed. Vapor pressures of DL-(±)-, L-(-)-methyl-, and DL-(±)-, L-(-)-n-butyl esters of lactic acid were measured by the transpiration method. The liquid phase standard molar enthalpies of formation of these esters were measured by using the high-precision combustion calorimetry. The standard molar enthalpies of vaporization of alkyl lactates at 298.15 K were derived from vapor pressure temperature dependencies. Thermochemical data of these compounds were collected, evaluated, and tested for internal and external consistency. The high-level G4 quantum-chemical method was used for mutual validation of the experimental and theoretical gas phase enthalpies of formation of alkyl lactates. A critical review of the available thermochemical data for the liquid and crystalline enantiopure and racemate pairs of optically active compounds has been performed. Useful general trends in energetics of sublimation, vaporization, and formation of optically active compounds have been revealed. This knowledge is required for evaluation of new and already available experimental data for the chiral compounds, and it can be helpful to assess volatility or feasibility of processes to separate enantiomers.

Renewable platform chemicals: Thermochemical study of levulinic acid esters

Abtract Equilibrium of the levulinic acid esterification with methanol, ethanol, and 1-butanol was studied in a broad temperature range (323 K–473 K) for reactions catalyzed by the enzyme Novozym 435 as well as for uncatalysed reaction systems. Thermodynamic equilibrium constants were derived with help of activity coefficients of reaction participants, which were predicted with the equation of state PC-SAFT. The liquid phase standard molar enthalpies of formation of methyl-, ethyl-, and n-butyl-esters of levulinic acid were measured by using the high-precision combustion calorimetry. Vapor pressures of these esters were measured by using the transpiration method. The standard molar enthalpies of vaporization of alkyl levulinates at 298.15 K were derived from vapor pressure temperature dependencies. Thermochemical data of alkyl levulinates were collected, evaluated, and tested for internal consistency. The high-level G4 quantum-chemical method was used for mutual validation of the experimental and theoretical gas phase enthalpies of formation of studied esters. Thermodynamic analysis of the levulinic acid esterification has been performed. Using the levulinic acid esterification with alcohols as the model reaction for an industrial processing of biomass conversion to fuels and useful platform chemicals, we have shown that qualitatively correct agreement between results from equilibrium study, from thermochemical data (combustion and transpiration), and from G4 calculations was observed. Reasonable combination of the quantum-chemical methods and of PC-SAFT modelling with empirical methods could serve to reduce experimental efforts for assessment of feasibility of the chemical processes of utilization of renewable feedstocks.

Aliphatic nitroalkanes: Evaluation of thermochemical data with complementary experimental and computational methods

Thermochemical properties of aliphatic nitroalkanes available in the literature are scarce and inconsistent. New standard molar enthalpies of vaporization and sublimation of 2-nitropropane, 2-methyl-2-nitropropane, and 2,3-dimethyl-2,3-dinitrobutane were derived from the vapor pressure temperature dependence measured by the transpiration method. Thermodynamic data on linear and branched aliphatic mono- and di-nitroalkanes available in the literature were combined with own experimental results and evaluated with help of empirical and theoretical methods aiming at recommendation of the sets of vaporization and formation enthalpies for aliphatic nitroalkanes as the reliable benchmark properties for further thermochemical calculations. Gas phase standard molar enthalpies of formation of aliphatic nitro-compounds derived by high-level quantum-chemical method G4 were found in a good agreement with the evaluated and recommended experimental data. Group-additivity procedure for calculation of vaporization and formation enthalpies have been developed and tested.