Fatty acids methyl esters: Complementary measurements and comprehensive analysis of vaporization thermodynamics
Introduction
The expected decline of oil supply in the near future makes the development and optimization of the manufacturing of alternative biofuels a hot topic for current science and engeneering. The prevailing share of the modern biofuel market includes bioethanol and biodiesel. Biodiesel is composed of alkyl esters of fatty acids and it usually synthesized by chemical or enzymatic catalysis mainly from renewable resources [1]. Thermodynamic data on esters are indispensable for optimization of the synthesis conditions, heat management, as well as for separation processes. Experimental thermodynamic studies of aliphatic esters has been a long-standing goal in our laboratory [2], [3], [4].
In this work, we focused on the Fatty Acids Methyl Esters (FAME) and their structure–property relationships. In a previous study of a series of n-alkyl acetates (from methyl acetate to tetradecyl acetate) [2], we observed a remarkable linear chain-length dependence for their vaporization enthalpy (referenced to T = 298.15 K). The dependence of vaporization enthalpy on the total number of C-atoms in alkyl chains (for nC ≥ 3), was expressed by the following equation:
This result can be rationalized in a simple way by the observation that monotonically growing chain length is characterized by a constant contribution of 4.56 kJ·mol−1 for each [CH2] group. From a theoretical as well a practical point of view, we could expect that this [CH2]-contribution is also valid for (FAME) where the monotonically growing chain length is extended from the side of carbonyl group (see Fig. 1).
In order to confirm our expectations, we have thoroughly collected the available literature on vapour pressures and vaporization enthalpies for FAME but we failed to draw any reasonable conclusion regarding the vaporization enthalpy (298.15 K) chain-length dependence due to a significant spread of the available literature data. Despite of that, the thermodynamic studies of FAME have been a popular endeavor in the past, since 1926 [5]. Many vapour pressure data of different quality and accuracy have been reported in the literature and some may be affected by systematic errors. Moreover, vapour pressures published in the literature were measured by different techniques and over significantly different temperature ranges. As a consequence, (Tav)-values, derived from these measurements, were referenced to different average temperatures Tav. For comparison, (Tav)-values must be adjusted to any common temperature, e.g. to the reference temperature T = 298.15 K. Obviously if the temperature Tav is close to T = 298.15 K, the contribution to vaporization enthalpy due to the temperature adjustment is rather small and it hardly would exceed the boundaries of experimental uncertainties (within the range of 1–2 kJ·mol−1). Otherwise, vaporization enthalpy derived e.g. from the high-temperature ebulliometry (e.g. [6]) are significantly affected by a contribution of (5–6) kJ·mol−1 due to large adjustment to T = 298.15 K. The temperature adjustment of (Tav)-values is usually performed according to the Kirchhoff's rule:where is the standard molar vaporization enthalpy and the difference between the isobaric heat capacities of the gaseous (g) and liquid phases, (l), is described by Eq. (3):
Recently [7], we successfully tested four methods to calculate the difference between the isobaric heat capacities of the gaseous and crystal phases required for adjustment of sublimation enthalpies to the reference temperature 298.15 K. Tests were performed for ferrocene, for which reliable experimental data are available in the literature. In this work, we focus on methods to evaluate the difference between heat capacities of the gaseous and liquid phases required for adjustment of vaporization enthalpies to the reference temperature 298.15 K. Numerous experimental vapour pressures available for FAME together with our new complementary measurements have been used to evaluate results of estimated using different methods. The reconciled (298.15 K)-values for FAME with the chain-length NC = 3–19 were analyzed in order to derive the chain length dependence for methyl esters and to compare the [CH2]-contributions for different homologous series. Moreover, the (298.15 K)-values of FAME have been used for interpretation of the gas phase dispersion interaction of the alkyl chain and the ester group.
Section snippets
Materials
Samples of FAME were of commercial origin with the mass fraction purities better than 0.99 according to certificate (see Table S1). The purity of the samples used for vapour pressure measurements was determined by gas chromatography (GC) using the Hewlett-Packard 4890 equipped with FID and HP5 capillary column (30 m × 0.32 mm), film thickness 0.25 µm. The final mass purity of FAME as determined by GC was better than 0.998 (see Table S1). Samples were additionally purified during the
General methods for estimation of
The isobaric heat capacity differences are required for vaporization enthalpy temperature adjustment according to the Kirchhoff's rule. There are at least four well-established methods I to IV, which can be applied for assessment -values.
Conclusions
New experimental vaporization enthalpies of the FAMEs were determmined using the static and transpiration methods. Four methods for assessment the heat capacity differences were discussed and applied for adjustment of vaporization enthalpies to the reference temperature 298.15 K. A set of vaporization enthalpies of FAMEs was evaluated and recommended for thermochemical calculations. Dispersion forces in methyl esters have been quantified and discussed. These results will facilitate evaluation
Acknowledgments
This contribution is a part of the special issue dedicated to the 80th birthday of Prof. Gennady Y. Kabo, the founder of thermochemical science school in Belarusian State University. His former students are working all around the world in the field of physical chemistry and thermodynamics. Authors gratefully acknowledge financial support from the Government of Russian Federation (decree №220 of 9 April 2010), agreement №14.Z50.31.0038. SPV acknowledges financial support from DFG, grant VE
References (95)
Industrial applications for plant oils and lipids
Bioprocess. Value-Added Prod. from Renew. Resour.
(2007)- et al.
Vapour pressures and enthalpies of vaporization of a series of the linear n-alkyl acetates
J. Chem. Thermodyn.
(2006) - et al.
Transpiration method: Vapour pressures and enthalpies of vaporization of some low-boiling esters
Fluid Phase Equilib.
(2008) - et al.
Vapour pressures and enthalpies of vaporization of aliphatic esters
Fluid Phase Equilib.
(2012) - et al.
Ferrocene: Temperature adjustments of sublimation and vaporization enthalpies
Fluid Phase Equilib.
(2018) - et al.
Vapour pressures and vaporization enthalpies of 5-nonanone, linalool and 6-methyl-5-hepten-2-one. Data evaluation
Fluid Phase Equilib. 386
(2015) - et al.
Vapour pressures and heat capacity measurements on the C7–C9 secondary aliphatic alcohols
J. Chem. Thermodyn.
(2007) - et al.
Phase equilibria and the thermodynamic properties of methyl and ethyl esters of carboxylic acids. 1. Methyl n-butanoate and ethyl propanoate
J. Chem. Thermodyn.
(2012) - et al.
Vapour pressure and thermal stability of ionic liquid 1-butyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)amide
Thermochim. Acta
(2005) - et al.
On the difference between isobaric and isochoric heat capacities of liquid cyclohexyl esters
J. Mol. Liq.
(2004)
Naphthalene as a reference substance for vapour pressure measurements looked upon from an unconventional point of view
J. Chem. Thermodyn.
Representation and assessment of vapour pressure data; a novel approach applied to crystalline 1-bromo-4-chlorobenzene, 1-chloro-4-iodobenzene, and 1-bromo-4-iodobenzene
J. Chem. Thermodyn.
Benchmark properties of diphenyl oxide as a potential liquid organic hydrogen carrier: Evaluation of thermochemical data with complementary experimental and computational methods
J. Chem. Thermodyn.
Isothermal vapour-liquid equilibria and excess molar volumes in the binary ethanol + methyl propanoate or methyl butanoate systems
Fluid Phase Equilib.
Excess thermodynamics functions of 1-propanol + methyl propanoate and 1-propanol + methyl butanoate systems
Fluid Phase Equilib.
Liquid–vapour equilibria of the methyl esters of alkanoic acids: vapour pressures as a function of temperature and standard thermodynamic function changes
Fluid Phase Equilib.
Experimental vapour pressures (from 1 Pa to 100 kPa) of six saturated Fatty Acid Methyl Esters (FAMEs): Methyl hexanoate, methyl octanoate, methyl decanoate, methyl dodecanoate, methyl tetradecanoate and methyl hexadecanoate
J. Chem. Thermodyn.
Vapour pressure measurements and prediction for heavy esters
J. Chem. Thermodyn.
Vapour pressure measurements on saturated biodiesel fuel esters by the concatenated gas saturation method
Fuel
PVT, saturated liquid density and vapour-pressure measurements of main components of the biofuels at high temperatures and high pressures: Methyl palmitate
Fuel
The vaporization enthalpies and vapour pressures of fatty acid methyl esters C18, C21 to C23, and C25 to C29 by correlation – gas chromatography
Thermochim. Acta
Express thermo-gravimetric method for the vaporization enthalpies appraisal for very low volatile molecular and ionic compounds
Thermochim. Acta
The vaporization enthalpies and vapour pressures of a series of unsaturated fatty acid methyl esters by correlation gas chromatography
Thermochim. Acta
Enthalpies of vaporization at 298.15 K for some 2-alkanones and methyl alkanoates
J. Chem. Thermodyn.
Enthalpies of vaporization of some 1-substituted n-alkanes
J. Chem. Thermodyn.
Enthalpies of vaporization of a series of aliphatic alcohols: Experimental results and values predicted by the ERAS-model
Fluid Phase Equilib.
Thermochemistry of 1-alkylimidazoles
J. Chem. Thermodyn.
Building blocks for ionic liquids: vapour pressures and vaporization enthalpies of 1-(n-alkyl)-imidazoles
J. Chem. Thermodyn.
Vapour pressures and enthalpies of vaporization of a series of the linear aliphatic nitriles
J. Chem. Thermodyn.
Vapour pressures and enthalpies of vaporization of a series of the linear n-alkyl-benzenes
J. Chem. Thermodyn.
Vaporization thermodynamics of ionic liquids with tetraalkylphosphonium cations
J. Chem. Thermodyn.
The accurate measurement of heats of vaporization of liquids
J. Am. Chem. Soc.
Vapour pressure and vapour-liquid equilibrium data for methyl esters of the common saturated normal fatty acids
J. Chem. Eng. Data
Estimation of the thermodynamic properties of C-H-N-O-S-halogen compounds at 298.15 K
J. Phys. Chem. Ref. Data
Heat capacity corrections to a standard state: a comparison of new and some literature methods for organic liquids and solids
Struct. Chem.
Heat capacity of room-temperature ionic liquids: a critical review
J. Phys. Chem. Ref. Data
Heat Capacities
Phase transition enthalpy measurements of organic and organometallic compounds. Sublimation, vaporization and fusion enthalpies from 1880 to 2015. Part 1. C1−C10
J. Phys. Chem. Ref. Data
Heats of vaporization of alkyl acetates and propionates
Collect. Czechoslov. Chem. Commun.
Enthalpies of vaporization of organic and organometallic compounds, 1880–2002
J. Phys. Chem. Ref. Data
Enthalpies of sublimation of organic and organometallic compounds. 1910–2001
J. Phys. Chem. Ref. Data
Structure-property relationships in ILs: A study of the alkyl chain length dependence in vapourisation enthalpies of pyridinium based ionic liquids
Sci. China Chem.
Making sense of enthalpy of vaporization trends for ionic liquids: new experimental and simulation data show a simple linear relationship and help reconcile previous data
J. Phys. Chem. B
Temperature and pressure dependence of the viscosity of the ionic liquids 1-hexyl-3-methylimidazolium hexafluorophosphate and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide
J. Chem. Eng. Data
Pressure dependence of the density of n-alkanes
Int. J. Thermophys.
Density, viscosity, speed of sound, and electrolytic conductivity for the ionic liquid 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide and its mixtures with water
J. Chem. Eng. Data
Evaluation of thermodynamic functions from equilibrium constants
Trans. Faraday Soc.
Cited by (34)
The vaporization enthalpies and vapor pressures of Vescepa® and related unsaturated marine FAME by correlation gas chromatography
2023, Chemical Thermodynamics and Thermal AnalysisExperimental and computational thermochemistry of methyl hydroxybenzoates revisited
2023, Journal of Chemical ThermodynamicsCompensation relationship in thermodynamics of solvation and vaporization: Features and applications. I. Non-hydrogen-bonded systems
2022, Journal of Molecular LiquidsCitation Excerpt :The solvation enthalpies in various solvents were available from Refs. [50–63]. The ΔlgG° and ΔlgH° values were derived from the original experimental articles on the vapor pressure measurement, as well as compilations and critical reviews [2,64–75]. ΔlgH° of aromatic/heteroaromatic compounds were obtained according to Ref. [10] from the calculated solvation enthalpies in benzene, while those of alkanes and alkenes were derived from the calculated solvation enthalpies in heptane [11] according to Eq. (2).
Biofuels energetics: Reconciliation of calorific values of fatty acids methyl esters with help of complementary measurements and structure–property relationships
2022, FuelCitation Excerpt :There we showed that TGA can provide reliable data, especially for low-volatility molecules such as long-chain aliphatic carboxylic acid esters. The findings from these two works have motivated the gathering of experience with the TGA measurement on FAMEs, for which the recommended enthalpies of vaporisation are already established [24]. This experience is valuable for the further development of the TGA method as an express method for measuring the vaporisation enthalpies.
Comprehensive thermodynamic study of alkyl-biphenyls as a promising liquid organic hydrogen carriers
2022, Journal of Chemical Thermodynamics