Phase equilibria and the thermodynamic properties of methyl and ethyl esters of carboxylic acids. 1. Methyl n-butanoate and ethyl propanoate

doi:10.1016/j.jct.2011.10.001

The Journal of Chemical Thermodynamics

Volume 47, April 2012, Pages 120-129

https://doi.org/10.1016/j.jct.2011.10.001 Get rights and content

Abstract

The heat capacity of methyl n-butanoate in crystalline and liquid states was measured by vacuum adiabatic calorimetry over the temperature range from (8 to 372) K. The triple point temperature, the enthalpy and entropy of fusion, and the purity of the sample were determined. The saturated vapour pressure and the boiling temperatures were determined by comparative ebulliometry in the “atmospheric” pressure range 10.8 ⩽ (p/kPa) ⩽ 99.6. The normal boiling temperature, T_n.b, and the enthalpy of vaporization at T = 298.15 K and T_n.b were derived. The thermodynamic functions (absolute entropy and changes of the enthalpy, and Gibbs free energy) were derived for the solid and liquid states in the temperature range studied and for the ideal gas state at T = 298.15 K. The ideal gas heat capacities and the absolute entropies of methyl n-butanoate (MeBu) and ethyl propanoate (EtPr) were calculated by statistical thermodynamics on the basis of the molecular constants determined by the use of density functional theory on the B3LYP level. The experimental vapour pressure of MeBu and EtPr [1] of moderate temperature intervals, Δ_expT = (59/65) K, were extended to the entire range of the liquids, Δ_liqT = (364.7/345.7) K by the methods of the corresponding states law and simultaneous treatment of the pT-parameters and low-temperature heat capacities of the ideal gas and liquid, respectively. An additive contribution of the carbonyl group CO–(C, O) connected with C and O atoms was determined for calculation of the absolute molar entropies at T = 298.15 K, $S_{m}^{0} (g) (298 K)$ , by additive Benson’s scheme.

Highlights

► Heat capacities, fusion properties of CH₃OC(O)C₃H₇ measured by adiabatic calorimetry. ► The temperature dependence of vapour pressure determined by comparative ebulliometry. ► The thermodynamic functions derived from experiment and calculated by DFT method. ► Extending vapour pressure of moderate interval to entire region of liquid. ► An increment of the entropy of carbonyl group was defined from experimental data.

Introduction

Biofuels provide alternative, renewable fuels for the motor cars. They are ecologically more acceptable than conventional fuels and also save significantly the fossil sources of the energy. Experimental study of the key thermodynamic properties of the biofuels is a very difficult task, as they are complex, largely in volatile mixtures of methyl and ethyl esters of fatty acids, C₁₈. Therefore, we start to explore some properties of main components of biofuels by experimental and calculation methods, including statistical thermodynamics coupled with density functional theory (DFT) on the B3LYP level, and additive principle. The capabilities of these methods was tested by studying the esters of the lower carboxylic acids C₃–C₄: namely ethyl propanoate (C₂H₅OC(O)C₂H₅, CAS:105-37-3) and methyl n-butanoate (CH₃OC(O)C₃H₇, CAS:623-42-7), for which some literature data on thermodynamic properties are available [2]. There are heat capacities at T = 298.15 K [3], [4], enthalpies of combustion and formation [2], [5], the saturation vapour pressures within the narrow temperature intervals 9 ⩾ (ΔT/K) ⩽ 43 [6], [7], [8], [9], the normal boiling temperature, T_n.b, the enthalpy of vaporization at T = 298.15 K and T_n.b [7], [8], [9], [10], [11] and the critical P_c and T_c parameters [2], [12]. Stull tabulated the saturation vapour pressures of MeBu [13], compiled from the pT-data of different authors over the temperature ranges from (246.3 to 545) K with accuracy 0.1 K. These data were approximated by NIST with Antoine equations [2]. A lack of reliable values on the low-temperature heat capacity makes it impossible to obtain the main thermodynamic functions ( $S_{m}^{0}, Δ_{0}^{T} H_{m}$ and $- {G_{m}^{0} (T) - H_{m}^{0} (0)}$ ) in crystal and liquid states, which are of interest for the science and technology.

In our previous papers [1], [14], thermodynamic properties of the ethyl esters of carboxylic acids C₃–C₅ were presented. The low-temperature heat capacities, the saturation vapour pressures, and the main thermodynamic functions of ethyl propanoate, ethyl n-butanoate, and ethyl n-pentanoate in three aggregate states were determined. On the basis of these data, the vapour pressures of the moderate pressure interval were extended to entire range of liquids from triple to critical points.

This work is a continuation of the exploration started in [1], [14] and deals with determination of the thermodynamic properties of the methyl ester of n-butanoic acid over the wide temperature region from 5 K to the critical temperature. The ideal gas absolute entropies of ethyl esters of carboxylic acids C₃–C₅ were employed for calculation of a contribution of the CO–(C, O) group, needed for calculation of the $S_{m}^{0}$ (g) values by the additive scheme of Benson. The additive $Δ C_{p,m}^{\circ} (g)$ values of the CH₃OC(O)CH₂- and C₂H₅OC(O)CH₂-groups at different temperatures, obtained on the basis of real gas heat capacities of methyl acetate and ethyl acetate [15], were used for computing the $C_{p,m}^{\circ} (g) = F (T)$ dependences for MeBu and EtPr. These $Δ C_{p,m}^{\circ} (g)$ group additivity values will be also used for calculation of appropriate dependences for same esters of the fatty acids, C₁₈, in our second paper of this series. The ideal gas heat capacities of MeBu at low temperatures are used in this work for a combined treatment with the pT-parameter for extending the vapour pressure of the esters to their triple point temperatures.

Section snippets

Experimental

The commercial sample of methyl n-butanoate of Acros Company had a certificate of mole fraction purity > 0.99. The total mole fraction of impurities, N₂ = 0.0035, was determined by calorimetric fractional melting study as described in [16]. A content of the impurities was analysed by gas chromatography and mass spectrometry (GC–MS) using a Pegasus IV D time-of-flight mass-spectrometer (Leco, USA). For gas chromatography, a DB-5MS capillary silicon column was used, with a length of 30 m, a diameter

Comparison of thermodynamic properties with literature data

The molar heat capacity of liquid MeBu at T = 298.15 K, obtained in this work, agrees within error with appropriate value of reference [3], that justifies their reliability. A relative deviation of C_p_,m (l)(298.15)/R = 24.151 value of reference [4] from our heat capacity (table 3) equals 1.4%, that is beyond the experimental errors.

Verification of available vapour pressures of MeBu were carried out by comparing s_p = (p_calc − p_exp) differences between experimental p values and calculated by equation (7).

Prediction of the vapour pressures for entire range of liquids

Extending the vapour pressure of methyl n-butanoate towards the triple point, T_tp = (190.10 ± 0.01) K, was conducted by simultaneous mathematical processing of the pT parameters and low-temperature differences of the heat capacities of the ideal gas, $C_{p,m}^{\circ} (g)$ , and liquid, С_р_,m(l), using a system of equations: $\ln (p / 〈 p 〉) = A^{'} + B^{'} / T + C^{'} \ln T + D^{'} \cdot T,$ $(Δ C_{p,m} / 2) / R = (1 / 2) \cdot [C_{p,m}^{\circ} (g) - C_{p,m} (l)] / R = C^{'} / 2 + D^{'} \cdot T .$ Here 〈p〉 denotes the pressure at the mean temperature 〈T〉 of the experimental pT-interval (table 3) and A′, B′, C′,

Conclusions

The phase equilibria and thermodynamic properties of methyl n-butanoate (MeBu) were investigated by experimental and calculation methods over wide temperature region from 8 K to critical temperature, Т_сr = 554.5 K. The heat capacity was measured by adiabatic calorimetry within the temperature region from (8 to 372) K with accuracy on the average 0.2%. The saturation vapour pressure and the boiling temperatures were determined by comparative ebulliometry for moderate pressure and temperature

Acknowledgement

This work was financially supported by Russian Foundation for Basic Research (Project No.10-08-00605а).

We are grateful to professor Olga. V. Dorofeeva for providing Gaussian programs and assistants in quantum-chemical calculations of ideal gas thermodynamic functions.

References (38)

R. Fuchs
J. Chem. Thermodyn.
(1979)
Aad C.G. van Genderen et al.
Fluid Phase Equilib.
(2002)
S.P. Verevkin et al.
Fluid Phase Equilib.
(2008)
D. Constantinescu et al.
Fluid Phase Equilib.
(2002)
S. Sunner et al.
J. Chem. Thermodyn.
(1979)
J.E. Connett et al.
J. Chem. Thermodyn.
(1976)
R.M. Varushchenko et al.
J. Chem. Thermodyn.
(1997)
R.M. Varushchenko et al.
Fluid Phase Equilibria
(2002)
R.M. Varushchenko et al.
J. Chem. Thermodyn.
(2001)
M. Мansson
J. Chem. Thermodyn.
(1972)

L.E. Agafonova et al.

Zh. Fiz. Khim.

(2011)

...

M. Pintos et al.

Can. J. Chem.

(1988)

E. Schjanberg

Z. Phys. Chem. Abt. A.

(1935)

J. Ortega et al.

J Chem. Eng. Data

(1990)

V. Majer, V. Svoboda, Enthalpies of Vaporization of Organic Compounds: A Critical Review and Data Compilation, Oxford,...

S. Young

Sci. Proc. R. Dublin Soc.

(1910)

D.R. Stull

Ind. Eng. Chem.

(1947)

L.E. Agafonova et al.

Moscow Univ. Chem. Bull.

(2010)

Cited by (9)

Vaporization/sublimation enthalpies of mono- and dimethyl-esters estimated by solution calorimetry method
2020, Thermochimica Acta
The additive scheme for calculating the solvation enthalpies of aliphatic compounds has been developed for linear mono- and dimethyl-esters. Ester group contribution to the enthalpy of solvation in n-heptane was obtained. Accuracy of the proposed approach for determination of solvation enthalpies of linear mono- and dimethyl-esters was tested by comparison with experimental solvation enthalpies. In most cases, deviations do not exceed 1 kJ·mol⁻¹.
It was found that the dependence of the solution enthalpies of mono- and dimethyl-esters on the number of carbon atoms in the molecule can be fitted by power function. This dependence and a group-additivity scheme for solvation enthalpy were used for estimation of the enthalpies of phase transitions of mono- and dimethyl-esters. Evaluated values of sublimation, vaporization, and fusion enthalpies at 298.15 K are in good agreement with experimental data obtained by conventional methods.
Fatty acids methyl esters: Complementary measurements and comprehensive analysis of vaporization thermodynamics
2019, Journal of Chemical Thermodynamics
Vapour pressures of methyl decanoate, methyl undecanoate, methyl tetradecanoate, methyl hexadecanoate and methyl octadecanoate were measured by using the static technique. Vapour pressures of methyl dodecanoate, methyl tridecanoate, methyl tetradecanoate, methyl heptadecanoate, and methyl octadecanoate were measured by using the transpiration method. In the present work, vapour pressures of methyl esters of the saturated fatty acids from methyl propanoate to methyl eicosanoate were collected from the literature. These data together with own complementary results were used for validation of methods for assessment of the difference $Δ_{l}^{g} C_{p, m}^{o}$ required for the correct adjustment of vaporization enthalpies to the reference temperature 298.15 K. The evaluated vaporization enthalpies for esters from methyl propanoate to methyl eicosanoate demonstrate impeccable linear chain-length dependence. The CH₂ group contributions for different homologous series were derived and compared. Quantitative analysis of dispersion interactions in the long-chained esters have been performed.
Heat capacities and thermal diffusivities of some n-alkanoic acid methyl esters
2019, Journal of Chemical Thermodynamics
The heat capacities and thermal diffusivities of n-alkanoic acid methyl esters C_nH_2n−1O₂CH₃ with n from 6 to 12 have been measured. The heat capacities have been measured in the temperature range from 303.15 K to 373.15 K; the measurements of thermal diffusivity have been carried out for a given methyl ester from 303.15 K to the temperature at which a noticeable evaporation of the ester took place. The temperature dependencies of the heat capacities and thermal diffusivities have been approximated by a third-order and a first-order polynomial, respectively. It has been shown that the dependence of the molar heat capacity on n (n = 1–14) at a temperature of 298.15 K is close to linear.
A group contribution model for determining the vaporization enthalpy of organic compounds at the standard reference temperature of 298K
2013, Fluid Phase Equilibria
Citation Excerpt :
The data compilation collected by Acree and Chickos [1] was used to provided the main database of vaporization enthalpy at the standard temperature of 298.15 K. The data compilation was supplemented with recently published enthalpies of vaporization taken from the chemical literature [64–156]. The database consists of 4320 experimental data points for 2811 compounds.
The vaporization enthalpy is regarded as a measure of molecular interactions in the vapor/liquid phase. It has a number of applications in chemical and petrochemical processes in which vapor–liquid equilibrium exists. Acree and Chickos [1], recently published a comprehensive compilation of phase change enthalpies, including vaporization enthalpies of pure organic compounds. This collection of vaporization enthalpies for 2811 compounds at the standard temperature of 298.15 K was used in this study for the development of a predictive model. The compounds in the collection are composed of a combination of the following atoms, viz. carbon, hydrogen, nitrogen, oxygen, phosphorous, sulfur, fluorine, chlorine, bromine, and iodine. This paper presents a reliable group contribution model for the prediction of the vaporization enthalpies of organic compounds. The group contribution model developed is able to predict the standard molar enthalpies of vaporization to within an average absolute relative deviation of 3.7%, which is of sufficient accuracy for many practical applications in chemical and petrochemical engineering.
Quantification of Dipolar Contribution and Modeling of Green Polar Fluids with the Polar Cubic-Plus-Association Equation of State
2021, ACS Sustainable Chemistry and Engineering
Anharmonic Effect in CH<inf>3</inf>CH<inf>2</inf>C(=O)OCH<inf>2</inf>CH<inf>3</inf> Decomposition
2017, Russian Journal of Physical Chemistry A

View all citing articles on Scopus

View full text

Phase equilibria and the thermodynamic properties of methyl and ethyl esters of carboxylic acids. 1. Methyl n-butanoate and ethyl propanoate

Abstract

Highlights

Introduction

Section snippets

Experimental

Comparison of thermodynamic properties with literature data

Prediction of the vapour pressures for entire range of liquids

Conclusions

Acknowledgement

J. Chem. Thermodyn.

Fluid Phase Equilib.

Fluid Phase Equilib.

Fluid Phase Equilib.

J. Chem. Thermodyn.

J. Chem. Thermodyn.

J. Chem. Thermodyn.

Fluid Phase Equilibria

J. Chem. Thermodyn.

J. Chem. Thermodyn.

Zh. Fiz. Khim.

Can. J. Chem.

Z. Phys. Chem. Abt. A.

J Chem. Eng. Data

Sci. Proc. R. Dublin Soc.

Ind. Eng. Chem.

Moscow Univ. Chem. Bull.