Characterizing second generation biofuels: Excess enthalpies and vapour-liquid equilibria of the binary mixtures containing 1-pentanol or 2-pentanol and n-hexane
Introduction
Energy policies in the European Union focus on the promotion of the use of biofuels, as is established in Directive «20-20-20» [1], which determines a minimum content of 10% of biofuels overall gasoline and diesel fuels.
Properties of these new biofuels change in comparison with fossil fuels, therefore a characterization of these properties is required in order to enhance their use. In this sense, our research group is involved in the measurement of thermodynamic and thermophysical properties, such as density, viscosity, heat capacity, excess enthalpy or vapour-liquid equilibria, of mixtures of interest for the formulation of biofuels.
In this paper, 1-pentanol and 2-pentanol are studied as oxygenated additives of renewable origin due to their qualities such as high octane rating or high combustion heat, and n-hexane was chosen as hydrocarbon. Excess enthalpies and vapour-liquid equilibria of the mixtures (1-pentanol + n-hexane) and (2-pentanol + n-hexane) are reported.
Section snippets
Materials
1-Pentanol, 2-pentanol and n-hexane were chromatography quality reagents of the highest purity available from Sigma-Aldrich. Their purities were >0.997 (GC), >0.98 (GC) and >0.99 (GC), respectively and were also checked by gas chromatography being better than 0.997. The details are summarized in Table 1.
Experimental techniques
Both techniques, used in this work, were described in detail in previous papers [2], [3] and a brief summary of their main characteristics is reported below.
A quasi-isothermal flow calorimeter,
Results
Excess enthalpies were measured at T= (298.15 and 313.15) K for the binary mixtures (1-pentanol + n-hexane) and (2-pentanol + n-hexane). These data, reported in Table 2 and in Fig. 1, were correlated using a modified Redlich-Kister [4] equation:
The parameters of equation (1) and the standard deviations are given in Table 3. The optimal number of parameters was selected by examining F-test [5].
As regards the use of a static technique for measuring VLE,
Discussion and conclusions
The study of the energy behavior of these mixtures shows that both systems have a strong endothermic effect due to the mixing process which increases with temperature. The highest excess enthalpies are 724 J mol−1 for the system with 1-pentanol at an alcohol mole fraction of 0.35and 1033 J mol−1 for a mole fraction of 2-pentanol of 0.40, both at 313.15 K. The maximum values decreases to 528 J mol−1 and 849 J mol−1 at 298.15 K and mole fractions of 0.35 and 0.45 for 1-pentanol and 2-pentanol,
Acknowledgments
The authors are grateful for financial support from the Spanish Minister de Science and Innovation (MICINN) for Project ENE2009-14644-C02-01 and the Project VA391A12-1 of the Junta de Castilla y León. Alejandro Moreau thanks the support from European Social Fund (ESF) and from Consejería de Educación de la Junta de Castilla y León.
List of symbols
- Ai
- adjustable parameters of Redlich-Kister equation, Eq. (1)
- Aij, Aji
- adjustable parameters of the VLE correlation models, Eqs. (2), (3), (4), (5)
- Bii, Bij, Bjj
- second virial coefficients
- C
- adjustable parameter of Redlich-Kister equation, Eq. (1)
- GmE
- excess molar Gibbs energy
- HmE
- excess molar enthalpy
- i,j
- constituent identification: 1 or 2
- lit.
- literature value
- max
- maximum value of the indicated quantity
- P
- total pressure
- Pis
- vapour pressure of pure constituent i
- R
- universal gas constant
- rms
- root mean square
- SmE
- excess
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