Measurement and correlation of density and viscosity of n-hexadecane with three fatty acid ethyl esters
Introduction
Biodiesels consist of mixtures of alkyl esters of fatty acid (typically methyl or ethyl) obtained by a transesterification reaction where a vegetable oil or an animal fat is combined with a short chain alcohol such as methanol or ethanol [1]. Biodiesel has a high cetane number, wherefrom reduced solid particle and hydrocarbons emissions. It is, therefore, considered as a renewable and environmental friendly alternative diesel fuel for diesel engine. In the last few years, researchers have made effort to establish novel approaches to improve the production or purification of biodiesels [2], [3], [4]. In addition, to study the thermophysical properties of fatty esters or biodiesels have attracted more and more attention [5], [6], [7], [8].
Due to the complete miscibility of biodiesel with diesel oil, the blending of both fuels in any proportion may improve fuel qualities and engine performance [9]. The knowledge of the thermodynamics and transport properties of the mixtures of biodiesel + diesel oil is essential to optimize the diesel engine. Density and viscosity are the most important properties of a fuel, influencing especially the injection system, atomization quality and combustion quality. Several investigations on the density and viscosity of biodiesel + diesel oil mixtures have been reported in the literature [10], [11], [12], [13]. As biodiesels and diesel oils are all multi-component mixtures, changes in compounds profile affect their densities and viscosities. The knowledge of the properties of the pure compounds or its mixtures enables the prediction of the properties of biodiesel + diesel oil mixtures. To the best of our knowledge, the density and viscosity of n-hexadecane (a reference molecule for modeling diesel oil thermodynamics properties) with pure fatty acid ethyl esters (for example, ethyl caprylate, ethyl caprate, or ethyl laurate) have not been reported in the literature. In this work, the density and viscosity of binary mixtures of n-hexadecane with ethyl caprylate, ethyl caprate, and ethyl laurate at temperatures from 298.15 to 323.15 K over the entire composition range were reported, and the excess molar volumes and viscosity deviations were obtained.
Section snippets
Samples
n-Hexadecane (CH3(CH2)14CH3), ethyl caprylate (CH3(CH2)6COOCH2CH3), ethyl caprate (CH3(CH2)8COOCH2CH3), and ethyl laurate (CH3(CH2)10COOCH2CH3) were supplied by Aladdin Chemistry and the mass purity was better than 99%. All samples were used without further purification. Table 1 shows the sample descriptions used in the present work. The densities and viscosities of the pure components were measured and compared to the literatures [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24]
Results and discussion
The experimental density and viscosity results of the binary mixtures n-hexadecane with ethyl caprylate, ethyl caprate, and ethyl laurate over the temperature range from 298.15 to 323.15 K at atmospheric pressure are listed in TABLE 3, TABLE 4, respectively.
The excess molar volume VE can be obtained from experimental density data according to the following equation:where xi, Mi, and ρi are the mole fraction, molar mass, and density of the pure component i, respectively. ρ is
Viscosity correlation
In this work, the rough hard-sphere theory, proposed by Chandler [31], was used to correlate the viscosity of the studied binary mixtures. The rough hard sphere expressions for the reduced viscosity () as functions of the reduced molar volume are as follows [32], [33], [34]:
The reduced viscosity is defined aswhere M is the molar mass, R is the gas constant, T
Conclusion
New experimental data for densities and viscosities of binary mixtures of n-hexadecane with ethyl caprylate, ethyl caprate, and ethyl laurate were reported at temperatures ranging from 298.15 to 323.15 K at atmospheric pressure. Results show that, for the studied systems, the excess molar volumes are positive for all the compositions at different temperatures. However, the deviations in viscosity are negative and show larger negative values with decreased temperature in every case. In addition,
Acknowledgment
The authors are grateful to acknowledge financial support for the work by National Natural Science Foundation of China (Grant No. 51476129).
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