Elsevier

Fluid Phase Equilibria

Volume 414, 25 April 2016, Pages 55-59
Fluid Phase Equilibria

Capillary constant and surface tension of dimethyl ether and n-butane at temperatures from 214 K to those close to the critical point

https://doi.org/10.1016/j.fluid.2016.01.001Get rights and content

Abstract

The capillary constant a2 has been measured by the differential capillary-rise technique and the surface tension σ of dimethyl ether and n-butane has been determined with the use of data on the densities of saturated liquid and gas. The experiments with dimethyl ether were performed at temperatures from 214 K to 390 K, for n-butane – from 278.15 K to 423.04 K. Equations that approximate the temperature dependences of a2 and σ have been suggested.

Introduction

In recent years, dimethyl ether and n-butane have been widely used in motor transport as fuels. Due to its high cetane number, lowered liability to soot formation during combustion, and almost no smoking at the exhaust, ether is regarded as an alternative to the traditional diesel fuel in future [1]. The boiling point of normal butane is higher than that for liquefied natural gas, so it is used in motor transport and household applications in mixture with propane and other hydrocarbons. As raw materials, dimethyl ether and n-butane are used in the processes of catalytic cracking and pyrolysis, in the manufacture of high – octane petrol and the production of synthetic rubber, and as propellants in deodorants, aerosol spray–on paints, etc.

For practical applications of dimethyl ether and n-butane reliable data on their physicochemical properties, in particular, on their surface tension are required. These data are necessary for studies of the character of fuel spray, boiling, condensation, and capillary phenomena.

This paper presents the results of our measurements of the capillary constant а2 and calculations of the surface tension σ of dimethyl ether at temperatures from 214 K, and those of n-butane from 278.15 K to temperatures near their critical points. All in all, 35 values of the capillary constant for dimethyl ether and 40 values of а2 for n-butane have been obtained. The surface tension of dimethyl ether was measured before by Maas and Boomer [2] (15 points, 231–263 К), Winkler and Maas [3] (6 points, 375.65–398.15 К), Soares et al. [4] (10 points, 131.7–139.1 К), Wu et al. [5] (31 points, 213–368 К). Experiments with n-butane were conducted before by Coffin and Maas [6] (19 points, 138.75–305.65 K), Reno and Katz [7] (1 point, 298.15 K), Katz and Saltman [8] (14 points, 275.2–318.5 K), Calado, McLure and Soares [9] (6 points, 238.0–273.3 K). The surface tensions of dimethyl ether [10] and n-butane [11] were measured before in our laboratory from the triple point temperature to 214 and 282.27 K, correspondingly.

Section snippets

Materials

A sample of dimethyl ether (methoxymethane, RE170, C2H6O, M = 46.0684 g/mol) was provided by Sigma–Aldrich (Germany), and a sample of n-butane (methylethylmethane, C4H10, M = 58.1222 g/mol) by VNIIGAZ (Russia). Details of the samples are presented in Table 1. In the experiments, use was made of substances from the same lots on which measurements of σ at low temperatures were previously conducted.

Apparatus and technique

The surface tension of dimethyl ether and n-butane was measured by the differential capillary-rise

Results

The surface tension of dimethyl ether was measured along the liquid–gas equilibrium coexistence curve in the temperature range 214–390, for n-butane – in the temperature range 278.15–423.04 K. The average values of a2 for 5–10 measurements of Δhij are listed in Table 2. In addition, the values of ρl and ρg from Ref. [19] [20], used in calculations of the surface tension are presented.

In the range from the triple to the critical point the temperature dependence of the capillary constant a2 was

Conclusion

Thus, in the present work and in our earlier work [10], [11] experimental data on the surface tension of dimethyl ether and n-butane were obtained with uniform measuring tools in the temperature range from the triple point to temperatures near the critical point.

All in all, the temperature range investigated with the exception of near-critical values of the uncertainty of the data obtained does not exceed 0.010 mN/m.

Within this error the result of measuring the surface tension of dimethyl ether

Acknowledgements

This study was financially supported by the Russian Foundation for Basic Research (project no. 15-08-03399-a), the complex program of basic research of the Ural Branch of the Russian Academy of Science (project no. 15-1-2-6) in the case of dimethyl ether. Measurements of the surface tension of n-butane were conducted in the framework of project no. 14-19-00567 of the Russian Scientific Foundation.

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