Physical and excess properties of binary and ternary mixtures of 1,1-dimethylethoxy-butane, methanol, ethanol and water at 298.15 K
Introduction
This paper completes a study on thermophysical properties of alcohol and ether mixtures used as octane-enhancing components in gasoline. On previous works [1], [2], [3], [4], physical and other thermodynamic properties of binary and ternary systems containing tertiary ethers, such as MTBE or TAEE, with methanol or ethanol, and with water have been published. All these ternary mixtures show a large heterogeneous region due to the immiscibility between the ethers and the water.
In this work, densities (ρ), refractive indices (nD), speeds of sound (u) and isentropic compressibilities (κs) are reported for complete miscible mixtures of the ternary systems 1,1-dimethylethoxy-butane (butyl tert-butyl ether or BTBE) + methanol + water and BTBE + ethanol + water, and for methanol + BTBE and ethanol + BTBE binary systems at 298.15 K. The results for excess molar volumes (VE) and molar refraction (ΔR) and isentropic compressibility (Δκs) changes of mixing, calculated from the measured properties and correlated with composition data using the Redlich–Kister [5] polynomial, are also reported. No comparable data were found in the surveyed literature for the binary or ternary systems studied in this work.
Section snippets
Materials
BTBE was supplied by Yarsintez (Yaroslav, Russia) with nominal purity >99.9 mass%. Methanol and ethanol were supplied by Merck (Madrid, Spain) and had a nominal purity >99.5 mass%. Water is purified using a Mili-Q Plus system. The water contents of BTBE was 0.1 mass%, and for methanol and ethanol were 0.05 and 0.04 mass%, respectively, determined with a Metrohm 737 KF coulometer. Information about pure components, i.e. experimental densities, refractive indices at 298.15 K, along with values
Results
The experimental values of densities (ρ), speeds of sound (u) and refractive indices (nD) for the binary and ternary mixtures of BTBE + methanol + water and BTBE + ethanol + water are listed in Supplementary data. This appendix also includes the values calculated for isentropic compressibility (κs), excess molar volumes (VE) and molar refraction (ΔR) and in isentropic compressibility (Δκs) changes of mixing. Corresponding data for water + methanol and water + ethanol binary systems were reported in
Data reduction
The VE, ΔR and Δκs calculated are correlated with composition data by means of the Redlich–Kister [5] polynomial, which for binary mixtures takes the shape:where Qij is VE or ΔR and xi is the mole fraction of component i, or Qij is Δκs, being xi the volume fraction of component i. Ak is the polynomial coefficient, and k is the number of the polynomial coefficient. For the ternary systems, the resulting equation as a function of the compositions, xi (in mole or volume
Conclusions
At 298.15 K and atmospheric pressure, for binary system methanol + BTBE, excess molar volumes are negative with a minimum of about −0.56 cm3 mol−1 at 0.61 in mole fraction of BTBE, for the binary ethanol + BTBE, a minimum value of −0.40 cm3 mol−1 is found at 0.60 in mole fraction of BTBE. The values of isentropic compressibility changes of mixing are relatively small and very similar for both binaries, these values are always negative and they did not exceed −7 or −6 TPa−1 for systems with methanol and
Acknowledgement
The authors are grateful to the Ministerio de Ciencia y Tecnología (Spain) for financial support under project PPQ2003-01236.
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