Wide-ranging densimetry of the compressed-liquid binary system ethanol + 2,2,4-trimethylpentane

S. Outcalt1, A. Laesecke1 and E. Lemmon1

1National Institute of Standards and Technology, Materials Measurement Laboratory, Thermophysical Properties Division, USA

Keywords: compressed-liquid, density, ethanol, 2,2,4-trimethylpentane
property: density
material: ethanol + 2,2,4-trimethylpentane (iso-octane)

The transition from petroleum-derived hydrocarbon fuels to biofuels poses considerable challenges for the fuels industry because it involves blends of nonpolar hydrocarbons with highly polar compounds such as alcohols, esters, and possibly heterocyclic compounds. It is well-known that mixtures of compounds of different molecular size, shape, and polarity are most challenging for property science because the complexity of their molecular interactions exceeds the capabilities of even of state-of-the-art models.

Even with our automated densimeter it is prohibitively time-consuming to characterize every actual fuel blend with wide-ranging measurements. Therefore, experimental studies need to focus on model systems that give the greatest insight into the molecular interactions while being closely related to actual fuel blends. The system of ethanol and 2,2,4-trimethylpentane (iso-octane) was chosen because it is a model for gasoline blends with ethanol which are increasingly used in internal combustion engines to mitigate global warming.

Density measurements of three compositions of the compressed-liquid ethanol blend were carried out in the temperature range from 270 K to 470 K with pressures to 50 MPa. Characterization over wide temperature ranges is particularly important for polar compounds because the contributions to their properties due to molecular size and shape and due to polarity can be resolved. Our measurement results are currently the only available data for this binary system at pressures above ambient. The data will be reported and compared to ambient pressure data in the literature. Our data formed the basis to develop new interaction parameters for an equation of state model for this binary system resulting in increased accuracy of the model over a larger range of temperature and pressure. The representation of our data by the equation of state model and its extrapolation capability will be discussed.

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