(695a) Density and Speed of Sound Measurements of Second-Generation Biofuels

While the conversion of biomass into ethanol is one of the oldest chemical processes, ethanol has never been optimized as a fuel for transportation but rather as a beverage. Its properties are too different from those of petroleum-based hydrocarbon fuels such as gasoline to be a feasible long-term replacement of the latter. The isomers of butanol (C4H9OH) are much more similar to conventional gasoline but their properties are much less known than those of either ethanol or hydrocarbons. To facilitate their use as fuels, measurements of their thermophysical properties have been started in our laboratory. Results of density and speed of sound measurements for 1- and 2-butanol will be reported in this presentation.

Thoroughly dried samples of the two alcohols were prepared with molecular sieves and confirmed by Karl-Fischer titration. A rapid characterization instrument was used for density and speed of sound measurements at ambient pressure from 278.15 K to 343.15 K. Compressed-liquid densities were measured from 270 K to 470 K at pressures from 0.5 MPa to 50 MPa with a fully automated vibrating-tube densimeter. The calibration and adjustment of the instruments will be discussed in detail because they were extended beyond existing standards.

The density results were correlated by Tait equations for comparisons with literature data. Density data for 1-butanol are available in the literature over the temperature and pressure range of the current measurements. However, they scatter significantly, particularly in the compressed liquid region. Literature data for 2-butanol are relatively scarce. Differences in the thermophysical properties and stability of these butanol isomers, some of the challenges associated with accurate measurements of hygroscopic, polar fluids as well as issues of correlating the measurement results will be discussed in the presentation.