Improvements in the Measurement of Distillation Curves. 3. Application to Gasoline and Gasoline + Methanol Mixtures

In previous work, several significant improvements in the measurement of distillation curves for complex fluids were introduced. The modifications to the classical measurement provide for (1) temperature and volume measurements of low uncertainty, (2) temperature control based upon fluid behavior, and, most important, (3) a composition-explicit data channel in addition to the usual temperature−volume relationship. This latter modification is achieved with a new sampling approach that allows precise qualitative as well as quantitative analyses of each fraction, on the fly. Moreover, as part of the improved approach, the distillation temperature is measured in two locations. The temperature is measured in the usual location, at the bottom of the takeoff in the distillation head, but it is also measured directly in the fluid. The measurement in the fluid is a valid equilibrium thermodynamic state point that can be theoretically explained and modeled. The usual temperature measurement location (in the head) provides a temperature that is not a thermodynamic state point for a variety of reasons but which is comparable to historical measurements made for many decades. We also use a modification of the Sidney Young equation (to correct the temperatures to standard atmospheric pressure) in which explicit account is taken of the average length of the carbon chains of the fluid. In this paper, we have applied the advanced approach to samples of 91 AI gasoline and to mixtures of this gasoline with methanol (10 and 15%, vol/vol) as examples of oxygenates. On the individual fractions, we have done chemical analysis by gas chromatography (using flame ionization detection and mass spectrometry). For the methanol blends, the approach allows characterization of the azeotropic inflections in terms of fraction composition and energy content.