Experimental test of the Sydney Young equation for the presentation of distillation curves

The distillation (or boiling) curve of a complex fluid is a critically important indicator of the bulk behavior or response of the fluid. For this reason, the distillation curve, usually presented graphically as boiling temperature against volume fraction distilled, is often cited as a primary design and testing criterion for liquid fuels, lubricants and other important industrial fluids. Clearly, the boiling temperatures that is measured near ambient conditions during the course of a distillation curve determination depend upon the local atmospheric pressure. For this reason, the user community is accustomed to data presented with an adjustment of the temperatures to those that would be observed at a standard atmospheric pressure of 101.325 kPa, or standard atmospheric pressure of 1 atm. Typically, this is done with a simplified Sydney Young equation. This correction makes little difference to measurements done consistently in a particular laboratory, or when the atmospheric pressure varies little. The correction can be quite large when measurements are done in laboratories at different elevations, however. In this paper, we describe an evaluation of this correction. Specifically, we performed measurements of the distillation curve of a binary mixture of (n-decane + n-tetradecane) at three elevations (and, therefore three different values of atmospheric pressures, (70.06, 82.73, and 101.00) kPa). Comparisons are made between the raw and adjusted values, and recommendations are presented as to when the equation might be inadequate.