Density Marching Method for Calculating Phase Envelopes

Abstract

Different methods have been proposed in the literature for the calculation of phase envelopes of mixtures. The phase envelopes of even simple mixtures have at least two stationary points on the P–T plane [∂P/∂T = 0 at the point of maximum pressure (cricondenbar) and ∂T/∂P = 0 at the point of maximum temperature (cricondentherm)]. Even more stationary points exist for complex mixtures. Therefore, a monotonic variation of either pressure or temperature cannot be used to trace the full phase envelope. Different methods have been proposed in the literature to help choose the right variable at the right location of the phase envelope to automatically trace the entire phase envelope. Although most methods work well for simple mixtures, many of them do not work well with wide-boiling mixtures or with mixtures that exhibit open-ended dew lines. In this article, we compare phase envelopes with space curves and show that the use of an independent variable helps trace complex phase envelopes automatically. It is sho...