Consistency tests for binary VLE data

Many VLE data papers are published each year for binary systems at either c onstant temperature or constant pressure. This manuscript examines consiste ncy checks via Gibbs-Duhem equations and finds most powerful a two-step met hod that (1) uses a combination of the liquid and vapor Gibbs-Duhem equatio ns to first check the internal consistency of (P, y, x) at constant tempera ture or (T, y, x) at constant; pressure and (2) then uses the liquid-side G ibbs-Duhem equation to check the liquid-phase activity coefficients in a te st more familiar to most workers. A new graphical method is developed in co njunction with step 1. The role of the assumed gas-phase model is examined. The common problem of published data of the activity coefficient of the so lvent falling slightly under unity upon approaching the pure solvent end on the familiar In gamma (i) versus x(1) diagram is explained as an artifact of usual data reduction procedures but corrected by the present procedures.