Consistency tests for binary VLE data

Many VLE data papers are published each year for binary systems at either constant temperature or constant pressure. This manuscript examines consistency checks via Gibbs-Duhem equations and finds most powerful a two-step method that (1) uses a combination of the liquid and vapor Gibbs-Duhem equations to first check the internal consistency of (P, y, x) at constant temperature or (T, y, x) at constant; pressure and (2) then uses the liquid-side Gibbs-Duhem equation to check the liquid-phase activity coefficients in a test more familiar to most workers. A new graphical method is developed in conjunction 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 solvent 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.