Wagner equation predicting entire curve for pure fluids from limited VLE data: Critical point & four Antoine analytic points

Abstract

Entire-curve Wagner analytics are treated as “true” or “best” values, and Antoine analytic values are used as surrogate experimental data. Limited-data Wagner constants are estimated from Antoine analytics for the fully-determined case for fifty-five species, from which reduced vapor pressures below and above the interval are predicted and compared with the entire-curve Wagner analytics to estimate the ability of limited VLE data to be used to accurately represent the entire two-phase curve. The Antoine intervals have a pressure range of 0.02–2 bars for most species, an average reduced temperature interval width of 0.20, and an average lower bound reduced temperature of 0.53. The Wagner constants estimated from Antoine analytics have an average entire-curve error of 4.8%, with the majority of the error occurring when extending down towards the triple point (9.55%), compared to 1.36% average error when extending up to the critical point. Such limited-data Wagner constants produce less predictive error for alcohols, while the semi-theoretical Riedel equation has the advantage for organic acids, and the empirical Ambrose-Walton equation produces less error for the remaining species. A comparison of Wagner and Antoine analytic values strictly over the Antoine interval indicates that disagreement of VLE data in the literature averages around 2% but varies considerably between species. Data disagreement is not found to be a strong indicator of predictive power of the limited-data Wagner constants; however, it is found to be a discriminator of performance relative to that of Riedel and Ambrose-Walton for some polar species.