Generalized vapor pressure behavior of substances between their triple points and critical points

Abstract

Several approaches are utilized for the estimation of the parameters associated with the normalized vapor pressure equation to develop a capability for the prediction of vapor pressures consistent with the theorem of corresponding states. In this development, conditions and restrictions associated with the critical point and the normal boiling point were used to establish the vapor pressure parameters a, p, y, and m. For the evaluation of these parameters, five different approaches were applied, and vapor pressures calculated with each of them were compared with corresponding experimental values presented in the literature. These comparisons were further examined using the results of four other well-known vapor pressure equations available in the literature. This evaluation included 138 substances of all types and involved a total of 7,633 literature reported vapor pressure values to show that improved results are possible through the involvement of the generalized vapor pressure equation of this investigation. SCOPEThe perennial involvement of the vapor pressure behavior of substances makes it mandatory that simple and exacting relationships be established that are capable of predicting vapor pressures over the complete liquid region included between the triple point and the critical point of a substance. In this context, a generalized vapor pressure equation, consistent with the theorem of corresponding states, has been examined and tested to show that improved results are possible with it. The capabiIity of this generalized relationship permits the calculation of vapor pressures that find use in vapor-liquid equilibria of both simple and complex mixtures, the estimation of latent heats of vaporization over the complete liquid range, and thermodynamic properties associated with the saturated vapor-liquid state. In addition, the analysis associated with this study constitutes a basis for evaluating parameters that find use in the application of the theorem of corresponding states for both gases and liquids. CONCLUSIONS A N D SIGNIFICANCEAverage percent deviations resulting from the use of in the literature. The capability of the vapor pressure this generalized vapor pressure equation are smaller than equation examined in this study has been extensively those obtained from corresponding relationships available tested using 138 substances and involving a total 7 633 vapor pressure values reported in the literature. One of y Technologia, Mbxico. the proposed schemes for estimating the vapor pressure

Estimation of Pure-Component Properties of Biodiesel-Related Components: Fatty Acid Methyl Esters, Fatty Acids, and Triglycerides

“…Vapor pressures of <1 kPa (region I in the tables), comprising about 60% of the data points, show the most significant deviations, in particular with the older corresponding-state models of Gomez-Nieto/Thodos (1977), Riedel (1954), and Lee/Kesler (1975), indicating, first, that, at these times, model development primarily focused on the representation of the normal boiling point region and, second, that the estimated critical data for the esters and acids might be questionable. It is evident from the tables that the newer approaches, notably the Moller/Rarey/Ramjugernath model and the Nannoolal/Rarey/Ramjugernath approach, show clear advantages in this pressure region.…”

Correlation and prediction of physical properties of hydrocarbons with the modified Peng-Robinson equation of state. 1. Low and medium vapor pressures

“…Results obtained are satisfactory in the high-pressure range and usually only roughly correct at medium (0.06-3 bar) and low pressures (less than 0.06 bar). As examples, the papers by Gomez-Nieto and Thodos (1977), Riedel (1954), Thek and Stiel (1966), and Willman and Teja (1985) can be quoted.…”

Vapour pressure measurements and prediction for heavy esters

“…The four methods based on the corresponding states principle are Willman-Teja, (10) Lee-Kesler, (11) Gomez-Thodos, (12) and Peng-Robinson. (13) All of them require the critical parameters, sometimes with the acentric factor (Lee-Kesler and Peng-Robinson), sometimes with the normal boiling temperature (Willman-Teja and Gomez-Thodos).…”