The PVT Behavior of Methane in the Gaseous and Liquid States

Abstract

Introduction Considerable time and effort frequently are expended to establish, with a degree of confidence, the PVT behavior of pure substances. In particular, a great deal of experimental information contributed by a number of investigators is available in the literature. The data of each investigator, although significant in themselves, cannot be used with a high degree of confidence until they are compared with the continuum of information presented by others. Current interest in thermodynamic and transport properties, for not only the gaseous state but the condensed state as well, requires that PVT information be presented for both regions. The density dependence on temperature and pressure, when presented as a continuum, is of considerable value in itself, especially since the available equations of state fail to properly account for the PVT behavior in the condensed state. For this reason and to incorporate PVT data recently presented in the literature, this investigation was carried out. In their studies concerned with the thermodynamic properties of methane, Matthews and Hurd in 1946 utilized the data of Kvalnes and Gaddy and Olds, Reamer, Sage and Lacey to establish the PVT behavior of methane in the superheated region and the saturated liquid densities of Keyes, Taylor and Smith in conjunction with the Clapeyron equation to develop the densities for the saturated envelope. Current activity sponsored by API Project No. 44 under the direction of F.D. Rossini has led to a tabular presentation of compressibility factors for gaseous methane in the superheated region. These values were obtained by using smoothed residuals, developed from experimental data and the Benedict-Webb-Rubin equation, to establish internally consistent compressibility factors for the real gas. This approach offers probably the most precise presentation of PVT information for gaseous methane to date. The PVT behavior of methane also can be represented accurately by equations of state such as the Benedict-Webb-Rubin equation or the Martin-Hou equation. These equations, although valuable for analytically representing the PVT behavior, lack precision in the compressed-liquid region.