Physical constants of pure fluids: critical points

Reliable data on the thermodynamic properties of substances is important for science and industry. We present here a review of data for three fundamental critical thermodynamic quantities of pure fluids that are very often used in calculations of thermodynamic and transport properties following the principle of corresponding states, namely the critical temperature T _c , the critical pressure p _c and the critical volume V _c . In addition, liquid-gas critical points, which define the upper limit of the behavior of two fluid phases, are of great interest in many industrial applications, including oil drilling and supercritical extraction. As there is a very wide variety of fluids for which there are no measurements of these quantities, either because they are new compounds or compounds that decompose before reaching the critical temperature, or compounds that have very high critical temperatures, we first describe the main equations that have been used to evaluate these quantities and that can be used to estimate those of new compounds.

These calculation methods use analytical equations or contributions from molecular groupings. Although the chemical industry is more interested in mixtures than in pure fluids, the critical coordinates of mixtures can be calculated from the critical coordinates of the individual components, using mixing laws. When the behavior of pure bodies deviates from that of the corresponding states, it is necessary to introduce additional parameters that characterize each molecule. Thus, based on the three critical coordinates T _c , p _c , V _c , formulations have been developed to calculate the critical point compressibility factor Z _c , the Pitzer acentric factor ω and the Riedel factor α _c . We then present, in tabular form, these critical thermodynamic quantities that have been measured or calculated for pure inorganic and organic fluids. In each case, we have tried to select the best experimental value. Over 300 inorganic and 2,400 organic compounds are referenced in this article.