Evaluating Characteristic Parameters for Carbon Dioxide in the Sanchez−Lacombe Equation of State

Abstract

For many different pure substances, large numbers of competing characteristic parameter sets exist in the literature for the Sanchez−Lacombe equation of state. This is due in part to differing research requirements or differing procedures used for determining the parameters. The existing parameters for carbon dioxide are reviewed in order to determine whether a single set of parameters can describe the equation of state over large ranges of temperature and pressure. It is found that by consideration of a large collection of experiments, a good fit can be achieved over much larger temperature and pressure ranges than previously thought possible. Properties directly related to the equation of state, such as the thermal expansivity and isothermal compressibility, are also predicted well; however, as expected, properties that depend on the internal degrees of freedom of molecules, such as the specific heats, do not correlate well. Closely agreeing parameter sets are found in the literature that fit the equation of state data reasonably well over a large range. A new set of parameters is found using a least-squares approach over the largest ranges of temperature and pressure to date. These parameters are found to be P* = 419.9 MPa, T* = 341.8 K, and ρ*= 1.397 g/cm3 using N = 556 experimental data points over the temperature range of 216.58−1800 K and the pressure range of 0.5−66.57 MPa.