The critical temperatures and pressures of binary systems: Hydrocarbons of all types and hydrogen



A method of the prediction of the critical temperatures and pressures of mixtures has been developed, primarily on the basis of data for binary hydrocarbon systems available in the literature. These mixtures may contain aliphatic (normal paraffinic, isoparaffinic, and olefinic), naphthenic, and aromatic hydrocarbons as well as hydrogen. The mixtures may be of varying complexity, and, although this method has been tested chiefly on binary systems, it has been applied to a limited number of mixtures containing more than two components.

This study introduces two dimensionless temperature parameters, γ and θ, which account for the composition of the mixture and for the nature of the components involved. These parameters are defined by the molar average boiling point, the boiling point, and the dew point, all at atmospheric pressure. For a given composition the ratios of the actual critical values to the pseudocritical values have been found to be functions of γ and θ. These relationships are presented graphically and permit the direct calculation of the critical temperature and pressure of the mixture.

The validity of this method has been checked not only on the binary systems used to obtain these correlations but also on binary and ternary systems which have not been included in this development. Critical values for eighteen systems, consisting primarily of two components, have been calculated for ninety-six compositions and have been compared with the experimental values presented in the literature. For temperature the average absolute deviation has been found to be 0.76% (based on degrees Rankine) and for pressure, 2.7%. The results for the majority of these systems have been compared with values calculated by the methods of Eilerts et al. (4), Organick and Brown (15), Kurata and Katz (11), Mayfield (12), and Smith and Watson (23).