A method of predicting the critical pressures of multicomponent hydrocarbon mixtures of known composition has been developed. These mixtures include ternary, quaternary, and quinary systems consisting of normal and isoparaffins, olefins, acetylenes, naphthenes, and aromatics. The method, based upon the mole fraction of the low-boiling component in the mixture, graphically presents the ratio of the actual critical pressure to the pseudocritical pressure as a function of a boiling parameter. For mixtures of more than two components the pseudocritical pressure is based on the critical pressure of the pure low-boiling component and on the actual critical pressure of the mixture consisting of all the remaining higher-boiling components. From an analysis of twenty-seven binary systems (139 compositions) the average deviation of calculated values from reported values is 1.27%. For thirty-four mixtures containing from three to seven components the average deviation is 1.64%.
Based upon a similar approach graphical relationships are presented for the estimation of the critical molar density of binary hydrocarbon mixtures of known composition, which also may contain normal and isoparaffins, olefins, nuphthenes, and aromatics. The same boiling point parameter is used to correlate the ratio of the critical density to the reciprocal of the molar average critical volume for nonmethane systems and the product of the critical pressure and the critical volume for methane systems. From an analysis of fifteen binary systems (eighty compositions) the average deviation of calculated values form reported values is 1.54%.