Equation of state of normal alkanes and thermodynamics of their mixtures

Abstract

The Prigogine principle of corresponding states for chain-molecule liquids is tested using published density, thermal expansion coefficient and isothermal compressibility data for the n-alkane series from methane to polymethylene. The principle is well obeyed allowing reduction parameters P*, V* and T* to be determined. The equation-of-state data for the pure liquids and the corresponding states theory applied to their mixtures permit the accurate prediction of excess volumes and their temperature and pressure dependence. Theoretical equations of state based upon the cell partition function (including the new Flory theory) show systematic errors. Analyses of experimental data using these theories produce, as artefacts, a variation of the reduction parameters with T, and an important decrease of P* with decreasing chain index. The present analysis shows P* to be constant to 3rl % from polymethylene to butane indicating that the terminal methyl groups and the interior methylene groups are similar in intermolecular contact energies. Without end-effects, the cell model theories predict an incorrect negative sign for H E of n-alkane mixtures at ordinary temperatures.

Comparison between some empirical equations of state for polymers

“…The cell model was first applied to polymer molecules by Prigogine ( 1). Good agreement with experimental data has been obtained from this The hole theory has been applied to polymer liquids with some success by Nanda et a1 (11) and Simha and Somcynsky (12) and others (13,14). However, this theory predicts the wrong trend for the variation of a with temperature.…”

The thermodynamics of solutions of some normal and branched alkanes in polyisobutylene: an investigation by gas‐liquid chromatography

“…3a, line b) and Q12 is found to be zero. Positive values of X12 and a zero value of Q12 are also found when the characteristic parameters of the solutes are brought into accordance with the principle of corresponding states, by calculating them from empirical correlations given by Patterson et al [14] instead of from Flory's equation of state (Fig. 2a, curve c).…”

Temperature dependence of the interaction between n‐heptane, carbon tetrachloride, and benzene and poly(vinyl methyl ether) between 120 and 180°C

“…Part of this temperature dependence can be traced to the equation of state used by Flory in the corresponding-states formulation, which does not fully account for the state behavior of the liquids. [21][22] In other words, doing calculations with temperature-independent characteristic variables results in an overestimation of the free volume contribution, which is a function of the difference of free volume between the probe and the polymer. Since the theory accounts only for part of this increase over increasing temperature and since the interaction contribution is calculated by subtracting the free volume difference contribution from the total xlz, then the net result is a value of XIz which is too negative.…”