Equation optimum binary deviation

Figure 1. Optimum binary deviation parameters (k and ji j) and confidence ellipses for the fit of the LHW equation of state to the Nz + Ar VE data of Ref. 11, pp. 166-168...

As expected, Equation 10 worked well for the 14 paraffin binaries the average deviation of the predicted from the optimum values was only 0.02. However, when all 26 hydrocarbon binaries were included, the average deviation increased to 0.05. 

Equation 11 was much less satisfactory, even when the coefficient was adjusted to minimize the deviation. The optimum value of the coefficient was 0.18, in agreement with Lin s conclusion for rare-gas mixtures, but the root-mean-square deviation of k j was 0.08. Any relationship involving I, the first ionization potential, is doomed to failure when applied to heavy hydrocarbon mixtures because I, for a given homologous series, is very weakly dependent on carbon number. For example, the I of n-decane is 10.19 eV, only 0.24 eV less than that of n-hexane, while that of n-eicosane should be about 10.04 eV. Thus, a correlation of kijs for methane-paraffin binaries based solely on ionization potentials would give the same result for all Ci0+ paraffins. 

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