TRIPLE POINT CORRESPONDING STATES IN LONG-CHAIN NORMAL ALKANES

Evidence for triple point corresponding states in temperature and pressure are presented for long-chain n-alkanes. As the carbon chain length exceeds n = 9, variations in triple point pressures, P(m), due to odd-even carbon number effects rapidly converge to a single line. Similar behavior is observed for the reduced value, P(rm) = P(m)/P(c). Likewise, odd-even variations in the reduced triple point temperature, T(rm) = T(m)/T(c), rapidly approach 0.4. T(rm) deviates less than 1 per cent from 0.4 between n = 12 and n = 100 when T(c) is based on a regression of experimental data to the Kreglewski-Zwolinski equation form. The rapid convergences in T(rm) and in P(rm) allow determination of T(c) and P(c) of thermally unstable n-alkanes based on triple point measurements. Triple point correlations for n-alkanes can be used to constrain vapor pressure correlations for conformal fluids at low pressures.