Vapor—Liquid Equilibria of Dilute Solutions of HT in e—H2 and DT in e—D2 from the Triple Points to the Critical Temperatures of the Solutions

Abstract

The liquid—vapor fractionation factors for dilute solutions of HT in e—H₂ and DT in e—D₂ have been measured over the temperature ranges 13.95°—30.26°K and 18.67°—32.48°K, respectively. At these temperatures the respective fractionation factors are 3.66, 1.24, 1.36, and 1.07. In all cases the heavy isotope concentrates in the liquid phase. The solutions obey Henry's law in the concentration range studied (1–2×10^—8M). The fractionation factors vanish at the critical temperatures of the respective solvents. The differences in the partial molal heats of vaporization of the isotopes are functions of the temperature. It is shown conclusively that the fractionation factors for the HT—H₂ mixtures are appreciably smaller (∼24%) than those to be expected for dilute mixtures of D₂ in H₂. The difference in behavior of HT from D₂ is a manifestation of the effect of the molecular structure on the phase equilibrium properties of the liquid. The principal structural effect is shown, by comparison of the experimental data with theoretical calculations, to be a coupling of the molecular rotation with the hindered translation of the molecule in the liquid.