Parameters of the UNIQUAC Model for Describing the Vapor–Liquid Phase Equilibrium of the Isotope Mixtures of Hydrogen H2–D2, H2–HD, HD–D2
摘要
The calculated and published experimental data on the activity coefficients of hydrogen isotopes in H2–D2, H2–HD, and HD–D2 mixtures were analyzed. The calculated data were obtained based on Sherwood’s theory of multicomponent liquid solutions of hydrogen, which takes into account the nonideality of the vapor–liquid equilibrium. The maximum relative deviation was 5.4%. The adequacy of the description of vapor pressure of the pure components H2, D2, and HD by empirical equations was checked, and equations were chosen for calculating the phase equilibrium in the vapor–liquid system. Based on the mathematical processing of published experimental data on the phase equilibrium of the isotope mixtures of hydrogen H2–D2, H2–HD, and HD–D2, the parameters of the binary energy interaction of the UNIQUAC model were found for calculating the activity coefficients of the H2, D2, and HD components. The separation coefficients for the H2–D2, H2–HD, and HD–D2 mixtures were calculated at different boiling points depending on the pressure and composition. Based on the results of calculations, phase equilibrium diagrams y–x and t–x,y were constructed at atmospheric pressure. The computational studies of the separation coefficient of these isotope mixtures revealed differences in the qualitative behavior of the dependence of the separation coefficient on the composition of the volatile component between the UNIQUAC model, Sherwood theory, and treatment of the mixture as an ideal one. The curve of the separation coefficient calculated using the UNIQUAC model is slightly convex relative to the abscissa axis; when calculated according to Sherwood’s theory, it is decaying; and when considering an ideal mixture that obeys Raoult’s law, this is an ascending and almost straight line with a significant angle of inclination to the abscissa. The calculated graphical dependences of the boiling temperature of the H2–D2 mixture on the H2 concentration in the liquid phase at various pressures are given. The distribution profile of the H2, D2, and HD components along the height of the 21st tray distillation column was studied for the H2–HD–D2 three-component model mixture with a composition (mol %):