Thermal Diffusion of Gas Mixtures in Chemical Equilibrium

Abstract

Theoretical expressions are developed for thermal‐diffusion ratios or factors in reacting gas mixtures. In general, these parameters can be related to λ_r, the increase in thermal conductivity due to chemical reaction. Calculations on the N₂O₄⇄2NO₂—argon system predict thermal‐diffusion factors as large as 2 and in satisfactory agreement with experiment. Reduced thermal‐diffusion factors are computed for separation of noble‐gas isotopes in the presence of the (HF)₆⇄6HF equilibrium and are predicted to be as much as an order of magnitude greater than factors which have been observed without added hydrogen fluoride. Reduced separation factors for argon, krypton, and xenon are negative, which means that the heavy isotope migrates to the hotter regions of the gas mixture. (In mixtures of isotopes alone, separation factors are always positive.) Finally, separation of reactants in a mixture without inerts is considered. Separation factors as large as 1 are predicted for the dissociation of PCl₅.