Studying the Kinetics of Mass Transfer in the Distillation of Water Hydrogen Isotopes in the Presence of Urea

The efficiency of mass transfer in the separation of hydrogen isotopes by water distillation in the presence of urea as a separating agent has been estimated. Experiments have been performed for vapor–liquid and vapor–aqueous salt solution systems under conditions with independent flows. Two regimes of mass transfer have been considered: the first one when the operating concentration of deuterium in the liquid phase is lower than that in equilibrium with the vapor (xD < $$x_{{\text{D}}}^{*}$$ ) and the second one when it is higher than that in equilibrium with the vapor (xD > $$x_{{\text{D}}}^{*}$$ ). A substantial difference in the number of theoretical separation stages for these regimes has been found. At xD > $$x_{{\text{D}}}^{*}$$ , in the presence of urea as a separating agent, the number of theoretical separation stages is three times lower than that for the vapor–water system. Thus, in the distillation of the hydrogen isotopes of water, urea hinders the transport of deuterium from the liquid phase to the vapor phase, forming nonvolatile complexes with water molecules that contain deuterium.