Dual pressure-dual temperature isotope exchange process and apparatus

The improvement described comprises operating the cold tower at a pressure of at least 5 atmospheres below the pressure of the corresponding hot tower within the pair of towers and simultaneously operating the cold tower at a temperature below the temperature at which solid hydrogen sulfide hydrate forms at the pressure of the hot tower. Another aspect employed to conserve the pressure related energy of the system includes expanding the hydrogen sulfide gas leaving the hot tower to the cold tower pressure through a turbine, reciprocal or other type engine for extracting mechanical work from the energy released in the expansion