Nitrogen-15 fractionation by countercurrent exchange between liquid N2O3-N2O4 mixtures and their vapor phases under pressured conditions

The nitrogen isotope exchange system for 15N-fractionation consisting of liquid mixtures of N2O3 and N2O4 and the vapor phase in equilibrium with the liquid (NO/N2O3 system) has been studied at temperatures between -9 and 200C under various pressures below 4 atm. A countercurrent isotope exchange apparatus and an associated product refluxer system are described. At 150C the effective separation factor, α/sub eff/, increases from 1.006 at 1 atm to 1.030 at 2.7 atm and levels off thereafter. The observed α/sub eff/ values are in good agreement with recent spectroscopic data. The height equivalent of theoretical plate (HETP) correlates well with the linear flow rate of gas phase, showing a dominant diffusion-control of the overall exchange rate. At 150C the HETP of the NO/N2O3 system under 3 approx. 4 atm can be smaller by factors of 7 to 10 than of the Nitrox (NO/HNO3 exchange) system having the same product rate, rendering the former system a possibility for significantly smaller plant volume. 40 references, 6 figures, 5 tables