Enrichment of Nitrogen-15 by Chemical Exchange of NO with Liquid N2O3

Abstract

The characteristics of the two-phase exchange system: N214O3(liq)+N15O(gas)⇄N14N15 O3(liq)+N14O(gas) have been studied in laboratory exchange columns to evaluate its usefulness for concentrating nitrogen-15. The effective single stage separation factor α has been determined both by direct equilibration of liquid and gas phases, and by measuring the over-all separation in an exchange column as a function of the rate of product with-drawal. The factor α varies from 1.035±0.005 at —14°C to 1.016±0.004 at +14°C. The system is complicated by the presence of additional oxides of nitrogen in both phases, and it is not yet possible to evaluate the contributions of each of the individual molecular species to the effective separation factor. The over-all separations achieved at total reflux in a 40-stage bubble plate column corresponded to a maximum plate efficiency of ∼60% at an interstage flow of ∼50 mM N/min cm2. Similarly, the separations obtained in a 95-cm column packed with stainless steel wire helices corresponded to stage heights of 1.1 and 1.2 cm for interstage flows of 23 and 31 mM N/min cm2, respectively. A comparison of the present system with the nitric acid-nitric oxide exchange system indicates that approximately equal volumes of column would be required for the same isotope separation task in spite of a considerably lower α for the N2O3 system. This is due to the higher rate of exchange as evidenced by lower stage height. The favorable stage height for this process makes it possible to prepare highly concentrated nitrogen-15 in shorter columns than those used for the nitric acid exchange.