Simulation of Multicomponent Isotope Distillation for 15N Production

Introduction Since their discovery in 1912, stable isotopes have received an increasing attention and they are now used in a variety of scientific applications, including industrial diagnostic methods, energy production, and physics. Although stable isotopes occur naturally, their utility can be greatly enhanced when they are isolated and enriched through several processes. Among them, distillation is only used in the separation of isotopes of light elements, such as carbon, nitrogen and oxygen, whose demand has increased sharply in recent years. Description of the Work or Project This work is focused on the separation of the various isotopic forms of nitric oxide (NO) by cryogenic distillation aiming at obtaining the heavy stable isotope 15N: it finds application in the form of 15N2, which allows to produce radioactive tracers that are used in the PET imaging technique and uranium nitrides (Un 15Nm) that are good candidates as fuels for IV generation nuclear reactors. The data available in the literature1 for the relative volatilities of the isotopic forms of NO have been used to describe the thermodynamic behavior of the system. To allow for rigorous calculations, the Aspen Plus® commercial process simulator, commonly used for dealing with systems other than isotopic ones, has been properly tuned to be used for isotope separation problems as well, and its reliability has been assessed by comparison with the experimental data presented in the literature by McInteer and coworkers1 for a NO distillation plant built for enriching both nitrogen and oxygen isotopes. For comparison purposes, the same 14N16O- 14N17O-14N18O-15N16O four-component system has been taken into account. Conclusions The adjustment of some features of Aspen Plus® properties and to numerical resolution methods has allowed to make this software suitable for the simulation of the multi-component isotope distillation, as proved by the agreement found with the experimental data made available for a pilot plant in a literature work.1 It has been then used for designing a process that allows to produce the heavy 15N isotope by means of a scheme which involves a column currently under construction within the DarkSide program for depleting the 39Ar-40Ar mixture from 39Ar.