Continuous Isotope Separation in Systems with Solid Phase. II. Separation of Nitrogen Isotopes with Use of Ion-Exchange Resin

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Abstract
This work deals with the separation of nitrogen isotopes by chemical exchange between ammonia in an aqueous solution and a cation-exchange resin in the NH± 4 form. Using this system, a continuous process in a simulated moving bed (SMB) is developed. Two operations, the column under total reflux and a continuous feed operation, have been studied. In the latter, the product enriched in heavy nitrogen 15N was removed from the unit. The operating conditions (2.1–30.5 cm/s superficial liquid velocity, 0.7 mm average resin granules size, and 0.98 N solution of a displacement agent) were close to those used in industrial applications. By studying the separation of nitrogen isotopes, it was shown that displacement ion-exchange chromatography in a practically standard liquid-phase SMB unit provides the opportunity for the flexible production of a number of isotopes of light elements. We found that flow converting is robust, and the operation and control are simple. It appears that the process design proposed in this work may also be applied for efficiently separating substances other than isotopic mixtures whenever a proper displacement band chromatographic system with nondispersive ends of the band is found.