Isotopic Separation and Labeled Compounds

Title: The Production of the Isotope ¹⁵N by Isotopic Exchange in Nitrox System at Pressure
Journal: Rev. Chim. (Bucharest) 70, 5, p.1530-1533 (2019)

Authors: Damian Axente, Ștefan Bugeac, Ștefan Gergely, Mihai Gligan, Cristina Marcu, Zsolt Szücs, Codruţa Varodi

The operation of  ¹⁵N production plant at pressure of 0.7 +/- 0.05 bar in stable conditions at total reflux and in production is demonstrated. The 10M HNO3 flows used  in the primary column were 6.6 L/h and 6.0 L/h, 47, respectively 33% higher than that of atmospheric pressure (4.5 L/h) and corresponding flow rates of the same column were 3.12 mL/cm² ∙ min, respectively 2.83 mL/cm² ∙ min for operation at pressure, compared to 2.12 mL/cm² ∙  min at atmospheric pressure. The 10M HNO3 flows used in the final column were 324 mL/ h and 264 mL/h, 62, respectively 32 % higher than that of the atmospheric pressure (200 mL/h) and flow rates of that column were: 3.05 mL/cm² ∙ min, respectively 2.49 mL/cm² ∙ min, compared to 1.86 mL/cm²∙ min for atmospheric pressure operation (Fig. 1). The HETP values are lower for both separation columns operated at pressure and higher 10M HNO3 flow rates, that being an argument in the favour of operation the  ¹⁵N production plant by isotopic exchange in Nitrox system at pressure. The nitrogen enriched in ¹⁵N losses in the waste sulphuric acid, evacuated at the bottom of product refluxer stage II, were : 5.18 -10.58 ppm of feeding with 10M HNO3 of the plant. Any losses of nitrogen enriched in  ¹⁵N represent an additional uncontrolled production, which  diminishes  the production of ¹⁵N plant. In the case of operation at pressure the flows of H ¹⁵NO3 extracted as plant product are higher than those corresponding to atmospheric pressure because the nitric acid solution is chemically equilibrated with nitrogen oxides at the operation pressure and temperature. At a pressure of 1 atm. in the ¹⁵N production plant the nitrogen content of nitric acid solution would be 10.919M instead of 10M.

Title: Method and installation for sulfur dioxide and oxygen recycling on the ¹⁵N production plant by isotopic exchange in the system (NO, NO₂)_(g) – HNO_3(s)

Authors: Axente Damian, Balla Ancuţa Carmen, Marcu Mariana Cristina, Gergely Ștefan

The invention refers to a method and installation for recycling of sulfur dioxide and oxygen in the plant for ¹⁵N production by isotopic exchange in the nitrogen oxides in gaseous phase and nitric acid solution (Nitrox). The method, according to the invention, consists in: the concentration of  the sulfuric acid, waste of the separation plant, to 96 – 98% by distillation, decomposition at 320^oC into sulfur trioxide and water vapors, which pass by a catalytic bed, where takes place the conversion of sulfur trioxide to sulfur dioxide and oxygen. The gaseous mixture is compressed at 15 atm for sulfur dioxide liquefaction, which is collected and then is recycled in the nitrogen oxides refluxers of the ¹⁵N separation plant and the gaseous oxygen, separated from the liquid sulfur dioxide, is recycled in the nitric acid refluxer of the ¹⁵N separation plant.

The installation according invention (Fig. 2) consists of: reactor (2) with a catalyst bed (3), an electric furnace (4) for heating the catalyst bed, a tank (1) for sulfuric acid, a metering pump (5), a heat exchanger (6) for water vapors condensation, which is collected in the vessel (7) together the unconverted sulfuric acid, a drying tower (8), a compressor (9), another heat exchanger (10), a pressure cylinder (11) for liquid sulfur dioxide collecting and gaseous oxygen separation.