Scale‐Up Studies of the Electrosynthesis of Dinitrogen Pentoxide in Nitric Acid

Abstract

The method for the electrosynthesis of in nitric acid by anodic oxidation of has been scaled up to produce quantities of 15 to 50 kg of solution containing 20 to 30 weight percent . A two‐ or three‐cell, divided, plate‐and‐frame electrolyzer operated in the bipolar mode was employed to test various combinations of candidate electrode coatings and separators, and to study the electrochemical characteristics of the process. Two sizes of electrolyzers were used each haying single‐electrode areas of 0.096 and 0.25 m2. The best performing anode/substrate materials were either Pt‐Ir on niobium, or on aluminum; the best cathode materials were Pt or Pt‐Ir on niobium. The preferred cell separator is a hydrophilic, porous polytetrafluorene‐ethylene diaphragm, but an FEP‐polymer anion‐exchange membrane is also satisfactory. Production of was achieved with chemical yields of 80 to 90% and current efficiencies of 50 to 70%. Maximum current densities were in the range of 0.1 to . Cell voltages were 3 to 5 V and specific energies were 1.6 to . In the electrolyzer catholyte, is generated at nearly theoretical yield, and could be recovered and recycled as an anolyte feedstock. The Eo' of the couple in anhydrous nitric acid was estimated to be +1.66 ± 0.02 V vs. SHE.