Electrochemical synthesis of N2O5 by oxidation of N2O4 in nitric acid with PTFE membrane

Electrochemical synthesis of dinitrogen pentoxide (N2O5) by oxidation of dinitrogen tetroxide (N2O4) in a plate-and-frame electrolyzer was investigated. As the separator, different porous polytetrafluoroethylene (PTFE) membranes were tested in this process and the effects of hydrophilicity and of hydrophobicity on the electrolysis were discussed. The transport of N2O4 and water from catholyte to anolyte through membrane occurred in the electrolysis, especially at the end of the electrolysis. The water transport had a much more effect on the electrolysis than that of the N2O4 diffusion. The hydrophobic PTFE membranes had better performance on control of water transport from catholyte to anolyte than that of the hydrophilic ones. Hydrophobicity can increase the chemical yield of N2O5. The membranes with a low hydrophobic surface were preferred. All the hydrophobic PTFE membranes with low resistance have the specific energy of 1.1-1.5 kWh kg(-1) N2O5. The current efficiency of 67.3-80.2% and chemical yield of 58.9-60.9% were achieved in production of N2O5. The technique of replacing the catholyte with fresh nitric acid can minimize the transport of N2O4 and water to a great extent, it can further improve the chemical yield and reduce the specific energy. (c) 2006 Elsevier Ltd. All rights reserved.