Chemical Reactions Involved in the Denitration Process with HCOOH and HCHO

Summary

Denitration reactions with HCOOH and HCHO proceed according to several reactions depending on the acidity and/or the redox potential of the reacting mixture. The parameters acting on the induction time — Inherent to these reactions — and the denitration rate have been identified and their possible effects discussed. These mainly deal with the concentration of the reacting mixture components, the pressure in the reactor and the nitrous acid concentration. The basic outcome of this study is that gaseous compounds in equilibrium with nitrous acid catalyze the denitration reaction. As a consequence, every action which could remove these products from the reacting mixture extends the induction time and are detrimental to the denitration rate.

The conditions whereby the noble metals can affect the denitration process by modifying the reactions stoichiometry and by entailing oscillations of the reacting mixture are also presented and discussed. These phenomena were showed to occur in presence of rather high amounts of noble metals (those existing in HLLW) and iron. At last, based on the various experimental data observed, a tentative reaction mechanism is proposed involving a reaction between NO₂ on HCHO/HCOOH as an intermediate reaction between HCHO/HCOOH and HNO₃.