Autocatalytic reaction mechanism of nitric acid and formic acid mixtures based on thermal and in situ Raman spectroscopi
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Autocatalytic reaction mechanism of nitric acid and formic acid mixtures based on thermal and in situ Raman spectroscopic analyses Mahoko Ando1 · Michiya Fujita1 · Yu‑ichiro Izato1 · Atsumi Miyake2 Received: 17 May 2020 / Accepted: 25 September 2020 © Akadémiai Kiadó, Budapest, Hungary 2020
Abstract The oxidation of organic compounds with nitric acid has the potential to undergo a runaway hazardous reaction and explosion after the thermal–neutral induction period. The purpose of this study is to obtain a better understanding of the oxidation reaction mechanism to clarify the specific conditions under which the exothermic reaction occurs. In this study, the oxidation reactions of formic acid with nitric acid were investigated to represent a typical mixture of organic compound and nitric acid. From the results of thermal analysis, the overall reaction rate in a 15% nitric acid and 10% formic acid aqueous solution was formulated using an autocatalytic reaction model. The apparent activation energy was 75.2 kJ mol−1, and the pre-exponential factor was 7.87 × 108 s−1. The reaction rate increased with either nitric or formic acid concentrations, emphasizing that it is important to treat the mixture at lower concentrations for thermal safety. As a result of the thermal and in situ Raman spectroscopic analyses, it was found that the concentration of nitrous acid increased with the progress of the reaction as nitric acid and formic acid changed into N O2, N2O4, HCO(O)NO, HCO(O)NO2, and so on. The reaction mechanism started from nitrous acid and the oxidation of formic acid with nitric acid is an autocatalytic reaction involving this nitrous acid-initiated cycle. Keywords Nitric acid · Formic acid · Autocatalytic reaction · Reaction mechanism analysis · Thermal and in situ Raman spectroscopic analyses
Introduction Nitric acid (HNO3) is a typical oxidizing agent that is widely used in industries such as metal cleaning and the production of adipic acid and other medicines [1–3]. In these processes, the oxidation of organic compounds by nitric acid, which occurs within mixtures containing nitric acid and organics (e.g., spent cleaning liquid), has the potential to cause a runaway reaction and explosion. In fact, several explosion Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10973-020-10311-y) contains supplementary material, which is available to authorized users. * Atsumi Miyake miyake‑atsumi‑[email protected] 1
Graduate School of Environmental and Information Sciences, Yokohama National University, 79‑5 Tokiwadai, Hodogaya‑ku, Yokohama 240‑8501, Japan
Institute of Advanced Sciences, Yokohama National University, 79‑5 Tokiwadai, Hodogaya‑ku, Yokohama 240‑8501, Japan
2
accidents have tragically occurred in the process of handling nitric acid together with organic compounds [4–6]. The oxidations of organic compounds with nitric acid are known to be autocatalytic reactions that exhibit induction periods [7–10] in which no remarkable thermal behavior can be observed
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