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Title: Safety Evaluation of Nitric Acid Reactions with Polysaccharides

Abstract

The hazards of polysaccharides in a transuranic (TRU) waste drum exposed to nitric acid (HNO3) and metal nitrate salts have been evaluated, based on considerations of how complex nitrogen redox cycles carry out the aqueous phase oxidation of alcohols and related organic functional groups. Of particular emphasis is how these exothermic reactions, coupled with a positive feedback loop inherent to nitrogen redox chemistry, can initiate an autocatalytic thermal runaway and explosive gas generation. This poses the most significant hazard for a TRU waste drum under ambient conditions where acidic solution may be present, either in small quantities as free liquid or sorbed within a solid matrix. Regarding specific mechanistic details, nitric acid is an extremely potent oxidant but is remarkably inert, rarely interacting directly with oxidizable substrates, instead exerting its vast potential energy through lower oxidation state reactants such as nitrogen dioxide (NO 2) and nitrous acid (HNO 2). These lower oxidation states of nitrogen are generated from the slow self-decomposition of nitric acid, as a result of which oxidation reactions involving nitric acid that have not been preloaded with these reactants commonly experience a quiescent induction period. It is the end of this induction period when exothermic reactivity increasesmore » rapidly that the system is most vulnerable to autocatalytic thermal runaway. Metal nitrate salts promote this ambient temperature solution chemistry (cf. traditional oxidizer properties of metal nitrate salts, which operate in the solid state at elevated temperatures) by releasing nitric acid into the system. Although less reactive than alcohols by virtue of extensive hydrogen bonding, carbohydrates are oxidized by nitric acid through the same fundamental mechanisms, potentially proceeding through a series of oxidation steps. For polymeric carbohydrates (polysaccharides) the chemistry is complicated by a variety of competing side reactions, including acid-catalyzed hydrolytic depolymerization to more reactive (ultimately monomeric) units, as well as other degradation reactions promoted by radical mechanisms. For this reason, polysaccharides that are more susceptible to hydrolysis such as starches are more reactive than cellulose, with the attendant microbial population in starch based kitty litter adding a special aspect of reactivity. A spectrum of nitrogen containing gas products is generated from polysaccharide oxidation by nitric acid depending on the reaction conditions - for example, fuel lean mixtures tend towards producing more oxidized gases such as NO 2, and thus favor an autocatalytic cycle, relative to fuel rich conditions that produce lower oxidation state gases such as nitrous oxide (N 2O). These nitrogen based gases may be accompanied by variable quantities of carbon dioxide (CO 2), which may be generated from small molecule (e.g., oxalic acid) oxidation or from decarboxylation of previously oxidized functional groups.« less

Authors:
 [1]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1467250
Report Number(s):
LA-UR-18-27835
DOE Contract Number:  
AC52-06NA25396
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Inorganic and Physical Chemistry

Citation Formats

Duval, Paul Bernard. Safety Evaluation of Nitric Acid Reactions with Polysaccharides. United States: N. p., 2018. Web. doi:10.2172/1467250.
Duval, Paul Bernard. Safety Evaluation of Nitric Acid Reactions with Polysaccharides. United States. doi:10.2172/1467250.
Duval, Paul Bernard. Thu . "Safety Evaluation of Nitric Acid Reactions with Polysaccharides". United States. doi:10.2172/1467250. https://www.osti.gov/servlets/purl/1467250.
@article{osti_1467250,
title = {Safety Evaluation of Nitric Acid Reactions with Polysaccharides},
author = {Duval, Paul Bernard},
abstractNote = {The hazards of polysaccharides in a transuranic (TRU) waste drum exposed to nitric acid (HNO3) and metal nitrate salts have been evaluated, based on considerations of how complex nitrogen redox cycles carry out the aqueous phase oxidation of alcohols and related organic functional groups. Of particular emphasis is how these exothermic reactions, coupled with a positive feedback loop inherent to nitrogen redox chemistry, can initiate an autocatalytic thermal runaway and explosive gas generation. This poses the most significant hazard for a TRU waste drum under ambient conditions where acidic solution may be present, either in small quantities as free liquid or sorbed within a solid matrix. Regarding specific mechanistic details, nitric acid is an extremely potent oxidant but is remarkably inert, rarely interacting directly with oxidizable substrates, instead exerting its vast potential energy through lower oxidation state reactants such as nitrogen dioxide (NO2) and nitrous acid (HNO2). These lower oxidation states of nitrogen are generated from the slow self-decomposition of nitric acid, as a result of which oxidation reactions involving nitric acid that have not been preloaded with these reactants commonly experience a quiescent induction period. It is the end of this induction period when exothermic reactivity increases rapidly that the system is most vulnerable to autocatalytic thermal runaway. Metal nitrate salts promote this ambient temperature solution chemistry (cf. traditional oxidizer properties of metal nitrate salts, which operate in the solid state at elevated temperatures) by releasing nitric acid into the system. Although less reactive than alcohols by virtue of extensive hydrogen bonding, carbohydrates are oxidized by nitric acid through the same fundamental mechanisms, potentially proceeding through a series of oxidation steps. For polymeric carbohydrates (polysaccharides) the chemistry is complicated by a variety of competing side reactions, including acid-catalyzed hydrolytic depolymerization to more reactive (ultimately monomeric) units, as well as other degradation reactions promoted by radical mechanisms. For this reason, polysaccharides that are more susceptible to hydrolysis such as starches are more reactive than cellulose, with the attendant microbial population in starch based kitty litter adding a special aspect of reactivity. A spectrum of nitrogen containing gas products is generated from polysaccharide oxidation by nitric acid depending on the reaction conditions - for example, fuel lean mixtures tend towards producing more oxidized gases such as NO2, and thus favor an autocatalytic cycle, relative to fuel rich conditions that produce lower oxidation state gases such as nitrous oxide (N2O). These nitrogen based gases may be accompanied by variable quantities of carbon dioxide (CO2), which may be generated from small molecule (e.g., oxalic acid) oxidation or from decarboxylation of previously oxidized functional groups.},
doi = {10.2172/1467250},
journal = {},
number = ,
volume = ,
place = {United States},
year = {2018},
month = {8}
}

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