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Understanding hydrogen in bayer process emissions. 1. hydrogen production during the degradation of hydroxycarboxylic acids in sodium hydroxide solutions / Allan Costine in Industrial & engineering chemistry research, Vol. 50 N° 22 (Novembre 2011) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 50 N° 22 (Novembre 2011) . - pp. 12324–12333 Titre : Understanding hydrogen in bayer process emissions. 1. hydrogen production during the degradation of hydroxycarboxylic acids in sodium hydroxide solutions Type de document : texte imprimé Auteurs : Allan Costine, Auteur ; Joanne S.C. Loh, Auteur ; Greg Power, Auteur Année de publication : 2012 Article en page(s) : pp. 12324–12333 Note générale : Chimie industrielle Langues : Anglais (eng) Mots-clés : Hydrogen  Hydroxycarboxylic  Acids Résumé : The formation of potentially explosive gas mixtures during Bayer process digestion and the wet oxidation of Bayer process liquors underscores the need for an improved understanding of the degradation reactions of organic compounds that produce flammable gases. This study is the first of a series investigating the production of hydrogen from different classes of organic compounds in sodium hydroxide solutions. The alkaline degradation of a range of aliphatic and aromatic carboxylates and hydroxycarboxylates was investigated under anaerobic conditions in an autoclave. It was found that aliphatic C4 carboxylates possessing a single β-hydroxy substituent are particularly reactive under these conditions, generating hydrogen gas and a range of low molecular weight (LMW) carboxylates. The effect of temperature (175–275 °C) and NaOH concentration (0–6 M) on the degradation of 3-hydroxybutanoate and hydroxybutanedioate (malate) was investigated in detail for reaction times up to 120 min. Under conditions that promote the total degradation of the organic compound, the β-hydroxycarboxylates have similar hydrogen production capacities, each generating about 1 mol of hydrogen gas per mole of organic compound consumed. The results provide direct evidence for an ionic degradation mechanism involving base-catalyzed oxidation by water, consistent with the stoichiometry of the formation of hydrogen gas and the other main reaction products (LMW carboxylates). These findings have important implications for the production of hydrogen in Bayer process digestion and the safe application of wet oxidation technologies for the treatment of organic compounds in alkaline liquors, such as those found in the Bayer and Kraft processes. The results also shed new light on the mechanism of hydrogen production during the base-catalyzed gasification of biomass at low temperature. DEWEY : 660 ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie201387x [article] Understanding hydrogen in bayer process emissions. 1. hydrogen production during the degradation of hydroxycarboxylic acids in sodium hydroxide solutions [texte imprimé] / Allan Costine, Auteur ; Joanne S.C. Loh, Auteur ; Greg Power, Auteur . - 2012 . - pp. 12324–12333. Chimie industrielle Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 50 N° 22 (Novembre 2011) . - pp. 12324–12333 Mots-clés : Hydrogen  Hydroxycarboxylic  Acids Résumé : The formation of potentially explosive gas mixtures during Bayer process digestion and the wet oxidation of Bayer process liquors underscores the need for an improved understanding of the degradation reactions of organic compounds that produce flammable gases. This study is the first of a series investigating the production of hydrogen from different classes of organic compounds in sodium hydroxide solutions. The alkaline degradation of a range of aliphatic and aromatic carboxylates and hydroxycarboxylates was investigated under anaerobic conditions in an autoclave. It was found that aliphatic C4 carboxylates possessing a single β-hydroxy substituent are particularly reactive under these conditions, generating hydrogen gas and a range of low molecular weight (LMW) carboxylates. The effect of temperature (175–275 °C) and NaOH concentration (0–6 M) on the degradation of 3-hydroxybutanoate and hydroxybutanedioate (malate) was investigated in detail for reaction times up to 120 min. Under conditions that promote the total degradation of the organic compound, the β-hydroxycarboxylates have similar hydrogen production capacities, each generating about 1 mol of hydrogen gas per mole of organic compound consumed. The results provide direct evidence for an ionic degradation mechanism involving base-catalyzed oxidation by water, consistent with the stoichiometry of the formation of hydrogen gas and the other main reaction products (LMW carboxylates). These findings have important implications for the production of hydrogen in Bayer process digestion and the safe application of wet oxidation technologies for the treatment of organic compounds in alkaline liquors, such as those found in the Bayer and Kraft processes. The results also shed new light on the mechanism of hydrogen production during the base-catalyzed gasification of biomass at low temperature. DEWEY : 660 ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie201387x

Understanding hydrogen in bayer process emissions. 2. hydrogen production during the degradation of unsaturated carboxylic acids in sodium hydroxide solutions / Allan Costine in Industrial & engineering chemistry research, Vol. 50 N° 22 (Novembre 2011) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 50 N° 22 (Novembre 2011) . - pp. 12334–12342 Titre : Understanding hydrogen in bayer process emissions. 2. hydrogen production during the degradation of unsaturated carboxylic acids in sodium hydroxide solutions Type de document : texte imprimé Auteurs : Allan Costine, Auteur ; Joanne S.C. Loh, Auteur ; Greg Power, Auteur Année de publication : 2012 Article en page(s) : pp. 12334–12342 Note générale : Chimie industrielle Langues : Anglais (eng) Mots-clés : Hydrogen  Carboxylic  acids  Sodium  hydroxide Résumé : This is the second in a series of studies of the production of hydrogen from the degradation of organic compounds in sodium hydroxide solutions. Unsaturated carboxylates, which are intermediate products in the wet oxidation of the types of monoaromatic compounds typically present in Bayer process liquors, have been found to produce significant amounts of hydrogen during alkaline degradation. The alkaline degradation of nine unsaturated carboxylates was investigated under anaerobic conditions in an autoclave, and the effect of temperature (175–275 °C) and NaOH concentration (0–6 M) on the degradation of acrylate, 2-butenoate, maleate, and 2-hexenoate was studied in detail for reaction times up to 120 min. All of the compounds investigated decompose to produce about 1 mol of hydrogen gas per mole of organic compound consumed, as well as a range of low molecular weight (LMW) carboxylates. The stoichiometries of the formation of hydrogen and LMW carboxylates from the unsaturated carboxylates observed here are consistent with the regioselective hydration of the C═C double bond to form the corresponding β-hydroxycarboxylates, which then undergo further degradation by an ionic mechanism involving base-catalyzed oxidation by water. These findings significantly advance the understanding of the production of hydrogen in Bayer process digestion and have implications for the safe application of wet oxidation of Bayer process liquors. The results also advance the fundamental understanding of the alkaline degradation of α,β-unsaturated carbonyl compounds in general. DEWEY : 660 ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie201388c [article] Understanding hydrogen in bayer process emissions. 2. hydrogen production during the degradation of unsaturated carboxylic acids in sodium hydroxide solutions [texte imprimé] / Allan Costine, Auteur ; Joanne S.C. Loh, Auteur ; Greg Power, Auteur . - 2012 . - pp. 12334–12342. Chimie industrielle Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 50 N° 22 (Novembre 2011) . - pp. 12334–12342 Mots-clés : Hydrogen  Carboxylic  acids  Sodium  hydroxide Résumé : This is the second in a series of studies of the production of hydrogen from the degradation of organic compounds in sodium hydroxide solutions. Unsaturated carboxylates, which are intermediate products in the wet oxidation of the types of monoaromatic compounds typically present in Bayer process liquors, have been found to produce significant amounts of hydrogen during alkaline degradation. The alkaline degradation of nine unsaturated carboxylates was investigated under anaerobic conditions in an autoclave, and the effect of temperature (175–275 °C) and NaOH concentration (0–6 M) on the degradation of acrylate, 2-butenoate, maleate, and 2-hexenoate was studied in detail for reaction times up to 120 min. All of the compounds investigated decompose to produce about 1 mol of hydrogen gas per mole of organic compound consumed, as well as a range of low molecular weight (LMW) carboxylates. The stoichiometries of the formation of hydrogen and LMW carboxylates from the unsaturated carboxylates observed here are consistent with the regioselective hydration of the C═C double bond to form the corresponding β-hydroxycarboxylates, which then undergo further degradation by an ionic mechanism involving base-catalyzed oxidation by water. These findings significantly advance the understanding of the production of hydrogen in Bayer process digestion and have implications for the safe application of wet oxidation of Bayer process liquors. The results also advance the fundamental understanding of the alkaline degradation of α,β-unsaturated carbonyl compounds in general. DEWEY : 660 ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie201388c