The Experts below are selected from a list of 252 Experts worldwide ranked by ideXlab platform
P.j. Van Den Berg - One of the best experts on this subject based on the ideXlab platform.
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The oxidation and absorption of nitrogen oxides in Nitric Acid in relation to the tail gas problem of Nitric Acid plants
Chemical Engineering Science, 2001Co-Authors: J.b. Lefers, F.c. De Boks, C.m. Van Den Bleek, P.j. Van Den BergAbstract:Abstract It has been suggested that concentrated Nitric Acid absorbs NO 2 very well. In this work it is demonstrated that concentrated Nitric Acid can also be used for the oxidation of NO to NO 2 , thus making an efficient removal of nitrogen oxides from tail gases in Nitric Acid plants possible. It is shown that the oxidation of NO takes place in the gas phase on a reaction plane parallel to the gas-liquid interface and that Danckwerts' solution for instantaneous irreversible reactions in the liquid phase can also be applied to gas phase reactions. The NO 2 and N 2 O 4 produced, which are in continuous equilibrium with each other, diffuse from the reaction plane to the gas bulk and to the gas-liquid interface. At the gas-liquid interface only N 2 O 4 dissolves physically into the concentrated Nitric Acid. The mathematical model to describe these diffusion processes agrees very well with the experiments.
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Absorption of NO2/N2O4 into diluted and concentrated Nitric Acid
Chemical Engineering Journal, 2001Co-Authors: J.b. Lefers, P.j. Van Den BergAbstract:Abstract The absorption rate and mechanism of NO2-N2O4 gas mixtures diluted with nitrogen into Nitric Acid solutions were investigated in a wetted wall column at 20 °C and 30 °C. It was found that N2O4, which is continuously in equilibrium with NO2, is preferentially absorbed into diluted Nitric Acid as well as into concentrated Nitric Acid. The absorption of N2O4 into diluted Acid is accompanied by a rapid pseudo-first order reaction with water. Values of HN2O4 were measured as a function of the Acid strength at 20 °C. Above 63% Nitric Acid the absorption was found to be purely physical. The solubility of N2O4 into concentrated Nitric Acid (63%) was derived from total vapour pressure data concerning the system NO2-N2O4-H2O-HNO3. It was found that Henry's law was valid within the condition considered.
Bernard Tribollet - One of the best experts on this subject based on the ideXlab platform.
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Mechanism of Nitric Acid Reduction and Kinetic Modelling
European Journal of Inorganic Chemistry, 2014Co-Authors: David Sicsic, Fanny Balbaud-célérier, Bernard TribolletAbstract:In France, the recycling of nuclear waste fuels involves the use of hot concentrated Nitric Acid. The understanding and prediction of the behaviour of the structural materials (mainly austenitic stainless steels) requires the determination and modelling of the Nitric Acid reduction process. Nitric Acid is indirectly reduced by an autocatalytic mechanism depending on the cathodic overpotential and Acid concentration. This mechanism has been widely studied. All the authors agree on its autocatalytic nature, characterized by the predominant role of the reduction products. It is also generally admitted that neither Nitric Acid nor the nitrate ion is the electroactive species. However, the nature of the electroactive species, the place where the catalytic species regenerates and the thermodynamic and kinetic behaviour of the reaction intermediates remain uncertain. The aim of this study was to clarify some of these uncertainties by performing an electrochemical investigation of the reduction of 4 M Nitric Acid at 40 °C at an inert electrode (platinum or gold). An inert electrode was chosen as the working electrode in a first step to avoid its oxidation and focus the research on the reduction mechanism. This experimental work enabled us to suggest a coherent sequence of electrochemical and chemical reactions. Kinetic modelling of this sequence was then carried out for a gold rotating disk electrode. A thermodynamic study at 25 °C allowed the composition of the liquid and gaseous phases of Nitric Acid solutions in the concentration range 0.5–22 M to be evaluated. The kinetics of the reduction of 4 M Nitric Acid was investigated by cyclic voltammetry and chronoamperometry at an inert electrode at 40 °C. The coupling of chronoamperometry and FTIR spectroscopy in the gaseous phase led to the identification of the gaseous reduction products as a function of the cathodic overpotential. The results showed that the reduction process is autocatalytic for potentials between 0.6 and 1.15 V/NHE. The electroactive species may be regenerated at the surface of the electrode for lower potentials, otherwise this regeneration process occurs in solution by a homogeneous chemical reaction. When the potential is less than 0.6 V/NHE, the fast reduction of nitrogen oxide may lead to rupture of the autocatalytic cycle.
Joanne M. Thwaites - One of the best experts on this subject based on the ideXlab platform.
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Vapour–liquid equilibria of Nitric Acid–water–sulphuric Acid mixtures
Journal of Chemical Technology & Biotechnology, 2007Co-Authors: S.r.m. Ellis, Joanne M. ThwaitesAbstract:New vapour–liquid equilibrium data have been obtained for the systems Nitric Acid–water and Nitric Acid–sulphuric Acid–water and have been applied to the design of a column for the concentration of Nitric Acid by extractive distillation with sulphuric Acid. The new data require an increase in the number of theoretical plates, and thus explain in part the present use of larger quantities of sulphuric Acid than should be necessary in a column designed according to previously published data.
J.b. Lefers - One of the best experts on this subject based on the ideXlab platform.
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The oxidation and absorption of nitrogen oxides in Nitric Acid in relation to the tail gas problem of Nitric Acid plants
Chemical Engineering Science, 2001Co-Authors: J.b. Lefers, F.c. De Boks, C.m. Van Den Bleek, P.j. Van Den BergAbstract:Abstract It has been suggested that concentrated Nitric Acid absorbs NO 2 very well. In this work it is demonstrated that concentrated Nitric Acid can also be used for the oxidation of NO to NO 2 , thus making an efficient removal of nitrogen oxides from tail gases in Nitric Acid plants possible. It is shown that the oxidation of NO takes place in the gas phase on a reaction plane parallel to the gas-liquid interface and that Danckwerts' solution for instantaneous irreversible reactions in the liquid phase can also be applied to gas phase reactions. The NO 2 and N 2 O 4 produced, which are in continuous equilibrium with each other, diffuse from the reaction plane to the gas bulk and to the gas-liquid interface. At the gas-liquid interface only N 2 O 4 dissolves physically into the concentrated Nitric Acid. The mathematical model to describe these diffusion processes agrees very well with the experiments.
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Absorption of NO2/N2O4 into diluted and concentrated Nitric Acid
Chemical Engineering Journal, 2001Co-Authors: J.b. Lefers, P.j. Van Den BergAbstract:Abstract The absorption rate and mechanism of NO2-N2O4 gas mixtures diluted with nitrogen into Nitric Acid solutions were investigated in a wetted wall column at 20 °C and 30 °C. It was found that N2O4, which is continuously in equilibrium with NO2, is preferentially absorbed into diluted Nitric Acid as well as into concentrated Nitric Acid. The absorption of N2O4 into diluted Acid is accompanied by a rapid pseudo-first order reaction with water. Values of HN2O4 were measured as a function of the Acid strength at 20 °C. Above 63% Nitric Acid the absorption was found to be purely physical. The solubility of N2O4 into concentrated Nitric Acid (63%) was derived from total vapour pressure data concerning the system NO2-N2O4-H2O-HNO3. It was found that Henry's law was valid within the condition considered.
David Sicsic - One of the best experts on this subject based on the ideXlab platform.
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Mechanism of Nitric Acid Reduction and Kinetic Modelling
European Journal of Inorganic Chemistry, 2014Co-Authors: David Sicsic, Fanny Balbaud-célérier, Bernard TribolletAbstract:In France, the recycling of nuclear waste fuels involves the use of hot concentrated Nitric Acid. The understanding and prediction of the behaviour of the structural materials (mainly austenitic stainless steels) requires the determination and modelling of the Nitric Acid reduction process. Nitric Acid is indirectly reduced by an autocatalytic mechanism depending on the cathodic overpotential and Acid concentration. This mechanism has been widely studied. All the authors agree on its autocatalytic nature, characterized by the predominant role of the reduction products. It is also generally admitted that neither Nitric Acid nor the nitrate ion is the electroactive species. However, the nature of the electroactive species, the place where the catalytic species regenerates and the thermodynamic and kinetic behaviour of the reaction intermediates remain uncertain. The aim of this study was to clarify some of these uncertainties by performing an electrochemical investigation of the reduction of 4 M Nitric Acid at 40 °C at an inert electrode (platinum or gold). An inert electrode was chosen as the working electrode in a first step to avoid its oxidation and focus the research on the reduction mechanism. This experimental work enabled us to suggest a coherent sequence of electrochemical and chemical reactions. Kinetic modelling of this sequence was then carried out for a gold rotating disk electrode. A thermodynamic study at 25 °C allowed the composition of the liquid and gaseous phases of Nitric Acid solutions in the concentration range 0.5–22 M to be evaluated. The kinetics of the reduction of 4 M Nitric Acid was investigated by cyclic voltammetry and chronoamperometry at an inert electrode at 40 °C. The coupling of chronoamperometry and FTIR spectroscopy in the gaseous phase led to the identification of the gaseous reduction products as a function of the cathodic overpotential. The results showed that the reduction process is autocatalytic for potentials between 0.6 and 1.15 V/NHE. The electroactive species may be regenerated at the surface of the electrode for lower potentials, otherwise this regeneration process occurs in solution by a homogeneous chemical reaction. When the potential is less than 0.6 V/NHE, the fast reduction of nitrogen oxide may lead to rupture of the autocatalytic cycle.
