Isothermal interpretations of oscillatory ignition during hydrogen oxidation in an open system. I. Analytical predictions and experimental measurements of periodicity

1986 ◽  
Vol 405 (1828) ◽  
pp. 117-128 ◽  
Keyword(s):  
Flow System ◽  
Hydrogen Oxidation ◽  
Mass Conservation ◽  
Stationary States ◽  
Third Body ◽  
Chain Reactions ◽  
Sequence Of Events ◽  
Oxidation Of Hydrogen ◽  
Branched Chain ◽  
Supercritical Reaction

The oxidation of hydrogen under well stirred, flowing conditions is the natural prototype of branched-chain reactions in open, gaseous systems. Experimentally, it exhibits the classical forms for the ( p - T a ) first and second ignition limits in the flow system. The constant reactant supply ensures that stationary states exist at subcritical conditions whereas the supercritical reaction is a repetitive, oscillatory sequence of events. In a linked pair of papers, we investigate isothermal criticality at the second limit in terms of changing nature of the singularities for the mass conservation equations and derive kinetic relationships that explain the oscillatory features. In this paper the origins of oscillatory ignition are traced analytically to chain-branching via H atoms coupled to the changing third-body efficiency in the elementary process H + O 2 + M → HO 2 + M, when water formed during ignition is displaced by the inflow of fresh hydrogen and oxygen. Analytical predictions are made of the periods between successive ignitions and of the conditions at which oscillatory reaction is transformed to a stationary state. A composition limit for the existence of oscillatory ignition in the (lean) mixture H 2 + 15O 2 + 14N 2 is located experimentally and explained in terms of the analytical inter­pretations presented here.

Branched-chain reactions in open systems: theory of the oscillatory ignition limit for the hydrogen+ oxygen reaction in a continuous-flow stirred-tank reactor

1984 ◽  
Vol 394 (1807) ◽  
pp. 243-258 ◽  
Keyword(s):  
Continuous Flow ◽  
Open Systems ◽  
Small Degree ◽  
Stirred Tank ◽  
Critical Conditions ◽  
Stirred Tank Reactor ◽  
Chain Reactions ◽  
Tank Reactor ◽  
Sequence Of Events ◽  
Branched Chain

The oxidation of hydrogen is the classic example of an ‘isothermal’, branched-chain reaction, and it is studied here from experimental and theoretical standpoints as the natural prototype of branched-chain reactions in open systems. With an inflow of reactants and a matching out-­flow of products, ignition now occurs as a repetitive, oscillatory sequence of events. By identifying the critical conditions as the marginal loss of stability of the stationary-state reaction, a simple criterion for ignition can be derived. This criterion is seen to be a generalization of the elementary treatments, going over to the classical results for closed vessels in the limit of zero flow-rate; it illustrates the stabilizing effect of opening the system. The experimental location of the p ─ T a limit for an equimolar H 2 +O 2 mixture in a continuous-flow, stirred-tank reactor (c. s. t. r.) reported here, shows good agreement with the new predictions (from a simple isothermal kinetic model). Extensive measurements of extents of reactant consumption and of the (small) degree of self-heating are also presented. These lead to rates of reaction and rates of heat release. We show how these are related under conditions of steady-state (non-explosive) reaction and, hence, how accurate measurements of the small temperature-excess can be used to give measurements of the reaction rate.

A gas-dispersed medium for pulsed chemical lasers based on photon-branched chain reactions

2001 ◽  
Vol 27 (8) ◽  
pp. 662-664
Author(s):  
V. I. Igoshin ◽  
V. S. Kazakevich ◽  
A. Yu. Kurov ◽  
A. L. Petrov ◽  
V. D. Shlyak
Keyword(s):  
Chain Reactions ◽  
Dispersed Medium ◽  
Branched Chain

scholarly journals The detection and inhibition of free radical chain reactions

1942 ◽  
Vol 180 (982) ◽  
pp. 237-256 ◽  
Keyword(s):  
Nitric Oxide ◽  
Free Radical ◽  
Chemical Analysis ◽  
Diethyl Ether ◽  
Pressure Increase ◽  
Stationary States ◽  
Decomposition Rates ◽  
Radical Chain ◽  
Chain Reactions ◽  
Limiting Values

Part I. Comparison of nitric oxide and propylene as inhibitors The reduction by propylene of the rate of pressure increase in the decomposition of propaldehyde at 550° has been shown by chemical analysis to represent a true inhibition of the reaction, and not to be due n an important degree to an induced polymerization of the propylene. With propaldehyde and with diethyl ether the limiting values to which the decomposition rates are reduced by nitric oxide and by propylene respectively are the same, although much more propylene is required to produce a given degree of inhibition. From this it is concluded that the limiting rates are more probably those of independent non-chain processes, than those characteristic of stationary states where the inhibitor starts and stops chains with equal efficiency.

Catalothermionic Power Generator Based on Internal Electron Emission in Ni/SiC Heterojunction Nanostructures

2009 ◽  
Author(s):  
Eduard G. Karpov ◽  
Ievgen I. Nedrygailov
Keyword(s):  
Energy Transfer ◽  
Electron Emission ◽  
Oxidation Reaction ◽  
Hydrogen Oxidation ◽  
Schottky Barriers ◽  
Gas Mixture ◽  
Hydrogen Oxidation Reaction ◽  
Power Generator ◽  
Oxidation Of Hydrogen ◽  
Internal Electron

We report on the unusual properties of single-faced SiC metal-semiconductor heterojunction nanostructures manifested by the ability to atalyze the hydrogen oxidation reaction, and also maintain internal electron emission over the Schottky barriers. As a result a stationary current has been detected in the preheated nanostructure when exposed to the oxyhydrogen gas mixture flux. The structures maintain both the non-adiabatic and electron-phonon channels of energy transfer, and the results of studies indicate the possibility for a very efficient conversion of chemical energy released in the catalytic oxidation of hydrogen into electricity.

Oscillatory excitation in branched chain reactions

1970 ◽  
Vol 19 (1) ◽  
pp. 149-151
Author(s):  
I. S. Zaslonko ◽  
S. M. Kogarko ◽  
E. V. Mozzhukhin
Keyword(s):  
Chain Reactions ◽  
Branched Chain

The Bakerian Lecture, 1966 The progress of photochemistry exemplified by reactions of the halogens

1967 ◽  
Vol 301 (1464) ◽  
pp. 1-37 ◽  
Keyword(s):  
Chemical Kinetics ◽  
Nuclear Reactions ◽  
Laser Action ◽  
Process Time ◽  
Propagation Time ◽  
Photochemical Process ◽  
Chain Reactions ◽  
Chlorine Reaction ◽  
Chemical Reaction Mechanisms ◽  
Branched Chain

It is appropriate for us to contemplate the growth of understanding of chemical kinetics which has taken place since the time of Planck. Understanding starts with the recognition by Stark in 1908 of the photon as an elementary particle in chemical reactions, and with the conception of the chain reaction by Bodenstein in 1913. Time was needed for the realization that the atom and the free radical are more often than not the entities responsible for chain propagation; time for Franck in 1924 to amplify Nernst’s conception of dissociation as the primary photochemical process; time for Semenov to give us the understanding of degeneracy in branched chain reactions; by 1930 the pattern had taken shape. When nuclear reactions were discovered their kinetic description needed no other modification than a change of time scale. In the evolution of chemical kinetics, the photochemistry of the halogens is not only typical but basic. From our early struggles with the hydrogen-chlorine reaction, through kinetic spectroscopy to population inversion of excited states and laser action, there is an unbroken thread, woven from the halogen staple, which knits together the fabric of chemical reaction mechanisms.

scholarly journals Catalytic activity of Pd-Ni in the oxidation of hydrogen for the safety of nuclear power plant

2016 ◽  
Vol 18 (1) ◽  
pp. 15-18
Author(s):  
Dariusz Łomot ◽  
Zbigniew Karpiński
Keyword(s):  
Bimetallic Catalysts ◽  
Nuclear Power ◽  
Power Plants ◽  
Hydrogen Oxidation ◽  
Precious Metals ◽  
Oxidation Of Hydrogen ◽  
Different Temperatures ◽  
Flowing System ◽  
Over Time ◽  
Excellent Stability

Abstract Pd-Ni/Al2O3 systems were investigated in the reaction of hydrogen oxidation in terms of their possible application as catalysts used in passive autocatalytic recombiners (PARs) used in nuclear power plants. Testing experiments were carried out in a flowing system at different temperatures and humidity of the reaction mixture. The bimetallic catalysts exhibited higher response to the increase of temperature and higher resistance to inhibit water than the monometallic palladium catalyst. They showed excellent stability during a few tens of hours, similarly, like their monometallic counterpart. Our bimetallic catalysts of hydrogen oxidation can be used as cheaper alternatives to catalysts based on the precious metals in the hydrogen oxidation without loss of their activity over time.

Spontaneous mirror symmetry breaking: an entropy production survey of the racemate instability and the emergence of stable scalemic stationary states

2020 ◽  
Vol 22 (25) ◽  
pp. 14013-14025 ◽  
Author(s):  
Josep M. Ribó ◽  
David Hochberg
Keyword(s):  
Symmetry Breaking ◽  
Entropy Production ◽  
Mirror Symmetry ◽  
Flow System ◽  
Stationary States ◽  
Open Flow ◽  
Continuous Range ◽  
Non Equilibrium

Stability of non-equilibrium stationary states and spontaneous mirror symmetry breaking, provoked by the destabilization of the racemic thermodynamic branch, is studied for enantioselective autocatalysis in an open flow system, and for a continuous range n of autocatalytic orders.

An E.S.R. study of the oxidation of some malonic and other acids by hydroxyl radicals

1981 ◽  
Vol 34 (2) ◽  
pp. 335 ◽  
Author(s):  
FR Hewgill ◽  
GM Proudfoot
Keyword(s):  
Hydroxyl Radicals ◽  
Ethylenediaminetetraacetic Acid ◽  
Flow System ◽  
Dicarboxylic Acids ◽  
Aliphatic Acids ◽  
Ph Values ◽  
Branched Chain

A series of terminal dicarboxylic acids, malonic acids and branched-chain aliphatic acids on oxidation with TiC13/H2O2 in a flow system give rise to e.s.r. spectra arising from mixtures of radicals. In most cases the dominant radical is that formed by abstraction of hydrogen from the β-carbon. Malonic acids complex with titanium(III) ions sufficiently strongly to be examined at elevated pH values without the need for added ethylenediaminetetraacetic acid.

Sign in / Sign up

Export Citation Format

Share Document