Atmospheric nitrogen kinetics

There are a large number of chain reactions that are significant in industrial processes or play an important role for the environment. Classes of chain reactions that are relevant industrially include hydrogen/halogen reactions and pyrolysis of hydrocarbons, which are both discussed below, and free-radical polymerization discussed in many textbooks on kinetics. As an example of a chain reaction of significant environmental consequence, we will discuss formation of nitric oxide from fixation of atmospheric nitrogen. 

A special place among kinetic studies in combustion is occupied by work on nitrogen oxidation. Begun at the AS USSR Institute of Chemical Physics in the mid-thirties on the initiative of N. N. Semenov, research to determine the feasibility of fixation of atmospheric nitrogen for the production of mineral fertilizers has today found application in the development of environmental protection measures for toxic components of combustion products, including nitrogen oxide. In December, 1939, Ya.B. defended his doctoral dissertation on The Oxidation of Nitrogen in Combustion and Explosions. It was precisely these studies, in which D. A. Frank-Kamenetskii, P. Ya. Sadovnikov, A. A. Rudoy, A. A. Kovalskii, and others actively participated, that led Ya.B. to the problems of combustion and detonation. 

Most of the cationic polymerizations and the polymer syntheses thereby, discussed in Chapters 4 and 5, may be carried out conveniently under the dry and inert gas atmosphere (nitrogen or argon) by the so-called syringe technique. Except for highly elaborated kinetic experiments, stringent high-vacuum technique is not required to maintain the control of the polymerizations and polymer architectures. 

Rate constants obtained at high concentrations are valid for estimating the rates of reaction at low partial pressures of atmospheric contaminants. Kinetic studies may be carried out at trace concentrations. Results are given for determining the rate of reaction of nitrogen dioxide with ozone. 

Earth s atmosphere is constantly being bombarded by cosmic rays of extremely high penetrating power. These rays, which originate in outer space, consist of electrons, neutrons, and atomic nuclei. One of the important reactions between the atmosphere and cosmic rays is the capture of neutrons by atmospheric nitrogen (nitrogen-14 isotope) to produce the radioactive carbon-14 isotope and hydrogen. The unstable carbon atoms eventually form C02, which mixes with the ordinary carbon dioxide ( C02) in the air. As the carbon-14 isotope decays, it emits f3 particles (electrons). The rate of decay (as measured by the number of electrons emitted per second) obeys first-order kinetics. It is customary in the study of radioactive decay to write the rate law as... 

Thermodynamics, Kinetics, and the Dream of Fixing Atmospheric Nitrogen... 

At the high temperatures found in MHD combustors, nitrogen oxides, NO, are formed primarily by gas-phase reactions, rather than from fuel-bound nitrogen. The principal constituent is nitric oxide [10102-43-9] NO, and the amount formed is generally limited by kinetics. Equilibrium values are reached only at very high temperatures. NO decomposes as the gas cools, at a rate which decreases with temperature. If the combustion gas cools too rapidly after the MHD channel the NO has insufficient time to decompose and excessive amounts can be released to the atmosphere. Below about 1800 K there is essentially no thermal decomposition of NO. 

Because hydrolytic reactions are reversible, they are seldom carried out in batch wise processes [26,28,36,70]. The reactor is usually a double jacket cylindrical flask fitted with a reflux condenser, magnetic stirrer, and thermometer connected with an ultrathermostat. The catalyst is added to the reaction mixture when the desired temperature has been reached [71,72]. A nitrogen atmosphere is used when the reactants are sensitive to atmospheric oxygen [36]. Dynamic methods require more complicated, but they have been widely used in preparative work as well as in kinetic studies of hydrolysis [72-74]. The reaction usually consists of a column packed with a layer of the resin and carrying a continuous flow of the reaction mixture. The equilibrium can... 

Since high temperatures and a nitrogen atmosphere are necessary to obtain measurable rates of polyesterification and to remove the reaction water, a loss of volatile reactants can hardly be avoided, especially in early stages of polyesterification. In the last stages, the decrease of the concentration of the volatile reactants can be of the same order of magnitude as their concentration. Consequently, the ultimate points of the kinetic plot have possibly no significance. 

Non-isothermal measurements of the temperatures of dehydrations and decompositions of some 25 oxalates in oxygen or in nitrogen atmospheres have been reported by Dollimore and Griffiths [39]. Shkarin et al. [606] conclude, from the similarities they found in the kinetics of dehydration of Ni, Mn, Co, Fe, Mg, Ca and Th hydrated oxalates (first-order reactions and all values of E 100 kJ mole-1), that the mechanisms of reactions of the seven salts are probably identical. We believe, however, that this conclusion is premature when considered with reference to more recent observations for NiC204 2 H20 (see below [129]) where kinetic characteristics are shown to be sensitive to prevailing conditions. The dehydration of MnC204 2 H20 [607] has been found to obey the contracting volume... 

C05-0014. Atmospheric temperature at the altitudes where jetliners fly is around -35 °C. Calculate the average and molar kinetic energies of molecular nitrogen at this temperature. 

Another point that one has to observe from analysis of Figure 10, is that despite the different precursor atmospheres, and consequently different N precursor partial pressures in the deposition, there is a coincidence of the deposition rate behavior upon nitrogen content (for mixtures other than C2H-N2). This points to a strong dependence of growth kinetics with nitrogen content. 

Abstract A review is provided on the contribution of modern surface-science studies to the understanding of the kinetics of DeNOx catalytic processes. A brief overview of the knowledge available on the adsorption of the nitrogen oxide reactants, with specific emphasis on NO, is provided first. A presentation of the measurements of NO, reduction kinetics carried out on well-characterized model system and on their implications on practical catalytic processes follows. Focus is placed on isothermal measurements using either molecular beams or atmospheric pressure environments. That discussion is then complemented with a review of the published research on the identification of the key reaction intermediates and on the determination of the nature of the active sites under realistic conditions. The link between surface-science studies and molecular computational modeling such as DFT calculations, and, more generally, the relevance of the studies performed under ultra-high vacuum to more realistic conditions, is also discussed. 

In this paper we summarize some of the results of our measurements of rates of dry oxidation. Results of chemical analyses of residues produced by heating in flowing nitrogen atmosphere (distillation) are also reported and combined with our kinetic data to obtain values of kinetic parameters. Preliminary results of measurements of rates of wet oxidation are presented. 

Figure 38 TGA results determined from a POM homopolymer and copolymer sample in a nitrogen atmosphere. The degradation kinetics differs because of their different structures.

General Methods. Methanol used in kinetic runs was distilled from sodium methoxide or calcium hydride in a nitrogen atmosphere before use. Freshly distilled cyclohexanol was added to the methanol in the ratio 6.0 ml cyclohexanol/200 ml MeOH and was used as an internal standard for gas chromatographic (GC) analysis. Benzaldehyde was distilled under vacuum and stored under nitrogen at 5°. Other aldehydes (purchased from Aldrich) were also distilled before use. The corresponding alcohols (purchased from Aldrich) were distilled and used to prepare GC standards. All metal carbonyl cluster complexes were purchased from Strem Chemical Company and used as received. Tetrahydrofuran (THF) was distilled from sodium benzophenone under nitrogen before use. 

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