Decomposition experiments

The results from the decomposition experiments clearly support the previous hypothesis of selective biogenetic collagen break-down by... 

Because rates change continuously with time, accurate rate determinations must use small time intervals. At the outset of the NO2 decomposition experiment shown in Figure 15-6. the time interval between measurements is 5 seconds. For the first 5 seconds, the average rate of O2 production is as follows ... 

The residue from vacuum distillation of crude material (contaminated with sodium hydroxide) exploded after showing signs of decomposition. Experiment showed that 2-chloro-4-nitrotoluene decomposes violently when heated at 170-200° C in presence of alkali. Thorough water washing is therefore essential before distillation is attempted [1], A similar incident was reported with mixed chloronitrotoluene isomers [2],... 

Cleveland CL, Neff JC, Townsend AR, Hood E (2004) Composition, dynamics, and fate of leached dissolved organic matter in terrestrial ecosystems. Results from decomposition experiment. Ecosystems 7 275-285... 

Many of the 25 C oxidation potential estimates of Latimer (54) were obtained simply from a knowledge of what reactions proceed and what do not. Hence preparative and decomposition experiments in simple autoclaves are also of considerable value provided that full experimental details are published. Swaddle s group has performed a number of such studies on the transition metals from which boiler water circuits are made (55,56,57) and also on species of more direct relevance to laboratory studies (58,59,60). Quite trivial unexpected observations in autoclave studies can be used to place limits on equilibrium constants. In complex systems, unique interpretations will usually be impossible but the observations may still prove useful if they can be supplemented by estimated data (10, 61). 

FIGURE 7.2. Typical in-situ dendrimer decomposition experiment in 20% O2. The supported DENs were pressed into a self-supporting wafer, loaded into the IR cell, and temperature was increased at approximately 5°C/min. The first 5 spectra shown are at intervals of approximately 30°C the bottom three spectra was collected after soaking at 300°C for 2 h. 

In-situ infrared spectroscopy has been used in much the same fashion at TGA, but temperature profiles have been combined with monitoring changes at constant temperature. " IR spectroscopy does not yield the same direct information about the complete removal of organic residues that TGA provides. On the other hand, CO adsorption experiments performed along with dendrimer decomposition experiments provide direct information regarding metal availability. Further, IR experiments provide... 

Complex 24 was used in thermal and Lewis acid-catalyzed decomposition experiments. Intramolecular C—H reductive elimination from 24 to form exo-2-phenyl-aminonorbornane was demonstrated with labeling experiments [7]. 

At temperatures below the ignition point, the thermal decomposition of black powder provides an interesting insight into the processes which are thought to control the reaction rate during subsequent burning. In decomposition experiments it has been shown that the overall reaction proceeds in several steps. As the temperature is increased the steps become shorter and the reaction faster. Since these reactions involve gases, the effect of pressure is also important. 

However, in the lignin fraction of the rotted straw, the ratio was 0.5 1 at the end of the decomposition experiment. Therefore, the syringyl components are split off more slowly from the polymeric lignin than the guaiacyl... 

Initial Rate of Temperature Initial Decomposition Experiment (°C) [N204] °f N204 (M/s)... 

Using the normal addition procedure (02 diffusion into a 75/25 benzene/THF solution of poly(styryl)lithium) the 37% dimer fraction analyzed for 19% alkyl radical dimer and 18% macroperoxide after LiAlH4 reduction. The yield of macroperoxide was also confirmed by thermal decomposition experiments in refluxing toluene, followed again by size exclusion chromatography analysis of the dimer fraction. The amount of hydroperoxide could be deduced from the difference between the amounts of total peroxide (determined by iodometric titration) versus the amount of macroperoxide determined by LiAlH4 reduction. 

Decomposition experiments for these CPs listed in Table 14.11 were carried out by the simultaneous action of UV radiation and Fenton s reagent (Benitez et al., 2000). Table 14.11 shows the first-order rate constants and half-lives. During the photo-Fenton s reagent reaction, the single photodecomposition rate constant, ku decreased as the number of chlorine substituents increased. In addition, combined rate constants, ku are much greater than the radical reaction constants, k,. Therefore, this confirms the additional contribution of the radical reaction due to generation of the hydroxyl radicals by Fenton s... 

The results of this calculation for the above-mentioned decomposition experiment are given in Fig. 6.14 by the continuous lines. The crosses illustrate the variation of the concentration of dithionite and sulphite in solution obtained by titration of samples taken at fixed times. It can be seen that the concentrations obtained by calculation from the experimental currents (continuous line) are in good agreement with the ones obtained by titration (crosses). Note also that the increase of the concentration of sulphite is twice as high as the drop of the sodium dithionite concentration. Indeed, for each dithionite ion that is decomposed, two sulphite ions are... 

I. Litter Decomposition Experiments. The rate of mass loss of fresh plant litter may be used to estimate litter decomposition rates, assuming first-order kinetics ... 

Following preliminary DSC studies, isothermal decompositions of small quantities (1-3 mg) of compound are performed at temperatures generally below the observed DSC exothermic maximum. Samples are usually thermolyzed in sealed Pyrex tubes. Use of Pyrex usually precludes reaction with the container that often occurs with metal reaction vessels. Sealed vessels also prevent corrosive decomposition products, e.g. NO2 or HF, from damaging laboratory instrumentation. Sealed reaction vessels confine the decomposition products where they can easily be identified and quantified. It is obvious that highly reactive decomposition products such as formaldehyde are not observed by this technique, but they would not be expected to survive over the time of these decomposition experiments (seconds to hours, depending on the temperature). Seal vessel thermoylses mimic real storage scenarios where the sample is self-confined. However, autocatalysis may occur in sealed vessels that would not be observed in open ones. On the other hand, in unsealed tubes sublimation of the sample may become competitive with decomposition. 

L.L. Bircumshaw, B.K Newman "The Thermal Decomposition of Ammonium Perchlorate I. Introduction, Experimental, Analysis of Gaseous Products and Thermal Decomposition Experiments," Proc. Roy. Soc. (London) A227 (1954) 115-132 ibid, "The Thermal Decomposition of Ammonium Perchlorate II. The Kinetics of the Decomposition, the Effect of Particle Size, and Discussion of Results" A227 (1955) 228-241. L.L.Bircumshaw, T.R. Phillips, "The Kinetics of the Thermal Decomposition of Ammonium Perchlorate" J. Chem. Soc. 122 (1957) 4741-4747. 

Methane decomposition experiments were conducted in a 5.0 ml fixed bed quartz microreactor using 0.3 g of catalysts. The catalysts were arranged within the reaction zone in several layers separated with ceramic wool to prevent clogging of the reactor due to produced carbon. The reactor temperature was maintained constant via a type K thermocouple and Love Controls microprocessor. The tubular reactor was made out of alumina and quartz tubings (I.D. 3-6 mm). 

The thermal decomposition experiments performed by Solomon and co-workers (5,12-15) were done in a thin bed under vacuum. Under these conditions, the tar molecules may be removed quickly from the reacting bed and undergo minimal secondary reactions. Therefore, many of the coal structural elements are preserved in tar and careful analysis of these products can supply clues to the original structure. For example, the average molecular weight of the PSOC 170 tar was determined to be about 370 by VPO and 490 and 385 by GPC (16). 

The relationship between the coal organic structure and the products of thermal decomposition has been incorporated into a general kinetic model. The model has proved successful in simulating the results of vacuum thermal decomposition experiments for a variety of bituminous coals and lignites (5,12,13). It has also proved to be successful in limited application to other conditions such as coal proximate... 

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