Exothermic reactions product distributions

Combination of SR and TOX is known as indirect partial oxidation (IPOX). Due to the fast nature of TOX, it occurs earlier than SR and elevates the reactor temperature via exothermic heat release. In IPOX, oxygen is always used as the limiting reactant, and once it is completely consumed, the remaining methane is converted to hydrogen via Reaction 11.32. While SR and TOX are the main reactions, product distribution is strongly affected by the water-gas shift (WGS) ... 

The reactions are highly exothermic. Under Uquid-phase conditions at about 200°C, the overall heat of reaction is —83.7 to —104.6 kJ/mol (—20 to —25 kcal/mol) ethylene oxide reacting (324). The opening of the oxide ring is considered to occur by an ionic mechanism with a nucleophilic attack on one of the epoxide carbon atoms (325). Both acidic and basic catalysts accelerate the reactions, as does elevated temperature. The reaction kinetics and product distribution have been studied by a number of workers (326,327). 

Thermal properties of several chlorinated phenols and derivatives were studied by differential thermal analysis and mass spectrometry and in bulk reactions. Conditions which might facilitate the formation of stable dioxins were emphasized. No two chlorinated phenols behaved alike. For a given compound the decomposition temperature and rate as well as the product distribution varied considerably with reaction conditions. The phenols themselves seem to pyro-lyze under equilibrium conditions slowly above 250°C. For their alkali salts the onset of decomposition is sharp and around 350°C. The reaction itself is exothermic. Preliminary results indicate that heavy ions such as cupric ion may decrease the decomposition temperature. 

In highly exothermic reactions such as this, that proceed over deep wells on the potential energy surface, sorting pathways by product state distributions is unlikely to be successful because there are too many opportunities for intramolecular vibrational redistribution to reshuffle energy among the fragments. A similar conclusion is likely as the total number of atoms increases. Therefore, isotopic substitution is a well-suited method for exploration of different pathways in such systems. 

Table IV. Product Distribution for Exothermic Reactions of Co+ with C5H10 Isomers...

The interaction of chemical and physical rate processes can affect the dynamic behaviour of reactors used for polymerisation or other complex reaction processes. This may lead to variations in the distribution of reaction products. As an example, consider a continuous-flow back-mixed reactor in which an exothermic reaction occurs. A differential material balance may be written for each reaction component... 

Effective temperature control of large fixed beds can be difficult because such systems are characterized by a low heat conductivity. Thus in highly exothermic reactions hot spots or moving hot fronts are likely to develop which may ruin the catalyst. In contrast with this, the rapid mixing of solids in fluidized beds allows easily and reliably controlled, practically isothermal, operations. So if operations are to be restricted within a narrow temperature range, either because of the explosive nature of the reaction or because of product distribution considerations, then the fluidized bed is favored. 

The alkenc 2 (1 mmol) was dissolved in anhyd MeOH (2 ml,). With stirring CsSO+F (0.32 g, 1.3 mmol) under N, at rt was slowly added within 5 min. The mixture was stirred at rt for 1 h (caution the reaction is exothermic ), C H2C12 (20 mL) was then added, the insoluble precipitate filtered olT. the Filtrate washed with H,0. the organic layer dried (Na,S04) and the solvent evaporated in vacuo. The crude product was analyzed by 1<1F NMR and GC for product distribution. Pure products were isolated by GC or preparative TLC. 

Methanol Conversion to Hydrocarbons. The conversion of methanol to hydrocarbons requires the elimination of oxygen, which can occur in the form of H20, CO, or C02. The reaction is an exothermic process the degree of exothermicity is dependent on product distribution. The stoichiometry for a general case can be written as in Eq. (3.45) ... 

In other words the enamine tautomers are clearly not in rapid equilibrium and, since further reaction of the low energy tautomer 229 is rapid and exothermic, the product ratio could well be a reflection of the isomer distribution. This does not mean that reaction does not occur via an aza-ene-like transition state, but merely that such a mechanism is not necessarily responsible for the observed regioselectivity of reaction. 

The products of the endothermic as well as the exothermic reactions are widely scattered, and their distribution is clearly consistent with the formation of a complex capable of surviving several rotations before dissociating to produce a symmetric (about 6 = 90°) c.m. distribution that is distorted in the lab system by the (v ju Y Jacobian factor. This conclusion was confirmed by the presence at wider lab angles of a strong, sticky-collision peak in the distribution of M, resulting from the break-up of the complex to reform the original reagents rather than new products. 

The formation of vibrationally excited products is nearly always energetically possible in an exothermic reaction, and these products can be detected by observing either an electronic banded system in absorption or the vibration-rotation bands in emission. In principle, rotational level distributions may be determined by resolving the fine structure of these spectra, but rotational energy is redistributed at almost every collision, so that any non-Boltzmann distribution is rapidly destroyed and difficult to observe. In contrast, simple, vibrationally excited species are much more stable to gas-phase deactivation and the effects of relaxation are less difficult to eliminate or allow for. 

For all the exothermic reactions between halogen atoms and hydrogen halides, product vibrational distributions have been obtained by infrared chemiluminescence measurements. Values of fv. are given in Table 1.9. In... 

Packed-bed reactors are commonly used in industrial practice for conducting solid-catalyzed reactions. Most often, they physically consist of tube-bundles, which are packed with pellets on which the active catalyst is deposited. The reactants enter at one end of the tubes, and the reaction products are withdrawn from the other end. The reaction(s) proceed over the length of the tube, and so the species concentrations, as well as the fluid and solid temperatures, vary as a function of position within the tube. The tube bundles are stacked in a shell, and because most industrial reactions are exothermic, cooling medium flows in the shell to maintain a desired temperature distribution over the tube length. 

Kinetics Studies. The sol-gel kinetics experiments were performed on a meth-anolic solution of 1.12 M dimer and 1.57 X 10" M chromium acetylacetonate [Cr(acac)3], a spin relaxation agent. Previous studies (12, 13) showed that Cr(acac)3 concentration does not affect the product distribution or reaction rate of TMOS-derived sol-gel solutions. The solutions were acid catalyzed (1.64 X 10" M HCl), and various amounts of water were added. To compensate for the exothermicity caused by dimer hydrolysis when water is added to the dimer-methanol solution, the alcoholic silicate solution was chilled in a thermostatically controlled bath prior to the addition of water. By adjusting the temperature to the appropriate level, the desired reaction temperature (25 1 °C) could be achieved within 60 s of mixing. At this time, the sample was removed from the thermostatically controlled bath and inserted into the spectrometer probe. 

The influence of the temperature distribution on selectivity varies according to the reaction scheme. Among such schemes, the ccmsecutive reaction (A —B — C) qualitatively represents many organic reactions with by-products. As shown in the previous section, the use of dilute phase is recommended for endothermic reactions, but prohibited for exothermic reactions. This conclusion agrees with the development of fluid bed reactors for partial oxidations (exothermic) and cracking (endothermic). This knowledge may help one to design or develop new fluid bed contactors. 

Kuntz. P.J.. Nemeth. E.M.. Polanyi. J.C.. Rosner. S.D. anf Young C.E. (1966). Energy distribution among products of exothermic reactions, n. Repulsive, mixed, and attractive eneigy release. J. Chem. Phys. 44, 1168-1184. 

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