Endothermic reaction kinetics

Microcell 545 and Microcell 546 are chemical foaming agents with endothermic reaction kinetics. At low doses the formulations produce very fine cell structures. They can also be used as nucleating agents for directly gassed systems or in masterbatch formulations. ... 

In classical examples of kinetics, such as the hydrolysis of cane sugar by acids in water solution, the reaction takes hours to approach completion. Therefore Whilhelmy (1850) could study it successfially one and a half centuries ago. Gone are those days. What is left to study now are the fast and strongly exothermic or endothermic reactions. These frequently require pressure equipment, some products are toxic, and some conditions are explosive, so the problems to be solved will be more difficult. All of them require better experimental equipment and techniques. 

Even at 1,500 F, equilibrium eonstants for the first two reactions are high enough (about 10) to expect reaction to go essentially to completion except for kinetic-rate limitations. The reaction zone might be expected to be sized by volume of rabbled carbon bed, considering that the carbon gasification reactions that occur in it are governed by kinetics and are reaction-rate limited. Actually, it is sized by hearth area. The area exposed to the gases controls mass transfer of reactants from the gas phase to the carbon and heat transfer to support the endothermic reactions. 

Gustafsson and Lindholm (19) have shown the effects of translational energy on charge transfer reactions with H2, N2, and CO. They observe that endothermic reaction cross-sections increase with increasing kinetic... 

A constant volume batch reactor is used to convert reactant. A, to product, B, via an endothermic reaction, with simple stoichiometry, A —> B. The reaction kinetics are second-order with respect to A, thus... 

The success of the phase space theory in fitting kinetic energy release distributions for exothermic reactions which involve no barrier for the reverse reaction have led to the use of this analysis as a tool for deriving invaluable thermochemical data from endothermic reactions. This is an important addition to the studies of endothermic reactions described above. As an example of these studies, consider the decarbonylation reaction 11 of Co+ with acetone which leads to the formation of the... 

Atomic metal ion-hydrocarbon reactions bond dissociation energies for fragments, 15,16t endothermic reactions, 13,15,17f Atomic transition metal ion reactions development of approach for real-time measurements of dissociation kinetics, 39 ion beam apparatus, 12,14f studies of... 

In practice, of course, it is rare that the catalytic reactor employed for a particular process operates isothermally. More often than not, heat is generated by exothermic reactions (or absorbed by endothermic reactions) within the reactor. Consequently, it is necessary to consider what effect non-isothermal conditions have on catalytic selectivity. The influence which the simultaneous transfer of heat and mass has on the selectivity of catalytic reactions can be assessed from a mathematical model in which diffusion and chemical reactions of each component within the porous catalyst are represented by differential equations and in which heat released or absorbed by reaction is described by a heat balance equation. The boundary conditions ascribed to the problem depend on whether interparticle heat and mass transfer are considered important. To illustrate how the model is constructed, the case of two concurrent first-order reactions is considered. As pointed out in the last section, if conditions were isothermal, selectivity would not be affected by any change in diffusivity within the catalyst pellet. However, non-isothermal conditions do affect selectivity even when both competing reactions are of the same kinetic order. The conservation equations for each component are described by... 

The SR reactors are well suited for long periods of steady-state operation. The high endothermicity of the primary SR reaction results in reactor performances limited by heat transfer more than by reaction kinetics. Consequently, the reactors are designed to promote heat exchange and tend to be large and heavy [22]. 

Endothermic reactions require the input of energy, which can include the input of thermal energy. This gives the molecules greater kinetic energy, which can help their collisions to be more effective. 

The mixers discussed in Sections 4-6 are particularly suitable for reactions where the required heat input (endothermic reaction) or heat production (exothermic reaction) is modest (i.e., temperature changes on reaction would be only a few degrees in the absence of any heat transfer). HEX reactors can be used for rapid, highly exothermic (or endothermic) reactions not only are the mixing rate and residence time of a reactor matched to the kinetic rate and reaction time, but heat transfer performance is also matched to heat production (Figure 9). 

Exploring different methods for the intramolecular radical cyclization of 78 (Scheme 15)95, Usui and Paquette observed that (TMS SiH under normal conditions affords the expected functionalized diquinane 79 in 80% yield and in a a fi ratio of 82 18. MM2 calculations suggest it is the result of a kinetic controlled process. It is worth mentioning that the endothermic reaction 42 is expected to be one of the propagation steps in this chain process (vide infra). By replacing the silane with tin hydride under similar experimental conditions, the unexpected product 80 was obtained in a 77% yield. 

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