Systems of reactions

Before we can proceed with the choice of reactor and operating conditions, some general classifications must be made regarding the types of reaction systems likely to be encountered. We can classify reaction systems into five broad types ... 

Consider now which of the idealized models is preferred for the five categories of reaction systems introduced in Sec. 2.2. 

There is one special class of reaction systems in which a simplification occurs. If collisional energy redistribution of some reactant occurs by collisions with an excess of heat bath atoms or molecules that are considered kinetically structureless, and if fiirthennore the reaction is either unimolecular or occurs again with a reaction partner M having an excess concentration, dien one will have generalized first-order kinetics for populations Pj of the energy levels of the reactant, i.e. with... 

There are a variety of reaction systems that allow the formation of cellulose trinitrate [9046-47-3]. HNO in methylene chloride, CH2CI2, yields a trinitrate with essentially no degradation of the cellulose chain (53). The HNO /acetic acid/acetic anhydride system is also used to obtain the trinitrate product with the fiber stmcture largely intact (51,52). Another polymer analogous reaction utilises a 1 1 mixture of HNO and H PO with 2.5% P2O5 to achieve an almost completely nitrated product (54). 

There are four types of reaction systems for the production of polyethylene of commercial importance ... 

Table 10. Ranges of Reaction System Variables in the Direct Oxidation Process for Ethylene Oxide ...

In this chapter we will discuss the results of the studies of the kinetics of some systems of consecutive, parallel or parallel-consecutive heterogeneous catalytic reactions performed in our laboratory. As the catalytic transformations of such types (and, in general, all the stoichiometrically not simple reactions) are frequently encountered in chemical practice, they were the subject of investigation from a variety of aspects. Many studies have not been aimed, however, at investigating the kinetics of these transformations at all, while a number of others present only the more or less accurately measured concentration-time or concentration-concentration curves, without any detailed analysis or quantitative kinetic interpretation. The major effort in the quantitative description of the kinetics of coupled catalytic reactions is associated with the pioneer work of Jungers and his school, based on their extensive experimental material 17-20, 87, 48, 59-61). At present, there are so many studies in the field of stoichiometrically not simple reactions that it is not possible, or even reasonable, to present their full account in this article. We will therefore mention only a limited number in order for the reader to obtain at least some brief information on the relevant literature. Some of these studies were already discussed in Section II from the point of view of the approach to kinetic analysis. Here we would like to present instead the types of reaction systems the kinetics of which were studied experimentally. 

Different type of reaction system containing organic solvent can be classified in a simple way. To accomplish this we first distinguished between microaqueous organic systems with a continuous organic phase, then reversed micelles stabilized with surfactant and a liquid-liquid biphasic system in which distinct organic and aqueous phase are mixed. The latter medium is discussed in this paper. 

Pressure measurements can be accomplished by any one of a number of different types of manometric devices without disturbing the system being observed. Another type of reaction system that can be monitored by pressure measurements is one in which one of the products can be quantitatively removed by a solid or liquid reagent that does not otherwise affect the reaction. For example, acids formed by reactions in the gas phase can be removed by absorption in hydroxide solutions. 

Paul, E. L. (1988). "Design of Reaction Systems for Specialty Organic Chemicals."... 

Rp is the local polymeriation rate—the rate at a layer located a distance D from the surface of the reaction system. Since Rp varies with the depth of penetration into the reaction system, it is useful to calculate the layer-averaged polymerization rate Rp, the average polymerization rate for a thickness D of reaction system. Rp is obtained by integrating the local rate over the layer thickness D and dividing by D to give... 

For most practical photopolymerizations there is appreciable attenuation of light intensity with penetration and the dependence of polymerization rate on monomer, photoinitiator, and light intensity is more complex (see Eqs. 3-54 and 3-55 for exact definitions). Equation 3-54 is especially useful for analyzing the practical aspects of a photopolymerization. When polymerizing any specific thickness of reaction system it is important to know Rp at various depths (e.g., front, middle, and rear surfaces) than to know only the total Rp for that system thickness. If the thickness is too large, the polymerization rate in the rear (deeper) layers will be too low, and those layers will be only partially polymerized—the result would be detrimental because the product s properties (especially the physical properties) would be... 

To achieve LCP, one needs to start by choosing the initiator, coinitiator, and other components of a reaction so that there is no nucleophile present that can irreversibly terminate the propagating cationic species. Basic components also need to be avoided to minimize P-proton transfer. However, even with the most judicious choice of reaction system, P-proton transfer is still present because monomer itself is a base. One needs to minimize P-proton transfer to monomer to achieve LCP. 

We answer the question What does it mean "to pick a multiscale system at random" We introduce and analyze a notion of multiscale ensemble of reaction systems. These ensembles with well-separated variables are presented in Section 3. 

I suggest that for certain types of reaction systems in solution it is useful to suppose that the energy, if it does arrive in increments, must arrive in a relatively short period of time compared to the lifetime of the cage. 

It is clear that several aspects of reaction systems with suspended substrates are significantly different from those in solution. The presence of solid substrates has important consequences for the reaction kinetics and thermodynamics, and it requires different strategies for reaction engineering. 

Table 12.1 Classification of reaction systems used for biocatalysis with undissolved substrates and/or products. Y Yes N No L Low H High A Aqueous media O Organic solvent. 

From the foregoing dicussion it is apparent that residuum hydroconversion processes can be influenced adversely by pore diffusion limitations. Increasing the catalyst porosity can alleviate the problem although increased porosity is usually accompanied by a decrease in total catalytic surface area. Decreasing the catalyst particle size would ultimately eliminate the problem. However, a different type of reaction system would be required since the conventional fixed bed would experience excessive pressure drops if very fine particles were used. A fluidized system using small particles does not suffer from this limitation. However, staging of the fluidized reaction system is required to minimize the harmful effects that backmixing can have on reaction efficiency and selectivity. 

Bailey, J. E. Horn, F. 1972 Cyclic operation of reaction systems the influence of diffusion on catalyst selectivity. Chem. Engng Sci. 27,109. 

It has long been appreciated that the occurrence of compensation effects in kinetic data could result from the specific selection of reaction systems for study on the criterion that conveniently measurable rates are obtained within the same selected temperature interval (4,5). If either A or varies significantly within such data, appropriate magnitudes of k are only possible if there is a measure of compensation. 

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