Heterogeneous non-catalytic

In heterogeneous non-catalytic reactors, the reaction medium is a two-phase medium. The two-phase reaction medium is composed of a gas phase and a solid phase for the reaction between a gaseous reactant and a solid reactant, whereas for the reaction between a gaseous reactant and a liquid reactant the reaction phase is a two-phase gas-liquid medium. The design of heterogeneous non-catalytic reactors for gas-solid reactions and gas-liquid reactions are discussed in this section. 

Homogeneous gas-phase reactions Heterogeneous non-catalytic reactions Heterogeneous catalytic reactions... 

Since the revised Biginelli mechanism was reported in 1997, numerous papers have appeared addressing improvements and variations of this reaction. The improvements include Lewis acid catalysis, protic acid catalysis, non-catalytic conditions, and heterogeneous catalysis. In addition, microwave irradiation (MWI) has been exploited to increase the reaction rates and yields. 

The first example cited is one in which the solid is totally consumed, whereas the second and third examples involve the formation of a new solid product which might be either a desired product, as in the second case, or a waste product (the gangue) as in the third example. Despite such fundamental differences from catalytic reactions, there are many similarities. In each case, chemisorption, surface chemical reaction emd diffusion through porous media occurs which is in common with heterogeneous chemical reactions. Hence, models representing the dynamics of these non-catalytic gas—solid processess incoporate the same principles of chemical reaction concomitant with diffusion and reaction in heterogeneous catalysts. 

All of the above discussion is strictly applicable only to homogeneous gas phase reactions. Usually the above considerations do apply reasonably well to non-polar liquids and nonpolar solutions, although normal Z values may be an order of magnitude less than for gas reactions. Reactions in solids are often much more complex, since they are usually heterogeneous, involve catalytic effects, reactions at preferential sites (dislocations, etc), and nucleation phenomena. These complicated processes are quite beyond the scope of the present article. For some description of these phenomena, and further references, the reader should consult Refs 9, 10 11... 

In industry, heterogeneous catalytic reactions are frequently performed not only at elevated temperatures but also at higher pressure. For EPR spectroscopy of catalysts under such practical conditions, suitable high-pressure/high-temperature reactors are needed, but there are only a few examples of EPR spectroscopy cells meeting these requirements. Moreover, they are more than 20 years old and were developed primarily for non-catalytic pyrolysis processes. Nevertheless, they seem to be suited without notable modifications for heterogeneous catalytic reactions, although no such applications are reported in the recent literature. 

Studies on the mechanisms of catalytic and non catalytic reac tions undertaken over the past 15-20 years have led to significant progress in the theory of reaction mechanisms. Most of the reactions involving homogeneous, metal-complex, and enzymatic catalyses were shown to be no less complex in terms of their mechanism compared with the mechanisms of radical chain processes. Infact, they appear to be much more complicated. Numerous examples of complicated mechanisms can be found in the literature. At present, multiroute mechanisms (with 2 to 4 reaction routes), involving as many as 8 intermediates and up to 12 elementary steps, are widely known to exist even in heterogeneous catalysis by metals and nonmetals where the simplest two-step schemes have hitherto been very popular. The existence of many routes and elementary steps is the most important general feature of the mechanisms of catalytic and also many noncatalytic reactions. 

The reaction mechanism in a heterogeneous catalytic process is more complicated than the mechanism in a non-catalytic reaction. In the first place, there is the influence of many physical stages of the catalysis on the reaction itself and on the reaction velocity. The main stages of the catalytic reaction can be represented as follows ... 

This classification is important not only for kinetics and for the equilibrium of the heterogeneous catalytic reactions with a doublet mechanism, but for the equilibrium of homogeneous catalytic and non-catalytic reactions as well, because the equilibrium does not depend on the mechanism of the reaction. It is interesting to note that the cyclic activated 4- and 6-complexes, postulated by Syrkin 355), are nothing but doublet and triplet index groups, and consequently the multiplet classification must be proper for them as well hence it can also be applied to the kinetics of catalytic reactions that are not heterogeneous. 

A great many reactions in physics and chemistry proceed via chain mechanisms. This large family of mechanisms includes free radical and ionic polymerization, Fischer Tropsch synthesis, gas phase pyrolysis of hydrocarbons, and catalytic cracking. Nuclear reactions, of both the power generating and the explosive kind, are also chain processes. Notice that chemical chain reactions can be catalytic or non-catalytic, homogeneous or heterogeneous. One is almost tempted to say that chain reactions are the preferred route of conversion in nature. 

DESIGN OF NON-IDEAL HETEROGENEOUS PACKED CATALYTIC REACTORS WITH INTERPELLET AXIAL DISPERSION... 

Among such oxidations, note that liquid-phase oxidations of solid paraffins in the presence of heterogeneous and colloidal forms of manganese are accompanied by a substantial increase (compared with homogeneous catalysis) in acid yield [3]. The effectiveness of n-paraffin oxidations by Co(III) macrocomplexes is high, but the selectivity is low the ratio between fatty acids, esters, ketones and alcohols is 3 3 3 1. Liquid-phase oxidations of paraffins proceed in the presence of Cu(II) and Mn(II) complexes boimd with copolymers of vinyl ether, P-pinene and maleic anhydride (Amberlite IRS-50) [130]. Oxidations of both linear and cyclic olefins have been studied more intensively. Oxidations of linear olefins proceed by a free-radical mechanism the accumulation of epoxides, ROOH, RCHO, ketones and RCOOH in the course of the reaction testifies to the chain character of these reactions. The main requirement for these processes is selectivity non-catalytic oxidation of propylene (at 423 K) results in the formation of more than 20 products. Acrylic acid is obtained by oxidation of propylene (in water at 338 K) in the presence of catalyst by two steps at first to acrolein, then to the acid with a selectivity up to 91%. Oxidation of ethylene by oxygen at 383 K in acetic acid in... 

Heterogeneous reactions in supercritical fluids can be catalytic or non-catalytic. Catalytic heterogeneous reactions are reactions carried out on solid catalysts and are of great impor-... 

We could not find any example of a heterogeneous catalytic reaction involving very reactive molecules such as chlorine or sulfur trioxide they are non catalytic or relevant to homogeneous catalysis. 

Heterogeneous reactors discussed in this section so far are reactors that handle multiphase reactions, which take place without the aid of catalysts. Hence, these reactors are called non-catalytic reactors. Non-catalytic heterogeneous reactors are essentially two-phase reactors broadly classified as gas-solid reactors and gas-liquid reactors based on the phases that are handled in them. We have already seen examples of these reactors in this section. 

Heterogeneous reactors are multiphase reactors in which the reaction medium is a multiphase medium. Heterogeneous reactors are broadly classified as reactors in which multiphase non-catalytic reactions take place and reactors in which multiphase catalytic reactions take place. Principles of multiphase reaction kinetics and design of multiphase reactors are discussed in this chapter. 

Consider a non-catalytic heterogeneous reaction between a reactant A in the gas phase and a reactant B in the solid phase ... 

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