Reactivity continued

GLS Fluidized with a Stable Level of Catalyst Only the fluid mixture leaves the vessel. Gas and liquid enter at the bottom. Liquid is continuous, gas is dispersed. Particles are larger than in bubble columns, 0.2 to 1.0 mm (0.008 to 0.04 in). Bed expansion is small. Bed temperatures are uniform within 2°C (3.6°F) in medium-size beds, and neat transfer to embedded surfaces is excellent. Catalyst may be bled off and replenished continuously, or reactivated continuously. Figure 23-40 shows such a unit. 

We expect the reactions complementary to equations (1) and (2), namely electrophilic attacks, to be faster for alkenes than for alkynes. Thus, reactivity ratios (/-ii and rj2) for corresponding alkynes and alkenes (PhC CH, PhCH=CH and BuC CH, BuCH=CH2) in radical copolymerizations favour the alkene over the alkyne . Electrophilic additions of Br, CI2, ArSCl and H3O+ to alkenes are usually much faster than those to alkynes . However, A (C=C)/A (C=C) can vary from 10 to < 1 for the different electrophilic processes and by 10 for one process (Br2 addition) when the solvent is changed from HjO to HOAc . This unexpected trend in reactivity continues undiminished in the rates of acid-catalysed hydration... 

FIGURE 4.6 The comparative shapes of the valence electrons to be engaged in chemical reactivity (continuous curve) computed using Eq. (4.151) based on the combined optimal Bohm total energy (4.148) with the golden ratio imbalance of Eq. (2.9), respecting the stable... 

The effectiveness and efficiency of microbicides result from the interplay of the chemicophysical properties of the active substance molecule, which are determined by the molecule s constitution. Solubility, polarity, ionicity and reactivity are examples of properties that influence effectiveness. Taking the N-trihalo-methylthio derivative as examples, Paulus Kiihle (1986) drew attention to an important principle that evidently applies to electrophilically active microbicides in general, namely that the relationship shown in Fig. 11 exists between the antimicrobial effectiveness and reactivity of microbicide molecules. As the reactivity increases, so, too, does the effectiveness—until it peaks at a moderately high reactivity level. Thereafter the antimicrobial activity decreases as the reactivity continues to rise because at this stage competition reactions — interactions of the reactive microbicide molecules with constituents of the surrounding medium — predominate. 

A major application of fluidized bed technology is to be found in the catalytic-cracking reactor, or Cat Cracker , which lies at the heart of the petroleum refining process. Here, the catalyst particles (which promote the breakdown of the large crude petroleum molecules into the smaller constituents of gasoline, diesel, fuel oil, etc.) are fluidized by the vaporized crude oil. An unwanted by-product of the reactions is carbon, which deposits on the particle surfaces, thereby blocking their catalytic action. The properties of the fluidized state are further exploited to overcome this problem. The catalyst is reactivated continuously by circulating it to another bed, where it is fluidized with air in which the carbon burns... 

Peixoto, F.C., de Medeiros, J.L. 1999. Modelling and parameter estimation in reactive continuous mixtures the catalytic cracking of alkanes. Part I. Braz. J. Chem. Eng. 16(1) 65-81. 

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