Scale reaction, heterogeneous

Time-scale of homogeneous reaction (1st order) Time-scale of heterogeneous reaction (1st order) Time-scale for reactor heat-up... 

Extracting Information ABOUT Surface Heterogeneity Effect on Heterogeneous Reactions Using Multifractal Scaling... 

The transformations described in this chapter include mostly heterogeneous reactions at the surface of metallic lithium. Processes of this type can become too slow on a preparative scale at low temperatures. This is why either they have to be carried out at elevated temperarnres (possible decomposition reactions) or an activation (e.g. ultrasound) of the lithium metal is necessary. In spite of the relatively high reaction temperatures, very selective reactions are observed, when this method is applied to the presented systems. Thus, in addition to Section II. A (Deprotonation), this section contains many visualisations of X-ray structural analyses. 

Furthermore, because these reactions result in the effective removal of NOx from ozone production, by removing N02, the model also predicts that O, concentrations will decrease. Figure 7.17, for example, shows the model results for the ratio of O, (R0i) with the heterogeneous removal of N03 and N2Os included to that without these aerosol reactions. In some locations, the 03 concentrations are predicted to be as much as 30% lower than they would have been in the absence of the heterogeneous reactions. Because 03 is also the major OH source on a global scale, via its photolysis to electronically excited oxygen atoms, O( D), which react in part with gas-phase water, this also decreases the predicted OH levels. 

The major drawback of CF processing, however, is the incompatibility with heterogeneous reaction mixtures and highly viscous liquids. Apart from the fact that obtaining a temperature measurement directly from a reaction mixture under flow can be complicated, the adaptation of conditions from small-scale batch reactions to a CF cell may be time-consuming. 

Heterogeneous reactions lend themselves to continuous flow reactors, which are desirable as they minimise the reacting volume. This reduces operation risks, and allows smaller, more efficient plants to be built. Flow reactors designed for fluorous reactions with both liquid and gaseous substrates have been demonstrated to be effective, at least on a bench scale [49]. Fluorous solvents have also recently found applications as liquid membranes to control the rate of addition of reagents and so control exothermic reactions such as alkene bromination (Fig. 6), and demethylation of anisoles by reaction with boron tribromide [50], This has potential as a clean route as the kinetic control gives improved selectivity. 

Heterogeneous reactions are basically surface reactions. However, the concentration of A can often be assumed to be nearly constant on the scale of the pore diameter and it is possible to treat these heterogeneous reactions as pseudohomogeneous reactions, as in Equation 3.29. Then, the homogeneous production rate may be defined according to... 

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