Plug flow reactor comparison with mixed

With Eqs. 6b and 7 we can compare performance of N reactors in series with a plug flow reactor or with a single mixed flow reactor. This comparison is shown in Fig. 6.5 for first-order reactions in which density variations are negligible. 

Eigure 2 shows that even materials which are rather resistant to oxidation ( 2/ 1 0.1) are consumed to a noticeable degree at high conversions. Also the use of plug-flow or batch reactors can offer a measurable improvement in efficiencies in comparison with back-mixed reactors. Intermediates that cooxidize about as readily as the feed hydrocarbon (eg, ketones with similar stmcture) can be produced in perhaps reasonable efficiencies but, except at very low conversions, are subject to considerable loss through oxidation. They may be suitable coproducts if they are also precursors to more oxidation-resistant desirable materials. Intermediates which oxidize relatively rapidly (/ 2 / i — 3-50 eg, alcohols and aldehydes) are difficult to produce in appreciable amounts, even in batch or plug-flow reactors. Indeed, for = 50, to isolate 90% or more of the intermediate made, the conversion must... 

Figure 6.6 Comparison of performance of a series of N equal-size mixed flow reactors with a plug flow reactor for elementary second-order reactions...

Figure 5. Comparison of performance of single mixed and plug flow reactors for the nth-order reactions. (Reprinted with permission from Ref 13, Fig. 6.1, 1972, John Wiley and Sons.)...

Table 5.2 Technical and economic running of a tubular turbulent reactor under quasi-plug flow conditions in turbulent flows in comparison with a perfect mixing reactor ...

Figure 6.36. Plot of the dimensionless concentration of cell mass x and substrate s for a continuous culture as a function of the dimensionless mean residence time I as in Fig. 6.1b with Xq > 0 Calculated comparison between a CSTR with maximum mixing (ST m) or one with total segregation (ST J and a continuous plug flow reactor (PF), assuming Monod kinetics with a death rate (Tsai et al., 1969).

Comparison of (10.3.1-2) and (10.3.1-3) shows that again there are differences between the yields obtained in the reactor types discussed here. A specific example is shown in Fig. 10.3.1-2, where it is seen that the batch or plug flow reactor has greater selectivity for Q relative to the perfectly mixed flow reactor. For sets of first-order reactions, Wei [1966] has shown that the convexity of reaction paths is decreased from plug flow to mixed reactors because of the intermingling of fluid elements with different extents of reaction, and so the... 

When the substrate concentration S is much greater than Km, Eqs. (12) and (13) reduce to the same form. In this case, the continuous flow stirred reactor and the plug flow device achieve similar conversion values in a given time. In contrast, when S Km, the reaction rate becomes first order in the substrate concentration (see Eq. (9)), and the plug flow reactor provides higher conversion values in comparison with the well-mixed continuous flow device. In the latter bioreactor, all the enzyme would be exposed to the same low concentration of the substrate which is not useful except when the reaction is inhibited by the substrate. 

The distribution of residence times of reactants or tracers in a flow vessel, the RTD, is a key datum for determining reactor performance, either the expected conversion or the range in which the conversion must fall. In this section it is shown how tracer tests may be used to estabhsh how nearly a particular vessel approaches some standard ideal behavior, or what its efficiency is. The most useful comparisons are with complete mixing and with plug flow. A glossary of special terms is given in Table 23-3, and major relations of tracer response functions are shown in Table 23-4. 

Equations 1 and 2 are displayed in graphical form in Fig. 6.1 to provide a quick comparison of the performance of plug flow with mixed flow reactors. For... 

Thus it seems that the type of comparison that should be made depends on the purpose of the model. For design of mixing vessels the tracer curves should be matched, and for reactor design conversions should be matched. Unfortunately, this means that a general approach is not possible for all cases. However, the various criteria of correspondence approach each other with approach to plug flow or... 

Model of ideal desaturation (model with plug flow regime) is the favorable approximation for calculation of reactor parameters [3,4,6] any cross-section normal for flow, weight hour space velocity w and flow s properties (pressure, temperature and reaction mixture structure) are uniform narrow distribution of reagents residence times in reaction zone Xpr diffusion in the axial line (coplanar mixing or turbulence) in comparison with weight hour space velocity is negligible low. 

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