Plug-flow reactors series reactions

The series byproduct reaction requires a plug-flow reactor. Thus, for the mixed parallel and series system above, if... 

But what is the correct choice a byproduct reaction calls for a continuous well-mixed reactor. On the other hand, the byproduct series reaction calls for a plug-flow reactor. It would seem that, given this situation, some level of mixing between a plug-flow and a continuous well-mixed reactor will give the best... 

Solution The byproduct reactions to avoid are all series in nature. This suggests that we should not use a continuous well-mixed reactor but rather use either a batch or plug-flow reactor. 

A system has been constructed which allows combined studies of reaction kinetics and catalyst surface properties. Key elements of the system are a computer-controlled pilot plant with a plug flow reactor coupled In series to a minireactor which Is connected, via a high vacuum sample transfer system, to a surface analysis Instrument equipped with XFS, AES, SAM, and SIMS. When Interesting kinetic data are observed, the reaction Is stopped and the test sample Is transferred from the mlnlreactor to the surface analysis chamber. Unique features and problem areas of this new approach will be discussed. The power of the system will be Illustrated with a study of surface chemical changes of a Cu0/Zn0/Al203 catalyst during activation and methanol synthesis. Metallic Cu was Identified by XFS as the only Cu surface site during methanol synthesis. 

A batch or plug-flow reactor should be used for multiple reactions in series. 

Comparison of performance of a series of N equal-size CSTR reactors with a plug flow reactor for the first-order reaction... 

ILLUSTRATION 9.2 QUANTITATIVE DEVELOPMENT OF SERIES REACTION RELATIONSHIPS FOR BATCH AND PLUG FLOW REACTORS... 

Comparison of maximum yields for series reactions in stirred tank and plug flow reactors. 

At present the liquid phase reaction, A + B = C + D, takes place in a plug flow reactor. A conversion of 96% is obtained with Ca0 = Cb0 = 1 mol/liter. A mixed reactor 10 times the volume of the PFR is connected in series. Find conversions with the PFR first and with the PFR second in series. In the PFR,... 

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. 

At present the elementary liquid-phase reaction A + B R + S takes place in a plug flow reactor using equimolar quantities of A and B. Conversion is 96%, Cao = Cbo = 1 mol/liter. If a mixed flow reactor ten times as large as the plug flow reactor were hooked up in series with the existing unit, which unit should come first and by what fraction could production be increased for that setup ... 

Figure 8.13 Distribution of materials in a batch or plug flow reactor for the elementary series-parallel reactions...

In the next example, we will compare a complete mixed reactor with a first-order degradation reaction at steady state for a plug flow reactor and a series of smaller complete mixed reactors. 

The compound formaldehyde is biodegrading in several systems simultaneously (1) a lake, modeled as a complete mix reactor (2) an estuary, modeled as three complete mixed reactors in series (3) a large river, modeled as 10 complete mixed reactors in series, and a small stream, modeled as a plug flow reactor. What is the nondimensional reaction/residence time, k p, that is required for each of these systems to reach a degradation of 50%, 90%, 99%, and 99.9% ... 

In Example 6.6, we saw that there is little difference between a plug flow reactor and 10 or more reactors-in-series when the constituent is undergoing a first-order reaction under steady-state conditions. This is not true for all circumstances. One example would be a conservative tracer under unsteady boundary conditions, as discussed in this section. 

It is expected that the conclusions reached in the analysis of the series reaction will also be valid for methane partial oxidation. The first objective of this study was to verify this expectation. The second objective of the study was to determine how much faster than methane formaldehyde must permeate for the membrane reactor to begin to outperform a plug-flow reactor. 

In all cases studied, the membrane reactor offered a lower yield of formaldehyde than a plug flow reactor if all species were constrained to Knudsen diffusivities. Thus the conclusion reached by Agarwalla and Lund for a series reaction network appears to be true for series-parallel networks, too. That is, the membrane reactor will outperform a plug flow reactor only when the membrane offers enhanced permeability of the desired intermediate product. Therefore, the relative permeability of HCHO was varied to determine how much enhancement of permeability is needed. From Figure 2 it is evident that a large permselectivity is not needed, usually on the order of two to four times as permeable as the methane. An asymptotically approached upper limit of... 

The main individual reactions that take place in the reformer (e.g., reactions (1), (2) and (5)) will be considered separately from the overall autothermal reaction for two reasons. First, in ATR the reactor can be considered as two plug-flow reactors in series (1) a very fast POX reaction occurs at the top of the catalyst bed and utilizes a small portion of the bed and (2) a slow SR utilizes the remainder of the reactor bed. Therefore, an optimal ATR catalyst must have excellent SR eatalytic properties. Second, there may be situations in which liquid fuels are reformed using only these individual reactions e.g., diesel fuel may be reformed using only SR (reaction (2)) or only by POX (reaction (1)). 

Fig. 1.25. Reaction in series—batch or tubular plug-flow reactor. Concentration Cr of intermediate product P for consecutive first order reactions, A -> P -> Q...

Fig. 1.28. Reactions in series—comparison between batch or tubular plug-flow reactor and a single continuous stirred-tank reactor. Consecutive first-order reactions,...

The same general conclusions apply since backmixing of products with reactants should be avoided, a tubular plug-flow reactor or a batch reactor is preferred. However, there is one respect in which a series reaction involving a second reactant B does differ from simple series reaction with one reactant, even when the orders are the same. This is in the stoichiometry of the reaction the reaction cannot proceed completely to the product Q, even in infinite time, if less than two moles... 

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