Reactor mixed flow

Mixed-flow reactor. Consider now the mixed-flow reactor in Figure 5.2b in which a feed of Component i is reacting. A material balance for Component i per unit time gives ... 

Figure 5.2 Rate of reaction in a mixed-flow reactor. 

Combining Equations 5.48 for the mixed-flow reactor with constant density and 5.50 gives ... 

Figure 5.4a compares the profiles for a mixed-flow and plug-flow reactor between the same inlet and outlet concentrations, from which it can be concluded that the mixed-flow reactor requires a larger volume. The rate of reaction in a mixed-flow reactor is uniformly low as the reactant is instantly diluted by the product that has already been formed. In a plug-flow or ideal-batch reactor,... 

A production rate of 10 tons per day equates to 0.0788 kmol-mkr1. For a mixed-flow reactor with equimolar feed CA0 = CB0 = 8.33 kmol-nr3 at 60°C ... 

As expected, the result shows that the volume required by a mixed-flow reactor is much larger than that for plug-flow. 

Maximum selectivity requires a minimum ratio r2/ri in Equation 5.65. A batch or plug-flow reactor maintains higher average concentrations of feed (CFeed) than a mixed-flow reactor, in which the incoming feed is instantly diluted by the PRODUCT and BYPRODUCT. If ax > a2 in Equations 5.64 and 5.65 the primary reaction to PRODUCT is favored by a high concentration of FEED. If ax < a2 the primary reaction to PRODUCT is favored by a low concentration of FEED. Thus, if... 

In general terms, if the reaction to the desired product has a higher order than the byproduct reaction, use a batch or plug-flow reactor. If the reaction to the desired product has a lower order than the byproduct reaction, use a mixed-flow reactor. 

For a certain reactor conversion, the FEED should have a corresponding residence time in the reactor. In the mixed-flow reactor, FEED can leave the instant it enters or remains for an extended period. Similarly, PRODUCT can remain for an extended period or leave immediately. Substantial fractions of both FEED and PRODUCT leave before and after what should be the specific residence time... 

But what is the correct choice if a < a2l Now the parallel byproduct reaction calls for a mixed-flow 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 mixed-flow reactor will give the best overall selectivity12. This could be obtained by a ... 

Styrene (A) and Butadiene (B) are to be polymerized in a series of mixed-flow reactors, each of volume 25 m3. The rate equation is first order with respect to A and B ... 

Solution As much as possible, the production of di- and triethanolamine needs to be avoided. These are formed by series reactions with respect to monoethanolamine. In a mixed-flow reactor, part of the monoethanolamine formed in the primary reaction could stay for extended periods, thus increasing its chances of being converted to di- and triethanolamine. The ideal batch or plug-flow arrangement is preferred to carefully control the residence time in the reactor. 

Solution The byproduct reactions to avoid are all series in nature. This suggests that a mixed-flow reactor should not be used, rather either a batch or plug-flow reactor should be used. 

However, the laboratory data seem to indicate that maintaining a constant concentration in the reactor to maintain 63% sulfuric acid in the reactor would be beneficial. Careful temperature control is also important. These two factors would suggest that a mixed-flow reactor is appropriate. There is a conflict. How can a well-defined residence time and a constant concentration of sulfuric acid be simultaneously maintained ... 

Example 14.1 Consider again the chlorination reaction in Example 7.3. This was examined as a continuous process. Now assume it is carried out in batch or semibatch mode. The same reactor model will be used as in Example 7.3. The liquid feed of butanoic acid is 13.3 kmol. The butanoic acid and chlorine addition rates and the temperature profile need to be optimized simultaneously through the batch, and the batch time optimized. The reaction takes place isobarically at 10 bar. The upper and lower temperature bounds are 50°C and 150°C respectively. Assume the reactor vessel to be perfectly mixed and assume that the batch operation can be modeled as a series of mixed-flow reactors. The objective is to maximize the fractional yield of a-monochlorobutanoic acid with respect to butanoic acid. Specialized software is required to perform the calculations, in this case using simulated annealing3. 

The first distinction to be drawn, as far as heat transfer is concerned, is between the plug-flow and mixed-flow reactor. In the plug-flow reactor shown in Figure 20.1, the heat transfer can take place over a range of temperatures. The shape of the profile depends on the following. 

Datta S, Bhattacharya PK, Verma N (2003) Removal of aniline from aqueous solution in a mixed flow reactor using emulsion liquid membrane. J Membr Sci 2269(1-2) 185-201... 

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