Choosing the reactor

As in any WW neutralization process, the reaction rime is very short relatively speaking. Reaction time is mainly defined by die diffusion time of the acid in a viscous environment and by die principle of pH regulation. 

It can vary from 6 to 12 min and the reactor must be closed either because harmful gases are released (H2S and HCN) or because they must be kept in solution by means of high back pressure. The reactor can be  

The equipment needs to be protected against the aggressiviry of the acid (H2SO4 is preferable to HCl), the presence of solvents (BTX) and the temperature (dilution of H2SO4 is highly exothermic). The following can be used  

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Raw materials efficiency. In choosing the reactor, the overriding consideration is usually raw materials efficiency (bearing in mind materials of construction, safety, etc.). Raw material costs are usually the most important costs in the whole process. Also, any inefficiency in raw materials use is likely to create waste streams that become an environmental problem. The reactor creates inefficiency in the use of raw materials in the following ways ... 

Figure 2.10 Choosing the reactor to maximize selectivity for multiple reactions producing byproducts.

In choosing the reactor conditions, particularly the conversion, and optimising the design, the interaction of the reactor design with the other process operations must not be overlooked. The degree of conversion of raw materials in the reactor will determine the size, and cost, of any equipment needed to separate and recycle unreacted materials. In these circumstances the reactor and associated equipment must be optimised as a unit. 

Figure 6.9 Choosing the reactor to maximize security for multiple reactants producing by products. (From Smith R and Petela EA, 1991, The Chemical Engineer, No. 509/510 12, reproduced by permission of the Institution of Chemical Engineers).

Therefore we choose the reactor inlet temperature setpoint as the... 

The preceding discussions serve to underline not only the importance of choosing the reactor with the promise of best performance, but also the need to anticipate scale-up difficulties. The approach we advocate in this article is to attack the problem of reactor selection in a systematic, structured manner, using some concepts borrowed from management... 

Problems in Choice of a Reactor. When a process engineer is faced with the problem of designing a commercial or semicommercial unit, he must first choose the reactor to be used. The type of reactor (tube, tower, or tank), the type of operation (batch, continuous, recycle, or once-through), and the means of temperature control (isothennal or adiabatic) may depend on the type of reaction involved. In order to choose the best reactor and method of operation, the specific type of reacting system must be considered. 

In choosing the reactor configuration for an electrosynthetic process, decisions will have to be made regarding the selection of a suitable cell system and its... 

The total mass balance is trivial. With no input, output, generation, or consumption there is no accumulation. What we seek, however, is a conservation statement for the nitrous oxide inside the reactor. Thus we choose the reactor as the system boundaries and consider only the mass of nitrous oxide. There is neither input nor output of N2O. The chemical reaction given by Eq. (6.64) tells us, however, that nitrous oxide is consumed by the reaction to produce nitrogen and oxygen. Thus we have... 

To operate the catalytic cracker at the required pressure, the reactor pressure Pr is chosen as a controlled variable. The pressure in the regenerator needs then to be controlled, to guarantee a reasonable pressure difference APrr, such that there is a guaranteed circulation of catalyst for regeneration. In this case we shall not control the pressure in the reactor and regenerator separately, but choose the reactor pressure and pressure difference between reactor and regenerator as controlled variables. 

What kind of continuous reactor system would you use if a final ester conversion of 0.60 were desired, and if the reaction were to take place isothermally. Choose the reactor or combination of reactors that has the smallest volume. Justify your answer. 

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