Reactor well-stirred tank

An alternative method to account for bed dispersion is to model the bed as a cascade of well stirred tank reactors, each with a uniform temperature and concentration (124,1 5) Transverse dispersion can be accounted for by staggering the cells so that each cell feeds into two different cells in the forward direction (126). When the value of L/d is large, say above 20, the two models are not very different if the number of cells in the cascade is chosen to equal N = PeL/2d. When Pe = 2, this amounts to considering... 

Table 11.4 lists reactors used for systems with two fluid phases. The gas-liquid case is typical, but most of these reactors can be used for liquid-liquid systems as well. Stirred tanks and packed columns are also used for three-phase systems where the third phase is a catal5hic solid. The equipment listed in Table 11.4 is also used for separation processes, but our interest is on reactions and on steady-state, continuous flow. 

The second important environment in which coupled reactions can occur is that of a batch reactor. We will assume that our batch reactor behaves as a well stirred tank reactor, such that all participants are well mixed and concentration gradients do not occur. We will also assume that our coupled reactions proceed only in the forward direction, such that our sequence of elementary steps is reduced to... 

In some cases, where the wall of the reactor has an appreciable thermal capacity, the dynamics of the wall can be of importance (Luyben, 1973). The simplest approach is to assume the whole wall material has a uniform temperature and therefore can be treated as a single lumped parameter system or, in effect, as a single, well-stirred tank. 

Solid catalysts can be conveniently studied in loop reactors, which allow measuring the rates by difference measurement across the catalyst bed. When operated continuously, they usually can be modelled as well-stirred tanks. Here the case of catalyst deactivation is studied. 

Chapter 3 concerns the dynamic characteristics of stagewise types of equipment, based on the concept of the well-stirred tank. In this, the various types of stirred-tank chemical reactor operation are considered, together with allowance for heat effects, non-ideal flow, control and safety. Also included is the modelling of stagewise mass transfer applications, based on liquid-liquid extraction, gas absorption and distillation. 

A reactor model based on solid particles in BMF may be used for situations in which there is deliberate mixing of the reacting system. An example is that of a fluid-solid system in a well-stirred tank (i.e., a CSTR)-usually referred to as a slurry reactor, since the fluid is normally a liquid (but may also include a gas phase) the system may be semibatch with respect to the solid phase, or may be continuous with respect to all phases (as considered here). Another example involves mixing of solid particles by virtue of the flow of fluid through them an important case is that of a fluidized bed, in which upward flow of fluid through the particles brings about a particular type of behavior. The treatment here is a crude approximation to this case the actual flow pattern and resulting performance in a fluidized bed are more complicated, and are dealt with further in Chapter 23. 

Experiment with the influence of recycle flow rate and show by simulation that the model has the limits of a well-stirred tank and a plug flow reactor. 

The process itself is stunningly simple [1, 6-8]. Propene and syngas are fed to a well stirred tank reactor containing the aqueous solution of the... 

The simplest form of flow system is the continuously fed well-stirred tank reactor or CSTR, represented schematically in Fig. 1.11. The behaviour of typical autocatalytic systems in a CSTR will be considered in chapters 4 and 5, but here we may quickly examine how multistability can arise, even with only one overall chemical reaction. We will take a CSTR in which just the... 

Fig. 1.11. Schematic diagram of a continuous-flow well-stirred tank reactor (GSTR), the...

A continuously fed well-stirred tank reactor (CSTR) for solution-phase reactions. 

There are two particularly common, and technically very important, manifestations of open systems and which have become increasingly used in the study of oscillatory processes. These are (i) the chemical engineers continuously fed well-stirred tank reactor (CSTR) and (ii) cells in which there is transport across a boundary or membrane from an external reservoir and in which diffusional processes are usually important. 

For a well-stirred tank reactor involving a second order irreversible reaction of the form aA + bB — rR + sS, the yield of R is... 

Generally, this implies the use of ideal reactors of the plug flow or well stirred tank type with well defined residence times and residence time distributions under isothermal conditions (with some exceptions, as will be indicated). By-passing part of the catalyst by channeling in a packed bed or uneven flow distributions must be avoided. In three-phase systems (gas/liquid/solid), the even distribution of both fluid phases over the catalyst is crucial. 

The simplest type of open system of interest in combustion is the continuous-flow well-stirred tank reactor or CSTR, which is an idealization of tank reactors used widely in industry. In essence, this is simply a tank into which reactants flow continuously at some known volumetric flow-rate and the reactant-intermediate-product mixture is efficiently stirred so that there are no spatial concentration or temperature gradients. In order to maintain a constant reaction volume, there is a matching volumetric outflow of the mixture from the CSTR so that molecules spend only a finite time in the reactor. This is known as the mean residence time t es and is determined by the volumetric flow-rates and the reactor volume. 

Exercise 7.7,4. A process for manufacturing X from A and B according to the reaction A + B—> X is being carried out in two well-stirred tanks in series. The reaction is second order, and the two reactants are fed in solution in equimolar proportions. For 90% efficiency of conversion find the ratio of tank volumes which gives the maximum output for a given total reactor volume. 

Example 3-1 Liquid benzene is chlorinated by bubbling gaseous chlorine into a well-stirred tank reactor containing the benzene. Three reactions can occur ... 

The process to produce Delos is simple yet effective. The two key pieces of equipment are a well-stirred tank-type reactor and a separation column. A simplified flow diagram is shown in Figure 2.8. 

R.T. Echols, J.F. Tyson, Determination of rate constants by a double-line flow injection method incorporating a well-stirred tank reactor, Talanta 41 (1994) 1775. 

In a CSTR, each element of monomer feed has an equal chance of being withdrawn from the reactor at any instant regardless of the time it has been in the reactor. Therefore, in a CSTR, unlike in batch and tubular reactors, the residence time is variable. The contents of a well-stirred tank reactor show an exponential distribution of residence times of the type shown in Equation 10.15. 

Semibatch operations usually employ a single well-stirred tank. In such cases it is possible to make the usual assumption that the composition and temperature of the fluid are uniform throughout the tank. For semibatch operation, the fraction conversion (f) is often ambiguous for many cases of interest. If reactant is present initially in the reactor and is added or removed in feed and effluent streams, the question arises as to the proper basis for the definition of /. In such cases it is best to work either in terms of the weight fraction of a particular component present in the fluid of interest or in terms of concentrations when constant-density systems are under consideration. In terms of the symbols shown in Figure 8.19 the fundamental material balance relation becomes... 

At 25°C this reaction is first-order in A in the forward direction with = 0.112 s . In the reverse direction, the reaction is pseudo-first-order in the lactone with = 0.042 A s . This reaction is being studied on a phot-plant scale in a single well-stirred tank reactor (volume =1.5 m ). 

This computer program calculates a well-stirred tank reactor and carries out a sensitivity analysis. It is part of the CHEMKIN system. 

This system consists of a well stirred tank so that the composition throughout the reactor is uniform but reactant is added continuously and a product stream is removed at the same rate. The exit stream will have the same composition as the fluid in the reactor. 

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