Perfectly mixed flow reactors

For a steady-state perfectly mixed flow reactor the energy balance can be made over the complete reactor ... 

Kinetics can also be studied at surface science conditions. Feed can be leaked at a constant rate into the chamber containing the crystal face, and the gas is removed at a constant rate by the pumps. The composition of the chamber gas can be continuously monitored by mass spectrometry. The pressure in the reaction chamber is low enough to ensure Knudsen flow The gaseous molecules collide almost exclusively with the exposed solid surfaces, and the system behaves as a perfectly mixed flow reactor (CSTR). Experiments in the transient regime with various forcing functions can be performed, and response times can be orders of magnitude smaller than those at atmospheric pressure. The catalytic oxidation of CO on Pt(llO) was one of the first studies of this type (33). 

Flush The flush reaction path model is analogous to the perfectly mixed-flow reactor or the continuously stirred tank reactor in chemical engineering (Figure 2.5). Conceptually, the model tracks the chemical evolution of a solid mass through which fresh, unreacted fluid passes through incrementally. In a flush model, the initial conditions include a set of minerals and a fluid that is at equilibrium with the minerals. At each step of reaction progress, an increment of unreacted fluid is added into the system. An equal amount of water mass and the solutes it contains is displaced out of the system. Environmental applications of the flush model can be found in simulations of sequential batch tests. In the experiments, a volume of rock reacts each time with a packet of fresh, unreacted fluids. Additionally, this type of model can also be used to simulate mineral carbonation experiments. 

Figure 2.5. Schematic representation of the perfectly mixed-flow reactor model. A refers to the component of interest C denotes the concentration and stands for the feed rate or reaction progress variable.

Finally, several alternate names have been used for what here is called the perfectly mixed flow reactor. One of the earliest was continuous stirred tank-reactor, or CSTR, which some have modified to continuous flow stirred tank reactor, or CFSTR. Other names are backmix reactor, mixed flow reactor, and ideal stirred tank reactor. All of these terms appear in the literature, and must be recognized. 

If this conversion were desired in a perfectly mixed flow reactor. Fig. 10.2.b-l gives k F/f ) = 6.5 (abcissa of the intersection of the ordinate level of0.865 and the n = 1 line) that is, for the given k, the reactor volume would have to be 6.5 limes the flow rate rather than only twice, as with plug flow. This example clearly illustrates that results obtained in a batch or plug flow tubular reactor cannot be directly extrapolated to a continuous flow stirred tank reactor—there may be large differences in conversion levels. 

These conclusions can be readily quantitatively visualized as shown in Fig. 10.2.b-3, which is based on the geometric nature of the plug flow or batch reactor design equation versus that for the perfectly mixed flow reactor. 

Figure I0.2.b-3 Comparison of plug flow and perfectly mixed flow reactor volumes. 

For the perfectly mixed flow reactor, the mass balances Eq. 10.2.b-2 lead to — -<0 ... 

Figure 4.1 Conceptual scheme of a continuous action of perfectly mixed-flow reactor (A.N. James, 1992 J. Crawford, 1999 ).

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