Chemical reactors complex configurations

The search for Turing patterns led to the introduction of several new types of chemical reactor for studying reaction-diffusion events in feedback systems. Coupled with huge advances in imaging and data analysis capabilities, it is now possible to make detailed quantitative measurements on complex spatiotemporal behaviour. A few of the reactor configurations of interest will be mentioned here. 

The additional complexity of real chemical processes comes from the fact that they are invariably multistage processes with many reactors and separation units linked with complex configurations. One must then design each unit individually and then see how its design must be modified to be integrated into the entire process. 

Thus far we have considered only two flow patterns the completely mixed reactor and the completely unmixed reactor. This is because only for these flow patterns can we completely ignore the fluid flow configurations in the reactor. In this chapter we will begin to see how reactors that have more complex flow patterns should be treated. We will not attempt to describe the fluid mechanics completely. Rather, we will hint at how one would go about solving more realistic chemical reactor problems and examine the errors we have been making by using the completely mixed and unmixed approximations. 

In recent years, membrane bioreactors, bioreactors combined with membrane separation unit have established themselves as an alternative configuration for traditional bioreactors. The important advantages offered by membrane bioreactors are the several different types of membrane modules, membrane structures, materials commercially available. Membrane bioreactors seem particularly suited to carry out complex enzymatic/microbial reactions and/or to separate, in situ, the product in order to increase the reaction efficiency. The membrane bioreactor is a new generation of the biochemical/chemical reactors that offer a wide variety of applications for producing new chemical compounds, for treatment of wastewater, and so on. 

A modular reactor similar to the approach of Adler et al. [11] was introduced by Muller and co-workers [37, 38, 56], The screening procedure was separated into a number of process operations. In chemical process engineering, these so-called unit operations are essential components of every complex plant. As catalyst screening involves many different processes such as heat exchange, flow distribution, sampling, analysis and reaction, such a subdivision into unit operations is justified. The flexibility of such a system was demonstrated with two exemplified configurations later, one of which was used for transient studies and one for steady-state experiments (Figure 3.30). 

For ease of fabrication and modular construction, tubular reactors are widely used in continuous processes in the chemical processing industry. Therefore, shell-and-tube membrane reactors will be adopted as the basic model geometry in this chapter. In real production situations, however, more complex geometries and flow configurations are encountered which may require three-dimensional numerical simulation of the complicated physicochemical hydrodynamics. With the advent of more powerful computers and more efficient computational fluid dynamics (CFD) codes, the solution to these complicated problems starts to become feasible. This is particularly true in view of the ongoing intensified interest in parallel computing as applied to CFD. 

A recycle reactor is a mathematical model describing a steady plug-flow reactor where a portion of the outlet is recycled to the Met, as shown schematically in Figure 9.5. Although this reactor configuration is rarely used in practice, the recycle reactor model enables us to examine the effect of mixing on the operations of continuous reactors. In some cases, the recycle reactor is one element of a complex reactor model. Below, we analyze the operation of a recycle reactor wifii multiple chemical reactions, derive its design equations, and discuss how to solve fiiem. 

In addition to heat transfer, mass transfer and mixing are also considerably enhanced in MSRs in comparison to conventional reactors [8-11]. In some configurations, mixing times of the order of milliseconds or even nanoseconds have been reported [12,13]. This quality renders MSRs extremely useful for reactions that require fast mixing. Hence, MSRs are of general interest for complex chemical reactions that are encountered in the synthesis of fine chemicals and pharmaceuticals. Examples are summarized in an excellent review by Jahnisch et al. [14]. 

From the chemical point of view, POs are simple materials composed of C and H. However, the configuration diversity of even the simplest polymethylene results in a spectrum of properties. The situation becomes more complex for polymers of the general formula (C H2 )dp where n>3 and the degree of polymerization, DP, is large. The next level of complexity is encountered with blends and copolymers, e.g., poly(ethylene-co-n-olefin) or poly(propylene-co-n-olefin). However, today the ultimate challenge for characterization is found in POs obtained during multi-catalyst/multi-reactor/multi-monomer polymerization processes. 

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