Optimal reactor type and operation

On the Optimal Reactor Type and Operation for Continuous Emulsion Polymerization... 

Nomura, M. and Harada, M. (1981) On the optimal reactor type and operations for continuous emulsion polymerization, in Emulsion Polymers and Emulsion Polymerization, (eds D. R. Bassett and A. E. Hamielec), ACS, Washington, pp. 121-144. 

Optimal reactor type and its operation method for the first stage in continuous emulsion polymerization was discussed in this paper. It was clarified theoretically and experimentally uaing a... 

Considerations based on the known physical phenomena can guide the choice of catalyst porosity and porous structure, catalyst size and shape and reactor type and size. These considerations apply both to laboratory as well as to large-scale operations. Many comprehensive reviews and good books on the problem of reactor design are available in the literature. The purpose of this book is to teach the reader the mathematical tools that are available for calculating interaction between the transport phenomena and true chemical kinetics, allowing optimization of catalyst performance. The discussed theories are elucidated with examples to provide training for application of the mathematics. 

Adesina [14] considered the four main types of reactions for variable density conditions. It was shown that if the sums of the orders of the reactants and products are the same, then the OTP path is independent of the density parameter, implying that the ideal reactor size would be the same as no change in density. The optimal rate behavior with respect to T and the optimal temperature progression (T p ) have important roles in the design and operation of reactors performing reversible, exothermic reactions. Examples include the oxidation of SO2 to SO3 and the synthesis of NH3 and methanol CH3OH. 

The comparison of the results obtained from model particle systems with experience of biological systems shows a similar tendency on many points. Therefore it proved to be very advantageous for the basic investigations, especially for the comparison of different reactor types, to use suitable model particle systems with similar properties to those of biological material systems. This permitted the performance of test series under technically relevant operating conditions, similar to those prevailing in bioreactors, in a relatively short time. The results are more reproducible than in biological systems and therefore permit faster and more exact optimization of reactors. 

Based on a detailed mathematical model, one can make computer simulations of the behaviour of various reactor types. Optimization of operating conditions and design parameters can be done for each reactor type. Downstream equipment should also be taken into account since the cost of product isolation and purification can heavily influence the final choice of all equipment items. A proper combination of investment and operating costs is used as the... 

The remainder of this text attempts to establish a rational framework within which many of these questions can be attacked. We will see that there is often considerable freedom of choice available in terms of the type of reactor and reaction conditions that will accomplish a given task. The development of an optimum processing scheme or even of an optimum reactor configuration and mode of operation requires a number of complex calculations that often involve iterative numerical calculations. Consequently machine computation is used extensively in industrial situations to simplify the optimization task. Nonetheless, we have deliberately chosen to present the concepts used in reactor design calculations in a framework that insofar as possible permits analytical solutions in order to divorce the basic concepts from the mass of detail associated with machine computation. 

For an autocatalytic reaction, Example 15-10 shows that a recycle PFR operating with an optimal value of R requires the smallest volume for the three reactor possibilities posed. (In the case of a PFR without recycle, the size disadvantage can be offset at the expense of maintaining a sufficient value of cBo (in the feed), but this introduces an alternative disadvantage.) A fourth possibility exists for an even smaller volume. This can be realized from Figure 15.8 (although not shown explicitly), if the favorable characteristics of both normal and abnormal kinetics are used to advantage. Since this involves a combination of reactor types, we defer consideration to Chapter 17. 

Separations are an important phase in almost all chemical engineering processes. Separations are needed because the chemical species from a single source stream must be sent to multiple destinations with specified concentrations. The sources usually are raw material inputs and reactor effluents the destinations are reactor inputs and product and waste streams. To achieve a desired species allocation you must determine the best types and sequence of separators to be used, evaluate the physical or chemical property differences to be exploited at each separator, fix the phases at each separator, and prescribe operating conditions for the entire process. Optimization is involved both in the design of the equipment and in the determination of the optimal operating conditions for the equipment. 

Kokossis and Floudas (1994) extended the MINLP approach so as to handle nonisothermal operation. The nonisothermal superstructure includes alternatives of temperature control for the reactors as well as options for directly or indirectly intercooled or interheated reactors. This approach can be applied to any homogeneous exothermic or endothermic reaction and the solution of the resulting MINLP model provides information about the optimal temperature profile, the type of temperature control, the feeding, recycling, and by-passing strategy, and the optimal type and size of the reactor units. 

Classification by Phase Despite the generic classification by operating mode, reactors are designed to accommodate the reactant phases and provide optimal conditions for reaction. Reactants may be fluid(s) or solid(s), and as such, several reactor types have been developed. Singlephase reactors are typically gas- (or plasma- ) or liquid-phase reactors. Two-phase reactors may be gas-liquid, liquid-liquid, gas-solid, or liquid-solid reactors. Multiphase reactors typically have more than two phases present. The most common type of multiphase reactor is a gas-liquid-solid reactor however, liquid-liquid-solid reactors are also used. The classification by phases will be used to develop the contents of this section. 

High conversion with an optimal reaction rate [7, 11, 75, 95], increase of the turnover numbers, i.e., the moles of substrate converted per mole of enzyme deactivated [3, 75, 95], and high stereospecificity of the compound of interest are targets of particular interest in the operation of these batch reactors [10,11,48, 77]. The achievement of these goals requires the study of different variables type and concentration of peroxide, substrates and cofactors, enzyme activity and purity, composition of the reaction medium, pH, temperature, or agitation. Such optimization requires a deep knowledge of the system and a mathematical model that represents it satisfactorily. The kinetic model obtained in batch experiments is the... 

The primary reason for choosing a particular reactor type is the influence of mixing on the reaction rates. Since the rates affect conversion, yield, and selectivity we can select a reactor that optimizes the steady-state economics of the process. For example, the plug-flow reactor has a smaller volume than the CSTR for the same production rate under isothermal conditions and kinetics dominated by the reactant concentrations. The opposite may be true for adiabatic operation or autocata-lytic reactions. For those situations, the CSTR would have the smaller volume since it could operate at the exit conditions of a plug-flow reactor and thus achieve a higher overall rate of reaction. 

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