Reactor type, and selectivity

Tubular Reactors Reactor Types and Selected Process Applications... 

The complexity of this relation depends on the reaction orders involved. Generally, one finds that it is not easy to arrive at expressions for the time dependence of the various species concentrations. However, it is often possible to obtain relations for the relative extents of reaction that are useful for design purposes. In Chapter 9 we will see the implications of such relations in the selection of reactor type and modes of contacting. 

The choice of reactor type and its design for a particular reaction netw ork may require examination of trade-offs involving reactor size and mode of operation, product distribution (selectivity), and production rate. If, as is often the case, selectivity is... 

An example of the effect of temperature on selectivity (yield) for the case of two reactions where A goes to product P by a first-order reaction, and P goes to impurity X by a second-order reaction is shown in Figure 3.9. Say that the undesired reaction is highly exothermic. If the product P is removed as soon as it is formed, the second (undesired) reaction will not occur. It is evident that the overall reaction would be more hazardous and the yield of product P less if an incorrect reactor type is selected. From Figure 3.9, it can be seen that the higher the temperature, the greater the decrease in selectivity. At low... 

In practice, most industrial processes are staged with multiple reaction processes and separation units as sketched in Figure 4-15. A is the key raw material and is the key product, it is clear that many factors must be included in designing the process to maximize the yield of E. The effectiveness of the separations are obviously critical as well as the kinetics of the reactions and the choice of reactor type and conversion in each reactor. If separations are perfect, then the yields are equal to the selectivities, so that the overall... 

Obviously, rpEi can be expressed in terms of reaction temperature and concentration or partial pressure of chemicals and so on. Therefore, the PEI rate-law expression can be helpful to analyze the effect of concentrations and temperature on the PEI transformation rate, rpEi, and to study the influence of back-mixing on process environmental performance. At least, the PEI rate-law expression can reveal the factors that control the transformation rate of PEI, so as to provide guidance for the selection of reactor type and operation conditions, and the inner structure of the reactor, which produce desired products while creating minimum undesired potential environmental impact. 

Reactor design is often discussed in terms of independent and dependent variables. Independent variables are choices such as reactor type and internals, catalyst type, inlet temperature, pressure, and fresH feed composition. Dependent variables result from independent variable selection. They may be constrained or unconstrained. Con-... 

Since it is impractical to fractionate the products and reformulate them into desirable ranges of molecular weights, immediate attainment of desired properties must be achieved through the correct choice of reactor type and operating conditions, notably of distributions of residence time and temperature. Reactor selection may be made on rational grounds, for historical reasons, or to obtain a proprietary position. 

In Figure 2.6 A stands for the reactants, P for the desired products and X and Y for the undesired products. In the same figure examples are given of industrial reactions, which in later chapters will be studied in further detail. Depending on the orders of the relevant reactions and the choice of reaction conditions, by careful selection of reactor type and concentration level the selectivity can be controlled favorably. These reactor properties were defined in Section 1.4. 

Historically, all the early neutron sources were of the conventional reactor type, and a large monochromating crystal was commonly employed (for single-crystal diffraction experiments) to select neutrons with a small wavelength spread in order to produce a monochromatic neutron beam. The rest... 

After selecting a reactor type and catalyst configuration, the next step is to calculate the reactor volume. Before undertaking a detailed calculation, we need to estimate the reactor volume. A quick estimate is sometimes needed to check an exact calculation or to prepare a budget for a proposal. For packed bed or homogenous reactors, the space velocity is a way of rapidly sizing reactors. Space velocity is defined as the ratio of the volumetric feed flow rate to the reaction volume or the ratio of mass feed flow rate to the catalyst mass. The volu-... 

The dependence of the selectivity to mono-alcohol, usually the desired product, on reactor type and conversion level is dramatic, as the data in Table 5.6 demonstrate. 

In this section we discuss various means of minimizing the undesired product, U, through the selection of reactor type and conditions. We also discuss the development of efficient reactor schemes. 

Select a suitable laboratory reactor type and scale, and analytical tools for kinetic measurements. 

Selection of the laboratory reactor type and size, and associated feed and product handling, control, and analytical schemes depends on the type of reaction, reaction time scales, and type of analytical methods required. The criteria for selection include equipment cost, ease of operation, ease of data analysis, accuracy, versatility, temperature uniformity, and controllability, suitability for mixed phases, and scale-up... 

---