Ideal multiple reactions

Computer simulation can also be used for relief sizing (see Annex 4). This may be the only safe alternative in cases where physical properties are non-ideal, multiple reactions occur or there are significant continuing.feed streams or external heating. It will be necessary to choose a computer simulation package which can handle multi-component mixtures comprising both volatile and permanent gas components. 

The chemical engineer almost never encounters a single reaction in an ideal single-phase isothermal reactor. Real reactors are extremely complex with multiple reactions, multiple phases, and intricate flow patterns within the reactor and in inlet and outlet streams. An engineer needs enough information from this course to understand the basic concepts of reactions, flow, and heat management and how these interact so that she or he can begin to assemble simple analytical or intuitive models of the process. 

Kinetic mechanisms involving multiple reactions are by far more frequently encountered than single reactions. In the simplest cases, this leads to reaction schemes in series (at least one component acts as a reactant in one reaction and as a product in another, as in (2.7)-(2.8)), or in parallel (at least one component acts as a reactant or as a product in more than one reaction), or to a combination series-parallel. More complex systems can have up to hundreds or even thousands of intermediates and possible reactions, as in the case of biological processes [12], or of free-radical reactions (combustion [16], polymerization [4]), and simple reaction pathways cannot always be recognized. In these cases, the true reaction mechanism mostly remains an ideal matter of principle that can be only approximated by reduced kinetic models. Moreover, the values of the relevant kinetic parameters are mostly unknown or, at best, very uncertain. 

As noted in the introduction, a major aim of the current research is the development of "black-box" automated reactors that can produce particles with desired physicochemical properties on demand and without any user intervention. In operation, an ideal reactor would behave in the manner of Figure 12. The user would first specify the required particle properties. The reactor would then evaluate multiple reaction conditions until it eventually identified an appropriate set of reaction conditions that yield particles with the specified properties, and it would then continue to produce particles with exactly these properties until instructed to stop. There are three essential parts to any automated system—(1) physical machinery to perform the process at hand, (2) online detectors for monitoring the output of the process, and (3) decision-making software that repeatedly updates the process parameters until a product with the desired properties is obtained. The effectiveness of the automation procedure is critically dependent on the performance of these three subsystems, each of which must satisfy a number of key criteria the machinery should provide precise reproducible control of the physical process and should carry out the individual process steps as rapidly as possible to enable fast screening the online detectors should provide real-time low-noise information about the end product and the decision-making software should search for the optimal conditions in a way that is both parsimonious in terms of experimental measurements (in order to ensure a fast time-to-solution) and tolerant of noise in the experimental system. 

Pyrolytic reactions can appear to be much more complicated compared to other reactions. However, this is mainly due to subsequent reactions that occur after the initial elimination step. A common cause of this problem is related to the fact that the reactions do not actually take place in ideal gas phase. Some pyrolytic processes may take place in true condensed phase. Multiple reaction paths and the interaction of the resulting molecules are, therefore, inevitable. Also, additional issues may affect the practical results of a pyrolysis. Some are related to the fact that the true pyrolysis can be associated with reactions caused by the presence (intentional or not) of non-inert gases such as oxygen or hydrogen that may be present during the heating. Also, the pyrolyzed materials may be in contact with non-inert surfaces that can have catalytic effects. In order to diminish these effects in the pyrolysis done for analytical purposes, an inert gas frequently is present during the pyrol ic reaction. 

The continuity equation for each ideal model reactor yields for multiple reactions (60, 61)... 

The results of Sections VI,B and C for multiple reactions still hold for flow reactors. The selectivity function [Eqs. (67), (69), or (71)] apply exactly to an ideal MER, within the reactor and at its exit. For an ideal CER, the same equations give the local selectivity along the reactor (60-62). The choice of suitable electrochemical reactors for parallel steps depends then on the reaction order of the desirable path with respect to the reactant. Although the surface and volume requirements of a MER are larger than those of a CER, the former would favor a low-order path. An economic trade-off exists, therefore, between reactor costs, subsequent separations of unwanted products, and waste of raw reactants. 

The choice of the carboxylic acid blocking group (R in Scheme 11.2) is very important, as it not only has to survive multiple reactions, it also has to be readily and cleanly removed at the end of the synthesis during the formation of the penultimate intermediate. In addition, there is an important third factor. The physical properties of the isolated intermediates need to be considered. The ideal blocking group will confer sufficient crystallinity on the key intermediates that they can easily be isolated as fairly pure defined compounds from the telescoped reaction sequences needed for commercial efficiency. 

When multiple reactions occur in the gas phase, the mass balance for component i is written for an ideal tubular reactor at high mass transfer Peclet numbers in the following form, and each term has units of moles per volume per time ... 

The important concept of selectivity is introduced here, and applied for multiple reactions in ideal single-phase reactors. 

Work-ups inevitably perturb the apparent reaction outcome to some extent, which may misrepresent or mask the important factors in a reaction, as some researchers have found initially. It is far better if the conversion to all products in solution, including the ratio of any stereoisomers before isolation, can be quantified before work-up by a technique such as LC or GC-MS. Representative sampling is of course required, and slurries can be particularly problematic. Ideally, solution sampling will allow results to be related back to the reaction conditions the work-up should be treated as a completely separate [i.e. derivative) process. But as noted, this does have advantages if multiple reactions can be worked up together to save time. 

The concentration of reactant A in a packet that was in the reactor for a time r is Cpft). This concentration can be calculated by solving the design equation for an ideal batch reactor, if a single reaction is taking place, or by solving the appropriate set of material balances (design equations), if multiple reactions are taking place. 

Of the two classes of reactions mentioned above, the use of a single catalyst to carry ont multiple reactions is a very promising approach. From a synthetic standpoint, it would be ideal since it is a relatively simple and economical approach [21], However, most cascade reactions of this type are essentially limited to reactions that have similar mechanisms (i.e., successive Pd-catalyzed cross-coupling), although some examples of sequence processes involving two or more different reactions have been described [22]. Here, we illustrate some monofunctional nanocatalyst examples and distinguish them from various catalytic active species. 

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