Types of Reaction Systems

Having made a choice of the reaction path, a choice of reactor type must be made, together with some assessment of the conditions in the reactor. This allows assessment of the reactor performance for the chosen reaction path in order for the design to proceed. 

Before proceeding to the choice of reactor and operating conditions, some general classifications must be made regarding the types of reaction systems likely to be encountered. Reaction systems can be classified into six broad types  

An example of this type of reaction that does not produce a byproduct is isomerization (the reaction of a feed to a product with the same chemical formula but a different molecular structure). For example, allyl alcohol can be produced from propylene oxide5  

An example of a reaction that does produce a byproduct is the production of acetone from isopropyl alcohol, which produces a hydrogen byproduct  

Multiple reactions in parallel producing byproducts. Rather than a single reaction, a system may involve secondary reactions producing (additional) byproducts in parallel with the primary reaction. Multiple reactions in parallel are of the type  

Single reactions. Most reaction systems involve multiple reactions. In practice, the secondary reactions can sometimes be neglected, leaving a single primary reaction to consider. Single reactions are of the type 

An example of this t3T)e of reaction which does not produce a byproduct is the production of allyl alcohol from propylene oxide  

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There are four types of reaction systems for the production of polyethylene of commercial importance ... 

In this chapter we will discuss the results of the studies of the kinetics of some systems of consecutive, parallel or parallel-consecutive heterogeneous catalytic reactions performed in our laboratory. As the catalytic transformations of such types (and, in general, all the stoichiometrically not simple reactions) are frequently encountered in chemical practice, they were the subject of investigation from a variety of aspects. Many studies have not been aimed, however, at investigating the kinetics of these transformations at all, while a number of others present only the more or less accurately measured concentration-time or concentration-concentration curves, without any detailed analysis or quantitative kinetic interpretation. The major effort in the quantitative description of the kinetics of coupled catalytic reactions is associated with the pioneer work of Jungers and his school, based on their extensive experimental material 17-20, 87, 48, 59-61). At present, there are so many studies in the field of stoichiometrically not simple reactions that it is not possible, or even reasonable, to present their full account in this article. We will therefore mention only a limited number in order for the reader to obtain at least some brief information on the relevant literature. Some of these studies were already discussed in Section II from the point of view of the approach to kinetic analysis. Here we would like to present instead the types of reaction systems the kinetics of which were studied experimentally. 

Different type of reaction system containing organic solvent can be classified in a simple way. To accomplish this we first distinguished between microaqueous organic systems with a continuous organic phase, then reversed micelles stabilized with surfactant and a liquid-liquid biphasic system in which distinct organic and aqueous phase are mixed. The latter medium is discussed in this paper. 

Pressure measurements can be accomplished by any one of a number of different types of manometric devices without disturbing the system being observed. Another type of reaction system that can be monitored by pressure measurements is one in which one of the products can be quantitatively removed by a solid or liquid reagent that does not otherwise affect the reaction. For example, acids formed by reactions in the gas phase can be removed by absorption in hydroxide solutions. 

I suggest that for certain types of reaction systems in solution it is useful to suppose that the energy, if it does arrive in increments, must arrive in a relatively short period of time compared to the lifetime of the cage. 

From the foregoing dicussion it is apparent that residuum hydroconversion processes can be influenced adversely by pore diffusion limitations. Increasing the catalyst porosity can alleviate the problem although increased porosity is usually accompanied by a decrease in total catalytic surface area. Decreasing the catalyst particle size would ultimately eliminate the problem. However, a different type of reaction system would be required since the conventional fixed bed would experience excessive pressure drops if very fine particles were used. A fluidized system using small particles does not suffer from this limitation. However, staging of the fluidized reaction system is required to minimize the harmful effects that backmixing can have on reaction efficiency and selectivity. 

Three types of reaction systems have been designed and applied for the enantioposition-selective asymmetric cross-coupling reactions so far. First example is asymmetric induction of planar chirality on chromium-arene complexes [7,8]. T vo chloro-suhstituents in a tricarhonyl("n6-o-dichlorobenzene)chromium are prochiral with respect to the planar chirality of the 7t-arene-metal moiety, thus an enantioposition-selective substitution at one of the two chloro substituents takes place to give a planar chiral monosubstitution product with a minor amount of the disubstitution product. A similar methodology of monosuhstitution can be applicable to the synthesis of axially chiral biaryl molecules from an achiral ditriflate in which the two tri-fluoromethanesulfonyloxy groups are enantiotopic [9-11]. The last example is intramolecular alkylation of alkenyl triflate with one of the enantiotopic alkylboranes, which leads to a chiral cyclic system [12], The structures of the three representative substrates are illustrated in Figure 8F.1. 

Several reactor types have been described [5, 7, 11, 12, 24-26]. They depend mainly on the type of reaction system that is investigated gas-solid (GS), liquid-solid (LS), gas-liquid-solid (GLS), liquid (L) and gas-liquid (GL) systems. The first three arc intended for solid or immobilized catalysts, whereas the last two refer to homogeneously catalyzed reactions. Unless unavoidable, the presence of two reaction phases (gas and liquid) should be avoided as far as possible for the case of data interpretation and experimentation. Premixing and saturation of the liquid phase with gas can be an alternative in this case. In homogenously catalyzed reactions continuous flow systems arc rarely encountered, since the catalyst also leaves the reactor with the product flow. So, fresh catalyst has to be fed in continuously, unless it has been immobilized somehow. One must be sure that in the analysis samples taken from the reactor contents or product stream that the catalyst docs not further affect the composition. Solid catalysts arc also to be fed continuously in rapidly deactivating systems, as in fluid catalytic cracking (FCC). 

Considerable progress has been made in recent years in obtaining solutions to the time-dependent Smith-Ewart differential difference equa> tions for various special types of reaction system in the nonsteady state. Although it has so far not proved possible to give an entirely general solution to these equations, it has proved possible to obtain a general solution to a modified set of equations which, under certain circumstances, approximate to the exact set of equations. 

Various resetirch groups have tried to overcome some of the difficulties outlined earlier and have developed methods for the investigation of particular types of reaction systems. The remainder of this section is devoted to typical arrangements used by some of the several workers in the field. 

Table 4-12 Effect of mixing on selectivity for various types of reaction systems...

In this section the permitted types of reaction system models are precisely defined. The simple, free format input language that has been developed to describe the model and its associated experimental data to the computer program is defined elsewhere 25 b) s this section is concerned with models that can be handled by CRAMS, some definitions differ slightly from those given in Section 1.1., where a more general model is discussed. 

Two major types of reaction systems have been observed coupling between two aryl groups (section 3.2.4.1) and coupling involving one or two heteroaryl groups (section 3.2.4.2). 

Industrially, coal gasification processes are differentiated by the type of reaction system used to gasify the coal such as 1) fixed bed, 2) fluidized bed, 3) entrained bed, and 4) molten salt. The processes utilizing these reactor configurations are shown in Table 2.13 the typical gas distributions from some common systems shown in Table 2.14 [5,37],... 

The opposite of entry 2 is the phase combination of entry 5, a fully organic reaction in the presence of an aqueous phase which contains the catalyst. This type of reaction system is the most often used for the technical realization of aqueous-phase organometallic-catalyzed reactions, for instance in the oligomerization of ethylene using the SHOP process (cf. Section 7.1) or in the Ruhrchemie/Rhone-Poulenc process (cf. Section 6.1.1) of propene hydroformylation (see also Section 4.2.2). 

The slow reaction regime is characterized by the fact that the amount of the aromatic reactant that reacts in the film at the interface between phases is negligible compared to the amount that diffuses into the acid phase. Either the intrinsic kinetics or the rate of bulk-diffusion of the aromatic reactant may be the rate controlling step. The second type of reaction system is designated as a fast reaction system, and benzene would react in... 

Table 15.5 shows the results of Mochel [22] for the effect of conversion upon the gel content of polychloroprene rubbers prepared by emulsion polymerization at 40 °C. In section (a) of this table are shown results for polymers produced in the absence of added sulfur section (b) shows results for polymers produced with the addition of 0.6 parts of sulfur per 100 parts by mass of chloroprene, before chemical peptization of the polymer. In both types of reaction system, polymer gel begins to form quite early in the reaction. However, these results indicate that sulfur has a slight tendency to act as a modifier during the polymerization, in that the onset of gel-formation is delayed when sulfur is present. Also delayed is the pdnt at which the polymer is virtually entirely gel. Mochel et al. [23] have reported results for the molar mass distribution of a thiuiam-modified polychloroprene rubber produced by emulsion polymerization at 40 °C,... 

In redox reactions, to an extent greater than found in other types of reactions, systems which are not reversible or are not in equilibrium are encountered. In such systems, although the predicted potential differences based on equilibrium behavior will not agree with observed values, such calculations are nevertheless useful in describing the relative strengths of oxidants and reductants. 

Reaction System - There are so many types of reaction systems in use throughout the world that no attempt will be made to identify all of them, The objective in designing the reaction system is to carry out the reaction between phosphate rock and sulfuric acid so as to recover a maximum percentage of the P2O5 from the rock as product phosphoric acid in the simplest and least expensive manner. Since the filtration step is the most critical and expensive step in the process, a primary objective in the reaction step is to form gypsum crystals of such size and shape that the filtration and washing can be carried out rapidly and efficiently. 

Besides of this classification including the above three processes, another classification is also made according to the way in which the reaction loci are formed. By this way, two types of reaction system are defined "ab initio emulsion polymerization" and "seeded emulsion polymerization" [29]. 

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