Reactions homogeneous batch

Runaway criteria developed for plug-flow tubular reactors, which are mathematically isomorphic with batch reactors with a constant coolant temperature, are also included in the tables. They can be considered conservative criteria for batch reactors, which can be operated safer due to manipulation of the coolant temperature. Balakotaiah et al. (1995) showed that in practice safe and runaway regions overlap for the three types of reactors for homogeneous reactions (1) batch reactor (BR), and, equivalently, plug-flow reactor (PFR), (2) CSTR, and (3) continuously operated bubble column reactor (BCR). 

When no traces of metal are observed in the products of a batch experiment, one cannot exclude the possibility that metal went into solution under reaction conditions. Then, the dissolved metal could catalyze the reaction homogeneously with re-adsorption on cooling down at the end of the experiment. 

It has been observed that enantioselective polymer-bound catalysts prepared by copolymerization produce in some cases better asymmetric inductions than systems prepared by grafting [175]. After much optimization, a monolithic polymer catalyst 51 suitable for a titanium-TADDOLate catalyzed Diels-Alder reaction was developed (Scheme 4.77). The monolith was applied in a flow system both under one pass and 24 h recirculation conditions, the latter producing the best yield (55%) and ee (23%) however, this contrasts poorly with the homogeneous batch reaction although the ee is comparable with the heterogeneous batch process. The reversal of topicity was also... 

Section 7 of this Handbook presents the theory of reaction kinetics that deals with homogeneous reactions in batch and continuous equipment. Single-phase reactors typically contain a liquid or a gas with (or without) a homogeneous catalyst that is processed in a reactor at conditions required to complete the desired chemical transformation. 

Much of the basic theory of reaction kinetics presented in Sec. 7 of this Handbook deals with homogeneous reactions in batch and continuous equipment, and that material will not be repeated here. Material and energy balances and sizing procedures are developed for batch operations in ideal stirred tanks—during startup, continuation, and shutdown—and for continuous operation in ideal stirred tank batteries and plug flow tubulars and towers. 

For homogeneous systems, the kinetic parameters k and tq are commonly determined by lab-scale batch experiments in which all reagents are combined at the start of the reaction. Following the concentration of all components (reactants and products) over the course of the reaction then allows for the estimation of the kinetic parameters. Since water has limited solubility in the reaction mixture at the start, conventional kinetic batch experiments could result in erroneous calculation of kj and tq if the limits for homogeneity are crossed. To ensure reaction homogeneity and reliable kinetic measurements, the gradual and continuous addition of water was selected as a suitable method for experimentation (semi-batch mode). The kinetic parameters were then recovered using an appropriate mathematical model with parameter estimation module. 

In this section we must be careful to respect our prior concern about the definition of rate with regard to the volume of reaction mixture involved. Further, since we wish to concentrate attention on the kinetics, we shall study systems in which the conservation equation contains the reaction term alone, which is the batch reactor of equation (1-12). It is convenient to view this type of reactor in a more general sense as one in which all elements of the reaction mixture have been in the reactor for the same length of time. That is, all elements have the same age. Since the reactions we are considering here occur in a single phase, the relationships presented below pertain particularly to homogeneous batch reactions, and the systems are isothermal. 

Type I. For parallel reactions with separate reactants, the analysis is easily handled, since the two steps are independent of each other. Indeed, the inclusion of Type 1 as a nearly complex scheme is not really necessary for the homogeneous batch reactions at constant volume treated here, since the yield and selectivity definitions are redundant in this case with rate and conversion. The system is important in heterogeneous systems, however, so we introduce it for later reference. For first-order, irreversible reactions ... 

Type II. For parallel reactions with the same reactant the selectivity and yield definitions are more meaningful for homogeneous batch reactions. For the reactant the rates are additive, so... 

The rate equations of Chapter 1 were given, for the most part, as they pertain to homogeneous batch reactions. While the purpose there was to treat descriptive kinetics, the results obtained pertain also to the operation of homogeneous batch reactors. One of the features of such a reactor was said to be that all the molecules in the reactor at a given time of reaction had been there for the same amount of time in other words, they had the same age. A second feature implied in the treatment was the intimate association, on a molecular scale, of all species contained in the reactor. 

Hie second case, the preliminary assessment of a homogeneous liquid phase reaction performed batch-wise, is somewhat more complex. First a batch process has to be defined. This term is used for the discontinuous production process in which all reactants involved are filled into the reaction vessel completely at the beginning. This charging is commonly followed by a heating phase up to a desired temperature. The continuously stirred mixture is usually kept at this temperature level until the desired extent of reaction has been reached. This is followed by different work-up procedures and product isolation steps. The reaction engineering characteristics, which form the basis for the safety assessment, are given in detail in Ch ter 4. 

FIRST-ORDER, HOMOGENEOUS BATCH REACTION WITH AGITATION... 

Table 6.3 Dimension Table for First-Order, Homogenous Batch Reaction With Agitation... 

In this chapter, we applied dimensional analysis to chemical processes. We used homogeneous batch reactions, plug flow reactions, and porous solid—catalyzed reactions as examples. We demonstrated how to derive the dimensionless parameters for these examples, then we showed how to combine them to form the Group I, II, III, and IV Damkohler numbers, as well as the Reynolds number. We demonstrated how these dimensionless parameters and numbers are used during upscaling and downscaling. 

Often homogeneous or homogeneously catalyzed reactions but even heterogeneous catalytic reactions exist batch, tank, and tube reactors, three-phase reactors, bubble columns Columns and mixer-settler... 

For a homogeneous reactor, it is characteristic that just one phase, usually a gas or a liquid phase, is present. Chemical reactions thus take place in this phase. In this chapter, we will examine three reactors most commonly used industrially for homogeneous reactions a batch reactor (BR), a tube reactor, and a tank reactor. Figure 3.1 illustrates a BR. A BR is operated by at first charging the reactor contents with a reaction mixture that is usually heated to the reaction temperature, allowing the reaction to proceed until the desired conversion of the reactants has been reached. After this, the reactor vessel is emptied. 

A Cu-Box complex supported on monolith (51) was developed for the enantio-selective cydopropanation of ethyl diazoacetate. The flow reactions using (51) provided an increase in enantioselectivities of about 20% relative to those for the homogenous batch process (Scheme 7.38) [142]. Pyridine-oxazolidine based monoliths (52) and (53), whose central metals were Ru and Cu, respectively, were also developed [143,144]. Mesoporous silica was utilized as a support for the Cu-Box complex for asymmetric cydopropanation in a flow reador. Aza(bisoxazoline) was easily immobilized on siliceous mesocellular foam MCF) microparticles, which are... 

We discuss two common types of reactors used for obtaining tme data the batch reactor, which is used primarily for homogeneous reactions, and the differential reactor, which Ls used for solid-fluid heterogeneous reactions. In batch reactor experiments, concentration, pressure, and/or volume are usually measured and recorded at different times during the course of the reaction. Data are collected from the batch reactor during transient operation, whereas measurements on the differential reactor are made during steady-state operation. In experiments with a differential reactor, the product concentration is usually monitored for different sets of feed conditions. 

Both batch and continuous reactors are used in industrial vinyl polymerization processes. Agitated kettles, tower reactors, and linear flow reactors are just a few examples of industrially used polymerization reactors. The choice of reactor type depends on the nature of polymerization systems, (homogeneous versus heterogeneous), the quality of product, and the amount of polymer to be produced. Sometimes, multiple reactors are used and operated at different reaction conditions. Whichever reactor system is used, it is always necessary to maximize the process productivity by reducing the reaction time (batch time or residence time) while obtaining desired polymer properties consistently. 

Recent Developments. A considerable amount of cellulose acetate is manufactured by the batch process, as described previously. In order to reduce production costs, efforts have been made to develop a continuous process that includes continuous activation, acetylation, hydrolysis, and precipitation. In this process, the reaction mixture, ie, cellulose, anhydride, catalyst, and solvent, pass continuously through a number of successive reaction zones, each of which is agitated (92,93). In a similar process, the reaction mass is passed through tubular zones in which the mixture is forced through screens of successively small openings to homogenize the mixture effectively (94). Other similar methods for continuous acetylation of cellulose have been described (95,96). 

Clearly, these groupings are not mutually exclusive. The chief distinctions are between homogeneous and heterogeneous reactions and between batch and flow reactions. These distinctions most influence the choice of equipment, operating conditions, and methods of design. 

In terms of cost and versatility, the stirred batch reactor is the unit of choice for homogeneous or slurry reactions and even gas/liquid reactions when provision is made for recirculation of the gas. They are especially suited to reactions with half-lives in excess of 10 min. Sam-... 

First, let us consider batch mixing processes, as exemplified by ordinaiy laboratory practice in solution kinetics. A portion of one solution (say, of the substrate) is added by pipet to a second solution (containing the reagent) in a flask, the flask is shaken to achieve homogeneity, and then samples are withdrawn at known times for analysis, or the solution is subjected to continuous observation as a function of time, for example, by spectrophotometry. For reactions on a time scale (measured by the half-life) of hours or even several minutes, the time consumed in these operations is a negligible portion of the reaction time, but as the half-life of the reaction decreases, it becomes necessary to consider these preliminary steps. Let us distinguish three stages ... 

Homogeneous reactions are those in which the reactants, products, and any catalysts used form one continuous phase (gaseous or liquid). Homogeneous gas phase reactors are almost always operated continuously, whereas liquid phase reactors may be batch or continuous. Tubular (pipeline) reactors arc normally used for homogeneous gas phase reactions (e.g., in the thermal cracking of petroleum of dichloroethane lo vinyl chloride). Both tubular and stirred tank reactors are used for homogeneous liquid phase reactions. 

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