Uses of Batch Reactors

In this chapter, we first consider uses of batch reactors, and their advantages and disadvantages compared with continuous-flow reactors. After considering what the essential features of process design are, we then develop design or performance equations for both isothermal and nonisothermal operation. The latter requires the energy balance, in addition to the material balance. We continue with an example of optimal performance of a batch reactor, and conclude with a discussion of semibatch and semi-continuous operation. We restrict attention to simple systems, deferring treatment of complex systems to Chapter 18. 

Batch reactors are used both in the laboratory for obtaining design and operating data 

The use of batch reactors in the laboratory is described in Section 2.2.2 for the interpretation of rate of reaction, in Section 3.4.1.1 for experimental methodology, and in Chapter 4 and subsequent chapters for numerical treatment of kinetics experimental 

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From diese various estimates, die total batch cycle time t(, is used in batch reactor design to determine die productivity of die reactor. Batch reactors are used in operations dial are small and when multiproducts are required. Pilot plant trials for sales samples in a new market development are carried out in batch reactors. Use of batch reactors can be seen in pharmaceutical, fine chemicals, biochemical, and dye industries. This is because multi-product, changeable demand often requues a single unit to be used in various production campaigns. However, batch reactors are seldom employed on an industrial scale for gas phase reactions. This is due to die limited quantity produced, aldiough batch reactors can be readily employed for kinetic studies of gas phase reactions. Figure 5-4 illustrates die performance equations for batch reactors. 

It is clear that the use of batch reactors has some serious drawbacks. For the production of larger quantities, mnltiple batch mns have to be performed and this often leads to batch to batch variation in prodnct qnahty and performance. Furthermore, the productivity is often lower than for dedicated continnons reactors and fixed costs are higher cansed by high operator efforts. Therefore, switching to continuons processes holds great appeal, if we can find a device that is snitable for multiple products. 

From an industrial viewpoint, scale-up means process development and highest possible throughput that virtually excludes the use of batch reactors. In fact, the productivity and not the size of the vessel is important, which clearly indicates that flow systems, regardless of whether applied in SF or CF manner, have distinct benefits over batch process reactors. 

The organic chemistry literature usually mentions, or almost always implies, the use of batch reactors with very little reference to other reactor types. An exception is Tundo s Continuous Flow Methods in Organic Synthesis (1991). 

CSTR s and batch reactors offer contrasting advantages and disadvantages as tools for studying the mechanisms and kinetics of emulsion pol mierization. Most fundamental kinetic studies are carried out in batch reactors because they are simple to build and operate and they consume a minimum amount of raw material. The use of batch reactor in a semi-batch mode is also rather straight forward. Under normal circumstances both of these reactor types offer another advantage namely the latex produced has a narrow PSD. Thus one does not need to account for the relative influence of particle size differences among the latex particles. 

Using a batch reactor, a constant concentration of sulfuric acid can be maintained by adding concentrated sulfuric acid as the reaction progresses, i.e., semi-batch operation. Good temperature control of such systems can be maintained, as we shall discuss later. 

Specific reactor characteristics depend on the particular use of the reactor as a laboratory, pilot plant, or industrial unit. AH reactors have in common selected characteristics of four basic reactor types the weH-stirred batch reactor, the semibatch reactor, the continuous-flow stirred-tank reactor, and the tubular reactor (Fig. 1). A reactor may be represented by or modeled after one or a combination of these. SuitabHity of a model depends on the extent to which the impacts of the reactions, and thermal and transport processes, are predicted for conditions outside of the database used in developing the model (1-4). 

A useful classification of lands of reaclors is in terms of their concentration distributions. The concentration profiles of certain limiting cases are illustrated in Fig. 7-3 namely, of batch reactors, continuously stirred tanks, and tubular flow reactors. Basic types of flow reactors are illustrated in Fig. 7-4. Many others, employing granular catalysts and for multiphase reactions, are illustratea throughout Sec. 23. The present material deals with the sizes, performances and heat effects of these ideal types. They afford standards of comparison. 

Unsteady material and energy balances are formulated with the conservation law, Eq. (7-68). The sink term of a material balance is and the accumulation term is the time derivative of the content of reactant in the vessel, or 3(V C )/3t, where both and depend on the time. An unsteady condition in the sense used in this section always has an accumulation term. This sense of unsteadiness excludes the batch reactor where conditions do change with time but are taken account of in the sink term. Startup and shutdown periods of batch reactors, however, are classified as unsteady their equations are developed in the Batch Reactors subsection. For a semibatch operation in which some of the reactants are preloaded and the others are fed in gradually, equations are developed in Example 11, following. 

The differential reactor is the second from the left. To the right, various ways are shown to prepare feed for the differential reactor. These feeding methods finally lead to the recycle reactor concept. A basic misunderstanding about the differential reactor is widespread. This is the belief that a differential reactor is a short reactor fed with various large quantities of feed to generate various small conversions. In reality, such a system is a short integral reactor used to extrapolate to initial rates. This method is similar to that used in batch reactor experiments to estimate... 

One other type of reactor allows this in principle. Dijferential reactors are so short that concentrations and temperatures do not change appreciably from their inlet values. However, the small change in concentration makes it very hard to determine an accurate rate. The use of dilferential reactors is not recommended. If a CSTR cannot be used, a batch or piston flow reactor is preferred over a dilferential reactor even though the reaction rate is not measured directly but must be inferred from measured outlet concentrations. 

Aim of this work was to optimise enzymatic depolymerization of pectins to valuable oligomers using commercial mixtures of pectolytic enzymes. Results of experiments in continuous and batch reactor configurations are presented which give some preliminary indications helpful to process optimisation. The use of continuous reactors equipped with ultrafiltration membranes, which assure removal of the reaction products, allows to identify possible operation policy for the improvement of the reaction yield. 

The fine chemicals business is characterized by a small volume of products manufactured. Therefore, batch production predominates and small-scale reactors are used. The need to implement fine chemistry processes into existing multiproduct plants often forces the choice of batch reactors. However, safety considerations may lead to the choice of continuous processing in spite of the small scale of operation. The inventory of hazardous materials must be kept low and this is achieved only in smaller continuous reactors. Thermal mnaways are less probable in continuous equipment as proven by statistics of accidents in the chemical industries. For short reaction times, continuous or semicontinuous operation is preferred. 

Rylander in Catalytic Hydrogenation Over Platinum Metals (p. 39, Academic Press, New York, 1967). Nitrobenzene in ethanol was hydrogenated at room temperature and 1 atm over various amounts of 5% Pd on carbon. Four loading levels of catalyst were used. At each level, the reduction was carried out in two different types of batch reactor. 

Shaw CB, Carliell CM, Wheatley AD (2002) Anaerobic/aerobic treatment of coloured textile effluents using sequencing batch reactors. Water Res 36(8) 1993-2001... 

The participant A is identified by subscript a. Thus the concentration is Ca, the number of mols is na, the fractional conversion is xa, the partial pressure is pa, the rate of decomposition is ra. The capital letter A also is used on occasion instead of Ca. The flow rate in terms of mols is na but the prime ( ) is left off when the meaning is clear, The volumetric flow rate is V, reactor volume is Vr or simply V of batch reactors, the total pressure is... 

Ford et al.60 also made a significant contribution to the metal carbonyl catalyzed shift reaction in acidic medium. A solution of Ru3(CO)i2 (0.006-0.024 M with 0.25-2.0 M H2S04 4.0-12.0 M H20) in 5 ml of diglyme had good catalytic activity at 100 °C. They used a batch reactor with Pqo = 0-9 atm. Typical H2 turnover activity was reported to be about 50 turnovers per day. Their in situ spectroscopic studies show that the principal component was HRu2(CO)8-. They found that, at low CO partial pressures (< 1 atm), the catalysis was first order in Ru. However, at high CO partial pressures, the rate was inhibited. On the basis of their studies, they proposed the catalytic cycle outlined in Scheme 15. 

Choice of operating conditions favoring the adsorption of the reactant molecules and the desorption of the product molecules fixed-bed reactor instead of batch reactor, high molar substrate/acylating agent ratio, low conversion, high temperature, use of solvents with adequate polarities. 

Batch operation For the design of batch reactors for biphasic conversion the type of stirring device is an essential aspect to generate a narrow distribution with small droplet sizes which is equivalent to high surfaces [36]. Together with the diffusion ability (diffusion coefficient) of the used sol-... 

A recycle reactor without through-flow becomes a batch reactor. This type of batch reactor was used by Butt et al. (1962). 

The half-hfe of vinyl chloride, C2H3CI, can be determined using a batch reactor. The components of reaction and the reactor are given in Figure E6.1.1. Without an inflow or outflow and with first-order kinetics, assuming that the other components in the reaction have a large concentration, equation (6.3) becomes... 

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