Stirred-tank reactor batch mode

Figure 3.1 Batch, continuous, and semibatch stirred tank reactors. The mode of operation is schematically indicated.

Therefore, many traditional designs, such as stirred tank reactors, incorporate heat transfer in the process (jacket, external or internal coil, etc.). However, in these devices, there is a significant distance between the heat transfer site and the site of the chemical reaction where heat is released. As a consequence semibatch mode is implemented while batch mode and/or systems are diluted. 

Crameri et al. (1997) have reported an asymmetric hydrogenation constituting an important step in the production of a new calcium antagonist, Mibefradil (POSICOR) (of Hoffmann-LaRoche). Pilot-scale synthesis of (S)-2-(4-flurophenyl)-3-methylbutanoic acid by the asymmetric hydrogenation of 2-(4-fluorophenyl)-3-methyl but-2-enoic acid with a [Ru (/ )-MeOBIPHEP)(OAc)2]-catalyst has been described. The hydrogenation was performed in a continuous mode in a cascade stirred-tank reactor system at a pressure of 270 bar. A large reduction in total reactor volume compared to the batch mode was realized. 

Factors re.sponsible for the occurrence of scale-up effects can be either material factors or size/shape factors. In addition, differences in the mode of operation (batch or semibatch reactor in the laboratory and continuous reactor on the full scale), or the type of equipment (e.g. stirred-tank reactor in the laboratory and packed- or plate- column reactor in commercial unit) can be causes of unexpected scale-up effects. A simple misuse of available tools and information also can lead to wrong effects. 

The esterification process can be carried out in either batch or continuous mode, the final decision depending most likely on the size of the flow rates involved. For most commercial sizes of 15 MM gal/yr or higher, the continuous process is probably more cost effective and for this option, two additional options are available continuous stirred tank reactor (CSTR) or a fixed-bed reactor (FBR). 

Stirred-tank reactors can be operated in batch, semi-batch, or continuous mode. In batch or semi-batch mode ... 

The ideal tank reactor is one in which stirring is so efficient that the contents are always uniform in composition and temperature throughout. The simple tank reactor may be operated in a variety of modes batch, semibatch, and continuous flow. These modes are illustrated schematically in Figure 8.1. In the simple batch reactor the fluid elements will all have the same composition, but the composition will be time dependent. The stirred tank reactor may also be... 

The chemical reactor is the unif in which chemical reactions occur. Reactors can be operated in batch (no mass flow into or out of the reactor) or flow modes. Flow reactors operate between hmits of completely unmixed contents (the plug-flow tubular reactor or PFTR) and completely mixed contents (the continuous stirred tank reactor or CSTR). A flow reactor may be operated in steady state (no variables vary with time) or transient modes. The properties of continuous flow reactors wiU be the main subject of this course, and an alternate title of this book could be Continuous Chemical Reactors. The next two chapters will deal with the characteristics of these reactors operated isothermaUy. We can categorize chemical reactors as shown in Figure 2-8. 

Figure 7.1 Modes of reactor operation (a) batch reactor, (b) semi-batch reactor, (c) continuous stirred-tank reactor, and (d) continuous plug flow reactor.

An analysis based on reaction kinetics suggests that up to 50% of manufacturing reaction steps in the fine chemical and pharmaceutical industries could benefit from being run continuously rather than in batch mode in a stirred tank reactor... 

Figure 1-2 Operating parameters necessary for ozone mass balance(s) on a continuous-flow stirred tank reactor (for operation in semi-batch mode Ol - 0).

For example, Beltran and Alvarez (1996) successfully applied a semi-batch agitated cell for the determination of kL k,a, and the rate constants of synthetic dyes, which react very fast with molecular ozone (direct reaction, kD = 5 105 to 1 108 L mol-1 s l). In conventional stirred tank reactors operated in the semi-batch mode the mass transfer coefficient for ozone kLa(03) was determined from an instantaneous reaction of ozone and 4-nitrophenol (Beltran et al., 1992 a) as well as ozone and resorchinol (l,3-c//hydroxybenzene) or phloroglucinol... 

A condensation reaction is to be in a stirred tank reactor in the semi-batch mode. The solvent is acetone, the industrial charge (final reaction mass) is 2500 kg, and... 

A reaction A——>P is to be performed in a PFR. The reaction follows first-order kinetics, and at 50 °C in the batch mode, the conversion reaches 99% in 60 seconds. Pure plug flow behavior is assumed. The flow velocity should be 1 m s"1 and the overall heat transfer coefficient 1000Wm 2 K"1. (Why is it higher than in stirred tank reactors ). The maximum temperature difference with the cooling system is 50 K. 

An attractive property of monolithic reactors is their flexibility of application in multiphase reactions. These can be classified according to operation in (semi)batch or continuous mode and as plug-flow or stirred-tank reactor or, according to the contacting mode, as co-, counter-, and crosscurrent. In view of the relatively high flow rates and fast responses in the monolith, transient operations also are among the possibilities. 

The semibatch reactor is a cross between an ordinary batch reactor and a continuous-stirred tank reactor. The reactor has continuous input of reactant through the course of the batch run with no output stream. Another possibility for semibatch operation is continuous withdrawal of product with no addition of reactant. Due to the crossover between the other ideal reactor types, the semibatch uses all of the terms in the general energy and material balances. This results in more complex mathematical expressions. Since the single continuous stream may be either an input or an output, the form of the equations depends upon the particular mode of operation. 

The slurry tank, when well mixed, can be considered a continuous-stirred tank reactor for both the gas phase and the liquid phase. When the solid is retained in the reaction vessel, it behaves in a batch mode however, catalyst can be removed and regenerated easily in a slurry tank, so activity can be maintained. 

In the production of 2, strains with entA - mutation have long-term stability and production rates are high. Typical cultivation of 2,3-trans-CHD 2 is performed at pH 6.8 and 37 °C in a stirred-tank reactor with glucose feeding in a fed-batch mode. Microbial production over a process time of 40 h affords 92 g 2 from 690 g glucose monohydrate in a 20-L cultivation experiment. This corresponds to a molar yield of 17% [13]. Advantageously, 2,3-trans-CHD 2 is the major product with no... 

Various laboratory reactors have been described in the literature [3, 11-13]. The most simple one is the packed bed tubular reactor where an amount of catalyst is held between plugs of quartz wool or wire mesh screens which the reactants pass through, preferably in plug flow . For low conversions this reactor is operated in the differential mode, for high conversions over the catalyst bed in the integral mode. By recirculation of the reactor exit flow one can approach a well mixed reactor system, the continuous flow stirred tank reactor (CSTR). This can be done either externally or internally [11, 12]. Without inlet and outlet feed, this reactor becomes a batch reactor, where the composition changes as a function of time (transient operation), in contrast with the steady state operation of the continuous flow reactors. 

After specifying the energy form, the catalyst and the phases in contact, the next task is to decide whether to conduct the reaction in a batch or continuous mode. In the batch mode, the reactants are charged to a stirred-tank reactor (STR) and allowed to react for a specified time. After completing the reaction, the reactor is emptied to obtain the products. This operating mode is unsteady state. Other unsteady-state reactors are (1) continuous addition of one or more of the reactants with no product withdrawal, and (2) all the reactants added at the beginning with continuous withdrawal of product. At steady-state, reactants flow into and products flow out continuously without a change in concentration and temperature in the reactor. 

The operating mode of a stirred-tank reactor may be either continuous or batch. A STR consists of a vessel to contain the reactants, a heat exchanger, a mixer, and baffles to prevent vortex formation and to increase turbulence, enhancing mixing. 

The stirred-tank reactor consists of a box or tank with a stirrer in it. The solid medium in the tank is stirred in batch or continuous mode to facilitate oxygen mass transfer. Figure 8 shows the rectangular pilot reactor (2 x 0.8 x 2.3 m) designed by Durand and Chereau [70] to culture T. viride with sugar beet pulp as raw material. The thickness of the substrate layer in the reactor is 1 m. Three vertical screws are bound to a conveyor with dual direction movement. The linear movement speed of the conveyor and the rotating rate of the screws are... 

Form and size of support The particle size will have an influence on filtration times from stirred tank reactors in repeated batch mode. Furthermore, this factor is important for the performance in column reactors regarding back pressure and flowrates, which of course are correlated. For this purpose a size of spherical particles in the range of 150-300 pm is preferred. 

Commercial industrial processes can be operated in a either batch or a continuous mode. Batch processes are suitable for small plants, while for larger plants (>100 000 ty ) continuous process tend to be more economical. In the ESTERFIP batch process (IFF license), transesterification occurs in a single stirred-tank reactor. Continuous transesterification processes include the Ballestra, Connemann CD and... 

The mode of reactor operation can be classified as batchwise or continuous . Batch reactions are started by filling a reactor with the reaction mixture and stopped after reaching the desired conversion. A steady state is only reached at equilibrium conversion of the reaction. A typical batch reactor is represented by the stirred tank reactor. 

The stirred tank reactor (STR) in batch mode exhibits a decreasing substrate concentration and increasing product concentration with time, independently of the position within the reactor (the reactor is well mixed , meaning that there are no gradients within the reactor). 

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