Stirred semi batch mode

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

Biochemical reactors can be operated either batchwise or continuously, as noted in Section 1.5. Figure 7.1 shows, in schematic form, four modes of operation with two types of reactors for chemical and/or biochemical reactions in Uquid phases, with or without suspended solid particles, such as catalyst particles or microbial cells. The modes of operation include stirred batch stirred semi-batch continuous stirred and continuous plug flow reactors (PFRs). In the first three types, the contents of the tanks arc completely stirred and uniform in composition. 

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... 

If we compare the sparged (BSCR) and mechanically stirred (MSSR) reactors, we can stress that the slurry bubble column may be operated in a semi-batch mode, does not use any moving parts, and requires minimal maintenance, smaller floor space and has lower power consumption. 

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... 

The condensation of an aromatic nitro compound with a second reactant should have been performed in an aqueous solution with DMSO in the semi-batch mode. The nitro-compound is initially charged into the reactor with water and DMSO as solvent. Before the progressive addition of the second reactant had been started, the initial mixture was heated to the process temperatures of 60-70 °C. Then a failure of the cooling water system of the plant occurred. It was decided to interrupt the process at this stage and to maintain the mixture under stirring until the failure had been repaired. The feed of the second reactant was postponed and the jacket of the reactor had been emptied. 

In slurry reactors (Fig. 8.8) small catalyst particles (10-100 pm) are suspended in a liquid phase by mechanical mixing. Stirring also improves the contact between the gas bubbles and the liquid phase and heat exchange with the surroundings. Slurry reactors can be operated in a batch, semi-batch or continuous mode. In the semi-batch mode often the gas-phase is supplied continuously. 

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 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 most commonly used mode of operation for precipitations in the life science and specialty chemicals field is the semi-batch operation, the fed-batch ( ometry D in Figure 12.1). One of the two solutions is present in a stirred tank vessel and the other solution is added. The goal of these precipitations is often not the (fine) particle size but rather the fact that no alternative and more gentle crystallization technique is available. 

Probably the main advantage of using a stirred tank reactor is the relatively easy temperature control that is possible with this reactor type. This applies both to the semi-batch and the continuous operation modes. 

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