Agitated-Kettle Type

If the reboiler is either a well-agitated kettle type or a thermosyphcm type with a high recirculation rate, the reboiler/column-base composition dynamics are essentially those of a simplified basic tray (see Figure 18.1). The chief difference is that the reboiler has no entering vapor flow from a lower tray. Usually, too, the reboiler has considerably more holdup than a typical tray. The holdup, Af, is that of the reboiler itself plus that of the column base. 

FIG. 11-56 Heat-transfer equipment for fusion of solids, a) Horizontal-tank type. (Coutiesy of Sttxithers Wells Corp. ) (h) Agitated kettle. (Cowtesy of Read-Standard Division, Capital Products Co.) (c) Donble-dnim mill. (Coutiesy of FaiTel-Bitmingham Co.)... 

Batch Mass Reactors. The batch-mass reactors used in these processes are of two types low conversion agitated kettles and high conversion static reactors with extended cooling surfaces. 

An example of a low conversion reactor would be a conventionally agitated kettle with large turbine agitators and jacket cooling. The utility of this type of reactor can be extended to intermediate conversions by the use of anchor or helical agitators to partially overcome heat transfer and mixing problems at higher viscosities. 

Example 2-8 Benzene is chlorinated in the liquid phase in a kettle-type reactor operated on a semibatch basis i.e., the reactor is initially charged with liquid benzene, and then chlorine gas is bubbled into the well-agitated solution. The reactor is equipped with a reflux condenser which will condense the benzene and chlorinated products but will not interfere with the removal of hydrogen,chloride. Assume that the chlorine is added sufiiciently slowly that (1) the chlorine and hydrogen chloride concentrations in the liquid phase are small and (2) all the chlorine reacts. 

Type Pfaudler type P glass-lined reaction kettle, unjaeketed, with agitator Kettle dimensions over-all Diameter 34 in., height 611. in. 

Industrially, styrene polymerizations are carried out in bulk, in emulsion, in solution, and in suspension. The clear plastic is generally prepared by mass polymerization. Because polystyrene is soluble in the monomer, mass polymerization, when carried out to completion, results in a tremendous increase in melt viscosity. To avoid this, when styrene is polymerized in bulk in an agitated kettle, the reaction is only carried out to 30-40% conversion. After that, the viscous syrup is transferred to another type of reactor for the completion of the reaction. According to one early German patent, polymerization is completed in a plate and frame filter press. Water circulating through the press removes the heat of the reaction and the solid polymer is formed inside the frames. This process is still used in some places. 

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. 

A simple jacketed pan or kettle is very commonly used in the processing industries as a reaction vessel. In many cases, such as in nitration or sulphonation reactions, heat has to be removed or added to the mixture in order either to control the rate of reaction or to bring it to completion. The addition or removal of heat is conveniently arranged by passing steam or water through a jacket fitted to the outside of the vessel or through a helical coil fitted inside the vessel. In either case some form of agitator is used to obtain even distribution in the vessel. This may be of the anchor type for very thick pastes or a propeller or turbine if the contents are not too viscous. 

The laboratory method was scaled up to the minimum amount that could be successfully processed in a 10-hter stainless-steel kettle (Figure 2). fitted with a 12-cm propeller-type agitator and a 2.5-cm-wide baffle. The reactants were 2.00 liters of filtered 2 N (340 g/liters) silver nitrate solution, 2.00 liters of filtered 2N (130 g/liters) sodium azide solution, 1.07 liters of filtered reagent-grade (28%) ammonium hydroxide. 

When liquids are to be evaporated on a small scale, the operation is often accomplished in some form of jacketed tank or kettle. This may be a batch or continuous operation The rate ofheat transfer is generally lower than for other types of evaporators and only a limited heat transfer area is available. The kettles may or may not be agitated. 

A typical batch sulfonation kettle is illustrated in Fig. 7-3. Two common types of agitators are shown on the same shaft propeller and turbine. These are used for reaction mixtures of low or moderate viscosity. For more viscous products, a close-fitting anchor agitator equipped with supplemental vertical arms is suitable, especially if the blades have knife edges on the leading sides. 

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