Mechanically Stirred Reactors

Among the earlier studies of reaction kinetics in mechanically stirred slurry reactors may be noted the papers of Davis et al. (D3), Price and Schiewitz (P5), and Littman and Bliss (L6). The latter investigated the hydrogenation of toluene catalyzed by Raney-nickel with a view to establishing the mechanism of the reaction and reaction orders, the study being a typical example of the application of mechanically stirred reactors for investigations of chemical kinetics in the absence of mass-transfer effects. 

Bubble columns and mechanically stirred reactors are the most common reactor types for slurry systems in laboratories, but they have many disadvantages from an industrialization perspective. Mechanically stirred reactors usually used for laboratorial studies are difficult to scale-up. In order to achieve good mixing and mass transfer between the gas and slurry phases, bubble column must be operated at a high space velocity, which leads to a relative low one-through conversion of the syngas. 

Conventional (semi)batch-operated, mechanically stirred reactors equipped with a multinozzle system for feeding components of the reaction mixture predominate at this stage. 

Comparison between mechanically stirred reactors and slurry bubble column reactors [71... 

The Difasol reaction involves a mechanically stirred reactor and settlers. An injection of fresh catalyst components is defined to compensate the detrimental effects of accidental impurities present in the feed and slight carryover of the catalyst. Mixing of the solvent phase with the organic phase ensures advantageous butene conversion. However, importantly, the stirring power combined with a high... 

Alkaline Extraction Tannins were extracted from samples (200 g) with 1000 ml NaOH, 1 % (w/w) (baik/solvent relation - 1 S) in a mechanically stirred reactor for 30 min at 90 C. The suspension was separated by centrifugation and the clear extract was neutralised with HCl and conditioned in recipients at 4 X. The extracted baric was dried to constant weight at 100 C. 

In WAO with solid catalysts, three-phase reactors are used trickle bed, bubble slurry column, and bubble fixed-bed (monolith) or three-phase fluidized-bed reactors. When the catalyst is present in the liquid phase (homogeneous) or absent, two-phase reaetors such as bubble columns, jet-agitated reactors, and mechanically stirred reactor vessels are used. The limitations and advantages of these reactors for the application to WAO are listed in Table 10.7. 

The stirred-tank reactor (STR) is one of the simplest and most widely used bioreactor types. For a preparative resolution of GPF, a mechanically stirred reactor was operated in batch mode under the above optimal conditions... 

The reaction mixture in ethyl acetate is then transferred to a 100-ml reactor, purged under a nitrogen atmosphere, 340 mg of Lil is added, and the whole mass is then heated, with mechanical stirring, on an oil bath, up to ethyl acetate reflux temperature. The heating is continued for 5 hours, until the disappearance of the epoxide (II), as evidenced by the thin-layer chromatography. 

In the second class, the particles are suspended in the liquid phase. Momentum may be transferred to the particles in different ways, and it is possible to distinguish between bubble-column slurry reactors (in which particles are suspended by bubble movement), stirred-slurry reactors (in which particles are suspended by bubble movement and mechanical stirring), and gas-liquid fluidized reactors (in which particles are suspended by bubble movement and cocurrent liquid flow). 

In stirred-slurry reactors, momentum is transferred to the liquid phase by mechanical stirring as well as by the movement of gas bubbles. Small particles are used in most cases, and the operation is usually carried out in tank reactors with low height-to-diameter ratios. The operation is in widespread use for processes involving liquid reactants, either batchwise or continuous— for example, for the batchwise hydrogenation of fats as referred to in Section II. 

Stirred-slurry reactors are of considerable industrial importance in batch-wise processing. The catalytic hydrogenation of fats and fatty acids is an example of a process that is carried out almost exclusively in mechanically stirred slurry reactors. The operation is of less significance with respect to continuous processing. 

Liquid residence-time distributions in mechanically stirred gas-liquid-solid operations have apparently not been studied as such. It seems a safe assumption that these systems under normal operating conditions may be considered as perfectly mixed vessels. Van de Vusse (V3) have discussed some aspects of liquid flow in stirred slurry reactors. 

The present research was focused on the study of acetaldehyde oxidation rising air with aqueous mangan acetate catalyst in mechanically stirred tank reactor. 

A continuous, mechanically stirred tank reactor with a sparger located below the agitator or... 

Laboratory reactor for studying three-phase processes can be divided in reactors with mobile and immobile catalyst particles. Bubble (suspension) column reactors, mechanically stirred tank reactors, ebullated-bed reactors and gas-lift reactors belong the class of reactors with mobile catalyst particles. Fixed-bed reactors with cocurrent (trickle-bed reactor and bubble columns, see Figs. 5.4-7 and 5.4-8 in Section 5.4.1) or countercurrent (packed column, see Fig. 5.4-8) flow of phases are reactors with immobile catalyst particles. A mobile catalyst is usually of the form of finely powdered particles, while coarser catalysts are studied when placing them in a fixed place (possibly moving as in mechanically agitated basket-type reactors). 

Studies in Table 1 refer to different types of reactors stirred tank (mechanically agitated reactors and rotary reactors), fixed bed and fluidized bed. Figure 2 reports an outline of the most common reactor typologies. The reactors may be operated... 

Mechanically stirred gas-liquid reactor performances are affected by the degree of mixing, apparatus geometry, stirring power, flow rate, discharge and feed locations for the gas and liquid. For a correct design, the following requirements must be satisfied ... 

The scale-up of mechanically stirred gas-liquid reactors mainly involves reactor size and stirrer size, and is generally based on homothetic designs from pilot tests. The similitude in the scale-up means that the following parameters are - or at least should be - kept constant ... 

Many correlations allow estimation of the gas-liquid volumetric mass transfer coefficient kLa in mechanically stirred tank reactors. The following intends not to provide a comprehensive review but rather a critical evaluation of selected correlations adapted to hydrogenations [Eqs. (40) to (43)] [25, 51-53]. 

The radiation-absorbing cell of the main unit (P) is the photochemical reactor, that is, it contains the solution to be examined. It is a Teflon-coated steel vessel with a volume of only 3 cm3, provided with mechanical stirring. The other radiation-absorbing cell, in the reference unit (R), is a steel rod with three holes for the optical fibers. 

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