Catalytic reactors batch slurry

In high pressure work, slurry reactors are used when a solid catalyst is suspended in a liquid or supercritical fluid (either reactant or inert) and the second reactant is a high pressure gas or also a supercritical fluid. The slurry catalytic reactor will be used in the laboratory to try different catalyst batches or alternatives. Or to measure the reaction rate under high rotational speeds for assessing intrinsic kinetics. Or even it can be used at different catalyst loadings to assess mass transfer resistances. It can also be used in the laboratory to check the deactivating behaviour. 

Bubble slurry column reactors (BSCR) and mechanically stirred slurry reactors (MSSR) are particular types of slurry catalytic reactors (Fig. 5.3-1), where the fine particles of solid catalyst are suspended in the liquid phase by a gas dispersed in the form of bubbles or by the agitator. The mixing of the slurry phase (solid and liquid) is also due to the gas flow. BSCR may be operated in batch or continuous modes. In contrast, MSSR are operated batchwise with gas recirculation. 

Monoliths exhibit a large flexibility in operation. They are well suited for optimal semibatch, batch, continuous, and transient processing. Catalytic conversion can be combined with in situ separation, catalytic reactions can be combined, heat integration is possible, and all lead to process intensification. In the short term, catalytic monoliths will be applied to replace trickle-bed reactor and slurry-phase... 

The liquid phase esterification of maleic acid with methanol in a batch slurry reactor was studied. The esterification of maleic acid is an example of a multistep catalytic reversible reaction. The first reaction involves formation of a monoester (monomethyl-meleate) which further reacts with methanol to form a di-ester (dimethyl-maleate). The reactions involved are ... 

The most common heterogeneous catalytic reaction is hydrogenation. Most laboratory hydrogenations are done on liquid or solid substrates and usually in solution with a slurried catalyst. Therefore the most common batch reactor is a stirred vessel, usually a stirred autoclave (see Figure 2.1.1 for a typical example). In this system a gaseous compound, like hydrogen, must react at elevated pressure to accelerate the process. 

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. 

In fine chemicals industries the batch reactor is used almost exclusively. For catalytic hydrogenations the batch reactor has a number of inconveniences in case a slurry catalyst is used. The complicated cooling coils, dead spaces behind baffles, etc. are difficult to clean if the catalyst has to be removed from the vessel. After each batch the vessel has to be emptied, which also implies that the catalyst falls dry. It is known that specially in this period all reactants and products, still contained in the pores of the catalyst, rapidly may deteriorate via unwanted side reactions and so deactivate the catalyst. Usually deactivation starts as soon as the catalyst is no more protected by the solvent. As a production series of one product consists of a number of batches, the exposure of the catalyst to deactivation conditions is frequent. 

With the batch reactors used in the fine-chemical industry, the rate of the catalytic reaction is generally not decisively important. The number of catalyst particles per unit volume of the liquid to be treated is one of the experimental factors determining the apparent activity of the catalyst. Because the size of the catalyst particles usually affects the apparent activity of the catalyst only, the size is not critical, provided the particles are no smaller than ca 3 pm. When the size of the particles is below this, separation of the catalyst from the reaction product(s) is difficult, and with still smaller sizes even impossible. The requirement to avoid particles smaller than ca 3 pm imposes fairly severe requirements on the mechanical strength of catalyst particles employed in slurry-phase reactors. When the catalyst particles are liable to attrition, which leads to particles smaller than 3 pm, it is difficult to purify the reaction product(s) completely from the catalyst. Especially with fine-chemicals to be used in the food or pharmaceutical industry, contamination of the reaction product with the catalyst is usually not acceptable. Either mechanically strong catalyst particles must therefore be employed with slurry-phase catalysts or the reactor must be adapted to minimize attrition. With a bubble-column reactor the attrition of suspended catalyst particles is much smaller than with a reactor equipped with a stirrer that vigorously agitates the suspension. 

The reaction progress is monitored ofF-Une by HPLC. Flow rates, residence times and initial concentrations of 4-chlorophenol are varied and kinetic parameters are calculated from the data obtained. It can be shown that the photocatalytic reaction is governed by Langmuir-Hinshelwood kinetics. The calculation of Damkohler numbers shows that no mass transfer limitation exists in the microreactor, hence the calculated kinetic data really represent the intrinsic kinetics of the reaction. Photonic efficiencies in the microreactor are still somewhat lower than in batch-type slurry reactors. This finding is indicative of the need to improve the catalytic activity of the deposited photocatalyst in comparison with commercially available catalysts such as Degussa P25 and Sachtleben Hombikat UV 100. The illuminated specific surface area in the microchannel reactor surpasses that of conventional photocatalytic reactors by a factor of 4-400 depending on the particular conventional reactor type. 

For the internal diffusion regimes the experimental runs in either continuous-fed tubular reactors or batch reactors are made with catalyst particles of different diameter (dp). In this case the constancy of the reagent conversion, changing dp, indicates the absence of internal diffusion. It is quite obvious that in such runs the value of dp must not change during the experiment. Ultrasonic irradiation of a slurry of catalytic particles in a liquid could reduce the value of dp due to a reciprocal abrasion of the solid. Therefore care must be taken to measure the value of the particle diameter before and after the runs. 

Catalytic particles of Ru02 (H20)y have been used in a slurry batch reactor to promote, under sonication (20 kHz), the reaction of hexacyanoferrate (III) to hexacyanoferrate (II) by thiosulfate ions7 The ultrasonic rate enhancement appears to be largely associated with the dispersive action of ultrasound on the aggregate particle of Ru02 (H20)y. 

FIGURE 8.3 Heterogeneous catalysis reactor types (a) fixed bed, (b) batch fluid bed, (c) slurry, (d) catalytic gauze, (e) trickle bed, (f) moving bed, (g) continuous fluid bed, and (h) transport line. 

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