Catalytic slurry reactors

In the third section an extensive writing on two types of slurry catalytic reactors is proposed Bubble Slurry Column Reactors (BSCR) and Mechanically Stirred Slurry Reactors (MSSR). All the variables relevant in the design and for the scale-up and the scale-down of slurry catalytic reactors are discussed particularly from the point of view of hydrodynamics and mass transfer. Two examples of application are included at the end of the section. 

High pressure catalytic processes are developed and carried out in both preformed and powdered catalysts. Preformed catalyst are useful for fixed bed operation. Preformed catalyst pellets, are used as packing in multiphase trickling flow reactors. Trickling flow reactors have been described in detail in another part of this book (see Laurent). In this section we deal with slurry catalytic reactors, where the catalyst is used in powdered form. 

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. 

Slurry catalytic reactors are the choice for a high pressure process whenever ... 

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. 

We review here the decisions to be made in choosing the relevant variables in the design of a slurry catalytic reactor. A fundamental selection refers to the raw materials. These include the catalyst and gas sources and their qualities. 

Heat transfer in mechanically slurry catalytic reactors... 

In summary, in the scale-up of a stirred slurry catalytic reactor, a certain number of adjustments may be necessary, as follows,... 

Strength against attrition is particularly important for catalysts in slurry-bed reactors, where physical breakage of the catalyst particles, ultimately to fines, can prevent their use for those reactions. The strength of the high surface area skeletal structures can be contrasted against activated carbon, which readily breaks down due to attrition in these types of environments. For the few environments where attrition is still a problem (e.g., oxidative dehydrogenation of alcohols), the skeletal catalytic material... 

The other major type of catalytic reactor is a situation where the fluid and the catalyst are stirred instead of having the catalyst fixed in a bed. If the fluid is a liquid, we call this a slurry reactor, in which catalyst pellets or powder is held in a tank through which catalyst flows. The stirring must obviously be fast enough to mix the fluid and particles. To keep the particles from settling out, catalyst particle sizes in a slurry reactor must be sufficiently small. If the catalyst phase is another Hquid that is stirred to maintain high interfacial area for reaction at the interface, we call the reactor an emulsion reactor. These are shown in Figure 74. 

The catalytic reactor is an example where reaction occurs only at the boundary with a solid phase, but, as long as the solid remains in the reactor and does not change, we did not need to write separate mass balances for the soHd phase because its residence time Tj is infinite. In a moving bed catalytic reactor or in a slurry or fluidized bed catalytic reactor... 

The ebullated, expanded, and slurry-bed reactors utilize a fluent catalyst zone unlike the stationary catalyst design of fixed-bed reactors. This design overcomes several of the problems encountered when processing residua in fixed-bed catalytic reactors. The commercial H-Oil process (Eccles et al., 1982 Nongbri and Tasker, 1985) employs the ebullated-bed, whereas the... 

Additional information on hydrodynamics of bubble columns and slurry bubble columns can be obtained from Deckwer (Bubble Column Reactors, Wiley, 1992), Nigam and Schumpe (Three-Phase Sparged Reactors, Gordon and Breach, 1996), Ramachandran and Chaudhari (Three-Phase Catalytic Reactors, Gordon and Breach, 1983), and Gianetto and Silveston (Multiphase Chemical Reactors, Hemisphere, 1986). Computational fluid mechanics approaches have also been recently used to estimate mixing and mass-transfer parameters [e.g., see Gupta et al., Chem. Eng. Sci. 56(3) 1117-1125 (2001)]. 

For the production of gasoline and other fuels by catalytic cracking of oils, a fluid bed reactor is used. This is a hybrid of a fixed bed and slurry phase reactor. The catalyst is fluidized as it interacts with the feed to be processed. This application is so important it... 

In comparison with fluidized-bed processes, the slurry bed offers the potential of lowering the reaction temperature to improve wax yields. Thus the slurry bed reactor offers the advantage of high flexibility with respect to operating conditions and product distribution 25). The catalytic activity is towei, however, which is explained by the reduced rates of transport of reactants from the gas... 

The EBR is one of the novel multiphase catalytic reactors which can be regarded as intermediate to slurry and fixed-bed operations. It is usually operated co-currently where the... 

Our objective here is to study quantitatively how these external physical processes affect the rate. Such processes are designated as external to signify that they are completely separated from, and in series with, the chemical reaction on the catalyst surface. For porous catalysts both reaction and heat and mass transfer occur at the same internal location within the catalyst pellet. The quantitative analysis in this case requires simultaneous treatment of the physical and chemical steps. The effect of these internal physical processes will be considered in Chap, 11. It should be noted that such internal effects significantly affect the global rate only for comparatively large catalyst pellets. Hence they may be important only for fixed-bed catalytic reactors or gas-solid noncatalytic reactors (see Chap. 14), where large solid particles are employed. In contrast, external physical processes may be important for all types of fluid-solid heterogeneous reactions. In this chapter we shall consider first the gas-solid fixed-bed reactor, then the fluidized-bed case, and finally the slurry reactor. 

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