Liquid-Gas-Solid Reactions

A hst of 74 GLS reacdions with hterature references has been compiled by Shah Gas-Liquid-Solid Reactions, McGraw-HiU, 1979), classified into groups where the solid is a reactant, or a catalyst, or inert. A hst of 75 reactions made by Ramachandran and Chaudhari (Three-Phase Chemical Reactors, Gordon and Breach, 1983) identifies reactor types, catalysts, temperature, and pressure. They classify the processes according to hydrogenation of fatty oils, hydrodesulfurization, Fischer-Tropsch reactions, and miscellaneous hydrogenations and oxidations. 

One goal of our experimental program with the bench-scale unit was to develop the necessary correlations for use in the ultimate design of large commercial plants. Because of the complexity inherent in the three-phase gas-liquid-solid reaction systems, many models can be postulated. In order to provide a background for the final selection of the reaction model, we shall first review briefly the three-phase system. 

Gas-liquid-solid reactions (catalytic hydrogenations and oxidations) 1-5 50-250 250 500... 

Column reactors for gas-liquid-solid reactions are essentially the same as those for gas-liquid reactions. The solid catalyst can be fixed or moving within the reaction zone. A reactor with both the gas and the liquid flowing upward and the solid circulating inside the reaction zone is called a slurry column reactor (Fig. 5.4-10). The catalyst is suspended by the momentum of the flowing gas. If the motion of the liquid is the driving force for solid movement, the reactor is called an ebullated- or fluidized-bed column reactor (Fig. 5.4-10). When a catalyst is deactivating relatively fast, part of it can be periodically withdrawn and a fresh portion introduced. 

The catalyst can, alternatively, be present in a basket located in the annular space at the wall. A reactor of this type is particularly useful for gas-liquid-solid reactions. 

Application Homogeneous reactions Liquid-Solid reactions Gas-Liquid-Solid reactions Gas-Liquid reactions Liquid-Liquid reactions... 

Heterogeneously catalyzed hydrogenation is a three-phase gas-liquid-solid reaction. Hydrogen from the gas phase dissolves in the liquid phase and reacts with the substrate on the external and internal surfaces of the solid catalyst Mass transfer can influence the observed reaction rate, depending on the rate of the surface reaction [15]. Three mass transfer resistances may be present in this system (Fig. 42.1) ... 

Liquid-liquid reactions 804. Gas-liquid-solid reactions 815... 

Reactions of cell growth or those using immobilized enzymes are instances of gas-liquid-solid reactions. In principle, accordingly, any of the types of reactors described in Section 8.3 could be employed as fermentors. Mostly, however, mechanically agitated tanks are the type adopted. Aeration supplies additional agitation as well as metabolic need, and moreover sweeps away C02 and noxious byproducts. 

Catalytic engineering, progress in, 26 949 Catalytic gas-liquid-solid reactions, 21 331 Catalytic gas-solid reactions, 21 331 steps in, 21 342... 

Testing of Catalysts in Liquid-Liquid, Gas-Liquid, and Gas-Liquid-Solid Reactions.411... 

TESTING OF CATALYSTS IN LIQUID-LIQUID, GAS-LIQUID, AND GAS-LIQUID-SOLID REACTIONS... 

Figure 11.32 Influence of essential reaction parameters exerted on the reaction rate of gas-liquid-solid reactions (a, impeller speed b, particle size).

TABLE 17.21. Examples of Industrial Gas-Liquid-Solid Reaction Processes... 

GAS-LIQUID-SOLID REACTORS 4.2.1. Gas-Liquid-Solid Reactions... 

At the present time, three-phase fluidised-beds are not often chosen for gas-liquid-solid reactions despite their advantages of good heat and mass transfer and, in principle, freedom from the blockages that can occur with fixed-beds(30). The reason may be that, because of the pronounced hydrodynamic interactions between the phases as indicated in Fig. 4.16, development of a three-phase fluidised-bed... 

In Table 3 the three common reactor types are compared. Obviously, the monolithic reactor in the Taylor-flow regime leads to a high degree of process intensification. When these numbers are recalculated into production rates, values of 40 mol/m3reactor-s were found. Figure 17 illustrates the high value in relation to the Weisz window of reality. This demonstrates the attractiveness of using monoliths in fast catalyzed gas-liquid-solid reactions. 

It has also been proposed that porous catalytic membranes may improve the efficiency of gas-liquid solid reactions when the gas-liquid interface is placed within the porous framework of the porous membrane [77], This postulated increase in efficiency has been experimentally supported by Cini and Harold in a comparative study of a CMR and a single-pellet model reactor [78] in the hydrogenation of a-mcthylstyrene into cumene. The authors ascribe this observation to a decrease in the mass transfer resistance. 

Internal recycle reactors are designed so that the relative velocity between the catalyst and the fluid phase is increased without increasing the overall feed and outlet flow rates. This facilitates the interphase heat and mass transfer rates. A typical internal flow recycle stirred reactor design proposed by Berty (1974, 1979) is shown in Fig. 18. This type of reactor is ideally suited for laboratory kinetic studies. The reactor, however, works better at higher pressure than at lower pressure. The other types of internal recycle reactors that can be effectively used for gas-liquid-solid reactions are those with a fixed bed of catalyst in a basket placed at the wall or at the center. Brown (1969) showed that imperfect mixing and heat and mass transfer effects are absent above a stirrer speed of about 2,000 rpm. Some important features of internal recycle reactors are listed in Table XII. The information on gas-liquid and liquid-solid mass transfer coefficients in these reactors is rather limited, and more work in this area is necessary. 

Recently, Manor and Schmitz (1984), Carberry et al. (1985), and Tipnis and Carberry (1984) illustrated a wiper-blade reactor for gas-liquid and gas-liquid-solid reactions. The reactor is a continuous flow reactor and incorporates a multibladed rotor that contacts the gas-liquid interface... 

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