Three-phase catalytic reactors continuous

Single phase Gas-liquid or liquid-liquid (semibatch reactors) Catalytic (three-phase) (semibatch or continuous) ... 

A reasonable throughput screening equipment consisting of six parallel reactor tubes was constructed. The system operates continuously and can be used for screening of various catalysts, different particle sizes and temperatures. Gas, gas-sohd and gas-solid-liquid applications are possible. The screening equipment is coupled to gas chromatographic-mass spectrometric analysis. The constraction principles, the equipment as well as the application of the equipment is demonstrated with three-phase catalytic systems. 

A second consideration is the operating mode continuous, batch, or semi-continuous. An extensive textbook on theory, design and scale-up of multiphase reactors was published by Gianetto and Silveston in 1986 [22], supplementing "Three-phase catalytic... 

Figure 8.31. Comparison between experimental and calculated according to eq. 8.117 data for three-phase catalytic hydrogenation in a fixed bed reactor (E. Toukoniitty, P. MSki-Arvela, A. Kalantar Neyestanaki, T. Salmi, D. Yu. Murzin, Continuous hydrogenation of l-phenyl-1,2 - propanedione under transient and steady-state conditions, regioselectivity, enantioselectivity and catalyst deactivation, Applied Catalysis A General, 235 (2002) 125).

Three phase catalytic slurry reactors are characterized by a continuous liquid phase in which a gas phase is dispersed and a solid (catalyst) is suspended. They are commonly used for catalytic hydrogenation, oxidation, halogenation or polymerization reactions such as edible oil hydrogenation, olefin oxidation or hydroformylation etc. But also fermenters can be included into this category of multiphase reactors. 

Column reactors can contain a draft tube - possibly filled with a packing characterized by low pressure drop - or be coupled with a loop tube, to make the gas recirculating within the reaction zone (see Fig. 5.4-9). In recent years, the Buss loop reactor has found many applications in two- and three-phase processes About 200 Buss loop systems are now in operation worldwide, also in fine chemicals plants. This is due to the high mass-transfer rate between the gas and the liquid phase. The Buss loop reactor can be operated semibatch-wise or continuously. As a semibach reactor it is mostly used for catalytic hydrogenations. 

Batchwise operating three-phase reactors are frequently used in the production of fine and specialty chemicals, such as ingredients in drags, perfumes and alimentary products. Large-scale chemical industry, on the other hand, is often used with continuous reactors. As we developed a parallel screening system for catalytic three-phase processes, the first decision concerned the operation mode batchwise or continuous. We decided for a continuous reactor system. Batchwise operated parallel sluny reactors are conunercially available, but it is in many cases difficult to reveal catalyst deactivation from batch experiments. In addition, investigation of the effect of catalyst particle size on the overall activity and product distribution is easier in a continuous device. 

Table 11.4 lists reactors used for systems with two fluid phases. The gas-liquid case is typical, but most of these reactors can be used for liquid-liquid systems as well. Stirred tanks and packed columns are also used for three-phase systems where the third phase is a catalytic solid. The equipment listed in Table 11.4 is also used for separation processes, but our interest is on reactions and on steady-state, continuous flow. 

The key issue in effective catalytic oxidation of organics is finding a suitable catalyst. Oxidation of aqueous phenol solutions by using different transition metal oxides as heterogeneous catalysts is already known [4-6]. On the other hand, the potential of molecular sieves to catalyze oxidative phenol destruction has not been examined yet. The objective of this contribution is to provide kinetic and mechanistic data on the catalytic liquid-phase oxidation of aqueous phenol solutions obtained in the presence of various transition metal oxides and molecular sieves. The reaction was studied in a semibatch slurry as well as two-and three-phase continuous-flow reactors. Another matter of concern was the chemical stability of catalysts under the reaction conditions. 

This case study is concerned with a three-phase gas-liquid-solid (catalytic) reaction. A systematic stepwise procedure has been described for determining the rate-controlling step, which depends on the catalyst type, particle size, operating pressure and temperature, mass transfer coefficient, and concentrations of reactants and products. As indicated, the rate-controlling step may change with location in a continuous reactor and with time in a batch reactor. 

Since the liquefaction of coal in a regular packed bed catalytic reactor would cause plugging problems, the data illustrate the feasibility of using a novel type of reactor to continuously operate a three-phase gas-liquid-solid (reactant) reaction in the presence of a catalyst. 

Several reactor types have been described [5, 7, 11, 12, 24-26]. They depend mainly on the type of reaction system that is investigated gas-solid (GS), liquid-solid (LS), gas-liquid-solid (GLS), liquid (L) and gas-liquid (GL) systems. The first three arc intended for solid or immobilized catalysts, whereas the last two refer to homogeneously catalyzed reactions. Unless unavoidable, the presence of two reaction phases (gas and liquid) should be avoided as far as possible for the case of data interpretation and experimentation. Premixing and saturation of the liquid phase with gas can be an alternative in this case. In homogenously catalyzed reactions continuous flow systems arc rarely encountered, since the catalyst also leaves the reactor with the product flow. So, fresh catalyst has to be fed in continuously, unless it has been immobilized somehow. One must be sure that in the analysis samples taken from the reactor contents or product stream that the catalyst docs not further affect the composition. Solid catalysts arc also to be fed continuously in rapidly deactivating systems, as in fluid catalytic cracking (FCC). 

Control of the temperature throughout the reforming catalyst bed can be established by use of a monolithic catalyst. The heat transfer control can be accomplished by combining three effects that monolithic catalyst beds can impact significantly (1) direct, uniform contact of the catalyst bed with the reactor wall will enhance conductive heat transfer (2) uniformity of catalyst availability to the reactants over the length of the flow will provide continuity of reaction and (3) coordination of void-to-catalyst ratio with respect to the rate of reaction will moderate gas-phase cracking relative to catalytically enhanced hydrocarbon-steam reactions. This combination provides conditions for a more uniform reaction over the catalyst bed length. 

Modeling of the reactor domain shown in Figure 11.8 requires simultaneous solution of continuity and conservation (of momentum, energy, and species mass) equations in the fluid and catalytic washcoat phases in every channel as well as of the heat flow between each channel in three dimensions. These sets of equations and the necessary boundary conditions, presented in Tables 11.2 and 11.3, respectively, can be simplified as a result of the following assumptions arising fi om the particular positioning of the channels ... 

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