Continuously-stirred tank catalytic

Fig. 12-3 Continuous stirred-tank catalytic reactor from D. G. Tajbl, J. B. Simons, and J. J. Carberry,...

Instead of the commonly used packed-tube reactor, IGT is using a continuous-stirred tank catalytic reactor (CSTCR) (3) which permits one to study these chemical events without any complicating control of the reaction rate by gas-solid mass or heat transfer. This reactor has several other advantages ... 

Figure 2. Continuous-stirred tank catalytic reactor...

Conditions for "perfect mixing were determined in a continuous-stirred tank catalytic reactor operated at 1000 p.s.i.g. "Perfect mixing was obtained at stirring speeds above 1500 r.p.m. over the flow range used in this study. 

We have used CO oxidation on Pt to illustrate the evolution of models applied to interpret critical effects in catalytic oxidation reactions. All the above models use concepts concerning the complex detailed mechanism. But, as has been shown previously, critical. effects in oxidation reactions were studied as early as the 1930s. For their interpretation primary attention is paid to the interaction of kinetic dependences with the heat-and-mass transfer law [146], It is likely that in these cases there is still more variety in dynamic behaviour than when we deal with purely kinetic factors. A theory for the non-isothermal continuous stirred tank reactor for first-order reactions was suggested in refs. 152-155. The dynamics of CO oxidation in non-isothermal, in particular adiabatic, reactors has been studied [77-80, 155]. A sufficiently complex dynamic behaviour is also observed in isothermal reactors for CO oxidation by taking into account the diffusion both in pores [71, 147-149] and on the surfaces of catalyst [201, 202]. The simplest model accounting for the combination of kinetic and transport processes is an isothermal continuously stirred tank reactor (CSTR). It was Matsuura and Kato [157] who first showed that if the kinetic curve has a maximum peak (this curve is also obtained for CO oxidation [158]), then the isothermal CSTR can have several steady states (see also ref. 203). Recently several authors [3, 76, 118, 156, 159, 160] have applied CSTR models corresponding to the detailed mechanism of catalytic reactions. 

There are numerous reactor types, but in this chapter the objective is to consider only a few common types. These are batch, continuous stirred tank, homogenous plug flow and fixed bed catalytic reactors. To size other reactor types and for a more thorough treatment of reactor design than presented here, the reader can consult books written on reactor design, such as Fogler [16], Smith [23], and Forment and Bischoff [31]. 

The simplicity and general utility of the Madon-Boudart criterion make it one of the most important experimental tests to confirm that kinetic data are free from artifacts. It can be used for heterogeneous catalytic reactions carried out in batch, continuous stirred tank, and tubular plug flow reactors. 

In Table I the high-vacuum (HV) range means a pressure of 10 to 10 Torr entries designated by Torr mean pressures between 0.1 and 10 Torr flow refers to an unspecified steady-state flow pattern. It is apparent from Table I that there is a great diversity in the different oscillation conditions and catalytic systems. The pressures under which oscillations have been observed vary from 10 Torr for the CO/NO reaction on Pt(lOO) 141, 142) to atmospheric pressure for a large number of systems. The reactors used in these studies include ultrahigh-vacuum (UHV) systems, continuous stirred tank reactors (CSTRs), flow reactors, and reactors designed as infrared (IR) cells, calorimeters, and ellipsometric systems. 

The simulations discussed above are focused on the behavior of single catalytic oscillators at fixed reactant pressures. In the full-scale analysis of reactions on nm-supported particles, the reactant pressures should be calculated self-consistently with the reaction kinetics. At present, due to computational limitations, the self-consistent treatment can, however, be done only by using the MF equations (see, e.g., recent simulations [57] of oscillations in CO oxidation in a continuously stirred tank reactor). The MF approach does not, however, make it possible to scrutinize the reaction kinetics on the nm scale. Under such circumstances, the MC and MF treatments are complementary. In particular, the MC results may be employed in order to understand the limits of applicability of the MF approximation. 

To derive the overall kinetics of a gas/liquid-phase reaction it is required to consider a volume element at the gas/liquid interface and to set up mass balances including the mass transport processes and the catalytic reaction. These balances are either differential in time (batch reactor) or in location (continuous operation). By making suitable assumptions on the hydrodynamics and, hence, the interfacial mass transfer rates, in both phases the concentration of the reactants and products can be calculated by integration of the respective differential equations either as a function of reaction time (batch reactor) or of location (continuously operated reactor). In continuous operation, certain simplifications in setting up the balances are possible if one or all of the phases are well mixed, as in continuously stirred tank reactor, hereby the mathematical treatment is significantly simplified. 

In fact, since the leaving group, methyl carbonate, decomposes (reaction 3), the base is restored and can be used in truly catalytic amounts. This feature allows utihzation of continuous-flow (c-f) procedures (i.e. gas-liquid phase-transfer catalysis, GL PTC, and continuously stirred tank reactor, CSTR ). 

Batch, semibatch, and continuous stirred tank reactors residence time 600 to 15,000 s (10 min to 4 h) heat of reaction primarily exothermic reaction rate slow to moderate. High-pressure autoclaves <100 L. Unique to semibatch phases liquid, gas-liquid, liquid-liquid, gas-liquid catalytic solid. Use where a batch operation is appropriate (Section 16.11.6.24), but one reactant (e.g., gas) needs to be added continuously or if the initial reaction rate is very high. Selectivity is best for parallel reactions. For more details, see CSTR, Section 16.11.6.26. 

Kinetic models can be used to link the reactor design with its performance. The reaction rate may be expressed by power law functions, by more complex expressions, as Langmuit-Hinselwood-Hougen-Watson (LHHW) correlations for catalytic processes, or by considering user kinetics. There are two ideal models, continuous stirred tank reactor (CSTR) or plug flow (PFR), available in rating mode (reaction volume fixed) or design mode (conversion specified). 

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