Kinetic regimes

Fig. 17. Transition between kinetic regimes of CO oxidation over platinum, where...

The rate of ammonia production was enhanced by more than 1100% in the nitrogen rich regime (Figs 9.33 and 9.34), upon potential application of -IV between the working electrode and the Ag reference electrode. The extent of the NEMCA effect depends strongly on the kinetic regime of the reaction. Very pronounced non-faradaic behavior is observed in the regime 0.33

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For small catalyst particles used in sugar hydrogenation (slurry reactors), one would intuitively conclude that the system is safely within the kinetic regime. 

Firstly, there are technical reasons concerning catalyst and reactor requirements. In the chemical industry, catalyst performance is critical. Compared to conventional catalysts, they are relatively expensive and catalyst production and standardization lag behind. In practice, a robust, proven catalyst is needed. For a specific application, an extended catalyst and washcoat development program is unavoidable, and in particular, for the fine chemistry in-house development is a burden. For coated systems, catalyst loading is low, making them unsuited for reactions occurring in the kinetic regime, which is particularly important for bulk chemistry and refineries. In that case, incorporated monolithic catalysts are the logical choice. Catalyst stability is crucial. It determines the amount of catalyst required for a batch process, the number of times the catalyst can be reused, and for a continuous process, the run time. 

Fig. 2 and 3 showed that increasing gas flow rate Qg) and temperature (7) at 500 rpm rotation speed (TV), will increase the acetaldehyde conversion. Fig. 2 also showed that the reaction is in kinetic regime at low temperature, while at higher temperature (Fig.3), the reaction approach the equilibrium condition or in thermodynamic region. 

The nucleation stage is followed by two different kinetic regimes of cluster growth (i) a diffusional one (occurring at the earlier stage of growth) which is characterized by a time dependence of cluster radius scaling as where... 

When diffusion of oxygen in the polymer occurs rapidly (Ak 1), we observe the kinetic regime of polymer oxidation (see Equation [13.16]). When penetration of oxygen into polymer is slow, the reaction rate v KXp02. 

Interpretation ofHatta Number (Ha) Criterion for Kinetics Regime... 

In a typical situation, as illustrated in Figure 24.3, the composition and flow rate of each feed stream (gas at the bottom and liquid at the top) are specified, directly or indirectly this enables evaluation of the quantities pAin, cAin, cB in, L, and G. The unknown quantities to be determined, in addition to h (or I, the packed volume), are Pa,out and c, our The determination involves use of the rate law developed in Section 9.2 for an appropriate kinetics regime (1) reaction in bulk liquid only (relatively slow intrinsic rate of reaction), or (2) in liquid film only (relatively fast reaction), or (3) in both bulk liquid and liquid film. For case (2), cA = 0 throughout the bulk liquid, and the equations developed below for the more general case (3), cA 0, are simplified accordingly. 

Calculate the required height of the tower (m), based on an assessment of the appropriate kinetics regime (for possible simplification), and on the following information ... 

Modem catalysts have to be very active and very (100%) selective, that is, they have to catalyze the desired reaction in the temperature window, where the equilibrium conversion is the highest possible and the reaction rate is high enough to permit suitable process economics. To engineer the reaction, one has to obtain first the intrinsic reaction rate, free of heat- and mass-transfer limitations. In many cases this is very difficult, because in the core of the catalytic process there are several physical and chemical steps that must occur and which may preclude the reaction running in the kinetic regime. These steps are as follows ... 

Kinetic regime This is the regime of small Thiele modules. The pore system of the catalyst with its interior surface is completely accessible for the educt. rj 1 and krj k, as In k In k0 -EpJRT, that the apparent activation energy is practically identical with the true activation energy. 

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