Catalyst distribution

Variables It is possible to identify a large number of variables that influence the design and performance of a chemical reactor with heat transfer, from the vessel size and type catalyst distribution among the beds catalyst type, size, and porosity to the geometry of the heat-transfer surface, such as tube diameter, length, pitch, and so on. Experience has shown, however, that the reactor temperature, and often also the pressure, are the primary variables feed compositions and velocities are of secondary importance and the geometric characteristics of the catalyst and heat-exchange provisions are tertiary factors. Tertiary factors are usually set by standard plant practice. Many of the major optimization studies cited by Westerterp et al. (1984), for instance, are devoted to reactor temperature as a means of optimization. 

Greater afterburn, particularly with an uneven air or spent catalyst distribution system... 

Air and spent catalyst distribution. Modifications to the air and spent catalyst distributors permit uniform dispersion of air and spent catalyst into the regenerator. Improvements are lower carbon on the catalyst and less catalyst sintering. The benefits are a cleaner and higher-activity catalyst, which results in more liquid products and less coke and gas. 

Oxygen enrichment. In a cat cracker, which is either air blower or regenerator velocity limited, enrichment of the regenerator air can increase capacity or conversion provided there is good air/ catalyst distribution and that the extra oxygen does not just burn CO to CO2. 

Any mechanical revamp to improve the unit yields should always begin with installing an efficient feed and catalyst distribution system. This is the single most-important component of the FCC unit. An efficient feed and catalyst injection system maximizes gasoline yield and conversion at the expense of lower gas, coke, and decant oil and allows downstream technology to perform at its full potential. 

Selective plugging/addition of air distributor jets to match the spent catalyst distribution... 

The regenerator review will include spent catalyst distribution, air distribution, and cyclones. If the test run with heavy feed indicates a temperature limitation, catalyst coolers, partial combustion, or riser quench should be considered. 

Figure 6.7 Catalyst distribution within a pellet of supported catalyst.

The T-STAR ebullated bed is shown schematically in Fig. 6. The figure demonstrates that a uniform catalyst distribution is maintained throughout the reaction chamber via the upward flow of the hydrogen, feed oil, and recycle oil. The internal recycle allows for increased conversion and assists in maintaining a uniform temperature throughout the reactor. Careful monitoring of the temperature in an ebullated bed... 

Let s note three important aspects followed from the model [4] application for description of reesterification reaction. At first as reesterification reactions with TBT and in it absence proceed in identical conditions, then from the comparison of figure 1 kinetic curves follows, that the reaction fractal-like behaviour in TBT presence is due to local fluctuations of catalyst distribution in reactive medium. Secondly the division of reaction duration into short and long... 

It is evident, that in any membrane reactor operation mode there are important parameters which determine the performance of the process (Shah, Remmen and Chiang 1970). These are (1) the total and partial pressures on both sides of the membrane, (2) the total and partial pressure differences across the membrane, (3) the diffusion mechanism through the support and the membrane layer (membrane structure), (4) the thickness of the membrane, (5) the reactant configuration (i.e. whether the reactants are supplied from the same or from opposite sides of the membrane, in counter or co-current flow) and (6) the catalyst distribution. 

An important aspect concerning catalytically active membrane reactors, is the distribution of the active phase within the membrane system. Modem modification techniques (van Praag et al. 1989, Lin, de Vries and Burggraaf 1989) allow control over the catalyst distribution and preferential deposition of the active phase at different places in the membrane (top layer/support) system. Studies on conventionally used plate-shaped and cylindrically-sha-ped catalytically active pellets (Vayenas and Pavlou 1987a, b, Dougherty and Verykios 1987) have shown that nonuniformly activated catalysts (catalysts with nonuniform distribution of active sites according to a certain profile)... 

Vayenas, C. G. and S. Pavlou. 1987a. Optimal catalyst distribution and generalized effectiveness factors in pellets single reactions with arbitrary kinetics. Chem. Eng. Sci. 42(11) 2633-2645. 

The results of this analysis of the product and catalyst distribution show that only a limited range of systems may be apphcable for the telomeriza-tion of butadiene and carbon dioxide. The reaction was performed in the biphasic systems EC/2-octanol, EC/cyclohexane and EC/p-xylene. The yield of 5-lactone reached only 3% after a reaction time of 4 hours at 80 °C. hi the solvent system EC/2-octanol triphenylphosphine was used as the hgand. With the ligand bisadamantyl-n-butyl-phosphine even lower yields were achieved in a single-phase reaction in EC or in the biphasic system EC/cyclohexane. The use of tricyclohexylphosphine led to a similar result, only 1% of the desired product was obtained in the solvent system EC/p-xylene, which forms one homogeneous phase at the reaction temperature of 80 °C. Even at a higher temperature of 100 °C and a longer reaction time of 20 hours no improvement could be observed. Therefore, we turned our interest to another telomerization-type process. 

Improve spent catalyst distribution to reduce afterburn... 

Another commercial nnit was revamped to improve spent catalyst distribution. This particular unit has a shallow bed of 8-10 deep with a bed L/D ratio of 0.4. The revamp resulted in a reduction of afterburn from 190 to 100°F and decrease in COP addition from 45 to 30 Ib/d (Figure 15.5). 

FIGURE 15.5 Spent catalyst distribution revamp performance. 

As discussed in this volume, the use of membrane reactors (Bernstein, et oL), monoliths (Hickman and Schmidt), optimized catalyst distribution in pellets (Gavriilidis and Varma), and supercritical conditions (Azzam and Lee) are examples of engineering developments that may provide improvements over existing processes. 

The effects of non-uniform distribution of the catalytic material within the support in the performance of catalyst pellets started receiving attention in the late 60 s (cf 1-4). These, as well as later studies, both theoretical and experimental, demonstrated that non-uniformly distributed catalysts can offer superior conversion, selectivity, durability, and thermal sensitivity characteristics over those wherein the activity is uniform. Work in this area has been reviewed by Gavriilidis et al. (5). Recently, Wu et al. (6) showed that for any catalyst performance index (i.e. conversion, selectivity or yield) and for the most general case of an arbitrary number of reactions, following arbitrary kinetics, occurring in a non-isothermal pellet, with finite external mass and heat transfer resistances, the optimal catalyst distribution remains a Dirac-delta function. 

Although this reaction network has been studied extensively, its mechanism is still under debate (10). In this study, a single-pellet reactor was used, and the pellet was prepared mechanically by pressing the active catalyst layer between two alumina layers. In this way a step-type catalyst pellet was produced, which approximated a Dirac-type catalyst distribution. 

The characterization of the flow in existing DPF materials has been assessed by experiments and macroscopic continuum flow in porous media approaches. However, when it comes to material design it is essential to employ flow simulation techniques in geometrically realistic representations of DPF porous media. Some first applications were introduced in Konstandopoulos (2003) and Muntean et al. (2003) and this line of research is especially important for the development of new filter materials, the optimization of catalyst deposition inside the porous wall and for the design of gradient-functional filter microstructures where multiple functionalities in terms of particle separation and catalyst distribution (for combined gas and particle emission control) can be exploited. 

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