Catalytic internals

The design of RD is currently based on expensive and time-consuming sequences of laboratory and pilot-plant experiments, since there is no commercially available software adequately describing all relevant features of reactions (catalyst, kinetics, holdup) and distillation (VLE, thermodynamics, plate and packing behavior) as well as their combination in RD. There is also a need to improve catalysts and column internals for RD applications (1,51). Figures 8 and 9 show some examples of catalytic internals, applied for reactive distillation. 

Figure 8 (a) Schematic of an RD column filled with catalytic internals CD TECH (1—catalytic balls, 2—feed, 3—distillate, 4—bottom product, 5—sieve tray) and (b) catalytic structured packing Sulzer Katapak-S. (Part a from Ref. 52.)... 

The key reactive separation topics to be addressed in the near future are a proper hydrodynamic modeling for catalytic internals, including residence time distribution account and scale-up methodology. Further studies on the hydrodynamics of catalytic internals are essential for a better understanding of RSP behavior and the availability of optimally designed catalytic column internals for them. In this regard, the methods of computational fluid dynamics appear very helpful. 

O rectification column with catalytic internals in the downcomers O rectification column with side stream reactors... 

The design of catalytic internals for RD is presently based on two general concepts, namely immobilization of commercial catalyst pellets and catalytic activation of conventional internals for vapor-liquid contactors. When using small solid catalyst particles under countercurrent flow conditions, the following additional requirements should be met ... 

Here we give another example of heterogeneously catalyzed ethyl acetate synthesis via RD, with two different column scales studied, namely a 50-mm and a 162-mm diameter columns (see [52]). The principal column setup is shown in Fig. 10.14. The columns consist of three packed sections, whereas the middle part is equipped with structured catalytic internals. The reactants are fed above and below the reactive section. 

Table 10.3 Characteristics of the applied structured catalytic internals for the ethyl acetate system.

Figure 10.16 Product purity (iv) and conversion (X) vs. heat duty for different catalytic internals (ethyl acetate system, lab-scale column).

The modeling of RD processes is illustrated by the heterogeneously catalyzed syntheses of methyl acetate, methyl tertiary butyl ether (MTBE), ethyl acetate and transesterification of dymethyl carbonate using different catalytic internals. These processes are described based on the pseudohomogeneous approach for the reaction kinetics. 

The key RD topics to be addressed in the near future are a proper hydrodynamic modeling for catalytic internals including residence-time distribution account and scale-up methodology. Further studies on the hydrodynamics of... 

The implementation of high-pressure reaction cells in conjunction with UFIV surface science techniques allowed the first tme in situ postmortem studies of a heterogeneous catalytic reaction. These cells penult exposure of a sample to ambient pressures without any significant contamination of the UFIV enviromnent. The first such cell was internal to the main vacuum chamber and consisted of a metal bellows attached to a reactor cup [34]- The cup could be translated using a hydraulic piston to envelop the sample, sealing it from... 

Physical properties affecting catalyst perfoniiance include tlie surface area, pore volume and pore size distribution (section B1.26). These properties regulate tlie tradeoff between tlie rate of tlie catalytic reaction on tlie internal surface and tlie rate of transport (e.g., by diffusion) of tlie reactant molecules into tlie pores and tlie product molecules out of tlie pores tlie higher tlie internal area of tlie catalytic material per unit volume, tlie higher the rate of tlie reaction... 

The components in catalysts called promoters lack significant catalytic activity tliemselves, but tliey improve a catalyst by making it more active, selective, or stable. A chemical promoter is used in minute amounts (e.g., parts per million) and affects tlie chemistry of tlie catalysis by influencing or being part of tlie catalytic sites. A textural (structural) promoter, on tlie otlier hand, is used in massive amounts and usually plays a role such as stabilization of tlie catalyst, for instance, by reducing tlie tendency of tlie porous material to collapse or sinter and lose internal surface area, which is a mechanism of deactivation. 

Terminal alkynes are only reduced in the presence of proton donors, e.g. ammonium sulfate, because the acetylide anion does not take up further electrons. If, however, an internal C—C triple bond is to be hydrogenated without any reduction of terminal, it is advisable to add sodium amide to the alkyne solution Hrst. On catalytic hydrogenation the less hindered triple bonds are reduced first (N.A. Dobson, 1955, 1961). 

Catalytic Oligomeri tion. Shell Chemical provides C —C linear internal olefin feedstock for detergent oxo alcohol production from its SHOP... 

The technological appHcations of molecular sieves are as varied as their chemical makeup. Heterogeneous catalysis and adsorption processes make extensive use of molecular sieves. The utility of the latter materials Hes in their microstmctures, which allow access to large internal surfaces, and cavities that enhance catalytic activity and adsorptive capacity. 

There are two types of stmctures one provides an internal pore system comprising interconnected cage-like voids the second provides a system of uniform channels which, in some instances, are one-dimensional and in others intersect with similar channels to produce two- or three-dimensional channel systems. The preferred type has two- or three-dimensional channel systems to provide rapid intracrystalline diffusion in adsorption and catalytic apphcations. 

PGM catalyst technology can also be appHed to the control of emissions from stationary internal combustion engines and gas turbines. Catalysts have been designed to treat carbon monoxide, unbumed hydrocarbons, and nitrogen oxides in the exhaust, which arise as a result of incomplete combustion. To reduce or prevent the formation of NO in the first place, catalytic combustion technology based on platinum or palladium has been developed, which is particularly suitable for appHcation in gas turbines. Environmental legislation enacted in many parts of the world has promoted, and is expected to continue to promote, the use of PGMs in these appHcations. 

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