Heterogeneously Catalyzed Processes in Industry

Modern industrial chemistry is based on catalytic processes. Heterogeneous catalysts are used on a large scale in the following areas  

We will now give an overview of the most important catal5dic processes and the process conditions. 

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Steam reforming is a heterogeneously catalyzed process, with nickel catalyst deposited throughout a preformed porous support. It is empirically observed in the industry, that conversion is proportional to the geometric surface area of the catalyst particles, rather than the internal pore area. This suggests that the particle behaves as an egg-shell type, as if all the catalytic activity were confined to a thin layer at the external surface. It has been demonstrated by conventional reaction-diffusion particle modelling that this behaviour is due to... 

The unique features of zeolites, and the possibility of tuning acidic and basic sites, as well as the creation of multifunctional catalysts, open a wide field of applications in the production of fine chemicals. In this article we present new heterogeneously catalyzed processes for the synthesis of industrially relevant fragrances, flavors and aromas. The emphasis of this review article will remain mainly on solid acids. 

A last important difference to combinatorial approaches in the pharmaceutical industry is the fact that reaction conditions in catalysis research are frequently much more demanding. While testing of drugs is usually carried out at room temperature in aqueous environments and at ambient pressure, a heterogeneously catalyzed process quite often is operated in the temperature range around 500°C, at pressures between ambient and several hundred bars, and in corrosive environments. A test system has to be adapted to such conditions, which clearly can be quite difficult. 

In the third part of this chapter, the experimental determination and the detailed theoretical analysis of reaction kinetics obtained at catalysts used in RD processes are discussed. For reliable column design, activity based microkinetic rate expressions are applied successfully to heterogeneously catalyzed processes. By increasing the particle size of heterogeneous catalysts to be used in RD processes, mass-transport resistances can become relevant and have to be considered for reliable column simulations. This is exemplified by the industrially relevant syntheses of the fuel ethers MTBE and ETBE. 

An intriguing influence of a cosolvent immiscible with water on the enantioselec-tivity of the enzyme-catalyzed hydrolysis was observed. It was proven that enzyme enantioselectivity is directly correlated with the cosolvent hydrophobicity. In the best example, for ethyl ether as cosolvent, the reaction proceeded with E = 55, and the target compound was obtained in 33% yield with 92.7% ee. This finding may be of great practical importance, particularly in industrial processes [24], since it will enable better optimization of enzyme-catalyzed processes. It is clear that, in future, immobilized enzymes, as heterogeneous catalysts, wiU be widely used in most industrial transformations, especially in the preparation of pharmaceuticals [25]. 

A heterogeneous catalyst exists in a phase that is different from the phase of the reaction it catalyzes. An important industrial use of heterogeneous catalysts is the addition of hydrogen to an organic compound that contains C = C double bonds. This process is called hydrogenation. Consider the hydrogenation of ethylene, shown below. 

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