Industrial processes heterogeneous catalysts used

Heterogeneous catalysts are defined as solids or mixture of solids that are used to accelerate a chemical reaction without undergoing change themselves. The types of solids used in industry as heterogeneous catalysts include simple oxides, mixed oxides, metal salts, solid acids and bases, metals, and dispersed metals. Catalysts are used in a wide variety of chemical and environmental processes worldwide. The global value of fuels and chemicals produced by catalytic routes is about US 2.4-3 trillion per year. About 20% of all products produced in the United States are derived from a catalytic process of some form. As important as catalysis is to the world economy, the number of various chemicals used as a catalyst as well as the form and shape of the material vary as much as the number of processes that use catalysts. Fig. 1 is a picture of a number of various types of catalysts and illustrates the numerous possibilities of shapes and sizes. Naturally, the preparation processes of such a wide variety of products is also numerous. 

Typical heterogeneous catalysts used in large-scale industrial processes are complex materials in terms of composition and structure. Catalytically active phases, supports, binders and promoters are common components. They typically are activated in some way before use, often by calcination. Heterogeneous catalysts have been prepared for many years and often the preparation procedure used in industry is based more on operator experience and tradition than on sound science. Generally the support is prepared or activated before use with the actual catalytic species and any promoters are added later, often as aqueous solutions of precursor compounds, which are then converted into their... 

Many very important chemical and physical processes occur at solid surfaces, as is well illustrated by a large number of heterogeneous catalysts used in industry. Then-heterogeneous nature is a remarkable characteristic of the chemical reactions that take place at surfaces/interfaces and so the principles usually followed to explain the chemical reactions that occur in the gaseous phase, Hquid phase, or in solution cannot be straightforwardly appHed to them. 

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

Sundmacher and Qi (Chapter 5) discuss the role of chemical reaction kinetics on steady-state process behavior. First, they illustrate the importance of reaction kinetics for RD design considering ideal binary reactive mixtures. Then the feasible products of kinetically controlled catalytic distillation processes are analyzed based on residue curve maps. Ideal ternary as well as non-ideal systems are investigated including recent results on reaction systems that exhibit liquid-phase splitting. Recent results on the role of interfadal mass-transfer resistances on the attainable top and bottom products of RD processes are discussed. The third section of this contribution is dedicated to the determination and analysis of chemical reaction rates obtained with heterogeneous catalysts used in RD processes. The use of activity-based rate expressions is recommended for adequate and consistent description of reaction microkinetics. Since particles on the millimeter scale are used as catalysts, internal mass-transport resistances can play an important role in catalytic distillation processes. This is illustrated using the syntheses of the fuel ethers MTBE, TAME, and ETBE as important industrial examples. 

Most industrial processes today still use heterogeneous Ziegler-Natta catalysts, although the market share of metallocene resins is increasing due to the enhanced... 

In industrial processes, heterogeneous and homogeneous catalysts are used. The processes are different, and here we want to address only the heterogeneous catalysts. The powdered catalysts can be metals, metal oxides, mixed oxides, zeolites, and nanostmctured materials. These materials can be synthetic or naturals. 

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]. 

Heterogeneous catalysts have been used industrially for well over 100 years. Amongst the first processes was the catalytic hydrogenation of oils and fats to produce margarine using finely divided nickel. It is quite likely that when this process was first operated in the late nineteenth century unhealthy amounts of nickel remained in the product. The issue of leaching and the avoidance of trace catalyst residues are still important aspects of research from both economic and environmental points of view. 

Organometallic chemistry has only recently been studied with the kind of intensity merited by its growing value to industrial chemistry. In the last fifteen years processes have been developed in which the transition metal carbon bond is an essential part of the structure of the catalysts used. Our knowledge of the mechanisms by which many of these reactions occur, however, is rather limited. This is because the majority of useful catalysts for practical reasons are heterogeneous and therefore unsuitable... 

It is well known that microwave drying of many solid materials is a very efficient and widely used process even on an industrial scale [3] it is also an attractive means of drying of heterogeneous catalysts. Microwave drying of catalysts and supported sorbents has several advantages ... 

---