Heterogeneous catalysts petrochemical industry

In heterogeneous catalysis, solids catalyze reactions of molecules in gas or solution. As solids - unless they are porous - are commonly impenetrable, catalytic reactions occur at the surface. To use the often expensive materials (e.g. platinum) in an economical way, catalysts are usually nanometer-sized particles, supported on an inert, porous structure (see Fig. 1.4). Heterogeneous catalysts are the workhorses of the chemical and petrochemical industry and we will discuss many applications of heterogeneous catalysis throughout this book. 

The heterogeneous catalysts have a profound impact on the chemical industry in general for example 60% of all chemical processes, 75% of oil refining processes, nearly 100% of polymers and about one hundred petrochemicals depend on the action of catalysts, as well as a significant part of environmental technologies (VOCs, automotive emissions control, stationary sources, etc.) and fine chemical production. Actually, the worldwide catalysts market is worth about 10 billion USD, (i.e. 10 x 109 USD) a year and, according to some... 

The relevance of the water-gas shift reaction in the petrochemical industry has already been discussed (see Section 1.1). The significance of the water-gas shift reaction in homogeneous systems is twofold. First, it plays a crucial role in stabilizing the rhodium catalyst in the Monsanto process. Second, studies carried out in homogeneous systems employing metals other than rhodium have provided useful mechanistic insights into the heterogeneous water-gas shift reaction. We first discuss the catalytic cycle with 4.1 as one of the catalytic intermediates, and then mechanistic results that are available from an iron-based catalytic system. 

In refining processes alkylation of isobutane with propene or butene is important in order to obtain all date which has a high octane number and a low vapour pressure. This process is not, however, directly relevant to the focus of attention of this paper and wifi therefore not be deah with in any detail It has been well reviewed recai% [36]. It is, however, worth noting that recent attempts to develop a zeolite as an ahemate to the currently used hydrofluoric or su huric acid do not appear to have been successful and it is now assumed that superacid catalysts are the most likely heterogeneous alternatives. For the petrochemical industry the alkylation of aromatics is an inportant route to the production of alkylaromatic such as ethylbenzene, xylenes, cume, alkylbenzoies, alky henol... 

In the chemical and the petrochemical industries, heterogeneous catalysts are typically operated in a narrow range of reaction conditions. These reaction conditions are chosen so as to achieve an optimal feedstock conversion at minimal catalyst deactivation and are typically either constant over time or are slightly modified to compensate for feedstock conversion loss due to deactivation of the catalyst. 

Figure 45. Comparison between the operating range of catalyst temperature and reactant space time for a three-way catalyst at two engine operation conditions (idling and full load operation), and for various heterogeneous catalytic processes used in the chemical and petrochemical industries. Reprinted with permission from ref. [34], 1994 Society of Automotive Engineers, Inc.

In the application of heterogeneous catalysts to the chemical and petrochemical industries, either all precautions are taken to minimize deactivation of the catalyst, or the process is designed for regular regenera-tion of the catalyst. In contrast, au-... 

Bond (1987) covers the basic principles of catalysis, adsorption on solid surfaces, chemisorption at metal and oxide surfaces, the kinetics of catalyzed reactions, the quantitative aspects of catalysis by metals and the structure, preparation and use of heterogeneous catalysts. The book also discusses the application of catalysts in different fields including energy conservation, production of hydrocarbon feedstocks, bifunctional catalysts in petroleum industry, oxidation catalysts in the petrochemical industry, heavy inorganic industry, hydrogenation of multiple bonds and catalysts used in atmospheric pollution control. 

Heterogeneous catalysis is especially important in industry. Some of the major industrial processes that use solid catalysts include the synthesis of inorganic chemicals such as NH3, SO3 and NO, the various reactions used in the refining of crude petroleum such as cracking, isomerisation and reforming, and many of the major reactions of the petrochemical industry, such as the synthesis of methanol, the hydrogenation of aromatics and various controlled oxidations. Some of the major industrial processes to be catalysed by inorganic solids are shown in Table 1.3. 

Disodium tetraborate is the source of many industrially important boron compounds. such as barium borate (fungicidal paints), zinc borate (fire-retardant additive in plastics), and boron phosphate (heterogeneous acid catalyst in the petrochemicals industry). 

Catalysts are very important for many applications and different processes, in particular in the chemical and petrochemical industries, also in energetic and environmental processes, and nowadays in material developments. Genetically, catalytic reactions are classified into homogeneous and heterogeneous or heterophase systems. 

ZSM-5, a heterogeneous solid acid catalyst with MFI cages connected by 10-ring micropores, has been widely used in the fields of oil refining and petrochemical industries [32]. 

There are a large number of processes where solid catalysts are employed. The process streams are either gaseous or liquid, or a combination of these. The catalysts usually have a high porosity. Especially in the petroleum and petrochemical industries one encounters catalytic reactors of a great variety. Well known reactor types are fixed bed, moving bed, fluidized bed, entrained bed, slurry reactor and three phase packed column. The choice between these reactor types is mostly based on the relative requirements for mass transfer, degree of conversion and heat transfer. Heterogeneous catalysis is a well developed science, with its own specific literature. In this chapter some technical acpects will be presented, particularly those related to scale-up. 

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