Industrial catalysts processes

This book aims to present the fundamentals of catalysis and applications illustrated with experiments performed in our laboratory, trying to understand why select the catalysts and processes. We seek to split the text into two parts. The first part presents the fundamentals addressing the activity patterns, adsorption-desorption phenomena, and advanced theories (Chaps. 1-5). The second part presents the most important conventional methods of characterizing properties (Chap. 6) the important methods of preparation with pre/posttreatment (Chap. 7) the most important traits (Chap. 8), with examples and practices spectroscopic characterizations, even in situ (Chaps. 8-12) Nanostructured catalysts (Chap. 13) the microkinetic chemistry and surface mechanisms (Chap. 14), and finally the evaluation of an industrial catalyst process (Chap. 15). 

Catalytic gas-phase reactions play an important role in many bulk chemical processes, such as in the production of methanol, ammonia, sulfuric acid, and nitric acid. In most processes, the effective area of the catalyst is critically important. Since these reactions take place at surfaces through processes of adsorption and desorption, any alteration of surface area naturally causes a change in the rate of reaction. Industrial catalysts are usually supported on porous materials, since this results in a much larger active area per unit of reactor volume. 

Several processes are available for the recovery of platinum and palladium from spent automotive or petroleum industry catalysts. These include the following. (/) Selective dissolution of the PGM from the ceramic support in aqua regia. Soluble chloro complexes of Pt, Pd, and Rh are formed, and reduction of these gives cmde PGM for further refining. (2) Dissolution of the catalyst support in sulfuric acid, in which platinum is insoluble. This... 

The catalysts used in the industrial alkylation processes are strong Hquid acids, either sulfuric acid [7664-93-9] (H2SO or hydrofluoric acid [7664-39-3] (HE). Other strong acids have been shown to be capable of alkylation in the laboratory but have not been used commercially. Aluminum chloride [7446-70-0] (AlCl ) is suitable for the alkylation of isobutane with ethylene (12). Super acids, such as trifluoromethanesulfonic acid [1493-13-6] also produce alkylate (13). SoHd strong acid catalysts, such as Y-type zeoHte or BE -promoted acidic ion-exchange resin, have also been investigated (14—16). 

Reaction and Heat-Transfer Solvents. Many industrial production processes use solvents as reaction media. Ethylene and propylene are polymerized in hydrocarbon solvents, which dissolves the gaseous reactant and also removes the heat of reaction. Because the polymer is not soluble in the hydrocarbon solvent, polymer recovery is a simple physical operation. Ethylene oxide production is exothermic and the catalyst-filled reaction tubes are surrounded by hydrocarbon heat-transfer duid. 

These siUca-supported catalysts demonstrate the close connections between catalysis in solutions and catalysis on surfaces, but they are not industrial catalysts. However, siUca is used as a support for chromium complexes, formed either from chromocene or chromium salts, that are industrial catalysts for polymerization of a-olefins (64,65). Supported chromium complex catalysts are used on an enormous scale in the manufacture of linear polyethylene in the Unipol and Phillips processes (see Olefin polymers). The exact stmctures of the surface species are still not known, but it is evident that there is a close analogy linking soluble and supported metal complex catalysts for olefin polymerization. 

Almost all industrial catalysts are developed by researchers who are motivated to improve processes or create new ones. Thus the organization that first uses a new catalyst is usually the one that has discovered it. This organization, however, only rarely becomes the manufacturer of the catalyst used on a large scale. Catalysts are for the most part highly complex specialty chemicals, and catalyst manufacturers tend to be more efficient than others in producing them. Catalyst manufacturing is a competitive industry. Catalyst users often develop close relations with catalyst manufacturers, and the two may work together to develop and improve proprietary catalysts. 

Hexachloroethane is formed in minor amounts in many industrial chlorination processes designed to produce lower chlorinated hydrocarbons, usually via a sequential chlorination step. Chlorination of tetrachloroethylene, in the presence of ferric chloride, at 100—140°C is one convenient method of preparing hexachloroethane (142). Oxychlorination of tetrachloroethylene, using a copper chloride catalyst (143) has also been used. Photochemical chlorination of tetrachloroethylene under pressure and below 60°C has been studied (144) and patented as a method of producing hexachloroethane (145), as has recovery of hexachloroethane from a mixture of other perchlorinated hydrocarbon derivatives via crystalH2ation in carbon tetrachloride. Chlorination of hexachlorobutadiene has also been used to produce hexachloroethane (146). 

The ACR Process. The first step in the SCR reaction is the adsorption of the ammonia on the catalyst. SCR catalysts can adsorb considerable amounts of ammonia (45). However, the adsorption must be selective and high enough to yield reasonable cycle times for typical industrial catalyst loadings, ie, uptakes in excess of 0.1% by weight. The rate of adsorption must be comparable to the rate of reaction to ensure that suitable fronts are formed. The rate of desorption must be slow. Ideally the adsorption isotherm is rectangular. For optimum performance, the reaction must be irreversible and free of side reactions. 

Some modes of heat transfer to stirred tank reacdors are shown in Fig. 23-1 and to packed bed reactors in Fig. 23-2. Temperature and composition profiles of some processes are shown in Fig. 23-3. Operating data, catalysts, and reaction times are stated for a number of industrial reaction processes in Table 23-1. 

The FCC process has a long history of innovation and will continue to play a key role in the overall success of the refining industry. The continuing developments will primarily be in the areas of catalyst, process, and hardware technologies. 

This in itself draws attention to one of the artistic aspects of the industrial catalyst designer s job. Money values are neither absolute, invariant, nor always logically desirable entities. For example, resource producing nations can increase feedstock prices and they may do so for political rather than for hard, technological reasons. One very important consequence is the fact that a catalytic process that is economic in one year but not in the next is not as attractive as one that can adapt. 

Most studies of the effect of alkalis on the adsorption of gases on catalyst surfaces refer to CO, NO, C02, 02, H2 and N2, due to the importance of these adsorbates for numerous industrial catalytic processes (e.g. N2 adsorption in NH3 synthesis, NO reduction by CO). Thus emphasis will be given on the interaction of these molecules with alkali-modified surfaces, especially transition metal surfaces, aiming to the identification of common characteristics and general trends. 

Firstly, there are technical reasons concerning catalyst and reactor requirements. In the chemical industry, catalyst performance is critical. Compared to conventional catalysts, they are relatively expensive and catalyst production and standardization lag behind. In practice, a robust, proven catalyst is needed. For a specific application, an extended catalyst and washcoat development program is unavoidable, and in particular, for the fine chemistry in-house development is a burden. For coated systems, catalyst loading is low, making them unsuited for reactions occurring in the kinetic regime, which is particularly important for bulk chemistry and refineries. In that case, incorporated monolithic catalysts are the logical choice. Catalyst stability is crucial. It determines the amount of catalyst required for a batch process, the number of times the catalyst can be reused, and for a continuous process, the run time. 

Much of the pioneering work which led to the discovery of efficient catalysts for modern Industrial catalytic processes was performed at a time when advanced analytical Instrumentation was not available. Insights Into catalytic phenomena were achieved through gas adsorption, molecular reaction probes, and macroscopic kinetic measurements. Although Sabatier postulated the existence of unstable reaction Intermediates at the turn of this century. It was not until the 1950 s that such species were actually observed on solid surfaces by Elschens and co-workers (2.) using Infrared spectroscopy. Today, scientists have the luxury of using a multitude of sophisticated surface analytical techniques to study catalytic phenomena on a molecular level. Nevertheless, kinetic measurements using chemically specific probe molecules are still the... 

Ethylene oxide synthesis is one of the largest-volume industrial processes with a produchon rate of some plants of several 100 0001 a (see original citahons in [4]). In 1995, the world capacity for ethylene oxide was approximately 11 200 0001 a. As industrial catalyst silver on alumina is employed. In addihon to large produc-... 

The industrial catalyst for n-butane oxidation to maleic anhydride (MA) is a vanadium/phosphoras mixed oxide, in which bulk vanadyl pyrophosphate (VPP) (VO)2P207 is the main component. The nature of the active surface in VPP has been studied by several authors, often with the use of in situ techniques (1-3). While in all cases bulk VPP is assumed to constitute the core of the active phase, the different hypotheses concern the nature of the first atomic layers that are in direct contact with the gas phase. Either the development of surface amorphous layers, which play a direct role in the reaction, is invoked (4), or the participation of specific planes contributing to the reaction pattern is assumed (2,5), the redox process occurring reversibly between VPP and VOPO4. 

Jpn. Pat. Tokkai, 86-1831 (cited as reference 22 by Muroi, T., in his review of selected industrial catalytic processes in Chemical Catalyst News, Engelhard Corp., March 1991). 

The task of developing a suitable catalyst for commercial applications involves many considerations, ranging from obvious factors like catalyst activity and selectivity to variables like the catalyst shape and the composition of the binder used in a pelletizing process. This section is devoted to a discussion of these considerations and of the techniques involved in manufacturing industrial catalysts. 

It must be noted that the heat capacity of the calorimeter cell and of its contents p, which appears in the second term of Tian s equation [Eq. (12)], disappears from the final expression giving the total heat [Eq. (19)]. This simply means that all the heat produced in the calorimeter cell must eventually be evacuated to the heat sink, whatever the heat capacity of the inner cell may be. Changes of the heat capacity of the inner cell or of its contents influence the shape of the thermogram but not the area limited by the thermogram. It is for this reason that heat-flow microcalorimeters, with a high sensitivity, are particularly convenient for investigating adsorption processes at the surface of poor heat-conducting solids similar in this respect to most industrial catalysts. 

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