Homogeneous catalytic reactions commercialization

Direct Chlorination of Ethylene. Direct chlorination of ethylene is generally conducted in Hquid EDC in a bubble column reactor. Ethylene and chlorine dissolve in the Hquid phase and combine in a homogeneous catalytic reaction to form EDC. Under typical process conditions, the reaction rate is controlled by mass transfer, with absorption of ethylene as the limiting factor (77). Ferric chloride is a highly selective and efficient catalyst for this reaction, and is widely used commercially (78). Ferric chloride and sodium chloride [7647-14-5] mixtures have also been utilized for the catalyst (79), as have tetrachloroferrate compounds, eg, ammonium tetrachloroferrate [24411-12-9] NH FeCl (80). The reaction most likely proceeds through an electrophilic addition mechanism, in which the catalyst first polarizes chlorine, as shown in equation 5. The polarized chlorine molecule then acts as an electrophilic reagent to attack the double bond of ethylene, thereby faciHtating chlorine addition (eq. 6) ... 

Industrial Problems. Problems have also been encountered in attempts to commercialize various homogeneous catalytic reactions. These, in addition to the highly corrosive nature of many metal solution systems involve general problems of large scale handling of liquid systems such as mass and heat transfer and the isolation of products from solution. Moreover, the recovery and/or regeneration of metals often presents difficulties. 

Another type of reactor that may have considerable future potential for use in homogeneous catalytic reactions is called the membrane reactor. These reactors have been successfully used for the commercialization of manufacturing processes based on enzyme catalysis. In fact, 75% of the global production of l-methionine is performed in an enzyme reactor. A membrane is basically an insoluble organic polymeric film that can have variable thickness. The catalyst... 

In many homogeneous catalyst-based industrial processes efficient recovery of the metal is essential for the commercial viability of the technology (see Section 1.4). This is especially true for noble metal-based homogeneous catalytic reactions. Apart from economic reasons spent catalyst recovery is also essential to prevent downstream problems, such as poisoning of other catalysts, deposition on process equipment, waste disposal, etc. Several different techniques are being followed industrially for the recovery of the catalyst from the reaction medium after the end of the reaction ... 

Aqueous catalysts offer facile catalyst separation for many homogeneous catalytic reactions [1] and several new processes have been commercialized (cf. Section 3.1.1.1). However, aqueous media cannot be used for chemical systems in which a component of the system undergoes undesired chemical reactions with water. Furthermore, the low solubility of many organic compounds in water could limit the applications of aqueous catalysts. Nonaqueous biphasic systems could overcome these limitations, provided the catalyst is preferentially soluble in the catalyst phase at the conditions under which the catalyst phase is separated from the product phase. It should be noted that there may be some catalyst loss into the product phase. The acceptable level of catalyst leaching depends on the quality specifications of the product, whether the residual catalyst could cause any health and/or environmental hazards, and the cost of the catalyst. When the leached catalyst has to be removed from the product phase, the cost of additional conventional catalyst separation and recycling must be considered also. 

As a natural development of the intense activity in CH activation see Alkane Carbon-Hydrogen Bond Activatiori since the 1970s, interest has arisen more recently in the closely allied area of CC activation. This process is much more difficult than CH activation and has so far been studied for its mechanistic interest rather than for any practical benefit. CX activation, on the other hand, is a major area of study because it is an initial step in many important and commercially valuable homogeneous catalytic reactions, such as Mizoroki-Heck, Suzuki-Miyaura, and Hartwig-Buchwald reactions. Here, an important practical goal is to avoid having to use the expensive iodides and bromides as ArX reagents in catalytic reactions and to work instead with chlorides and tosylates. 

In the late 1930s, Otto Roelen discovered the hydroformylation, or 0x0 process, one of the first commercially important homogeneous catalytic reactions. He found that a C alkene can be converted to a C +i aldehyde by the addition of H2 and CO, catalyzed by Cc CCOjs further reduction to the alcohol can occur, depending on conditions (Eq. 9.16). 

Sulfided bimetallic clusters which mimic the metal composition of commercial hydrodesulfurization (HDS) catalysts have been prepared and their homogeneous catalytic behavior studied. Reaction of thiophenol with [Mo2Co2(/z4-S)... 

This complex and structurally related molecules served as a functional homogeneous model system for commercially used heterogeneous catalysts based on chromium (e.g. Cp2Cr on silica - Union Carbide catalyst). The kinetics of the polymerization have been studied to elucidate mechanistic features of the catalysis and in order to characterize the potential energy surface of the catalytic reaction. 

Examples of catalytic reactions and processes relevant to hydrocarbon chemistry are numerous. The technologies of the oil refinery with extremely low (<0.1) E factors are excellent examples demonstrating the possibilities that can be achieved by the development of selective catalytic methods, particularly by the use of various solid acids (see detailed discussions in Chapter 2). Further examples of commercially highly successful processes are the oxidation catalyst TS-1 developed by Enichem researchers160 161 (see Sections 9.1.1, 9.2.1, and 9.4.1), the homogeneous aqueous-phase Rh-catalyzed hydroformylation (see Sections 7.1.3 and 7.4.1), and single-site metallocene polymerization catalysts, which allow the preparation of tailored polymers with new properties (see Sections 13.3.2).162-164... 

This reaction is used in the production of hydrogen in several commercial processes. It is an example of a heterogeneous catalytic reaction, hut the principles derived from it are also applicable to homogeneous and enzymatic catalytic reactions. A simplified scheme fur the reaction is given as follows ... 

The homogeneous catalytic asymmetric hydrogenations of 2-arylacrylic acids have been studied. Both rhodium and ruthenium catalysts have been examined. The reaction temperatures and hydrogen pressures have profound effects on the optical yields of the the products. The presence of a tertiary amine such as triethylamine also significantly increases the product enantiomer excess. Commercially feasible processes for the production of naproxen and S-ibuprofen have been developed based on these reactions. 

All the forward reactions are important steps in commercial homogeneous catalytic processes. Reaction 2.2 is a step in methanol carbonylation (see Chapter 4), while reaction 2.3 is a step in the hydrogenation of an alkene with an acetamido functional group. This reaction, as we will see in Chapter 9, is... 

Three commercial homogeneous catalytic processes for the hydroformyla-tion reaction deserve a comparative study. Two of these involve the use of cobalt complexes as catalysts. In the old process a cobalt salt was used. In the modihed current version, a cobalt salt plus a tertiary phosphine are used as the catalyst precursors. The third process uses a rhodium salt with a tertiary phosphine as the catalyst precursor. Ruhrchemie/Rhone-Poulenc, Mitsubishi-Kasei, Union Carbide, and Celanese use the rhodium-based hydroformylation process. The phosphine-modihed cobalt-based system was developed by Shell specih-cally for linear alcohol synthesis (see Section 7.4.1). The old unmodihed cobalt process is of interest mainly for comparison. Some of the process parameters are compared in Table 5.1. 

Among the several types of homogeneously catalyzed reactions, oxidation is perhaps the most relevant and applicable to chemical industry. The well-known Wacker oxidation of ethylene to ethylene oxide is the classic example, although this is not a true catalytic process since the palladium (II) ion becomes reduced to metallic palladium unless an oxygen carrier is present. Related to this is the commercial reaction of ethylene and acetic acid to form vinyl acetate, although the mechanism of this reaction does not seem to have yet been discussed publicly. Attempts to achieve selective oxidation of olefins or hydrocarbons heterogeneously do not seem very successful. 

The term applied indicates the application-oriented objective of this work. It was an important criterion of selection not to supply merely a collection of unweighted facts and various practical examples of homogeneous catalysis. In this context applied means a selection of homogeneous catalyzed processes, which on the one hand have already arrived at industrial success (e. g., cai bonyla-tion of alcohols, hydroformylation, Wacker-Hoechst process). On the other hand, the book also includes homogeneously catalyzed reactions of which the state-of-the-art indicates commercialization in the near future. Moreover, for scientific reasons the inclusion of newer catalytic reactions or reaction principles is required, even when commercialization is not yet in sight. Both aspects are covered by the sections Applied Catalysis and Recent Developments . 

The term reactive distillation (RD) refers to both catalyzed and uncatalyzed reaction systems. Catalytic distillation systems may use a homogenous or heterogenous catalyst to accelerate the reaction. Reactive distillation is a well-known example of reactive separation process, and is used commercially. The first patent and early journal articles deal mainly with homogenously catalyzed reactions such as esterifications, transesterifications, and hydrolysis.f Heterogenous catalysis with RD is a more recent development. The key advantages for a properly designed RD colunm are complete conversion of reactants and attainment of high selectivity. An example of the benefits of RD is the acid catalyzed production of methyl acetate by... 

The successful industrial application of the homogeneous catalytic asymmetric hydrogenation of prochiral olefins depends on the ability of the catalyst systems to offer high activity both in terms of reaction rate and efficient utilization of the catalyst (as the molar substrate to catalyst ratio S/C). It is also essential for the reaction to deliver the product with high enantiomeric excess and in good yield under conditions appropriate for industrial manufacture. In addition, the catalysts should be accessible in appropriate quantities for commercial manufacture. 

Carbonylation of methanol catalyzed by soluble Group IX transition metal complexes remains the dominant method for the commercial production of acetic acid. The Monsanto process stands as one of the major success stories of homogeneous catalysis, and for three decades it was the preferred technology because of the excellent activity and selectivity of the catalyst. It has been demonstrated by workers at Celanese, however, that addition of iodide salts can significantly benefit the process by improving the catalytic reaction rate and catalyst stability at low water concentrations. Many attempts have been made to enhance the activity of... 

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