Chemical selective oxidation processes

Catalytic selective oxidation processes play a central role in the chemicals industry as well as in the development of new catalysts as the key contributions to modern manufacturing, because a large proportion of materials and commodities in daily use undergo a selective oxidation process as a critical step in their production cycle. More than half of the products obtained using catalytic processes are obtained by selective oxidation, and nearly all the monomers used in the production of fibers and plastics are obtained in this way [241-243]. 

One of the most important selective oxidation processes in the production of chemicals is the side chain oxidation of alkyl aromatics, which are then further reacted to higher value products that end up in a variety of polymer compositions and specialised chemicals.The largest oxyfunctionalised aromatic products with regard to world production are terephthalic acid, phthalic anhydride and benzoic acid which are produced worldwide with capacities of >30,000, 5,000 and 500 kt a respectively. Worldwide production capacities for benzaldehyde and pyromel-litic dianhydride do not rise above 50 kt a In smaller capacities as specialty chemicals for the pharmaceutical industry, halo-substituted oxyfunctionalized aromatics are also produced. Of the aforementioned products, phthalic anhydride and pyromellitic dianhydride are produced from gas-phase processes using V20s-Ti02 catalysts and a liquid-phase alternative process does not appear immediately desirable. On the other hand, terephtalic and benzoic acids, and benzaldehyde are... 

The fact that gold is active under very mild conditions means that its potential as a selective oxidation catalyst is high, and many selective oxidation processes are important in the chemical industry [1,2]. Papers have been published on the selective oxidation of propene to propene oxide in the presence of hydrogen, oxidation of sugars and aldehydes to acids, and the oxidation of alcohols and other hydroxyl-compounds. Au-Pd catalysts have been used to oxidize ethene to vinyl acetate in the presence of acetic acid and oxygen and this is a process used by a number of manufacturers worldwide. The selective oxidation of hydrogen to hydrogen peroxide, rather than water, is also catalyzed efficiently by supported Au-Pd catalysts [49]. 

Qean and efficient processes production of at) mc chemicals witiiout salt, replaconent of HE or H2SO4, catalytic combustion, hi tempoature selective oxidation firel cells ... 

New materials are also finding application in the area of catalysis reiated to the Chemicals industry. For example, microporous [10] materials which have titanium incorporated into the framework structure (e.g. so-calied TS-1) show selective oxidation behaviour with aqueous hydrogen peroxide as oxidizing agent (Figure 5). Two processes based on these new catalytic materials have now been developed and commercialized by ENl. These include the selective oxidation of phenol to catechol and hydroquinone and the ammoxidation of cyclohexanone to e-caproiactam. 

There is not much to be said about the use of micro reactors for bulk chemicals and commodities. Worz et al. are so far the only ones who have disclosed their work on the potential of micro-structured reactors for the optimization of chemical processes performed on a large scale ofindustrial relevance [110,112,154,288-290]. This included a fast exothermic liquid/liquid two-phase reaction, which was used for the industrial production of a vitamin intermediate product, and a selective oxidation reaction for an intermediate, a substituted formaldehyde derivative. 

Compared with ketoreductases, the synthetic application of alcohol oxidases has been less explored. However, selective oxidation of primary alcohols to aldehydes is superior to the chemical methods in terms of conversion yields, selectivity, and environmental friendliness of reaction conditions. In addition, coupling of alcohol oxidase with other enzymes provides a tremendous opportunity to develop multi-enzyme processes for the production of complex molecules. Therefore, a growing impact of alcohol oxidases on synthetic organic chemistry is expected in the coming years. 

Metal complexes, especially involving transition metals, are known for their role as catalysts in a broad variety of chemical processes including isomerization, oxidization, hydrogenation, and polymerization. Such catalytic reactions play an important role not only in many industrial processes, such as petroleum and polymer industries, but also in many biological systems, e.g., a variety of selective oxidation catalysts with heme (1) and nonheme (2) iron centers. The transition metals in these systems usually constitute a fundamental part of the catalyst, due to their... 

The selective oxidation of ra-butane to give maleic anhydride (MA) catalyzed by vanadium phosphorus oxides is an important commercial process (99). MA is subsequently used in catalytic processes to make tetrahydrofurans and agricultural chemicals. The active phase in the selective butane oxidation catalyst is identified as vanadyl pyrophosphate, (V0)2P207, referred to as VPO. The three-dimensional structure of orthorhombic VPO, consisting of vanadyl octahedra and phosphate tetrahedra, is shown in Fig. 17, with a= 1.6594 nm, b = 0.776 nm, and c = 0.958 nm (100), with (010) as the active plane (99). Conventional crystallographic notations of round brackets (), and triangular point brackets (), are used to denote a crystal plane and crystallographic directions in the VPO structure, respectively. The latter refers to symmetrically equivalent directions present in a crystal. 

It is expected that in the very near future, the application of closed water loops will show an intensive growth, strongly supported by the further development of separate treatment technologies such as anaerobic treatment, membrane bioreactors, advanced biofilm processes, membrane separation processes, advanced precipitation processes for recovery of nutrients, selective separation processes for recovery of heavy metals, advanced oxidation processes, selective adsorption processes, advanced processes for demineralisation, and physical/chemical processes which can be applied at elevated temperature. 

From the above it can be concluded that only the reaction with component B may enhance mass transfer of ozone substantially. And only if the Hatta number HaB is much higher than 1. Therefore it can be expected that whenever we have to deal with an enhancement of mass transfer due to chemical reactions, this influences the selectivity of the oxidation process in a negative way. The factor which has to be considered in this respect is the Hatta number for the reaction of ozone with component B (equation 29). HaB increases with increasing value of kB and CBb and with decreasing value of the mass transfer coefficient for ozone, kHq,... 

Scheme 9.1 shows a generalized sequence of reactions for the oxidation of an alkane, via alcohol, ketone and carboxylic acid, to the completely oxidized products, water and carbon dioxide. The latter are often referred to as combustion products as they are the same as those formed by burning hydrocarbons. These are not normally desirable chemical products unless it is necessary to destroy a toxic, hazardous or otherwise unwanted waste material. Oxidation itself is not difficult to achieve, and is a highly exothermic or even explosive process. Selective oxidation, however, is a much greater challenge, as it is important to stop the sequence at the desired product without proceeding further down the oxidation pathway. 

---