Ethylene oxide oxygen-based

Figure 3 Flow diagram for ethylene oxide oxygen-based process.

CHLORURE PERRIQUE (French) (7705-08-0) Very hygroscopic contact with moisture in air forms ferric chloride hexahydrate. Aqueous solution is highly acidic, precipitating hydroxide and phosphate salts, and forming corrosive fumes. Violent reaction with strong bases, allyl chloride, bromine pentafluoride, ethylene oxide, oxygen difluoride. Shock- and friction-sensitive explosive is formed with potassium, sodium, potassium-sodium aUoy, and possibly with other active metals. Aqueous solution is incompatible with sulfuric acid, caustics, ammonia, aliphatic amines, alkanolamines, amides, organic anhydrides, isocyanates, vinyl acetate, alkylene oxides, epichlorohydrin. Attacks metals in the presence of moisture. 

Equation 1 is referred to as the selective reaction, equation 2 is called the nonselective reaction, and equation 3 is termed the consecutive reaction and is considered to proceed via isomerization of ethylene oxide to acetaldehyde, which undergoes rapid total combustion under the conditions present in the reactor. Only silver has been found to effect the selective partial oxidation of ethylene to ethylene oxide. The maximum selectivity for this reaction is considered to be 85.7%, based on mechanistic considerations. The best catalysts used in ethylene oxide production achieve 80—84% selectivity at commercially useful ethylene—oxygen conversion levels (68,69). 

There are 12 producers of ethylene oxide ia the United States. Table 9 shows the plant locations, estimated capacities, and types of processes employed. The total U.S. production capacity for 1992 was ca 3.4 x 10 metric tons. The percentages of total domestic production made by the air- and oxygen-based processes are ca 20 and 80%, respectively. The largest producer is Union Carbide Corp. with approximately one-third of the United States ethylene oxide capacity. About 94% of domestic ethylene oxide capacity is located on the Gulf Coast near secure and plentiful ethylene suppHes. Plans for additional U.S. production ia the 1990s have been announced by Union Carbide (incremental expansions), Eormosa Plastics (at Pt. Comfort, Texas), and Shell (at Geismar, Louisiana) (101). 

Fig. 3. Oxygen-based direct oxidation process for ethylene oxide (96,102,103,109,117—119,127).

Process Technology Considerations. Innumerable complex and interacting factors ultimately determine the success or failure of a given ethylene oxide process. Those aspects of process technology that are common to both the air- and oxygen-based systems are reviewed below, along with some of the primary differences. 

For the same production capacity, the oxygen-based process requires fewer reactors, all of which operate in parallel and are exposed to reaction gas of the same composition. However, the use of purge reactors in series for an air-based process in conjunction with the associated energy recovery system increases the overall complexity of the unit. Given the same degree of automation, the operation of an oxygen-based unit is simpler and easier if the air-separation plant is outside the battery limits of the ethylene oxide process (97). 

Because the epoxidation with Tl(III) is stoichiometric to produce Tl(I), reoxidation is needed. Halcon has patented processes based on such epoxidation to yield ethylene oxide (200—203). The primary benefits of such a process are claimed to be high yields of ethylene oxide, fiexibihty to produce either propylene oxide or ethylene oxide, and the potential of a useful by-product (acetaldehyde). Advances usiag organic hydroperoxides ia place of oxygen for reoxidation offer considerable promise, siace reaction rates are rapid and low pressures can be used. 

Ethylene is selectively oxidized to ethylene oxide using a silver-based catalyst in a fixed-bed reactor. Ethylene and oxygen are supplied from the gas phase and ethylene oxide is removed by it. The catalyst is stationary. Undesired, kinetically determined by-products include carbon monoxide and water. Ideally, a pure reactant is converted to one product with no by-products. 

Based on these experimental findings it is drawn that adsorbed oxygen species should play an important role to form adsorbed intermediates and adsorption sites for reaction gas components. Therefore, to know the detailed reaction mechanism of ethylene oxidation, it is necessary to clarify a situation of the adsorbed layer formed during the reaction, especially on the adsorbed oxygen species available for the progress of reaction. 

Ethylene oxide is a polar molecule with an excess of electron density on the oxygen making it the site for acid attack, whereas the ethylene moiety is electron-poor and the site for nucleophillic attack by the base. 

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