Direct Oxidation of Ethylene

The first industrial process for the production of ethylene oxide was based on the chlorohydrin reaction (indirect oxidation of ethylene), discovered by Wurtz. In the chlorohydrin process ethylene reacts with hypochlorous add (chlorine dissolved in water) to give ethylene chlorohydrin [Eqs. (6.12.1) and (6.12.2)]. In the second step ethylene chlorohydrin is converted with hydrated lime or caustic soda to form the final product ethylene oxide [Eq. (6.12.3)]  

In 1931 the basis for another, more economical ethylene oxide manufacturing process was laid by the French chemist Lefort. He discovered the formation of ethylene oxide from ethylene and oxygen over a metallic silver catalyst. Only six years later, in 1937, the first process based on this reaction was commercialized by UCC (Union Carbide Corporation). 

The main reaction involved in this process is the partial oxidation of ethylene [Eq. (6.12.4)]. Two side reactions, which form the major by-products carbon dioxide and water, can occur the total oxidation of ethylene [Eq. (6.12.5)] or the consecutive oxidation of ethylene oxide to the same products [Eq. (6.12.6)]. 

All three reactions are highly exothermic (especially the two side reactions) and the activation energies of the undesired side reactions are higher than that of the desired main reaction. This effect causes a high temperature sensitivity of the ethylene oxide selectivity (even at small temperature changes). Therefore precise temperature control of the reactor is necessary. 

In the literature numerous studies exist on the kinetics and reaction network of the direct ethylene oxidation to ethylene oxide catalyzed by silver (see Example 6.12.1). The surface reaction is considered to proceed via the Langmuir-Hinshelwood mechanism (adsorption of ethylene and oxygen — surface reaction desorption of ethylene oxide, see Section 4.5.2). The rate expression for the selective oxidation can be expressed in the following equation  

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At one time acetaldehyde was prepared on an industrial scale by this method Modern methods involve direct oxidation of ethylene and are more economical... 

Acetaldehyde, first used extensively during World War I as a starting material for making acetone [67-64-1] from acetic acid [64-19-7] is currendy an important intermediate in the production of acetic acid, acetic anhydride [108-24-7] ethyl acetate [141-78-6] peracetic acid [79-21 -0] pentaerythritol [115-77-5] chloral [302-17-0], glyoxal [107-22-2], aLkylamines, and pyridines. Commercial processes for acetaldehyde production include the oxidation or dehydrogenation of ethanol, the addition of water to acetylene, the partial oxidation of hydrocarbons, and the direct oxidation of ethylene [74-85-1]. In 1989, it was estimated that 28 companies having more than 98% of the wodd s 2.5 megaton per year plant capacity used the Wacker-Hoechst processes for the direct oxidation of ethylene. 

From Acetylene. Although acetaldehyde has been produced commercially by the hydration of acetylene since 1916, this procedure has been almost completely replaced by the direct oxidation of ethylene. In the hydration process, high purity acetylene under a pressure of 103.4 kPa (15 psi) is passed into a vertical reactor containing a mercury catalyst dissolved in 18—25% sulfuric acid at 70—90°C (see Acetylene-DERIVED chemicals). 

The direct oxidation of ethylene is used to produce acetaldehyde (qv) ia the Wacker-Hoechst process. The catalyst system is an aqueous solution of palladium chloride and cupric chloride. Under appropriate conditions an olefin can be oxidized to form an unsaturated aldehyde such as the production of acroleia [107-02-8] from propjiene (see Acrolein and derivatives). 

For many years ethylene chlorohydrin was manufactured on a large iadustrial scale as a precursor to ethylene oxide, but this process has been almost completely displaced by the direct oxidation of ethylene to ethylene oxide over silver catalysts. However, siace other commercially important epoxides such as propylene oxide and epichlorohydrin cannot be made by direct oxidation of the parent olefin, chlorohydrin iatermediates are stiU important ia the manufacture of these products. 

Ethylene oxide [75-21-8] was first prepared in 1859 by Wurt2 from 2-chloroethanol (ethylene chlorohydrin) and aqueous potassium hydroxide (1). He later attempted to produce ethylene oxide by direct oxidation but did not succeed (2). Many other researchers were also unsuccesshil (3—6). In 1931, Lefort achieved direct oxidation of ethylene to ethylene oxide using a silver catalyst (7,8). Although early manufacture of ethylene oxide was accompHshed by the chlorohydrin process, the direct oxidation process has been used almost exclusively since 1940. Today about 9.6 x 10 t of ethylene oxide are produced each year worldwide. The primary use for ethylene oxide is in the manufacture of derivatives such as ethylene glycol, surfactants, and ethanolamines. 

In addition to ethylene oxide, carbon dioxide, and water, small quantities of acetaldehyde and traces of formaldehyde are also produced in the process. They generally total less than 0.2% of the ethylene oxide formed. Acetaldehyde is most likely formed by isomerization of ethylene oxide, whereas formaldehyde is most likely formed by direct oxidation of ethylene (108). 

Extend Range of Feedstocks for the Process. Feedstock flexibility can enable maximum advantage to be taken of market fluctuations in the price and availability within the range of feedstocks which can be used. Obviously this is inappropriate in some cases where there is a close chemical link between feedstock and product, e.g. direct oxidation of ethylene to ethylene oxide, but in some processes, e.g. steam-reforming, flexibility is possible and may be advantageous. 

Heteropolyacids are also beginning to emerge from academic laboratories and find commercial applications. Showa Denko, for example, claim to have a process [14] for the direct oxidation of ethylene to acetic acid employing a bifunctional Pt/heteropolyacid catalyst system. 

In the 1940s and 1950s, a considerable amount of research was funded to find and develop the chemists impossible dream a process for the direct oxidation of ethylene to EO, without any by-products. Finally, Union Carbide found the silver bullet that did the joE)—a catalyst made of silver oxide. Silver oxide is the only substance found having sufficient activity and selectivity. (Activity relates to the amount of conversion, selectivity relates to the right yield.) Moreover, ethylene is the only olefin affected in this way. The others, propylene, butylene, etc., tend to oxidize completely, forming carbon dioxide and water. But when silver oxide is used as a catalyst with ethylene, the dominant reaction is the formation of EO. Some ethylene still ends up being further oxidized, as much as 25% in some processes, as shown in Figure 10—2. 

Oxidation of ethyl alcohol was one of the two important commercial routes to acetaldehyde until the 1950s, The other, much older route was the hydration of acetylene. The chemical industry was always after a replacement of acetylene chemistry, not just for acetaldehyde production, but all its many applications. Acetylene was expensive to produce, and with its reactive, explosive nature, it was difficult to handle. In the 1950s, acetylene chemistry and the ethyl alcohol oxidation route were largely phased out by the introduction of the liquid phase direct oxidation of ethylene. Almost all the acetaldehyde produced uses the newer process. 

Acetaldehyde is made by the direct oxidation of ethylene, C2H4. It is a liquid at room temperature and is an intermediate in the production of acetic acid, acetic anhydride, butyl, and 2-ethyl hexyl alcohol. 

Acetaldehyde may be made (1) from ethylene by direct oxidation, with the Wacker-catalyst containing copper(II) and palladium(II) salts (2) from ethanol by vapor-phase oxidation or dehydrogenation or (3) from butane by vapor-phase oxidation. The direct oxidation of ethylene is the most commonly used process, accounting for 80% of acetaldehyde production. 

The direct oxidation of ethylene to EO by O2 has now replaced the chlorohydrin process entirely because it is cheaper and involves less byproducts, but propylene oxide (a monomer in polyurethanes) is still made by the chlorohydrin route. 

Example 4 Seven-Tenths Rule A company is considering the manufacture of150,000 tons annually of ethylene oxide by the direct oxidation of ethylene. According to Remer and Chai (1990), the cost capacity exponent for such a plant is 0.67. A subsidiary of the company built a 100,000-ton aimual capacity plant for 70 million fixed capital investment in 1996. Using the seven-tenths rule, estimate the cost of the proposed new facility in the third quarter 2004. 

The Carbide and Carbon Co began large scale manuf of EtnO thru ethylene chloro-hydrin in 1925 and by the direct oxidation of ethylene in 1937. Dow entered the field in 1939 Si 1941 Jefferson and Wyandotte in 1941 and Mathieson Chem Corp in 1951. These four Co s used the chlorohydrin method. US consumption, which was in 1939 108 million pounds, increased in 1949 to 354 million Several laboratory methods of prepn are described in Ref 17, pp 75—7. In one of them hydroxide is added gradually to a soln of 2-chloroethyI acetate heated to a temp betwn 40 150°C. An excess of unreacted base is avoided. The reaction proceeds as follows ... 

Ethylene Chlorohydrin. Two industrial processes were used in the synthesis of ethylene chlorohydrin,182 191 which, in turn, was transformed to ethylene oxide. Since the direct oxidation of ethylene to ethylene oxide is more economical, these technologies are being abandoned. 

Ethylene Oxide. Essentially all ethylene oxide produced industrially is manufactured by the direct oxidation of ethylene catalyzed by silver 867,887-889... 

A method of considerable industrial importance for the large-scale preparation of ethylene oxide is direct oxidation of ethylene at elevated temperatures over a suitably prepared metallic silver catalyst. Although the reaction may be written aa indicated in Eq. (09), in actual practice only about half the ethylene is converted into ethylene oxide, the remainder being oxidized further to carbon dioxide and water. In spite of this seeming disadvantage, catalytic oxidation appears at present to bo economically competitive with chlorohydrin formation aa a means for the commercial production of ethylene oxide.MM Unfortunately, other olefins, such as propylene and mo-butylene for example, apparently give only carbon dioxide and water under the usual oxidation conditions,1310 so that until now the patent hu balance ethylene oxide has been the only representative accessible by tins route. 

In tonnage production, acetaldehyde may be manufactured by (1) the direct oxidation of ethylene, requiring a catalytic solution of copper chloride plus small quantities of palladium chloride, (2) the oxidation of ethyl alcohol with sodium dichromate, and (3) the dry distillation of calcium acetate with calcium formate. 

The commercial process of choice for acetaldehyde production is the direct oxidation of ethylene. 

In the direct oxidation of ethylene to yield acetaldehyde (Table 3, entry 23), aqueous solutions of a catalyst and slightly elevated temperatures (100-150 °C) are used [34], For process development the corrosion caused by the CuCl2 and PdCl2 solutions used as catalysts was crucial. 

In the industrial production of acetic acid the main production routes are based on the carbonylation of methanol, a process which was first developed in the 1940s. Although the process remains cheap, the availability and pricing of raw materials have forced the development of new processes based on the direct oxidation of ethylene to form acetic acid (Table 3, entry 24). Complex multimetal oxide... 

Ethylene oxide was discovered in 1859 by Wurtz. He stated that ethylene oxide could not be made by direct oxidation of ethylene, and it was nearly 80 years before this was disproved. Wurtz made ethylene oxide by the method known today as the chlorohydrin process, in which ethylene is reacted in turn with hypochlorous acid and base. This process was commercialized during World War I in Germany, and until 1985 was still used commercially in the United States. 

Since 1985, processes for the direct oxidation of ethylene using either air or oxygen and... 

Acetaldehyde. Acetaldehyde has been made from ethanol by dehydrogenation and by catalytic hydration of acetylene. Today direct oxidation of ethylene in the liquid phase catalyzed by palladium and copper has replaced these earlier methods. Figure 10.14 shows an ethylene-to-acetaldehyde unit based on this last route. 

A process for preparing acetaldehyde is by direct oxidation of ethylene. (This process is described in Prob. 8 of Chap. 2.) Completely analyze the various factor which should be considered in choosing a plant site for this process. With this information, outline possible geographical locations for the plant, noting the advantages and disadvantages of each site. 

The industrial production of ethylene oxide is based on the direct oxidation of ethylene in the gas phase on a silver catalyst in cooled, tubular reactors. For a large excess of ethylene the reaction scheme can be simplified to ... 

Application To produce ethylene oxide (EO) from the direct oxidation of ethylene using the Dow Meteor process. 

A familiar example of multiple reaction paths is the catalytic oxidation of ethylene to ethylene oxide, where the by-products water and carbon dioxide are produced both by direct oxidation of ethylene and by further oxidation of ethylene oxide. For this example, the equations may be written in the form... 

Applications of POMs to catalysis have been periodically reviewed [33 0]. Several industrial processes were developed and commercialized, mainly in Japan. Examples include liquid-phase hydration ofpropene to isopropanol in 1972, vapor-phase oxidation of methacrolein to methacrylic acid in 1982, liquid-phase hydration of isobutene for its separation from butane-butene fractions in 1984, biphasic polymerization of THE to polymeric diol in 1985 and hydration of -butene to 2-butanol in 1989. In 1997 direct oxidation of ethylene to acetic acid was industrialized by Showa Denko and in 2001 production of ethyl acetate by BP Amoco. 

Acetic anhydride is produced by the direct oxidation of ethylene in the presence of air. The synthesis of salicylic acid involves the combination of several reactants. Sodium hydroxide (NaOH) reacts with phenol (CeHsOH) to give sodium phenolate and water. Sodium phenolate reacts with carbon dioxide (CO2) to obtain sodium salicylate. The subsequent acidification with H2SO4 leads to pure salicylic acid and sodium sulfate. 

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