Commercial Production of Propylene Oxide

In comparison to ethylene oxide, propylene oxide - also known as 1,2-epoxypropane and methyloxirane - is less reactive and less hazardous. However, propylene oxide is also an important raw material for a wide range of intermediates. Propylene oxide is a chiral epoxide, but is commonly used as its racemic mixture. 

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Use Catalyst for commercial production of propylene oxide using hydroperoxides. 

Alkene epoxidation is a very useful reaction in industry and organic s)mthesis. The resultant epoxides are essential precursors in the s)mthesis of various important substances like plasticizers, perfumes, and epoxy resins [1]. For example, over 5,000,000 and 70,000 metric tonnes of propylene and butene oxides, respectively, are produced per year [2]. Current commercial production of propylene oxide (PO) usually employs the chlorohydrin process or the Halcon process, which gives rise to disposal problem for the resultant salts or large amounts of coproducts. As a result of increasing stringent enviromnent legislation, there is currently much interest in the research and development of environmentally friendly methods for preparation of PO without any coproduct. 

The most well-known example is the catalytic epoxidation of olefins with alkyl hydroperoxides that is used for the commercial production of propylene oxide (see earlier). The reaction is catalyzed by high-valent compounds of early transition metals, e.g. Movl, WVI, Vv and TiIV, and involves a peroxometal type mechanism [6,7] as shown (reaction 12). Mo compounds are particularly effective homo-... 

There are other commercial processes available for the production of butylenes. However, these are site or manufacturer specific, eg, the Oxirane process for the production of propylene oxide the disproportionation of higher olefins and the oligomerisation of ethylene. Any of these processes can become an important source in the future. More recentiy, the Coastal Isobutane process began commercialisation to produce isobutylene from butanes for meeting the expected demand for methyl-/ rZ-butyl ether (40). 

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. 

There has been a great deal of commercial interest in an electrochemical process for the production of propylene oxide from propene via anodic generation of halogen 70>171). The reactions are summarized below ( X = Cl, Br) ... 

Hiis method, initially intended for the more selective production of propylene oxide, is commercialized by ARCO Chemical (formerly Oxirane an Atlantic Richfield Co subsidiary, and by Sheli The first industrial plant was built in 1973 by Montoro, a Joint venture of Oxirane and Empecrol, at Alcudia, Spain. This plant can now manufacture 100.0CX) t/year of styrene and 40,000 t/year of propylene oxide. Two other facilities based on this technology are also in operadoo, one at Channelview, Texas, and the second in Japan, owned jointly by Sumitomo and Showa Denka (Nippon Oxirane), capable of producing 455,000 and 225,000 t year of styrene respectively, as well as about 180,000 and 90.0001/ year of propylene oxide. Shell has also built production capacities of 330,000 and 12SJXX) tf year of these two products at its Moerdijk complex in the Netherlands. 

ARGO (ATLANTIC RICHFIELD) Landau s entrepreneurial inventiveness further yielded Arco Chemical, Atlantic Richfield s chemical subsidiary, another highly profitable new process. In this case, however, the innovation was developed not through licensing, but through a joint venture to commercialize Landau s process for the production of propylene oxide, the principal ingredient in urethane foams and other polyurethane polymers (as reviewed in Chapter 4). 

Table 7.5 lists the average commercial specifications of propylene oxide. Table 7.6 presents the main uses in 1984, as well as the production, capacities and consumption figures for Western Europe, the United States and Japan. 

Methyl terf-butyl ether (MTBE) is an important industrial product used as oxygenate additive in reformulated gasoline. Environmental concern makes its future uncertain, however. Although mainly manufactured by reaction of isobutylene with methanol, it is also produced commercially from methanol and fcrr-butyl alcohol, a by-product of propylene oxide manufacture. Numerous observations from the use of heteropoly acids have been reported. These compounds were used either as neat acids [74], or supported on oxides [75], silica or K-10 montmorillonite [76]. They were also used in silica-included form [77] and as acidic cesium salts [74,77]. Other catalysts studied were sulfated ZrOj [76], Amberlyst 15 ion-exchange resin [76], HZSM-5 [76], HF-treated montmorillonite, and commercial mineral acid-activated clays [75]. Hydrogen fluoride-treatment of montmorillonite has been shown to furnish particularly active and stable acid sites thereby ensuring high MTBE selectivity (up to 94% at 413 K) [75]. 

Commercial production of acetic acid has been revolutionized in the decade 1978—1988. Butane—naphtha Hquid-phase catalytic oxidation has declined precipitously as methanol [67-56-1] or methyl acetate [79-20-9] carbonylation has become the technology of choice in the world market. By-product acetic acid recovery in other hydrocarbon oxidations, eg, in xylene oxidation to terephthaUc acid and propylene conversion to acryflc acid, has also grown. Production from synthesis gas is increasing and the development of alternative raw materials is under serious consideration following widespread dislocations in the cost of raw material (see Chemurgy). 

More than a decade after the publication of the MoVNb catalyst system, scientists at Mitsubishi Chemical reported that modifying this family of mixed metal oxides with Te produced a catalyst for the amoxidation of propane to acrylonitrile [4] and the oxidation of propane to acrylic acid [5], Modification of the Union Carbide catalyst system with Te was probably not a random choice as it is a known propylene activator [5 b] and the molybdate phase TeMoO oxidizes propylene into acrolein and ammoxidizes propylene to acrylonitrile [6], a key intermediate in the commercial production of acrylic acid using Mo-based oxides. Significant efforts to optimize this and related mixed metal oxides continues for the production of both acrylic acid and acrylonitrile, with the main participants being Asahi, Rohm Hass, BASF, and BP. 

Acetylene once was the raw material for commercial production of acrylic acid and esters, but in 1970 production of acrylic acid by oxidation of propylene was first practiced commercially. In a few years, the new process had essentially replaced the old. In 2000, acrylic acid production in the U.S. was of the order of 2.0 billion lb, and that of acrylate esters was of the order of 1.8 billion lb. 

The direct oxidation of propylene on silver catalysts has been intensively investigated, but has failed to provide results with commercial potential. Selectivities are generally too low and the isolation of propylene oxide is complicated by the presence of many by-products. The best reported selectivities are in the range 50-60% for less than 9% propylene conversion. The relatively low selectivity arises from the high temperature necessary for the silver catalysts, the radical nature of molecular oxygen, as well as the allylic hydrogens in propylene. Thus alternative routes have been studied based on the use of oxidants able to act heterolytically under mild conditions. Hypochlorous acid (chlorine+water) and organic hydroperoxides fulfill these requirements and their use has led to the introduction of the chlorohydrin (Box 2) and the hydroperoxide processes, both currently employed commercially. 

Acrolein and condensable by-products, mainly acrylic acid plus some acetic acid and acetaldehyde, are separated from nitrogen and carbon oxides in a water absorber. However in most industrial plants the product is not isolated for sale, but instead the acrolein-rich effluent is transferred to a second-stage reactor for oxidation to acrylic acid. In fact the volume of acrylic acid production ca. 4.2 Mt/a worldwide) is an order of magnitude larger than that of commercial acrolein. The propylene oxidation has supplanted earlier acrylic acid processes based on other feedstocks, such as the Reppe synthesis from acetylene, the ketene process from acetic acid and formaldehyde, or the hydrolysis of acrylonitrile or of ethylene cyanohydrin (from ethylene oxide). In addition to the (preferred) stepwise process, via acrolein (Equation 30), a... 

All the styrene monomer (bpi.oia - 145.2 C, s/J == 0.906. ) produced throughout the world is obtained directly or indiiectly from etbylbenzeoe. Most is product by dehydrogenation, while a certain amount is also obtained as a co-product of Ae manu- ctuie of propylene oxide. Some attempts have been made to extract styrene from liyrolysis C5- gasolines (Stex process by Toray, deserflied in Section 4.2J), but they have. not culminated in commercial plants. 

Selectivity is an especially tough challenge in the case of autoxidation of small olefins in fluid phase because of diversion of the radical chain reaction by termination steps that result in the formation of oxy radicals. These are very reactive species that attack indiscriminately the starting hydrocarbon and primary products. The photochemical reaction in zeolites opens up much better controlled oxidation of low olefins, which are illustrated here briefly for the commercially important case of propylene oxidation. 

The Isolated chromophores in a polymer of type A are in general adventitious, being due to end-groups resulting from the polymerization process commercial additives such as plasticizers, antioxidants, and pigments products of thermal, oxidation or occasionally probes added deliberately. Typical examples of type A chromophores are the ketonic species present in thermally oxidized poly(propylene)6 (IV and V) (6). 

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