Propylene oxide organic hydroperoxides

Indirect oxidation of propylene is an important route for propylene oxide production that proceeds in two reaction steps. The first step is the formation of a peroxide from alkanes, aldehydes, or adds by oxidation with air or oxygen. The second reaction step is the epoxidation of propylene to PO by oxygen transfer from the peroxide with formation of water, alcohol, or acid. The catalytic oxidation of propylene with organic hydroperoxides is nowadays a successful commercial production route (51% of world capacity). Two organic hydroperoxides dominate the processes (i) a process using isobutane (peroxide tert-butyl hydroperoxide, co-product tert-butyl alcohol), which accounts for 15% of the world capacity and (ii) a process using ethylbenzene (peroxide ethylbenzene hydroperoxide, co-product styrene) that accounts for 33% of the world capacity. The process via isobutane is presented by ... 

As of this writing, the process has not been commercialized, but apparendy the alcohol can be separated from its propylene oxide coproduct process to maintain an economically competitive position. The formation of organic hydroperoxides is a concern, as it was in the Shell process. 

Propylene oxide [75-56-9] (methyloxirane, 1,2-epoxypropane) is a significant organic chemical used primarily as a reaction intermediate for production of polyether polyols, propylene glycol, alkanolamines (qv), glycol ethers, and many other useful products (see Glycols). Propylene oxide was first prepared in 1861 by Oser and first polymerized by Levene and Walti in 1927 (1). Propylene oxide is manufactured by two basic processes the traditional chlorohydrin process (see Chlorohydrins) and the hydroperoxide process, where either / fZ-butanol (see Butyl alcohols) or styrene (qv) is a co-product. Research continues in an effort to develop a direct oxidation process to be used commercially. 

The hydroperoxide process involves oxidation of propjiene (qv) to propylene oxide by an organic hydroperoxide. An alcohol is produced as a coproduct. Two different hydroperoxides are used commercially that result in / fZ-butanol or 1-phenylethanol as the coproduct. The / fZ-butanol (TBA) has been used as a gasoline additive, dehydrated to isobutjiene, and used as feedstock to produce methyl tert-huty ether (MTBE), a gasoline additive. The 1-phenyl ethanol is dehydrated to styrene. ARCO Chemical has plants producing the TBA coproduct in the United States, Erance, and the Netherlands. Texaco has a TBA coproduct plant in the United States. Styrene coproduct plants are operated by ARCO Chemical in the United States and Japan, Shell in the Netherlands, Repsol in Spain, and Yukong in South Korea. 

Hydroperoxide Process. The hydroperoxide process to propylene oxide involves the basic steps of oxidation of an organic to its hydroperoxide, epoxidation of propylene with the hydroperoxide, purification of the propylene oxide, and conversion of the coproduct alcohol to a useful product for sale. Incorporated into the process are various purification, concentration, and recycle methods to maximize product yields and minimize operating expenses. Commercially, two processes are used. The coproducts are / fZ-butanol, which is converted to methyl tert-huty ether [1634-04-4] (MTBE), and 1-phenyl ethanol, converted to styrene [100-42-5]. The coproducts are produced in a weight ratio of 3—4 1 / fZ-butanol/propylene oxide and 2.4 1 styrene/propylene oxide, respectively. These processes use isobutane (see Hydrocarbons) and ethylbenzene (qv), respectively, to produce the hydroperoxide. Other processes have been proposed based on cyclohexane where aniline is the final coproduct, or on cumene (qv) where a-methyl styrene is the final coproduct. 

Ethylbenzene Hydroperoxide Process. Figure 4 shows the process flow sheet for production of propylene oxide and styrene via the use of ethylbenzene hydroperoxide (EBHP). Liquid-phase oxidation of ethylbenzene with air or oxygen occurs at 206—275 kPa (30—40 psia) and 140—150°C, and 2—2.5 h are required for a 10—15% conversion to the hydroperoxide. Recycle of an inert gas, such as nitrogen, is used to control reactor temperature. Impurities ia the ethylbenzene, such as water, are controlled to minimize decomposition of the hydroperoxide product and are sometimes added to enhance product formation. Selectivity to by-products include 8—10% acetophenone, 5—7% 1-phenylethanol, and <1% organic acids. EBHP is concentrated to 30—35% by distillation. The overhead ethylbenzene is recycled back to the oxidation reactor (170—172). 

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. 

Oxirane A general process for oxidizing olefins to olefin oxides by using an organic hydroperoxide, made by autoxidation of a hydrocarbon. Two versions are commercial. The first to be developed oxidizes propylene to propylene oxide, using as the oxidant f-butyl hydroperoxide made by the atmospheric oxidation of isobutane. Molybdenum naphthenate is used as a... 

The activity of titanium based catalysts for the oxidation of organic compounds is well known. Wulff et al. in 1971 [1] patented for Shell Oil a process for the selective epoxidation of propylene with hydroperoxides like ethylbenzene hydroperoxide (EBH) or tertiary-butyl hydroperoxide (TBH) with the use of a catalyst made of Ti02 deposited on high surface area Si02. A Shell Oil plant for the production of 130,000 tons/y of propylene oxide at Moerdijk, Holland, is based on this technology. 

The search for a new epoxidation method that would be appropriate for organic synthesis should also, preferably, opt for a catalytic process. Industry has shown the way. It resorts to catalysis for epoxidations of olefins into key intermediates, such as ethylene oxide and propylene oxide. The former is prepared from ethylene and dioxygen with silver oxide supported on alumina as the catalyst, at 270°C (15-16). The latter is prepared from propylene and an alkyl hydroperoxide, with homogeneous catalysis by molybdenum comp e ts( 17) or better (with respect both to conversion and to selectivity) with an heterogeneous Ti(IV) catalyst (18), Mixtures of ethylene and propylene can be epoxidized too (19) by ten-butylhydroperoxide (20) (hereafter referred to as TBHP). 

Styrene, one of the world s major organic chemicals, is derived from ethylene via ethylbenzene. Several recent developments have occurred with respect to this use for ethylene. One is the production of styrene as a co-product of the propylene oxide process developed by Halcon International (12). In this process, benzene is alkylated with ethylene to ethylbenzene, and the latter is oxidized to ethylbenzene hydroperoxide. This hydroperoxide, in the presence of suitable catalysts, can convert a broad range of olefins to their corresponding oxirane compounds, of which propylene oxide presently has the greatest industrial importance. The ethylbenzene hydroperoxide is converted simultaneously to methylphenyl-carbinol which, upon dehydration, yields styrene. Commercial application of this new development in the use of ethylene will be demonstrated in a plant in Spain in the near future. 

The selective epoxidation of alkenes by alkyl hydroperoxides in the presence of d° transition metals (equation 64), reported in 1965,234 has been widely applied in organic chemistry and has been developed into a commercial process for the manufacture of propylene oxide by Halcon (M = Mo)99 and by Shell (M = Ti/SiO2).10°... 

Propylene oxide (PO) is a major bulk chemical that is useful as an intermediate for the production of glycols, polyethers and polyols. World PO production is about 7 million tons per year, with the market growing by approximately 5% annually. PO comes from two current industrial processes the chlorohydrin process and the organic hydroperoxide process (Scheme 3.1). These processes require multiple steps and suffer from the additional drawback of not producing the desired PO alone. 

Eight catalyst generations of 21 samples have been synthesised and tested, and a highly active and selective catalyst for the epoxidation of cyclohexene with tert-bu-tyl hydroperoxide found, which can be applied to the epoxidation of other olefins, especially propylene, using organic peroxides as oxidants [25]. 

PO is produced by one of two commercial processes the chlorohydrin process or the hydroperoxide process. The chlorohydrin process involves reaction of propylene and chlorine in the presence of water to produce the two isomers of propylene chlorohydrin. This is followed by dehydrochlorination using caustic or lime to produce PO and salt. The hydroperoxide process involves oxidation of propylene to PO by an organic hydroperoxide. 

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. 

Epoxidation with hydroperoxides is the basis for the large-scale indirect production of propylene oxide by a process that has been called the Oxirane or Halcon processes. Early work was reported by Smith in a patent issued in 1956 [457], which described soluble heteropoly acids containing transition metals such as chromium, molybdenum, and tungsten that could be employed as homogeneous catalysts for the reaction of olefins with organic hydroperoxides and hydrogen peroxide. 

Propylene oxide (PO) is an important chemical intermediate, which is mainly used in the manufacture of polyols, propylene glycols, and propylene glycol ethers [1]. The world annual production capacity of PO is about 7 million metric tons [2]. PO is mainly produced commercially by either the chlorohydrin (about 43%) or organic hydroperoxide processes. The chlorohydrin route produces large amounts of salt by-product, and new plants have used the hydroperoxide processes [3]. 

Propylene oxide (PO) is an industrially important chemical for the manufacture of polyurethane, unsaturated resins, surfactants and other products. Industrially PO is produced using two processes Chlorohydrin process and Halcon (hydroperoxide) process [1]. The former process produces environmentally unfriendly chlorinated organic byproducts as well as calcium chloride, while the latter process produces equimolar amounts of co-products and requires heavy capital investment. 

The epoxidation of propylene to PO using organic hydroperoxides instead of H2O2 as oxidants is also facile, but a compHcation in this case is the coproduct formation, that is, the formation of stoichiometric amounts of the reduced form of the oxidant. Teri-butyl hydroperoxide (TBHP) (194), ethylbenzene hydroperoxide (195), and cumene hydroperoxide (CHP, systematic name hydroperoxide, 1-methyl-1-phenylethyl) (196) are the most frequently used organic hydroperoxides for the oxidation of propylene to PO. 

Sumitomo developed a recirculation process for manufacture of PO using CHP as oxidant (196). The company developed both a new catalyst and a new process for PO production. The production method is fundamentally similar to known methods involving organic peroxides as oxidants the major difference is that cumene is used as the reaction medium and hence the process is referred to as the cumene PO-only process. Laboratory tests started in 2000 and pilot plant testing in 2001. A plant was completed in 2002 and started up in 2003. This commercial plant was the first PO-only plant in Japan, producing PO by oxidation of propylene with cumene hydroperoxide without a significant formation of coproducts. The plant is located in the Chiba prefecture, operated by a joint venture between Nihon Oxirane Co. and Lyondell, and produces aroimd 200,000 t of PO/year. A second plant was started in May 2009 in Saudi Arabia, as a joint project of Sumitomo with Saudi Arabian Oil Co. 

In recent years, the liquid phase oxidation of organic substrates using transition metal compounds as catalysts has become a profitable means of obtaining industrially important chemicals. Millions of tons of valuable petrochemicals are produced in this manner annually [1]. Typical examples of such processes are the production of vinyl acetate or acetaldehyde via the Wacker process, equations (1) and (2) the Mid-Century process for the oxidation of methyl aromatics, such as p-xylene to tereph-thalic acid, equation (3) and the production of propylene oxide from propylene using alkyl hydroperoxides, equation (4). 

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