Propylene oxide Halcon process

The addition of an oxygen atom to an olefin to generate an epoxide is often catalyzed by soluble molybdenum complexes. The use of alkyl hydroperoxides such as tert-huty hydroperoxide leads to the efficient production of propylene oxide (qv) from propylene in the so-called Oxirane (Halcon or ARCO) process (79). 

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. 

The reaction of olefin epoxidation by peracids was discovered by Prilezhaev [235]. The first observation concerning catalytic olefin epoxidation was made in 1950 by Hawkins [236]. He discovered oxide formation from cyclohexene and 1-octane during the decomposition of cumyl hydroperoxide in the medium of these hydrocarbons in the presence of vanadium pentaoxide. From 1963 to 1965, the Halcon Co. developed and patented the process of preparation of propylene oxide and styrene from propylene and ethylbenzene in which the key stage is the catalytic epoxidation of propylene by ethylbenzene hydroperoxide [237,238]. In 1965, Indictor and Brill [239] published studies on the epoxidation of several olefins by 1,1-dimethylethyl hydroperoxide catalyzed by acetylacetonates of several metals. They observed the high yield of oxide (close to 100% with respect to hydroperoxide) for catalysis by molybdenum, vanadium, and chromium acetylacetonates. The low yield of oxide (15-28%) was observed in the case of catalysis by manganese, cobalt, iron, and copper acetylacetonates. The further studies showed that molybdenum, vanadium, and... 

The second manufacturing method for propylene oxide is via peroxidation of propylene, called the Halcon process after the company that invented it. Oxygen is first used to oxidize isobutane to r-butyl hydroperoxide (BHP) over a molybdenum naphthenate catalyst at 90°C and 450 psi. This oxidation occurs at the preferred tertiary carbon because a tertiary alkyl radical intermediate can be formed easily. 

About 50% of the current worldwide propylene oxide capacity is based on a newer process called hydroperoxide (coproduct or oxirene) route (Halcon-Arco technology919,920). According to this process, hydroperoxides synthesized by the oxidation of certain hydrocarbons, such as ethylbenzene or isobutane, are used for epoxidation of propylene in the presence of a transition-metal catalyst ... 

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°... 

Inserting oxygen into the C-H bond of an alkane initially leads to hydroperoxides. When this reaction is performed with atmospheric oxygen it is also called autooxidation. It usually leads to a multitude of products, because of further spontaneous reactions, so this reaction is of limited synthetic use. An exception is oxidation of isobutane with oxygen, which leads to 70 % yield of tert-butyl hydroperoxide at a conversion of 80% (Table 1, entry 7). Hydrogen bromide is used, among other compounds, as an initiator [15]. tert-Butyl hydroperoxide is used as an oxidant in propylene oxide production by the Halcon process. In the formation of phenol by the cumene process cumene is oxidized into the corresponding hydroperoxide in a similar way. 

Molybdenum complexes are the most effective catalysts known for the selective epoxidation of olefins with alkyl hydroperoxides (210-212). Commonly known is the Arco or Halcon process for the large-scale manufacture of propylene oxide from propylene. This process uses t-BuOOH or ethyl benzene hydroperoxide (EBHP) as an oxidant and Mo(CO)6, for example, as a source of Mo. The Mo(CO)6 acts as a catalyst precursor, which is converted into a soluble active form by complexation with diols (3). Chemists have designed several supported versions of the catalysts for this epoxidation chemistry. A clear classification can be made on the basis of the nature of the support. 

This process was originally developed and commercialized by Oxirane (a joint venture company between ARCO Chemical, now Lyondell, and Halcon) and independently by Shell Petrochemical Company. At present, this is one of the main processes for the commercial manufacture of propylene oxide (the other is a variant of the same that starts with isobutane instead of ethylbenzene, and produces propylene oxide together with tert-butyl alcohol, isobutylene, and... 

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. 

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. 

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 bottoms product from the isobutane separation is a mixture of tertiary butyl alcohol and tertiary butyl hydroperoxide. This mixture enters the epoxidation reactor where it reacts with propylene to form propylene oxide. The catalyst is either molybdenum based as in the process developed by Halcon and practiced by ARCO or TiOj on silica in the Shell process. 

Transition Metai-Catalyzed Epoxidation with Alkyl Hydroperoxides. Alkyl hydroperoxides are attractive oxidants on a technical scale because they can be produced by autoxidation of branched alkanes with oxygen. This concept has been realized on the largest scale in the so-called Halcon process, i.e., the transition metal-catalyzed epoxidation of propylene to propylene oxide (35) (Fig. 9). Homogeneous and heterogeneous titanium, vanadium, and molybdenum catalysts are capable of catalyzing the C=C-epoxidation by alkyl hydroperoxide (for a review see Ref. 36). 

Methylphenylcarbinol is also an intermediate in the Halcon process, in which ethylbenzene is oxidized to a hydroperoxide at around 130 °C with air, then converted with propylene into propylene oxide and carbinol. The carbinol is subsequently dehydrated on a titanium catalyst at 180 to 280 °C to styrene. This process, first commercialized by Atlantic Richfield, has found large-scale application in a few isolated cases (e.g. Shell (Netherlands), Alcudia (Spain) and Nihon Oxirane (Japan)) it is only viable if there is sufficient demand for propylene oxide. 

In 1962, researchers at Scientific Design discovered a direct oxidation reaction for making propylene oxide, which was then made by a variant of the chlorhydrin process. The new process involved the air oxidation of isobutene to -butylhydroperoxide, which in turn is used to oxidize propylene in the presence of a soluble molybdenum compound. The coproduct is f-butanol. To develop this process, Scientific Design reorganized to form Halcon International, a joint venture with Atlantic Richfield called Oxirane. The first plants were built in 1969... 

Ethylene oxide is manufactured hy direct oxidation of ethylene, in contrast PO is only obtained in coproduct processes. The classical process, chlorination of propylene, is still used by Dow, one of the world s largest producer of polyether polyols. In contrast, all other producers use the Halcon process, based on the simultaneous production of PO and styrene monomer or t-butyl alcohol. In view of the demise of AITBE (methyl-f-butyl ether based on t-butyl alcohol) as a fuel additive, the styrene coproduct process (POSM) will remain as the economically viable route to PO. A recent example is the new (SMPO) plant of Basell at Moerdijk in the Netherlands. The largest producer of PO, the former Arco (now Lyondell), has sold its global polyol business to Bayer in 1999. Lyondell will also provide Bayer a long-term, low cost supply of PO. Recently, Dow annoimced that it also will use the POSM route to PO in a new facility. 

The indirect propylene oxidation process via ethylbenzene hydroperoxide (Halcon process) is displayed in Eq. (6.12.12). Ethylbenzene, obtained by the acid-catalyzed Friedel-Crafts alkylation of benzene with ethylene, is converted with air into ethylbenzene hydroperoxide. The hydroperoxide epoxidizes propylene and generates the co-product a-phenylethanol that is later dehydrated to styrene. Styrene is a major industrial chemical used mainly as monomer for polymers such as polystyrene or styrene-containing copolymers ... 

The yield of PO in the Halcon process is in the range 87-91% and more than 2 t of the co-product styrene are generated for each produced ton of propylene oxide. The investment costs for the ethylbenzene process are higher than for the tert-butanol process, because of the isolation and purification demands for polymer-grade styrene, figure 6.12.6 shows the plant design for an indirect propylene oxidation process via ethylbenzene hydroperoxide. 

Figure 6.12.6 Flow sheet of the Halcon process for propylene oxide production. Adapted from Kahlich et a. 2000) and Fedtke eto/. (1992).

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