Organic hydroperoxide process

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. 

Scheme 3.2 shows recently established industrial processes for PO production. The cumene recycling process uses an organic hydroperoxide process combined with hydrogenation of cumyl alcohol to cumene. This process consumes only hydrogen... 

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]. 

In the organic hydroperoxide processes, PO (CsHgO) is synthesized by the catal)d ic reaction of propylene (CaH ) and an alkyl hydroperoxide (ROOH), according to the following reaction scheme ... 

Suitable catalysts are /-butylphenylmethyl peracetate and phenylacetjdperoxide or redox catalyst systems consisting of an organic hydroperoxide and an oxidizable sulfoxy compound. One such redox initiator is cumene—hydroperoxide, sulfur dioxide, and a nucleophilic compound, such as water. Sulfoxy compounds are preferred because they incorporate dyeable end groups in the polymer by a chain-transfer mechanism. Common thermally activated initiators, such as BPO and AIBN, are too slow for use in this process. 

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. 

Organic hydroperoxides can be prepared by Hquid-phase oxidation of selected hydrocarbons in relatively high yield. Several cycHc processes for hydrogen peroxide manufacture from hydroperoxides have been patented (84,85), and others (86—88) describe the reaction of tert-huty hydroperoxide with sulfuric acid to obtain hydrogen peroxide and coproduct tert-huty alcohol or tert-huty peroxide. 

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). 

The original SBR process is carried out at. 50° C and is referred to as hot polymerization. It accounts for only about 5% of aU the mbber produced today. The dominant cold polymerization technology today employs more active initiators to effect polymerization at about 5°C. It accounts for about 85% of the products manufactured. Typical emulsion polymerization processes incorporate about 75% butadiene. The initiators are based on persulfate in conjunction with mercaptans (197), or organic hydroperoxide in conjunction with ferrous ion (198). The rest of SBR is produced by anionic solution polymerization. The density of unvulcanized SBR is 0.933 (199). The T ranges from —59" C to —64 C (199). 

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 formation of some organic hydroperoxides by oxidation with molecular oxygen is catalytically promoted by metals like silver or copper 171). A dissociative chemisorption of oxygen cannot be active in these processes they probably proceed via the chemisorption of O7 ions (or O2 molecules forming a covalent bond resonating with an ionic bond). 

Methyloxirane is an important building block for the manufacture of polyurethane, of various organic intermediates and solvents7-13 (Section 14.3.6). It is currently made in one of two ways (i) the chlorohy-drin process and (ii) the hydroperoxide process.7-10,12 The former is not environmentally friendly, due to the formation of calcium chloride and... 

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. 

Nucleophilic attack by water on coordinated ethylene, as shown by Reaction 2.12, is the key step in the manufacture of acetaldehyde by the Wacker process (see Chapter 8). In Reaction 2.13 the high oxidation state of titanium makes the coordinated oxygen atom sufficiently electrophilic for it to be attacked by an alkene. As we will see in Chapter 8, this reaction is the basis for the homogeneous catalytic epoxidation of alkenes, using organic hydroperoxides as the oxygen atom donors. 

A major aspect of the cytotoxicity of organic hydroperoxides is their ability to decompose into free radicals which can stimulate autoxidation of organic molecules bearing labile hydrogen atoms. The autoxidation process may be decomposed in three basic steps ... 

Radicals generated during peroxidation of lipids and proteins show reactivity similar to that of the hydroxyl radical however, their oxidative potentials are lower. It is assumed that the reactive alkoxyl radicals rather than the peroxyl radicals play a part in protein fragmentation secondary to lipid peroxidation process, or protein exposure to organic hydroperoxides (DIO). Reaction of lipid radicals produces protein-lipid covalent bonds and dityrosyl cross-links. Such cross-links were, for example, found in dimerization of Ca2+-ATPase from skeletal muscle sarcoplasmic reticulum. The reaction was carried out in vitro by treatment of sarcoplasmic reticulum membranes with an azo-initiator, 2,2/-azobis(2-amidinopropane) dihydrochloride (AAPH), which generated peroxyl and alkoxyl radicals (V9). 

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. 

On decomposition of hydroperoxides phase separation of the pair of primary radicals may occur. It is suggested that a similar process applies to the initiation systems in which radicals are produced by reaction of an oil-soluble initiator and a water-soluble activator. For example, the reaction between an organic hydroperoxide and complexed ferrous ions provides an eflFective source of free radicals in emulsion polymerization ... 

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