Propylene oxide Hydrocarbon hydroperoxides

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. 

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... 

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... 

This indirect oxidation route takes two steps. In the first, a hydrocarbon, such as iso butane or ethylbenzene, is oxidized. The source of the oxygen is air. The reaction takes place just by mixing the ingredients and heating them to 250-300°F at 50 psi, producing a hydroperoxide. In the second step, the oxidized hydrocarbon reacts with propylene in a liquid phase and in the presence of a metal catalyst at 175-225°F and 550 psi to produce PO yields of better than 90%. The process flow is shown in Figure 11—3. 

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 ... 

A more economic process has been commercialized. In one version, the hydroperoxide is produced by catalytic air-oxidation of a hydrocarbon such as ethylbenzene (see top of page). Reaction of this hydroperoxide with propylene yields propylene oxide as a co-product. 

I to 5. 0 mol per mol of hydroperoxide. The presence of sodium naphtheoate, by prevenling side reaction, helps to reduce the excess propylene required (from lO/l to 2/1 in moles). In the Shell technology, epoxidation is catalyzed by metallic oxides (molybdenum, vanadium, titanium, etc.) supported on sih cau The liighiy exothe c reaction takes place around 100 to 130 at 3.5.10 Pa absolute. Hydroperoxide conver> sion is very hi (> 97 per cent). Propylene oxide molar selectivity exceeds 70 per cent and that of the styrene precursors 93 per cent As for propylene, its once-through conversion is about 15 per cent, for a oxide molar selectivity greater than 90 per cent, and the main by-products are dimers and heavier hydrocarbons. 

The selective oxidation of hydrocarbons into hydroperoxides, primary products of oxidation is the most difficult problem because of the high catalytic activity of the majority of applied catalysts in ROOH decomposition. At the same time, the problem of selective oxidation of alkylarens (ethylbenzene and cumene) with molecular 02 in ROOH, is of current importance from the practical point of view in connection with ROOH use in large-tonnage productions such as production of propylene oxide and styrene (a-phenylethylhydroperoxide, PEH), or phenol and acetone (cumyl hydroperoxide) [1],... 

A variety of hydrocarbons can be used to form hydroperoxides in situ which can then be used to make propylene oxide however, in each case, a coproduct is formed. The quantity of the coproduct, on a weight basis, is larger than the propylene oxide produced therefore, the economics of the processes are sensitive to the market and price for both propylene oxide and the coproduct. Two hydrocarbon feedstocks have been commercialized isobutane which yields tert-butyl alcohol as coproduct and ethylbenzene which yields styrene as coproduct. Both of these feedstocks are readily available and there are large established markets for both coproducts. Styrene is a large volume and well established petrochemical monomer and tert-butyl alcohol can be easily dehydrated to isobutylene which can be used as a feedstock for the gasoline additive methyl-tert-butyl ether (MTBE). 

In the peroxidation processes, propylene oxide is obtained by reaction of propylene with either a hydroperoxide or with peracetic acid. In the United States, manufacture is limited to oxidation of propylene by either of two hydroperoxides t-butyl hydroperoxide or ethylbenzene hydroperoxide. A hydrocarbon, either isobutane or ethylbenzene, is first oxidized to the corresponding hydroperoxide and then the hydroperoxide is used to oxidize propylene to give propylene oxide with a useful alcohol by-product. 

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