Epoxidation of propylene

The polycondensation reaction to give the desired polymer, 8.18, is carried out at high temperatures ( 260°C) in the presence of Sb203 and Ti-alkoxide catalysts. The roles of the catalysts at the molecular level are not known in any detail. As shown by reaction 8.26, in the polycondensation reaction one molecule of ethylene glycol is also generated for each molecule of the monomer. 

Nylon 6,6 and nylon 6 are polyamides. These polymers are used in carpets, in hosiery, and in certain cases as engineering plastics. Nylon 6,6 8.19, is the condensation product between adipic acid and 1,6-diamino hexane. Nylon 6 8.20 is made from caprolactam by ring-opening polymerization. 

A homogeneous catalytic process, developed by Oxirane, uses a molybdenum catalyst that epoxidizes propylene by transferring an oxygen atom from tertiary butyl hydroperoxide. This is shown by 8.28. The hydroperoxide is obtained by the auto-oxidation of isobutane. The co-product of propylene oxide, /-butanol, finds use as an antiknock gasoline additive. It is also used in the synthesis of methyl /-butyl ether, another important gasoline additive. The over- 

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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. 

Although this process has not been commercialized, Daicel operated a 12,000-t/yr propylene oxide plant based on a peracetic acid [79-21-0] process during the 1970s. The Daicel process involved metal ion-catalyzed air oxidation of acetaldehyde in ethyl acetate solvent resulting in a 30% peracetic acid solution in ethyl acetate. Epoxidation of propylene followed by purification gives propylene oxide and acetic acid as products (197). As of this writing (ca 1995), this process is not in operation. 

Selectivity of propylene oxide from propylene has been reported as high as 97% (222). Use of a gas cathode where oxygen is the gas, reduces required voltage and eliminates the formation of hydrogen (223). Addition of carbonate and bicarbonate salts to the electrolyte enhances ceU performance and product selectivity (224). Reference 225 shows that use of alternating current results in reduced current efficiencies, especiaHy as the frequency is increased. Electrochemical epoxidation of propylene is also accompHshed by using anolyte-containing silver—pyridine complexes (226) or thallium acetate complexes (227,228). 

Epoxidation of propylene with ethylbenzene hydroperoxide is carried out at approximately 130°C and 35 atmospheres in presence of molybdenum catalyst. A conversion of 98% on the hydroperoxide has been reported ... 

Table 8-2 shows those peroxides normally used for epoxidation of propylene and the coproducts with economic value... 

A particularly interesting system for the epoxidation of propylene to propylene oxide, working under pseudo-heterogeneous conditions, was reported by Zuwei and coworkers [61]. The catalyst, which was based on the Venturello anion combined with long-chained alkylpyridinium cations, showed unique solubility properties. I11 the presence of hydrogen peroxide the catalyst was fully soluble in the solvent, a 4 3 mixture of toluene and tributyl phosphate, but when no more oxidant was left, the tungsten catalyst precipitated and could simply be removed from the... 

The latest industrial strides in PO synthesis are liquid phase epoxidation of propylene with H2O2 over TS... 

Currently there are four major lines of approach towards gas-phase epoxidation of propylene (1) mechanistic studies of Au/Ti02 catalysts through kinetics, spectroscopic identification of adsorbed species and... 

The disadvantage of the chlorohydrin process is the use of toxic, corrosive, and expensive chlorine the major drawback of the peroxide process is the formation of co-oxidates in larger amounts than the desired PO. The direct epoxidation of propylene using 02 (i.e., partial oxidation of propylene) from air has been recognized as a promising route. 

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... 

SMPO [styrene monomer propylene oxide] A process for making propylene oxide by the catalytic epoxidation of propylene. The catalyst contains a compound of vanadium, tungsten, molybdenum, or titanium on a silica support. Developed by Shell and operated in The Netherlands since 1978. 

Xi and coworkers [135-137] reported on the epoxidation of alkenes performed with (CP)3[P04(W03)4] catalyst. This insoluble catalyst formed soluble active species, (CP)3[P04 W02(02) 4], by the reaction with H202. When H202 was consumed completely, the catalyst became insoluble again. Therefore, the catalyst recovery was simple. When coupled with the 2-ethylanthraquinone/2-ethylanthrahydroquinone redox process for H202 production, 02 could be used as an oxidant for the epoxidation of propylene in 85% yield based on 2-ethylanthrahydro-quinone which was obtained without ary by-products (Figure 13.8). 

G. Jenzer, T. Mallet, M. Maciejewski, F. Eigenmann, and A. Baiker, Continuous epoxidation of propylene with oxygen and hydrogen onaPd-Pt/TS-1 catalyst, A/j/jZ. Catal. A208(l-2), 125-133 (2001). 

T. Hayashi, K. Tanaka, and M. Haruta, Selective vapor-phase epoxidation of propylene over Au/Ti02 catalysts in the presence of oxygen and hydrogen, J. Catal. 178(2), 566-575 (1998). 

R. Meiers, and W. F. Holderich, Epoxidation of propylene and direct synthesis of hydrogen peroxide by hydrogen and oxygen, Catal. Lett. 59, 161-163 (1999). 

C. Qi, T. Akita, M. Okumura, and M. Haruta, Epoxidation of propylene over gold catalysts supported on non-porous silica, Appl. Catal. A Gen. 218, 81-89 (2001). 

The epoxidation of propylene to propylene oxide is a high-volume process, using about 10% of the propylene produced in the world via one of two processes [127]. The oldest technology is called the chlorohydrin process and uses propylene, chlorine and water as its feedstocks. Due to the environmental costs of chlorine and the development of the more-efficient direct epoxidation over Ti02/Si02 catalysts, new plants all use the hydroperoxide route. The disadvantage here is the co-production of stoichiometric amounts of styrene or butyl alcohol, which means that the process economics are dependent on finding markets not only for the product of interest, but also for the co-product The hydroperoxide route has been practiced commercially since 1979 to co-produce propylene oxide and styrene [128], so when TS-1 was developed, epoxidation was looked at extensively [129]. 

Jenzer, G., Mallat, T., Madejewski, M., Eigenmann, F., and Baiker, A. (2001) Continuous epoxidation of propylene with oxygen and hydrogen on a Pd-Pt/... 

Let us recall that by the sol-gel method one can obtain very efficiently very well-defined systems such as Ti silicalite, which can be considered as a single site system where titanium is tetracoordinated in a zeolitic matrix and undergoes epoxidation of propylene or hydroxylahon of benzene to phenol. Bear in mind that it took industry more than 20 years to realize such an industrial processes (Dow-BASF process) [1]). 

The other third comes from t-butyl alcohol by dehydration, with the t-butyl alcohol being made available as a by-product by oxidation of isobutane followed by epoxidation of propylene with t-butyl hydroperoxide. 

The epoxidation of propylene is discussed in Chapter 10, Section 2. Some isobutane can be made by isomerizing -butane. The isomerization of -butenes to isobutylene is also being commercialized. 

Epoxidation of olefins over Mo containing Y zeolites was studied by Lunsford et al. [86-90]. Molybdenum introduced in ultrastable Y zeolite through reaction with Mo(C0)g or M0CI5, shows a high initial activity for epoxidation of propylene with t-butyl hydroperoxide as oxidant and 1,2-dichloroethane as solvent [88]. The reaction is proposed to proceed via the formation of a Mo +-t-butyl hydroperoxide complex and subsequent oxygen transfer from the complex to propylene. The catalyst suffers however from fast deactivation caused by intrazeolitic polymerization of propylene oxide and resulting blocking of the active sites. 

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 problem of the role of acidity in the oxidation reaction has been examined. To this end silicalites containing both Ti(IV) and Al(III),- or Fe(III) or Ga(III) have been synthesized [24-26] and used in the epoxidation of propylene. It is well known that trivalent elements introduced in the framework impart definite acidic character to the material. The results obtained under very similar experimental conditions are given in Table 2. 

For the epoxidation of propylene with HO—ONO, both the QCISD and CISD calculations result in a Markovnikov-type transition structure, where the electrophile is slightly skewed toward the least substituted carbon, with a small difference in the bond lengths between the spiro-oxygen and the double-bond carbons (0.106 and 0.043 A, respectively Figure 8). The B3LYP calculations also lead to an unsymmetrical Markovnikov-type transition structure (b). However, the MP2/6-31G geometry optimization results in an anti-Markovnikov-type structure (c) (Figure 8). The CCSD(T)/6-31G and BD(T)/6-31G barriers for ethylene epoxidation with HO—ONO calculated with the QCISD/6-31G ... 

The epoxidations of propylene and isobutylene with peroxyformic acid proceed in a concerted way via slightly unsymmetrical Markovnikov-type transition stmctnres where the differences in the bond distances between the donble-bond carbons and the spiro oxygen are only 0.021 and 0.044 A at the QCISD/6-31G level. In contrast, the more polarizable natnre of the carbon-carbon double bond of o ,/ -unsaturated systems results in a highly nnsymmetrical transition structure for the epoxidation of 1,3-butadiene with an order-of-magnitnde difference in the carbon-oxygen bond distances of 0.305 A at the QCISD/6-31G level. A highly unsymmetrical transition structure has been also found for the epoxidation of acrylonitrile. 

One molybdenum-catalyzed epoxidation, which is of indnstrial importance, needs special mention the Halcon process , which is the molybdennm-catalyzed epoxidation of propylene with TBHP or 1-phenylethyl hydroperoxide on a large scale (Scheme 74), and has been developed and patented by researchers from Halcon and Atlantic Richfield . 

Supported Au catalysts have been extensively studied because of their unique activities for the low temperature oxidation of CO and epoxidation of propylene (1-5). The activity and selectivity of Au catalysts have been found to be very sensitive to the methods of catalyst preparation (i.e., choice of precursors and support materials, impregnation versus precipitation, calcination temperature, and reduction conditions) as well as reaction conditions (temperature, reactant concentration, pressure). (6-8) High CO oxidation activity was observed on Au crystallites with 2-4 nm in diameter supported on oxides prepared from precipitation-deposition. (9) A number of studies have revealed that Au° and Au" play an important role in the low temperature CO oxidation. (3,10) While Au° is essential for the catalyst activity, the Au° alone is not active for the reaction. The mechanism of CO oxidation on supported Au continues to be a subject of extensive interest to the catalysis community. 

Figure 1. In situ formation of oxidant for the epoxidation of propylene in CXLs.

Research Focus Epoxidation of propylene using palladium/titanium zeolite-1 as catalyst Originality This propene epoxidation method occurs in a neutral medium and is... 

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