Direct epoxidation of propylene

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. 

N. Mimura, S. Tsubota, K. Murata, K. K. Bando, J. J. Bravo-Suarez, M. Haruta, S. T. Oyama, Gas-phase radical generation by Ti oxide clusters supported on silica Application to the direct epoxidation of propylene to propylene oxide using molecular oxygen as an oxidant, Catal. Lett. 110 (2006) 47. 

W. Mueller-Markgraf, (Ed.), Process for the direct epoxidation of propylene to propylene oxide, German Patent DE 0019,529,679Al, Feb. 13,1997, To Linde AG. 

T. A. Nijhuis, B. J. Huizinga, M. Makkee, J. A. Moulijin, Direct epoxidation of propylene using gold dispersed on TS-1 and other titanium-containing supports, Ind. Eng. Chem. Res. 38 (1999) 884. 

Direct epoxidation of propylene to propylene oxide by Ti02 (MCM48)-supported AuNPs [9d], sensors able to simultaneously detect H2 and CO at low level using C02O3-supported AuNPs [9e]. 

Au catalysts have received considerable attention recently because of the extraordinary performance in the low temperature oxidation of CO and high selectivities of over 99% in the direct epoxidation of propylene in the presence of hydrogen. Besides the extraordinary... 

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). 

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]. 

A so far still unsolved problem is the direct enantioselective epoxidation of simple terminal olefins. For example the epoxidation of propylene that was achieved with a 41% ee almost twenty years ago by Strukul and his coworkers using Pt/diphosphine complexes is still unsurpassed. Unfortunately such low ee s are of no practical interest. The problem was circumvented by Jacobsen using hydrolytic kinetic resolution of racemic epoxides (Equation 26) and is practised on a multi 100 kg scale at Chirex. The strategy used is to stereose-lectively open the oxirane ring of a racemic chiral epoxide leaving the other enantiomer intact. Reactions are carried out to a 50% maximum conversion. The catalyst belongs to the metal-salen class described above and can be recycled. The products are separated by fractional distillation. 

C. Qi, T. Akita, M. Okumura, M. Haruta, Effect of surface chemical properties and texture of mesoporous titanosilicates on direct vapor-phase epoxidation of propylene over Au catalysts at high reaction temperature, Appl. Catal. A Gen. 253 (2003) 75. 

A. Zwijnenburg, M. Saleh, M. Makkee, J. A. Moulijn, Direct gas-phase epoxidation of propylene over bimetallic Au catalysts, Catal. Today 72 (2002) 59. 

A process for the epoxidation of propylene with in situ generation of hydrogen peroxide was proposed in the 1990s by the Tosoh Corporation (283). The company suggested that PO could be made in a flow system via a direct reaction between H2 and O2 in the presence of propylene by using a catalyst made of palladium supported on crystaUine titanium sihcate. A propylene conversion of 0.8% was reported, with a selectivity to PO of 99%. ARCO (now Lyondell) described catalysts that produce PO with better selectivity and yield as compared with those reported earher (284). BASF has also claimed the use of framework metal-modifled TS-1 catalysts for this catalytic chemistry (266). Various catalyst compositions were described that can be... 

Direct air epoxidation of propylene to propylene oxide suffers from selectivity problems. Epoxidation by alkyl hydroperoxide, as practiced by Arco, is based on the use of Mo(CO)g as a homogeneous catalyst. The most impressive use of homogeneous catalysis in epoxidation, however, is in the Sharpless asymmetric oxidation of allylic alcohols. In view of its importance, this enantioselective reaction is included in Chapter 9 which is devoted mainly to asymmetric catalysis. 

Direct oxidation of propylene with air or pure oxygen (equivalent to ethylene oxide manufacturing) is not efficient, since the silver catalysts used in the direct ethylene oxidation are not suitable for the reaction of alkenes with allylic hydrogen atoms (like propylene). Direct oxidation of propylene results mainly in acrolein formation and total oxidation. Some 3% of the world capacity of PO is produced by very recently developed processes, for example, hydroperoxidation of cumene and propylene and catalytic epoxidation of propylene using H2O2. 

Compared to EO, propylene oxide (PO) is less reactive and less hazardous. PO is mainly used for the production of polyether, polyols, polyurethane, glycols, and ethers. Direct oxidation of propylene with air or pure oxygen is not efficient, and PO is produced either by the chlorohydrin process (46% share) or by indirect oxidation. Indirect oxidation of propylene proceeds in two steps. The first step is the formation of a peroxide from iso-butane or ethylbenzene by oxidation with air/oxy-gen (peroxides tert-butyl hydroperoxide and ethylbenzene hydroperoxide, respectively). The second step is the catalytic epoxidation of propylene to propylene oxide by oxygen transfer from the peroxide. In future, oxidation processes based on H2O2 will probably also play an important role. In 2008, the first commercial plant of this kind went on stream. 

Unlike ethylene epoxide, which is produced from ethylene and oxygen on a silver catalyst, the epoxide of propylene cannot be obtained by direct catalytic... 

For many years ethylene chlorohydrin was manufactured on a large iadustrial scale as a precursor to ethylene oxide, but this process has been almost completely displaced by the direct oxidation of ethylene to ethylene oxide over silver catalysts. However, siace other commercially important epoxides such as propylene oxide and epichlorohydrin cannot be made by direct oxidation of the parent olefin, chlorohydrin iatermediates are stiU important ia the manufacture of these products. 

The catalysts which have been tested for the direct epoxidation include (i) supported metal catalysts, (ii) supported metal oxide catalysts (iii) lithium nitrate salt, and (iv) metal complexes (1-5). Rh/Al203 has been identified to be one of the most active supported metal catalysts for epoxidation (2). Although epoxidation over supported metal catalysts provides a desirable and simple approach for PO synthesis, PO selectivity generally decreases with propylene conversion and yield is generally below 50%. Further improvement of supported metal catalysts for propylene epoxidation relies not only on catalyst screening but also fundamental understanding of the epoxidation mechanism. 

---