Styrene monomer propylene oxide reaction process

Olefin epoxidation is an important industrial domain. The general approach of SOMC in this large area was to understand better the elementary steps of this reaction catalyzed by silica-supported titanium complexes, to identify precisely reaction intermediates and to explain catalyst deachvahon and titanium lixiviation that take place in the industrial Shell SMPO (styrene monomer propylene oxide) process [73]. (=SiO) Ti(OCap)4 (OCap=OR, OSiRs, OR R = hydrocarbyl) supported on MCM-41 have been evaluated as catalysts for 1-octene epoxidation by tert-butyl hydroperoxide (TBHP). Initial activity, selechvity and chemical evolution have been followed. In all cases the major product is 1,2-epoxyoctane, the diol corresponding to hydrolysis never being detected. 

Scheme 4.51 shows the process known to the bulk chemicals industry as SMPO, the styrene monomer-propylene oxide process. Styrene is used in polymers, and propylene oxide derivatives have a wide variety of uses, including as surfactants and in anti-freeze. For the bulk industry, the process is as follows. Addition of ethylene to benzene gives ethylbenzene, which undergoes air oxidation to give the hydroperoxide. Reaction of this with propylene, in the presence of a suitable catalyst, gives styrallyl alcohol and propylene oxide. Styrallyl alcohol is readily dehydrated to styrene. 

Monomers devoid of polar groups generally undergo anionic polymerization in a predictable manner. With polar monomers sometimes side reactions occur during the process transfer reactions in the case of acrylonitrile, or propylene oxide, and even more so with alkylacrylates deactivations (or "killing") reactions in the case of halogen substituted styrene or dienes. 

The styrene is separated from the product mix, which also contains unreacted ethylbenzene and other impurities, by vacuum distillation. The monomer can easily autopolymerize into a hard solid and is therefore inhibited from polymerization during storage by mixing in a few parts per milhon of a free-radical reaction inhibitor (generally f-butyl catechol). A relatively small amount of styrene is also made by the oxidation of ethyl benzene in a process introduced by Union Carbide. The ethylbenzene hydroperoxide formed by oxidation is reacted with propylene to form propylene oxide and 2-phenyl ethanol. The latter compound is dehydrated to obtain styrene. 

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