January 16, 2012
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Rhenium improves the hydrogen peroxide oxidation of propylene. Propylene oxide (PO) production technology has undergone somewhat of a renaissance recently. In the 1970s, Halcon developed (and later, in partnership with ARCO Chemical, commercialized) two coproduct routes to PO. The first route coproduced PO and tert-butyl alcohol, a key intermediate for making methyl tert-butyl ether (MTBE). A two-for-one process, also developed by Halcon, produced PO and styrene. This process, often called POSM, dominated the PO business.
No new technology for PO production was introduced until 2004, when Sumitomo Chemical commercialized a process that produces PO with no coproducts. This technology uses cumene hydroperoxide to oxidize propylene. The byproduct cumyl alcohol is converted back to cumene and recycled. In 2008, BASF and Dow jointly commercialized another coproduct-free route to PO that is based on oxidizing propylene with hydrogen peroxide and a titanium catalyst.
B. Subramaniam and co-inventors disclose conditions for epoxidizing C2–C5 olefins with hydrogen peroxide and rhenium as a catalyst. In one example, a reactor is charged with 0.012 g methyltrioxorhenium, 0.61 mL 50% aq H2O2, and 4.956 mL of pyridine N-oxide in 4.14 mL MeOH solvent. After 100 mg propylene is introduced, 2.37 mL CO2 is added at a pressure of 700 psi and a temperature of 25 °C. The reaction conditions are chosen so that all of the liquid in the reactor is in one phase. The temperature is raised to 40 °C and monitored for 3 h. The yield of PO is 79%, and the selectivity to PO is 96%. (University of Kansas [Lawrence]. US Patent 8,080,677, Dec. 20, 2011; Jeffrey S. Plotkin)