June 10, 2013
Here’s a better direct epoxidation of propylene. Oxidizing propylene directly to propylene oxide (PO) continues to be a goal of industrial research laboratories. Unlike ethylene oxide, which is commercially manufactured by the reaction of ethylene with oxygen over a supported silver catalyst, direct propylene oxidation to PO is much more challenging because the allylic hydrogen atoms in propylene can oxidize to give CO2. Consequently, propylene is catalytically epoxidized to PO by treating it with peroxides such as ethylbenzene hydroperoxide, t-BuOOH, or H2O2.
V. A. Dang and co-inventors found that the metal-catalyzed reaction of propylene with an O2–H2 mixture moderated by a buffer solution containing a quinone acid salt gives PO in good conversion and selectivity. The reaction apparatus is a 450-mL stainless steel continuously stirred tank reactor.
In an example, 8 g Pd/Ti-MWW zeolite catalyst and 211 g of a buffer solution that contains the sodium salt of anthraquinone-2-sulfonic acid are added to the reactor. The system is pressured to 600 psig with a feed gas made up of 3.1 vol% H2, 4.4 vol% O2, 6 vol% propylene, 0.4 vol% CH4, and the balance N2. The feed gases are continuously passed through the reactor at 2800 mL/min. The buffer solution is continuously added to the reactor at 115 g/h. The slurry is heated to 60 °C, and the pressure is maintained at ≈600 psig.
The production rate is 0.516 g POE/(g catalyst·h). (POE is propylene oxide equivalents, which includes ring-opened products in addition to PO.) The H2-to-PO and O2-to-PO selectivities are 38% and 68%, respectively. (Lyondell Chemical Technology [Houston]. US Patent 8,440,846, May 14, 2013; Jeffrey S. Plotkin)