Chemical News

Tuesday, January 20, 2009

Propylene Oxide Process

Propylene oxide (PO) production technology is undergoing something of a renaissance. After 1974, when the first propylene oxide–styrene monomer technology plant came on stream, no new PO technology was put into use until 2003, when Sumitomo Chemical started up its new coproduct-free route to PO that was based on cumene hydroperoxide as the propylene epoxidizing agent.

This innovation spurred others to develop alternative ways to make PO, such as direct-oxidation and H2O2-based routes. Another method is the so-called hydro-oxidation route, in which propylene is exposed to a mixture of oxygen and hydrogen. This route has been plagued by low productivity because of very low conversions per pass.

H. Abekawa, T. Kawabata, and M. Yako disclose a technique in which the productivity of propylene hydro-oxidation is increased and selectivity to PO is maintained at relatively high levels. The key to the inventors’ method is adding polycyclic compounds such as anthracene, naphthalene, tetracene, and pyrene to the reaction solvent in the presence of titanium silicalite and supported palladium catalysts. For example, a propylene oxide reaction was carried out in an autoclave at 60 °C and 0.8 MPa pressure by feeding a 4:4:10:82 propylene–oxygen–hydrogen–nitrogen gas mixture at 20 L/h and a H2O–MeCN 20:80 w/w solution containing 0.7 mmol/kg of anthracene and 0.7 mmol/kg of NaH2PO4 at 108 mL/h. Ti-silicalite (0.133 g) and Pd/C (0.33 g) activated carbon were added to the reaction mixture. PO was made in 87% selectivity based on the amount of propylene consumed; almost all of the remaining propylene was converted to propane. Productivity, defined as the amount of PO made per unit weight of titanium catalyst, was 33.5.

Source: CAS & Patent Watch