January 21, 2013
Recycle ethylene glycol in the manufacture of dimethyl carbonate. In the early 1990s, General Electric Plastics (GEP) developed a technology that allowed polycarbonate to be produced without starting from toxic phosgene (COCl2). The GEP process is based on the reaction of diphenyl carbonate [CO(OPh)2] with bisphenol A in the melt phase. Since GEP’s breakthrough, several of its competitors developed similar non-COCl2 routes to polycarbonate.
In all of these routes, CO(OPh)2 provides the carbonate functionality for the polymer backbone. The competitors, however, developed different routes for making CO(OPh)2. GEP (now owned by SABIC) uses oxidative MeOH carbonylation to give dimethyl carbonate [CO(OMe)2], which undergoes transesterification with PhOH to give CO(OPh)2. The released MeOH is recycled to the front end of the process.
Competitor Asahi Chemical uses the reaction of ethylene oxide with CO2 to give ethylene carbonate (EC), which reacts with MeOH to give CO(OMe)2 and coproduct ethylene glycol (EG). Like GEP, Asahi converts CO(OMe)2 to CO(OPh)2 by treating it with PhOH.
C. Gurtler and co-inventors at Bayer, a leading polycarbonate producer, disclose an alternative process for making CO(OMe)2 from EC. Instead of removing EG as a coproduct, as in the Asahi process, the EG undergoes oxidative carbonylation to regenerate EC. This process avoids producing EG, which can complicate the market strategy and economics of the overall process.
To demonstrate the efficacy of the oxidative carbonylation of EG to EC, the inventors give the following example: An autoclave is charged with a mixture of EG (80.33 wt%), Pd(OAc)2 (0.23 wt%), Mn(acac)3 (7.22 wt%), and KBr (12.22 wt%) in dimethyl ether solvent (2 parts by volume); acac is acetoacetate. Then, 20 bar of a gas mixture of N2, O2, and CO (91:3:6 w/w/w) is injected into the reactor, and the contents are heated at 60 °C for 20 h.
EC is produced in 20.3% yield, corresponding to a turnover number of 255 relative to palladium. EC is the only detectable product. (Bayer Intellectual Property GmbH [Monheim, Germany]. US Patent 8,304,509, Nov. 6, 2012; Jeffrey S. Plotkin)