Chemical News

Thursday, November 8, 2007

New catalyst for Dimethyl Carbonate (DMC)

The demand for dimethyl carbonate (DMC) is increasing as it has evolved from a specialty chemical to larger-scale use as an intermediate in phosgene-free polycarbonate processes. DMC has also been mentioned as a possible gasoline blending component because of its very high oxygen content, good blending octane, freedom from phase separation, low toxicity, and rapid biodegradability. These qualities may be more attractive with the ban on MTBE as a gasoline oxygenate.

The classic route to DMC uses phosgene as the starting material. The disadvantage of this route is the danger of handling highly toxic phosgene and the environmental problem of disposing of the NaCl byproduct.

Three relatively new nonphosgene routes to DMC are in commercial operation:
  1. Oxidative carbonylation using a CuCl “catalyst” (actually a redox agent).

  2. Transesterification between ethylene carbonate and MeOH, and

  3. urea methanolysis.

The tin-catalyzed reaction of MeOH with urea to give DMC is a well-known synthesis; however, yields are typically low because the intermediate methyl carbamate is prone to decompose to isocyanic acid or isocyanuric acid. Y. Sun and colleagues disclose a new catalyst that allows the methanolysis of urea to proceed in good yield.

One of the best catalysts described in the patent consists of 2 wt% K2O, 31 wt% ZnO, and 67 wt% Al2O3. Urea (60.08 g) was dissolved in 60.7 g of MeOH. The solution was fed into a fixed bed reactor containing the catalyst that was maintained at 200 ˚C and a pressure of 2.0 MPa. Urea conversion was 100% and selectivity to DMC was 76.9%. The patent did not indicate which impurities were produced.

Source: Chemical Abstracts