June 13, 2011
Here’s a biobased route to propylene glycol. Green chemicals and polymers continue to generate increasing interest and activity in the chemical industry. It is clear that a certain percentage of end users, primarily in the packaging industry, are willing to pay a premium for so-called “green” polymers and plastics. The question is: Can viable green chemical and plastics industries be built on the premise of premium pricing?
In the long run, green products must compete on price with conventional hydrocarbon-based chemicals and plastics. There is therefore a need to develop new processes and catalysts that can transform biobased feedstocks into monomers and intermediates with very high selectivity.
G. J. Suppes, W. R. Sutterlin, and M. Dasari describe a process and catalyst system for converting biodiesel glycerol to propylene glycol in good selectivity. The invention is based on the idea that glycerol can be first dehydrated to hydroxyacetone (“acetol”), which can then be hydrogenated to propylene glycol.
The inventors conducted two experiments to support the process:
- Glycerol was converted to acetol over a copper chromite [(CuO)x(Cr2O3)y] catalyst at 180–220 °C and 34–96 MPa pressure. Hydrogen was not used in this step. The acetol was formed in this step, but no data are given as to selectivity or conversion.
- The catalyst used in the first step was used to hydrogenate the acetol at a temperature of 180–220 °C and a pressure of 1–25 bar. Again, no yield data are given.
In separate experiments, glycerol was converted directly to propylene glycol with the same catalyst. The inventors found that glycerol water content plays a major role in propylene glycol yield. If the water content is 80%, conversion is only 33.5% and propylene glycol selectivity is only 64.8%. If the water content is reduced to 20%, however, glycerol conversion increases to 54.8% and selectivity to 85.0%. (The Curators of the University of Missouri [Columbia]. US Patent 7,943,805, May 17, 2011; Jeffrey S. Plotkin)