Scientific Achievement
For the hydrogenolysis of polyethylene, product molecular weight was independent of the starting molecular weight and was instead controlled by the length and density of branches. Conversely, for polypropylene, tacticity significantly affected product molecular weight, however, the same product microstructure was observed in all cases.
Significance and Impact
Modern solutions to plastic waste will need to combat mixed and varied polymer waste streams. This work highlights that certain properties, such as stereochemistry in branching, affect product molecular weight and microstructure, while others, such as molecular weight, have little effect and are therefore less of a concern when evaluating catalyst design.
Research Details
- Polyethylenes of varying molecular weight and branch density and polypropylenes of varying molecular weight and tacticity were converted to lower molecular weight liquid products using a Pt nanoparticle on strontium titanate nanocuboids (Pt/STO) catalyst under solvent free-conditions with 170 psi of H2 at 300 °C.
- Gaseous product distributions were obtained by direct headspace analysis, while liquid products were evaluated for yield, molecular weight, branch density, and branch length.
- Hydrogenolysis of isotactic polypropylene was also conducted using D2 to determine the extent of dehydrogenation, C–C bond cleavage, and skeletal rearrangement mechanisms.
R. Hackler, J.V. Lamb, I. Peczak, R. Kennedy, U. Kanbur, A. LaPointe, K. Poeppelmeier, A. Sadow, M. Delferro, “The effect of the macro- and microstructure on catalytic hydrogenolysis of polyolefins” Macromolecules 2022, https://doi.org/10.1021/acs.macromol.2c00805
Supported by the Institute for Cooperative Upcycling of Plastics (iCOUP), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under contracts DE-AC-02- 06CH11357 and DE-AC-02-07CH11358.