Pyrolytic Depolymerization of Polyolefins Catalysed by Zirconium-based UiO-66 Metal-Organic Frameworks

Area of Science:

• Materials Science
• Catalysis
• Polymer Chemistry

Background:

• Polyolefins, including polyethylenes and polypropylenes, are major plastic waste streams.
• Their chemical inertness makes them challenging to recycle into valuable products.
• Pyrolysis offers a scalable method for converting mixed, contaminated plastics into petrochemicals.

Purpose of the Study:

• To investigate the efficacy of Metal-Organic Frameworks (MOFs) as catalysts for polyolefin depolymerization via pyrolysis.
• To address the limitations of MOFs, such as thermal instability and pore accessibility, in polyolefin conversion.
• To demonstrate the potential of MOFs to enhance hydrocarbon yields and reduce waste in plastic recycling.

Main Methods:

• Utilized UiO-66 MOFs with coordinatively-unsaturated zirconium nodes as catalysts for polyolefin pyrolysis.
• Characterized the penetration of polyolefins into MOF pores at pyrolytic temperatures.
• Analyzed the resulting hydrocarbon products and residual solids.

Main Results:

• UiO-66 MOFs significantly enhanced the yields of liquid and gas hydrocarbons from polyolefin pyrolysis.
• The amount of residual solid waste was reduced by half compared to non-catalytic pyrolysis.
• Demonstrated unambiguous polyolefin penetration into UiO-66 pores, enabling C-C bond cleavage within the MOF structure.
• Achieved aliphatic hydrocarbon product distributions distinct from zeolite-catalyzed reactions.

Conclusions:

• UiO-66 MOFs are effective heterogeneous catalysts for the pyrolysis of polyolefins, offering a promising route for plastic waste valorization.
• The catalytic activity stems from Lewis-acidic Zr-oxo nodes accessible within the MOF pores.
• MOFs represent a highly designable class of catalysts that can complement existing technologies for plastic depolymerization.