Researchers at the University of Delaware have shown that ruthenium deposited on titania is an active and selective catalyst for breaking down polypropylene into valuable lubricant-range hydrocarbons with narrow molecular weight distribution and low methane formation at low temperatures of 250 °C with a modest H2 pressure.
They were able to convert amorphous polypropylene and everyday bags and bottles effectively to lubricants with yields up to 80+%. A paper on their work is published in the journal ACS Catalysis.
Quantification of critical properties, including pour point, kinematic viscosity, and viscosity index, indicates that the products are promising alternatives to currently used base or synthetic oils. The reaction network involves the sequential conversion of polymer into the oil with a gradual decrease of molecular weight until ∼700–800 g/mol and slow liquid gasification to methane and ethane.
NMR, ATR-IR, GCMS, and isotopic labeling experiments expose the complexity of structure and reaction evolution whereby hydrogenolysis involves intermediate dehydrogenation with synchronous loss of polypropylene stereoregularity.
Conventional plastics recycling uses mechanical processes in which post-consumer plastics are collected, processed, and reintroduced into a plastics manufacturing stream. Plastic recycling and upcycling are required to combat the environmental crisis from landfilling consumer products. Chemocatalytic technologies—such as that described in the paper—are emerging as a more promising approach to achieve plastic recycling and upcycling.
Pavel A. Kots, Sibao Liu, Brandon C. Vance, Cong Wang, James D. Sheehan, and Dionisios G. Vlachos (2021) “Polypropylene Plastic Waste Conversion to Lubricants over Ru/TiO2 Catalysts” ACS Catalysis doi: 10.1021/acscatal.1c00874