Researchers at the Swiss Federal Institute of Technology (ETH) Zurich, Switzerland, have developed a carbon-supported platinum nanoparticle catalyst that can achieve complete hydrocracking of polypropylene into liquid hydrocarbons (C₅–C₄₅). With tuning, the catalyst can achieve a selectivity of 80% toward motor oil (C₂₁–C₄₅).

A paper on their work is published in ChemSusChem.

The recycling of plastic waste plays a large conceptual role in the quesst for the realization of a circular economy. As an indication of the industrial interest in this field, Neste and and Ravago recently announced plans to set up a joint venture to focus on chemical recycling of mixed waste plastic using a thermochemical liquefaction technology from Alterra Energy.

The Alterra technology transforms plastic destined for landfills back into petrochemical products that can be further refined into fuels, waxes and plastic production.

Polypropylene constitutes about 30% of all plastic waste. However, the ETH team notes, chemical recycling of polypropylene usually yields a mix of solid, liquid, and gaseous compounds as cleavage products. This suggests that the design of catalysts that can control the selectivity of this process is challenging.

In their work, the ETH researchers used a surfactant-free colloidal synthesis to obtain monodisperse Pt nanoparticles. The nanoparticles were supported on a carbon material synthesized via the carbonization of an aniline/phytic-acid-based polymer.

The team found that the metal and carrier phases work together. The platinum phase controls the activity, while the carbon carrier regulates selectivity. The carrier readily adsorbs large polypropylene chains and desorbs shorter hydrocarbon products of specific lengths.

The chain length at which products desorb can be tuned by changing the surface oxygen concentration on the carrier. Following this strategy, the selectivity of 80% toward motor oil (C₂₁–C₄₅) can be achieved.

The work provides some guidelines for catalyst design in the field of plastic hydrocracking.

Resources

• Shibashish D. Jaydev, Antonio J. Martin, Javier Pérez-Ramírez (2021) “Direct Conversion of Polypropylene into Liquid Hydrocarbons on Carbon‐Supported Platinum Catalysts,” ChemSusChem doi: 10.1002/cssc.202101999