Consumer Grade Polyethylene Recycling via Hydrogenolysis on Ultrafine Supported Ruthenium Nanoparticles

• Published in: Angewandte Chemie Vol. 136; no. 11
• Main Authors: Jaydev, Shibashish D., Martín, Antonio J., Usteri, Marc‐Eduard, Chikri, Katia, Eliasson, Henrik, Erni, Rolf, Pérez‐Ramírez, Javier
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 11.03.2024
• Subjects: Additives; Alkanes; Anatase; Catalysts; Catalytic converters; Chemical Plastic Recycling; Cleavage; Heterogenous Catalysis; High density polyethylenes; Hydrogenolysis; Isomerization; Low molecular weights; Molecular weight; Nanoparticles; Plastic debris; Polyethylene; Polyethylene Hydrogenolysis; Ruthenium; Ruthenium Nanoparticles; Selectivity; Ultrafines
• ISSN: 0044-8249; 1521-3757
• DOI: 10.1002/ange.202317526

Catalytic hydrogenolysis has the potential to convert high‐density polyethylene (HDPE), which comprises about 30 % of plastic waste, into valuable alkanes. Most investigations have focused on increasing activity for lab grade HDPEs displaying low molecular weight, with limited mechanistic understanding of the product distribution. No efficient catalyst is available for consumer grades due to their lower reactivity. This study targets HDPE used in bottle caps, a waste form generated globally at a rate of approximately one million units per hour. Ultrafine ruthenium particles (1 nm) supported on titania (anatase) achieved up to 80 % conversion into light alkanes (C1−C45) under mild conditions (498 K, 20 bar H2, 4 h) and were reused for three cycles. Small ruthenium nanoparticles were critical to achieving relevant conversions, as activity sharply decreased with particle size. Selectivity commonalities and peculiarities across HDPE grades were disclosed by a reaction modelling approach applied to products. Isomerization cedes to backbone scission as the reaction progresses. Within this trend, low molecular weight favor isomerization whilst high molecular weight favor cleavage. Commercial caps obeyed this trend with decreased activity, anticipating the influence of additives in realistic processing. This study demonstrates effective hydrogenolysis of consumer grade polyethylene and provides selectivity patterns for product control. Ruthenium particles of ∼1 nm supported on titania achieved via hydrogenolysis up to 80 % conversion of HDPE used in bottle caps into light alkanes at mild conditions and showed reusability. General selectivity trends were disclosed across HDPE types. Isomerization cedes to backbone scission as reaction progresses, nuanced by HDPE type.