Consumer Grade Polyethylene Recycling via Hydrogenolysis on Ultrafine Supported Ruthenium Nanoparticles

Abstract

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.

Hierarchical FAU Zeolites Boosting the Hydrocracking of Polyolefin Waste into Liquid Fuels

“…The exponential surge in plastic consumption and waste accumulation, with polyolefins alone constituting 70% of the total, poses a global environmental challenge. − The C–C backbone in polyolefins makes them durable as consumer goods but resistant to degradation after service life. − Upcycling polyolefin wastes into value-added fuels represents a promising approach, including the hydrocracking technique that employs a bifunctional metal-acid catalyst and produces highly branched gasoline, diesel, and jet fuels. , …”

Chemical Upcycling of Polyolefin Plastics Using Structurally Well-defined Catalysts

“…However, the pyrolysis reaction is typically endothermic and requires high temperatures (>400 °C), , which increases energy cost of the process and simultaneously lowers product selectivity. , More thermodynamically favorable hydrocracking can be carried out at lower temperatures (250–375 °C) than pyrolysis, but it leads to heavily isomerized branching alkane products. , Compared to pyrolysis and hydrocracking, catalytic hydrogenolysis is usually exothermic, which can convert PO into more desirable linear alkane products under milder conditions (≤300 °C) . The H 2 -rich environment during hydrogenolysis can promote the cleavage of C–C bonds, the hydrogenation of intermediates to form alkanes, and the suppression of coke deposition and isomerization, the main obstacle of pyrolysis and hydrocracking. − ,, …”

“…22 The H 2 -rich environment during hydrogenolysis can promote the cleavage of C−C bonds, the hydrogenation of intermediates to form alkanes, and the suppression of coke deposition and isomerization, the main obstacle of pyrolysis and hydrocracking. [17][18][19][20]22,23 Previous studies on C−C hydrogenolysis were mostly carried out on small alkanes in the gas phase. This could be very different from PO hydrogenolysis, which needs to be carried out in the condensed phase.…”

“… 22 The H 2 -rich environment during hydrogenolysis can promote the cleavage of C–C bonds, the hydrogenation of intermediates to form alkanes, and the suppression of coke deposition and isomerization, the main obstacle of pyrolysis and hydrocracking. 17 − 20 , 22 , 23 …”