Polypropylene Plastic Waste Conversion to Lubricants over Ru/TiO₂ Catalysts

Abstract

Plastic recycling and upcycling are required to combat the environmental crisis from landfilling consumer products. Chemocatalytic technologies are the most promising approach to achieve this. Here, we show that ruthenium deposited on titania is an active and selective catalyst in polypropylene breakdown into valuable lubricant-range hydrocarbons with narrow molecular weight distribution and a low methane formation at low temperatures of 250 °C with a modest H 2 pressure. Amorphous polypropylene and everyday bags and bottles were also effectively converted to lubricants with yields up to 80+%. 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.

Sustainable chemical upcycling of waste polyolefins by heterogeneous catalysis

“…Thus, the reported reaction temperatures for Pt catalysts on polyolefin hydrogenolysis are relatively high (250−300°C) and the degradation time is fairly long 59,60 . As a cheaper active metal for hydrogenolysis, Ru‐based catalysts have drawn much attention in recent studies to catalyze polyolefins (including HDPE, LDPE, PP, waste polyolefins) to liquid fuels under mild conditions, with a reaction temperature of 200−250°C, H 2 pressure of 0−6 MPa, and reaction time from 0−12 h 56,61–64 . However, the following challenges still exist in this reaction: (1) high yield of low‐value gases (predominantly methane), generally above 10%, and (2) the long reaction time compared to the hydrocracking reaction.…”

Expanding Plastics Recycling Technologies: Chemical Aspects, Technology Status and Challenges

“…Ruthenium supported on metal oxides or carbon has been reported to catalyze the production of alkanes, aromatics, and liquid fuels from polyolefins (i.e., LDPE, HDPE, PP), PS, and PC. [881][882][883][884][885][886][887] LDPE, HDPE, and PP can be converted to liquid fuel (C5-C21) and lubricants/waxes (C22-C45) at low temperature and low H2 pressure (i.e., 200-250 °C, 20-30 bar) on metal oxides-supported Ru (e.g., Ru/TiO2, Ru/CeO2). [881][882] Over multifunctional Ru/Nb2O5, monocyclic aromatics can be selectively produced from single or mixed aromatic plastics (i.e., PET, PC, PS, polyphenylene oxide) at 200-320 °C in the presence of hydrogen and solvent (e.g., water, octane etc.).…”

“…[881][882][883][884][885][886][887] LDPE, HDPE, and PP can be converted to liquid fuel (C5-C21) and lubricants/waxes (C22-C45) at low temperature and low H2 pressure (i.e., 200-250 °C, 20-30 bar) on metal oxides-supported Ru (e.g., Ru/TiO2, Ru/CeO2). [881][882] Over multifunctional Ru/Nb2O5, monocyclic aromatics can be selectively produced from single or mixed aromatic plastics (i.e., PET, PC, PS, polyphenylene oxide) at 200-320 °C in the presence of hydrogen and solvent (e.g., water, octane etc.). 883 Ru hydrogenation sites with low coordination numbers (i.e., 5-6) prevent the over-hydrogenating of the aromatics, while the surface Lewis acid and Brønsted acid sites on NbOx species act in concert to selectively adsorb, activate C-O bonds, and cleave C-C bonds of the plastics.…”

Effect of reaction conditions on the hydrogenolysis of polypropylene and polyethylene into gas and liquid alkanes

“…[10][11][12][13] Numerous recent reports are focusing on hydrogenolysis as a conversion strategy (Table 1 (ref. [14][15][16][17][18][19][20][21][22][23][24]). While several platinum (Pt)-group metals are being explored, Ru-based catalysts are attracting most of the attention from the research community.…”