H₂‐free Plastic Conversion: Converting PET back to BTX by Unlocking Hidden Hydrogen

Abstract

The strong desire for a circular economy makes obtaining fuels and chemicals via plastic degradation an important research topic in the 21st century. Here, the first example of the H 2 -free polyethylene terephthalate (PET) conversion to BTX (benzene, toluene and xylene) was achieved by unlocking hidden hydrogen in the ethylene glycol part over Ru/Nb 2 O 5 catalyst. Among the whole process (hydrolysis, reforming and hydrogenolysis/ decarboxylation), the parallel hydrogenolysis and decarboxylation were competing and the rate-determining step. Ru/Nb 2 O 5 exhibited superior hydrogenolysis and poorer decarboxylation performance in direct comparison with Ru/NiAl 2 O 4 , accordingly contributing to the distinct selectivity to alkyl aromatics among BTX. Ru species on Nb 2 O 5 , unlike those on NiAl 2 O 4 , showed more Ru δ + species owing to the strong interaction between Ru and Nb 2 O 5 , restricting the undesired decarboxylation. Along with NbO x species for CÀ O bond activation, excellent reactivity towards the H 2 -free conversion of PET back to BTX with alkyl aromatics as dominant species was achieved. This H 2 -free system was also capable of converting common real PET plastics back to BTX, adding new options in the circular economy of PET.

Recent Advancements in Plastic Packaging Recycling: A Mini-Review

“…More complex phosphine ligands have also been tested, but the economic viability on an industrial scale seems to be rather limited [147] (Table 1, entries 2-3). Two very important studies have been published on the efficient conversion of postconsumer PET to benzene, toluene, and xylenes by reportedly "unlocking hidden hydrogen in the ethylene glycol part" with Ru/Nb 2 O 5 catalyst [156,157]. The hydrogen is formed in situ during the reaction from ethylene glycol, and it appears that, in the presence of Ru/Nb 2 O 5 , two different pathways (decarboxylation and hydrogenolysis) compete to determine the selectivity toward alkyl-aromatic compounds (Table 1, entries 4-5) [156].…”

Waste to Wealth: Chemical Recycling and Chemical Upcycling of Waste Plastics for a Great Future

“…From the perspective of chemical bond activation and cleavage, Wang et al fabricated a multifunctional Ru/Nb 2 O 5 catalyst to break CÀ O and CÀ C bonds in various aromatic waste plastics (e. g., PET, PPO, PS, and PC) for the production of monocyclic arenes by hydrogenolysis. [39] The hydrogen species is either from external added H 2 or from the reforming of the ethylene glycol units in PET. [39a] Main products obtained over Pd/Nb 2 O 5 and Pt/Nb 2 O 5 were saturated ring products due to the strong hydrogenation ability of Pd and Pt (Figure 6a).…”

“…With the assistance of the hydrogen species dissociated from the small particle Ru, the precise activation and cleavage of CÀ O and CÀ C bond within aromatic plastics is achieved (Figure 6d). [39] Interestingly, it was found that Ru/Nb 2 O 5 also exhibited poor decarboxylation performance than Ru/NiAl 2 O 4 , because the strong interaction between Ru and Nb 2 O 5 results in the presence of more positively charged Ru species (Figure 6c), restricting the undesired decarboxylation reaction. [39a] The Ru/ Nb 2 O 5 catalyst can not only convert a single aromatic plastic, but also realize the direct conversion of mixed aromatic plastics into arenes with high selectivity, resulting in aromatic yields as high as 75-85 % (Figure 6e).…”

Recent Progress in the Chemical Upcycling of Plastic Wastes

“…The Ru/Nb 2 O 5 system enables a selective and effective way for the chemical upcycling of waste aromatic plastics into the valuable arenes contributing to the future establishment of the circular plastic economy. Afterwards, Wang and co-workers developed a H 2 -free route to convert PET into BTX (benzene, toluene, xylene) products in water by using the Ru/Nb 2 O 5 catalyst, [42] in which the reaction of hydrolysis [the H 2 needed originated from the ethylene glycol (EG) intermediate], reforming and hydrogenolysis/decarboxylation happened, adding new options in the circular economy of PET.…”