私たちのプラスチック廃棄物は、改良された触媒法のおかげで、洗剤の原料として使用することができる。(Our plastic waste can be used as raw material for detergents, thanks to an improved catalytic method)

2023-08-16 カリフォルニア大学サンタバーバラ校(UCSB)

＜関連情報＞

• https://www.news.ucsb.edu/2023/021175/our-plastic-waste-can-be-used-raw-material-detergents-thanks-improved-catalytic-method
• https://www.cell.com/chem/fulltext/S2451-9294(23)00249-8

ポリエチレンの二官能性タンデム触媒による界面活性アルキルアロマティックへのアップサイクル Bifunctional tandem catalytic upcycling of polyethylene to surfactant-range alkylaromatics

Jiakai Sun,Yu-Hsuan Lee,Ryan D. Yappert,Anne M. LaPointe,Geoffrey W. Coates,Baron Peters,Mahdi M. Abu-Omar,Susannah L. Scott
Chem  Published:June 07, 2023
DOI:https://doi.org/10.1016/j.chempr.2023.05.017

Highlights

•H₂ redistribution converts polyethylene to surfactant-range alkylaromatics
•Metal/acid bifunctional catalysts are more effective than either component separately
•Strong Brønsted acid sites control rates of C–C bond scission, isomerization, and cyclization
•Metal and acid sites are not required to be in close proximity

The bigger picture

Exponential growth in the worldwide use of plastics, as well as in the generation of plastic waste, have combined to create an increasingly visible environmental burden and have elicited calls for a broader range of recycling strategies to mitigate the problem. Conversion of waste polyolefins to large-scale chemicals has the potential to divert plastic waste from landfills and municipal incinerators, displace fossil feedstocks used in conventional chemical manufacturing, and provide economic incentives for collection and recycling.

In this report, strong Brønsted acid sites act in concert with Pt nanoparticles to accelerate the selective transformation of polyethylene to surfactant-range aromatic chemicals. The bifunctional catalysts improve the viability of chemical upcycling of waste polyolefins as an alternative strategy complementary to mechanical recycling.

Summary

Catalytic conversion of waste polyolefins to value-added alkylaromatics could contribute to carbon recycling. Compared with tandem hydrogenolysis/aromatization of polyethylene (PE) catalyzed by Pt/γ-Al₂O₃ at 280°C, both a 5-fold enhancement in the rate of C–C bond scission and a doubling of the molar yield of alkylaromatics were achieved using a more acidic Pt/F-Al₂O₃ catalyst instead. Bifunctional (metal/acid) catalysts also generate alkylaromatic products with lower average carbon numbers (ca. C₂₀), similar to conventional anionic surfactants. Because physical mixtures of weakly acidic Pt/γ-Al₂O₃ or non-acidic Pt/SiO₂ with strongly Brønsted acidic Cl-Al₂O₃ or F-Al₂O₃ are also effective, the tandem reaction does not require nanoscale intimacy between metal and acid active sites. Kinetic studies using triacontane (norm-C₃₀H₆₂) as a model for PE show that the Pt-catalyzed dehydrogenation/hydrogenation reactions are quasi-equilibrated, while the acid-catalyzed C–C bond scission and skeletal transformations (isomerization and cyclization) determine the overall rates of depolymerization and aromatic formation.