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)

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2023-08-16 カリフォルニア大学サンタバーバラ校(UCSB)

◆カリフォルニア大学サンタバーバラ校(UCSB)の研究者たちは、使い捨てのプラスチック包装を有用な原料に再構築する革新的なプロセスを改善し、それを価値あるアルキルアロマティックス(界面活性剤の基となる分子)に変換する方法を開発しました。
◆このプロセスにより、石油由来の原料から分子を作る代わりに、廃プラスチックから再利用されることで、環境への負荷を軽減し、プラスチックの有効活用が促進されます。これにより、プラスチックごみ処理の新たなアプローチが提案され、持続可能な環境への貢献が期待されています。

<関連情報>

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

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)

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.

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