Smak Tom J, de Peinder Peter, Van der Waal Jan C, Altink Rinke, Vollmer Ina, Weckhuysen Bert M
Inorganic Chemistry and Catalysis group, Debye Institute for Nanomaterials Science and Institute for Sustainable and Circular Chemistry, Utrecht University, Universiteitsweg 99, 3584 CG, Utrecht, The Netherlands.
TNO, Brightsite, Urmonderbaan 22, 6167 RD, Geleen, The Netherlands.
ChemSusChem. 2024 Apr 8;17(7):e202301198. doi: 10.1002/cssc.202301198. Epub 2023 Dec 13.
To reduce the pressure on the environment created by the increasing amount of plastic waste, the need to develop suitable plastic recycling methods has become more evident. However, the chemical recycling toolbox for polyethylene (PE), the most abundant type of plastic waste, remains underdeveloped. In this work, analytical methods were developed to explore the possibility to oxidatively convert PE into di-carboxylic acids as reaction products. A multi-analytical approach including gas chromatography-mass spectrometry, gas chromatography-flame ionization detection, several (2D) nuclear magnetic resonance methods as well as in-situ transmission infrared spectroscopy was used. This led to a thorough qualitative and quantitative analysis on the product mixture, which extends and clarifies the existing literature. Without a catalyst (thermally) already up to 7 mol % di-carboxylic acids can be formed. Furthermore, it was found that the majority of the oxidized functionalities are carboxylic acids, (methyl) ketones, γ-lactones, γ-ketones and esters. An intra-molecular hydrogen shift seemed key in the cleavage step and the formation of late-stage side products. In addition, crosslinking reactions due to esterification reactions seem to limit the di-carboxylic acid yield. Therefore, these two handles can be taken into account to study and design similar (catalytic) systems for the oxidative conversion of plastic waste.
为了减轻日益增多的塑料垃圾对环境造成的压力，开发合适的塑料回收方法的需求变得愈发明显。然而，针对聚乙烯（PE）这种最常见的塑料垃圾的化学回收方法仍不完善。在这项工作中，我们开发了分析方法来探索将PE氧化转化为二羧酸作为反应产物的可能性。我们采用了多种分析方法，包括气相色谱 - 质谱联用、气相色谱 - 火焰离子化检测、几种（二维）核磁共振方法以及原位透射红外光谱法。这使得我们能够对产物混合物进行全面的定性和定量分析，扩展并澄清了现有文献。在无催化剂（热反应）的情况下，已能形成高达7 mol%的二羧酸。此外，我们发现氧化官能团主要是羧酸、（甲基）酮、γ - 内酯、γ - 酮和酯。分子内氢迁移似乎是裂解步骤和后期副产物形成的关键。此外，酯化反应导致的交联反应似乎限制了二羧酸的产率。因此，在研究和设计类似的用于塑料垃圾氧化转化的（催化）系统时，可以考虑这两个因素。
