Chemical upcycling of PVC-containing plastic wastes by thermal degradation and catalysis in a chlorine-rich environment.

Autor: Kang, Jisong, Kim, Ju Young, Sung, Suhyeon, Lee, Yerin, Gu, Sangseo, Choi, Jae-Wook, Yoo, Chun-Jae, Suh, Dong Jin, Choi, Jungkyu, Ha, Jeong-Myeong
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Zdroj: Environmental Pollution; Feb2024, Vol. 342, pN.PAG-N.PAG, 1p
Abstrakt: Chlorine (Cl)-containing chemicals, including hydrogen chloride, generated during thermal degradation of polyvinyl chloride (PVC) and corresponding mixture impede the chemical recycling of PVC-containing plastic wastes. While upgrading plastic-derived vapors, the presence of Cl-containing chemicals may deactivate the catalysts. Accordingly, herein, catalytic upgrading of pyrolysis vapor prepared from a mixture of PVC and polyolefins is performed using a fixed-bed reactor comprising zeolites. Among the H-forms of zeolites (namely, ZSM-5, Y, β, and chabazite) used in this study, a higher yield of gas products composed of hydrocarbons with lower carbon numbers is obtained using H-ZSM-5, thus indicating further decomposition of the pyrolysis vapor to C 1 –C 4 hydrocarbons on it. Although the formation of aromatic compounds is better on H-ZSM-5, product distributions can be adjusted by further modifying the acidic properties via the alteration of the Si/Al molar ratio, and maximum yields of C 1 –C 4 compounds (60.8%) and olefins (64.7%) are achieved using a Si/Al molar ratio of 50. Additionally, metal ion exchange on H-ZSM-5 is conducted, and upgrading of PVC-containing waste-derived vapor to aromatic chemicals and small hydrocarbon molecules was successfully performed using Co-substituted H-ZSM-5. It reveals that the highest yield of gas products on 1.74 wt% cobalt (Co)-substituted H-ZSM-5 is acquired via the selection of an appropriate metal and metal ion concentration adjustment. Nevertheless, introduction of excess Co into the H-ZSM-5 surface decreases the cracking activity, thereby implying that highly distributed Co is required to achieve excellent cracking activity. The addition of Co also adjusted the acid types of H-ZSM-5, and more Lewis acid sites compared to Brønsted acid sites selectively produced olefins and naphthenes over paraffins and aromatics. The proposed approach can be a feasible process to produce valuable petroleum-replacing chemicals from Cl-containing mixed plastic wastes, contributing to the closed loops for upcycling plastic wastes. [Display omitted] • PVC-containing mixture was converted to hydrocarbons by thermolysis and catalysis. • Chlorine from PVC was removed by thermal and catalytic processes. • 15.9% yield of aromatics using H-ZSM-5 with Si/Al = 100 mol/mol. • 91.7% yield of C 1 –C 12 hydrocarbons using 1.74 wt% Co-substituted H-ZSM-5. [ABSTRACT FROM AUTHOR]
Databáze: Supplemental Index
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