Theoretical study on the catalytic pyrolysis mechanism of polyethylene terephthalate dimer

ABSTRACT

In this paper, the density functional theory of B3P86/6–31++G(d,p) method was used to study the mechanism of the catalytic pyrolysis reactions of PET dimer. The calculated results show that the reaction energy barrier for calcium oxide to capture a proton on carboxyl group (at 112.6 kJ/mol) is lower than that on alkyl group (at 153.3 ~ 170.0 kJ/mol), which is more conducive to decarboxylation reaction. The protons provided by the acid catalyst attack the oxygen atoms of the C=O bond of PET main chain to form the cationic intermediate, and then the cleavage reaction occurs on the C_alkyl-O bond, of which the bond dissociation energy is the lowest at 46.9 ~ 62.4 kJ/mol. Compared with pure pyrolysis, catalysts have little effect on the components of initial pyrolysis products, but it has effects on the components of secondary pyrolysis products of PET. The addition of catalysts can change the components of secondary pyrolysis products by changing the optimal reaction path of degradation. During the reaction processes, both alkaline and acidic catalysts can reduce the reaction energy barriers of the main elementary reactions to a certain extent (from 251.3 ~ 264.6 kJ/mol to 112.6 ~ 170.0 and 46.9 ~ 169.1 kJ/mol, respectively), making the reactions easier to proceed.

KEYWORDS:

• Polyethylene terephthalate dimer
• density functional theory method
• catalytic pyrolysis
• reaction mechanism
• waste recycling

Disclosure statement

No potential conflict of interest was reported by the authors.

Author Contributions

Guiying Pan: writing – original draft preparation. Yao Wang: investigation, reviewing, and editing. Qiujing Jin and Hanxian Meng: data arrangement and analysis. Jinbao Huang: methodology, reviewing, and funding acquisition. Sijia Li and Weifeng Xu: supervision. Hong Wang: supervision and project administration. Weiwei Xu and Li Jin: conceptualization, reviewing, and editing. All authors read and approved the final manuscript.

Data availability statement

The data that support the findings of this study are available from the corresponding author, Jinbao Huang, upon request.

Additional information

Funding

This work was supported by Guizhou Provincial Science and Technology Projects (No. ZK[2021]278, ZK[2022]198) and Construction Project of Characteristic Key Laboratory in Guizhou Colleges and Universities (No. KY[2021]003).