Theoretical study on the catalytic pyrolysis mechanism of polyethylene terephthalate dimer

Abstract

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 Calkyl-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.