Insights into the hydrolysis/alcoholysis/ammonolysis mechanisms of ethylene naphthalate dimer using density functional theory (DFT) method.

Hydrolysis, alcoholysis and ammonolysis are viable routes for the efficient degradation and recycling of polyethylene naphthalate (PEN) plastic waste. Various possible hydrolysis/alcoholysis/ammonolysis reaction pathways for the degradation mechanism of the ethylene naphthalate dimer were investigated using the density functional theory (DFT) B3P86/6-31++G(d,p). To determine the thermodynamic and kinetic parameters, geometric structure optimization and frequency calculation were performed on a range of intermediates, transition states, and products associated with the reaction. The calculation results show that the highest energy barrier of the main element reaction step in hydrolysis is about 169.0 kJ/mol, the lowest is about 151.0 kJ/mol for ammonolysis, and the second is about 155.0 kJ/mol for alcoholysis. The main hydrolysis products of the ethylene naphthalate dimer are 2,6-naphthalenedicarboxylic acid and ethylene glycol; the main products of alcoholysis are dimethyl naphthalene-2,6-dicarboxylate and ethylene glycol, and the main products of ammonolysis are naphthalene-2,6-dicarboxamide and ethylene glycol. Furthermore, in the process of ethylene naphthalate dimer hydrolysis/alcoholysis/ammonolysis, the decomposition reaction in the NH3 atmosphere is better than that in methanol, and the reaction in CH3OH is better than that in the H2O molecular environment, and the increase in reaction temperature can increase its spontaneity. Our study presents the molecular mechanism of PEN hydrolysis/alcoholysis/ammonolysis and provides a reference for studying the degradation of other plastic wastes.

Insights into the thermal degradation mechanisms of polyethylene terephthalate dimer using DFT method.

The thermal degradation mechanisms of polyethylene terephthalate (PET) dimer were studied by the B3P86 density functional theory (DFT) approach at 6-31++G (d, p) base set in this paper. Seven possible reaction paths were designed and analyzed, and the thermodynamic parameters for all reactions were computed. The calculated results indicate that the bond dissociation energy values (BDEs) of C-C bonds on the main-chain are the smallest, followed by those of C-O bonds. The kinetics analysis indicates that the concerted reactions are obviously liable to occur rather than radical reactions in the initial thermal decomposition process. In the processes of initial reactions, all concerted reactions occurred by six-membered cyclic transition states (TSs) are more prone to carry out than those happened by four-membered cyclic transition states. The research results show that the primary products of PET dimer pyrolysis are terephthalic acid, vinyl terephthalate, CH3CHO and divinyl terephthalate. CH3CHO is mainly formed by a concerted reaction in the initial degradation process, and CO2 is mainly produced by the decarboxylation via a concerted reaction and CO is mainly produced by the decarbonylation of a radical in secondary degradation.

DFT studies on pyrolysis mechanisms of tetrabromobisphenol A (TBBPA).

Tetrabromobisphenol A (TBBPA) is the most widely used brominated flame retardant. In order to better understand the decomposition process of TBBPA and clarify the evolution process of the main pyrolysis products, the density functional theory (DFT) method PBE0/6-311G(d) has been used to investigate the pyrolysis mechanisms of TBBPA in this study. Seven possible pyrolysis reaction paths were proposed, and the kinetic parameters in all pyrolysis paths were calculated. The calculation results indicate that in initial degradation of TBBPA without the involvement of hydrogen radical, the demethylation reaction is the main pyrolysis reaction channel, and the keto-enol tautomerization reaction is the main competitive pyrolysis reaction channel. The brominated cyclohexadienone formed through the keto-enol tautomerization is prone to further debromination to generate Br radical. The involvement of hydrogen radical significantly lowers the energy barrier of TBBPA decomposition. When a hydrogen radical is involved in the pyrolysis process, the debromination reaction becomes the major pyrolysis reaction channel, and the homolytic cleavage of Caromatic-C bond becomes the major competitive pyrolysis reaction channel.

[Experimental study on methane potentials of source-separated BMW and individual waste materials].

A laboratory procedure is described for measuring methane potentials of source-separated bio-organic municipal waste (BMW). Triplicate reactors with about 20 grams fresh material were incubated at 37 degrees C with 300 mL inoculum from Shenyang wastewater treatment plant and the methane production was followed over a 50 d period by regular measurement of methane on a gas chromatograph. At 37 degrees C, the methane production efficiency of source-separated BMW and individual waste materials was: starch > BMW > protein > food oil > fat > paper. For the source-separated BMW,starch,protein,food oil,fat and paper, the methane potential (CH4/VS) of 218.15, 209.11, 194.20, 238.86, 257.82 and 131.41 mL/g were found,and ultimate biodegradability of 6 difference materials were 67.73%, 72.88%, 65.84%, 78.38%, 74.11% and 47.98%, respectively.