Density functional theory study on thermal degradation mechanism of ethylene terephthalate
Mechanism degradation of ethylene terephthalate momer was investigated by density functional theory B3P86/6-31 + +G(d,p)method,the possible reaction paths of pyrolysis/hydrolysis/alcoholysis and catalytic degradation were designed,the geometric structures of various intermediates,transition states,and products in-volved in the reaction were optimized,and their frequencies were calculated to gain the thermodynamic and ki-netic parameters.The calculation results show that:When water or methanol is used as a catalyst in the ethylene terephthalate process of thermal degradation,the use water or methanol O-H provides H to the main chain of the ethylene terephthalate ester bond on the carbonyl O atom is form terephthalic acid,and ethyl C off H atoms and(water)hydroxyl(-OH)or(methanol)methoxy group(-OCH3)are combined to form new water or methanol,thereby reducing the reaction energy barriers during the pyrolysis of ethylene terephthalate(251.4 kJ/mol→181.1 kJ/mol(methanol)and 187.5 kJ/mol(water)).When water or methanol is reactant in the ther-mal degradation process of ethylene terephthalate,H in water or methanol O-H is supplied to the carbonyl O at-om of the main chain of ethylene terephthalate to form ethylene glycol.Hydroxy group(-OH)in water or me-thoxy group(-OCH3)in methanol binds to the carbonyl C atom of the carbonyl group of ethylene terephthalate backbone to form terephthalic acid or mono-methyl terephthalate,it further reduces the reaction energy barriers(156.4 kJ/mol(methanol)and 170.1 kJ/mol(water))during the pyrolysis of ethylene terephthalate.In the reaction process,either water/methanol as catalysis or water/methanol as reactants can reduce the reaction ener-gy barrier of the main element step to a certain extent,so that the reaction is easy to proceed.
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