Kinetics of glycolysis of poly(ethylene terephthalate) melts

Abstract

SYNOPSISThe reaction of poly(ethy1ene terephthalate) (PET) melts with ethylene glycol was examined in a pressure reactor at temperatures above 245°C. The reaction rate was found to depend on temperature and on the concentrations of liquid ethylene glycol and of ethylene diester groups in the polymer. A kinetic model proposed for the initial period of the reaction was found to be consistent with experimental data. It was found that internal catalysis by ethylene glycol does not play a n important role in the glycolytic depolymerization of PET.The rate constants for glycolysis were calculated for three different temperatures, yielding an activation energy of 92 kJ/mol. Zinc salts, which have a catalytic effect on glycolysis of P E T below 245"C, do not appear to influence glycolysis rates above that temperature.

Recent Developments in the Chemical Recycling of PET

“…Studies on the kinetics of PET glycolysis (Campanelli et al, 1994b;J. Chen & L. Chen, 1999) have shown that glycolysis without a catalyst is very slow and complete depolymerization of PET to BHET cannot be achieved.…”

“…Although metal salts are effective in increasing the PET glycolysis rate, it should be noted that zinc salts, and presumably other metal salts, have a catalytic effect on glycolysis of PET only below 245 °C, and apparently do not promote any further increase in the reaction rate above that temperature due to mass transfer limitations (Campanelli et al, 1994b). Thus, a need to develop new catalysts that can overcome this limitation.…”

Despolimerização do poli (tereftalato de etileno) - PET: efeitos de tensoativos e excesso de solução alcalina

“…• b -uso de altas temperaturas [8][9][10] ; e • c -altas pressões [10,11] . Em trabalhos recentes Ruvolo Filho e colaboradores estudaram a despolimerização do PET [12][13][14][15] e mostraram usando soluções de NaOH em etilenoglicol 1,1 mol.L -1 [12] que a cinética de despolimerização abaixo da temperatura de fusão do PET é um processo heterogêneo que ocorre na superfície do PET e depende da velocidade de agitação em que é realizada a reação.…”

“…Outros pesquisadores tem estudado a reciclagem do PET [16][17][18][19][20][21][22][23][24] e encontrado resultados semelhantes usando solução aquosa de NaOH em proporções equimolares com PET em temperaturas e ou pressões menores mas, em maiores tempos de reação [16][17][18][19][20] . Existem poucos trabalhos usando catalisadores [9] para aumentar o rendimento da reação de despolimerização do PET.…”

Synthesis of Unsaturated Polyester Resins from PET Wastes: Effect of a Novel Co-catalytic System on Glycolysis and Polyesterification Reactions

“…The activation energy for the uncatalyzed glycolysis is about 32 kcal/mol, whereas a proper catalyzed process requires less than 20 kcal/mol [25]. Thus, various metal-containing catalysts, such as zinc acetate [26][27][28][29][30], lead-, cobalt-or manganese acetate [26,29,30] and titanium alkoxides [31] or other titanium compounds [5,25] such as titanium (IV)-phosphate compound were used to facilitate the process. Zinc acetate is the most efficient catalyst in comparison with other metal-acetate compounds.…”