Chemical Recycling and Kinetics of Aqueous Alkaline Depolymerization of Poly(Butylene Terephthalate) Waste

Abstract

reactions of poly(butylene terephthalate) (PBT) waste in aqueous sodium hydroxide solution were carried out in a batch reactor at 80±140 C at atmospheric pressure by varying PBT particle size in the range of 50±512.5 lm. Reaction time was also varied from 10±110 min to understand the influence of PBT particle size and reaction time on the batch reactor performance. Agitator speed, particle size of PBT and reaction time required were optimized. Disodium terephthalate (salt) and 1,4-butanediol (BD) remain in the liquid phase. BD was recovered by the salting-out method. Disodium terephthalate was separated by acidification to obtain solid terephthalic acid (TPA). The produced monomeric products (TPA and BD) and PBT were analyzed. The yields of TPA and BD were in agreement with PBT conversion. The depolymerization reaction rate was first order to PBT concentration as well as first order to sodium hydroxide concentration. The acid value of TPA changes with the reaction time as well as particle size of PBT. This indicates that PBT molecules get fragmented and hydrolyze simultaneously with aqueous sodium hydroxide to produce BD and disodium terephthalate. Activation energy, Arrhenius constant, equilibrium constant, Gibbs free energy, enthalpy and entropy were determined. The dependence of the hydrolysis rate constant on reaction temperature was correlated by the Arrhenius plot, which shows an activation energy of 25 kJ/mol and an Arrhenius constant of 438 L/min/cm 2 .

Fast Hydrolyzable Constitutional Isomer of Poly(butylene terephthalate) and Its Copolyesters with 1,4-Butanediol

“…The 1 H and 13 C NMR spectra of all compositions are given in the Supporting Information (SI) (Figures S2 and S3) and mainly confirm the condensation of S with BDM and B. A closer look at the NMR spectra showed small additional signals with an increase in the BDM content.…”

“…In addition, two signals at 4.49 and 3.46 ppm (10″ and 3′) could be seen for PB 54 BDM 46 S. These signals show the presence of unavoidable ether linkages in the polymer backbone by self/crosscondensation of diols at high temperatures. 33,34 The microstructure of the PB x BDM y S copolyesters was determined by 13 C NMR analysis to clarify the distribution of B and BDM units along the polymer chain. Therefore, the signals of the carbonyl carbon atoms of succinic acid in the S2, showing the total randomness of the microstructure in all cases.…”

“…Analytical Methods. 1 H (300 MHz) and 13 C (75 MHz) NMR spectra were recorded on an Ultrashield-300 spectrometer (Bruker) in CDCl 3 , using the undeuterated solvent's residue peak as an internal standard. ACD/NMR Processor Academic Edition, version 12.01, was used for the analysis of NMR spectra.…”

Polyoxometalate-Induced Efficient Recycling of Waste Polyester Plastics into Metal–Organic Frameworks

“…11 Besides, these stringent reaction conditions, many complicated steps are involved, thus, imposing large energy consumption and enormous environmental threats. Except for PET, other polyester plastics such as PBT also face similar problems; 12 hence, strategies that could efficiently hydrolyze polyester plastics and further convert them into economically valuable products without incurring additional pollution concerns are long-sought-after.…”

Pyrolysis versus hydrolysis behavior during steam decomposition of polyesters using18O-labeled steam

“…The ester bonds in polyester chains are well known to be cleaved by pyrolysis and hydrolysis. Both reactions enable the depolymerization of high-molecular-weight polyesters into monomers; thus, are commonly applied for the feedstock recycling of waste polyesters such as polyethylene terephthalate (PET), [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] polybutylene terephthalate (PBT), 8,[20][21][22] and polyethylene 2,6naphthalate (PEN). 13,14,22,23 On the other hand, pyrolysis is an attractive method because it only requires heat.…”