Kinetics of glycolysis of poly(ethylene terephthalate) waste powder at moderate pressure and temperature

The reaction of poly(ethylene terephthalate) waste (PETW) powder with ethylene glycol (EG) was carried out in a batch reactor at 2 atm of pressure and a 220°C temperature. The particle size range of 50–512.5 μm and the reaction time of 40–180 min that are required for glycolysis of PETW were optimized. To avoid the carbonization and oxidation of reactants and reaction products and to reduce corrosion, the reaction was undertaken below 250°C using a lower reaction time. To increase the yield of dimethyl terephthalate and EG, an external catalyst was introduced during the reaction. The degree of depolymerization of PETW was proportional to the reaction time. The reaction rate was found to depend on the concentrations of liquid EG and of ethylene diester groups in the polyester. A kinetic model was used for the reaction was found to be consistent with experimental data. The rate constant was inversely proportional to the reaction time, as well as the particle size, of PETW. The degree of depolymerization of PETW was inversely proportional to the particle size of PETW. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1569–1573, 2003     

Kinetics of neutral hydrolytic depolymerization of PET (polyethylene terephthalate) waste at higher temperature and autogenious pressures

Neutral hydrolytic depolymerization of PET (Polyethylene terephthalate) waste was studied using 0.5‐L high pressure autoclave at the temperatures 100, 150, 200, 230, and 250°C at autogenious pressures 15, 80, 230, and 451 psi (pound per square inch) and time intervals of 60, 90, 120, and 150 min, respectively. The obtained terephthalic acid (TPA) was characterized by measuring its acid value and recording FTIR spectra. Depolymerization of the PET by neutral hydrolysis was found to be first order with velocity constant in the order of 10^?2 min^?1. Energy of activation and frequency factor were obtained by slope and intercept of Arrhenius plot, which were found to be 99.58 KJ mole^?1 and 2.9 × 10⁸ min^?1respectively. Effect of temperature on rate of depolymerization reaction was also studied and optimized: rate of reaction increased drastically on increase in temperature from 150 to 200°C. Modified shrinking core model based on acid values focused the light on depolymerization of the PET into TPA by fragmentation due to formation of pores and cracks. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Kinetics and thermodynamics of hydrolytic depolymerization of poly(ethylene terephthalate) at high pressure and temperature

Hydrolytic depolymerization of PET (polyethylene terephthalate) waste in excess of water was studied using a 0.5‐L stirred high‐pressure autoclave at temperatures of 100, 150, 200, and 250°C and at 200, 300, 400, 500, 700, and 800 psi (pounds per square inch) pressure. Velocity constants of hydrolysis were calculated from the experimental data obtained. Maximum depolymerization (91.38%) of PET into monomer was obtained at 250°C and 800 psi. pressure. However, the maximum rate of reaction was recorded at 200°C and 500 psi temperature and pressure, respectively. The energy of activation and frequency factor were calculated, as 64.13 KJ/g mol and 7.336 × 10⁴ min^?1, respectively, for higher pressure and temperature conditions. It was also reported that the hydrolytic depolymerization is first order with the velocity constant 1.773 × 10^?2 min^?1 at 250°C. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3305–3309, 2003     

Isothermal gravimetric analysis of poly(trimethylene terephthalate)

Poly(trimethylene terephthalate) was investigated by isothermal thermogravimetry in nitrogen at six temperatures, including 304, 309, 314, 319, 324, and 336°C. The isothermal data have been analyzed using both a peak maximum technique and an iso‐conversional procedure. Both techniques gave apparent activation energies of 201 and 192 kJ mol^?1, respectively, for the isothermal degradation of poly(trimethylene terephthalate) in nitrogen. The decomposition reaction order is calculated to be 1.0. The natural logarithms of the frequency factor based on the peak maximum and the iso‐conversional techniques are 36 and 34 min^?1, respectively, for poly(trimethylene terephthalate) decomposed isothermally in nitrogen. These isothermal kinetic parameters are in good agreement with those derived by the Kissinger technique on the basis of the dynamic thermogravimetric data reported elsewhere (209 kJ mol^?1, 1.0 and 37 min^?1). The isothermal decomposition of poly(trimethylene terephthalate) in nitrogen undergoes two processes, a relative fast degradation process in the initial period and a subsequent one with a slower weight‐loss rate. The former process may be due to the removal of ester groups, trimethylene groups, and aromatic hydrogen atoms from the chain of poly(trimethylene terethphalate). The latter one may be ascribed to the further pyrolysis of the carbonaceous char. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1600–1608, 2002; DOI 10.1002/app.10476     

Chemical Kinetics,Simulation, and Thermodynamics of Glycolytic Depolymerization of Poly(ethylene terephthalate) Waste with Catalyst Optimization for Recycling of Value Added Monomeric Products

Reaction of poly(ethylene terephthalate) (PET) waste powder with ethylene glycol (EG) was carried out in a batch reactor at 1 atm pressure and at various temperatures ranging from 100–220 °C at the intervals of 10 °C. Particle size from 50–512.5 μm, reaction time from 30–150 min, amount of catalyst from 0.001–0.009 mol, and type of catalysts required for glycolysis of PET were optimized. To increase the PET weight (%) loss, various external catalysts were introduced during the reaction at different reaction parameters. Depolymerization of PET was increased with reaction time and temperature. Depolymerization of PET was decreased with increase in the particle size of PET. Reaction rate was found to depend on concentrations of liquid ethylene glycol and ethylene diester groups in the polyester. Analyses of value added monomeric products (DMT and EG) as well as PET were undertaken. Yields of monomers were agreed with PET conversion. A kinetic model was proposed and simulated, and observed consistent with experimental data. Comparisons of effect of various amounts of catalysts and type of catalysts on glycolysis rate were undertaken. Dependence of the rate constant on reaction temperature was correlated by Arrhenius plot, which shows activation energy of 46.2 kJ/mol and Arrhenius constant of 99 783 min^?1.

Arrhenius plot of the rate constant of glycolysis at 1 atm pressure for 127.5 μm PET particle size (KZA = rate constant using zinc acetate as a catalyst, KMA = rate constant using manganese acetate as a catalyst).     

PET Recycling – Contributions of Crystallization to Sustainability

Polyethylene terephthalate (PET) is one of the most common thermoplastic polymers and its durability has become a major environmental concern. The current public debate on plastic debris also triggered the revision of PET recycling technologies. This Research Article focuses on the chemical recycling of PET by means of methanolysis. The process degrades PET into two main reaction products, dimethyl terephthalate (DMT) and ethylene glycol (EG). Subsequent separation by distillation combined with crystallization removes critical impurities and non-PET components from co-polymers, providing monomers of high purity needed for re-polymerization purposes.     

Recycling of waste PET‐bottles using dimethyl sulfoxide and hydrotalcite catalyst

The degradation of PET bottles has been successfully achieved using hydrotalcite as catalyst and dimethyl sulfoxide (DMSO) as solvent. The reaction was carried out at boiling point of DMSO (190°C) and degradation was complete in 10 min. The oligomer (tetramer) obtained was treated with NaOH at room temperature in methanol to get dimethyl terephthalate (DMT) and ethylene glycol (EG). Thus, it is a safe and cleaner process. Oligomer was characterized by MS, 13 C‐NMR, X‐ray diffractometric, and thermogravimetric analysis. DMT and EG were characterized by GC‐MS. DMT was also characterized by FT‐IR. GC‐MS analysis shows that the purity of DMT was 99%. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2012     

Effects of injection‐molding processing parameters on acetaldehyde generation and degradation of poly(ethylene terephthalate)

The acetaldehyde (AA) generation behavior of poly(ethylene terephthalate) (PET) has been investigated in terms of its relationship to changes in various processing conditions. A single‐cavity injection‐molding machine was used to prepare preforms in order to relate changes in barrel temperature, screw shear rate, back pressure, cooling time and total residence time to levels of AA generated during processing. Within the temperature range 280–300 °C, a 10 °C rise in processing temperature causes AA production to double. Shear rate increases from 20 to 40 m min^?1 result in 13–21 % increases in AA generation at temperatures from 300 to 280 °C. Increased back pressures from 0 to 200 bar result in AA concentration increases of about 1.2 ppm for each 50 bar pressure increase. The majority of this change is caused by increased polymer residence time. Longer cooling times also increase overall cycle times and result in higher levels of AA generation, at the rate of almost 7 ppm per additional minute at 290 °C processing conditions. Apparent activation energies of 167 kJ mol^?1 were calculated for samples prepared at various shear rates. These results are in agreement with literature values obtained under conditions of static mixing and indicate that shear rate and plastication do not significantly affect reaction mechanisms for AA generation. Copyright © 2005 Society of Chemical Industry     

Depolymerization of poly(ethylene terephthalate) in dilute aqueous ammonia solution under hydrothermal conditions

BACKGROUND: Various methods, such as glycolysis, methanolysis, and hydrolysis with supercritical water, have been investigated for chemical recycling of poly(ethylene terephthalate) (PET), which is used in large quantities for beverage containers. However, a more effective process is needed. RESULTS: PET was depolymerized in aqueous ammonia in a batch reactor and a semi‐batch reactor over a temperature range 463 to 573 K, at a pressure 10 MPa, and with up to 3 mol L^?1 ammonia. Total organic carbon in the product solution and yields of the major products such as terephthalic acid (TPA) and ethylene glycol (EG) were measured. The PET pellet sample was thoroughly solubilized in aqueous ammonia under hydrothermal conditions, and more than 90% of the initial PET samples were recovered as TPA + EG on a carbon weight basis. Depolymerization rates were represented by 2/3‐order reaction kinetics with respect to unreacted PET, where the reaction took place on the PET pellet surface. The rate increased slightly with increasing ammonia concentration. CONCLUSION: Ammonia was effective for depolymerization of PET, allowing the recovery of TPA and EG under hydrothermal conditions. Copyright © 2008 Society of Chemical Industry     

Recycling of off‐grade pet via partial alcoholysis to synthesize functionalized pet oligomer nanocomposites

Off‐grade poly(ethylene terephthalate) (PET) of industrial manufacturers was partially depolymerized using excess ethylene glycol in the presence of manganese acetate as a transesterification catalyst to synthesize PET oligomers. Influences of reaction time, Ethylene Glycol (EG)/PET molar ratio, catalyst concentrations, and particle size of off‐grade PET on yield of partial glycolysis reaction were investigated based on Box–Behnken's design of experiment. Thermal analyses of glycolyzed products are examined by differential scanning calorimetry. The optimum samples were also well‐characterized by Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy (¹H‐NMR and ¹³C‐NMR). The optimal conditions to synthesize PET oligomer (melting point of about 180°C) for a 120‐min glycolysis reaction time were EG/PET molar ratio of 2 with no catalyst using granule‐shaped PET. The same results were obtained for a 60‐min glycolysis reaction time, including EG/PET molar ratio of 1 with the weight ratio (catalyst to PET) of 0.5% using average particle size of PET. Then, maleated PET as a compatibilizer for preparing PET nanocomposites was produced via reaction between maleic anhydride/phthalic anhydride composition and optimized PET oligomers based on central composite design of experiment. The combination of reaction time of 106 min and PhA/MA molar ratio of 0.85 gave the best results based on d‐spacing and peak shift of nanocomposite samples. Hence, melt mixing of maleated PET with organoclay produced a good intercalation of layered silicate and good dispersion of clay in maleated PET matrix. Analysis of variance (ANOVA) was studied for both glycolyzed products and functionalized PET oligomers. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Acetophenone‐assisted main‐chain photocrosslinking of poly(ethylene terephthalate)

Maximum gel fraction of 99.1% was obtained under continuous UV irradiation of a UV energy of 200 J cm^?2 on poly(ethylene terephthalate) (PET) containing only in presence of 2.9%(w/w) acetophenone (AP). The fragmented AP radicals abstract the hydrogen atoms of methylene units in PET, producing secondary methine radicals which couples to main‐chain crosslinks. The crystal structure of the crosslinked PET became disordered remarkably. The glass transition temperature disappeared and the peak thermal decomposition temperature was significantly retarded as much as 85°C. The crosslinking density and molecular weight between crosslinks reaches up to 0.129 mol g^?1 and 7.7 g mol^?1, respectively. Also tensile modulus and strength increased by 200 and 72% compared with those of the pristine PET respectively, resulting in more toughened PET. The solid‐state photocrosslinking may extend high‐temperature applications of PET with enhanced thermal and mechanical properties. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39802.     

Alkali decomposition of poly(ethylene terephthalate) with sodium hydroxide in nonaqueous ethylene glycol: A study on recycling of terephthalic acid and ethylene glycol

Pellets of poly(ethylene terephthalate) (PET; 0.48–1.92 g) were heated in anhydrous ethylene glycol (EG; 5 mL) with 2-equivs of NaOH at 150°C for 80 min or 180°C for 15 min to convert them quantitatively to disodium terephthalate (Na₂-TPA) and EG. The disodium salt was precipitated quantitatively in pure state from the EG solution and separated readily. The other product EG, being the same component to the solvent, remains in the solution and can be obtained after distillation as a part of the solvent. The rate of decomposition was significantly accelerated by the addition of ethereal solvents to EG, such as dioxane, tetrahydrofuran, and dimethoxyethane. The reaction system is simple; no water and no extra reagent other than NaOH and EG are used. A few recycling systems of PET can be designed on the basis of the present alkali decomposition reaction. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 595–601, 1997     

Kinetic and thermodynamic studies of depolymerisation of poly(ethylene terephthalate) by saponification reaction

Depolymerisation reaction of polyester waste was carried out by a saponification reaction. Yields of depolymerised products were up to 85% for a 2.5‐h reaction time. Products obtained were characterized by chemical as well as instrumental analysis such as mp (sublimation), acid value and FTIR spectra. The valued obtained for terephthalic acid (TPA) agreed with those for the pure substance. Chemical kinetics of this reaction shows that it is a first‐order reaction with respect to poly(ethylene terephthalate) (PET) concentration with a velocity constant of the order of 10^?2 min^?1. In the light of the Yashioka modified shrinking core model, a simultaneous fragmentation and depolymerisation model was proposed for the kinetics of hydrolysis of PET. The modified model is based on change in acid value of the product obtained, which is directly related to the change in surface area of particle. The energy of activation and the Arrhenius constant (frequency factor) obtained by Arrhenius plot were 59.71 kJ g^?1 and 8.325 × 10⁶ min^?1 respectively. © 2002 Society of Chemical Industry     

Poly(ester-ether) fibres

Ester-ether copolymers were prepared by melt condensation reaction using dimethyl terephthalate (DMT) and different quantities of ethylene glycol (EG) and poly(ethylene glycol) (PEG) (MW 400) in the initial monomer feed. Five copolymer samples were prepared by varying the contents of PEG on the basis of EG from 0.5 to 2.5 mol-%. The polymer samples were characterized by determination of melting points (mp) and intrinsic viscosities. The mp decreased from 258°C to 248°C on increasing the poly(ethylene oxide) segments in the backbone. Thermal stability of the copolymers also decreased by the introduction of PEG units in the backbone. The polymers were melt spun into fibres. With the increase of PEG in the copolymer fibres a decrease in tensile strength and initial modulus was observed while the elongation increased. The dye uptake and moisture regain of the copolyester fibres was considerably enhanced in comparison of poly(ethylene glycol terephthalate) (PET) fibres.     

Glycolysis of poly(ethylene terephthalate) wastes in xylene

To reclaim the monomers or prepare intermediates suitable for other polymers zinc acetate catalayzed glycolysis of waste poly(ethylene terephthalate) (PET) was carried out with ethylene or propylene glycol, with PET/glycol molar ratios of1 : 0.5–1 : 3, in xylene at 170–245°C. During the multiphase reaction, depolymerization products transferred to the xylene medium from the dispersed PET/glycol droplets, shifting the equilibrium to glycolysis. Best results were obtained from the ethylene glycol (EG) reaction at 220°C, which yielded 80 mol % bis-2-hydroxyethyl terephthalate monomer and 20 mol % dimer fractions in quite pure crystalline form. Other advantages of employment of xylene in glycolysis of PET were improvement of mixing at high PET/EG ratios and recycling possibility of excess glycol, which separates from the xylene phase at low temperatures. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2311–2319, 1998     

Effect of particle size on thermal decomposition and devolatilization kinetics of melon seed shell

Thermogravimetric analysis (TGA) and devolatilization kinetics of melon seed shell (MSS) at different particle sizes (150?µm and 500?µm) and at different heating rates (10, 15, 20, and 25?°C/min) were investigated with the aid of TGA. The results of the TGA analysis show that the TGA curves corresponding to the first and third stages for 150?µm particle sizes exhibited some bumps that developed at the first and third stages of pyrolysis. It was also observed that at constant heating rate, the maximum peak temperature increases as the particle sizes increase from 150 to 500?µm, whereas 500?µm particle sizes exhibited higher peak temperatures compared to 150?µm particle sizes. The resulting TGA data were applied to the Kissinger (K), Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO) methods and kinetic parameters (activation energy, E and frequency factor, A) were determined. The E and A obtained using K method were 74.27?kJ mol^?1 and 3.84?×?10⁵?min^?1 for 150?µm particle size, whereas for 500?µm particle size were 97.12?kJ mol^?1 and 3.74?×?10⁷?min^?1, respectively. However, the average E and A obtained using KAS and FWO methods were 82.35?kJ mol^?1, 1.29?×?10⁷?min^?1, and 88.50?kJ mol^?1, 1.32?×?10⁷?min^?1 for 150?µm particle sizes. While for 500?µm particle sizes, the E and A were 108.46?kJ mol^?1, 3.14?×?10⁹?min^?1, and 113.05?kJ mol^?1, 7.56?×?10⁹?min^?1, respectively. It was observed that E and A calculated from FWO and KAS methods were very close and higher than that obtained by K method. It was observed that the minimum heat required for the cracking of MSS particles into products is reached later at higher peak temperatures since the heat transfer is less effective as they are at lower peak temperatures.     

Synthesis of poly(ethylene terephthalate) in benzyl imidazolium ionic liquids

In order to improve the method of synthesis of poly(ethylene terephthalate) (PET), a series of ionic liquids (ILs) based on benzyl imidazolium ([YBMIM][X], Y = NO₂, CH₃, F; B = benzyl; X = Tf₂N) were used to investigate the formation of PET at low temperature and pressure. High molecular weight PET (M_w up to 2.6 × 10⁴ g mol^?1) was obtained by two‐step polycondensation in these ILs at lower temperature (230–240 °C) than with traditional melt polycondensation (270–290 °C). Moreover, the molecular weight of the resulting PET was found to depend on the activities of the catalysts used in the ILs. The catalysts (Sb₂(OCH₂CH₂O)₃, Sb(OAc)₃, Sb₂O₃) used in the preparation of PET have little effect on the thermostability of the ILs. The ILs can decrease the viscosity of the reaction system, and thus small molecules can be easily removed. Copyright © 2012 Society of Chemical Industry     

Ultrafast preparation of branched poly(methyl Acrylate) through single electron transfer living radical polymerization at room temperature

Ultrafast preparation of branched poly(methyl acrylate) (BPMA) with high‐molecular weight through single electron transfer living radical polymerization (SET‐LRP) of inimer at 25°C has been attempted, atom transfer radical polymerization (ATRP) at 60°C was also carried out for comparison. Gas chromatography, proton nuclear magnetic resonance, and triple detection size exclusion chromatography were used to analyze these polymerizations. As expected, SET‐LRP system showed much faster polymerization rate than ATRP system, the calculated apparent propagation rate constants (k_p^app) are 3.69 × 10^?2 min^?1 and 6.23 × 10^?3 min^?1 for SET‐LRP and ATRP system, respectively. BPMA with high‐molecular weight (M_w._MALLS = 86,400 g mol^?1) compared with that in ATRP (M_w.MALLS = 61,400 g mol^?1) has been prepared. POLYM. ENG. SCI., 54:1579–1584, 2014. © 2013 Society of Plastics Engineers     

Kinetics of polycondensation and copolycondensation of Bis(3‐hydroxypropyl terephthalate) and Bis(2‐hydroxyethyl terephthalate)

The kinetics of polycondensation and copolycondensation reactions of bis(3‐hydroxypropyl) terephthalate (BHPT) and bis(2‐hydroxyethyl) terephthalate (BHET) as monomers were investigated at 270°C, in the presence of titanium tetrabutoxide (TBT) as a catalyst. BHPT was prepared by ester interchange reaction of dimethyl terephthalate (DMT) and 1,3‐propanediol (PD). Applying second‐order kinetics for polycondensation, the rate constants of polycondensation of BHPT and BHET, k₁₁ and k₂₂, were calculated as 3.975 and 2.055 min⁻¹, respectively. The rate constants of cross‐reactions in the copolycondensation of BHPT and BHET, k₁₂ and k₂₁, were obtained by using the results obtained from a proton nuclear magnetic resonance spectroscopy. The rate constants during the copolycondensation of BHPT and BHET at 270°C decreased in the order k₁₁ > k₁₂ > k₂₂ > k₂₁, indicating the block nature of the copolycondensation. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 693–698, 2000     

Kinetics of glycolysis of polyethylene terephthalate with zinc catalyst

The glycolysis reaction of poly(ethylene terephthalate) (PET) melts with ethylene glycol has been examined in a pressurized reactor. The kinetics of the glycolysis reaction are studied. The rate constants for glycolysis without addition of catalyst are calculated at four different temperatures, yielding an activation energy of 108 kJ mol⁻¹. By comparison, the rate constants for glycolysis with addition of zinc acetate are also calculated at four different temperatures, yielding an activation energy of 85 kJ mol⁻¹. It is found that the activation energy of glycolysis with addition of zinc acetate is lower than that of glycolysis without addition of catalyst. Therefore, zinc acetate has a catalytic effect on PET glycolysis at temperatures between 235 and 275 °C. The effect of catalyst concentration on reaction rate constants is also discussed. Below a critical catalyst concentration, the rate constant for glycolysis is linearly dependent on catalyst concentration. © 1999 Society of Chemical Industry