Heat Transfer Studies in an Agitated Vessel During Aqueous Alkaline Depolymerization of Poly(Ethylene Terephthalate) (PET) Waste

Depolymerization reactions of poly(ethylene terephthalate) (PET) waste in aqueous sodium hydroxide solution were carried out in a batch reactor at 150°C at atmospheric pressure. Disodium terephthalate (terephthalic acid salt) and ethylene glycol (EG) remain in the liquid phase. Terephthalic acid (TPA) salt was converted into TPA. The produced monomeric products (TPA and EG) were recovered. Various design parameters were estimated. Design of a batch reactor was undertaken for depolymerization of PET waste in aqueous sodium hydroxide solution. As expected, the Reynolds numbers, Prandtl numbers, Nusselt numbers, coil-side heat transfer coefficients, and overall heat transfer coefficients were consistent with the fluid velocities. It shows excellent potential for commercialization of the depolymerization of PET waste.     

Auto-Catalyzed Hydrolytic Depolymerization of Poly(Butylene Terephthalate) Waste at High Temperature

Auto-catalyzed hydrolytic depolymerization of poly(butylene terephthalate) (PBT) waste in neutral water was carried out in an autoclave at 200°, 215°, 230°, and 245°C under autogenously pressure. The effects of particle size, agitator speed, charge ratio, and reaction time on PBT hydrolyses were studied. Reaction products were terephthalic acid (TPA) and 1,4-butanediol (BD) that were recovered, analyzed, and confirmed. Yields of TPA and BD were almost equal to PBT conversion. Analyses of PBT waste samples were also undertaken. A kinetic model for PBT hydrolysis was fitted with the experimental data. Moreover, a noncatalytic PBT hydrolysis was studied to understand the effect of auto-catalyzed action during reaction. Various kinetic parameters (i.e., hydrolysis rate constant, equilibrium constant, backward rate constant, Gibbs free energy, enthalpy, and entropy) of reaction were calculated. The transfer of laboratory data is required during process commercialization through pilot plant. The dependence of the rate constant on the reaction temperature was correlated by the Arrhenius plot giving activation energy of 87 kJ/mol and the corresponding Arrhenius constant of 5.56 × 10⁹[(g ET/mol)^1.5 min^?1] for PBT hydrolysis.     

聚对苯二甲酸丁二醇酯在亚临界水中的催化解聚

研究间歇高压反应釜中聚对苯二甲酸丁二醇酯(PBT)以醋酸铜为催化剂在亚临界水中的解聚反应.主要考察反应时间(10-50min)和反应温度(493～553 K)对PBT解聚率以及产物产率的影响.反应产物分别采用气相色谱、气-质联用仪、傅里叶红外光谱、高效液相色谱和液-质联用仪进行分析,主产物为对苯二甲酸(TPA)和四氢呋喃(THF),产物中并未检测出1,4-丁二醇,与相关文献的研究结果不同.实验结果表明:PBT的解聚率随温度的升高、反应时间的延长而增加.在投料比8∶1(24.0g H2O/3.0 g PBT),催化剂醋酸铜0.03 g/3.0 g PBT,反应温度523K,时间50 min条件下,PBT可完全解聚,TPA和THF的产率分别为99.3％和83.1％.根据PBT在亚临界水中催化解聚产物的分析,提出PBT催化水解反应机理.通过实验数据关联,得出催化解聚反应级数为一级,反应活化能为141.6 kJ·mol-1.在微型毛细管反应器中结合显微镜研究了PBT在醋酸铜水溶液相态变化,温度上升至553 K停留19 min后PBT能完全溶解于水中,解聚反应在液相均相中进行.     

Production of agrochemical from waste polyesters

In this study, agrochemical was produced from waste polyesters. Reactions of waste polyesters [poly (ethylene terephthalate) (PET) and poly (butylene terephthalate) (PBT)] powder with ethylene glycol (EG) in the presence of tetrahydrofurane (THF) using 0.003 mol lead acetate as a catalyst were carried out in a batch reactor at 470 K and at atmospheric pressure conditions. Reactions were undertaken with various particle size ranges from 50 to 512.5 μm, and reaction time from 30 to 70 min for reactions of polyesters. Low molecular weight product of polyester was obtained during this process. In the next stage, hydroxylamine hydrochloride (HAHC), cyclohexylamine (CHA), and potasium hydroxide (KOH) solution were introduced to convert low molecular weight product of polyester into terephthalohydroxamic acid (TPHA) by introduction of HCl (Hydrochloric Acid) as per stoichiometric requirement. TPHA can be used as an agrochemical (insecticide) with appreciable efficiency. To increase the polyester conversion rate, external catalyst (0.003 mol lead acetate) was introduced during the reaction. The product was deposited on the surface of unreacted polyester, which was removed from the surface by introducing dimethyl sulfoxide (DMSO). To accelerate the reaction rate, DMSO, CHA, and THF were introduced during the reaction, which has an industrial significance. Depolymerization of polyester was proportional to the reaction time. Depolymerization of polyester was inversely proportional to the particle size of polyester. Analyses of value‐added product (TPHA) and byproducts [EG and BD (1,4‐butanediol)] as well as polyesters were undertaken. A kinetic model is developed, and experimental data simulated with it, which was consistent with the model. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2504–2510, 2006     

Poly(ethylene terephthalate) Recycling and Recovery of Pure Terephthalic Acid. Kinetics of a Phase Transfer Catalyzed Alkaline Hydrolysis

Poly(ethylene terephthalate) (PET) taken from post‐consumer soft‐drink bottles was subjected to alkaline hydrolysis with aqueous sodium hydroxide after cutting it into small pieces (flakes). A phase transfer catalyst (trioctylmethylammonium bromide) was used in order the reaction to take place in atmospheric pressure and mild experimental conditions. Several different reaction kinetics parameters were studied, including temperature (70–95°C), NaOH concentration (5–15 wt.‐%), PET average particle size, catalyst to PET ratio and PET concentration. The disodium terephthalate received was treated with sulfuric acid and terephthalic acid (TPA) of high purity was separated. The ¹H NMR spectrum of the TPA revealed an about 2% admixture of isophthalic acid together with the pure 98% terephthalic acid. The purity of the TPA obtained was tested by determining its acidity and by polymerizing it with ethylene glycol using tetrabutyl titanate as catalyst. A simple theoretical model was developed to describe the hydrolysis rate. The apparent rate constant was inversely proportional to particle size and proportional to NaOH concentration and to the square root of the catalyst amount. The activation energy calculated was 83 kJ/mol. The method is very useful in recycling of PET bottles and other containers because nowadays, terephthalic acid is replacing dimethyl terephthalate (the traditional monomer) as the main monomer in the industrial production of PET.     

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     

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).     

Sodium Methoxide Catalyzed Depolymerization of Waste Polyethylene Terephthalate Under Microwave Irradiation

Chemical recycling of polyethylene terephthalate (PET) to produce terephthalic acid (TPA) was studied using in situ hydrolysis with sodium methoxide in methanol and dimethyl sulfoxide (DMSO) as solvent under microwave irradiation. The microwave-assisted reaction was carried out at different temperatures, and reaction time between 5 to 30 min. High degrees of depolymerization were examined at temperature near 70°C at microwave power 300 W. The reaction was carried out in a sealed microwave reactor in which the time and temperature were controlled and recorded. The products were mainly monomers such as TPA and ethylene glycol (EG) which were isolated and purified for further analysis. Monomethyl terephthalate, dimethyl terephthalate, and terephthalic acid were formed initially then converted to TPA as a single monomer product. Purified, TPA was analyzed and identified by NMR, TGA, DSC and FTIR. It was observed that the reaction greatly depends on the amount of sodium methoxide, the volume of methanol and DMSO used, the reaction time, and temperature. Compared to conventional heating methods, the time needed to achieve complete degradation of PET was significantly reduced to 5 min by using microwave irradiation and sodium methoxide catalyst. This has led to substantial saving in energy and cost supporting the conclusion that this proposed recycling process is very beneficial for the recycling of PET wastes.     

Degradation of poly(butylene terephthalate) in different supercritical alcohol solvents

Reactions were carried out in a batch autoclave reactor. Poly(butylene terephthalate) (PBT) and different alcohol solvents were used in the vessel. The reaction products were analyzed by infrared spectroscopy and gas chromatography/mass spectrometry. Alcoholysis of PBT occurred in supercritical methanol, ethanol, and propanol, and we obtained dimethyl terephthalate (DMT), diethyl terephthalate (DET), and dipropyl terephthalate (DPT), respectively. The conversion of PBT at different temperatures showed similar trends but different degradation degrees. The reactivity for the alcoholysis of PBT in supercritical methanol was much higher than those in supercritical ethanol and propanol. DMT and 1,4‐butanediol obtained from the depolymerization of PBT in supercritical methanol reached 98.5 and 72.3%, respectively, at 583 K for 75 min. The yield of DET reached 76% for 75 min. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Depolymerization of poly(trimethylene terephthalate) in supercritical methanol

The depolymerization of poly(trimethylene terephthalate) (PTT) in supercritical methanol was carried out with a batch‐type autoclave reactor at temperatures ranging from 280 to 340°C, at pressures ranging from 2.0 to 14.0 MPa, and for reaction time of up to 60 min. PTT quantitatively decomposed into dimethyl terephthalate (DMT) and 1,3‐propaniol (PDO) under the designed conditions. The yields of DMT and PDO greatly increased as the temperature rose. The yields of the monomers markedly increased as the pressure increased to 10.0 MPa, and they leveled off at higher pressures. The final yield of DMT at 320°C and 10.0 MPa reached 98.2%, which was much closer to the extent of the complete reaction. A kinetic model was used to describe the depolymerization reaction, and it fit the experimental data well. The dependence of the forward rate constant on the reaction temperature was correlated with an Arrhenius plot, which gave an activation energy of 56.8 kJ/mol. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2363–2368, 2004     

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     

Depolymerization of waste polybutylene terephthalate in hot compressed water in a fused silica capillary reactor and an autoclave reactor: Monomer phase behavior,stability, and mechanism

Depolymerization is a potentially viable means of recycling waste polymers, converting them back into monomers or other useful compounds. Terephthalic acid (TPA) and 1,4‐butanediol (1,4‐BD) are the depolymerization monomer products of polybutylene terephthalate. Their yields from depolymerization in hot compressed water (HCW) were previously found to be lower than reported theoretical values. Thus, the phase behavior, stability, and mechanism of monomers in HCW were investigated in a fused silica capillary reactor (FSCR) and a stainless steel autoclave reactor. Phase change observations showed that TPA was completely dissolved in water at 300°C, was relatively stable at 320 to 350°C, and that its recovery significantly decreased at temperatures above 350°C. The decomposition of TPA increased with increasing heating time. However, the recovery of 1,4‐BD decreased rapidly with increasing temperature or heating time. A mechanism for the stability of TPA and 1,4‐BD is proposed based on their depolymerization products. The products were quantified by Fourier transform‐infrared spectroscopy, high‐performance liquid chromatography, and gas chromatography coupled with mass spectrometry. The wall effect of the stainless steel autoclave promoted the decomposition of TPA and 1,4‐BD in HCW. POLYM. ENG. SCI., 57:544–549, 2017. © 2016 Society of Plastics Engineers     

Depolymerization of poly(butylene terephthalate) using high‐temperature and high‐pressure methanol

Poly(butylene terephthalate) (PBT) was depolymerized in excess methanol at high‐temperature (473–523 K) and high‐pressure (4–14 MPa) conditions. Considering the critical point of methanol (512.6 K, 8.09 MPa), the reaction pressure was varied over the range of 6–14 MPa at the reaction temperature of 513 K. As a result, ca. 20 min was required to recover dimethyl terephthalate and 1,4‐butanediol, quantitatively, at any pressure, indicating that the supercritical state of methanol is not a key factor of degradation of PBT and that the effect of pressure is little. On the contrary, when the reaction temperature was varied over the range of 473–523 K at the pressure 12 MPa, the decomposition rate constant of PBT at the reaction temperatures (503–523 K) higher than the melting temperature of PBT (500 K) was much higher than that at 473–483 K. This result indicates that melting of PBT is an important factor for the short‐time depolymerization of PBT. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 3228–3233, 2000     

Kinetic and thermodynamic study of methanolysis of poly(ethylene terephthalate) waste powder

Depolymerization of poly(ethylene terephthalate) waste (PETW) was carried out by methanolysis using zinc acetate in the presence of lead acetate as the catalyst at 120–140 °C in a closed batch reactor. The particle size ranging from 50 to 512.5 µm and the reaction time 60 to 150 min required for methanolysis of PETW were optimized. Optimal percentage conversion of PETW into dimethyl terephthalate (DMT) and ethylene glycol (EG) was 97.8% (at 120 °C) and 100% (at 130 and 140 °C) for the optimal reaction time of 120 min. Yields of DMT and EG were almost equal to PET conversion. EG and DMT were analyzed qualitatively and quantitatively. To avoid oxidation/carbonization during the reaction, methanolysis reactions were carried out below 150 °C. A kinetic model is developed and the experimental data show good agreement with the kinetic model. Rate constants, equilibrium constant, Gibbs free energy, enthalpy and entropy of reaction are also evaluated at 120, 130 and 140 °C. The methanolysis rate constant of the reaction at 140 °C (10.3 atm) was 1.4 × 10^?3 g PET mol^?1 min^?1. The activation energy and the frequency factor for methanolysis of PETW were 95.31 kJ mol^?1 and 107.1 g PET mol^?1 min^?1, respectively. © 2003 Society of Chemical Industry     

Investigation of alkaline hydrolysis of polyethylene terephthalate by differential scanning calorimetry and thermogravimetric analysis

The hydrolytic depolymerization of polyethylene terephthalate (PET) with alkaline hydroxides was investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The reactions of the mixtures were conducted in their solid states under nitrogen atmosphere. The experimental results showed that potassium hydroxide possessed the hydrolytic activity of depolymerizing PET into small molecules such as ethylene glycol; in contrast, sodium hydroxide did not. The production rate of ethylene glycol was enhanced by increasing charge ratio of potassium hydroxide to PET. The presence of water facilitated the alkaline hydrolysis of PET; however, the presence of metal acetates decreased the hydrolysis rate. The activation energy for alkaline hydrolysis of PET determined by the thermograms was in good agreement with the value obtained from the experiments in a batch reactor. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1939–1945, 1998     

Kinetics and mechanistic analysis of caustic magnesia hydration

The kinetics of magnesia hydration to produce magnesium hydroxide is crucial for process design and control, and for the production of an Mg(OH)₂ powder with desirable particle morphology. In this study, highly pure magnesia has been hydrated in a batch reactor. The effects of the following variables were evaluated experimentally: temperature (308–363 K), reaction time (0.5–5 h), initial slurry density (1–25%wt) and particle size in the ranges ?212 + 75 µm and ?45 + 38 µm. Experimental data indicate increasing magnesia hydration rates with increasing temperature, as expected. In addition, it has been observed that the hydration of magnesia increases significantly up to about 4–5%wt initial slurry density, stabilising afterwards. On the other hand, the reaction was almost unaffected when magnesia with different particle sizes were hydrated because of similar specific surface areas involved. A reaction mechanism to explain the oxide dissolution and the hydroxide precipitation has been proposed, assuming no significant change in the initial solids size and dissolution rate as the controlling step. The calculated activation energy value of 62.3 kJ mol^?1 corroborates the mechanism proposed in this study and compares well with values previously reported in the literature. Copyright © 2004 Society of Chemical Industry     

Phase transfer catalysis of alkaline hydrolysis of n-butyl acetate: Comparison of performance of batch and micro-reactors

The hydrolysis of n-butyl acetate with aqueous sodium hydroxide was studied in the batch mode as well as in the continuous mode in a micro-reactor. The progress of the reaction was analyzed both with and without a phase transfer catalyst. The concentration of the unreacted sodium hydroxide in the aqueous phase was determined by titration with hydrochloric acid to monitor the progress of the reaction. The performance of the two systems is studied for different operating conditions, i.e. concentrations of reactants, stirring speeds (in batch mode) and flow rates (in continuous mode). Conditions are identified when the performance of the micro-reactor system is superior to that of the batch system. To understand this better the performance of a 1 mm channel and a 0.4 mm channel are compared with that of the batch reactor.     

The synthesis of poly(butylene terephthalate) from terephthalic acid,part II: Assessment of the first stage of the polymerization process

The production of poly(butylene terephthalate) (PBT) struggles with the formation of substantial amounts of tetrahydrofuran (THF). When PBT is synthesized from terephthalic acid (TPA) instead of dimethyl terephthalate (DMT), even more THF is formed, mainly during the first stage of the melt polymerization process. Although a lot of literature reports on the existence of this side reaction in both processes, to the best of our knowledge, a comparison, which reveals the importance of the acidity and insolubility of TPA on the THF formation, was never described. Finally, an interesting study was performed on the THF formation during the synthesis of PBT from mixtures of DMT and TPA as well as from the completely soluble monomethyl terephthalate (MMT). © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Post Consumer Pet Depolymerization by Acid Hydrolysis

The reaction of post-consumer poly(ethylene terephthalate) with aqueous solutions of sulfuric acid 7.5 M was investigated in terms of temperature, time and particle size. The reaction extent reached 80% in four days at 100°C and 90% in 5 hours at 135°C. TPA obtained was purified and considered in the same level of quality of the commercial one after tests of elemental analysis, particle size and color. It was concluded that the hydrolysis occurred preferentially at the chain ends and superficially, having as controller mechanism the acid diffusion into the polymer structure. The shrinking-core model can explain the reaction kinetics.     

Diffusion of butanediol in poly(butylene terephthalate) (PBT) melt and analysis of pbt polymerization reactor with surface renewal

A reactor with surface renewal, originally designed for poly(ethylene terephthalate) (PET) polymerization, was applied for poly(butylene terephthalate) (PBT) polymerization. A comprehensive model including side reactions was developed and compared with the experimental results. The diffusivity of butanediol (BD) in PBT melt was measured separately by desorption experiments (D_b ? 1.08 × 10⁶ exp(?32600 / RT) (m²/min)). Optimum operating temperature for PBT polymerization was found to be around 250°C in order to avoid degradation.