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.     

Hydrolytic depolymerization of poly(ethylene terephthalate) under microwave irradiation

This article covers the depolymerization of poly(ethylene terephthalate) (PET) under microwave irradiation in neutral water. The reaction was carried out in a sealed reaction vessel in which the pressure (or temperature) was controlled. The hydrolytic product contained terephthalic acid, ethylene glycol, and diethylene glycol characterized by IR spectrometry and gas chromatography. The undepolymerized PET was identified by gel permeation chromatography. Both the yield of terephthalic acid and the degree of PET depolymerization were seriously influenced by pressure (or temperature), the weight ratio of water to PET, and the reaction time. The applied irradiation power had little influence on the degree of PET depolymerization. With a pressure of 20 bar (temperature = 220°C), a reaction time of 90–120 min, and a weight ratio of water to PET of 10:1, the PET resin was depolymerized completely. The molecular weight and the molecular weight distribution indicated that the hydrolytic depolymerization of PET obeyed the regular chain‐scission mechanism to some extent. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 719–723, 2005     

Aminolytic depolymerization of poly(ethylene terephthalate) waste in a microwave reactor

The aminolytic depolymerization of poly(ethylene terephthalate) (PET) taken from waste soft‐drink bottles, under microwave irradiation, is proposed as a recycling method with possible substantial energy savings. The reaction was carried out with ethanolamine and without the use of any other catalyst in a sealed microwave reactor in which the pressure and temperature were controlled and recorded. Experiments under constant temperature or microwave power were carried out for several time periods. The main product, bis(2‐hydroxyethyl) terephthalamide, was identified from Fourier transform infrared (FTIR) spectra and DSC measurements. It was found that PET depolymerization is favoured by increasing temperature, time and microwave power. The average molecular weight of the PET residues, determined using viscosity measurements, was found to decrease with the percentage of PET degradation, indicating a random chain scission mechanism to some extent. From a simple kinetic model, the activation energy of the reaction was evaluated. Complete depolymerization was found to occur in less than 5 min when the irradiation power applied was 100 W or the temperature was 260 °C. These results support the use of microwave‐assisted aminolytic degradation as a very beneficial method for the recycling of PET wastes. Copyright © 2010 Society of Chemical Industry     

Methanolysis of Poly（ethylene terephthalate）in Supercritical Phase

1 INTRODUCTIONPoly(ethylene terephthalate), commonly known as PET polyester, is extensively used for making synthetic fibers and package containers. The volume of PET consumed is rising by year, and thus the chemical recycling and reuse of waste PET are drawing much attention for the preservation of resources and the protection of environment. Through chemical recycling, waste PET is depolymerized into its valuable monomers such as dimethyl terephthalate (DMT), bis (hydroxyethyl) ter…     

有色废弃PET材料化学回收新工艺

为了解决有色废弃PET材料回收难的问题,促进资源循环利用,研究了有色PET以超临界甲醇技术进行解聚,并脱色提纯得到对苯二甲酸二甲酯的工艺流程。探讨了有色PET在超临界甲醇中的降解规律,并对脱色方案进行了筛选。探索了不同级别的PET材料解聚条件的差异。结果表明：纤维级材料在265 ℃,11 MPa下,超临界甲醇解聚30 min后,用溶解-热过滤-沉析的方法脱色提纯,对苯二甲酸二甲酯的产率可达到85%,纯度达到99.9%以上,白度达到87.5%;瓶片级材料呈现的解聚规律与纤维级变化趋势相同,但达到相同的解聚率,明显需要更长的反应时间。     

超/亚临界水中聚对苯二甲酸乙二醇酯的解聚

采用间歇式高压反应装置研究了聚对苯二甲酸乙二醇酯(PET)在超/亚临界水中的解聚,考察了投料比、反应温度及反应时间对PET解聚率及主产物对苯二甲酸(TPA)和乙二醇(EG)产率的影响.固相产物采用傅里叶红外光谱(FT-IR)、液相色谱(HPLC)进行分析,液相产物采用气相色谱(GC)和气-质联谱(GC-MS)进行分析....     

Hydrolysis of poly(ethylene terephthalate) and poly(ethylene 2,6-naphthalene dicarboxylate) using water at high temperature: Effect of proton on low ethylene glycol yield

Depolymerization of poly(ethylene terephthalate) (PET) to terephthalic acid (TPA) and ethylene glycol (EG) and poly(ethylene 2,6-naphthalene dicarboxylate) (PEN) to 2,6-naphthalene dicarboxylic acid (2,6-NPA) and EG in water at high temperature (>523 K) was investigated for the purpose of monomer recycling. In case of the depolymerization of PET in water, the yield of TPA increased to 90% with increasing reaction temperature up to 693 K while the maximum yield of EG achieved was 60% at 573 K. For PEN depolymerization, the yield of 2,6-NPA also increased to 97% with increasing reaction temperature up to 693 K and the maximum yield of EG obtained was 60% at 573 K. The higher yield of 2,6-NPA than that of TPA was ascribed to the higher stability of 2,6-NPA than that of TPA. The lower yields of EG than the corresponding monomers (TPA and 2,6-NPA) in the decomposition of the two kinds of polyesters were caused by the catalytic dehydroxylation of EG by protons derived from dicarboxylic acids.     

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     

N,N-二甲基乙酰胺二甲基缩醛的合成工艺优化

报道了一种优化的N,N-二甲基乙酰胺二甲基缩醛(DMACA)合成工艺。该工艺使用液体甲醇钠,蒸除甲醇后悬浮在正己烷中,再和亚胺络合物反应。甲醇钠和硫酸二甲酯的摩尔比为1.2∶1,-10℃滴加亚胺络合物,滴加时间为1 h,反应时间为1.5 h。本合成工艺产品收率高(由文献值25%~35%提高到75%~85%),纯度好(HPLC≥98%)。     

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     

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.     

Microwave assisted glycolysis of poly(ethylene terephthalate) catalyzed by 1‐butyl‐3‐methylimidazolium bromide ionic liquid

The combination of ionic liquid (IL) associated with microwave energy may have some potential application in the chemical recycling of poly (ethylene terephthalate). In this processes, glycolysis of waste poly (ethylene terephthalate) recovered from bottled water containers were thermally depolymerized with solvent ethylene glycol (EG) in the presence of 1‐butyl‐3‐methyl imidazolium bromide ([bmim]Br) as catalyst (IL) under microwave condition. It was found that the glycolysis products consist of bis (2‐hydroxyethyl) terephthalate (BHET) monomer that separated from the catalyst IL in pure crystalline form. The conversion of PET reach up to 100% and the yield of BHET reached 64% (wt %). The optimum performance was achieved by the use of 1‐butyl‐3‐methyl imidazolium bromide as a catalyst, microwave irradiations temperature (170–175°C) and reaction time 1.75–2 h. The main glycolysis products were analyzed by ¹H NMR, ¹³C NMR, LC‐MS, FTIR, DSC, and TGA. When compared to conventional heating methods, microwave irradiation during glycolysis of PET resulted in short reaction time and more control over the temperature. This has allowed substantial saving in energy and processing cost. In addition, a more efficient, environmental‐friendly, and economically feasible chemical recycling of waste PET was achieved in a significantly reduced reaction time. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41666.     

Simulation of Continuous Direct Esterification Process between Terephthalic Acid and Ethylene Glycol

Owing to its excellent end-use performance, demand for the general-purpose polymer poly(ethy1ene terephthalate) (PET) has increased each year, and PET has long been the leading feedstock polymer for synthetic fiber, film, and other uses. The manufacturing method used for PET has moved from a batch process to a continuous process and the starting raw materials have changed from dimethyl terephthalate and ethylene glycol (EG) to terephthalic acid (TPA) and EG.     

Microwave irradiation as an energy source in poly(ethylene terephthalate) solvolysis

Solvolysis by glycols and alcohols is an established method for the chemical recycling of poly(ethylene terephthalate) (PET). In our work, we investigated the use of microwave radiation as the energy source in PET solvolysis reactions, and the conditions that govern its effectiveness. The main advantage of microwave use are short reaction times, between 4 and 10 min, in which complete PET degradation is achieved. Solvolysis reagents used were methanol, propylene glycol, and polyethylene glycol 400. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1115–1118, 1998     

Kinetics of glycolysis of poly(ethylene terephthalate) under microwave irradiation

The glycolysis of poly(ethylene terephthalate) (PET) was carried out using excess ethylene glycol (EG) in the presence of zinc acetate as catalysts under microwave irradiation. The effects of particle size, microwave power, the weight ratio of EG to PET, the weight ratio of catalyst to PET, reaction temperature and stirring speed on the yield of bis(hydroxyethyl terephthalate)(BHET) were investigated. The experimental results indicated that the glycolysis rate was significantly influenced by stirring speed and initial particle size. The optimal parameters of glycolysis reactions were the weight ratio of catalyst to PET of 1%, the weight ratio of EG to PET of 5, 500 W and 196°C, the yield of BHET reached to 78% at only 35 min. The glycolysis products were analyzed and identified by FTIR, differential scanning calorimetry, and elemental analysis. The kinetics of glycolysis of PET under microwave irradiation could be interpreted by the shrinking core model of the film diffusion control. The apparent activation energy was evaluated using the Arrhenius equation and it was found to be 36.5 KJ/mol, which was lower compared to the same process using conventional heating. The experimental results also showed that the reaction time was significantly decreased under microwave irradiation as compared with it by conventional heating. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Aminolytic depolymerization of poly (ethylene terephthalate) bottle waste by conventional and microwave irradiation heating

Poly (ethylene terephthalate) (PET) is the most popular thermoplastic polymer. The ever-growing production and utilization of PET has led to postconsumer waste disposal problems because of its nonbiodegradability. The chemical depolymerization of PET waste is a possible remedy, as it results in some recyclable products. The aminolytic depolymerization of PET bottle waste with hydrazine monohydrate by conventional and nonconventional (with microwave irradiation) heating was carried out with simple chemicals as catalysts, such as sodium acetate and sodium sulfate. The yield of the product was optimized through variations in the time of aminolysis, the catalyst concentration, and the PET:hydrazine monohydrate ratio. The pure product obtained in good yield (86%) was analyzed by Fourier transform infrared spectroscopy, NMR, and differential scanning calorimetry and was identified as terephthalic dihydrazide. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

PET pyrolysis and hydrolysis mechanism in the fixed pyrolyzer

In the conventional polyethylene terephthalate (PET) pyrolysis process, the formation of char by excessive pyrolysis is mainly due to the dehydration mechanism, so water is considered an auxiliary agent that can effectively inhibit excessive pyrolysis. The preparation of terephthalic acid (TPA) by steam-assisted pyrolysis of PET is an effective method to achieve closed-loop recycling of waste PET. To ensure that the reaction is mild enough to reduce excessive cracking products such as char and benzoic acid and thus increase the yield of TPA, it is critical to reduce the reaction rate while maintaining a sufficient excess steam coefficient. Under the optimal operating conditions, when the temperature rise rate was 0.5 °C min⁻¹ and the excess steam coefficient was 150, the yield of TPA was 72.5 wt.%, and the purity was 85.5%. Noticeably, the steam-assisted pyrolysis system is a heterogeneous reaction system whose reaction mechanism is different from the conventional hydrolysis and pyrolysis reactions and has a unique reaction path. The mechanistic study indicates that, in addition to the thermal cracking of PET molecules occurring in conventional pyrolysis, hydroxyl attack and transfer, and supplementation of benzene ring hydrogen also occur between water and intermediate molecules. Meanwhile, it has also been proven that the intermolecular hydrogen transfer between intermediate molecules and water molecules is the key to reduce the intensity of the reaction and inhibit the formation of char. This discovery illustrates the mechanism of the reaction between water and PET in the steam-assisted pyrolysis process in the fixed pyrolyzer and justifies the distinction between it and the pyrolysis and hydrolysis processes of PET. It provides a theoretical basis for optimizing the pyrolysis process of PET, which is essential for the industrialization of TPA preparation from PET steam-assisted pyrolysis.     

Identification of kinetics of direct esterification reactions for PET synthesis based on a genetic algorithm

In this study we propose a method to identify the kinetics of direction esterification reactions for polyethylene terephthalate (PET) based on a genetic algorithm. The reaction rate parameters could be identified successfully by using a genetic algorithm and plant data. The effects of key operating variables (temperature, pressure, monomer feed ratio and residence time) on the reactor performance were also investigated. It was observed that the reactor performance strongly depends on the degree of dissolution of the solid terephthalic acid (TPA) in the reaction mixtures.     

Hydrolysis of poly(ethylene terephthalate) waste bottles in the presence of dual functional phase transfer catalysts

The hydrolysis of poly(ethylene terephthalate) (PET) obtained from waste bottles was studied. The dual functional phase transfer catalyst [(CH₃)₃N(C₁₆H₃₃)]₃[PW₁₂O₄₀] exhibited outstanding catalytic activity to the hydrolysis of PET. Fourier transform infrared spectroscopy and proton nuclear magnetic resonance spectroscopy were used to confirm the main product terephthalic acid (TPA) of hydrolysis. The effects of temperature, time, particle size of PET and dosage of catalyst on hydrolysis reaction were examined. Under the optimum conditions of reaction temperature 145°C, time 2 h, particle size of PET at 0.5–1 mm and dosage of catalyst at 7 wt %, the conversion of PET and the yield of TPA were almost 100% and 93%, respectively. After easily separated from the product, the catalyst could be reused more than three times without obvious decrease in the conversion of PET and yield of TPA. An economical and convenient process was developed for hydrolysis of PET. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2790–2795, 2013     

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