Glycolytic aminolysis of poly(ethylene terephthalate) waste for recovery of value‐added comonomer at atmospheric pressure

Reaction of poly(ethylene terephthalate) waste (PETW) powder with ethylene glycol (EG) using 0.003 mol lead acetate as a catalyst was carried out in a batch reactor at 470 K under atmospheric pressure. Reactions were undertaken with various particle sizes ranging from 50 to 512.5 μm and reaction times ranging from 10 to 60 min at 10‐min intervals. A low molecular weight product of PETW was obtained using this reaction. Then hydrazine monohydrate, chlorobenzene, and cyclohexylamine (CHA) were introduced to convert the low molecular weight product of PETW into terephthalohydrazide (TPHD). To increase the PETW conversion rate, an external catalyst (lead acetate) was introduced during the reaction. The reaction product was deposited onto the surface of unreacted PETW that was removed from the surface by introducing dimethyl sulfoxide. To accelerate the reaction rate CHA was introduced during the second stage of reaction, which has industrial significance. Depolymerization of PETW was proportional to the reaction time and inversely proportional to the particle size of PETW. Analyses of value‐added products (TPHD and EG) as well as PETW were undertaken. A kinetic model was developed and experimental data were simulated consistent with the model. A thermodynamic study was undertaken because this is required during the transfer of laboratory data through the pilot plant for commercialization. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3437–3444, 2003     

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.     

Preparation and characterization of water‐extended polyester based on recycled poly(ethylene terephthalate)

An unsaturated polyester resin was prepared that was based on the reaction of oligomers obtained from the depolymerization of poly(ethylene terephthalate) waste products, with both maleic anhydride and sebacic acid. The structure of the produced polyester was compared with that prepared from the reaction of dimethyl terephthalate with both maleic anhydride and sebacic acid with IR and NMR spectroscopy. Water‐extended polyester resins were prepared from these two polyesters through curing with styrene in the presence of various amounts of water with benzoyl peroxide as an initiator. The mechanical properties of the prepared water‐extended polyesters, as well as scanning electron microscopy, were investigated. The use of water‐extended polyesters based on recycled poly(ethylene terephthalate) waste for the preparation of decorative art objects and statues was investigated. Therefore, three pharaonic statues representing Tutankhamen, Nefertiti, and a black head of a cat were prepared. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3693–3699, 2003     

Recycling of Waste PET: Usage as Secondary Plasticizer for PVC

Postconsumer water bottle poly(ethylene terephthalate) (PET) flakes were depolymerized with ethylene glycol (EG) by the glycolysis reaction in the presence of zinc acetate as the catalyst. In the depolymerization reactions, different weight ratios of PET/EG were used. In order to obtain polyesters used as PVC plasticizers, these glycolysis products containing hydroxyl end groups were reacted with an adipic acid (AA)–containing diacid group at equivalent amounts. In order to obtain PVC plastisols, PVC was dispersed into a plasticizers' mixture composed of di-isooctyl phthalate (DOP) and polyester products by using a high-speed mixer (PVC/plasticizers, 65/35 w/w). For the preparation of plasticizer mixture polyester products were used at a weight ratio of 20%, 40%, 60% of DOP. Plasticized PVC sheets were prepared from plastisols and their glass transition temperatures (T_g), migration, and mechanical properties were determined. The results show that the polyester products obtained from glycolysis products of waste PET can be used as secondary plasticizers, with DOP for PVC.     

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     

含氟PET的非等温结晶动力学

通过分子设计,在聚对苯二甲酸乙二酯(PET)大分子主链上同时引入耐热性的芳杂酰亚胺环和含氟基团。以六氟二酐和氨基十一酸为原料,通过热环化反应合成酰亚胺二酸,再用制备的酰亚胺二酸单体按照不同配比和对苯二甲酸二甲酯、乙二醇按一定比例调节投料比进行酯化缩聚反应,合成一系列含氟PET。利用差示扫描量热(DSC)法研究了聚合物非等温结晶行为,发现纯PET的结晶能力最强,随着含氟量的增加,结晶能力减弱。采用Jeziorny法分析了纯PET和含氟PET的非等温结晶动力学,发现结晶速率常数随着含氟链段的加入而减小,表明含氟链段的加入降低了PET的结晶能力。     

聚酯废丝的化学回收研究

使用乙二醇(EG)对有色聚酯(PET)废料解聚,经分离提纯,得到对苯二甲酸二乙二醇酯(BHET)。研究了物料比、反应温度、反应时间、催化剂对醇解率的影响。结果表明,在m(乙二醇)∶m(PET)=2∶1,反应温度196℃,反应时间3 h,催化剂用量为PET质量的0.5%条件下,聚酯解聚很彻底,产物羟值可达434 mg/g以上,主要成分是BHET单体及其低聚物。并通过IR,DSC,HPLC验证了产物的组成,BHET单体纯度可达96.457%。     

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.     

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).     

Synthesis and properties of UV-curable waterborne unsaturated polyester for wood coating

UV-curable waterborne unsaturated polyesters for wood coatings were prepared. The effects of different polyols and acids on the properties of the UV-curable waterborne unsaturated polyesters were investigated. Several different unsaturated polyester prepolymers were prepared from three different polyols [ethylene glycol (EG), diethylene glycol (DEG), and propylene glycol (PG)] and three different acids [tetrahydrophthalic anhydride (THPAn), terephthalic acid (TPA), and trimellic anhydride (TMAn)]. UV-curable coating materials were formulated from the prepolymers and 2-hydroxy-2-methylphenyolpropane-1-one as a photoinitiator with distilled water as a diluent. Trimethylolpropane diallyl ether was used as an air inhibitor of cure. The dynamic mechanical studies showed the properties of those unsaturated polyesters were well correlated with their glass transition temperature behaviors. It was found that the unsaturated polyester prepared with 60/40 (mol %) TMAn/THPAn and the equimolar mixture of EG, DEG, and PG showed balanced coating properties such as good tensile properties and weatherability, as well as proper viscosity (ca. 2500 cps) when using distilled water as a diluent. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 695–708, 1998     

Unsaturated polyesters based on bis(2-hydroxyethyl)terephthalate

A series of unsaturated polyesters based on bis(2-hydroxyethyl)terephthalate, ethylene glycol, propylene glycol, diethylene glycol, maleic anhydride and styrene were prepared. Properties of these castings were investigated and compared with those analogues based on dimethyl terephthalate or polyester oligomers formed by depolymerization of poly(ethylene terephthalate). It is found that properties of castings based on bis(2-hydroxyethyl)terephthalate are superior to those based on polyester oligomer. When compared with those based on dimethyl phthalate, the castings have higher hardness and heat distortion temperature, but lower tensile strength and elongation; other properties are very similar.     

Blends of thermoplastic polyesters with amorphous polyamide. I. Thermal and crystallization behavior

The thermal and crystallization behavior of blends of three thermoplastic polyesters with different degrees of crystallizability, with an amorphous aromatic polyamide is reported. The thermoplastic polyesters used in the investigation were poly(butylene terephthalate) (PBT), poly(ethylene terephthalate) (PET) and a co-polyester of 1,4 cyclohexane-dimethanol, ethylene glydol and terephthalic acid (PETG). The blends exhibited a single glass transition temperature indicating mlseibility in the amorphous phase. The results of thermal analysis indicated that the crystallization of all the three polyesters is facilitated in the molten phase as a result of blending. The blending significantly Increased the degree of crystallinity of PET, but there was no change in the crystallinity of PBT. It is thus observed that the extent of change in both the crystallization rate and the degree of crystallinity of polyesters depend on the inherent crystallizability of the individual polyester.     

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.     

A study of aromatic polyester/chlorinated polymer blends

A large number of studies have been devoted in recent years to the miscibility behavior of linear polyesters with chlorinated polymers, including poly(vinyl chloride) (PVC), chlorinated PVC, chlorinated poly(ethylenes), and copolymers of vinylidene chloride (Saran). However, similar studies with aromatic polyesters are lacking. It is the purpose of this paper to compare the properties of blends made of poly(ethylene terephthalate), poly(butylene terephthalate) or poly(hexamethylene terephthalate) and of various chlorinated polymers. It is shown that a high concentration of chlorine atoms is required to achieve miscibility. Moreover, there is a “miscibility window” in terms of the carbonyl concentration of polyesters, immiscibility being found for carbonyl concentrations outside this window, A similar behavior was observed before for linear polyester/chlorinated polymer blends and for polyester/polycarbonate blends. Solid state small-angle light scattering experiments were also conducted to follow the morphology of the blends as a function of composition. Spherulites were found but their size vary with composition.     

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     

聚氨酯用二聚酸聚酯二醇的合成

研究了以辛酸亚锡为催化剂、二聚酸（DA）与乙二醇（EG）为原料、制备聚氨酯用二聚酸聚酯二醇的方法,讨论了催化剂的类型和用量、反应温度、原料醇酸比、反应时间等对酯化率的影响,并用红外光谱对合成产物进行了表征。结果表明,DA与EG摩尔配比为1：2．4,催化剂辛酸亚锡用量为原料总质量的0．3％,反应温度在1h内缓慢升温到190℃,然后保温反应4h,并在130℃、2．66kPa下减压3h,酯化率可达99．7％,产品羟值为95mgKOH／g,酸值0．26mgKOH／g。     

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     

Network formation in poly(ethylene terephthalate) by thermooxidative degradation

Gelation of poly(ethylene terephthalate) by heating at 263°–300°C was investigated. Under nitrogen flow, crosslinks were scarcely formed. However in air, degradation and crosslinking were common, and these were accelerated by purging gaseous and sublimable degradation products out of the system with a stream of air. The main component of the sublimate was terephthalic acid. Infusible and insoluble gel was treated with methanol at 260°C, and then the methanolysis products were separated into two parts. The methanol-insoluble part exhibited a polyene structure with ester groups, and the methanol-soluble part contained dimethyl terephthalate, ethylene glycol, and some 1,2,4-butanetriol. To clarify the relation between the crosslinking and the formation of vinyl ester groups, the degradation of vinyl methyl terephthalate was studied. Thermoxidative degradation of linear polyesters other than poly(ethylene terephthalate) was also studied. Poly(ethylene isophthalate) and poly(ethylene sebacate) were easily gelated. However, poly(trimethylene terephthalate) and poly(neopentyl terephthalate) were scarcely gelated. The primary reaction leading to crosslinking is assumed as follows. At first, the random scission of polyester chain may take place forming carboxylic acids, vinyl esters, aldehydes, etc. After accumulation of vinyl esters to some extent, vinyl polymerization of the esters takes place and network structures are formed.