Supercritical methanol for polyethylene terephthalate depolymerization: observation using simulator

To apply PET depolymerization in supercritical methanol to commercial recycling, the benefits of supercritical methanol usage in PET depolymerization was investigated from the viewpoint of the reaction rate and energy demands. PET was depolymerized in a batch reactor at 573 K in supercritical methanol under 14.7 MPa and in vapor methanol under 0.98 MPa in our previous work. The main products of both reactions were the PET monomers of dimethyl terephthalate (DMT) and ethylene glycol (EG). The rate of PET depolymerization in supercritical methanol was faster than that of PET depolymerization in vapor methanol. This indicates supercritical fluid is beneficial in reducing reaction time without the use of a catalyst. We depicted the simple process flow of PET depolymerization in supercritical methanol and in vapor methanol, and by simulation evaluated the total heat demand of each process. In this simulation, bis-hydroxyethyl terephthalate (BHET) was used as a model component of PET. The total heat demand of PET depolymerization in supercritical methanol was 2.35 x 10(6)kJ/kmol Produced-DMT. That of PET depolymerization in vapor methanol was 2.84 x 10(6)kJ/kmol Produced-DMT. The smaller total heat demand of PET depolymerization in supercritical methanol clearly reveals the advantage of using supercritical fluid in terms of energy savings.     

Kinetics and Thermodynamics of Hydrolytic Depolymerization of Polyamide Waste at Various Temperature and Autogenious Pressure by High-Pressure Autoclave

Hydrolytic depolymerization of polyamide waste in water was studied using 0.5 L high pressure autoclave at temperatures of 235, 240, 245, 250 °C and at autogenious pressure 480, 500, 520, and 600 psi (pound per square inch).The reaction rate constant, energy of activation, enthalpy of activation, entropy of activation and equilibrium constant were calculated from the experimental data obtained. The maximum depolymerization (59.2%) of polyamide waste into monomer caprolactum was obtained at 250 °C and 600 psi pressure. The reaction rate constant was obtained on basis of measurement of amine value and residual weight. The depolymerization reaction was found to be pseudo first order with reaction rate constant of the order of 10⁻³ min⁻¹. The enthalpy, entropy and free energy of activation were recorded as 85.75, −0.1354 and 156.59 kJ mol⁻¹ respectively at the experimental conditions for maximum depolymerization of polyamide waste. The thermodynamic equilibrium constant for this hydrolysis reaction was found to be 2.3 × 10⁻¹⁶.     

Depolymerization of Waste PET with Phosphoric Acid–Modified Silica Gel Under Microwave Irradiation

Chemical recycling of waste poly(ethylene terephthalate) (PET) using phosphoric acid–modified silica gel as a solid catalyst is reported. Advantageously, microwave irradiation was used to progress the depolymerization of PET. In this study, depolymerization of PET with a small amount of water is suggested as a suitable method. The depolymerized product, terephthalic acid was obtained and assigned by ¹H NMR and FT-IR spectroscopy. Finally, over 90 % conversion to terephthalic acid was achieved when waste plastic bottles were treated with the method. This results confirm the importance of the microwave power technique as a promising recycling method for plastic bottles made from PET, resulting in monomer recovery in addition to substantial energy saving.     

Improved method for the formation of recycled resins from depolymerized products of waste fiber-reinforced plastics: simple and effective purification of recovered monomers by washing with water

The synthesis of recycled plastics from recovered monomeric materials obtained from the depolymerization reaction of fiber-reinforced plastics (FRP) was examined. The depolymerization reaction of FRP in the presence of N,N-dimethylaminopyridine (DMAP) smoothly yielded the corresponding monomers, which mainly consisted of dimethyl phthalates. The polymerization reaction with this monomer failed to form the corresponding unsaturated polyesters due to contamination by N-methyl-4-pyridone, a decomposition product of DMAP. An efficient purification of the recovered monomer was achieved by washing with water, and the purified monomer successfully yielded the corresponding polymers. A hardness test revealed that the polymers were as hard as the polyester made from virgin materials. The present modification provides a practical method for the preparation of recycled plastics from depolymerized plastics.     

Recycling of waste PET into useful textile auxiliaries

Polyethylene terephthalate (PET) waste fibers were initially depolymerized using a glycolysis route in the presence of sodium sulfate as a catalyst, which is a commonly used chemical and ecofriendly as compared to heavy metal catalysts. Good yield of the pure monomer bis(2-hydroxyethylene terephthalate) (BHET) was obtained. Further, to attempt its reuse, the purified BHET was converted to different fatty amide derivatives to obtain quaternary ammonium compounds that have a potential for use as softener in the textile finishing process. The products were characterized by infrared spectroscopy. Application of these synthesized compounds was carried out on cotton fabric; they were evaluated for performance and were found to give good results. The chemicals used during depolymerization and reuse of PET are inexpensive and comparatively less harmful to the environment, and thus offer advantages in the chemical recycling of polyester waste fibers.     

Evaluation of Poly(ethylene-terephthalate) Products of Chemical Recycling by Differential Scanning Calorimetry

Poly (ethylene-terephthalate), (PET) bottles waste was chemically recycled by glycolysis and hydrolysis. The depolymerization processes were carried out in different time intervals from 5 to 360 min, in two different molar ratios of PET/EG, 1:5 and 1:18 and at different temperatures. The PET glycolysis leads to formation of bis(2-hydroxy-ethyl)terephthalate (BHET) monomer and PET oligomers with hydroxyl and carboxyl end groups while PET hydrolysis is followed by formation of monomers terephthalic acid (TPA) and ethylene glycol (EG). Fractions of monomers and oligomers were further characterized by FTIR spectroscopy and by differential scanning calorimetry (DSC). The results show that DSC is successful method to describe the different structures of oligomers formed during chemical recycling of PET.     

Investigation of conventional analytical methods for determining conversion of polyethylene terephthalate waste degradation via aminolysis process

Journal of Material Cycles and Waste Management - There is a growing interest in the depolymerization of polyethylene terephthalate (PET) waste for both environmental and economic reasons by...     

One-Pot Reaction of Waste PET to Flame Retardant Polyurethane Foam,via Deep Eutectic Solvents-Based Conversion Technology

Depolymerization of polyethylene terephthalate (PET) is a promising technology for producing recycled monomers. Using a deep eutectic solvent (DES)-based catalyst, the PET glycolysis process produces bis-(2-hydroxyethylene terephthalate) (BHET). This recycled monomer reacts with isocyanate and forms polyurethane foam (PUF). The DES-based one-pot reaction is advantageous because it is a low-energy process that requires relatively lower temperatures and reduced reaction times. In this study, choline chloride/urea, zinc chloride/urea, and zinc acetate/urea based DESs were adopted as DES catalysts for glycolysis. Subsequently, the conversion of PET, BHET yield, and OH values were evaluated. Both filtered and unfiltered reaction mixtures were used as polyols for PUF polymerization after characterization of the acid and hydroxyl values of the polyols, as well as the NCO (–N=C=O) value of isocyanate. In the case of unfiltered reaction mixtures, PUF was obtained via a one-pot reaction, which exhibited higher thermal stability than PUF made from the filtered polyols. This outcome indicated that oligomeric BHET containing many aromatic moieties in unfiltered polyols contributes to the thermal stability of PUF. This environmentally friendly and relatively simple process is an economical approach for upcycling waste PET.

     

镁铝水滑石制备复合金属氧化物及其催化处理废弃聚酯材料

采用共沉淀法合成了镁铝水滑石并将其在不同温度下煅烧得到复合金属氧化物。将两者作为催化剂用于醇解聚对苯二甲酸乙二醇酯(PET)反应中。实验结果表明:复合金属氧化物的催化活性明显高于其前体,最佳煅烧温度为500℃;在催化剂与PET质量比为1.0%、醇解反应时间为50 min时,产物对苯二甲酸乙二醇酯(BHET)的产率可达到81%。镁铝水滑石煅烧后得到的复合金属氧化物是一种高效、环境友好型醇解PET催化剂,可以替代目前常用的均相催化剂。     

Chemical Recycling of PET Waste with Multifunctional Pentaerythrytol in the Melt State

Chemical recycling of poly(ethylene terephthalate) PET waste in the melt state through alcoholysis with multifunctional alcohol—pentaerythrytol (PENTE)—was performed in a internal mixer Haake Rheomix 600, at 250 °C, 60 rpm, for 10 min, in presence of zinc acetate. The following PET:PENTE molar ratios 1:0; 1:0.16; 1:0.48 and 1:3.4 were studied. The chemical structure of the end-products was characterized by FT-IR. Thermal properties and X-ray diffractograms were also assessed. The esterification and alcoholysis reactions took place and were dependent on the molar ratio. The first one is dominant in compositions rich in PET leading to the formation of star-branching copolymer. The second one brings about the PET oligomerization and an oligoester named herein bis(tri-hydroxylneopentyl) terephthalate (BTHNPT) was obtained. The end-products have potential application as asphalt additive or adhesive.     

Lactic Acid Production by Hydrolysis of Poly(Lactic Acid) in Aqueous Solutions: An Experimental and Kinetic Study

Poly(lactic acid) (PLA) is increasingly utilized as an alternative to petroleum-based polymers in order to reduce their impact on the environment. The monomer of PLA is mainly produced from corn, which, in addition to its food utilization, can be also used for the production of bioethanol or biofuels. In this work the depolymerization (chemical recycling) of PLA pellets in a batch reactor at temperatures near the melting temperature of solid PLA has been investigated to produce lactic acid. New experimental data are presented and a kinetic model is provided for a first analysis. With a residence time less than 120 min, a yield of lactic acid greater than 95 % has been obtained at temperatures of 160 and 180 °C for pressure equal to water vapour pressure and a water/PLA ratio by weight equal ~10.     

Synthesis of unsaturated polyester resin from glycolysed postconsumer PET wastes

The purpose of this study was to explore ways to extend the chemical recycling of poly(ethylene terephthalate) (PET) as a valuable feedstock for chemical processes. First, PET wastes were depolymerised using a glycolysis method in the presence of sodium carbonate, which is considered to be a less environmentally damaging option for a catalyst. Good yields of the monomer bis(2-hydroxyethyl) terephthalate (BHET) were obtained (80 %). Second, to develop an economically viable recycling programme for the reclaimed BHET, the conversion of purified BHET into unsaturated polyester resins (UPR) was studied. The recovered monomer was thus polyesterified with maleic anhydride and subsequently mixed with styrene monomer to prepare UPRs. The resins were casted by a crosslinking reaction using methyl ethyl ketone peroxide and cobalt 2-ethylhexanoate as the initiator and catalyst, respectively. The polyesterification reaction was followed by gel permeation chromatography. The curing process was studied by differential scanning calorimetry and infrared spectroscopy. The cured resin was subjected to various characterisation methods in order to determine its chemical, physical and mechanical properties. Resins with suitable properties for commercial application were obtained.     

Catalytic hydrothermal depolymerization of nylon 6

Depolymerization of nylon 6 to produce ε-caprolactam using an environmentally friendly heteropoly acid catalyst was studied at temperatures between 553 and 603 K in water. The products of depolymerization were analyzed qualitatively and quantitatively by means of mass spectrometry and high-performance liquid chromatography. The results showed that the depolymerized product was mainly ε-caprolactam with a little 6-aminocaproic acid and oligomers. The phosphotungstic heteropoly acid used as a catalyst can improve the hydrolysis rate and yield of ε-caprolactam. The optimum hydrolysis conditions for ε-caprolactam yield were as follows: phosphotungstic heteropoly acid content, 3%; reaction temperature, 573 K; and reaction time, 85 min. Under these conditions, the yield of ε-caprolactam was 77.96%. In the temperature range 553–603 K, the activation energy of 3% phosphotungstic heteropoly acid-catalyzed depolymerization was evaluated as 77.38 kJ/mol, which is lower than the 86.64 kJ/mol value for no catalyst.     

Synthesis and Characterization of Polyols and Polyurethane Foams from PET Waste and Crude Glycerol

In this study, polyethylene terephthalate (PET) waste from post-consumer soft-drink bottles and crude glycerol from the biodiesel industry were used for the preparation of polyols and polyurethane foams. PET waste was firstly depolymerized by the glycolysis of diethylene glycol. The glycolyzed PET oligomers were then reacted with crude glycerol at different weight ratios to produce polyols via a series of reactions, such as esterification, transesterification, condensation, and polycondensation. The polyols were characterized by titration, viscometry, gel permeation chromatography (GPC), and differential scanning calorimetry. Subsequently, polyurethane (PU) foams were made via the reaction between the produced polyols and polymeric methylene-4,4′-diphenyl diisocyanate and were characterized by mechanical testing, scanning electron microscopy, and thermogravimetric analysis. Polyols from crude glycerol and their PU foams were also prepared to compare properties with those of polyols and PU foams from PET and crude glycerol. The influence of aromatic segments existing in glycolyzed PET and glycerol content on the properties of the polyols and PU foams was investigated. It was found that aromatic segments of polyols from glycolyzed PET helped increase their molecular weights and improve thermal stability of PU foams, while high glycerol content in polyols increased the hydroxyl number of polyols and the density and compressive strength of PU foams.     

Chemical depolymerisation of PET complex waste: hydrolysis vs. glycolysis

The huge increase in the generation of post-consumer plastic waste has produced a growing interest in eco-efficient strategies and technologies for their appropriate management and recycling. In response to this, PROQUIPOL Project is focused on developing, optimizing and adapting feedstock recycling technologies as an alternative for management for the treatment of complex plastic waste. Among the different plastic wastes studied, PROQUIPOL Project is working on providing a suitable treatment to the highly colored and complex multilayered post-consumer waste fractions of polyethylene terephthalate (PET) by chemical depolymerisation methods. Glycolysis and alkali hydrolysis processes have been studied with the aim of promoting the transformation of PET into the bis(2-hydroxyethyl) terephthalate monomer and terephthalic acid, respectively. In both cases operational conditions such as temperature, reaction time, catalyst to PET rate and solvent to PET rate have been considered to optimize product yield, achieving values near to 90 % and monomer purities over 95 % in both processes. This paper presents results obtained for each treatment as well as a simplified comparison of technical, economic and environmental issues.     

Combination of three-stage sink-float method and selective flotation technique for separation of mixed post-consumer plastic waste

The aim of this research was to separate the different plastics of a mixed post-consumer plastic waste by the combination of a three-stage sink-float method and selective flotation. By using the three-stage sink-float method, six mixed-plastic wastes, belonging to the 0.3-0.5 cm size class and including high density polyethylene (HDPE), polypropylene (PP), polyvinylchloride (PVC), polystyrene (PS), polyethylene terephthalate (PET) and acrylonitrile-butadiene-styrene copolymers (ABS) were separated into two groups, i.e., a low density plastic group (HDPE and PP) and a high density plastic group (PET, PVC, PS and ABS) by tap water. Plastic whose density is less than that of the medium solution floats to the surface, while the one whose density is greater than that of the medium solution sinks to the bottom. The experimental results elucidated that complete separation of HDPE from PP was achieved by the three-stage sink-float method with 50% v/v ethyl alcohol. To succeed in the separation of a PS/ABS mixture from a PET/PVC mixture by the three-stage sink-float method, a 30% w/v calcium chloride solution was employed. To further separate post-consumer PET/PVC and PS/ABS based on plastic type, selective flotation was carried out. In order to succeed in selective flotation separation, it is necessary to render hydrophilic the surface of one or more species while the others are kept in a hydrophobic state. In flotation studies, the effects of wetting agent, frother, pH of solution and electrolyte on separation were determined. The selective flotation results showed that when using 500 mg l(-1) calcium lignosulfonate, 0.01 ppm MIBC, and 0.1 mg l(-1) CaCl2 at pH 11, PET could be separated from PVC. To separate ABS from PS, 200 mg l(-1) calcium lignosulfonate and 0.1 mg l(-1) CaCl2 at pH 7 were used as a flotation solution. Wettability of plastic increases when adding CaCl2 and corresponds to a decrease in its contact angles and to a reduction in the recovery of plastic in the floated product.     

Chemical Recycling of Polyamide Waste at Various Temperatures and Pressures Using High Pressure Autoclave Technique

Chemical recycling of polyamide waste in water was studied using 0.5 L high pressure autoclave at temperatures of 150, 200, 210, 220,230 and 240 °C and at various pressures of 100, 200, 300, 400, 500, 600 and 700 psi (pound per square inch). Viscosity average molecular weight of the polyamide waste sample was determined by Ostwald method and recorded as 1.928 × 10³. The reaction was found to be first order with velocity constant in order of 10⁻² min⁻¹. The velocity constant and percent conversion of depolymerization reaction at 240 °C and 700 psi pressure were recorded as 2.936 × 10⁻² min⁻¹ and 99.99% respectively. The velocity constant was obtained on the basis of measurement of amine value. Kinetic and thermodynamic parameters such as energy of activation, frequency factor, enthalpy of activation were found to be 10.6 kJ mole⁻¹, 0.3719 min⁻¹ and 6.3 kJ mole⁻¹ respectively, at the optimum conditions for maximum depolymerization of polyamide waste.     

黑索金废水的处理

以球形活性炭为吸附剂，用吸附法处理黑索金（ＲＤＸ）废水，出水能够达到国家排放标准，球形活性炭的动态饱和吸附量为０．１２３－０．１４０ｇ／ｇ，吸附带长为２ｍ。吸附饱和的球形活性炭，可用碱液以复再生。笔者还提出了数学模型，导出了处理实验数据公式，此公式可推广应用于同类吸附实验数据处理。     

Characterisation of sugar cane straw waste as pozzolanic material for construction: calcining temperature and kinetic parameters

This paper reports on the influence of calcining temperature (800 and 1000 degrees C) on the pozzolanic activation of sugar cane straw (SCS). The reaction kinetics of SCS ash-lime mixtures were inferred from physicochemical characteristics (X-ray diffraction patterns and thermogravimetry analysis. The fitting of a kinetic-diffusive model to the experimental data (fixed lime versus time) allowed the computing of the kinetic parameters (reaction rate constant) of the pozzolanic reaction. Results obtained confirm that the sugar cane straw ash (SCSA) calcined at 800 and 1000 degrees C have properties indicative of very high pozzolanic activity. No influence of calcining temperature on the pozzolanic activity was observed. Also, no crystalline compounds during the pozzolanic reaction were identified up to 90 days of reaction. Environmental durability and strength of the consequential mortars remain to be assessed.     

Use of plastic waste (poly-ethylene terephthalate) in asphalt concrete mixture as aggregate replacement.

One of the environmental issues in most regions of Iran is the large number of bottles made from poly-ethylene terephthalate (PET) deposited in domestic wastes and landfills. Due to the high volume of these bottles, more than 1 million m3 landfill space is needed for disposal every year. The purpose of this experimental study was to investigate the possibility of using PET waste in asphalt concrete mixes as aggregate replacement (Plastiphalt) to reduce the environmental effects of PET disposal. For this purpose the mechanical properties of plastiphalt mixes were compared with control samples. This study focused on the parameters of Marshall stability, flow, Marshall quotient (stability-to-flow ratio) and density. The waste PET used in this study was in the form of granules of about 3 mm diameter which would replace (by volume) a portion of the mineral coarse aggregates of an equal size (2.36-4.75 mm). In all prepared mixes the determined 6.6% optimum bitumen content was used. In this investigation, five different percentages of coarse aggregate replacement were used. The results showed that the aggregate replacement of 20% by volume with PET granules would result in a reduction of 2.8% in bulk compacted mix density. The value of flow in the plastiphalt mix was lower than that of the control samples. The results also showed that when PET was used as partial aggregate replacement, the corresponding Marshall stability and Marshall quotient were almost the same as for the control samples. According to most of specification requirement, these results introduce an asphalt mix that has properties that makes it suitable for practical use and furthermore, the recycling of PET for asphalt concrete roads helps alleviate an environmental problem and saves energy.