Pyrolysis kinetics of waste PVC pipe.

The pyrolysis kinetics of waste PVC pipe was investigated with a thermal gravimetric analysis system at heating rates of 5, 10, and 30 degrees C/min in a nitrogen atmosphere. Freeman-Carroll method was employed to evaluate kinetic parameters. Two dominant peaks were observed on derivative gravimetric curves, hypothetically suggesting a two-stage apparent reaction model. The first-stage reaction was likely to be represented by stoichiometric reaction to yield volatiles (mainly HCl) and intermediates. The second-stage reaction might be described by thermal degradation of intermediates competitively into gas, liquid, and solid by-products. Quasi-isothermal operations were introduced to verify the reaction types of the first and second reaction. The generation reaction of intermediates achieved at lower temperatures was carried out independently with their decomposition reaction at higher temperatures. The effects of additives on the pyrolysis kinetics of waste PVC pipe seem to be significant, especially on the first-stage reaction. The first-stage reaction was retarded. A merged peak at low temperatures was observed on the derivative thermogravimetry (DTG) curve instead of two peaks usually observed for that of pure PVC resin. The first peak on the DTG curve of pure PVC resin may shift more, resulting in the complete overlap of two peaks. The quantity of evolved HCl was likely to decrease because of interaction of metal components of stabilizers with either HCl or active chlorine atom or both. The final residual fraction increased as a result of pyrolysis of organic forms of additives to yield extra char. On the other hand, the second-stage reaction kinetics demonstrates a similar pattern to that of pure PVC resin, implying that the effects of additives may be less significant in comparison with that at the first-stage reaction.     

Effect of additives on dechlorination of PVC by mechanochemical treatment

Polyvinyl chloride (–CH₂–CHCl–) _n (PVC) was ground with a powdered inorganic material (CaO, CaCO₃, SiO₂, Al₂O₃, or slag) in a planetary ball mill under atmospheric conditions to investigate the effect of additions on its dechlorination. The grinding causes a dehydrochlorinating reaction, forming a mixture of partially dechlorinated PVC and inorganic chloride, depending on the grinding time. The dechlorination increases as the grinding progresses, and is improved with increasing amounts of additives. The most effective additive is a mixture of CaO, SiO₂, and Al₂O₃, which has the same constituent components as blast furnace slag. CaO, a mixture of CaO, SiO₂, and blast furnace slag, are also effective, but CaCO₃ is the least effective additive tired. Received: August 3, 2000 / Accepted: September 21, 2000     

Influence of poly(bisphenol A carbonate) and poly(ethylene terephthalate) on poly(vinyl chloride) dehydrochlorination

Recycling of poly(vinyl chloride) (PVC) waste is a serious problem because of its high chlorine content. Dehydrochlorination of PVC-containing polymer waste produces solid residue char, for which conversion to pyrolysis oil in a petrochemical plant seems to be an attractive way of recycling PVC waste. Unfortunately, some polymer admixtures react with HCl and cause formation of chloroorganic compounds in a char. This article describes the influence of polycarbonates and poly(ethylene terephthalate) on thermal feedstock recycling of PVC wastes using a two-stage method. It was found that the presence of polycarbonate causes the formation of small amounts of benzyl chloride and other chloroaryl or chloroalkylaryl compounds. Poly(ethylene terephthalate) interacts with HCl forming significant amounts of various chlorocompounds – mainly chloroethyl esters of terephthalic and benzoic acids, but derivatives possessing chlorine directly connected to the aromatic ring are also formed.     

Vinyl 2010 — nearing the target date

For almost 10 years, Vinyl 2010 has provided original approaches to technical, environmental, and political problems relating to poly(vinyl chloride) (PVC) material cycles and waste management. On the one hand, PVC has outstanding qualities in a wide range of applications; on the other hand, concerns about potential impacts attributed to production, additives, and waste management led to calls for PVC-specific regulations and mandatory substitution in certain applications. Considering the entire life cycle of PVC products, the industry proposed a comprehensive set of measures rendering production cleaner, eliminating controversial additives, and promoting responsible management of waste, favoring recycling. Vinyl 2010 can now be regarded as a highly successful example of applying voluntary commitments instead of the more usual command and control approach from regulatory authorities.     

Dehydrochlorination behavior of polyvinyl chloride and utilization of carbon residue: effect of plasticizer and inorganic filler

The dehydrochlorination behavior of plasticizer (DOP) and inorganic filler (CaCO₃) contained in PVC samples and the properties of the activated carbons produced from those carbon residues have been investigated. In the dehydrochlorination process, both additives contributed not only to a decrease in HCl yield but also to the prolonged evolution of HCl. Part of the Cl species were observed to be stabilized as CaCl₂ by reaction with calcium ions when CaCO₃ was added. More than 80% of chlorine removal was achieved in all samples at 533 K. The use of potassium as an activation agent led to the production of activated carbon with a specific surface area greater than 1000 m²/g at the low temperature of 1023 K and assisted also in the elimination of residual Cl species by the formation of KCl during activation. Chemical Feedstock Recycling & Other Innovative Recycling Techniques 6     

Carbon accounting for Japanese petrochemicals

This paper discusses two bottom-up models for the estimation of carbon storage and CO₂ emissions related to the nonenergy use of fossil energy carriers. The models show how material flow accounting can be applied to policy making. The nonenergy use emission accounting tables model is a static model, while the chemical industry environmental strategy assessment program (CHEAP) model is a dynamic model of the flows of synthetic organic materials. Both models provide detailed and more accurate estimates of carbon storage in materials than the accounting method that is currently used in the framework of the Intergovernmental Panel on Climatic Change (IPCC) guidelines. The results for both models suggest that carbon storage in synthetic organic materials has been overestimated, and consequently CO₂ emissions have been underestimated. Japanese CO₂ emissions in 1996 were at least 1.9% higher than reported previously. The CHEAP model results indicate that the net carbon storage (storage − emissions in waste incineration) will decrease during the next few decades. This decrease is mainly driven by changing waste management practice. Received: December 8, 2000 / Accepted: August 15, 2001     

Energy recovery from waste incineration: Assessing the importance of district heating networks

Municipal solid waste incineration contributes with 20% of the heat supplied to the more than 400 district heating networks in Denmark. In evaluation of the environmental consequences of this heat production, the typical approach has been to assume that other (fossil) fuels could be saved on a 1:1 basis (e.g. 1 GJ of waste heat delivered substitutes for 1 GJ of coal-based heat). This paper investigates consequences of waste-based heat substitution in two specific Danish district heating networks and the energy-associated interactions between the plants connected to these networks. Despite almost equal electricity and heat efficiencies at the waste incinerators connected to the two district heating networks, the energy and CO₂ accounts showed significantly different results: waste incineration in one network caused a CO₂ saving of 48 kg CO₂/GJ energy input while in the other network a load of 43 kg CO₂/GJ. This was caused mainly by differences in operation mode and fuel types of the other heat producing plants attached to the networks. The paper clearly indicates that simple evaluations of waste-to-energy efficiencies at the incinerator are insufficient for assessing the consequences of heat substitution in district heating network systems. The paper also shows that using national averages for heat substitution will not provide a correct answer: local conditions need to be addressed thoroughly otherwise we may fail to assess correctly the heat recovery from waste incineration.     

Degradation of PVC Containing Mixtures in the Presence of HCl Fixators

Degradation of a model polymer mixture (PVC/PS/PE) and a waste polymer mixture in the presence of HCl fixators (Red Mud, precipitated CaCO₃ and dolamite) was studied using thermal gravimetric analysis (TGA) and a cycled-spheres-reactor. The experiments in cycled-spheres reactor model were performed by stepwise pyrolysis. Liquid products and HCl from each step were collected separately. For the model polymer mixture, the precipitated CaCO₃ showed the best effect on the fixation of evolved HCl and the reduction of chlorine content in the liquid products whereas RM yielded the best result for the waste polymer mixture. In addition, using HCl fixator also affected the degradation of both types of polymer mixture, leading to the formation of more gaseous and less residue.     

Reductive decomposition of waste gypsum with SiO<Subscript>2</Subscript>, Al<Subscript>2</Subscript>O<Subscript>3</Subscript>, and Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> additives

From the point of view of a sustainable and environment-friendly society based on the recycling of material resources, it is preferable to utilize waste gypsum as a substitute for lime, which is currently produced by the calcination of limestone. In the present work, the reductive decomposition of CaSO₄ was investigated under an atmosphere of CO: 2 vol%, CO₂: 30 vol%, with N₂ as a carrier gas without and with the addition of SiO₂, Al₂O₃, or Fe₂O₃. It was found that the decomposition temperature of CaSO₄ was significantly reduced from 1673 K to 1223 K when only 5 wt% Fe₂O₃ was added to CaSO₄. In the case of the addition of SiO₂ or Al₂O₃ to CaSO₄, the decomposition temperature was reduced from 1673 K to 1623 K. This was due to the formation of composite oxides (calcium ferrite, calcium silicate, or calcium aluminate) during the reaction of CaSO₄ with the additives at a lower temperature. In addition, the formation of unfavorable product CaS was inhibited in the presence of 5 wt% Fe₂O₃, and this inhibition effect further increased as the addition of Fe₂O₃ was increased. In contrast, no significant effect on the inhibition of CaS formation was observed on the addition of SiO₂ or Al₂O₃.     

Studies on the dechlorination and oil-production technology of waste plastics

 Recycle technology for waste plastics containing polyvinyl chloride (PVC) has been developed in the Hokkaido National Industrial Research Institute for the production of solid and liquid fuel, and has established a recycling process which includes a dechlorination process for PVC plastics, and a two-stage catalytic pyrolysis process for plastics using zeolite catalysts. The dechlorination equipment consists of a two-axis screw extruder with a heating element, which can remove chlorine up to 99.9 wt. % from PVC containing plastics as hydrogen chloride. The product had about 44 000 kJ/kg calorific value and was fed into the next oil production process, although it could also be used as a solid fuel. Natural and synthetic zeolite were used as catalysts for the two-stage catalytic process, which produced a light oil with a boiling point which was between those of kerosene and gasoline. The yield of this oil reached 82 wt. %. The chemical type was analyzed using liquid chromatography, and was found to have many aromatic compounds. These technologies make it possible to produce a nonpolluting, high-calorie solid fuel and a liquid fuel very efficiently. Received: July 19, 2000 / Accepted: September 21, 2000     

Development of a catalytic dehalogenation (Cl,Br) process for municipal waste plastic-derived oil

Dehalogenation is a key technology in the feedstock recycling of mixed halogenated waste plastics. In this study, two different methods were used to clarify the effectiveness of our proposed catalytic dehalogenation process using various carbon composites of iron oxides and calcium carbonate as the catalyst/sorbent. The first approach (a two-step process) was to develop a process for the thermal degradation of mixed halogenated waste plastics, and also develop dehalogenation catalysts for the catalytic dehydrochlorination of organic chlorine compounds from mixed plastic-derived oil containing polyvinyl chloride (PVC) using a fixed-bed flow-type reactor. The second approach (a single-step process) was the simultaneous degradation and dehalogenation of chlorinated (PVC) and brominated (plastic containing brominated flame retardant, HIPS–Br) mixed plastics into halogen-free liquid products. We report on a catalytic dehalogenation process for the chlorinated and brominated organic compounds formed by the pyrolysis of PVC and brominated flame retardant (HIPS–Br) mixed waste plastics [(polyethylene (PE), polypropylene (PP), and polystyrene (PS)], and also other plastics. During dehydrohalogenation, the iron- and calcium-based catalysts were transformed into their corresponding halides, which are also very active in the dehydrohalogenation of organic halogenated compounds. The halogen-free plastic-derived oil (PDO) can be used as a fuel oil or feedstock in refineries.     

Mechanochemical dechlorination of polyvinyl chloride with calcium sulfates

Polyvinyl chloride (PVC) was milled with hydrated or unhydrated calcium sulfates (CaSO₄·2H₂O or CaSO₄) in air by using a planetary mill to investigate mechanochemical dechlorination behavior. The milling process resulted in size reduction and in the breaking of bonds leading to mechanically induced solid state reaction, forming CaCl₂ and dechlorinated hydrocarbon with C=C double bonds in the product. Washing the milled mixtures with water at room temperature allowed removal of the chloride formed during milling, and more than 95% of the chlorine in PVC was removed from a mixture milled for 4 h. This process could offer a potential route for the handling and disposal of both PVC and gypsum wastes. H₂S gas was generated during milling; more H₂S was released from the unhydrated sample than from the hydrated sample.     

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.     

Preparation and Characterization of PVC Matrix Composites with Biochemical Sludge

Biochemical sludge (BS), generated in the waste water treatment of paper mills, was pretreated by enzyme hydrolysis. The effect and action mechanism of the enzymatic treatment on the properties of polyvinyl chloride (PVC) matrix composites with BS were discussed. Results showed that when the filler content was 30 wt%, the tensile strength of the PVC composites filled with BS and its modified products which were pretreated by laccase, cellulase and hemicellulase can be increased by 38.64, 67.4, 63.5 and 66.3% than the PVC composite filled with calcium carbonate. When the dosage of filler was 40 wt%, the elastic modulus of PVC composites filled with BS and its above three modified products decreased by 53.3, 52.3, 50.0 and 46.3%, respectively. Meanwhile, the thermal stability of PVC composites can also be improved at the temperature of over 340 °C. It can be concluded that the enzyme pretreatment can improve the application performance of BS usage in PVC matrix composites.     

Feasible conversion of solid waste bauxite tailings into highly crystalline 4A zeolite with valuable application

Bauxite tailings are a major type of solid wastes generated in the flotation process. The waste by-products caused significant environmental impact. To lessen this hazardous effect from poisonous mine tailings, a feasible and cost-effective solution was conceived and implemented. Our approach focused on reutilization of the bauxite tailings by converting it to 4A zeolite for reuse in diverse applications. Three steps were involved in the bauxite conversion: wet-chemistry, alkali fusion, and crystallization to remove impurities and to prepare porous 4A zeolite. It was found that the cubic 4A zeolite was single phase, in high purity, with high crystallinity and well-defined structure. Importantly, the 4A zeolite displayed maximum calcium ion exchange capacity averaged at 296 mg CaCO₃/g, comparable to commercially-available zeolite (310 mg CaCO₃/g) exchange capacity. Base on the optimal synthesis condition, the reaction yield of zeolite 4A from bauxite tailings achieved to about 38.43%, hence, this study will provide a new paradigm for remediation of bauxite tailings, further mitigating the environmental and health care concerns, particularly in the mainland of PR China.     

The city of San José's integrated waste management program: a case study for reaching high levels of diversion

The city of San José, California, USA, has a widely recognized integrated waste management program and is currently diverting close to 50% of its waste stream from landfill disposal. This paper describes the residential and commercial components of the city's waste management program. Information is presented on performance (e.g., types and quantities of materials that are collected, processed, and disposed of), customer service, and costs associated with the program. Received: October 4, 2000 / Accepted: February 15, 2001     

Simultaneous treatment of PVC and oyster-shell wastes by mechanochemical means

This work presents a new process for dechlorinating poly-vinyl chloride (PVC) by the use of oyster-shell waste. The process consists of milling of PVC waste with oyster-shell waste, followed by washing the milled sample with water. The milling of PVC and oyster-shell mixture results in size reduction and rupture in bonds, leading to mechanically induced reactions between the two to form CaCl2 and hydrocarbon with C=C bonds. Washing the milled mixtures with water at room temperature allows complete removal of chlorine from the milled sample. More than 95% of chlorine in PVC was removed when 2h grinding is conducted for the mixture. The present process could offer a potential route to the handling and disposal of oyster-shell and PVC wastes.     

Preparation of MgCr<Subscript>2</Subscript>O<Subscript>4</Subscript> from waste tannery solution and effect of sulfate,chloride, and calcium on leachability of chromium

This paper presents a study regarding the preparation of MgCr₂O₄ from waste tannery solution, and chromium leaching behavior is also investigated with varying amounts of sulfate, chloride and calcium. The phase transformation, crystallinity index and crystallite diameter were characterized using XRD, FT-IR and thermal analysis. A well-crystallized MgCr₂O₄ was successfully prepared at 1400 °C. The sintering temperature had a major impact on the formation of MgCr₂O₄ compared with sintering time. The MgCr₂O₄ phase was observed initially at 400 °C and its crystallite diameter increased with increasing temperature. The concentration of total chromium leached and Cr(VI) decreased gradually with increasing temperature. The considerable amount of Cr(VI) was found in the leachate at 300–500 °C caused by Cr(VI) intermediary products. Sulfate and chlorine could impact the transformation efficiency of chromium adversely, and chlorine has a more significant effect than sulfate. The presence of calcium disturbed the formation of MgCr₂O₄ and new chromium species (CaCrO₄) appeared, which resulted in a sharp increase in the concentration of leached Cr(VI). Incorporating Cr(III) into the MgCr₂O₄ spinel for reusable products reduced its mobility significantly. This was demonstrated to be a promising strategy for the disposal of chromium containing waste resource.     

Determination of specific gravity of municipal solid waste

This investigation was conducted to evaluate experimental determination of specific gravity (G_s) of municipal solid waste (MSW). Water pycnometry, typically used for testing soils was adapted for testing MSW using a large flask with 2000 mL capacity and specimens with 100–350 g masses. Tests were conducted on manufactured waste samples prepared using US waste constituent components; fresh wastes obtained prior and subsequent to compaction at an MSW landfill; and wastes obtained from various depths at the same landfill. Factors that influence specific gravity were investigated including waste particle size, compaction, and combined decomposition and stress history. The measured average specific gravities were 1.377 and 1.530 for as-prepared/uncompacted and compacted manufactured wastes, respectively; 1.072 and 1.258 for uncompacted and compacted fresh wastes, respectively; and 2.201 for old wastes. The average organic content and degree of decomposition were 77.2% and 0%, respectively for fresh wastes and 22.8% and 88.3%, respectively for old wastes. The G_s increased with decreasing particle size, compaction, and increasing waste age. For fresh wastes, reductions in particle size and compaction caused occluded intraparticle pores to be exposed and waste particles to be deformed resulting in increases in specific gravity. For old wastes, the high G_s resulted from loss of biodegradable components that have low G_s as well as potential access to previously occluded pores and deformation of particles due to both degradation processes and applied mechanical stresses. The G_s was correlated to the degree of decomposition with a linear relationship. Unlike soils, the G_s for MSW was not unique, but varied in a landfill environment due both to physical/mechanical processes and biochemical processes. Specific gravity testing is recommended to be conducted not only using representative waste composition, but also using representative compaction, stress, and degradation states.     

Waste polyvinylchloride derived pitch as a precursor to develop carbon fibers and activated carbon fibers

Polyvinylchloride (PVC) was successfully recycled through the solvent extraction from waste pipe with an extraction yield of ca. 86%. The extracted PVC was pyrolyzed by a two-stage process (260 and 410 degrees C) to obtain free-chlorine PVC based pitch through an effective removal of chlorine from PVC during the heat-treatment. As-prepared pitch (softening point: 220 degrees C) was spun, stabilized, carbonized into carbon fibers (CFs), and further activated into activated carbon fibers (ACFs) in a flow of CO2. As-prepared CFs show comparable mechanical properties to commercial CFs, whose maximum tensile strength and modulus are 862 MPa and 62 GPa, respectively. The resultant ACFs exhibit a high surface area of 1200 m2/g, narrow pore size distribution and a low oxygen content of 3%. The study provides an effective insight to recycle PVC from waste PVC and develop a carbon precursor for high performance carbon materials such as CFs and ACFs.