Dechlorination Of Polyvinyl Chloride Research Articles

Low-temperature dechlorination of polyvinyl chloride (PVC) for production of H2 and carbon materials using liquid metal catalysts.

Polyvinyl chloride (PVC) is ubiquitous in everyday life; however, it is not recycled because it degrades uncontrollably into toxic products above 250°C. Therefore, it is of interest to controllably dechlorinate PVC at mild temperatures to generate narrowly distributed carbon materials. We present a catalytic route to dechlorinate PVC (~90% reduction of Cl content) at mild temperature (200°C) to produce gas H2 (with negligible coproduction of corrosive gas HCl) and carbon materials using Ga as a liquid metal (LM) catalyst. A LM was used to promote intimate contact between PVC and the catalytic sites. During dechlorination of PVC, Cl is sequestrated in the carbonaceous solid product. Later, chlorine is easily removed with an acetone wash at room temperature. The Ga LM catalyst is reusable, outperforms a traditional supported metal catalyst, and successfully converts (untreated) discarded PVC pipe.

Hydrothermal carbonisation of polyvinyl chloride in ethanol-water/water system for solid fuels: Dechlorination, characteristics analysis of hydrochar, and reaction path

Polyvinyl chloride (PVC) waste plastic is a typical solid waste. In this paper, the dechlorination and carbonization behavior of PVC in ethanol-water/water system under different process parameters (temperature, residence time, solid-liquid ratio) was studied, and hydrothermal carbon was characterized by SEM, elemental analysis, TG-DTG, XPS, Py-GC/MS. The results show that temperature is the key to the hydrothermal dechlorination of PVC, and the dechlorination efficiency of PVC is the highest by parameter optimization (220°C-90 min-10% S/D-80% E/D), which can reach 96.33 %. With the removal of Cl, the surface of the PVC matrix changed from full and smooth flocculent to honeycomb with uniform pore size distribution. Thermogravimetric analysis shows that the combustion of hydrochar can be divided into three stages: HCl precipitation and volatile combustion, semi-coke and coke combustion, and fixed carbon combustion. The combustion parameters and kinetic parameters of hydrochar were measured, and it was found that the hydrothermal carbonization of PVC at higher temperatures and ethanol-water ratio could improve the combustion performance of hydrochar. The highest calorific value can reach 36.68 MJ/mol. Py-GC/MS analyzed the distribution of the pyrolysis products, and alkylbenzene and aliphatic were the main products of pyrolysis. The structural analysis of hydrochar showed that C–C and CC accounted for the largest proportion, accompanied by a small amount of C–O and CO and trace C–Cl. The possible reaction mechanism of the hydrothermal carbonization of PVC was analyzed based on the distribution of functional groups and compound composition. This work provides an effective and sustainable method for the recycling of refractory chlorinated plastics.

Synergetic treatment of waste tantalum capacitors and polyvinyl chloride by subcritical water: Tantalum recovery, benzoic acid production and dechlorination

The rapid upgrading of electronic products led to the generation of a great deal of waste tantalum capacitors (WTCs). The recovery of WTCs is of great interest due to the high-value metal tantalum and resin materials. However, it is difficult to separate/recover the materials from WTCs because of the special structure and composition. Polyvinyl chloride (PVC) waste with high level of chlorine could result in severe corrosion and emission of chlorinated pollutants in the conventional disposal process. In this study, a synergetic and high-efficiency treatment of WTCs and PVC by subcritical water (SubCW) process was developed based on the interaction of the two kinds of wastes. The interaction between WTCs and PVC in SubCW could significantly reduce the treatment temperature and shorten the reaction time for recovering high-purity metal tantalum from WTCs, and it could also markedly improve the dechlorination efficiency (DE) of PVC. The optimized conditions for the synergetic treatment of WTCs and PVC were 325 ℃, 30 min, solid-to-liquid ratio of 1:5 g/mL, and PVC-to-WTCs ratio of 6:1 g/g. The resin conversion efficiency (RCE) of WTCs and the DE of PVC could reach 100% and 97.39% under the optimized conditions. The HCl released from PVC in SubCW could significantly promote the acid-catalytic hydrolysis of resin materials in WTCs and resulted in the production of abundant phenol/phenol derivates. In turn, hydroxyl functional group of phenol/phenol derivates could enhance the dechlorination of PVC by promoting the hydroxyl substitution reaction pathway. High level of benzoic acid (72.52%) could be obtained from the interaction between the decomposition products of WTCs and PVC by radical and oxidation reactions. The SubCW synergetic process developed in this study provided a high-efficiency and low-energy strategy for metal tantalum recovery, benzoic acid production, and dechlorination from WTCs and PVC wastes.

Hybridization of the thermo-chemical process of polyvinyl chloride in the production of bioethanol using horse hay

The improper disposal of polyvinyl chloride (PVC) is hazardous to the environment. To rectify the inappropriate disposal of PVC, this study proposes a sustainable method to valorize hydrogen chloride (HCl) (from the thermolysis of PVC) in bioethanol (BE) production. Prior to saccharification, lignocellulosic biomass (horse hay) was treated with HCl. The optimized parameters for acid treatment were determined from a series of saccharification tests. In detail, the sugar recovery yield was 75 % after 2 % HCl, 120 °C, and 2 h treatment of horse hay. In addition, this study suggests that a nitrogen source is required during fermentation to enhance BE productivity. To valorize the residual materials from the saccharification of horse hay and dechlorination of PVC, they were pyrolyzed. Co-pyrolysis of the residues was performed in a CO2 gas environment. The gas-phase reaction of CO2 and volatiles stemming from the two residues was observed, which directly led to the enhanced generation of carbon monoxide (CO). These observations are attributed to the simultaneous redox mechanisms of CO2 and volatiles. To accelerate the reaction rate of the redox mechanisms, catalytic co-pyrolysis of the residues over Co/SiO2 was performed, and such attempts were confirmed by the enhanced formation of H2 and CO. This study highlights that the hybridization of the thermochemical process of PVC in the production of BE could be a viable approach for waste valorization.

Extraction of valuable metals from waste lithium iron phosphate batteries by subcritical water leaching method with synergistic waste polyvinyl chloride

In this paper, the effect of leaching valuable metals from waste lithium iron phosphate (LiFePO4) using waste polyvinyl chloride (PVC) as a source of hydrochloric acid under subcritical water treatment conditions was investigated. The effects of various parameters including temperature, reaction time, PVC/LiFePO4 mass ratio, and solid-to-liquid ratio on metal leaching were investigated. The results showed that the leaching of metals and dechlorination of PVC could be achieved simultaneously under subcritical hydrothermal conditions. The solid residues were analyzed using XRD, XPS and SEM-EDS elemental mapping to identify the compounds in the leached solids. ICP-OES analysis showed that optimal reaction conditions, including a temperature of 275 °C, a reaction time of 120 min, a PVC/ LiFePO4 mass ratio of 3:2, and a solid/liquid ratio of 1:10 (g/mL), could effectively leach 99.10 % of Li and 83.12 % Fe. Finally, the Li in the leachate was recovered in the form of Li3PO4 by precipitation. These findings suggest that subcritical water synergistic waste PVC technology is a promising and eco-friendly method to recover Li and Fe from waste lithium iron phosphate.

Effect of iron-nickel cations on urea-assisted hydrothermal dechlorination of polyvinyl chloride: Appropriateness of using steel reactors for determining intrinsic degradation chemistry

Hydrothermal dechlorination of polyvinyl chloride (PVC) is primarily performed in stainless-steel reactors prone to chlorine-induced pitting corrosion, contaminating the reaction media with Fe2+, Ni2+, and Cr2+ possibly triggering shifts in the degradation chemistry. This study investigated the single and synergistic effects of Fe2+ and Ni2+ on urea-assisted hydrothermal dechlorination of PVC under mild conditions. Significant improvement in dechlorination degree was observed at 210 °C when 5 mmol/L Fe2+ or 10 mmol/L Ni2+ was added. Furthermore, positive interaction between the cations was confirmed when the simultaneous use of 1 mmol/L Fe2+ and 0.25 mmol/L Ni2+ achieved the same catalytic performance. The presence of these ions prevented adhesive contact of PVC particles, thus limiting the mass-transfer resistance and autocatalytic effect. The experimental design revealed that dechlorination and its improvement were temperature-dependent (p < 0.0001). Ni2+ and Fe2+ exerted quadratic and linear effects, respectively, on dechlorination. The highest catalytic activity occurred in the temperature range of 217.5–222.5 °C. The results show that total concentrations of as low as 1.08 mmol/L accelerated dechlorination, indicating the inappropriateness of using steel reactors for determining intrinsic PVC degradation chemistry. However, Fe–Ni composites have the potential to be used as catalysts.

Preparation of carbon nanotubes by catalytic pyrolysis of dechlorinated PVC

Plastic waste is attracting growing interest for its utilization potential as a valuable resource. However, conventional thermochemical methods can hardly achieve high-value utilization of certain plastics, such as polyvinyl chloride (PVC) characterized with high chlorine content. Here, a low-temperature aerobic pretreatment method was introduced to realize high-efficiency dechlorination of PVC, and then the dechlorinated PVC was used to prepare carbon nanotubes (CNTs) by a catalytic pyrolysis. The results demonstrate that oxygen can significantly promote the HCl release in a pretty low-temperature range (260–340 °C). Chlorine was almost completely eliminated at 280 °C under 20 % oxygen concentration. Compared to untreated PVC, using the dechlorinated PVC as raw material, higher carbon deposition was obtained and over 60 % CNTs could be collected from the carbon deposition. This study provides a high-value utilization way for the production of CNTs from waste PVC.

High-efficiency promotion on dechlorination of polyvinyl chloride in subcritical water treatment by introducing waste concrete

Polyvinyl chloride (PVC) is one of the most widely used plastics in the world. Due to the generation of corrosive HCl and chlorine-containing organic pollutants during the recycling process, waste PVC can cause great environmental risks. At the same time, a large number of waste concrete in the construction industry have not been effectively utilized. Subcritical water (SubCW) has showed good prospect for treatment of PVC due to that dechlorination can be carried out with lower energy consumption. In this study, a high-efficiency and low-temperature SubCW treatment for dechlorination of PVC using waste concrete as an enhancer was proposed. The effects of temperature, residence time, solid-to-liquid ratio and PVC-to-Concrete ratio on dechlorination efficiency, chlorine distribution and weight loss ratio were studied. The PVC dechlorination efficiency could be enhanced to as high as 95.04% by introducing waste concrete. Significant dechlorination occurred under the conditions of 220 ℃, 60 min, solid-to-liquid ratio of 1:30 g/mL, and PVC-to-Concrete ratio of 4:1. Under the optimal conditions, all the removed chlorine from PVC was transferred into the liquid phase in the form of inorganic chlorine. Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscope (SEM), and elemental analysis were used to analyze the PVC dechlorination mechanism. The dechlorination pathway of PVC was found to include both direct dehydrochlorination and hydroxyl substitution. The enhancement mechanism of the waste concrete on the PVC dechlorination could be attributed to the rapid capture ability of CaCO3 for HCl. The SubCW-Concrete process proposed in this study was beneficial to both the low-temperature dechlorination of PVC and the resource utilization of waste concrete.

Polyvinyl chloride (PVC) derived microporous carbons prepared via hydrothermal dechlorination and potassium hydroxide activation for efficient CO2 capture

Hydrothermal dechlorination has been widely studied for recycling end-of-life polyvinyl chloride while the impact of embedded metal additives, a major component of many waste PVC products, has rarely been reported. In this study, hydrothermal treatment of used polyvinyl chloride pipe was carried out at a temperature range between 220 and 280 °C to understand the role of metal additives in the dechlorination process. The potential application of chlorine-free hydrochar as the precursor to prepare CO2 sorbents via chemical activation was also evaluated. The results demonstrated that the well-distributed calcium carbonate in the polyvinyl chloride matrix, acting as an in-situ neutralization agent, could accelerate the dechlorination of PVC, over 98.4% of chlorine was removed at 260 °C or higher. Using the hydrochar prepared at 260 °C as a single precursor, a series of activated carbons were successfully prepared via a facile chemical activation process. Those hydrochar-derived carbons have a microporous dominant structure with high surface area and total pore volume reaching up to 1927 m2 g−1 and 0.85 cm3 g−1, which showed great potential as CO2 sorbents. Tested at 25 °C, the microporous carbons exhibited both remarkable CO2 adsorption capacities of 1.60 mmol g−1 and 4.05 mmol g−1 at 100 kPa and high CO2/N2 selectivity of 42 at 15 kPa CO2. Advanced characterization demonstrated that the excellent CO2 adsorption performance originated from a unique combination of ultra-microporosity and surface chemistry. This work provides an effective and sustainable strategy to recycle hard-to-handle chlorinated plastic waste and reduce carbon emissions.

Photoaging process and mechanism of four commonly commercial microplastics

Microplastics (MPs) are the widespread emerging pollutants in the terrestrial systems, and photo-oxidation is an effective process for aging MPs on land. Here, four common commercial MPs were exposed to ultraviolet (UV) light to simulate the photo-aging of MPs on soil, and the changes in surface properties and eluates of photoaging MPs were studied. Results revealed that polyvinyl chloride (PVC) and polystyrene (PS) exhibited more pronounced physicochemical changes than polypropylene (PP) and polyethylene (PE) during photoaging on the simulated topsoil, due to the dechlorination of PVC and the debenzene ring of PS. Oxygenated groups accumulated in aged MPs were strongly correlated with dissolved organic matters (DOMs) leaching. Through analysis of the eluate, we found that photoaging altered the molecular weight and aromaticity of DOMs. PS-DOMs showed the greatest increase in humic-like substances after aging, whereas PVC-DOMs exhibited the highest amount of additive leaching. The chemical properties of additives explained their differences in photodegradation responses, which also accounted for the greater importance of chemical structure of MPs to their structural stability. These findings demonstrate that the extensive presence of cracks in aged MPs facilitates DOMs formation and the complexity of DOMs composition poses a potential threat to soil and groundwater safety.

Degradation of polyvinyl chloride by a bacterial consortium enriched from the gut of Tenebrio molitor larvae

Polyvinyl chloride (PVC), a carbon backbone synthetic plastic containing chlorine element, is one of six widely used plastics accounting for 10% global plastics production. PVC wastes are recalcitrant to be broken down in the environment but release harmful chlorinated compounds, causing damage to the ecosystem. Although biodegradation represents a sustainable approach for PVC reduction, virtually no efficient bacterial degraders for additive-free PVC have been reported. In addition, PVC depolymerization by Tenebrio molitor larvae was suggested to be gut microbe-dependent, but to date no additive-free PVC degraders have been isolated from insect guts. In this study, a bacterial consortium designated EF1 was newly enriched from the gut of Tenebrio molitor larvae, which was capable of utilizing additive-free PVC for its growth with the PVC-mass reduction and dechlorination of PVC. PVC films inoculated with consortium EF1 for 30 d were analyzed by diverse polymer characterization methods including atomic force microscopy, scanning electron microscope, water contact angle, time-of-flight secondary ion mass spectrometry, Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis technique, and ion chromatography. It was found that bio-treated PVC films were covered with tight biofilms with increased –OH and –CC- groups and decreased chlorine contents, and erosions and cracks were present on their surfaces. Meanwhile, the hydrophilicity of bio-treated films increased, but their thermal stability declined. Furthermore, Mw, Mn and Mz values were reduced by 17.0%, 28.5% and 16.1% using gel permeation chromatography, respectively. In addition, three medium-chain aliphatic primary alcohols and their corresponding fatty acids were identified as PVC degradation intermediates by gas chromatography-mass spectrometry. Combing all above results, it is clear that consortium EF1 is capable of efficiently degrading PVC polymer, providing a unique example for PVC degradation by gut microbiota of insects and a feasibility for the removal of PVC wastes.

PVC dechlorination residues as new peroxidase-mimicking nanozyme and chemiluminescence sensing probe with high activity for glucose and ascorbic acid detection

Polyvinyl chloride (PVC) dechlorination residues urgently need to be used to improve PVC recycling efficiency. Herein, PVC dechlorination residues were used for visual colorimetry and chemiluminescence (CL) sensing for the first time. It was found that the dechlorination residues of PVC and iron chips treated by subcritical water showed excellent peroxidase-mimicking activity and could catalyze enzyme substrate 3,3′,5,5′-tetramethylbenzidine (TMB) oxidation to produce blue product. Based on this, residues colorimetric analysis was developed to detect hydrogen peroxide in the range of 3.2 × 10−8–9.5 × 10−5 M and glucose in the range of 8.9 × 10−6–9.2 × 10−4 M. The detection limits were estimated to be 4.5 × 10−9 M for hydrogen peroxide and 6.8 × 10−7 M for glucose, respectively. The kinetic investigation of enzymatic reaction confirmed that the simulated enzyme activity of the residues was much stronger than that of the previously synthesized nanocomposite (The Km and Vmax of the residue system with TMB as the substrate were 0.298 mM and 207.3 × 10−8 M S−1, respectively). In addition, the residues could alone trigger luminol CL reaction to produce strong CL signal with no need for oxidant, and the residues CL analysis was developed for detection of ascorbic acid (AA) in the range of 1.5 × 10−12 M to 7 × 10−8 M with the detection limit of 0.32 pM. The results affirmed that the residues were fantastic colorimetric and CL sensing material, which not only provided vital reference for residues applications in other sensing assays, but also was important for construction of the sensing platforms using wastes.

Dechlorination of Polyvinyl Chloride via Solvothermal Treatment with Glycerol

Solvothermal treatment using glycerol effectively removes chlorine from polyvinyl chloride (PVC). Additive-free PVC was dechlorinated by treatment with glycerol in an autoclave at 200–240 °C. Liquid glycerol was coexistent with a red powder after the reaction at 200 °C. At reaction temperatures of 220 and 240 °C, the liquid glycerol disappeared, and carbonization proceeded to form a black powder. In this reaction, the glycerol was directly converted into glycidol. Epichlorohydrin was also produced from the glycerol via 1,3-dichloro-2-propanol as an intermediate. The PVC was converted into the polyethylene oxide structure, following the generation of the polyene structure by zip-elimination. Finally, the converted PVC was resinified by an epoxidation reaction with the glycidol and epichlorohydrin. Thus, glycerol acted as a useful reaction medium for this reaction system. The analysis of the decomposition ratio and dechlorination yield showed that the PVC was converted into solid products in high yields via chlorine release, and 30% of the glycerol was solidified by resinification at 240 °C. The effects of the additives on dechlorination were investigated using commercially available PVC sheets. Elemental analysis showed that the calorific value of the solid product dechlorinated at 240 °C was found to be higher than that of standard bituminous coal.

Thermal Degradation and Organic Chlorine Removal from Mixed Plastic Wastes

Plastic waste accumulation has been growing due to the increase in plastic generation and the lack of infrastructure for recycling. One of the approaches is to treat the mixed plastic waste (MPW) through thermal processes to produce feedstocks for other applications. However, the presence of polyvinyl chloride (PVC) in MPW would produce HCl during processing and has negative impacts (emission, catalyst poisoning, etc.). In addition, due to the high heterogeneity of MPW, it is difficult to generate consistent experimental data. In this study, MPW was homogenized through double compounding–extrusion and then formed into a sheet to be treated at 400 °C. The solid products at various mass losses were characterized by heat and chlorine content, Fourier-transform infrared (FTIR) spectroscopy, and elemental composition analysis. It was found that the thermal degradation of MPW started at ~260 °C. The chlorine removal efficiency increased with mass loss and reached an asymptotic value of ~84% at ~28% mass loss, and the remaining chlorine can be attributed to inorganic sources. A PVC de-chlorination model was developed for MPW using TGA data for PVC and MPW to determine organic chlorine removal efficiency. These results show that PVC de-chlorination was not affected by other plastics at this temperature. As the mass loss increases, the heat content first increases and then decreases. It was found that mass loss is a universal parameter for organic chlorine removal efficiency and heat content. The elemental composition analysis and FTIR spectroscopy also shed more light into the chemical changes during MPW thermal degradation.

Solid Base Assisted Dual-Promoted Heterogeneous Conversion of PVC to Metal-Free Porous Carbon Catalyst.

Polyvinyl chloride (PVC) is widely used in daily life, but its waste has become a serious environmental problem. A solid base assisted low-temperature solvothermal dehalogenation was developed in this work to sustainably and efficiently transform PVC into high-value dimethylamine hydrochloride (DMACl) chemical and N,O co-doped carbon monolith with hierarchically porous structure. The synergistic promotion of solid-base catalyst and solvent decomposition with the removal of HCl can shift forward the chemical equilibrium to promote the dechlorination of PVC and increase the carbon yield. Meanwhile, the solid-base catalyst can also act as a pore-forming additive to fabricate the carbon monolith with hierarchical pores. Induced by the high specific surface area, hierarchical pores and N,O co-doped structure, the generated carbon monolith exhibits superior electrocatalytic performance towards H2 evolution. These discoveries shed light on the design of synergistically coupled solvent and solid catalyst to promote the heterogeneous conversion of waste chlorinated plastics into high-value chemicals for a sustainable future.

Co-treatment of plastics with subcritical water for valuable chemical and clean solid fuel production

Plastic nylon 66, ethylene-vinyl acetate (EVA) and polyvinyl chloride (PVC) were treated in subcritical water to produce value-added liquid chemicals and clean solid fuels. A synergistic effect was found in the co-treatment of PVC and the other two plastic polymers. Nylon 66 was totally decomposed to water-soluble oligomers with the reaction at 330 °C for 45 min. The same condition was required for the complete hydrolysis of EVA to produce acetic acid and deacetylated solid fuel. The activation energy for nylon 66 and EVA hydrolysis were 99.30 and 146.46 kJ/mol, respectively. However, a relatively low temperature (250 °C) was adequate for PVC dechlorination (efficiency >80%). The hydrochloric acid released from PVC worked as the acidic catalyst, which significantly accelerated the hydrolysis of nylon 66 and EVA, consequently more moderate reaction conditions (250 °C for 60 min) are required. Co-treatment of PVC with other polymers by subcritical water showed a great perspective.

Co-treatment of PVC and used LCD panels in low-temperature subcritical water: Enhanced dechlorination and mechanism

The dechlorination of polyvinyl chloride (PVC) and the removal of organic materials from used liquid crystal display (LCD) are the primary difficulties and steps in the safe disposal of these two types of waste. In this study, the dechlorination of PVC and the removal of organic materials from waste LCD were simultaneously accomplished by using a low-temperature subcritical water (SubCW) co-treatment due to the low dielectric constant and mass transfer resistance of SubCW. The dechlorination efficiency of PVC could be significantly enhanced by introducing waste LCD in the SubCW co-treatment with lower PVC-to-H2O ratio (1:20 g/mL and 1:30 g/mL). The temperature, time, PVC-to-H2O ratio, and PVC-to-LCD ratio have significant influence on the dechlorination efficiency and chlorine distribution. The optimal parameters of the co-treatment were as follows: 220 °C, 90 min, PVC-to-LCD ratio of 4:1, and PVC-to-H2O ratio of 1:30 g/mL. In the optimal conditions, the PVC dechlorination efficiency could reach as high as 100 %. The removed chlorine was completely transferred to the aqueous phase and could be recovered as inorganic chlorine, eliminating the risk of chlorine. It is a remarkable improvement for the PVC dechlorination at low temperature with lower PVC-to-H2O ratio. The organic materials contained in used LCD could be efficiently removed by the SubCW co-treatment above 200 °C, and part of inorganic substances in used LCD could dissolve during the co-treatment due to the interaction between metallic oxides in LCD and HCl removed from PVC. The stable alkene-carbonyl structure (CCO) could be formed in the PVC residue during the SubCW co-treatment of PVC + LCD, promoting the dechlorination reaction of PVC. It is believed that the SubCW co-treatment is a high-efficiency strategy both for the dechlorination of PVC and the pre-treatment of used LCD.

Comparative study on the pyrolysis and leachability of washed/unwashed electric arc furnace dust-PVC mixtures and their residues

In this work, the pyrolysis behavior of electric arc furnace dust (EAFD) mixed with poly(vinyl) chloride (PVC) was studied under inert conditions. Unwashed (UW) EAFD was found to contain lead hydroxychlorides which were converted to hydrocerrusite upon washing. It also contains appreciable amounts of soluble salts such as halite and sylvite; the effect of these salts on the pyrolysis behavior of EAFD-PVC mixtures was investigated. These salts delayed the dechlorination of PVC, by at least 20 ⁰C, during the pyrolysis of EAFD-PVC and altered the mineral composition of the pyrolysis residue. The later was rich in PbCl2, FeCl2. H2O for both unwashed (UW) and washed (W) EAFD samples. However, the W-EAFD-PVC residue was rich with ZnCl2. H2O, which was not detected in the UW-EAFD-PVC pyrolysis residue. Instead, it is believed that UW-EAFD-PVC pyrolysis residue is rich with the metastable Na2ZnCl4 as well as K2FeCl5. H2O and NaFeCl4. The capturing and monitoring of the released gases during the pyrolysis of UW- and W-EAFD-PVC mixture, confirmed the inhibiting effect of the halite and the sylvite on the dehydrochlorination of PVC. The released gases demonstrate a strong evidence of the solid-solid reaction between EAFD compound (mainly ZnO) and PVC without evolution of hydrochloric acid (HCl) at temperatures below 200 ⁰C. The subsequent leaching of the pyrolysis residue has resulted in the recovery of Zn (up to 100%), Fe (up to 64%) and Pb (up to 76%) in water. It is inferred that decreasing iron recovery can be achieved by oxidizing Fe+2, while increasing Pb recovery can be achieved by controlling the pH of the leachate solution.

Cohydrothermal carbonization of waste polyvinyl chloride and wood chip for dechlorination

The co-hydrothermal carbonization (Co-HTC) of polyvinyl chloride (PVC) film and wood chip (WC) was conducted at 200-260oC in an autoclave filled in air or nitrogen for the chemical recycling of wastes with dechlorination of PVC. Effects of the Co-HTC temperature and the oxidation reaction during the Co-HTC on the decomposition behaviors were investigated. The percentage decomposition in nitrogen atmosphere increased with increasing the reaction temperature and reached 76.1% at 260oC. The percentage decompositions in nitrogen were several percent higher than those in air. The synergistic effect of PVC and WC for the decomposition was observed at 220oC in N2. When the Co-HTC was performed in air, decomposition was suppressed, indicating the increase in hydrochar yield. The dechlorination yield was determined from the Cl content in the recovered PVC after the Co-HTC reaction. Under nitrogen atmosphere conditions, the dechlorination yield increased slightly with increasing the temperature. At a carbonization temperature of 260oC, the dechlorination yield of PVC was about 40%.

Dechlorination of polyvinyl chloride by hydrothermal treatment with cupric ion

Hydrothermal treatment (HTT) is able to remove chlorine effectively from polyvinyl chloride (PVC), however, the reaction temperature is critical in practical application. Less energy-intensive hydrothermal dechlorination condition with cupric ion (Cu2+) has been proposed in this study. In particular, Cu2+ was applied in HTT of PVC at temperature ranging from 200 °C to 240 °C. It has been found that the introduction of Cu2+ distinctly accelerated PVC decomposition and dechlorination at 220 °C. When Cu2+ concentration was increased from 0.01 mol/L to 0.20 mol/L, the dechlorination efficiency was significantly improved from 15.46 %–67.89 %. Dramatic dechlorination occurred as residence time was longer than 15 min during HTT. Besides, both elimination and substitution dominated the HTT dechlorinaton. The facilitated dechlorination after the addition of Cu2+ was mainly due to the enhanced dispersion and formation of micropores in hydrochar. On the whole, HTT could be a promising pretreatment technology for copper-containing PVC in electronic wastes to prepared chlorine free hydrochar for combustion or pyrolysis applications, the optimal HTT condition would be 220 °C, 60 min with 0.1 mol/L Cu2+.