An integrated utilization strategy of printed circuit boards and waste tire by fast co-pyrolysis: Value-added products recovery and heteroatoms transformation.

Fast co-pyrolysis has been suggested as a promising technique to solve the environmental issues and simultaneously recover value-added products from polymer wastes. However, to date, no studies have focused on fast co-pyrolysis of printed circuit boards (PCB) and waste tire (WT). Therefore, we comprehensively investigated the fast co-pyrolysis of PCB and WT using pyrolysis-gas chromatography/mass spectrometry. The results show that an increase in temperature during fast pyrolysis improved the interactions between the PCB and WT pyrolyzates, increasing the formation of aliphatic and aromatic compounds. The formation of p-cymene was greatly induced by the isomerization and dehydrogenation reactions of D-limonene. Co-pyrolysis reduced the formation of brominated phenols and benzothiazole from PCB and WT pyrolysis, respectively, whereas promoted the interactions between Br- and S/N-containing radicals, concentrating them into heavy compounds. Increasing the temperature enhanced the release of heteroatom compounds. The findings suggest that debromination of PCB achieved via dehydrogenation of WT pyrolysis provoked secondary reactions of olefins and interactions of heteroatom radicals. The major products were accurately predicted by different fitting models using response surface methodology, indicating the synergistic interactions during co-pyrolysis. The results were beneficial for optimizing the experimental parameters to obtain the maximum yield of desired products.

New insights into the capture performance and mechanism of hazardous metals Cr3+ and Cd2+ onto an effective layered double hydroxide based material.

The phosphonate functionalized layered double hydroxide constructed through intercalation reaction, and efficiently applied to capture toxicant metal ions. The characterization results indicated that the functionalized composite with many functional groups has adsorption potential to heavy metals. The strong chelation of the phosphonate groups with heavy metal ions proved it an excellent adsorbent leading to a maximum adsorption capacity of 156.95 mg/g (Cr3+) and 198.34 mg/g (Cd2+) separately. The data of kinetics and isotherm revealed that the chelating adsorption was dominated by chemisorption and monolayer interaction. Notably, the spent adsorbent presented satisfactory reusability after six cycles. Furthermore, the Forcite simulation with the CLAYFF-CVFF force field implied that the critical mechanism for modifiers and the surface sites of the interlayer is electrostatic interaction. Our in-depth exploration in terms of the weak interactions not only demonstrated the strength and nature but also provided a novel way to intuitively capture the type of interactions that occurred around interesting regions. In the end, we made detailed investigations on the chelation mechanism, and the covalent nature played a leading role in the binding interaction. This work provides a valuable strategy for researchers to design novel materials in practice.

Prediction of pyrolyzate yields by response surface methodology: A case study of cellulose and polyethylene co-pyrolysis.

There are numerous combinations of biomass, plastic, and co-pyrolysis conditions. The presence of synergies, which make pyrolyzate distribution more complex, has been supported by research. In this study, the potential of response surface methodology (RSM) to predict the pyrolyzate yields affected by synergies during co-pyrolysis (500-700 °C) of cellulose and polyethylene was investigated, beyond gas, oil, and char yields. The results indicated that co-pyrolysis promoted liquid and C5-28 hydrocarbon production with increasing temperature. The quadratic model could predict the total gas, CO, CO2, and liquid yields, including the synergy. The cubic model could predict the levoglucosan and C5-28 hydrocarbon yields due to various synergies under different conditions. The linear model was suitable for the char yield distribution without interaction. Thus, this study reveals that RSM has a significant potential to predict pyrolyzate yields, enabling co-pyrolysis condition setting to maximize the desired product recovery with the fewest experiments.

Quantification of Cellulose Pyrolyzates via a Tube Reactor and a Pyrolyzer-Gas Chromatograph/Flame Ionization Detector-Based System.

Pyrolysis of cellulose primarily produces 1,6-anhydro-ß-d-glucopyranose (levoglucosan), which easily repolymerizes to form coke precursors in the heating zone of a pyrolysis reactor. This hinders the investigation of primary pyrolysis products as well as the elucidation of cellulose pyrolysis mechanisms, particularly because of the significant buildup of coke during slow pyrolysis. The present study discusses the applicability of a pyrolysis-gas chromatography/flame ionization detection (Py-GC/FID) system using naphthalene as the internal standard, with the aim of substantially improving the quantification of pyrolyzates during the slow pyrolysis of cellulose. This method achieved quantification of levoglucosan with a yield that was 14 times higher than that obtained from offline pyrolysis in a simple tube reactor. The high yield recovery of levoglucosan was attributed to the suppression of levoglucosan repolymerization in the Py-GC/FID system, owing to the rapid escape of levoglucosan from the heating zone, low concentration of levoglucosan in the gas phase, and rapid quenching of levoglucosan. Therefore, this method facilitated the improved quantification of primary pyrolysis products during the slow pyrolysis of cellulose, which can be beneficial for understanding the primary pyrolysis reaction mechanisms. This method can potentially be applied to other polymeric materials that produce reactive pyrolyzates.

Direct Gas-Phase Derivatization by Employing Tandem µ-Reactor-Gas Chromatography/Mass Spectrometry: Case Study of Trifluoroacetylation of 4,4'-Methylenedianiline.

Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) is a promising technique allowing the rapid characterization of the polymer structure and additives of microgram-scale plastics. However, the Py-GC/MS analysis of polymers with urethane bonds is challenging because they produce highly reactive pyrolyzates such as amines and isocyanates polymerizing in the GC column, which limits the efforts to elucidate the pyrolysis mechanism and plastic characterization by online GC analysis. Herein, a novel pyrolysis-gas-phase derivatization-GC/MS (Py-GPD-GC/MS) technique was developed, allowing the pyrolysis of polymers and the subsequent direct gas-phase derivatization of pyrolyzates, employing a modified tandem µ-reactor-GC/MS system. This work conducted the gas-phase trifluoroacetylation of 4,4'-methylenedianiline (MDA), which is one of the major polyurethane (PU) pyrolyzates, using N-methyl-bis-trifluoroacetamide (MBTFA) as a derivatization agent. The trifluoroacetylation gas-phase reaction was monitored by in situ GC/MS analysis and the effects of derivatization conditions were investigated. The highest MDA conversion observed was 65.6 area %. Furthermore, the sequential PU pyrolysis and direct trifluoroacetylation of PU pyrolyzates in the first µ-reactor and second µ-reactor, respectively, were successfully operated, achieving the inhibited polymerization and detection of trifluoroacetylated derivatives. Thus, the Py-GPD-GC/MS method has a significant potential to be applied for other combinations of pyrolyzates and derivatization reactions, enabling deeper characterization of plastics producing highly reactive pyrolyzates that cannot be accurately analyzed by conventional Py-GC/MS analysis.

Simultaneous recovery of high-purity Cu and poly(vinyl chloride) from waste wire harness via swelling followed by ball milling.

Poly(vinyl chloride) (PVC) swelling coupled with ball milling was employed for the simultaneous recovery of high-purity Cu and PVC from waste wire harness under ambient conditions. The experimentally determined performances of 15 organic solvents for PVC swelling and phthalate plasticiser extraction were compared with those predicted considering Hansen solubility parameters. As a result, n-butyl acetate and acetone were identified as the two best solvents for adequate PVC swelling without PVC dissolution and almost complete plasticiser extraction within 60 min. The swelling was concluded to contribute to the control of phthalate plasticisers, the use of which in wire harness has recently been limited by the Restriction of Hazardous Substances (RoHS) directive. Cables swollen with n-butyl acetate or acetone were subjected to dry ball milling for ~ 60 min to completely separate PVC and Cu and achieve the quantitative recovery of these components from 20-cm-long cables. Thus, this work unveils the high potential of recycling the otherwise non-recyclable long and non-uniform waste wire harness cables and is expected to impact the related (e.g., automotive, electrical, and electronics) industries, contributing to the establishment of a more sustainable society.

Practical dechlorination of polyvinyl chloride wastes in NaOH/ethylene glycol using an up-scale ball mill reactor and validation by discrete element method simulations.

To avoid the formation of undesired Cl compounds during polyvinyl chloride (PVC) wastes treatment and facilitate the recycling of valuable NaCl and dechlorinated hydrocarbons as feedstocks, advanced dechlorination (de-Cl) process should be developed. Here, an up-scale ball mill reactor was established for the de-Cl of real PVC wastes, including sealing strips from waste refrigerators and crushed cable coverings from waste cables. The effects of NaOH on de-Cl were validated with lab-scale studies and the influences of mechanical conditions were innovatively investigated. A maximum de-Cl degree of 99% was obtained with 1 M NaOH in ethylene glycol for sealing strips, whereas a maximum de-Cl degree of 92% was obtained with Φ1.27 cm stainless steel balls at a moderate rotation speed for cable coverings. The remaining Cl content in the sample residues was small and decreased with decreasing residue size, resulting in minimum contents of 0.49% and 0.61% for sealing strips and cable coverings, respectively. The de-Cl behavior was consistent with a shrinking-core model and the meaning of kinetic parameters was illustrated. The ball milling process was simulated by discrete element method (DEM). A positive correlation was observed between the apparent rate constant of the experimental de-Cl process and the specific impact energy calculated using DEM simulations. The combined experimental and simulation approach suggested that the surface of PVC is first dechlorinated and then crushed into fine particles by ball milling to expose the inner unreacted surface. For industrial application, the balance of chemical and mechanical conditions should be optimized.

Separation mechanism of polyvinyl chloride and copper components from swollen electric cables by mechanical agitation.

In this study, a high-accuracy separation process is proposed for recycling pure polyvinyl chloride (PVC) and Cu from the thin electric cables of electrical, electronic, and automotive wastes by PVC swelling and mechanical agitation in hydrophobic organic solvent mixed with water. The high stirring speed and low blade height combined with proper blade type and reactor tank shape ensure a separation rate of over 98%. By conducting computational fluid dynamic and discrete element model simulations, quantitative force, fluid velocity, and data visualization analyses were performed. The obtained separation rate exhibited strong positive correlations with the resultant, drag, and centripetal forces at various stirring speeds and blade heights. Using the experimental and simulation data, a plausible separation mechanism was suggested. It was found that Cu pieces could slip out from swollen PVC covers under the action of external forces, while the stirring speed should be high enough to apply sufficient external forces to cables via either blade-to-cable collisions or fluid drag. Furthermore, the vertical motion of cables induced by the low blade height was essential because the rotation in the bottom reactor part inhibited the slipping of Cu pieces.

Separation of copper and polyvinyl chloride from thin waste electric cables: A combined PVC-swelling and centrifugal approach.

Waste electric cables from end-of-life vehicles and electronic and electrical equipment present a significant problem in terms of environmental protection and resource recycling. Herein we detail a novel recycling method for thin waste electric cables, by combining polyvinyl chloride (PVC) swelling and centrifugal separation to simultaneously recover PVC and high-purity copper. PVC coverings were swollen in an organic solvent at ambient temperatures, which creates a gap between the covering and the copper wire and facilitates centrifugal separation. Electric cables (12 g) were 100% separated, and more than 95% of the plasticizer was extracted by stirring in 100-mL acetone or ethyl acetate that facilitated the separate recovery of copper, the PVC covering, and the plasticizer. In contrast, >97% separation, with <10% extraction of the plasticizer, was achieved with a mixture of 10 mL butyl acetate and 90 mL water. High-purity copper and PVC with controlled plasticizer content were recovered, which is highly advantageous for recycling both copper and PVC.

A combined kinetic and thermodynamic approach for interpreting the complex interactions during chloride volatilization of heavy metals in municipal solid waste fly ash.

This study elucidated complex interactions during the chloride volatilization of heavy metals (Pb, Cu, Zn, Mn, and Cr) from municipal solid waste fly ash by combining thermodynamic and kinetic approaches. Chloride volatilization tests under HCl flow at 900 °C and subsequent rinsing with water achieved almost complete removal of Pb, Zn, and Mn. In contrast, almost 100 % of Cr and ∼40 % of Cu were not removed by either volatilization or rinsing processes. Kinetics indicated that the chlorination of Pb, Zn, and Mn followed a pseudo second order reaction and their apparent activation energies were 96.3, 89.2, and 43.5 kJ/mol, respectively. Further thermodynamic calculation revealed that the components contained in fly ash greatly influenced the chlorination of each heavy metal. Unburned carbon facilitated the chlorination of Pb, Zn, and Mn, while it inhibited Cu chlorination. MgO immobilized Cr and inhibited chlorination. KCl and NaCl promoted Zn and Mn chlorination, respectively. The revealed chloride volatilization behavior and effects of co-existing elements could be useful in the design of high-efficiency recovery process of heavy metals from fly ash and the utilization of residues as raw materials for cement. Furthermore, these findings could guide the realization of a recycling-oriented society in terms of reducing waste disposal.

Beech Wood Pyrolysis in Polyethylene Melt as a Means of Enhancing Levoglucosan and Methoxyphenol Production.

Recycling wood/plastic composites in municipal and industrial wastes currently represents a challenge which needs to be overcome. In this work, we considered the concept of independent pyrolysis of wood and plastic in wood/plastic mixtures for enabling a versatile catalytic process design which is capable of producing recoverable final products from both components. In order to reveal the influence of plastic on wood pyrolysis, the pyrolysis of beech wood (BW, wood material) in a polyethylene (PE) melt (polyolefin material) was performed at 350 °C. The combined use of thermogravimetric analysis, product recovery studies, in situ radical characterisations, and microscopic analysis revealed the influence of the PE melt on the BW pyrolysis. More specifically, a physical prevention of the intermolecular condensation and hydrogen abstraction from PE pyrolysates in the liquid/solid phase was observed. These interactions enhanced the production of levoglucosan and methoxyphenols by factors of 1.7 and 1.4, respectively, during the BW pyrolysis in the PE melt. Based on these results, we concluded that the observed synergistic effects could potentially control the yield and quality of useful products, as well as the utilisation of mixed wood/plastic wastes, which cannot be effectively recycled otherwise.

Degradation of PVC waste into a flexible polymer by chemical modification using DINP moieties.

In consideration of the toxicity and high migration capacity of plasticizers, the possibility to obtain flexible PVC via chemical modification of PVC was investigated for feedstock recycling. In this work, some Cl atoms of PVC were substituted with fragments of the common plasticizer DINP (diisononyl phthalate) in the presence of K2CO3 (potassium carbonate) or DIEA (N,N-diisopropylethylamine), and the simultaneous elimination of PVC was suppressed. 1H NMR (1H nuclear magnetic resonance spectroscopy) and 1H-1H COSY (1H-1H correlation spectroscopy) were used to evaluate the substitution while a novel method of calculating the substitution and elimination ratios was developed using a combination of 1H NMR and elemental analysis. A maximum substitution rate of 35.7% was achieved using thiophenol as a nucleophile in the presence of DIEA, while the corresponding elimination of HCl was just 4.4%. In addition, the thermal stability of the modified PVCs was very close to that of pure PVC, which suggested that the main characteristics of PVC were preserved. Moreover, the T g values of all the modified PVCs were less than that of PVC, which means it is feasible to improve the plasticity of PVC via substituting some Cl on PVC with DINP moieties. Therefore, an alternative approach for feedstock recycling of PVC by chemical modification was developed in this work.

Validation of a deplasticizer-ball milling method for separating Cu and PVC from thin electric cables: A simulation and experimental approach.

There is increasing demand in the electronics recycling industry for an effective method to separate polyvinyl chloride (PVC) and Cu from thin electric cable waste. Herein, a novel separation technique involving PVC embrittlement via plasticizer extraction and crushing by ball milling is proposed. The method was developed by varying the size, quantity, and hardness of the cables, as well as the size and quantity of the milling balls, to determine a combination that resulted in complete separation of PVC and high-purity Cu (>99.9%) from thin electric cables. The experimental crushing behavior was demonstrated via a sphere-to-cylinder discrete element model combined with a statistical approach. The mechanism of PVC crushing generated cracks from the edge to the center of the cable via ball impacts that were strong enough to overcome the elastic repulsion force of the PVC. The resulting method was found to be effective at separating PVC and high-purity Cu (>99.9%) from de-plasticized thin electric cables with diameters of 1.5-2.7 mm.

Selective phenol recovery via simultaneous hydrogenation/dealkylation of isopropyl- and isopropenyl-phenols employing an H2 generator combined with tandem micro-reactor GC/MS.

The pyrolysis of bisphenol A (BPA), an essential process ingredient used in industry and many everyday life products, helps produce low-industrial-demand chemicals such as isopropenyl- and isopropyl-phenols (IPP and iPrP). In this study, tandem micro-reactor gas chromatography/mass spectrometry combined with an H2 generator (H2-TR-GC/MS) was employed for the first time to investigate the selective recovery of phenol via simultaneous hydrogenation/dealkylation of IPP and iPrP. After investigating the iPrP dealkylation performances of several zeolites, we obtained full iPrP conversion with over 99% phenol selectivity using the Y-zeolite at 350 °C. In contrast, when applied to IPP, the zeolite acid centres caused IPP polymerisation and subsequent IPP-polymer cracking, resulting in many byproducts and reduced phenol selectivity. This challenge was overcome by the addition of 0.3 wt% Ni on the Y-zeolite (0.3Ni/Y), which enabled the hydrogenation of IPP into iPrP and subsequent dealkylation into phenol (full IPP conversion with 92% phenol selectivity). Moreover, the catalyst deactivation and product distribution over repetitive catalytic use were successfully monitored using the H2-TR-GC/MS system. We believe that the findings presented herein could allow the recovery of phenol-rich products from polymeric waste with BPA macro skeleton.

A novel method to delaminate nitrate-intercalated MgAl layered double hydroxides in water and application in heavy metals removal from waste water.

Nitrate-intercalated MgAl layered double hydroxide (LDH) was successfully delaminated in water by a facile and effective method upon reflux at 120 °C for 24 h followed by sonication at 40 °C for 5 h. This process is environmentally friendly since water is the only solvent used. The delaminated nanosheets were characterized by microscopic, spectroscopic, and particle size analyses. The delamination process successfully produced octahedron-shaped single-layer nanosheets 50-150 nm in size. X-ray photoelectron spectroscopy (XPS) data confirmed that the surface elements and their chemical status are consistent with the basic layer of MgAl LDH. The delaminated nanosheets displayed higher adsorption capacity for removing heavy metals from waste water than the original powdered LDH. After treating the waste water, a sharp and intense peak in the X-ray powder diffraction (XRD) pattern of the precipitate confirms the restacking of the LDH nanosheets.

Identification of number and type of cations in water-soluble Cs+ and Na+ calix[4]arene-bis-crown-6 complexes by using ESI-TOF-MS.

The treatment of cesium-contaminated wastewater has become one of the biggest issues. The selective Cs+ removal from wastewater containing competitive alkali metal ions such as Na+ is desired to reduce the volume of sludge. Therefore, the present work focused on water-soluble calix[4]arene-bis-crown-6 (W-BisC6) to selectively capture Cs+. For characterization of the complex, UV-vis spectroscopy is commonly used, however, due to the limited availability of information it can be hard to quickly identify the specific structures of some complexes. In this work, the electrospray ionization time of flight spectrometry (ESI-TOF-MS) is successfully utilized to identify the number and type of cations in W-BisC6-cation complexes. ESI-TOF-MS accurately recognized 4 types of complex (W-BisC6-Na+, W-BisC6-Cs+, W-BisC6-2Na+, W-BisC6-Na+-Cs+), and the experimental and simulated results were almost perfectly matched. It also revealed the difficulty of W-BisC6-2Cs+ complex formation under the present conditions. Thus, this technique is significantly helpful for rapid identification of the specific structures of complexes during Cs+-contaminated wastewater treatment.

Simultaneous recovery of high-purity copper and polyvinyl chloride from thin electric cables by plasticizer extraction and ball milling.

Herein, we introduce a combination of plasticizer extraction from polyvinyl chloride (PVC) and ball milling for the simultaneous, effective recovery of PVC and copper (Cu) from thin electric cables. PVC coverings typically contain plasticizers for flexibility. As such, PVC cables become brittle after plasticizer extraction, causing them to be easily crushed by physical impact. Hence, we extracted the plasticizers from the PVC coverings of electric cables using organic solvents, and then crushed the obtained cable samples by ball milling. The influences of the plasticizer extraction yield and PVC morphologies before and after extraction on separation by ball milling were investigated. After a series of treatments to PVC coverings including quantitatively de-plasticizing for 5 h by Soxhlet-extraction in diethyl ether, 6 h ball milling and 1 h shaking in the sieve shaker, a maximum separation rate of 77% was achieved and the purity of the obtained separated Cu reached >99.8%.

Removal of boron and fluoride in wastewater using Mg-Al layered double hydroxide and Mg-Al oxide.

Mg-Al layered double hydroxide intercalated with NO3- and Mg-Al oxide were found to remove hazardous materials such as B and As, as well as Cl- and SO42-, from artificial and real hot spring wastewater. However, compared with the mixture of Al2(SO4)3 and Ca(OH)2, both adsorbents were inferior for the removal of B from real hot spring wastewater. Both adsorbents were also found to remove F- and PO43- from artificial semiconductor plant wastewater. Both adsorbents have the same ability to remove B from landfill wastewater as the mixture of Al2(SO4)3 and Ca(OH)2; furthermore, both remove Cl-, Br-, and SO42-. The benefit of Mg-Al layered double hydroxide intercalated with NO3- is that it does not require neutralization after the treatment. Overall, it can be stated that among the materials tested, Mg-Al layered double hydroxide intercalated with NO3- is the most suitable adsorbent for the treatment of hot spring and landfill wastewater.

Use of Mg-Al oxide for boron removal from an aqueous solution in rotation: Kinetics and equilibrium studies.

Mg-Al oxide prepared through the thermal treatment of [Formula: see text] intercalated Mg-Al layered double hydroxides (CO3·Mg-Al LDH) was found to remove boron (B) from an aqueous solution. B was removed by the rehydration of Mg-Al oxide accompanied by combination with [Formula: see text] . When using twice the stoichiometric quantity of Mg-Al oxide for Mg/Al = 4, the residual concentration of B dropped from 100 to 2.8 mg/L in 480 min, and for Mg/Al = 2, it decreased from 100 to 2.5 mg/L in 240 min. In both cases, the residual concentration of B was highlighted to be lower than the current Japanese effluent standards (10 mg/L). The removal of B can be explained by way of pseudo-first-order reaction kinetics. The apparent activation energy of 63.5 kJ mol(-1), calculated from the Arrhenius plot indicating that a chemical reaction dominates the removal of B by Mg-Al oxide (Mg/Al = 2). The adsorption of B acts upon a Langmuir-type phenomena. The maximum adsorption (qm) and equilibrium adsorption constants (KL) were 7.4 mmol g(-1) and 1.9 × 10(3), respectively, for Mg-Al oxide (Mg/Al = 2). [Formula: see text] in B(OH)4·Mg-Al LDH produced by the removal of B was observed to undergo anion exchange with [Formula: see text] in solution. Following regeneration, the Mg-Al oxide maintained the ability to remove B from an aqueous solution. This study has clarified the possibility of recycling Mg-Al oxide for B removal.

Steam Pyrolysis of Polyimides: Effects of Steam on Raw Material Recovery.

Aromatic polyimides (PIs) have excellent thermal stability, which makes them difficult to recycle, and an effective way to recycle PIs has not yet been established. In this work, steam pyrolysis of the aromatic PI Kapton was performed to investigate the recovery of useful raw materials. Steam pyrolysis significantly enhanced the gasification of Kapton at 900 °C, resulting in 1963.1 mL g(-1) of a H2 and CO rich gas. Simultaneously, highly porous activated carbon with a high BET surface area was recovered. Steam pyrolysis increased the presence of polar functional groups on the carbon surface. Thus, it was concluded that steam pyrolysis shows great promise as a recycling technique for the recovery of useful synthetic gases and activated carbon from PIs without the need for catalysts and organic solvents.