Low-temperature subcritical water dechlorination composites of waste PVC/coal fly ash with powerful sensing activity for chemiluminescent detection of acetamiprid and imidacloprid.

Pesticide residues in agricultural products are serious threat to people's health. Real-time monitoring of pesticides residues in the environment and agricultural products posed challenges to sustainable methods with high analytical performance for pesticide detection. Herein, waste PVC/coal fly ash (the mass ratio of PVC and coal fly ash was 4:1) was dechlorinated in subcritical water at low temperature to achieve nearly 100 % dechlorination of PVC and obtain carbon-based composite materials (CM-Fe/Al/Si-dPVC) with strong sening activity. For CM-Fe/Al/Si-dPVC, CFe bonding resulted in strong electron migration, and nano/µm SiO2 and Al2O3 doping in the layered polyene C matrix provided large specific surface area, and silicon hydroxyl created good heterogeneous catalytic interfaces. CM-Fe/Al/Si-dPVC could strongly trigger luminol chemiluminescence (CL) reaction and produce intense CL signals. Neonicotinoid pesticides (acetamiprid and imidacloprid) bonded with CM-Fe/Al/Si-dPVC through coordination chelation and hydrogen bonding, which shielded the catalytic active site and increased the Fermi level of system, thus quenching CL reaction. Inspired by these, a cheap CL assay was constructed for detecting neonicotinoids combinations of acetamiprid and imidacloprid (NICs). The detection limits of NICs were 0.7 ng/L. Satisfactory recoveries were obtained for real agricultural products and environmental samples. The results of life cycle evaluation (LCA) revealed that the strategy had significantly small global warming potential (GWP). This work presented a sustainable method with environmental benefits for the detection of neonicotinoids, and also opened up new way for the recycling of organic solid wastes.

Low-cost and sensitive chemiluminescence detection of phthalates in environment by signal sensing of carbon-based materials from PVC/coal gangue dechlorination.

BACKGROUND: The detection of plasticizers in the environment is important to prevent environmental risks and people's health hazards. Improving recycling efficiency of waste PVC still faced challenges. RESULTS: In this work, it was found that solid products from waste PVC/coal gangue dechlorination in subcritical water (dPVC) had strong catalysis activity for luminol-H2O2 chemiluminescence (CL) reaction. Phthalates, common plasticizers, could bond and adsorb on dPVC, which greatly inhibited the luminol-H2O2-dPVC CL reaction. Based on this, a low-cost CL analysis was constructed for the detection of phthalates combinations (PACs) and di-(2-ethylhexyl) phthalate (DEHP) in the environment. The detection limit for PACs and DEHP was 0.048 ng/L and 0.13 ng/L, respectively. Compared with HPLC standard method, the dPVC CL analysis had accuracy and reliability for the detection of phthalates in actual environmental samples. Besides, the results of life cycle assessment (LCA) revealed that dPVC for CL sensing materials had significantly small global warming potential (GWP). SIGNIFICANCE: The use of dPVC for CL sensing not only improved the recycling efficiency of PVC, but also reduced carbon emissions of obtaining CL sensing materials.

Upcycling of waste disposable medical masks to high value-added gasoline fuel and surfactants products by sub/supercritical water degradation and partial oxidation.

The amount of waste disposable medical masks (DMMs) and the potential environmental risk increased significantly due to the huge demand of disposable medical surgical masks. In this study, two effective and environmentally friendly processes, supercritical water degradation (SCWD) and subcritical water partial oxidation (SubCWPO), were proposed for the upcycling of DMMs. The optimal conditions for the SCWD process (conversion ratio>98 %) were 410 â„ƒ, 15 min, and 1:5 g/mL. The oil products obtained from the SCWD process were mainly small molecule hydrocarbons (C7-C12) with a content of 86 % and could be recycled as fuel feedstock for gasoline. Alkyl radicals in the SCWD reaction formed double bonds and ring structures through hydrogen capture reactions, ß-scission, and dehydrogenation reactions, and aromatic hydrocarbons were formed by olefin cyclization and cycloalkane dehydrogenation. The introduction of an oxidant (H2O2) to the reaction system could significantly reduce the reaction temperature and shorten the reaction time. At 350 â„ƒ, 15 min, 1:20 g/mL, V(H2O2): V (H2O) of 1:1, the conversion ratio of the SubCWPO process was 88 %, which was higher than that of the SCWD process at 400 â„ƒ (71.49 %). Oil products produced from the SubCWPO process were rich in alcohols and esters, which could be used as raw materials for nonionic surfactant of polyol and fatty acid ester. The abundant hydroxyl radical in the SubCWPO system trapped hydrogen atoms on PP and reacted with the resulting alkyl radical to form alkanols, which was oxidized to form acids. The esterification of acids and alkanols formed high level of esters. The SCWD and SubCWPO processes proposed in this study are believed to be promising strategies for DMMs degradation and the recovery of high value-added hydrocarbons.

A novel subcritical water synergistic co-treatment of brominated epoxy resin and copper-based spent catalysts: debromination, phenol production, and copper recovery.

In this study, a high-efficiency co-treatment strategy for brominated epoxy resin (BER) and copper-based spent catalyst (CBSC) was developed by using subcritical water (SubCW) process. Multivalent species of copper released from CBSC could accelerate the electron transfer of the SubCW system and efficiently catalyze radical reactions to promote the debromination and decomposition of BER, and had an effect on the capture and binding of bromine species. Meanwhile, the formation of HBr by the BER debromination resulted in a decrease in the system pH and markedly enhanced the leaching/recovery of Cu from CBSC. The optimal conditions of the SubCW co-treatment process were as follows: reaction temperature of 350 °C, solid-to-liquid ratio of 1:30 g/mL, BER-to-CBSC mass ratio of 10:1 g/g, and reaction time of 60 min. Under the optimal conditions, 97.12 % of the Br could be removed from BER by the SubCW co-treatment process and a high-purity phenol (64.09 %) could be obtained in the oil phase product, and 86.44 % of Cu in the CBSC could be leached and recovered. The introduction of CBSC significantly changed the decomposition path of BER. Compared to the SubCW process without CBSC, bromine-free oils products could be obtained by the co-treatment process of BER and CBSC at low-temperature. This study provided a novel understanding of resource conversion mechanism of BER and CBSC in subcritical water medium via the synergistic effect between the two different waste streams to improve treatment efficiency and synchronously recover high-value products.

An alkali-enhanced subcritical water treatment strategy of short-chain chlorinated paraffins: Dechlorination and hydrocarbons recovery.

As persistent organic pollutants, short-chain chlorinated paraffins (SCCPs) have attracted wide attention in the field of environmental health risk and hazardous waste management. Efficient dechlorination of high content of SCCPs in plastic waste is the committed step for its detoxification and safety treatment. In this study, a high-efficiency and low-temperature process for dechlorination and hydrocarbons recovery from typical SCCPs (52#SCCPs) by subcritical water (SubCW) with alkali enhancer was developed. The introduction of alkali enhancer in the SubCW process had significantly enhanced effect on the dechlorination of 52#SCCPs, and the order of the enhanced effect of alkali enhancer for the dechlorination was NaOH > Na2CO3 > NaHCO3 > NH3·H2O > KOH. The dechlorination behaviors of 52#SCCPs in the NaOH-enhanced SubCW process were studied systematically under different conditions including temperature, residence time, alkali concentration, and volume ratio. The results showed that high-efficiency dechlorination (100 %) of 52#SCCPs could be achieved by the NaOH-enhanced SubCW process at low temperature for a short time (250 °C, 5 min). All of the chlorine released from the molecular chain of 52#SCCPs was transferred to the aqueous phase in the form of inorganic chlorine. The continuous HCl elimination reaction was the primary dechlorination mechanism for 52#SCCPs in the NaOH-enhanced SubCW process. After the dechlorination of 52#SCCPs, high value-added hydrocarbons such as 2,4-hexadiyne (31.74 %) could be obtained. The alkali-enhanced SubCW process proposed in this study is believed to be an environmentally friendly and high-efficiency method for dechlorination/detoxification and resource recovery of SCCPs.

Ultrafast colorimetric detection of Cr(VI) based on competition of 8-HQ to Cr(VI) and TMB oxides using GO/AuNPs nanocomposites as peroxidase mimic.

Rapid detection of ultra-trace heavy metal chromium is very important for ecological environment. Herein, a rapid colorimetric assay was constructed for detecting hexavalent chromium (Cr(VI)) in environment water through the strong peroxidase mimicking activity of graphene oxide/gold nanoparticles (GO/AuNPs) nanocomposites and competition of Cr(VI) to 3,3',5,5'-tetramethylbenzidine (TMB) oxides and 8-hydroxyquinoline (8-HQ). Cr(VI) could effectively prevent the reaction between 8-HQ and TMB oxides to restore the blue color of the system. The detection limit for Cr(VI) was as low as0.018 µM by spectroscopic absorption. Paper-based colorimetric analysis had the detection limit of0.153 µM. The high sensitivity was basically due to the strong peroxidase mimicking activity of GO/AuNPs nanocomposite from synergistic coupling action and the firm chelation between 8-HQ and Cr(VI) from inner-sphere surface complexation. The detection results for real water sample showed that the analysis had feasibility in practical application. It is worth mentioning that the assay is performed by one-step mixing mode at room temperature, and a single test can be completed in half a minute. Indeed, this work not only provided an extremely easy method for real-time detecting Cr(VI) in the environment, but also verified the vitality of colorimetric strategy based on the strong peroxidase mimicking activity and competitive reaction.

Treatment of DEHP-rich PVC waste in subcritical urine wastewater: Efficient dechlorination, denitrification, plasticizer decomposition, and preparation of high-purity phthalic acid crystals.

It is difficult to dispose diethylhexyl phthalate-rich polyvinyl chloride (DEHP-rich PVC) waste due to the high level of chlorine and plasticizer. On the other hand, the denitrification of urine wastewater with high nitrogen content also faces great challenges. In this study, a synergistic treatment strategy was developed for the DEHP-rich PVC waste and urine wastewater by a subcritical water process. Subcritical urine wastewater (SUW) was used as a reaction medium in the synergistic treatment. PVC dechlorination, DEHP decomposition, and denitrification of urine wastewater were synchronously achieved in the one pot SUW. Under the optimal conditions (300 °C, 15 min, 1:5 g/mL), the PVC dechlorination ratio, urine wastewater denitrification ratio and DEHP decomposition ratio could reach 98.4%, 64.9%, and 99.2%, respectively. The decomposition of DEHP mainly included hydrolysis, nucleophilic substitution, and acylation. DEHP could be converted into phthalic acid crystal at 220 °C with a yield of 66.25% due to the efficient hydrolysis action of SUW. All the removed Cl was transferred from PVC matrix to aqueous phase. Hydroxyl nucleophilic substitution is the principal dechlorination path of PVC. The reactions between N-containing species and DEHP in SUW resulted in the high-efficiency denitrification of urine wastewater, and the N element was fixed in solid residue or transferred to oil phase as amides compounds. It is believed that the proposed SUW process is a promising technology for the synergistic treatment of DEHP-rich PVC waste and urine wastewater.

A novel conversion strategy for organic compounds in waste liquid crystal displays based on the near/supercritical methanol process.

Waste liquid crystal displays (LCD) contain a large number of organic compounds such as cellulose triacetate (CTA), poly(vinyl alcohol) (PVA), triphenyl phosphate (TPP), and liquid crystal (LC). It is important to recover organic compounds from waste LCD due to their value and environmental toxicity. However, it is challenging to recover organic compounds from waste LCD because of the heterogeneous mixture of glass, organics and metals contained therein. In this study, an environment-friendly near/supercritical methanol (NSCM) process was developed as a closed cycle technology for the conversion of organic compounds from waste LCD. The acid-base catalytic activity and nonpolar property of the NSCM could efficiently promote the conversion of organic compounds from waste LCD. TPP could be extracted below 200 °C in the NSCM process. Below 250 °C, the conversion ratio of organic compounds from waste LCD ranged from 5 % to 68 % due to the extraction or decomposition of TPP, LC, and PVA. The main products obtained at 250 °C included long-chain alcohols and alkanes with a similar composition to industrial liquid paraffin, which could be widely used in other industrial processes. Under the optimal operation parameters (300 °C, 30 min, and 1:20 g/ml), the conversion ratio of organic compounds could reach 98 % due to the efficient decomposition of CTA. The main products obtained included ketones and esters chemicals, which could be further used as a chemical feedstock. No secondary pollutant was generated in the whole process. The low-boiling methanol could easily be recycled, which could make the NSCM a clean process for the production of high value-added organic products from waste LCD.

Rapid color-fading colorimetric sensing of Hg in environmental samples: regulation mechanism from DNA dimension.

It was found that dimension change of aptamer DNA significantly weakened the mimicking activity of gold nanozyme, which was contrary to previous research. Based on this, a rapid colorimetric method for the detection of low concentrations of mercury in environmental media was fabricated. It was observed that 40 nM Hg2+ causes color changes in solution. The detection limit of absorbance measurements was estimated to be 9.3 × 10-11 M. The assay was fast and could complete a single test in half an hour. The detection results for real environment samples confirmed the reliability of the colorimetric analysis in practical application. The proposed assay provides an alternative method for real-time monitoring of mercury in the environment. In particular, the charge effect on the affinity of nanozyme consummated the DNA regulation mechanism for the simulated enzyme activity.

Degradation and partial oxidation of waste plastic express packaging bags in supercritical water: Resources transformation and pollutants removal.

Millions of waste plastic express packaging bags (PEPBs) were generated with the rapid development of the express delivery industry due to the boom of electronic commerce. Waste PEPBs contain polyethylene (PE) material and large number of pollutants such as plasticizers and flame retardants. In this study, two effective and environmental-friendly methods were proposed to produce valuable products and remove pollutants from waste PEPBs by supercritical water degradation (SCWD) and supercritical water partial oxidation (SCWPO) treatments. Both SCWD and SCWPO treatments could effectively obtain valuable products (wax, liquid oil, CaCO3) and remove bisphenol A (BPA) and di-(2-ethylhexyl) phthalate (DEHP) from waste PEPBs. No obvious difference about the conversion could be found between SCWD and SCWPO treatments. 425 °C, 60 min, solid-to-liquid ratio of 1:20 g/mL, and V(H2O2):V(H2O) ratio of 1:3 mL/mL were the optimal conditions for the conversion of waste PEPBs by SCWD and SCWPO treatments. The maximum conversion could reach 98.13%. The produced wax and liquid oil were easily separated from each other. The produced wax mainly included long-chain olefins or long-chain alkanes, and a small amount of alcohols, ethers and aldehydes. SCWD treatment was favorable for obtaining long-chain alkenes, while SCWPO treatment was favorable for obtaining long-chain alkanes. The main chemical compounds contained in the produced liquid oil were decomposed from DEHP and BPA. DEHP was decomposed to produce 2-ethyl-1-hexanol and acetophenone. BPA was decomposed to produce 4-tert-butylphenol and other alkylated derivatives of benzene and phenol. In comparison with SCWD treatment, DEHP and BPA could be decomposed more thoroughly by SCWPO treatment.

Determination of Cr(VI) based on the peroxidase mimetic catalytic activity of citrate-capped gold nanoparticles.

Highly negatively charged gold nanoparticles (AuNPs) are shown to have strong simulated oxidase activity and effectively boosted the oxidation of enzyme substrate 3,3',5,5'-tetramethylbenzidine (TMB) by hexavalent chromium ion Cr(VI), resulting in the formation of oxidation product with blue color. Based on this, a facile colorimetric assay was developed to detect Cr(VI) at a range 0.008~0.156 mg/L with r = 0.996. The detection limit was estimated to be 0.52 µg/L. In addition, the colorimetric assay showed high selectivity against 28 other interfering ions. It was performed at room temperature and required about half an hour including the preparation of AuNPs. The assay was successfully applied to the determination of Cr(VI) in spiked water samples, and recoveries in the range 95.00-105.40% were obtained. This work paves a way for design of high performance sensor based on highly active nanozymes and also provides an extremely practical analytical tool for the monitoring of Cr(VI) in the environment.

Efficient low-temperature debromination and high selectivity products recovery from brominated epoxy resin waste by subcritical water-urea treatment.

In this study, a subcritical water-urea (SubCW-urea) process was developed for the treatment of brominated epoxy resin powder (BRP) waste. The SubCW-urea process had two significant advantages: efficient low-temperature debromination and highly selective products recovery. The NH3 and CO2 released from urea in the SubCW medium had a prominent enhancement effect on the decomposition and debromination of BRP waste when the SubCW temperature was below 300 °C. The debromination efficiency of SubCW-urea treatment was significantly enhanced in comparison with that of SubCW-NH3 and single SubCW treatments. The debromination efficiency of BRP could reach 38.21%, 85.3%, and 99.92% at 200 °C, 250 °C, and 300 °C, respectively. The debromination rate constant of BRP in SubCW-urea, SubCW-NH3, and single SubCW system was 0.1363, 0.1254, and 0.0146 min-1, respectively. No brominated chemical compound could be detected in the oil phase products when the treatment temperature was higher than 250 °C. The decomposition products of BRP waste could be easily regulated by controlling the treatment temperature of SubCW-urea. 2-bromo-phenol with the purity of 72.5% could be selectively prepared from BRP by SubCW-urea process at 200 °C. The purity of the recovered phenol could reach as high as 81.5% at 250 °C. The selectivity of the products decreased greatly at 300 °C due to the secondary reactions. The SubCW-urea process has an application prospect in the safe treatment of BRP waste with the aim of high-efficiency debromination and high selectivity products recovery at low temperature.

DEHP degradation and dechlorination of polyvinyl chloride waste in subcritical water with alkali and ethanol: A comparative study.

In this study, subcritical water-NaOH (CW-NaOH) and subcritical water-C2H5OH (CW-C2H5OH) processes were developed for diethylhexyl phthalate (DEHP) degradation and dechlorination of polyvinyl chloride (PVC) waste. The introduction of NaOH or C2H5OH in subcritical water had a noticeable influence on the mechanism of DEHP degradation and dechlorination. For both CW-NaOH and CW-C2H5OH treatments, the increase in temperature could increase dechlorination efficiency (DE) of PVC. The DE of CW-NaOH is much higher than that of CW-C2H5OH under the same conditions. The DE of CW-NaOH could exceed 95% at 300 °C. Hydroxyl nucleophilic substitution was the main dechlorination mechanism in CW-NaOH, while nucleophilic substitution and direct dehydrochlorination were equally important in CW-C2H5OH. In CW-NaOH treatment, 2-ethyl-1-hexanol, benzaldehyde, and toluene were obtained by hydrolysis and reduction reactions of DEHP. Acetophenone was produced by the further cyclization, dehydrogenation and rearrangement reactions of 2-ethyl-1-hexanol. Transesterification was the main degradation pathway of DEHP in CW-C2H5OH at 300 °C. The cyclization and dehydration of 2-ethyl-1-hexanol resulted in producing a high level of ethyl-cyclohexane and 1-ethyl-cyclohexene in CW-C2H5OH at 350 °C. Furthermore, high concentration of ethyl palmitate and ethyl stearate could be prepared in CW-C2H5OH system by the strong reactivity of C2H5OH with the lubricants in PVC.

Practical aptamer-based assay of heavy metal mercury ion in contaminated environmental samples: convenience and sensitivity.

Due to heavy metals' magnified pollution from their accumulation in the ecosystem, practical detection of ultra-low concentration of heavy metals in environmental sample is of great significance for environmental supervision and maintenance of people's health. Herein, a practical and sensitive assay of heavy metal mercury was developed by visually observing (or spectrum detecting) the change of cationic gold nanoparticles (AuNPs), which is directly caused by mercury ion induced hybridization between non-canonical base pairs. In this assay, signal probe's response was direct rather than the indirect salt induction, thus avoiding the defect of salt-induced indirect response. It makes the analysis more sensitive. The results showed that the response of 8.2 × 10-8 M Hg2+ could be observed with naked eye and the detection limit of Hg2+ in spectrometric determination was 4.9 × 10-11 M, which is more than one order of magnitude lower than that from indirect response pattern of signal probe. In addition, high specificity of the affinity chemistry for T-Hg-T renders the assay to be highly selective. Compared with the results of cold vapor atom adsorption spectroscopy (CVAAS), this analysis has good reliability for the detection of mercury. The results fully indicate that the developed assay is an ideal alternative for online detection of heavy metal mercury in environmental pollution samples.

A novel safety treatment strategy of DEHP-rich flexible polyvinyl chloride waste through low-temperature critical aqueous ammonia treatment.

Flexible polyvinyl chloride (f-PVC) contains high content of plasticizers and chlorine. Improper treatment of waste f-PVC can easily lead to resource wasting and bring environmental risks. In this work, a novel strategy for resource recycling and dechlorination of waste f-PVC containing high content of di-(2-ethylhexyl) phthalate (DEHP) was developed by using low-temperature critical aqueous ammonia (LCA) process. The LCA treatment of waste DEHP-rich f-PVC (WDP) was performed at the temperature range of 200-400 °C with the ammonia concentration of 1%-5%. The results indicated that the LCA temperature had a significant effect on the chemical composition of decomposition products. High concentration of 2-ethyl-1-hexanol (86.12%), which is an important chemical feedstock and is derived from the decomposition of DEHP, could be obtained from WDP by the LCA process at 250 °C, and the concentration of 2-ethyl-1-hexanol decreased markedly with increasing the temperature. Benzaldehyde and acetophenone were generated when the temperature increased to 300 °C, and their concentrations increased with the rise of temperature. The increase of the ammonia concentration and the temperature could enhance the dechlorination efficiency of WDP. The dechlorination could reach 98.7% at 300 °C. This result showed that the LCA process was a promising and high-efficiency strategy for the sustainable management of WDP.

A novel management strategy for removal and degradation of polybrominated diphenyl ethers (PBDEs) in waste printed circuit boards.

Waste printed circuit boards (PCBs) contain a high level of brominated flame retardants (BFRs), among which polybrominated biphenyl ethers (PBDEs) are the most widely used additive BFRs. PBDEs are considered to be a type of persistent organic pollutants (POPs). The efficient removal/degradation of PBDEs in waste PCBs is an urgent problem in electronic waste treatment, but the degradation of PBDEs is a great challenge due to their extreme stability and persistence in nature. In this study, a novel management strategy was developed for removal and degradation of PBDEs in waste PCBs by using a simple subcritical methanol (SubCM) process. The results showed that reaction temperature, residence time, solid-to-liquid ratio, and additive NaOH are key factors influencing the removal of PBDEs from waste PCBs. Under optimal conditions (200 °C, 60 min, 1:20 g/mL), the removal efficiency of ∑8PBDEs from waste PCBs could reach 91.3% and 98.8% for the proposed process of SubCM and SubCM + NaOH, respectively. When the temperature is below 200 °C, highly brominated PBDEs congeners in waste PCBs were degraded into 2,'3,4',6-Tetrabromodiphenyl ether (BDE71) and 2,4,4'-Tribromodiphenyl ether (BDE28) after SubCM treatment. 4-Bromophenyl ether (BDE4) and diphenyl ether were generated by the further debromination of BDE71 and BDE28 with the increase of treatment temperature. The debromination temperature of PBDEs congeners in SubCM could be markedly lowered by adding 4 g/L of NaOH. The complete debromination of PBDEs congeners in waste PCBs could be achieved at 300 °C and 250 °C for the developed process of SubCM and SubCM + NaOH, respectively.

A facile chemiluminescence sensing for ultrasensitive detection of heparin using charge effect of positively-charged AuNPs.

Heparin is a glycosaminoglycan with the highest negative charge density of any known biological molecule. Herein, this highly negative charge structure of heparin and the charge effect from positively-charged AuNPs for luminol chemiluminescence (CL) reaction were combined to build a facile and sensitive CL strategy for detection of heparin. The highly negative charge structure of heparin molecules (four negatively-charged side groups per repeat unit) and the effective signal amplification of charge effect from positively-charged AuNPs make this analysis to display high sensitivity for heparin detection, and the detection limit is as low as 0.06 ng/mL. It is about two orders of magnitude lower than the previously reported colorimetric assay and far lower than the current analysis methods. The established CL strategy is to use the electrostatic interaction between heparin and signal probe (positively-charged AuNPs). Since polyanionic heparin has the highest negative charge in biological system, this CL sensing shows high selectivity for the detection of heparin, and hyaluronic acid (HA), an analogue of heparin, cannot cause interference. This CL sensing succeeded in detecting heparin in human serum samples. Besides, polycationic protamine, heparin antidote, can respond to the system's CL signals through its strong interactions with heparin, thus indirectly detecting protamine. For protamine in serum samples, the detection result was basically consistent with Coomassie brilliant blue assay.

A novel treatment of waste printed circuit boards by low-temperature near-critical aqueous ammonia: Debromination and preparation of nitrogen-containing fine chemicals.

In waste printed circuit boards (PCBs), brominated epoxy resin (BER) and copper are the two types of material that attracts the most attention due to their environmental risk and resource value. In this study, a novel and high-efficiency process for debromination and resource recovery of waste PCBs by low-temperature near-critical aqueous ammonia (NCAA) was successfully developed. A batch reactor was used in experiments with the temperatures ranging from 200 to 350 °C and the reaction times from 30 to 90 min. The ammonia water in near critical conditions can act not only as a medium but also as a reactant. Approximately 100% of the Br in waste PCBs could be removed and trapped by the NCAA at 300 °C. Copper foil could be easily separated and recovered from waste PCBs after the NCAA process. No brominated organic compounds could be detected in the oil phase products after the NCAA treatment of waste PCBs even at low temperature of 200 °C. Two new products (pyrazine and pyridine compounds) with high value-added were obtained for the first time by the treatment of waste PCBs. This study provides a novel and efficient strategy for the debromination, the recovery of copper, and the preparation of high value-added nitrogen-containing fine chemicals from waste PCBs. The low-temperature NCAA processing of waste PCBs could effectively reduce the energy consumption in comparison with traditional thermal decomposition processes, and promote the sustainable waste management strategy for waste electrical and electronic equipment (WEEE).

A novel treatment method of PVC-medical waste by near-critical methanol: Dechlorination and additives recovery.

Before PVC-medical waste is subjected to a waste-to-energy recovery process, the dechlorination and the recovery of additives such as plasticizer, stabilizer, and lubricant are quite important and attractive. In this work, a novel process was developed for the dechlorination and the recovery of additives from PVC-medical waste such as tube for transfusion (TFT) and sample collector for urine (SCFU) by using near-critical methanol (NCM). Reaction temperature, solid-to-liquid ratio, and reaction time have significant effect on the dechlorination of TFT and SCFU in NCM. The order of dechlorination efficiency of the samples at the same reaction conditions is as follows: TFT > Pure PVC > SCFU. When reaction temperature was controlled at 250 °C (solid-to-liquid ratio of 1:10 g/mL, reaction time of 60 min), the dechlorination efficiency reached 90%. Plasticizer such as dibutyl phthalate (DBP), dioctyl phthalate (DOP), and dimethyl phthalate (DMP) could be efficiently extracted and recovered from TFT at 250 °C by the NCM process. The recovery efficiency of DBP, DOP, and DMP decreased significantly with increasing temperature due to the further decomposition and other secondary reactions. High level of hexadecanoic acid methyl ester and octadecanoic acid methyl ester can be obtained from SCFU at 250 °C by the NCM process because of the esterification between methanol and hexadecanoic acid/octadecanoic acid, which are the important stabilizers and lubricants generally used in rigid PVC. It is noteworthy that methanol can be circulated and reused in the NCM process. This result showed that the NCM process was beneficial for both the dechlorination and the additives recovery from PVC-medical waste, and had a widespread application prospect for the waste management of PVC wastes.

Application of critical water-alcohol composite medium to treat waste printed circuit boards: Oil phase products characteristic and debromination.

Critical water system used for decomposition and debromination of waste printed circuit board (PCBs) has two disadvantages: low value-added oil phase products and halfway debromination at low temperature condition. In this study, critical water-alcohol composite medium was found to be a promising method to surmount these disadvantages. Critical water-ethanol (CWE) and critical water-methanol (CWM) were selected as the composite medium. The temperature of CWE and CWM had a significant effect on the oil phase composition. At low temperature CWE/CWM of 300°C, 4-(1-methylethyl)-phenol with high concentration could be recovered. CWM of 400°C was beneficial to the generation of ether compounds and high level of anisole could be obtained, while 450°C was beneficial to the generation of high level of multi-alkyl substituted phenol derivatives or benzene derivatives such as p-xylene. Br-free oil phase products could be obtained when the temperature of CWE/CWM ≥300°C. Different oil phase products with high level of chemicals or chemical intermediates could be obtained by controlling the reaction conditions of CWE/CWM. It is believed that the additional value of the oil phase products derived from waste PCBs can be greatly improved by this new process.