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

Photo-aging of brominated epoxy microplastics in water under simulated solar irradiation

Microplastics have become an increasingly concerning pollutant in aquatic environments, and photodegradation is their main degradation pathway in water. Gaining insight into the transformation process of microplastics will enhance our understanding of their behavior and destiny in natural environments. This paper studied the aging process of BER microplastics in aquatic environments under simulated sunlight and investigated the changes in the physical and chemical properties of microplastics and the changes in the leachate. During the photodegradation process, BER-MPs underwent extensive oxidation and reduction in particle size, and the originally smooth surface developed numerous voids, accompanied by yellowing. Introduction of O atoms in the molecular chains increased their hydrophilicity, resulting in the polymer chains breaking away from the plastic particles and dissolving in water. Also, once BER was excited by light, environmentally persistent free radicals are produced on its surface. Moreover, the breaking of C-Br bonds occurred during the photodegradation process of BER-MPs, which suggested that tetrabromobisphenol A would be transformed during the photoaging process of BER even if it was covalently bound to BER.

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.

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.

Laboratory Research on Design of Three-Phase AC Arc Plasma Pyrolysis Device for Recycling of Waste Printed Circuit Boards

Accumulation of electronic waste (e-waste) will place a heavy burden on the environment without proper treatment; however, most ingredients contained in it are useful, and it could bring great economic benefits when recycled. A three-phase alternating current (AC) arc plasma pyrolysis device was designed for resourcing treatment of waste printed circuit boards (WPCBs). This paper focuses on the analysis of plasma pyrolysis gas products, and the results showed that the plasma could operate stably, and overcame the problems of the poor continuity and low energy of single-arc discharge. Air-plasma would generate NOx contaminants, burn the organics, and oxidize the metals; therefore, air had not been selected as a working gas. Ar-plasma can break the long chains of organic macromolecules to make a combustible gas. Moreover, the strong adhesion between the metals and fiberglass boards would be destroyed, which facilitates subsequent separation. Ar/H2-plasma promoted the decrease of carbon dioxide and the increase of combustible small molecular hydrocarbons in the pyrolysis product compared with Ar-plasma, and the increase of the H2 flow rate or plasma power intensified that promotion effect. The percentage of other components, except the hydrogen of CO2, CO, CH4, C2H4, and C3H6, accounted for 55.7%, 34.2%, 5.6%, 4.5%, and 0% in Ar-plasma, and changed to 35.0%, 29.0%, 11.2%, 24.3%, and 0.5% in Ar/H2-plasma. Ar/H2-plasma could provide a highly chemically active species and break chemical bonds in organic macromolecules to produce small molecules of combustible gas. This laboratory work presents a novel three-phase AC arc plasma device and a new way for recycling WPCBs with high value.

Microwave-assisted chemical recovery of glass fiber and epoxy resin from non-metallic components in waste printed circuit boards

An efficient, microwave-assisted chemical recovery approach for epoxy resin and glass fiber from non-metallic components (NMC) in waste printed circuit boards (WPCBs) for resource reutilization was developed in this research. HNO₃ was selected as the chemical reagent because epoxy resin has low corrosion resistance to HNO₃. The influence of reaction parameters such as reaction time, temperature, concentration of HNO₃, liquid-solid ratio, and power of the microwave synthesizer on the separation efficiency of NMC (epoxy resin and glass fiber) and the reaction mechanism were investigated. The physical and chemical properties of NMC, reaction solvent, and decomposed products were analyzed using energy dispersive X-ray Spectroscopy (SEM-EDX) and Fourier transform infrared spectroscopy (FT-IR). The results showed that up to 88.42% of epoxy resin and glass fiber ((5 g) 10 mL/g) could be separated under the action of 300 W microwave power at 95 ℃ for 12 h and a HNO₃ concentration of 7 mol/L. During the reaction, C-N bonds formed by the crosslinking agent and the three-dimensional network structure of the thermosetting epoxy resin were destroyed. The carbon chain structure and chemical properties of epoxy resin did not change significantly and the functional groups of ethyl acetate maintained the chemical structure before and after the reaction. This uncomplicated and efficient inorganic acid chemical microwave-assisted process holds promise for use as a feasible recovery technology for epoxy resin and glass fibers in NMC. The proposed process is particularly appealing because of its high selectivity, considerable economic advantages, and environmental benefits.