Catalytic effect and mechanism of in-situ metals on pyrolysis of FR4 printed circuit boards: Insights from kinetics and products

New insights into brominated epoxy resin type WPCBs pyrolysis mechanisms: Integrated experimental and DFT simulation studies

Pyrolysis is a recycling technology for waste circuit boards (WPCBs) with a wide range of applications. In this research, the brominated epoxy resin (BER) type WPCBs were taken as the research object, and the optimal pyrolysis process parameters were determined. Combined with experiments and density functional theory (DFT) calculations, the pyrolysis gaseous generation pattern and product distribution of BER type WPCBs were analyzed, and the generation mechanism of phenol, bromide and other pyrolysis products was investigated in depth. The results of the study showed that the pyrolysis rate of WPCBs exceeded 95 % under optimal reaction conditions. In the initial phase of the pyrolysis of WPCBs, the BER's CO bonds and a portion of Ph-Br bonds will be broken, leading to the production of intermediates such propylene oxide, bisphenol A, isopropyl alcohol, tetrabromobisphenol A and HBr. Among them, propylene oxide can generate ethylene oxide through free radical reaction. In the second stage, intermediates such as bisphenol A undergo homolytic cleavage and radical addition to form phenols, bromides, alcohols, ketones and other pyrolysis products.

Debromination with Bromine Recovery from Pyrolysis of Waste Printed Circuit Boards Offers Economic and Environmental Benefits

Bromine is an important resource that is widely used in medical, automotive, and electronic industries. Waste electronic products containing brominated flame retardants can cause serious secondary pollution, which is why catalytic cracking, adsorption, fixation, separation, and purification have gained significant attention. However, the bromine resources have not been effectively reutilized. The application of advanced pyrolysis technology could help solve this problem via converting bromine pollution into bromine resources. Coupled debromination and bromide reutilization during pyrolysis is an important field of research in the future. This prospective paper presents new insights in terms of the reorganization of different elements and adjustment of bromine phase transition. Furthermore, we proposed some research directions for efficient and environmentally friendly debromination and reutilization of bromine: 1) precise synergistic pyrolysis should be further explored for efficient debromination, such as using persistent free radicals in biomass, polymer hydrogen supply, and metal catalysis, 2) rematching of Br elements and nonmetal elements (C/H/O) will be a promising direction for synthesizing functionalized adsorption materials, 3) oriented control of the bromide migration path should be further studied to obtain different forms of bromine resources, and 4) advanced pyrolysis equipment should be well developed.

Distributed Activation Energy Modeling and Py-GC/MS Studies on Pyrolysis of Different Printed Circuit Boards for Resource Recovery

Printed circuit boards (PCBs) constitute an important segment of electronic waste that can be effectively utilized to recover valuable metals and organics. The present work is focused on the kinetics and product distribution from pyrolysis of three different PCB samples, viz., television PCB (TV PCB), motherboard PCB (MB PCB), and hard disk PCB (HD PCB). The PCBs were pretreated to eliminate most of the metallic constituents. Kinetic analysis was performed using Vyazovkin's isoconversional method and distributed activation energy model (DAEM). The average apparent activation energies obtained from the Vyazovkin method were 207.2, 158.9, and 179.7 kJ mol^-1 for the TV PCB, MB PCB, and HD PCB, respectively. The DAEM with five, four, and four pseudo-components was used to describe the decomposition kinetics of the TV PCB, MB PCB, and HD PCB, respectively. Importantly, two types of distributions, viz., Gaussian and Weibull, were utilized to effectively model the nonisothermal data obtained from thermogravimetric analysis at 10 and 20 °C min^-1. The evolution of pyrolysates belonging to functional groups such as phenolics, aromatics, aliphatics, halogenated compounds, N-containing compounds, and oxygenates was studied at two different temperatures (500 and 700 °C) using analytical pyrolysis-gas chromatograph/mass spectrometry (Py-GC/MS). The Py-GC/MS results demonstrated an increase in selectivity to aromatics and straight-chain aliphatics at 700 °C with a concomitant decrease in selectivity to phenols and oxygenates.

Co-pyrolysis of waste printed circuit boards with iron compounds for Br-fixing and material recovery

Waste printed circuit boards (WPCBs) were co-pyrolyzed with iron oxides and iron salts. Solid, liquid, and gaseous products were collected and characterized. Co-pyrolysis with FeCl₂, FeCl₃, or FeSO₄ was able to increase the yield of liquid product which was rich in phenol and its homologues. Also, the addition of co-pyrolysis reagents reduced the release of brominated organics to liquid as Br was either fixed as FeBr₃ in solids or released as HBr. In particular, FeCl₂ showed the best ability to reduce the release of Br-containing organics to liquid compared with FeCl₃ and FeSO₄. Solid residuals were rich in iron oxides, glass fibers, and charred organics with surface areas of 20.6-26.5 m²/g. CO₂ together with a small amount of CH₄ and H₂ were detected in the gaseous products. Overall, co-pyrolysis could improve the quantity and quality of liquid oil which could be reused as chemical or energy sources. Pyrolysis of waste printed circuit board was promising as a method for recycling.