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Recovery of Printed Circuit Boards Non-Metalic Fraction by Pyrolysis

Haghi, Mahdi | 2025

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 58009 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Yaghmaei, Soheyla; Fotovat, Farzam
  7. Abstract:
  8. Waste printed circuit boards (WPCBs) account for approximately 4–7 wt. % of all types of electronic waste. Due to the content of organic materials (resins and halogenated flame retardants), recycling and disposal of WPCBs are associated with the production of hazardous materials. With the aim of maximizing the pyrolysis oil recovery, this study focuses on optimizing the temperature (T), retention time (t), and WPCB-to-additive ratio (FR2/A) as the parameters controlling the co-pyrolysis of paper-laminated phenolic PCB (FR2-PCB) with a 50:50 mixture of CaO and Ca(OH)2 in a lab-scale fluidized bed reactor. According to the results of the experiments designed based on the response surface methodology, the maximum recovery of pyrolysis oil (40.6%) was obtained at T = 620 °C, t = 22 min, and FR2/A= 5.4 g/g. The results showed that a non-linear quadratic model accurately predicted the relationship between the liquid recovery value and the variables that influence it, with the model's predictions matching closely with the experimental data collected. Additional tests were then carried out under these conditions in fixed and fluidized bed pyrolyzers to separately explore the impact of CaO, Ca(OH)2, and CaO+Ca(OH)2 on the liquid recovery (LR) and the halogen content of the non-solid products. The performance of the fluidized bed pyrolyzer was deemed more effective, as it yielded higher liquid recovery when using CaO, Ca(OH)2, and their mixture (CaO+Ca(OH)2). The results showed that the liquid recoveries were 34.5%, 41.2%, and 38.9% by weight, respectively, while the halide distribution in the residual solid were 89%, 80%, and 91% respectively. The fraction of phenolic compounds in the pyrolysis oil ranged from 86% to 93%, about 1-3% higher than the corresponding values in the fixed bed. Using additives led to lower halide content in the pyrolysis oil of the fluidized bed than that of the fixed bed. However, the opposite trend was observed in the absence of additives. Regardless of the type of pyrolyzer, Ca(OH)2 was more successful than CaO in increasing LR, whereas CaO was more effective than Ca(OH)2 in pyrolysis oil dechlorination. Co-pyrolysis of FR2-PCB and CaO+Ca(OH)2 in a fluidized bed reactor was identified as a practical approach to enhance the recovery of pyrolysis oil comprising only 5% of the original halogen content of the feedstock. Furthermore, the thermogravimetric analysis (TGA) was performed to investigate the influence of the tested additives on the pyrolysis behavior and the kinetic characteristics of FR2-PCB. By employing three iso-conversional model-free approaches, i.e., the Kissinger-Akahira-Sunose (KAS), Flynn-Wall-Ozawa (FWO), and Starink integral methods, it was found that adding CaO+Ca(OH)2 to FR2-PCB can reduce the activation energy of the pyrolysis reactions by 20%
  9. Keywords:
  10. Pyrolysis ; Fluidized Bed Reactor ; Fixed Bed Reactor ; Waste Printed Circuit Boards ; Halogenated Flame Retardant ; Kinetic Analysis ; Calcium Based Additive ; Liquid Recovery

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