Co-pyrolysis of phenolic printed circuit boards with CaO and Ca(OH)2 mixture in a fluidized bed reactor: Optimization of the operating conditions and the kinetic analysis

Abstract

In a previous study (Haghi et al., 2023), we demonstrated that co-pyrolysis of paper-laminated phenolic PCB (FR2-PCB) with a mixture of CaO and Ca(OH)2 in a fluidized bed reactor results in the simultaneous enhancement of the production of the pyrolysis oil and a significant decrease in its halide content. To advance the utilization of a blend of CaO and Ca(OH)2 for scaling up the pyrolysis of FR2-PCB beyond laboratory-scale pyrolyzers, especially in fluidized bed reactors renowned for their effectiveness in large-scale pyrolysis of polymeric materials, the optimal operating conditions, as well as the kinetic parameters in the presence of CaO and Ca(OH)2 should be explored. To this end, this study focuses on optimizing the temperature (T), retention time (t), and PCB-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 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. Additional tests were carried out to explore the impact of CaO+Ca(OH)2 concentration on the halogen content of the pyrolysis products. 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 %.