In-situ debromination mechanism based on self-activation and catalysis of Ca(OH)2 during pyrolysis of waste printed circuit boards

Gao, Ruitong; Liu, Binyang; Zhan, Lu; Guo, Jie; Zhang, Jie; Xu, Zhenming

doi:10.1016/j.jhazmat.2020.122447

Cited by 31 publications

(16 citation statements)

References 41 publications

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“…The co-pyrolysis debromination reaction for NM-WPCBs was conducted at 500 °C with different amounts of NaOH–KOH (NaOH/(NaOH–KOH) = 0.5). It can be seen from Figure a that the debromination efficiency was increased with the mass fraction of NaOH–KOH because of the increase of active reaction sites . However, when the mass fraction of NaOH–KOH was greater than 0.15, the debromination efficiency remained almost unchanged due to the presence of sufficient active sites.…”

Section: Resultsmentioning

confidence: 94%

“…It can be seen from Figure 3a that the debromination efficiency was increased with the mass fraction of NaOH−KOH because of the increase of active reaction sites. 13 However, when the mass fraction of NaOH−KOH was greater than 0.15, the debromination efficiency remained almost unchanged due to the presence of sufficient active sites. Compared to calcium-based catalysts, the dosage of NaOH−KOH was significantly reduced.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…At the middle stage of pyrolysis, large amounts of pyrolysis oil and gas were generated. The organic bromides (OB), such as bromoethane, 4-bromophenol, 2-bromophenol, and 2,4-dibromophenol, were captured by the molten NaOH–KOH, and then debromination reaction occurred, similar to the initial stage (eq –). At this time, the reaction between NaOH–KOH and pyrolytic char could further facilitate the pyrolysis of NM-WPCBs.…”

Section: Resultsmentioning

confidence: 99%

“…To further remove the HBr and improve the debromination efficiency, calcium-based catalysts were applied. 20 Gao et al 13 used Ca(OH) 2 as the debromination agent to remove bromide during the catalytic pyrolysis process; the results showed that the removal efficiency of HBr, 2-bromophenol, 4-bromophenol, and 2,4-dibromophenol reached 100, 74.6, 87.5, and 54.5%, respectively. However, previous studies on the catalytic pyrolysis for NM-WPCBs' debromination had some unsolved problems.…”

Section: ■ Introductionmentioning

confidence: 99%

“…Pyrolysis can be regarded as one of the most promising technologies for energy and resource recovery from NM-WPCBs because of its high efficiency and easy operation . Gao et al. , used thermogravimetry-coupled Fourier transform infrared spectroscopy (TG-FTIR) and thermogravimetry-mass spectroscopy (TG-MS) techniques to reflect the thermal decomposition process of WPCBs in real time, and measure the conversion of pyrolysis products. Liu et al calculated the kinetic parameters of NM-WPCBs’ pyrolysis, and found that the presence of copper could decrease the apparent activation energy ( E a ).…”

Section: Introductionmentioning

confidence: 99%

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NaOH–KOH Capillary Action Enhances the Pyrolysis and Debromination of Waste Printed Circuit Boards

Wang

Chen

et al. 2021

ACS Sustainable Chem. Eng.

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Catalytic pyrolysis was one of the most promising technologies for energy recovery and bromide removal from nonmetals of waste printed circuit boards (NM-WPCBs). However, the low efficiency of debromination, large dosage of catalysts, and high consumption of energy were the main reasons for limiting the application and popularity of catalytic pyrolysis. To solve these problems, the capillary action of molten NaOH–KOH was used to enhance the pyrolysis and debromination of NM-WPCBs. In this paper, the molten state of NaOH–KOH was achieved at an NaOH/(NaOH–KOH) mole ratio of 0.5 and a temperature of 182 °C. The maximum debromination efficiency reached 95.0%, while the average activation energy decreased from 201.4 to 112.6 KJ/mol. Kinetic results suggested that nucleation and diffusion action played key roles when α was below 0.6. Herein, the enhancing mechanism for the capillary action of catalysts was analyzed. First, molten NaOH–KOH spontaneously spread out on the surface of NM-WPCBs with the capillary force. Then, the Br atoms coordinated with Na/K to form [NM-WPCBs-Br···NaOH/KOH], in which the electrons transfer from Br to Na/K, resulting in the cleavage of the C–Br bond. Afterwards, the bromine radical (Br*) bonded with the hydroxyl radical (H*) to form HBr, which was removed by NaOH–KOH. This work offers inspiration for recycling other plastics by removing contamination and improving the efficiency.

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Section: Resultsmentioning

confidence: 94%

Section: ■ Results and Discussionmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%