Chemical Recycling of Printed Circuit Board Waste by Depolymerization in Sub- and Supercritical Solvents

Abstract

Disposal of waste printed circuit boards is regarded as a potential major environmental problem due to their heavy metal content. Therefore, recycling waste printed circuit boards represents an opportunity to recover the high value resin chemicals and the high value metals that are present. In this study, the solvo-thermal depolymerisation of waste printed circuit boards obtained from desktop computer monitors was carried out using water, ethanol and acetone between 300 -400 °C. Alkalis (NaOH, KOH) were used as additives to promote the removal of the resin fraction of the printed circuit boards. At 400 °C, 94% resin removal was achieved when water was used as the solvent, in the presence of NaOH. The liquid produced in the process was analysed by GC/MS and the results showed that it was mainly composed of phenol, and some phenolic compounds, with up to 62.5 wt% present as phenol in the liquid phase.

Screening of common synthetic polymers for depolymerization by subcritical hydrothermal liquefaction

“…Single synthetic polymers subcritical HTL has been reported for specific materials in several publications, including reports on HTL of: high-impact polystyrene, poly-acrylonitrile-butadiene-styrene (ABS), polycarbonate and polyamide 6 (Iwaya et al, 2006;Zhao et al, 2018a); epoxy printed circuit boards (Yildirir et al, 2015); polyethylene naphthalate and terephthalate (Arai et al, 2010;Zenda and Funazukuri, 2008); polystyrene-butadiene (Park et al, 2001); polyurethane (Dai et al, 2002). These studies show that monomers, other valuable chemical compounds or an oil product may be recovered using HTL.…”

Potential use of natural rubber to produce liquid fuels using hydrous pyrolysis – a review

“…138 Various studies were conducted on the depolymerization of kraft lignin, polystyrene, polytrimethylene terephthalate, nylon-6, circuit board waste, shale, kerogen, and coal through hydrous pyrolysis. [139][140][141][142][143][144][145][146] Chen et al 147 performed hydrous pyrolysis of nylon-6 using phosphotungstic heteropoly acid as catalyst at 280°C-330°C. Under the optimum conditions, the main product of hydrous pyrolysis was found to be caprolactum, with a yield of 77.96 wt.%, and a small amount of 6-aminocaproic acid and oligomers.…”

Evaluating waste printed circuit boards recycling: Opportunities and challenges, a mini review

“…The chemical process is mainly focused in metal dissolving, such as copper, lead and tin in solution, leaving precious metals in residue, and then isolate and purify precious metals from the residue (Ali et al, 2013;Huang et al, 2014;Yazici and Deveci, 2013;Yildirir et al, 2015). The commonly used chemical are nitric acid, sulphuric acid and hydrogen peroxide as a pretreatment agent.…”