Highly selective conversion of tetrabromobisphenol A epoxy resin waste to high-purity phenolic chemicals by subcritical water-CuO process

Abstract

Tetrabromobisphenol A epoxy resin (TBBPA-ER) is the most important nonmetallic composition of waste printed circuit boards (PCBs). Currently, the TBBPA-ER waste is mainly sent to incineration or landfills. The great obstacle of the recovery of the TBBPA-ER waste is the low value-added products obtained by existing technologies. In this study, a novel resource conversion strategy was developed to produce high-purity phenolic chemicals from the TBBPA-ER waste by subcritical water-CuO (SubCW-CuO) process. The high selectivity of the SubCW-CuO process for the recovered products from the TBBPA-ER waste could be attributed to the regulating effect of CuO. The CuO could preferentially trigger the rupture of C-O and C-Ph bonds in the TBBPA-ER chain, resulting in the producing of high-purity phenol (91.47 %) at 300 °C. The reaction between phenol and methyl radical (derived from β-scission of ternary carbon chain groups in the TBBPA-ER waste) resulted in the recovery of high-purity p-cresol (90.30 %) at 350 °C. The optimal conditions of the SubCW-CuO process were solid-liquid ratio of 1:30 g/mL, M(TBBPA-ER):M(CuO) ratio of 10:1 g/g, and 60 min. The conversion ratio of the TBBPA-ER waste could reach 70 % under the optimal conditions. Approximately 3 % of the bromine was transferred into the oil phase products after the SubCW-CuO process at 250 °C, while no organic bromine could be found in the oil phase products at 300 and 350 °C. More than 70 % of the bromine was fixed in the solid residue after the SubCW-CuO process at 300 and 350 °C. The bromine contained in the solid residue mainly existed in the form of CuBr and the Cu species had efficient capture ability for the bromine released from the molecular chain of the TBBPA-ER. It is believed that the SubCW-CuO process developed in this study is a promising alternative technology for the high-efficiency resource conversion of the TBBPA-ER waste.