Separation of bromine and hydrocarbons from polymeric constituents in e-waste through thermal treatment with calcium hydroxide

Complete and deep removal of bromine from polymeric constituents in waste printed circuit boards (WPCBs) signifies the prime aim of the commonly deployed catalytic/pyrolytic approach in the treatment of e-waste. To attain this aim, a wide array of debromination agents were utilized with varying degree of effectiveness, scalability, and economic viability. Through the use of a multitude of techniques (flow reactor experiments, chemical analysis, surface characterization, and molecular simulation), this work presents conclusive evidence that co-pyrolysis of tetrabromobisphenol A (TBBA; as a model compound for the bromine content in WPCBs) with calcium hydroxide (Ca(OH)2) results in a complete fixation of the bromine content and produces bromine-free pyrolysis oil. For instance, measurements by IC and FTIR (gas sampling cell) confirms the disappearance of HBr from the gaseous stream during co-pyrolysis of a TBBA (1):Ca(OH)2 (2) mixture between 200 and 500 °C. Likewise, no brominated compounds could be detected from the analysis of the condensate and gas fractions. As the collected oil is dominated by n-alkanes, it is concluded that Ca(OH)2 displays both cracking and debromination capacity. DFT calculations maps out reaction pathways for the transformation of Ca(OH)2 into CaBr2 via the dissociative addition of HBr molecules. Formed CaBr2 could open a venue for a complete recovery of bromine in the thermal treatment of e-waste. Outcomes reported herein shall be instrumental in the design and operation of an effective chemical recycling facility for the ever-increasing loads of e-waste.