Degradation of brominated flame-retarded plastics (Br-ABS and Br-HIPS) in supercritical water

Two of the most commonly used brominated plastics in electrical and electronic goods, Br-ABS and Br-HIPS have been degraded in supercritical water up to 450 °C and 31 MPa in a batch Hastelloy-C reactor. The plastics were reacted both in the absence and presence of alkaline additives, NaOH and Ca(OH)_2. The main reaction products were oils with near-zero bromine and antimony content in the presence of NaOH additive. The compositions of the oils were similar, comprising compounds like toluene, ethylbenzene, propylbenzene, cumene, butyl benzene, acetophenone, naphthalenes, phenylnaphthalenes, diphenylpropane, diphenylcyclopropane and a variety of multi-benzene compounds. Ethylbenzene was the predominant compound in the oils from both plastics. Phenols and substituted phenols were present in the oils from Br-ABS. Sodium hydroxide was more effective than Ca(OH)₂ in the removal of organobromine compounds or in suppressing their formation in the oils. Up to 99 wt% of the bromine atoms in the plastics was removed into the aqueous phase. Nearly, the entire antimony in the plastics was found in the solid residues obtained after the reactions. The NH₃ and HBr released during the degradation of Br-ABS, reacted together forming ammonium bromide while keeping the reaction medium almost neutral. Carbon dioxide was the major component of the gas product from Br-ABS. In addition, both plastics produced hydrogen and hydrocarbon gases of which alkane gases were predominant.