Production of oil with low organobromine content from the pyrolysis of flame retarded HIPS and ABS plastics

Abstract

Pyrolysis of flame retarded plastics often leads to high concentrations of toxic organobromine compounds in the pyrolysis oil. In this work, we have investigated the pyrolysis of flame retarded high impact polystyrene (HIPS) and acrylonitrile–butadiene–styrene (ABS) over long residence times in a tube reactor with the aim of producing an oil that is free from organobromines. The tube reactor was fitted with a distillation column so that the pyrolysis products could be separated into heavy oil, middle distillate, light oil, and gases. The light pyrolysis products were characterised using GC–MS and GC-FID/ECD, while the total bromine content of the oils was determined by bomb calorimetery. The bromine content of heavy fractions and antimony content of all fractions of pyrolysis (light oil, middle distillates, heavy oil and char) was determined by inductively coupled plasma atomic adsorption spectroscopy (ICP-AAS). Heavy oil fractions were characterised using Fourier Transform-Infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy disperse X-ray analysis (EDAX), and gel permeation chromatography (GPC) techniques. It was found that the light oil produced by the pyrolysis of both flame retarded HIPS and flame retarded ABS mostly consisted of toluene, ethylbenzene, and cumene and had a relatively low bromine content, all of which was inorganic. The middle distillate oils produced by the same plastics had much higher bromine content, but the vast majority of the bromine was inorganic in the form of antimony bromide. The average molecular weights of heavy fractions were affected by the cracking temperature, while the structure of the mentioned fractions did not change considerably with temperature. Light oil fractions had very low amount of contaminants (bromine and antimony), while heavy oils contained them in enormous concentrations.