Influence of Feedstock Particle Size on the Certain Determination of Chlorine and Bromine in Pyrolysis Oils from Waste Electrical and Electronic Equipment Plastics

Abstract

Rejected streams emerging from waste sorting and recycling plants are still capable of being valorized by unconventional recycling routes. This is the case of the plastic-rich fraction generated after the treatment of waste electrical and electronic equipment (WEEE). However, the material complexity of this stream supposes a handicap when it comes to obtaining repetitive results in laboratory-scale recycling processes. This work aims to highlight the influence that the pretreatment (mainly particle size reduction) of a real WEEE plastic-rich stream has on the variability of the concentration of halogens (representative pollutants) in the oils obtained from its recycling via pyrolysis. The pretreatment steps were based on the standards of the European Committee for Standardization (ECN) for the analysis of waste samples. Four samples were studied: the WEEE plastics as received; two milled samples (2 and 1 mm particle size) derived from the original one; and a simulated sample composed of virgin polymers. All the samples were treated under the same conditions: 500 °C reaction temperature, 15 °C min–1 heating rate, 30 min dwell time, and a 1 L min–1 nitrogen purge flow. The oils obtained in, at least, two pyrolysis tests performed on the same sample were deeply characterized, and the results were compared. The oils derived from the “as-received” sample showed an unacceptable relative standard deviation (RSD, ∼42%) in the chlorine concentration. The sample milled to 2 mm reduced the RSD on the concentration of chlorine in the oils down to 8%, while no enhancement in the results was observed for the further milled sample. The other two major pyrolysis fractions were also characterized, showing an overall enhancement in the RSD of the analysis of the main components of the gases, while no improvement in the solids pollutants’ characterization was achieved.