The behavior of heteroatom compounds during the pyrolysis of waste computer casing plastic under various heating conditions

Single step and two-step pyrolysis of waste computer casing plastic were conducted to optimize both the product distribution and characteristics of liquid products. The single step pyrolysis was performed under various final temperatures ranging from 350 to 600 °C. The two-step pyrolysis was undertaken by initially increasing the temperatures to 350–380 °C and holding for 15 min, followed by a further increase to a peak temperature of 500 °C. The pyrolysis kinetic studies showed the activation energy of the two stages against conversion and revealed the synergistic reactions between BFR additives and plastic matrix. In the single step pyrolysis, fixed bed experiments showed that the final pyrolysis temperature had a significant influence on the product yield. The highest yield of 45.3 wt% oil was produced at 500 °C. The oil products mainly consisted of aromatic compounds, phenolic compounds, nitrogen-containing compounds, and approximately 11.3–15.9 wt% of toxic bromine. For the two-step pyrolysis, the impurities of O-, N- and Br-containing compounds were mainly enriched in the pyrolytic oils from the first step. Comparatively, more than 57% of single aromatic compounds was obtained in the pyrolytic oils from the second step, with less than 2.0 wt% of bromine. Meanwhile, the depolymerization of the plastic for the formation of styrene was promoted at the second step. The results suggested that in the two stage pyrolysis, bromine can be transferred into the liquid phase in the first stage, thus producing bromine containing compounds deficient oil in the second stage.