Separate Two-Step and Continuous Two-Stage Pyrolysis of a Waste Plastic Mixture to Produce a Chlorine-Depleted Oil

Abstract

In this study, a separate two-step pyrolysis (using auger and fixed-bed reactors) and a continuous two-stage pyrolysis (using auger and fluidized bed reactors) were conducted. This two-step pyrolysis was conducted to understand the effect of a 300 °C thermal pretreatment with the auger reactor before main pyrolysis on the chlorine removal. The fixed-bed pyrolysis of a solid product obtained after the pretreatment produced an oil with 464 ppm chlorine. An oil with only 14 ppm of organic chlorine could be obtained when a solid containing CaO was pyrolyzed in the fixed-bed reactor. Thermal pretreatment also caused changes in the yield and product composition; pretreatment led to an increase in gas yield and aromatic content of the oil. In the continuous two-stage pyrolysis of a waste plastic mixture having 3 wt.% polyvinyl chloride at 730 °C, chlorine in the feed material was removed in parallel from the outlet of the auger reactor line and through a CaO hot filter; this produced an oil with 6.3 ppm organic chlorine. In the two-stage pyrolysis, an aromatic-rich oil (80 wt.%) was obtained. The two-stage pyrolysis successfully converted the waste plastic mixture into an oil which could be acceptable as a feedstock for petrochemical industries.