Uncovering the differences: A comparison of properties of crude plastic pyrolytic oil and distilled and hydrotreated plastic diesel produced from waste and virgin plastics as automobile fuels

Abstract

Thermal pyrolysis of mixed waste plastics (MWP) and mixed virgin plastics (MVP) containing high-density polyethylene (HDPE), polypropylene (PP) and polystyrene (PS) at 1:1:1 ratio were performed in a 20L pyrolytic pilot-scale batch reactor. The pyrolysis was conducted at 540 °C temperature and atmospheric pressure for 6 h. The properties of the produced crude plastic pyrolytic oil (CPPO or crude PPO), such as higher heating value (HHV), cetane index, lubricity, flash point, etc, obtained by pyrolysis of MWP, and MVP samples, confirmed that the oil was not suitable for direct use as an automobile fuel. Therefore, CPPO was further refined by vacuum distillation to match the properties of standard diesel more closely, herein referred as distilled plastic diesel (DPD). Some of the properties of DPD did not meet the standard diesel criteria, which is why DPD was further refined through a hydrotreatment process to ensure it was directly comparable to standard diesel, herein referred as hydrotreated plastic diesel (HPD). The fuel properties of all crude PPO, DPD and HPD were analysed and compared to standard (consumer) diesel according to Australian, ASTM and EN standards to assess their suitability as automobile fuel. With the aid of a 20L pyrolizer and a pilot-scale distillation and hydrotreatment plant, this comprehensive study demonstrated the importance of distillation and hydrotreatment for CPPO and found that DPD and HPD are well suited for use as drop-in diesel fuels. The results signify that with the right choice in refining technologies, waste plastics can be used as a source of automobile fuel.