Automobile fuels (diesel and petrol) from plastic pyrolysis oil—Production and characterisation

Abstract

Plastics like high-density polyethylene (HDPE), polystyrene (PS), and Polypropylene (PP) constitute a large portion of municipal solid waste. Plastics can be pyrolysed for reuse, but the end-product qualities are critical to industry refining processes. Pilot-scale pyrolysis and vacuum distillation were used to thermally degrade the plastics and convert it to petrol (gasoline) and diesel. Batch pyrolysis of HDPE, PS, and PP at 540 oC yielded plastic pyrolysis crude oils. The crude oil was separated into different fractions starting with distillation temperatures of less than 170 OC, 170 to 380 °C, and above 380 °C. The quality of the produced crude oil, gasoline, and diesel cuts was evaluated analytically according to the fuel specifications. This study demonstrated that pyrolysis of plastics can convert up to 80% of solids by weight) into liquid crude oil. HDPE pyrolysis produces lower quantities of oil due to the production of wax. A high calorific value (38.1 to 42.9 MJ/kg) similar to fossil fuels indicates that the liquid product of plastic pyrolysis could be a viable energy source. Plastic pyrolysis crude oil from PS mostly yielded gasoline at around 70% by weight, while HDPE and PP yield predominantly diesel at more than 50% by weight. The distilled oil characterisation results were outstanding, confirming that the quality of produced petrol and diesel from plastics pyrolysis oil suppress minimum specifications for automotive fuel standards. The cetane index of HDPE and PP diesel was found to be 60 and 55 respectively, significantly above the required value of 46 for automotive diesel. Higher heating values of most petrol cuts were in the range of 41.1 to 44.6 MJ/kg. These and other fuel qualities are within or near the approved range for automotive fuel. Thus, the findings can be used to build a foundation for the industrial manufacture of automotive quality fuels from plastic solid waste.