Design of a pyrolyser model for the conversion of thermoplastics into fuels.

This study focuses on alternatives to the sustainable management of plastic wastes through the development of a pyrolyser model, adapted to the recycling of plastics into fuel. It is a batch reactor, fixed bed, designed and built for the extraction of pyrolysis oil that can be recycled into petrol or diesel. The pyrolyser consists of a reactor with a volume of 0.0424 m3 and a copper spiral condenser with 2.31 m length. The plastics used for this study were Low Density PolyEthylene (LDPE), polypropylene (PP), polystyrene (PS) and polyethylene terephthalate (PET). They were collected from surrounding companies, washed, sampled, cut and sieved. Two different sizes of pyrolysis material: 1-3 cm (G1 ) and 3-7 cm (G2 ) were obtained and tested. The pyrolysis reactor and the plastics entering at an ambient temperature of 25 °C were heated. Plastics were then melted at 110 °C and vaporised at 450 °C. The hot vapour produced circulated through a copper coil and condensed. The resulting liquid was called pyrolysis oil. The results of this study show that the pyrolysis of LDPE, PP and PS yields two liquids: the heavy and majority fraction which arelike the conventional diesel and the light fraction which is like gasoline. Yields of 6-12.4% for the light fraction and 43.2-63.8% corresponding to the heavy fraction are observed. PE has the highest yield, 63.8% for the heavy fraction and 12.4% for the light fraction. The study further underscores that the size of the pyrolysis material influences the yields, i.e. an increase of 12.5, 9.1 and 7 % for LDPE, PS and PP respectively when the size of the pyrolysis material is increased from G2 to G1 . In contrast, the results of PET have shown a liquid that solidifies 46 s later. It was also noticed that 2061.34 kJ of energy was required to pyrolyse 1 kg of plastic and produce 0.762 l of fuel. The simple physico-chemical characterisation of the majority fraction shows a great similarity with diesel fuel, as the distillation went beyond 200 °C. Therefore, we can say that the diesel fraction is similar to diesel fuel. We equally observed a high cetane number (52.1-55.1) and a high calorific value (42.9-55.5 MJ/kg). Consequently, there are some points of non-conformity with the European 590 standard and Cameroonian specifications for diesel fuel. These include a low density (767.8-815.1 kg/m3 ) and a low viscosity at 40 °C (1.108-1.346 mm2 /S). A thorough physico-chemical analysis will complete this study before any recommendation for appropriate use.