Prediction of liquid yields from the pyrolysis of waste mixtures using response surface methodology

The main objective of this work was to predict the influence of experimental conditions on product yields formed by waste mixtures pyrolysis, using response surface methodology (RSM). Accurate prediction of liquid yields at different experimental conditions and pyrolysis optimisation was achieved. The waste mixture studied contained 10% of pine, 10% of scrap tyres and 80% recycled plastic, whose main components were polyethylene (PE), polypropylene (PP) and polystyrene (PS). Experiment Factorial Design was used for the optimisation of reaction time, temperature and initial pressure to maximise the yield and composition of liquid products for the waste mixture studied. Experimental yields of liquids were fitted with a linear and second order model by the method of least squares with good correlation and high statistical significance. According to the model, the production of total pyrolysis liquids (including those obtained by solvent extraction) was maximised when the following conditions were used: reaction temperature of 350 °C, reaction time of 30 min and initial pressure of 0.2 MPa, leading to liquid yield of 91.3% (w/w). The yield of only decanted liquids (not considering those obtained by solvent extraction) was maximised to the value of 54.9% at 426 °C, 28 min and 0.2 MPa. The total liquid production at these conditions was 79.1%. The results obtained also showed that the approach used may be suitable for optimizing the experimental conditions that favour the formation of chosen gaseous and liquid compounds.