Improving the catalytic pyrolysis of polyethylene and polypropylene with acidic clay catalysts using pre-degradation method

• Pre-degradation over clay-based catalysts improves contact between melted polymer and solid catalyst particles. • Pre-degradation improves the yield to liquid hydrocarbon products and its quality. • Pre-degradation method improves coke characteristics. • Best pre-degradation conditions: 150 °C for 10 min. Catalytic pyrolysis of plastics with clay catalysts was studied using pyrolysis reactor experiments and GC analysis of the formed liquid. In quest for improving the quantity and quality of the product yields, during catalytic pyrolysis of plastic pellets rather than fine powder, pre-degradation was used as a pre-treatment method. A detailed study of the effect of various experimental conditions of the method was carried out and applied to the catalytic pyrolysis of polyolefins with clay catalysts. As revealed by the experiments, pre-degradation as a pre-treatment method increased the liquid yield while decreased the coke yield compared to conventional mixing with optimal operating conditions of 150 °C temperature and 10 min holding time. Increasing the temperature or reaction time beyond this limit continued to decrease coke yield and improved coke volatility but decreased liquid yield. No coke from normal mixing volatilised below 500 °C, in contrast to pre-degradation pyrolysis coke, in particular at holding times of 10 min and above. Furthermore, specific effects of clay based catalyst type and polymer type were investigated on liquid product yield as well as product distribution.