Catalytic pyrolysis of waste polypropylene using Ahoko kaolin from Nigeria

The aim of this study is to convert polypropylene waste into usable liquid fuel via pyrolysis technique using kaolin as a low-cost catalyst. Waste polypropylene was thermally and catalytically degraded in a chemical vapour deposition (CVD) horizontal glass reactor at a temperature of 450 °C, residence time of 30 min, and heating rate of 30 °C/min. The kaolin clay was characterized by XRF analysis while the ultimate and proximate analysis of the polypropylene feed carried out gave combustible materials content of 93.77 wt%, fixed carbon of 1.62 wt%, calorific value of 45.20 MJ/kg and elemental composition with carbon (83.65%), hydrogen (14.27%), oxygen (0.15%), sulphur (0.1%), chlorine (1.16%), and nitrogen (0.67%). Thermal cracking was carried out in the absence of catalyst and the process gave a yield of liquid, gaseous, and solid products of 67.48, 8.85, and 23.67 wt%, respectively. Furthermore, kaolin clay was employed as a catalyst in catalytic pyrolysis of the same feedstock for catalyst-to-plastic ratio of 1:1, 1:2, 1:3, and 1:4 at the same operating parameters as in thermal cracking. Optimum yield was obtained at a catalyst-to-plastic ratio of 1:3 with a yield of 79.85, 1.48, and 18.67 wt% for liquid, gaseous, and solid products, respectively. The liquid products obtained for both thermal and catalytic cracking at optimum conditions were characterized for their suitability as fuel. The properties determined were density, viscosity, flash point, fire point, pour point, and calorific value. The results suggest that catalytic pyrolysis produced liquid products, whose properties are comparable to conventional fuels (gasoline and diesel oil) than that produced through thermal pyrolysis. FTIR analysis of the liquid product from catalytic pyrolysis also shows that it contains hydrocarbons with different functional groups such as aromatics, olefins, carbonyl, amines, sulphides, and hydroxyl.