Investigations on the effect of kaolin catalyst on the yield of various products obtained from pyrolysis of low-density polyethylene (LDPE) wastes and reaction kinetics

The pyrolysis characteristics of low-density polyethylene (LDPE) wastes were investigated in a batch pyrolyzer in the temperature range of 550–650 °C for a varying heating rate (5, 10, 15, 20, and 25 °C/min) alone and using kaolin catalyst (10, 15, and 20% w/w). The yield distribution of various products under varying operating conditions was investigated, and the corresponding favourable conditions for maximum yield of pyrolytic oil (PO) were identified. The possible effect of the catalyst on pyrolysis kinetics was explored by extracting activation energies from the TGA experiments. The various model-free iso-conversion methods estimated the activation energy of 162–166 kJ/mol during thermal degradation of LDPE, while it shifted to a lower range (138–145 kJ/mol) on catalytic treatment. The catalytic pyrolysis with a 20% (by mass) catalyst in a batch pyrolyzer provided the maximum PO yield with the least solid residue at 600 °C using a heating rate of 20 °C/min, while the temperature of  600 °C with 10% catalyst showed the least liquid product with more solid residue. The presence of a catalyst improved the oil quality with transparency and lower viscosity due to lighter hydrocarbons and higher aromatic content. The FTIR analysis detected various organic groups—alkanes, alkenes, cyclic, and aromatics in the oil. GC tests of gaseous products confirmed the gases like hydrogen, propane, butane, and propylene. The present study aims to provide technical know-how for the effective utilization of LDPE wastes towards clean energy sources and create a plastic-free green environment.