Conversion of PP, HDPE and LDPE Plastics into Liquid Fuels and Chemical Precursors by Thermal Cracking

The inappropriate disposal of plastic waste causes serious environmental problems. Nowadays, alternative processes are being studied for the sustainable reutilization of plastics. One of these options is the cracking into shorter liquid hydrocarbon fractions, while maintaining its basic chemical structure. The energetic potential from the original plastics structure remains and the fractions can be used as fuels and chemical precursors. This research addresses the kinetic study of thermal cracking of polypropylene (PP) and high- and low-density polyethylene (HDPE and LDPE) in a batch reactor. The kinetics of the reaction can be described as a first-order rate with the lowest activation energy using PP, followed by HDPE and LDPE with values of 367.28 kJ/mol, 453.37 kJ/mol and 457.96 kJ/mol, respectively. The yield obtained for the liquid fraction is highest for LDPE, with a value of 72% at 390 °C, followed by HDPE and PP with 69% and 62% at 375 °C. The liquid fractions obtained from the process were characterized according to ASTM standards, obtaining that LDPE and HDPE fractions have similar properties to diesel, while PP is closer to gasoline. The fractions were also analyzed by means of gas chromatography identifying the main products of the reaction and establishing a possible reaction mechanism.