Influence of retention time and catalyst concentrations on catalytic pyrolysis yields of polyethylene and polystyrene

The present work focuses on enhancing the liquid fraction yields having hydrocarbons in the diesel fuel range from pyrolysis of PS/PE (1:1 wt.%) under the influence of ZSM–5 catalysts in an autoclave reactor. The pyrolysis product yields and their compositions were investigated for varied catalyst concentrations (0%, 5%, 7.5%, and 10%), reaction temperatures (250–500°C), and retention times (20–60 min). The physical and chemical characterization of the feedstocks, catalysts, and thermally and catalytically derived oils were carried out along with elemental analysis of the liquid products. It was observed that 7.5% catalyst concentration exhibited the maximum liquid fraction yields (71.2 wt.%) at 350°C and a retention time of 30 min. Catalytic cracking with a retention time of 20–30 min produced maximum liquid yields with aromatic, aliphatic, and isomerized hydrocarbon contents of 42.9%, 30.15%, and 14.3%, respectively. Expedite weakening of the catalytic activity of the ZSM-5 catalyst was observed with process retention time higher than 30 min. The calorific values of catalytically derived oils were found to be in the range of 44.2–44.8 MJ/kg, and their carbon numbers were between C11 and C19. Thus, these characteristics make these oils a potential candidate to be used as an alternative to diesel fuel. Further, the higher proportions of aromatics and aliphatic compounds present in catalytically derived oils compared to that obtained from thermal pyrolysis affirmed its superiority as a potential diesel substitute.