Cracking of plastic pyrolysis oil over FCC equilibrium catalysts to produce fuels: Kinetic modeling

Abstract

The kinetics of the catalytic cracking of plastic pyrolysis oil (PPO) over three FCC (fluid catalytic cracking) equilibrium commercial catalysts has been modeled. The PPO comes from the fast pyrolysis of high-density polyethylene (HDPE). The cracking runs have been carried out in a laboratory-scale reactor under FCC conditions: 500–560 °C; catalyst/oil weight ratio of 5 gcat gPPO-1; and contact time of 1.5–6 s. Four different reaction schemes composed of six lumps have been compared and it has been obtained by statistical means that the simplest one is the most appropriate for describing the process. The differences in the kinetic parameters have been related to the properties of the catalysts. Among them, total acidity and mesoporous structure have a key role. The former for promoting the cracking reactions and the latter for limiting the diffusional restrictions of both the bulky compounds within the PPO and the formed coke precursors. This way, ECAT-3 that is the most acid and most mesoporous catalyst, maximizes the yields of naphtha (33.6 wt%) and liquefied petroleum gases (LPG) (18.9 wt%). In contrast, ECAT-1 and ECAT-2 should be chosen for producing light cycle oil (LCO). For ECAT-3, the apparent activation energies of the conversion of heavy cycle oil (HCO) into light cycle oil (LCO), LCO into naphtha, and LCO into LPG are 60.5 42.5 and 58.3 kJ mol-1, respectively. In addition, those of the formation of coke from HCO, LPG and dry gas are 129.0, 4.4 and 40.7 kJ mol-1, respectively.