4-Lump kinetic model of the co-pyrolysis of LDPE and a heavy petroleum fraction

Pyrolysis of post-consumer plastics is a promising strategy to recover valuable hydrocarbons from waste streams. In this study, the lumping approach is adopted to model the kinetics of a continuous co-pyrolysis process for lowdensity polyethylene (LDPE) and a heavy petroleum residue fraction (HPR). All evolving species are merged in four lumps based on their boiling range: residue (R,> 410 degrees C), spindle oil (SO, 350-410 degrees C), light liquids (LL, IBP - 350 degrees C) and gas (G, noncondensable at 0 degrees C). The experimental results of a tubular laboratory cracker with a mixture of LDPE and HPR at different reactor lengths between 19.4 and 33m provide data to estimate kinetic parameters for all six considered reactions and the overall reaction enthalpy. Based on the rate equations for irreversible, monomolecular, first-order reactions and the mass and heat balance of an incrementally modeled tubular reactor, a MATLAB algorithm solves the optimization problem including a bottom-up approach to find suitable initial values. The calculated frequency factors vary over a wide range from 10(2) to 10(8) s(-1) and the obtained activation energies are between 147 and 313 kJ mol(-1). The determined value for the overall reaction enthalpy is 4669 kJ mol(-1). The results of the modeled system are in good agreement with experimental yields and can be implemented into a process model of the LDPE-HPR co-pyrolysis for simulation and optimization purposes.