César Pernalete

Ghent University
Hydroprocessing pyrolysis oil from waste mixed polyolefins: experimental and kinetic study

Hydrotreating is a promising route for upgrading pyrolysis oils derived from plastic waste [1] . This study investigates the hydrotreating of a pyrolysis oil composed of polyolefins, employing a three-phase continuous stirred tank reactor (CSTR) of the Robinson-Mahoney type with a commercial NiMoP/Al₂O₃ catalyst [2]. Comprehensive characterization of feed and product streams using GC × GC-FID enabled detailed insights into PIONA composition by carbon number [3].

Key process parameters, including feed flowrate-to-catalyst mass ratio and temperature, were found to critically influence total olefin conversion, which varied between 5 % and 75 % mol/mol. Conversion trends demonstrated a pronounced dependence on olefin type, consistently favoring linear over branched olefins across carbon numbers ranging from 10 to 26. A kinetic model based on the classical Horiuti-Polanyi mechanism quantified thermodynamic parameters associated with adsorption and reaction steps for linear and branched olefins. The study revealed that iso-olefins, particularly those with lower molecular weights, exhibit favorable adsorption due to enhanced π-metal interactions driven by electron-donating alkyl groups. However, steric hindrance near the reactive center in branched olefins elevated activation energy requirements, which were determined to be 87.2 kJ/mol for linear olefins and 132.8 kJ/mol for branched olefins, irrespective of olefin size.

Keywords: Hydroprocessing, Pyrolysis Oil, Mixed Polyolefins, Upgrading, Olefins conversion

References

[1] M. Kusenberg, M. Roosen, A. Zayoud, M. R. Djokic, H. Dao Thi, S. De Meester, K. Ragaert, U. Kresovic and K. M. Van Geem, “Assessing the feasibility of chemical recycling via steam cracking of untreated plastic waste pyrolysis oils: Feedstock impurities, product yields and coke formation,” Waste Management, vol. 141, p. 104–114, March 2022.
[2] J. Lauwaert, C. S. Raghuveer and J. W. Thybaut, “A three-phase Robinson-Mahoney reactor as a tool for intrinsic kinetic measurements: Determination of gas-liquid hold up and volumetric mass transfer coefficient,” Chemical Engineering Science, vol. 170, p. 694–704, October 2017.
[3] W. Zeb, M. Roosen, P. Knockaert, S. Janssens, D. Withoeck, M. Kusenberg, J. Hogie, P. Billen, S. Tavernier, K. M. Van Geem and S. De Meester, “Purification and characterisation of post-consumer plastic pyrolysis oil fractionated by vacuum distillation,” Journal of Cleaner Production, vol. 416, p. 137881, September 2023.

César Pernalete, Ir. MSc., is a chemical engineer with a master’s degree in systems modeling and simulation. He has 13 years of experience in distinct roles in the oil refining industry that range from technical (process/research engineer leader) to corporate (strategic planning analyst). He is currently a PhD fellow on the SEMK modelling of plastic-waste pyrolysis oil hydroprocessing in close collaboration with major operators of the refining industry.