Effect of Particle Size and Heating Rate on Formation of Polycyclic Aromatic Hydrocarbons During Corn Cob Biomass Pyrolysis

Teka Tesfaye Mengesha (), Venkata Ramayya Ancha, Abebe Nigussie, Million Merid Afessa and Ramchandra Bhandari ()
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Teka Tesfaye Mengesha: Oromia Agricultural Research Institute, Jimma Agricultural Engineering Research Center, Renewable Energy Engineering Case Team, Jimma P.O. Box 386, Ethiopia
Venkata Ramayya Ancha: Faculty of Mechanical Engineering, Jimma Institute of Technology, Jimma University, Jimma P.O. Box 378, Ethiopia
Abebe Nigussie: College of Agriculture, Jimma University, Jimma P.O. Box 307, Ethiopia
Million Merid Afessa: Faculty of Mechanical Engineering, Jimma Institute of Technology, Jimma University, Jimma P.O. Box 378, Ethiopia
Ramchandra Bhandari: Institute for Technology and Resources Management in the Tropics and Subtropics (ITT), TH Köln (University of Applied Sciences), Betzdorfer Strasse 2, 50679 Cologne, Germany

Sustainability, 2025, vol. 17, issue 11, 1-34

Abstract: Polycyclic aromatic hydrocarbons (PAHs) in biochar, as opposed to those in pyrolysis liquid products that exit the reactor without adhering to the solid product, are particularly undesirable due to their environmental persistence and potential toxicity. When applied as a soil amendment, biochar containing PAHs poses risks to soil ecosystems and human health. Their formation during pyrolysis presents a significant challenge in biochar production, requiring the optimization of pyrolysis process parameters to minimize PAH content for safe soil amendment applications. This study explored the effects of particle size and heating rate on PAH formation during corn cob pyrolysis. Thermogravimetric analysis (TGA) was employed to heat corn cob powder of varying sample masses from ambient temperature to 550 °C at heating rates of 5, 10, and 20 °C/min. Simultaneously, the Chemical Reaction Engineering and Chemical Kinetics (CRECK) model simulated the pyrolysis of spherical corn cob biomass particles with a radius ranging from 1 to 40 mm, using feedstock chemical compositions as inputs. Tar species generated from the solid biomass model were introduced into a gas-phase batch reactor model to evaluate PAH formation. The results demonstrate that the particle size and heating rate significantly affect PAH formation, shedding light on the complex dynamics of biomass pyrolysis. A single spherical particle with a radius close to 1 mm approximates ideal TGA conditions by minimizing temperature and mass transfer limitations. The CRECK model suggested that a particle radius of 5–10 mm, combined with a low heating rate of 5 °C/min, optimally reduces PAH formation. Future research should focus on using thermogravimetric analysis coupled with gas chromatography–mass spectrometry (TGA-GC-MS) to comprehensively quantify PAH species formation.

Keywords: biomass; pyrolysis; heating rate; particle size; polycyclic aromatic hydrocarbons; biochar (search for similar items in EconPapers)
JEL-codes: O13 Q Q0 Q2 Q3 Q5 Q56 (search for similar items in EconPapers)
Date: 2025
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