Dielectric and physico-chemical behavior of single thermally thick wood blocks under microwave assisted pyrolysis (Open Access)--颗粒学报PARTICUOLOGY

Vorhauer-Huget, N., Seidenbecher, J., Bhaskaran, S., Schenkel, F., Briest, L., Gopalkrishna, S., . . . Dieguez-Alonso, A. (2024). Dielectric and physico-chemical behavior of single thermally thick wood blocks under microwave assisted pyrolysis. Particuology, 86, 291-303. https://doi.org/10.1016/j.partic.2023.07.004

Dielectric and physico-chemical behavior of single thermally thick wood blocks under microwave assisted pyrolysis (Open Access)

Nicole Vorhauer-Huget ^a *, Jakob Seidenbecher ^a, Supriya Bhaskaran ^a, Francesca Schenkel b, Lucas Briest ^a, Suresh Gopalkrishna ^a, Jan Barowski ^b, Andrea Dernbecher ^a, Liane Hilfert ^a, Ilona Rolfes ^b, Alba Dieguez-Alonso ^a

a Otto von Guericke University Magdeburg, Universitätsplatz 2, 39106, Magdeburg, Germany
b Ruhr University Bochum, Institute of Microwave Systems, Universitätsstraße 150, 44801, Bochum, Germany

10.1016/j.partic.2023.07.004

Volume 86, March 2024, Pages 291-303

Received 10 January 2023, Revised 28 June 2023, Accepted 7 July 2023, Available online 23 July 2023, Version of Record 3 August 2023.

E-mail: nicole.vorhauer-huget@ovgu.de

Highlights

• Microwave assisted pyrolysis of thermally thick beech wood blocks in a lab-scale reactor operated at 2.45 GHz.

• Process conditions monitored based on sample weight, temperature and reflected power.

• Power-level dependent mass conversion and formation of hot spots observed.

• Similar product properties as with conventional pyrolysis at 700 °C obtained at 600 W.

• Dielectric and physico-chemical properties affected by the process conditions.

Abstract

Pyrolysis of thermally thick beech wood blocks with a size of around 2.5 × 8 × 6 cm³ (width × length × height) was carried out in a lab scale microwave reactor with a frequency of 2.45 GHz, operated, both, at 300 W and 600 W under inert conditions, using N2 at around 400 mbar absolute pressure. The microwave cavity had a size of 20 × 20 × 20 cm³. The specific energy supply referred to the untreated wood block was 4–8 W/g, with slight variations depending on the initial water content. The mass loss and the reflected microwave power were in-situ monitored during the experiments. The sample surface and chamber temperatures were measured with a pyrometer and a thermocouple, respectively. Physico-chemical and dielectric properties of the produced solids were investigated and compared to those of chars produced under conventional pyrolysis using the same raw materials. It is shown that the complex dielectric permittivity of the solid products changed drastically during the pyrolysis process, with increasing heating properties as the conversion process evolved. This was easily achieved using 600 W without susceptors. However, 300 W was not enough to achieve a high conversion degree, independently of the irradiation time. This, together with the physico-chemical analyses of the solids, hinted to the importance of the transport kinetics in thermally thick materials, although further investigation is still required.

Graphical abstract

Keywords

Microwave assisted pyrolysis; Conventional pyrolysis; Dielectric measurements; Penetration depth; Elemental analysis

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