Microwave pyrolysis of sargassum: how to scale-up?
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Randal De La Cruz Iturbides, Ulises Jauregui Haza, Isabelle Polaert*
Microwave pyrolysis has emerged as a promising alternative to conventional pyrolysis, offering volumetric heating, fast processing, and the ability to handle larger biomass particles. Sargassum, that invades Caribbean coasts fron 2011, represents an abundant third-generation biomass with significant valorization potential. Until now, studies on microwave pyrolysis of sargassum have been limited to laboratory-scale experiments. This work investigates the scale-up of microwave pyrolysis of sargassum from laboratory to a pilot reactor capable of treating approximately 1 kg per hour, addressing the technical challenges associated with dielectric property variations and wave propagation. Sargassum collected in Punta Cana (Dominican Republic) was air-dried, ground, and characterized.Reactor design was supported by wave propagation simulations using COMSOL Multiphysics. Pilot experiments were conducted in a semi-batch cylindrical reactor (2 kW magnetron, 2.45 GHz) with screw agitation, stepwise power increase, and nitrogen as inert gas. At pilot scale, semi-batch experiments (1 kg, 1 h) produced pyrolytic gas, bio-oil, and biochar, but residual solids remained high (~65%), indicating incomplete conversion. Energy absorbed per gram was 5–10 times lower than at lab scale. Simulations confirmed strong field concentration near the wave inlet, with limited penetration once biochar and oil formed due to their high dielectric constants. Pre-drying below 9% moisture was found essential to ensure wave propagation. Microwave pyrolysis of sargassum at kilogram scale is technically feasible, but reactor design and operating strategies must be improved to achieve complete conversion. Continuous operation, optimized geometry, and controlled pre-drying are recommended to overcome limitations observed in semi-batch mode.
Keywords: microwave, pyrolysis, sargassum, pilot scale, biochar
Proscience vol. 10
Pp 7-12