Evolution of Char Structure and Its Influence on Reactivity During Biomass Pyrolysis: Spatial Scale Effects from...

Area of Science:

• Biomass conversion
• Thermochemical processes
• Chemical engineering

Background:

• Biomass pyrolysis converts natural polymers into chemical feedstocks.
• Char conversion is the rate-limiting step in thermochemical processes.
• Char reactivity is crucial for efficient pellet-based thermochemical conversions.

Purpose of the Study:

• To investigate the effect of pellet size on char structure and reactivity.
• To analyze the spatiotemporal evolution of char structure within a single pellet.
• To understand how pellet size influences volatile-char interactions and aromatization.

Main Methods:

• Pyrolysis experiments on rice straw pellets (8, 10, 12 mm) at 700 °C.
• Analysis of char chemical structure using Raman spectroscopy and FTIR.
• Sampling chars at different stages and locations within a 10 mm pellet.

Main Results:

• Increased pellet size promotes polycyclic aromatic structure growth and bio-oil aromatic compounds.
• Volatile-char interactions lead to enhanced char aromatization on the char surface.
• Char structure exhibits spatial heterogeneity within pellets due to coupled heat/mass transfer and reactions.
• Reactivity shifts from the center (devolatilization) to the surface (aromatization) over time.

Conclusions:

• Pellet size significantly impacts char aromatization and surface properties.
• Spatiotemporal evolution of char structure dictates localized reactivity.
• Understanding these effects is key to optimizing pellet-based thermochemical conversion efficiency.