CO₂ Gasification Reactivity of Char from High-Ash Biomass

Area of Science:

• Biomass pyrolysis and gasification
• Renewable energy materials
• Catalysis and surface chemistry

Background:

• Biomass char from pyrolysis is a promising renewable fuel and material.
• High-ash biomass feedstocks, like forest residues and agricultural wastes, often exhibit high char reactivity.
• Understanding the influence of ash-forming elements on char gasification is crucial for optimizing its utilization.

Purpose of the Study:

• To investigate how chemical and physical properties of high-ash biomass char influence CO2 gasification rates.
• To analyze the interactions between these properties, particularly the role of inorganic elements.
• To assess the impact of acid leaching on char properties and gasification reactivity.

Main Methods:

• Chars were produced from pine bark, forest residue, and corncobs (4-30 mm particle size).
• Acid leaching (diluted acetic acid) was performed to modify inorganic element content.
• Char properties (elemental composition, specific surface area, carbon structure) were analyzed.
• CO2 gasification rates were measured at 800 °C with 20% CO2 in N2.

Main Results:

• Inorganic content, especially potassium (K), had a greater impact on gasification reactivity than surface area or aromatic cluster size.
• K volatilized and mobilized on the char surface at 800 °C, significantly enhancing reactivity.
• Calcium (Ca) showed a low catalytic effect due to limited mobilization at this temperature.
• Acid leaching effectively reduced K content, leading to reactivity being governed by active carbon surface area.

Conclusions:

• The dispersion and mobilization of inorganic elements, particularly K, are key drivers of catalytic activity in biomass char gasification.
• Temperature plays a critical role in the mobilization and catalytic effect of ash-forming elements like K and Ca.
• For low-K biomass char, gasification reactivity is primarily determined by the specific surface area.