Pyrolysis of wood to biochar: increasing yield while maintaining microporosity

Area of Science:

• Biomass conversion
• Pyrolysis technology
• Materials science

Background:

• Biochar production typically involves heating biomass in the absence of oxygen.
• Volatile pyrolysis species are often lost during conventional biochar production.
• Optimizing biochar yield while preserving its properties is crucial for applications.

Purpose of the Study:

• To investigate increasing biochar yield through in-situ deposition of volatile pyrolysis species.
• To assess the impact of this deposition on biochar's microporosity and adsorption characteristics.
• To evaluate the efficacy of bio-oil recycling for enhancing biochar yield.

Main Methods:

• Aspen wood chips were pyrolyzed in a vertically stacked, multi-zone reactor (420-650°C) under nitrogen.
• Volatile species were allowed to deposit and carbonize in subsequent reactor zones.
• Bio-oil from prior pyrolysis runs was recycled back into the reactor bed.
• Microporosity and organic vapor uptake (1,1,1,2-tetrafluoroethane) were analyzed.

Main Results:

• Biochar yield increased progressively from the inlet to the outlet zones of the reactor.
• Deposited carbonized species exhibited similar microporous structure to primary biochar.
• Recycling bio-oil further boosted biochar yield.
• Desirable adsorption properties were maintained throughout the process.

Conclusions:

• In-situ deposition of volatile pyrolysis species effectively increases biochar yield.
• Recycling bio-oil is a viable strategy to further enhance biochar production.
• The method preserves key biochar properties, making it suitable for adsorption applications.