Pyrolysis of rice husk using CO₂ for enhanced energy production and soil amendment

Anthropogenic CO₂ generations from use of fossil resources has led to catastrophic climate problems. Biochar is a promising material for CO₂ capture and storage in soil, because it does not require additional storage space. To produce biochar, pyrolysis is required in an oxygen-limited condition. In an attempt to offer more environmentally benign route for biochar formation, this study introduced CO₂ as a reaction agent. Using rice husk as a model compound, biochars were produced under CO₂ and N₂ condition. Porosity of rice husk biochars (RHBs) were enhanced under CO₂ condition, because CO₂ affected to formation of nano-sized pores. pH and moisture retention capacity of garden soil was controlled with an addition of RHBs. Mixtures of garden soil and RHB were also used as cultivation media for growth of barley grass, and plant growth in the mixtures was improved by 20% comparing to garden soil. Moreover, CO₂ contributed to enhanced syngas generation during biochar production through gas phase reactions between CO₂ and volatile compounds. Thus, this study proved that CO₂ is a useful reactant for pyrolysis of biomass waste.