Biochar production by coconut shell gasification in supercritical water and evolution of its porous structure

Biochar produced by pyrolysis is more and more widely applied in industrial and agricultural fields. The properties of biochar depend largely on its pore structure. Supercritical water has special physical and chemical properties, and may result in unique evolution rule of pore structure during the gasification process. In this paper, supercritical water gasification (SCWG) experiment of coconut shell was conducted, and porous structure in biochar was characterized. The results showed that micropores were formed and enlarged during the SCWG process; size of mesopores focused on 12 nm and 41 nm, and its content increased with time. Specific surface area of biochar increased first then decreased, and the peak value reached 279.3 m²/g at 30 min, 78 times higher than that of raw material. As for pore volume, it almost increased continually throughout the gasification process and up to 0.32 m³/g at 60 min, 43 times higher than raw material.