Characterization of biochars derived from pyrolysis of biomass and calcium oxide mixtures

This study forms the fundamental foundation for the development of a novel carbon arrestor process to produce a functionalized biochar. In this study, an experimental investigation was carried out on the production and characterization of biochar produced using a novel carbon arrestor process, which operates under the principle of in situ pyrolysis of biomass with lime (CaO) to produce a functionalized biochar product for use as an agronomic soil amendment. Two biomass sources were used, a woody biomass, Eucalyptus pilularis (or blackbutt) sawdust, and a herbaceous biomass, wheat stem. Characterization of the biochars produced as well as the gaseous products was completed via thermogravimetric analysis, micro gas chromatography, solid-state Fourier transform infrared (FTIR) spectroscopy, nitrogen adsorption, and scanning electron microscopy. The addition of CaO to the pyrolysis process resulted in a significant reduction in CO2 evolution via the carbonation reaction of CaO and the formation of H2 and CH4 at lower temperatures in significantly higher quantities in comparison to biomass pyrolysis alone. This was achieved via carbonation and hydration reactions of CaO with pyrolysis gases and catalytic effects of CaO. Biochar produced with no CaO from blackbutt had the highest surface area (201 m2/g), while the wheat stem was considerably lower (6.7 m2/g), and both had morphology resembling the parent biomass. The addition of CaO resulted in a drop in the surface area (37 m2/g) for blackbutt biochars, with wheat stem biochar presenting similar surface areas to the respective blackbutt biochars. Greater swelling of char particles, a significant reduction in the particle size, and considerable fracturing of the CaO particles were evident. Biochars produced with the addition of CaO resulted in a reduction in oxygenated functional groups on the surface, determined via FTIR and, to a lesser extent, elemental analysis, which may be beneficial for char stability and longevity in soil.