Effect of Protective Gas and Pyrolysis Temperature on the Biochar Produced from Three Plants of Gramineae: Physical and Chemical Characterization

Purpose Biochars are carbon-rich products derived from biomass through pyrolysis, and are useful for soil fertility enhancement and carbon sequestration. Most agricultural and forestry residues could be used for biochars production. In this study, biochars were produced from rice straw, bamboo culm, and reed straw under different pyrolysis temperatures. The physiochemical and morphological properties, and PAHs content of biochars were investigated for determining the effect of protective gas and pyrolysis temperatures on biochars under different pyrolysis processes. Method Rice straw, bamboo culm (8 years old), and giant reed straw were used in this study. These three organic materials were converted into biochars by slow pyrolysis using a lab-scale fixed bed pyrolysis reactor. Treatment temperatures of slow pyrolysis were 400, 500, 600 and 700 °C with or without the application of high purity nitrogen (>99.999 %) as the protective gas. Results We found that the high-temperature pyrolysis produced lower biochar yield (25.84–28.84 %) than the low-temperature pyrolysis (29.44–34.4 %). However, the BET and C content of biochar under the high-temperature pyrolysis process was higher. The low H/C and O/C ratios of the biochars produced at higher temperature pyrolysis, was 0.08–0.10, 0.01–0.22, respectively, which showed that the carbon in these biochars was unsaturated. The PAHs content decreased with increasing pyrolysis temperature. Bamboo culms pyrolysed at 700 °C had the lowest concentration of ∑ 16 PAH (10.06 μg kg −1 ). Conclusion The pyrolysis temperature significantly affected the properties of the resultant biochars ( P 0.05).