Comparison of corn straw biochars from electrical pyrolysis and microwave pyrolysis

In this study, biochar production from electrical pyrolysis and microwave-assisted pyrolysis of corn straw was detailed. The yields and surface topographies of biochars produced from electrical pyrolysis and microwave pyrolysis at different pyrolysis temperatures (700, 750, 800, 850, and 900°C), biomass loads (9, 12, 15, 18, and 21 g), and residence times (60, 90, 120, 150, and 180 min) were elaborated in the study. The results showed that the biochar yields were in the range of 21.14–38.7 wt. %, and they gradually decreased when there were decreases in the biomass loads or increases in the pyrolysis temperatures or residence times. Increases in pyrolysis temperatures and residence times or decreases in biomass loads increased the porosity and pore densities and reduced the pore sizes. As compared with electrical pyrolysis, microwave pyrolysis increased the bochar yields, i.e. by 21.24% at 800°C, 180 min, and 15 g (21.4 wt. % vs. 25.3 wt. %). Biochar produced from electrical pyrolysis had heterogeneous pore size distribution, whereas biochar obtained from microwave pyrolysis had identical sizes and round shapes on its surface. This study quantitatively revealed the relationships between biochar yields and experimental conditions (pyrolysis temperature, biomass load, residence time).