Evaluation of the physiochemical development of biochars obtained from pyrolysis of wheat straw, timothy grass and pinewood: Effects of heating rate

Biochar is a major product obtained from conversion of biogenic waste via pyrolysis, which is recognized to have both bioenergy and remarkable environmental benefits. This biochar is mainly composed of aromatic carbon with several degrees of aromaticity. The effectiveness of biochar produced from three different biomass species such as wheat straw, timothy grass and pinewood was estimated through two different conversion scenarios. The first scenario employed slow heating rate (SHR) to generate biochars that had an advantage of high yields and a limitation of producing relatively low-energy product. The second scenario employed high heating rate (HHR) pyrolysis with low yields of biochar and pyrolysis gas, and higher yields of bio-oil. HHR pyrolysis produced substantially high-energy products (bio-oils), while SHR pyrolysis resulted in high amount of biochars with agronomic values. The HHR and SHR biochars were characterized physiochemically through CHNS, ICP-MS, SEM, Raman spectroscopy, FT-IR, TG–DTG and XRD analysis. The composition of N, P, K, Na, Ca and Mg was retained in higher amounts in SHR biochars. The highly alkaline nature of SHR biochars indicated their application to croplands for increasing crop yield and soil fertility.