Production and characterization of biochar produced from slow pyrolysis of pigeon pea stalk and bamboo

Sustainable management of agricultural residues has gained momentum worldwide as an environmentally benign process. This study focused on the impact of pyrolysis temperature on biochars' physicochemical properties derived from two agricultural residue materials (pigeon pea stalk and bamboo) pyrolysed at different pyrolysis temperatures (400, 500 and 600 °C) for a holding time of 1 h. The bamboo and pigeon pea stalk were characterized, as well as their resulting biochar samples (proximate, ultimate, SEM, BET, FTIR and XRD). For both the biomass materials, biomass composition had great influence on the biochar yield and properties. More mass fraction of lignin in the bamboo biomass yields more biochar (32.20–27.00%) compared to pigeon pea stalk biomass (29.80–21.70%) at the same pyrolysis temperature. The mass fraction of fixed carbon of biochars was observed to be in the range of 81.85–85.68%, which were much higher than the biomass. The mass fraction of carbon in the derived biochars were in the range of 76.17–88.43%. The biochar with the highest mass fraction of carbon was found at a pyrolysis temperature of 600 °C for both biomass-derived biochars. Biochars with low atomic ratio of H/C (0.03–0.06) and O/C (0.09–0.25) confirmed their highly carbonized, aromatized and hydrophobic nature. The BET surface area of biochar samples were ranged from 16.90 to 307.10 m2 g−1, biochar with the higher surface area was obtained at pyrolysis temperature of 600 °C. At the same pyrolysis temperature, bamboo derived biochars were higher total pore volume (0.057–0.18 cm3 g−1) in respect to pigeon pea stalk derived biochars. The alkalinity of all biochars increased in tandem with the pyrolysis temperature and found to be in the range of 7.25–10.14. The acidic and polar functional groups were successively removed and resulted in a more hydrophobic well-organized carbon layered biochar at a temperature of 600 °C. The biochars were enriched with sylvite, calcite, and silicates of Mg, Mn, and Ca signifying its heterogonous characteristics and increased ash content.