Physiochemical properties and yields of corn-stalk-biocharunder different pyrolyzed temperatures

Objectives The physiochemical properties of corn-stalk-biochar were largely determined by the carbonization temperature. The aim of the experiment was to investigate the yields and physiochemical properties of corn-stalk-biochar at different pyrolyzed temperatures (100℃–800℃), looking for the suitable temperature in which biochar has a high use value.

MethodsCorn-stalk-biochar was prepared through the hypoxia carbonization method. The furnace temperatures were set at 100℃, 200℃, 300℃, 400℃, 500℃, 600℃, 700℃ and 800℃, respectively, and the rate of heating up was 20℃/min and finally held at that temperature for 2 hours. We studied the properties, including pH, total N and total C content, and CEC of biochar.

ResultsThe yields of corn-stalk-biochar were decreased with the rising of pyrolysis temperature. The total C contents were increased with the increase of pyrolysis temperature, the total N contents started to decrease when the temperature was higher than 400℃. The CEC of corn-stalk-biochar reached peak values between 400℃–600℃, which were 70.87–83.48 cmol/kg. With the increase of carbonization temperature, the alkaline functional groups contents on the corn-stalk-biochar surface were increased significantly, while the acidic functional groups contents were reduced significantly. The pH values of corn-stalk-biochar became alkaline after 400℃ and would continue to increase to strong alkaline with the further increase of temperature. When the pyrolysis temperature reached 500℃, the cellulose and hemicellulose were completely decomposed, and the groups of –OH, –CH₃, –CH₂, –C=O would be associated or eliminated to form new aromatic groups. With the carbonization temperature increasing, the specific surface area and pore volumes of corn-stalk-biochar were both increased firstly and then declined. However, the pore sizes showed an opposite trend. The porosity of corn-stalk-biochar was relatively more abundant at 400℃–600℃. The specific surface area showed a significant highly positive correlation with the pore volume.

Conclusions Comprehensively considering the effects of yields and physiochemical properties, the optimum carbonization temperature of corn-stalk-biochar should be remained at 400℃–500℃.