Effect of pyrolysis conditions on the characteristics of biochar produced from a tobacco stem

To investigate the potential use of tobacco stems as feedstock for biochar production, a variety of pyrolysis conditions were studied to determine their effects on the distribution of pyrolysis products, as well as the physicochemical properties, energy yield and porosity characteristics of the biochar. The results showed that a moderate temperature of 400–450°C, a retention time of three hours and a slow heating rate of 5°C min⁻¹ was better to get high energy yield from biochar. In this study, the highest calorific value of biochar was 28.128 MJ kg⁻¹. The highest biochar yield occurred at a moderate retention time of three hours. The heating rate had an important influence on the characteristics of biochar, and the physiochemical properties of biochar produced at a heating rate of 10°C min⁻¹ were better than other levels. Also, the oil yield decreased and gas yield increased as retention time and heating rate increased. Biochar produced at a high temperature of 600°C, a retention time up to four hours and a heating rate of 10–15°C min⁻¹ had a larger BET surface area and cumulative pore volume than that of others. The highest change rate of pore volume of biochar almost occurred at the pore size of 2–5 nm.