Carbonization and Activation of Lignocellulosic Biomass in Liquid Phase at Sub-200 °C Temperatures

This work presents a novel solvothermal carbonization and activation method for lignocellulosic biomasses at sub-200 °C temperatures. Common agricultural and forestry biowastes, such as corncobs, rice husks, straw, and sawdust were carbonized and activated by solvothermal treatment in chlorinated solvents in the presence of H₂SO₄. Unactivated carbonaceous materials were also obtained by omitting H₂SO₄ from the reaction. The resulting materials were characterized by using nitrogen porosimetry, scanning and transmission electron microscopy, and thermogravimetric analysis. The activated materials achieved specific surface areas as high as 830 m² g^–1 and total pore volumes up to 0.38 cm³ g^–1. The porosity consisted mostly of micropores, indicating that the present activation method favors the development of microporosity. The effects of H₂SO₄ amount, solvent type, temperature, and time on the activated materials were elucidated. To the best of our knowledge, this is the first report of (i) a liquid-based activation process and (ii) an activation process at sub-200 °C temperatures. In addition, the process has many advantages compared with the traditional activation methods that involve temperatures of 500–1000 °C. First, it is less energy-intensive due to the significantly lower temperature. Second, it is less resource intensive due to the smaller amount of activating agent required and no pretreatment or post-treatment steps. Third, it is less polluting, as no VOCs/CO/CO₂ fumes are expelled into the atmosphere. Lastly, it involves only a single one-pot step. Overall, the present carbonization and activation process offers an excellent alternative to the common high-temperature carbonization and activation methods.