Synthesis and properties of activated carbon from lignin

A series of activated carbons have been synthesized from Kraft lignin by different methods. The lignin has been found containing Na+ (∼10%) and S (∼2%) and is water soluble at high pH (∼9.5). The preparation of these carbons is divided two major steps: pre-carbonization in N₂ and air, and activation at 600–850°C of the carbon with CO₂ or K₂CO₃ and KOH catalysts. Carbon I specimens are prepared in air, N₂/O₂, or carbon dioxide while retaining large fraction of inorganic compound (27–36%); Carbon II are prepared with catalyst (K₂CO₃ or KOH) in nitrogen; Carbon III are prepared with catalyst (K₂CO₃ or KOH) in carbon dioxide.; Properties of the carbons have been characterized by TGA, Py-MS, ICP, and elemental analysis. This study revealed that in the carbonization stage most of the thermal degradation products are non-aromatic fragments, resulting in a high yield of carbon material (>50%). The apparent activation energy of degradation of lignin is ∼136 kJ/mol. These results confirm our supposition that lignin, which is polyphenol based, is a good precursor for activated carbon.; Nitrogen adsorption studies show types I, II and IV isotherms for all carbons, indicating that most pores are in the micropore range. The BET-surface area, microporosity, pore diameters, and fractal dimension have been obtained from nitrogen adsorption measurements. Carbon II displays high surface area (up to ∼1800 m2/g), narrow pore size distribution with average diameter of ∼2 nm, and pore volume of 0.85 mL/g. Some correlations between the micropore volume, surface area, fractal dimension, micropore size and filling up pressure have been obtained. The fractal dimension has been found to be inversely proportional to the micropore's square diameter.