Activated Carbons Derived from High-Temperature Pyrolysis of Lignocellulosic Biomass

Biomass pyrolysis to produce biofuel and hydrogen yields large amounts of charred byproducts with low commercial value. A study was conducted to evaluate their potential for being converted into higher value activated carbons by a low-cost process. Six chars derived from various lignocellulosic precursors were activated in CO2 at 800 °C to 30–35% weight loss, and their surface area and porosity were characterized by nitrogen adsorption at 77 K. It was found that, in similar activation conditions, the surface area of the activated carbons correlates with the activation energy of the oxidation reaction by CO2, which in turn varies inversely with the carbon yield after thermolysis in nitrogen at 1000 °C. Since lignin is the most thermally-stable component of lignocellulosic biomass, these results demonstrate, indirectly, that robust, lignin-rich vegetal precursors are to be preferred to produce higher quality activated carbons. The chars derived from white pine (pinus strobus) and chestnut oak (quercus prinus) were converted to activated carbons with the highest surface area (900–1100 m2/g) and largest mesopores volume (0.85–1.06 cm3/g). These activated carbons have properties similar to those of commercially-available activated carbons used successfully for removal of pollutants from aqueous solutions.