Adsorption properties of active carbon from lignin

Regularities of changing the adsorption characteristics of lignin-based active carbon (AC) with the temperature and time of activation with steam are studied. The extreme changes in the plots of the specific surface and adsorption activity with respect to methylene blue (MB) and iodine with maxima at 800°C are observed with an increase in the activation temperature from 400 to 900°C. The dependence of the AC yield on the activation time at 800°C indicates the presence of two regions of interaction of lignin with steam. The gasification rate in region I (τ_a up to 30 min) is by 33 times higher than that in region II (τ_a = 30–120 min), which is determined by different reactivities of structural fragments of two types. The gasification of the highly reactive structural fragments of the type I results in the formation of a porous system of AC, and their complete burning-out corresponds to limiting values of the specific surface and adsorption activity with respect to iodine. Subsequent activation is determined by the gasification of the structural fragments of the type II and leads to the formation of AC characterized by the maximum adsorption activity with respect to MB.