Statistical approach to describe the properties of nanoporous carbons from lignin by chemical activation

Black liquor (BL), being a residue of pulp and paper industries, composed of lignin, sulphides and carbonates of alkaline metals. BL valorisation into activated carbon is one of possible solutions to manage waste from the mentioned industry sectors. A number of studies from the literature reported the preparation of activated carbon from lignin through metallic salt and hydroxide activation. Relying on the existing massive experimental data set, this paper proposes regression models that describe the variation of the textural properties of lignin-derived activated carbon as a function of operation conditions, such as temperature, activation time and impregnation ratio for different activators (KOH, NaOH). Statistical significance of model parameters was verified by relying on results of t-test. Using the proposed models, it was highlighted that activation temperature and impregnation ratio parameters are the principal factors controlling the activation process, while activation time has less significant effect on the development of porous structure. Carbons produced by lignin activation in the presence of KOH exhibit higher specific surface area (SSA) and micropore volume (MPV) than NaOH-activated carbons and require shorter activation time to reach high porosity. KOH activation of lignin-derived char requires lower activation temperature in comparison with a direct KOH-activation of lignin.