Using alkali metals to control reactivity and porosity during physical activation of demineralised kraft lignin

Abstract

Demineralised kraft lignin was impregnated with between 6.2% and 50% NaCl or KCl and physically activated in CO2 at 750 C. The results presented show that a considerable reduction in activation time even at a comparatively low activation temperature could be achieved, particularly when using KCl. Considering a fixed level of burn-off, the impregnation did not affect the pore volume and only increased the pore width by about 0.1–0.2 nm, depending on the concentration of NaCl or KCl used. By controlling the conditions it was possible to obtain predominantly ultramicroporous materials with mean pore widths over the range 0.53–0.77 nm. On the other hand, at high levels of burn-off there was evidence for micropore widening into the small mesopore range and also for the formation of a secondary mesopore structure. Under these conditions it was possible to obtain materials with pore volumes as high as 0.82 cm3 g 1.