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

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.