Preparation of granular activated carbon from hydrothermally treated and pelletized deciduous wood

Dense mechanically strong granular activated carbon (GAC) was prepared from hydrothermally modified and pelletized grey alder (Alnus incana (L.) Moench) (GA) wood by direct carbonization and physical activation with superheated steam under a self-generated atmosphere. Hemicellulose autohydrolysis products, formed during hydrothermal treatment, provide a bounding and bulking effect during the modified wood pelletization process. After carbonization and activation, a mechanically strong activated carbon structure containing up to 45% micropores was developed. The influence of the moisture content of the modified wood (MW) before pelletization in a range of 4–12 wt% as well as the carbonization temperature of the obtained pellets 300–700 °C on the thermochemical and mechanical properties, and the developed porous structure of the GAC was studied. It has been found that MW pellets, derived from GA wood treated at 180 °C for 2 h, are thermally more stable than the raw GA wood. Samples with a higher content of cellulose and lignin reached higher char yields. The mechanical and surface properties of GAC depend on the combined effect of the employed conditions. If mechanically strong high-density granular adsorbents are necessary, pelletization of MW with the moisture content 6–12 wt% is preferable, and the optimal carbonization temperature is 600 °C.