1996 Effect of steam and carbon dioxide activation in the micropore size distribution of activated carbon

    The three series of activated carbons were prepared from a common char, prepared by the carbonization of olive stones (nitrogen flow of 80 ml min^-1; 850℃; heating rate, 5℃ min^-1; residence time 2 hours).

    Activated carbons prepared by carbon dioxide activation exhibit a larger micropore volume and a narrower micropore size distribution than those prepared by steam activation.

    2001 Mesoporous high-surface-area activated carbon

    The shells or seeds were dried at 110^oC, crushed and sieved to a uniform size of 1.0–2.0 mm. Subsequently, ZnCl₂ in the form of a powder and about 10 ml of water were added to the raw material to provide ZnCl₂-to-shell ratios varying from 0.25 to 3 by weight. The mixtures were dehydrated overnight at 110^oC and pyrolysed under a flow of nitrogen in a quartz tube held in a horizontal furnace (Carbolite). The temperature was ramped at 10^oC/min up to 800^oC. Nitrogen was replaced by CO₂ when the temperature reached 800^oC and the carbon soaked at these conditions for 2–3 h. The activated products were then cooled, washed successively with deionised water, hydrochloric acid (0.1 mol/l) and hot deionised water to remove the zinc and chloride compounds. After overnight drying in air at 110^oC, N₂ adsorption–desorption isotherms of the carbons were measured using a gas sorption analyser (Nova-1000, Quantachrome) to determine surface area and pore volume.

    At low ZnCl₂-to-shell ratios, micropore formation is the dominating mechanism; pore widening becomes important as the ratio increases. Pore widening takes place at the expense of micropore formation for high ZnCl₂-to-shell ratios, thereby reducing the micropore content.

    Almond, walnut, hazelnut shells and apricot stones were used as starting materials. These raw materials were broken with a Waring commercial blender and sieved to a particle size of 1–1.25 mm in diameter.   

    Granulated raw materials were dried at 110^oC for 24 h. Dried raw materials were mixed with a solution of ZnCl2 (30 wt.%). The mixture was dehydrated at 103^oC for 6–10–18–24 h and subsequently activated at 750–800–850^oC for 2 h in the presence of N₂ (40 ml min^-1 flow rate). The activated samples were washed initially with 1.2 M hydrochloric acid solution. Further washing was done with hot distilled water. Products were dried
at 110^oC for 24 h in a thermostatically controlled oven.