Active carbons from almond shells as adsorbents in gas and liquid phases

Almond shells have been used as raw material to prepare activated carbons. The preparation conditions, by direct activation of the raw material with CO 2 or air, or by activation after carbonisation under nitrogen, have been compared in respect to the percentage burn‐off and the adsorptive properties of the resulting carbons. It is shown that direct activation with CO 2 in the temperature range 1023–1173 K (750–900°C) gives activated carbons with similar or larger surface areas than those obtained by the conventional method (carbonisation followed by activation). On the other hand, the results show the role played by the particle size of the carbonised products on the adsorptive properties of the activated carbons prepared from them. Activation with air (in the temperature range from 573 to 673 K) does not produce carbons with large surface areas, but the yield is large and this could be of practical interest. The adsorption of methylene blue and phenol, both in aqueous solution, has allowed further comparison of the adsorptive properties of the activated carbons. In all, the direct activation with CO 2 seems to be a very good way to prepare activated carbons from almond shells; they can be favourably compared with commercial activated carbons, two of which have been used in this study.