Steam- or carbon dioxide-activated carbons from almond shells: physical, chemical and adsorptive properties and estimated cost of production

A series of steam- or carbon dioxide (CO2)-activated, granular activated ca rbons (GACs) were made from almond shells using six different activation or activation/oxidation conditions for each series. Unoxidized/oxidized pairs of GACs were compared among treatments and to two commercial GACs in order to determine the relative value of the carbons. Comparative terms included yield, surface area, attrition, surface charge, copper ion (Cu2+) uptake, adsorption of a mixture of six polar and non-polar organic compounds and an estimated cost of carbon production. Of the six conditions investigated fo r steam activation, two treatments consisting of a 1 h pyrolysis at either 700 degrees C or 800 degrees C, followed by a 2 h activation at 800 degrees C with the introduction of water at a rate of 7.0 ml/min were the best ove rall performing unoxidized/oxidized pairs in terms of copper ion or organic s adsorption, respectively. Of the six conditions investigated for carbon d ioxide activation, a treatment consisting of a 1 h pyrolysis at 700 degrees C, followed by a 2 h activation at 800 degrees C using a 75% CO2/25% N-2 g as mixture was the best overall performing unoxidized/oxidized pair. Our es timated costs of production indicate that steam-activated, unoxidized and o xidized carbons appear to be the most economical GACs to manufacture and al so the most economical for removal of copper ions and organic compounds. (C ) 2000 Elsevier Science Ltd. All rights reserved.