Air-activated carbons from almond tree pruning: Preparation and characterization

In this work the results obtained in the preparation and characterization of carbons made from almond tree pruning by non-catalytic and catalytic gasification (using K and Co) with air are analyzed and discussed. The main aim was to obtain high quality activated carbons at the lowest possible cost. The variables studied have been the temperature (190–260 8C) and the time (1–10 h) in non-catalytic gasification and the influence of the catalyst type (K and Co, 1 wt.% referred to cation, at 190 8C and 1 h) and the time (1–4 h) in catalytic gasification with Co at 190 8C. The air flow rate used in all the series was 167 cm3 min 1. In non-catalytic gasification the reaction normalized rate versus the conversion degree was maintained until a conversion value of 10% for the experiment made at 260 8C since, at lower temperatures, this rate drops quickly for low conversion values. The N2 adsorption isotherms for the carbons of this series resemble type I, although there is an increase of N2 adsorbed volume at relatively high pressures. A temperature rise produced an increase of the carbon porosity and BET specific surface (116–469 m2 g 1). The activation time has a positive effect on the N2 volume adsorbed by the carbons. The isotherms shapes were similar to those previously commented. A concentration equal to 1 wt.% was used to study the influence of the catalyst type. Under the studied experimental conditions, Co drives to a bigger porosity development than K, although with both catalysts a very similar pore size distribution is obtained. The activation time, in the gasifications catalyzed with Co, gives rise to a very important porosity development in the carbons. This produces a strong increase of the carbon specific surface area with very high values in the 4 h experiment, in which a BET specific surface of 959 m2 g 1 was obtained.