Activated carbon from olive stones by a two step process: Influence of production parameters on textural characteristics

Crushed olive stones in the 1.25-4.00 mm size range, a by-product of oil factories in south Tunisia, were used as granular activated carbon precursor. The raw material was at first thermally carbonized in a fixed bed reactor in nitrogen stream. BET apparent specific area measurements showed that heating for a period of 2 hours at 600 degrees C gives optimum char characteristics with a specific area of 240 m(2)/g and 0.12 cm(3)/g micropore volume. Three important reaction groups were observed in the thermogravimetric analysis of carbonization with peaks at 280 degrees C and 320 degrees C and a long tail for temperatures higher than 400 degrees C. In a second step, the char was activated by steam at high temperature. A high steam content was favorable to the activation process. The specific area and the total pore and micropore volumes increased with residence time and activation temperature with a relatively higher development of mesoporosity. However, experiments showed that there is an optimum activation temperature and residence time giving the highest specific area and pore volume. A temperature of 700 degrees C and 8 h activation time with 70% steam-nitrogen flow produced an activated carbon with 789 m(2)/g and 1122 m(2)/g specific area estimated by BET and Langmuir equation, respectively. Under these conditions, the micropore volume was 0.34 cm(3)/g and the total pore volume was about 0.63 cm(3)/g.