The effect of the activating agent and temperature on the porosity development of physically activated coal chars

An experimental work on the influence of temperature and the activating agent on the development of surface area and porosity for activated carbons was carried out. Three coals from different regions of Colombia were activated with CO2, steam and a CO2-steam mixture. Coal from the Antioquia Region (La Capotera) was activated with a CO2-stearn mixture at 1073, 1123 and 1173 K and with CO2 and steam at 1073 K. Other two coals from Antioquia and Cesar regions (La Grande and Borrego) regions were activated with a CO2-steam mixture at 1073 K and these were compared with the La Capotera char for the same conditions. The content of ash was confirmed to affect the development of surface area: coals with lower amount of ash developed higher specific surface areas. Activation temperature also affected the development of surface area: the use of high temperature produced low surface areas. Results indicate that CO2-steam produces larger surface areas than CO2 and steam alone, and reactions with CO2 -steam and CO2 develop a more uniform porosity than reaction with steam. The pore sizes are larger when steam is used and smaller when CO2 is used. (C) 2004 Elsevier Ltd. All rights reserved.