Activated Carbons from Spanish Coals. 2. Chemical Activation

Abstract

Activated carbons from Spanish coals have been prepared by chemical activation with alkali and alkaline-earth hydroxides. The paper analyzes the following aspects:  presence of water during pyrolysis, extension of the impregnation and drying processes, activating agent, temperature and time of pyrolysis, activating agent/coal ratio, coal rank, and mineral matter content. KOH and NaOH activation provides very successful results in which N2 apparent surface areas of 2500 m2/g are obtained; contrarily, Ca(OH)2 produces a small porosity development. A pyrolysis temperature of 700 °C yields activated carbons with a wider pore size distribution than those prepared at 500 °C. The pyrolysis time does not affect the microporosity development but an important reduction in the ash content is observed when the time is increased. The use of an activating agent/coal ratio of 2/1 compared to 1/1 has favorable effects:  (i) a decrease in the ash content and (ii) a wider pore size distribution. The addition of a drying st...