The Production of Activated Carbons Using Greek Lignites by Physical and Chemical Activation Methods: A Comparative Study

Abstract

Twenty-six lignite samples, from eleven different basins of Greece, were examined as a precursor material to produce activated carbons. Two different experimental procedures were compared, a physical one, using CO₂ as the activation agent after carbonization in N₂, and a chemical one where lignites impregnated with KOH were thereafter activated. Raw materials and activated products were characterized using a variety of analytical techniques, including ultimate, proximate analysis, and X-ray diffraction. Specific surface areas and pore size distributions were also determined by means of liquid nitrogen isotherms. It was found that the obtained surface area and texture of the activated lignites depend mainly on the nature of the precursor material. The inorganic content had a negative effect on the developed surface area and the pore volume of the CO₂ activated carbons. This effect was minor for the KOH activated samples, due to leaching reactions. Regardless of the activation procedure, the samples exhibited a quite similar pore texture consisting of narrow micropores and narrow mesopores. Especially for the KOH activated carbons, the mesopores occupied the higher portion of the total pore volume.

Keywords:

• activation
• active carbon
• BET
• KOH
• lignite