Although potassium hydroxide (KOH) is known to be effective in generating highly porous activated carbons, the mechanism of KOH activation has not been well elucidated. To develop porosity in carbon, a high KOH/carbon mass ratio must be maintained. Consequently, KOH, as the activating agent, represents a major part of the cost of the activation process. Focusing on the mechanism, particularly the activation products, the present work attempted to establish the technical feasibility of recycling KOH. Experiments revealed that the major products of KOH activation at 600–900°C are metallic K, K2CO3, CO and H2, which is supported by thermodynamic analysis. The overall reaction may be written as 6KOH + 4C = K2CO3 + 4K + 3H2 + 3CO. At temperatures over 900°C, K2CO3 becomes unstable and participates in activation reactions with carbon; a more suitable overall reaction would be KOH + C = CO + K + 0.5H2. As potassium ion is reduced to metallic K which is readily converted into KOH and hydrogen gas upon reacting with water, KOH recycling is feasible. The reuse of KOH in chemical activation could substantially reduce the cost of activation process. © 2011 Canadian Society for Chemical Engineering
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