Transforming micropores to mesopores by heat cycling KOH activated petcoke for improved kinetics of adsorption of naphthenic acids

Abstract

Formation of activated carbon from petroleum coke by KOH, results in high specific surface area materials that are predominantly microporous. This initial microporosity means that the adsorption kinetics of target species are not as rapid as they could be, thus limiting environmental remediation applications for the material. To address this problem a series of additional heat cycles with no additional chemical inputs were applied after activation but prior to the removal of activating agents. This process resulted in the oxidation of residual potassium metal from the initial activation which allows it to function again as an activating agent for the subsequent cycles. The heat cycling resulted in an increase in mesoporosity by 10–25% with each successive cycle independent of the KOH to feedstock ratio. This was shown to be demonstrably different than equivalently extended heating times, thus identifying the importance of thermal cycling. Adsorption kinetics of three model naphthenic acids showed faster kinetics for the pore widened activated carbon. The t1/2 times dropped from 20 to 6.6 min for diphenyl acetic acid, 34.3 to 4.5 min for cyclohexane acetic acid, and 51.4 to 12.0 min for heptanoic acid.

Keywords

• Activated carbon
• Petroleum coke
• KOH
• Mesoporosity
• Naphthenic acid