Preparation of activated carbon from Hawaii nut shell via CO₂ activation using response surface methodology

Spent Hawaii nut shell was converted into a high-quality activated carbon via CO₂ physical activation. The operational variables including activation temperature, activation duration and CO₂ flow rate on the adsorption capability and yield of activated carbon were identified. The operating variables were optimized utilizing the response surface methodology and were identified:activation temperature of 766℃, an activation duration of 36 min and a CO₂ flow rate of 186 mL/min with the methylene blue adsorption number of 186 mg/g and yield of 71.35%. The key parameters that characterize quality of the activated carbon such as the BET surface area, total pore volume and average pore diameter were estimated to be 1 267 m²/g, 0.97 mL/g and 4.13 nm, respectively. Additionally, through the SEM analyzing of char and activated carbon, the surface of activated carbon has large number of pores of irregular.