Chemical activation and cold plasma surface modification of olefin plant waste pyrolytic coke and its effectiveness for elimination of an azo dye from aqueous solutions

Pyrolytic coke is formed in olefin plants of petrochemical complexes that is considered as a detrimental waste material. However, it could be used as a suitable carbon source for value-added activated carbon production due to its high carbon and low sulfur content. The aim of this is to convert Pyrolytic coke into activated carbon by KOH activation and cold oxygen plasma treatment as the chemical and physical treatment methods, respectively. First, effective parameters of plasma modification such as vacuum pressure and retention time as well as effective parameters of chemical activation such as temperature, activation time and weight ratio of KOH to the coke was optimized by the adsorption performance of Acid Yellow 17 dye (AY17). In the second step, the novel plasma treated activated pyrolytic coke was introduced at the optimum conditions. Vacuum of 0.2 mbar and residence time of 15 min were determined as optimal plasma modification conditions with almost 40 % AY17 removal efficiency. For chemical activation, temperature of 825 °C, activation time of 1 h and KOH to coke ratio of 1:2 were obtained as the optimal conditions. Optimum waste-base adsorbent's characteristics were investigated by SEM, BET, XRD, XRF, FTIR, CHNS and AFM analysis. Surface area of plasma treated activated pyrolytic coke (PTAPC) was reached up to 102.4 m2/g. Isotherm model and adsorption kinetics showed that this adsorbent follows the Langmuir isotherm with a maximum adsorption capacity of 48.52 mg/g and the pseudo second-order kinetic model. Adsorption at acidic pH, especially at pH = 3, has the best results. The main adsorption mechanism at pHs below zero potential is electrostatic interaction between the dye sulfonate anions and oxygenated groups such as hydroxyl.