Development of Activated Carbon Fibers for Organic Removals

Abstract

Phenols are classified to be one of the most hazardous pollutants found in wastewater. They are discharged into rivers, lakes and seas, causing adverse effects on the enviromental and human health. Adsorption is a well-known technique used to treat wastewater. Activated carbon fibers (ACFs) are highly microporous efficient adsorbents due to their small diameters, high surface area and excellent volumetric capacity. In this work, ACFs were produced using polyacrylonitrile (PAN) fibers using different methods and tools. The fibers were stabilized initially at 250°C followed by carbonization at 850°C at a heating rate of 10°C/min and under the flow of nitrogen gas at a flow rate of 135ml/min. The carbonized fibers were subjected to physical (carbon dioxide) and chemical (potassium hydroxide) activation. The results showed that chemical activation using 3:1 ratio of KOH (wt/wt) produced fibers with a higher surface area of 2885m2/g compared to the physically activated fibers (774m2/g). The synthesized ACFs (Syn-ACFs) were compared and characterized in terms of morphology, thermal stability, composition and pore characteristics using SEM, EDS, TGA, CHN and nitrogen isotherm (Quantachrome). Bench scale batch experiments were carried out to determine and compare the adsorption efficiency, optimum parameters and the capacity of Syn-ACF and commercial ACFs (C-ACFs) for p-cresol removal. The adsorption optimum conditions using Syn-ACFs are: Syn-ACFs dosage = 1 g/l, contact time = 30 minutes, temperature = 25°C and initial pH = 4.6. The adsorption study on (Syn-ACFs) gave a higher removal efficiency of 91.0% of p-cresol compared to 71.6% (C-ACFs) at a concentration of 350ppm. In addition, the adsorption isotherms of p-cresol on C-ACFs and Syn-ACFs were found to follow the Langmuir isotherm equation; however, Syn-ACFs revealed a higher adsorption capacity (500mg/g) compared to C-ACFs (294 mg/g) at 25°C. The Syn-ACFs regeneration method was evaluated thermally at elevated temperatures and chemically using ethanol and n-hexane solvents. The thermal regeneration at 600°C achieved a higher removal efficiency of 84% compared to n-hexane (78%). The Syn-ACFs were evaluated for the treatment of produced water to ensure a removal of 71.2%. The results indicated that Syn-ACFs could be used as an efficient adsorbent for p-cresol removal in wastewater.