Improving Porosity of Activated Carbon Nanotubes via Alkali Agents for the Enhancement of Adsorptive Desulfurization Process

Abstract

This work was focused on the removal of sulfur compounds via adsorption process from heavy naphtha using alkali agents-activated carbon nanotubes (ACNTs). Commercial CNTs were activated using three alkali agents (KOH, NaOH, and CaCl2) to amend their surfaces for application in the petroleum industry. The characterization of the physicochemical properties of as-received CNTs and CNTs/alkali agents was performed using a scanning electron microscope (SEM), N2 adsorption/desorption isotherm, and Fourier transform infrared spectroscopy (FTIR). The effects of three operating conditions including adsorbent dosage (1-3 g), agitation speed (330-1500 rpm), and contact time (30-70 min) on the removal efficiency of sulfur compounds at constant pressure and temperature were investigated. Studying of the removal efficiency at different operating conditions was adopted to effectively evaluate the surface modifications of adsorbents on the present process. The specific surface areas of the CNTs were found to be increased upon treatment with alkali agents especially KOH and NaOH. SEM images demonstrated the formation of many defects on the CNTs surface due to the strong etching effect of both alkali agents KOH and NaOH. FTIR spectra showed different relative intensities around band 3440 cm-1 for CNTs/KOH and CNTs/NaOH which was potentially attributed to the presence of hydroxyl functional groups. The sulfur removal experiments from heavy naphtha (initially had a sulfur concentration of 350 ppm) showed that the largest sulfur removal efficiency and adsorption capacity were 69.6% and 6.6 mg/g adsorbent respectively and obtained with CNTs/KOH which presented a superior adsorption efficiency over others. The highest sulfur removal efficiency was gained at adsorbent dosage=3 g, agitation speed=1500 rpm, and contact time=70 min. The study of adsorption kinetics demonstrated that the adsorption of organosulfur compounds from heavy naphtha obeyed the pseudo-second order kinetics