Adsorptive desulfurization of model fuels using ferrite nickel-silica in continues system: Modelling of breakthrough curves, thermodynamic study and experimental design

Abstract

• NiFe 2 O 4 -SiO 2 nanosorbent was synthesized and used for adsorption of DBT. • The effects of bed height, flow rate, and initial sulfur concentration parameters were investigated. • Optimal continuous column conditions were obtained using the experimental design. • The kinetic and thermodynamic aspects of the dibenzothiophene adsorption process were investigated. Utmost of the adsorption testing is restricted to batch trials which do not give precise scale-up data that can be applied to the bulky ruler of handling. In this regard, ferrite nickel-silica (NiFe 2 O 4 -SiO 2 ) nanocomposite is synthesized by an auto-combustion sol–gel method. The removal of dibenzothiophene (DBT) from model fuel ( n -hexane and DBT) was studied by conducting adsorption process in fixed-bed column using NiFe 2 O 4 -SiO 2 nanocomposite. The synthesized nanocomposite was characterized by vibrating sample magnetometer (VSM), temperature programmed desorption (TPD), SEM, FTIR, XRD, BET, and TEM analyses. In addition, to evaluate the effective parameters of the adsorption process in the continuous column, a central composite design was used. The optimal values of influential factors such as bed height, initial sulfur concentration, and flow rate to maximize the percentage of sulfur removal were 10 cm, 150 mg.l −1 , 0.75 ml.min −1 , respectively. The maximum amount of DBT adsorbed from model fuel by nickel ferrite-silica nanosorbent under optimal column conditions was 382.455 mg.g −1 . Additionally, the thermodynamic studies of the fixed-bed column showed that the adsorption process is endothermic ( Δ H >0), and spontaneous ( Δ G <0). Also, the positive value of Δ S indicates that the increase in temperature increases the stochaticity between the adsorbent and the model fuel in the adsorption process. Moreover, Thomas, Adams-Bohart, and Yoon-Nelson models were used for kinetic modeling of continuous system data. Adams-Bohart and Yoon-Nelson models with correlation coefficient values of 0.85, and 0.86, respectively, showed good agreement with experimental results. In addition, three isotherms (i.e., Freundlich, Langmuir, and Dubinin-Kaganer–Radushkevick) were investigated for the adsorption process of DBT by NiFe 2 O 4 -SiO 2 nanosorbent in a continuous system. The results showed that the Langmuir isotherm fits well with the results.