Asphaltene adsorption on MgO, CaO, SiO2, and Al2O3 nanoparticles synthesized via the Pechini-type Sol−Gel method

Abstract

Basic, amphoteric, and acidic metal oxide nanoparticles including MgO, CaO, SiO2 and Al2O3 were synthesized via the Pechini-type sol–gel process and evaluated for adsorption of two types of asphaltenes (Ap1, Ap2) extracted from two different Iranian crude oils. The adsorbents were characterized by the N2 adsorption–desorption, XRD, FE-SEM, TEM, and EDS and the asphaltene samples were examined using FTIR analysis. The effects of citric acid to metal precursor molar ratio (M), calcination temperature, type of adsorbent, textural properties, adsorption temperature, and regeneration on the adsorbent performance were investigated. The SiO2 nanoparticle with the highest specific surface area and an amphoteric character was an excellent adsorbent capable of removing more than 70% of asphaltene from a model oil with initial asphaltene concentration of 3000 ppm. However, CaO exhibited the highest specific adsorption capacity, indicating that basic sites were active centers for asphaltene adsorption. It was demonstrated that with increasing the calcination temperature, the crystallite sizes of MgO and SiO2 increased and their BET surface areas decreased. The maximum asphaltene adsorption capacities of MgO and SiO2 nanoparticles were obtained at optimal calcination temperatures of 600 °C and 500 °C, respectively. Moreover, the optimum M value for the synthesis of MgO nanoparticle, in terms of asphaltene adsorption capacity, was M = 1, while it was M = 2 (for Ap1) and M = 1 (for Ap2) for SiO2. The adsorption isotherms were best fitted by the Jovanovic model. Moreover, kinetic data for the best adsorbents (MgO and SiO2) were in maximum agreement with the Elovich model. The adsorbents could be easily regenerated by calcination at 600 °C.