An experimental and modeling study of asphaltene adsorption by carbon nanotubes from model oil solution

Abstract

The adsorption of asphaltene on the surface of nanoparticles in the crude oil industry is a significant issue. In this regard, carbon nanostructures can be applied as an adsorbent for the removal of asphaltene from crude oil. In this paper, carbon nanotubes (CNTs) were used for the adsorption of three different asphaltenes from toluene solutions. The CNTs were synthesized by Chemical Vapor Deposition (CVD) method. The synthesized CNTs were characterized by Brunauer–Emmett–Teller (BET), Field Emission Scanning Electron Microscopy (FESEM) and Transmission Electron Microscopy (TEM). The asphaltenes were analyzed by X-ray Diffraction (XRD) and elemental analysis techniques. In addition, asphaltene adsorption isotherms and kinetics were offered. The adsorption of asphaltene was fast since equilibrium was reached in 1 h. The kinetic data were fitted well to the pseudo-second-order kinetic model. The equilibrium data of asphaltene A and B was fitted well to the Freundlich model. However, for asphaltene C, Temkin model was consistent with the experimental data due to the strong interactions between asphaltene C and surface arising from pyridinic, pyrrolic, sulfide and disulfide functional groups which existed on the surface of asphaltene C. The results indicated that the capacity and affinity depend on the molecular structure of the asphaltenes. The high adsorption capacity of asphaltene A was attributed to its high aromaticity. An increase in the aromatic nature of asphaltenes increases the self-association of asphaltenes and π−π interactions between asphaltenes and CNTs, which increases the asphaltene adsorption. The thermodynamic parameters indicated that the adsorption of asphaltenes on CNTs is exothermic and spontaneous. According to the results, CNTs showed high adsorption capacity and can be considered as an appropriate choice for asphaltene removal from crude oil.