Periodic mesoporous organosilicas containing naphthalenediimides within the pore walls for asphaltene adsorption

Abstract

Abstract Periodic mesoporous organosilicas (PMO) containing 1,4,5,8-naphthalenediimides (NDI) as integral part of the pore walls were employed for the adsorption of asphaltenes from toluene solutions. The adsorbents, which were named PMONDI, contained variable amounts of NDI co-condensed with inorganic silica. The PMONDI showed a better performance for asphaltene adsorption than purely inorganic mesoporous silica SBA-15, which was used for comparison. Adsorption isotherms of the PMONDI showed asphaltene adsorption capacities reaching up to 224 mg/g, which is higher than most reported adsorbents. The best fit for the adsorption isotherms was achieved with the Langmuir model (developed for homogeneous surfaces) for SBA-15 and with the Sips model (which deals with heterogeneous surfaces) for the PMONDI. It was concluded that the homogeneous surface in SBA-15, where asphaltene binding is mainly due to hydrogen bonding to silanol groups, was converted to heterogeneous surfaces in the presence of the NDI, indicating that hydrophobic and π-stacking interactions between wall-embedded NDI units and asphaltene molecules contributed for binding. These conclusions were supported by contact angle measurements. The adsorbents could be reused for at least three adsorption cycles, and the adsorbed asphaltenes could be easily regenerated by desorption with organic solvents. In conclusion, the PMONDI are novel materials with great potential for applications such as oil upgrading and the remediation of oil spills.