Understanding the nature of non-covalent interactions (NCIs) between asphaltene molecules is not only theoretically interesting but also important for practical application. We performed quantum chemical calculations to reveal the configuration feature and intermolecular interaction characteristics of asphaltene dimers using three representative asphaltene model compounds and their derivatives. The frontier molecular orbitals and electrostatic potential map of the model asphaltenes were analyzed to reveal the nature of interaction between the asphaltene monomers. The calculation of binding energies indicates that the stability of asphaltene dimers not only depends upon the number of aromatic rings but also relies on the presence of heteroatoms in the aromatic core and aliphatic side chains, which could change the electrostatic charge distribution on the molecular van der Waals surface. In addition, NCIs and the natural bond order analysis method were used to identify the interactions that promote the formation of asphaltene dimers. It was found that the reduced density gradient isosurfaces could clearly reveal the type of interactions between two asphaltene monomers in their dimers. The results indicate that various interactions possess either an electrostatic or a dispersive nature, including hydrogen-bonding, θ–θ, θ–π, and π–π interactions, among which the π–π stacking interaction is believed to be the major driving force for asphaltene aggregation.

•The M-GO was a high efficiency demulsifier which could be reused for 6–7 times.•The non-covalent interaction analysis proved that π-π and σ-π interactions between GO materials and asphaltene molecules are the major driven forces for demulsification.Graphene oxide (GO) nanosheets have been experimentally proved to be a highly efficiency, rapid and universal demulsifier to break up the crude oil-in-water emulsion and/or the emulsified oily waste water in our previous study. To recycle the GO nanosheets and avoid the possible contamination of GO for crude oil, in this work, the magnetic graphene oxide (M-GO) was successfully synthesized and used for separating oil/water emulsions. Demulsification tests indicated that M-GO could separate the oil/water emulsions within a few minutes and recycle 6–7 times without losing its demulsification capability. The residual oil content in the separated water was as low as ∼10 mg/L, corresponding to a demulsification efficiency of 99.98% at an optimal dosage. Quantum chemical calculation results indicated that the π-π/σ-π interactions between GO materials and asphaltene molecules are the major driven forces for the high demulsification performance of M-GO nanosheets. This work not only provides a promising demulsifies to demulsify the crude oil-in-water emulsion or the oily wastewater but also give a deep understanding on the intrinsic interaction between demulsifiers and asphaltenes.

It is well known that asphaltene molecules play a significant role in stabilizing emulsions of water in crude oil or diluted bitumen solutions. Molecular dynamics simulations were employed to investigate the aggregation and orientation behaviors of asphaltene molecules in a vacuum and at various water surfaces. Two different continental model asphaltene molecules were employed in this work. It was found that the initially disordered asphaltenes quickly self-assembled into ordered nanoaggregates consisting of several molecules, in which the aromatic rings in asphaltenes were reoriented to form a face-to-face stacked structure. More importantly, statistical analysis indicates that most of the stacked polycyclic aromatic planes of asphaltene nanoaggregates tend to be perpendicular to the water surface. If the asphaltene molecules are considered as “stakes”, then the asphaltene nanoaggregate can be regarded as a “fence”. All the fence-like nanoaggregates were twined and knitted together, which pinned them perpendicularly on the water surface to form a steady protective film wrapping the water droplets. The mechanism of stabilization of the water/oil emulsions is thereby well understood. Demulsification processes using a chemical demulsifier were also studied. It was observed that the asphaltene protective film was destroyed by a demulsifier of ethyl cellulose molecules, leading to exposure of the water droplet. The results obtained in this work will be of significance in guiding the development of demulsification technology.

Seeking highly efficient, rapid, universal, and low-cost demulsification materials to break up the crude/heavy oil-in-water emulsion and emulsified oily wastewater at ambient conditions has been the goal of the petroleum industry. In this work, an amphiphilic material, graphene oxide (GO) nanosheets, was introduced as a versatile demulsifier to break up the oil-in-water emulsion at room temperature. It was encouraging to find that the small oil droplets in the emulsion quickly coalesced to form the oil phase and separated with the water within a few minutes. The demulsification tests indicated that the residual oil in separated water samples was as low as ∼30 mg/L, corresponding to a demulsification efficiency over 99.9% at an optimum GO dosage. More importantly, GO not only is useful for ordinary crude oil emulsion but also can be used to break up the extra heavy oil emulsion. The effect of the emulsion pH on the demulsification was also investigated. It was interesting to find that the distribution of GO either in oil or in water phase after demulsification was dependent on the pH value of the solution, which was attributed to the pH-dependent amphiphilicity of GO. The prominent demulsification ability of GO was attributed to the strong adsorption between the GO nanosheets and molecules of asphaltenes/resins driven by π–π interactions and/or n−π interactions. The findings in this work indicate that the GO nanosheets are a simple, highly efficient, and universal demulsifier to separate the oil from the crude/heavy oil-in-water emulsions at ambient conditions, which shows a good application prospect in the oil industry.

Nitrogen-functionalized mesoporous carbon (NMC) materials with high nitrogen content were synthesized through a hard template method using ionic liquid of 1-cyanomethyl-3-methylimidazolium bromide as the precursor and LUDOX HS-40 colloidal silica as the template. The obtained NMCs were characterized by X-ray diffraction, transmission electron microscopy, N2 adsorption and desorption analysis, X-ray photoelectron spectroscopy, and elemental analysis. It was shown that the carbonization temperature played a critical role in determining the physiochemical properties and the nitrogen content of the carbon materials. The obtained nitrogen-functionalized mesoporous carbon carbonized at 800 °C possessed disordered mesoporous structure with very high specific surface area of 1028 m2 g−1, large pore volume of 0.94 cm3 g−1, and high nitrogen content of 21.0 wt%. The adsorption performance of the prepared NMCs was investigated by removing Cu2+ from aqueous solutions and the adsorption capacity could attain 117.1 mg g−1 at an optimal condition. The kinetic and isothermal analysis revealed that the removal of Cu2+ by the NMCs belongs to chemical monolayer adsorption, suggesting the strong interaction between Cu2+ and the adsorbent. The XPS spectra of N1s before and after adsorption of Cu2+ suggested that the pyridinic-type nitrogen was the dominant groups of the adsorbent in the adsorption process. Furthermore, the material was separated from solution by filtration and displayed a superior reusability in the recycling test.

In order to explore the addition effect of fluorinated graphene (FG) on the mechanical and thermal performances of polyimide (PI) matrix, FG sheets are first prepared and employed as the nanofillers to construct PI/FG nanocomposite films. The prepared film is optically transparent at low content of FG and experimental results demonstrate that the addition of FG can effectively enhance the properties of PI matrix. Especially, compared with pure PI matrix, the addition of 0.5 wt% FG in PI can endow 30.4% increase in tensile stress and 115.2% increase in elongation at break. Experimental analyses considering the morphology and microstructure are also conducted, and the results indicate that the improved mechanical properties of the PI/FG nanocomposite films are mainly attributed to the good dispersibility of FG sheets in PI host, and the effective stress transfer between the polymer and the FG.

•Surfactant and metallic ions play synergistic effect on bitumen–silica interactions.•Ca2+ and Mg2+ act as either barrier or bridge affecting the surfactants adsorption.•The interaction forces could be well interpreted by the extended DLVO theory.•The findings have a guideline of controlling the oil sands processing condition.Synergistic effects of surfactants and divalent metal ions on bitumen–silica interaction were investigated in various pH solutions by using atomic force microscope (AFM). Zeta potential measurements were carried out and the extended DLVO theory was employed to interpret the bitumen–silica interaction behaviors. The AFM force measurements showed that the presence of cationic surfactant of dodecyltrimethylammonium chloride (DTAC) caused a strong long-range attractive force and high adhesive force, which were considerably reduced as divalent metal ions of Ca2+ or Mg2+ added in the acid solutions. However, the long-range repulsive force changed to attractive force compounded with a relative high adhesion when both the anionic surfactant of sodium dodecylbenzene sulfonate (SDBS) and divalent metal ions of Ca2+ or Mg2+ presented in the alkaline solution. Mechanism on bitumen–silica interaction behaviors at various conditions was discussed. It was suggested that changes of surface wettability arising from the adsorption of surfactants on silica and bitumen surfaces were responsible for the variation of the bitumen–silica interactions. The preferential adsorption of the divalent metal ions of Ca2+ or Mg2+ on silica and bitumen surfaces acted as either a barrier to prevent the cationic surfactants from adsorbing or a bridge to anchor the anionic surfactants. The generation of the hydrophobic attraction between bitumen and silica was supported by the extended DLVO theory. It is believed that the findings in this work have a guideline of controlling the oilsands processing condition to obtain a high bitumen recovery and good froth quality.

Low bitumen recovery and poor froth quality are always encountered when processing poor oil sands using water-based extraction processes. Application of microbial treatment of the ore prior to bitumen extraction was proposed to resolve the challenges and develop a more versatile and effective extraction process. Microbial treatment was carried out by placing a poor processing ore in the culture solution with strain of Bacillus subtilis for a restricted period of time. Flotation tests showed that an improved bitumen recovery of 97% was obtained after the poor ore was microbially treated. The wettability of solids was found to be changed from hydrophobic to hydrophilic, leading to a great decrease of the long-range attractive force and adhesion between bitumen and solids. Saturate, aromatic, resin, and asphaltene (SARA) fraction analysis indicated that the content of heavy components of asphaltenes and resins was decreased with an increase in saturate and aromatic fractions after the microbial treatment of the ore. This was well-correlated with the rheological characterization of bitumen. The improved processability was attributed to the biosurfactant production in the culture solutions, alteration of solids wettability, and decrease in bitumen viscosity, which collectively promoted the liberation of bitumen from the solids surface, and gives a better oil quality.

Water-assisted solvent extraction processes (WASEPs) were developed by introducing a water layer between the oil sands and solvent to extract bitumen from oil sands. The extraction condition was well investigated using the naphtha as the extraction solvent. Considering the extraction cost, the advised extraction processes for industrial application were conducted under stirring at temperature of 50–60 °C for 30 min using a ratio of oil sands to naphtha to water in 1:1:0.5 (wt/wt/wt). At such conditions, bitumen recovery of about 72–74% was obtained on processing a weathered ore. In the case of some types of oil sands such as the weathered ore, surfactant needs to be added in the aqueous phase to eliminate the solids aggregation suspended in the oil–water interface. The function of the water layer introduced in the WASEPs is to reduce the fines content in the extracted bitumen solution and make it easy to separate the bitumen solution from the solids. In the examination of the solvent recovery, it was found that there was 7% of the solvent still remaining in the solids. The loss of the solvent greatly depends upon the surface wettability of the solids. Studies on the effect of various solvents on bitumen recovery indicated that using toluene as the extraction solvent gave the highest bitumen recovery of about 95%. However, considering the extraction cost and environmental problems, the water-assisted naphtha extraction processes were advised and might find its application in the oil sands processing industry, although some issues need to be resolved in the future work.

Liberation of bitumen from sand grains is a key step on processing oil sands using water-based extraction processes. In this study, effects of diluent addition on bitumen liberation from a solid surface were investigated under various conditions, including the washing temperature, pH value of the water, and washing time. It was found that more effective bitumen liberation could be achieved by adding diluents, such as kerosene and fatty acid methyl ester (FAME), in the bitumen. Especially, FAME addition was found more efficient to accelerate bitumen liberation than that of kerosene. Rheological characterization showed that bitumen viscosity was greatly decreased with diluent addition, which was responsible for the improved bitumen liberation. The findings in this study might find their applications in the oil sands processing industry.