6 research outputs found

    Molecular Dynamics Simulation of Self-Aggregation of Asphaltenes at an Oil/Water Interface: Formation and Destruction of the Asphaltene Protective Film

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    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

    Molecular Dynamics Simulation of Self-Aggregation of Asphaltenes at an Oil/Water Interface: Formation and Destruction of the Asphaltene Protective Film

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    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

    Functionalized carbon black nanoparticles used for separation of emulsified oil from oily wastewater

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    <p>Functionalized carbon black (F-CB) nanoparticles were synthesized by covalently grafting the polyvinyl alcohol on carbon black (CB) surfaces and used as demulsifier to separate the oil from the emulsified oily wastewater. The bottle test showed that the residual oil content in the separated water was as low as ∼50 mg/L corresponding to a demulsification efficiency of about 99.90% at an optimal condition within a few minutes. It was believed that the surface wettability of the carbon black could be tuned by modifying with the PVA molecules, which enables the F-CB nanoparticles to be readily migrated to the oil/water interface and have the opportunity to interact with and/or displace the stabilizers of the emulsion. As a result, the demulsification process was accomplished with the coalescence of the oil droplets promoted by the F-CB nanoparticles. The interaction behavior between F-CB nanoparticles and asphaltenes was investigated by quantum chemical calculations. The results showed that the F-CB nanoparticles have strong interaction with the asphaltene molecules in form of π−π and θ−π forces. The findings in present study are significant for understanding the demulsification mechanism and also provide a novel demulsifier for the demulsification of emulsified oily wastewater.</p

    Revealing the Intermolecular Interactions of Asphaltene Dimers by Quantum Chemical Calculations

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    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

    Demulsification of Crude Oil-in-Water Emulsions Driven by Graphene Oxide Nanosheets

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    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

    Demulsification of Crude Oil-in-Water Emulsions Driven by Graphene Oxide Nanosheets

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    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
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