Interfacial Behaviors Of Ionic Liquids And Asphaltenes At Oil-Water Interface

In the production process of residual oil and unconventional oil,oil-solid separa-tion and oil-water separation are generally involved:liberation of oil from solids,and demulsification.In these two processes,ionic liquids(ILs)act as surfactants.However,the interaction mechanism between ILs and petroleum interfacial surfactants(such as asphaltenes)at oil-water interface is complex,such as dynamic interfacial behaviors,due to the complexity and interfacial activity of petroleum components.Thus,this paper studied the dynamic adsorption behaviors of ILs and asphaltenes at oil-water interface,and interaction mechanism of ILs at oil-water interface,aiming to reveal the effect of ILs on the asphaltenes-stabilized interface.In this paper,three imidazolium-based ILs[C₈mim][Br],[C₁₀mim][Br],and[C₁₂mim][Br]were selected as interfacial surfactants.The dynamic interfacial tensions were measured and fitted by the equation to explore the dynamic adsorption behaviors of ILs and asphaltenes at oil-water interface.The experimental results show that when ILs and asphaltenes are simultaneously added to the water phase and oil phase,respec-tively,both of them could diffuse to the interface and adsorb at the interface.However,the ILs has stronger adsorbability than asphaltenes.As the alkyl chain length of the IL cation increases,the time required for reaching adsorption equilibrium is shortened,and the equilibrium interfacial tension is much lower.The fitting results show that when ILs and asphaltenes coexist in the system,adsorption and rearrangement time of them at the interface are shortened.In order to further explore the effect of ILs on interfacial asphaltene films,the spreading and diffusion protocols were designed to determine the interfacial pressure-area isotherms and morphology of interfacial films by atomic force microscopy.The results show that the interfacial films are broken under these two protocols.In addition,the final pressure of the interface film is decreased.The above results prove that the ILs could compete with the asphaltene for adsorption and hinder the formation of the cross-network structure between asphaltenes.In addition,for the preformed asphaltene inter-facial film,ILs could replace the adsorbed asphaltenes and destroy the network struc-ture.What's more,the hindrance and destruction by ILs on interfacial films are signif-icant due to the increase of alkyl chain length.According to the above experimental results,the interfacial molecular orientations and surface free energy of ILs and asphaltenes at oil-water interface were simulated by COSMOtherm software.The simulation results show that the IL cations could penetrate into the asphaltene film by squeezing the asphaltenes out from the interface.In addition,the absolute surface free energy of ILs decreases with the addition of asphaltenes.It confirms the competition adsorption between ILs and asphaltenes.The simulation re-sults are in good agreement with the experimental results.In this paper,the dynamic diffusion and adsorption processes of IL cations and asphaltenes from the aqueous phase and the toluene solution to oil-water interface are clarified.It provides basic theory for the IL flooding(oil-water interface aspect)and demulsification processes.Besides,it proposes new ideas and methods for the subse-quent investigation about dynamic interfacial behaviors of surfactants(including natu-ral petroleum components)at oil-water interface.