Molecular Dynamics Simulation Of Emulsification And Demulsification Of Surfactant In Oily Wastewater

In practical production and application,surfactants are widely used to reduce the viscosity of heavy oil and increase the fluidity of crude oil,thus reducing the difficulty of crude oil exploitation and transportation,but the widespread use of surfactants will bring a lot of oily sewage.The composition of oily wastewater is complex and the oil phase can be suspended in the water phase in the form of small oil droplets to form emulsified oil,which undoubtedly increases the difficulty of sewage treatment.The common demulsification methods can be roughly divided into chemical method and physical method,and their main mechanisms are inducing chemical instability and increasing oil phase aggregation by physical means respectively.Molecular dynamics simulation has become a powerful means to study surfactants and heavy oil components at the micro-scale,and can reasonably explain the micro-process and mechanism of demulsification.In this paper,the emulsification mechanism of surfactants in different scenarios is studied by using molecular dynamics simulation,and the dynamic process of different demulsification methods is studied on this basis.The main research contents include:(1)Molecular Dynamics Study on Emulsified Oil Droplets with Nonionic SurfactantsGROMACS software was used to simulate the emulsification process of nonionic surfactant(NP-4),and the internal stacking structure and surface properties of emulsified oil droplets were analyzed.The results show that the emulsification process of nonionic surfactant is different from that of anionic surfactant.Nonionic surfactants can not only be adsorbed on the surface of oil droplets to increase surface hydrophilicity,but also enter the interior of oil droplets to destroy the internal stable stacking structure.Through our simulation,the role of nonionic surfactant in viscosity reduction of heavy oil can be reasonably explained.(2)Molecular Dynamics Study on the Emulsification Stability of Oil Droplets Enhanced by NanoparticlesThe process of emulsifying oil droplets by combining nanoparticles with anionic surfactant(SDS)was simulated,and the emulsified oil droplets were also analyzed from the inside and outside.The results show that nanoparticles can enhance the expression of SDS emulsifying properties.The addition of nanoparticles can change the stacking structure of molecules inside oil droplets and increase the maximum capacity of SDS molecules on the surface.thus enhancing the emulsification effect of oil droplets.(3)Molecular Dynamics Simulation of Demulsification of O/W Emulsion Containing Soil in Direct current Electric FieldBy simulating the movement and coalescence of oil droplets in O/W emulsion containing surfactants and solid particles,the micro-mechanism of demulsification by direct current(DC)electric field was studied.Firstly,the movement and deformation process of emulsified oil droplets under six different electric field intensities were simulated,and the movement of all molecules in the system under the action of DC electric field and the coalescence behavior without electric field were observed respectively,and the reasons for the different behaviors of different molecules under the action of electric field and the micro-mechanism of electric field demulsification were determined.(4)Molecular Dynamics Simulation of Oily Wastewater Treatment by Air FlotationThe process of capturing suspended oil droplets by rising bubbles in air flotation was simulated by molecular dynamics,and the micro-mechanism of treating oily wastewater by air flotation was studied.The results show that the foam film can carry oil droplets in the water phase by deformation.After the moving foam film collides with the oil droplets,the oil droplets are deformed on the bubble surface,and the oil droplet molecules will form a stable stacking structure on the surface.The foam film will also deform inward where the oil droplets are located to form a depression,and the oil droplets that are close to each other coalesce,while the oil droplets that are far away will exist side by side in the depression.