Preparation Of Magnetic Fe₃O₄ Nanocomposites And Its Effect On Oil-water Separation Of Hexadecane-water Emulsion

Most of the oilfields in the country have entered the middle and late stages.Tertiary oil recovery technology is widely used to increase oil production.A large amount of oily wastewater discharged from this process,shows negative impact on the economy and the environment.The traditional water treatment method is not effective and will cause secondary pollution.In recent years,Fe₃O₄ nanomaterials with excellent adsorption performance,low toxicity and magnetic properties in the treatment of oily wastewater are getting more and more attention.In order to improve the oil-water separation performance,it is necessary to deeply study the influence of the surface properties of the materials on oil-water separation performance.The content of this paper is to design and synthesize Fe₃O₄ magnetic nanoparticles(MNPs)modified with humic acid and cationic poly dimethyl diallyl ammonium chloride(PDDA)to regulate the surface charge and wettability,and use in the separation oil and water of hexadecane-water emulsion.the purpose is to explore the relation between the surface properties of MNPs and the oil-water separation performance.The main work is as follows:(1)In this paper,Sodium Humate(HA)and PDDA-modified Fe₃O₄ magnetic nanoparticles(Fe₃O₄/HA,Fe₃O₄/HA/PDDA MNPs)were synthesized by co-precipitation method,which was used for oil-water separation of cetane-water emulsion that was stabilized by anionic surfactant sodium dodecyl sulfate(SDS)and cationic surfactant cetyl trimethyl ammonium bromide(CTAB).The results showed that Fe₃O₄/HA/PDDA MNPs have excellent demulsification performance for SDS-stabilized emulsions,while its demulsification performance for CTAB-stabilized emulsions was generally good,indicating that electrostatic force plays a leading role in the process of oil-water separation.(2)In order to investigate the effect of surface charge quantity of MNPs on oil-water separation performance,a series of Fe₃O₄/FA/PDDA MNPs with different positive charges on the surface were prepared and used for oil-water separation of cetane-water emulsion.It was found that with the increase of the positive potential of the material,the demulsification rate and efficiency gradually increased.The calculation results based on the DLVO theory showed that the attraction between the oil droplets and MNPs was mainly influenced by the electrostatic force,indicating that both the material's surface electrical property and quantity have an impact on the oil-water separation effect.(3)In order to further explore the influence of the material's surface wettability on oil-water separation performance,Fe₃O₄/HA/PDDA MNPs modified by PDDA with different molecular weights were synthesized,whose contact angle with water was increased from 37.5°to 56.0°with the change of molecular weight.The preliminary results using the material for oil-water separation of cetane-water emulsion showed that the separation rate increases with the contact angle,indicating that for hydrophilic materials,the oil-water separation effect increases with the increase of contact angle.To sum up,in this paper,MNPs modified by HA,FA and PDDA were synthesized,the effects of electrostatic action and wettability of the material on the oil-water separation performance of emulsion were investigated,which laid a theoretical foundation for the design and synthesis of oil-water separation materials.