Study On Emulsification And Demulsification Of Oil Products

It is well known that refined oils have been indispensable in economical society and our daily life.With the rapid developments of our country and enhancements of people's life-level such as popularity of cars,the transportation amount of various oil products increases substantially.However,the oil transportation usually suffers from high safety risks due to the inflammable and explosive characteristics of the oil products,and usually needs specific vehicles and well trained drivers.One way to solve this problem is to transform the oil products into oil-in-water emulsions,in which the oil is surrounded by water with flashing point significantly increased.The emulsions can then be transported and stored as non-dangerous goods by using ordinary vehicles,which not only increases the safety but also reduces significantly the transportation cost,if the emulsion can be demulsified quickly and the oil can be recovered in good quality after reaching destinations.Based on such an idea in this thesis the preparation,stabilization mechanism and demulsification methods of three species of O/W oil product emulsions are studied systematically by using either an ionic surfactant solely or a surfactant in combination with inorganic nanoparticles as emulsifiers,respectively.In the first section,ordinary O/W emulsions with diesel oil,white oil,and gasoline as oil phases respectively were successfully prepared using a typical anionic surfactant sodium dodecyl benzene sulfonate?SDBS?as emulsifier at a concentration close to critical micelle concentration?cmc?.Due to the sensitivity of the SDBS to the hard water,the emulsions prepared using tap water are less stable than those prepared using deionized water,but the stability can be improved by increasing SDBS concentration.Stable emulsions can also be prepared using a typical cationic surfactant,cetyltrimethyl ammonium bromide?CTAB?,as emulsifier at concentration close to cmc.Since CTAB is less sensitive to hard water the emulsions prepared using tap water have similar stability to those prepared using deionized water.These emulsions stabilized by ionic surfactant solely can be demulsified by addition of equimolar oppositely charged ionic surfactant,which neutralized the charge of the emulsifier adsorbed at oil/water interface and thus eliminated the Zeta potential of the droplets leading to demulsification.In the second section,Pickering emulsions with diesel oil and gasoline as oil phase respectively stabilized by inorganic nanoparticles hydrophobized in situ by the oppositely charge ionic surfactants were prepared.Using negatively charged silica?SiO₂?nanoparticles in combination with cationic surfactant CTAB,stable diesel oil-in-water emulsions and gasoline-in-water emulsions have been prepared,in which silica nanoparticles are in situ hydrophobized to be surface active by adsorbing CTAB via electrostatic interaction in aqueous phase.Similarly using tap water is not as good as using deionized water.But in general the formation and stability of the Pickering emulsions are less sensitive to hard water than the ordinary emulsions stabilized solely by anionic surfactants.Specifically stable diesel oil-in-water Pickering emulsions can be obtained using alumina?Al₂O₃?nanoparticles solely as emulsifiers.By analyzing the composition of the diesel oil,measuring surface and interfacial tensions and Zeta potentials of relative systems,and examining the emulsification properties of the diesel oil passing through a column filled with micro-alumina particles,it is proved that diesel oil contains trace amount of anionic surface-active components which adsorb on the surface of the alumina nanoparticles to endow particles surface activity.However demulsification of the Pickering emulsions by addition of oppositely charged ionic surfactant is less efficient and more efficient methods should be discovered.In the last section,novel diesel oil-in-water and gasoline-in-water emulsions were prepared using silica nanoparticles and same charged SDBS.The lowest concentrations of the particles and surfactant required for stabilization of the emulsions can be as low as 0.001 wt.%and 0.001 cmc,respectively.In the emulsion the droplets are covered by a dilute surfactant film and particles are proved to distribute in aqueous phase,giving thick lamellae separating droplets from each other.The van der Waals attraction between droplets is significantly reduced and the electrical double layer repulsion between particles,droplets and between particles and droplets prevents flocculation and coalescence of the droplets.The stability of the emulsion is high enough by using deionized water as aqueous phase,but is not as good as expected for practical application by using tap water as aqueous phase,since the electrolytes in tap water inhibits the Zeta potential of the particles dispersed in aqueous phase.The presence of the trace amount anionic surface-active components in diesel oil made it possible to prepare novel diesel oil-in-water emulsions using silica nanoaprticles solely as emulsifier at concentrations between 0.1 wt.%and 0.5 wt.%.The emulsions can be stabilized for at least two weeks.However,no stable emulsion can be prepared using tap water because the Zeta potential of the silica nanoparticles in tap water is less than-18 mV,a critical value for the stabilization of the emulsions.The novel emulsions can be demulsified by addition of equimolar oppositely charged ionic surfactant or addition of inorganic electrolytes,where the former is more efficient than the latter for demulsification.