Research On Demulsification Performance And Mechanism Of A New Gemini Quaternary Ammonium Salt Diesel Demulsifier

The straight-run diesel oil containing naphthenic acid will be emulsified in the process of alkaline-washing electro-refining,which will affect the quality of diesel oil.In addition,the discharge of oily wastewater has aggravated environmental pollution and water pollution.Therefore,it is of great significance to study the demulsification process of naphthenic straight-run diesel oil.In the first part of this paper,the demulsification performance of three novel Gemini double-headed quaternary ammonium surfactants(5a-c)and a single-headed quaternary ammonium salt(CTAB)in diesel/water systems were investigated.The relationship between demulsifier structure and demulsification performance was further examined by varying the concentration,temperature and pH.The results showed that the optimum demulsification concentration of 5a-c and CTAB was 10 ppm at 50 °C,and 5c showed the best demulsification performance,which can completely separate the diesel/water within 30 s.Moreover,The temperature and pH value had a significant effect on demulsification performance.Increasing the temperature is benefit to break the emulsion,but when the temperature is higher than 50 °C,the demulsification efficiency tends to decrease,and optimum demulsification temperature is 50 °C.As the pH value increases,the stability of the emulsion increases,and the demulsification performance of the four demulsifiers decreases as the pH value increases.In the second part of this paper,the demulsification mechanism of the 5a-c and CTAB in the diesel/water system were investigated.The mechanism of demulsification for the Gemini double-headed quaternary ammonium surfactants were obtained by the interfacial tension and interfacial dilational viscoelasticity measurements.The results indicated that there was no obviously relationship between interfacial tension and demulsification performance,which also indicated that 5a-c and CTAB do not affect their demulsification performance through interfacial tension.Moreover,the interfacial film of 5a-c and CTAB mainly exhibit elastic properties,and and the lower expansion modulus results in a shorter demulsification time.The 5a-c and CTAB cationic surfactants mainly cause the destruction of the original structure of the diesel-water interfacial film by electrostatic interaction,thereby accelerating the coalescence of the emulsion droplets.In addition,there may be adsorption,displacement,bridging and other mechanisms to achieve achieve a synergistic demulsification.In the third part of this paper,using n-octane as the oil phase and sodium naphthenate as the interface active substance,a diesel oil simulation system was established.The demulsification performance of 5a-c and CTAB in the model oils with different concentrations naphthenic acid were studied.The results showed that the demulsification performance of the model oil containing 100 ppm naphthenic acid showed a similar to that of diesel emulsion.5c shows the best demulsification performance,and the optimum concentration is 10 ppm.