Oil Removal Efficiency Of Alkali/Surfactant/Polymer Flooding Produced Water Using Perlite Modified By Quaternary Ammonium Salt

With the increase of oil demand in China,the alkaline/surfactant/polymer(ASP)flooding technology has been widely applied.However,while the ASP flooding technology improves the crude oil recovery rate,the residual oil displacement agent in produced water leads to very dense oil-in-water emulsion,which brings great difficulties to the surface oil-water separation.Adsorption method is one of the effective methods to treat produced water in ASP flooding.It is of great significance to develop adsorption materials with excellent performance and low price for oil and water separation of produced water in ASP flooding.In this study,perlite with abundant reserves was used as raw material and modified by quaternary ammonium surfactant dioctadecyl dimethyl ammonium bromide(DDAB).Four kinds of organic perlite composites(0.5 CEC-organo-perlite,1.0 CECorgano-perlite,1.5 CEC-organo-perlite,and 1.5 CEC-organo-perlite)were synthesized under different cation exchange capacity(CEC)equivalents.The microstructure and surface properties of perlite before and after modification were characterized by water contact angle determination(WCA),zeta potential determination,scanning electron microscopy(SEM),X-ray diffraction(XRD),specific surface area and pore volume determination,Fourier transform infrared spectroscopy(FT-IR),dissipative microgravity balance(QCM-D),and atomic force microscopy(AFM).The effect of characterization and adsorption experiments were used to select the most effective organic perlite from the four organic perlites for the subsequent series of experiments,and then to investigate the effects of organic perlite dosing,initial pH,contact time and reaction temperature on the emulsified oil removal efficiency,combined with thermodynamic experimental analysis,further explore the mechanism of organic pearlite to remove emulsified oil.The results of the study showed that.(1)The results of SEM,CA,FT-IR,zeta potential and other images proved the successful synthesis of organic perlite.The water contact angle measurements showed that the water contact angle of natural perlite was 14.9° and the contact angles of the four organic perlites(0.5 CEC-organo-perlite,1.0 CEC-organo-perlite,1.5 CECorgano-perlite,and 2.0 CEC-organo-perlite)were 92.5°,109.8°,1 17.8°and 125.4°.The zeta potential results indicated that the surface charge of the modified perlite was reversed from negative to positive.(2)It was found that 2.0 CEC-organo-perlite has better hydrophobicity and positive charge and has the best oil removal effect.Adsorption experiments were performed with 2.0 CEC-organo-perlite.The adsorption process reached equilibrium within 24h.The optimum reaction conditions were a dosage of 10 g/L,pH of 4 and a reaction temperature of 60℃.At this time,the oil removal efficiency reached 99.75%.Organic perlite(2.0 CEC-organo-perlite)is reusable and still shows good degreasing effect after 5 cycles.(3)The results of adsorption kinetics and adsorption isotherm model show that the adsorption process of emulsified oil droplets by organic perlite(2.0 CEC-organo-perlite)is more consistent with the quasi-second-order kinetic model and Langmuir isotherm model.The maximum adsorption amount was 333.7 mg/g at the reaction temperature of 60℃.(4)Thermodynamic calculations showed that the adsorption of organic perlite(2.0 CEC-organo-perlite)on emulsified oil was a spontaneous heat absorption process,and the adsorption mechanism involved electrostatic attraction and hydrophobic interactions.