| In order to improve oil displacement efficiency and meet additional demand for crude oil in the future,the application of Enhanced Oil Recovery(EOR)processes have been attempted at oilfields.In particular,alkaline/surfactant/polymer(ASP)flooding has been demonstrated to be an effective candidate.However,due to the residual of three oil displacements,produced water from ASP flooding possesses stronger emulsion stability,resulting in the inefficiency of conventional treatment technologies.Hence,finding a rapid,high-efficiency and economical treatment technology for ASP flooding produced water is an urgent issue.This study presents an effective and economical method to decontaminate emulsified oil via in situ formed magnesium hydroxide(IFM).IFM was directly synthesized in ASP flooding produced water by a wet precipitation method,and the emulsified oil was simultaneously removed during the precipitation process of IFM.The roles of dosage,contact time,pH,interface-active components,temperature,and initial oil concentration in oil removal were systematically investigated.The characterization of IFM and IFM-EOs precipitates were done.Combining zeta potential measurement and the species distribution diagram for magnesium simulated by Visual MINTEQ,the removal mechanism was elucidated in depth.The experimental results are listed below.(1)The effect of three conditions of the way to add adsorbents on oil removal efficiency was studied.The drop MgCl2 and drop NaOH systems,considered as in situ formed magnesium hydroxide,exhibited excellent removal efficiencies and removal rates for emulsified oil compared to commercial Mg(OH)2,considered as ex situ formed magnesium hydroxide.The excellent removal efficiency was relied on the high surface free energy,the large surface energy and the fresh active adsorption sites of IFM.(2)Under optimal experimental conditions(MgCl2 dosage of 1 g/L,contact time of 8 min,equilibrium pH of 11.0),the residue oil concentration could be reduced below 5.0 mg/L,meeting rejection standard of low permeability layer and discharge standard for oily wastewater.(3)When equilibrium pH was higher than 11.0,the oil removal performance was different between the drop MgCl2 and drop NaOH systems.Using the species distribution diagram for magnesium simulated by Visual MINTEQ,it was demonstrated that the synergistic effect of MgOH+ and the IFM network structure played a significant role in complete oil removal.(4)The effect of interface-active components on oil removal efficiency was conducted.It was indicated that the oil removal by IFM was mainly relied on the electrostatic attraction between IFM and interface-active components(WPS,HPAM).Even if the emulsion stability was enhanced by an increase in concentration of interface-active components,efficient oil removal could still be achieved.The series of characterizations also illustrated that oil droplets,WPS,and HPAM was adsorbed on IFM.(5)The adsorption isotherms were fitted at 293,313,and 333 K,respectively.It was revealed that the adsorption process of oil droplets on IFM was not solely exothermic or endothermic due to the different interfacial activity between WPS and HPAM.The adsorption capacity of IFM for oil was 10959 mg/gat 293 K.(6)The recycle experiment revealed that crude oil could be recovered via HCl.And the regenerated IFM maintained an oil removal efficiency of 91%in the fifth cycle. |
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