Investigation Of Surfactant/polymer Flooding Produced Water Removed By Surfactant-modified Sepiolite

Adsorption is one of the most promising technologies for treating emulsified oils(EOs)in produced water,and organoclay materials have great potential in this field.Electrostatic adsorption and hydrophobicity constitute the main functions of effective removal of EOs in produced water.Here,sepiolite(Sep)is modified with single-chain and double-chain organic cation surfactants,stearyl trimethyl ammonium bromide(STAB)and dimethyl dioctadecyl ammonium bromide(DDAB).Analyses of SEM,CA and ζ-potential indicated that individually-dispersed Sep fibers modified to form Sep fibrous aggregates with a more hydrophobic and electropositive surface,which greatly improved EOs adsorption and oil-water separation efficiency,and EOs removal efficiency exceeded 99%.The adsorption experiments have studied the effects of modifier concentration and the number of alkyl chains,contact time,initial pH,and temperature on the adsorption of EOs.It was found that double-chain modified Sep has higher affinity with EOs.Both the Langmuir and the Freundlich isotherms could be used to explain the adsorption process.Thermodynamic parameters proved that the adsorption process was a spontaneous endothermic physical process.This study provides a theoretical foundation for the design of high-efficiency and low-cost organoclay adsorbents.The experimental results are as follows:(1)FT-IR,XRD,and SEM analysis of the samples showed that the modification of Sep and the adsorption of organo sepiolites(organo-Seps)on EOs were successfully completed.And the two processes mainly occurred on the surface of Sep without changing its crystal structure.BET experiments showed that the modification reduced the specific surface area of Sep from 344.2 to 37.2 m2/g.organo-Seps has a more hydrophobic surface,and water contact angle measurements have found that the water contact angles of STAB-Sep and DDAB-Sep(1.0,1.5,2.0 CEC)are 56,58,63°,and 65,71,75°,respectively.At the same time,Zeta potential measurements also showed that the modified Sep has a positively charged surface.(2)Modifier concentration experiments showed that in the range of 0.5-2.0 CEC,as the modifier concentration increased,the adsorption performance of organo-Seps to EOs would increase.However,the adsorption effect did not change significantly under 2.5 CEC.And it was found in adsorption experiments that double-chain surfactant-modified sepiolite had a better adsorption effect than single-chain Adsorption equilibrium could be reached at a contact time of 60 min.Relatively lower initial pH value and higher temperature are favorable for the adsorption of EOs by organo-Seps.(3)Through Langmuir isotherm and Freundlich isotherm simulation,the R2 values of Organo-Seps were 0.9815-0.9705 and 0.9731-0.9595,respectively.Therefore Langmuir and Freundlich isotherm models were suitable for this adsorption process.The maximum adsorption capacities of STAB-Sep and DDAB-Sep were 957.0 and 1031.5 mg/g,respectively.(4)Calculated by thermodynamics,the value of △Go was<0,and the adsorption process was spontaneous.The values of △H°and △S° were>0.The adsorption process was endothermic.The adsorption heat was between 9.95 and 17.18 KJ/mol-1,so the process was a physical adsorption.(5)The regeneration experiment showed that the adsorption capacity of the recycled organo-Seps gradually decreased,but the organo-Seps maintained a high removal rate of EOs after eight cycles.