| A large amount of fracturing flowback water will be produced during shale gas exploitation,in which polyacrylamide（PAM）,surfactant,micro-iron oxide（nano Fe2O3）and other substances will interact to form complexes,resulting in serious membrane pollution of ultrafiltration（UF）membrane in reuse treatment process.Therefore,it is urgent to study micro and nano particles from the perspective of complex formation and UF membrane pollution control.In this study,the formation mechanism and influencing factors of the composite were studied rom the micro point of view by quartz crystal microbalance with dissipation（QCM-D）,and the pollution of ultrafiltration membrane by XDLVO theory,on this basis,the feasibility of inorganic nanoparticles modifying UF membrane to reduce the pollution of the composite membrane was explored.The results show that:（1）The effect of ion concentration,ionic strength and PAM molecular weight on the formation of the complex.The results show that the smaller the molecular weight of PAM,the higher the ionic strength and the ionic concentration,the easier the aggregation and the larger the particle size of the complex.The viscosity of the system decreases after the formation of the composite,which is consistent with adsorption experimental results,and the viscosity decreases more under the condition of high temperature and high pressure.（2）When studying the interfacial interaction energy of the composites,it is found that increasing the concentration of the background solution,the free energy of adhesion between the composites decreased and the hydrophobicity of the composites increased,that is,the gravity between the composites increased.（3）PAM-nano Fe2O3compound was used as model pollutant to analyze the interface interaction between the compounds.The results show that the membrane pollution caused by simulated fracturing fluid is greater than that caused by complex.This conclusion has been verified in micro adsorption experiment and membrane filtration experiment.When the pollutant is simulated fracturing fluid,the amount adsorbed on the membrane surface is more,the membrane pollution flux decreases faster.（4）The membrane chips of different nano particles（Fe2O3,CuO,Ce O2and Ti O2）were prepared and QCM-D adsorption experiment were carried out.The results showed that the affinity order between the modified membrane and the composite was Fe2O3>Ce O2>Ti O2>CuO,indicating that the composite was more difficult to deposit on the surface of the membrane containing CuO.Four kinds of nanoparticles were coated on PVDF membrane.CuO concentration,modification time and different nanoparticles were used as optimization conditions.From the perspective of water flux and antifouling effect,when CuO concentration was 0.03mg/cm2,dopamine hydrochloride and KH550 concentration was 0.5 mg/cm2,and modification time was 16 h,the antifouling performance of CuO modified membrane was the best,and the flux of modified membrane was increased by about 11%,indicating that CuO modified performance effectively improved the antifouling capacity of membrane,this is also consistent with the results of QCM-D. |
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