| In recent years,membrane distillation has been used more and more to treat domestic and industrial wastewater.These wastewaters often contain oil contaminants.The existing membranes used for membrane distillation have strong hydrophobicity on the surface.In the application process,due to strong hydrophobic-hydrophobic interaction between the membrane and the pollutants in the water,the membrane is easily polluted by hydrophobic pollutants,and the flux decreases after the pores of the membrane are blocked.Therefore,the preparation of a hydrophilic/hydrophobic composite membrane by constructing an underwater oleophobic coating on a hydrophobic substrate can not only reduce the adsorption of oil stains on the membrane to enhance the membrane's resistance to oil stains,but also make the membrane flux promoted.In this paper,firstly the PDMS-PVDF hydrophobic porous membrane was prepared by steam induction method.Membrane structure and performance can be tuned by varying the relative humidity and the residence time of the humid air,respectively.All membranes was characterized by scanning electron microscopy(SEM),Fourier infrared spectroscopy(ATR–FTIR),pore structure and water contact angle(WCA),and membrane performance was tested.The results showed that in the process of preparing the membrane by the steam induction method,there is a mass exchange process between the solvent on the membrane surface and the non-solvent in the air,the gel layer is formed on the membrane surface,which limits the formation of finger pores and makes the membrane more porous.Membrane distillation performance has also been improved.After analysis,the 70%relative humidity and 70%the residence time,membrane performance of the membrane are the most excellent.Furthermore,using the prepared PDMS-PVDF hydrophobic porous membrane as the base membrane,Ag/PDMS-PVDF composite membranes are modified by silver membrane prepared by chemical reduction method.Membrane structure and performance can be tuned by varying the activation time,reaction ratio and reaction time.All membranes was characterized by the X-ray diffraction(XRD),SEM,Pore structure and WCA,and membrane performance was tested.The results showed that after the modification of the silver membrane,the surface of the membrane changes from hydrophobic to hydrophilic,The flux of the modified membrane is improved compared with the original membrane;the membrane is more closely compounded with silver membrane;when the activation time is 20 minutes,the ratio of silver nitrate solution and sodium tartrate is 60:120 and the reduction reaction time is 50 min,membrane performance of the membrane are the most excellent.Finally,the separation performance of the PDMS-PVDF pristine membrane and Ag/PDMS-PVDF modified membrane in the vacuum membrane distillation for treating oily brine were studied.The results showed that the surface of the modified membrane is hydrophilic in the air and oleophobicity under the water;And under the long-term membrane operation of pure brine system,the performance of the original membrane and the modified membrane is stable;When the modified membrane treated crude oil-containing brine system,the membrane flux decreased less,and there is no significant increase in leakage,And after running for 10 hours,the flux is 13.41kg/(m~2·h),which is18%higher than the initial flux of 11.32 kg/(m~2·h)... |
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