Study On Hydrophilization Modification Of Polyvinylidene Fluoride Membrane And Its Application In Oil-Water Separation

In recent years,the problem of water pollution is serious.How to efficiently treat wastewater has become the key to protecting the ecological environment.Membrane separation technology with high separation efficiency and low energy consumption has played an important role in wastewater treatment.Although polyvinylidene fluoride?PVDF?separation membrane has excellent chemical resistance and thermal stability,it has serious membrane fouling problems in the treatment of water-based fluids.Studies have shown that the hydrophilization of the separation membrane surface can effectively improve anti-fouling performance.In view of this,PVDF membrane was firstly prepared by non-solvent phase separation method,then hydrophilic modification of PVDF membrane was carried out by bionic co-deposition method,and on this basis,the performance of PVDF membrane was further optimized by in-situ formation of micro-nano structure.?1?PVDF separation membrane was prepared by non-solvent induced phase separation method.The study found that with the increase of PVDF content in the casting solution,the porosity and pure water flux of the PVDF membrane prepared gradually decreased,and the BSA rejection rate gradually increased.In the process of increasing the amount of porogen PVP K30 from 2%to 8%,the PVDF membrane pure water flux showed a trend of increasing first and then decreasing.When the amount of PVP K30 is 6%,the PVDF membrane has the best pure water flux of 556.1 L/?m²·h?,and with the addition of PVP,the contact angle of the PVDF membrane decreases from 92.4°to 76.8°,flux recovery rate increased from 62.6%to 76.4%.At the same time,as the molecular weight of PVP increases,the pure water flux of PVDF membranes tends to increase first and then decrease.The rejection rate of BSA gradually decreases with the increase of molecular weight of PVP.As the temperature of the coagulation bath increases,the pure water flow of the PVDF membrane gradually increases,and the BSA rejection rate gradually decreases.?2?Using the adhesion of tannic acid?TA?to the substrate and its crosslinking reaction with polyethyleneimine?PEI?,build a stable TA/PEI coating on the surface of the separation membrane to improve the hydrophilicity of the membrane surface.The effects of co-deposition time,TA content and molecular weight of PEI on the properties of modified films were mainly studied.The study found that with the increase of co-deposition modification time,the pure water flux of the modified membrane showed a trend of increasing first and then decreasing.When the TA/PEI co-deposition time is 6h,the comprehensive performance of the modified membrane is the best,its pure water flux is1612 L/?m²·h?,BSA rejection rate reaches 81.9%,and contact angle is 48°.In the process of co-deposition,with the increase of TA content in the solution,the hydrophilic property and anti-pollution property of the membrane are obviously improved.Compared with the unmodified separation membrane,the water contact angle on the surface of the separation membrane after modification was reduced from 79°to 38°,the flux recovery rate was increased from 63.7%to 82.6%;the total pollution rate was reduced from 86.0%to 74.7%.During the TA/PEI co-deposition process,the increase in the molecular weight of PEI is not conducive to the deposition of the TA/PEI coating on the membrane surface,resulting in an increase in the contact angle of the modified membrane and a decrease in pure water flux.?3?The TA-PEI co-deposited layer is used as the intermediate layer,and the amide groups present in the intermediate layer are used to induce Zr?SO₄?₂and?NH₄?₂Ti F₆to hydrolyze in situ on the surface of the separation membrane to form micro-nano structures of Zr O₂and Ti O₂.Mainly studied the effect of hydrolysis time on membrane hydrophilicity,permeability,retention performance and anti-fouling performance,and used two modified membranes for the separation process of dyes and emulsified oils,and studied the separation performance of two different microstructures impact.The study found that the in-situ induced hydrolysis of Zr?SO₄?₂built a tightly packed nanosphere particle structure on the surface of the PVDF separation membrane,and the surface hydrophilicity and separation performance of the Zr O₂/TA-PEI/PVDF separation membrane were significantly improved.When the treatment time is 30min,compared with the unmodified separation membrane,the water contact angle of the membrane surface is reduced from 79.0°to12.2°,the BSA rejection rate is increased from 65.9%to 98.2%,For Congo red and methyl blue dye,the rejection rates were 96.8%and 93.5%,respectively.?NH₄?₂Ti F₆hydrolysis was used to construct a network structure composed of nanowires on the surface of the PVDF separation membrane.The Ti O₂/TA-PEI PVDF separation membrane had good hydrophilicity and pure water flux.When the treatment time was 30 min,the water contact angle of the modified membrane dropped to 26.9°,and the pure water flux was 1222.3L/?m²·h?.In addition,Zr O₂/TA-PEI/PVDF and Ti O₂/TA-PEI/PVDF separation membranes have good separation performance for oil-in-water emulsions.