Study On The Preparation Of PA/PVDF Tubular Nanofiltration Membrane And The Performance Of Waste Emulsion Treatment

In this study,polyvinylidene fluoride(PVDF)tubular ultrafiltration membrane was used as the base membrane.Anhydrous piperazine is an aqueous monomer.N-hexane is an organic solvent.Trimethylbenzene chloride is an organic monomer.Triethylamine is used as acid absorbent.The optimum technological conditions for preparing polypiperazine amide tubular nanofiltration membranes by interfacial polymerization were studied.The properties and storage methods of tubular nanofiltration membranes were analyzed and explored.The application effect of tubular nanofiltration membrane in emulsion treatment was also studied.Polyvinylidene fluoride tubular ultrafiltration membrane was used as the base membrane.The optimum technological conditions for preparing nanofiltration membranes by interfacial polymerization are as follows:the concentration of organic phase is 0.7 wt%,the residence time is 60 seconds,water phase concentration is 0.6 wt%,residence time is 6 min,Ultrafiltration membrane takes 90 seconds to blow out in water phase,the concentration of acid absorbent is 0.3wt.%,the heat treatment temperature is 50 °Cand the time is 5 min.Under this condition,the tubular composite nanofiltration membrane was prepared at 0.4 MPa,and the rejection rate of 2000 mg/L MgSO4 aqueous solution at 25 0C was 95±1%.The corresponding flux was 45±3 L/(m2·h).The thickness of the functional layer of the nanofiltration membrane was about 200 nm by scanning electron microscopy(SEM).Fourier transform infrared spectroscopy(FTIR)showed the existence of functional groups in polypiperazineamide,which indicated that a layer of nanofiltration membrane was formed on the surface of the ultrafiltration membrane.The cut-off molecular weight of tubular nanofiltration membranes was 273 Da by testing the retention of PEG by nanofiltration membranes,the pore size distribution of nanofiltration membranes was calculated by solute transport method between 0.4 and 0.6 nm.The optimum operating pressure range of nanofiltration separation process was 0.4-1.0 MPa,and the optimum testing time was 15 minutes after the membrane separation process.Natural drying and preservation of nanofiltration membranes with different concentrations of glycerol can ensure that the performance of nanofiltration membranes remains unchanged with the change of time when the glycerol concentration is 10%.The acid and alkali resistance of nanofiltration membranes was tested,and the performance of nanofiltration membranes was stable when the pH of feed solution was between 2 and 11.The effects of concentration,temperature and type of electrolyte solution on the performance of nanofiltration membranes were also studiedThe prepared tubular nanofiltration membrane and tubular ultrafiltration membrane were connected in series to filter the whole emulsified liquid and semi-emulsified liquid prepared by ourselves.The influence of filtration time and pressure on membrane separation process was studied.The water quality of tubular ultrafiltration and tubular nanofiltration was analyzed and compared.The results show that the optimum filtration pressure for the emulsion is 0.6 MPa,and the flux tends to decrease with the extension of filtration time,because the emulsion deposits on the surface of the membrane,blockages some of the membrane holes,increases the filtration resistance and decreases the flux.The indexes of water production of tubular nanofiltration membranes are better than those of tubular ultrafiltration membranes.The total water production of the emulsion was analyzed.The removal rate of COD,turbidity and conductivity was above 97%,99%and 70%,respectively.The water quality was still good even when the concentration was 10 times.