Study On Modification And Preparation Of Polyamide Composite Membrane Based On Diazotization

In order to reduce the energy consumption of water and reduce the production cost,the final purpose of solving the problem of human water shortage.In this paper,the improvement of commercial reverse osmosis membrane flux was realized by using the diazo reaction of aromatic amine,and the new nanofiltration membrane was prepared by using the diazotization reaction of hyperbranched polyamide.First,the effects of factors（temperature of the solution,reaction time,concentration of sodium nitrite solution,and pH of the solution）on the permeation performance of the membrane were investigated through orthogonal experiments,then it is obvious that reaction time can improve the flux of membrane.The data shows that when the concentration of sodium nitrite is 0.3%（w/v）,the modification effect is the best when it is modified for 30 min.The water flux of the membrane can be increased by 35%and the salt intercept rate can also be increased by 0.5%,which overcomes the trade-off phenomenon of the traditional modification method.The modification method has enormous commercial value.Characterization of the membrane by ATR-FTIR,UV,SEM,AFM,contact angle,Zeta potential,etc.showed that the increase of the flux was due to the reaction of the amino groups on the membrane surface,which changed the degree of cross-linking on the membrane surface.The structure becomes looser,which increases the flux of the membrane;at the same time,to achieve the goal of further increase membrane salt intercept taking the preprocessing（m-phenylene diamine,para-phenylene diamine solution immersion treatment）and subsequent crosslinking phenolic solution（anhydrous phloroglucinol,tannic acid,3-methoxy phenol）experiment of the modificed membrane.The result showed that the membrane achieve the largest increase in salt rejection at 99.2%,which 0.3%（w/v）PDA solution was soaked by pretreatment for 10 min,and after 0.3%（w/v）sodium nitrite coating treatment for 10 minutes,the last 0.1%of the phloroglucinol solution coating treatment for10 minutes.The modified membrane have potential application value for the users with higher water quality undoubtedly.The sodium nitrite solution with pH=1 and 0.3%（w/v）was used as the modified solution in the pilot test.It is obvious that the flux of membrance had improved by NaNO₂.From the mechanism of liquid-solid kinetics,inline modification in the pilot experiment is driven by pressure,and the reaction molecules is difficult to be adsorded on the membrane surface by the running water to reach the activation energy of the reaction,and the final online modification effect is far less than that of the soaking modification,which explains the reason why the two modification differences in the pilot experiment.A novel nanofiltration membrane was prepared by its diazotization and cross-coupling reaction with tannic acid on polyethersulfone ultrafiltration membrane.The membrane was prepared without using organic solvents,reducing the damage to the enviro nment and the human body,and haing the advantages of simple operation,mild experimental conditions,and low raw material costs.It showed that a new type of nanofiltration membrane was prepared by multilayer coating of synthetic product and tannic acid mixed solution with sodium nitrite solution.It was found that the membrane prepared with 3 layers was best.The rejection of 2 g/L（Na₂SO₄、MgSO₄、NaCl、MgCl₂）were 98.96%,93.08%,86.00%and75.17%,respectively.And the flux of novel NF membrane is 18 L/m²·h.