| The research and development of solvent-resistant nanofiltration membranes have attracted much attention at home and abroad,and the development of membrane materials with excellent comprehensive performance is the key to the development of solvent-resistant nanofiltration membranes.Polyimide is a polymer material with excellent comprehensive properties,but it still has some common problems as a film mater:ial.Conventional polyimide is difficult to melt under ordinary heating conditions,and it is difficult to dissolve in most organic solvents,which limits its processing performance.In this paper,based on the molecular structure design of diamine monomer,combined with the optimization of imidization process,a new polyimide membrane material with excellent film-forming properties was prepared,and a series of polyimide-based nanofiltration membranes were prepared by phase separation,sol-gel method,etc.The structure and application characteristics of the membranes were investigated.Related research can provide reference for the creation of high-performance nanofiltration membrane materials,enriching the theory of solvent-resistant nanofiltration membrane construction and structural regulation.The main research contents and conclusions are as follows:(1)Based on the design of molecular structure,3,3'-dimethyl-4,4'-diaminodiphenylmethane(DMMDA)diamine monomer was synthesized and its structure was verified by infrared,nuclear magnetic and other characterization methods,and BTDA-DMMDA type polyimide was prepared by chemical imidization.The results showed that the polyimide materials could not only tolerate common organic solvents,but also be dissolved in a membrane-forming solvent such as NMP.(2)Polyimide nanofiltration membranes were prepared by phase separation method using polyimide as the membrane material.The effects of casting solution concentration,post-treatment temperature and post-treatment time on the microstructure and separation performance of the membrane were investigated.The results showed that the nanofiltration membrane has a typical integrally skinned asymmetric structure.The membrane is electronegative.The membrane can effectively separate the monovalent salt and the divalent salt,and the rejection rate of the acid red 94 is higher than 92%.Under the pressure of 0.5 MPa,the flux of the membrane to different separation systems is 10-30 L/(m2·h).Nanofiltration membranes have good reusability and long-term stability.At the same time,the application characteristics of nanofiltration membrane in the separation of spiramycin extract were investigated.The results showed that the membrane exhibits good solvent resistance and maintains stable structure and performance under various solvent conditions.The effects of operating pressure,feed liquid concentration,feed liquid flow rate,temperature,pH and other conditions on the actual separation performance of the membrane were analyzed.Under optimal operating conditions,the membrane flux is 23 L/(m2·h)and the rejection of spiramycin is higher than 90%.(3)A silicon dioxide/polyimide nanofiltration membrane was prepared by sol-gel and phase separation method.The effects of tetraethyl silicate(TEOS)content on the microstructure and separation performances of the membrane were investigated.The membrane structure was characterized by infrared,SEM,AFM,XPS,EDX,water contact angle,etc.,and the separation performance of the membrane was investigated.The results showed that the structure of silicon dioxide/polyimide nanofiltration membrane was greatly affected by TEOS content.With the increase of TEOS content,the membrane cross-section structure shows a transition from finger-hole to sponge-like pore.The surface roughness of membrane increases with increasing of TEOS content.The hydrophilicity,mechanical strength and thermal stability of silica/polyimide nanofiltration membranes are superior to those of pure polyimide nanofiltration membranes.When the content of TEOS is 9%,the performance of silicon dioxide/polyimide nanofiltration membrane is the best.Under the pressure of 0.4 MPa,the water flux of the membrane is 80 L/(m2·h)and the rejection of Na2SO4 is higher than 85%. |
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