| Membrane separation technology has gradually replaced the heat-based separation process based on distillation because of its flexible solute separation range,high separation efficiency,and low energy consumption,and is widely used in sewage treatment,food processing,seawater desalination,and other fields.At present,the separation and purification of chemical products in the petroleum industry,biopharmaceuticals and organic synthesis,and other fields require the use of a large number of organic solvents,so the purification of solutes and the recovery of organic solvents is very important,and heat-sensitive solutes and solvents are easy to decompose during the distillation process,so an efficient,inexpensive and gentle method is required for separation and purification,and the separation scale and separation efficiency of nanofiltration membrane separation technology meet such needs well.However,although the traditional separation membrane shows excellent performance in the separation of the water system,due to its poor resistance to organic solvents,swelling,and even dissolution will occur in the organic solvent system,thereby reducing the separation efficiency and limiting its use scenarios.Therefore,the development of separation membranes with excellent solvent resistance and efficient separation performance in organic solvent systems has become a hot spot in scientific research and a bottleneck in application technology.The mainstream separation membranes for organic solvent systems are mainly composite nanofiltration membranes composed of a solvent-resistant substrate and a high-efficiency separation layer.Currently,the main research direction of separation membranes used in organic solvent nanofiltration systems focuses on constructing special separation resins with high solvent resistance and precision,and efficient separation layers.At present,the polymer materials used for organic solvents are mainly polyimide,polybenzimidazole,and other polymers with a certain solvent resistance base,but their resistance to harsh polar aprotic solvents（such as N,N-dimethylformamide,etc.）is poor,and additional crosslinking treatment is required,which makes the process cumbersome and costly.At present,the direction of development is the preparation of solvent-resistant polymer film materials with high solvent resistance,simple process flow,and high repeatability.The high-efficiency separation layer is mainly cross-linked polyamide prepared on a solvent-resistant substrate by interfacial polymerization,which has the advantages of high separation accuracy and good separation ability for solutes in organic solvents,but the traditional molecular structure of polyamide has poor solvent permeability due to its small free volume,so the current development direction is to develop a polyamide separation layer with large free volume and high solvent permeability.Based on this,from the perspective of molecular structure design,this paper selects polyaryletherketone materials with crystallization and excellent solvent resistance as solvent-resistant membrane materials,designs and prepares a crystalline sulfonated polyaryletherketone polymer with excellent solvent resistance,and prepares it into a separation membrane,controls the sulfonation degree of polyaryletherketone through molecular structure design,improves the shortcoming of the uncontrollable sulfonation ratio of polyaryletherketone separation membrane in previous literature reports,and the introduction of sulfonic acid groups also improves the permeability of the membrane to polar solvents.Subsequently,to obtain the composite nanofiltration membrane with high solvent permeability,a large free-volume polyamide separation layer containing diphenyl fluorene and triphenylmethane structure was introduced to the polyaryletherketone substrate by co-solvent interface polymerization,and a series of composite nanofiltration membranes were prepared and their properties studied.In the first part of the work,to prepare a separation membrane with excellent solvent resistance,the polyether ketone-sulfonated diphenyl polyetheretherketone copolymer（PEK-SPEDEK）with precise sulfonic acid group ratio was prepared by controlling the sulfonated biphenyl content in the copolymer by molecular structure design.Copolymers exhibit excellent resistance to organic solvents.It was prepared into a crystalline separation membrane by the NIPs method.The effects of the change of film concentration and the sulfonation degree of polymer on the micromorphology and surface properties of the film were studied.The relationship between membrane molecular structure,microscopic morphology,and properties was explored.The results showed that the polyaryletherketone separation membrane prepared at a lower concentration of casting solution would have higher solvent permeability due to its thinner cortex,and the sulfonic acid group with strong negative electricity would improve the permeability of the membrane to common polar solvents（such as methanol,ethanol,etc.）,and showed excellent separation ability for large-size anionic dyes（such as tiger red sodium salt with a molecular weight of 1017 Da）.And because the polyarylenetherketone membrane is crystalline,it shows good structural and property stability in the face of harsh organic solvents such as N,N-dimethylformamide（DMF）.It has been proved that it can meet the solvent resistance requirements of membrane materials in organic solvent separation.In the second part of the work,a polyamide separation layer with high solvent permeability and high solute retention capacity was constructed based on a solvent-resistant polyaryletherketone separation membrane.Through the structural design of polyamide,we pioneered the use of a co-solvent interfacial polymerization method,using 9,9-bis（4-aminophenyl）fluorene（BAF）,an aqueous amine monomer with a rigid twisted structure,to prepare a polyamide separation layer with a large free volume segment.Subsequently,a tightly compounded polyaryletherketone/polyamide composite membrane between the substrate and the separation layer was prepared by the vacuum-assisted method.The causes of membrane micromorphology were discussed from the perspective of the diffusion behavior of monomers at the interface.The effects of co-solvent composition and amine concentration on membrane properties and morphology were studied.With the increase of amine concentration,the surface of the prepared composite membrane showed the ridge-like change law of characteristic point-like connection,which effectively increased the effective area of contact between the membrane and the solvent,and then improved the permeability of the membrane to the solvent.The polyamide separation layer with a rigid twisted structure prepared in this work has an order of magnitude higher methanol solvent flux than that of the traditional polyamide separation layer.It also has excellent dye separation ability.Therefore,through the scientific preparation of the interfacial polymerization solvent system,the problem of insoluble high-rigidity amine monomer in the traditional process was overcome,and the preparation of an efficient loose polyamide separation layer was realized.However,since the composite effect between the substrate membrane and the separation layer still needs to be improved,and the hydrolysis of acid chloride will cause the crosslinking degree of the polyamide separation layer to be relatively low,there is still room for improvement in the solute separation performance of the composite membrane,so the preparation process of the composite membrane needs to be further optimized.In the third part of the work,the experiment of in situ interfacial polymerization was carried out to improve the interface composite effect between the solvent-resistant polyaryletherketone membrane and the polyamide separation layer.At the same time,focusing on the problem of acid chloride hydrolysis in the aforementioned polyamide separation layer,a new interfacial polymerization system was created to improve membrane hydrolysis,improve the cross-linking degree of the functional layer,and achieve the purpose of improving the separation effect of the functional layer.Firstly,starting from the root of polyamide hydrolysis,a three-component pure organic interface polymer system of n-hexane-ethylene glycol/DMF was constructed,which realized the rigid polyamide solvent and fully participated in the interfacial polymerization reaction while completely abandoning water and avoiding the hydrolysis of acid chloride in the interfacial polymerization process.Secondly,9,9-bis（4-aminophenyl）fluorene（BAF）and tetra（4-aminophenyl）methane（TAM）with different amino functions were prepared for two composite membranes with large free-volume separation layers.The influence of membrane structure on membrane properties was studied.The composite membranes prepared with BAF increased the rejection of rhodamine B and acid fuchsin by 9.9%and 6.7%.The composite membrane prepared with TAM has high solvent permeability,excellent separation effect for dyes with a molecular weight of 696 Da and above,and an ultra-high methanol permeance of 46.32 L m-2 h-1 bar-1.Finally,the in-situ polymerization experiment of solvent-resistant polyaryletherketone membrane was carried out,and the in-situ interface polymer of n-hexane-ethylene glycol/DMF three-component pure organic interface polymer system was realized.At the same time,it was found that the sulfonic acid group can adsorb amines on the surface of the substrate membrane,and improve the composite effect of the substrate membrane material and the polyamide separation layer.At the same time,ethylene glycol as a co-solvent can effectively avoid the hydrolysis of acid chloride to improve the crosslinking degree of polyamide,and the solvent permeability of the two composite membranes far exceeds that of the traditional polyamide composite membrane in maintaining the high methanol flux of 22.40 L m-2h-1bar-1 while improving the separation accuracy of organic pollutants.In summary,we prepared a crystalline solvent-resistant polyaryletherketone separation membrane by molecular structure design,which has excellent solvent resistance.On this basis,a polyaryletherketone/polyamide composite film with a large free volume of separation layer was prepared through a new interfacial polymerization solvent system,which showed excellent solvent permeability and realized the combination of a new solvent-resistant film material and an efficient separation layer. |
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