Studies On Preparation And Modification Of Polyamide Composite Forward Osmosis Membranes

At present,osmosis(FO)technology has a huge application potential in the fields of power generation,desalination,and sewage treatment.FO has many advantage,but it also faces many problems,one of which is the development of high-performance FO membranes.This experiment is based on the thin-film composite polyamide forward osmosis(TFC FO)membrane that is the most widely used at present,and the TFC FO membrane with higher performance is prepared by modifying the TFC membrane.The traditional TFC FO membrane contains a polyamide(PA)active layer and a porous support layer,which is formed by the polymerization reaction of m-phenylenediamine(MPD)and trimesoyl chloride(TMC)on the surface of the polysulfone(PSf)bottom membrane.However,due to the strong steric hindrance between the molecules caused by the benzene ring,some of the acid chloride groups on the TMC failed to react,making it difficult to network the polyamide active layer.This work proposes three easy and effective methods to improve the density and hydrophilia of the active layer of the membrane.Amino groups are introduced to the Polyamide layer to react with the exposed acid chloride groups after a small molecule of 1,3-diamino-2-propanol(DH)or 2-aminoethanethiol(AE)or1,3-diamino-2-propanol/2-aminoethanethiol(DH-AE)being introduced.This may lead to a higher degree of crosslinking and form a more complex and networked aggregate structure.In this work,three modified membranes are successfully prepared,and a series of characterizations are carried out.The result is that all methods could improve the density of the active layer and increase the salt rejection without adversely affecting the selectivity.The hydrophilicity of the thin-film composite of1,3-diamino-2-propanol(TFC-DH)film is significantly improved,the reverse salt flux of the thin-film composite of 2-aminoethanethiol(TFC-AE)film is remarkably improved,and the effect of the thin-film composite of1,3-diamino-2-propanol/2-aminoethanethiol(TFC-DH-AE)film is between the TFC-DH film and the TFC-AE film.Therefore,the method of adding a small molecular material can increase the degree of polymerization.The method of introducing an inorganic element provides a valuable solution for designing and developing a novel and efficient FO film.And the method is simple,and easy to be operated.In order to explore the effect of modifier concentration on TFC membrane performance,this paper also takes TFC-DH modified membrane as an example,using three modifier concentrations(0.2 g / 100 m L,0.4 g / 100 m L,0.6 g / 100 m L)Three modified membranes were prepared: TFC-DH-0.2 membrane,TFC-DH-0.4membrane,and TFC-DH-0.6 membrane.The result obtained is that as the concentration of the modifier increases,the degree of modification will increase,the degree of crosslinking of the polymer on the membrane surface will become higher and higher,and the active layer will become denser and denser.The hydrophilicity of the membrane will also become stronger and stronger,and the water flux of the membrane will become larger and larger in the forward osmosis performance test.In this paper,three methods were modified to improve the membrane performance while comparing the difference between the alcohol hydroxyl group and the thiol group.Through microscopic infrared,new components on the surface of the film can be seen,and there are changes in the bonds between the molecules.In addition,DH also introduced hydroxyl groups.From the contact angle and water flux test,it can be seen that the modified membrane improved the active layer in terms of hydrophilicity and increased the water flux of the forward osmosis membrane.After adding AE,through scanning electron microscopy and atomic force microscopy,it can be seen that the introduction of inorganic sulfur element has changed the membrane structure,the concentration polarization phenomenon also has been improved to a certain extent.The innovation of this paper is that,taking the steric hindrance and the degree of polymerization as the starting points,the unreacted acid chloride groups on trimesoyl chloride are reacted by introducing small molecules,so that the structure,morphology and performance of the forward osmosis membrane change greatly.