Preparation And Properties Of Composite Membranes Based On Bisaminoguanidine Salt Monomer

Lithium is an important energy element.With the advent of new energy era,the global energy demand is increasing.Lithium plays an important role and is widely used in various fields.Salt lake brines are rich in lithium resources,but the mass ratio of magnesium to lithium in most salt lake brines in China is very high,and the lithium ion radius is similar to that of magnesium,which limits the development of lithium extraction technology from salt lake brines.Therefore,it is very important to find a suitable and effective method to separate magnesium and lithium.Ultrafiltration(UF)as a pressure driven process for the removal of harmful substances has attracted more and more attention.NF membrane,with its advantages of high water flux,high separation efficiency and energy saving,has shown broad application prospects in many fields,including the separation of monovalent/divalent ions,the removal of heavy metal ions and small organics,and the softening of water.Therefore,nanofiltration membrane has unique advantages in the separation of magnesium and lithium.In this paper,1,3-diaminoguanidine hydrochloride was selected as the aqueous phase monomer and trimethoyl chloride(TMC)as the organic phase monomer.The composite nanofiltration membrane was prepared by interfacial polymerization.The effects of interfacial polymerization conditions and heat treatment conditions on the magnesium lithium retention performance of the composite nanofiltration membrane were investigated,and the aqueous phase additives were introduced to improve the retention efficiency of the composite nanofiltration membrane for magnesium chloride(Mg Cl₂)And the mechanism was analyzed.In the first part of this dissertation,the effects of different interfacial Polymeriza-tion time,heat treatment conditions,different proton acceptors and aqueous monom-er concentration on the rejection flux performance of composite nanofiltration membrane were studied.The optimal preparation conditions of composite nanofiltration membrane were determined,and the change of rejection flux with pressure and molecular weight of composite nanofiltration membrane were tested.The optimum conditions were 2.4wt%1,3-diaminoguanidine hydrochloride,1wt%tea as proton acceptor,0.1wt%TMC,interfacial polymerization for 2min,and heat treatment at 80?for 5min.Under these conditions,the rejection of Mg Cl₂and Li Cl was 55.89%and 30.51%respectively.When the pressure increased from 0.2MPa to 0.7MPa,the water flux of the composite nanofiltration membrane increased with the increase of pressure,and the retention rates of Mg Cl₂ and Li Cl increased first and then decreased,and the molecular weight of the composite nanofiltration membrane was about 2000Da.In the second part of this dissertation,the optimum conditions for the preparation of composite nanofiltration membrane were selected.On the basis of this,the effects of sodium 2-ethylhexanoate,pva1788,sodium citrate,sodium benzoate,Na₂SO₄ and Na Cl as water phase additives on the performance of the composite nanofiltration membrane were studied.The performances of Mg Cl₂,Li Cl interception and water flux,and the change of the retention flux with pressure were measured.Finally,the surface properties of the composite nanofiltration membrane were characterized.The experimental results show that the performance of the composite nanofiltration membrane is affected by the use of 2-ethylhexanoate as water additive.The surface roughness and hydrophilicity of the composite nanofiltration membrane can be reduced to the greatest extent by using2-ethylhexanoate as water additive.