Study On The Coupling Performance Of Polyelectrolyte Type Draw Solution And Charged Forward Osmosis Membrane

In this study,polyelectrolytes were used as the draw solution,polyamide forward osmosis membranes was prepared by interfacial polymerization,with sulfonated polyphenylsulfone(sPPSU)as the charged support layer.The coupling system of ionic polyelectrolyte and charged forward osmosis membranes was established.In the process of forward osmosis,polyelectrolytes can provide higher osmotic pressure,and in the FO mode and PRO mode,there is an interaction force between charges when the charged support layer and charged active layer contact with the polyelectrolyte.With the increase of running time,the charge properties of the contact interfaces will be changed by polyelectrolytes.Through the study of this system,the interaction mechanism between different types of polyelectrolytes and charged forward osmosis membranes was mastered,while a forward osmosis coupling system with higher water flux and smaller reverse solute flux was obtained.(1)The osmotic pressure,viscosity and diffusion coefficient of four kinds of polyelectrolyte solutions including polyhexamethylene biguanide hydrochloride(PHMG),polyacrylic acid sodium(PAAS)and polyethyleneimine PEI 1800 and PEI 10000 were preliminarily measured.Among them,the osmotic pressure of PHMG is 791 mOsmol/kg at 0.2 g/mL,and the viscosity is the smallest.The diffusion coefficient in aqueous solution of PHMG is greater than PEI 10000 with similar molecular weight.(2)By measuring the penetration rate of four polyelectrolytes in the support layer of different structures and membrane materials,the structure of the sPPSU support layer with PVP K30 as the pore-forming agent is most suitable for the penetration of polyelectrolyte solutions.In the range of pH 3-11,the permeability rate of PAAS has the largest change range,while the permeability rate of PHMG has a small change range with pH,and the permeation rate of polyelectrolytes increase with the increase of temperature.By comparing the permeability rate of polyelectrolyte in the support layer with the diffusion coefficient in aqueous solution,it is found that the support layer can promote the permeability of cationic polyelectrolyte.(3)Two aqueous monomers,1,4-phenylenediamine-2-sulfonic acid(PDS)and 1,3-diaminoganidine hydrochloride,were used for interfacial polymerization to obtain the polyamide charged active layer,and the optimal interfacial polymerization conditions of the two aqueous monomers were obtained by orthogonal test.The water flux and reverse solute flux of the charged forward osmosis membranes were determined with four polyelectrolytes as draw solution.Among them,when PHMG as draw solution,the PDS-TMC composite forward osmosis membranes with sPPSU as the supporting layer ran stably under FO and PRO modes,and the membrane fluxes were 8.0 L/m2·h and 9.4 L/m2·h,respectively.Through the analysis and verification of the running results,it is found that the coupling between polyelectrolyte and charged membrane causes the charge transformation of the contact interface and can reduce the reverse solute flux.