Preparation And Properties Of Sulfonated Poly(Phthalazinone Ether Ketone) Membranes For Electrodialysis

Ion exchange membranes are the key part of electrodialysis.Their properties,such as area resistance and transport number,determine the separation efficiency and energy consumption.In general,ion exchange membranes include cation and anion exchange membranes.Expensive commercial cation exchange membranes,such as Nafion and ASTOM,limit further application in industry.Therefore,the development of novel cation exchange membranes for electrodialysis has been investigated extensively in recent year.Sulfonated poly（phthalazinone ether ketone）s（SPPEKs）with different ion exchange capacities(0.77,1.02,1.45,1.82 mmol·g^-1)were prepared and labeled as SPPEK-1,SPPEK-2,SPPEK-3 and SPPEK-4 from poly（phthalazinone ether ketone）（PPEK）by controlling reaction time.¹H-NMR and FT-IR spectra were used to confirm the structure of polymer.The inherent viscosity of SPPEK was between 1.01-3.61 dL·g^-1.The TGA curves showed that 5%weight loss of SPPEKs was about 360℃,suggesting good thermal stability.The properties of SPPEK membranes,including area resistance,transport number,and limiting current density,were investigated.With the increase of IEC from 0.77 to 1.82 mmol·g^-1,the area resistance of SPPEK membranes decreased,while transport number and limiting current density increased.SPPEK-4 exhibited the best properties and its area resistance was only 0.62Ω·cm²,transport number was 0.97,and the limiting current density was 39.8 mA·cm^-2.Compared with the commercial Tianwei CMX membrane,the SPPEK-3 and SPPEK-4 membranes showed better performance.The desalination and concentration performance of SPPEK membranes were investigated and compared with the commercial Tianwei CMX membrane.The electrodialysis tests showed that for 0.1 mol·L^-1 NaCl solution,the desalination curves of SPPEK-3 and SPPEK-4membranes were similar and the desalination rate was 99%in 180 minutes Whereas the commercial membrane could have desalination rate of 90%.In concentration test of 0.6 mol·L^-1 NaCl solution,SPPEK-3 has the best concentration property and lowest energy consumption.The concentration rate was 94%and energy consumption was 3.59 kWh·kg^-1,which were superior to SPPEK-4 membrane(74%,3.61 kWh·kg^-1)and commercial membrane(72%,3.76kWh·kg^-1).With high transport number and low water uptake,SPPEK-3 membrane had the best performance in desalination and concentration.SPPEK-3 membrane was used as cation exchange membrane for further electrodialysis tests.The effects of volume ratio,flow rate and operation current on desalination of low concentration solution and concentration of high concentration solution were investigated.The results showed that volume ratios of between concentration cell and desalination cell played invisible influence on desalination of low concentration solution,but played important effect on concentration for saline water,which final concentration rate increased from 94%to 223%,when volume ratio increased from 1:1 to 1:100.Increasing flow rate adversely affected the desalination process of low concentration solution.The desalination rate decreased from 76%to 71%at 105 min,whereas final concentration of high concentrated solution increased from191%to 223%and energy consumption decreased from 1.85 kWh·kg^-1 to 1.28 kWh·kg^-1.The desalination rate of low concentration solution and concentration rate of high concentration solution increased with an increase in operating current（0.10-0.18 A）,while the operation potential and energy consumption would be increased.