Polysulfone Anion Exchange Membranes And Their Application For Electrodialysis Purifying Phosphoric Acid

Phosphoric acid solution,as the one of the most critical mineral acid for the chemical industry,suffers from lots of metal impurities material by sulfuric acid leaching,resolving these purified issues more pressing to meet industry requirements.Electrodialysis(ED)technology is one of the membrane separation technologies which has the advantages of easy to operate and process greening.It is a great potential process for phosphoric acid purification.As the most important component to influence the phosphoric acid purification in ED technology,the anion exchange membrane(AEM)needs to has the essential qualities,including excellent ion transport efficiency,low membrane area resistance and high dimensional stability.In this work,a series of polysulfone(PSU)AEMs with different structure were prepared.Then,the purification efficiency of wet phosphoric acid in ED technology with all resultant AEMs were further investigated.The main contents are as following:(1)Chloromethylation polysulfone(CMPSU)was synthetized through the reaction between PSU and non-toxic chlorotrimethylsilane,followed by adding trimethylamine(TMA)ethanol solution to produce quaternary ammonium polysulfone(QAPSU)AEMs.A series of QAPSU membranes with different ion exchange capacity(IEC)values were obtained by controlling the chloromethylation time.Notably,the QAPSU with IEC of 1.61 mmol/g has the best performance,i.e.swelling ratio of 9.4 %,membrane area resistance of 6.0 ??cm2,transport number of 0.95,and the tensile strength of 10.6 MPa.When the AEM was applied in ED technology for purifying phosphoric acid solution,all the metal ions removal rates reach over 65 %.(2)A series of comb-shaped quaternized ammonium polysulfone(Cx-QAPSU)AEMs which have low swelling ratio and membrane area resistance as well as high transport number and tensile strength were synthesized.The Cx-QAPSU membranes show enhanced hydrophilic-hydrophobic phase separation structure with the increase of side chain length.The C16-QAPSU with IEC of 1.55 mmol/g has the best performance.Its swelling ratio and membrane area resistance are reduced to 5.3 % and 2.5 ?·cm2 while transport number and tensile strength are increased to 0.98 and 16.7 MPa comparing with those of QAPSU with IEC of 1.61 mmol/g.Moreover,C16-QAPSU AEM exhibits the highest metal ions removal rate over 78 % in phosphoric acid purification among all Cx-QAPSU membranes.(3)The olefin crosslinked quaternized ammonium polysulfone(VQAPSU)AEMs were prepared by thermal crosslinking of the N,N-Dimethylvinylbenzylamine with flexible unsaturated side chains during the membrane formation process,which can improve the dimensional and mechanical stabilities of the AEM.When /VBN CMPSUn n is about 1.5,the VQAPSU with IEC of 1.89 mmol/g has the best performance,i.e.swelling ratio of 6.3 %(in plane direction)and 9.1 %(in thick direction),membrane area resistance of 4.3 ??cm2,transport number of 0.98,tensile strength of 36.4 MPa(hydrated membrane)and 29.0 MPa(dried membrane).When the AEM was applied in ED technology for purifying phosphoric acid solution,the metal ions removal rates reach over 80 %.(4)A series of diamine crosslinked quaternized ammonium polysulfone(TQAPSU and TTQAPSU)AEMs were synthesized by means of diamine N,N,N',N'-tetramethyl-1,6-hexanediamine(TMHDA)and TMHDA/TMA modifying the CMPSU to achieve the high IEC and conductivity of AEM.The performances of the resulting crosslinked AEMs were determined by the quaternization reagents.The TQAPSU and TTQAPSU with six methylene side chains will facilitate the formation of micro-phase separation structure,which would improves not only the conductivity and selectivity but also the dimensional stability,strength and toughness of the AEMs.When / / 3:1:1TMA TMHDA CMPSUn n n(28),the TTQAPSU membrane exhibits the lowest membrane area resistance of 1.2 ?·cm2 and swelling ratio of 7.4 %(in plane direction)and 9.7 %(in thick direction)as well as the highest transport number of 0.98 and appropriate tensile strength of 15.0 MPa at IEC of 1.88 mmol/g and crosslinking degree of 49.6 %.Moreover,the metal ions removal rate in phosphoric acid purification of this TTQAPSU membrane is higher than 72 %.