Study On Quaternization Modification Of Polysulfonamide Alkaline Anion Exchange Membrane

An anion exchange membrane is a kind of membranes which is selectively permeable to anions. Polystyrene-based anion exchange membrane as a typical anion exchange membrane is widely applied in fields like separation, purification. Anion exchange membrane still cannot meet the requirement of special application under certain rigorous circumstance like high temperature, acid and alkaline environment. Recently, anion exchange membrane as a electrolyte membrane in fuel cell also requires alkaline resistance, high temperature tolerance and high conductivity. How to conquer these problems is becoming a research point in ionic exchange membrane field.PSA posses great chemistry stability and thermal resistance. In this work, the quaternary ammonia polysulfonamide(QAPSA) was prepared via chloromethylation, quaternization and alkalization process. The effects of experimental conditions on the structure and properties of QAPSA were studied. PTFE porous membrane as matrix material was used to reinforce QAPSA/PTFE composite anion exchange membrane. The mechanical and electrochemical properties were measured. The main conclusions are summarized as follows:1. Synthesis experiment results indicated that the degree of chloromethylation increased with the increasing of chloromethyl methyl ether/PSA mass ratio, reaction time and reaction temperature, while decreased with the increasing of PSA concentration. Based on the obtained Chloromethylated Polysulfonamides(CMPSA), the QAPSA were successfully prepared via further quaternization and alkalization process.2. PSA with the different ratio of meta-position and para-position were used to prepare QAPSA. The results indicated that para-position structure is easier to be chloromethylated. The degree of para-position CMPSA chloromethylation was16%, which is100%,60%, and33%higher than that of meta-position PSA,3:1PSA and1:1PSA respectively. The thermal stability was determined by the matrix material and the modification had no effect on the thermal stability. 3. The rheological behavior of QAPSA/DMAc solution was also investigated. Properties of newtonian fluid has been found in low shear rate in QAPSA/DMAc solution. With shear rate rising, shear thinning behavior has been observed. Guarant viscosity can be effectively decreased by the increase of temperture in highly concentrated solutions(≥48%). The48%QAPSA/DMAc solution presented even and stable characters.4. QAPSA/PTFE composite anion exchange membrane was successfully prepared using dipping method. The surface of membrane was smooth and dense. The membrane shows good mechanical properties with35MPa of breaking strength and55.1%of breaking elongation ratio. Also, it showed excellent dimensional stability and have9.90%of water uptake and2.91%of swelling degree. Ion exchange capacity(IEC) of QAPSA/PTFE membrane made from41%of the chloromethylation degree CMPSA reached1.46mmol/g. The membrane ionic conductivity was1.025×10-2S/cm at room temperature.