Preparation And Characterization Of Low-resistivity Heterogeneous Cation-exchange Membranes

Although being inferior to a homogeneous ion exchange membrane in electro-chemical properties, the heterogeneous ion exchange membrane is still marketable due to its typical advantages, such as low cost, easy manufacturing, favorable oxidative stability, good mechanical strengths and dimensional stability. Therefore, the improvement of some relevant properties to heterogeneous membrane has attracted much attention from whether academic or practical points of view. Among all the properties of an ion exchange membrane, membrane conductivity and membrane permselectivity can directly affect energy consumption and separation efficiency in the application, therefor are two of the most important. In this study, the attempt for an improved preparation of heterogeneous cation exchange membrane have been taken in two ways, ion exchange resin and resin binder respectively.In this study, The homemade Sulfonated Polystyrene Microspheres (SPM) of different ion exchange capacity have been used by replacing part of commercial cation exchange resin (CR) particles, Sulfonated Polyethersulfone (SPES) with different sulfonation degree have been used by replacing part of res in binder (PVC), both to decrease the inert regions formed by the random accumulation of CRs. Then membrane properties in different aspects, for example, ion-exchange properties, electrical properties and mass transfer performance, have been thoroughly investigated through conventional characterization methods then contrastively analyzed, to study the effect of SPM and SPES on those membrane properties.The micro-size SPM are prepared by dispersion polymerization and sulfonation with concentrated sulfuric acid as sulfonating agents, with average particle size and average variance of the size distribution of 11.02 μm and 1.61 respectively, showing monodispersity and little damage capability to membrane structure. SPES need to be sulfonated with high reactive chlorosulfonic acid due to more stable molecular structure, meanly applied as a kind of binder in the membrane. All homemade heterogeneous cation-exchange membranes are prepared by casting solution technique.Membrane characterization indicates that the increase of SPM replacement in total cation exchange resins (from 0,5wt%,10wt%), and ion exchange capacity of SPM implied in the membrane (from 0.62 mmol/g (dry),1.21 mmol/g (dry)) both can help reduce the electrical resistivity of the homemade heterogeneous cation-exchange membrane, especially when contents of total resins is not big. Only the former may meanwhile do harm on membrane permselectivity if ion exchange capacity of SPM implied is not big enough. however, by increasing ion exchange capacity of SPM implied in the membrane, membrane permselectivity can be well reserved when membrane conductivity being improved; for the same ratio of SPES replacement (14wt%)in the resin binder, the increase of sulfonation degree of SPES (0～15.29%) can help improve membrane permselectivity but do little help in improving membrane conductivity, however, as the ratio of SPES (sulfonation degree:15.29%)replacement raised, both electrical properties and mass transfer performance of the homemade heterogeneous cation-exchange membranes can be obviously improved.