The current density is rather low in solid bipolar membranes, because the water transfer rate is relatively slow across solid bipolar membranes made of solid ion-exchange materials. This paper describes the use of polymer solutions, such as phosphatic poly(vinyl alcohol) solution, poly(acrylic acid) solution and poly(vinyl alcohol) solutions with dispersed cation/anion-exchange resin particles to prepare bipolar membranes. The 0.1 mol/L NaOH and the 0.05 mol/L H2SO4 were used to test the performance of the bipolar membranes. For a fixed liquid layer thickness, both the current density and the selectivity increase with the concentration increase of a polyelectrolyte solution. The maximum current density measured in the experiment was 1497 A/m2 with a selectivity of 96.8%.
A bipolar membrane-based process was proposed to regenerate sodium p-toluenesulfonate (or sodium 4-methylbenzenesulfonate) in the production of D-(-)-p-hydroxyphenylglycine (or R- α-amino-4-hydroxy-benzeneacetic acid). The conversion of pure sodium p-toluenesulfonate solution and actual feed solution that contains small amount of R-α-amino-4-hydroxy-benzeneacetic acid besides sodium p-toluenesulfonate was compared and a new processing route was proposed. The removal ratio of Na+ was typically around 80% with an average current efficiency of 20–50%.
To achieve organic mixture separation at higher temperatures, organic inorganic hybrid membranes were prepared from 3 aminopropyltriethoxysilane(APST) and terephthaloyl chloride (CTPH) membrane material using the Sol Gel method. Experiments showed that many factors, such as acid content, solution concentration, hydrolysis time, temperature and type of support membranes, can affect the preparation process. The mechanical properties, heat resistance and structure of the membrane were characterized and analyzed. Experimental results showed that the membrane has good heat resistance with a decomposition temperature around 333 ℃. The polytetra fluor ethylene (PTFE) microporous membrane is an ideal support for the active layer except that the membrane is brittle.
