The characteristics of citric acid separation using electrodialysis with bipolar membranes

摘要

The conversion of salts into their corresponding acids and bases using electrodialysis with bipolar membranes shows specific characteristics. Considering for example the generation of HCL and NaOH from NaCl, the process efficiency strongly decreases with increasing product concentration, a process behaviour typical of strong acids. In this report the separation and production of a (weak) organic acid, specifically the conversion of sodium citrate into citric acid and NaOH in a three-compartment cell arrangement, will be described and characterized. Using model solutions, and varying the current density between 300 and 1000 A/m~2 the current efficiency, the conversion rate and the specific energy consumption were determined. Furthermore, by changing both the base concentration (1N-3.5N) and the acid content (20-60%), the resulting effects upon the process behaviour were examined. In addition to these experiments the product impurities and water transport were measured and noted. Another goal was to investigate the highest attainable acid concentration which was close to the saturation point.