Synthesis and transport of impurities in electrodialysis metathesis: Production of choline dihydrogen phosphate

Abstract

The production of ionic liquids involves a metathesis step in which the desired anion and cation are combined. Depending on the desired product purity, this step can be accomplished by different methods, including acid base neutralisation reactions, the use of silver salts and electrodialysis. In this paper, electrodialysis metathesis is used for the production of choline dihydrogen phosphate. The influence of operating parameters was investigated. It was found that a high current density, low diluate and choline dihydrogen phosphate concentration yield the highest product purity. Furthermore, it was illustrated for the first time that electrodialysis metathesis is able to yield a product purity comparable with that obtained by using silver salts. An electrical efficiency of 94.0% for choline and 58.6% for dihydrogen phosphate was achieved. The total cost of the electrodialysis process was estimated at 0.06€ per mole of choline dihydrogen phosphate. The second aim of this paper is the characterization of the flow of impurities in electrodialysis metathesis. In addition, the effect of operating variables on this flow of impurities was quantified. In the further optimization of the electrodialysis metathesis process, this knowledge is likely to be of great interest in conducting salt metathesis reactions.