IDENTIFICATION OF THE IONIC SPECIES IN ANION-EXCHANGE MEMBRANES EQUILIBRATED WITH SULFURIC-ACID-SOLUTIONS BY MEANS OF RAMAN-SPECTROSCOPY AND RADIOTRACERS

The ARA anion exchange membrane which has been designed for the recovery of acid by electrodialysis shows a reduced proton leakage compared with other commercial membrane. The ion exchange fixed site of this membrane is the vinylpyridinium group. The purpose of this work is to identify the chemical species present in this membrane equilibrated with an aqueous sulphuric acid solution up to 6 M. Using radiotracers and Raman spectroscopy, it can be established that: (i) the undissociated sulphuric acid is not present in the membrane, (ii) the hydrogenosulphate anion is the only counter-ion equilibrating the charge of the ion exchanging fixed sites, and (iii) the sulphate anion is only present in the interstitial solution of the membrane. In this inner solution, the ratio of the number of hydrogenosulphate anions and the number of sulphate ions increases steadily when the sulphuric acid concentration in the membrane phase is increased.