Online Gas-Free Electrodialytic KOH Eluent Generator for Ion Chromatography

An online gas-free KOH electrodialytic eluent generator (EDG) with two-membrane configuration is described for ion chromatography (IC). A central eluent channel is separated from two outer regenerant channels bearing KOH solution (or one is water) by stacked cation-exchange membranes (sCEMs) and a bipolar membrane (BPM) plus stacked CEMs (BPM-sCEMs), in which the anion-exchange membrane (AEM) of BPM is facing the central channel (the anode direction). Independent fluid input or output ports address all channels. One platinum screen electrode is put in each outer channel, and the sCEM side is anode with respect to the cathode of the BPM-sCEM side. Under the electric field, enhanced water splitting at the intermediate layer of BPM will occur, offering hydroxide and hydronium; hydroxide electromigrates through AEM into the central channel, while the potassium of KOH feed solution at the anode migrates into the central channel to combine with hydroxide to form a solution of KOH. Because the central eluent channel is spatially isolated from both electrodes, the generated KOH solution is gas-free and no gas-removal device is required. More important, the AEM side of BPM is contactless with the alkaline solution, nearly avoiding possible AEM degradation when immersed into concentrated alkaline solution. This ensures long-term running stability of the EDG and high purity of the produced KOH solution (as indicated by the typical suppressed background conductance of 0.28 μS/cm). The EDG has a pressure tolerance (at least 21 MPa), and the produced KOH concentration is up to 101 μeq/min with near-unity faradaic efficiency. When operated in both isocratic and gradient modes, the EDG demonstrates excellent reproducibility, as indicated by the retention time of RSD ≤ 0.08% and the peak area of RSD ≤ 0.6%. To the best of our knowledge, this is the first description of gas-free EDG matched conventional IC system.