Novel membrane concept of internal pH control in electrodialysis of amino acids using a segmented bipolar membrane (sBPM)

In electrodialysis of amino acids, pH-changes play an important role in terms of the efficiency of the process. Due to the zwitterionic character of amino acids, small pH changes may result in significant changes in the charge of the amino acids. This decreases either the recovery of the target ions or the product purity. An example of this is the separation of the modification product of serine (Ser) from ethanolamine (Etn) where the decrease in the pH in the feed compartment leads to a decrease in the product purity due to co-transport of alanine (Ala), that becomes charged at low pH. External pH control, like acid/base dosage or the use of a buffer, adds smaller ions that compete with the amino acids during the separation and decreases the process performance. Here we investigate the separation of Etn and Ala using electrodialysis with a segmented bipolar membrane (sBPM). The designed sBPM has both monopolar and bipolar areas. The transport of positively charged Etn at neutral pH is allowed through the monopolar areas without decreasing the separation performance. At the same time water splitting is enhanced at the bipolar areas keeping the pH constant during the experiment. This approach resulted in a recovery of 37% of Etn, while Ala was completely retained in the feed stream. These results show the strength of the concept of using a segmented bipolar membrane to combine ionic transport and water splitting to control the pH simultaneously.