Capacitive deionization has gained increasing interest for the desalination of brackish water. Within the CDI process, ions are stored in an electric double layer at the electrode-electrolyte interface due to a potential bias or due to chemical surface charges (inverted CDI). The ions are released upon releasing or reversing the potential bias. This principle works well for simple salts; here we show that this mechanism can also be applied to macro molecules such as proteins. Contrary to salts, proteins are known to adhere to surfaces, therefore polyelectrolytes were incorporated into the electrodes that carry either positive, or negative charge to bind the proteins, or prevent undesired adsorption (zwitter-ionic polymers). The proteins can be stored at the charged polymers that subsequently can be regenerated upon applying a potential bias, therewith releasing the proteins. In our experimental work, we used various options to examine the potential of (inverted) capacitive protein separation: cationic, anionic or zwitterionic polymers were either mixed into the matrix of the electrodes (activated carbon or graphene oxide is used as base material), or attached to their surface. Subsequently the electrodes were paired and assembled into a flow cell, which was connected to a conductivity and UV meter. These sensors allowed us to trace the ion and protein concentration in the outlet, while applying different potential biases. We found that next to the ion concentration also the protein content in the outlet can be alternated using electrochemical stimuli, and we will report on the proof of principle that we obtained. While the ion concentration decreases when applying a potential bias the protein concentration increases. After releasing the bias the trends switch, ions get released and proteins adsorb. The amount of ion and protein separation can further be influenced by the choice of polyelectrolytes in the electrode. We compare various process conditions and use classical (adsorbed amount) and new (exergy loss) parameters to compare efficiency, also with established methods. This separation procedure can be of great interest for the food, chemical and pharmaceutical industry that aim at purification or desalination of protein streams, and it opens new application fields for CDI technology.

Capacitive protein separation: From electrode preparation to process design that also affects salt removal

2019 Fall National Meeting

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