(496g) Sulfonated Polyamide Thin Film Composite Cation Exchange Membrane (CEM) Synthesis By Electrospray

Cation exchange membranes (CEMs), with the ability to separate cations from anions due to their negative charge groups in their structure, have broad implications in both water and energy sectors. Their properties are crucial for desalination applications, namely electrodialysis (ED) and ED derivatives (bipolar membrane electrodialysis, electrodeionization, reverse electrodialysis), and energy conversion technologies, namely fuel cells and redox flow batteries. Therefore, customizing ion exchange membranes (IEMs) is critical to meet the expectations for these various applications. Numerous ionomers have been developed for ion exchange membranes within years. These ionomers are all processed in the same approach (typically through extrusion or casting). Those ionomers are also combined with several types of nanoparticles to obtain desired properties. However, the production method of ion exchange membranes remains more or less the same in terms of large-scale production, and lab-scale productions could not translate into industrial large-scale productions. Besides, researchers did not focus on customizing the membrane properties based on applications despite different requirements for different applications.

For desalination applications (ED and ED derivatives), mostly used CEMs are divinylbenzene-styrene copolymer with sulfonated charged groups fabricated via solution casting. However, those membranes are highly resistant, expensive compared to other desalination membranes, and their production requires an extensive amount of solvent leading to safety concerns. To circumvent those disadvantages, in-situ polymerization can be an alternative way to make ion exchange membranes, particularly CEMs.

It is known that polyamide membranes are widely used in the desalination process synthesized via interfacial polymerization of m-phenylene diamine (MPD) and trimesoyl chloride (TMC) onto the support layer. Those membranes mainly consist of two layers (active polyamide layer, which functions to reject ions, and support layer which functions to provide physical durability of a relatively thin and fragile selective layer of membrane). Those membranes also have shown relatively low ion exchange capacity due to the low amount of negatively charged COOH- in their structure, but those membranes do not contain enough negatively charged COOH- groups in their structure to achieve a high ion exchange capacity, making these membranes unsuitable for use in ED and ED derivative processes. The method, interfacial polymerization, is relatively inexpensive and easy to use, but it cannot be adapted to make ion exchange membranes with different materials.

To increase the selectivity between cations and anions, ion exchange capacity, and decrease the electrical resistance of IEMs, charged co-monomers such as the sulfonated analog of MPD (SMPD) are necessary. However, the use of charged and uncharged comonomers together can only be applied by electrospray due to the reactivity and solubility difference between charged and uncharged co-monomers. Additionally, the controls over the deposition of materials via electrospray offer precise control over the thickness and indirect control over electrical resistance. The number of negatively charged groups swelling degree of polymer can also be controlled by the amount of incorporation of SMPD directly. This approach allows for the synthesis of ion exchange membranes with tunable parameters, specifically designed for applications such as desalination and allows us to chance adapt inexpensive TFC membrane technology has been used over 40 years in other membrane-based desalination technologies to ED and ED derivative desalination technologies.

In this study, we will synthesize sulfonated polyamide membranes by using both MPD and SMPD and TMC via electrospray by using different support membranes. This novel approach has the potential to control CEMs of selectivity, resistance, and scalability based on process requirements.