Degree

Doctor of Philosophy (PhD)

Department

The Gordon A. and Mary Cain Department of Chemical Engineering

Document Type

Dissertation

Abstract

Chemical separations are critical processes for chemical and industrial plants to purify and isolate products however current separation technologies, such as distillation, rely on energy intensive processes. Electrochemical separation processes, such as electrodialysis and electrodeionization, are an energy efficient alternative that are emerging as an alternative for thermal-based separations. Organic acids are weakly ionizable species and susceptible for purification from process streams using electrochemical processes. Recently the fermentation route has garnered greater attention as a means for producing value-added chemicals, such as organic acids, from a renewable feedstock and aiding the circular economy. Some of the challenges electrodialysis faces for organic acid recovery from fermentation broths include requiring chemicals for pH adjustment, poor selectivity for the targeted organic acids, large energy use and fouling of the membranes.

One goal of this dissertation was to investigate bipolar materials, such as Janus bipolar resin wafers for pH adjusting the fermentation streams without the use of chemical additives, thus improving the simplicity of the process. The Janus bipolar resin wafer featured individual layers of anion- and cation-conducting materials with a water-splitting catalyst (aluminum hydroxide nanoparticles) at the interface of the individual layers. This type of interface represents a bipolar junction, and it promotes water splitting to hydroxide and hydronium ions under applied electric fields. For further improvement of capturing organic acids, an imidazolium functionalized anion exchange membrane (AEM) was synthesized and tested as a material for selectively targeting the carboxyl group in organic acid molecules. These AEMs have been successful in carbon dioxide reduction to value-added chemicals. The imidazolium AEMs exhibited exceptional lactate permeability and increased the ionic flux two-fold when benchmarked against a quaternary ammonium functionalized AEM. Molecular dynamics simulations demonstrated that the lactate molecule interacts with a smaller binding distance to the imidazolium group than the quaternary ammonium group and this reduced binding distance is posited to be the dominant mechanism leading to the increased transport properties. Lastly the capture and purification of aromatic acids are a promising product to increase the economic competitiveness of bioderived products to compete with petroleum-derived chemicals. However aromatic acids traditionally have low transport rates through anion exchange membranes which increases separation costs and decrease efficiency. A new, single unit integrated membrane-wafer assembly was devised that minimized the interfacial resistance between the membrane and resin wafer. This new membrane-wafer assembly with reduced interfacial transport resistances increased the capture of p-coumaric acid by three-fold while co-currently reducing energy use for the separation by half. Further, a reengineered electrodialysis gasket was designed to accommodate the material and the design was found to decrease the required ion-exchange membrane area by >60%. This has significant implications for reducing the overall cost of EDI units for ionic separations.

Date

3-21-2022

Committee Chair

Arges, Christopher G.

DOI

10.31390/gradschool_dissertations.5774

Available for download on Sunday, March 19, 2023

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