Charged polymer membranes are widely used for water purification applications involving control of water and ion transport, such as reverse osmosis and electrodialysis. Efforts are also underway worldwide to harness separation properties of such materials for energy generation in related applications such as reverse electrodialysis and pressure retarded osmosis. Additional applications, such as energy recovery ventilation and capacitive deionization, rely on polymer membranes to control transport rates of water, ions, or both. Improving membranes for such processes would benefit from more complete fundamental understanding of the relation between membrane structure and ion sorption, diffusion and transport properties in both cation and anion exchange membrane materials. Ion-exchange membranes often contain strongly acidic or basic functional groups that render the materials hydrophilic, but the presence of such charged groups also has a substantial impact on ion (and water) transport properties through the polymer.
We are exploring the influence of polymer backbone structure, charge density, and water content on ion transport properties. Results from some of these studies will be presented, focusing on transport of salt, primarily NaCl, through various neutral, positively charged and negatively charged membranes via concentration gradient driven transport (i.e., ion permeability) and electric field driven transport (i.e., ionic conductivity). One long-term goal is to develop and validate a common framework to interpret data from both electrically driven and concentration gradient driven mass transport in such polymers and to use it to establish structure/property relations leading to rational design of membranes with improved performance.
Ion sorption and permeability data were used to extract salt diffusion coefficients in charged membranes. Concentrations of both counter-ions and co-ions in the polymers were measured via desorption followed by ion chromatography or flame atomic absorption spectroscopy. Salt permeability, sorption and electrical conductivity data were combined to determine individual ion diffusion coefficients in neutral, cation exchange and anion exchange materials. Manning’s counter-ion condensation models and the Mackie/Meares model were used to correlate and, in some cases, predict the experimental data.
Benny Freeman is the William J. (Bill) Murray, Jr. Endowed Chair of Engineering in the Chemical Engineering department at The University of Texas at Austin. He is a professor of Chemical Engineering and has been a faculty member for 30 years. He completed graduate training in Chemical Engineering at the University of California, Berkeley, earning a Ph.D. in 1988. In 1988 and 1989, he was a postdoctoral fellow at the Ecole Supérieure de Physique et de Chimie Industrielles de la Ville de Paris (ESPCI), Laboratoire Physico-Chimie Structurale et Macromoléculaire in Paris, France. Dr. Freeman was a member of the chemical engineering faculty at NC State University from 1989 – 2002, and he has been a professor of chemical engineering at The University of Texas at Austin since 2002. Dr. Freeman’s research is in polymer science and engineering and, more specifically, in mass transport of small molecules in solid polymers. His research group focuses on structure/property correlation development for desalination and gas separation membrane materials, new materials for hydrogen separation, natural gas purification, carbon capture, and new materials for improving fouling resistance in liquid separation membranes. He leads the Center for Materials for Water and Energy Systems (M-WET), a DOE Energy Frontier Research Center and serves as Challenge Area Leader for Membranes in the National Alliance for Water Innovation (NAWI), a five-year, DOE sponsored Energy-Water Desalination Hub to address critical technical barriers needed to radically reduce the cost and energy of water purification.
His research is described in nearly 450 publications and 30 patents/patent applications. He has co-edited 5 books on these topics. He has won a number of awards, including a Fulbright Distinguished Chair in Disruptive Separations (2017), Fellow of the North American Membrane Society (NAMS) (2017), the Distinguished Service Award from the Polymeric Materials: Science and Engineering (PMSE) Division of the American Chemical Society (ACS) (2015), Joe J. King Professional Engineering Achievement Award from The University of Texas (2013), American Institute of Chemical Engineers (AIChE) Clarence (Larry) G. Gerhold Award (2013), Society of Plastics Engineers International Award (2013), Roy W. Tess Award in Coatings from the PMSE Division of ACS (2012), the ACS Award in Applied Polymer Science (2009), AIChE Institute Award for Excellence in Industrial Gases Technology (2008), and the Strategic Environmental Research and Development Program Project of the Year (2001). He is a Fellow of the AAAS, AIChE, ACS, and the PMSE and IECR Divisions of ACS. He has served as chair of the PMSE Division of ACS, chair of the Gordon Research Conference on Membranes: Materials and Processes, President of the North American Membrane Society, Chair of the Membranes Area of the Separations Division of the AIChE, and Chair of the Separations Division of AIChE. His research has served as the basis for several startup companies, including Energy-X and NALA Systems.
Reilly Lecture sponsored by the Department of Chemical and Biomolecular Engineering