Benny D. Freeman, winner of the 2009 American Chemical Society Award in Applied Polymer Science, is cited for his “pioneering polymer science research that has defined the state of the art in polymer-based gas, liquid, and vapor separation membranes.”
Benny is the Kenneth A. Kobe and Paul D. and Betty Robertson Meek & American Petrofina Centennial Professor of Chemical Engineering at the University of Texas at Austin. He received a B.S. from North Carolina State University in 1983 and a Ph.D. from the University of California, Berkeley in 1988, all in chemical engineering. He was a NATO Postdoctoral Fellow during 1988-89 at the Ecole Supérieure de Physique et Chimie Industrielles de la Ville de Paris (ESPCI) in the laboratories of Professor Lucien Monnerie and Liliane Bokobza. He served on the chemical engineering faculty of North Carolina State University during 1989-2002. He joined the faculty at the University of Texas at Austin in 2002.
Benny supervises the research of a large group of graduate students in the area of membranes for separations. Some highlights from his productive career are given below.
Over the past 40 years, gas separation properties of thousands of polymers were measured. Empirically, a tradeoff is observed between gas permeability and gas selectivity: more permeable polymers are less selective and vice versa. This behavior was widely recognized, but not well understood. Benny developed a model using fundamental facts that predicts this tradeoff behavior [Macromolecules, 32, 375 (1999)]. This publication helped change the direction of research away from Edisonian structure/property studies seeking higher permeability and higher selectivity and towards issues such as membranes with improved chemical stability and membranes based on materials other than polymers (e.g., polymer/inorganic hybrids and inorganic materials).
His group, in collaboration with Dr. Ingo Pinnau at Membrane Technology and Research, Inc., pioneered dispersion of nonporous inorganic nanoparticles in rigid polymers to produce nanocomposites that are, counterintuitively, more permeable and more selective than the native polymer. Their landmark work [Science, 296, 519 (2002)] expanded the portfolio of strategies to rationally manipulate permeation properties.
Removal of organic vapors from mixtures with air or nitrogen and removal of higher hydrocarbons from natural gas requires membranes that selectively remove larger molecules from mixtures with smaller molecules (so-called reverse-selective membranes). Working with Ingo Pinnau and Prof. Toshio Masuda of Kyoto University catalyzed the preparation of libraries of new reverse-selective materials. These materials harness higher solubility of larger molecules to promote high permeability of larger, more soluble components (e.g., n-butane) in mixtures with light gases (e.g., CH4), a concept not previously appreciated. A review article co-authored by Benny [Prog. Polym. Sci., 26, 721-798 (2001)] summarizes the literature in this area.
In contrast to the traditional approach of using rigid, glassy polymers for gas separation materials, Benny’s group has tuned the molecular structure of polar, rubbery polymers to remove CO2 from gas mixtures. For CO2/H2 separations, these materials, based on poly(ethylene oxide) diacrylate, have among the highest combinations of CO2 permeability and CO2/H2 selectivity ever reported, and their mixed gas selectivity improves as CO2 partial pressure increases [Science, 311, 639 (2006)], which is opposite to conventional polymer membranes, where selectivity decreases, often catastrophically, at high CO2 partial pressures. In natural gas separations, these membranes exhibit good CO2/CH4 selectivity at high CO2 partial pressures and are an order of magnitude more permeable than conventional polymers [Adv. Matls., 18, 39 (2006)]. Traditional rigid polymers rely on high diffusivity selectivity to achieve high permeability selectivity whereas these rubbery polymers work based on high solubility selectivity. Membranes based on these materials are being deployed commercially for hydrogen purification.
While working on polymer materials design principles that challenge conventional wisdom, such as those described above, Benny and colleagues from Hanyang University in Seoul, Korea (Professors Young Moo Lee and Ho Bum Park) and CSIRO in Melbourne, Australia (Dr. Anita Hill) pushed the envelope on traditional, highly size selective materials by using biomimetic principles to design gas separation membranes having very high CO2 permeability (1610 Barrer) and high CO2/CH4 selectivity (40) under strongly plasticizing conditions [Science, 318, 254 (2007)] to achieve what has been called a “breakthrough in the development of polymers for gas separation.”
In liquid separations, Benny has challenged conventional notions regarding wastewater purification membrane design. Such membranes are typically porous and the major factor limiting their service life is pore blockage by contaminants, which leads to irreversible loss in membrane flux (membrane fouling). Ingo Pinnau and Benny used thin (< 1 micrometer), nonporous membranes of self-assembled block copolymers to provide continuous hydrophilic channels for water permeation through a mechanically stable, high strength matrix. These membranes have very high water flux but block contaminant transport, reducing membrane fouling by more than 90% for oily wastewater purification, which effectively increases membrane throughput by more than 10x. These membranes are being installed aboard a Navy ship to purify oily wastewater.
A recent collaboration with Professor James McGrath at Virginia Tech has yielded new desalination membranes with previously unattainable property profiles. This research has identified sulfonated polysulfones having uniquely outstanding chlorine resistance and excellent desalination properties. Current desalination membranes are degraded by chlorine, a widely used disinfectant. Consequently, this discovery is important because it eliminates a processing step, dechlorination, which currently limits the productivity of desalination plants. Initial results have garnered worldwide attention [Science, 313, 1088 (2006)].
Benny has organized major ACS and AIChE symposia, chaired the PMSE Division of ACS, chaired the Gordon Research Conference on Membranes, co-chaired the annual meeting of the North American Membrane Society and the International Congress on Membranes, the largest membrane meeting in the world. His students have taken high-profile positions in the field, further extending his influence to the next generation of scientists.
Benny also received the 2008 Award for Excellence in Industrial Gases Technology from the American Institute for Chemical Engineers for his work on gas separations using membranes and a 2008 IBM Faculty Award, which is an internationally competitive award given to university faculty who have an outstanding reputation for contributions to their field. In 2002, he received the PMSE Cooperative Research Award. He has received numerous additional teaching and research awards. He is an Associate Editor of Industrial & Engineering Chemistry Research (published by ACS) and is a member of the Editorial Board of the Journal of Membrane Science.