departmental Seminar

DePARTMENT OF CHEMICAL AND BIOMOLECULAR ENGINEERING
Faculty of Engineering
National University of Singapore
4Engineering Drive4 Singapore 117576
Tel: (65) 65162186 Fax: (65) 67791936 /
TOPIC/TITLE / Novel Functionalized Polybenzimidazole Membranes for Forward Osmosis Applications
SPEAKER / Prof Isabel C. Escobar
HOST / Professor Chung Tai-Shung, Neal
DATE / 7 June 2010, Monday
TIME / 10.30 a.m.
VENUE / E5-02-32
SYNOPSIS / While pressure-driven membrane processes, such as reverse osmosis (RO), have dominated for several decades, new desalination processes are now emerging, such as forward osmosis (FO). Like RO, FO uses a semi-permeable membrane to separate water from dissolved solutes. The semi-permeable membrane acts as a barrier that allows water to pass through while blocking salts. Thus, FO may offer the advantage of rejection of a wide range of contaminants. Instead of employing hydraulic pressure as the driving force for the separation as in RO, FO uses the osmotic pressure gradient across the membrane to induce a net flow of water through the membrane into a draw solution (generally a high concentration salt solution); thus, efficiently separating the fresh water from its solutes. Because it is driven by an osmotic pressure gradient, FO does not require significant energy input, only stirring or pumping of the solutions. This process has a number of salient advantages; for example, FO consumes only about 20-30% of the energy required by other desalination processes and may use very low quality heat, such as the “waste” heat from a power plant, as its energy input. FO may have higher recovery, resulting in less brine discharge to the environment. FO applications in real-world water purification have long been hindered by three key challenging issues:
  • Presently available membranes are mostly made for pressure-driven processes; development of membranes tailor-made and fully effective for osmotically driven FO processes is still in its infancy stage. The support layer of an FO membrane should be much thinner or have very low transport resistance in order to minimize internal concentration polarization and enhance membrane flux.
  • Compared to abundant research in pressure-driven processes, a mechanistic understanding of the unique solute transport phenomena and fouling/cleaning behavior of FO processes is basically lacking. This knowledge gap has severely discouraged systematic development (vs. trial-and-error approaches) of FO membranes.
  • Suitable draw solution that is able to create high osmotic pressure while containing solutes that can be removed efficiently and completely have not been readily available when FO is used as a stand-alone water purification process.
This presentation focuses on the first issue – FO membrane materials. One approach to overcome current obstacles with respect to low efficiency FO membranes is by surface modification or functionalization of existing membranes to provide targeted properties. To develop the ideal membrane, a polybenzimidizole (PBI) membrane was cast as the baseline membrane since PBI membranes have robust mechanical strength, and excellent chemical and thermal stability over a wide range of pH. It is important to design the surface functionality to optimize the balance between maximizing surface charge while minimizing flux decline; thus, three monomeric groups (taurine, ethylene diamine, and para-phenyl diamine) were investigated for the purpose of adding charge to the PBI membrane along with hydrophilicity.
BIOGRAPHY
/ Isabel Escobar an associate professor in the Department of Chemical and Environmental Engineering at the University of Toledo, Ohio. In 1997, she was awarded an Environmental Protection Agency (EPA) Science To Achieve Results (STAR) Fellow, which allowed her to study impacts of water treatment changes on organic parameters relevant to biological stability. In 2000, Isabel Escobar received a Ph.D. degree in Environmental Engineering from the University of Central Florida. That same year, she joined the Chemical and Environmental Engineering Department at The University of Toledo as a tenure-track assistant professor. While at The University of Toledo, she has graduated 2 doctoral student, 8 masters students, and over 10 undergraduate students. Currently, she is advising 3 doctoral students.
Dr. Escobar’s research focuses on developing and/or improving polymeric membrane materials for water/wastewater treatment and water reuse operations through (i) membrane post-synthesis modifications, (ii) the use of dynamic membranes, and (iii) process modifications. These projects are funded by industry, local and federal government, and amount to over US$1,000,000. She has published/submitted over 30 articles in peer-reviewed journals; have made over 70 presentations at national/international conferences, and 10 invited presentations. She was invited to present at the 2004 Gordon Conference Membranes: Materials and Processes. She has also guest edited two special issues of the Environmental Progress Journal and one issue of Separation Science and Technology on Membrane Filtration.
Between 2004 and 2008, she was the Chair of the American Water Works Association (AWWA) Membrane Technology Research Committee and produced a committee report on the state of the art in membrane fouling. She also participated in the planning committee for the 2005 AWWA Membrane Technology Conference, was invited to participate in the student committee for the 2006 North American Membrane Society (NAMS) Annual Conference, and was chosen to chair the 2007 NAMS Annual Conference. She was chosen to chair the 2007 NAMS Annual Conference. In 2009, she was awarded the US YWCA Milestone Award for Education.
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