NAMS 2002 Workshop - ICOM 2008

Nanofiltration and Reverse Osmosis I - Membranes – 3
Monday July 14, 3:30 PM-4:00 PM, Maui
Structure-Property Relationships in PEG-Based Hydrogel Membrane
Coatings
A. Sagle (Speaker), University of Texas at Austin
H. Ju, University of Texas at Austin
B. Freeman, University of Texas at Austin, freeman@che.utexas.edu
M. Sharma, University of Texas at Austin
The search for new water resources continues as demand for fresh water
increases worldwide. One potential resource is produced water, a byproduct of
oil and natural gas production, which is a complex emulsion composed of oil and
other organics, salts, and particulate matter. Currently, 92% of produced water is
reinjected, but cost-effective treatment could provide new water resources for
beneficial uses in applications such as irrigation, power generation, and even
human consumption.
Reverse osmosis (RO) membranes are a potential option to purify produced
water because they are capable of removing up to 99.9% of monovalent salts as
well as particulates and emulsified oil. However, RO membranes foul strongly in
the presence of oily feed waters. One proposed solution to reduce membrane oil
fouling is to apply a hydrophilic coating to the membrane surface. An ideal
coating would be hydrophilic, resist oil droplet adhesion, and minimally impact
the water flux and salt rejection of the underlying desalination membrane.
As a first step towards preparing fouling-resistant coatings for RO membranes,
three series of copolymer hydrogel networks were synthesized using
poly(ethylene glycol) diacrylate (PEGDA) as the crosslinker and acrylic acid (AA),
2-hydroxyethyl acrylate (HEA), or poly(ethylene glycol) acrylate (PEGA) as
comonomers. Materials were prepared using varying amounts of PEGDA and
comonomer. Glass transition temperatures in these materials obeyed the Fox
equation. Both water and NaCl transport properties were studied, and ethylene
oxide content and crosslink density influenced these transport properties. For
example, the volume fraction of water sorbed by a 100 mole% PEGDA hydrogel
was 0.61. However, introducing comonomers into the network reduced hydrogel
crosslink density, and in hydrogels having the same ethylene oxide content,
water sorption increased as crosslink density decreased. Water permeability
increased systematically with increasing water sorption, and water permeability
coefficients ranged from 10 - 26 L micron/(m 2 hr bar). NaCl partition coefficients
ranged from 0.36 to 0.53 (g NaCl/cm 3 hydrogel)/(g NaCl/cm3 solution) and
correlated strongly with water sorption. NaCl diffusion coefficients varied little
with polymer composition; in this regard, diffusion coefficient values ranged from