Ammonium Bicarbonate Transport in Anion Exchange Membranes for Salinity Gradient Energy
KAUST Grant NumberKUS-I1-003-13
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AbstractMany salinity gradient energy technologies such as reverse electrodialysis (RED) rely on highly selective anion transport through polymeric anion exchange membranes. While there is considerable interest in using thermolytic solutions such as ammonium bicarbonate (AmB) in RED processes for closed-loop conversion of heat energy to electricity, little is known about membrane performance in this electrolyte. The resistances of two commercially available cation exchange membranes in AmB were lower than their resistances in NaCl. However, the resistances of commercially available anion exchange membranes (AEMs) were much larger in AmB than in NaCl, which would adversely affect energy recovery. The properties of a series of quaternary ammonium-functionalized poly(phenylene oxide) and Radel-based AEMs were therefore examined to understand the reasons for increased resistance in AmB to overcome this performance penalty due to the lower mobility of bicarbonate, 4.59 × 10-4 cm2/(V s), compared to chloride, 7.90 × 10-4 cm2/(V s) (the dilute aqueous solution mobility ratio of HCO3 - to Cl- is 0.58). Most membrane resistances were generally consistent with the dilute solution mobilities of the anions. For a few key samples, however, increased water uptake in AmB solution reduced the ionic resistance of the polymer compared to its resistance in NaCl solution. This increased water uptake was attributed to the greater hydration of the bicarbonate ion compared to the chloride ion. The increased resistance due to the use of bicarbonate as opposed to chloride ions in AEMs can therefore be mitigated by designing polymers that swell more in AmB compared to NaCl solutions, enabling more efficient energy recovery using AmB thermolytic solutions in RED. © 2013 American Chemical Society.
CitationGeise GM, Hickner MA, Logan BE (2013) Ammonium Bicarbonate Transport in Anion Exchange Membranes for Salinity Gradient Energy. ACS Macro Letters 2: 814–817. Available: http://dx.doi.org/10.1021/mz4003408.
SponsorsThis research was supported by funding through the King Abdullah University of Science and Technology (KAUST) (Award KUS-I1-003-13). The authors acknowledge Dr. Nanwen Li and Mr. Sean Nunez for preparing the aPPO and aRadel polymers, respectively. A portion of this research at Oak Ridge National Laboratory's High Flux Isotope Reactor was sponsored by the U.S. Department of Energy, Office of Basic Energy Sciences. The authors acknowledge Dr. Lillin He for assistance with SANS.
PublisherAmerican Chemical Society (ACS)
JournalACS Macro Letters