Chemical and Biomolecular Engineering - Research Publications
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ItemSingle and binary ion sorption equilibria of monovalent and divalent ions in commercial ion exchange membranes.(Elsevier, 2020-05-15)The co-ion and counter-ion sorption of monovalent (Na+, K+, Cl- and NO3-) and divalent ions (Ca2+ and SO42-) in commercial Neosepta ion exchange membranes were systemically studied in both single and binary salt systems. The new generation of Neosepta cation exchange membrane (CSE) showed a significant difference in water uptake and co-ion sorption compared to the earlier generation (CMX). Use of the Manning model confirmed that there were significant differences between these membranes, with the estimated value of the Manning parameter changing from 1.0 ± 0.1 for CMX to 2.8 ± 0.5 for CSE. There were fewer differences between the two Neosepta anion exchange membranes, AMX and ASE. In single salt solutions, potassium sorbed most strongly into the cation exchange membranes, but in binary salt mixtures, calcium dominated due to Donnan exclusion at low concentrations. While these trends were expected, the sorption behaviour in the anion exchange membranes was more complex. The water uptake of both AMX and ASE was shown to be the greatest in Na2SO4 solutions. This strong water uptake was reflected in strong sorption of sulphate ions in a single salt solution. Conversely, in a binary salt mixture with NaCl, sulphate sorption fell significantly at higher concentrations. This was possibly caused by ion pairing within the solution, as well as the strongly hydrophobic nature of styrene in the charged polymer. Water uptake was lowest in NaNO3 solutions, even though sorption of the nitrate ion was comparable to that of chloride in these single salt solutions. In the binary mixture, nitrate was absorbed more strongly than chloride. These results could be due to the low surface charge density of this ion allowing it to bond more strongly with the hydrophobic polymeric backbone at the exclusion of water and other ions.
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ItemAn investigation of the impact of fouling agents in capacitive and membrane capacitive deionisation(Elsevier, 2019-05)The effect of organic fouling on both capacitive deionisation (CDI) and membrane capacitive deionisation (MCDI) was studied using two model foulants, the sodium salt of alginic acid and humic acid. Fouling of the activated carbon electrodes in the CDI cell was significant. The salt adsorption fell to 75% and the charge efficiency to 90% of their initial values after 18 cycles of operation with 0.5 mM CaCl 2 and 60 mg L −1 of sodium alginate. Similarly, the salt adsorption fell to 70% and the charge efficiency to 65% of their initial values after 18 cycles of operation with 60 mg L −1 of humic acid. The effect on MCDI was much more limited with these two foulants. The ability to clean the CDI cell with alkali cleaning agents was also investigated. While this cleaning was effective in restoring the salt adsorption, the alkali solution caused erosion of the activated carbon electrode or its PVDF binder, evidenced by an accumulation of carbon within the cleaning solution. Alternative electrode designs or alternative cleaning solutions will be needed if this approach is to be used in systems with similar foulants.
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ItemThe Role of Ion Exchange Membranes in Membrane Capacitive Deionisation(MDPI, 2017-09)Ion-exchange membranes (IEMs) are unique in combining the electrochemical properties of ion exchange resins and the permeability of a membrane. They are being used widely to treat industrial effluents, and in seawater and brackish water desalination. Membrane Capacitive Deionisation (MCDI) is an emerging, energy efficient technology for brackish water desalination in which these ion-exchange membranes act as selective gates allowing the transport of counter-ions toward carbon electrodes. This article provides a summary of recent developments in the preparation, characterization, and performance of ion exchange membranes in the MCDI field. In some parts of this review, the most relevant literature in the area of electrodialysis (ED) is also discussed to better elucidate the role of the ion exchange membranes. We conclude that more work is required to better define the desalination performance of the proposed novel materials and cell designs for MCDI in treating a wide range of feed waters. The extent of fouling, the development of cleaning strategies, and further techno-economic studies, will add value to this emerging technique.
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ItemA comparison of multicomponent electrosorption in capacitive deionization and membrane capacitive deionization(PERGAMON-ELSEVIER SCIENCE LTD, 2018-03-15)In this study, the desalination performance of Capacitive Deionization (CDI) and Membrane Capacitive Deionization (MCDI) was studied for a wide range of salt compositions. The comprehensive data collection for monovalent and divalent ions used in this work enabled us to understand better the competitive electrosorption of these ions both with and without ion-exchange membranes (IEMs). As expected, MCDI showed an enhanced salt adsorption and charge efficiency in comparison with CDI. However, the different electrosorption behavior of the former reveals that ion transport through the IEMs is a significant rate-controlling step in the desalination process. A sharper desorption peak is observed for divalent ions in MCDI, which can be attributed to a portion of these ions being temporarily stored within the IEMs, thus they are the first to leave the cell upon discharge. In addition to salt concentration, we monitored the pH of the effluent stream in CDI and MCDI and discuss the potential causes of these fluctuations. The dramatic pH change over one adsorption and desorption cycle in CDI (pH range of 3.5-10.5) can be problematic in a feed water containing components prone to scaling. The pH change, however, was much more limited in the case of MCDI for all salts.