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Partitioning of Inorganic Contaminants into the Polyamide Active Layers of Thin-film Composite Membranes for Water Purification
- 1. Partitioning of Inorganic Contaminants into the Polyamide Active Layers of Thin-film Composite Membranes for Water Purification Jingbo Wang, Lamar A. Perry, Orlando Coronell Department of Environmental Sciences and Engineering University of North Carolina at Chapel Hill 1
- 2. Background 2
- 3. RO/NF Membrane structure Polyamide ~20-200 nm Polysulfone ~30-50 μm Background 3 Polyester ~40-100 μm Active layer Support layers
- 4. RO/NF Membrane structure Polyamide ~20-200 nm Polysulfone ~30-50 μm Background 4 Polyester ~40-100 μm Active layer Support layers
- 5. Solution-diffusion model Background 5 Feed water Permeate Membrane active layer NaCl partition partition diffusion
- 6. Solution-diffusion model Background 6 𝑩 = 𝑫𝑲/𝜹 𝒎 𝑱 𝒔 = 𝑩 ∙ ∆𝑪 Diffusion coefficient Partition coefficient
- 7. Membrane rejection can be as high as 99.95% Study Mi et al Zhang et al Kotelyanskii et al Partitioning solute arsenic(III) CsCl, KBr Membrane type Thin film composite FT30 Technique RBS RBS Atomistic modeling Partition coefficient 6±2 3.6~8.1 estimation~2 7 Partition coefficients in literature Background
- 8. To develop a simple and accurate method for measuring the partition coefficient of inorganic solutes between aqueous solution and polyamide active layers of RO/NF membranes. 8 Objective
- 10. 10 Quartz Crystal Microbalance (QCM) Materials and methods Constant water/solution flow Isolated active layer (AL) QCM sensor
- 11. 11 NaCl NaCl NaCl QCM sensor QCM sensor Membrane active layer SolutionWater Quartz Crystal Microbalance (QCM) Materials and methods
- 12. 12 Partition coefficient Materials and methods K = CM: solute concentration in membrane, M Cs : solute concentration in solution, M Obtain from QCM CM Cs
- 13. 13 Membranes and solutes Materials and methods Membrane SWC4+ (seawater RO), ESPA 3(brackish water RO) , XLE (brackish water RO), NF90 (nanofiltration) Solutes Alkali metal chlorides, Boric acid Concentration range 0.001M-1M pH=5.3
- 14. Results 14
- 16. 16 Data analysis – membrane charge Results Na+ Cl- Cl- - - Na+ Membrane active layer- - - Na+Na+ Na+ Na+ Cl- Cl- Cl- Na+ Cl- Cl- Cl- Cl- Cl- Cl- Cl- Na+ Na+ Na+ Na+ Na+ Na+ Cl- - - Increasing mass= ion neutralizing fixed charge + partitioning solute Na+ Na+ Na+ Cl- Na+ Na+ Cl- Cl- Na+ Na+ Na+Na+ Cl-Cl- Cl- Cl-
- 17. 17 Baseline of data analysis Results water 0.001M NaCl water 0.01M NaCl 0.1M NaCl 0.4M NaCl 1.0M NaCl 2 Control Sample
- 18. 18 0 150 300 450 600 750 0 0.2 0.4 0.6 0.8 1 CM(ng/cm2) Cs (M) NaCl KCl Boric acid
- 19. 19 0 150 300 450 600 750 0 0.2 0.4 0.6 0.8 1 CM(ng/cm2) Cs (M) NaCl KCl Boric acid K = CM Cs
- 20. 20 Data analysis Results Mass reading from QCM = weight of partitioning solutes, ng/cm2 Unit conversion from ng/cm2 to M CM: solute concentration in membrane, M Cs : solute concentration in solution, M K = CM Cs
- 21. QCM sensorQCM sensor 21 NaCl·xH2O NaCl Scenario D Hydrated solute partitioning + Membrane dehydration QCM sensor NaCl NaCl NaCl NaCl H2O NaCl·xH2O NaCl·xH2O QCM sensor NaCl·xH2O NaCl·xH2O H2O Scenario C Non-hydrated solute partitioning + Membrane dehydration Scenario B Hydrated solute partitioning only Scenario A Non-hydrated solute partitioning only
- 22. 22 Partition coefficient Results 0 0.2 0.4 0.6 0 0.2 0.4 0.6 0.8 1 CM(M) Cs (M) KCl K = 0.64
- 23. Scenario Hydrated solute? Membrane dehydration? K KCl NaCl H3BO3 A No No 0.64 0.63 0.54 B Yes No 0.48 0.31 – C No Yes 0.82 0.86 – D Yes Yes 1.17 0.90 – Table.1. A summary of partition coefficients obtained with SWC4+ membrane at pH=5.3 23
- 24. 24 Partition coefficient Results This study (QCM) Previous studies (RBS) Partition coefficient 0.31~1.17 3.6~8.1
- 25. Conclusion 25
- 26. 26 Conclusion 1. We successfully developed a bench top method to measure solute partition coefficients using a QCM as an analytical tool. 2. The partition coefficients of chloride salts of all alkali metals and of the weak acid studied were all lower than or very close to 1. 3. The results are not in agreement with the results obtained using RBS as an analytical tool in which the partition coefficients of inorganic salts and arsenious acid were reported to be in the 3.6 to 8.1 range.
- 27. Future Work 27
- 28. 28 Future work 𝑱 𝒔 = 𝑫𝑲 ∙ ∆𝑪/𝜹 𝒎 Diffusion coefficient Partition coefficient Solute flux Concentration gradient Active layer thickness
- 29. 29 Acknowledgment • Funding sources • Coronell research group Lin Lin • National Science Foundation (NSF) Grants Opportunities for Academic Liaison with Industry (GOALI) and Chemical and Biological Separations programs under Award#1264690 • NSF Environmental Engineering program under Award#1336532.
- 30. 30 References cited [1] Freger, V., & Ben-David, A. Use of attenuated total reflection infrared spectroscopy for analysis of partitioning of solutes between thin films and solution. Analytical chemistry, 2005, 77(18), 6019-6025. [2] Ben-David, A., Oren, Y., & Freger, V. Thermodynamic factors in partitioning and rejection of organic compounds by polyamide composite membranes. Environ. Sci. Technol. 2006, 40(22), 7023-7028. [3] Geise, G. M., Falcon, L. P., Freeman, B. D., & Paul, D. R.. Sodium chloride sorption in sulfonated polymers for membrane applications. Journal of Membrane Science, 2012, 423, 195-208. [4] Lonsdale, H. K., Merten, U., & Riley, R. L.. Transport properties of cellulose acetate osmotic membranes. Journal of Applied Polymer Science, 1965, 9(4), 1341-1362. [5] Mi, B., Mariñas, B. J., & Cahill, D. G. RBS characterization of arsenic (III) partitioning from aqueous phase into the active layers of thin-film composite NF/RO membranes. Environ. Sci. Technol. 2007, 41(9), 3290- 3295. [6] Zhang, X., Cahill, D. G., Coronell, O., & Mariñas, B. J. Partitioning of salt ions in FT30 reverse osmosis membranes. Applied Physics Letters, 2007, 91(18), 181904. [7] Kotelyanskii, M. J.; Wagner, N. J.; Paulaitis, M. E. Atomistic simulation of water and salt transport in the reverse osmosis membrane FT-30. J. Membr. Sci. 1998, 139, 1–16. [8] Sauerbrey, G. (1959). Verwendung von Schwingquarzen zur Wägung dünner Schichten und zur Mikrowägung. Zeitschrift für physik, 155(2), 206-222. [9] Perry, L. A., & Coronell, O. Reliable, bench-top measurements of charge density in the active layers of thin- film composite and nanocomposite membranes using quartz crystal microbalance technology. J. Membr. Sci. 2013, 429, 23-33.
- 31. Thank you! 31 Jingbo Wang (jingbo_wang@unc.edu) Orlando Coronell (coronell@unc.edu)
Editor's Notes
- -Most widely used RO/NF membranes are thin film composite membranes. -The three layer configuration gives the desired properties of high rejection of undesired materials (like salts), high filtration rate, and good mechanical strength. The polyamide top layer is responsible for the high rejection and is chosen primarily for its permeability to water and relative impermeability to various dissolved impurities including salt ions and other small, unfilterable molecules.
- Water and solute permeation are controlled by the interactions between the permeating molecule and the active layer. My research will focus on polyamide active layer.
- -The starting point for the mathematical description of permeation in all membranes is the proposition, solidly based in thermodynamics, that the driving forces of pressure, temperature, concentration, and electromotive force are interrelated and that the overall driving force producing movement of a permeant is the gradient in its chemical potential. -The solution-diffusion model assumes that when a pressure is applied across a dense membrane, the pressure everywhere within the membrane is constant at the high-pressure. As a result, the chemical potential gradient across the membrane is expressed only as a concentration gradient.
- Parameters in equations correspond to major steps of solute permeation. B is hard to calculated theoretically due to the difficulty of D and K measurement. However, B can be treated with a fitting parameter to obtain from experiments with known Js and ∆𝑪. Diffusion happens in very short amount of time so very difficult to measure. If partition coefficient can be measured, diffusion coefficient can be obtained. All transport phenomenon in 3 steps of solution-diffusion model can be characterized quantitatively.
- There are only 3 papers can be found that studied inorganic molecule partition coefficient in polyamide active layer, including 2 experimental measurement and 1 atomistic modeling. The fact is inconsistent with the result in the literature cited above ***There is no reason to believe that inorganic salts would have partition coefficients larger than 1 b/c there is no reason to believe that there is some specific interaction between polyamide and e.g. sodium or chloride other than electrostatic interactions
- by “partitioning solute” I mean the mobile salt
- Assumptions!!!
- -All partition coefficients in all scenarios are lower or very close to 1.
- -Compared to RBS results, this is much lower. This goes along with the fact of high membrane salt rejection. I trust more the values in our study. -Important limitation of RBS for measuring partition coefficient: inability to characterize partitioning while the active layer is in contact with the solution of interest. Samples need to be dried up which may introduce error
- -Compared to RBS results, this is much lower. This goes along with the fact of high membrane salt rejection. More studies are needed to figure out more accurate value of partition coefficients.
- There are studies of partition coefficients with organic molecules. Regarding transportation of inorganic small molecules, there are studies done with cellulose membranes and sulfonated polymers, but very few TFCs (the main barrier-polyamide active layer is too thin so it’s difficult to measure). Techniques from measuring organic molecules cannot be applied to inorganic small molecules.
- -incomplete polymerization and cross-linking of the PA -Membrane charges--deprotonation of functional groups from R-COOH to R-COO- -carboxylic group pKa=4
- incomplete polymerization and cross-linking of the PA Membrane charges--deprotonation of functional groups from R-COOH to R-COO-