Partitioning of Inorganic Contaminants into the Polyamide Active Layers of Thin-film Composite

Membranes for Water Purification

Jingbo Wang, Lamar A. Perry, Orlando CoronellDepartment of Environmental Sciences and Engineering

University of North Carolina at Chapel Hill

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Background

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RO/NF Membrane structure

Polyamide ~20-200 nm

Polysulfone ~30-50 μm

Background

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Polyester ~40-100 μm

Active layer

Support layers

RO/NF Membrane structure

Polyamide ~20-200 nm

Polysulfone ~30-50 μm

Background

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Polyester ~40-100 μm

Active layer

Support layers

Solution-diffusion modelBackground

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Feed water

Permeate

Membrane active layer

NaCl partition

partition

diffusion

Solution-diffusion modelBackground

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𝑩=𝑫𝑲 /𝜹𝒎

𝑱 𝒔=𝑩 ∙∆𝑪

Diffusion coefficient Partition coefficient

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

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Partition coefficients in literatureBackground

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.

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Objective

Materials and Methods

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Quartz Crystal Microbalance (QCM)

Materials and methods

Constant water/solution flow

Isolated active layer (AL)

QCM sensor

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NaClNaCl

NaCl

QCM sensor QCM sensor

Membrane active layer

SolutionWater

Quartz Crystal Microbalance (QCM)

Materials and methods

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Partition coefficientMaterials and methods

K =

CM: solute concentration in membrane, M

Cs : solute concentration in solution, M

Obtain from QCM

CM

Cs

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Membranes and solutesMaterials 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

Results

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QCM raw dataResults

water

0.001M NaCl

water

0.01M NaCl

0.1M NaCl

0.4M NaCl

1.0M NaCl

2 ControlSample

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Data analysis – membrane chargeResults

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-

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Baseline of data analysisResults

water

0.001M NaCl

water

0.01M NaCl

0.1M NaCl

0.4M NaCl

1.0M NaCl

2 ControlSample

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0 0.2 0.4 0.6 0.8 10

150

300

450

600

NaCl KCl

Boric acid

Cs (M)

CM

(ng/

cm2)

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0 0.2 0.4 0.6 0.8 10

150

300

450

600

NaCl KCl

Boric acid

Cs (M)

CM

(ng/

cm2)

K =CM

Cs

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Data analysisResults

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

QCM sensorQCM sensor

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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

partitioningonly

Scenario A

Non-hydrated solute

partitioning only

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Partition coefficientResults

0 0.2 0.4 0.6 0.8 10

0.2

0.4

0.6 KCl

Cs (M)

CM

(M) K = 0.64

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

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Partition coefficientResults

This study(QCM)

Previous studies(RBS)

Partition coefficient 0.31~1.17 3.6~8.1

Conclusion

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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.

Future Work

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Future work

𝑱 𝒔=𝑫𝑲 ∙∆𝑪 /𝜹𝒎

Diffusion coefficient Partition coefficient

Solute fluxConcentration

gradientActive layer thickness

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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.

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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.

Thank you!

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Jingbo Wang (jingbo_wang@unc.edu)Orlando Coronell (coronell@unc.edu)