Results

Modified Nanofiltration Membranes for Hydraulic Fracturing Water FiltrationBlake Johnson1, Brian Walker2, Dr. Matthew McIntosh2, Dr. Jamie Hestekin1

1Department of Chemical Engineering, 2Department of ChemistryUniversity of Arkansas, Fayetteville

Methods Conclusions• Commercial membranes do not reject enough calcium to recycle.• Reaction to chloromethylate polysulfone nearing desired substitution

percentage.• Further testing and optimization is required before quality membranes

can be produced using modified polymer.• Optimization of casting process may be necessary for flux tests.

Introduction• Nanofiltration can remove divalent salts at a lower osmotic pressure than

reverse osmosis:• Positively charged membranes can separate ions based on ion charge

strength.• Monovalent sodium ions are retained to concentrations of 50%, while

divalent calcium ions are retained to concentrations of near 90%.• Commercial membranes are negatively charged and do not remove

enough calcium for reuse (1,000 ppm).• Polysulfone (PS), while usually used in the formation of ultrafiltration

membranes, can be modified to hold a positive charge.• Filtration tests are conducted using a tangential flow system.• Salt water will be fed at membrane with fresh water permeating the

membrane and salt water being retained.

Background• Flowback water from fracking is highly contaminated:• Organics, hydrocarbons, and high concentrations of salts.• Divalent salts have high concentrations (10,000 ppm) and can

precipitate. These must be removed before reuse.

Chloromethylation1. Dissolve 5 g PS in 250 mL chloroform at 40oC for

24 hours.2. Mix paraformaldehyde and TMSCl in a 1:10:10

mole ratio with 10:1 mole ratio to stannic chloride catalyst to the PS.

3. Mix for 24-120 hours at 50oC.4. Precipitate the reacted polymer in methanol and dry.

Amination5. Mix in a 30 wt% mixture with NMP.6. Cast polymer to 200 µm on a paper backing.7. Immerse in 5oC DI water for phase inversion.8. Immerse in trimethylamine to aminate the

chloromethyl group.9. Immerse in hydrochloric acid to protonate.

• Commercial membranes rejected less than 70% of chlorine (lowest reduction to 3,000).

• Initial FTIR and NMR results were inconclusive and showed no distinct differences between original polysulfone membranes and chloromethylated polysulfone.

• After modification of the reaction procedure, NMR results show significant improvement in substitution of chloromethyl group to polysulfone monomers.

Future Research• Optimize the chloromethlation reaction:• New reagents with higher purity will be tested.• Reaction conditions will be altered to test the effect of increased

temperature, reaction time, and molar ratios of reactants and catalyst.

• Aminate and protonate the chlormethylated membranes.• Run FTIR to determine degree of substitution of amine group.

• Test aminated membranes in filtration system:• Determine water flux and rejection of sodium and calcium.• Test collected flowback solutions to determine actual rejection.

• Blend chlormethylated polysulfone with standard polysulfone to modify charge density.• A fully charged membrane may result in too high of an osmotic

pressure and too much separation of monovalent salts.

Acknowledgements• Funding for research was provided by Flexible Water Solutions, LLC.• Reactions and NMR were carried out in the with the assistance of

Brian Walker and permission of Dr. Matthew McIntosh.• SEM and FTIR were conducted by Kevin Roberts.• Commercial NF membrane flux tests conducted by George Marshall

and Long Tran.• Research was conducted in conjunction with Brigitte Rodgers and Dr.

Dmytro Demydov.

ReferencesGregory, K. B., Vidic, R. D., & Dzombak, D. A. (2011). Water management challenges associated with the production of shale gas by hydraulic fracturing. Elements, 7(3), 181-186. Mulder, M. (1996). Basic principles of membrane technology. (pp. 56-58, 77-78, 299-303) Springer Science & Business MediaAvram, E., Butuc, E., Luca, C., & Druta, I. (1997). Polymers with pendant functional group. III. polysulfones containing viologen group. Journal of Macromolecular Science, Part A, 34(9), 1701-1714. Dong, H., Xu, Y., Yi, Z., & Shi, J. (2009). Modification of polysulfone membranes via surface-initiated atom transfer radical polymerization. Applied Surface Science, 255(21), 8860-8866.

(b) (a)

Fig 6: NMR of reacted polysulfone using updated procedure at 72 hours. Substitution of chloromethyl group (a) at 25%.

(b) (a)

Fig 5: NMR of reacted polysulfone using original procedure at 72 hours. Substitution of chloromethyl group (a) less than 10%.

Fig 3: Reaction mechanism of polysulfone to aminated polysulfone.

Fig 1: Representation of the operation of hydraulic fracturing to extract natural gas from shale.

PumpFeed Tank

Retentate Flow ValvePermeate Flow Valve

Membrane UnitFeed

Retentate

Sample Collection

Permeate

Fig 2: Schematic of a tangential flow filtration unit.

250 400 600 700 8000.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

54.7 54.7

62.3

69.8 69.8

29.234.8

40.4

29.2

40.4

7.1 7.1

25.0

7.1 7.110.7 10.7

20.2 20.2 20.2

49.7

29.1

63.6

49.7

NF3A NF3.1A NF2A NF6 XN45

Pressure psi

Rej

ectio

n %

Fig 4: Calcium rejection from a flowback solution using commercials nanofiltration membranes.