Di-sulfonated Poly(Arylene Ether Di-sulfonated Poly(Arylene Ether Sulfone) Copolymers as Novel Sulfone) Copolymers as Novel

Candidates for Chlorine-Resistant Candidates for Chlorine-Resistant Reverse Osmosis MembranesReverse Osmosis Membranes  

M. Paul, H. B. Park*, B. D. Freeman*, Z. Zhang, G. Fan, A. Roy, J. S. Riffle and J. E.

McGrath. Macromolecular Science and Engineering

Program, Macromolecules and Interfaces Institute (MII),

Virginia Polytechnic Institute and State University,

Blacksburg, VA 24061 *Center for Energy and Environmental Resources

The University of Texas at Austin$$$- ONR

Objective Develop new reverse osmosis membrane materials showing

excellent chlorine-tolerance, high water flux, good salt

rejection, anti- fouling and arsenic removalproperties relative to the state of the art.

Approach• Synthesize systematic series of directly copolymerized

sulfonated copolymers and vary their structures

• Study fundamental properties (water permeability, salt

permeability and water/salt selectivity) of sulfonated polymers

• Preparing the most promising new materials as thin

membranes.

Project GoalProject Goal

1

Problem: a Shortage of Clean WaterProblem: a Shortage of Clean Water

• 41% of the Earth’s population (2.3 billion) live in water-stressed areas; 3.5 billion by 2025.

• The number of people living without clean, piped water is 1.2 billion (WHO).

• Water shortages limit economic development and threaten human life.

Source: www.abc.net.au/news/newsitems/200609/s1733920.htm1

• There are currently more than 15,000 desalinization plants worldwide (1/4 in US)

• Membranes (reverse osmosis and nano-filtration) provide the most economical desalinization.

• >98% of U.S. water treatment facilities use chlorine - the most economical disinfectant to deactivate pathogenic microorganisms in drinking water

Water Desalinization Report, 42(35), 1, 2006, www.bp.com, Ultrapure Water, 23(3), 14, 2006

Desalination MarketDesalination Market

$0

$200

$400

$600

$800

$1,000

$1,200

$1,400

Sale

s ($ m

illions)

2010

2005

VALUE OF REVERSE OSMOSIS (RO) SYSTEM COMPONENTS

Ann

ual s

ales

($ m

illio

ns)

New

Des

alin

atio

n C

apac

ity

(mill

ion m

3 /d)

Prediction

Issues Facing Commercially Available Issues Facing Commercially Available Membranes for Water DesalinationMembranes for Water Desalination

• Polyamideslow chlorine tolerance prevents use in potable water applications and especially food and beverage, medical, biochemical, and pharmaceutical applications where chlorination and other similar oxidative cleaners or

sterilants are commonly employed.

T. Knoell, Ultrapure Water, 2006, 23, 24-31

Chlorinate(0.2-5 ppm)

Dechlorinate(Free chlorine < 0.01 ppm)

Polyamidedesalinationmembrane

Rechlorinate(1-2 ppm)

Feed water

Product water

To protectmembranefrom chlorine

Costly Pretreatment Steps

Search for Chlorine Resistant RO Search for Chlorine Resistant RO Membranes-Previous Sulfonated Polymer Membranes-Previous Sulfonated Polymer

StudiesStudiesH3C

H3C

O

SO3H

n

Sulfonated poly(2,6-dimethyl phenylene oxide) (SPPO)

C

CH3

CH3

O S

O

O

SO3H

n

Sulfonated polysulfone (SPS)

•Fouling and chlorine tolerance of sulfonated polysulfone was superior to that of aromatic polyamides.

Parise et al., Ultrapure Water, pp. 54-65 (Oct. 1987); Allegrezza et al., Desalination, 64, 285-304 (1987).

Howerver, manufacturing reproducibility issues and inability to prepare a product with flux/rejection capabilities equivalent to aromatic polyamides led to limited commercial success.

VT Breakthrough- VT Breakthrough- Chlorine Tolerant Chlorine Tolerant sulfonated Poly (arylene ether sulfone) ROsulfonated Poly (arylene ether sulfone) RO

MembranesMembranes

0 4000 8000 12000 16000

40

50

60

70

80

90

100

SW30HR(FilmTec)

BPS 40N

NaC

l rej

ection (%

)

Chlorine exposure (ppm-hours)

BPS 40H

33 h16 h0 h 24 h8 h

Cross-flowpH = 9.5Feed = 2000 ppmNaClPressure = 400 psigFlow rate = 0.8 GPMChlorine = 500 ppm

BPS 40 (X = 0.4; M = H+ or Na+)

ChlorinateNew

membraneFeedwater

Productwater

Cost savings via elimination of dechlorination required by current membranes

Extended membrane lifetime

• reproducible to manufacture & stable against chemical attack.

• Access to structural variations (e.g., new comonomers, block copolymers, controlled crosslink structures, etc.) to achieve high rejection and high flux.

Sulfonated Poly (arylene ether sulfone) (BPS)

Proposed New Process with VT Proposed New Process with VT MembraneMembrane

VT membrane (BPS) outperforms commercial polyamide membrane (SW30HR) under chlorine exposure

S

O

O

ClClS

O

O

ClCl

NaO3S SO3Na

OH Ar OH

CH3

CH3

CF3

CF3

O S

O

O

O

SO3HHO3S

Ar O S

O

O

O Ar

S

O

O

ClCl S

O

O

ClCl

NaO3S SO3Na

+

140 oC / 4 h 190 oC / 24 h

+

K2CO3

NMP / Toluene

Ar =

n 1-n

H2SO4

SO3

110 oC 6 h

NaCl NaClNaOH

x

pH~7

O S

O

O

O

SO3-M+

+M-O3Sx

O S O

O

O 1-xn

CO

Hydrophilic Hydrophobic

Acronym: BPS-xx Bi Phenyl Sulfone: salt (M =Na+) form (BPS), acid (M = H+) form (BPSH) xx= molar fraction of disulfonic acid units, e.g., 30, 40, etc.Copolymer Synthesis by Nucleophilic Aromatic

Substitution

Disulfonated Poly(arylene ether sulfone) (BPS)

Effect of Sulfonation Degree (Ion Exchange Capacity) on Effect of Sulfonation Degree (Ion Exchange Capacity) on Water and Salt Transport in Random BPS CopolymersWater and Salt Transport in Random BPS Copolymers

0

1

2

3

4

5

0.8 1 1.2 1.4 1.6 1.8

Wat

er p

erm

reab

ilit

y (L

.m

/m2 .h

.bar

)

IEC value (meq/g)

O

S

O

O

O O S

O

O O

HO3S SO3H

x 1-x

80

85

90

95

100

0.8 1 1.2 1.4 1.6 1.8

NaC

l rej

ect

ion

(%

)

IEC value (meq/g)

B P S 20H

B P S 30H

B P S 35H

B P S 40HB P S 20H

B P S 30H

B P S 35H

B P S 40H

2000 ppm NaC l400 ps i25 oCC ros s flow

0

20

40

60

80

100

70

40

12

4

70

35

1

95

2

50

90

20

30

10

1015

Sulfonation degree

Rej

ectio

n (%

)

Sulfonation degreeNa

2SO

4 NaCl MgSO4 MgCl

2 CaCl2

Various Types of Salt RejectionVarious Types of Salt Rejectionby BPS in Comparison to Commercial Membraneby BPS in Comparison to Commercial Membrane

Salt rejection: Na2SO4 > KCl ≥ NaCl > MgSO4 > MgCl2 > CaCl2

• Dead-end• Feed pressure: 400 psig• Feed temperature: 25 oC

0

20

40

60

80

100

MgCl2

KCl MgSO4

CaCl2

Na2SO

4

Sal

t re

ject

ion (%

)

NaCl

BPS 35H

(IS: Ionic strength) IS (M) = 0.03 0.01 0.01 0.04 0.01 0.03

Commercial SPS composite membranes(Hydranautics)

(www.membranes.com)Chemically tolerant NF membranes for

aggressive industrial application

BPS Type Materials with NaCl Rejection > BPS Type Materials with NaCl Rejection > 97%97%

Name Commentmol%

sulfonation or IEC

Water permeability

(L.μm/m2.h.bar)

NaCl rejection (%)

PAEB35Random

copolymer (salt form)

35 mol% 0.24 97.8

PA40Random

copolymer(salt form)

40 mol% 0.43 97.5

6F25PAEB35Random

copolymer(salt form)

35 mol% 0.64 98.0

BPS20Random

copolymer (acid form)

20 mol% 0.11 98.7

Epoxy-crosslinked

BPS50

Crosslinked(salt form)

50 mol% 1.41 97.2

BPS35:RadelBlend (90:10)

Blend(salt form)

35 mol% 0.71 97.2

BPS35:6F35Blend (95:5)

Blend(salt form)

35 mol% 0.86 98.0

BPSH-15-BPS-15

Block copolymer(salt form)

IEC = 1.36 meq/g

0.05 99.2

Lab-Scale FabricationLab-Scale Fabrication of Thin-Film Thin-Film Composite Membrane from BPS-40 Composite Membrane from BPS-40

0.5 % (wt./vol.)Polymer solution

in formic acid (1 day)

Drying wet support (PSf)

at 105 oC (5 min)

Brush coating(2~3 times)

Air drying at 50 oCfor 5 min.

Chlorine-Tolerance ofChlorine-Tolerance ofThin-Film Composite (TFC) MembranesThin-Film Composite (TFC) Membranes

30

40

50

60

70

80

90

100

0 5000 10000 15000 20000

NaC

l re

ject

ion

(%

)

Chlorine exposure (ppm-hours)

0

0.5

1

1.5

2

2.5

3

0 5 10 15 20 25 30 35

Pe

rme

ate

flu

x (

L/m

2 .h.b

ar)

Chlorine exposure time (hr)

Cross-flow, pH = 9.5, Feed = 2000 ppm NaCl, Pressure = 400 psig, Flow rate = 1.2 GPM, Chlorine = 500 ppm

30 h20 h0 h 25 h10 h

BPS 40H TFC

BPS 40H TFC

SW30HR (FilmTec)

1 GFD/psi = 24.6 LMH/bar

80

85

90

95

100

1 2 3

pH = 4.5pH = 8

As

(V) re

ject

ion (%

)

BPS 30H BPS 40H BPS 40N80

85

90

95

100

1 2 3

pH = 4.5pH = 8

As

(III)

rej

ection (%

)

BPS 30H BPS 40H BPS 40N

Arsenic RejectionArsenic Rejectionof Sulfonated Copolymer Membranesof Sulfonated Copolymer Membranes

O

S

O

O

O O S

O

O O

SO3-M+

-O3S

x 1-x

+M

Sulfonated poly(arylene ether sulfone) (M = H+ or Na+)

A: BPS 30H, B: BPS 40H, C: BPS 40N

Summary: Trade-off Relationship Between Summary: Trade-off Relationship Between Permeate Flux and NaCl Passage Permeate Flux and NaCl Passage

0.01 0.1 1 10 100100

10

1

0.1

0.01

NaCl

Pas

sage

(%)

Permeance (L/(m2.h.bar))

PA (for brackish water)

PA (for sea water)

PA (for NF)

Millipore SPS

SPS (this work)

SPS composite (BPS40)

Conclusions & Future WorksConclusions & Future Works

Sulfonated poly(arylene ether sulfone) copolymer membranesSulfonated poly(arylene ether sulfone) copolymer membranes

• Stable and reproducible properties• High water permeability• Moderate salt rejection (between that of NF and RO) with excellent chlorine tolerance • Excellent arsenic removal properties

• Further fundamental studies to define structure/property relations.

• Prepare and characterize chlorine-resistant composite membrane with higher salt rejection.