vanderbruggen_nanofiltration

7/27/2019 VanderBruggen_Nanofiltration

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Nanofil tration: drawbacks

for application

- research challenges

Bart Van der Bruggen

Department of Chemical Engineering

K.U.Leuven, [email protected]

BMG-NMG Posterdag

Antwerpen (BE), 26 Nov. 2008

Applied

pressure

Flux range

(l/m/h/bar)

Transport

mechanism

Application range

Microfiltration 0.1-2 bar > 50 Sieving Removal of particles

Ultrafiltration 1-5 bar 10-50 Sieving Removal of

macromolecules

Nanofiltration 5-15 bar 1.4-12 Sieving

Diffusion

Charge effects

Removal of

multivalent ions and

relatively (small)

organic molecules

Reverse

osmosis

10-100 bar 0.05-1.4 Diffusion Removal of ions and

(small) organic

molecules

Nanofiltration compared to other pressure driven

membrane processes
mailto:[email protected]:[email protected]


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Nanofil tration: some history 1970s: low pressure reverse osmosis becomes

nanofiltration (NF)

1980s: NF applications: softening, NOM removal in

drinking water treatment

1987: first journal publication on NF

BMG-NMG Posterdag



nanofiltration (NF)



1987: first journal publication on NF- Conlon, W.J., McClellan, S.A., 1989. Membrane softening: treatment

process comes of age, J. AWWA 81(11), 47-51.

- Eriksson, P., 1988. Nanofiltration extends the range of membrane filtration.

Environm. Prog. 7 (1), 58-62.

- D. Watson, C.D. Hornburg, Low energy membrane nanofiltration for

removal of color organics and hardness from water supplies, Desalination

72 (1989) 11


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nanofiltration (NF)



1987: first journal publication on NF

1990s: process coming to age- Scientific research booming

- Applications from small scale to large scale (Mry-sur-Oise)

>2000: fouling resistant membranes, ceramic NF

membranes, solvent resistant NF

BMG-NMG Posterdag


Research on nanofiltration

1

10

100

1000

10000

1985 1988 1991 1994 1997 2000 2003 2006

Year

Number

ofpublications

UF

NF

RO


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Some principles Tight vs. loose NF membranes

near RO

Ca, SO4 > 99%

Na, Cl 60-90%

MW 200 organics

PA, PI

Tight vs. loose NF membranes

near UF

Ca, SO4 90-99%

Na, Cl 10-60%

MW 500-1000organics

P(E)S, ceramics

BMG-NMG Posterdag


Process performance Flux equation: Hagen-Poiseuille

Rejection:

(MWCO?)

Spiegler & Kedem:

surface porosity ()

pore radius (r)

tortuosity ()

membrane thickness (x)

x

PrJ

8

.

100).1((%),

,

if

ip

ic

cR

RF

F

.( )

.

1

1).

1exp( J

PF

s


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Not only MW

02040

6080

100

0 50 100 150 200Molecular weight

Reten

tion(%

Desal-HL-51, MWCO

= 150-300

Desal-HL-51

0

20

40

60

80

1 00

- 4 - 2 0 2 4

log P

Retentie(%)

BMG-NMG Posterdag


Molecular weight cut-offCut- off curve: sharp or diffuse

0%

10 0%

Rejection(%)

10 0 500 750 1 000


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NF: Challenges?1. Advanced Membrane Technology and

Applications (Eds. Norman N. Li,

Anthony G. Fane, W.S. Winston Ho,

Takeshi Matsuura), Wiley, 2008.

2. Van der Bruggen, B.; Mnttri, M.;Nystrm, M. Drawbacks of applying

nanofiltration and how to avoid them: a

review. Separ. Purif. Technol. 2008,

63, 251-263.

BMG-NMG Posterdag


NF: ChallengesI. avoiding membrane fouling, and possibilities to

remediate

II. improving the separation between solutes that can be

achieved

III. further treatment of concentrates

IV. chemical resistance and limited lifetime of membranes

V. insufficient rejection of pollutants in water treatment

VI. the need for modelling and simulation tools


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NF: Challenges Not exhaustive in particular towards engineering

aspects

- module development for special applications

(solvents, extreme pH)

- membrane configurations with improved performance

(surface area per volume, hydrodynamics) NF applications will not wait for answers and are already

successful improvements will broaden up the range

and make life easier

BMG-NMG Posterdag


Membrane fouling Interactions to be understood at nanoscale

Pretreatment, membrane cleaning, limited recoveries and

feed water loss, and short li fetimes of membranes

0

20

40

60

80

100

120

0 100 200 300 400

time (min)

relativeflux(%)

NF270 (HP11)

water cleaning NF270 (HP11)

NF270 (rim cleaner)

water cleaning NF270 (rim cleaner)

0

20

40

60

80

100

120

0 100 200 300 400

time (min)

relativeflux(%)

NFPES10 (HP11)

water cleaning NFPES10 (HP11)

NFPES10 (rim cleaner)

water cleaning NFPES10 (rim cleaner)


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Parameters influencing NOM fouling

Value NOM fouling Rate Cause

Ionic strength concentration Increased Increased Electrostatic repulsion

pH High pH

Low pH

Increased

Increased

Hydrofobic forces

Electrostatic repulsion

Divalent cations Presence Increased Electrostatic repulsion and bridging

between NOM and surface

NOM fraction Hydrophobic

Hydrophilic

Increased

Decreased

Hydrophobicity

Molecule or membrane charge High charge Increase Electrostatic repulsion

CP High Increased

Surface morphology Higher Increased Valley blocking

Permeate flux (High recovery) Higher Increased Hydrophobicity

Pressure Higher Increased Compaction

BMG-NMG Posterdag


Membrane fouling

Fouling vs. compaction

Membrane thickness

170 m Membrane thickness

150 m


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Membrane fouling Organic fouling

- Adsorption on the membrane surface

- Parameters of influence: log P, dipole moment, solubility

membrane hydrophobicity (contact angle)

- Electrostatic attraction repulsion for charged solutes

Colloidal fouling- Related to surface roughness of membranes

- Hydrophobicity and charge interaction play a role

- Concentration and size of the colloids

BMG-NMG Posterdag


Membrane fouling Scaling

- Calcium carbonate, gypsum, barium/strontium sulphate and silica

- Thermodynamical problem module design?

Biofouling

- Mainly bacteria and (in some cases) fungi

- Biofilms 20-30 m

- Indirect problems: cake layer, exopolymeric substances


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Solutions to fouling Pretreatment

- When? Provide UF quality feed water

- Ultrafiltration and microfiltration, ozonation or UV/H2O2 oxidation,

adsorption (PAC) and flocculation

BMG-NMG Posterdag


Solutions to fouling Cleaning

- When? In al l cases

- Physical cleaning by flushing (backflush, forward flush, reverse

flush), scrubbing, air sparging, vibrations and sonication

- Chemical cleaning: hydrolysis, saponification, solubilisation,dispersion, chelation, and peptisation

- Various cleaning solutions and protocols


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Solutions to fouling Membrane modifications

- Hydrophilic groups into a polymeric structure: grafting, ion beam

irradiation, plasma treatment, adsorption, self-assembling

nanoparticles

- Ceramic membranes (titania, alumina, zirconia)

- Development, upscaling needed

BMG-NMG Posterdag


Solutions to fouling Membrane manufacturing

- Surface charge

- Surface roughness

- Biofouling: e.g., silver nanoparticles

25 years of experience but many aspects

yet to learn


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Synthesis of polymeric membranes

Parameters determining the

membrane structure:

wt% polymer

Type of solvent

Temperature

Air humidity

Additives

BMG-NMG Posterdag


The concept of crit ical flux The membrane has a limited

capacity

- represents the shift from repulsive

interaction (dispersed matter-

polarised layer) to attractive

interaction (condensed matter-deposit)

- Sustainable flux: protection

against fouling

- depends on hydrodynamics, feed

conditions and process time0

20

40

60

80

100

120

0 2 4 6 8 10 12 14 16

Pressure, bar

Flux,l/(m2h)

a)


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Membranes are not an absolute barrier

Filtration in series: removal of a given compound

increases with each step added

Rejection is not only determined by solute size

vs. pore size

II. Can we achieve complete

separation?

0.110 1 0.01

BMG-NMG Posterdag


Typical rejection curve

01020304050

60708090

100

0 50 100 150 200 250 300 350 400 450 500

Molecular size

Rejectio

n(%)


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Ideal rejection curve

0102030405060708090

100

0 50 100 150 200 250 300 350 400 450 500

Molecular size

Rejection(%)

BMG-NMG Posterdag


and possibly:

01020304050

60708090

100

0 50 100 150 200 250 300 350 400 450 500

Molecular size

Rejectio

n(%)


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How to achieve this?

Membrane stack: N membranes in a

single module

N modules in series

BMG-NMG Posterdag


Combined cascades:

distillationTotal condensor

Feed

Overheadvapour

BoilupN

2

1

Distillation

f

Reflux drum

Enrichment section

Stripping section

Feed tray

Bottom products

Partial reboiler

Reflux Distillate


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Membrane cascades

2

3

BMG-NMG Posterdag


Rejection curvesN30F

0

10

20

30

40

50

60

70

80

90

100

0 100 200 300 400 500 600

MW

R

ejection(%)

(1)

(2)

(3)

NF270

0

10

20

30

40

50

60

70

80

90

100

0 100 200 300 400 500 600

MW

Rejection(%)

(1)

(2)

(3)

Desal-HL-51

0

10

20

30

40

50

60

70

80

90

100

0 100 200 300 400 500 600

MW

Rejection(%)

(1)

(2)

(3)

Desal-5-DL

0

10

20

30

40

50

60

70

80

90

100

0 100 200 300 400 500 600

MW

Retjection(%)

(1)

(2)

(3)


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Separation of solutes from

one another?

Applications in pharmaceutical industry

Diafiltration may be possible for product

recovery, not for separation

Food industry: xylose/glucose, stevioside, tailor-made milk products

BMG-NMG Posterdag


Ion separation, organic-

inorganic separation?

NF270, rejection (single passage) NaCl 59% -

CaCl2 63% - Na2SO4 96%

Rejections too high to apply in cascade (no

separation)

Rejections organic inorganic not feasible

Membrane optimisation: lower salt rejections

required


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Ion separation, organic-

inorganic separation?

N30F: rejection (single passage) NaCl ca. 10% -

rejection maltose 63%

In cascade: NaCl overall rejection ca. 20% -

rejection maltose 97%

Not (yet) perfect

Membrane tailoring in terms of separation

potential

BMG-NMG Posterdag


V. Insufficient rejection of

individual compounds

Originally: partial softening, bulk organics

removal

New trend = complete absence of all possible

pollutants, even at ultra-low concentrations

- Subjective customer criterion not necessarily based

on risks or toxicity

- But a reality


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Nitrate removal

Health effects?

- None for adults

- Methemoglobinemia (children < 6 m) related to nitrite

- Synergetic toxic effects?

Standards are under debate

NF: partial removal

BMG-NMG Posterdag


Membrane Nitrate rejection (%)

NF90 94-98

HG19 9

SX10 32

SV10 28

SX01 25

BQ01 12

MX07 8

NF70 76

NF45 16

UTC-20 32

UTC-60 11

MPS44 90 50

NF70 90 85

Desal 60 33

ESNA-1 LF 75-80

NF 65-80

NF90 85-95

OPMN-K 25-50

OPMN-P 40-70


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Boron removal

Micronutrient with narrow range between deficiency andexcess

Not a primary target compound but the times they area-changin ( low concentration by preference)

Neutral pH: undissociated boric acid, removal with

complexes (e.g., mannitol) Acid conditions (or alkaline conditions): removal in ionic

form

NF has a disadvantage

BMG-NMG Posterdag


Organic micropollutants

Including: natural and synthetic hormones; industrialpollutants such as phthalates, alkylphenols, bisphenol-A,PCBs (polychlorinated biphenyls), PAHs (polyaromatichydrocarbons), NDMA (N-nitrosodimethylamine) and

MTBE (methyl tertiarybutyl ether); pesticides;pharmaceuticals; personal care products and disinfectionby-products (DBPs)

priority compounds in view of drinking water production:Verliefde, Environ. Pollut. 2007, 146 (1), 281-289


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Organic micropollutantsCompon ent Type MW Log Kow S iz e [nm] pKa Compone nt Type MW Log Kow S iz e [nm] pKa

2-naftol Surrogate 144 2,7 9,5 Estrone EDC 270 3,43 0,8 10,4

4-phenylphenol EDC 170 3,28 9,55 Fenacetine PhAC 179 1,58 /

1,5-naftal ene

disulfonic acid

Surrogate 288 -3,15 0,71 / Fluoranthene EDC 202 4,93 /

2-naftalene

sulfonic acid

Surrogate 208 0,63 0,55 / Ibuprofen PhAC 206 3,79 0,5 4,91

9-ACA Surrogate 222 3,85 3,65 Isopropylantipyrine PhAC 231 1,94 /

Atrazine Pes ticide 216 2,82 0,8 1,7 (weak

base)

Isoproturon Pesticide 206 2,84 0,81 /

Mecoprop Pesticide 215 2,94 0,49 3,78

Metamitron Pesticide 202 1,44 0,5 /

Metazachlorine Pesticide 278 2,38 /

Metribuzin Pes ticide 214 1,49 0,44 1 (weak base)

Bisphenol A EDC 228 3,64 0,33 10 Pirimicarb Pes ticid e 238 1,4 0,79 4,53 (w eak

base)

Carbamazepin

e

PhAC 236 2,25 / Primidone PhAC 218 0,73 /

Cyanazine Pe sticide 240 2,51 0,83 0,63 (w ea k

base)

Salicylic acid Surrogate 138 2,24 2,97

DCAA DBP 129 0,92 1,26 Simazine Pes ticid e 202 2,4 0,75 1,67 (we ak

base)

Diclofenac PhAC 296 4,02 4,15 Sulphamethoxazole PhAC 253 0,48 /

Diuron Pesticide 233 2,67 0,49 / TCAA DBP 163 1,33 0,51

Estradiol EDC 272 3,94 10,7 Terbutylazine Pesticide 230 3,27 2 (weak

base)

0,8 3,3Bentazone Pes ticide 240 1,67

BMG-NMG Posterdag


Organic micropollutants

Modelling and prediction of rejections is still difficult

qualitative appraisal of rejections- classification of compound/membrane combinations

- based on molecular weight, molecular weight cut-off of the

membrane, pKa (solute charge) and log Kow (hydrophobicity)- See J. Chem. Technol. Biotechnol. 2006, 81 (7), 1166-1176

Relatively low rejections for uncharged hydrophobiccompounds, e.g., 2-naphtol, 4-phenylphenol, estradiol,ibuprofen, fluoranthene and bisphenol-A, estradiol,estrone, atrazine, simazine, diuron, and isoproturon

Small hydrophilic compounds (e.g., NDMA) areproblematic


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Acknowledgements

-My colleagues from Lappeenranta University of Technology (LUT): Mika Mnttri &

Marianne Nystrm

vanderbruggen_nanofiltration

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