Transport properties of hydrophobic microporous … properties of hydrophobic microporous polymeric...

Transport properties of hydrophobic

microporous polymeric membranes

Enrico Drioli1,3,4,5

Zhaoliang Cui1, Naser Tavajohi Hassankiadeh1, Young Moo

Lee1,2, Francesca Macedonio3,4, Alberto Figoli4, Elena Tocci4,

1WCU Energy Department, Hanyang University, Seoul 133-791 S. Korea2Department of Energy Engineering, College of Engineering, Hanyang University, Seoul 133-791,

Republic of Korea3Department of Environmental and Chemical Engineering, University of Calabria, via P. Bucci, Rende 4Institute on membrane Technology, National Research Council of Italy, ITM-CNR, c/o University of

Calabria, via P. Bucci cubo 17/C, Rende Italy5Center of Excellence in Desalination Technology, King Abdulaziz University, Saudi Arabia

Membrane processes impact on

the most strategic problems:

water, energy, rationalization of

productive processes

4

Improvement of desalination

Solutions for

tomorrow

• Energy production

• Mineral recoveryProblems of today

• Electric energy consumptions

• Brine disposal

• Water recovery

T. Pankratz, GWI, 24th WateReuse Symposium 2009

Membrane based desalination systems

Seawater reverse osmosis

desalination

MEDINA

(2006-2010)

MEGATON

(2009-2014)

SEAHERO

(2007-2012)

Major desalination projects aims

to increase the water production

and decrease water costs by

integrating various membrane

operations for improved

production of water, energy and

minerals.

HOW THE IMPROVEMENT CAN BE REACHED?

•New membrane modules and materials (e.g., multifunctional

and auto-restored membranes)

•New membrane operations

• More efficient pre-treatment (e.g., MF/UF, MBr, MDBR, etc.)

and post-treatment operations (e.g., MD, MCr, etc.)

•Integrated membrane systems

•Possibility to address contemporaneously water, energy and

raw materials production

Membrane Distillation

A process based on the vapor pressure gradient created across a micro-porous hydrophobic membrane.Membrane requirement Hydrophobic High overall porosity Narrow pore size distribution Low thermal conductivityAdvantages Concentration independent operation Complete rejection of all non volatiles Possibility to use waste grade heat Less stringent mechanical requirements for membrane usedChallenges Unavailability of specific membranes Control of thermal polarization Control of non traditional fouling including wetting and surface scaling

MD Configurations

The performance of various

configurations in terms of flux,

energy efficiency and operational

stability (resistance to wetting and

scaling) can be different under the

same process conditions due to

different thermal polarisation and

resistance to mass transfert.

In SGMD, AGMD and VMD, the

wetting does not affect the product

quality significantly.

The selectivity of volatile

components can differ according

to the configuration used.

MD vs Conventional Distillation

• Membrane Distillation • Conventional Distillation

Compact design with very small foot print.

Can use waste grade heat or solar energy

No corrosion related issues

Can be used for heat sensitive materials (no hot spots)

The process is emerging

Large footprint

Intensive energy nature and

conventionally based on the

fossil fuel.

Corrosion and surface

scaling is a big problem

The applications are usually

typical and temperature

distribution is less uniform.

Well established technology

Membrane Crystallization

Driving force: partial pressure

difference )c,T(pJ

Advantages compared to traditional techniques

High specific area for mass transfer

Optimal control of the supersaturation level

Shorten induction periods

Surface effect (heterogeneous nucleation)

p

M

RT

RT

rJ

2/1

81

3

2

11

Reduction in the free energy of nucleation as a

function of the contact angle with the polymeric

surface

High values of the crystal growth rate at low

supersaturation

Control of crystals habit

0 45 90 135 180

Contactangle(°)

0

0.25

0.5

0.75

1

DGhe

t / DG

hom

(-)

PANCA

PCPEIPSf

PVDFPP

PTFE

Production of catalytic crystals

with a well defined size and shape

400 600 800 1000 1200 1400

0

1

2

3

4

5

6

v, Solution velocity / m s-1

G, G

row

th r

ate

/

m h

-1

-10,0

-7,5

-5,0

-2,5

0,0

2,5

5,0

7,5

r, Len

gth

to w

idth

ratio

Protein: Bovine Pancreas Trypsin, M.W. = ~ 24000 Da

12

Application in

anti-solvent

crystallization

process

Uniform crystals. Control of crystal

size distribution

Crystallization of inorganic, organic

and “bio” materials

Control of the kinetic/thermodynamic

balance in the polymorphic

crystallization of organic molecules

0 50 100 150 200 250 300

0

5

10

15

20

25

30

35

Bovine Pancreas Trypsin Crystallization Trials

Crystal Size Distribution

Fre

qu

en

cy / %

Crystal size / m

Dynamic, V=423 m s-1



Batch, without membranes

Quiescient, 4 Membranes

Selective polymorphs crystallization

Solvent

Vapor

Solvent

Vapor

Solvent

Vapor

Solvent

Vapor

Strip

pin

g S

olu

tion

-

Polymorph

-

Polymorph

Low

flow

rate

High

flow

rate

Gly

cin

e S

olu

tio

n

13

Example 1: The polymorphism of Glycine

Glycine polymorphs: , , and . At room conditions the -form is stable,

the -form is metastable, the -form is instable.

-

Polymorph

-

Polymorph

-

Polymorph

pH

6 8 1

0

1

2

42

STATIC MEMBRANE

CRYSTALLIZER

DYNAMIC MEMBRANE

CRYSTALLIZER

Flowrate (m/s)

Evaporation rate (L/h)

250 500 750 1000 1250 1500

Form Form

126 18 24 30 36

Di Profio, G.; Tucci, S.; Curcio, E.; Drioli, E. Crystal Growth & Design 2007, 7, 526.

14

Example 2: The polymorphism of Paracetamol

Monoclinic form I : The thermodynamically stable modification at room temperature

Orthorhombic form II : The metastable form at ambient conditions

The form III: The unstable polymorph

J/(mL/h) tind/h S(tind)* Polymorph

1.37 x 10-2 64.3 1.34 II

1.94 x 10-2 53.6 1.52 II (+ I)

4.33 x 10-2 23.5 1.91 I

4.37 x 10-2 31.0 1.83 I

5.89 x 10-2 24.3 1.93 I

6.60 x 10-2 23.0 1.96 I

7.90 x 10-2 19.5 2.00 II

8.98 x 10-2 17.5 2.05 II

Form I

Form II

Thermodynamic control

(Path 1)

The stable product prevails at the

nucleation stage

The stable product grows to become a

macroscopic crystal

Kinetic control

(Path 2)

The metastable phase nucleate first and

the growth rate (G) determinate which

form will be present at the end

If supersaturation increases slowly, the

metastable phase converts into the

thermodynamic product; if supersaturation

changes quickly, the kinetic form will

growth. )( )( ABdB SSkG

)( ABgA SkG

Kinetic and thermodynamic

control

Chen et al. Cryst. Growth Des. 2011, 11, 887

17

Super-satured flue gas

Dehydrated gaseous stream

Condensed water retained in the retentate

Microporous hydrophobic membrane

Membrane Condenser

Recycling

to the

plant

Macedonio F., Brunetti A., Barbieri G., Drioli E., Membrane Condenser

as a new technology for water recovery from “waste” humidified

gaseous streams, Ind. Eng. Chem. Res., 2013, 52 (3), pp 1160–1167

Membrane condenser allows the condensation of evaporated “waste” water by using hydrophobic membranes.Water condensation and recovery happens on one side of the membrane, whereas the dehydrated stream, passing through the membrane, is purged on the other side, under atemperature difference between the feed gas and the membrane condenser.

18

The membrane surface can be

cooled with a cold gas fed on

the retentate side of the

membrane module.

The cooling gas can consist of

air coming out from the

surrounding that can be cooled

in an heat exchanger if

necessary.

The membrane module can be

placed at a certain distance

from the chimney of the tower

and its cooling can occur

exploiting the temperature

difference between the feed

gas and the environment.

The membrane surface can be

cooled with a sweep gas fed

on the permeate side of the

membrane module.

The sweep can consist of air

coming out from the

surrounding that can be cooled

in an heat exchanger if

necessary.

Configuration 1: cooling of the membrane condenser by external sources

Configuration 2: cooling of fibers with coldsweep gas

Air (Surrounding)

Cooling tower(six parallel stacks)

Flue gasRH=80-100%T= 40-50°C

Balance

Feed

Waterxx L h-1

Temperature=….pH=….

[salt]=….

Microporous hydrofobicMembrane

DehydratedGaseous stream

Is anHeat Exchanger

necessary?

Permeateside


Air (Surrounding)

at 35°C (noon) or 15°C (midnight)

Flue gasRH=80-100%

Balance

Feed

Waterxx L h-1


[salt]=….



Configuration 3: Cooling of the membrane condenser by cold auxiliary

gas fed on retentate side


Is anHeat Exchanger

necessary?Air (Surrounding)at 35°C (noon) or 15°C (midnight)

Flue gasRH=80-100%

Balance

Feed

Waterxx L h-1


[salt]=….



Permeateside

• Low energy consumption

if low ΔT requirement

• Difficult to removing

water from the fiber.

• Difficult to control the

temperature of the

module.

• Can only be used for

small systems.

• Control of the temperature

of the fibers

• Condensation inside the

membrane pores

• Easy removal of water • Dilution of the Feed

current ,consequent

reduction of the relative

humidity and therefore

decrease of water

recovered.

Advantages Disadvantages

Membrane condenser vs conventional technologies

Liquid sorption [1]Cooling with condensation[2]

Dense Membranes [3]Membrane condensers

Water recovery

22-62% < 70% 20-40% > 70%

Water purity >95%Sufficient for cooling towermake upContaminants

>95%Sufficient for coolingtower make upContaminants

Maintananceand durability

Corrosion and salt crystalsformation due to saltdessicants presence and O2

in the flue gas

Corrosion due to the formation of a thin liquidlayer of diluted acids and flyashes forming deposits

Ashes removal and FGDnecessary to avoidmembrane damaging

Ashes removal toavoid membrane damaging

Environmentalaspects

Increase of CO2 emissionsReduction of SOx emissionCaCl2 losses

Co-capture of SOx and NOxcould results in a environmental profit reducing the DENOx and FGD systems

Clean operation Clean operation

Investmentscosts

5.8 mln $ (2006) +200.000$/year (2006)as operational costs

6.4 mln EURO (2011) To be determined To be determined

Economicviability

4.4 $/m3 1.5-2 EURO/m3

1.5 Euro/m3 (WET regions)10 EURO/m3 (DRY regions)

1.5- 2.5 Euro/m3

(*)

[1]Folkedahl, B., Weber, G.F., Collings, M.E. Water extraction from coal-fired power plant flue gas. Final report. DOE Cooperative

Agreement No. DE-FC26-03NT41907. December 2006 . http://www.netl.doe.gov/technologies/coalpower/ewr/water/pp-

mgmt/pubs/41907/41907%20Final.pdf

[2] Michels, B., Adamczyk, F., Koch, J. Retrofit of a flue gas heat recovery system at the Mehrum power plant. An example of power plant

lifetime evaluation in practice. VGB PowerTech, Nr. 10, 2004.

[3] http://www.watercapture.eu/downloads/paper-powergen-europe.pdf

Membrane Emulsification

Emulsions are dispersed systems of two (or more) insoluble liquids,

e.g. water and oil.

Oil in water and water in oil emulsionsa) Cross flow membrane emulsification

b) Batch membrane emusification

c) Pre-emulsification

d) Membrane tube emulsification

e) CME system

Schematic diagram of the membrane emulsification process

Emulsions play an important role in the formulation

of cosmetics, pharmaceuticals, paints and foods and

petroleum industry.

Membrane Emulsification

Advantages of ME

Membrane properties including

material of construction, pore

size, pore size distribution and

overall porosity are crucial in

obtaining the stable emulsion of

desired droplet size and size

distribution.

Process parameters including

cross flow velocity and TMP are

important to control droplet size

and droplet size distribution.

Phase properties including

viscosity and surfactants also

affect the process and emulsion

properties.

Parameters affecting ME

Energy consumption of membrane

emulsification (104–106 Jm−3) is

lower than its conventional

counterparts (106–108 Jm−3).

The droplet size can be tuned by

changing the pore size of

membranes. ME can be utilized to produce

monodispersed micro and

nanoemulsions depending upon

membrane characteristics used. Membrane emulsification can be

particularly suitable for shear-

sensitive ingredients such as

proteins and starch.

Membrane Dryer (1)

Membrane Dryer is a membrane-based system able to dry solid particles

contained in liquid streams, while producing a liquid particle-free.

The main principles are those of Membrane Distillation: the liquid stream

(feed) to be treated is in contact with one side of a microporous

membrane and the liquid permeates as vapor thanks to a driving force

that can be established across the membrane in different ways: by

applying vacuum; by creating an air gap; by sending a cold liquid or a

sweep gas.

Vacuum

Air gap

Cold liquid

Sweep gas

Microporous

Membrane

Vapor Flux

Feed

Membrane Dryer (2)

Main Properties of the membranes to be used:

1. Microporous;

2. Hydrophobic (for aqueous feeds);

3. Hydrophilic (for organic feeds);

4. Pore size smaller than the solid particle size.

Membrane Dryer (3)

Main Advantages:

1. Ability to work with feeds of different concentration (dilute or

concentrated feeds);

2. Ability to work with feeds containing solid particles of different size;

3. Production of liquid particle-free without the need of a separation step

downstream;

4. Modularity, flexibility, easy scale-up and scale-down, low footprint (all

typical advantages of membrane processes).

HOW THE IMPROVEMENT CAN BE REACHED?

•New membrane modules and materials (e.g., multifunctional

and auto-restored membranes)

•New membrane operations

• More efficient pre-treatment (e.g., MF/UF, MBr, MDBR, etc.)

and post-treatment operations (e.g., MD, MCr, etc.)

•Integrated membrane systems

•Possibility to address contemporaneously water, energy and

raw materials production

Membrane characteristics

Morphology: symmetric or asymmetric porous

Thickness: 20-100 m

Pore size: 0.1 – 1.0 m (even if 0.2-0.3 m is better)

Membrane material:

- hydrophobic

- resistant to alchools and surfactants

Membrane porosity: 70-80%

High liquid entry pressure (LEP)

High permeability

Low fouling problem

High chemical stability

High thermal stability

High overall porosity

Narrow pore distribution

Desired membrane characteristics

7.0 um

2.5 um

AFM photos of fluor polymeric membranes

with ordered structures


Membrane materialswith low thermalconductivity

Simulation results of the effects of the membrane thermal conductivity onthe DCMD performance

S. Al-Obaidani et al. / Journal of Membrane Science 323 (2008) 85–98


Membrane with properthickness

Simulation and experimental results of the effects of the membrane thickness on the MD performance .

S. Al-Obaidani et al. / Journal of Membrane Science 323 (2008) 85–98

Perfluoro polymers for new

membrane operations

The most important fluoropolymers for membrane operations are

CH2 CF2n

CF2 CF2n

CH2 CH2 C

Cl

F

CF2 n

PVDF homopolymer PTFE homopolymer ECTFE copolymer

Most of the fluoropolymers for membranes are homopolymers and copolymers

based on PVDF and PTFE.

ECTFE , which is starting to catch researchers’ attention, is a novel

fluoropolymers for membranes.

Membrane processes based on fluoropolymers

Fluoropolymer Membrane process

Poly(vinylidene fluoride) (PVDF) homopolymer MF, UF, MD, MCr, ME, PV

PVDF copolymer Poly(vinylidene fluoride-co-tetrafluoroethylene) (P(VDF-co-

TFE))

MF/UF, MD

Poly(vinylidene fluoride-co-hexafluoropropene) (P(VDF-co-

HFP))

MF/UF, MD, PV, fuel cell, lithium

ion battery

Poly(vinylidene fluoride-co-chlorotrifluoroethylene) P(VDF-

co-CTFE)

MF/UF, NF, MD, PV, fuel cell

Poly(vinylidene fluoride)-graft-poly-(styrene sulfonic acid)

PVDF-g-PSSA

Fuel cell

Poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) Lithium ion battery, tissue

regeneration

Poly(tetrafluoroethylene) (PTFE) homopolymer MD, MC, PV, MGA

PTFE copolymer Perfluorosulfonic acid (PFSA) Fuel cell, lithium ion battery, chlor-

alkali industry

Poly(tetrafluoroethylene-co-perfluoropropyl vinyl ether) (PFA)Fuel cell

Poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) MD, fuel cell

Poly(ethylene-alt-tetrafluoroethylene) (ETFE) Fuel cell

Poly(ethylene chlorotrifluoroethylene) (ECTFE) PV, has potential in MD, MC and

MF/UF

Other fluoropolymers Poly(chlorotrifluoroethylene) (PCTFE)

Poly(vinyl fluoride) (PVF) Fuel cell

Poly(fluorenyl ether) (PFE) Fuel cell

Hyflon® AD, Teflon® AF, Cytop® Gas separation, have potential in

MD, MC

PVDF homopolymers

Homopolymers of PVDF are semicrystalline and long chain macromolecules

which contain 59.4 wt.% fluorine and 3 wt.% hydrogen.

PVDF typically has a crystallinity of 35-70%, depending on the preparation

and thermal mechanical history.

Ameduri B. Chem. Rev 2009; 109: 6632-86; Dillon DR, et al. Polymer 2006; 47: 1678-88;

Hasegawa R, et al. Polym J 1972; 3: 600-10; Boccaccio T, et al. J Membr Sci 2002; 210: 315-29.

Three molecular conformations are TGTG’ (α

and δ phases), TTT (β phase) and TTTGTTTG’

(γ and ε phases).

The α-form is kinetically favorable, while the β-

form is the most thermodynamically stable

form.

α phase is non-polar, β and γ phases are polar.

The polar property and the relatively higher

mechanical strength makes β phase is the most

interesting phase.

γ phase presents higher melting point and

solvent resistance.

α and δ phases

β phase

γ and ε phase s

PVDF membrane preparations

Li CL, et al., J Membr Sci 2010; 361: 154-66; Mu CX, et al., J Membr Sci 2010; 361: 15-21;

Feng C, et al., J Membr Sci 2008; 311: 1-6

Publication numbers related PVDF

and its copolymer membranesWet-inversion membranes

Casting-freezing membranes

VIPS membranes

New methods like VIPS,

casting-freezing and

electrospinning are conducted

to prepare PVDF membranes.

• Publication number is

increasing dramatically.

Electrospinning membranes

The most important methods for PVDF membrane preparation are still non-solvent

induced phase separation (NIPS) and thermally induced phase separation (TIPS).

Citroflex A4 (ATBC)

Formula C20H34O8

Molecular weight, g/mol 402.5

Purity, % >97 (GC)

Specific gravity 1.05

Boiling point, oC 343

Flash point, oC 204

Melting point/freezing point, oC -80

Soluble in Ethanol, alcohol ether

Insoluble in Water

ATBC has a solubility parameter of 18.34 MPa1/2.

The cloud points curve intersects the crystallization curve at the temperature about 117 oC and

the polymer concentration about 25 wt%.

A bicontinuous structure is expected to be formed by preparing the membranes with polymer

concentration lower than 25 wt% without adding nonsolvent or stretching process

36

10 15 20 25 30 35

80

90

100

110

120

130

140

150

160

170

Te

mp

era

ture

(o

C)

Polymer concentration (wt.%)

PVDF 1010

10 15 20 25 30 35

80

90

100

110

120

130

140

150

160

170

Te

mp

era

ture

(o

C)


PVDF 1015

10 15 20 25 30 35

80

90

100

110

120

130

140

150

160

170

Te

mp

era

ture

(o

C)


PVDF 6020

0 5 10 15 20 25 30 35 400

20

40

60

80

100

120

140


Te

mp

era

ture

(oC

)

PVDF 1010-fitted curve

PVDF 1010- experimental data


PVDF 1015-experimental data


PVDF 6020-experimental data Effect of cooling rate, polymer molecular weight and

polymer concentration on cloud point. (a) Solef 1010, (b)

Solef 1015, (c) Solef 6020,( cooling rate: 1 oC /min (▲),

15 oC /min (●) and 30 oC /min (■)). (d) Solef 1010, Solef

1015 and solef 6020 (cooling rate: 30 oC /min).

Phase diagram for different molecular weight of PVDF

Cloud points in the PVDF/ATBC system decreased with the molecular weight of

PVDF. In fact, the high molecular weight of the polymer enhances the interaction

parameter between the polymer and diluent.

37

Morphology of flat sheet membranes

37a, b, c and d: PVDF concentration 15, 20, 25,

and 30 wt%

a, b and c: quenching temperature

30, 50, 100 oC

Bicontinuous structure was formed.

The membrane structure becomes

spherical from concentration of 25 wt%

38

Polymer structure (flat sheet) vs. Polymer concentration

Polymer concentration

(wt%)

Thickness

(μm)

Mean pore size

(μm)

Porosity

(%)

15 186 0.56 76.32

20 175 0.35 75.91

25 193 0.31 69.61

30 262 0.27 66.95

Liquid–liquid phase separation takes place when the polymer concentration is

lower than 25 wt%.

When the polymer concentration is higher than 24 wt%, the higher polymer

concentration reduces spherulite size, and consequently reduces mean pore size.

Porosity decreases with an increase in polymer concentration because the fraction

of the polymer-lean phase is reduced during phase separation.

39

Polymer structure (flat sheet) vs. Quenching temperature

Mean pore size decreases with increase in quenching temperatures.

Porosity increases with quenching temperature, the reason is that larger

pore sizes were induced on the bottom surfaces of the membranes prepared

at relatively higher temperatures.

Quenching temperature

(°C)

Thickness

(μm)

Mean pore size

(μm)

Porosity

(%)

30 175 0.35 77.05

50 294 0.27 79.64

100 312 0.16 81.14

40

Polymorph

40

FTIR

ATBC always induces α-phase PVDF during PVDF membrane preparation via

TIPS method without additives.

Z. Cui, et al., Poly(vinylidene fluoride) membrane preparation with an environmental diluent via thermally induced

phase separation, J Membr Sci (2013), http://dx.doi.org/10.1016/j.memsci.2013.05.031

20mer chain in ATBC

solvent box

Alpha form PVDF

Molecular Dynamics simulations

Crystalline (super)unit cell

interfacing ATBC solvent

42

Properties and performance of the membranes

42

The prepared membranes are MF membranes.

High porosity about 80% can be obtained.

The pure water flux is competitive used in MF/UF.

Z. Cui, et al., Poly(vinylidene fluoride) membrane preparation with an environmental diluent via thermally induced

phase separation, J Membr Sci (2013), http://dx.doi.org/10.1016/j.memsci.2013.05.031

4343

Mechanical strength (flat sheet)

Polymer concentration

(wt%)

Young's modulus

(MPa)

Tensile stress

(MPa)

Extension at break

(%)

15 27.65 1.02 9.28

20 38.58 0.94 13.99

25 59.39 1.47 14.87

30 126.18 4.83 11.97

In the case of solid–liquid TIPS membrane preparation, crystal nucleation and

growth determined the morphology and mechanical strength of the membrane.

The space between crystalline domains became pores upon extraction of the

diluents. Thus, higher polymer concentrations resulted in higher nucleation

density, forming membranes with higher mechanical strength because of

increased integrity.

4444

Mechanical strength (hollow fiber)

Tensile strength

(MPa)

Elongation

(%)

Fiber one 2.18 ± 0.08 89 5.0

Fiber two 3.08 ± 0.03 128 2.0

Fiber three 3.02 ± 0.25 105 7.3

PVDF 1015/30% DBP and 70% DEHP 0.43 69

PVDF 1015/40% DBP and 60% DEHP 0.59 6.81

PVDF 1015/DBP 0.91 8.91

Decreasing air gap from 2.5 cm (fiber one) to 4 mm (fiber two), the

mechanical properties of the membranes improved.

The reduction of mechanical properties of fiber three compared with fiber two

was due to high bore fluid temperature, which decreased the cooling rate of

the inner parts of the fibers.

Superior mechanical strengts compared to other published studies.

45

24

68

1012

1416

1012

1416

1820

60

65

70

75

80

Washing bath temperature (oC)

Quenching bath temperature (oC)

Po

ro

sit

y (

%)

67

68

69

70

71

72

73

74

75

76

24

68

1012

1416 10

12

14

16

18

20

60

65

70

75

80



Po

ro

sit

y (

%)

64

66

68

70

72

74

24

68

1012

1416

1012

1416

1820

1

2

3

4

5

6

7

8



Ten

sil

e s

tre

ng

th (

MP

a)

1.5

2

2.5

3

3.5

4

4.5

5

5.5

6

6.5

24

68

1012

1416

10

12

14

16

18

20

12345678



Ten

sil

e s

tre

ng

th (

MP

a)

2

2.5

3

3.5

4

4.5

The effect of preparation conditions on overall porosity and tensile strength when the air gap is 4 mm (a and c) where air the

gap is 2 cm (b and d). The black points represent experimental data.

The effect of preparation condition on hollow fiber properties

46

60 65 70 750

1

2

3

4

5

6

7 Quenching bath temperature = 3

oC

Quenching bath temperature = 10 o

C


C

Ten

sil

e s

tren

gth

(M

Pa)

Porosity (%)

Tensile=(-0.2237×Porosity)+18.73

60 65 70 75 80

100

1000

10000 Quenching bath temperature = 3

oC


C


C

Wate

r p

erm

eab

ilit

y (

LM

H)

Porosity (%)

Overall porosity of the membrane versus tensile strength and water permeability.

The effect of preparation condition on hollow fiber properties

By increasing the quenching bath temperature the overall porosity increase

and mechanical properties decrease

47

0.10 0.15 0.20 0.25 0.30

Inte

ns

ity

Average diameter (m)

0.176 m 0.222 m

Mean pore size and pore size distribution for different

molecular weights of PVDF Solef® 1015 (red) and Solef®

6020 (blue).

1500 1400 1300 1200 1100 1000 900 800 700

Tra

ns

mit

tan

ce

(%

)

Wave number (cm-1

)

Inner surface of PVDF 1015 hollow fiber

Outer surface fo PVDF 1015 hollow fiber

Inner surface of PVDF 6020 hollow fiber

Outer surface of PVDF 6020 hollow fiber

(840 cm-1)

(1270 cm-1)

FTIR results for different molecular weights of PVDF.

The effect of PVDF molecualr weight on hollw fiber properties

PVDF hollow fiber with very narrow pore size distribuition is prepared by green

solvent

Changin molecular weight of PVDF did not have significant effect on polymorphisim

of prepared membrane.

48

DCMD for the prepared hollow fibers the test was done using 3.5 wt.% NaCl solution at different flow velocity

and the Solef® 6020 hollow fiber membrane. Flux and temperature polarization coefficient increase as Re

increases.

500 750 1000 1250 1500

17

18

19

20

21

22

Flux

Temperature polarization coefficient

Ref

Flu

x (

Kg

/m2

.hr)

0.65

0.70

0.75

0.80

Te

mp

era

ture

Po

lariza

tion

Co

effic

ien

t

One of the potential applications of prepared hollow fiber membrane

Rejection in all experiments was more than 99.99%

49

ECTFE

CH2 CH2 C

Cl

F

CF2 n

Properties:

• High mechanical properties

• Excellent chemical stability

• Wear resistance

• Outstanding stability in pH

• Limited solubility in organic solvents

Chemical structure

Because of the limited solubility in organic solvents, ECTFE is difficult to be

fabricated into membranes by NIPS process, but it is possible by TIPS process.

Phase diagram of ECTFE/DBP system

Ramaswamy S, et al., J Membr Sci 2002; 210: 175–80; Roh IJ, et al., J Membr Sci 2010; 362: 211–20.

ECTFE (Ethylene–Chlorotrifluoroethylene copolymer) is a copolymer of formula

–(–CH2–CH2–CFCl–CF2–)n–, composed of alternating ethylene and

chlorotrifluoroethylene units.

Since it is very hydrophobic, an ECTFE porous membrane is more suitably

used in membrane processes in which vapor or gas passes through the

membrane pores, like MD, and a dense ECTFE membrane can be used in PV.

This material has been studied primarily in preparing flat sheet and hollow fiber

membranes, microporous membranes for UF/MF processes, and dense

membranes for the PV process.

C CC C C C

H

H

F

Cl

F

F

H

H

F

Cl

F

F

H

H

C

ECTFE membranes

Two different additives have been used in order to improve

the polymer processability: glycerol triacetate (GTA), known

also as triacetin and tri-ethyl citrate (Citroflex™, CTF).

CTF

GTA

Polymeric solution

T=180°C

Preparation of ECTFE membranes

Solvent: N-methyl pyrrolidone

Simone, Figoli, Galiano, Drioli et al. Sep and Purif Tech, 90 (2012)147-161

Cloud point DETERMINATION

0

20

40

60

80

100

120

140

160

180

0 5 10 15 20 25

T

(°C)

Weight fraction of ECTFE (%)

NMP NMP+GTA 5% NMP+CTF 5%

The cloud point temperature of a polymer/diluent system depends on the

affinity between the two: the lower the cloud point the more compatible are

the two components.

As shown in the graph, the compatibility of the polymer/diluent system can be further

improved by using CTF or GTA, which work as plasticizer additives.


Preparation of ECTFE membranes

Morphology: Scanning Electron Microscope

Cross section Top side Bottom side

Cross section Top side Bottom side

ECTFE Membrane with GTA 5%

ECTFE Membrane with CTF 5%

ECTFE membranes presented an asymmetric dense structure.

CHARACTERISATION OF ECTFE MEMBRANE


Hydrophobicity: Contact angles

98.990.5

102

119.3

0

30

60

90

120

GTA CTF

q()

Additive

Top Side Bottom Side

C.A. measurements confirm the hydrophobicity of ECTFE membranes.

The contact angle of top side (dense) is lower than the bottom side (sferulitical).


CHARACTERISATION OF ECTFE MEMBRANE

When ECTFE membranes are fabricated, lower temperatures of the casting

block result in anisotropic membrane structure, even with the formation of a

dense skin layer at the quenched surface. On the other hand, if the

casting temperature is high, a dense skin layer also might be induced at the

top surface of flat sheet membranes because of evaporation.

To produce a porous membrane, the formation of a dense skin layer can

be avoided, and more porous membranes can be obtained by co-extrusion

of hot solvent on both sides of the polymeric dope during casting.

Stretching the membrane film during casting has been found to be an

interesting way to improve ECTFE membrane surface porosity and effective

surface pore size. Another method to improve the porosity is incorporating

particles such as silica.

Z. Cui et al. / Progress in Polymer Science. In press.

ECTFE microporous flat sheet membranesC

ross

Se

ctio

n

Surf

ace

: TO

P S

ide

Surf

ace

: B

OT

TOM

Sid

e

113±3µm

ECTFE membranes showed a symmetric porous morphology.The roughness of the surface TOP side is lower than the Surface BOTTOM Side.

ECTFE flat-sheet membrane

Higher contact angles were observed for the bottom side (~139°) than air side (~91°) because of the higher as a consequence of the higher roughness .

ECTFE membrane is hydrophobic and can be used, for example, as a barrier to water transport.

Porosity

0

20

40

60

80

100

ECTFE PVDFP

oro

sit

y(%

)

New hydrophobic flat sheetmembrane and PVDF hollow fibrepresented porosity of around 80%.

Mechanical Tests

MembraneYoung's Modulus

(N/mm2)

Elongation at

Braeak (%)

ECTFE 88±6 123±2

PVDF 53±7 22±4

New polymer(≈83%) (≈80%)

ECTFE flat-sheet membrane

Composite hollow fibres: ECTFE on PP support

Dip-coating, using PP fibers as support, of ECTFE polymeric solution (from 1wt% to

5wt%) in NMP at 135°C. In order to modulate the morphology of the coated

layer of ECTFE, the time of dip-coating was varied from 1 s to 5 s.

ACCUREL® PP S6/2 hollow fibre supplied by Membrana has been used as support of the ECTFE skin layer

• As a consequence of the deposition of the ECTFE on the external surface, the

mean pore size dramatically decreased from ca. 0.4 μm for PP support to values

lower than 0.2 μm for ECTFE/PP composite fibers.

• The time of immersion did not influence the size of the mean pore. Generally,

composite membranes prepared by dipping PP support in a polymeric solution

containing 1wt% ECTFE presented pores bigger than the once prepared using a

dope solution of 3wt% or 5wt% of ECTFE in NMP that showed similar pore size.

0,0

0,1

0,2

0,3

0,4

0,5

0 1 2 3 4 5 6

Me

an p

ore

, μm

Time of dip-coating, s

ECTFE(1wt%) ECTFE(3wt%) ECTFE(5wt%) PP

Composite hollow fibres: ECTFE on PP support

61

Other fluoropolymers for membranes

Name Chemical structure Membrane process

Hyflon® AD Gas separation, have potential in

MD, MC

Teflon® AF Gas separation, have potential in

MD, MC

Cytop® Gas separation, have potential in

MD, MC

CF C

O

CF2

O

CF2

OF3C

CF2

m

n

CF CF

O

C

O

CF2 CF2m n

F3C CF3

CF CF

O

CF2

CF2

CF2 CF2n

DCMD VMD

50 60 70

6

9

12

15

18

21

Flu

x (

kg/m

2.h

)

Temperature (°C)

M1

M2

M3

PP

50 60 706

9

12

15

18

21

Flu

x (

kg

/m2.h

)

Temperature (°C)

6 L/h

7.8 L/h

9.6 L/h

11.4 L/h

E. Drioli et al., Separation and Purification Technology 115 (2013) 27–38

62

Fiber VMD flux (H2O)

(kg/h m2)

M1 15.06

M2 22.37

M3 41.78

Permeate temperature: 25 C

Permeate flow-rate: 6 l/h

Membrane performance in VDM and DCMD

Pvacuum 40 mbar, Tfin 50 °C, Qfeed 6 l/h

Morphology vs performanceFiber Morphology Thickness

(mm)

Porosity

(%)

Ref. 18 fiber 4b Spongy with some fingers at outer surface 0.174 81.23

Ref. 18 fiber 4d Spongy with some fingers at outer surface 0.202 78.09

Ref. 18 fiber 4g Spongy with some fingers at outer surface 0.139 78.45

M1 Spongy with some fingers at outer surface 0.38 80.9

M2 Asymmetric with fingers at inner and outer surface 0.45 79.11

M3 Asymmetric with fingers towards inner surface 0.23 83.39

63E. Drioli et al., Separation and Purification Technology 115 (2013) 27–38,S. Simone et al. / Journal of Membrane Science 364 (2010) 219–232

Comparison with literature dataMembrane type DCMD

Flux

(kg/m2.h)

VMD

flux

(kg/m2.h)

Operating parameters Reference

VMD DCMD

PVDF 18.9 22.4 Tfin=73 oC,P=315mbar

,35g/L NaCl solution

DCMD Feed=35g/L NaCl, solution

Tfin=73 oC Tpin=25oC

[1]

PVDF ~16.5 ~23.5 65+0.2 oC, P=900 mbar, 9.09% NaCl DCMD Feed=9.09% NaCl, Tfin=65-65.2

oC Tpin=25oC

[2]

PVDF 83.4+3.66 - - DCMD Feed=3.5% NaCl solution,

Tfin=80 oC, Tpin=17+0.5oC

[3]

PVDF–

PTFEPVDF–

PTFE

40.4 - - DCMD, 3.5% NaCl solution, Tfin=80+0.5

oC, Tpin=17.5+0.5oC

[4]

PVDF-Clay

nanocomposite

~5.7 - - DCMD, 3.5% NaCl solution, Tfin=80 oC

Tpin=17+2 oC

[5]

PVDF-FS 1.39 Tfin=25 oC, P=9.33-30 mbar [6]

PVDF-HF 0.5 Tfin=50 oC, P=16.7mbar [7]

PVDF-HF 18.5 Tfin=50 oC, P=20mbar [8]

PVDF 21.9 50 50 oC, P=40 mbar Distilled water, Tfin=70oC, TPin=25 oC Current study

[1] Fan et al, Chem. Eng. Sc., 79 (2012) 94–102[2] Tang et al, Desalination 287 (2012) 326–339[3] Edwie et al, Chemical Engineering Science 68 (2012) 567–57[4] Chung et al, Separation and Purification Technology 66 (2009) 229–236[5] Prince et al, Journal of Membrane Science 397–398 (2012) 80–86[6] Khayet and Matsuura, Industrial & Engineering Chem-istry Research 40 (2001) 5710–5718.[7] Khayet et al, Journal of Membrane Science 238 (2004) 199–211[8] Simone et al, Journal of Membrane Science 364 (2010) 219-232, doi:10.1016/j.memsci.2010.08.013 64

http://www.sciencedirect.com/science/journal/00092509

http://www.sciencedirect.com/science/journal/03767388

http://www.sciencedirect.com/science/journal/03767388/397

65

High lights of Rhodiasolv® PolarClean

O O

CH3-O-C- -C-NBranched

C4

CH3

CH3

Polar and water soluble.

Excellent toxicological & ecotoxicological profiles

Non-flammable and with very low vapour pressure

Based on Rhodia raw material Reduced carbon foot print

Hansen parameters close to solvents such as e.g. NMP, ADMA etc.

A new environmental friendly solvent

PVDF 1015 was used to investigate the potential of Polarclean for membrane production

66

No PVP PVP 10K PVP 55K PVP 360K PVP 1300K

A-5 oC A-5 oC A-5 oC A-5 oC

A-15 oC A-15 oC A-15 oC A-15 oC A-15 oC

A-25 oC A-25 oC A-25 oC A-25 oC A-25 oC

B-5 oC B-5 oC B-5 oC

B-5 oC

B-5 oC

B-15 oC B-15 oC B-15 oC B-15 oC B-15 oC

B-25 oC B-25 oC B-25 oC B-25 oC B-25 oC

C-5 oC C-5 oC C-5 oC C-5 oC C-5 oC

A-5 oC

Preparation porous membrane

5 10 15 20 250

250

500

750

1000

1250

Wate

r p

erm

eab

ilit

y (

LM

H)


PVP 10k

PVP 55k

PVP 360k

PVP 1300k

67

5 10 15 20 25

20

40

60

Rq

(nm

)


No PVP

PVP (Mw= 10 K)

PVP (Mw= 55 K)

PVP (Mw= 360 K)

PVP (Mw= 1300 K)

(a)

5 10 15 20 250

20

40

Ra(

nm

)


No PVP

PVP (Mw= 10 K)

PVP (Mw= 55 K)

PVP (Mw= 360 K)

PVP (Mw= 1300 K)

(b)

0

1

2

3

4

5

6

7

1300K

360K

55K

10K

No PVP

Molecular weight o

f PVP

PVP Mw=1300K

PVP Mw=360K

PVP Mw=55K

PVP Mw=10K

No PVP

Tens

ile s

tren

gth

(MP

a)

Quenching bath temperature ( oC)

5

15

25

(a)

010

20

30

40

50

60

70

80

90

100

1300K

360K

55K

10K

No PVP

Molecular weight o

f PVP

PVP Mw=1300K

PVP Mw=360K

PVP Mw=55K

PVP Mw=10K

No PVP

Ove

rall

poro

sity

(%)

Quenching bath temperature ( oC)

5

15

25

(b)

By increasing the quenching bath

temperature the roughness of

prepared hollow fibers increase

By increasing the molecular weight of PVP

the overall porosity increase and mechanical

properties decrease

68

The effect of PVP molecular weights on polymorphism. A, B, C, D and E are No PVP, PVP 10k, PVP 55k, PVP

360k, PVP 1300k.

1500 1400 1300 1200 1100 1000 900 800 700

Tra

nm

itta

nce (

%)

Wavenumber (cm-1)

A

B

C

D

E

(cm-1) (cm

-1)

1400 1300 1200 1100 1000 900 800 700

Tra

nsm

itta

nce (

%)

Wavenumber (cm-1)

A

B

C

D

E

(1270 cm-1

)

(1270 cm-1

)

1400 1300 1200 1100 1000 900 800 700

Tra

nsm

itta

nce (

%)

Wavenumber (cm-1)

A

B

C

D

E

(cm-1

)

(cm-1

)

Quenching bath temp= 5 oC Quenching bath temp= 15 oC Quenching bath temp= 25 oC

The result of FTIR confirm the existence of β phase in the skin layer of prepared hollow fibers

By increasing the molecular weight of PVP the amount of β phase increase and then decrease

The effect of additive on polymorphism

69

1400 1300 1200 1100 1000 900 800 700

Tra

nsm

itta

nce (

%)

Wavenumber (cm-1)

5 o

C

15 o

C

25 o

C

(840 cm-1

)

(1270 cm-1

)

The effect of quenching temperature in polymorphism

10 15 20 25 30

Inte

nsit

y

2q(o)

(o)

(20.26o

)

PVP 360k- 25 oC

PVP 360k- 15 oC

PVP 360k- 5 oC

No PVP- 5 oC

XRD results of produced hollow fiber membranes

The amount of β phase changed in the skin layer while it was constant in the bulk of membrane

By increasing the quenching bath temperature the amount of β phase decreased

The effect of additive on polymorphism

70

Morphology of the hollow fibers by using glycerol as additive. A and B are 5 and 15 wt.% glycerol, respectively. C,

O and I are cross section, outer part and inner part of hollow fibers, respectively.

A B

C- 5 oC

C- 15 oC

C- 25 oC

C- 40 oC

O-5

oC

O-15

oC

O-25

oC

O-40

oC

I-5 oC

I-15 oC

I-25 oC

I-40 oC

A A AB B B

Using glycerol as additive

71

0 5 10 15 20 25 30 35 40 45

10

100

1000

Tra

ns

-me

mb

ran

e f

lux

(lit

/m2.h

r.b

ar)


PVDF/PVP

PVDF/glycerol (5 wt.%)


PVDF/PMMA

(a)

0 5 10 15 20 25 30 35 40 450

1

2

3

4

5

6

7

8

Ten

sil

e s

tren

gth

(M

Pa)


PVDF

PVDF/Glycerol (5 wt. %)


PVDF/PVP

PVDF/PMMA

(b)

0 5 10 15 20 25 30 35 40 4560

65

70

75

80

85

90

95

Po

rosit

y (

%)

Quenching bath tempeature (oC)

PVDF

PVDF/glycerol (5 wt. %)


PVDF/PVP

PVDF/PMMA

Water permeability, mechanical property and overall porosity of prepared hollow fibers

10 15 20 25 30

Inte

nsit

y

2q(o

)

PVDF without additive



PVDF/PMMA

PVDF/PVP

(20.26o

)

Effect of different additive on the formation of β phase. A, B,

C and D are PVDF without additive, PVDF/glycerol (5 wt.%), PVDF/glycerol (15 wt. %), PVDF/PVP and PVDF/PMMA

0 5 10 15 20 25 30 35 40 45

10

100

1000

Tra

ns

-me

mb

ran

e f

lux

(lit

/m2.h

r.b

ar)


PVDF/PVP



PVDF/PMMA

(a)

0 5 10 15 20 25 30 35 40 450

1

2

3

4

5

6

7

8

Ten

sil

e s

tren

gth

(M

Pa)


PVDF



PVDF/PVP

PVDF/PMMA

(b)

1500 1400 1300 1200 1100 1000 900 800 700

Tra

nsm

itta

nce (

%)

Wave number (cm-1

)

A

B

C

D

E

(1270 cm-1

)

(840 cm-1

)

Effect of different additive on the formation of β phase. A, B, C

and D are PVDF without additive, PVDF/glycerol (5 wt. %),

PVDF/glycerol (15 wt. %), PVDF/PVP and PVDF/PMMA

72

Conclusions and outlook

PVDF and PTFE homopolymers and their copolymers are the most important

fluoropolymers for membranes in the past and now.

ECTFE is a new novel materials for membranes with high properties and

performances and, it has higher processability than PTFE.

In the past, hydrophilicity was the first consideration, but now hydrophobicity

is obtaining more and more attention.

Some amorphous fluoropolymers such as Hyflon® AD, Teflon® AF and

Cytop® are very interesting for gas separation.

New methods such as VIPS, TIPS/NIPS combination, Casting-freezing and

electrospinning becomes novel approaches to prepare good membranes.

Blending amphiphilic copolymers to modify fluoropolymers is an interesting

method to realize preparation and modification in one step.

73

Conclusions and outlook

PVDF membrane with compatible properties were prepared with green

solvent

By using the additives the amount of β phase was controlled in the skin layer

of the membrane

The prepared membranes were used in membrane distillation as one of

potential application

Thank you for your attention

Transport properties of hydrophobic microporous … properties of hydrophobic microporous polymeric...

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