Teknik Pembuatan Membran

Phase Inversion Membrane●●

Membranes are fabricated by a process known as phase inversion.Membranes are fabricated by a process known as phase inversion.

●●

Phase inversion has been universally accepted as a standard tecPhase inversion has been universally accepted as a standard technique hnique for fabricating commercial membranes.for fabricating commercial membranes.

--

A homogeneous polymer solution is transformed or inverted in a A homogeneous polymer solution is transformed or inverted in a controlled condition into a gel comprising a polymer rich phase controlled condition into a gel comprising a polymer rich phase and and polymer poor phase.polymer poor phase.

--

This is a very versatile technique.This is a very versatile technique.

Motor

Vessel clip

Stirrer

Feed tunnel

Dope solution

Heating elementHeater

Proses pembuatan larutan membran

--

precipitation by solvent evaporationprecipitation by solvent evaporation,

-

precipitation by controlled evaporation,

-

thermal precipitation,

-

precipitation from the vapour

phase and

-

immersion precipitation

●●

The differences between these techniques are based on differenceThe differences between these techniques are based on differences in s in the the desolvenationdesolvenation

mechanisms.mechanisms.

Phase inversion dapat dibagi:

4.1.1: Precipitation by Solvent Evaporation

●●

This is the simplest technique for preparing phase inversion memThis is the simplest technique for preparing phase inversion membranes.branes.

●●

In this method a polymer is dissolved in a solvent and the polymIn this method a polymer is dissolved in a solvent and the polymer er

solution is cast on a suitable support, e.g. a glass plate.solution is cast on a suitable support, e.g. a glass plate.

●●

The solvent is allowed to evaporate in an inert atmosphere, in The solvent is allowed to evaporate in an inert atmosphere, in order to order to

exclude water vapour, allowing a dense homogeneous membrane to bexclude water vapour, allowing a dense homogeneous membrane to be e

obtained.obtained.

4.1.2: Precipitation from the Vapour Phase

●●

A cast film, consisting of a polymer and a solvent, is placed inA cast film, consisting of a polymer and a solvent, is placed in

a a vapourvapour

●●

atmosphere where the atmosphere where the vapourvapour

phase consists of a phase consists of a nonsolventnonsolvent

saturated saturated

with the same solvent.with the same solvent.

●●

The high solvent concentration in the The high solvent concentration in the vapourvapour

phase prevents the phase prevents the

evaporation of solvent from the cast film.evaporation of solvent from the cast film.

●●

Membrane formation occurs because of the penetration (diffusion)Membrane formation occurs because of the penetration (diffusion)

of of

nonsolventnonsolvent

into the cast film.into the cast film.

●●

This leads to a porous membrane without skin layer.This leads to a porous membrane without skin layer.

4.1.3: Precipitation by Controlled Evaporation

●●

In this technique the polymer is dissolved in a mixture of solveIn this technique the polymer is dissolved in a mixture of solvent and nt and

nonsolventnonsolvent..

..

●●

Since the solvent is more volatile than the Since the solvent is more volatile than the nonsolventnonsolvent, the composition , the composition

shifts during evaporation to a higher shifts during evaporation to a higher nonsolventnonsolvent

and polymer content.and polymer content.

●●

This leads eventually to the polymer precipitation leading to tThis leads eventually to the polymer precipitation leading to the he

formation of skinned membrane.formation of skinned membrane.

4.1.4: Thermal Precipitation

●●

A solution of polymer in a mixed or single solvent is cooled to A solution of polymer in a mixed or single solvent is cooled to enable enable

phase separation to occur.phase separation to occur.

●●

Evaporation of the solvent often allows the formation of a skinnEvaporation of the solvent often allows the formation of a skinned ed

membranemembrane

●●

This method is frequently use to prepare This method is frequently use to prepare microfiltrationmicrofiltration

membrane.membrane.

4.1.5: Immersion Precipitation

●●

Most commercially available membranes are prepared by immersion Most commercially available membranes are prepared by immersion

precipitation.precipitation.

●●

The The polymer solution is cast on a suitable support and immersed in the

coagulation bath containing a nonsolvent.

●●

Precipitation occurs because of the exchange of solvent and Precipitation occurs because of the exchange of solvent and nonsolventnonsolvent..

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The membrane structure ultimately obtained results from the The membrane structure ultimately obtained results from the

combination of mass transfer and phase separation.combination of mass transfer and phase separation.

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Membranes can be produced in the form of flat sheets and hollow Membranes can be produced in the form of flat sheets and hollow fibers.fibers.

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These geometries are commercially produced by the phase inversioThese geometries are commercially produced by the phase inversion n

processprocess

●●

Although the phase inversion mechanism involved in these two Although the phase inversion mechanism involved in these two

geometries is similar, the production techniques are not the samgeometries is similar, the production techniques are not the same.e.

●●

The flat sheet is a very simple geometry which is normally produThe flat sheet is a very simple geometry which is normally produced by ced by

spreading a polymer solution on a support glass plate using a caspreading a polymer solution on a support glass plate using a casting sting

knife knife --

the phase separation occurs from one side only.the phase separation occurs from one side only.

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Hollow fibers are selfHollow fibers are self--supporting and give a higher surface area per unit supporting and give a higher surface area per unit

volume of membrane module.volume of membrane module.

Teknik Pembuatan dengan immersion precipitation

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Hollow fibers are formed by simultaneous phase separation from bHollow fibers are formed by simultaneous phase separation from both oth

the bore side and the outer side.the bore side and the outer side.

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The The behaviourbehaviour

of the dope is crucialof the dope is crucial.

●●

This section will briefly discuss the manufacturing techniques aThis section will briefly discuss the manufacturing techniques and nd

procedures for the fabrication of these two membrane geometries.procedures for the fabrication of these two membrane geometries.

Membrane Fabrication

Spinning Machine

Melt Spinning Machine

Casting Machine

Flat Sheet Casting

●●

Flat sheet casting is the oldest technique used to form membraneFlat sheet casting is the oldest technique used to form membraness.

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The dope is then cast over a suitable base or support (e.g. glasThe dope is then cast over a suitable base or support (e.g. glass plate or s plate or

nonnon--woven polyester) by a casting knife.woven polyester) by a casting knife.

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The cast film undergoes a partial evaporation of solvent or mixtThe cast film undergoes a partial evaporation of solvent or mixture of ure of

solvents before immersion into a coagulation bath.solvents before immersion into a coagulation bath.

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The partial evaporation may result in solidification and preThe partial evaporation may result in solidification and pre--orientation of orientation of

the skin.the skin.

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When the film is immersed in the coagulation bath the phase sepaWhen the film is immersed in the coagulation bath the phase separation ration

is completedis completed

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Water is often used as a Water is often used as a nonsolventnonsolvent

for many types of polymersfor many types of polymers

Casting machine

●●

Parameters influencing membrane structure and properties includeParameters influencing membrane structure and properties include

solvent/solvent/nonsolventnonsolvent, polymer concentration, evaporation time, humidity, , polymer concentration, evaporation time, humidity,

temperature and composition of the casting solution.temperature and composition of the casting solution.

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The membranes obtained after precipitation can be used directly The membranes obtained after precipitation can be used directly or or

subjected to dryingsubjected to drying.

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The resultant membranes are used in plateThe resultant membranes are used in plate--andand--frame and spiral wound frame and spiral wound

systems.systems.

Hollow Fiber Spinning

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Spinning is a physical process involving the extrusion of a polySpinning is a physical process involving the extrusion of a polymer mer

solution through an annular spinneretsolution through an annular spinneret.

●●

The term spinning originates from the production of manThe term spinning originates from the production of man--made textile made textile

fibersfibers

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Hollow fiber spinning is a tricky practical process and generallHollow fiber spinning is a tricky practical process and generally involves y involves

four main steps namely, solution formulation, extrusion, coagulafour main steps namely, solution formulation, extrusion, coagulation and tion and

treatment of the coagulated fibers.treatment of the coagulated fibers.

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A number of processing parameters influence the structure and heA number of processing parameters influence the structure and hence nce

the separation performance of hollow fiber membranes.the separation performance of hollow fiber membranes.

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Hollow fiber membranes can be fabricated in the form of dense anHollow fiber membranes can be fabricated in the form of dense and d

asymmetric structures.asymmetric structures.

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These structures differ only in the method used to solidify the These structures differ only in the method used to solidify the gel gel

filament.filament.

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A dense structure is usually fabricated by melt spinning while sA dense structure is usually fabricated by melt spinning while solution olution

spinning (phase inversion) yields asymmetric membranes.spinning (phase inversion) yields asymmetric membranes.

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The major techniques used in the fabrication of hollow fiber memThe major techniques used in the fabrication of hollow fiber membranes branes

as as summarisesummarise

in Figure 2in Figure 2

Figure2

Quench Bath

Spinneret

Nitrogen CylinderSteel MixingVessel

Metering Pump

Explosion-proof ovenTake-up drum

AIR GAP

Purge valve

Mass flow controller

Hollow Fiber Spinning Techniques

Melt Spinning Solution Spinning

Dry Spinning Wet Spinning Dry/Wet Spinning

Figure 4.1: Hollow fiber spinning techniques.

Membrane Fabrication –

Melt Spinning

Membrane Characterization

Table 4.1: Characteristics of the experimental membranes _________________________________________________________________ Parameter PSF membrane CA membrane _________________________________________________________________ Membrane type Hollow fiber Hollow fiber Membrane material Polysulfone Cellulose acetate aContact angle 56° 28º b Zeta potential (mV) -27 -15.5 MWCO 68 kDa 50 kDa cPure water flux Jpwf 13.9±1.65 27.62±2.27 (Lm-2h-1)

Pure water specific flux 43 ± 5 85 ± 7 (Lm-2h-1bar-1) Surface property Hydrophobic Hydrophilic Nominal surface area (300mm) 565.48 mm2 565.48 mm2

Internal diameter 300 µm 300 µm Outside diameter 600 µm 600 µm Effective area potted bundle of 100 filaments 565 cm2 565 cm2 _________________________________________________________________

Membrane autopsy by contact angle

Membrane Before contactAngle (°)

After contact Angle (°)

% of contact angleIncremental

Fouled with Sg. Ulu Pontian PSF (68 kDa) 56 48 - 14.2 CA (50 kDa) 28 21 - 25.0 Fouled with Bekok Dam PSF (68 kDa) 56 53 - 5.3 CA (50 kDa) 28 23 - 17.8 Fouled with Yong Peng PSF (68 kDa) 56 68 + 21.4 CA (50 kDa) 28 30 + 7.1

Contact angle characterization of clean and fouled membrane

SCANNING ELECTRON MICROSCOPE

Filamentaperture

Condenser aperture

Sample holderSample

Detector

Primary electron

Prinsip Kerja Scanning Electron Microscope

•

Scanning electron microscope (SEM) is a very simple and useful technique to determine the membrane structure. The samples of membrane were snapped under liquid nitrogen to give a clean break. The samples are taken out and mounted on sample stubs using double surface scotch tape with the surface to view facing up. These are then spurred-coated with gold using SEM sputter coater before being view with the scanning electron microscope.

Membrane Structures

Dense skin layer

Porous substructure

Symmetric

Integrally-skinned Asymmetric Composite membrane

Asymmetric membrane

Figure 4: PSF membrane

a) cross section b) outer edge

c) inner edge d) partial cross section

Figure 5: CA membrane

a) cross section b) outer edge cross section

Morphological analyses

Fouled SEM image of Yong Peng

water Clean surface of PSF membrane

Fouled SEM Image of Bekok

Dam Fouled SEM image of Ulu

Pontian

Figure 27: SEM micrograph of fouled UF PSF membrane

Fourier Transform Infra Red•

Molecular orientation in the active layer of flat sheet membranes was directly measured using plane polarized reflectance infrared spectroscopy because the preferred orientations of specific functional groups

can be easily and clearly determined.

••

Infrared spectroscopy measures vibrational

energy levels of molecules and records characteristics band parameters in terms of frequency (energy), intensity (polar character), band shape (environment of band) and polarization of various modes.

•

This technique can reveal anisotropy on the molecular level within a sample. A preferential alignment of randomly coiled chain molecules leads to differences in absorption of plane-polarized infrared spectra between parallel and perpendicular directions. This phenomenon is known

as linear dichroism.

•

The samples of membranes were mounted at the sample position with the outer skin surface facing the infrared beam and were rotated according to the shear direction (either vertical or horizontal). Then, spectra of linear dichroism

were obtained by straightforward subtraction of plane polarized

infrared spectra perpendicular to shear direction from plane polarized infrared spectra parallel to shear direction.

0.01

0.05

0.09

0.13

800 1000 1200 1400 1600 1800 2000

a

b

c

d

Wavenumbers (cm-1)

Yong Peng

water

Ulu

Pontian

riverBekok

Dam reservoir

1723 cm-1

-

C=O carboxylic groups

1725 cm-1

– COOH-1

1640 cm-1

amide I

1550 cm-1

amide II

1034 -1040 cm-1

–

C-O polysacc-N-acetyl sugar

1720 cm-1

-

C=O Carboxylic groups

Higher than BD

Figure 9: Figure 10:

Figure 11:

Differential Scanning Calorimetry

•

Differential scanning calorimetry

(DCS) is performed using a Mettler

Toledo DSC at

a heating rate of 10 oC/min to measure Tg that will provide a qualitative estimation of

the flexibility of polymer chains.

Glass Tr ansitionOnset 216.74 °CMidpoi nt 220.10 °C

Glass TransitionOnset 218.36 °CMidpoint 220.29 °C

mW2

min

°C40 60 80 100 120 140 160 180 200 220 240 260 280 300 320

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28

mg5

min0 10 20 30 40 50 60 70 80

^exo

STARe SW 9.00Lab: METTLER

X-Ray Diffraction (XRD) Analysis

• X-ray diffraction analysis were carried out on a Siemens Diffractometer

D5000

using a Cu-Kα

radiation source. Each sample was grounded using agate mortar in order to get very fine powder. Scanning speed and interval of the data collection was 0.05 °

and 2 θ/s. The

diffraction patterns were recorded over a range 2θ

of from 5 °

to 70 °

.

Hydrogen Nuclear Magnetic Resonance (H-NMR)

• H-NMR spectroscopy was used to determine the degree of sulfonation, DS of SPEEK. The spectrometers were recorded on a Varian Unity Inova

spectrometer at a resonance frequency of 399.961 MHz at room temperature. For each analysis, 3 wt% polymer solution was prepared in deutrated

dimethyl

sulfoxide

(DMSO-d6).

Water Uptake

• The membranes were first dried at 60 °C for 48 hours. The dried films were then immersed in deionized

water overnight at ambient

temperature. The water on the surface of wetted membranes was removed using tissue paper before weighing. Water uptake was then calculated as follows:-

• Water Uptake (%) = (Ww-Wd)/Wd

• where Ww

and Wd

are the weight of the

membranes after keeping in water and initial dried membranes, respectively

Methanol Permeability

1 M methanolA

Distilled waterB

Sampling point

Membrane

1) Gas Cylinder

3) F

lexi

ble

Hos

e

4) P

erm

eatio

nC

ell

5) Valve

6) Pressure Purge

7) Bubble Flow Meter

To Atmosphere2) Pressure Regulator

5) Valve

Gas Permeability

Calculation

•

Permeability/Fluks= Q/A.ΔP•

Rejection = 1-(Cp/Cf) x 100%