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
●●
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
●●
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.
●●
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%