Membrane Separation
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Transcript of Membrane Separation
MEMBRANE TEST UNIT
1 | P a g e
ABSTRACT 2
INTRODUCTION 3
AIMS 4
THEORY 5
APPARATUS 9
PROCEDURE 9
RESULTS 11
DISCUSSION 12
CONCLUSION 14
RECOMMENDATIONS 16
REFERENCES 17
APPENDICES 18
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ABSTRACT
This experiment is conducted to study the characteristics on 4 different types of membranes
which are AFC 99 (polyamide film), AFC 40 (polyamide film), CA 202 (cellulose acetate)
and FP 100 (PVDF) by using membrane test unit (TR14). Membrane separation is a
technology which fractionates materials through pores and minutes of gaps in the molecular
arrangement of a continuous structure. Membrane separation can be classified by pore size
and by the separation driving force for example Microfiltration (MF), Ultrafiltration (UF),
Nanofiltration (NF), Ion-Exchange (IE) and Reverse Osmosis (RO). We need to operate the
plunger pump, control the valves, and collect the samples as well as weighing the samples.
After weighing the sample, graph of permeates weight versus time is plotted. Based on the
graph, membrane 1 and membrane 3 used in membrane process that operates at higher
pressure while membrane 2 and membrane 4 used in membrane that operates at lower
pressure. Membrane 1 used in reverse osmosis process and membrane 3 is in nanofiltration
which both of the tubes in these membranes are fitted with polyamide. The tubes fitted in
membrane 2 is polyethersulphone which for ultrafiltration while for membrane 4 is PVDF
which for microfiltration. This experiment is conducted successfully.
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INTRODUCTION
This Membrane Test Unit (Model: TR 14) has been designed to demonstrate the technique of
membrane separations which has become highly popular as they provide effective separation
without the use of heating energy as in distillation processes. This type of membrane is
widely used biotechnology and process industry. Heat sensitive materials, such as fruit juices,
can be separated or concentrated by virtue of their molecular weights. The unit consists of a
test module supplied with four different membranes, namely the reverse osmosis (RO),
nanofiltration (NF), ultrafiltration (UF) and microfiltration (MF) membranes, thus allowing
students or researchers to carry out membrane separation processes that are most widely used
in the food, dairy, pharmaceutical and chemical industries. This self-contained unit on a
mobile epoxy coated steel framework, requires only connection to a suitable electricity
supply and a normal cold water supply to be fully operational. It consists of a feed tank, a
product tank, a feed pump, a pressure regulator, a water bath, and a membrane test module.
All parts in contact with the process fluid are stainless steel, PTFE, silicone rubber or nitrile
rubber. The unit comes with a high pressure feed pump for delivering the feed to the
membrane unit at the desired flow rate and pressure. The retentate line can be either returned
to the feed tank or straight to the drain. Appropriate sensors for flow, pressure and
temperature are installed at strategic locations for process monitoring and data acquisitions.
In this experiment we need to study the characteristic on 4 different types of membranes. The
TR 14 unit is supplied with 4 membranes which are:
Membrane 1: AFC 99 (polyamide film)
Membrane 2: AFC 40 (polyamide film)
Membrane 3: CA 202 (cellulose acetate)
Membrane 4: FP 100 (PVDF)
The AFC 99 is rated with 99% NaCl rejection at maximum pressure and temperature which is
64 bar and 80 whereas the AFC 40 has 60% CaCl2 rejection at 60 bar and 60 Both of
these membranes use in operation of reverse osmosis. Meanwhile, the CA 202 is rated with
apparent retentation of 2000 MWCO and the FP 100 is 100000 MWCO. Both of these two
membranes use in ultrafiltration process which CA 202 operates at 25 bars and 30 while
the FP 100 is at 10 bar and 80
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The advantages of cross-flow membrane separations are the concentrate remains in a mobile
from suitable for further processing, possible to fractionate solutes of different sizes, can
prevent solid buildup on membrane surface so that higher overall liquid removal rate is
achieved and solute content of the concentrate ma be varied over a wide range.
AIMS
To study the characteristics of membrane by performing a characteristic study on 4
different types of membranes.
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THEORY
Membrane separation is a technology which fractionates materials through pores and minutes
of gaps in the molecular arrangement of a continuous structure. Membrane separation can be
classified by pore size and by the separation driving force for example Microfiltration (MF),
Ultrafiltration (UF), Nanofiltration (NF), Ion-Exchange (IE) and Reverse Osmosis (RO).
This figure is examples of different substance that correspondence to the pore size of the
membrane separation method.
Reverse osmosis separates aqueous ionic solutions of different concentration. There is an
osmotic pressure when the solvent moves from an area of high water potential to low water
potential so that equal ionic concentrations on each side of membranes. When a hydraulic
pressure is applied to the concentrated solution which is greater and in reverse to the osmotic
pressure, water molecules will pass to dilute solution side through the membrane. This
process can separate water from ions and low-molecular weight organic constituents.
Ultrafiltration enables precise separation, concentration and purification of dissolved and
suspended constituents based on the relative molecular size of substance. Microfiltration
membranes enable efficient and precise separation as well as concentration of suspended and
colloidal particles.
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REVERSE OSMOSIS ULTRAFILTRATION
MICROFILTRATION
The membrane separation techniques utilized in the dairy industry serve different purposes:
RO -used for dehydration of whey, UF permeate and condensate.
NF -used when partial desalination of whey, UF permeates or retentate is required.
UF -typically used for concentration of milk proteins in milk and whey and for
protein standardization of milk intended for cheese, yoghurt and some other products.
MF -basically used for reduction of bacteria in skim milk, whey and brine, but also
for defatting whey intended for whey protein concentrate (WPC) and for protein
fractionation.
Many theoretical models and the identification of new factors controlling flux, J or mass
transfer through membranes have been proposed. The build-up of deposited materials on the
surface has introduced the terms of hydrodynamic resistance which are the best outlined basic
operating patterns.
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The flux J will be given by:
J =
=
=
(1)
For most biological materials, is a variable depending on the applied pressure and time (the
compressible deposit), so that the expression requires a numerical solution.
A useful method for the effects of cross-flow removal of depositing materials is to write:
J =
(2)
Removal of solute by cross-flow is sometime assumed constant, and equal to the convective
particle transport at steady state which can be obtained experimentally or from an
appropriate model. In many situation however, steady state of filtration is seldom achieve. In
such case, it is possible to describe the time dependence of filtration by introducing an
efficiency factor, , representing the fraction of filtered material remaining deposit rather
than being swept along by the bulk flow. This gives:
RC =
, where o < < 1 (3)
Although deposition also occurs during ultrafiltration, an equally important factor controlling
flux is concentration polarization.
a) Applied pressure b) ln CA c) ln (cross-flow velocity)
Figure: typical dependence of membrane flux
a) applied pressure difference
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b) Solute concentration
c) cross-flow velocity
Solution containing molecular gel-forming solute will form a gel on the surface of the
membrane. The gel formation will contribute to formation of dynamic membranes. The
mechanism is as follows;
Due to convective flux through the membrane a concentration of the solution at the surface
CW increase and eventually reaches a gel formation concentration Cg (figure b) the flux, J
through the membrane depends on a concentration according to the relation;
J = k ln
(4)
Combining equation (1) and (4)
ln
=
(5)
As long as concentration Cw is less than Cg, Cw will increase with pressure, but the moment
Cw equals to Cg, an increase in bring about an increase of the layer resistance Rp, and the
flux will no longer vary with pressure.
Assuming no fouling effect, the membrane resistance Rm can be calculate from the flux
equation below:
J =
(6)
The slope obtain from the plot of flux J vs is equals to
the retention of any solute can
be express by the rejection coefficient, R
R =
(7)
Where Cf is final macrosolute concentration in the retentate
C0 is initial macrosolute concentration
V0 is initial volume
Vf is final retentate volume
This expression assumed complete mixing of retentate seldom accomplishes due to
concentration polarization. The apparent rejection coefficient depends on factors affecting
polarization including UF rate and mixing. For material entirely rejected, the rejection
coefficient is 1 (100% rejection); for freely permeable material it is zero.
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Rejection is a function of molecular size and shape. Nominal cut-off levels, defined with
model solute, are convenient indicators.
Fractional rejection membrane with low MW cut-off spans a narrower range of molecular
size than by more open membranes. For maximum retention of a solute, select a membrane
with nominal cut-off well below the MW of the species.
Many biological macromolecules tend to aggregate so that effective size may be much larger
that the native molecule, causing increase rejection. Degree of hydration, counter ions and
steric effect can cause molecule with similar molecular weights to exhibit very different
retention behaviour.
APPARATUS
The membrane test unit (TR14)
Sodium chloride solution
PROCEDURE
General start-up procedures
1. Ensure all valves are initially closed.
2. Prepare a sodium chloride solution by adding 100 gram of sodium chloride into 20
litre of water.
3. Fill up the tank with the salt solution prepared in step 2. The feed shall always be
maintained at room temperature.
4. Turn on the power for the control panel. Check that all sensors and indicators are
functioning properly.
5. Switch on the thermostat and make sure that the thermo oil is above the coil inside
thermostat. Check that the thermostat connections are properly fitted.
6. The unit is now ready for experiments.
General shut-down procedures
1. Switch off the plunger pump (P2).
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2. Close valve V2.
3. Drain all liquid in the feed tank and product tank by opening valves V3 and V4.
4. Flush all the piping with clean water. Close V3 and V4, fill the clean water to feed
tank until 90% full.
5. Run the system with the clean water until the feed tank is nearly empty.
Procedures
1. The general start-up is performed.
2. Valves V2, V5, V7, V11 and V15 are opened.
3. The plunger pump (P1) is switched on and valve V5 is slowly closed to set the
maximum working pressure at 20 bars. The pressure value at pressure gauge is
observed and the pressure regulator is adjusted to 20 bars.
4. Valve V5 is opened. Membrane maximum inlet pressure is set to 18 bars for
membrane 1 by adjusting the retentate control valve (V15).
5. The system is allowed to run for 5 minutes. The sample is collected from permeate
sampling port and the sample is weighed using digital weighing balance. The weight
of permeates every 1 minutes for 10 minutes.
6. Step 1 to 5 for membrane 2, 3 and 4 are repeated. The respective valves are open and
close and membrane maximum inlet pressure is adjusted for every membrane.
Membrane Open valves (step
2)
Sampling valves Retentate
control valve
Membrane
maximum inlet
pressure(bar)
1 V2, V5, V7, V11,
and V15
Open V19 and
closed V11
V15 18
2 V2, V5, V8, V12
and V16
Open V20 and
closed V12
V16 12
3 V2, V5, V9, V13
and V17
Open V21 and
closed V13
V17 10
4 V2, V5, V10, V14
and V18
Open V22 and
closed V14
V18 8.5
7. The graph of permeate versus time is plotted.
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RESULTS
Time (min) Weight of permeates (g)
Membrane 1 Membrane 2 Membrane 3 Membrane 4
1 49.21 236.63 265.43 536.17
2 83.43 394.11 297.60 768.43
3 117.27 465.75 327.29 1001.07
4 151.59 536.07 357.81 1233.24
5 185.40 605.49 386.91 1465.07
6 221.04 676.01 418.09 1696.85
7 255.55 746.12 448.69 1924.43
8 290.83 817.00 479.79 2153.87
9 327.34 889.99 512.76 2393.55
10 367.77 959.10 539.92 2608.04
0
500
1000
1500
2000
2500
3000
1 2 3 4 5 6 7 8 9 10
we
igh
t o
f p
erm
eat
es(
g)
Membrane 1
Membrane 2
Membrane 3
Membrane 4
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DISCUSSION
Membrane separation is based on separation mechanisms and size of the separated particles.
The membrane processes that have been widely used are microfiltration, ultrafiltration,
nanofiltration, reverse osmosis, electrolysis, dialysis, electrodialysis, gas separation, vapour
permeation, pervaporation, membrane distillation and membrane contactors. Pervaporation is
the only process that involves phase change. All processes except electrodialysis are pressure
driven.
We conduct this experiment to study the characteristics on 4 different types of membranes
which are AFC 99 (polyamide film), AFC 40 (polyamide film), CA 202 (cellulose acetate)
and FP 100 (PVDF). From the graph that has been plotted, the slope of the membrane 4 is the
steepest compared to other membranes. This followed by membrane 2, membrane 3 and
membrane 1 respectively.
Based on the graph, membrane 1 is used for reverse osmosis process. This is because the
weight of permeates for membrane 1 have the lightest weight. Reverse osmosis operates at
very high pressure which is more than 20 bras. Reverse osmosis require the greatest operating
pressure as it has the smallest pore-size range and has the ability to remove solids as small as
salts. Only small amounts of very low molecular weight solute can pass through the
membranes. Membrane 1 is nonporous, asymmetric, and composite with homogeneous layer
which has dense pore size. Reverse osmosis is mainly applied in production of pure water.
Apart from that, nanofiltration is a type of membrane process that uses membrane 3. This is
also same as reverse osmosis that operates at high pressure but not as higher as pressure used
in reverse osmosis. The driving force used in nanofiltration is between 4 to 20 bars.
Nanofiltration is used for organic, color and contaminant removal as well as for softening.
Membrane 3 is also asymmetric, microporous which has pore size between 1 to 5 nm. Main
application of nanofiltration is to separate small organic compounds and multivalent ions.
Membrane 2 operates in ultrafiltration. Ultrfiltration designates a membrane separation
process, driven by a pressure gradient, in which the membrane fractionates components of a
liquid as a function of their solvated size and structure. The membrane configuration is
usually cross-flow. The feed water flows across the membrane surface by limiting the extent
of particle deposition and formation on the membrane surface. The membrane pore size is
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larger allowing some components to pass through the pores with the water. Ultrafiltration
operates at lower pressure compared to nanofiltration and reverse osmosis. A type of
membrane 3 is asymmetric microporous and the size of pore is 5-100nm. The driving force
for this membrane is between 1-9 bars. Nanofiltration is applied in separation of
macromolecular solutions.
The membrane process for membrane 4 is microfiltration. In microfiltration, the membrane
separation process is similar to ultrafiltration but it has larger membrane pore size. Thus, this
will allow particles in the range of 0.1 to 10 micrometers to pass through. The pressure used
is basically lower than that of ultrafiltration process which is 0.5 to 2 bars. The membrane
configuration is usually cross-flow. This membrane is symmetric and asymmetric porous.
Microfiltration used in the clarification and sterile filtration.
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Reverse osmosis have been used to remove nitrate from contaminated groundwater as well as
remove high concentrations of naturally occurring fluoride from deep groundwater. It is also
effective in removing specific synthetic organic contaminates from contaminated
groundwaters. Nanofiltration is used as an alternative treatment method to lime softening in
order to reduce the level of calcium and magnesium in hard waters. NF also can remove
naturally occurring color and dissolved organic species which is responsible for the formation
of THMs and DBPs regulated by US EPA.
Microfiltration and ultrafiltration can be used for particulate removal to comply with surface
water treatment rule. Both of MF and UF can precede by pretreatment systems to precipitate
or co-precipitate dissolved inorganic and dissolved organic compound. MF used in separation
of bacteria and cells from solution whereas UF used in separation of protein and virus,
concentration of oil-in-water emulsions.
CONCLUSION
From this experiment, it can be concluded that membrane 1 is operate in reverse osmosis
process while membrane 3 is in nanofiltration process. Both of this membrane process
operate at very high pressures and are typically deployed for the removal of dissolved
inorganic and organic constituents. Low pressure membrane processes which are
microfiltration and ultrafiltration are applied for the removal of particulate and microbial
contaminants and can be operated under negative or positive pressure. Membrane 2 and
membrane 4 has been used in ultrafitration and microfiltration respectively.
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RECOMMENDATIONS
In this experiment, there are some recommendations that can be done in order to get the best
results which are:
During taking the weight of permeates by using digital weighing balance, the reading
should be taking in more significant figures so that the reading of the actual weight of
permeates are more accurate and the value of true error could be minimized.
The average weight of permeates should be calculated by taking the weight of
permeates in three times in order to get more accurate value of weight of permeates.
When collecting the sample from permeates sampling port, make sure that we used a
big container to support the volume of the sample and to avoid the sample from spill
out in order to get more accurate weight of permeates.
The system should be run in more than 5 minutes so that the system and membrane
maximum inlet pressure is more stabilized in order to get the accurate value of weight
of permeates.
To collect the sample, the sampling valves should be open and close simultaneously
so that there is no interruption during collecting the sample from permeates sampling
port.
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REFERENCES
1. (1986). Dairy Processing Handbook. In Dairy Processing Handbook (p. 125). sweeden:
Tetra Pak Processing Systems AB.
2. Eliane Rodrigues dos Santos Goes,Elisabete Scolin. Mendes, Nehemias Curvelo
Pereivela, Sueli Teresa Davantel de Barros. (2005). influence at different condition on the
concentration by reverse osmosis. Retrieved 9 april, 2012, from Alim.Nutr.Araquara:
http://serv-bib.fcfar.unesp.br/seer/index.php/alimentos/article/viewFile/489/452
3. http://www.solution.com.my/pdf/TR14(A4).pdf. (n.d.). membrane test unit. Retrieved 9
april, 2012, from solteq: http://www.solution.com.my/pdf/TR14(A4).pdf
4. membrane separation technology primer. (n.d.). Retrieved 8 april, 2012, from asahi kasei
chemicals: http://www.asahi-kasei.co.jp/membrane/microza/en/kiso/index.html
5. nakagawa, o. (2012, february 12). membrane separation. Retrieved april 8, 2012, from
wikipedia:
http://en.wikipedia.org/wiki/Membrane_technology#Membrane_separation_processes
6. Ripperger S., Schulz G. (1986). Microporous membranes in biotechnical applications. In
Bioprocess Engineering (pp. 43-49).
7. Zeman, Leos J., Zydney, Andrew L. (Inc,1996). Microfiltration and Ultrafitration,
Principles and Applications. In M. Dekker, Microfiltration and Ultrafitration, Principles
and Applications. New York.
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APPENDICES
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