ABSTRACT

This is a report from the experiment to study the characteristics of different types of

membrane. The development of the filter medium has helped the industry, specifically

filtration industry to achieve very fine levels of separation today. In its early days as a

separating medium, the membrane was a thin flexible sheet or a thin-walled flexible tube,

rendered semi-permeable by its production process. Its earlier applications covered reverse

osmosis and ultrafiltration. Then, the appearance of nanofiltration has overlapped the top end

of reverse osmosis and the lower end of ultrafiltration. Furthermore, appearance of

microfiltration has greatly increased the applicability of membrane media in separation

processes. In addition, though membranes are better known for liquid separation, they are

also widely used for gas and vapour separations. Ken Sutherland (2009) stated that, the

ability to make smart of functional membranes is an important development in membrane

materials, and the rotating or vibrating membrane unit offers a great promise. Even the

application of membrane has also been developed, as such; sterilisation of a liquid flow or

treating waste liquid.

1.0 INTRODUCTION

Semipermeable membranes involve in many separation processes of gaseous or liquid

mixture. Semipermeable membranes; which usually are of thin layers of a rigid material such

as porous glass or sintered metal allow one or more constituents of a mixture to pass through

more readily than the others. However, in some cases, the membranes are purposely designed

to be of flexible films which have a high permeability for certain types of molecules, and

made from synthetic polymers. (Warren L., 2005)

Out of the three groups of filtration, the principle of crossflow filtration; membrane

filtration was applied in this equipment, Membrane Test Unit (Model : TR 14). The

membrane in crossflow filtration is made up of ceramic, metal or polymer. The pores are

small enough to exclude most of the suspended particles. The feed suspension, in a crossflow

filter flows across the filter medium under pressure at a moderate velocity. There may be a

build up of a thin layer of solids on the surface of the medium, but the formation of the layer

is prevented by the high liquid velocity. (Warren L., 2005)

There are severel types of filters involve in the crossflow filtration. The first one is the

microfiltration. This type of filter is generally used for particles of the size range between 0.5

to10 μm. Besides that, ultrafiltration is also one of the types of filter in crossflow filtration. It

covers a wider range of particles sizes, from 0.5 μm to molecules with the size of about

10−3 μm. Next, for the separation of small molecules or ions, hyperfiltration and nanofiltration

is used. However, in such operation, reverse osmosis would also be applied when the osmotic

pressure has a major effect on the flux. The difference between these two filters is their type

of membrane. (Warren L., 2005)

2.0 OBJECTIVE

This experiment was carried out to study the characteristics of four different types of

membrane.

3.0 THEORY

The term membrane most commonly refers to a thin, film-like structure that separates

two fluids. It acts as a selective barrier which allow some particles or chemicals to pass

through but not others. In anatomy cases, membrane may refer to a thin film that is primarily

a separating structure rather than a selective barrier.

A membrane is a layer of material which serves as a selective barrier between two

phases and remains impermeable to specific particles, molecules, or substances when

exposed to the action of a driving force. Components that are not allowed to pass through the

membrane membrane retained in the retentate stream while the other allowed components

pass through the membrane into a permeate stream.

In reverse osmosis membrane process, a membrane must allow passage of certain

molecules and exclude or greatly restrict passage of others. In osmosis, a spontaneous

transport of solvent occurs from a dilute solute or salt solution to a concentrated solute or salt

solution across a semipermeable membrane which allows passage of the solvent but impedes

passage of the salt solutes. The solvent water normally flows through the semipermeable

membrane to the salt solution. The solvent can be reduced by exerting a pressure on the salt

solution, equilibrium is reached and the amount of solvent passing in opposite direction is

equal. The chemical potentials of the solvent on both sides of the membrane are equal.

Ultrafiltration membrane procedded has quite similarity with reverse osmosis. It is

pressure driven process where the solvent and small solute molecules pass through the

membrane and are collected as a permeate. Larger solute molecules do not pass through the

membrane and recovered in a concentrated solution. The solutes or molecules to be separated

generally have molecular weights greater than 500 and up to 1 000 000 or more.

Ultrafiltration membranes are too porous to be used for desalting. It is also used to separate a

mixture of different molecular weight proteins.

In microfiltration membrane processes, pressure-driven flow through a membrane is

used to separate micron-sized particles from liquids. The size range of particles ranges from

0.02 μm to 10 μm. This microfiltration separates particles from solutions. The particles are

usually larger than the solutes in reverse osmosis and ultrafiltration. Hence, osmotic pressure

is negligible. At the very low end of the size range, very large soluble macromolecules are

retained. The dividing line between ultrafiltration and microfiltration is not very distinct. The

pore sizes of the membranes and the permeate flux are typically larger than for reverse

osmosis and ultrafiltration. Usually the pressure drop used across the membranes varies from

1 psi to 50 psi.

4.0 APPARATUS AND MATERIALS

4.1 Membrane Test Unit ( Model TR 14 )

4.2 Digital weighing balance

4.3 Stopwatch

4.4 Beaker

4.5 Sodium Chloride and Water

5.0 EXPERIMENTAL PROCEDURES

5.1 The general start-up procedures had been performed by the laboratory technician.

5.2 The experiment for Membrane 1 was started. Valves V2, V5, V7, V11 and V15

were opened.

5.3 The working pressure was set to maximum at 20 bars by switching on the plunger

pump (P1), and slowly closing the valve V5. The pressure value at the pressure

gauge was observed and the pressure regulator was adjusted to 20 bars.

5.4 Valve V5 was opened. Then, the membrane maximum inlet pressure was set to 18

bars for Membrane 1 by adjusting the retentate control valve (V15).

5.5 The system was allowed to run for 5 minutes. The sample was stared to be

collected from permeate sampling port. To collect sample, valve V19 was opened,

and valve V11 was closed, simultaneously. The sample was weighed using digital

weighing balance. The weight of permeates was recorded at every 1 minute

interval, within 10 minutes.

5.6 Step 1 to 5 was repeated for Membrane 2, 3 and 4. The respective sets of valves

were opened and closed, and the membrane maximum inlet pressure for every

membrane was adjusted, according to the table below;

Membrane Open Valves

(step 2)

Sampling Valves Retentate

Control

Valve

Membrane

Maximum

Inlet Pressure

(bar)

1 V2, V5, V7,

V11, V15

Open V19, close

V11

V15 18.0

2 V2, V5, V8,

V12, V16

Open V20, close

V12

V16 12.0

3 V2, V5, V9,

V13, V17

Open V21, close

V13

V17 10.0

4 V2, V5, V10,

V14, V18

Open V22, close

V14

V18 8.5

Table 5.1 : Respective sets of valves for every membrane

5.7 The graph of weight of permeate versus time was plotted.

6.0 RESULTS

Time (min)Weight of Permeates (gram)

Membrane 1 Membrane 2 Membrane 3 Membrane 4

1.0 28.06 76.42 210.0 708.99

2.0 55.07 148.57 437.40 1371.42

3.0 68.85 218.84 641.95 2002.80

4.0 81.57 284.21 863.57 2655.76

5.0 106.69 352.08 1015.08 2703.28

6.0 132.68 421.15 1184.86 3378.67

7.0 157.99 488.43 1340.34 3926.87

8.0 182.88 555.79 1497.15 4449.29

9.0 206.78 625.14 1635.37 4529.13

10.0 233.42 693.08 1780.28 5249.47

Table 6.1 : Table of experimental results

1 2 3 4 5 6 7 8 9 100

1000

2000

3000

4000

5000

6000

Weight of Permeates VS Time

Weight of Permeates(gram) Membrane 1Weight of Permeates(gram) Membrane 2Weight of Permeates(gram) Membrane 3Weight of Permeates(gram) Membrane 4

Time (min)

Wei

ght o

f Per

mea

tes (

g)

Graph 6.1 : Graph of Weight of Permeates VS Time

7.0 DISCUSSIONS

The experiment was conducted to distinguish between four types of membranes. In this

experiment, the Membrane Test Unit (Model : TR 14) used has four membranes. They are;

reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF) and microfiltration (MF). This

experiment was started by preparing the sodium chloride solution first, by adding 100 gram

of sodium chloride into 20 litre of water. The solution was then filled into the feed tank of the

unit. Then, the experiment was conducted as in the experimental procedures.

The membranes that were used in this experiment were different from each other. They were

manufactured by PCI system, and were categorized according to their membrane types. The

type of membrane used in membrane 1, 2, 3 and 4 were made up of mostly polyamide film

and cellulose acetate. Polyamide film was widely used to make membrane because of its

permeability to water and its relative impermeability to various dissolved impurities

including salt ions and other small non-filtrable molecules. On the other hand, cellulose

acetate has an extremely low binding characteristic. This was why it is suitable and an ideal

type of membrane to be used for protein and enzyme filtrations. Another material that made

up the membrane is polyvinylidene difluoride (PVDF), a material that can provide high

protein and nucleic acid binding capacity.

One of the characteristics of membrane is hydrophilic membrane, which it has an attractive

response to water and can readily absorb water. This allows the material to be wetted forming

a watter film or coating on the surface of the membrane. In contrast, hydrophobic membrane

does not absorb water and have less charge than hydrophilic.

Based on the plotted graph, it can be seen that the permeation rate differs for each of the

membrane. Membrane 4 had the highest permeation rates. Next, it followed by Membrane 3,

then Membrane 2 and lastly, Membrane 1. Hence, permeates moves fastest through

Membrane 4 and slowest through membrane 1. The high permeation rate of Membrane 4 is

most likely due to its hydrophobic property, while as for membrane 3, its hydrophilic

property caused its permeation to be the slowest.

There were several errors occurred during the experiment which affect the results obtaind.

One of the errors is the digital weighing scale cannot measure the accurate weight of the

permeate due to the vibration of the pump, which made the reading of the weighing scale was

inconsistent. In order to reduce this error, the weighing scale should be put outside of the

unit. Besides that, the weight of the permeate that was permeated from the membrane

changed too fast, which eventually causing the weight recorded to be less accurate. Then, to

reduce this error , the experiment need to be repeated three time to get tha average reading of

the permeate weight.

8.0 CONCLUSION

Based on the results obtained, it was observed that permeation rate differs for each

membrane. Membrane 4 has the highest permeation rates, followed by Membrane 3, then

Membrane 2, and lastly Membrane 1.

Since Membrane 4 has the highest permeation rates, then, permeate moves fastest through it.

On the other hand, the permeate moves the slowest through Membrane 1.

9.0 RECOMMENDATIONS

9.1 The pressure must be ensured to be measured according to the experimental

procedure.

9.2 All valves must be ensured to be well functioning to avoid pressure drop during

experiment.

9.3 The weighing balance should be put outside of the unit to avoid inaccurate

measurement due to vibration.

9.4 Repeat the experiment 3 times to get more accurate permeate weight

measurements

REFERENCES

Christie John Geankoplis, Transport Processes and Separation Process principle 4th Edition,

Pearson Education Inc, United States, 2003

Warren L. McCabe, Unit Operations of Chemical Engineering 7th Edition, McGraw-Hill

Companies, Inc., 2005

Ken Sutherland, Membrane Filtration : What’s New in Membrane Filtration?, accessed from

http://ac.els-cdn.com.ezaccess.library.uitm.edu.my/S0015188209701934/1-s2.0-

S0015188209701934-main.pdf?_tid=50b5de28-dc0d-11e4-b751-

00000aab0f27&acdnat=1428291227_e5f2e2063039afca4a582f9f653582fd at 6th April 2015

APPENDIX