Membrane Separation

INTRODUCTION Separation by the use of membranes are becoming increasingly important in the process industries. In this relatively new separation process, the membrane acts as a semipermeable barrier and separation occurs by the membrane controling the rate of the movement of various molecules between two liquid phase, two gas phases, or a liquid and a gas phase. The two fluid phases are usually miscible and the membrane barrier prevents actual, ordinary hydrodynamic flow. A classification of the main types of membrane separation follows. Membrane separation processes have very important role in separation industry. This Membrane Separation Unit has been designed to demonstrate the techniques of membrane separations which are becoming highly popular as they provide effective separation without the use of heating energy as in distillation processes. For the mass transfer at the membrane, two basic models can be distinguished: the solution-diffusion model and the hydrodynamic model. In real membranes, these two transport mechanisms certainly occur side by side, especially during the ultra-filtration. Depending on the type of membrane, the selective separation of certain individual substances or substance mixtures is possible. Important technical applications include drinking water by Reverse Osmosis (RO), filtrations in the food industry, the recovery of organic vapors such as gasoline vapor recovery and the electrolysis for chlorine production. But also in wastewater treatment, the membrane technology is becoming increasingly important. In this experiment, we use the SOLTEQ Membrane Test Unit (Model : TR 14) as the device to run this experiment. This apparatus has to be desingn to demonstrate the techinuque of membrane separations which has become hinghly popular as they provide effective separation without the use of the heating energy in distilation process. Heat sensitive materials, such as fruit juices can be separated or concentrated by virtue of their molecular weights. The unit consits of a test module supplied with four different membranes, namely Reverse Osmosis (RO), nano filtiration (NF), and microfiltration (MF) membranes

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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.

Reverse osmosis (RO) is a membrane-technology filtration method that removes many types of large molecules and ions from solutions by applying pressure to the solution when it is on one side of a selective membrane. The result is that thesolute is retained on the pressurized side of the membrane and the pure solvent is allowed to pass to the other side. To be "selective," this membrane should not allow large molecules or ions through the pores (holes), but should allow smaller components of the solution (such as the solvent) to pass freely. Nanofiltration describes a process of water purification that remove contaminats from the water to produce clean, clear and pure water. Nanofiltrition is a form a reverse osmosis, that will remove bivalent hardness, calcium, and magnesium plus sulphate but leave in most of the single valent sodium ion. Ultrafiltration is a separation process using membranes with pore sizes in the range of 0.1 to 0.001 micron. Typically, ultrafiltration will remove high molecular-weight substances, colloidal materials, and organic and inorganic polymeric molecules. Low molecular-weight organics and ions such as sodium, calcium, magnesium chloride, and sulfate are not removed. Because only high-molecular weight species are removed, the osmotic pressure differential across the membrane surface is negligible. Low applied pressures are therefore sufficient to achieve high flux rates from an ultrafiltration membrane. Flux of a membrane is defined as the amount of permeate produced per unit area of membrane surface per unit time. Generally flux is expressed as gallons per square foot per day (GFD) or as cubic meters per square meters per day. 2

Microfiltration is a membrane technical filtration process which removes contaminants from a fluid (liquid and gas) by passage through a microporos membrane. A typical microfiltration membrane pore size range is 0.1 to 10 micrometers (µm). Microfiltration is fundamentally diffrenent from reverse osmosis and nanofiltration because those systems use a pressure as a meaans of forcing water to go from low pressure to high pressure.Microfiltration can use a pressurized system but it does not need to include pressure.

AIM/OBJECTIVE To study the characteristics of 4 different types of membrane silicon in terms of separation process. THEORY The term membrane most commonly refers to a thin, film-like structure that separates two fluids. It acts as a selective barrier, allowing some particles or chemicals to pass through, but not others. In some cases, especially in anatomy, membrane may refer to a thin film that is primarily a separating structure rather than a selective barrier. A membrane is a selective barrier that permits the separation of certain species in a fluid by combination of sieving and sorption diffusion mechanism. Separation is achieved by selectively passing (permeating) one or more components of a stream through the membrane while retarding the passage of one or more other components Membrane processes are characterized by the fact that a feed stream is divided into 2 streams: retentate and permeate. The retentate is that part of the feed that does not pass through the membrane, while the permeate is that part of the feed that does pass through the membrane. The optional "sweep" is a gas or liquid that is used to help remove the permeate. The component(s) of interest in membrane separation is known as the solute. The solute can be retained on the membrane and removed in the retentate or passed through the membrane in the permeate.

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Figure 1.0 – process of membrane technology

The concept of a membrane has been known since the eighteenth century, but it remained as only a tool for physical or chemical theories development until the end of World War II, when drinking water supplies in Europe were compromised and membrane filters were used to test for water safety. However, due to the lack of reliability, slow operation, reduced selectivity and elevated costs, membranes were not widely exploited. The first use of membranes on a large scale was with microfiltration and ultra-filtration technologies. Since the 1980’s, these separation processes, along with electrodialysis, are employed in large plants and, today, a number of experienced companies serve the market. 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. Some components are allowed passage by the membrane into a permeate stream, whereas others are retained by it and accumulate in the retentate stream. Some advantages of membrane separation are less energy-intensive, since they do not require major phase changes, do not demand adsorbents or solvents, which may be expensive or difficult to handle and the equipment simplicity and modularity, which facilitates the incorporation of more efficient membranes. The particular advantage of membrane separation processes is that it operate without heating and thus are energetically usually lower than conventional thermal separation processes (distillation, Sublimation or crystallization). This

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separation process is purely physical and, thanks to its gentle separation, the use of both fractions (permeate and retentate) is possible.

APPARATUS 1) Membrane Test Unit (Model TR14) 2) Digital Weighing Balance 3) Stopwatch 4) Beaker

MATERIAL 1) Sodium chloride. 2) Water.

PROCEDURE General start-up procedure 1.

All the valves were making sure initially closed.

2.

A sodium chloride solution was prepared by adding 100g of sodium chloride into 20L of water.

3.

The tank was filled up with the salt solution that was prepared in step 2. The feed was maintained at room temperature.

4.

The power for control panel was turned on. All sensors and indicators were checked to functioning properly.

5.

Thermostat was switched on and the thermo oil level was checked to make sure it is above the coil inside thermostat. The thermostat was checked if connections were properly fitted. The temperature was adjusted at the thermostat to maintain feed temperature.

6.

The unit is now ready for experiments.

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Experiment procedure

1.

The experiment was started with membrane 1. Valves V2, V5, V7, V11 and V15 were opened.

2.

To set the maximum working pressure at 20 bars, the plunger pump (P1) was switched on and valve V5 was slowly closed. The pressure value at pressure gauge was observed and the pressure regulator was adjusted to 20 bars.

3.

Valve V5 was opened. Then, membrane maximum inlet pressure was set to 18 bars for Membrane 1 by adjusting the retentive control valve (V15).

4.

The system was allowed to run for 5 minutes. Sample from permeate sampling port was collected and the sample was weighed using digital weighing balance. The weight of permeates was recorded every 1 minute for 10 minutes.

5.

The 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 was adjusted for every membrane.

Membrane

Open Valves

Sampling

Retentive

Membrane

Valves

control valve

maximum inlet pressure(bar)

1

V2, V5, V7, Open V19 and V11 and V15

2

3

4

6.

12

V17

10

V18

8.5

close valve V13

V2, V5, V10, Open V22 and V14 and V18

V16

close valve V12

V2, V5, V9, Open V21 and V13 and V17

18

close V11

V2, V5, V8, Open V20 and V12 and V16

V15

close V14

The graph of permeate weight versus time was plotted.

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General shut-down operation 1.

The plunger pump was switched off.

2.

Valve 2 was then closed.

3.

All liquid in the feed tank and product tank were drained by opening valves V3 and V4.

4.

The entire pipes were flushed with clean water. V3 and V4 were closed; the clean water was filled to the feed tank until 90% full.

5.

The system was run with the clean water until the feed tank is nearly empty.

RESULTS Membrane 1 Times (mins)

Weight of sample (g)

0

0

1

30.45

2

19.22

3

19.07

4

18.86

5

18.98

6

17.33

7

18.69

8

19.33

9

20.44

10

19.26

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Membrane 2

Times (mins)

Weight of sample (g)

0

0

1

75.23

2

64.24

3

59.23

4

69.88

5

66.03

6

66.25

7

64.50

8

67.39

9

64.81

10

67.80

Times (mins)

Weight of sample (g)

0

0

1

14.43

2

5.44

3

5.00

4

5.28

5

5.61

6

5.39

7

5.10

8

4.90

9

4.95

10

4.95

Membrane 3

8

Membrane 4

Times (mins)

Weight of sample (g)

0

0

1

112.30

2

127.38

3

128.16

4

133.84

5

147.35

6

145.02

7

146.77

8

146.51

9

144.23

10

145.71

DISCUSSION This experiment has been done to fulfil the objective which is to perform a characteristic study on four different types of membrane. In doing this experiment, the apparatus used to accomplish the objective is SOLTEQ Membrane Test Unit (Model: TR14). This unit has been designed to demonstrate the technique of membrane separations which has become highly popular as it provide separation in effective way without using heat energy as used in distillation process. Heat sensitive materials, such as fruit juices can be separated or concentrated by virtue of their molecular weight. In this unit, there are four types of membrane which each of them is differ with each other. The four membranes I, II, III and IV are namely first, reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF) and lastly microfiltration (MO) membranes respectively while in the case of membrane type are AFC99, AFC40, CA202 and FTP100 respectively. Every type of this membrane has its own characteristics which differ in each other as shown in table below;

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Membran

Material

e type

1

AFC99

Max

Max

Max

Apparent

Hydro

Solvent

pH

pressur

Temperatur

Retention

Philicit

Resistanc

e

e

character

y

e

Range

(bar)

1.5-12

64

80

99% NaCl

3

++

Polyamid

1.5-

60

60

60%

4

++

e

9.5

Polyamid

(

e Film

2

AFC40

Ca

Film

3

CA202

Cellulose

2-7.25

25

30

2000 MW

5

+

1.5-12

10

80

100,000M

1

+++

Acetate

4

FP100

PVDF

W

From the table above, its show that each membrane type have different characteristic in each other. The first characteristics are based on its material. Membrane I and membrane II were made up from the same element which is Polyamide Film while the other two membranes were made up from cellulose acetate and PVDF. Polyamide film (membrane I and II) is known as its permeability to water and its relative impermeability to various dissolved impurities including salt ions and other small non-filterable molecules. Membrane III is made of cellulose acetate which has an extremely low binding characteristic that made it ideal for protein and enzyme filtrations. The material that membrane IV is made of is polyvinylidene difluoride (PVDF). PVDF is a material that can provide high protein and nucleic acid binding capacity. In terms of maximum pH range, membrane I and IV have the maximum capacity of range while membrane II and II were the least. While in properties of maximum operating 10

pressure, membrane IV shows the least operation while membrane I is the most maximum operating unit in term of pressure. The other characteristics of the membrane is apparent retention character with membrane I rated as 99% NaCl rejection, membrane II with 60% CaCl2 rejection, membrane III with 2,000 MWCO and membrane IV with 100,000 MWCO. Furthermore, the membranes are characterized with their own hydrophilicity level. Hydrophilic membrane is a membrane that has an attractive response to water and can readily adsorb water. This allows the material to be wetted forming a water film or coating on the surface of the membrane. Hydrophobic membrane is the opposite of it. Usually hydrophilic membrane has more charge than hydrophobic membrane. Membrane III has the highest hydrophilic property followed by membrane II, I and IV. These mean that membrane IV has the highest hydrophobic property and usually known as hydrophobic membrane. In addition, membrane IV became the highest solvent reistent other than the three membrane (I, II and III). In doing this experiment, approximately about 100mL sodium chloride has been used as the reagent (feed). The membrane has been set to a certain maximum pressure inlet for a safety regulation so as not to exceed the maximum operation pressure of the membrane. Then, the sample from permeate was collected for 10 minutes. In each 1 minute interval, the weight of permeate was recorded. After the 10 minutes past, these steps were carried out again for the others membranes unit. All the data got from this experiment was tabulated in the table in result section. From the result, it shows the increasing in weight of permeate with time (as time increase, weight of permeate increase) for all four membranes. Permeate is actually a part of the feed stream that passed through the membrane, while a part of the feed that did not pass through the membrane is called the retentate. In the graph plotted, it shows that there are different permeation rate for each of membrane, with membrane IV has the highest permeation rate followed by membrane II, I and lastly III. Thus, permeates moves faster through membrane IV and slower in membrane III. The high permeation rate of membrane 4 is most probably due to its hydrophobic property, whereas the low permeation rate of membrane 3 is most probably due to its hydrophilic property. The membrane separates a wide range of particle sizes ranging from monoions to macromolecules. In doing this experiment, the result get may be not 100% accurate although it follows the theory. The error could be due to the lack of attention in doing the experiment, such as not alert in taking the record in 1 minute’s interval and not accurate in adjusting the maximum 11

inlet pressure. This experiments can be improve by followed the recommendations suggested at recommendation sections. CONCLUSSIONS As the conclusions, it can be said that the increase and decrease in the membrane were almost similar to each other. Even though it was kind of hard to be detected, however, if the graph were properly analyzed, the curves for each and one of the membranes were almost the same. However, the only things that distinguish these curves were the value plotted in each curve. It can be seen based on the graph plotted; the value plotted for the first membrane was the smallest. The value of the weight collected for each membrane increases along with the membranes used. It can be seen that the forth membrane carried the largest value of weight of the collected. This shows that every membrane will give out the same pattern at the outlet however, only the values of the weight were different from each other. Therefore, this shows that the separation process was the fastest in the forth membrane and the first membrane was the slowest.

RECOMMENDATION 1) Repeat the experiment 2 or 3 times for each membrane in order to calculate the average reading. 2) The digital weighing balance should not be put near the pump as it is moving while taking reading. Thus error could be happen. 3) Wearing the gloves during taking the sample. 4) You must be alert with time during taking the sample.

REFERENCES 1) http://en.wikipedia.org/wiki/Membrane_technology 2) http://vedyadhara.ignou.ac.in/wiki/images/6/63/Unit_11_Membrane.DOC_1.pdf 3) http://www.epa.gov/ogwdw/disinfection/lt2/pdfs/guide_lt2_membranefiltration_final. pdf

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APPENDIX

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