Membrane Test Unit

ABSTRACT

The experiment of membrane separation unit is mainly conducted to study the performance of characteristics of four different types of membrane. All of the four different types of membrane are basically based on the size of porous. The experiment is done with four different membranes and with four respective pressures that are (18, 12, 10 & 8.5 bars). The four membranes are Polyamide Film (AFC 99 & AFC40) for membrane 1 & 2. Membrane 3 is cellulose acetate (CA 202) while membrane 4 is PVDF (FP 100). This experiment is conducted by using water (H2O) and sodium chloride (NaCl). The data taken within 10 minutes and graph of weight of permeates versus time taken has been plotted. From the graph, it shows that membrane 4 which is the microfiltration membrane has the highest number of weight of permeates entering the membrane. This is followed by membrane 2, which is nanofiltration(NF), membrane 3 ultrafiltration(UF) and finally membrane 1 which is the reverse osmosis (RO). This experiment has been conducted successfully.

INTRODUCTION Membrane permeation is a separation process involving the selective transport of gas molecules through a permeable polymeric film. Unlike most chemical engineering separation processes which are governed by phase equilibrium relations, membrane separation is based primarily upon the relative rates of mass transfer. The membrane test unit (Model: TR14) 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. 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. Ultrafiltration and microfiltration membranes are usually specified in terms of their “molecular weight cut-off” (MWCO), whereas the nanofiltration and reverse osmosis membranes are specified in terms of their “percentage rejection of salts”. Polymeric membranes are widely used and supplied in the form of modules that give membrane areas in the range of 120m2.The membranes that are supplied with the model TR 14 unit is classifies as tubular type which is widely used and have turbulent flow conditions. The system is in a cross flow configuration where the feed solution is pumped parallel to the membrane at a velocity in the range of 1-8ms-1 with a pressure difference of 0.1-0.5MPa across the membrane. Liquid

1

permeates through the membrane and feed emerges in a more concentrated form on exit form module.

Figure 1: A tubular (multi-channel) type of membrane

OBJECTIVES To perform a characteristic study on 4 different types of membranes

THEORY

Membrane separation technology has evolved from a small-scale laboratory technique to a large-scale industrial process during the past 30 years. Numerous theoretical models for ultrafiltration have been proposed along with the identification of new factors controlling flux or mass transfer through membranes. The basic operating patterns are best outlined in terms of the hydrodynamic resistance resulting from the build up of deposited materials on the membrane surface. The flux, J will be given by:

2

For most biological materials, α 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:

Removal of solute by cross-flow is sometimes assumed constant, and equal to the convective particle transport at steady state (JssCb), which can be obtained experimentally or from an appropriate model. In many situations however, steady state of filtration is seldom achieved. In such cases, it is possible to describe the time dependence of filtration by introducing an efficiency factor β, representing the fraction of filtered material remaining deposit rather than being swept along by the bulk flow. This gives:

Although deposition also occurs during ultrafiltration, an equally important factor controlling flux is concentration polarization (Figure 2). Typical operating patterns of ultrafiltration are shown in Figure 3c.

Figure 2: Concentration Polarization at a Membrane Surface. (Cw = Solute Concentration at Membrane Surface, Cb = Bulk-Solute Concentration)

3

Figure3: Typical Dependence of Membrane Flux. (a) Applied Pressure Difference, (b) Solute Concentration, (c) Cross-Flow Velocity

Solution containing macromolecular 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 increases and eventually reaches a gel formation concentration Cg (Figure 8b). The flux, J through the membrane depends on a concentration according to the relationship:

Combining Equations (1) and (4),

4

As long as concentration Cw is less than Cg, Cw, will increase with pressure, but the moment Cw, equals Cg, an increase in brings about an increase of the layer resistance RΔΡp, and the flux will no longer vary with pressure (Figure 8a).

Assuming no fouling effect, the membrane resistance Rm can be calculated from the flux equation below:

The slope obtained from the plot of flux, J versus ΔΡ is equal to 1/mRv. While the retention of any solute can be expressed by the rejection coefficient, R.

Where; Cf = final macrosolute concentration in the retentate C0 = initial macrosolute concentration V0 = initial volume V f = final retentate volume This expression assumes complete mixing of retentate seldom accomplished 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. Rejection is a function of molecular size and shape. Nominal cut-off levels, defined with model solute, are convenient indicators. % Removal can be calculated from the relation:

5

Where; Cf = Concentration in feed Cp = Concentration in permeate Fractional rejection by membranes 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 than native molecule, causing increased rejection. There are various laboratory applications of ultrafiltration (UF) systems, such as: • Apple juice clarification • Pineapple/lime/orange/sugar cane juice clarification • Clarification of fermentation broths • Enzyme separation and concentration

MATERIALS & APPARATUS

Sodium chloride, water, weighing balance, Membrane Test Unit (Model: TR 14), stop watch.  Membrane 1 : AFC 99 (Polyamide Film)  Membrane 2 : AFC40 (Polyamide Film)  Membrane 3 : CA 202 (Cellulose Acetate)  Membrane 4 : FP 100 (PVDF)

6

PROCEDURE General start-up procedures 1. Ensures that all valves are initially closed. 2. Sodium chloride solution was prepared by adding 100 gram of sodium chloride into 20liter of water. 3. The feed tank is filled with the salt solution prepared in step 2. The feed shall always be maintained at room temperature. 4. The power for the control panel is turned on. All sensors and indicators are checked to function properly. 5. Thermostat is switched on and make sure the thermo oil level is above the coil inside thermostat. The thermostat connections are properly fitted. 6. The unit is now ready for experiments. Experimental Procedures

1. The experiment is started for membrane 1. Valves V2, V5, V7, V11 and V15 are opened. 2. The plunger pump (P1) is switched on to set the maximum working pressure at 20 bars and slowly close valve V5. Pressure value at pressure gauge is observed and the regulator is adjusted to 20 bars. 3. Valve V5 is opened. Maximum inlet pressure is set to 18 bars for membrane 1 by adjusting the retentate control valve (V15). 4. The system is allowed to run for 5 minutes. After 5 minutes, the sample is collected and weight using digital weighing balance. The weight of permeates is recorded every 1 minutes for 10 minutes. 5. Step 1 to 5 is repeated for membrane 2, 3 and 4. The respective valve is open and close and the membrane maximum inlet pressure is adjusted for every membrane.

7

Membrane

Open valves

Sampling

Retentate

Membrane

(step 2 )

valves

control valve

maximum inlet pressure (bar)

1

V2, V5, V7,

Open V19 and

V11 and V15

close V11

V2, V5, V8,

Open V20 and

V12 and V16

close V12

V2, V5, V9,

Open V21 and

V13 and V17

close V13

V2, V5, V10,

Open V22 and

V14 and V18

close V14

2

3

4

V15

18

V16

12

V17

10

V18

8.5

6. The graph of permeate weight versus time is plotted General shut-down procedures 1. Plunger pump (P2) is switched off. 2. Valve V2 is closed. 3. All the liquid in the feed tank and product tank is drained by opening valves V3 and V4. 4. The piping is flushed with clean water. V3 and V4 is close, the clean water is filled to the feed tank until 90% full. 5. The system is run with the clean water until the feed tank is nearly empty.

8

RESULTS

time (min)

membrane 1

Membrane 2

Membrane 3

Membrane 4

1 2 3 4 5 6 7 8 9 10

27.38 45.50 64.19 83.84 101.65 120.43 139.38 157.96 176.56 195.82

62.53 119.53 178.17 280.55 286.76 342.33 398.02 453.59 511.57 567.63

19.86 29.39 39.94 48.98 60.41 66.85 76.51 85.70 93.46 99.52

184.11 278.36 418.06 580.95 732.81 890.05 1048.56 1205.16 1363.33 1521.06

Membrane 1

Graph Of Permeate Weight Vs. Time 250

permeate weight (g)

200 150 100

membrane 1

50 0 0

2

4

6

8

10

12

Time(min)

9

Membrane 2

Graph Of Permeate Weight Vs. Time 600

permeate weight (g)

500 400 300 membrane 2

200 100 0 1

2

3

4

5

6

7

8

9

10

time (min)

Membrane 3

Graph Of Permeate Weight Vs. Time 600

permeate weight (g)

500 400 300 Membrane 3

200 100 0 1

2

3

4

5

6

7

8

9

10

Time (min)

10

Membrane 4

Graph Of Permeate Weight Vs. Time 1600

permeate weight (g)

1400 1200 1000 800 membrane 4

600 400 200 0 0

2

4

6

8

10

12

Time (min)

11

DISCUSSION

According to the results of the experiment, it shows graphs of weight of permeate against time for 4 types of membranes. All the graphs shows straight line which shows the weight of permeates entering all four membranes increasing as the time increase. For membrane 4, the graph shows that it has the most weight of permeate entering the membrane with total weight of sample collected is 8222.45g within 10 minutes. By referring to the theory, membrane 4 is has the biggest pores than other membranes. It is rated with apparent retention character of 100000 MWCO and Membrane 3 is CA 202 which only 2000 MWCO. The graph also shows the consistent increment in weight of permeates entering the membrane. Thus, membrane 4 is known as microfiltration. Membrane 3 has the least total of permeates weight entering which is 620.62g within 10 minutes. It is known as ultrafiltration. Ultrafiltration membranes are usually specified in terms of their "molecular weight cut-off" (MWCO). Membrane 1 is reverse osmosis. Reverse osmosis is a high-pressure process as the permeate contains a very low concentration of dissolved solids. Membrane 2 is nanofiltration in which a pressure driven membrane process with performance characteristics between reverse osmosis and ultrafiltration. The results also shows that membrane 2 has higher weight of permeate entering than membrane 1. This is due to membrane 2 which AFC 40 has 60% CaCl2 rejection compared with Membrane 1; AFC 99 which rated with 99% NaCl rejection. The results obtained quite similar to the theory which shows that the experiment was successfully conducted. At the end of this experiment, we have been encountering some error in conducting this experiment. There might be some blockage inside the pipeline which affecting the flow of the permeates entering the membranes which lead to inaccurate reading from the weight balance and thus affecting the overall results.

12

CONCLUSION In conclusion, the objective of the experiment which is to study the different 4 types of membrane the experiment is successfully conducted. It can be concluded that membranes consists of several types and has different characteristics compare to each other. The most effective membrane is microfiltration, followed by nanofiltration , ultrafiltration and reverse osmosis.

RECOMMENDATION 1. Always run the experiment after fully understanding the equipment and procedures 2. Dispose all liquids immediately after each experiment. 3. Do not leave solutions or waste over long period of time. 4. Always tare the digital weighing balance before taking weight readings

5. Always observe all safety precautions in laboratory. 6. Always wear protective shoes and helmet throughout the laboratory session.

REFERENCES 

Warren L. McCabe, Julian C. Smith, Peter Harriott, “Unit Operations of Chemical Engineering”, 5th Edition, McGraw Hill, 1993



Christi J. Geankoplis, “Transport Processes and Unit Operations”, 3rd Edition, Prentice Hall International Edition, 1995



http://www.solution.com.my/pdf/TR14(A4).pdf



http://www.scribd.com/doc/102685260/10/About-Membrane-SeparationProcesses



http://chemical.eng.usm.my/ekc394/exp_manual/Experiment%2013%20%20Study%20of%20Ultrafiltration%20Operation.pdf

13

APPENDICES

14