Introduction5+Prelab... · Web view(McCabe 1035) There are several membrane modules used, these include plate and frame, spiral-wound, and hollow-fiber. The one that will be used

Ultrafiltration University of Illinois

Ultrafiltration

Ultrafiltration uses a membrane filter to mechanically filter unwanted components from a feed solution based on varying molecule sizes. In the case of this lab skim milk will be removed from water by proper utilization of the membrane by varying pressure at the inlet and outlet of the filtering column.

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Unit Operations ChE 382 Group 5 Spring 2011 2/15/2011

Damo, Duffy, Guerrero, Hsu, Kosak, Qamar, Tyska


Lab Prep Report

Unit Operations II Lab 2

February 15, 2011

Group 5

Andrew Duffy

Daniyal Qamar

Jeff Tyska

Bernard Hsu

Ryan Kosak

Tomi Damo

Alex Guerrero

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1. Introduction

The purpose of this unit operation is to separate a solution using the ultrafiltration method.

Ultrafiltration utilizes membranes in order to separate components from the feed stream. The

operational description of ultrafiltration is that a mixed stream at high pressure comes into the

tube side and as it flows the permeate is removed radially outwards. This method of separation

is used to either remove a desired component, the permeate, or concentrate a stream, the

retentate, by selectively removing undesired components from it. The membrane should have a

high permeability for permeate and a low permeability for retantate (Wankat, 541). Membrane

separators are used when applications such as evaporation are impractical for the process in

mind. The key component in membrane separation is the membrane; it is responsible for

successfully selecting out the desired components by pore size. The operation is based on

selecting not only a membrane than separates correctly but one that can operate at desired

conditions such as high pressure, high temperature and possible highly corrosive conditions.

This operation uses a bundle of hollow fiber tubes in order to concentrate a water based

colloidal solution, milk, within the retantate. On the outer side, the shell side, of the membrane

the solvent, water, will be removed thereby concentration the milk. This separation is

accomplished by the pores in the membrane and also by the high pressure in the tubes forcing the

solution against the membrane.

The feed is held and prepare in a tank where water is used to dilute the milk. Then the

stream gets pumped into the membrane system where it separates. The retantate is directed back

into the feed tank while the water is directed to a permeate tank. This operation also involves a

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rigorous cleaning process due to the fouling affects of the feed. It is crucial to proper separation

that the membrane and transport pipes are free of buildup it improve efficiency of the system.

2. Literature Review/Theory

Ultrafiltration is a separation that takes advantage of the differing physical sizes of the

individual molecules to separate solute from solvent. In Ultrafiltration a hydrostatic pressure is

utilized as a driving force to transport certain components through a membrane which shows

different permeability for different components. As a result a feed solution is converted into a

purer filtrate and a retentate. The filtrate contains all components that have permeated the

membrane, and the retentate contains the components that are retained or rejected by the

membrane. The performance of a membrane in a pressure-driven separation process is

determined by its filtration rate, the membrane flux, and by the membrane separation properties.

Membrane flux and separation properties are a function of membrane permeability for the

different components of the solution and the applied hydrostatic pressure. (Strathmann 702) In

our experiment, the skim milk molecules are much larger than the water molecules so they will

be removed in the retentate, while the smaller particles will be removed in the permeate.

Examples of some other particles that get rejected by ultrafiltration are oils, particulate matter,

bacteria and suspended solids large macromolecules and proteins. (Koch) Below is a diagram of

a single tube ultrafilter that illustrates the principle of ultrafiltration.

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Figure 1: Simple diagram of a single-tube ultrafilter. (Strathmann 686)

The structure of an ultrafiltration membrane is asymmetric, with the smallest pores on the

surface facing the feed solution. Their diameters at the feed side surface of the membrane are

between 2 and 10 nm and the components retained by an ultrafiltration membrane have a

molecular weight between 5000 and several million Dalton. (Strathmann 686) Ultrafiltration

membranes have a range of pore sizes in the selective layer, and they are often characterized by a

molecular weight cutoff based on measurements of fraction rejected versus molecular weight.

Molecules larger than the cutoff size are almost completely rejected, but there is a wide range of

sizes for which partial rejection occurs. (McCabe 1035) There are several membrane modules

used, these include plate and frame, spiral-wound, and hollow-fiber. The one that will be used in

this lab is the hollow-fiber Ultrafiltration membrane. These have diameters of 0.2 to 2.0 mm, and

hundreds of thousands of fibers are sealed in each cylindrical module. Flow through the fibers is

usually laminar, but the velocity is kept high to give high shear at the wall and improve the flux.

The area per unit volume is greatest for the smallest fibers, but these are most susceptible to

plugging by suspended matter in the feed. Since ultrafiltration membranes also retain some

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relatively low molecular weight solutes, osmotic pressure differences between the feed and the

filtrate can be significant. (Strathmann 686)

Figure 2: Cross section of a polysulfane Ultrafiltration membrane. (McCabe 1034)

There are several other separation methods such as reverse osmosis, nanofiltration,

microfiltration, and particle filtration. Reverse Osmosis rejects the finest of particles ranging in

the 0.001 microns size while simple particle filtration only gets rid of particles that are about

1000 microns big. (Koch Membrane). Dialysis is another method for the purification of solutions

and ultrafiltration is often confused with dialysis. Although both these methods have a semi

permeable membrane they utilize different driving forces dialysis makes use of the concentration

difference between two solutions while, as stated earlier, ultrafiltration is pressure driven.

(Neligan)

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Figure 3: Filtration methods and the particles rejected

This experiment is primarily concerned with measuring the flux and pressure drop across

the membrane at different recoveries. Flux is defined as the amount that flows over a unit area

per unit time:

Flux= Transfer RateTransfer Area

=Perme ability∗(Driving Force)Separation T h ickness

(1)

With a clean membrane water is assumed to pass by laminar flow through the small pores

of the selective layer, and the driving force is the pressure difference Δp minus the difference in

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osmotic pressures across the membrane Δπ. The flux is proportional to the void fraction ε and the

square of the average pore size, D. The pores are at random angles to the surface, and the

nominal thickness of the active layer L is multiplied by a tortuosity factor τ. (McCabe 1037)

Although it is difficult to get independent measurements of ε, D, τ, and L, these characteristics

are incorporated in the membrane permeability for the solvent where the solvent flux Q through

the membrane is a function of applied pressure:

Q=LP ∆ P (2)

Where:

Q = solvent flux (L/ (m^2*time))

Lp = membrane permeability (L/(atm*m^2*time))

ΔP = pressure drop (atm)

In this relation permeability is a measure of the ability of a porous material to transmit

fluid. The permeability of a membrane is often determined in lab by the application of Darcy’s

law. It is useful to view these equations in another form so the components will make more sense

physically. In "Separation Process Engineering" by Wankat, this equation is described using

different terminology. The solvent flux is described by equation 16-41. (Wankat 575) *Note that

Ksolv/tms yields the Lp constant shown in equation 2. In this experiment the flux relation of

importance is:

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Jsolv=K solv∗¿¿ (3)

Where:

Jsolv = flux of solvent leaving the ultrafilter (m/s)

Ksolv = permeability of the solvent through membrane (m2 / (psi-s))

Pr = total pressure on the retentate or high pressure side (psi)

Pp = total pressure on the permeate or low pressure side (psi)

tms = thickness of the membrane skin during separation (m)

To determine the optimum operating pressure differential for the filter it is necessary to

plot the concentration factor versus the flux. The pressure differential where the greatest flux is

obtained is the optimum operating pressure differential. When the filter is at the optimum

operating pressure differential the best possible separation can be achieved. The concentration

factor is defined as:

CF=V original

V concentrate=

V original

V original−V permeate(4)

Where:

CF = concentration factor (unitless)

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Voriginal = volume of the original solution (L)

Vconcentrate = volume of concentrated skim milk (L)

Vpermeate = volume of the permeated water (L)

An alternative definition of the concentration factor (CF) that is dependent on the

recovery ( R ) is the following:

CF= 11−R (5)

Where:

CF = concentration factor (unitless)

R = recovery of the feed stream that becomes permeate (unitless)

In this equation the recovery is defined as:

R=V permeate

V original(6)

Where:

R = recovery of the feed stream that becomes permeate (unitless)

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Vpermeate = volume of the permeated water (L)

Voriginal = volume of the original solution (L)

The objective in this experiment is to measure the pressure differentials and fluxes at

different recoveries so that it is possible to determine which pressures will yield the maximum

flux. The pressures that yield the maximum flux will have achieved the greatest separation and

consequently should become the standard operating conditions.

3. Experimental

3.1 Apparatus

# Equipment Description Manufacture

1 Membrane Column Membrane Type: PM10

Effective Area 25 cubic feet

Max Pressure: 40 PSIG

Serial Number:4PX 14069

Romicon INC

2 Jet Pump Power: 2 HP @ 3050 RPM Reliance

3 Back Jet Flush Pump Power: 1/3 HP @ 3450 RPM

Mod. Number 14010

Dayton

4 Power Switch Box A-B Quality

5 Permeate Tank

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6 Process Tank

7 Large On/Off Valve 1” Full-Flo PVC ball valve Hayward

8 Inlet Pressure Gauge Max Pressure: 30 PSI Omega Engineering

9 Small On/Off Valve Ball Valve Hill-McCanna

10 Back Flush Pressure Gauge

Max Pressure: 15 PSI US Gauge

Figure 4: Ultrafiltration Apparatus

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1

2

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5

6

7

7

7

8

10

89

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Figure 5: Ultrafiltration P&ID

3.2 Materials and Supplies

Equipment Manufacture Description

Bleach Clorox Used to sanitize system

Deionized Water Used as solvent

Phosphoric Acid Fisher Scientific A242-212 85%. Used as cleaning agent.

Solid Sodium Hydroxide Fisher Scientific BP359-212 White Pellets. Used as cleaning agent.

Skim Milk Deans Used as solute.

pH Paper EM Science & Micro Essentials

Used to measure acid concentration in system.

1000 ml Beaker Nalgene Used for volume measurement.

200 ml Beaker Nalgene Used for volume measurement.

3.3 Experimental Procedure

Membrane Cleaning Procedure

1. Check all valves and be sure that there is no pressure head generated during startup.

2. Fill the process tank (6) with 80L of deionized water at 105ºF.

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3. Place the valve connected to the green water hose in line with the flow. This directs the

permeate flow to the tank as recycle.

4. Build up pressure head by closing the inlet pressure valve and opening the outlet pressure

control valve. This pressure head will be required to fill inlet pipe with water and

ejecting all excess air in the system.

5. Turn pump on.

6. Slowly open the inlet pressure control valve so that the adjacent pressure gauge reads 20

psig.

7. Close the outlet pressure control value so that a pressure between 8 and 10 psig is reached

on the corresponding pressure gauge.

8. Readjust the inlet and outlet pressure control value so that 25 and 10 psig, respectively,

are achieved.

9. Run system for 15 minutes. Check the system for leaks and air bubbles in the tank.

10. Open the outlet pressure control valve completely and close the inlet pressure control

valve.

11. Turn off pump.

12. Drain and rinse process tank.

Acid Cycle

1. Create a 2.5 pH phosphoric acid solution in Deionized Water at 105 ºF. Use the pH paper

to determine the pH.

2. Repeat steps 4-8 of Membrane Cleaning Procedure.

3. Run for 10 minutes. Close the permeate outlet valve and run the phosphoric acid solution

through the filter for 5 more minutes.

4. Repeat steps 10-12 of Membrane Cleaning Procedure.

Drain and Rinse Cycle

1. Fill process tank to 50L with 105ºF Deionized water.

2. Set permeate outlet valve to drain.

3. Set process outlet line to drain.

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5. Turn pump on.


psig.



8. Open the drain valves briefly during the rinse cycle to flush out excess acid trapped in the

apparatus.

Caustic Cycle

1. Prepare 1 wt% NaOH solution using 105ºF Deionized water. This is done with 500g

solid NaOH pellets in 50L of water.




3. Turn pump on.


psig.




are achieved.




valve.

10. Turn off pump.


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12. Do not flush permeate solution. Save it for the next cycle.

Back Wash Mode

1. Close inlet and outlet pressure control valves and close the permeate outlet valve so that

flow will go be into the permeate tank.

2. Close back flush pressure control valve.

3. Open the lower process drain valve.

4. Attach and turn on the back flush pump.

5. Open back flush pressure control valve to change adjacent pressure gauge to 15 psig.

6. Open the upper process drain, close the lower process drain valve to change the flow of

back washing from countercurrent to current. This is done with volume in the back wash

tank has dropped approximately by half.

7. Let the system run until water in the permeate tank decreases to the level of inlet pipe to

pump.

8. Close back wash pressure control valve.

9. Open the outlet pressure control valve and repeat the drain and rinse cycle.

Bleach Cycle

1. Make 200ppm NaClO4 solution in Deionized water.




3. Turn pump on.


psig.




are achieved.


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valve.

10. Turn off pump.


Testing Water Flux

1. Calculate permeate water flux at inlet pressure 25 psig and outlet pressure 5 psig in

graduated cylinder.

2. The time between runs is >30 seconds.

3. Repeat for outlet pressures of 5, 10, 15, 20 psig.

Skim Milk

1. Fill process tank with 80L of 105ºF DI water.

2. Add 1 gallon skim milk.

3. Operate system at 25 psi inlet pressure and 5 psi outlet pressure.

4. Run feed through membrane until solvent is removed and until 10% recovery is obtained.

5. Measure the flux and direct flow back to feed tank.

6. Repeat for outlet pressures 5, 10, 15, 20 psi and for 30 and 70% recovery.

Shutdown


valve.

2. Turn off pump.


4. Ensure back wash pump is disconnected.

5. Rinse process and permeate tanks.

6. Clean the area around apparatus.

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4. Anticipated Results

In this lab we are investigating the effect of different process variables on the solvent flux

through an ultrafiltration membrane. In particular, the effect of outlet pressure sand recovery

percentages on solvent flux will be found. As noted in the theory section, the solvent flux, Q,

does not depend on pressure when osmotic pressure is significant. When the solution is dilute,

however, the solvent flux is proportional to the pressure drop, as seen in equation (NOTE THE

EQUATION FROM THE THEORY, it’s 1 in the packet). This means that the flux should not

increase when we vary the outlet pressure from 5 to 20 psig, if the solution is concentration. The

solvent flux should change, however, when we change the percent recoveries. This is because

different recoveries have different boundary layer sizes, and cause there to be different

concentrations at the surface. In general, increasing the recovery should increase both the length

of the boundary layer and the concentration at the surface. When we increase the pressure, the

solvent flux should increase for the 10 percent, and possible the 30 percent recoveries, since the

solution should still be dilute. At 70 percent concentration, the solution will probably be too

concentrated for pressure to have a large effect on the solvent flux. Increasing the recovery

percentages should decrease the solvent flux by a small factor, since the concentration at the

surface will increase, but the boundary layer length will probably decrease quicker.

Possible sources of error in this lab include the water temperature and air bubbles in the

column. As seen in equation (NOTE EQUATION FROM THEORY, EQUATION 6 IN LAB),

the time to concentrate a solution depends on temperature. The membrane’s properties are also

specified at a certain temperature. Since we are constantly circulating water and it is difficult to

regulate the temperature, it will be hard to keep the temperature at a precise value. Air bubbles

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may appear in the column like they did during one of the cleanings in the pre-lab, which can

decrease the effect area of the membrane during the trial. This may results in a slower flux.

Despite these possible sources of error, we should be able to determine the effect of

higher recoveries and different pressures on solvent flux with an acceptable amount of accuracy

and precision.

5. References

Strathmann, Heinrich. "Membranes and Membrane Separation Processes." Ullmann's Encyclopedia of Industrial Chemistry. 7th. 40. New York, NY: Wiley-VCH Verlag GmbH & Co., 2010. (pp: 667-724) Print.

Wankat, Phillip C. Separation Process Engineering. (2nd Edition). Boston, MA: Pearson Education, Inc., 2007. (pp: 573 – 579) Print

McCabe, Warren L., Julian C. Smith, and Peter Harriott. Unit Operations of Chemical

Engineering. New York: McGraw-Hill, 1993. (pp: 1058-1065) Print.

"Koch Membrane :: Ultrafiltration." Koch Membrane Systems. Web. 13 Feb. 2011. <http://www.kochmembrane.com/sep_uf.html>.

Neligan, Patrick. "What Is the Difference between Dialysis and Ultrafiltration?" Welcome to Critical Care Medicine Tutorials. Web. 13 Feb. 2011. <http://www.ccmtutorials.com/renal/rrt/page2.htm>

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6. Appendix I: Job Safety Analysis

What is the purpose of this experiment?

The purpose of this experiment is to operate a membrane separation unit in order to separate

water from a skim milk solution. During the operation the inlet tube side pressure is keep higher

than the shell side in order to achieve separation. The difference in pressure is used to investigate

the affect it has of separation efficiency.

What are the hazards associated with the experiment?

Since the system requires a series of cleaning procedures a combination of concentrated

phosphoric acid then caustic sodium hydroxide and water will be run through the system. These

chemical pose a health hazard since handling could lead to skin contact with them. This would

result is severs burns to the individual. A pump with an exposed turning shaft will be used to

pump the fluid. It is important that clothing and body parts are kept at a distance since they could

be caught up in the mechanism and do bodily harm.

How will the experiment be conducted in a safe manner?

The feed and permeate tank will be monitored for overflow. The pump will be operated properly

meaning the outlet stream will not be closed when the pump is running and the pumps pressure

outputs will be monitored. The handling of the cleaning acid and base will be done while

wearing gloves and the required preparation will be done in the hood to prevent fume exposure

and minimize spillage hazards. As always, close-toed shoes and safety goggles will be worn at

all times in the experiment area to decrease the chance of potential hazards.

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What safety controls are in place?

Recycle streams are connected to maintain a constant flow for the running pump. Most

importantly, the laboratory area around the experiment will be kept dry using paper towels and a

mop to clean any spilled liquid promptly to avoid wet working conditions. The water levels will

be monitored to ensure that the water does not overflow and cause a spill in the laboratory.

Safety goggles will be worn at all times to ensure eye protection.

Describe safe and unsafe ranges of operations.

De-ionized water at approximately 100F will be used to dilute the milk, this is not a safety concern

though. The pump discharge pressure is limited to 25 psi.

I have read relevant background material for the Unit Operations Laboratory entitled:

“Ultrafilteration” and understand the hazards associated with conducting this experiment. I have

planned out my experimental work in accordance to standards and acceptable safety practices

and will conduct all of my experimental work in a careful and safe manner. I will also be aware

of my surroundings, my group members, and other lab students, and will look out for their safety

as well.

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Electronic Signatures:

Bernard Hsu

Daniya l Qamar

Jeff Tyska

Alex Guerrero

Tomi Damo

Ryan Kosak

Andrew Duffy

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Documents

Introduction5+Prelab... · Web view(McCabe 1035) There are several membrane modules used, these include plate and frame, spiral-wound, and hollow-fiber. The one that will be used