TKP4105/TKP4110Oldershow perforated plate distillation

Workplan

Audun F. Bueneaudunfor@stud.ntnu.no

Elise Landsemelisel@stud.ntnu.no

Group B19Supervisor: Vladmiros Minasidis

Laboratory: K4-213To be conducted on: 15th of October 2012

Contents

1 Introduction 2

2 Theory 32.1 Distillation theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32.2 Weeping point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32.3 Flooding point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32.4 Column efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42.5 Reflux . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42.6 MacCabe-Thiele Method . . . . . . . . . . . . . . . . . . . . . . . . 42.7 Gas Chromatography with FIR (far infrared) sensors . . . . . . . . 5

3 Method and apparatus 63.1 Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

3.1.1 The making of ethanol mixture . . . . . . . . . . . . . . . . 73.1.2 Column startup . . . . . . . . . . . . . . . . . . . . . . . . . 73.1.3 Time required for reaching steady state condition . . . . . . 83.1.4 Efficiency vs. Vapor velocity . . . . . . . . . . . . . . . . . . 83.1.5 Column shutdown . . . . . . . . . . . . . . . . . . . . . . . . 9

3.2 How to perform gas chromatography . . . . . . . . . . . . . . . . . 93.2.1 Prepare sample . . . . . . . . . . . . . . . . . . . . . . . . . 93.2.2 Using micropipettes - the reversed pipetting technique . . . 10

A Calculations 14A.1 Calculation required amount of ethanol . . . . . . . . . . . . . . . . 14A.2 Assignment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15A.3 McCabe-Thiele diagram . . . . . . . . . . . . . . . . . . . . . . . . 18

B Risk assessment and chemical data sheets 19

1

1 Introduction

In this laboratory exercise an 11 volume percent mixture of ethanol and waterwas distilled by Oldershaw perforated plate distillation. This experiment wasperformed as a part of the subject TKP4105, Separasjonsteknikk, in the autumn2012, at NTNU. An 11% mixture of ethanol and water was distilled by Older-show perforated plate distillation. The purpose was to understand and investigatethe distillation principles, the parameters affecting the operation of distillationcolumns and how to find optimal operating conditions. The time required to reachstedy state condition was determined, as well as the efficiency of a column as afunction of the vapour velocity. The weeping condition of the column was alsostudied and determined.

2

2 Theory

2.1 Distillation theory

Destillation is a process where a mixture gets physically separated into two or moreproducts with different boiling points. This is done by partial vaporization of aliquid mixture, and/or by partial condensation of a gas mixture. This results in aliquid phase richer in less volatile component, while the gas phase will be richer inmore volatile component.

2.2 Weeping point

When the velocity of the vapor through the perforations of a tray is so low thatthe liquid weeps through the holes of a sieve tray, the condition of the systemis called weeping point. Massive weeping is known as dumping, and results inparticularly severe phase maldistribution. When weeping point is reached, thecontact between the gas- and liquid phase will practically disappear. Note thatthis definition doesn’t apply to packed columns.

2.3 Flooding point

Any countercurrent flow separation device is subject to a capacity limitation dueto flooding. The phenomenon is related to the ability of the two phases to flow insufficient quantity in opposite directions past one another and is a result of highvapor velocity. The pressure exerted by the vapor from below balances the gravityhead of the liquid, and as a result the liquid starts to build up in the column.The condition of a flooding point is reflected by a sudden increase in the pressuredrop. This condition will not be studied in the laboratory, because of the highcapasity of the oldershow destillation column which makes it impossible to reachsuch high vapor velocity.

3

2.4 Column efficiency

The total column efficiency in a destillation column is defined as the ratio of totalnumber of ideal equilibrium stages to the number of actual trays in the column:

Column Efficiency =Nt − 1

Na

× 100% (2.1)

Nt is the number of theoretical stages which can be found from a McCabe Thielediagram, while Na is the number of actual trays. One stage is deducted from thenumerator due to the fact that the reboiler is counted as one stage. It’s worthnotice that this equation does not apply to the case of a packed column.

If the outgoing liquid and vapor phase establish an equilibrium with each other,the distillation stage is viewed as an ideal one. To reach a high column efficiencyits necessary to obtain a thorough contact between the gas and the liquid.

2.5 Reflux

The condensersystem in the distillation apparatus takes the overhead vapor fromthe column and liquifies a portion of it to return to the tower as reflux. For thisparticular experiment the distillation columns will work with a total reflux mostof the time, but condensate will also be taken out from the top of the column asa product.

2.6 MacCabe-Thiele Method

The McCabe-Thiele Method is a matemathical-graphical method for determingthe number of ideal (theoretical) stages needed for a given separation of a binarymixture. The main assumption made in this method is that there must be equimo-lar overflow through the tower between the feed inlet and the top tray, and alsothe feed inlet and the bottom tray. This assumption leads to a straight operatingline.

4

2.7 Gas Chromatography with FIR (far infrared) sensors

Gas Chromatography (GC) is an analytic technique which is commonly used inmany research and industrial laboratories. Several different kinds of samples canbe analyzed this way, as long as the compounds are sufficiently thermal stable andvolatile enough.

The technique requires a mobile and a stationary phase, whereas the mobile phase,or carrier gas, is an inert gas. The stationary phase consist of a packed columnwhere the packing or solid support itself acts as stationary phase, or is coated withthe liquid stationary phase. It’s also common to use capillary columns and havethe stationary phase cover the walls.

Different compounds can be separarted with GC because of the interaction of thecompound with the stationary phase. Stronger interaction leads to a longer timeintervall before the compound releases and goes through the column. This time iscalled retention time and is unique for each solute[3]

5

3 Method and apparatus

The experiment is described in the document Felleslab: Distillation Columns, Sep-aration [1], and the illustration in figure 3.1 is taken from page 6 in this document.

Figure 3.1: An illustration of a destillation column at NTNU with reference to thedifferent components.

6

3.1 Experiment

The experiment was divided into two main parts, the study of approaching steadystate and the study of column efficiency vs. vapor velocity. The procedures arenevertheless divided into several subsections to make the execution of the experi-ment well arranged.

3.1.1 The making of ethanol mixture

The column was to be charged with 5800mL of an ethanol-water mixture withxEtOH = 0.11. This was made by mixing 1724.17 mL of a solution with 96 vol.%ethanol with 4075.83 mL of water. The calculations that led to these numbers canbe found in Appendix A.1 .

3.1.2 Column startup

This procedure was followed in the laboratory:

1. Turn on the PC

2. Turn on the cooling water

3. Make sure that the bottom and distillate tap lines are closed

4. Charge the column with 5800mL of the mixture with xethanol = 0.11

5. Set the column to total reflux

• Set T=105◦C using the control box

• When the top temperature substantially changes, or the pressure dif-ference over the column rises quickly, set the boiler’s power duty to50%

6. Wait until the vapor stream starts condensing, and let this be "zero" time(t=0 min)

7

3.1.3 Time required for reaching steady state condition

The purpose of this exercise was to calculate the time it took the column to reacha stedy state condition. This procedure was followed in the laboratory:

1. Set the reboiler to 50% and wait until the column starts to give condensate

• This is actually the same as the last step in the column start up, so itshould already be done

2. Take samples every 5 minutes within 1 hour, so that there’s 12 top-samplesin total

3. After taking the twelfth sample, take one sample from the bottom of thecolumn.

• The composition of this sample will be used in the next part of theexercise

4. Analyze all samples and find out approximately how long it takes for thecolumn to reach steady state

• When the composition of the top-samples is constant from one sampleto the next, it can be assumed that steady state is reached

3.1.4 Efficiency vs. Vapor velocity

The goal of this part of the experiment was to find out how the column efficiencyvaries as a function of vapor velocity. To study this, the column was run with a to-tal reflux for five different boiler powers, which produced different vapor velocities.The following procedure was repeated until these five measures was done:

1. Set the reboiler power to 40%

2. Wait until the column reaches the steady state

• Assume that steady state is reached at the same amount of time as inthe previous part of the experiment

8

3. Take two samples of 20mL, one from the top and one from the bottom

4. Write down the reflux rate at the time of sampling

5. Increase the reboiler power by 10% and redo the steps, starting at 2

6. Analyze the 10 samples

7. Identify the weeping point and record the values of pressure drop and vaporvelocity. Also, write down the power of the boiler

3.1.5 Column shutdown

When the last sample was taken, the column was shut down by the followingprocedure:

1. Turn off the heater

2. Let the column with contents cool down

3. Empty the column and turn off the cooling water

4. Turn of the rest of the equipment

3.2 How to perform gas chromatography

3.2.1 Prepare sample

• Isopropanol is used as a standard component, so pour some of it into a smallglass container (about 5mL)

• Prepare sample for GC by mixing 500µL of ethanol sample with 250µL ofisopropanol into a glass vial using the micropipettes.

• Use the reversed pipetting technique describes in the subsequent section

• Seal the vial with an appropriate cap

• Important: mark the vial clearly!

9

3.2.2 Using micropipettes - the reversed pipetting technique

Air displacement is used to dispense the liquid. The pipetteshave fixed dispensingvolumes with the quantity marked at the top button. Before use, a disposable tipmust be attached. There are three steps(stops) in the pipette:

1. for aspirating and dispensing liquid into and out of the tip

2. used to blow out the remaining liquid from the tip

3. the last step detaches the disposable tip

The reversed pipetting technique contains of five steps:

1. Wetting

2. Aspiration

• Both 1 and 2 is done by submerging the tip about 3mm into the liquid,push the plunger down to step 2 and release it slowly. This is donetwice.

3. Dispensing

4. Blow-out

5. Tip-release

• Step 3,4 and 5 is done by holding the tip at an angle against the glasswall, and dispensing the liquid into the glass vial by pushing the plungerdown to the first stop. Then hold the plunger at this position, and liftthe tip out of the vial. Blow out the remaining liquid into a glass con-tainer marked for waste by pushing the plunger down to the secondstop. release the tip into the trash by pushing the plunger down to thethird step.

10

The prepared samples are then put into the auto sampler tray. The position ofthe respective samples should be noted. The Chrom-Card program is started bydoubleclicking the Focus#1 GC icon.

To enter the sample information, open the sample table by clicking "edit", then"sample table". These fields needs to be filled in:

• ID: Grey is for sample ID number. White is the active sample that the GCanalyzes. If several samples are analyzed, write in the first sample and theGC will analyze the rest in incrementing order.

• Sample name: This must be logic, so that there are no mix-up of the results.For the first part of the experiment, use the time. Example: t_20min. Forthe bottom sample, use tb_60min. For the second part, use boiler powerand also define if its top(t) or bottom(b) sample. Example: p_60per_b.

• Filename: This is the name of the file with the results. Start with group-number, B19, to make sure no other groups uses the same name. Example:B19_t_20min.

• Type: Tell the GC that the sample is unknown. (This may also be used forcalibration, but that should not be needed).

• S.A, I.S, X.F: Don’t fill in anything here.

• The GC method filename: C:\Focus\June 2011\ethanol.gsm

• The AS method filename: C:\Focus\June 2011\ethanol.asm

– These two last fields only needs to be filled in at the first sample.

• Vial: The position of the sample on the auto sampler tray is noted here.

– It’s very important to write the correct position!

• When all the samples are registered in the sample table, press OK.

The samples are now ready to be analyzed. Use the following procedure:

11

• Push the button with a green arrow and save the method as ethanol.mth

• Press START

• Each sample takes about 4 minutes to analyze, and the chromatograms canbe watched by clicking "View", then "Sample Being Acquired"

• After all the samples are analyzed, press "Reprocessing" and "summarizeresults". Here the results are given in vol.% of ethanol.

• Print the results from the summarized results by first entering B19, thenmark one of the samples and push print.

After analyzing the samples, remove the vials from the auto sampler tray. Removethe caps, empty the content into the container marked "organic waste" , discardthe vials into the glass waste basket and the caps into the waste basket.

12

Trondheim, October 11, 2012

Elise Landsem Audun F. Buene

References

[1] Laboratory exercise: Felleslab: Distillation Columns, Separation, September2011.

[2] Chemical card, ethanol: http: // app. ecoonline. no/ documents/ msds/

285_ 2991719. pdf

[3] Theory about Gas Chromatography: http: // www. chem. ucla. edu/

~bacher/ General/ 30BL/ gc/ theory. html

[4] MATLAB code for MacCabe Thiele diagram: http: // folk. ntnu.

no/ oyas/ fag/ felleslab/ Distillation/ Workplan/ McCabe_ Thiele_

Plotting_ Tool. pdf

13

A Calculations

A.1 Calculation required amount of ethanol

The following properties were found using wolfram alpha:δEtOH = 0.789 g/cm3

MEtOH = 46.0684 g/molδH2O

= 0.997 g/cm3

MH2O= 18.0153 g/mol

A solution of 96 vol.% ethanol is handed out, and a solution of 11 mol % ethanolis to be made.The mole fraction of ethanol in an aqueous solution is given by:

xEtOH =nEtOH

nEtOH + nH2O

(A.1)

Calculating the number of moles of ethanol is done by:

nEtOH =VEtOH · δEtOH

MEtOH

(A.2)

Analogous for water:

nH2O=VH2O

· δH2O

MH2O

(A.3)

Substituting Equation (A.2) and (A.3) into Equation (A.1), gives:

xEtOH =

VEtOH ·δEtOH

MEtOH

VEtOH ·δEtOH

MEtOH+

VH2O·δH2O

MH2O

(A.4)

The volume of water can be calculated using Vtot = VEtOH + VH2O. Substituting

this into Equation (A.5) gives:

xEtOH =

VEtOH ·δEtOH

MEtOH

VEtOH ·δEtOH

MEtOH+

(Vtot−VEtOH)·δH2O

MH2O

(A.5)

14

For this calculation, xEtOH = 0.11, and using the data listed over, Equation (A.5)can be solved for VEtOH . This yeilds the volume of pure ethanol needed:

VEtOH, 100 % = 1655.2 mL (A.6)

Converting the answer to 96 vol % ethanol is done by:

VEtOH, 96 % =1655.2 mL

0.96= 1724.17 mL (A.7)

This means that the required volume of water to make the given solution is:

VH2O= Vtot − VEtOH = 5800 mL− 1724.17 mL = 4075.83 mL (A.8)

A.2 Assignment

These measurments were given in the assignment:

• Weight of empty pycnometer 1: 11.98170 g

• Weight of empty pycnometer 2: 11.77385 g

• Weight of pycnometer 1 with water: 16,95955 g

• Weight of pycnometer 2 with water: 16.75745 g

• Weight of pycnometer 1 with distillate: 16.0903 g

• Weight of pycnometer 2 with bottom product: 16.6962 g

From the GC anaylsis, the following data are found:

• Distilate composition: xEtOH = 0.744

• Bottom composition: xEtOH = 0.033

First step is to find the volume of each pycnometer, by using the weight of purewater, and the known density of water, ρwater = 0.997 cm3/mL. This gives:

V1 = 4.992 cm3 V2 = 4.998 cm3 (A.9)

15

Then the densities of the distillate and bottom product are found using:

ρ =weight of sample

volume pycnometer(A.10)

This gives the densities:

ρdistillate = 0.8229 g/cm3 ρbottom product = 0.9847 g/cm3 (A.11)

From data in Green and Perry, the weight % of the distilate is estimated to 88.1wt.% and of the bottom product 8.0 wt.%. The mole fraction of ethanol in wateris:

xEtOH =nEtOH

nEtOH + nH2O

(A.12)

Using the fact that ni = mi

Mi, converting the number of moles to mass gives:

xEtOH =

mEtOH

MEtOH

mEtOH

MEtOH+

mH2O

MH2O

(A.13)

Substituting the mass with weight % gives the following equation:

xEtOH =

wt.%EtOH

MEtOH

wt.%EtOH

MEtOH+ (100−wt.%EtOH)

MH2O

(A.14)

Substituting for wt. %EtOH for the bottom product and the distilate gives:

xEtOH, bottom product = 0.0328

xEtOH, distilate = 0.7433

Calculating the gas velocity of the vapor in the column is done by using Equation(A.15). The reflux rate is given, 53 mL/min, the temperature is 25◦, and thepresure is 1 bar:

ν =VgasA · t

[m/s] (A.15)

16

where A is the cross section area of the distillation column, t is the time, and Vgasis the volume of the gas which can be found, assuming one can use the ideal gaslaw:

Vgas =ngas ·R · T

P(A.16)

A general mass balance for the two components in the column:

mtot = mEtOH +mH2O= xEtOH · ntot ·MEtOH + (1− xEtOH) · ntot ·MH2O

(A.17)

Rearranging this for ntot gives:

ntot =mtot

xEtOH ·MEtOH + (1− xEtOH) ·MH2O

(A.18)

Knowing that the reflux ratio is 1, and that mtot = ρ ·Vtot, this can be substitutedinto Equation (A.19), to give:

ntot =ρ · Vtot

xEtOH ·MEtOH + (1− xEtOH) ·MH2O

(A.19)

This will give, using ρ1 = 0.8229 for the distillate, the total number of moles:

ntot = 1.1215 [mol/min] (A.20)

Substituting this into Equation (A.16) yields:

Vgas =1.1215 [mol

min] · 8.314 [m3Pa

K·mol ] · (79 + 273) [K]100.000 [Pa]

= 0.0328 m3/min (A.21)

Substituting into Equation (A.15), with a column diameter of 0.07 m, gives thegas velocity of the column:

ν =0.0328 [ m

3

min]

π40.072 [m2] · 60 [s]

= 0.1420 [m/s] (A.22)

17

A.3 McCabe-Thiele diagram

Figure A.1 shows a McCabe-Thiele diagram made in MATLAB. The code is writ-ten by Øyvind Eraker and Kjetil Sonerud[4], but the values for top and bottomcomposition is changed to the ones from the exercise. The equilibrium data at 1atm was found in Gmelin and Unken. Five theoretical steps are estimated fromthe diagram.

Figure A.1: McCabe-Thiele diagram for ethanol-water binary solution. For thedistilate composition, xEtOH = 0.744. For the bottom composition, xEtOH = 0.033.

18

NTNUNorges teknisk-

naturvitenskapelige universitet

Chemical card

NAMEEthanol

FORMULAC2H5OH

HEALTH HAZARDS No special health risk.

PHYSICAL DATA

Melt.p./fr.p.

Boil.p Fl. p. Molar mass Expl.lim. FIRE HAZARDSExtremely inflammable

-114 °C 78 °C 363 °C 46,07 g/mol 3,3-19,0% REACTION HAZARDSAvoid alkali metals, ammonia, oxidizing agents and peroxides.

PROTECTIVE MEASURES

Use respirator if necessary. Use safety gloves. Use safety goggles. Choose other safety equipment that suits the risk of your experiment.

ADMINISTRATIVE NORM

HELSEFARE

Inhaling

Ingestion

Skin

Eyes

May be harmful. May lead to irritation of the air passage.

May be harmful.

May be harmful if absorbed through the skin. May cause skin irritation.

May cause eye irritation.

FIREFIGHTING“Alcohol”-foam, dry chemicals or carbon dioxide. Water as fog or spray.

First aid EYESRinse with water.

SKINWash with soap and water. Contact doctor.

INGESTIONDo NOT induce vomiting. Rinse mouth with water. Contact doctor.

INHALINGMove person to fresh air. Provide artificial breath if needed. Contact doctor.

SPECIAL MARKS

WASTE Contact a licensed treatment- or terminal station for hazardous waste for destruction of this material. Use a incinerator.

STORAGE Keep away from fire sources. Keep in a cool, dry and ventilated place.

B Risk assessment and chemical data sheets

NTNUNorges teknisk-

naturvitenskapelige universitet

Kjemikaliekort

Name: Distilled water

Formula:H2O

Health risk:-

Physical dataMolar mass Melt.p./

fr.p. Boiling pointFire risk:-

18.0153 g/mol 0 °C 100 °C

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LABJOURNAL:  Time  required  for  reaching  steady  state  condition,  measurments    Sample  nr.   t  [min]   xEthanol   xWater   Comments  

 1  

 5    

     

 2  

 10    

     

 3  

 15    

     

 4  

 20  

 

     

 5  

 25  

 

     

 6  

 30  

 

     

 7  

 35  

 

     

 8  

 40    

     

 9  

 45    

     

 10  

 50    

     

 11  

 55  

 

     

 12  

 60  

 

     

   13    

(Bottom)  

 60  

 

     

 Estimated  time  until  steady  state  were  reached:                                                [min]    Other  comments:      

LABJOURNAL:  Efficiency  vs.  Vapor  velocity    Measurment    number  

Boiler  power  

Reflux  rate   xEthanol   yEthanol   Comments  

 1    

 40%  

       

 2    

 50%  

       

 3    

 60%  

       

 4    

 70%  

       

 5    

 80%  

       

 For  calculations:  Dcolumn=                                      [  cm  ]=                                        [  m  ]    Other  comments:                        Weeping  point:      Pressure  drop    

 

 Vapor  velocity    

 

 Boiler  power    

 

   Other  comments: