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Binary Distillation University of Illinois at Chicago

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Binary Batch Distillation

Final Lab ReportUnit Operations Lab 2

19 February, 2011

Group 4Tien Diep

Kevin EstacioSebastian IskraZack LabaschinKevin ThompsonFelix Velazquez

Unit Operations ChE-382 Group No. 4 p. 1 Spring 2011 02/19/2011Diep, Estacio, Iskra, Labaschin, Thompson, Velazquez


1. Summary

The purpose of this lab is to run a batch binary distillation in order to separate methanol

and water. By heating the mixture to near its boiling point, the more volatile component will

vaporize first and travel up the distillation column. Data will be collected from the column at

various trays and compared with a calibration curve in order to determine weight fraction. Once

the weight fractions are determined, the tray efficiency can then be calculated. This was tested

with a 10 wt% methanol solution.

For this experiment the distillation column featured six bubble cap type trays and was set

up to operate at total reflux. At each stage there were two sample ports, one for collecting vapor

product and the other for liquid, with a single liquid sample port at the top just below the

condenser for drawing off a sample of reflux. Temperature probes were placed all over the

apparatus and connected to a digital thermometer unit used to monitor the temperature at each

tray, in the condenser, where the reflux was collecting, and the reboiler. The water pipes feeding

the condenser featured mechanical temperature gauges for monitoring the change in temperature

of the cooling water as it flowed through the condenser. Each sample taken from the column was

then put into a refractometer and analyzed against a calibration curve to determine its

composition.

The methanol concentration increased moving up the column, which makes sense as the

concentration should be increasing moving up the column as the methanol boils sooner than the

water; it is thus the lighter component and should be recovered in the distillate. The liquid

concentration consequently decreased up the column due to a high relative volatility (McCabe,

578). The vapor and liquid fractions of methanol per stage do not add up to 1 which means that

the species mass balance is not satisfied. This indicates a problem in the experiment, possibly



with the design of the apparatus. The diameter of the column is most likely too small causing

entrainment of the liquid. Another source of this error is that the methanol may have escaped the

system through the top of the column thus creating false results.



2. Results

The distillation module required that operators set up a calibration curve in order to

determine weight fractions at each tray via index of refraction (Figure 2.2). Different wt%

methanol/water solutions were placed on the cooled refractometer at intervals of 10 wt%

methanol. The purpose of this calibration curve is to compare it to the provided index of

refraction curve of the system (Figure 2.1) and to find out how to analyze the data collected from

the different stages of the distillation column after it has reached steady state.

A 32 Liter sample of 10wt% methanol was prepared in a side tank and then added to the

boiler pot of the column. The column was then heated to steady state (approx. 2 hours). Steady

state was distinguished by a lack of increase in temperature. Once reached, the compositions of

the system at each stage of the column along with the reflux was collected and analyzed in the

refractometer. The results for the gas composition at each stage showed that the methanol weight

fraction increases as gas at each stage of the column moving upward. At the same time, the

weight fraction of methanol in liquid decreased at each stage moving up the column (Bird, 698-

702). The total weight fraction of methanol did not add to one though, often being over or less

than 1. The final vapor weight percent exiting the column was found to be 79.51 wt% methanol.

For the liquid portion, there was a general trend for the weight fraction of the methanol to

decrease going from the top to the bottom of the column, but this was not the case for the liquid

reflux stage (Figure 2.4). The weight percent of the liquid leaving the column above the reflux

stage was found to be 1 wt% methanol, but the reflux stage was found to be 28.64 wt%.



0 20 40 60 80 100 1201.32

1.325

1.33

1.335

1.34

1.345

f(x) = − 4.75177418664593E-06 x² + 0.000459340581979334 x + 1.3317190382118R² = 0.977641176987116

Known Index of Refractions for the Methanol/Water System at 22C

nPolynomial (n)

Weight Percent of Methanol

Inde

x of

Ref

ract

ion

Figure 2.1: Index of Refractions for the Methanol/Water System at 22 °C

0 20 40 60 80 100 1201.32

1.325

1.33

1.335

1.34

1.345

1.35

f(x) = − 5.45454545454553E-06 x² + 0.000564272727272736 x + 1.33078181818182R² = 0.946621153836576

Calibration Index of Refraction for Gas Phase Methanol/Water System at 34F

Weight Percent of Methanol

Inde

x of

Ref

ract

ion

Figure 2.2: Calibration Index of Refraction for Methanol/Water System at 34 ˚F



0 1 2 3 4 5 61.326

1.328

1.33

1.332

1.334

1.336

1.338

1.34

1.342

1.344

Index of Refraction for Gas Comp. vs. Stage

Comp.

Figure 2.3: Index of Refraction vs Vapor Stage of Distillation

0 1 2 3 4 5 6 7 81.32

1.325

1.33

1.335

1.34

1.345

Index of Refraction for Liquid Comp. vs. Stage

Comp.

Figure 2.4: Index of Refraction vs Liquid Stage of Distillation



3. Discussion

In this experiment, a 10 wt% methanol water solution was prepared to gather the VLE

data of the distillation system to determine the batch column efficiency for the system at total

reflux. The 10% wt. methanol solution took about 2.5 hours to reach an equilibrium temperature

across the 6-stages in the distillation column. The compositions of vapor and liquid samples

collected at various stages of the column were determined using the calibration curve. The

calibration curve was plotted by measuring the refractive indices of methanol and water solutions

of known compositions (0-100 wt% methanol in increments of ten). The feed was assumed to be

saturated vapor. The liquid that gathers on the trays was then reheated via convection of upward

flowing vapor to allow for more of the volatile component to become a vapor and for water to

flow downward as liquid. This allowed for a high purity in both the top and bottom of the

distillation column and the component with the higher volatility was easier to vaporize.

The data indicates that the higher stages contained more methanol vapor, which is

expected as methanol is the more volatile component of the methanol-water system. The index of

refractions of the liquid and vapor compositions were analyzed at each stage of the distillation

system in the refractometer and a corresponding index of refraction was recorded. In Figure 2.3,

stage 0 in the index of refraction was 1.3431 and 1.3321 at stage 6. Since the calibration curve is

a parabola, the higher the index of refraction, the closer to 50% wt for each component. As the

stage height increases, the lower index of refraction is expected to increase the weight fraction of

methanol in gas and decrease in liquid. Therefore the index of refraction is much higher at stage

0, where there is a higher concentration of both methanol and water, than is at stage 6, which is

at the top of column.



As a result, to achieve a higher percentage of separation, more stages are needed or the

vapor collected should be fed to another column for purification. The experimental errors were

due to the fact that the concentration of the binary mixture was taken as an approximation. The

temperature kept fluctuating from time to time, so the steady-state temperature might not have

been at steady-state when taking stage readings for both liquid and gas.

4. Conclusions

A 10 wt% methanol solution was to be distilled from water and analyzed for purity.

Solutions of differing concentrations of methanol were analyzed with a refractometer and a

calibration curve, shown in Figure 2.2, was generated. This calibration curve was used to classify

the composition of methanol in the samples analyzed. Once the column reached steady state

samples were drawn from each stage of the column in the vapor and liquid phases. Each sample

was then analyzed using the refractometer and compared against the calibration curve.

The final vapor weight percent exiting the column was found to be 79.51 wt% methanol.

For the liquid portion, there was a general trend for the weight fraction of the methanol to

decrease going from the top to the bottom of the column. The weight percent of the liquid

leaving the column above the reflux stage was found to be 1 wt% methanol, but the reflux stage

was found to be 28.64 wt%. The methanol concentration increased moving up the column in the

gaseous state as it is the lighter component (Wankat, 26).

The composition of the product was not equal to 100% methanol. Methanol present in

the column from previous experiments could be a source of impurity that may have oxidized to

formaldehyde. Even though there were impurities present while conducting the experiment, the

separation of two components was observed applying the concept of binary distillation.



5. References

"Binary Batch Distillation." University of Illinois at Chicago - UIC. Web. 14 Feb. 2011. <http://www.uic.edu/depts/chme/UnitOps/che382-2005f-frame.html>.

Bird, R. Byron, Warren E. Stewart, and Edwin N. Lightfoot. Transport Phenomena. New York: J. Wiley, 2007. Print.

"Fractional Distillation." Engineering. Web. 14 Feb. 2011. <http://engineering.wikia.com/wiki/Fractional_distillation>.McCabe, Warren L., Julian C. Smith, and Peter Harriott. Unit Operations of Chemical Engineering. Boston: McGraw-Hill, 2005. 576-78. Print.

Wankat, Phillip C. Separation Process Engineering. Upper Saddle River, NJ: Prentice Hall, 2007. Print.



6. Appendix I: Data Tabulation/Graphs

Gas Weight FractionStage Index of Refraction Weight Fraction Efficiency

0 1.3431 0.51859 -0.0599137621 1.3405 0.54175 -0.1161022872 1.3391 0.573386 -0.2057832433 1.3379 0.602508 2.420898384 1.3345 0.7 0.2594613565 1.3321 0.7951 3.085329478

Table I.1

Liquid Weight FractionStage Index of Refraction Weight Fraction Efficiency

1 1.3419 0.45825 0.154447192 1.3432 0.5138 -0.1125699333 1.3404 0.45607 -0.3046110734 1.3375 0.387298 1.1631489165 1.3331 0.248897 0.2618546236 1.3305 0.1 -0.309287681

Reflux 1.3341 0.286356 0.478263469Table I.2



7. Appendix II: Error Analysis

Component Uncertainty Expected Description

100 mL Graduated Cylinder ± 0.5mL

The 100mL graduated cylinder measures liquid in increments of 1mL. The lines can be accurately

read to within ± 0.5mLDigital Temperature

Monitor ± 0.1 oC The temperature monitor measures in increments of 0.1 oC and is accurate to ± 0.1 oC.

Refractometer ±0.0001The refractometer measures the refractive index of a mixture in increments of 0.0001 and values can

be read accurately to the nearest 0.0001.Table II.1

Error existed all throughout this lab. The preceding table shows the uncertainties of

equipment used in the experiment. This uncertainty comes from the approximated error that

comes from the reading of the instrumentation as these readings are fairly objective.

There was also error in the running of the operation of the experiment. The calibration

curve itself was an error as it is a polynomial regression of data points. This regression was done

over as many data points as possible in order to minimize this error, but this regression is only an

estimate and not exact. Also, when mixing the solutions due to the uncertainty of the equipment

more error was added into the polynomial regression. A polynomial regression was chosen due

to the shape of the graph being a parabola as well as the polynomial regression being the best fit

with a correlation factor of 0.94.

During column operation, when taking samples of low stage liquid or gas, the column

sputtered and leaked, making contact with the operator. Not only is contamination of stage

composition possible, but also the operator is put at risk by making undesired contact with

methanol.

One improvement that can be made would be to obtain a different refractometer or

different cooling system for the current refractometer, as the constant fluctuating coolant



temperature of the system may have contributed to error in this lab’s results. Potential error in

results may have occurred at the refractor station, as the refractor surface must be cleaned after

every test, and the potential for accidental spills or contamination is high. Also, it would be more

accurate to use fresh methanol as opposed to methanol that has been sitting in a drum for a long

time since it’s possible that the old methanol oxidized over time.



8. Appendix III: Sample Calculations

The quadratic equation is obtained from plotting the index of refraction versus the weight percent

of methanol:

-5*10-06x2 + 0.0001x + 1.331

For vapor composition:

-5*10-06x2 + 0.0001x + 1.331= 1.3431 (stage 1)

x = 51.85wt% vapor

mol% ratio: Molecular weight of Methanol

Molecular weight of Methanol∧water = = 0.6403

mol% methanol = 0.6403 * 0.5185 = 0.3319 mol% methanol

For liquid composition:

-5*10-06x2 + 0.0001x + 1.331= 1.3419 (stage 1)

x = 45.82 wt% liquid

mol% ratio = 0.6403

mol% methanol =0.6403 * 0.4582 = 0.2933 mol% methanol

For Murphee efficiency:

= 0.5189−0.5417

1−0.51850.5185

−0.5417 = - 0.05991



9. Appendix IV: Individual Team Contributions Name: Kevin Sean Thompson

Time (HOURS) DescriptionOperator (Both Lab Days) 8.00 Operator both daysPre- Lab Editing 0.50 Final compilationFinal-Lab Editing 1.00 Final compilationSummary 1.00 Wrote sectionIntroduction 0 ---Literature Review/Theory 0 ---Apparatus 0 ---Materials and Supplies 0 ---Procedure 0 ---Anticipated Results 1.50 ---Results 0.50 ReformattingDiscussion 0 ---Conclusion 0.50 Editing grammar and contentReferences 0.50 Found and formatter all referencesData Tabulation/Graphs 0 ---Error Analysis 1.00 Wrote sectionSample Calculations 0 ---Job Safety Analysis 0 ---Power Point Presentation 2.00 Wrote powerpointTotal 16.50

Name: Zachary Daniel LabaschinTime (HOURS) Description

Operator (Both Lab Days) 8.00 Operator both daysPre- Lab Editing 0 ---Final-Lab Editing 0 ---Summary 0.50 Proof readIntroduction 0 ---Literature Review/Theory 4.00 Wrote sectionApparatus 0 ---Materials and Supplies 0 ---Procedure 0 ---Anticipated Results 0 ---Results 0 ---Discussion 1.00 Restyled emphasisConclusion 0.50 Proof readReferences 0 ---Data Tabulation/Graphs 3.00 Did calculationsError Analysis 0 ---Sample Calculations 0 ---Job Safety Analysis 0 ---Power Point Presentation 0.50 Proof readingTotal 17.50



Name: Kevin Manuel EstacioTime (HOURS) Description

Operator (Both Lab Days) 8 Day 1 – OperatorDay 2 – Lab writer

Pre- Lab Editing 1 Grammar and content editingFinal-Lab Editing 1.50 Grammar and content editingSummary 0 ---Introduction 1 Wrote entire sectionLiterature Review/Theory 0 ---Apparatus 0 ---Materials and Supplies 0 ---Procedure 0 ---Anticipated Results 0 ---Results 1 Wrote first draft of sectionDiscussion 0 ---Conclusion 0 ---References 0 ---Data Tabulation/Graphs 1 Compiled data into excel, composed index of

refraction curvesError Analysis 0 ---Sample Calculations 0 ---Job Safety Analysis 0 ---Power Point Presentation 0 ---Total 13.50

Name: Felix VelazquezTime (HOURS) Description

Operator (Both Lab Days) 8 Day 1 – WriterDay 2 – Operator

Pre- Lab Editing 0 ---Final-Lab Editing 0 ---Summary 0 ---Introduction 0 ---Literature Review/Theory 0 ---Apparatus 2 Gathered information on each specific part

and label on pictureMaterials and Supplies 1.50 Provided a brief description of each

component and manufacturer if availableProcedure 0 ---Anticipated Results 0 ---Results 0 ---Discussion 2 Wrote discussion and editConclusion 0 ---References 0 ---Data Tabulation/Graphs 0 ---Error Analysis 0 ---Sample Calculations 0 ---



Job Safety Analysis 0 --Power Point Presentation 0 --Total 13.50

Name: Tien DiepTime (HOURS) Description

Operator (Both Lab Days) 8 Day 1- Lab writerDay 2 – operator

Pre- Lab Editing 0 ---Final-Lab Editing 0 ---Summary 0 ---Introduction 0 ---Literature Review/Theory 0 ---Apparatus 0 ---Materials and Supplies 0 ---Procedure 0 ---Anticipated Results 0 ---Results 0 ---Discussion 0 ---Conclusion 0 ---References 0 ---Data Tabulation/Graphs 0 ---Error Analysis 0 ---Sample Calculations 1.50 ---Job Safety Analysis 1.50 ---Power Point Presentation 0 ---Total 11.00

Name: Sebastian Tadeusz IskraTime (HOURS) Description

Operator (Both Lab Days) 8.00 Operator both daysPre- Lab Editing 0 ---Final-Lab Editing 0 ---Summary 0 ---Introduction 0 ---Literature Review/Theory 0 ---Apparatus 0 ---Materials and Supplies 0 ---Procedure 0.50 ---Anticipated Results 0 ---Results 0 ---Discussion 0 ---Conclusion 0.50 Wrote sectionReferences 0 ---



Data Tabulation/Graphs 0 ---Error Analysis 0 ---Sample Calculations 0 ---Job Safety Analysis 0 ---Power Point Presentation 0 ---Total 9.00


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