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Continuous Binary Distillation University of Illinois

Continuous Binary Distillation

Lab Prep ReportUnit Operations Lab 2

January 24, 2011

Group 6

Sana Buch

Priya Chetty

Liliana Gutierrez

Linda Quan

Vijeta PatelLipi Vahanwala

Unit Operations ChE-382 Group No. 6 p. 1 Spring 2011 01/24/2011Buch, Chetty, Gutierrez, Patel, Quan, Vahanwala

Alan Zdunek, 09/05/22,

Total: 87/100


1. Introduction

Distillation is the most widely used separation process that separates a mixture

based on differences in the conditions required to change the phase of components of the

mixture. Distillation contributes to more than 50% of plant operating costs (Modeling &

Simulation of Binary Distillation Column). Distillation is used mainly for commercial

purposes, such as production of gasoline, distilled water, xylene, alcohol, paraffin, and

kerosene (Modelling & Simulation of Binary Distillation Column). In large chemical

complexes, the distillations are continuous with the feed entering at some point near the

middle of the column and the product being taken off the top and the bottom. Distillation

is very flexible and there are schemes which include multiple feeds to the column and the

take-off of multiple products. However, a distillation column can produce only two

products (the top and the bottom) which are of high purity. Sequences of distillation

columns are commonly used to produce numerous high-purity products.

The process of distillation can be categorized according to the following (Guzman

4).

1) Method of separation (Guzman 5)

a. Simple distillation is distillation without reflux, where no condensate is

allowed to return to the single stage still pot to contact the rising vapors.

b. Fractional distillation is distillation with reflux in which a portion of the

condensate is allowed to return to the distilling column to contact the

rising vapors.

2) Nature of the process feed (Guzman 5)

a. Binary component

b. Multi-component

3) Method of operation (Guzman 5)

a. Batch Column is the design of a batch column, which is more complex

than a continuous distillation column as it requires consideration of

unsteady-state behavior (Diweker, Madhvan 713). Batch distillation is

most often used with smaller volume products (“The Distillation Group,

Inc”). The batch column distillation column can be designed by keeping

two modes of operation (Diweker, Madhvan 713).



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Be consistent with reference citation; you use author names below .


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i. Variable reflux and constant product composition of all or one

component

ii. Constant reflux and variable product composition

b. Continuous Column, on the other side, is an ongoing distillation in which

a liquid mixture is continuously fed into the process and separated

fractions are removed continuously (M&S). The simulation of continuous

distillation for multi-component mixture is well developed in chemical

engineering due to its commercial importance. Continuous distillation is

most often used with big volume products like jet fuel, benzene, and

plastic monomers (“The Distillation Group, Inc”).

4) Types of columns used (Guzman 5)

a. Plate/staged column type provides each plate contact between vapor and

liquid in continuous countercurrent flow. Each plate constitutes a single

stage where there’s a simultaneous partial condensation of vapor and

partial vaporization of liquid.

b. Packed column type are plate columns containing packing columns that

provides high interfacial area for the exchange of the components

between the vapor and liquid phases.

This lab is mainly designed to separate binary components including methanol

and water using the fractional distillation method in the six stages batch column. The 32

liter mixture is created using 5vol% of 99.8% anhydrous methanol and water. Then

sufficient amount of steam is supplied to begin the process of distillation. After it starts

boiling, the feed reaches equilibrium and samples of liquid and vapor from each stage are

collected. The collected sample is observed under a refractometer, a device that measures

the index of refraction. The data obtained from the refractometer is compared with the

calibration data obtain at room temperature in order to determine the composition.

2. Literature Review/Theory

Distillation is the separation or partial separation of a liquid feed mixture into

components or fractions by selective boiling (or evaporation) and condensation (Wankat



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What is the ultimate objective of the lab? Compare theoretical stages? Determine efficiency?


The unit ops distillation column doesn’t use steam, it uses electric heaters surrounding the bottom flask.


“on the other hand”


86). In a distillation column, the separation occurs because different components have

different volatilities. The component with more volatility is easy to vaporize therefore

the output vapor from distillation column will be enriched with more volatile component

while the output liquid phase will be more enriched with less volatile component

(Wankat 91). When a mixture reaches a specific temperature and pressure a certain

amount of the mixture moves into the vapor phase until the vapor reaches the mixture’s

vapor pressure (Wankat 98). This point is known as the vapor-liquid equilibrium.

Volatility is a measure of a pure component’s vapor pressure at a set pressure and

temperature in a specific mixture. It is incorrectly assumed that the components of a

mixture will separate based on their boiling points when pure. Rather, the boiling point of

a mixture is based on the total vapor pressure of a mixture, which is a sum of the vapor

pressures of each individual component in the mixture. This is known as the Dalton’s law

and can be expressed as:

psat=Σ(vpa+vpb .. . .. ) (1)

Psat=Vapor pressure of mixture (kPa)

vpa=Vapor pressure of component a (kPa)

vpb=Vapor pressure of component b (kPa)

This means that a component will not boil off “cleanly” meaning it is impossible through

distillation to obtain a pure substance. The vapor created above a mixture is also a

mixture of components. The composition of the vapor is based on the volatility of each of

the substances. Raoult’s law helps us to determine what the volatility, or “K value” of a



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substance. This in turn allows us to find the mole fraction of a component in the vapor

phase.

ya=vpa∗xa

psat (2)

ya=Mole fraction of component a in vapor phase (dimensionless)

vpa = Vapor pressure of component a (kPa)

xa = Mole fraction of component a in liquid phase (dimensionless)

Psat = Vapor pressure of mixture (kPa)

Equation 2 (Raoult’s law) holds true only for those components that do not form

azeotrope (J.M. Smith, H.C. Van Ness, M.M Abbott 350. Not all components obey

Raoult’s law because some components have high solubility with each other which leads

to the formation of azeotrope. An azeotrope is a mixture of two or more liquids in such a

ratio that its composition cannot be changed by simple distillation. This occurs because,

when an azeotrope is boiled, the resulting vapor has the same ratio of constituents as the

original mixture (Azeotrope). The simplest of all distillation techniques is called flash

distillation. Flash distillation occurs when a mixture at a specific temperature and

pressure is allowed to drop in pressure. This changes the vapor-liquid equilibrium of the

mixture and creates a vapor rich in the most volatile component(s). This is also the

crudest form of distillation and does not allow for refinement of the distillates.

A more complicated form of distillation is batch distillation. Batch distillation

uses both a boiler and a condenser, but only allows one separation, or cut, to be taken

from the mixture.



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Continuous distillation is the most complicated and most common form. It has a

boiler, condenser and multiple trays or packing which allows the vapor to condense as it

moves up the column and cools. The trays or packing allows for a better separation of the

components in the mixture which in the end gives purer products. It also adds a lot of

complexity to the system.

Figure 1

The McCabe-Thiele method greatly simplified the process of determining the size

of the tower and the number of trays. The method uses a graphical representation of the

material balance equations as operating lines on a graph of the liquid composition (x-

axis) and the vapor composition (y-axis). The bottom line in Figure 1 is the x-y line. This

starts at the origin and ends where x and y both equal 1.This line would represent a

distillation column that operated at total reflux and total boil-up, meaning that all of the

vapor and all of the liquid is recycled back into the system. The next line added is the

vapor –liquid equilibrium line for a binary system which is found experimentally. By

moving step-wise between the two lines we can find the number of theoretical plates



need figure caption, y-axis and x-axis title didn’t show up in your scanned pic.


needed for a specific separation of a binary mixture and the liquid and vapor composition

at any point in the distillation column. These stage lines can be seen in Figure 1.

Figure 2: McCabe-Thiele diagram with operating lines and feed line added.

In practice, we want to draw a purified product out of the column in the form of

either a distillate (top of the column) or the bottoms product (bottom of the column) or

both. This requires a column that operates at a partial reflux and/or a partial boil-up ratio.

This means that we cannot use the x-y line for such a column. In Figure 2 we see the

addition of a line for reflux ratio (slope L/V) and a line for the boil-up (slope L’/V’). The

boil-up line’s slope increases as we increase the amount of bottoms product that we

remove from the system. Subsequently, as we remove more distillate as product we

decrease the slope of the top operating line, which is the line for the reflux ratio. By



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changing the amount of liquid re-boiled, which is liquid returned to the column as a

vapor, or by changing the amount of vapor refluxed, returned to the column as a liquid,

we change the number of theoretical plates necessary for a given separation. The q

(quality) line in Figure 4 is the feed line which is the composition of the stream entering

the distillation column. We can see from the diagram in Figure 4 that where that line

intersects with the two operating lines is the feed stage, or the tray at where the incoming

stream enters.

The quality q is defined as:

(3)

Where:

[=] quality of the feed (dimensionless)

[=] liquid flow rate below the feed (mole/hr)

L [=] liquid flow rate above the feed (kJ/kg)

F [=] feed flow rate (mole/hr)

H [=] saturated vapor enthalpy of feed (kJ/kg)

hf [=] enthalpy of feed (kJ/kg)

h [=] saturated liquid enthalpy of feed (kJ/kg)

The feed line can then be defined as:

(4)

Where:

y [=] vapor mole fraction of methanol (dimensionless)

q [=] quality of the feed (dimensionless)



This is the case where the feed stream enters somewhere in the column. What does Figure 2 look like for batch distillation? In our lab, we don’t have a liquid flow rate above/below the stream so how will this effect the McCabe Thiele analysis?


Figure 2


x [= ] liquid mole fraction of methanol (dimensionless)

ZF [=] mole fraction of methanol in feed (dimensionless)

The top operating line is defined as

(5)

Where:

y [=] vapor mole fraction of methanol (dimensionless)

L0 [=] liquid reflux rate into column (mole/hr)

D [=] distillate flow rate (mole/hr)

x [=] liquid mole fraction of methanol (dimensionless)

xD [=] mole fraction of methanol in distillate (dimensionless)

The McCabe-Thiele method is widely used for binary mixtures. Multi-component

distillation is much more complicated and the calculations involved are trial-and-error, so

it is convenient to do them on computers (Wankat 176).

3. Experimental

3.1 Apparatus


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What is the effect of reflux on distillation? What type of reflux do we have in the lab experiment?


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No. Manufacture Component Description/Usage/Safety1 N/A Condenser Condenses the water.2 N/A Water supply A bulb valve used to fill the filling tank with

water. Be cautious of splashing water when opening the valve.

3 F&P Co Liquid Rotameter

Measures the flowrate of the water flowing into the condenser.

4 N/A Stages 1-6 There are 6 stages of the distillation column. At each stage, both liquid and vapor can be extracted. When extracting samples, be careful. Use a ladder or the staircase. Do not climb on the metal bars to extract samples.

5 N/A Filling tank The filling tank holds the methanol and water until it can be drained into the round bottom flask of the distillation column.

6 N/A Ladder Used to fill the holding tank and to extract


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samples at various stages of the distillation column.

7 N/A Ball valve for draining distillation column

Ball valve is used to drain the distillation column at the end of the experiment. Make sure the system is cooled to room temperature before draining; otherwise, it will break the glass.

8 N/A Fill/Drain valve

Needle valve used to fill the distillation column with the methanol and water solution from the filling tank. When the knob is pointing towards “fill” the filling tank can be filled with solution. When the knob is pointing towards drain, the filling tank will be drained of the solution and transported into round bottom flask of the distillation column.

9 N/A Pressure gauge Reads the pressure of the water flowing into the condenser.

10 N/A Flow rate control valve

Needle valve used to control the flow rate of the water flowing into the condenser.

11 N/A Valve for pressure gauge

Needle valve used to control the pressure of the condenser.

12 Powerstat Heater box Controls the boiler of the distillation column. Team must ask instructor to unlock and turn on the reboiler.

13 N/A Thermometer gauge

Reads temperature at the top of the distillation column.

14 Newport Digital Thermometer

Reads the temperature at each thermocouple location at each stage of the distillation column.

15 N/A Large round bottom flask

Holds the methanol and water solution while the boiler heats it up.

16 N/A Reboiler Heats up the round bottom flask containing the methanol and water solution.

17 N/A Valve to release the vapor

For each stage there is a ball valve labeled “GAS” and the stage number. This releases the vapor into a tube in which a vapor sample at that stage can be collected.

18 N/A Tube for gas A clear tube is connected to a valve in order to transfer the vapor from the distillation column to a small test tube.

19 N/A Valve to release the liquid

For each stage this is a ball valve labeled “LIQ” with the stage number. This releases the liquid into a tube in which the liquid sample at that stage can be collected.

20 N/A Tube for liquid A clear tube connected to the liquid valve allows for an easy transfer of the liquid from the distillation column to a small test tube.

21 N/A Filling funnel There if a funnel located at the mouth of the



filling tank in which water and methanol can be easily poured into the tank.

22 N/A Filling tank valve

A green valve that drains the fluid out of the tank. When the green valve is facing the left side, the solution is contained in the tank. When the green valve is facing the right side, the solution is transported through the pipes and into the distillation column.

23 Eyepiece Used to see the sample.24 Thermometer Reads the temperature of the water flowing into

the refractometer from the ice bath.25 Light switch Turns on the light source of the refractometer.26 Adjusting

KnobUsed to align the horizontal refracting line to the center of the X.

27 Refocusing knob

Used to focus the refracting line.

28 Light source29 Scale

illuminationThis button makes the refractor index scale appear. Read the top numbers.

30 Illuminating Prism

A small droplet of the sample is placed here. Be sure to clean the lens using distilled water and kimwipes in between samples.

31 Tubing for cold water

The cold water from the ice bath is transported through the refractometer.

32 Ice bath Used to keep the water flowing through the refractometer cold.

33 Capacity Controller

Controls the amount of fluid flowing through the refractometer.

34 Temperature controller

Controls the heating coil that melts the ice to form water which flows through the refractometer.

35 On/Off Switch Turns the ice bath machine on and off.36 Digital

thermometerReads the temperature of the ice bath.

37 Heating coil Melts the ice into water which flows through the refractometer.

3.2 Materials and Supplies

No.

Materials/Supplies Description/Use

1 Goggles Used to protect the eyes 2 Gloves Used to protect your hands from Methanol because it can


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dry out your hands.3 Tap Water Used to make the 5 wt % methanol and supplied to the

condenser4 Methanol 99.8% anhydrous methanol used to make the 5wt% water-

methanol solution that is then fed into the distillation column.

5 Graduated Cylinders

Measure the amount of Methanol needed to make methanol solutions.

6 Ladder Used to add methanol to the filling tank.7 Small test tubes Used to collect samples of the liquid and vapor at each stage

of the distillation column.8 Distilled water Used to clean the refractometer in between readings.9 Kimwipes Used to clean and dry off the refractometer.10 Ice Used in the ice bath for the refractometer to maintain the

temperature at approximately 33°F11 Digital

ThermometerUsed to read the temperature of the ice bath.

12 Refractometer Used in the experiment to obtain the refractive index that be used to calculate density once calibrated.

3.3 Experimental Procedure

Starting the batch distillation column:

1. Make sure the filling tank is closed and the knob of the Fill/Drain valve is

pointing in the direction of “Fill”.

2. Make a 5% of 99.8% anhydrous methanol solution by mixing it with water in the

13 gallon feed tank using graduated cylinders for measurement.

3. Pour the methanol-water mixture into the feed container and turn on the water

valve and fill the filling tank to the 32 liter mark, indicated by the black line.

4. Once the filling tank is full, turn off the water supply and carefully climb back

down to ground level. Turn the Fill/Drain valve so that the knob is pointing in the

direction of “Drain”. Make sure the yellow ball valve of the distillation column is

closed which is indicated by the knob facing perpendicular to the pipe.


Ruzica, 01/29/11,

Please number all the equipment parts used throughout the procedure section, so that the reader can easily look back at the apparatus section and know exactly what you are referring too.

Ruzica, 01/29/11,

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Ruzica, 01/29/11,

And to make various methanol wt% solutions when doing a calibration curve


5. Open the filling tank valve by turning the green knob all the way to the right. The

solution should start to fill the round bottom flask of the distillation column.

6. Once filling tank is completely drained, close the filling tank valve by turning the

green knob all the way to the left.

7. Call the instructor or the TA to turn on the reboiler.

8. Record the temperature of thermocouples at each stage every 20 minutes until the

temperature has reached steady-state.

9. Obtain samples of liquid and vapor at each stage.

10. Use the refractometer to determine the refractive index for each of the sample.

Instructions are listed below.

Using the refractometer:

1. Make solutions of 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, and 100 wt% methanol

solutions and cover each solution with parafilm.

2. Obtain ice from the CHE office on the 2nd floor.

3. Turn on the ice bath and add ice to cool the water to approximately 32 or 33°F.

Try to maintain this temperature throughout the experiment.

4. Turn on the light switch for the refractometer.

5. Open the illuminating prism and add a droplet of solution or sample. Close the

illuminating prism. And adjust the light source upwards.

6. While looking into the eyepiece, use the refocusing knob to obtain a clearly

defined horizontal line in which the bottom is green and the top is white.

7. Use the adjusting knob to raise or lower the line until it is exactly centered at the

middle of the X.



8. Press the scale illumination button to make the refraction index scale appear.

Record the value.

9. Repeat these steps for all the solutions of the calibration curve and the liquid and

vapor solutions from the distillation column after it has reached steady-state.

4. Anticipated Results

In this lab experiment, the mixture of methanol and water will be distilled using a

six stage batch distillation system at total reflux. The liquid and vapor compositions of

each stage will be determined using the refractometer, which will be calibrated using the

samples of known composition at constant temperature. From the values of refraction

index (n) of the known composition of methanol-water mixture, a second order

polynomial will be constructed. The vapor and liquid compositions for the each stage will

be calculated using the polynomial equation. The polynomial equation (ax2+bx+c) will

give two solutions for each refraction index. The correct refraction index will be

determined using the temperature of each stage.

From the collected data, the McCabe-Thiele diagram for the methanol-water

system will be constructed. This data will be compared to the theoretical VLE (vapor-

liquid-equilibrium) data of methanol-water system. Using this plot, the number of stages

and the fraction of the distillate will be calculated. The feed will be saturated vapor.

Using the Murphee plate efficiency equation, the efficiency of each stage will be

calculated.

(6)

Where,

= the composition in equilibrium with xn

η = efficiency of the stage

y = vapor fraction of methanol

The overall efficiency can be calculated from the equation below (Wankat 133):



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(7)

Where,

= the overall efficiency of the column

= number of the equilibrium stages

= actual number of the stage required

The overall energy balance for the distillation after it reaches the steady state can

be written as below:

(8)

Where,

m = mass of the component entering in the column at the top (kg)

= heat capacity of water at constant pressure (J/kg*K)

= the difference between inlet and outlet temperature of condenser (K)

From the above equation q of the distillation system will be calculated.



A couple of terms here will be zero in our case because we are not removing product from the top or bottom but are running at total reflux.


Any speculation on how your analysis will turn out compared to the theoretical?


5. References

1. “Azeotrope” < http://en.wikipedia.org/wiki/Azeotrope >

2. Diwekar, Urmila M., and K. P. Madhavan. "Multicomponent Batch Distillation

Column Design." Industrial & Engineering Chemistry Research 30.4 (1991): 713-

21. Print.

3. Guzman, Manuel De. Distillation. Scribed. Electronic.

4. Introduction to Chemical Engineering Thermodynamics (7th Ed.), J.M. Smith,

H.C. Van Ness., M.M. Abbott. McGraw-Hill, 2005. Pages 350-353.

5. MODELLING & SIMULATION OF BINARY DISTILLATION COLUMN.

Working paper. Scribed. Print.

6. Separation Process Engineering (2nd Ed.), Wankat, Phillip, Prentice Hall, 2007.

Pages 86-105.

7. "The Distillation Group, Inc. Distillation." The Distillation Group, Inc

Distillation. The Distillation Group, Inc, 11 Jan. 2002. Web. 23 Jan. 2011.

<http://www.distillationgroup.com/distill.htm>.

8. Website: < http://www.chemsep.com/downloads/data/fri_1982_tr.png>

9. Website: http://commons.wikimedia.org/wiki/File:McCabe-Thiele_diagram.png>

REFERENCES for this Lab Report Template:

Final Report Template Fall 2009, Department of Chemical Engineering, University of Illinois at Chicago, Chicago, Illinois.CHE4162 Syllabus Spring 2010, Department of Chemical Engineering, Louisiana State University, Baton Rouge, LA.



Good except you didn’t cite references 8 and 9. 4/5

http://commons.wikimedia.org/wiki/File:McCabe-Thiele_diagram.png

http://www.chemsep.com/downloads/data/fri_1982_tr.png


6. Appendix I: Job Safety Analysis (formerly called WP &C)

What is the purpose of this experiment?

The purpose of this experiment is to separate a mixture of a 5% (by volume) methanol-water solution in a binary distillation column. Methanol-water mixture will be introduced into the round bottom flask of the column and the column will operate at temperatures ranging from 0-100oC. Water will be used to condense the methanol rich product. The column will be run and allowed to reach steady state. Samples from the six stages will then be obtained and tested with a Refractometer to eventually obtain the methanol concentration in each stage.

What are the hazards associated with the experiment?

1. Methanol is a relatively toxic fluid. It can cause eye, skin and respiratory tract irritation when carelessly exposed to lab personnel.

2. The persistent use of fluids like water and methanol could lead to fluid spillage. If lab personnel were to walk over an affected area, they run the risk of injuries due to a fall

How will the experiment be conducted in a safe manner?

1. Lab personnel should wear gloves, goggles, slip resistant shoes, and a facemask when conducting experiment especially when handling the methanol.

2. Paper towels or task wipers should be in close proximity to clean up any fluid spills that may occur during experiment.

3. The Distillation column should not be heated until the mixture has reached the Reboiler section of unit.

What safety controls are in place?1. There is a failsafe valve present that allows the removal of fluids incase the unit

gets flooded.

Describe safe and unsafe ranges of operations.1. The operating flow rates of water should be between 0-2 GPM. All relevant data

can be obtained in this range. An increase flow rate between 3-10 GPM could be hazardous due to increased pressure.

I have read relevant background material for the Unit Operations Laboratory entitled: “Batch Distillation” 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


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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.

Signatures: _Sana Buch______________________________________

_Priya Chetty____________________________________

_Liliana Gutierrez_________________________________

_Vijeta Patel_____________________________________

_Linda Quan_____________________________________

_Lipi Vahnwala__________________________________


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