Binary Distillation University of Illinois at Chicago

(Image from "Fractional Distillation.")

Binary Batch Distillation

Lab Prep ReportUnit Operations Lab 2

14 February, 2011

Group 4Tien Diep

Kevin EstacioSebastian IskraZack LabaschinKevin ThompsonFelix Velazquez

Unit Operations ChE-382 Group No. 4 p. 1 Spring 2011 02/14/2011Diep, Estacio, Iskra, Labaschin, Thompson, Velazquez

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1. Introduction

Distillation is a separation process that takes place in a column which is able to separate a feed

into two components which exit in either the top or the bottom of the column. It works by

heating the fluid, which causes the more volatile component to evaporate. As the vapor phase

flows up, the liquid phase flows down as it gathers on the many trays. The liquid that gathers on

the trays is then able to be reheated to allow for more of the more volatile component to become

a vapor. This allows for a high purity in both the top and bottom of the distillation column. It is

important to chemical engineers because it “is the most widely used separation process in

chemical engineering” (Lab Manual, 1).

The advantage to using a distillation column over other methods of separation is that the

products produced are usually of very high purity. The disadvantage to using distillation is that it

can only separate a mixture into two different components; this can be offset by using a sequence

of distillation columns. In industry, distillation columns are used for a large amount of processes,

including the production and refinement of petroleum, pharmaceutical drugs, and alcoholic

beverages. Although there are several types of distillation methods, such as batch (used mostly in

the pharmaceutical industry), this lab will focus on continuous distillation, which allows for a

process to be run at steady state for an unspecified amount of time.

In this lab, a methanol/water system will be analyzed. First, a calibration curve will be

calculated for the index of refraction of the system using a refractometer. This will allow for later

analysis of the composition of binary mixtures present at each stage of the distillation column.

The distillation column will then be operated and a material balance will be carried out in order

to find the amount of methanol recovered in the distillate and the amount of water recovered in

the bottoms.

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2. Literature Review/Theory

The purpose of this module is to perform a binary distillation on a feed of methanol and water.

Distillation is defined as a process by which components are separated at equilibrium into gas

and liquids phases. This occurs on each tray present in the system, and the result is the vapor

components move up as the liquid products move down. This process is controlled by adjusting

the temperature and pressure of the system. Components with lower boiling points will become

vapor and components with high boiling points will remain liquid (or become liquid). In this way

a mixture can be separated, and when distillation columns are put in seris, the vapor/liquid

products can be further purified with the same process. Because of this simplicity, distillation

columns are iconic structures in chemical engineering . This particular unit operates at total

reflux – the vapor product does not exit the system. In this way the Methanol, the lighter of the

two components, will be separated from the water. In this way water will be purified. The

overall picture of a distillation column includes a mass and energy balance on the column

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(overall and for each compoenent) and a mass and energy balance on each tray.

Figure 1 (Binary Distillation w/ overall Mass Balanace, Wankat 2009)

Figure 2 (Tray Mass Balance, Wankat 2009)

The basic equation for a Mass Balance in a Binary Column:

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F = B + L EQ 1

F = Feed (mol / hr)

B = Bottoms (mol / hr)

D = Distilate (mol / hr)

In this way, we see that the mass entering the system is equal to the mass coming out of the top

and bottom of the column. In order to analyze the system, the McCabe – Thiele method is used.

The McCabe – Thiele method allows for the equilibrium relationship to be solved from the

vapor-liquid fraction curve and the mass balances from the operating line. An example of an

operating line (top):

y=L/V * x + (1-L/V) * x_d EQ 2

This top operating line is graphed for the rectifying or top section of the column (also known as

the absorbing section). The same equation is used for calculating the bottom half of the column,

the stripping section, except the L and V are calculated for the bottom section and the y-intercept

utilizes the liquid mole fraction of the bottoms product. Plotting such a graph results in the

following:

Unit Operations ChE-382 Group No. 4 p. 5 Spring 2011 02/14/2011Diep, Estacio, Iskra, Labaschin, Thompson, Velazquez

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Figure 3 (McCabe – Thiele diagram, Wankat 2009)

The McCabe – Thiele diagram thus shows the number of trays needed in a system and the

optimal placement for the feed stream to be place between. While the McCabe – Thiele method

is very useful, assumptions include vapor-liquid equilibrium at each stage, which is not practical

in reality. An efficiency is associated with the system.

n = (y_n – y_n+1) / (y*_n – y_n+ 1) EQ 3

n = efficiency

y_n = vapor fraction at tray nUnit Operations ChE-382 Group No. 4 p. 6 Spring 2011 02/14/2011Diep, Estacio, Iskra, Labaschin, Thompson, Velazquez

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y_n+1 = vapor fraction of tray n +1

y*_n = composition at equilibrium with X_n

With the McCabe – Thiele method and a method for accounting for the efficiency of the system,

this module can successfully be anaylized for a separation of Methanol and Water.

3. Experimental

3.1 Apparatus

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Figure 3.1 Distillation Column (Shown above)

No. Manufacture

Component Description/Safety

1 N/A Condenser Condenses the water in the system.2 N/A Water supply A bulb valve used to fill the tank with water. Be cautious of

splashing water when opening the valve.3 F&P Co. Liquid

RotameterMeasures the flow rate of the water going 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. Use caution when extracting samples. Use a ladder or the staircase. Do not climb on the metal bars to extract samples.

5 N/A Filling tank The filling tank retains 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 of the distillation column.

7 N/A Ball valve for draining distillation column

Used to drain the distillation column. System must be cooled to room temperature before draining, or else the glass might break.

8 N/A Fill/Drain 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

valveControlS 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. Instructor must 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 from each stage of the distillation column.

15 N/A Large round bottom flask

Retains 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.

3.2 Materials and SuppliesNo.

Materials/Supplies Description/Use

1 Goggles Used to protect the eyes 2 Napkins Used to clean excess water to prevent spillage3 Mop Used to mop any excess water around lab area to prevent spillageUnit Operations ChE-382 Group No. 4 p. 9 Spring 2011 02/14/2011Diep, Estacio, Iskra, Labaschin, Thompson, Velazquez

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2 Gloves Used to protect your hands from Methanol because it can dry out your hands.

3 Water Used to make the 10 wt % methanol and supplied to the condenser4 Methanol 99.8% anhydrous methanol used to make the 10wt% methanol

solution.5 Graduated

CylindersMeasure 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 Refractometer Samples of different wt% methanol solutions are placed in the

refractometer to later obtain the refraction index scale8 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.

3.3 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. Using a graduated cylinder, measure 1.6 liters of 99.8% anhydrous methanol. Using the

ladder, carefully climb up to the top of the tank and pour the methanol into the funnel.3. 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.

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 steadystate.9. Obtain samples of liquid and vapor at each stage.10. Use the refractometer to determine the refraction index for each of the sample.

Instructions are listed below. Unit Operations ChE-382 Group No. 4 p. 10 Spring 2011 02/14/2011Diep, Estacio, Iskra, Labaschin, Thompson, Velazquez

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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

The purpose of this lab is to study the process of continuous binary distillation, a

common physical separation process which works by exploiting the difference in volatilities of

the two components of the mixture (McCabe, 576-578). By heating the mixture to near its

boiling point, the more volatile component (Methanol) will vaporize first and travel up the

distillation column (Wankat, 280). In cases where the boiling points of the two pure components

are less than 25C apart, a simple distillation column will not be sufficiently effective,

necessitating the use of a fractional distillation column.

For this experiment a two-component system consisting of water and methanol will be

studied at differing mass fractions. This mass fraction difference will be directly proportional to

the mass flux rate which is also directly proportional to the rate of separation (Bird, 515).

Thermocouples are in place to measure the temperature at each stage. Using the refractometer, a

calibration curve will be generated for differing methanol concentrations and used as a reference

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for the experimental data. The higher the stage in the distillation column the higher the

concentration should be as well as the stage temperature decreasing up the column. The stage

temperatures also should have ranged between 65-100C, as pure methanol boils at 65C and

pure water boils at 100C. Methanol will be collected in the distillate as it is the more volatile

component and will evaporate out of the mixture at a rate faster than that of water.

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.

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6. Appendix I: Job Safety Analysis

What is the purpose of this experiment? 

The main purpose of this experiment is to understand the process of distillation by separating a binary mixture of 5 vol% methanol and water at total reflux. The compositions of vapor and liquid samples will be collected at various stages of the column and will be determined by using the calibration curve. The calibration curve can be plotted by measuring the refractive indices of methanol and water solutions of known compositions. (0, 10, 20, 30, 40, 50, 60, 70, 80, 90 and 100 wt% methanol)

What are the hazards associated with the experiment? 

This experiment involves heating a mixture in a pressurized system. Potential hazards from the heating component involve boiling liquid and the hot pipes coming into contact with the operator. Potential hazards from the steam also involve hot pipes coming into contact with the operator as well as pressurized steam. Another hazard includes handling the methanol solution since methanol is a highly flammable concentration. Methanol is moderately irritating to the skin. Methanol can be absorbed through the skin and harmful effects have been reported. Inhalation of methanol concentrations can also irritate mucous membranes, cause headaches, sleepiness, nausea, confusion, loss of consciousness, digestive and visual disturbances. Methanol is a mild to moderate eye irritant. High vapour concentration or liquid contact with eyes causes irritation, tearing and burning.

How will the experiment be conducted in a safe manner? 

To work in safe manner, eye protection should be worn at all time to avoid exposure to methanol solution. It is highly recommended to wear gloves and face mask when attempting to handle the methanol solution during the transferring and mixing the binary mixture in the column to avoid inhalation or skin contact. Conduct an inspection of the electrical outlet and make sure the heater is working properly before conducting experiment.

What safety controls are in place? 

If methanol or water spills on floor, clean up immediately to prevent slippery surface. Quickly breathe in fresh air if methanol is inhaled. Use eye wash station in the event of eye contact with methanol. When the heater is not in use, make sure to turn off the switches to prevent overheating and burning.

Describe safe and unsafe ranges of operations.

Safe ranges of operations include working with methanol wearing protective gear, gloves and face mask. When heating up the mixture solution, do not exceed the desired temperature and pressure. Unsafe ranges of operations include working with methanol when transporting samples to the refractometer station for further examination.

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

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