Experiment No. 1

Batch & Continuous Distillation

Date Performed:February 12, 2013

Date Completed:February 12, 2013

Submitted by:Group 4

MembersChing, Hans Elstin E.Gildo, Peniel Jean A.

Lam, Angelo W.Uy, Marc Louie T.

Submitted to:Nathaniel P. Dugos, PhD

Chemical Engineering DepartmentGokongwei College of Engineering

Date Submitted:March 26, 2013

I. Objectives

1. To investigate Rayleigh’s equation in describing differential distillation.

2. To determine the temperature and concentration profile in a differential

distillation process.

3. To determine the concentration profile in a packed column operating under total

reflux conditions at steady state.

4. To determine HETP and Kya of a packed column.

II. Theory

Distillation is a unit operation to separate the components of liquid mixture into

individual (or groups) of components by vaporization. Volatile liquids are readily

vaporized at low pressure and the boiling point of the more volatile components drive

the distillation process. The components are separated based on their physical

properties, specifically relative volatility, a tool used to express the magnitude of the

equilibrium distribution:

α=ya/ xa

yb/ xb

Where y is the vapor composition, x is the liquid composition, a is the more volatile

component and b is the less volatile component. There are two kinds of distillation:

batch and continuous. Batch distillation has the advantage of being able to handle

different mixtures simply by changing its operating conditions, but with higher

energy requirements and needs to be processed on a per batch basis. On the other

hand, in continuous distillation, as the name implies, feed is continuously supplied

and distilled.

In differential distillation, at any given time, the concentrations may be related by

material balance, with W the amount in the still at any time of concentration x:

wx−( w−dW ) ( x−dx )=vdW

wx−wx+xdW +Wdx−dWdx= ydW

Wdx= ( y−x ) dW

dWW

= dxy−x

Integrating and considering the initial feed as F and concentration xF, we obtain

Rayleigh’s equation:

lnFW

=∫X w

X f

dxy−x

The Rayleigh equation can be simplified into various forms such as:

1. When Henry’s Law applies, y=mx where m=H/P. This, however, is only

applicable for dilute solutions, where partial pressure of the vapor is a linear

function of composition. The integrated equation yields

lnFW

= 1m

lnXfXw

2. If the relative volatility is assumed to be practically constant, and substituting the

relative volatility equation and integrating, we obtain in terms of the individual

components,

lnA1

A2

=α AB ,ave lnB1

B2

Where subscript 1 refers to initial amounts and subscript 2 refers to the final amounts

found in the solution. If the assumptions above cannot be applied, then the integral is

evaluated by graphical or numerical methods.

In a packed column distillation, the advantages include simpler design, ease of

operation, and lower pressure drop. In this experiment, total reflux was chosen for

better and simpler data collection. A packed column may be expressed in terms of the

number and height of a transfer unit. If we base it on the mass transfer in the

interfacial contact between the liquid and vapor around a differential volume element:

d N A=K ya ( y∗− y ) sdZ∧d N A=VdY=Vdy

Substituting and solving for Z,

Z=V /SKya∫

dyy∗− y

∧Z=(N TU )(HTU )

The NTU can be determined from the experimental data by plotting the equilibrium

curve together with the concentrations collected. Since the column is operated at total

reflux, the operating line coincides with the diagonal thus the driving force (y*-y) is

the vertical line from the equilibrium curve to the operating line. One can plot 1/(y*-

y) versus y or x since y=x at total reflux. The area under the curve yields the NTU.

Since the height of the packing is known, then the HTU is evaluated. To measure the

vapor flow rate, one can use the heat or wattage of the heater to estimate the vapor

generated at steady state:

V= Heat suppliedγ of solution

III. Setup

IV. Summary of Procedures:

A. Preparation of a Calibration Curve1. Prepare a 0, 10, 20, 30, 40, 50, 60, 70, 80, 90 (% v/v) ethanol solution.2. Determine each refractive indices of the different ethanol solution by using a

refractometer.3. Plot the refractive indices to the ethanol solution.

B. Batch or Differential Distillation Experiment1. Setup the batch distillation apparatus.2. Prepare a 10% (250 mL) ethanol solution3. Heat the setup until the first drop then record the initial temperature reading alongside

start the time.4. Take every 10 mL of distillate until 100 mL and for every 10 mL record the time and

temperature.5. Determine the refractive index of every 10 mL sample by using a refractometer.

C. Packed Column Distillation at Total Reflux Conditions Experiment1. Setup the Packed Colmn Distillation and prepare the ethanol solution.2. Heat the setup for at least 45 to 60 minutes and make sure that every outlet is closed.3. Every after 10 minutes, record the 4 temperature reading and take a sample for every

outlet then determine the refractive index of each sample.4. Repeat the previous step until the refractive index stabilizes.

V. Data

Part I. Batch Distillation

A. Calibration Data

EtOH Conc in Water

Refractive Index

0 1.331910 1.334520 1.341130 1.345540 1.353550 1.357160 1.357770 1.359580 1.361490 1.361599 1.3605

B. Calibration Curve of EtOH-Water System

0 10 20 30 40 50 60 70 80 90 1001.315

1.321.325

1.331.335

1.341.345

1.351.355

1.361.365

f(x) = 0.000314816946042865 x + 1.33557868151113R² = 0.875764381799626f(x) = − 3.99839131223765E-06 x² + 0.000712323265522784 x + 1.32966153753436

R² = 0.983173001332173

Calibration Curve for EtOH-Water

Concentration of EtOH in Water (%v/v)

Refr

activ

e In

dex

C. Batch Distillation Data

Refractive Index Volume FractionVolume

(mL) FlaskDistillat

eFlask

(x)Distillat

e (y)

101.339

5 1.3625 0.1535 0.8967

201.338

1 1.3614 0.1296 0.8600

301.337

0 1.3611 0.1114 0.8500

401.335

5 1.3611 0.0872 0.8500

501.334

3 1.3587 0.0684 0.6735

601.333

5 1.3550 0.0561 0.5102

701.332

8 1.3484 0.0455 0.3290

801.332

0 1.3397 0.0335 0.1569

901.331

9 1.3350 0.0320 0.0793

1001.331

8 1.3330 0.0305 0.0485

D. Plot of 1/(y-x)

0.0200

0.0400

0.0600

0.0800

0.1000

0.1200

0.1400

0.1600

0.1800

0.20000.0000

10.0000

20.0000

30.0000

40.0000

50.0000

60.0000

x

1/(y

-x)

E. Area Calculation

Area under the curve

b1 b2 h Area

A1 55.6728 21.1351 0.0015 0.0562A2 21.1351 8.1010 0.0015 0.0220A3 8.1010 3.5270 0.0120 0.0696A4 3.5270 2.2023 0.0106 0.0304A5 2.2023 1.6526 0.0123 0.0237A6 1.6526 1.3455 0.0663 0.0993

Total 0.3012

Part II. Continuous Distillation

A. Data

Steady-State ValuesT y* RI y 1/(y*-y) Area80.1 0.822 1.3451 0.258066 1.773258 1.616965

81 0.794 1.3536 0.465004 3.039553 1.21937686.5 0.6735 1.3517 0.410664 3.804653 -1.58286

98 0.198 1.3342 0.066826 7.623461Total 1.253479

VI. Results and Analysis

The calibration curve of ethanol-water system is used to compute for the actual

concentrations of Ethanol in water using the measured refractive indexes. Two models were

used to maintain accuracy. For RI values that are more than 1.3603, the linear model is used.

RI = 0.0003 (Concentration) + 1.3356

For values below, the more fitted quadratic curve is used:

RI = -4×10-6(Concentration)2 + 0.0007(Concentration) + 1.3297

From the data obtained, it can be computed that the area under the batch distillation

curve is 0.3012. This means that the term ln(F/W) is equal to 0.3012 and thus, the Feed to

Residue Ratio is equal to 1.3415.

As for the continuous distillation, the calculated number of transfer unit is 1.2535.

Knowing that the height of the tower is 0.9 m, the height of a transfer unit, HTU would be 0.717

m.

VI. Conclusions and Recommendations:

The group was able to utilize the Rayleigh Equation for the determination of the Feed to

Residue ration, which is 0.3012. For the continuous distillation, the height of a transfer unit was also

computed as 0.717 m. The calibration curve of the system turns out to be an accurate fit for the data

but care must be taken from determining the actual data.

Appendix

I. References Olaño, S. (2007). Experiments in Chemical Engineering, 2nd Ed. De La Salle

University Press.

Geankoplis, C. J. (2003). Transport Processes and Separation Process Principles, 4th ed. New Jersey: Pearson Education, Inc.