che291 manual spring 2011 revised and po

CHEMICAL ENGINEERING LABORATORY 2

CHE-291

DEPARTMENT OF CHEMICAL ENGINEERING

Spring 2011 Instructor: Jennifer Moll/John Zhang

Edition: April 2007

Rev: May 2011

INTRODUCTION 1

ACADEMIC OFFENCES .............................................................................. 2

EXCERPTS FROM THE UNIVERSITY OF WATERLOO

POLICY #71 ...................................................................................... 2

LABORATORY SAFETY ............................................................................. 3

LABORATORY REPORTS ........................................................................... 5

A. Preliminary Reports ............................................................................. 5

B. Group Memo Reports ............................................................................ 6

Evaluating Errors ........................................................................................ 8

Propagation of Error Equations ................................................................ 10

Error in Linear Regression Analysis ......................................................... 10

Assessing Quality of Fitted Data .............................................................. 11

Tables and Figures .................................................................................... 12

LENGTH of MEMO REPORTS for ChE291 .............................................. 17

ORAL PRESENTATIONS ........................................................................... 18

EXPERIMENT 1: Double-Pipe Heat Exchanger ........................................ 19

Physical properties of Paratherm NF heat transfer oil .............................. 26

Physical properties of water and steam ..................................................... 26

Table 1-1: Double-pipe heat exchanger properties .................................. 26

PRELIMINARY REPORT QUESTIONS ................................................ 30

MEMO REPORT QUESTIONS ............................................................... 31

EXPERIMENT 2: Distillation Column ..................................................... 32



EXPERIMENT-3: Liquid-Vapour Equilibrium .......................................... 44



EXPERIMENT 4: Phase Diagram: 3–Component Liquid System .............. 52



General Lab Info 1

INTRODUCTION

Progress in the field of science or technology depends not only on a clear

grasp of relevant theoretical principles, but also on the quality of

experimental investigations carried out in that field. Solutions to many

complex problems of interest to chemical engineers can be approached by a

carefully designed and properly executed experimental program.

Laboratory courses allow the student to study numerous experimental

arrangements, equipment details, and measuring devices which cannot be

covered adequately in a lecture course. An appreciation is also gained of the

difficulties involved in obtaining accurate data under properly controlled

conditions.

Basically, the three main course objectives of this laboratory course are:

To assist in the understanding of basic principles of chemical

engineering through actual observations of the behaviour of

physicochemical systems.

To help develop skills in experimentation, data analysis and

interpretation of results.

To practice in the art of writing effective engineering reports.

General Lab Info 2

ACADEMIC OFFENCES

EXCERPTS FROM THE UNIVERSITY OF WATERLOO POLICY #71

"STUDENT ACADEMIC DISCIPLINE POLICY"

Original text available at:

http://www.adm.uwaterloo.ca/infosec/Policies/policy71.htm

"A university is a community of scholars in which knowledge is generated and

disseminated through scholarship and teaching. All members of the community - faculty,

students and staff are bound to conduct themselves with honesty, integrity, fairness and

concern for others. Any action which unnecessarily impedes the scholarly activities of

members of the University is an offence punishable by appropriate disciplinary action."

Some of the academic offences outlined by the University include:

Infringing unreasonably on the work of other members of the University

community (disrupting classes or examinations; harassing, intimidating or

threatening others).

Cheating on examinations, assignments, work-term reports, or any other work

used to judge student performance. Cheating includes copying from another

student's work or allowing another student to copy from one's own work,

submitting another person's work as one's own, fabrication of data,

consultation with an unauthorized person during an examination or test, and

use of unauthorized aids.

Plagiarism, which is the act of presenting the ideas, words or other intellectual

property of another as one's own. The use of other people's work must be

properly acknowledged and referenced in all written material such as take-

home examinations, essays, laboratory reports, work-term reports, design

projects, statistical data, computer programs and research results.

Submitting an essay, report, or assignment when a major portion has been

previously submitted or is being submitted for another course without the

express permission of all instructors involved.

http://www.adm.uwaterloo.ca/infosec/Policies/policy71.htm

General Lab Info 3

LABORATORY SAFETY

It is essential that engineers develop a habit of safety in all experimental work. Dealing

with flammable corrosive liquids, spattering reagents, violent chemical reactions, or the

escape of steam can be quite dangerous in the absence of sensible protective measures or

devices.

All students are required to have completed a WHMIS course. If you have any

doubts about a procedure, ask the TA for assistance.

Safety goggles must be worn when in the undergrad labs. Lab coats are required.

Closed-toe shoes and long pants are required. Contact lenses are not permitted to be

worn in labs.

Read the Material Safety Data Sheets (MSDS) prior to experiment. Evaluate

hazards involved in procedures to be used.

All hazardous wastes must be emptied into the appropriate waste containers. Read

waste labels before disposing into any receptacle.

Keep chemical bottles closed tightly when not in use.

Immediately inform your Teaching Assistant of any injuries or spills. For cuts,

burns and if a chemical comes in contacts with your skin, eyes or mouth, flush

immediately with water at the sink or safety station. You must file an accident

report with the department. In the event of a serious injury, inform the TA that you

wish to go to Health Services. The TA will send someone to accompany you.

Dispose of any broken glass in the bucket labeled “Broken Glass”.

Clean up work area before leaving.

Make sure to know the location of the following:

Fire extinguisher

Safety shower

First aid kit

Fire alarm

Telephone

GENERAL INSTRUCTIONS

FOOD and BEVERAGES ARE STRICTLY PROHIBITED FROM THE LAB

General Lab Info 4

Most of the experiments require several students working together in order

to manipulate the equipment, take readings, and record the data.

Accordingly, students are assigned to groups of three.

Before commencing an experiment, all members of a group should have a

thorough understanding of:

Theoretical principles involved in the experiment.

Type and amount of data to be recorded.

Expected results.

Whenever the foregoing requirements are met, the experiment can become a

true learning experience which will immeasurably assist in understanding

the underlying principles; otherwise, the exercise becomes merely one of

manipulation of equipment and the reading of various instruments.

Every member of a lab group is expected to actively participate in the lab. The

pre-assigning of duties to each member of the group is strongly advised in order

for the experiment to be performed effectively and quickly.

Professional conduct: Although you are going to work as a group, some

marks are allocated for individual professional conduct. Marks will be

deducted for horse-play and lack of participation in the experiment.

Attendance: Marks are reduced for latecomers to the lab. If you have a

conflict with a co-op interview, you must inform the TA in advance in order

to make alternate arrangements to fulfill your lab requirements.

In the event of a lab missed due to an illness, contact the TA or lab instructor

asap. You must provide the chemical engineering undergraduate secretary or the

lab instructor with a Verification of Illness form (can be downloaded from:

http://www.healthservices.uwaterloo.ca/Health_Services/verification.html)

completed by a doctor. Arrangements will be made for you to make up for the

missed lab.

http://www.healthservices.uwaterloo.ca/Health_Services/verification.html

General Lab Info 5

LABORATORY REPORTS

Two types of laboratory reports are required in this course. The

requirements for each type of report are outlined below:

A. Preliminary Reports

The purpose of a Preliminary Report is to prepare the student for the

experiment. Each group prepares one Preliminary Report for each

Physical Chemistry experiment. The report should contain the following:

1) Statement of the objective.

2) Summary of theory and Equations to be used in calculation of results.

3) Brief summary of experimental procedure, number of runs and range

over which the experiment is to be carried out. Constraints on

experiment. Diagram of equipment.

4) Datasheet with appropriate headings to be filled in during experiment.

Prepare an extra copy for use during the lab.

5) Review of safety protocol for experiment. Identify potential physical and

health hazards of chemicals and equipment that could be encountered in

the experiment. Summarize safe handling procedures and personal

protection equipment required. Summarize MSDS for chemicals to be

used (can find online via Safety Office).

6) Answers to the Preliminary Report Questions from the lab manual.

7) This report should be submitted to the Teaching Assistant at the start of

the laboratory period. It will be checked during the laboratory period to

see that the group is not pursuing some erroneous task; graded and then

returned.

8) Graded prelab report should be attached to back of Memo or Data

Analysis Report be submitted.

General Lab Info 6

B. Group Memo Reports

A Memo Report is a complete record of your experiment. It describes:

Why the experiment was performed.

What data were obtained, and

Your interpretation of the data

A scientific report is not merely a list of facts or observations; it must provide an

interpretation of the findings and show their significance. A good engineering

report is organized logically and the wording chosen carefully so that the reader

knows exactly what you mean and where to find the evidence that supports your

conclusions.

The Memo Report should include the following:

1) Title Page

a) Name of the University and Department.

b) Course name and number.

c) Group number and names all the members of the group.

d) Date experiment was performed.

e) To whom and the date that the report was submitted.

2) Table of Contents

List the divisions of the report with page numbers opposite. Lengthy

divisions should be subdivided into appropriate headings.

General Lab Info 7

3) Introduction

The purpose of the Introduction is to guide the reader to consider the

importance of the topic being presented. It should include:

a) Brief statement of the objective.

b) General background information relating to the experiment.

c) Significance to Chemical Engineering of the data obtained.

4) Theoretical Principles

This section should include:

a) Brief discussion of the theoretical foundation of the experiment.

b) Include all necessary equations to be used in the calculations. Derivations of

equations go in the Appendix.

c) Conclude with a brief statement indicating how the objectives will be met using

the theoretical principles involved.

5) Experimental

In this section:

a) Summarize what you will be doing in the laboratory based on what you have read

in the Laboratory Manual

b) Include a labeled sketch or schematic of the equipment.

c) State all modifications made to the procedure.

The Introduction and Theoretical Principles must be written in your own words.

Do not copy from the Lab Manual. Research your topic. Use library resources.

General Lab Info 8

6) Observations and Results

In this section, you should present your qualitative and quantitative

observations. Then guide the reader through the manipulation of the data

in fitting it to the theoretical model.

a) Qualitative Observations

b) Describe the experimental observations and, if required, refer to the appendix

which contains your original measurements.

c) Report any irregularities in the experimental procedure that might explain

outlying data points.

Original datasheet should go in an appendix

d) Quantitative Results

e) Present results which were calculated based on the data recorded during the

experiment. Place sample calculations in the appendix but refer to them here.

f) Use tables or figures to clearly demonstrate trends in data (Refer to Tables and

Figures section below).

g) List the estimated precision of your measurements, as well as, any other

observations which may help to explain the results. Refer to the Evaluating Error

section.

h) Use significant digits. Remember to include units.

Always maintain significant figures when reporting values. The number

of digits used to express a measured or calculated value is extremely

important. It indicates the precision of the value. The last significant

digit is considered to vary by 10 % unless the error is specified. It is

incorrect and misleading to report values to higher precision than

possible from the equipment used in the experiment. Refer to Chapter 11

section 6.2 in Introduction to Professional Engineering in Canada by

Andrews et. al. (2003) for more information on determining significant

figures through algebraic operations.

Evaluating Errors

Unless one is counting individual objects, there is error inherent in all

measurements. Two types of errors occur: Systemic (or determinate) and

Random errors.

General Lab Info 9

Systemic errors are constant or proportional biases in a measurement

occurring due to the investigator’s habits or poor calibration or drift of

the analytical equipment. For example, the ruler was misread by +0.5 mm each time,

or the pressure gauge was zeroed when the system pressure was actually 10 psi however, the

upper range was accurate. Large differences between experimentally-derived

results and commonly-accepted or cited values of a parameter are likely

due to the occurrence of systemic errors. Fortunately, systemic errors

may be identified and correction factors used to compensate for them if

they can be quantified. Systemic errors can also be minimized by regular

recalibration of analytical equipment and by standardizing experimental

procedures.

Random errors, on the other hand, are inevitable and vary from reading to

reading. It is an estimate of these random errors which must be included

when reporting any measurement or derived experimental value. Unlike

systemic errors, random errors cannot be quantified exactly but they can

be approximated. For example, you measure the length of your pen to be 16.0 cm using

a ruler with gradations to the nearest 0.5 cm. Those markings are thick and imprecise so you

might assume that you can read precisely to, say, the nearest 0.1 cm. This is the “external

error” of this measurement. You would report the length as 16.0 ± 0.1 cm. Depending

on the size of the scale of measurement, the human eye can differentiate

up to 1/10 of the interval between markings. For digital displays, the

precision is to half of one decimal place below the last stable digit or to

the manufacturer’s specifications. Use judgment in assessing the

precision of the measurement.

Random errors tend to offset each other so, for any given parameter the

average of several repeated measurements will be more precise than any

single measurement. You can estimate this higher precision by

calculating the average value ( x ) and the standard deviation (s) of n

repeats. Your measurement would be reported as x ± SE where the

standard error SE can be approximated by:

n

sSE

General Lab Info 10

Propagation of Error Equations

If the precision of individual measurements are known, the overall

precision of any value derived from these measured values can be

approximated using the equations shown below:

Addition and Subtraction

Multiplication and Division

Exponential In General

Where: k, n are constants, a, b, c, d, x and y are measured variables, Δx is

the standard deviation of x which can be approximated by the standard

error of a repeated measurement or the estimated precision or “external

error” of a single measurement.

Error in Linear Regression Analysis

Linear regression uses the Method of Least Squares to determine the line

which best fits N experimental data points. The relationship is plotted as:

y = mx + b. Generally in the 291 experiments, the values of interest from a

regression line are the intercept, b or the slope of line, m. Unless the data fit

perfectly to a straight (i.e. R2=1), then some error is inherent in these

regressed values and this error must be reported.

...

...

23

22

21

321

ckbkaky

ckbkakky

2222

d

d

c

c

b

b

a

a

y

y

cd

kaby

b

bn

y

y

by n

dx

dyxy

xfy

)(

General Lab Info 11

To simplify the calculations, some key quantities need first be defined:

N

xxS

iixx

22

N

yyS

iiyy

22

2

2

N

SmSS

xxyyr where (xi,yi) are the individual data points.

Use the following equation to find the standard deviation of the slope, sm:

xxrm Sss /

The standard deviation of the y-intercept, sb, is given by:

2

2

1

i

i

rb

x

xN

SS

The standard deviation, sc, of any point taken from the regressed line

based on an average of M replicate measurements, is

found using:

xx

crc

Sm

yy

NMm

SS

2

211

where: y is the mean (average) of all values of yi (where i = 1….N) used

to determine the regression line.

Assessing Quality of Fitted Data

When regressing data, it is assumed that the random deviations from the

model are independent, normally distributed, and have a constant

variance. For any modeling of fitted data, you should assess the quality

of the fit of the model using the coefficient of determination and residual

plots. Outliers should be identified. Justify any data points removed

from the assessment.

General Lab Info 12

Tables and Figures

Any tables and figures must be explicitly mentioned (“cited”) in the text

and should be inserted in the report as closely after they have been cited

as possible. All figures and tables must have titles and they must give

units for all data presented. Number tables using Roman numerals (i.e.

Table ΙI).

Tables must contain enough information to stand alone. The reader

should not have to refer to the report to understand it. An example of a

table is shown below.

“… The experimental conditions and the measurement results are shown in Table Ι. ”

TABLE I: pH of the reaction product in the titration of 1.0 mmol/L Copper perchlorate

using 0.04 wt % Ethylenediamine [en] solution (298 K).

[en] in Cu

solution mmol/L

pH

0.00 2.80

1.46 2.89

2.93 3.05

4.41 3.05

Figures should be prepared by computer. Label all figures with Arabic

numerals (i.e. Figure 1, Figure 2, etc.) and a relevant title. As with

tables, be sure to include all information that is necessary for the reader

to interpret or identify the image (i.e. reaction temperature, pressure, etc.)

in the title or in a caption.

For graphs, label each axis with a scale and title. Remember to include

units. If several sets of data are being plotted, use a legend to identify the

different symbols.

Depict observed data as discrete points. Plot trendlines or fitted models

using lines.

Sign and date all the figures in ink.

General Lab Info 13

Figure 1:

7) Discussion of Results and Error Analysis

This is the most important aspect of the report! Many students have

trouble knowing what to discuss. A good guideline is to think of the

experiment not merely as a school exercise but as an experiment being

performed as engineering research. Indicate which observations or

calculated results would be useful to other engineers who might read

your report. Guide the reader through your analysis of the observed

results. Explain any discrepancies with the theory and what may have

occurred to cause the discrepancy?

(a) Discuss the quality of your experimental data. Are there any data

points which may be unreliable? State the reasons for the

unreliability. Consider the purity of the reagents used.

Note that you must support your ideas and this will usually require

finding and reading reference material.

Microbial Growth Curves (grown at 37ºC in Tryptose Phosphate broth

with 2.5 g/L dextrose added)

0.000

0.500

1.000

1.500

2.000

2.500

3.000

0 100 200 300 400 500 600

Incubation Time (min)

Op

tic

al

Den

sit

y (

AB

S)

Bacillus subtilis

Streptococcus faecalis

All the equations should be presented in the theoretical principles

section and referred here in the discussion section only by equation

number.

General Lab Info 14

(b) Discuss your calculated results. It may be necessary to review

briefly how the calculations were performed. Mention any

assumptions made, such as, the values assigned to constants in

equations or data points that were excluded from the calculations.

(c) Relate your results to the theory. How do they relate to the physical

phenomenon being studied? Do your results agree with values

presented in literature? Include references. Are your values

reasonable? If not, try to explain the course of the discrepancy.

(d) Discuss the significance of your results, and any new information

that has been learned.

(e) Finally, discuss the error analysis. Include a discussion of the

individual measurement errors that contributed to the overall error in

the calculated results. Which measurement error had the largest

effect on the results? Could the results be improved by taking

replicate measurements, by using different equipment, or by taking

measurements under different conditions? Is the precision in your

results comparable to experiments in the literature?

8) Conclusions

This section should include a summary statement of the relation between

the results and the objectives of the experiment.

What are the principal results of the experiment? List them, stating the

most important ones first. Summarize the significance of the results

obtained as they relate to applications in engineering.

9) Recommendations

Recommendations to improve the experiment should be included here.

Most important recommendation should be made first. Make sure your

recommendations are feasible from a practical point of view and give

estimates of the costs involved when making such suggestions.

10) Nomenclature

Define all the symbols used in the report in alphabetical order.

General Lab Info 15

11) References

For journals, give complete information, including names of all the

authors, title of the article, name of the journal, volume, page number(s)

and the year of publication. For example:

1. Reilly, P.M., B.M.E. van der Hoff, and M. Ziogas, “Statistical study of the

application of the Huggins equation to measure intrinsic viscocity”, J. Appl.

Polym. Sci., 24, 2087-2100 (1979)

For references to books give author(s), “Title”, edition, publisher, place

and (year of publication), and the page number(s).

2. Laidler, K.J. and Meisner, J.H., "Physical Chemistry", Benjamin/Cummings

Publ. Co. Inc., Menlo Park, California (1982), p. 789.

For websites give the author’s name, Title of section used, URL, (date

accessed)

3. Shuzon Ohe, Distillation Computation, http://www.s-ohe.com/McCabe-

Thiele.html (accessed Jan. 19, 2005).

The abbreviation et al. should not be used in the reference list. List the

names of all authors.

Do not repeat references. If the next reference refers to the same article or

book write:

4. Ibid., p.238.

If referring to a reference already listed, refer to its reference number and

give page number:

5. Ref. 2, p. 237.

General Lab Info 16

12) Appendices

The purpose of putting extraneous material, such as, experimental data

into the appendix is to prevent disruption of the coherence of the report

by long derivations or large columns of numbers. Materials that should

be in the appendix include:

Long tables of original observations.

Lengthy derivations of equations

Sample calculations

Answers to “Memo Report Questions”.

Graded Prelab Report.

Material essential for understanding the report must remain in the body

of the report.

General Lab Info 17

LENGTH of MEMO REPORTS for ChE291

To reduce the time spent writing and to help you produce organized and

concise reports, the following guidelines regarding the length of Memo

Reports for the CHE-291 course are recommended:

Title or cover page

Table of contents 1 page

Introduction 1-2 pages

Theoretical principles 1-2 pages

Experimental 1 page

Observation of results 1-2 pages

Discussion of results and Error Analysis 2-3 pages

Conclusions and Recommendations 1 page

References ½ page

Appendices 2+ pages

Your reports should be as straightforward and concise as possible.

Note that Figures and Tables are not included in the guidelines above.

General Lab Info 18

ORAL PRESENTATIONS

Each group will give one oral presentation that is 15 minutes in length

followed by a 5-minute question period.

A paper copy of the overheads should be prepared and submitted to the Lab

Instructor and three TAs just before the presentation.

All group members must participate in the presentation and answering of

questions. The presentation will be graded on an individual basis.

Some guidelines for presentation overheads:

Present an outline at the start of your presentation. It provides a

chance for you to inform audience of where the presentation will lead.

Use 24 pt font or larger. Check that titles and axis labels on graph are

legible from back of presentation room. Avoid red lettering. Make

use of contrast (light font on dark background or vice versa).

Generally one minute per overhead is good timing. Use judgment.

Give audience sufficient time to absorb all content of the overhead.

Limit # of words per overhead to approximately 25. Use headings

and then list only key words and phrases. Excessive writing hides key

values and points and distracts the audience.

Give sufficient detail in figures and tables for audience to comprehend

without verbal explanation. Give a brief explanation of the table or

figure then draw attention to key values or trends by pointing them out

as they are discussed. Use a pointer.

Animation can be useful for highlighting key points. However, keep

in mind that excessive animation is very distracting.

Double-check presentation for spelling mistakes and equation typos.

Practice your presentation. Ask for access to presentation room

beforehand to check how overheads will look. Note that the vibrancy

of certain colours sometimes changes from computer to projector.

Exp1: Double Pipe Heat Exchanger 19

EXPERIMENT 1: Double-Pipe Heat Exchanger (Contributed by L. Coleman)

INTRODUCTION:

Heat transfer is a fundamental component of chemical engineering education. The

addition or removal of heat is essential in many industrial processes. Heat transfer often

occurs in combination with other unit operations, such as chemical reactors, distillation

columns, evaporators, steam generators, and the burning of fuel. However, it can also be

used as a unit operation by itself to condition the temperature of fluid streams. In most

chemical processes, heat is added or removed at a specific rate to ensure the stable and

efficient operation of the process. Therefore, a particular heat exchanger is designed to

transfer heat at a specified rate.

The driving force for the transfer of heat is the temperature difference between two

points. Heat transfers from a region of high temperature to a region of low temperature.

There are three modes of heat transfer: conduction, convection, and radiation. In this

experiment heat transfer by radiation will be assumed to be negligible and will not be

discussed. Conductive heat transfer generally describes the transfer of heat in solids, and

slow moving or stagnant fluids. For moving fluids, heat is transferred by convection. In

this experiment, both conductive and convective heat transfer play significant roles.

One of the most common heat exchangers used in industry is the double-pipe heat

exchanger (DPHE). A schematic drawing of a DPHE is shown in Figure 1-1. One fluid

flows through the inside pipe and the other flows in the annular space between the two

pipes, see Figure 1-2. The fluids can flow in either co-current or counter-current

directions.

Figure 1-1: Double-pipe heat exchanger1.


Figure 1-2: Cross-section of a double-pipe heat exchanger (concentric tube arrangement).

When analyzing the performance of heat exchangers it is helpful to begin with a plot of

the temperature profile. A temperature profile graphically describes the temperature

change for each stream over the length of the heat exchanger. Several temperature

profiles commonly found in double-pipe heat exchangers are shown in Figure 1-3. For

co-current flow systems, the temperature difference between the hot and cold streams

continually decreases over the length of the heat exchanger and it can be shown that the

maximum cold stream outlet temperature is the temperature of the exiting hot stream. In

contrast to this, counter-current flow maintains a higher temperature difference and thus a

high heat transfer driving force. Because of the flow arrangement, it is possible for the

exiting temperature of the cold fluid to be greater than that of the exit temperature of the

hot fluid.

Figure 1-3: Typical temperature profiles for double-pipe heat exchangers1.


When a vapour contacts a surface that is at or below its saturation temperature,

condensation occurs. For steam at atmospheric pressure, the saturation temperature is

100°C, or 373.15 K. The condensation process involves the removal of the latent heat of

vaporization (ΔHV) from the vapour, to produce a liquid condensate. The temperature

profile for condensation in a double-pipe heat exchanger is quite interesting. The cold

fluid gains heat as it passes through the heat exchanger, but the temperature of vapour

(the hot fluid) does not change. The temperature remains constant since only the energy

required to condense the vapour is removed. This energy is termed the latent heat of

condensation and is equal in magnitude to the heat of vaporization (in which the energy

transfer would be in the opposite direction) but opposite in sign. No sensible heat is

removed while the temperature remains constant, since by definition a temperature

change must be “sensed” to drive this process.

Heat (Energy) Balances

One of your most important duties as a chemical engineer will be to evaluate the overall

energy requirement of a process unit and determine its efficiency. To begin, an energy

balance of the process unit is necessary. An energy balance for a process unit operating at

steady state accounts for energy transferred to and from the process unit. A general

steady state energy balance is given in equation (1-1),

q = Energy Out – Energy In (1-1)

where q represents the heat gained (+) or lost (-) by the process unit. A steady-state heat

balance allows an engineer to quantify heat losses from a system. For the DPHE used in

this experiment two heat balances can be performed; (1) for the heating section and (2)

for the cooling section. Any discrepancy between the heat supplied by the hot stream and

that recovered by the cool stream in a section demands an explanation, such as, a source

or loss of energy not accounted for or an error in the measurements. For example, in our

DPHE set-up, low-pressure steam is introduced to the heating section. Although most of

the outer surface of our DPHE is insulated, some points are exposed to the atmosphere

and so, some steam may condense on the interior wall of the outer tube due to heat loss to

the environment. The amount of energy lost by the steam to the environment can be

quantified, as will be demonstrated in the experimental portion of this experiment.

Unlike the heating section, the cooling water does not gain a significant amount of heat

from or lose a significant amount of heat to the environment since the temperature

difference between the cooling water and the ambient room temperature is very small.

Latent Heat Exchange

Low-pressure steam flows through the annular space of the first three passes and

condenses on the exterior surface of the inside tube and transfers the latent heat of

vaporization, ΔHV, to the colder oil flowing through the inside pipe (refer to figures 1-2

and 1-4). The condensate flow is collected at the outlet and its mass flowrate, is

measured. The amount of energy transferred from the steam to the oil, qsteam can be


calculated via equation (1-2) as:

(1-2)

where a negative value represents a loss of heat from the hot stream. Heat of vaporization

values are commonly found in saturated steam tables.

Sensible Heat Exchanges

A heat input or loss which leads to a temperature increase in a stream without a

corresponding change in state can be attributed to sensible heat changes. In the cooling

section of the DPHE (the last three passes), cooling water flows through the annular

space removing heat from the exterior wall of the inside tube. The amount of heat gained

or lost by a stream via sensible heat exchanges is related to its heat capacity, Cp and mass

flowrate, by equation (1-3):

(1-3)

Log-mean temperature difference

The temperature difference between hot and cold streams can vary considerably over the

length of the heat exchanger as seen in the temperature profiles shown in figure 1-3.

Since this temperature difference is the driving force for the transfer of heat, the rate of

heat transfer also varies over the length of the heat exchanger. Integrating the varying

temperature difference over the length of the tube gives rise to a special type of mean

temperature difference called the log-mean temperature difference (LMTD). The log-

mean temperature difference is described algebraically in equation (1-4).

(1-4)

Applied to the counter-current DPHE, shown in Figure 1-3, ΔT1 represents the

temperature difference between the fluid streams on the right-hand side and ΔT2

represents the difference between the temperatures of the fluid on the left-hand side

within each section of the DPHE.


Overall heat transfer coefficient, U

The heat balance, although very important, does not shed light on the performance or

operation of the heat exchanger. Heat balances do not contain information concerning the

behaviour of the heat exchanger. The heat transfer driving force, heat exchanger

properties (e.g., construction materials, surface area, and direction of flow), fluid

properties, and flow conditions all affect the performance of the heat exchanger and

determine how much heat is actually transferred. Therefore, a more thorough analysis of

heat exchangers is necessary. To aid in this analysis, an analogy between heat transfer

and electrical current (Ohm’s Law) can be considered.

In an electrical circuit, the flow of electrons is from a point of high electric potential to a

point of low electrical potential with the driving force for this flow being the electrical

potential difference (ΔV). The rate of flow of charges (I) is inversely proportional to the

driving force by a constant defined as resistance, R:

The transfer of heat is analogous to the flow of electricity. Heat flows from areas of high

temperature to areas of low temperature.

ΔV ΔT

I q

R 1/hA

where h is a heat transfer coefficient, and

A is the specific surface area

The transfer of heat in a heat exchanger from the hot fluid to the cold fluid through the

wall separating the two fluids is analogous to the flow of electricity through a series of

three resistors. Each resistor represents a phase that heat must transfer through: 1) the hot

fluid, 2) the tube, and 3) the cold fluid. As in the study of electricity, the total resistance

to the flow of heat is equal the sum of the individual resistances.

i Averagei ii

iTotalUA

1

Ah

1RR

(8)

From Ohm’s Law, the transfer of heat can be described as,

TUA

UA

Tq Average

Average

1

(9)


The term U is generally known as the overall heat transfer coefficient, and represents the

total resistance to the transfer of heat.

Reynolds Number

Fluid flow through a conduit can be laminar (stratified), turbulent (well-mixed) or

transitional (some indefinable combination of the two). It is important for engineers to

establish the type of flow regime present in a pipe or channel as it influences both heat

and mass transfer properties and behaviours. The flow profile across a pipe or channel is

typically not visible however, an assumption of the type of flow present inside can be

made based on a comparison of the inertial to viscous forces present in the stream in the

calculation of a dimensionless number called the Reynolds Number, Re or NRe.

Where: = density of fluid (kg/m3)

= flow velocity (m/s)

= hydraulic diameter (m)

=dynamic viscosity of fluid (kg/m·s)

Table 1-1 below shows the commonly accepted ranges of Re for the various flow regimes

in pipe flow.

FLOW REGIME REYNOLDS NUMBER, RE

Laminar < 2300

Transitional 2300 < Re < 4000

Turbulent > 4000

OBJECTIVE:

The overall objective of this experiment is to determine the effect of flow conditions on

the performance of a double-pipe heat exchanger. This will be achieved by performing

heat balances on the heating and cooling sections of a double-pipe heat exchanger and

evaluating the effect of oil/water flowrates on the overall heat transfer coefficients in

each section of the DPHE.


APPARATUS:

A schematic drawing of the double-pipe heat exchanger (DPHE) apparatus is given in

figure 1-4. The DPHE consist of six individual lengths of concentric copper tube. Refer

to figure 1-2 for a graphical depiction of a cross-section of the concentric tube

arrangement. A heat transfer oil called Paratherm NF is circulated in the inner tube

passing through the heating and cooling sections and returning to the oil storage tank for

recycle. The oil is circulated by a centrifugal pump in a closed loop system. A panel-

mounted electronic flow controller controls the oil flow rate between 10 and 70 L/min.

In the oil heating section, oil is heated by low-pressure steam occupying the annular

space (i.e. between the inside and outside tubes). A pressure regulator maintains the

preset steam pressure and an electronic pressure indicator displays the steam pressure and

temperature on the main indicator panel. The steam trap, located on the steam outlet line,

is used to ensure that only liquid condensate can exit the system and that the uncondensed

steam remains in the heat exchanger. The condensate sample valve is used to allow

collection of the liquid condensate aiding in the measurement of the condensate mass

flow rate. The temperature of the oil entering and exiting the heating section are given by

thermocouples (TC) #1 and #4 respectively.

Figure 1-4: Schematic drawing of the double-pipe heat exchanger apparatus


In the cooling section, cooling water from the city supply line flows in a counter-current

direction through the annular space to cool the oil. The cooling water flow rate is set and

controlled by an electronic flow controller. The temperature of the cooling water entering

and exiting the cooling section are given by thermocouples (TC) #8 and #11 respectively.

Similar to the heating section, the temperature of the oil entering and exiting the cooling

section are given by thermocouples (TC) #4 and #7 respectively.

The physical characteristics of the DPHE apparatus are given in Table 1.

Physical properties of Paratherm NF heat transfer oil

Valid for the temperature range: 310.93 K < T < 366.48 K

Density:

Specific Heat Capacity:

Viscosity refer to product info sheet:

http://www.paratherm.com/_engineering/NFEngBul.pdf

Physical properties of water and steam

Valid for the temperature range: 277.15 K < T < 303.15 K

Density of water: where T is in Kelvins.

The viscosity and specific heat capacity of water and the latent heat of vaporization can

be found in most water and steam property tables.

Table 1-1: Double-pipe heat exchanger properties

Heating Section Cooling Section

Outer Copper Tube

Inside Diameter (cm) 5.042 3.823

Outside Diameter (cm) 5.398 4.128

Inner Copper Tube

Inside Diameter (cm)

Outside Diameter (cm)

2.604

2.858

2.604

2.858

Length per pass (m) 2.743 2.794

Outside Area of Inside Pipe (m2) 0.739 0.753

Inside Area of Inside Pipe (m2) 0.674 0.686

Average Area of Inside Pipe (m2) 0.706 0.719

http://www.paratherm.com/_engineering/NFEngBul.pdf


EXPERIMENTAL PROCEDURE:

Part A: Energy Losses to the Environment

To estimate the energy losses from the steam to the environment, steam is admitted to

the heating section of the DPHE without oil circulating in the inner tube and the

flowrate of condensate is measured. The exchanger is in this configuration when you

arrive to the lab session.

1. Vent the 6 ports of the steam line using buttons on left-side panel to release any

air that has accumulated in the steam annulus. Repeat this venting every 10

minutes unless collecting a condensate sample.

2. Record the temperature profile (Thermocouples 1-4). Check that system has

achieved steady-state by confirming that the temperature at positions 1, 2 and 3

are within 0.2ºC over a 5 minute interval.

3. At steady-state record the steam pressure and temperature.

4. Place a bucket below the condensate sampling line at lower left side of exchanger,

open its valve and close the steam trap outlet. Ask your TA for help if necessary.

CAUTION: Wear heat-resistant gloves when collecting condensate!!!

5. Wait for condensate to start flowing from the sample line then, tare a large plastic

beaker on the weighing scale and collect liquid condensate from the sample line

for 5 minutes. Weigh and record the mass of condensate collected.

6. Repeat 5-minute sampling of condensate two more times then close the

condensate sampling line and open the steam trap drain to prevent condensate

from accumulating inside the DPHE.

Part B: Starting the first run

Once the measurement of the losses to the environment is complete, the DPHE is put

into full operation. Generally, it takes about 20-25 minutes to achieve steady-state

after an operating condition is adjusted.

7. Start the cooling water and set the water flow rate to approximately 20 L/min

using the controller on the right-side of the equipment. Press button below

controller screen until small square highlights above “Water”. Use the lower

right-hand-side keys to adjust flowrate (note: upper key is to decrease flow, lower

key is to increase flow).


8. Start the oil pump and set the oil flow rate to approximately 60 L/min. Controller

adjustment is same as for cooling water except square should be above “Oil”.

9. Use a wrench to adjust the steam pressure to the original setting from Part A.

Your TA will demonstrate.

10. Allow the system to run and record the following measurements every 5 minutes

until steady-state is achieved (that is, temperatures are not varying by more than

0.2°C over 5-minute period):

a. Oil and water flow rates

b. Steam pressure and temperature

c. Oil temperatures, Thermocouple channels 1-7

d. Water temperature, Thermocouple channels 8-11

11. At steady-state, collect the water condensate from the steam trap outlet for 5

minutes. Weigh and record the mass of condensate collected. Repeat condensate

sample two more times.

Part C: Varying the Operating Conditions

12. Change the oil flow rate to approximately 12 L/min.

13. Repeat from step 9.

14. If time permits, decrease the cooling water flowrate water to 10 L/min and repeat

from step 9. You need approx 30-40 minutes for a complete run.

Part D: Shutdown of the DPHE

15. Switch off the steam (middle position on switch) and vent the heating section

using 6 steam ports until pressure is reduced to atmospheric.

16. Increase the cooling water flowrate to 25 L/min and increase the oil flowrate to 40

L/min.

17. Allow oil to circulate through DPHE until max temperature in the exchanger is

30ºC. Then, decrease oil and water flowrates to zero, switch off the oil pump and

open valve above oil storage tank on side wall to drain oil from heating section.

18. Switch off air, water and main switch and all instrument panels.


SAFETY CONCERNS:

This experiment has very few obvious safety hazards, but as in all laboratories, safety

should come first. Always wear your safety glasses and lab coat when working in the lab.

Remember that other experiments are being performed around you. Of major concern for

this experiment is the use of low-pressure steam. Low-pressure steam is quite hot,

ranging in temperature between 110ºC to 125°C. The DPHE is constructed of insulated

copper tubing but some portions such as, the condensate sampling line and piping near

the steam pressure controller, are exposed and could cause burns. Always wear heat-

resistant gloves when working near the DPHE. Also note that the condensate exiting the

sample line is approximately 100°C. Do not stand near the sampling bucket when the

condensate sample valve is open as the line may sputter hot condensate. In the event of a

burst steam line, turn off steam switch if safe to do so. If not, evacuate area and inform

lab instructor or TA.

DATA ANALYSIS

Draw and label a flowchart for both the oil heating and oil cooling sections.

Draw the temperature profile for the heating and cooling sections.

Calculate how much heat was lost to the environment from the heating section?

Perform a heat balance for the heating and cooling sections.

Determine the overall heat transfer coefficient, U, for both sections at all flow rates

tested.

Determine the Reynold Number for both the oil and water streams in each section of

the exchanger.


PRELIMINARY REPORT QUESTIONS

1. Why is a burn from steam at 100°C often much more serious than a burn from

scolding water at 100°C?

2. How much energy does it take to vaporize 1 liter of water if the water is initially at

a temperature of 98oF.

Heat capacity of water = 4.18 kJ / oC kg

Density of water = 1000 kg / m3

Latent heat (Enthalpy) of vaporization of water = 2260 kJ / kg

3. Calculate the amount of heat required to completely convert 500gm of ice at 0oC to

steam at 100oC.

Latent heat (Enthalpy) of fusion of ice = 334 kJ / kg

Latent heat of vaporization of water = 2260 kJ / kg

Heat capacity of water = 4.18 kJ / oC kg

4. Are the mechanisms for transfer of heat the same in both the cooling and heating

sections of the double-pipe heat exchanger? Develop the heat balance equations

for the heating and cooling sections of the DPHE.

5. Why is temperature difference along length used for the heat balances on the

DPHE while log mean temperature difference is used for the heat transfer

expression?

6. Define Reynolds Number for flow in both the inner pipe and the annulus.

Calculate the hydraulic diameter of the inner and annulus in our DPHE for the

heating and cooling sections?


MEMO REPORT QUESTIONS

1. Draw the flow velocity profiles across the exchanger diameter for laminar and

turbulent oil flow.

2. Is there a difference between the calculated overall heat transfer coefficients in the

heating and cooling sections? Are they similar under the different flow regimes?

3. Overall heat transfer coefficient for the heating section represents the ease at which

heat can be conveyed from the steam in the annulus to the oil flowing through the

inner pipe. Which resistances to heat transfer are accounted for in this overall

coefficient? Are the same resistances observed in the cooling section?

4. Does the volume of condensate formed affect the heat transfer in the heating

section? Discuss.

5. Which heat exchanger configuration: co-current or counter-current would require a

longer contact length between hot and cold streams? Show mathematical proof.

6. You wish to cool an 82ºC stream of n-C16 to 45ºC within an 8 m long section of 4

cm diam. pipe using a shell heat exchanger and city supplied water (typical

temperature of 12ºC). The hexadecane stream is flowing at 30 L/min. City water

is controlled at How much heat must be removed from the system? Would a shell

heat exchanger rated at 0.71 kW/m-2·K-1

at a water flowrate of 10 L/min be

sufficient to cool the process line? Show mathematical proof.

REFERENCES

Welty, J.R., C.E. Wicks, and R.E. Wilson, Fundamentals of Momentum, Heat and

Mass Transfer, Chapter 22, John Wiley and Sons Inc., Toronto, 1969.

Felder, R.M., and R.W. Rousseau, Elementary Principles of Chemical Process, 2nd

Ed, Chapter 7, John Wiley and Sons Inc., Toronto, 1986.

Macdonald, I.F., “Chemical Engineering Laboratory 040 Undergraduate Manual”,

Department of Chemical Engineering, University of Waterloo, 2001.

Exp2: Distillation 32

EXPERIMENT 2: Distillation Column

INTRODUCTION:

Distillation is a separation process in which a liquid mixture of two or more substances is

separated into component fractions of desired purity. It is based on the principle that the vapour

of a boiling mixture will be richer in the components of lower boiling points. Rectification is the

distillation method used most widely in industries. Feed to the column is continuous and vapour

formed moves up through the column and is cooled to form a top product rich in the more

volatile components in a condenser located at the top. The distillate product is collected from the

condenser outlet but a portion of the condensate stream called “reflux” is returned to the column

where it makes contact with the ascending vapour. Industrial columns are designed to have

multiple contacts (mostly in the form of trays) between liquid and vapour streams that flow

counter-currently through the column. These trays also called stages are designed such that

intimate mixing between the vapor and liquid phases is facilitated at each stage in the column.

Industrial distillation columns, particularly the giant ones of the petroleum industry, are designed

to handle several thousand gallons of feed per hour. The diameter of the column could be up to

16 m and height about 90 m or more.

McCabe Thiele Method and Column Efficiency

In the design of a distillation column, the flow rate and the concentration of the feed stream are

known and the flow rate and concentration of the desired product is usually specified. The goal

is to determine the size of distillation column, in terms of its height and diameter, needed to

effect the specified separation. To determine the height of the column, we need to first estimate

the number of theoretical stages (plates) required for the separation.

In the preliminary design, a simple graphical method called McCabe and Thiele method is used

to estimate the number of theoretical stages. This method is base on the assumption of ideal

stages (i.e. equilibrium between the vapor and liquid phases is assumed in each stage) and

constant molar overflow. Fenske developed a formula to calculate the number of theoretical

plates for a given separation at total reflux.

Where: n = Number of theoretical plates

xA = mole fraction of more volatile component A in liquid phase

xB = mole fraction of less volatile component B in liquid phase

= average relative volatility between A and B,

Subscripts d, b indicate distillate and bottom respectively


The actual number of stages required for the design separation is always higher than the

theoretical stages because equilibrium is never truly achieved. Consequently, an efficiency

factor is applied to calculate the number of actual stages required in the design of a distillation

column. Estimates of efficiency are made from pilot plant studies.

Overall column efficiency is defined as the ratio of the number of theoretical stages to the

number of actual stages:

Column Efficiency (E) =

× 100 %

In actuality, efficiency varies from stage to stage and is a function of many complex variables

(e.g. tray type, perforation area, hole diameter, weir height, loading parameters, etc). Murphree

Tray Efficiency, EM accounts for these variations in plate design and column operating conditions

and is an indication of the extent of separation achieved relative to equilibrium in each tray.

In Vapour Phase:

In Liquid Phase:

Overall column efficiency and average Murphree tray efficiency cannot be compared directly.

However, Garcia and Fair (2000) have attempted to correlate Murphree vapour tray efficiency to

overall column efficiency.

Energy balance calculations

A process-side energy balance consists of an account of the heat of vaporization in the re-boiler

and the heat of condensation in the condenser.

Reboiler

Where: : Reboiler duty

: Molar flow rate of species i

: Total molar flow rate obtained from Boil Rate vs Power calibration

: Heat of vaporization of species i

Condenser

Where: : Condenser duty

: Heat of condensation of species i

: Heat capacity of species i


OBJECTIVES:

The two main objectives of this experiment are (1) to investigate the relationship between the

boil-up rate and overall column efficiency at total reflux and (2) to perform an overall energy

balance on the column.

APPARATUS:

There equipment for Lab 2 consists of a Process Unit and a Control Console.

Process Unit:

The main part of the process unit is a 50 mm diameter glass column containing 8 sieve plates and

downcomers. Each plate has a temperature sensor positioned to accurately measure the

temperature of the liquid phase on each plate. These sensors are labeled T1 –T8 on Figure 2-1.

A miscible mixture of methanol and isopropanol is initially charged to the reboiler (a) at the base

of the column. The reboiler is heated by an electrical coil. Its temperature is measured with

thermocouple T9 and samples of the reboiler can be collected via valve V2. The power input to

the reboiler is controlled via the Control Console. All overhead vapour exiting the top of the

column is collected in the condenser (b) which is cooled by a water flow that is regulated by a

needle valve (V5) and monitored using a calibrated rotameter (Fl 1). The inlet and outlet

temperature of the cooling water is monitored with thermocouples T11 and T12, respectively.

The condenser is vented to the room. The condensate drains into the decanter (c) which empties

through valve V10 into the reflux solenoid valve which is set for total reflux back to the column

top. The temperature of the reflux stream is measured using thermocouple T13. Samples of the

reflux can be collected via valve V3.

Devices attached to the column include:

(a) An electrically heated re-boiler

(b) An overhead condenser with cooling water flow measurement and adjustment

(c) A condensate collecting vessel, equipped with double overflow weirs and exit pipes to

allow separation of immiscible liquids

(d) A return reflux valve, solenoid operated to provide for 0% to 100% reflux adjustable by

electric signal.

(e) Two 5L feed vessels

(f) Peristaltic feed pump, range 0 –0.25 L/min, adjustable by voltage input variation to the

pump motor controller.

(g) A differential manometer connected to the top and bottom of the column to monitor

column pressure drop

(h) A vacuum system with gauge to allow distillation at reduced pressures down to 200 mbar

(absolute).


Figure 2-1: Schematic Diagram of Apparatus

REBOILER

FEED TANKS

T12

CONDENSER

T11

FI1

V5

V14

P1

V15

DECANTER

TOP

PRODUCT

RECEIVER

V10

REFLUX

VALVE

V3

T13

T10V7

MANOMETER

T

V8

T1

T2

T3

T4

T5

T6

T7

T8V6

BOTTOM

PRODUCT

RECEIVER

V11

T

HEAT EXCHANGER

T14

FEED PUMPT

V4V12

T9

V2

V1

VENT

VACUUM

PUMP

HEATER

CO

LU

MN COOLING

WATER

(a)

(b)

(d)

(c)

(f)

(e)

(g)

(h)


Control Console:

The control console is located to the right of the distillation column and includes a

computer with software to monitor and adjust parameters. The control console has the

following features:

Monitoring and selectable display of temperatures

Monitoring, display and manual adjustment of

(a) The electrical power to the re-boiler heater.

(b) The reflux ratio setting

Front panel connections to allow the user to connect Programmable Logic

Controller (PLC) to provide online control of the boil-up rate or reflux ratio

from chosen column temperature measurements.

PROCEDURE:

Column Start-Up (performed by lab instructor/TA)

The distillation column will have been operating for at least 30 minutes before the start of

the lab session and should have reached steady-state for the first operating condition.

The start-up procedure was as follows:

1. Open valve V5 (cooling water inlet) slightly then open cold water tap at sink.

Use valve V5 to set cooling water flow rate between 2000 to 2500 cc/min.

2. Open valve V10 (bottom drain of decanter) and ensure all other valves: V1

(bottoms line), V2 (reboiler drain), V3 (reflux sample), V4 (distillate sample), V6

(manometer bottom) , V7 (manometer top), V8 (separatory funnel), V11 (bottoms

sample), V12 (distillate return) are closed.

3. Switch on lower two control units and computer with login: “User”. Open

UOP33 Armfield Unit Ops Software. Click on icon (next to “Paste”) to

open the view diagram in manual operation mode.

4. Start the reboiler by setting the percent power output to the reboiler in the PID1

PWR input box on the view diagram. The reboiler power range of 0 - 100%

corresponds to 0 - 2.5 kW input. Press the red power ON/OFF button on the

control console under Reboiler Heater. The column should be set for Total

Reflux.

NOTE: Reboiler power input should not exceed 90%.


5. Open “View Real Time Data” and “View Data History” windows to monitor the

process profiles. It takes approx. 30-40 minutes for the column to reach a steady-

state operation. Look for bubbling on the top trays, a steady flow of liquid from

the condenser through the decanter and back into the top of the column through

the reflux line and for all thermocouples in the column to show stable readings on

the software monitoring window.

Sampling from Distillation Column (lab groups start from here)

6. GC software password is “test”. Start program “Peak 393”. Click on “123” icon

to check that the method analysis time is set to 2.7 minutes. The graph axes may

also be changed from this window. When GC column temperature is constant,

rinse the 10 μL syringe in your condensate sample and then collect and inject

approx. 1μL into the GC injection port.

7. Take a sample from the feedstock container located in the fumehood. Analyze for

the concentrations of methanol and isopropanol using GC (refer to GC Calibration

Data, Figure 2-3 in Appendix).

8. Once the column has reached stable values for T1 through T8, remove a small

sample (~1 mL) of the condensed reflux stream via valve V3 and analyze it using

GC. Fresh condensate samples should be collected and analyzed every 5 minutes.

Steady-state is confirmed when the composition of three consecutive condensate

samples is within 0.5 wt%.

9. Once steady-state has been confirmed, record the process data by pressing the

green “GO” button on the diagram window. Use the “Attach Note” button to

annotate the data acquisition file to record the associated operating condition.

10. Take a sample from the re-boiler via valve V2. Analyze using GC to determine its

composition.

CAUTION: the liquid and reboiler are hot, avoid touching them directly!!!

11. Change the operating conditions by varying the power to the reboiler as in step 4

and repeat sampling procedure (step 6 onwards). Test at least 3 reboiler power

settings over the lab session.


DATA ANALYSIS:

At each reboiler power setting:

Determine the Boil-up Rate (refer to Figure 2-2 in Appendix).

Use the McCabe-Thiele method to determine the number of theoretical trays at total

reflux and minimum reflux ratio. Equilibrium data is given in Appendix.

From the condensate and reboiler compositions, calculate the relative volatilities at

the top of the column and at the bottom of the column (use equilibrium data).

Calculate the average relative volatility in the column.

Use Fenske equation to calculate the number of theoretical stages at total reflux and

compare to value from graphical method.

Calculate the Overall Column Efficiency.

Calculate the Murphree Tray Efficiencies at plates 3 and 7.

Plot a curve of Boil-up Rate vs. Column Efficiency (use the calibration graph to

determine the Boil-up Rate at different heater power input)

Calculate the Boiler Duty and Condenser Duty. Comment on the heat balance


1. Define volatility of a component. Assuming ideal behavior in both vapor and

liquid phases, derive an equation for relative volatility of components A and B in a

binary mixture.

2. Most liquid mixtures are non-ideal (i.e. do not obey Raoults law). How do you

account for non-ideality in calculating the relative volatility of a binary mixture?

3. How does the reflux ratio affect the capital and operating costs of a distillation

unit? Sketch appropriate graphs to explain.

4. A mixture of butane and pentane is at equilibrium at 3 atm and 100 ºF. Assuming

ideal conditions, calculate the composition of the liquid and vapor phases.

Vapor pressure of pentane at 100 ºF = 830mm Hg.

Vapor pressure of butane at 100 ºF = 2650mm Hg


5. A distillation column operating at 1 atm pressure is to be designed for separating

an ethanol-water mixture. The feed is 20 mole % ethanol and the feed flow rate is

1000 kg mole/hr of saturated liquid. A distillate composition of 80 mole % ethanol

and a bottoms composition of not more than 2 mole% ethanol are desired. The

reflux ratio is 5/3. Determine:

a. The total number of equilibrium stages required.

b. The optimum feed plate location

c. The distillate and bottom flow rates in kg mole/hr

d. Equilibrium data for ethanol-water system at 1 atm pressure is given below

Temperature (°C) Mol % Ethanol in Liquid Mol % Ethanol in Vapour

100 0 0

95.5 1.90 17

89 7.21 38.91

86.7 9.66 43.75

84.1 16.61 50.89

82.7 23.37 54.45

80.7 39.65 61.22

78.7 67.63 73.85

78.1 89.43 89.43


1. In this experiment, you sample a point on trays 3 and 7 and determine the liquid

and vapour Murphree Tray efficiencies. What are the assumptions of the

Murphree Tray efficiency equation? Are these samples representative of “tray” or

“point” efficiencies? Could the same be said of such a sample taken from an

industrial scale column?

2. Tray distillation columns are designed for specific ranges of operational vapour

flowrates. In proper column operation, liquid will pool on each tray of the column

with the excess overflowing through the downcomers while vapours readily move

up through the perforations in the trays to bubble through the pooled liquid.

Describe four conditions of adverse or undesirable vapour flow conditions in a tray

distillation column.

3. Explain how the pressure in the column affects its performance.


4. For a water–glycerol system, the difference in normal boiling points is 190ºC. The

values of relative volatility (α) are very high (190 – 250). Is distillation using a

tower an economical process to separate the components in this system? Explain.

5. Use Raoults law to calculate the vapor and liquid compositions at equilibrium (in

mole fractions) for the Benzene-Toluene system using vapor pressure data at a

pressure of 101.32 kPa as shown in the table below.

Temp (°C) Vapor Pressure (kPa)

Benzene Toluene

80.1 101.32 16.1

85 116.9 46

90 135.5 54

95 155.7 63.3

100 179.2 74.3

105 204.2 86

110.6 240 101.32

a. Plot the phase diagram (T-x-y).

b. Plot the equilibrium curve for benzene-toluene system at 101.32 kPa.

REFERENCES

Garcia, J. A., and Fair, J. R (2000) Ind. Eng. Chem. Res. v.39 p.1809-1817.

Hines, A.L and Maddox,R.N., “Mass Transfer-Fundamentals and Applications,

Prentice Hall, NJ, 1985.

King, C.J., “Separation Processes”, McGraw Hill, NY,1981

McCabe,W.L and Smith, J.C., “Unit Operations of Chemical Engineering”, McGraw-

Hill, NY., 1985.

Perry, R.H., and Green, D.W., Perry’s Chemical Engineers’ Handbook, 8th

ed.,

McGraw-Hill, NY, 2008.

Treybal, R.E., “Mass Transfer Operations”, McGraw Hill, NY

Yaws, Carl L., “Yaws’ Handbook of Thermodynamic Properties for Hydrocarbons

and Chemicals”, Knovel, 2009.


APPENDIX

BOIL- UP RATE VS. POWER

Mass Fraction Methanol

Mole Fraction Methanol

Reboiler PWR (kW)

Boil Rates (g/min) Boil Rates

(mmol/sec) Tops Tops

0.888 0.9370 1.10 12.71 6.278

0.868 0.9250 1.32 33.36 16.305

0.859 0.9195 1.54 53.31 25.939

0.844 0.9103 1.76 68.78 33.215

Regression Line Parameters: slope: 85.527, y-intercept: -80.264

y = 85.527x - 80.264R² = 0.9958

0

10

20

30

40

50

60

70

80

1 1.2 1.4 1.6 1.8 2

Bo

il-u

p R

ate

(g/

min

)

Power to Reboiler (kW)

Figure 2-2: Boil-up Rate (g/min) versus Reboiler Power (kW)


GAS CHROMATOGRAPHY DATA

GC Operating Conditions GC calibration (refer to Figure 2-3 below)

GC CONDITIONS

Column Oven

Local 160 oC

Total 161 oC

Actual 162 oC

Detector Heat

Local 140 oC

Total 140 oC

Actual 146 oC

Carrier

Local 50 psi

Total 51 psi

Actual 50 psi

Mass Fraction Methanol GC Data

1 1

0.8486 0.8703

0.7192 0.7538

0.6288 0.6712

0.5639 0.6069

0.5041 0.5489

0.4535 0.4980

0.3818 0.4233

0.2935 0.3303

0.1744 0.1995

0.1038 0.1343

0 0

y = 0.172x2 + 0.8284x - 0.002R² = 0.9999

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Me

than

ol M

ass

Frac

tio

n

GC Data

Figure 2-3: GC calibration for a Methanol-Isopropanol System


METHANOL-ISOPROPANOL BINARY SYSTEM

T-x-y data for Methanol-isopropanol binary system

Ideal (at 760 mmHg)

Mole Fraction of Methanol Boiling Point (oC)

x y

0 0 82.19

0.1 0.176 80.02

0.2 0.328 77.97

0.3 0.458 76.03

0.4 0.571 74.18

0.44 0.612 73.47

0.5 0.669 72.42

0.6 0.755 70.75

0.7 0.829 69.15

0.8 0.894 67.62

0.9 0.950 66.15

1 1.000 64.75

Physical Properties of Methanol and Isopropanol

Component Density

( 3/ cmg )

Molar mass ( molg / )

Boiling Point (oC)

methanol 0.792 32.0 64.2

iso-propanol 0.786 60.1 82.2

Heat Capacity Coefficients ( )/ KmolJ from Perry's Handbook Table 2-153

32 dTcTbTaC p

Component a b c d

methanol 105800 -362.23 0.9379 isopropanol 471710 -4172.1 14.745 -0.0144

Component Heat of Vaporization ( )/ molkJ

methanol 35.14

isopropanol 39.87 from Yaws' Handbook of Thermodynamic Properties.

Exp3: Liquid Vapour Equilibrium 44

EXPERIMENT-3: Liquid-Vapour Equilibrium

INTRODUCTION

Chemical engineering involves the control of industrial processes in a chemical plant to

convert raw materials into useful products. A chemical plant is an integrated system of

different units, the most important of which is the reactor where reactions are performed

under set conditions to optimize production.

For most chemical reactions, the intended products must be separated from inevitable

byproducts of the reaction in order to achieve the required product purity. There are

some equilibrium-limited reactions in which conversions are very low. The economics of

processes involving such reactions may be improved by separating the un-reacted

components from the product stream and recycling them back into the reactor.

Although a chemical plant will not exist without reactors, the largest equipment and

hence, the biggest expense will often be the separation equipment. Distillation is the

most common separation process; it is the workhorse of chemical process industries.

When a liquid containing two or more components is heated to its boiling point, the

composition of the vapour will normally differ from that of the liquid. It is this

difference in composition of the two phases at equilibrium that forms the basis of the

distillation process. An important requirement of a distillation unit is the provision of

intimate contact between the liquid and vapor streams so that equilibrium may be

approached.

A phase diagram shows the phases existing in equilibrium at any given condition.

According to the Phase Rule, a maximum of three intensive variables (intensive

properties) must be specified to define completely the state of a two-component system.

The intensive variables typically chosen are: temperature, pressure, and concentration.

Since there are three degrees of freedom, a complete representation of the conditions of

equilibrium would require three dimensions. However, 3-D models are difficult to

construct and inconvenient to use. Instead, it is common practice to use 2-D

representations with one of the intensive variables held constant. Usually, pressure is

held constant and the equilibrium compositions of the liquid and vapor phases are plotted

against temperature. These plots are sometimes called Boiling Point Diagrams and they

are necessary for the design of distillation columns for separating binary mixtures. The

successful application of distillation methods depends greatly upon a thorough

understanding of the equilibria which exist between the vapour and liquid phases of the

mixtures encountered.


Figure 3-1: Temperature–Composition Phase Diagrams (Z denotes an azeotrope)

(a) Simple system: Boiling points of mixtures lie between those of pure

components.

(b) Maximum boiling point systems: Azeotrope has a higher boiling point than

both pure components.

(c) Minimum boiling point systems: Azeotrope has a lower boiling point than

both pure components.

OBJECTIVE

In this experiment, the liquid-vapour equilibrium phase diagram in the two component

system, consisting of any of acetone, ethanol, iso-propanol with heptanes, hexane, and

cyclohexane, will be determined at atmospheric pressure using a simple still.

APPARATUS

The apparatus is a simplified liquid-vapour equilibrium still of Daniels and Alberty

(1962). The liquid in the flask is heated by an Electrothermal mantle with Heater and

Controller. The temperature in the pot is measured using a digital thermometer with

type-K thermocouple. Analysis of pot liquid and condensed equilibrium vapour is

carried out using a model 8500 Basic Gas Chromatograph. The Gas Chromatograph

(GC) is equipped with a Thermal Conductivity Detector and a SF-96 column. A Hewlett

Packard integrator is connected to the GC to quantify the chromatographic peaks.

a) b) c)

Z


Figure 3-2: Stilling Apparatus for Binary System Distillation

PROCEDURE

Each group will split up and operate two stills. One half of the group will carry out part

A of the experiment and the other half will perform part B (see Table II). The results

from both sets of experiments will be combined to create a complete liquid-vapour phase

diagram. The mass ratio of each component in the liquid and vapor phases may be

approximated by the ratio of corresponding peak areas on chromatograms from GC

analysis of samples from the still and condenser, respectively.

Operation of the stills

1. Ensure that the still is assembled properly (see Figure 3-2 above). The interior of

the still is open to the atmosphere via a tube containing a drying agent. Check

that the drying agent is blue in colour.

2. Add the specified initial amount of solution (see Table II) and some anti-bump

granules to the still flask and begin heating by increasing the mantle power

output.

3. Monitor the liquid phase temperature by reading the temperature directly from the

digital thermometer. Observe closely. The temperature change will level-off near

the boiling point. Record the boiling point for the solution then tilt the apparatus

Digital Thermometer

Stilling flask

Drying Tube

Type K Thermocouple

Electric Heating Mantle

Condensate Collection Cup

Condenser

H2O in

H2O out

Open to

atmosphere


to spill the condenser cup back into the still and wait for the system to reach

boiling again. (*NOTE* DO NOT HEAT beyond boiling point).

4. Switch off the heating mantle. Once the boiling has stopped, remove the

condenser and collect ~1.5 mL of condensate from the collection cup and store in

a sealed GC vial. Label the vial.

5. Remove the stopper from the stilling flask and collect ~1.5 mL from the still.

Store in a different sealed GC vial. Label the vial.

6. When GC is ready, flush 10 L syringe with still sample. Then, collect and inject

approx. 0.3 L into GC injection port and immediately press START on

integrator. Sample should pass through GC is less than 2 minutes. Check that

integrator output has two well-defined Gaussian peaks, then press STOP to end

integration. GC results (% area) are approx. equal to weight percent

composition.

7. If GC peaks are flat-topped, the GC detector was saturated. Collect a smaller

volume of sample and reanalyze. Repeat until an appropriate sample volume is

found that allows for two clearly-defined Gaussian (i.e. normally-distributed

about the mean retention time) peaks. Use this volume for remainder of GC

analyses unless flat tops occur again.

8. When GC is ready again flush, collect and inject condensate sample for GC

analysis. Remember to START integrator. Check peaks. Are your results as

expected? If not, repeat procedure or reanalyze samples.

9. Return all condensate to the still.

10. Remove X ml of solution from the stilling flask, as per Table II, and discard. Add

X ml of the underlined component to the stilling flask. Then repeat the procedure

outline above to determine the boiling point of the new solution and compositions

of the liquid and condensed vapor phases.

* NOTE * The microlitre syringe is very delicate. Take special care when using

the syringe so as not to remove the plunger completely from the barrel when

collecting samples nor to bend the plunger or syringe tip when injecting sample

into the GC.


Table II: Initial Still Compositions and Incremental Adjustments for Parts A and B

in Determining the Boiling Point Diagram

a) Hexane/Ethanol System b) Heptane/Ethanol System

Part A Part B Part A Part B 40 mL hexane 33 mL hexane +

7 mL ethanol

40 mL heptane 25 mL heptane +

15 mL ethanol

X mL exchanged X mL exchanged X mL exchanged X mL exchanged

1.0 2.0 3.0 5.0

2.0 5.0 4.0 8.0

2.0 10.0 5.0 10.0

3.0 15.0 5.0 15.0

4.0 20.0 5.0 20.0

c) Hexane/Isopropanol System d) Heptane/Isopropanol System

Part A Part B Part A Part B 40 mL hexane 34 mL hexane +

6 mL isopropanol

40 mL heptane 25 mL heptane +

15 mL isopropanol


1.0 2.0 3.0 4.0

2.0 5.0 4.0 8.0

2.0 10.0 4.0 10.0

3.0 15.0 5.0 15.0

4.0 25.0 10.0 20.0

e) Cyclohexane/Ethanol System f) Cyclohexane/Isopropanol

Part A Part B Part A Part B 40 mL

cyclohexane

30 mL cyclohexane

+ 10 mL ethanol

40 mL

cyclohexane

28 mL cyclohexane+

12 mL isopropanol


1.0 4.0 1.0 5.0

2.0 5.0 2.0 5.0

3.0 10.0 3.0 10.0

4.0 15.0 5.0 15.0

4.0 25.0 6.0 30.0


11. Continue removing solution from the still and adding underlined component in

steps to obtain the boiling point curve over the whole composition range. Be sure

to include pure component runs.

12. Record all data necessary to estimate the precision of your results. Remember to

record the pressure of the room.

DATA ANALYSIS

From your GC data, determine the mol % of each component for each sample tested.

Plot the LV phase diagram for your system. Use mol % for x-axis.

Locate the azeotrope composition and boiling point at ambient conditions of

experiment.

Using the data from your plot and van Laar equations to determine the azeotrope

point at 101.3 kPa (Mukhopadhyay, 1975). Convert your pure component boiling

points from ambient to 101.3 kPa.

Compare your azeotrope point to value(s) found in literature. What is the % error?

Identify the major sources of error in the experiment. What unquantifiable errors are

inherent in the procedure?

Plot the vapour-liquid equilibrium for this system using the same scale unit for both

axes. For a helpful discussion on the reliability of your data refer to Livingston

(1957).


1. Define azeotrope.

2. Verify the fact that the maximum number of degrees of freedom in a two

component system is 3. What is the reason that time is not a degree of freedom in

the Phase Rule? Using the Phase Rule, show that the point Z in figure 3-1(b) has

no degrees of freedom once the pressure is fixed.

3. Draw the vapour pressure-composition curves (at constant temperature)

corresponding to figures 3-1(a), (b) and (c).


4. Label all points, lines, and areas on the phase diagram shown below. Draw in

typical tie lines. A copy of the diagram can be downloaded from ChE291 UW-

ACE. In our system the two components are miscible. Will the phase diagram

differ from the one shown below? If so, how?

5. Which of the two components in the figure above (A or B) is more volatile? If a

35 wt % solution of A in B was heated to T*, would the vapour phase have a

higher or lower concentration of A than the liquid phase in equilibrium with it?

Which phase at equilibrium would have a higher concentration of A for a 25 % B

in A solution heated to T2*? What proportion of an 80 wt % A solution will be

vapourized at T2*?


1. Briefly discuss one of the factors that cause negative and positive deviations from

“ideal solution behaviour” (Raoult’s law behaviour)

2. Experience has shown that inaccurate results for the vapour composition are

obtained if the solution is boiled vigorously. Explain why this is so.

3. Describe how a GC can separate the components of an injected sample. What GC

parameters can be manipulated to improve peak separation?

4. Ethanol forms an azeotrope with water under normal distillation conditions (i.e. 1

atm) and yet chemical manufacturers are still able to provide supplies of alcohol at

concentrations of up to 99+%. Describe such a process that allows for the

production of absolute alcohol.

T2*


REFERENCES

"Analytical Methods for Atomic Absorption Spectrophotometry", Perkin-Elmer,

1968.

Braun, R.D., "Introduction to Instrumental Analysis", McGraw-Hill, N.Y., 1987.

Dean, J.A., "Flame Photometry", McGraw-Hill, N.Y., 1960.

De, Anil K., Khopkar, Shripad M., and Chalmers, Robert A., "Solvent Extraction of

Metals", Van Nostrand Reinhold Company Ltd, London, 1970.

Ives, D.J.G., "Principles of the Extraction of Metals", Royal Institute of Chemistry,

W. Heffer and Sons Ltd., Cambridge, 1979.

Livingston, R, “Physico Chemical Experiments”, 3rd

ed. Macmillan, New York, 1957.

Movrodineanu, R. and Boiteus, H., "Flame Spectroscopy", Wiley, N.Y., 1965.

Mukhopadhyay, M. Ind Eng Chem, Process Des Dev, v14 n2, 1975 p195.

Paterson, Russell, "An Introduction to Ion Exchange", Heyden & Son Ltd., London,

1970.

Price, W.J., "Spectroscopic Analysis by Atomic Absorption", Heyden, London, 1979.

Ramirez-Munoz, J., "Atomic Absorption Spectroscopy", Elsevier, N.Y., 1968.

Reiman, William III and Walton, Harold, "Ion Exchange in Analytical Chemistry",

Vol. 38, Pergamon Press, Oxford, 1970.

Robinson, J.W., "Atomic Absorption", Marcel Dekker Inc., N.Y. 1966.

Skoog, D.A. and West, D.M., "Principles of Instrumental Analysis", 2nd Ed., Holt

Reinhart, N.Y., 1980.

Welz, B., "Atomic Absorption Spectrometry", 2nd Ed., Verlag Chemie, Weinheim,

FRG, 1985.

Willard, H.H., Merritt, L.L., Dean, J.A. and Settle, F.A. Jr., "Instrumental Methods of

Analysis", 6th Ed., D. Van Nostrand, N.Y., 1981.

Exp4: Ternary Phase Diagram 52

EXPERIMENT 4: Phase Diagram: Three–Component Liquid System

INTRODUCTION A phase diagram shows the phases existing in equilibrium at any given set of conditions.

According to the Phase Rule,

F = C + 2 – P

Where F is the degrees of freedom or variance, C is the number of constituent

components and P indicates the number of phases present.

For example, in a three-component system, F = 5 – P, and hence the degrees of freedom

may reach 4. Therefore, a maximum of four intensive variables (intensive properties)

must be specified to define the state of a three-component system completely. The

intensive variables that are usually chosen are pressure, temperature and concentration. If

the system consists of only one phase (P=1), the four variables required are temperature,

pressure and mol fractions x1 and x2 [i.e. two out of three compositions, since x3 is given

by 1-(x1+x2)]. Since four variables cannot be represented graphically, it is usual to

consider the system at constant pressure and temperature leaving only two degrees of

freedom (i.e. the mole fractions of two components). One of the best ways of showing

how phase equilibria vary with the composition of the system is to use triangular phase

diagrams. These three-component liquid phase diagrams are of considerable value in the

design of extraction equipment used to effect a separation by solvent extraction methods.

In certain binary mixtures where separation of the individual components is desired,

extraction of one component by a third solvent frequently offers advantage over

distillation, evaporation, crystallization or other possible methods of separation. Some

applications in which liquid-liquid extraction is frequently used are given below:

Separation of solutions of components having low relative volatility, especially when

vacuum distillation is expensive.

Solutions of close boiling and azeotrope-forming components.

Dissolved solute when evaporation may be impractical.

Solutions of heat-sensitive components, such as, antibiotics.

Components of differing chemical type whose boiling points may overlap as in the

case of petroleum hydrocarbons.

In liquid-liquid extraction, the solute substance is transferred from one liquid phase to

another liquid (solvent) phase. Hence, accurate knowledge of the phase equilibrium

relationship of the components involved is of primary importance in the design of liquid

extraction equipment. By studying the phase diagrams for the components in question

and various solvents, it is possible to deduce whether the separation sought can be

accomplished and to define the best operating conditions for an optimum result.


THEORY

The phase equilibrium among three components is usually represented on a triangular

diagram. This triangular representation is based on the fact that from any point within an

equilateral triangle, the sum of the distances perpendicular to each side is equal to the

height of the triangle.

The height is set equal to 100 % and is divided into 10 equal parts. A network of small

equilateral triangles is formed by drawing lines parallel to the three sides through the ten

equal divisions. For example, in Figure 4-1, each apex of the equilateral triangle

represents one of the three pure components, namely 100 % A, 100 % B or 100 % C.

The three edges of the triangle represent the three possible binary systems and 0 % of the

third component.

A point within the triangle represents a mixture of three components. The composition of

such a mixture can be determined in the following way: consider the point G in Figure 4-

1. Any line a-a’ parallel to side BC represent a line of constant weight percent of A.

Therefore the line a-a’ which intersects at G determines the percentage of A in the

mixture and is the value at a. Similarly, lines b-b’ and c-c’ determines the composition of

B and C, respectively.

So, the composition at point G is: 40 % A, 30 % B and 30 % C. The composition at

point H is 15% A, 17% B and 68 % C.

Figure 4-1: The triangular diagram representing a three-component system at constant

temperature and pressure.

In a three-component system where species C is completely miscible in all proportions

with B as well as with A, but where A and B are only sparingly soluble in each other, the

ternary phase diagram would like something like that of Figure 4-2. The limited

C

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40

10

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80

90

10

20

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30

50

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90

G

H a

a’

c c’

b

b'

A B


solubility causes the two saturated solutions to form near the apexes of the triangle at L

(A-rich) and at K (B-rich).

Figure 4-2: Sketch of a ternary phase diagram for A-B-C.

Curve LRPEK is the bimodal solubility curve indicating the solubility of the A- and B-

rich phases upon addition of component C. Any mixture outside this curve will be a

homogeneous solution of the liquid phase. Any ternary mixture underneath the curve

(such as at J) will form two insoluble, saturated liquid phases. The equilibrium

compositions of these phases are indicated by the ends of the “tie-line” which passes

through the point that represents the overall composition of the mixture as a whole. For

example, at point M, two phases exist: an A-rich phase with composition R and a B-rich

phase with composition E. The relative proportions of the two phases are determined

using the Lever Rule.

There are an infinite number of tie lines in the two-phase region. Only a few are shown

in the figure. Tie-lines are rarely parallel and usually change slope slowly in one

direction, as shown. In figure 4-2, the slope of the tie-lines indicates that C is more

soluble in B than in A. As the two liquid solutions become more nearly the same, the tie-

lines become shorter and shorter until they finally reduce to a point called the Plait point

(P in figure 4-2). The Plait point generally does not occur at the top of the solubility

curve. At P, both layers are present in approximately the same proportion and have the

same composition of solute.

OBJECTIVE In this experiment, the phase diagram for a 3 component liquid system (water-toluene-

acetic acid) will be determined under ambient conditions.


PROCEDURE

* PLEASE NOTE * If your skin comes into contact with concentrated acetic acid wash

the affected area immediately with plenty of water.

To establish several tie-lines, the following four mixtures should be prepared in the

separatory funnels. Dispensers are provided for transferring toluene and acetic acid.

Prepare these mixtures at least one day before the scheduled

laboratory session to allow time for equilibrium to be established.

1. Add 45 ml of toluene to each of the four separatory funnels.

2. Using a burette, add x ml of water and (55-x) ml of acetic acid, where x = 45, 35,

25 and 15, to each respective separatory funnel.

3. Cap and shake vigorously to mix.

The day of the lab:

4. Prepare a series of samples (in glass-stoppered bottles) made up of x ml of water

and (10 - x) ml of toluene, where x = 0.5, 1.0, 2.0, 4.0, 6.0, 8.0, 9.0 and 9.5 in each

of eight respective bottles. Also prepare two more solutions with (20 - y) ml of

toluene, where y = 0.4 and 19.6 mL of water added, respectively.

5. Titrate each of the samples with acetic acid, shaking the two-phase system

vigorously after each addition of acid, to determine the quantity of acetic acid

required to form a clear homogeneous liquid. (*Note* the shaker mixture

becomes cloudy as it nears the miscible point. Continue adding acid in small

increments until it turns clear again. At this point only one phase should be

present.)

Analyze the mixtures prepared in the previous day as follows:

6. Record the volumes of the clear phases and separate the phases into flasks using

the funnel.

7. Withdraw a 5-mL sample from the toluene phase using the autopipettor.

8. Titrate the sample with 0.5 M NaOH solution using a few drops of

phenolphthalein indicator.


9. Titrate a 2 mL sample from the aqueous phase with 0.5 M NaOH solution and

indicator.

10. Titrate three times a 1.00 mL sample of concentrated acetic acid.

DATA ANALYSIS

Convert all results to a mass percent basis.

Draw the solubility curve on triangular coordinate paper. For the convenience of the

person who is going to mark the report, let the lower left-hand corner of the triangle

represent toluene and the right-hand corner water. Assume the densities shown in

Table III on next page for each phase at room temperature.

Label your tie lines and Plait point on the triangle diagram.

Plot a Distribution Diagram to show the equilibrium compositions between the

extract (y-axis) and raffinate (x-axis) phases for the binary phase region.

Comment on the sources of error. Use error propagation equation to determine the

major source(s) of error in the experiment.

Table III: Density of Components at Room Temperature

Substances Density, kg / m3

Toluene 866

Water 1000

Acetic acid 1049

Toluene “phases” 935

Water “phases” 1020



1. Define extensive and intensive variables (properties) and give examples.

2. Define Phase Rule and the term “degree of freedom”. In this experiment, the three

components are water, toluene, and acetic acid. Would a mixture of water,

toluene, and a 50:50 (by mass) mixture of benzene and acetic acid have the same

number of degrees of freedom? Explain.

3. What are conjugate solutions?

4. Demonstrate the use of a triangular phase diagram similar to the one shown in

Figure 4-3 by describing in detail what happens when an a solution containing 50

wt % C in B is gradually diluted with a solution of 10 wt % C in A.

5. Working on a copy of Figure 4-3 determine the amount of mixture X (50 % C, 40

% A) that must be added to 30 g of mixture Y (70% B, 25% C) to achieve a

system which has only 10 % A. How much to achieve a two-phase system in

which the A-rich phase contains 10%B? What is the composition of the resulting

B-rich phase?


1. In analyzing the toluene phases for acetic acid by titration with aqueous base,

what problem(s) in end point detection will arise? Use your results to estimate the

error in the determination of [acetic acid] of each toluene sample by the titration

technique?

2. Suggest a better method of determining [acetic acid] in toluene samples.

3. There are several methods to determine the position of the Plait Point. Describe

at least two different methods. Comment on the precision of the results of these

methods. What is the significance of the Plait Point in respect to solvent

extraction?

4. In water, acetic acid exists at least partially as the dimer (CH3COOH)2; in toluene

it is almost entirely dimeric. Is it valid to consider monomeric acetic acid as a

component in this system? Explain. How does this difference in form affect the

observed results?

5. List and explain some of the properties that are desirable in an extraction solvent.

6. Referring to Figure 4-4, state two reasons why Solvent B is more useful than

Solvent D in extracting C from solution in A?


Figure 4-3: Ternary Diagram for Prelab Questions 4 and 5.

Figure 4-4 Ternary diagrams for mixtures of A-B-C and A-D-C.

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C

B

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P, T constant

Composition in mass

percent


ADDITIONAL SOURCES

Barrow, G.M.,”Physical Chemistry”, 6th ed., McGraw-Hill, New York (1996).

Burns, C.M., “Applications of Phase Equilibria”, Sandford Educational Press,

Waterloo (1984), chapter 6.

Bromberg, J.P.,”Physical Chemistry”, Allyn and Bacon, Inc., New York (1984).

Castellan, G.W., “Physical Chemistry”,3rd ed., Addison-Wesley, New York (1983),

Sections 15.1-15.11.

Daniels, F. and R.A. Alberty,”Experimental Physical Chemistry”,7th ed., McGraw-

Hill, New York (1970).

Francis, A.W., “Liquid-Liquid Equilibrium”, John Wiley & Sons, New York (1963).

Laidler, K.J. and Meiser, J.H., “Physical Chemistry”, Benjamin/Cummings Pub Co.,

Menlo Park, Calif. (1982).

Maron, S.H., and C.F. Prutton,”Principles of Physical Chemistry”, 4th ed., Macmillan

Co., New York (1965),pp. 344-349 and 376-380.

Moore, W.J., “Physical Chemistry”, 4th ed., Prentice-Hall, Inc., Englewood Cliffs

(1972), pp. 207-208.

che291 manual spring 2011 revised and po

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