ABSTRACT

This experiment is conducted using Plug Flow Reactor to carry out a saponification

reaction between Sodium Hydroxide (NaOH) and Ethyl Acetate ( Et(Ac) ). The other objective is

to determine the reaction rate constant. This experiment also carried out to determine the effect

of residence time on the conversion of the reactions by plotting a graph of residence time against

conversion. The experiment were using 0.1 M of NaOH, 0.1 M of Et(Ac), 0.25 M of

hydrochloric acid and the deionized water as the materials involved in the reactions. The

temperature and the pressure were constant but the flowrate are changed. The sample from the

experiment are mixed with the 0.25 M of HCl and titrated against the NaOH solution. The

volume of NaOH that being titrated are recorded and being calculated to find the conversion of

the reaction. The result shows that the conversion increase as the time residence increase. The

experiment was conducted successfully.

1

INTRODUCTION

Chemical reactors can be defined as the vessels that contain chemical reactions. A reactor

is one of the important roles in many production facilities involving the chemical transformation

of the substances. The performance of the reactor determines the reliability and suitability of the

process that take place in the reactor such as its environmental safety, the consumption of energy

and the raw materials required. Back then, it was difficult to classify industrial chemical

apparatus due to diversity and the differences of the reactors. However, a distinction and

integration have been made between stirred tank reactors and plug flow reactors.

The plug flow reactor (PFR) is a model used to describe the chemical reactions in

continuous flowing system. It is consist of hollow pipe or tube through which reactants flow. The

reactor also consist of a cylindrical pipe with opening at each end. It is provided to allow the

reactants and the product to flow through. The water at controlled temperature is circulated

through the tank that consist of a tube wrapped around an acrylic mold to constant reactants

temperature. The plug flow reactor are operate on steady state condition. (Encyclopedia of

Chemical Engineering Equipment)

Plug flow reactor can be used to model the tubular flow reactors in which there is no

moxing in the horizontal direction and perfect mixing in radial direction. (Bryan Research and

Engineering, Inc) in pharmaceutical industry, the plug flow reactor have been used which

contributed to the drug development and also scale up the process. By using the plug flow

reactor, they are able to perform the chemical reactions process that would be difficult to perform

in batch system process. This reactor also increase the safety of the reactions and the process as

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well. The plug flow reactor has the ability to allow the rapid condition screening to accelerate

early phase development. (Characterization and Selection of Continuous Plug Flow Reactors in

Pharmaceutical Development, 2012)

AIM

1. To carry out a saponification reaction between NaOH and Et(Ac).

2. To determine the reaction rate constant.

3. To determine the effect of residence time on the conversion.

3

THEORY

In a pug flow reactor, the feed enters at one end of a cylindrical tube and the

product stream leaves at the other end. The long tube and the lack of provision for stirring

prevents complete mixing of the fluid in the tube. Hence the properties of the flowing stream will

vary from one point to another, namely in both radial and axial directions.

In the ideal plug flow reactor, which is called the tubular reactor, specific assumptions are

made about the extent of mixing:

1. no mixing in the axial direction, i.e., the direction of flow

2. complete mixing in the radial direction

3. a uniform velocity profile across the radius.

Besides, this experiment is conducted to study the saponification reaction between NaOH and

Et(Ac).

CH3COOCH2CH3 + OH- CH3COO- + CH2CH3OH

This reaction will give the acetate ion and ethyl alcohol.

The rate of reaction can be obtained from the experimental data. The expression of general

chemical reaction rate is ,

a A + b B c C + d D

The rate law of a reaction can be expressed in the form;

Rate= k [A]n[B]m

Where

- k is the rate constant

-n and m are the reaction order with respect to each reactant.

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For constant volume, flowrate and initial concentration, the rate constant can be calculate as,

k¿v0

v CA0( X1−X )

where,

V0 =Total inlet flowrate

V =volume of reactor

CA0 =inlet concentration of NaOH

X =conversion of reactant

5

APPARATUS

1. The unit used in this experiment is SOLTEQ Plug Flow Reactor (Model: BP101)

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2. The other laboratory apparatus used,i. Burreteii. Conical flaskiii. Measuring cylinderiv. Beakers

3. The materials used are,i. 0.1 M of NaOHii. 0.1 M of Et(Ac)iii. 0.25 M of hydrochloric acidiv. deionized water

7

PROCEDURE.

General Start-Up Procedures:

1. All valves are initially closed except valves V4,V8 and V17.

2. All the following solutions are prepared:

20 liter of sodium hydroxide, NaOH (0.1M)

20 liter of ethyl acetate, Et(Ac) (0.1M)

1 liter of hydrochloric acid, HCl (0.25M) for quenching.

3. Feed tank B1 is filled with the NaOH solution and tank B2 with the Et(Ac) solution.

4. Water jacket B4 and pre-heater B5 is filled with clean water.

5. The power for the control panel turned on.

6. Valves V2, V4, V6, V8,V9 and V11 is opened.

7. Both pumps P1 and P2 is switched on. P1 and P2 is adjusted to obtain flow of approximately 300 ml/min at both flow meters FI-01 and FI-02. Both of the flow rates must be identical.

8. Both solutions is allowed to flow through the reactor R1 and overflow into the waste tank B3.

9. V13 and V18 is opened. Pump P3 is switched on to circulate the water through pre –heater B5. Stirrer motor M1 is switched on and the speed is dey about 200 rpm to ensure homogenous water jacket temperature.

General Shutdown Procedures:

1. Pumps P1, P2 and P3 were switched off. Valves V2 and V6 were closed.2. The heaters were switched off.3. The cooling water was kept circulating through the reactor while the stirrer motor was

running to allow the water jacket to cool down to room temperature.4. All all liquid from the unit by was drained by opening valves V1 to V19. The feed tanks

was cleansed with clean water.5. The power for the control panel was turned off.

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Preparation of Calibration Curve for Conversion vs. Conductivity:

1. 1 L of 0.1M sodium hydroxide,NaOH, 1 L of 0.1M sodium acetate Na(Ac) and 1 L of deionised water, H2O were prepared.

2. The conductivity and NaOH concentration for each conversion values were determined by mixing the following solutions into 100 ml of deionised water:

a) 0% conversion : 100 ml NaOH

b) 25% conversion : 75 ml NaOH + 25 ml Na(Ac)

c) 50% conversion : 50 ml NaOH + 50 ml Na(Ac)

d) 75% conversion : 25 ml NaOH + 75 ml Na(Ac)

e) 100% conversion : 100 ml Na(Ac)

Back Titration Procedures for Manual Conversion Determination

1. The burette was filled up with 0.1 M NaOH solution.

2. 10 ml of 0.25 M HCl was measured in a flask.

3. 50 ml sample was obtained from the experiment and was immediately added to the HCl in the flask to quench the saponification reaction.

4. A few drops of pH indicator were added into the mixture.

5. The mixture was titrated with NaOH solution from the burette until the mixture was neutralized. The amount of NaOH titrated were recorded.

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EXPERIMENT 3: Effect of Residence Time on Reaction

The general start-up procedures were performed.

1) Valves V9 and V11 were opened.Both the NaOH and Et(Ac) solutions were allowed to enter the plug reactor R1 and empty into the waste tank B3.

2) P1 and P2 were adjusted to give a constant flow rate of about 300 ml/min at flow meters FI-01 and FI-02.Both flow rates were adjusted to the same value and the value was recorded.

3) The inlet (QI-01) and outlet (QI-02) conductivity values were monitored until they do not change over time to ensure that the reactor has reached steady state.Both inlet and outlet steady state conductivity values were recorded.The concentration of NaOH exiting the reactor and extent of conversion from the calibration curve were to be determined.

4) Sampling valve V15 was opened and a 50 ml sample was collected.A back titration procedure was carried out to manually determine the concentration of NaOH in the reactor and extent of conversion (Section B).

5) Steps 4 to 7 were repeated for different residence times by reducing the feed flow rates of NaOH and Et(Ac) to about 250, 200, 150, 100 and 50 ml/min. Both flow rates were kept constant.

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RESULT

TABLE OF PREPARATION FOR CALIBRATION CURVE

ConversionSolution Mixture (mL) Concentration

of NaOH (M)Conductivity

(mS/cm)0.1 M NaOH 0.1 M Et(Ac) H 2O

0 % 100 - 100 0.0500 7.89

25 % 75 25 100 0.0375 5.39

50 % 50 50 100 0.0250 3.55

75 % 25 75 100 0.0125 3.42

100 % - 100 100 0.0000 3.37

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0% 20% 40% 60% 80% 100% 120%0

1

2

3

4

5

6

7

8

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A Calibration Curve of Conductivity vs Con-version

conversion, X (%)

Cond

uctiv

ity (m

S/cm

)

12

13

6.67 8 10 13.3 20 400

10

20

30

40

50

60

70

80

90

A graph of Conversion,X vs Residence Time

Residence Time, (min)𝞃

Conv

ersio

n, X

(%)

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CALCULATION

Sample calculation at flowrate of 300 mL/min ;

a) Residence time,r

Residence time,ᴦ =

reactor volume,V (L )

total flowrate ,V 0( Lmin )

V0 = flowrate NaOH + flowrate Et(Ac)

=(300+300)ml/min

= 600ml/min

=0.6L/min

Residence time , ᴦ= 4 L0.6 L/min

=6.667min

b) Conversion, X

Moles NaOH reacted,n1 = concentration of NaOH × volume of NaOH titrated

=0.1 M X (10.2 / 1000) L

= 0.00102 moles

Moles of unreacted HCl = moles reacted NaOH

=0.00102 moles

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Volume of unreacted HCl,

v= nconcentration of HCl quench

¿¿

¿ 0.001020.25M

=0.00408 L

Volume of HCl reacted = total volume HCl volume HCl unreacted

= (10/1000) L - 0.00408L

= 0.00592 L

Moles of reacted HCl = concentration of HCl × volume of HCl reacted

= 0.25 × 0.00592

= 0.00148 moles = moles of unreacted NaOH

Concentration of unreacted NaOH = moleof unreacted NaOHVOlumeof sample

=0.00148mole

0.05L

=0.0296 M

Conversion of NaOH in the reactor, X;

X=1−C NaOH

CNaOH ,0

16

¿1−0.02960.05

×100 %=40.8 %

The other calculations of conversion,X for other flowrates are calculated using the same

formula and solutions.

c) Rate constant, k

k=v 0

v CA0( X

1−X )

k= 0.64 (0.1) ( 0.408

1−0.408 )=1.034 L .mol/min

d) Rate of reaction, −r A

-rA = k(CA0)2(1-X)2

= 1.034(0.1)2(1-0.408)2

= 0.00362 mol /Lmin

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DISCUSSION

The objectives of this experiment is to carry out the saponification reaction between

NaOH and Et(Ac) in plug flow reactor, to determine the reaction rate constant and to determine

the effect of residence time on the conversion, X. From this experiment, the value of the reaction

rate constant can be determined by using the formula and to determine the effect of residence

time on the conversion in the plug flow reactor.

In this experiment, the solution with 0%, 25%, 50% 75% and 100% conversion was

prepared in other to prepare a calibration curve. Moreover, the concentration of solution is

calculated and recorded in result section. Calibration apparatus also was used to measure the data

for the conductivity and the conductivity measured was recorded in the result section. The result

of the conductivity of the solution is 7.89, 5.39, 3.55, 3.42 and 3.37 mS/cm for 0% to 100% of

conversion. Then, the graph of Conductivity versus conversion is plotted (Graph 1).

Saponification can be defined as a chemical reaction in which an ester is heated with an

alkali. The experiment is about saponification, thus the experiment is done by running up the

equipment in order to start the saponification process. Based on the theory of the experiment, the

coiled reaction tube is where the saponification process to occur. Basically, the saponification

process can be done in two ways of method whether variation in the temperature of the system

or variation in contact time. The flowrate of both solutions let as the varying components

because the flowrate of both solutions is controlled by the temperature of the reactor. From the

experiment and data collected it can be summarized that the saponification process in this

experiment is successfully and nicely done.

Variation in flowrate for both solution sodium hydroxide and ethyl acetate was needed in

order to determine the reaction rate constant and the rate of the reaction for the saponification

process. The reaction of saponification process is as stated below:

CH3COOC2H5 (A)+ NaOH (B) → CH3COONa + C2H5OH

It is noted that the overall reaction order for the saponification process is second ordered,

the reaction rate constant can be determined by applied the equations below:

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−r A = k (C A0 ¿¿2(1−X)2.

For constant plug flow reactor volume, flow rate and initial concentrations, the reaction

rate constant:

k=v0

V TFRCA 0

( X1−X

).

For the calculation of rate constant for flowrate 600ml/min to 100 ml/min is calculated as

shown in calculation section and tabulated in table 2 in result section .There are some error

occurs during the experiments resulting the 100% conversion, such as the sample is not well

mixed, therefore the volume of NaOH used is lot, and the conversion is perfect.

Lastly, the rate of reaction also can be determined after find the reaction rate constant.

Calculation of rate of reaction for 600ml/min is shown in calculation section and tabulated in

table 2, also for other flowrate. Same as rate constant, the rate of reaction for 100 and 200ml/min

also cannot be calculated due to 100%. After all value of rate of reactions has been calculated, a

graph of conversion factor against residence time is plotted. From the graph that has been

plotted, it shows that conversion factor not directly proportional to residence time. There is

fluctuation in the graph as shown in graph 1.

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CONCLUSION

This experiments is conducted to perform the saponification reaction between NaOH and

Et(Ac) and to determine the reaction rate constant. Besides, this experiment also perform to

determine the effect of residence time on the conversion. For the preparation of calibration curve,

the result of the conductivity of the solution is 7.89, 5.39, 3.55, 3.42 and 3.37 mS/cm for 0%,

25%, 50%, 75% and100% of conversion respectively. Then, the graph of Conductivity versus

conversion is plotted (Graph 1). Lastly, a graph of conversion factor against residence time is

plotted. From the graph that has been plotted, it shows that conversion factor not directly

proportional to residence time.

RECOMMENDATION

There some recommendations can be made to improve the experiment result and data.

1. Make sure before carry out the experiment, consult with technician on how to

run the equipment so that you can save students time and energy while doing

the experiment. The experiment also will run smoothly with nice result and

data.

2. This experiment should be repeated at various other temperatures to investigate

the relationship between the reaction rate constant and the rate of reaction.

3. It is recommended that the experiment be repeated using dissimilar flow rates

for the NaOH solution and ethyl acetate solutions to investigate the effect that

this will have upon the saponification process.

4. Be careful when doing the titration because we only want the last drop of

NaOH that will convert the solution to light pale purple colour. The excess of

drop of NaOH will give effect on the result in the calculations.

5. Students should avoid careless mistake such as parallex error.

6. Lastly, students should wear a safety uniform to that have been fixed by the lab

safety law to avoid incident that might make the student harm.

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REFFERENCE

1. Fogler, H.S (2006). Elements of Chemical Reaction Engineering (3rd Edition).

PrenticeHall.

2. Encyclopedia Of Chemical Engineering Equipment

http://encyclopedia.che.engin.umich.edu/Pages/Reactors/PFR/PFR.html

3. Bryan Research and Engineering, Inc.

http://www.bre.com/promax/capabilities/reactors.aspx

4. The Essential Chemical Industry Online, Department of Chemistry, University of York.

http://www.essentialchemicalindustry.org/index.php

5. Characterization and Selection of Continuous Plug Flow Reactors in Pharmaceutical

Development, 2012 AiChE Annual Meeting.

http://www3.aiche.org/proceedings/Abstract.aspx?PaperID=263817

6. http://en.wikipedia.org/wiki/Plug_flow_reactor_model

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APPENDIX

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