ABSTRACT

From this experiment, our objectives are to carry out the saponification reaction between NaOH and Et(Ac) in plug flow reactor, to determine the reaction rate constant and the rate of reaction of the saponification process. A unit called SOLTEQ Plug Flow Reactor (Model: BP 101) is used in this experiment, commonly known as PFR. During the reaction we used Sodium hydroxide (NaOH) and Ethyl acetate Et(Ac) as the reactant .The value of reaction rate constant and rate of reaction were calculated from the data recorded. The reaction rate constant for 600ml/min flow rate was 102.19L/mol.min, for the 500mL/min reaction rate constant was 52.60L/mol.min, for the 400mL/min reaction rate constant was 52.50L/mol.min, for the 300mL/min reaction rate constant was 29.26L/mol.min, for the 200mL/min reaction rate constant was 28.78L/mol.min and for the 100mL/min reaction rate constant was 13.13L/mol.min. Other than that, the rate of reaction for this process also determined. The rate of reaction we got for flow rate of 600ml/min was 0.0170mol/L.min, for the 500mL/min the rate of reaction was 0.0190mol/L.min,for the 400mL/min the rate of reaction was 0.0130mol/L.min, for the 300mL/min the rate of reaction was 0.0120mol/L.min, for the 200mL/min the rate of reaction was 0.0063mol/L.min and for the 100mL/min the rate of reaction is 0.0034mol/L.min. . A graph of conductivity against conversion was plotted. From the graph, the conversion is inversely proportional to the conductivity. So that, as the conversion increases, the conductivity decreases. A graph of conversion against residence time also plotted. From the graph we can see that, the conversion of reaction changes constantly as the residence time increases.

INTRODUCTION

Reactors play an important role in many production facilities involving the chemical

transformation of substances. Their performance determines the reliability and suitability of a process,

it’s environmental safety, the consumption of energy and the raw materials required. Chemical reactors

are vessels that contain chemical reactions. Different types of chemical, biological and physical

processes take place in reactors. Some examples of reactors include lakes, rivers, and sedimentation

tanks. The degree of mixing and residence time in reactors affect the degree of completion of reactions

within the reactor. (Dipa Dey et.al , 2007).

A plug flow reactor (PFR) is a type of chemical reactor where the influent is pumped into the

pipe. Chemical reactions occur through the length of the PFR and the reaction rate is not a constant. It is

also a vessel through which flow is continuous, usually at steady state with conversion of the chemicals

and other dependent variables are functions of position within the reactor rather than of time. In the

ideal plug flow reactor, the fluids flow as if they were solid plugs or pistons, and reaction time is the

same for all flowing material at any given tube cross section. Flow in these reactors can be laminar, as

with viscous fluids in small-diameter tubes while turbulent, as with gases. Turbulent flow generally is

preferred to laminar flow, because mixing and heat transfer are improved. (Laboratory of Environmental

and Science Engineering, n.d). For slow reactions and especially in small laboratory and pilot-plant

reactors, establishing turbulent flow can result in inconveniently long reactors or may require

unacceptably high feed rates.

Figure 1: Plug flow reactor

It is difficult to classify industrial chemical apparatus due to their diversity; however, a distinction is

made between stirred tank reactors and plug flow reactors.

Stirred tank reactors are mainly characterized by the following features:

o Perfect mixing allows the reaction to take place in the entire reactor volume and avoids the

formation of stagnant zones.

o Inlet concentration is not equal to the outlet concentration.

o The particle residence time distribution is the arithmetic mean of the residence time of all

particles.

o The reactor can be operated under isothermal conditions at steady state. This condition allows

the reactor to be easily controlled.

o The process temperature can be varied in a cascade of stirred reactors from one reactor to

another. The stable mode of operation can be achieved when each reactor in the cascade is

under isothermal conditions.

The features of a plug flow continuous reactor are as follows:

Flow is laminar, the properties of the reaction medium (i.e. pressure, temperature, reactant and

product concentrations) are the same throughout the entire cross section of flow.

All the elemental volumes of the reaction medium remain in the reactor for the same period of

time, and the change in concentration, temperature, and pressure with time are identical for

each elemental volume.

Additionally, there are temperature and reactant concentration gradients along the length of

the reactor.

The rate of chemical reactions vary along the length of the reactor.

OBJECTIVE

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

To determine the reaction rate constant.

To determine the effect of residence time on the conversion in a TFR

THEORY

The Plug Flow Reactor (PFR) is used to model the chemical transformation of compounds as they

are transported in pipes. The pipe may represent a river, a region between two mountain ranges

through which air flows, or a variety of other conduits through which liquids or gases flow. Besides, it

can even represent a pipe.(Richard E. Honrath, n.d).In an ideal tubular flow reactor, specific assumptions

are made regarding the extent of mixing:

No mixing in the axial direction

Complete mixing in the radial direction

A uniform velocity profile across the radius

Rate of reaction and rate law

Simply put, rate of reaction can be roughly defined as the rate of disappearance of

reactants or the rate of formation of products. When a chemical reaction is said to occur, a reactant(or

several) diminishes and a product(or several) produced. This is what constitutes a chemical reaction. For

example

aA + bB → cC + dD (Equation 1.1)

Where A and B represent reactants while C and D represent products. In this reaction, A and B is

being diminished and C and D is being produced. Rate of reaction, concerns itself with how fast the

reactants diminish or how fast the product is formed. Rate of reaction of each species corresponds

respectively to their stoichiometric coefficient. As such :

−r Aa

= −rBb

= rCc

= rDd

(Equation 1.2)

Rate of equation for reactant A is:

−r A = k C Aα CB

β (Equation 1.3)

k =rate constant

C A = concentration of A species

CB =concentration of B species

α =stoichiometric coefficient of A

β =stoichiometric coefficient of B

The rate expression can be shown to be

-rA = k [A] [B] (Equation 1.4)

Where if [A] is equal to [B], this simplify to

-rA = k [A]2 (Equation 1.5)

In the general case the order of the reaction η is not known and is shown by

-rA = k [A]η

If the inlet concentration, [A] is known, k can be determined. The reaction:

NaOH + CH3COOC2H5 → CH3COONa + C2H5OH

Sodium Hydroxide + Ethyl Acetate → Sodium Acetate + Ethyl Alcohol

can be considered equal-molar and first order with respect to both sodium hydroxide and ethyl acetate

i.e. second order overall, within the limits of the concentration (0-0.1M) and temperature (20-40oC)

studied. (Instruction Manual Turbular Flow Reactor,2006)

Conversion

While conversion shows how many moles of products are formed for every mole of A has consumed.

X A=molesof A reactedmolesof A fed (Equation 1.6)

Residence Time Distribution (RTD)

Residence Time Distribution is a characteristic of the mixing that occurs in the chemical reactor.

There is no axial mixing in a plug flow reactor, PFR and this omission can be seen in the Residence Time

Distribution, RTD which is exhibited by this class of reactors. The continuous stirred tank reactor CSTR is

thoroughly mixed and its RTD is hugely different as compared to the RTD of PFR.

APPARATUS

Plug Flow Reactor Model Bp101

Burette

Measuring cylinder

Beakers

pH indicator

Conical flask

0.1M Sodium Hydroxide, NaOH

0.1M Ethyl Acetate, Et(Ac)

0.1M Hydrochloric Acid, HCl

De-ionized water

Figure 2 : Plug flow reactor

PROCEDURE

General Start-up Procedures

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

2. The following solutions are prepared: 20 liter of NaOH (0.1M) 20 liter of Et(Ac) (0.1M)1 liter of

HCL (0.25M) for quenching

3. Feed tank B1 was filled with NaOH while feed tank B2 was filled with the Et(Ac).

4. The water jacket B4 was filled with water and pre-heater B5 was filled with clean water.

5. The power for the control panel was turned on.

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

7. Both pumps P1 and P2 were switched on. P1 and P2 were adjusted to obtain flow rate

approximately 300mL/min at both flow meters Fl-01 and Fl-02. Both flow rates were made sure

to be equal.

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

B3.

9. Valves V13 and V18 was opened. Pump P3 then was switched on in order to circulate the water

through pre-heater B5. The stirrer motor M1 was switched on and set up to speed about200

rpm to ensure homogeneous water jacket temperature.

Experiment Procedures

1) The general starts up procedures were performed.

2) Valves V9 and V11 were opened.

3) Both the NaOH and Et(Ac) solutions were allowed to enter the plug reactor R1 and empty into

the waste tank B3.

4) P1 and P2 were adjusted to give a constant flow rate of about 300 ml/min at flow metersFI-01

and FI-02. Both flow rates were ensured same. The flow rates were recorded.

5) The inlet (QI-01) and outlet (QI-02) were started to monitor the conductivity values until they

do not change over time. This is to ensure that the reactor has reached steady state.

6) 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.

7) Optional: Sampling was opened from valve V15 and 50ml of sample was collected. A

back titration procedure was carried out manually to determine the concentration of NaOH in

the reactor and extent of conversion.

8) The experiment was repeated from step 4 to 7 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 made sure to be equal.

Titration Procedures

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

2. 10 mL of 0.25 M HCl was poured in a flask.

3. 50 mL samples that were collected from the experiment at every controlled flow

rate (300,250, 200, 150, 100 and 50 mL/min) were added into the 10mL HCl to quench the

saponification reaction.

4. 3 drops of phenolphthalein were dropped into the mixture of sample and HCl.

5. The mixture then was titrated with NaOH until it turns light pink.

6. The amount of NaOH titrated was recorded.

RESULT

Conversion Solution Mixtures Concentration of NaOH (M)

Conductivity (mS/cm)

0.1M NaOH 0.1M Na(Ac) Water

0% 100mL - 100mL 0.0500 6.31

25% 75mL 25mL 100mL 0.0375 5.25

50% 50mL 50mL 100mL 0.0250 4.55

75% 25mL 75mL 100mL 0.0125 3.71

100% - 100mL 100mL 0.0000 2.55

Table 1: Preparation of Calibration Curve

Reactor volume: 4L

Concentration of NaOH in feed tank: 0.1M

Concentration of Et(Ac) in feed tank: 0.1M

No

Flow rate of NaOH (mL/min)

Flow rate of Et(Ac) (mL/min)

Total flow rate of solutions, V 0 (mL/min)

Residence time, τ (min)

Outlet conductivity (mS/cm)

Volume of NaOH

(ml)

Conversion, X (%)

Reaction Rate Constant (L/mol.min)

Rate of Reaction (mol/L.min)

Q1 Q2

1 300 300 600 0.667 7.7 6.9 0.0218 87.2 102.19 0.0170

2 250 250 500 0.800 7.2 6.2 0.0202 80.8 52.60 0.0190

3 200 200 400 1.000 6.8 5.7 0.0210 84.0 52.50 0.0130

4 150 150 300 1.333 6.7 5.5 0.0199 79.6 29.26 0.0120

5 100 100 200 2.000 6.4 5.2 0.0213 85.2 28.78 0.0063

6 50 50 100 4.000 5.8 4.5 0.021 84.0 13.13 0.0034

Table 2: Experiment 3

CALCULATION

Residence time

Residence time, τ= reactor volume ,V (L)total flow rate ,V 0 (L/min )

For flow rate of 300 mL/min

Total flow rate, V0 = Flow rate of NaOH + Flow rate of Et(Ac)

= 300 mL/min NaOH + 300 mL/min Et(Ac)

= 600 mL/min = 0.6 L/min

Reactor volume, V = 0.4 L

Residence time, τ= 0.4 L0.6 L/min

=0.667min

Conversion

X=(1−concentrationof unreacted NaOH∈reactor ,CNaOH

concentration of NaOH∈reactor ,CNaOH ,0)×100 %

For flow rate of 300 mL/min

Volume of sample, Vs = 50 mL = 0.050 L

Concentration of NaOH in the feed vessel, CNaOH, f = 0.1 mol/L

Volume of HCl quenching, VHCl = 10 mL = 0.010 L

Concentration of HCl in standard solution, CHCl = 0.25 mol/L

Volume of NaOH titrated, V1 = 21.8 mL = 0.0218 L

Concentration of NaOH used for titration, CNaOH, s = 0.1 mol/L

Concentrationof NaOH enteringthe r eactor ,CNaOH ,0=C NaOH ,f

2

CNaOH , 0=0.1mol /L

2=0.05mol

L

Volumeof unreacted quenchingHCl ,V 2=CNaOH , s

CHCl×V 1

V 2=0.1

0.25×0.0218 L=8.72×10−3 L

Volumeof HCl reacted withNaOH∈sample ,V 3=V HCl−V 2

V 3=0.010L−8.72×10−3 L=1.28×10−3 L

Molesof HCl reacted withNaOH∈sample , n1=CHCl−V 3

n1=0.25molL× (1.28×10−3 ) L=3.2×10− 4mol

Molesof unreacted NaOH∈sample ,n2=n1

n2=n1=3.2×10−4mol

Concentrationof unreacted NaOH ∈reactor ,CNaOH=n2

( V s

1000 )

CNaOH=3.2×10−4mol

( 501000 )L

=6.4×10−3mol/L

Conversion ,X=(1−CNaOH

C NaOH ,0)×100 %

X=(1−6.4×10−3mol /L0.05mol/L )×100 %=87.2%

Reaction rate constant, k

k=v0

V C A0( X1−X )

X = extent of conversion

v0 = total flow rate of solution (L/min)

CA0 = Inlet concentration of reactant NaOH in the reactor (mol/L)

V = Reactor volume (L)

For flow rate of 300 mL/min

k= 0.6 L/min0.4 L×0.1mol/L ( 0.872

1−0.872 )=102.19 Lmol .min

Rate of reaction, -rA

-rA = kC2A0 (1-X)2

For flow rate of 300 mL/min

−rA=(102.19 ) (0.1 )2 (1−0.872 )2=0.0170 molL .min

0% 20% 40% 60% 80% 100% 120% 140%0

1

2

3

4

5

6

7

Conductivity (mS/cm) vs. Conversion

Conversion

Con

duct

ivity

(mS/

cm)

Figure 3: Conductivity (mS/cm) versus Conversion(%)

0.5 1 1.5 2 2.5 3 3.5 4 4.574

76

78

80

82

84

86

88

Conversion, X (%) vs. Residence time,τ(min)

Residence time,τ (min)

Con

vers

ion,

X (%

)

Figure 4: Conversion, X (%) versus Residence time, τ (min)

DISCUSSION

The objective of this experiment to carry out a saponification reaction between NaOH and Et(Ac)

in a plug flow reactor. Besides, we determine the reaction rate constant and the effect of residence time

on the conversion in plug flow reaction. Saponification is a process that produces soap, usually from fats

and lye. The process involves a reaction between a base, usually sodium hydroxide (caustic soda), and

an ester group on a compound. For this experiment, we conducted saponification process in plug flow

reactor Model Bp101.So the reaction occurred different resulted. During the reaction we used Sodium

hydroxide (NaOH) and Ethyl acetate Et(Ac) as the reactant .

NaOH + CH3COOC2H5 → CH3COONa + C2H5OH

Sodium Hydroxide + Ethyl Acetate → Sodium Acetate + Ethyl Alcohol

By using a Plug Flow Reactor, PFR, these two substances were flowed into the reactor, mixed

and react for a certain period of time to completing the saponification process .Both the NaOH and

Et(Ac) solutions were allowed to enter the plug reactor and empty into the waste tank .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 ensured same. The flow rates were recorded. The flow rate of reaction was set up from 300

ml/min to 50 ml/min for both NaOH and Et(Ac) flow rate. Sampling was opened from valve V15 and

50ml of sample was collected. A back titration procedure was carried out to determine the

concentration of NaOH in the reactor and extent of conversion. Titration was carried out between 0.1 M

of NaOH with 0.1M HCI and sample from reaction added 3 drops of phenolphthalein. The volume of

NaOH change the colour of solution to light pink was recorded.

After that, the conversion of the reaction and rate constant can be calculated. The reaction rate

constant for flow rate 600ml/min is 102.19 L/mol.min while flow rate 500 ml/min is 52.60 L/mol.min.

Next, for flow rate 400ml/min,300 ml/min and 200 ml/min the rate constant are 52.50

L/mol.min,29.26L/mol.min and 28.78 L/mol.min respectively. The reaction rate constant is 13.13

L/mol.min for flow rate 100 ml/min. From these results, we can see that as the flow rate increases, the

reaction rate also increases.

Conversion is a property that shows how much of the reaction has taken place.For the

conversion of reaction, at flow rate 600ml/min and 500 ml/min are 87.2% and 80.8 % respectively. For

flow rate 400ml/min the conversion reaction was 84%.Besides that, conversion reaction for flow rate

300ml/min ,200 ml/min and 100 ml/min are 79.6%,85.2% and 84% respectively.As a result, the

conversion of reaction depends on the volume of NaOH from titration. The increase volume of NaOH

from titration, the more conversion of reaction occurred.

The rate of reaction also can be determined after we had done find the reaction rate constant.

From the resulted, the rate of reaction for 600ml/min was 0.0170 mol/L.min and for 500ml/min was

0.0190 mol/L.min. Other than that, reaction rate for 400ml/min,300 ml/min and 200ml/min was 0.0130

mol/L.min,0.0120 mol/L.min and 0.0063 mol/L.min respectively. The reaction rate was 0.0034mol/L.min

for flow rate 100ml/min. Therefore, the rate of reaction increases as the flow rate increases. At 600

ml/min the reaction rate decrease from 0.019 mol/L.min to 0.017 mol/L.min. This is maybe due to the

same value of the flow rate and the volume of the tank reactor.

A graph of conductivity against conversion was plotted. From the graph, the conversion is

inversely proportional to the conductivity. So that, as the conversion increases, the conductivity

decreases. Furthermore, a graph of conversion against residence time also plotted. From the graph we

can see that, the conversion of reaction changes constantly as the residence time increases.Therefore,

residence time is not a factor of reaction conversion. This is because PFR lacks a good mixing process.

Since the PFR is designed not to stir the solution vigorously to maximise mixing process, the conversion

of the reaction by using PFR is fairly low.

CONCLUSION

As a conclusion, we had carried out a saponification reaction between NaOH and Et(Ac) in a plug

flow reactor. Besides ,we had determined the reaction rate constant and the effect of residence time

on the conversion in PFR. The reaction rate constant for flow rate 600ml/min is 102.19 L/mol.min while

flow rate 500 ml/min is 52.60 L/mol.min. Next, for flow rate 400ml/min,300 ml/min and 200 ml/min the

rate constant are 52.50 L/mol.min,29.26L/mol.min and 28.78 L/mol.min respectively. The reaction rate

constant is 13.13 L/mol.min for flow rate 100 ml/min. So that, the flow rate increases, the reaction rate

also increases. Other than that, we also determined the rate of reaction. From the resulted, the rate of

reaction for 600ml/min was 0.0170 mol/L.min and for 500ml/min was 0.0190 mol/L.min. Then, reaction

rate for 400ml/min,300 ml/min and 200ml/min was 0.0130 mol/L.min,0.0120 mol/L.min and 0.0063

mol/L.min respectively. The reaction rate was 0.0034mol/L.min for flow rate 100ml/min. Therefore, the

rate of reaction increases as the flow rate increases. At 600 ml/min the reaction rate decreases from

0.019 mol/L.min to 0.017 mol/L.min. This is maybe due to the same value of the flow rate and the

volume of the tank reactor. A graph of conductivity against conversion was plotted. From the graph, the

conversion is inversely proportional to the conductivity. So that, as the conversion increases, the

conductivity decreases. A graph of conversion against residence time also plotted. From the graph we

can see that, the conversion of reaction changes constantly as the residence time increases.Therefore,

residence time is not a factor of reaction conversion. The experiment is conducted and completed

successfully.

RECOMMENDATION

There are several recommendations that can be taken in order to get more accurate result that are:

1. Before carry out the experiment, please consult with technician on how to run the equipment so that you can save your time and energy while doing the experiment.

2. It is recommended that 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 further 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. For obtained more accurate results, run several trials on tubular flow reactor so we can take the average value from each different molar rates.

5. 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.

REFERENCE

Laboratory of Environmental and Science Engineering. (n.d) .Bioreactors for metal bearing wastewater treatment: Tubular Reactor or Plug flow reactor. Retrieved from: http://www.metal.ntua.gr/~pkousi/e-learning/bioreactors/page_07.htm

Dipa Dey, Amanda, Herzog , Vidya Srinivasan.(2007).Tracer Studies In a Plug Flow Reactor. Retrieved from: http://www.egr.msu.edu/~hashsham/courses/ene806/docs/Plug%20Flow%20Reactor.pdf

Richard E. Honrath.(n.d).CPE521,Mass and energy balance . Retrieved from :http://www.cee.mtu.edu/~reh/courses/ce251/251_notes_dir/node3.html

Instruction Manual Turbular Flow Reactor.(2006).Retrieved from :http://eleceng.dit.ie/gavin/DT275/CET%20MKII%20manual%20issue%2016.pdf

Laboratory Manual Tubular Flow Reactor .Retrieved from: http://www.solution.com.my/pdf/BP101(A4).pdf

APPENDIX