1. ABSTRACT

For this experiment, we have done two different experiments which are by titration and by using plug

flow reactor. The purpose of titration process is to determine the concentration of NaOH and the

conductivity. The conductivity of 0.050 M NaOH is 6.31 ms/cm whereas the conductivity of 0.0000 NaOH

is 2.55 ms/cm. This particular result shows that, the concentration id directly proportional to the

conversion factor.

The second experiment is by using the plug flow reactor for the purpose of to determine the effect of

residence time on conversion. From the result obtained, when the residence time taken at 0.667 min,

the conversion factor is at 50.6 % at highest flow rate of NaOH at 304 ml/min. whilst, when the

residence time taken at 3.883 min, the conversion is 51.0 % at lowest flow rate of 52 ml/min. thus, this

result shows that, the residence time is directly proportional to the conversion. When longer time taken,

the conversion factor increase.

2. INTRODUCTION

Tubular reactors are one category of flow reactors. These reactors have continuous inflow and outflow

of materials. In the tubular 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 prevent 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.

1

Ideal tubular reactor is referred as a plug flow reactor (PFR). PFRs are frequently referred to as piston

flow reactors. The key assumption is that as a plug flows through a tubular reactor, the fluid is perfectly

mixed in the radial direction but not in the axial direction (forwards or backwards). Each plug of

differential volume is considered as a separate entity, effectively an infinitesimally small batch reactor,

limiting to zero volume. As it flows down the tubular PFR, the residence time (τ) of the plug is a function

of its position in the reactor. In the ideal PFR, the residence time distribution is therefore a Dirac delta

function (small and tall) with a value equal to τ. The PFR model works well for many fluids: liquids, gases,

and slurries. An ideal plug flow reactor has a fixed residence time: Any fluid (plug) that enters the

reactor at time t will exit the reactor at time t + τ, where τ is the residence time of the reactor.

Residence time in the reactor is equal to the space time if the conditions in the reactor like pressure and

temperature are same as those at the entrance. In the ideal tubular reactor, which is called the “plug

flow” 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.

The absence of longitudinal mixing is the special characteristics of this type of reactor. It is an

assumption at the opposite extreme from the complete mixing assumption of the ideal stirred tank

reactor. The validity of the assumptions will depend on the geometry of the reactor and the flow

conditions. Deviations, which are frequent but not always important, are of two kinds:

1. mixing in longitudinal direction due to vortices and turbulence

2. incomplete mixing in radial direction in laminar flow conditions

3. OBJECTIVES

1. To determine the reaction rate constant.

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

2

4. THEORY

Tubular flow reactor consists of a cylindrical pipe and operated at steady state condition. For

analytical purposes, the flow in the system is considered to be highly turbulent and may be modeled by

that of a plug flow. Therefore, there is no radial variation in concentration along the pipe. Tubular

reactors are one type of flow reactors. It has continuous input and output of materials. 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 prevent complete mixing of the fluid in the tube. Hence the properties of

the flowing stream will vary from one point to another. In an ideal tubular flow reactor,

specific assumptions are made regarding the extent of mixing:

1. No mixing in the axial direction

2. Complete mixing in the radial direction

3. A uniform velocity profile across the radius.

Rate of reaction is defined as the rate of disappearance of reactants or the rate of formation of

products. Rate of reaction shows how fast the reactants diminish or how fast the product is formed. A

reactant disappeared and a product produced when a chemical reaction occurred. For example:

aA + bB cC + dD

In the chemical equation above, A and B represent reactants while C and D represent products.

A and B is being disappeared and C and D is being produced. Rate of reaction of each species

corresponds respectively to their stoichiometric coefficient. The negative sign indicates reactants and

the positive sign indicates products.

−r A

a =

−rBb

= rCc

= rDd

Rate of equation for reactant A is:

3

−rA = k C Aα CB

β

k rate constant

C A concentration of A species

CB concentration of B species

α stoichiometric coefficient of A

β stoichiometric coefficient of B

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

consumed.

X A=molesof A reactedmolesof A fed

Residence time 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. The

continuous stirred tank reactor CSTR is thoroughly mixed and its residence time is hugely different as

compared to the residence time of PFR.

4

5. APPARATUS

SOLTEQ Tubular Reactor (Model: BP 101-B)

Conical flask

Calibration meter

Sodium hydroxide, NaOH (0.1M)

Sodium Acetate, Na(Ac) (0.1M)

Deionised water, H2O

5

6. PROCEDURE

General Start-Up Procedures for Experiments 3 & 4

1. Ensured that all valves are initially closed except valves V4, V8 and V17.

2. The following solutions was prepared:

a. 20 liter of sodium hydroxide, NaOH (0.1 M)

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

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

3. Filled the feed tank B1 with the NaOH solution and feed tank B2 with the Et(Ac) solution.

4. Filled the water jacket B4 and pre-heater B5 with clean water.

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

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

7. Both pumps P1 and P2 were Switch on. Adjust P1 and P2 to obtain flow of approximately 300

ml/min at both flow meters FI-01 and FI-02. Make sure both flow rates are the same.

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

B3.

9. Valves V13 and V18 were opened. Switch on pump P3 to circulate the water through pre-heater

B5. Switch on stirrer motor M1 and set the speed to about 200 rpm to ensure homogeneous

water jacket temperature.

10. For experiment 4, the following additional steps performed:

a. Switch on the heaters.

b. Valve V19 was opened to let the cooling water to flow through the cooling tubes. Adjust

valve V19 to obtain reasonable cooling water flow in order to minimize the temperature

overshoot at the TIC-01 during heater cut-off.

c. Set the temperature set point on TIC-01 to the desired temperature.

11. The unit is now ready for experiment.

6

General Shut-Down Procedures

12. Both pumps P1, P2 and P3 were switch off. Valves V2 and V6 were closed.

13. The heaters was Switch off.

14. Keep the cooling water circulating through the reactor while the stirrer motor is running to

allow the water jacket to cool down to room temperature.

15. If the equipment is not going to be used for long period of time, drain all liquid from the unit by

16. Opening valves V1 to V19. Rinse the feed tanks with clean water.

17. Turn off the power for the control panel.

Experimental procedures

A. Preparation of Calibration Curve for Conversion vs. Conductivity

The reaction to be studied is the saponification reaction of ethyl acetate Et(Ac) and sodium hydroxide

NaOH. Since this is a second order reaction, the rate of reaction depends on both concentrations of

Et(Ac) and NaOH. However, for analysis purposes, the reaction will be carried out using equimolar feeds

of Et(Ac) and NaOH solutions with the same initial concentrations. This ensures that both concentrations

are similar throughout the reaction.

NaOH + Et(Ac) →Na(Ac) + EtOH

The following procedures will calibrate the conductivity measurements of conversion values for the

reaction between 0.1 M ethyl acetate and 0.1 M sodium hydroxide:

1. The following solutions were prepared:

a) 1 liter of sodium hydroxide, NaOH (0.1 M)

b) 1 liter of sodium acetate, Na(Ac) (0.1 M)

c) 1 liter of deionized water, H2O

2. The conductivity and NaOH concentration for each conversion values were determined by

mixing the following solutions into 100 ml of deionized water:

a) 0% conversion: 100 ml NaOH

7

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)

B. Back Titration Procedures for Manual Conversion Determination

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

2. Measured 10 ml of 0.25 M HCl in a flask.

3. A 50 ml sample from the experiment was obtained and immediately added the sample 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 is neutralized.

Record the amount of NaOH titrated.

Experiment 3: Effect of residence time on the reaction

1. The general start-up procedures were performed.

2. Valves V9 and V11 were opened.

3. Allowed both the NaOH and Et(Ac) solutions 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 meters FI-01

and FI-02. Make sure that both flow rates are the same. Record the flow rates.

5. Start monitoring the inlet (QI-01) and outlet (QI-02) 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.. Find the concentration of

NaOH exiting the reactor and extent of conversion from the calibration curve.

7. The experiment (steps 4 to 7) was 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. Make sure that both

flow rates are the same.

8

7. RESULT

Experiment A: preparation of calibration curve

Conversion

(%)

Solution mixtures Conc. Of NaOH

(M)

Conductivity

(ms/cm)0.1 M NaOH

(mL)

0.1 M Na(Ac)

(mL)

H20

(mL)

0 100 - 100 0.050 6.31

25 75 25 100 0.0375 5.25

50 50 50 100 0.0250 4.55

75 25 75 100 0.0125 3.71

100 - 100 100 0.0000 2.55

9

Experiment 3:

Reactor Volume : 0.4 L

Concentration of NaOH in the reactor, CNaOH : 0.1M (2L)

Concentration of NaOH in the feed vessel, CNaOH,f : 0.1M (2L)

Concentration of HCl quench, CHCl,s : 0.25 M (0.01L)

Volume of sample, Vs : 0.05L

10

FLOWRATE OF NaOH

(ml/min)

FLOWRATE OF Et(Ac)

(ml/min)

TOTAL FLOWRATE OF SOLUTION,t 0

RESIDENCE TIME , T (min)

VOLUME OF NaOH

CONVERSION x (%)

REACTION RATE

CONSTANT (L/mol.min)

RATE OF REACTION

(mol/L.min)

Q1 Q2

304 307 611 0.667 0.3 8.1 6.0 50.6 15.65 0.0382

252 253 505 0.792 0.2 8.2 5.9 50.5 15.58 0.0382

203 205 408 0.980 0.1 8.0 5.5 50.4 15.52 0.0382

152 150 302 1.325 0.1 7.7 5.2 50.3 15.46 0.0382

104 102 206 1.942 0.2 7.4 5.0 50.2 15.40 0.0382

52 51 103 3.883 0.2 6.5 4.1 51.0 15.90 0.0382

11

OUTLET CONDUCTIVITY

(ms/cm)

12

8. SAMPLE OF CALCULATION

Residence Time

For flow rates of 304 ml/min :

Residence Time, τ= Reactor volume (L ) ,V

Total flow rate( Lmin ) , v0

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

= 304 mL/min NaOH + 307 mL/min Et(Ac)

= 611 mL/min

= 0.611 L/min

Hence,

Residence Time, τ=0.4 L

0.611L /min = 0.667 min

Other residence times were calculated by the same way, and varying the flow rates.

Conversion

For flow rates of 304 ml/min :

Moles of reacted NaOH, n1,

n1= Concentration NaOH x Volume of NaOH titrated

= 0.1 M x 0.000304 L

= 0.0000304 mole

Moles of unreacted HCl, n2,

Moles of unreacted HCl = Moles of reacted NaOH

13

n2 = n1

n2 = 0.0000304 mole

Volume of unreacted HCl, V1,

V1 = n2

concentrationHCl quench

= 0.00003040. 25

= 0.0001216 L

Volume of HCl reacted, V2,

V2 = Total volume HCl – V1

= 0.01 – 0.0001216

= 0.00988 L

Moles of reacted HCl, n3,

n3 = Concentration HCl x V2

= 0.25 x 0.00988

= 0.00247 mole

Moles of unreacted NaOH, n4,

n4 = n3

= 0.00247 mole

Concentration of unreacted NaOH,

CNaOH unreacted = n4

volume sample

=0.002470.05

= 0.0494 M

14

Xunreacted,

Xunreacted = Concentrationof NaOH unreacted

concentrationNaOH

=0.04940.1

= 0.494

Xreacted,

Xreacted = 1 - Xunreacted

= 1 - 0.494

= 0.506

Conversion for flow rate 304mL/min

0.506 x 100% = 50.6 %

Hence, at flow rate 304mL/min of NaOH in the reactor, about 50.6% of NaOH is reacted with

Et(Ac). Other conversions were calculated by the same way, and varying the flow rates.

Reaction Rate Constant,k

k=v0

V TFRC AO( X1−X )

For flow rates of 304 ml/min :

V0 = Total inlet flow rate

= 0.611 L/min

VTFR = Volume for reactor

15

=0. 4 L

CAO = inlet concentration of NaOH

= 0.1 M

X = 0.506

k= 0.611(0. 4)(0.1) ( 0.506

1−0.506 ) = 15.65L.mol/min

Other Reaction Rate Constants were calculated by the same way, and varying the flow rates.

Rate of Reaction, -rA

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

For flow rates of 304 ml/min :

-rA = 15.65 (0.1)2 (1-0.506)2

= 0.0382 mol.L/min

Other Rate of Reactions were calculated by the same way, and varying the flow rates.

16

9. DISCUSSION

The objectives of this experiment are to determine the reaction rate constant and to determine the

effect or residence time on the conversion of the reaction. A tubular reactor is a vessel through which

flow is continuous, usually at steady state, and configured so that conversion of the chemicals and other

dependent variables are functions of position within the reactor rather than of time. 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 in the ideal tubular reactor. Tubular reactors resemble batch reactors in providing initially

high driving forces, which diminish as the reactions progress down the tubes.

From this experiment, we conduct two different methods which are by using titration for the

calibration curve and we use plug flow reactor for the calculation of calibration curve. For the first

experiment, we titrate 0.1 M OF NaOH with 0.1 Na(Ac) to obtain the concentration of NAoH which are

0.050, 0.0375, 0.0250, 0.0125 and 0.000M for the conversion of 0,25, 50 75 and 100 % respectively.

From this titration, we constant the value of water added which is at 100Ml. For the conversion of

0% ,the titration of 100 ml of NaoH and 100ml water without Na(Ac), the conductivity obtain is 6.31

ms/cm whereas for 100% conversion with the titration of 100ml of Na(Ac) and 100ml water without

NaOH, the conductivity obtain is 2.55 ms/cm. Thus, it is shows that when the volume of NaOH increase,

the conductivity of the mixture decrease.

For the experiment using the plug flow reactor with the condition of the reactor volume of 0.4 L, the

concentration of NaOH in the reactor is 0.1 M, concentration of NaOH fed in the vessel is 0.1 M and the

volume of sample taken is 0.05L it was done to determine the residence time on the conversion of the

reaction. For the NaOH flow rate of highest rate which is at 304 ml/min the residence time is at 0.667

min with the conversion of 50.6 %. Whilst, for the least flow rate of NaOH at 52 ml/min,the residence

time taken is 3.883 min which far longer than 0.667 min of 304 ml/min flowrate. The conversion of 52

ml/min is 51.0 % which is faster than 50.6%. this can be coclude that, the residence time is inversely

proportional to the conversion unit of the mixture. When higher flow rate used,the residence time

decrease and the conversion of the mixture increase.

The tubular flow reactor has both advantages and disadvantages. The advantages of this flow

reactors are its have a high volumetric unit conversion, can be run for long periods of time without

maintenance, and the heat transfer rate can be optimized by using more, thinner tubes or fewer, thicker

tubes in parallel. While the disadvantages of this flow reactors are that temperatures are hard to control

17

and can result in undesirable temperature gradients. PFR maintenance is also more expensive than

continuous stirred tank reactor (CSTR) maintenance. Tubular flow reactor is mainly used for large scale

reactions, fast reactions, homogeneous or heterogeneous reaction, and continuous production and also

for the high temperature reactions.

10.CONCLUSION

As the conclusion, the objective of this experiment was achieved. The reaction rate constant obtained

are 15.65, 15.58, 15.52, 15.46 ,15.40 ,and 15.90 L/mol.min respectively by calculate using the value of

conversion obtain. Next, the residence time is inversely proportional to the conversion mixture. This is

because when the volume flow rate lower, the residence time increase and the conversion of the

mixture slightly decrease

11.REFERENCES

http://www.metal.ntua.gr/~pkousi/e-learning/bioreactors/page_07.htm

http://solve.nitk.ac.in/dmdocuments/Chemical/theory_plugflow.pdf

18

12.APPENDIX

Conical flask

Calibration meter

19