cstr joe's

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ABSTRACT

This Continuous Stirred-Tank Reactor experiment which commonly known as CSTR is

conducted to observe the order of the saponification reaction and also to find the rate

constant. This experiment is conducted by mixing two different solution which is Ethyl

cetate and Sodium !ydroxide "#a$!% with e&ual volume using Continuous stirred-tank

reactor. The sample of mixed solution is then mixed with !Cl after ' minutes and titrate with

(.) * #a$!. The amount of #a$! used by the titration will be recorded for the result of the

experiment. The same procedure for the next sample will be conducted repeatedly with

continuous time taken which is )(+ )'+ ,( and ,' minutes. ifferent flowrate are been

adusted for each time taken in this experiment that is (.)(+ (.)'+ (.,(+ (.,' and (./( 01min.

ll the data are collected for the result. 2ased on the calculation and graph that have been plotted from the result obtained+ we can determine the rate of the reaction. The temperature is

fixed for the residence temperature that have been calculated in our calculation which is /( C

due to limited time to conducting the second experiment which varying the temperature.

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INTRODUCTION

Chemical reaction and reactor design are important in producing almost all in industrial

chemicals. The selection of a reaction system that operates in the safest and most efficient

way is the key to success or failure of a chemical plant. Reactor is the e&uipment that changes

the raw materials to the product that we want. good reactor will give a high production and

economical. $ne of criteria to design or to choose a reactor knows the effectiveness of the

reactor itself. There are many reactors depending on the nature of the feed materials and

products. $ne of the most important we need to know in the various chemical reaction is the

rate of reaction.

The reaction occurred in a reactor is exothermic or endothermic. reactor is generally

assembled with a acket or coil in order to maintain the temperature in the reactor. 3f the heat

is evolved due to exothermic reaction+ a coolant stream is re&uired to pass through the acket

or coil to remove the extra heat. $n the other hand+ if endothermic reaction occurs in the

stream+ the flow of heating medium is passing through acket or coil for maintain the reaction

temperature. reactor operates at constant temperature+ then that is called as the isothermal

reactor. 3f any exothermic or endothermic reactions are involved in the reactor mixture varies

with time and we need to develop the energy balance e&uation for this non-isothermal reactor.

3n adiabatic reactor+ no interchange of heat occurs between the system and surroundings.

Thus no heating and cooling medium is re&uired. chemical reactor is a vessel where

reactions are carried out purposely to produce products from reactants by means of one or

chemical reactions. chemical reactor may be characteri4ed by the mode operation

according to the flow condition. 3n this experiment+ the Continuous Stirred Tank Reactor has

been used to conduct a chemical process.

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OBJECTIVES

• 5reparation of Calibration Curve for Conversion versus Conductivity

). To determine the conductivity at certain percent conversions.

,. To obtain a calibration curve of conductivity versus conversion.

• Effect of Residence Time on the Reaction in a CSTR

). To carry out the saponification reaction between #a$! and Et"c% in a CSTR.

,. To determine the effect of residence time+ τ on the extent of conversion.

/. To determine the reaction rate constant+ k.

THEORY

The continuous stirred-tank reactor "CSTR% or sometimes called back mix reactor was a very

typical reactor used in the industry as a part of the continuous-flow reactor. 6)+,+/7 The other

types of the continuous-flow reactor were plug-flow reactor "58R% and packed bed reactor

"52R%. 6,7 These reactors were classified as a continuous-flow reactor since the feed entered

the reactor continuously. The CSTR was named due to the special characteristic that it has

which is the stirrer as shown in the figure below. The function of the stirrer was to ensure allthe contents in well mixed condition and the concentration of the fluid was uniform

throughout the reaction.

Figure 1 The cross-sectional view of the CSTR

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The CSTR was generally designed to avoid the spatial variations in terms of the

concentrations+ temperature+ or even the reaction rate along the reaction process. Thus the

CSTR was operated in a steady state and it is normally used primarily for li&uid phase

reactions.6,7 3n such perfect mixing reaction+ the output composition was same to the material

inside the reactor where it is actually a function of residence time+ τ and rate of reaction+

−r .6/7 ll the variables such as the temperature and the concentration were the same at

every point either inside or at the exit of the reactor since the CSTR operated at steady state .6,7

The calculation performed by a CSTR was assumed as perfect mixing processes may be

initiated with the general mole balance e&uation+

F j0− F j+∫❑

V

r j dV =dN j

dt

Since the CSTR was operated at steady state+ thusdN j

dt =0 .6,+/7 This is due to no change

on the number of moles at steady state. *eanwhile+ the ∫❑

V

r j dV =V r j as there was no

spatial variations in the rate of reaction in a perfect mixing process. 6,7 Thus+ the general

mole balance became+

V = F j0− F j−r j

Theoretically+ the flow rate of a species was known as the product of the concentration of

species with the volumetric rate+

F j=C j×v

. 9hen inserting the flow rate e&uation into

the derived general mole balance+ 6,7

V =v0

C A 0−v C A−r A

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s for the effect of residence time on the percent of conversion in the CSTR+ the percent of

conversion should increase linearly as the time increase. 8or the experiment conducted+ the

residence time can be known based on the e&uationτ =

V CSTR

V 0.6)7

The e&uation used to find the conversion percent+ :+ 6)7

X =(1− C NaOH

C NaOH 0❑)×100

3n the experiment carried out+ in order to calculate the conversion percent+ the first thing that

should be determined was the volume of (.) * #a$! solution used to titrate '( ml of thesample collected from the CSTR. The sample solution initially being added with (.,' * !Cl

solution and three drops of phenolphthalein before conducting the titration process. The !Cl

was added for the &uenching purposes while the phenolphthalein was acted as an indicator.

The volume of the #a$! used was recorded as the colour of the sample changed from

colourless into light pink.

The calibration curve was also being carried out during this experiment by mixing the (.) *

of #a$! solution+ (.) * of Et"c% solution and also )(( ml of deionised water. The volume

for the #a$! solution and Et"c% solution were varied to achieve at certain percentage

conversion. The conductivity of all the solutions prepared based on their conversion were

then being observed by taking the value shown from a device called conductivity probe.

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APPARATUS AND MATERIALS

). The continuous-stirrer tank ;(0 "*$E0< 25);/%<

A. B. C. D. E.

F. G. H. I. J. K. L.

. Control 5anel =. Samples> *easuring Tank

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2. 8eed tanks "#a$! ? Et"c%% !. 5ipeline 9ith 8ittings

C. Stirrer 3. 9aste Tank

. *otor @. Aalves

E. Condenser B. Samples> ischarge 5ipe

8. 5umps 0. Tank Reactor

,. Retort stand with clamp./. '( ml burette.

;. '( ml+ )(( ml+ (( ml beakers

'. )( ml+ '( ml measuring cylinders

. ,'( ml conical flask

D. Sample of mixture<

a% '( ml sample solution

b% / drops of phenolphthalein

c% )( ml of (.,' * !Cl solution

. (.) * #a$! solution

F. (.) * Et"c% solution

)(. ropper )). Conductivity probe

),. eionised water

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PROCEDURE

A) GENERAL STARTUP PRCEDURE

). ll the following solutions are prepared<

a% ;( 0 of sodium hydroxide+ #a$! "(.)*%

b% ;( 0 of ethyl acetate+ Et"c% "(.)*%c% ) 0 of hydrochloric acid+ !C0 "(.,'*%+ for &uenching

,. ll valves are initially closed.

/. The feed vessels are charged as follows<

a% The charge port caps are opened for vessels 2) and 2,.

b% The #a$! solution are poured carefully into vessel 2) and the Et"c% solution

into vessel 2,.

c% The charge port caps are closed for both vessels.

;. The power for the control panel are turned on.'. Sufficient water in the thermostat T) tank are checked and refilled as necessary.

. Cooling water valve A)/ are opened and let the cooling water flow through the

condenser 9). "$nly for Experiment ,%

D. The overflow tube are adusted to give a working volume of )( 0 in the reactor R).

. Aalves A,+ A/+ AD+ A and A)) are all opened.

F. The unit is now ready for experiment.

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B) E!PERIMENTAL PROCEDURES

5reparation of Calibration Curve for Conversion vs. Conductivity

). ll the following solutions are prepared<

a% ) liter of sodium hydroxide+ #a$! "(.) *%

b% ) liter of sodium acetate+ Et"c% "(.) *%

c% ) liter of deionised water+ !,$

,. The conductivity and #a$! concentration for each conversion values are determined

by mixing the following solutions into )(( ml of deionised water<

a% (G conversion < )(( ml #a$!

b% ,'G conversion < D' ml #a$! H ,' ml Et"c%

c% '(G conversion < '( ml #a$! H '( ml Et"c%

d% D'G conversion < ,' ml #a$! H D' ml Et"c%e% )((G conversion < )(( ml Et"c%

C) BACK TITRATION PROCEDURES FOR MANUAL CONVERSION

DETERMINATION

). burette is filled up with (.) * #a$! solution.

,. )( ml of (.,' * !Cl is measured in a flask.

/. '( ml sample is obtained from the experiment and the sample is immediately added

to the !Cl in the flask to &uench the saponification reaction.

;. few drops of p! indicator is added into the mixture.

'. The mixture with #a$! solution is titrated from the burette until the mixture is

neutrali4ed. The amount of #a$! titrated is recorded.

D) EFFECT OF RESIDENCE TIME OF THE REACTION IN A CSTR

). The general start-up procedures are performed.

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,. 2oth pumps 5) and 5, are switched on simultaneously and valves A' and A)( are

opened to obtain the highest possible flow rate into the reactor.

/. 0et the reactor fill up with both the solution until it is ust about to overflow.

;. The valves A' and A)( are readusted to give a flow rate of about (.)( 01min. *ake

sure that both flow rates are the same. The flow rate are recorded.'. The stirrer *) is switched on and the speed are set to about ,(( rpm.

. The conductivity value at I3-;() is been monitored until it does not change over

time. This is to ensure that the reactor has reached steady state.

D. The steady state conductivity value is recorded and find the concentration of #a$! in

the reactor and extent of conversion from the calibration curve.

. Sampling valve A), is opened and collect a '( m0 sample. 2ack titration procedure

is carried out to manually determine the concentration of #a$! in the reactor and

extent of conversion.

F. The experiment "steps ' to F% are repeated for different residence times by adusting

the feed flow rates of #a$! and Et"c% to about (.)'+ (.,(+ (.,' and (./( 01min.

*ake sure that both flow rates are the same.

E) GENERAL SHUTDO"N PROCEDURE

). The cooling water valve A)/ is keep opened to allow the cooling water to continue

flowing.

,. 2oth pumps 5) and 5, are switched off. Stirrer *) is switched off.

/. The thermostat T) is switched off. 0et the li&uid in the reaction vessel R) cooled

down to room temperature.

;. Cooling water valve A)/ is closed.

'. Aalves A,+ A/+ AD and A are closed. Aalves A;+ AF and A), are opened to drain any

li&uid from the unit.

. The power for the control panel is turned off.

RESULT

A. PREPARATION OF CALIBRATION CURVE

Conversio

n

Solution *ixtures "0% Concentration of

#a$! "*%

Conductivity

"mS1cm%(.) * #a$! (.) * Et"c% !,$

(G (.) - (.) (.('(( );.;F(

,'G (.(D' (.(,' (.) (.(/D' .FF(

'(G (.(' (.(' (.) (.(,'( ;.D'(

D'G (.(,' (.(D' (.) (.(),' /.)'(

)((G - (.) (.) (.(((( (.),D

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Figure #$ =raph Conductivity against Conversion

B. E%%e&' (% Rei*e+&e Ti,e (% T-e Re&'i(+ i+ CSTR

• Reactor volume < ;( 0

• Concentration of #a$! in feed vessel < (.) *

• Concentration of Et"c% in feed vesssel < (.) *

Temperatu

re "oC%

8low

Rate

of

#a$!

"01mi

n%

8low

Rateof

Et"c

%

"01mi

n%

Total

8low

Rate of

Solution

s+ 8o

"01min%

Residen

ce Time+

J "min%

Conductivi

ty

Exit

Concentrati

on of

#a$!+ "*%

Conversio

n+ : "G%

,F. (.)( (.)( (.,( ,((.(( ,.; .; x )(-/ D.,

/(.( (.)' (.)' (./( )//.// ,., D.; x )(-/ '.,

/(., (.,( (.,( (.;( )((.(( ,.; . x )(-/

.(/(.; (.,' (.,' (.'( (.(( ,.D D.( x )(-/ D.,

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/(.' (./( (./( (.( .D ,.D) D.; x )(-/ '.,

Total 8low Rate of Solution+ 01min Aolume of #a$! titrated "m0%

(., ,).(./ ,)./

(.; ,).D

(.' ,).'

(. ,)./

Aolume of #a$!

titrated+A) "ml%

KAolume of unreacted

&uenching !Cl+ A, "ml%

Aolume of !Cl

reacted with #a$!

in sample+ A/ "ml%

*oles of !Cl

reacted with #a$!

in sample+n) "x)(-;%

,). .D, )., /.,(

,)./ .', ).; /.D(

,).D . )./, /./(

,).' .( ).;( /.'(

,)./ .', ).; /.D(

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CALCULATIONS

• Concentration of #a$! entering the reactor+ "C #a$!+o%<

C NaOH ,f

2

L

0.1 M

2

L (.(' *

• Aolume of unreacted &uenching !Cl+ "A,%<

C NaOH ,s

C HCl, s × V 1

L0.1 M

0.25 M x 21.8 mL

L .D, m0

• Aolume of !Cl reacted with #a$! in sample+ "A/%<

V HCl , s−V 2

L )( m0 M .D, m0

L )., m0

• *oles of !Cl reacted with #a$! in sample+ "n)%<

C NaOH , s× V 3

1000

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L0.25 M x1.28mL

1000

L /., x )(-;

• *oles of unreacted #a$! in sample+ "n,%

n2=n1 L /., x )(-;

• Concentration of unreacted #a$! in the reactor+ "C #a$!%<

n2

V s

1000

L3.2 x10−4

50×1000

L .; x )(-/ mol L

• Conversion of #a$! in the reactor+ :<

(1− C NaOH C NaOH , o )×100

L ") ‒6.4 x 10−3

0.05 ) x 100

= 87.2

• Reaction rate constant<

B L "C$- C%

CƬ ,

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= 0.05 ‒ (.; x )(-/%

,(( ‒ (.; x )(-/%,

L './,,/

-r L kC,

L ,.)(( x )(-;m

s

DISCUSSION

NOH / E'0A&) N0A&) / E'OH

The experiment was carried out by using special Sodium hydroxide "#a$!% and Ethyl

acetate and is conducted to carry out a saponification reaction between #a$! and Et"c% in

CSTR+ to carry out the manual conversion determination on experiment samples to verify the

conductivity measurement values of respective substances in the chemicals+ to determine the

effect of residence time onto the reaction extent of conversion and finally to determine the

reaction rate constant. 3n order to accomplish all of these obectives+ the Continuous Stirred

Tank Reactors "CSTR% ;(0 "model< 25 );/% is used. 2asically+ this experiment will mainly

be focusing on the saponification reaction of sodium hydroxide "#a$!% and Ethyl cetate+

Et"c%. Nsing the CSTR+ the behavior of the chemical reactors can be predicted+ therefore+

the key factors of a reactor such as the dimensions of the reactor+ can be estimated. The effect

of residence time onto the reaction extent of conversion and the reaction rate constant can be

determined after this experiment is carried out. 8or the titration part of the experiment+ it is to

determine the extent of conversion of the reaction using the manual conversion. fter all

these results are obtained+ both of these results will be compared.

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The saponification process+ which is one type of continuous process+ is a process to make

soap. 3n this experiment+ the reaction of saponification will involve &uenching with

hydrochloric acid to stop the reaction of neutrali4ation. The acid+ which is the Ethyl cetate+

Et"c% will be mixed with phenolphthalein in a beaker. The mixture will then be titrated with

Sodium !ydroxide in the burette. The titration process goes on until the mixture in the beaker

turns pink+ indicating the end point of the reaction that is the mixture has become neutral. The

reaction rate is very rapid+ and one must be very careful when reaching the end point of the

titration. $ther than that+ back titration is done to investigate the volume of Sodium

!ydroxide reacted.

3nside the reactor+ the saponification of #a$! and Ethyl cetate producing sodium acetate

and ethanol. $rder of the reaction is based on the powers of the concentration which areraised in the kinetic law. 8rom the data obtained+ a graph had been plotted which are

conductivity against conversion for manual conversion experiment "Titration% to determine

the conductivity of the reaction between #a$! and Et"c%. This graph should be plotted

before the beginning of the experiment so as to compare the results obtained later in the

experiment with the data shown in the calibration curve. 9ith the calibration curve+ one can

predict that conductivity of the reaction at any particular point in the reaction. 8rom =raph )+

it is observed that the conductivity will decrease when the volume of #a$! decreases.

Therefore+ it can be concluded that the conductivity decrease proportionately with

conversion+ :. This is because when volume of #a$! used decreases+ less #a$! will be

reacted with the acid in the titration. 9hen both reactants with different moles were used+ the

result will be different as this will give a significant difference in the conductivity of the

reaction. The product of the neutrali4ation are ethyl acetate and ethanol. 2ecause both of

these substances are not electric conductor and both Sodium ions and hydroxide ions ioni4e

easily in solution+ the conductivity of the mixture measurement depicts more or less+ the

concentration of #a$! that remains in the mixture. Therefore+ from the reading of

conductivity values of the mixture+ one can determine the concentration of unreacted #a$!

that remains in the solution relative to the conversion.

Aolumetric flow rate is related to the residence time therefore the experiment is repeated with

different flow rates+ that is (.)+ (.)'+ (.,(+ (.,' and (./( 01min. 8rom the data collected+ it

can be concluded that the conversion+ : increases as the volumetric flow rate decreases. The

fluid will enter the reactor at time+ t and will exit at time t H 2. Residence time+ 2 is the timethat the fluid elements spend in the reactor. t high flow rates+ the velocity of fluid moving in

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the reactor is high. This means the reactants spend less time within the reactor. 8rom the

second graph+ it can be observed that conversion+ : increases+ linearly with residence time.

Therefore+ it can be concluded that the longer the residence time+ the more conversion of the

reactant.

The reaction between #a$! and Et"c% is an e&uimolar reaction with the same initial

concentrations. 8rom the data obtained+ the order of the reaction was determined to be a

second order reaction. The rate law is Mr LkCC2. The rate of reaction is in 01mol.s. Relative

to the rate constant+ k for this order of reaction+ when the k value increases+ that means+ more

volume of #a$! is re&uired to convert one mole of #a$! in ) second. Calculated results

showed that the reaction rate constant increases as the volumetric flow rate decreases. 9hen

the reaction rate constant decreases+ the rate of reaction will increase. This is because thereare more moles of #a$! converted for a less volume of #a$! solution that is re&uired. This

is a very important fact to remember when designing a reactor so as to enable a reactor to

have a high conversion for large scale production. 2ased on result and the sample of

calculation+ the value of data was fitted to second order reaction. Therefore the rate law for

this experiments is<

*C3*' 4 5C#

The time taken for each sample taken is from the first minute the time started and followed

by the next 'th minute+ )(th minute and so on. The volume of titrating sodium hydroxide to

calculate the amount of &uenching hydrochloric acid+ phenolphtalein is used to be the

indicator of the mixture to be in neutral condition. Aolume of &uenching hydrochloric acid

unreacted with sodium hydroxide in sample is calculated using the amount of sodium

hydroxide titrated with the mixture.

The slopes of the graph are representing the specific reaction rate constant+ B. B constant can

be obtained by considering all the data obtained throughout the experiment. 2ased on the

calculation present on the sample of calculation+ B can be calculated.

8or the first temperature which is at ,F.OC+ since the reaction is second order+

-r L kC, L ,.)(( x )(-;

m

s . Then+ for this experiment+ the volume of &uenching !Cl

unreacted with #a$! in Sample "ml% is .D, ml. #ext+ the volume of !Cl reacted with

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#a$! in Sample "ml% is )., ml. The volume of titrating #a$! for this experiment are ,).

ml+ ,)./ ml+ ,).D ml+ ,).' ml+ and ,)./ ml.

This experiment also need to have the some precaution+ for example when if needed to read

the value of the sodium hydroxide from the burette+ make sure to look the value at eye level

to get the accurate value from the burette. The same person should be taking the reading since

everyone might have different opinion of the value.

CONCLUSION

s the result+ all of the aims and obectives are achieved. The reaction rate constant as well as

the effect of residence time on the conversion of Sodium !ydroxide has been determined.

8rom the result+ we obtained the order of the rate reaction which is second order.

Therefore

the reaction rate by the rate law is in the form of −r A=k C A2 and the result shows that the

conversion will decreases when the flow rate increases. This verifies the data and thus+ the

theory from the calibration curve from the first experiment. 9hen increasing the flow rate+

the reaction rate constant will be smaller and the rate of reaction will increase. The

experiment is has been achieved its obectives and successful.

RECOMMENDATION

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There are a few recommendations and precautions that have to be considered when

conducting this experiment in order to get accurate data and smoothly in progressing the

experiment. 8irstly+ general set-up must be conducted as given then followed by the

experimental procedures and end with the general shut-down procedures correctly. This is to

ensure that the experiment can be progress successfully. #ext is make sure reactor does not

have any leaks and valve closed and opened as needed. ll the valve must be controlled

carefully and slowly when adusting the flow rate to obtain (.)( 01min. 3t is to make sure

flow rate will stabili4e and the experiment will run smoothly and the result will be obtained

accurately. The titration process must be repeated for two or three times due to the errors

which is mostly came from the titration process. ll the apparatus that are been used in 2ack

Titration must be clean before proceed the next step and rinse after use it to make sure that it

will not affect the result. ue to saving the time used for finishing this experiment+ two

groups can be divided for conducting the CSTR while others carry out the back titration

process.

APPENDICES

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Figure 6$

Retort stand with burette which Figure 7$ *easuring cylinder

been used for back titration

Figure 8$ !ydrochloric acid "!Cl% Figure 9$ Sodium !ydroxide

"#a$!%

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cstr joe's

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