Cstr Batch Grup 1

7/27/2019 Cstr Batch Grup 1

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ABSTRACT

Data obtained in batch reactors can be well defined and used to predict performance of larger

scale, continuous-flow reactors. The saponification reaction between NaOH and Et(ac) done

in a batch reactor at different temperature.The effect of temperature on the reaction rateconstant, k in CSTR batch operation was conducted with the addition of back titration process

in order to determine the realtionship between the time, the concentration of unreacted sodium

hydroxide, CNaOH, the rate law and the reaction rate constant at three temperatures, 26oC, 40oC

and 50oC. It was concluded that the higher the temperature of the reaction, the higher the

reaction rate constant by the means of the 1:4 ratio of rise in temperature and the reaction

rate.The longer the reaction is allowed to take place, the slower the reaction proceeds.

INTRODUCTION

A process in which all the reactants are added together at the beginning of the process and

products removed at the termination of the reaction is called a batch process. In this process,

all the reagents are added at the commencement and no addition or withdrawal is made while

the reaction is progressing .

In the majority field of chemical processes, the reactor vessel in which the reaction process

take place is the key component of the equipment.The design of the reactors is very important

to the success of the production.Batch reactors are used widely in industry at all scales. These

commonly provided with agitation and a method of heat transfer (usually by coils or external

jacket). This type of reactor is primarily employed for relatively slow reactions of several

hours duration, since the downtime for filling and emptying large equipment can be

significant.

The stirred tank batch reactor is still the most widely used reactor type both in the laboratory

and industry. Batch reactors may be preferred for small-scale production of high priced

products, particularly if many sequential operations are carried out to obtain high product

yields. Batch reactors may also be justified when multiple, low volume products are produced

in the same equipment or when continuous flow is difficult, as it is with highly viscous or

sticky solids-laden liquids. Because residence time can be more uniform in batch reactors,

better yields and higher selectivity may be obtained than with continuous reactors.
http://wiki.biomine.skelleftea.se/wiki/index.php?title=Yield&action=edithttp://wiki.biomine.skelleftea.se/wiki/index.php?title=Yield&action=edit


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OBJECTIVE

To measure the rate of saponification reaction between NaOH and ethyl acetate, using a batch

reactor as function of temperature and determine the rate law constants.

THEORY

Batch reactors are often used because of their convenience mainly in laboratory

experimentation. Data obtained in batch reactors can be well defined and used to predict

performance of larger scale, continuous-flow reactors

The reaction chosen in this experiment is the saponification of ethyl acetate (EtOAc) with

dilute sodium hydroxide (NaOH):

NaOH + EtOAc NaOAc + EtOH

This type of reaction is called a saponification because of its importance in themanufacture of

soap.The reaction is relatively slow and the changing ester concentration can be followed

quite easily by analyzing samples from the reaction mixture every few minutes. The second

order rate constant is determined by integrated rate law method:

Assuming the reaction to be a simple, irreversible, second order process, then the rate law for

a batch process may be written;

where is concentration of NaOH and is concentration of ethyl acetate.

Suppose that the concentrations of the ester and hydroxide are equimolar at the start of the

experiment and equal to CA0 mol/dm3, and that at some time tlater,both the NaOH and ethyl

acetate concentration have fallen to CA. Therefore,

Intergrating the equation give;


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Where is concentration of unreacted NaOH, is initial concentration, k is rate constant(L/mol.s) and tis time.

A plot of 1/CA against tgive a straight line with the slope t, k value.

In any single homogenous reaction, temperature, composition, and reaction rate are uniquely

related. They can be represented graphically in one of three ways as shown in Figure 8 below:

Concentration vs Time Rate appearence vs Time Rate appearence vs Concentration

Rate, k vs Temperature


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APPARATUS

1. Stopwatch2. 100mL Beakers

3. 100mL graduated cylinder

4. Burette and retort stand5. 250 mL conical flasks6. Continuous stirrer tank reactor (SOLTEQ model:BP100)

Chemicals

1. 0.1 M sodium hydroxide

2. 0.1 ethyl acetate3. 0.25M hydrochloric acid

4. Phenolphtalein

Figure A: Continuous stirrer tank reactor (SOLTEQ model:BP100)


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METHODOLOGY

Effect of Temperature on Reaction Rate Constant

1. General start-up procedures were performed. (See Appendix A)

2. Prior to the start of the batch reactor experiment, the overflow tube was adjusted to

give a working volume of about 2.5 liters. Pump P1 was switch on and 1.25 liters of

0.1M of ethyl acetate from the feed were pumped into the reactor. The stirrer was

switched on at a medium speed followed by the heater which the reaction temperature

was set at room temperature of 26oC.

3. Consequently, pump P2 was switched on with the valve was set at maximum flowrate

where as the 0.1M NaOH pumped into the reactor at the same volume of ethyl acetate,

1.25 liters. As soon as the level of the reactants reached 2.5 liters, pump P2 were

switched off and the timer starts immediately at t0.

4. At the same time, 25ml of 0.25 M HCl was prepared in a flask ready for quenching

process with the collected sample.

5. After 1 minute of reaction time, 100ml sample was collected by opening the sampling

valve and the sample was immediately quenched with the prepared HCl solution.

6. The sample was then titrated with 0.1M NaOH under the hood, to determine the

amount of unreacted HCl in the sample. Three drops of phenolphthalein were added

prior to the titration.

7. The steps 4 to 6 were repeated for reaction times of 5, 10, 20 and 25 minutes.

8. Subsequently, the steps 1 to 7 were repeated for temperatures of 40 and 50oC.

9. All the switches were switch off after the experiment finished and general shut-down

procedures were done, consequently.


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RESULT

Temperature: 26C

Time

(min)

Volume of

NaOH titrated

(mL)

Conversion,

X

Concentration of

unreacted NaOH in

reactor, CA

1/Ca -rA

1 40 0.775 0.0225 44.44 0.0070

5 45 0.825 0.0175 57.14 0.0042

10 51 0.885 0.0115 86.96 0.0018

15 55 0.925 0.0075 133.33 0.0008

20 58 0.955 0.0045 222.22 0.0003

25 60 0.975 0.0025 400 0.0001

Temperature: 40C

Time

(min)

Volume of

NaOH titrated

(mL)

Conversion,

X

Concentration of

unreacted NaOH in

reactor, CA

1/Ca -rA

1 53 0.905 0.0095 105.26 0.0058

5 57 0.945 0.0055 181.82 0.0020

10 60 0.975 0.0025 400 0.0004

15 61 0.985 0.0015 666.67 0.0001

20 61.8 0.989 0.0007 1428.57 0.0000

25 62.5 1 0 0.0000


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Temperature: 50C

Time

(min)

Volume of

NaOH titrated

(mL)

Conversion,

X

Concentration of

unreacted NaOH in

reactor, CA

1/Ca -rA

1 56.5 0.947 0.0060 166.67 0.0039

5 61.2 0.987 0.0013 769.23 0.0002

10 61.8 0.993 0.0007 1428.57 0.00005

15 61.9 0.994 0.0006 1666.67 0.00004

20 62.5 1 0 0

25 62.5 1 0 0

Figure 1:Concentration of NaOH versus Time at specific temperature

-0.005

0

0.005

0.01

0.015

0.02

0.025

0 5 10 15 20 25 30

CNaOH

Time

50

40

26


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Figure 2: The reciprocal of Concentration of NaOH versus Time at specific temperature

Figure 3: The rate of dissapearance of NaOH,-rA versus Time at specific temperature

y = 13.75x - 16.88

y = 64.766x - 98.531

y = 108.8x + 164.0

0

200

400

600

800

1000

1200

1400

1600

1800

2000

0 5 10 15 20 25 30

1/CA

Time,min

26

40

50

-0.001

0

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0.008

1 5 10 15 20 25

-rA

Time, min

26

40

50


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Figure 4: The rate of dissapearance of NaOH,-rA versus concentration of NaOH at specific

temperature

Figure 5: The reaction rate constan,k versus Temperature

-0.001

0

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0.008

0 0.005 0.01 0.015 0.02 0.025

-rA

Concentration of NaOH (mol/L)

26

40

50

y = 3.9401x - 1165.6

0

20

40

60

80

100

120

295 300 305 310 315 320 325

rateconstant,k

Temperature (K)


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CALCULATIONS

Sample calculation for conversion of NaOH in the reactor, X for temperature = 26C at 1

minute

Unknown quantity:

Concentration of NaOH in the reactor = CNaOH = ? mol/L

Known quantities:

Volume of samples = VS = 100 mL

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

Volume of HCl for quenching = VHCl,s = 25 mL

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

Volume of titrated of NaOH = V1 = 40 mL

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

Calculations:

Conc. Of NaOH entering the reactor, CNaOH, 0 = (CNaOH, f) = (0.1) = 0.05 mol/L

Volume of unreacted quenching HCl, V2 =

xV1 =

x 40= 16 mL

Vol. of HCl reacted with NaOH in sample, V3 = VHCl,s - V2 = 2516 = 9 mL

Moles of HCl reacted with NaOH in sample, n1 = CHCl s x V3 = 0.25 x 0.009

= 2.25x10-3 mol

Moles of unreacted NaOH in sample, n2 = n1 = 2.25x10-3 mol

Conc. of unreacted NaOH in reactor, CNaOH = (n2/ Vs) x 1000 = (2.25x10-3 /100) x1000

= 0.0225 mol/L

Conversion of NaOH in the reactor, X = (1-) = (1-

) = 0.55


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DISCUSSION

Continuous stirred tank reactor (CSTR) is the experiment which to study the effect of

temperature on the reaction rate constant, k in standard batch operating process. The aim

involves a saponification reaction between sodium hydroxide, NaOH and ethyl acetate which

were conducted at three different temperatures, room temperature which was 26oC, 40 oC and

50 oC.

According to the figure 1, as the time of reaction increases at the same temperature,

the concentration of the unreacted NaOH, CNaOH decreases.Based on the trendline of the

graph, at higher temperature, the rate of decreasing of concentration of NaOH is faster. Thus,

by means of the back titration calculation, the CNaOH was obtained from the experiment were

greatly effects on each temperature. At higher temperature of 40

o

C and 50

o

C, theconcentration of NaOH appear 0 because the conversion was completed

The rate reaction constant however, was determined by the figure 2 as the slope of the

straight line at each corresponding temperature. The, k at 26oC, 40oC and 50oC are

13.75L/mol.minutes, 64.766L/mol.minutes and 108.80L/mol.minutes, respectively. As the

rule of thumb, a 10oC in temperature causes the reaction rate constant to double. Though in

this case, from that figure, the reaction rate constant is 2.4 times from the calculated 30oC to

40oC however further temperature at 50oC was 1.7 times of the reaction rate constant at 40 oC.

(

)

( )

Sample calculation of reaction rate constant, k for temperature = 26C at 1 minute:

= 54.3210

Sample calculation of rate of reaction, -rA for temperature = 26C at 1 minute :

= 13.75(0.0225)2 = 0.0070Where k value is determined from the slope of the graph of the reciprocal of Concentration

of NaOH versus Time at specific temperature.


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The slight error in the experiment was to install the cooling water when the process undergo

at 50oC which leads to decrease of 5oC of the desired temperature.

While in figure 3, it shows the relationship between the rates of disappearance of

NaOH with the time increment. At the start of the experiment of 26oC of temperature, the rate

of disappearance of NaOH also called the rate law was 0.007. The rate law decreases as the

time increases to 25 minutes of reaction. Comparing to the trendline at different

temperature,at higher temperature, the rate of disappearance of NaOH is faster to achieve the

maximum conversion. Once the sodium hydroxide entered the reactor with half full of ethyl

acetate, the reaction already started thus the rate of disappearance of sodium hydroxide is high

at this starting period. At that period, the reactions already occur as time proceeds is not

considered could lead to inaccurate data taken.

The relation between the rate of disappearance of NaOH with respect to time shown in figure

4. As the concentration of NaOH increase, the rate of disappearance of NaOH increase.

Otherwise,the rate of dissapearence of NaOH decrease as there is more product form can

reduce the contact between the reactants of NaOH and ethyl acetate.

Figure 5 illustrates the relationship between the rate constant and temperature.From that

figure, it shown that the reaction rate increase as the temperature increase. This is because the

effect of temperature to increase the rate of reaction by lowering the activation energy and

increase the effective collision between molecules of reactants. Thus, the reaction become

faster.

CONCLUSION

In the experiment, the evaluation on the effect of temperature on the reaction rate constant, k

in CSTR of batch process where crucial in order to determine the trend of these two properties

in chemical reaction engineering. A batch titration process was also conducted to determine

the concentration of unreacted sodium hydroxide values thus in addition to verify the values,

the conversion also calculated. It was concluded at the higher the temperature of reaction,

more reactions were precede at higher reaction rate resulting decreases of CNaOH throughout

the time period. Though there was a slight contrast between the result of the experiment and

the theory where as in the theory it stated that a 10

o

C rise in temperature causes a reaction rate


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constant to double. However, the values of rate constant from 30 to 40 and 40 to 50 oC are 2.4

and 1.7 respectively are appear double.

RECOMMENDATIONS

It is impossible to get the precise result same as the imaginary result without any errors in the

experiment but possible to minimize the error that exists in this experiment. There are some

recommendations and precautions need to be considered in order to ensure that the result of

experiment is accurate.

i. The sample needs to be added with 0.25 M of Hydrochloric Acid quickly in order to

stop the reaction.

ii. Make sure the temperature controller was set for desired value before run the pump

P2.

iii. In order to get more accurate data, make sure that you not use the same conical flask

in order to keep away from contamination of previous sample

iv. Make sure to cool down the reactor when the temperature reaches 45C to avoid the

reactor becomes too hot.

v. The experiment can be repeated and the value of average reaction time can be taken to

make more precise value. This will having a better data than only conducting the

experiment only once..

REFERENCES

1. Frogler, H.S., (2006). Elementary of Chemical Reaction Engineering (4th Edition).

Prentice Hall.

2. CSTR in series Model: BP 107. Retrieved on 15 November 2011 from

http://www.solution.com.my/pdf/BP107%28A4%29.pdf

3. Hafiz Muhammad Zaheer Aslam (2006). Chemical Reaction Engineering Lab.

Retrieved on 15November 2011 from

http://www.uet.edu.pk/export/sites/UETWebPortal/faculties/facultiesinfo/chemical/La

bs/ChemicalReactionEngineering.pdf

4. Prof. William H. Green (2007).Lecture 5: Continuous Stirred Tank Reactors

(CSTRs). Retrieved on 15

October 2011 from http://ocw.mit.edu/courses/chemical-
http://ocw.mit.edu/courses/chemical-engineering/10-37-chemical-and-biological-reaction-engineering-spring-2007/lecture-notes/lec05_02212007_g.pdfhttp://ocw.mit.edu/courses/chemical-engineering/10-37-chemical-and-biological-reaction-engineering-spring-2007/lecture-notes/lec05_02212007_g.pdf


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engineering/10-37-chemical-and-biological-reaction-engineering-spring-2007/lecture-

notes/lec05_02212007_g.pdf

5. Smith, J.M., Chemical Engineering Kinetics, McGraw Hill Book Co., Singapore,

1981.

6. Fogler, H.S., Elements of Chemical Reaction Engineering, Prentice Hall, New Jersey,

1992.

7. Levenspiel, O., Chemical Reaction Engineering, Third ed., Wiley Int. Co., New York,

1999.
http://ocw.mit.edu/courses/chemical-engineering/10-37-chemical-and-biological-reaction-engineering-spring-2007/lecture-notes/lec05_02212007_g.pdfhttp://ocw.mit.edu/courses/chemical-engineering/10-37-chemical-and-biological-reaction-engineering-spring-2007/lecture-notes/lec05_02212007_g.pdfhttp://ocw.mit.edu/courses/chemical-engineering/10-37-chemical-and-biological-reaction-engineering-spring-2007/lecture-notes/lec05_02212007_g.pdfhttp://ocw.mit.edu/courses/chemical-engineering/10-37-chemical-and-biological-reaction-engineering-spring-2007/lecture-notes/lec05_02212007_g.pdf

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Cstr Batch Grup 1