continuos stirred tank reactor

Table of Contents

ABSTRACT................................................................................................................................3

INTRODUCTION......................................................................................................................4

OBJECTIVES.............................................................................................................................4

THEORY....................................................................................................................................5

APPARATUS& MATERIALS..................................................................................................8

PROCEDURE.............................................................................................................................9

RESULTS.................................................................................................................................10

CALCULATIONS....................................................................................................................15

DISCUSSION...........................................................................................................................17

CONCLUSION.........................................................................................................................18

RECOMMENDATIONS..........................................................................................................18

REFERENCES.........................................................................................................................19

APPENDIX

ABSTRACT/SUMMARY

The objectives of the experiment were to study the effect of temperature on reaction constant, k

of the saponification reaction between NaOH and ethyl acetate and also to determine the

activation energy of saponification. The reaction rate, rA was measured throughout 5 minutes

interval for 25 minutes at temperature of 30, 40, 50 and 60 °C. Then the samples were titrated to

determine the reactions that occur in the reactor. The samples were taken for every 5 minutes for

all temperatures. The reaction constant, k was obtained from slope of graph of 1/Ca vs. time. At

30, 40, 50 and 60 °C, the reaction constant, k was 5.9447, 5.4616, 9.7958 and 14.769 Lmol-1min-1

respectively. The results can be referring to table 1 to table 4 for each temperature. The results

obtained were according to the theory but for temperature 40°C, some error has occurred because

of mishandling the sample. For the second objective, the activation energy was the slope obtained

by comparing the equation of the straight line from the graph to the equation of ln k= -E a/(RT) +

ln A as we can get from figure 7, graph of ln k vs. 1/T the activation energy was +4.2269 kJ . All

the objectives were achieved. The values of the reaction constant were obtained and the

activation energy was calculated. The experiments were supposed to be conducted carefully so

that the results obtained for calculation are correct.

2

INTRODUCTION

Reactor is one of the most important parts in industrial sector. Reactor is equipment that changes

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

economical. One of criteria to choose or to design a good reactor is to know the effectiveness of

the reactor itself. There a many types of reactor depending on the nature of the feed materials and

products. One of the most important we need to know in the various chemical reaction was the

rate of the reaction.

By studying the saponification reaction of ethyl acetate and sodium hydroxide to form

sodium acetate in a batch and in a continuous stirred tank reactor, we can evaluate the rate data

needed to design a production scale reactor.

A stirred tank reactor (STR) may be operated either as a batch reactor or as a steady state

flow reactor (CSTR). The key or main feature of this reactor is that mixing is complete so that

properties such as temperature and concentration of the reaction mixture are uniform in all parts

of the vessel. Material balance of a general chemical reaction described below. The conservation

principle requires that the mass of species A in an element of reactor volume dV obeys the

following statement:

(Rate of A into volume element) - (rate of A out of volume element) + (rate of A produced

within volume element) = (rate of A accumulated within vol. element)

OBJECTIVES

The objectives of this experiment are:

1. To determine the effect temperature i=on reaction rate constant, k for batch reaction.

2. To determine the activation energy of saponification.

3

THEORY

IDEAL STIRRED-TANK REACTOR

A stirred-tank reactor (STR) may be operated either as a batch reactor or as a steady-state

flow reactor (better known as Continuous Stirred-Tank Reactor (CSTR)). The key or main

feature of this reactor is that mixing is complete so that properties such as temperature and

concentration of the reaction mixture are uniform in all parts of the vessel. Material balance of a

general chemical reaction is described below.

The conservation principle required that the mass of species A in an element of reactor volume

∆V obeys the following statement:

Rate of

A

Rate of

A Rate of A Rate of A

into - out of + produced =

Accumulate

d

volume volume

within

volume

within

volume

elemen

t

elemen

t element Element

BATCH STIRRED-TANK REACTOR (BSTR)

In batch reactions, there are no feed or exit streams and therefore equation (1) can be simplified

into:

Rate of A Rate of A

produced =

accumulate

d

within

volume

within

volume

4

element element

The rate of reaction of component A is defined as:

-rA = 1/V (dNA/dt) by reaction = [moles of A which appear by reaction]

[unit volume] [unit time]

By this definition, if A is a reaction product, the rate is positive; whereas if it is a reactant which

is consumed, the rate is negative.

Rearranging equation,

(-rA) V = NAO dXA

dt

Integrating equation gives,

t = NAO ∫ dXA__

(-rA)V

where t is the time required to achieve a conversion XA for either isothermal or non-isothermal

operation.

Ca

5

Area = t

1/-rA

EFFECT OF TEMPERATURE ON RATE OF REACTION

As we increase the temperature the rate of reaction increases. This is because, if we heat a

substance, the particles move faster and so collide more frequently. That will speed up the rate of

reaction. Collisions between molecules will be more violent at higher temperatures. The higher

temperatures mean higher velocities. This means there will be less time between collisions. The

frequency of collisions will increase. The increased number of collisions and the greater violence

of collisions result in more effective collisions. The rate for the reaction increases. Reaction rates

are roughly doubled when the temperature increases by 10 degrees Kelvin.

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:

C r3

r2

r1

6

T

APPARATUS AND MATERIALS

Apparatus

1. Continuous stirred tank reactor (Model BP:100)

Figure 1: CSTR

2. Stopwatch

3. Beaker

4. Pipet

5. Volumetric cylinder

Material

1. 0.1M NaOH

2. 0.1M Ethyl acetate

3. 0.25M HCl

7

PROCEDURE

1. General start-up procedures are perform earlier.

2. Then, overflow tube was adjusted to give a working volume of about 2.5 liters. Pump P1

was switched on and pumping 1.25 liters of 0.1 M of ethyl acetate from the feed pump

into the reactor. Then, stirrer is switched on at a medium speed follow by the heater which

the reaction temperature was set at room temperature of 26oC.

3. Consequently, switched on Pump P2 with the valve was set at maximum flow rate and

pump 0.1 M NaOH into the reactor at same volume of ethyl acetate, 1.25 liters. As soon

as the level of the reactants reached 2.5 liters, switched off Pump P2 and the timer starts

immediately at t0.

4. At the same time, 25 ml of 0.25 M HCl was prepared in a flask to quench with the

sample.

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

valve and immediately quench the sample with prepared HCL solution.

6. Then, the sample was titrated with 0.1 M NaOH under the hood, to determine the amount

of unreacted HCL in the sample. 3 drops of phenolphthalein was added into the solutions

as prior to the titration.

7. Step 4 to 6 was repeated for reaction times 5, 10, 20, 25 minutes.

8. Step 1 to 7 was repeated for temperatures of 40, 50 and 60oC.

9. All switched are turned off after the experiment done and general shut – down procedure

was done immediately.

8

RESULT

Temperature = 30°C

Table 1

Time (min)

Volume of

titrating NaOH

(mL),V1

Volume of

unreacted quenching HCl, V2

(mL)

Volume of HCl reacted

with NaOH in sample, V3 (mL)

Moles of HCl

reacted with

NaOH in sample, n1 (mol)

Moles of unreacted NaOH in sample, n2

(mol)

Concentra-tion of

unreacted NaOH in the reactor, Ca

(M)

Conversion of NaOH

in the reactor, X

(%)

1/Ca

1 17 6.8 3.2 0.0008 0.0008 0.016 68 62.5

5 18.7 7.48 2.52 0.00063 0.00063 0.0126 74.879.3650

8

10 19.7 7.88 2.12 0.00053 0.00053 0.0106 78.894.3396

2

15 21.3 8.52 1.48 0.00037 0.00037 0.0074 85.2135.135

1

20 22.1 8.84 1.16 0.00029 0.00029 0.0058 88.4172.413

825 22.5 9 1 0.00025 0.00025 0.005 90 200

9

0 5 10 15 20 25 300

50

100

150

200

250

f(x) = 5.94470580645161 x + 48.6593264516129R² = 0.980458268959379

1/Ca vs. time(min)

time (min)

1/Ca

Figure 2: graph of 1/Ca vs. time (min)

Rate constant, k (Lmol-1min-1) = 5.9447

Temperature = 40°C

Table 2

Time (min)

Volume of titrating NaOH (mL),V1

Volume of unreacted quenching HCl, V2

(mL)

Volume of HCl reacted with NaOH in sample, V3 (mL)

Moles of HCl reacted with NaOH in sample, n1

(mol)


(mol)

Concentra-tion of unreacted NaOH in the reactor, Ca

(M)

Conversion of NaOH in the reactor, X (%)

1/Ca

1 18 7.2 2.8 0.0007 0.0007 0.014 72 71.428575 19.5 7.8 2.2 0.00055 0.00055 0.011 78 90.9090910 20.6 8.24 1.76 0.00044 0.00044 0.0088 82.4 113.636415 21.1 8.44 1.56 0.00039 0.00039 0.0078 84.4 128.205120 22 8.8 1.2 0.0003 0.0003 0.006 88 166.666725 22.6 9.04 0.96 0.00024 0.00024 0.0048 90.4 208.3333

10

0 5 10 15 20 25 300

50

100

150

200

250

f(x) = 5.46164008064516 x + 60.6824256451613R² = 0.970054992598211

1/Ca vs time (min)

time (min)

1/Ca



Temperature = 50°C

Table 3

Time (min)

Volume of titrating NaOH (mL)


(mL)



(mol)


(mol)

Concentra-tion of unreacted NaOH in the reactor, Ca (M)


1/Ca

1 17.8 7.12 2.88 0.00072 0.00072 0.0144 71.2 69.444445 20.3 8.12 1.88 0.00047 0.00047 0.0094 81.2 106.38310 21.6 8.64 1.36 0.00034 0.00034 0.0068 86.4 147.058815 22.5 9 1 0.00025 0.00025 0.005 90 20020 22.9 9.16 0.84 0.00021 0.00021 0.0042 91.6 238.095225 23.4 9.36 0.64 0.00016 0.00016 0.0032 93.6 312.5

11

0 5 10 15 20 25 300

50

100

150

200

250

300

350

f(x) = 9.795775 x + 54.8337500000001R² = 0.990286626183072

1/Ca vs. time (min)

time (min)

1/Ca



Temperature = 60°C

Table 4

Time (min)

Volume of titrating NaOH (mL)


(mL)



(mol)


(mol)

Concentra-tion of unreacted NaOH in the reactor, Ca (M)


1/Ca

1 19.2 7.68 2.32 0.00058 0.00058 0.0116 76.8 86.20695 21.1 8.44 1.56 0.00039 0.00039 0.0078 84.4 128.205110 22.4 8.96 1.04 0.00026 0.00026 0.0052 89.6 192.307715 22.9 9.16 0.84 0.00021 0.00021 0.0042 91.6 238.095220 23.5 9.4 0.6 0.00015 0.00015 0.003 94 333.333325 23.9 9.56 0.44 0.00011 0.00011 0.0022 95.6 454.5455

12

0 5 10 15 20 25 300

50100150200250300350400450500

f(x) = 14.769162983871 x + 51.7062188709678R² = 0.967787505305028

1/Ca vs. time (min)

time (min)

1/Ca



0 5 10 15 20 25 300

50

100

150

200

250

300

350

400

450

500

f(x) = 14.769162983871 x + 51.7062188709678R² = 0.967787505305028

f(x) = 9.795775 x + 54.8337500000001R² = 0.990286626183072

f(x) = 5.46164008064516 x + 60.6824256451613R² = 0.970054992598211f(x) = 5.94470580645161 x + 48.6593264516129R² = 0.980458268959379

1/Ca vs. time (min)

T = 30 oC"Linear (T = 30 oC")

time (min)

1/Ca

Figure 6: graph of 1/Ca vs. time (min) for 30, 40, 50 and 60 °C

13

0.016 0.018 0.02 0.022 0.024 0.026 0.028 0.03 0.032 0.0340

2

4

6

8

10

12

14

16

f(x) = − 508.412436115843 x + 21.0675703577513R² = 0.680163068661989

ln K vs. 1/T

1/T

ln K

Figure 7: graph of ln K vs. 1/T

SAMPLE OF CALCULATION

Volume of sample, Vs = 50 mL

Concentration of NaOH in feed vessel, Ca,f = 0.1 M

Volume of HCl for quenching, VHCl,s = 10 mL

Concentration of HCL in standard solution, CHCl,s = 0.25 M

At temperature = 30 °C

Concentration of NaOH entering the reactor, CNaOH,0 = (CNaOH,f) / 2

= 0.1 mol/L / 2

= 0.05 mol/L

Volume of unreacted quenching HCl, V2 = (CNaOH,s / CHCI,s) x V1

= (0.1 / 0.25) x 17

= 6.8 mL

14

Volume of HCl reacted with NaOH in sample, V3 = VHCl,s – V2

= 10 –6.8

= 3.2 mL

Moles of reacted HCl with NaOH in sample, n1 = (CHCI,s x V3 ) / 1000

= (0.25 x 3.2) / 1000

= 0.0008 mol

Moles of unreacted NaOH in sample, n2 = n1

= 0.0008 mol

Conc. of unreacted NaOH in the reactor, Ca = (n2 / Vs) x 1000

= 0.0008 / (50/1000)

= 0.016 mol/L

Conversion of NaOH in the reactor, X = (1 – Ca / Ca0 ) x 100%

= ( 1- (0.016 / 0.05) x 100%

= 68 %

To determine the rate constant, k

From the graph of 1/Ca vs. T plotted, the equation of straight line obtained is compared with

equation 1/Ca = kt + 1/Cao

From figure 5, y = 5.9447x + 48.659

Compared to equation, 1/Ca = kt + 1/Cao

The value of k = 5.9447 Lmol-1min-1.

Rate of reaction, -rA = kCA2

= (5.9447)(0.016)2

= 1.5218 x 10-3

15

To determine the activation energy, Ea

According to the graph plotted in Figure 6, the equation of straight line obtained was

Y = - 508.41 x + 21.068

Comparing to equation ln k=−E a /(RT )+ln A

−Ea

R=−508 .41

Ea=508.41× 8.314

¿4226.92 J

¿4.2269 kJ

DISCUSSION

The objective of the experiment was to study the effect of temperature on reaction constant, k of

the saponification reaction between NaOH and ethyl acetate. The reaction rate, rA was measured

throughout 5 minutes interval for 25 minutes at temperature of 30, 40, 50 and 60 °C.

From Arrhenius’s equation, k = Ae-E/RT it show that the temperature has an effect to the

reaction rate constant. It states that when the rate constant doubles, so wills the rate of reaction.

The higher the temperature the faster the molecules move producing much more kinetic energy

than normal. More collision is happen in order for a reaction to occur and thus larger fraction of

molecules to provide the activation energy needed for the reaction. Activation energy, Ea is the

minimum energy needed for the reaction to occur.

In the experiment, the reaction constant, k was obtained from slope of graph of 1/Ca vs.

time. At 30, 40, 50 and 60 °C, the reaction constant, k was 5.9447, 5.4616, 9.7958 and 14.769

16

Lmol-1min-1 respectively. From the graph plotted it can be seen that the reaction constant is

increases with temperature except at temperature 40 °C. This was happen because of the

misconduct procedure during the experiment where the sample was not titrated immediately. The

sample collected from the reactor supposed to be titrated immediately under the hood to

determine the amount of unreacted HCL in the sample.

The activation energy was the slope obtained by comparing the equation of the straight

line from the graph to the equation of ln k= -Ea/(RT) + ln A. From figure 7, graph of ln k vs. 1/T

the activation energy was +4.2269 kJ . The reaction was endothermic in which the reaction

absorb energy to form bonds in the reaction. The bonds of the products are higher than the bonds

of the reactants.

CONCLUSION

All in all, all the objectives were achieved. The values of the reaction constant were obtained and

the activation energy was calculated. The experiments were supposed to be conducted carefully

so that the results obtained for calculation are correct. As an example for temperature 40 °C. We

should know that the sample should be titrated immediately because it may react with the

surroundings. All the mistakes can be corrected for the next experiment for the next time.

RECOMMENDATIONS

1. Make sure all the flask, apparatus that involved in titration process is cleaned from

chemicals because it will affect the titration results.

2. Wait until the system stable before taking the reading, because sometimes, the system is

not well reacted, but students already take the readings.

17

3. Make sure all valves are in their right positions before starting the experiments to prevent

any damages into the equipment.

4. Before taking the sample, make sure flush the products a little bit, just to ensure there are

no previous product in the outlet stream

5. Do not let the temperature shoot higher or lower than the temperature needed. Make sure

the temperatures are well controlled.

REFERENCES

Levenspiel, O, Chemical Reaction Engineering, John Wiley, 1972

Robert H.Perry, Don W.Green, Perry’s Chemical Engineers’ Handbook, McGraw

Hill,1998.

Smith,J.M, Chemical Engineering Kinetics, McGraw Hill, 1981.

Rate Constants and The Arrhenius Equation. Retrieved on OCTOBER 30, 2013 from

http://www.chemguide.co.uk/physical/basicrates/arrhenius.html

APPENDIX

Please refer to the next page.

18

continuos stirred tank reactor

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