Continuos Stirred Tank Reactor
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Transcript of 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)
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 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
Figure 3: graph of 1/Ca vs. time (min)
Rate constant, k (Lmol-1min-1) = 5.4616
Temperature = 50°C
Table 3
Time (min)
Volume of titrating NaOH (mL)
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 17.8 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
Figure 4: graph of 1/Ca vs. time (min)
Rate constant, k (Lmol-1min-1) = 9.7958
Temperature = 60°C
Table 4
Time (min)
Volume of titrating NaOH (mL)
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 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
Figure 5: graph of 1/Ca vs. time (min)
Rate constant, k (Lmol-1min-1) = 14.769
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