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7/30/2019 Exp5 Teo Resultsanddiscussion
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1. THEORY
1.1 Classification of Reactors
Chemical reactors may be operated in batch, semi-batch, or continuous modes.
When a reactor is operated in a batch mode, the reactants are charged, and the vessel is closed
and brought to the desired temperature and pressure. These conditions are maintained for the time
needed to achieve the desired conversion and selectivity, that is, the required quantity and quality
of product. At the end of the reaction cycle, the entire mass is discharged and another cycle is
begun. Batch operation is labor-intensive and therefore is commonly used only in industries
involved in limited production of fine chemicals, such as pharmaceuticals.
In a semi-batch reactor operation, one or more reactants are in the batch mode, while the other
reactant is fed and withdrawn continuously.
In a chemical reactor designed for continuous operation, there is continuous addition to, and
withdrawal of reactants and products from, the reactor system. [1]
1.2 Design Equations of Reactors
1.2.1 Batch Reactors
General Mole Balance on System Volume V
InOut + Generation = Accumulation
(1)
There is no inflow or outflow during the process in batch reactors.
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Assumptions
Well mixed
(2)
(3)
Rearranging and integrating with limits
t = 0 NA = NA0
t = t1 NA = NA1
(4)
Multiplying by -1 for the reagent A that becomes consumed and changing the limits of
integration
(5)
This equation gives the time t1 necessary to reduce the number of moles in a batch reactor from
NA0 initially to NA1. [2]
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1.2.2 Perfect Mixture Continuous Reactors
Assumptions
Steady State
(6)
Well mixed
(2)
(7)
(8)
Figure 1.1. CSTR diagram [3]
This equation gives the CSTR volume necessary to reduce the entering molar flow rate from FA0
to the exit molar flow rate FA1 when species A is disappearing at a rate -rA. [2]
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1.2.3 Tubular Reactor Design
Figure 1.2 Cut through a tubular reactor showing (PFR) showing the volume part [4]
Steady State
(6)
(9)
Differentiate with respect to V
(10)
(11)
Rearranging and integrating between
V = 0 FA = FA0
V = V1 FA = FA1
(12)
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This equation gives the PFR Volume, V1 necessary to reduce the entering molar feed rate from
FA0 to the exit molar feed rate FA1 by chemical reaction. [2]
Table 1.1 Reactor Mole Balances In Terms of Conversion [2]
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2. EXPERIMENTAL METHOD
2.1 The Aim of the Experiment
The aim of the experiment is to learn batch and CSTR systems, their working principles and
differences, investigation of the reaction rate constant and reaction order. The experiment was
also performed to understand how the reaction rate constant changes with temperature according
to Arrhenius Equation and also to learn how to find the conversion.
2.2 Equipment Description
2.2.1 Base Module and Interface
In this part, the necessary elements for the use of the diverse reactor modules were provided.
Constituted by;
Feeding circuits of reagents
Flow control system: Two dosing pumps two flowmeters of direct measure for the feeding
pumps and also another rotation meter to measure the flow of liquids.
Temperature control system
Data acquisition and process control system
Collecting circuit of products
2.2.2 Chemical Reactor Module in Liquid Phase
Pyrex-glass reactor insulated with its maximum capacity of 2 liters. Agitation system with speed
control helped the study of the influence of agitation in continuous or discontinuous system.
Conductivity cell with conductimeter connected to the electronic module and allowed measuring
the evaluation of the reaction in real time.
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2.2.3. Accessories used in the experiment
Ethyl acetate and Sodium hydroxide are necessary as chemical reagents, as laboratory materials
5L plastic cans, draining containers are needed and they are required as services 210 V /50 Hz.
Electric supply and water supply.
2.3 Experimental Procedure
2.3.1 Discontinuous Isothermal Operation (Batch System)
2.3.1.a Obtaining the reaction rate constant (k) and the reaction order ( ) with respect to
ethyl-acetate
In this experiment, firstly, computer controlled system was started and water was recirculated
until a constant flow was obtained. Thermal system was started and the desired working
temperature was set to 25 C. Sodium hydroxide valve was opened to the to reactorposition
and it was allowed 0.02M and 1 L solution to the reactor. When the desired amount of reactant
had been in the reactor, the valve was arranged to the recirculationposition. Then the stirrer
was started and waited for the temperature of 25 C. After that, ethyl-acetate valve was arranged
to the to reactor module and it was allowed 1L of 1M solution to the reactor and, the valve was
arranged to the recirculation position. When the conductivity had been stayed constant, the
reaction was finished. Then, the stirrer was closed and the reactor was emptied. Also experiment
was finished with clearing equipment with pure water.
2.3.1.b Variation of the kinetic constant with temperature, Arrhenius Equation
In the first part of experiment repeated in temperature of 35 C and k changing with temperature
was obtained according to Arrhenius Equation.
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2.3.2 Continuous Operation, CSTR System
In this part of the experiment, as in the first part, firstly, the program was started and the working
temperature was set to 25 C. An equal flow for both reactants was set and the system was kept in
recirculationposition. When a steady flow was achieved, the valve was turned to the to
reactorposition. After the reactant level had been reached the stirrers blades, the stirrer system
was started. The system was kept working for 1 hour. After that, the reactant valves were turned
to the recirculation position and the system was stopped.
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3. RESULTS AND DISCUSSION
3.1 Semi-batch/Batch System (25C)
For a semi-batch system, reaction was started with 1 L of 0,02 M NaOH solution in the reactor. 1
L of 1M CH3COOC2H5 solution was added gradually with constant flow rate to the reactor. By
the time conductivity values was recorded by computer program with 60 s intervals. End of the
reaction determined by observing stabilizing of conductivity values.
Ethyl Acetate was used as excess reactant in this process. Table 3.1 shows the moles and
concentration values of produced Sodium Acetate after the reaction ended.
Table 3.1 Stoichiometric Table
Species Initially Change
(moles)
Remaining
(moles)
Concentration
(mol/L)
Conversion
CH3COONa 0 0,0188 0,0188 0,0011 0,85
The data that was used in the experiment is shown below for 25C. The calculation methods can
be seen from sample calculations part in appendix. Colored rows shows when the reactor became
batch reactor (reaches 2 L volume).
Table 3.2 Experimental Value at 25C
Time
(s)
Conductivity
(mS)
Volume
(L)
CEtoNa(mol/L)
NEtoNa(mol)
NNaOH -
NEtoNa (mol)
CnaOH(mol/L)
(dCNaOH/dt)
(mol/L.s)
CNaOH. v/V
(mol/L.s)
60 3,525193115 1,06 0,0011 0,0012 0,0188 0,0178 -0,00010651 1,56529E-05
120 3,064170410 1,11 0,0031 0,0035 0,0165 0,0149 -9,7485E-05 1,24047E-05
180 2,223489746 1,17 0,0047 0,0055 0,0145 0,0124 -6,2676E-05 9,84172E-06
240 1,543054810 1,22 0,0056 0,0068 0,0132 0,0108 -3,9207E-05 8,17772E-06300 1,197494995 1,28 0,0059 0,0076 0,0124 0,0097 -2,9042E-05 7,05597E-06
360 1,052932251 1,33 0,0061 0,0081 0,0119 0,0089 -2,5054E-05 6,19281E-06
420 0,982966370 1,39 0,0062 0,0086 0,0114 0,0082 -2,2639E-05 5,46760E-06
480 0,934389404 1,44 0,0063 0,0091 0,0109 0,0076 -1,9508E-05 4,84355E-06
540 0,896102112 1,50 0,0064 0,0095 0,0105 0,0070 -1,9553E-05 4,30735E-06
600 0,868851929 1,56 0,0064 0,0100 0,0100 0,0064 -1,7867E-05 3,81803E-06
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660 0,832312744 1,61 0,0065 0,0105 0,0095 0,0059 -1,6634E-05 3,38885E-06
720 0,801241028 1,67 0,0066 0,0110 0,0090 0,0054 -1,5421E-05 3,00864E-06
780 0,773123657 1,72 0,0066 0,0114 0,0086 0,0050 -1,4729E-05 2,67225E-06
840 0,748850220 1,78 0,0067 0,0119 0,0081 0,0046 -1,2107E-05 2,37505E-06
900 0,729047791 1,83 0,0067 0,0123 0,0077 0,0042 -1,0662E-05 2,12779E-06
960 0,726464844 1,89 0,0067 0,0126 0,0074 0,0039 -1,0470E-05 1,91088E-06
1020 0,728982544 1,94 0,0067 0,0130 0,0070 0,0036 -9,7343E-06 1,71114E-06
1080 0,728025391 2,00 0,0067 0,0134 0,0066 0,0033 1,94869E-05 1,53110E-06
1140 0,727817871 2,06 0,0067 0,0138 0,0062 0,0030 -8,2316E-05 1,36604E-06
1200 0,726019226 2,11 0,0084 0,0178 0,0022 0,0010 -5,1990E-05 4,56037E-07
dCNaOH+CNaOH. v/V
(mol/L.s)
ln(-dCNaOH-
CNaOH. v/V)
ln(CNaOH)
(mol/L)
9,08615E-05 -9,306174448 -4,02607
8,50808E-05 -9,371909371 -4,20735
5,28340E-05 -9,848355786 -4,39000
3,10296E-05 -10,38056982 -4,52870
2,19860E-05 -10,72510525 -4,63178
1,88613E-05 -10,87839918 -4,71970
1,71717E-05 -10,97225038 -4,80343
1,46642E-05 -11,13010175 -4,88540
1,52453E-05 -11,09124220 -4,96498
1,40489E-05 -11,17296972 -5,04920
1,32449E-05 -11,23189482 -5,13335
1,24120E-05 -11,29684868 -5,21845
1,20570E-05 -11,32586692 -5,30423
9,73227E-06 -11,54006300 -5,39037
8,53373E-06 -11,67148392 -5,46954
8,55953E-06 -11,66846495 -5,54721
8,02320E-06 -11,73317305 -5,628621,01000E-06 -13,80217981 -5,71162
8,09504E-05 -10,42167336 -5,79829
5,15344E-05 -10,87326078 -6,86872
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Figure 3.1 Variations of Concentrations with Time
Obviously, meantime reaction is going on reactants (CH3COOC2H5 and NaOH) concentrations
are decreasing, and the products (CH3COONa and C2H5OH) concentrations are increasing with
time until equilibrium is achieved. Decrease in the CH3COOC2H5 is negligible. Because of it is
assumed excess reactant. This part of the experiment is done at approximately at 25 C.
Figure 3.2 Determination of the Reaction Order () and the Reaction Rate Constant (k)
0
0,005
0,01
0,015
0,02
0,025
0 500 1000 1500
Concentration
(mol/L)
Time (s)
NaOH
EtONa
y = 0,8528x - 6,6611
R = 0,3334
-16
-14
-12
-10
-8
-6
-4
-2
0
-8 -7 -6 -5 -4 -3 -2 -1 0
ln(-d
CNaOH+CnaOH.
v/V)
lnCNaOH
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ln(-dCNaOHCNaOH.v/V) and ln(CNaOH) values was calculated at the Table 3.2 to find the reaction
rate and reaction rate constant k from the semi -batch design equation. To calculate dCA/dt
values one of the differential methods (finite differential method) is used. From the slope of the
curve the reaction rate is determined. The reaction rate constant is determined by using the
intercept of x-coordinate.
T(oC) k Xfinal tfinal (min)
25 0,85 0,0965 0,85 35,45
It can be seen that at 25C reaction rate is found as 0, 85 and reaction rate constant is found as
0,0965. Theoretically reaction of ethyl acetate is first order and our result is acceptable accuracy.
Also reaction is assumed isothermally for this operation.
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3.2 Semi-batch/Batch System (35C)
To study the effect of temperature on reaction order and reaction coefficient, temperature value
changed 25oC to 35
oC. As in the first part of the experiment the reactor was filled with 1 L of
0,02 M NaOH solution, 1 L of 1M CH3COOC
2H
5solution was added to the reactor gradually.
Table 3.3 shows the moles and concentration values of produced Sodium Acetate after the
reaction ended.
Table 3.3 Stoichiometric Table
SpeciesInitally
(mol)
Changing
(mol)
Remaining
(mol)
Concentration
(mol/l)Conversion
CH3COONa 0 0,01367 0,01367 0,006478045 0,69
The data that was used in the experiment is shown below for 35C. The calculation methods can
be seen from sample calculations part in appendix. Colored rows shows when the reactor became
batch reactor (reaches 2 L volume).
Table 3.4 Experimental Value at 35C
Time
(s)
Conductivity
(mS)
Volume
(L)
CEtoNa(mol/L)
NEtoNa(mol)
NNaOH -
NEtoNa(mol)
CnaOH(mol/L)
(dCNaOH/dt)
(mol/L.s)
CNaOH.
v/V
(mol/L.s)
60 3,202790527 1,05556 1,11294E-09 1,17E-09 0,02 0,018947 -0,000126227 1,6620E-05
120 2,193194824 1,11112 0,002375520 0,002639 0,017361 0,015624 -9,66378E-05 1,3020E-05
180 1,539539062 1,16668 0,003913534 0,004566 0,015434 0,013229 -5,31839E-05 1,0499E-05
240 1,281099121 1,22224 0,004521628 0,005527 0,014473 0,011842 -3,47971E-05 8,9709E-06
300 1,170795654 1,27780 0,004781166 0,006109 0,013891 0,010871 -2,91156E-05 7,8772E-06
360 1,097239014 1,33336 0,004954240 0,006606 0,013394 0,010045 -2,54243E-05 6,9759E-06
420 1,042470459 1,38892 0,005083107 0,007060 0,012940 0,009317 -2,31883E-05 6,2109E-06
480 0,996847595 1,44448 0,005190455 0,007498 0,012502 0,008655 -2,02734E-05 5,5482E-06
540 0,963058899 1,50004 0,005269958 0,007905 0,012095 0,008063 -1,95520E-05 4,9770E-06
600 0,927184753 1,55560 0,005354368 0,008329 0,011671 0,007502 -1,75409E-05 4,4656E-06
660 0,899407104 1,61116 0,005419727 0,008732 0,011268 0,006994 -1,63068E-05 4,0192E-06
720 0,873949890 1,66672 0,005479626 0,009133 0,010867 0,006520 -1,49540E-05 3,6221E-06
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780 0,850325195 1,72228 0,005535214 0,009533 0,010467 0,006077 -1,49928E-05 3,2673E-06
840 0,821458862 1,77784 0,005603134 0,009961 0,010039 0,005646 -1,36099E-05 2,9408E-06
900 0,799355713 1,83340 0,005655142 0,010368 0,009632 0,005254 -1,28494E-05 2,6532E-06
960 0,781799927 1,88896 0,005696450 0,010760 0,009240 0,004891 -1,08725E-05 2,3976E-06
1020 0,776269531 1,94452 0,005709462 0,011102 0,008898 0,004576 -1,02030E-05 2,1789E-06
1080 0,772639404 2,00008 0,005718004 0,011436 0,008564 0,004282 -9,24329E-06 1,9821E-06
1140 0,772503357 2,05564 0,005718324 0,011755 0,008245 0,004011 -0,000450806 1,8067E-06
1200 0,772023804 2,11120 0,005719452 0,012075 0,007925 0,003754 -1,34033E-05 1,6463E-06
-dCNaOH-CNaOH.
v/V (mol/L.s)
ln(-dCNaOH- CNaOH.
v/V)ln(CNaOH)(mol/L)
0,00010961 -9,11861 -3,96609
8,3618E-05 -9,38926 -4,15893
4,2685E-05 -10,0617 -4,32533
2,5826E-05 -10,5641 -4,43612
2,1238E-05 -10,7597 -4,52168
1,8448E-05 -10,9005 -4,60063
1,6977E-05 -10,9836 -4,67596
1,4725E-05 -11,1260 -4,74958
1,4575E-05 -11,1362 -4,82047
1,3075E-05 -11,2448 -4,89253
1,2288E-05 -11,3069 -4,96275
1,1332E-05 -11,3879 -5,03288
1,1725E-05 -11,3537 -5,10319
1,0669E-05 -11,4482 -5,17672
1,0196E-05 -11,4935 -5,24885
8,4748E-06 -11,6784 -5,32028
8,0241E-06 -11,7331 -5,38696
1,0134E-06 -13,8022 -5,45343
0,00044900 -7,70849 -5,51871
1,1757E-05 -11,3511 -5,58498
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Figure 3.3 Variations of Concentration with Time
As seen in the Figure 3.3, concentration changes of CH3COONa and NaOH were plotted with
respect to time. Same as first part it can be observed limiting reactant NaOH concentration is
decreasing, desired product CH3COONa concentration is increasing.
Figure 3.4 Determination of the Reaction Order () and the Reaction Rate Constant (k)
0
0,005
0,01
0,015
0,02
0,025
0 500 1000 1500
Concentration(mol/L)
Time (s)
EtONa
NaOH
y = 1,1226x - 5,4301
R = 0,1859
-16
-14
-12
-10
-8
-6
-4
-2
0
-6 -5 -4 -3 -2 -1 0
ln(-dCNaOH
/dt-CNaOH
v/V)
lnCNaOH
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From Figure 3.4 the slope and x- intercept of the graph were determined. Reaction rate constant
is calculated. (see Sample Calculation)
T(oC) k Xfinal tfinal (min)
35 0,162 0,69 32
It can be seen that at 35C reaction rate constant is found as 0,162. Theoretically reaction of ethyl
acetate is first order and our result is acceptable. Also reaction is assumed isothermally for this
operation. Data show that temperature values usually around 35C.
3.3 Arrhenius Equation
Table 3.5 compares the change of reaction constant with temperature. Theoretically it is higher at35oC and also experimentally, k is higher at 35oC as expected. the error between experimental
and theoretical values are 13,1% and 33,1% respectively.
Table 3.5 Changes of Reaction Constant according to T emperature
TemperatureoC ktheoretical kexperimental Error %
25 0,111 0,0965 13,1
35 0,242 0,1620 33,1
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3.4 Continuous Operation (CSTR System)
Table 3.8 Stoichiometric Table for CSTR Sytem
Species
Initally
(mol)
Changing
(mol)
Remaining
(mol)
Concentration
(mol/l)
CH3COONa 0 4,7 x 10-4 4,7 x 10-4 2,35 x 10-4
As it can be seen, calculated concentration datas are very small. And conductivity values are
nearly same during the reaction. It is obvious that there are some mistakes on the measured
conductivity values.
Xtheo Xexp % Error
1.25 1.82 45
Normally observed conductivity values must decrease with time. But recorded conductivity value
was higher than the initial value. And this situation causes to wrong calculations.
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4. CONCLUSION
The aim of this experiment is to learn the working principles and types of chemical reactors.
There are three types of reactors that we study on (Batch, semi-batch and CSTR).
In the first part of the experiment, conductivity values had been recorded during the reaction.
With using the data other values were calculated. Using this values and k values were
determined. These values calculated as; for ; 0,85 and for k 0,0965.
Same procedures had been done at the temperature of 35oC. After calculations k was found as
0,162. This higher value was expected because k values are proportional to temperature.
Although, when theoretical and experimental k values were compared, error values found
respectively high. This error can occur because of the position of the conductometer. Or error can
come from the quite small concentration values. We dont know how used conductometers work
with such small concentration values in the experiment setup. More effective concentration
measurement equipments can be used (pH meter, refractometer). Molarity of solutions can be
increased or more suitable reactions can be used for this experiment.
In the second part, CSTR setup was started and the desired working temperature was set to 35oC.
Two components were fed to the reactor at same time and same concentrations (0,02 M). For the
CSTR design equation, some assumptions were made. For example, we are assuming that the
reactor volume is constant and reactor is stirred well. But it was clearly seen blades of the stirrer
was too close to bottom of the reactor. And conductometer was taking the data from near to feed
line. According to the calculations, there are very big mistakes in the conductivity measuring.
As a result it can be said that experiment was helpful and
really instructive. The difference between batch and continuous systems can obviously be seen
with respect to this experiment results. In addition application of the Arrhenius Equation
evidently observed.
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5. NOMENCLATURE
A ; pre-exponential factor
CA0 ; concentration of the reagent A at he beginning, mol/L
Ci ; concentration of I, mol/L
Ci0 ; initial concentration, mol/L
EA ; activation energy of the gases, J/mol
FA0 ; molar flow of reagent A that is fed to the reactor, mol/s
k ; reaction rate constant
NA0 ; moles of reagent A at the beginning of the process, mole
Q ; volumetric flow rate of the reagent, L/s
-rA ; disappearance velocity of I component
ri ; reaction rate of i component
R ; constant of the gases, J/mol.K
t ; time, s
T ; temperature, K
V ; volume occupied by the reaction mixture, L
xA ; conversion factor
; spatial time
V ; differentia element of volume, L
; resident time, s
, ; reaction order
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6. REFERENCES
[1] McGraw-Hill Encyclopedia of Science and Technology, 5th edition, published by The
McGraw-Hill Companies, Inc.
[2] http://www.engin.umich.edu/~cre/344/index.htm
[3] http://commons.wikimedia.org/wiki/File:Continuous_bach_reactor_CSTR.svg
[4] http://www.schwiedernoch.de/english/work/dipl_sim1.htm
http://www.engin.umich.edu/~cre/344/index.htmhttp://commons.wikimedia.org/wiki/File:Continuous_bach_reactor_CSTR.svghttp://www.schwiedernoch.de/english/work/dipl_sim1.htmhttp://www.schwiedernoch.de/english/work/dipl_sim1.htmhttp://commons.wikimedia.org/wiki/File:Continuous_bach_reactor_CSTR.svghttp://www.engin.umich.edu/~cre/344/index.htm