Exp5 Teo Resultsanddiscussion

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reactant is fed and withdrawn continuously.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

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