1. EFFECT OF MIXING IN A
STIRRED TANK REACTOR

2. ESSENSE OF THE PROJECT
 To study the performance of a Stirred Tank Reactor
using different parameters.
 To design a better and a controlled mixing process that
utilizes raw materials and avoids pollution.
 To cut down the mixing expenditure.

3. MIXING
• Mixing isdefined as the reduction of in-homogeneity in
order to achieve a desired process result.
• The primary objective of the mixing is to achieve a
homogeneous mixture, generally this means, attaining a
nearly uniform distribution of the ingredients.
• The in-homogeneity can be one of concentration, phase,
or temperature. Secondary effects, such as mass
transfer, reaction, and product properties are usually
the critical objectives.

4. A horse-driven mixer is a pug mill preparing clay for brick
making……………

5. MIXING TANK
Agitated mixer are increasingly used to perform a variety of mixing
tasks in
 chemical products
 Food
 Biochemical
 Pharmaceutical
 Medicine
 Energy,
 Environment protection,
 dealing with fining,
 homogenizing,
 dissolution,
 gas dispersion,
 solid suspension,
 heat transfer and diffusive transport of multiple raw materials.

6. GEOMETRY OF MIXING TANK
 A conventional stirred tank consists of a vessel equipped with a
rotating mixer.
 The vessel is generally a vertical cylindrical tank.
 Nonstandard vessels such as those with square or rectangular
cross-section, or horizontal cylinder vessels are sometimes used.
 The rotating mixer has several components: an impeller, shaft,
shaft seal, gearbox, and a motor drive.
 Wall baffles are generally installed for transitional and turbulent
mixing to prevent solid body rotation (sometimes called fluid swirl )
and cause axial mixing between the top and bottom of the tank . .

7. Schematic of a mixing tank

8. MIXING MECHANISMS
 Dispersion or diffusion is the act of spreading out.
 Molecular diffusion is diffusion caused by relative molecular motion
and is characterized by the molecular diffusivity.
 Eddy diffusion or turbulent diffusion is dispersion in turbulent flows
caused by the motions of large groups of molecules called eddies; this
motion is measured as the turbulent velocity fluctuations.
 Convection (or bulk diffusion) is dispersion caused by bulk motion.
 Taylor dispersion is a special case of convection, where the dispersion
is caused by a mean velocity gradient. It is most often referred to in
the case of laminar pipe flow, where axial dispersion arises due to the
parabolic velocity gradient in the pipe.

9. MEASURES OF MIXEDNESS
 Scale of segregation is a measure of the large scale breakup
process (bulk and eddy diffusivity) without the action of
diffusion. It is the size of the packets of B that can be
distinguished from the surrounding fluid A.
 Intensity of segregation is a measure of the difference in
concentration between the purest concentration of B and the
purest concentration of A in the surrounding fluid. Molecular
diffusion is needed to reduce the intensity of segregation, as
even the smallest turbulent eddies have a very large
diameter relative to the size of a molecule.

11. RESIDENCE TIME DISTRIBUTION
 Residence time distributions represent the first generation of
mixing models. The residence time distribution measures features
of ideal or non ideal flows associated with the bulk flow patterns or
macro mixing in a reactor or other process vessel.
 In RTD analysis, a tracer is injected into the flow and the
concentration of tracer in the outlet line is recorded over time.
When the mixing is ideal or close to ideal and the reaction kinetics
are known, the RTD can be used to obtain explicit solutions for the
reactor yield .
 The chief weakness of RTD analysis is that from the diagnostic
perspective, an RTD study can identify whether the mixing is ideal
or non ideal, but it is not able to uniquely determine the nature of
the non ideality.
contd……

12. RESIDENCE TIME DISTRIBUTION
 Residence time distributions are the first characteristic of
mixing. The characteristic time scale for a residence time
distribution is the mean residence time of the vessel. The
characteristic length scale is the vessel diameter, or volume.
 The conclusion is that improvements in CFD codes and still
faster computers are needed for accurate design calculations
in complex geometries. Residence time calculations will be a
useful tool for their validation

13. PARAMETERS CONSIDERED
 Type of mixing process
Lateral mixing
Axial mixing
 Type of flow
Laminar Flow
Turbulent Flow
 Type of reactor
Batch reactor
 Type of mixers to be used
Mechanical Agitators
 Materials taken for the mixing process

14. KEY PROCESS VARIABLES
 Residence time (τ)
 Volume (V)
 Temperature (T)
 Pressure (P)

15. TYPES OF IMPELLERS
Three blade marine type Double flight ribbon type:.
 A high efficiency turbulent flow  It is the most efficient blender of
impeller used on our smallest all existing close clearance
turbine agitators at direct drive agitators
motor speeds.  . Generally used for applications
 The high solidity permits where viscosities are ordinarily
operation nearer the boiling greater than 30,000 MPa.
point without cavitations.

16. TYPES OF IMPELLERS
Axial impeller : Straight Blade Impeller :
 A reasonably cost effective impeller  A cost effective impeller
in both turbulent and laminar flow.
 Good impeller for applications where
for operation very near the
the viscosity changes over a wide floor of a tank for agitating
range causing the flow regime to the heel in solids
vary between turbulent and laminar
flow. suspension applications.
 A reasonably cost effective impeller
for solids suspension.

17. CASE STUDY
PROCEDURE:
1. Fill the overhead tanks with NaOH and Ethyl Acetate.
2. Adjust the flow rates of NaOH and Ethyl Acetate until the flow
reaches steady state.
3. Switch on the stirrer.
4. Add 10 ml of Glacial Acetic Acid to the reactor
5. Collect the samples from outlet for every 30 seconds of time
interval.
6. Take 10ml from each sample and transfer it to the conical flask
which contains 10ml HCl.
7. Titrate the sample with NaOH by adding phenolphthalein
indicator, till colorless solution turns to pink.
8. Note down the volume of NaOH rundown.
9. Repeat the same procedure for different flow rates.

18. FORMULAE
QNaOH * NNaOH
CAO =
QNaOH + QETHYL ACETATE
VETHYL ACETATE *ᵨ
SETHYL ACETATE =
M.W.(1+VETHYL ACETATE )

19. CBO = QETHYL ACETATE *SETHYL ACETATE
QNaOH + QETHYL ACETATE
M = CBO
CAO
CA = GNaOH
VSAMPLE
XA = 1 - CA
CAO
τ = V
QNaOH + QETHYL ACETATE

20. OBSERVATIONS AND CALCULATIONS

21. EFFECT OF MIXING WITHOUT STIRRER
S.NO QNaOH QETHYL ACETATE V NaOH
(LPH) (LPH) RUNDOWN
ml
1 12.5 15 6.5
2 10 12.5 4.7
3 7.5 10 3.3
4 5 7.5 3.0
5 2.5 5 2.0

22. S NO τ XA
sec
1 0.03709 0.0001
2 0.0453 0.010
3 0.0582 0.0109
4 0.0816 0.112
5 0.136 0.119

23. RESIDENCE TIME Vs CONVERSION
0.14
0.12
0.1
A
0.08
0.06
o
n
X
e
v
c
s
r
i
0.04
0.02
0
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16
Residence time, τ (sec)

24. CONVERSION BY VARYING RPMs
S.No XA AT 400 RPM XA AT 600 RPM XA AT 1000 RPM τ
sec
1 0.0512 0.0841 0.112 0.03709
2 0.0740 0.099 0.344 0.045
3 0.0911 0.156 0.499 0.058
4 0.202 0.331 0.546 0.0816
5 0.335 0.584 0.844 0.136

25. RESIDENCE TIME Vs CONVERSION
0.9
XA @
0.8
400 RPM
0.7
0.6
A
XA @
0.5 600 RPM
0.4
0.3 XA @
o
n
X
e
v
c
s
r
i
0.2 1000
0.1 RPM
0
0 0.025 0.05 0.075 0.1 0.125 0.15
Residence time, τ (sec)

26. CONVERSION WITH A THREE BLADE MARINE TYPE
IMPELLER
S.No QNaOH QETHYL ACETATE Volume of NaOH
(LPH) rundown
(LPH)
ml
1 12.5 15 6.9
2 10 12.5 6.5
3 7.5 10 6.3
4 5 7.5 6.1
5 2.5 5 6.0

27. S.No XA τ
Sec
1 O.O114 0.037
2 0.02021 0.045
3 0.02117 0.058
4 0.19905 0.0816
5 0.20704 0.136

28. RESIDENCE TIME Vs CONVERSION
0.25
0.2
A
0.15
0.1
o
n
X
e
v
c
s
r
i
0.05
0
0 0.025 0.05 0.075 0.1 0.125 0.15
Residence time, τ (sec)

29. CONVERSION WITH A STRAIGHT BLADE TYPE
IMPELLER
S NO QNaOH QETHYL ACETATE V NaOH RUNDOWN
(LPH) (LPH) ml
1 12.5 15 7.5
2 10 12.5 6.9
3 7.5 10 6.5
4 5 7.5 6.3
5 2.5 5 6.1

30. S NO XA τ
Sec
1 0.0321 0.0370
2 0.05705 0.045
3 0.06774 0.058
4 0.18905 0.0816
5 0.33903 0.136

31. RESIDENCE TIME Vs CONVERSION
0.4
0.35
0.3
A
0.25
0.2
0.15
o
n
X
e
v
c
s
r
i
0.1
0.05
0
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16
Residence time, τ (sec)

32. CONVERSION WITH AN AXIAL HIGH EFFICIENCY
IMPELLER
S NO QNaOH QETHYL ACETATE V NaOH RUNDOWN
(LPH) (LPH) ml
1 12.5 15 9.0
2 10 12.5 8.5
3 7.5 10 7.0
4 5 7.5 6.9
5 2.5 5 6.5

33. S NO XA τ
Sec
1 0.045 0.037
2 0.101 0.045
3 0.194 0.058
4 0.310 0.0816
5 0.381 0.136

34. RESIDENCE TIME Vs CONVERSION
0.45
0.4
0.35
0.3
A
0.25
0.2
0.15
o
n
X
e
v
c
s
r
i
0.1
0.05
0
0 0.025 0.05 0.075 0.1 0.125 0.15
Residence time, τ (sec)

35. CONVERSION WITH A DOUBLE FLIGHT RIBBON
IMPELLER
S NO QNaOH QETHYL ACETATE VOLUME OF NaOH
(LPH) (LPH) RUNDOWN
ml
1 12.5 15 8.4
2 10 12.5 7.5
3 7.5 10 6.7
4 5 7.5 6.5
5 2.5 5 6.4

36. S NO XA τ
Sec
1 0.0421 0.037
2 0.0631 0.045
3 0.082 0.058
4 0.210 0.0816
5 0.348 0.136

37. RESIDENCE TIME Vs CONVERSION
0.4
0.35
0.3
A
0.25
0.2
0.15
o
n
X
e
v
c
s
r
i
0.1
0.05
0
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16
Residence time, τ (sec)

38. COMPARISION OF VARIOUS TYPES OF IMPELLERS BY
TAKING CONVERSION AS FACTOR
0.45
0.4 with out impeller
0.35
three blade marine
0.3
type impeller
A
0.25
flat 4-blade type
0.2 impeller
o
n
X
e
v
c
s
0.15
r
i
double flight ribbon
impeller
0.1
0.05 axial impeller
0
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16
Residence time, τ (sec)

39. APPLICATIONS
 Stirred tank reactors are frequently used in the
chemical and biochemical industry to accomplish mixing
tasks.
 Stirred tank reactors are used for the mixing of various
types of polymerizations, precipitations and
fermentations.
 A better designed and controlled mixing process leads
to significant pollution prevention, better usage of raw
materials and avoids expensive separation costs
downstream in the process.

40. CONCLUSION
• From our project we were able to study the
following:
– Inefficient mixing has large negative effects on the yield
and selectivity of a broad range of chemical reactions,
because slow mixing can retard desired reactions.
– The speed of the agitators and its involvement in the
effect of mixing using a Tachometer and a Dimmerstat.
– We have taken different stirrers and achieved maximum
conversion and studied the effect of mixing varying RPM
and found out the properties of different impellers and
their rate of mixing using different liquids.
– The best conversion we have achieved for axial impeller
because of the twisted blade structure when compared
with other three impellers.

41. SCOPE FOR FUTURE WORK
This study can be extended by varying different
reactors , agitators and solutions
The study can be done in closed type vessels
where different fluids can be taken.

42. REFERENCES
Schmidt, Lanny, The Engineering Of Chemical
Reactions. NY Oxford Press, 1998.
Octave Levenspiel, The Chemical Omnibook,Oregon
St Univ Bookstores 1993.
Effect Of Mixing in a Stirred Tank Reactor- Chemical
Engineering Journal.
Warren L.McCabe, Julian Smith, Peter Harriot. Unit
Operations Of Chemical Engineering-2005.
Bakker R A, “Micro mixing in Chemical Reactors”
Thesis ,Delft University,1996.

43. THANK YOU