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Saponification of Ethyl Acetate in Batch and Mixed Flow Reactors
February 16, 2005Travis Quarles (Team Leader)
Team members:Hannah Tuinstra (Operations Coordinator)Cory Tolzman (Safety Coordinator)
Presentation Overview Project Objectives Project Planning Background Experimental Methods Results Conclusions Questions?
Project Objectives We were asked to develop reaction kinetic data for
the saponification of ethyl acetate by sodium hydroxide using:1. Batch Reactor (stirred beaker)
Find true rate constant, compare to literature values
2. Mixed Flow Reactor (CSTR) Reaction Rate as a function of residence time
Both experiments were run at 30°C and 45°C - this allowed for us to see the effect of temperature
It was necessary to calibrate the conductivity probes accurately first
Project Planning and Execution Important to understand and assign primary tasks
Everyone researched, I developed lab plans and individual tasks for each day
Cory completed the safety report by the first wet lab session and monitored safety in the lab
Hannah completed the operations manual by the second wet lab session and updated the project plan
All members participated in Batch and CSTR runs, as well as solution preparation and conductivity calibration
Project Plan was updated along the way to keep track of progress towards goals
Project Planning and Execution Safety First
PPE – Lab coat, indirectly vented goggles, gloves when handling any chemicals, face shield when pouring ethyl acetate out of stock bottle
Any solutions not in use were kept in the hood, properly labeled
CSTR waste container filled quickly when running high flows Operations
The CSTR rotameters were assumed to be correct, though we believe they read about 10% over the actual flow
The conductivity probe calibrations were done using solutions at known conversions of hydroxide (X)
Lessons Learned Plan more ahead of time, in order to use full
amount of lab time for experimentation Allow more time for CSTR runs, more data
would be helpful Make sure reactants are prepared accurately
each time *Understand something before you attempt it
Nomenclature COH - concentration of hydroxide (mol/L) k - rate constant (L*min/mol) rOH - rate of depletion of hydroxide (mol/L*min) t - time (min) V - volume of reactor (L) - volumetric flow rate of reactants (L/min) X - conversion of hydroxide τ - residence time (min-1)
v
Background Saponification Reaction: CH3COOC2H5 + NaOH CH3COONa + C2H5OH
Significance of this project Study the use of a CSTR and the effects of flow
changes Determining rate constant from batch data Studying temperature effects for reactions
Background - Batch Since the reaction is second-order, the following
equation applies:
If 1/COH is plotted vs. time, then the resulting line will have a slope equal to k, and an intercept equal to 1/COHo
The literature value is 0.122 L/mol*min for 30 °C and 0.273 L/mol*min for 45 °C
*values obtained from JACS
oOHOH Ckt
C
11
Background - CSTR The reaction rate can be expressed as follows:
Plotting the reaction rate vs. residence time should result in a curve that shows that longer residence times result in slower reaction rates
The volume of the reactor was 1.75 L, determined by filling and then draining
v
VXCr
OHOH
OHo
;
Experimental Methods – Conductivity Calibration
We did not neglect the conductivity of the sodium acetate (NaAc) formed
The following solutions were used for calibration: 0.05M NaOH (X=0) 0.025M NaOH and 0.025M NaAc (X=0.5) 0.05M NaAc (X=1)
The conversion can be plotted against conductivity, yielding a way to get concentration vs. time data
o
o
OH
OHOH
C
CCX
Experimental Methods - Batch
Beaker
Conductivity Probe
Conductivity Readout
Experimental Methods - Batch The runs were performed with 100 mL of
each 0.1M reactant Reactants were preheated to reaction
temperature in water bath The conductivity probe was used to stir the
reaction The readings were taken every five seconds
for three minutes
Experimental Methods -CSTR
Experimental Methods - CSTR
Ethyl Acetate Feed
Reaction Vessel
Mixer Speed Adjustment
Armfield Unit
Brownsfield UnitNaOH Ethyl
Acetate
Temperature Adjustment
On/Off
Flowrate Adjustment
NaOHEthyl
Acetate
Sample Port
On/Off
Waste Container
NaOH Feed
Temperature Probe
Conductivity Probe
Experimental Methods - CSTR The CSTR was loaded with the feed
solutions Temperature was allowed to equilibrate Equal flows were then sent to the reactor After the conductivity stabilized, the reading
was taken The flows were changed to a new steady
state
Results - Conductivity Calibration
[NaAc]: 0.05M = 3.8 mS [NaOH]: 0.05M = 10.9 mS This means that when conversion is complete,
the conductivity would still read 3.8 mS Sodium acetate conductivity is not negligible,
this might explain why other groups had trouble last time
Results - Conductivity Calibration
This probe was used for the batch reactions
Calibration of Conductivity Probe #5
y = -0.14x + 1.53
R2 = 0.9989
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0 2 4 6 8 10 12
Conductivity (mS)
Co
nve
rsio
n
Results - Conductivity Calibration
This probe was used for the CSTR runs
Calibration of Conductivity Probe #1
y = -0.12x + 1.42
R2 = 0.9996
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0 2 4 6 8 10 12 14
Conductivity (m S)
Co
nve
rsio
n
Results - BatchBatch 30 °C - 1/COH vs. Time
0
10
20
30
40
50
60
70
0 50 100 150 200
Time (s)
1/C
OH
(L
/mo
l)
Run A 1/[NaOH]
Run B 1/[NaOH]
Run C 1/[NaOH]
Results - BatchBatch 30 °C - 1/COH vs. Time
y = 0.24x + 20.3
R2 = 0.97
y = 0.19x + 19.0
R2 = 0.99
y = 0.18x + 18.0
R2 = 0.99
0
5
10
15
20
25
30
35
40
45
50
0 10 20 30 40 50 60
Tim e (s )
1/C
OH
(L
/mo
l)
Run A 1/[NaOH]
Run C 1/[NaOH]
Run D 1/[NaOH]
Results - BatchBatch 45 °C - 1/COH vs. Time
0
10
20
30
40
50
60
0 50 100 150 200
Tim e (s)
1/C
OH
(L
/mo
l)
Run E 1/[NaOH]
Run F 1/[NaOH]
Run G 1/[NaOH]
Results - BatchBatch 45 °C - Initial Reaction Rate
y = 0.23x + 19.2
R2 = 0.9963
y = 0.25x + 19.8
R2 = 0.9993
y = 0.24x + 20.0
R2 = 0.9978
0
5
10
15
20
25
30
35
0 10 20 30 40 50
Time (s)
1/C
OH
(L
/mo
l)
Run E 1/[NaOH]
Run F 1/[NaOH]
Run G 1/[NaOH]
Results - CSTR
The longer the reaction is allowed to take place, the slower the reaction proceeds
CSTR - Reaction Rate vs. Residence Time
0.000
0.002
0.004
0.006
0.008
0.010
0.012
0.014
0 2 4 6 8 10 12 14 16 18 20
Residence Time (min-1)
Rea
ctio
n R
ate
(mo
l/L
/min
)
45 °C
30 °C
Conclusions Batch
1. The rate constant at 30 °C is 0.203 L/mol*min; compared to the literature value, our value is 66% higher
2. The rate constant at 45 °C is 0.24 L/mol*min; compared to the literature value, our value is 12% lower
3. The temperature had the correct effect, but it was not to the degree expected
CSTR
1. The shapes of the reaction rate vs. residence time fit with expectations
2. The reaction rates are greater for 45 °C, but the effect of the temperature decreases with residence time
Conclusions - Possible Sources of Error Batch
Conductivity probe had some stability problems while stirring
Incorrect conductivity calibration CSTR
Inconsistent flows Incorrect flow readings Poor temperature control Varying initial concentrations in feed solutions
Recommendations for Future Work Research conductivity probe calibration more
carefully to determine actual effects of all components
Develop more accurate rotameter calibration for CSTR
Prepare a lot of solution at once, the CSTR can use a lot quickly at higher flows, and this ensures constant feed concentration
Questions?