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?