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Rate Constant Determination for

Saponification in Batch & CSTR

February 17, 2005

Presentation by Trevor Binney


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Group Members

Jay Berndt Me Eric Houchin

Operations Manager Team Leader Safety Coordinator


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Nomenclature

CSTR- Continuous Stirred Tank Reactor

EtAc- Ethyl Acetate

NaAc- Sodium Acetate

EtOH- Ethyl Alcohol (Ethanol) PPE- Personal Protective Equipment

Soln- Solution

Xa- Extent of Reaction of NaOH Conc- Concentration in mol/L

Ca- mol/L NaOH


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What is Saponification,and what is it used for?

http://www.dictionary.com/defines saponificationas: A reaction in which an ester is heated withan alkali, such as sodium hydroxide, producing a

free alcohol and an acid salt, especially alkalinehydrolysis of a fat or oil to make soap.

EtAc + NaOH NaAc + EtOH

CH3COOC2H5 + NaOH

CH3COONa + C2H5OH Saponification is primarily used for the

production of soaps.
http://www.dictionary.com/http://www.dictionary.com/


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Project Objectives

Our team was asked to meet several goalswhile running saponification experiments

1. Develop conductivity calibration curves for thereactants used in the process. (NaOH & EtAc)

2. Verify feed concentration throughstandardization using titration

3. Determine the true rate constant for reaction ina batch reactor

4. Obtain reaction rate data for the CSTR as afunction of the solution residence time


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Safety Considerations

NaOH- Corrosive

EtOH & EtAc- Flammable

EtAc will corrode various plastics

Standard PPE worn, as well as face shield andrubber gloves for handling dangerous chemicals.

Clean up spills and broken glass immediately

Be aware of where other people in the lab are Open windows for ventilation and work under

the fume hood when mixing solutions


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Assumptions

Conductivities EtAc & EtOH negligible

Solution inside the CSTR is well mixed

Solution inside batch reactor well mixed Ethyl acetate bottle wasnt contaminated

Liquid pulled from the 1 M EtAc is 1 M

The CTSR flow meters were accurate Conductivity linearly proportional to Conc


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Conductivity Probe Calibration


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Conductivity Probe Calibration

NaOH Conductivity vs Concentration

y = 214.03x

0

10

20

30

40

50

60

0 0.05 0.1 0.15 0.2 0.25 0.3

Molarity NaOH

Conductivity(mho

)

Literature Data

Calibration

Linear (LiteratureData)


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Continuous Stirred Tank Reactor


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CSTR procedure

1. Enter setpoint temperatures using set point 2

2. Drain reactant tanks as much as possible

3. Prepare three liters of reactant solutions

4. Fill tanks equally and heat to set temp5. Make sure the bottom reactor drain is closed

6. Turn on the CSTR stirring device

7. Open the flow valves to equal levels8. Wait until SS reached and record conductivityusing a calibrated conductivity probe


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Batch Reactor and Heating Bath


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Batch Procedure

1. Preheat bath to desired reaction temp

2. Prepare the NaOH and ethyl acetate solutions

3. Fill two erlenmeyer flasks, one with NaOH and

the other with EtAc

4. Allow reactants to heat to desired temp

5. Pour one flask into the other submerged flask

6. Using the conductivity probe, recordconductivities of the solution every 15 seconds

7. Record data until the conductivity stabilizes


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Equations Used for Data Analysis

Arrhenius law: k = k0e-E/RT

ln(k2/k1)=E/R*(1/T1 1/T2)

Ca0*(214-136*Xa)

Xa = (Ca0 Ca)/Ca0 Ca = (Cond/Ca0 214)*Ca0/136 + Ca0


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Results and Conclusions


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(k) Determined rate constant for saponification

Experimental k = 0.178 L/mol*sec @ 30 C

Experimental k = 0.192 L/mol*sec @ 45 C

As listed in in the Bulletin of the ChemicalSociety of Japan k = 0.112 L/mol*sec

According to this source, the rate constant wedetermined was about 59% too large

A possible reason for this is that the EtAc solutionconcentration was higher than predicted


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CSTR Results and Conclusions

Data recorded was very inconsistent

For equal feed concentrations, we had runsthat yielded conductivities of 6-7 mS and also

3 mS/m, with no results falling in between Reagent bottle contamination?

Inability to completely drain feed tanks

Difficulty in maintaining stirring speed

CSTR operations were abandoned for thefinal lab period to focus on Batch data


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Temperature Dependence Results

Multiple trials were run at both 30 & 45 C

Arrhenius law: k = k0e-E/RT

Rewritten: ln(k2/k1)=E/R*(1/T1 1/T2) R = 8.314 J/mol*K

E = Activation energy of this reaction

We were unable to find the value for E in literaturek30 = 0.178 L/mol*sec < k45 =0.192 L/mol*sec

Experimental E = 4040 J/mol


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Overall Conclusions

Saponification rxn is a 2nd order reversible reaction

(1/Ca vs time linear at low time)

-Ra = k*Ca*Cb

Considerable error comparing experimentalrate constant to that in literature

Batch data fairly reproducible and precise

CSTR data and operation inconsistent


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Difficulties Encountered During Lab

Creation and mixing of ethyl acetate solns

Attempted creation of 1 M stock solution

Attempted to dissolve 9.6 g EtAc/100 mL

Max Solubility of EtAc in water is 8 g/100 mL

Possible reagent bottle contamination

Evident through formation of unknown precipitate

CSTR temperature reading inconsistency Inability to completely drain CSTR tanks


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Recommendations For Future Work

Do research before entering the lab

Become familiar with analytical equipment

Begin trials with CSTR as early as

possible

Split up tasks for each person to do duringlab prior to running the labs

Make an in depth Design of Experimentbefore entering the lab


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References

Levenspiel, Octave. Chemical ReactionEngineering, Third Edition. USA: John Wiley &Sons, 1999.

Levenspiel, Octave. The Chemical Reactor

Omnibook. Corvallis, OR: OSU Book Stores, 2002. Pecaj, Arta. Personal Interview. February 16, 2005.

Tsujikawa, H. and Inoue, H. 1965. The Rate of theAlkaline Hydrolysis of Ethyl Acetate. Bulletin of the

Chemical Society of Japan. 39: 1837-1839 http://www.woodlandsinstruments.com/conductivity_

values.htm
http://www.woodlandsinstruments.com/conductivity_values.htmhttp://www.woodlandsinstruments.com/conductivity_values.htmhttp://www.woodlandsinstruments.com/conductivity_values.htmhttp://www.woodlandsinstruments.com/conductivity_values.htm


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Questions ??

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