Ideality of a CSTR

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Ideality of a CSTR
Jordan H. Nelson
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Brief Overview
Introduction General CSTR Information
Three Questions
Experimental Conclusions
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Schematic of the CSTR
Item Description
1 Mixing Point
2 Mixing Point
3 Mixing Point
4 Mixing Points
5 Water Bath Inlet and Outlet
6 Four Wall Mounted Baffles
7 Mixer Drive
8 Marine Type Impeller
9 CSTR Vessel
10 Water Bath Vessel
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3 Questions ?

• Where is the best mixing in the CSTR?
• What is tmean and how does it compare to tideal?
• What configuration of PFR-CSTR will produce the
  greatest conversion?

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Where is the Best Mixing?

• Impeller selection
• Food Dye Test
• Dead Zones
• Impeller Speed

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Flow Patterns of different impellers
Rushton Impeller
Marine Impeller
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tMean vs tIdeal ?

• tMean Measured mean residence time
• The amount of time a molecule spends in the
  reactor
• tIdeal Ideal residence time is calculated from
  the following equation

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Experiment

• Fill reactor with low concentration salt
  (baseline)
• Spike reactor at most ideal mixing
• Create spike concentration at least one order of
  magnitude larger than baseline
• Measure change in conductivity over time
• Run experiment at different impeller speeds

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Yikes!
Plot of Concentration vs Time with Error
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Measured Concentration over time in the CSTR.
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RTD Function E(t)

• Measured concentrations are used to create the
  residence time distribution function

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Plot of an ideal residence time distribution
function
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Residence time distributions
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Mean Residence Time

• Using E(t) the following equations produce the
  mean residence time

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Comparison of Residence Times
RPM Mean Residence Time Standard Deviation Sigma Sigma/Tau
15 357.57 11.58 206.87 0.58
30 358.14 11.58 206.35 0.58
Ideal CSTR 466.97 5.90    
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Loss of Data

• Over an hour of data was lost from Opto 22
• Calculation of Reynolds number over 4000
  (Turbulent)
• Equation applies to a baffled CSTR
• RPM speed of 300 obtained full turbulence

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CSTR-PFR Configurations ?

• Schematic of arrangements
• Levenspiel Plot
• Conduct saponification reaction in the reactor at
  different RPMs
• Use Equimolar flow rates and concentrations of
  reactants
• Quench reaction with a HCl and titrate with NaOH

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Series Reactor with CSTR Before PFR.
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Series Reactor with PFR Before CSTR.
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CSTR-PFR Configurations ?

• Schematic of arrangements
• Levenspiel Plot
• Conduct saponification reaction in the reactor at
  different RPMs
• Use Equimolar flow rates and concentrations of
  reactants
• Quench reaction with a HCl and titrate with NaOH

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Measured Conversion for PFR-CSTR Configuration
Speed (RPM) Conversion () Conversion Error ()
30 19.7 /- 4.30
60 21.7 /- 3.91
200 21.2 /- 4.00
400 24.3 /- 3.48
875 24.7 /- 3.41
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Measured Conversion for CSTR-PFR Configuration
Speed (RPM) Conversion ()   Conversion Error ()
30 21.5 /- 3.94
60 21.2 /- 4.00
200 21.4 /- 3.97
400 20.9 /- 4.06
875 21.5 /- 3.94
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3 Questions ?

• Where is the best mixing in the CSTR?
• What is tmean and how does it compare to tideal?
• What configuration of PFR-CSTR will produce the
  greatest conversion?

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Conclusions

• Better mixing for a Rushton impeller is below the
  impeller
• The reactor is far from ideal at low impeller
  speeds
• The PFR-CSTR arrangement provided better
  conversions
• Run the PFR-CSTR reactor at RPMs of higher than
  300

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Opportunities

• Run the experiment again to obtain the lost
  residence time values
• Run the saponification reaction at higher
  temperatures
• Exit sampling stream should be at the bottom of
  the reactor

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Acknowledgements

• Taryn Herrera
• Robert Bohman
• Michael Vanderhooft
• Dr. Francis V. Hanson
• Dr. Misha Skliar

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• REFERENCES
• De Nevers, Noel, Fluid Mechanics, McGraw Hill,
  New York N.Y. (2005)
• Fogler, H. Scott, Elements of Chemical Reaction
  Engineering, Prentice Hall, Upper Saddle River,
  N.J. (1999)
• Havorka, R.B., and Kendall H.B. Tubular Reactor
  at Low Flow Rates. Chemical Engineering
  Progress, Vol. 56. No. 8 (1960).
• Ring, Terry A, Choi, Byung S., Wan, Bin., Phyliw,
  Susan., and Dhanasekharan, Kumar. Residence Time
  Distributions in a Stirred Tank-Comparison of CFD
  Predictions with Experiments. Industrial and
  Engineering Chemistry. (2003).
• Ring, Terry A, Choi, Byung S., Wan, Bin., Phyliw,
  Susan., and Dhanasekharan, Kumar. Predicting
  Residence Time Distribution using Fluent Fluent
  Magazine. (2003).

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What to expect from your CSTR.
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Question?
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Design Equations
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Design Equations