Effects of Mixing on Adipic Acid Crystallization

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Effects of Mixing on Adipic Acid Crystallization

• Susan Philyaw,
• Kathryn Baker, Randal Nelson, Jessica Moffitt,
  Joy Sroykum and Dr. Terry Ring

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Outline of Talk

• Introduction- What is Adipic Acid?
• Background- Purpose for Study.
• Previous Research- Comparison.
• Experimental System- Equipment.
• Experimental Procedure- How we did it.
• Results- What we found
• Conclusions

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Introduction

• Adipic acid 2 Billion tonne /yr.
• Adipic acid used in Nylon Manufacture
• WH. Carothers at Dupont discovered Nylon in
  1930s
• Adipic acid is a natural product found in some
  plants
• Adipic acid is produced by an oxidation reaction
• oxidation of cyclo-hexane
• oxidation of phenol (minor route).
• Other uses
• Resins, Polyurethanes, and Plasticizers

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Background

• Purpose of study Increase Quality Control
• Adipic acid is crystallized from an aqueous
  solution by cooling.
• Aggregation/Agglomeration
• Advantages
• Easy to Filter
• Challenges
• Difficult to control crystal size distribution
• Adheres to the reactor walls and other parts
• Aggregates trap impurities/solvent in the voids
  of particles

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Previous Research

• Rene Davids Paper
• Stirred tank with cooling
• Aqueous Adipic Acid Solution
• S. Derenzos Paper
• Batch with cooling
• Aqueous Solution of Adipic Acid
• Ethanol Solution of Adipic Acid
• A. Meyersons Paper
• Batch with cooling
• Alcohol Solution of Adipic Acid

• Tulocks Paper
• Batch with cooling
• Aqueous Adipic Acid Solution
• Cesar and Ng
• Batch with cooling
• Aqueous Adipic Acid Solution
• Williams-Seton, et. al.
• Batch with cooling
• Aqueous Adipic Acid Solution

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Experimental System

• Reactor- Continuous Stirred Tank (CSTR)
• Volume 1.243 liters
• Operating Condition
• Impeller RPM varied 400 to 800 rpm
• Flow rate held constant 120.0 ml/min
• Reactor Temperature T15 C.
• Solution Properties
• Concentration and Temperature
• 18.2 gm/liter at 22.0 C.

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Solubility
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On-Line Analysis Computer Data Logging

• Feed Flow Rate
• Product Flow Rate
• Reactor
• Temperature - ?
• Stirrer RPM - ?
• Stirrer Torque - ?
• Heat Balance - ?

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Tank Internals
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Off-line Analysis

• Steady State Sample
• Yield
• Particle Size Distribution
• Beckman Coulter LS-230 (40 nm to 2000µm)
• Particle Morphology
• SEM

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Residence Time Measurements
T,C
T,C
Time(min)
Time(min)
T(To-Tin)exp(-t/tau)Tin
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Residence Time Measurements

• Pulse Addition to Steady State CSTR
• Visual Blue Dye
• Salt Conductivity
• Hot Temperature
• Acid pH converted to H concentration
• Done Simultaneously
• All the results are similar!

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GOOD vs BAD MIXING
20 RPM
300 RPM
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Mean Residence Time Results
Vreactor 1280 ml
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RDT Variance Results
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Experimental Procedure

• Experimental Procedure
• Saturated Solution of Adipic acid feed to CSTR
• Mean Residence time of 10 minutes
• Steady state time of 50 minutes
• Flow rate constant 120 ml/min
• Rpm of impeller varied - 400, 800 rpm
• Samples taken at steady state
• Sample filtered, dried weighed to get yield
• PSD, Beckman-Coulter LS 230 small volume
  particle distribution unit
• Particle Morphology - SEM

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Results-2 400 rpm
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Results 2 - 800 rpm
50 micro meters
500 micro meters
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Results-3

• Yield
• 400 rpm 645
• 800 rpm 61 5
• Particle Size Distribution

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Particle Size Distribution
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Conclusions

• Mixing speed must be greater than 200 rpm
• Ideal Mixing in Stirred Tank
• Mixing speed controls the aggregate size
• Smaller aggregates give less impurities
• Smaller aggregates are more difficult to filter

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Acknowledgement

• DOE/OIT
• Industries of the Future Research Program