Effects of Mixing on Adipic Acid Crystallization

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

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

Introduction Adipic acid = 2 Billion tonne /yr.

Adipic acid used in Nylon Manufacture WH. Carothers’ at Dupont discovered Nylon in 1930’s

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

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

Previous Research Rene David’s Paper

Stirred tank with cooling Aqueous Adipic Acid

Solution

S. Derenzo’s Paper Batch with cooling

Aqueous Solution of Adipic Acid

Ethanol Solution of Adipic Acid

A. Meyerson’s Paper Batch with cooling

Alcohol Solution of Adipic Acid

Tulock’s 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

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 T=15 C.

Solution Properties Concentration and Temperature

18.2 gm/liter at 22.0 C.

Solubility

Adipic Acid Solubility

0

10

20

30

40

50

60

70

80

90

100

0 5 10 15 20 25 30 35 40 45 50

Temperature (C)

gm

/lite

r

On-Line Analysis – Computer Data Logging Feed Flow Rate Product Flow Rate Reactor

Temperature - Stirrer RPM - Stirrer Torque - Heat Balance -

Tank Internals

Off-line Analysis Steady State Sample

Yield Particle Size Distribution

Beckman Coulter LS-230 (40 nm to 2000µm) Particle Morphology

SEM

Residence Time Measurements

Time(min)

T,C

T,C

Time(min)T=(To-Tin)exp(-t/tau)+Tin

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!

GOOD vs BAD MIXING

0

0.0005

0.001

0.0015

0.002

0.0025

0:00:00 0:07:12 0:14:24 0:21:36 0:28:48 0:36:00 0:43:12 0:50:24

H+

300 RPM

0

0.0005

0.001

0.0015

0.002

0.0025

0:00:00 0:07:12 0:14:24 0:21:36 0:28:48 0:36:00 0:43:12 0:50:24

Time

H+

20 RPM

Mean Residence Time Results

Comparison of tm with different flow rate & mixer rpm

0:00:00

0:02:53

0:05:46

0:08:38

0:11:31

0:14:24

0:17:17

0:20:10

0 100 200 300 400

Mixer rpm

Me

an

Re

sid

en

t T

ime

(t

m)

127ml/min_01

127ml/min_02

243ml/min_01

243ml/min_02

359ml/min_01

359ml/min_02

475ml/min_01

475ml/min_02

591ml/min_01

591ml/min_02

Vreactor ~ 1280 ml

RDT Variance Results

Comparison of Sigma/tm with different flow rate & mixer rpm

0.6

0.65

0.7

0.75

0.8

0.85

0.9

0.95

1

1.05

1.1

0 100 200 300 400

Mixer rpm

Sig

ma

/tm

127ml/min_01

127ml/min_02

243ml/min_01

243ml/min_02

359ml/min_01

359ml/min_02

475ml/min_01

475ml/min_02

591ml/min_01

591ml/min_02

Experimental Procedure Experimental Procedure

Saturated Solution of Adipic acid feed to CSTR

Mean Residence time of 10 minutes Steady state time of 50 minutesFlow rate constant 120 ml/minRpm of impeller varied - 400, 800 rpmSamples taken at steady stateSample filtered, dried weighed to get yield

PSD, Beckman-Coulter LS 230 small volume particle distribution unit

Particle Morphology - SEM

Results-2 – 400 rpm

Results 2 - 800 rpm

50 micro meters 500 micro meters

Results-3 Yield

400 rpm 64±5% 800 rpm 61 ±5 %

Particle Size Distribution

Differential Volume Vs. Particle Size

0

1

2

3

4

5

6

7

1 10 100 1000 10000

Particle Size (micro meter)

Dif

fere

inti

al

Vo

lum

e%

Diff Volume 800

Diff Volume 400

Particle Size Distribution

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

Acknowledgement DOE/OIT

Industries of the Future Research Program