This document discusses improved operation of a caustic tower through complex system evaluation and chemical treatment. It identifies that caustic tower fouling occurs through aldol condensation, free radical polymerization, and Diels Alder reactions. Testing identified specific fouling precursors. A treatment program using POLYFREE additives to inhibit each reaction mechanism was successful, extending the caustic tower run length to over 18 months without unplanned outage.

1. Improved Caustic Tower Operation
by Complex System Evaluation
Hua Mo, David Dixon
Baker Hughes Incorporated
Sugar Land, TX 77478

2. Agenda
• Introduction of caustic tower
• Caustic tower fouling mechanism
• Identify caustic tower fouling mechanism
• Treatment summary
• Conclusion

3. Acid Gas Removal
• Acid gas
- Organic acids
- Carbon dioxide (CO2)
- Hydrogen sulfide (H2S)
• Acid gas removal
RCOOH OH-
H2ORCOO-
2H2S OH-
H2OS2-
CO2 2 OH - CO3
2-
H2O

4. Caustic Tower Design

5. Fouling Mechanism (1)
• Aldol condensation
• Diels Alder reaction
Red Oil
R1CH2CH
OH- -
R1
-H2O
R2CH2CHR1CHCH R2CH2CHCHCH
R1
R2CH2CH=CCH

6. Fouling Mechanism (2)
• Free radical polymerization

7. Keys Questions
• Why does the caustic tower foul?
• What chemical treatment(s) can be used to
mitigate the fouling?

8. Test Protocols
• Pre-treatment system evaluation
• Skim oil analysis
• Deposit analysis
• Caustic reflux test

9. Pre-treatment System Evaluation
Filterable Solids
(ppm)
Soluble Polymer
(ppm)
Strong Section 329 490
Weak Section 1986 1895

10. Skim Oil Analysis
• Aldol condensation
- Aldehyde
• Free radical polymerization
- Vinyl monomer
• Solvent help to mitigate the fouling
- Aromatic components

11. Deposit Analysis
• Organic foulants
• Hydrogen/Carbon mole ratio similar to aldol polymer
• Precursor of free radical polymerization trapped in
deposit matrix
- Styrene, Indene, etc
• Deposits matrix contained:
– products of free radical polymerization
– Diels Alder reaction products
– aldol polymer

12. Summary
• All reaction mechanism involved in the caustic
tower fouling
How to treat it?

13. Treatment Recommendation
• Aldol condensation inhibitor
- POLYFREE™ 305C additive
• Free radical polymerization inhibitor
- POLYFREE 300R1 additive
• Antifoulant for controlling Diels Alder fouling
- POLYFREE 350 additive
POLYFREE is a trademark of Baker Hughes Incorporated

14. Caustic Reflux Results
Chemical Additives Percentage inhibition (%) *
Blank 0
POLYFREE 300R1 Additive 18.9
POLYFREE 305C Additive 27.9
POLYFREE 300R1 /
POLYFREE 305C Additives
81.5
*Percentage Inhibition (%)=
[(Foulants with additive) – (Foulant without additives)]/
(Foulant without additives) x 100

15. Treatment Results (1)
• Soluble Polymer
• Skim Oil Quality
Before Treatment (ppm) After Treatment (ppm)
1895 640

16. Treatment Results (2)
• Process Data
y = 0.013x - 529.19
y = 0.0076x - 305.68
2
3
4
5
6
7
8
9
12/23/11 4/1/12 7/10/12 10/18/12 1/26/13 5/6/13 8/14/13
CausticTowerDP
Date
Before Treatment After Treatment Linear (Before Treatment) Linear (After Treatment)

17. Treatment Summary
• The POLYFREE treatment program was
successful
• The column run length extended to 18+
months
– It reached turnaround

18. Conclusion
• A complex proprietary caustic tower system evaluation
can identify fouling mechanisms
• Free radical polymerization, Aldol condensation and
Diels Alders reaction mechanisms are involved in
caustic tower fouling
• From the analysis, a successful POLYFREE chemical
treatment program was recommended
• Field test data indicates fouling was controlled
• The caustic tower run length was significantly extended
• A costly unplanned outage was avoided

19. Acknowledgement
• The analytical group in Baker Hughes
• Unit personnel for their collaboration,
communication and discussions of caustic
tower operations

20. Questions ?