Novel classes of organic corrosion inhibitors

1
Novel classes of organic corrosion inhibitors

• Dr. S. U. Rahman
• Associate Professor, Chemical Engineering
  Department
• King Fahd University of Petroleum Minerals,
• Dhahran-31261, Saudi Arabia

2
Applications of Corrosion Inhibitors

• Water
• Potable Water
• Silicates, Popyphosphates, CaCO3
• Cooling Water
• Chromate, Nitrate, Polyphosphates,
• Automotive Coolants
• Nitrite, Benzoate, Borax,
• Steam Condensates
• Mophines, cyclohexamine, Long chain aliphatic
  amines
• Brine and Seawater
• Nitrite, Chromates, Phosphates
• Acid Pickling
• Sulfur and nitrogen containing organic compounds
• Oil Production and Refining
• Sulfur and nitrogen containing organic compounds

3
Factors Affecting Inhibition of Cooling Systems

• Oxygen saturation
• Water soluble gases
• pH
• TDS
• Silt and solids
• Sulfate bearing bacteria

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Requirements of Inhibitors

• Surface coverage
• Low concentration
• Wide range of conditions (T, pH and water
  quality)
• Should not produce solid deposits
• Low/nil toxicity
• Antiscaling properties

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Organic Inhibitors (Literature)

• Mechanism
• Adsorb (chemisorb) to form barrier
• Coordinate covalent bond between metal and
  inhibitor
• React with environment to form thin coating
• Bond strength depends on
• Density of one pair or ? electrons
• Polarizibility of the functional group
• Contain O, S or N
• Mostly surfactant-like compounds
• Contain polar head and nonpolar chain
• Polar head helps in adsorption and impart
  solubility
• Nonpolar chain provides the required coverage

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New Classes of Inhibitors

• Following N containing compounds were studied
• Isoxazolidines1
• Cyclic Hydroxylamines2
• Cyclic Nitrones3
• Some of these compounds were synthesized first
  time
• None of them have been tested as corrosion
  inhibitors

1 Ali, Saeed,, Rahman, Corrosion Science, 45
(2003) 253-266. 2 Saeed, Ali, Rahman,
Anti-Corrosion Methods and Materials, 50 (2003)
201-207. 3 Rahman, Saeed, Ali, Anti-Corrosion
Methods and Materials (Accepted).
7
Isoxazolidines

• Ali, A. A., Saeed, M. T., Rahman, S. U.,
  Corrosion Science, 45 (2003) 253-266.

8
Isoxazolidines1
Nitrone
isoxazoidines
Diadducts
Cycloadducts
1 Ali, A. A., Saeed, M. T., Rahman, S. U.,
Corrosion Science, 45 (2003) 253-266.
9
Quaternary Ammonium Salts1
Quaternary Amm. Salt
Isoxazolidine
Quaternary Amm. Salt
1 Ali, A. A., Saeed, M. T., Rahman, S. U.,
Corrosion Science, 45 (2003) 253-266.
10
Summary of all isoxazolidines
isoxazoidines
Cycloadducts
Quaternary Ammonium Salts
Diadducts
1 Ali, A. A., Saeed, M. T., Rahman, S. U.,
Corrosion Science, 45 (2003) 253-266.
11
Gravimetric Tests (Inhibition Efficiencies)
Compound 50 ppm 100 ppm 200ppm 400ppm
3a 40.7 53.6 73.8 86.7
3b 34.7 50.0 70.8 87.3
3c 98.0 98.2 98.5 98.5
3d 97.5 98.0 98.6 98.8
5a 97.0 97.2 98.5 98.8b
5b 95.2 95.7 96.0 98.3
7aa 81.9 82.3 83.4 88.1
7b 8.60 46.4 88.7 93.5
8 93.9 97.3 98.3 99.1
9 96.0 98.0 99.0 99.5
Substrate metal Mild steel, Temperature 60
?C, Exposure 6 hrs, Base solution 1 N HCl
a soluble in 10 acetone in 1N HCl bIE for 10
and 25 ppm were 87.2 and 91.8, respectively.
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Isotherms

• Isotherms provide insight into adsorption process
• Surface coverage (?) can be evaluated as
  inhibition efficiency.
• Langmuir Isotherm
• ?/(1- ?)aC
• Tempkin Isotherm
• ?(1/f)log(aC)

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Isotherms of compounds 3a and 3b
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Tafel Tests
Solution fcorr, V SCE ?a,, V/decade ?C V/decade Icorr(mA/cm2) CR (mpy) Inhibition Efficiency
Blank - 0.480 0.1777 0.1813 2.2563 1031.8 0
3c - 0.491 0.0976 0.1325 0.1057 48.3 95.32
3d - 0.479 0.1330 0.1269 0.2255 103.1 90.01
5a - 0.475 0.0970 0.1170 0.1794 82.0 92.05
8 - 0.463 0.0867 0.1210 0.1107 50.6 95.10
Substrate metal Mild steel, Temperature 60
?C, Exposure 20 minutes, Base solution 1 N
HCl, Inhibitor Concentration 400 ppm
1 Ali, A. A., Saeed, M. T., Rahman, S. U.,
Corrosion Science, 45 (2003) 253-266.
15
Cyclic Hydroxylamines

• Saeed, M. T., Ali, A. A., Rahman, S. U.,
  Anti-Corrosion Methods and Materials, 50 (2003)
  201-207.

16
Cyclic Hydroxylamines2
Hydroxylamines
Nitrone
Hydroxypyrrolidine
Cyclic Nitrones
Hydroxylamines
Hydroxylamines
1 Saeed, M. T., Ali, A. A., Rahman, S. U.,
Anti-Corrosion Methods and Materials, 50 (2003)
201-207.
17
Hydroxylamines
1 Saeed, M. T., Ali, A. A., Rahman, S. U.,
Anti-Corrosion Methods and Materials, 50 (2003)
201-207.
18
Gravimetric Tests (Inhibition Efficiencies)
Comp. 50 ppm 100ppm 200ppm 400ppm
1 24.6 39.2 59.3 77.4
3 7.3 33.4 49.5 80.8
4 6.8 28.0 57.4 85.3
5 66.4 82.6 96.1 96.8
6 90.2 91.9 94.4 98.0
7 86.1 86.8 90.5 94.1
9a 81.8 95.7 96.7 98.0d
9ba 95.1 96.1 97.2 97.4
10 12.0 27.3 45.8 66.1
11 17.9 35.0 58.7 90.0
Substrate metal Mild steel, Temperature 60
?C, Exposure 6 hrs, Base solution 1 N HCl
asoluble in 10 acetone in 1 N HCl d IE for
inhibitor concentration of 10 and 25 ppm was
determined to be 26.7 and 62.5, respectively.
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Isotherms of compounds 9a, 1 and 10
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Tafel Tests
Solution fcorr, V SCE ?a,, V/decade ?C V/decade Icorr(mA/cm2) CR (mpy) Inhibition Efficiency
Blank - 0.480 0.1777 0.1813 2.2563 1031.8 0
4 -0.5015 0.1004 0.1375 0.5010 229.1 77.8
5 -0.4976 0.09034 0.1383 0.2254 103.1 90.0
10 -0.4659 0.1591 0.2006 0.9015 412.3 60.0
Substrate metal Mild steel, Temperature 60
?C, Exposure 20 minutes, Base solution 1 N
HCl, Inhibitor Concentration 400 ppm
1 Saeed, M. T., Ali, A. A., Rahman, S. U.,
Anti-Corrosion Methods and Materials, 50 (2003)
201-207.
21
Cyclic Nitrones

• Rahman, S. U., Saeed, M. T., Ali, S. A,
  Anti-Corrosion Methods and Materials (Accepted).

22
Cyclic Nitrones3
1 Rahman, S. U., Saeed, M. T., Ali, S. A,
Anti-Corrosion Methods and Materials (Accepted).
23
Gravimetric Tests (Inhibition Efficiencies)
Comp. 50 ppm 100 ppm 200ppm 400ppm
6 66.1 78.9 91.1 91.0
7 30.7 50.0 68.6 94.4
8 37.6 58.9 76.3 94.1
10a 92.3 97.0 97.7 98.3
13a 72.6 82.7 89.4 90.0
15a 97.1 97.4 97.5 98.2
Substrate metal Mild steel, Temperature 60
?C, Exposure 6 hrs, Base solution 1 N HCl
asoluble in 10 acetone in 1N HCl
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Isotherms of compounds 13, 6, 8 and 7
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Tafel Tests1
Solution fcorr, V SCE ?a,, V/decade ?C V/decade Icorr(mA/cm2) CR (mpy) Inhibition Efficiency
Blank - 0.480 0.1777 0.1813 2.2563 1031.8 0
(7) -0.4805 0.0717 0.10767 0.1914 87.5 91.52
(13) -0.4717 0.1473 0.1661 0.2594 118.6 88.51
(15) -0.4878 0.09996 0.1731 0.1303 59.6 94.22
1 Rahman, S. U., Saeed, M. T., Ali, S. A,
Anti-Corrosion Methods and Materials (Accepted).
26
Conclusions

• Following new compound exhibited excellent
  corrosion inhibition of mild steel in hot acidic
  medium

Polar compounds with substantially bulky
non-polar chains were better inhibitors.
Isoxazolidines
Cyclic Hydroxylamines
Cyclic Nitrones
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Future work

• Gather more data in different corrosive
  environments.
• Use mixtures of these compounds. Statistical
  experimental design will be beneficial
• Perform toxicity studies
• Study their antiscalent properties.
• Study their synergy with commercial antiscalents.

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Acknowledgement

• Prof. S. A. Ali,
• Dr. M. T. Saeed,

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Thank you