On-site Additive Depletion and Oxidation Monitoring in ... · Turbine Oil Beer’s Law (Absorbance...

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On-site Additive Depletion and Oxidation Monitoring in Turbine Oils by FTIR Spectroscopy

By Christopher SassoOut of Lab Product SpecialistAgilent Technologies

FT-IR Spectroscopy Fundamentals

Overview of Antioxidants and Oxidation

Measuring Phenolic and Aminic Antioxidants in Turbine Oil

Relationship Between AO Depletion and Oxidation

Remaining Useful Life Results• Portable FT-IR • Other Methods

Contaminant Detection

Portable FT-IR Spectrometers

• “Spectroscopy” is the study of how electromagnetic radiation interacts with the atoms and molecules that compose matter

• “Infrared” spectroscopy is specifically the study of how infrared light (heat) is absorbed by the bonds between atoms that form molecules

What is Spectroscopy?

Microwave

(Rotation)

Radio Wave

(Nuclear Spin)

Visible

Infrared

(Molecule Vibration)

Wavelengths:

770 nm – 50 µm

Wavenumbers:

12,900 – 200 cm-1Ultraviolet

(Electron States)

X-ray

(Nuclei)

n Wavelengths of light in the infrared (heat) region have energies that are on the same order of magnitude as vibrating bonds in molecules

Infrared Radiation

Peaks appear where sampleabsorbs light

Infrared(heat)

Source

InfraredDetector

A spectrum is a graph of how much infrared light is absorbed by molecules at each wavenumber of infrared light

Infrared Spectrum

Bend

~ 1600 cm-1

Symmetric stretch

~ 3300 cm-1

Antisymmetric stretch

~ 3400 cm-1

Ab

sorb

ance

Wavenumber (cm-1)

Oxygen

Hydrogen

Infrared Spectrum of Water (H2O)

Simple IR Group Frequency Chart

H – C – C – C – C – C – C – H

H|

H|

H|

H|

H|

H|

|

H

|

H

|

H

|

H

|

H

|

HC – H stretch

H – C – H bend

Ab

sorb

ance

Wavenumber (cm-1)

Hexane

H – C – C – C – C – C – C – O – H

H|

H|

H|

H|

H|

H|

|

H

|

H

|

H

|

H

|

H

|

H

C – O stretchO – H stretch

Ab

sorb

ance

Wavenumber (cm-1)

Hexanol

H – C – C – C – C – C – C – H

H|

H|

H|

H|

H|

O||

|

H

|

H

|

H

|

H

|

HC = O stretch

Ab

sorb

ance

Wavenumber (cm-1)

Hexanal

H – C – C – C – C – C – C – O – H

H|

H|

H|

H|

H|

O||

|

H

|

H

|

H

|

H

|

H

C – O stretch

C = O stretch

O – H stretch

Ab

so

rban

ce

Wavenumber (cm-1)

Hexanoic acid

Ephedrine

Pseudoephedrine

Specificity of Infrared Spectra

IR Spectral Overlay of an Additive in an Aromatic Solvent

4600 4400 4200 4000 3800 3600 3400 3200 3000 2800 2600 2400 2200 2000 1800 1600 1400 1200 1000 800 600

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0.0

Wavenumber

Ab

sorb

ance

1710 1700 1690 1680 1670 1660 1650 1640

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0.0

Wavenumber

Abs

orba

nce

Calibration Curve for Additive in Aromatic Solvent

1

2

3

4

5

6

7

8

R²=1.000

5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

3.0

1.5

0.0

Peak Area

Con

cent

ratio

n

Overview of Antioxidants

Aminic and Phenolic Based Additives

Sulfur based, ZDDP

Function as preservatives

• Prevent oxidation• Inhibit the oxidation mechanism

Will not reverse oxidation damage

Once consumed oxidation skyrockets

Antioxidants

Phenolic Antioxidants (AO)

• Common in most mineral based lube oils• Similar in function to natural antioxidants such as vitamin E,

(tocopherols)• Efficient free radical scavengers• Terminate the oxidation chain reaction• Sacrificial additive, first to be consumed• Better performance at low temperatures

R

OH

Antioxidants

Aminic Antioxidants

• Also common in most mineral based lube oils• Functions similarly to phenolics, quenches oxidation free radicals• Synergistic Relationship with phenolic AO

– Can be recharged by phenolic AO• High thermal stability• Performs better than phenolics at high temperatures

NH

R R

Oxidation

Conditions that lead to oil oxidation• Heat• Extreme Pressures• High sheer conditions• Water

– Accelerates oxidation by forming peroxides– Can cause wash out of antioxidants and other additives

• Metal wear particles– Acts as a catalysts that accelerate oxidation

• Electrostatic sparking – Introduces nitrates

Oxidation

The Oxidation Chain Reaction• Held in check by AO• Skyrockets without AO

– Exponential growth

– Hockey stick model

– Reaches a critical saturation point before taking off

Point of no return• Adding AO after critical saturation point has little benefit

Varnish consists of mostly oxidation products• Observed increase in varnish as AO’s are consumed


IR bands are distinctive for aminic and phenolic functional groups

Phenolic functional group creates a sharp band at 3650cm-1

Aminic functional group is at 3430cm-1 (broad), and sharp p-aromatic at 1510cm-1

Multiple bands in the IR spectra for both AO


3680 3675 3670 3665 3660 3655 3650 3645 3640 3635 3630 3625 3620 3615 3610Wavenumber

Abs

orba

nce

3680 3675 3670 3665 3660 3655 3650 3645 3640 3635 3630 3625 3620 3615 3610Wavenumber

Abs

orba

nce

3460 3455 3450 3445 3440 3435 3430 3425 3420 3415 3410 3405 3400 3395Wavenumber

Abs

orba

nce

3460 3455 3450 3445 3440 3435 3430 3425 3420 3415 3410 3405 3400 3395Wavenumber

Abs

orba

nce

R

OH

R

OH

NH

R R

NH

R R

Aminic aDPA, alkyl di-phenylaminePhenolic DBPC, di-tertiary-butyl paracresol

Infrared Spectrum of Turbine Oil

433

2.0

4259

.9

4168

.7

406

8.7

365

2.6

360

9.7

348

7.5

336

3.0

2727

.326

75.

1

2406

.123

39.2

2185

.2

203

1.5

189

0.8

160

6.1 15

16.1

130

5.5

125

1.5

114

4.4

112

3.1

106

7.3

937

.489

1.1

846

.0

770

.47

23.1

4600 4400 4200 4000 3800 3600 3400 3200 3000 2800 2600 2400 2200 2000 1800 1600 1400 1200 1000 800 600

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0.0

Wavenumber

Abs

orb

ance

3993.2 am 5995 phen w surf(1)

4332

.0

4259

.9

4168

.7

4068

.7

3652

.6

3609

.7 3487

.5

3363

.0

2727

.3

2675

.1

2406

.1

2339

.2

2185

.2

2031

.5

1890

.8

1606

.1

1516

.1

1305

.5

1251

.5

1144

.4

1123

.1

1067

.3

937.

4

891.

1

846.

0

770.

4

723.

1

3750 3700 3650 3600 3550 3500 3450 3400 3350 3300 3250 3200

0.05

0.04

0.03

0.02

0.01

0.00

-0.01

-0.02

-0.03

-0.04

-0.05

-0.06

-0.07

Wavenumber

Abs

orba

nce

3993.2 am 5995 phen w surf(1)

4332

.0

4259

.9

4168

.7

4068

.7

3652

.6

3609

.7

3487

.5

3363

.0

2727

.3

2675

.1

2406

.1

2339

.2

2185

.2

2031

.5

1890

.8

1606

.1

1516

.1

1305

.5

1251

.5

1144

.4

1123

.1

1067

.3

937.

4

891.

1

846.

0 770.

4

723.

1

1670 1660 1650 1640 1630 1620 1610 1600 1590 1580 1570 1560 1550 1540 1530 1520 1510 1500 1490

0.26

0.24

0.22

0.20

0.18

0.16

0.14

0.12

0.10

0.08

0.06

0.04

0.02

0.00

-0.02

-0.04

-0.06

Wavenumber

Abs

orba

nce

3700 3690 3680 3670 3660 3650 3640 3630 3620 3610

Wavenumber

Abs

orb

anc

e


Peak Area

1

4

7

10

13

16

19

22

25

28

Quant Validation Plot for Phenolic (ppm)R²=1.000

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

10000

9000

8000

7000

6000

5000

4000

3000

2000

1000

0

Con

cent

ratio

n


Beer’s Law (Absorbance Law): IR absorbance is directly proportional to concentration

A=abc

A is Absorbance, b=thickness, c=concentration, a=absorptivity constant

FT-IR measures each AO separately

FT-IR measures all compounds in a mixture at the same time (one spectrum can yield concentrations for dozens of components)

Relationship Between Antioxidant Depletion and Oxidation

Goal: Predict oxidation before the critical saturation point is reached

Performed a modified thermal oxidation stability test (TOST D943)

• Universal Oxidation Test (D6514, D5846)• Similarity to RPVOT (D2272)

Started with 250mL used Chevron ISO 32 turbine oil

• heated in a lab oven at 135°C • Cu and Fe catalysts added

2mL removed and tested every 2-3 days

• Experiment lasted 26 days• Trended phenolic, aminic and oxidation FT-IR measurements over time

Oxidation Experiment


0.00

20.00

40.00

60.00

80.00

100.00

120.00

NewISO 32

Oil

Day 1 Day 2 Day 5 Day 6 Day 8 Day 9 Day 12 Day 13 Day 16 Day 19 Day 22 Day 23 Day 24 Day 26

Phe

nolic

and

Am

inic

Ant

ioxi

dant

s (%

of

Con

c. in

New

Oil)

0.00

5.00

10.00

15.00

20.00

25.00

Oxi

dati

on (

Pea

k A

rea

Abs

orb

ance

)

Aminic Antioxidant

Phenolic Antioxidant

Oxidation

PASS MONITOR FREQUENTLY CHANGE IMMEDIATELY

Critical Saturation of Oxidation Products


Phenolic Diminishes 40% right away

• Evaporation, Low molecular weight flash off

Aminic stays above 80% until near the end of useful life

Aminic Stages of depletion

• Stage 1: Initial slight increase to 110%• Stage 2: Mid-way point in oil lifespan, 25% depletion• Stage 3: Decent from 80% to 40% after phenolic reaches 30%

0.00

20.00

40.00

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NewISO 32

Oil


Ph

en

oli

c a

nd

A

min

ic A

ntio

xid

an

ts (

% o

f C

on

c.

in N

ew

Oil

)

0.00

5.00

10.00

15.00

20.00

25.00

Ox

ida

tio

n (

Pea

k A

rea

Ab

so

rb

an

ce)

Aminic Antioxidant


Oxidation




AO levels give a larger window of warning than oxidation alone

• TAN tracks oxidation• Viscosity tracks oxidation

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20.00

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NewISO 32

Oil


Phe

nolic

an

d A

min

ic A

ntio

xid

ants

(%

of C

onc.

in N

ew O

il)

0.00

5.00

10.00

15.00

20.00

25.00

Oxi

dati

on (

Pea

k A

rea

Ab

sorb

ance

)

Aminic Antioxidant


Oxidation



1 Day in the Lab Experiment = 3-6 months in real world oil life (assuming 6-10y oil life)

Rapid oxidation spiked on day 22• Day 20-21

– Aminic Rapid decrease– Phenolic modest decrease– Slight growth in oxidation

Day 22-23 = 1200% increase in Oxidation• Equal to 400% increase in one month real world in-service oil life


Re-additize, bleed & feed, or top-off at day 19• Outcome greatly delayed by preventive

measures

Aminic perhaps the best indicator for Oxidation

Varnish layer in Day 22 and later samples• 65-80% more oxidation products in varnish

compared to free flowing oil


Oxidation products are complex mixtures

Oxidation carbonyls are the most visible

• 1700-1720cm-1 region of IR spectrum

– Ketones

– Carboxylic Acids

– Aldehydes

– All contribute to the strong band at 1713cm-1


C O O H

C H O

O H

O


184

4.7

177

8.5

17

13.2

165

3.9

151

5.0

2020 2000 1980 1960 1940 1920 1900 1880 1860 1840 1820 1800 1780 1760 1740 1720 1700 1680 1660 1640 1620 1600 1580 1560 1540 1520 1500

0.65

0.60

0.55

0.50

0.45

0.40

0.35

0.30

0.25

0.20

0.15

0.10

0.05

0.00

-0.05

Wavenumber

Abs

orba

nce

184

4.7

177

8.5

17

13.2

165

3.9

151

5.0

2020 2000 1980 1960 1940 1920 1900 1880 1860 1840 1820 1800 1780 1760 1740 1720 1700 1680 1660 1640 1620 1600 1580 1560 1540 1520 1500

0.65

0.60

0.55

0.50

0.45

0.40

0.35

0.30

0.25

0.20

0.15

0.10

0.05

0.00

-0.05

Wavenumber

Abs

orba

nce

184

4.7

177

8.5

17

13.2

165

3.9

151

5.0

2020 2000 1980 1960 1940 1920 1900 1880 1860 1840 1820 1800 1780 1760 1740 1720 1700 1680 1660 1640 1620 1600 1580 1560 1540 1520 1500

0.65

0.60

0.55

0.50

0.45

0.40

0.35

0.30

0.25

0.20

0.15

0.10

0.05

0.00

-0.05

Wavenumber

Abs

orba

nce

Oxidation,Ester

Preventive Action Zone

Oxidation at Critical Saturation Point (Day 22)

Day 23, Oxidation

AminicAntioxidant

Oxidation Carbonyl,Ketone, Carboxylic Acid, Aldehyde

Oxidation,Perester,Organic Carbonate,Cyclic Anhydride,Acid Chloride

184

4.7

177

8.5

17

13.2

165

3.9

151

5.0

2020 2000 1980 1960 1940 1920 1900 1880 1860 1840 1820 1800 1780 1760 1740 1720 1700 1680 1660 1640 1620 1600 1580 1560 1540 1520 1500

0.65

0.60

0.55

0.50

0.45

0.40

0.35

0.30

0.25

0.20

0.15

0.10

0.05

0.00

-0.05

Wavenumber

Abs

orba

nce

184

4.7

177

8.5

17

13.2

165

3.9

151

5.0

2020 2000 1980 1960 1940 1920 1900 1880 1860 1840 1820 1800 1780 1760 1740 1720 1700 1680 1660 1640 1620 1600 1580 1560 1540 1520 1500

0.65

0.60

0.55

0.50

0.45

0.40

0.35

0.30

0.25

0.20

0.15

0.10

0.05

0.00

-0.05

Wavenumber

Abs

orba

nce

184

4.7

177

8.5

17

13.2

165

3.9

151

5.0

2020 2000 1980 1960 1940 1920 1900 1880 1860 1840 1820 1800 1780 1760 1740 1720 1700 1680 1660 1640 1620 1600 1580 1560 1540 1520 1500

0.65

0.60

0.55

0.50

0.45

0.40

0.35

0.30

0.25

0.20

0.15

0.10

0.05

0.00

-0.05

Wavenumber

Abs

orba

nce

Oxidation,Ester

AminicAntioxidant

Oxidation Carbonyl,Ketone, Carboxylic Acid, Aldehyde

Oxidation,Perester,Organic Carbonate,Cyclic Anhydride,Acid Chloride

Ester Oxidation products absorb at 1720-1745cm-1• Shoulders on main COOH and ketone components

1778cm-1 band likely a perester and/or an organic carbonate


O

O

O

O

O

O O

O

Best practice to save new oil to compare to used in-service oil• Enables % deletion of additives• Enables top offs and/or bleed and feed

Agilent Technologies MicroLab Software stores the IR spectrum of new oil• Overlays new oil spectrum with used oil• Provides weight percent value for aminic and phenolic antioxidants,

Oxidation % of upper limit


Yellow “Monitor Frequently” warning when AO’s reach critical depletion points

Red “Change Immediately” warning = critical thresholds reached

Phenolic and aminic are red = critical saturation point is imminent

Water is measured in ppm with yellow at 200ppm and red at 400ppm


Remaining Useful Life Measurements- Portable FT-IR and Other Methods

Remaining Useful Life (RUL)

• Rotating Pressure Vessel Oxidation Test (RPVOT)

– Specifically designed to measure RUL

– Overall quality of oil base stock and additives

– Accelerates oxidation reaction with heat, pressure, and pure oxygen

– Requires lab set up• Pure Oxygen gas cylinders (highly flammable)• Significant sample prep and monitoring• Expensive initial costs


RUL by Voltammetry

• Measures antioxidants

– Not a direct measurement, introduces errors • Electrochemical Technique: electrodes

– Current flow relative to applied voltage• Need new oil to compare to used oil

– Mixed oil and contaminant interference

– Wear metals, basic detergents, antifoam, and oxidation products (organic salts) cause interference

RUL by Voltammetry

Require Sample Preparation

• Careful Pipetting• Extraction step with an electrolyte solution

– Assumes a contsant extraction efficiency

– Extraction efficiencies are variable for additives in oil

– Some additives remain in oil = not measured

Voltammetric Electrodes need maintenance

• Cleaning and conditioning in buffer solutions


RUL by 4500 Portable FT-IR

• Exact direct measurements

– Aminic antioxidant wt.%

– Phenolic antioxidant wt.%

– Oxidation Products: via carbonyl bands

– Water (ppm), calibrated to Karl Fischer

– Nitration Products: occur in electrostatic spark conditions and combustion engine oils

• Single drop of neat oil + ~30seconds to scan

– KF precision water requires a stabilizer additive


RUL by Portable FT-IR

• No interference by wear metals or other contaminants• New oil comparison is recommended but not necessary

– Weight percent values are absolute regardless of mixed oils• Monitors the effectiveness of top-offs, bleed & feed, filtration, re-

additization, and dehydration


Detects common contaminations of oil• Phosphate ester (EHC) hydraulic in turbine, gear, or mineral

based hydraulic fluids• “Fingerprint” IR bands for EHC• Cross contamination from filtration & dehydration units• ID and/or Quantify a range of impurities

– WD-40 in Hydraulics– High particulates like Soot, Dirt, and wear metals

Contaminant Detection By Portable FT-IR

Contaminant Detection By Portable FT-IR

0

.2

.4

.6

3500 3000 2500 2000 1500 1000

0

.2

.4

.6

3500 3000 2500 2000 1500 1000

Absorbance / Wavenumber (cm-1)

0

.2

.4

.6

3500 3000 2500 2000 1500 1000

0

.2

.4

.6

3500 3000 2500 2000 1500 1000

Absorbance / Wavenumber (cm-1)

EHC, Phosphate Ester Bands

Methods Development – Portable FT-IR

• Other 4500 FT-IR Water Calibrations

• Gear Oil• EHC hydraulic, phosphate

ester based• Polyester hydraulic, Quintolub• Grease• Crankcase oil

• ASTM E-2412 method also available for condition monitoring of mineral oil basestocks

• ASTM D2668 Transformer Oil Phenolic

Conclusions

4500 Portable Full Scanning FT-IR Spectrometers Can Provide:

• Independent phenolic and aminic antioxidant concentrations• Fast results – helps prevent an unscheduled shutdown• Eliminates calibrating, maintaining, and conditioning other systems

require• Total analysis time per sample less than 3 minutes, immediately ready

for the next sample

On-site Additive Depletion and Oxidation Monitoring in ... · Turbine Oil Beer’s Law (Absorbance...

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Transcript of On-site Additive Depletion and Oxidation Monitoring in ... · Turbine Oil Beer’s Law (Absorbance...