Additives III - Anti-oxidants/Oxidation Inhibitors

[MolaKule]

Oxidation occurs when oxygen is introduced in large quantities to oils. This process is accelerated by heat, metal catalysis, and the presence of moisture, acids, or solid contaminants. The oxidation process leads to increased viscosity and deposit formation (as in varnish and sludge).

This Class of additive decomposes peroxides and terminates free radicals so as to retard oxidation of the oil.

1. What is this class of additive?
2. Name at least one of the additive compounds in this class.

[ July 22, 2003, 01:29 PM: Message edited by: Patman ]

 

[Pablo]

Anti-oxidants

My mind ain't workin'...uh, reducing agents, but none as strong as sodium perborate....and maybe some synthesized organic (carbon) compounds, and some bases and I know Mo and even some S compounds.

 

[68redlines73]

2. Alkylated diphenylamines, or, my personal favorite...2,6-Di-t-butyl-p-cresol

[ June 03, 2003, 12:00 PM: Message edited by: 68redlines73 ]

 

[rugerman1]

quote:

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To fight oxidation in oil we use antioxidants. This fights and terminates free-radical reactions that attack the Carbon hyd bond and destroys the base oil thus creating higher levels of oxidation and putting more demand on the detergents.

Detergents are used to clean up the by product of oxidized oil which occurs when antioxidants can't neutralize the acids effectively by creating a chemical reaction with sludge, and varnish precursors so to neutralize them and keep them soluble.

Zinc dithiophosphates, hindered phenols, aromatic amines, sulfurized phenols are typical compounds used as antioxidants.

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Mark

[ June 03, 2003, 01:50 PM: Message edited by: rugerman1 ]

 

[MolaKule]

Korrect! Antioxidants it is. Whew, this is one tough group.

Recall that there are three main additive classifications:
A. Surface Prtective Additives,
B. Performance Additives
C. Protective Additives.


Antioxidants fall into the Protective Additive Category, No. 3.

Organometallic Antioxidants:
1. ZDDP
2. MoTDC
3. Antimony (SbTDC)

Other Chemicals:
1. Hindered Phenols such as dioctyldiphenolamine
2. Organic Amines such as, Aromatic Amineoctylated and butylated
diphenylamines; amine phosphate,
3. Tolutriazoles
4. alkyl polycarboxylates
5. heterocyclic S-N compounds
6. Sodium XX-benzothizole (Used in antifreezes as well).
7. Hydroxyalkyl and Alkenylcarboxylic acids in ester form
3. Sulferized phenols.

[ June 03, 2003, 10:47 PM: Message edited by: MolaKule ]

 

[MolaKule]

Most lubricants have a primary and secondary anti-oxidant.

Please explain why.

 

[Mickey_M]

quote:

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Originally posted by MolaKule:
Most lubricants have a primary and secondary anti-oxidant.

Please explain why.

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As oils oxidize they turn into organic acids which attack metals and oxyhydrocarbons causing oil thickening and sludge.

To deal with both problems there are two categories of anti-oxidants.

The first slows down the rate of oxidation, which is what most people think of when they think "anti-oxidant".

The second forms a protective coating on metal surfaces (particularly bearing surfaces) to shield sensitive metals.

 

[MolaKule]

Excellent answer Mickey_M.

Add to this the fact that primary and secondary anti-oxidants react at different temperatures and pressures.

Generally speaking, the primary anti-oxidants take care of thigs at the lower temperatures, while the seconmdaries are for higher temp situations.

 

[MolaKule]

The amines are a class of aliphatic organic nitrogen "rich" compounds that are useful as dispersants (in ester formats) and as anti-oxidants in other complex compounds.

You have to careful to apply the correct complex amine to the right application. The ethanolamine, diethanolamine, triethanolamine series, etc can exhibit hydrolosis issues in conjuction with certain compounds.

Most of these compounds are made by reacting ammonia with ethylene oxide or ethylene chloride.

Secondary and tertiary amines were most often compounded for anti-oxidants, but have been replaced by the butylated phenols, the complex amine esters, Tolutriazoles, and the thiadiazoles.

 

[Bill]

quote:

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Oxidation occurs when oxygen is introduced in large quantities to oils. This process is accelerated by heat, metal catalysis, and the presence of moisture, acids, or solid contaminants. The oxidation process leads to increased viscosity and deposit formation (as in varnish and sludge).

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Molekule,

I was told that that a petroleum oil can 'Oxidize' in two ways:

a) The oil can Oxidize against itself, as in the lube basestock can have impurities that may work against the host lube.

b) The oxidation occurs from the presence of oxygen with heat, etc, as you stated above.


A synthetic (PAO, Ester) lube will need less Anti-Oxidants (or will not need to depend on the Anti-Oxidants as much as petro lube) because they do not have the impurities that Petro lubes have and will not oxidize as much or as quickly.

Is this true?

 

[bruce381]

You would think a PAO would not need an AO but they are by themselves with out a AO very poor
in resisiting oxidation. However with a small amount .2-.5% they will shine and offer protection out past 10,000 hours on the
ASTM D-943 test. Compared to 2,000 hours or so from GP I base stocks. That said GP II and GP III will also go past 10,000 hours with correct AO.
Bruce