Ester Content and Oxidation (abs/cm) on Virgin Analysis

Joined
Aug 25, 2018
Messages
3,761
Location
South Carolina
I'm looking for information regarding the different esters used with group IV PAO oils to increase solubility and how they effect the oxidation value on VOAs. It seems when it comes to polyol ester, the oxidation value seems to increase approximately 5 abs/cm for every 1% content. I know that's not exact, but just a rough estimate based on what I've seen before. What esters out there are used for this purpose and concentration that doesn't effect oxidation? Would any type of ester provide the same or better solubility at a lower concentration compared to another type?
 
The VOA's that I got on Redline 5w30 had oxidation numbers around 108, which Polaris flagged as severe.
Sorry I don't know what the percentage of ester is in Redline.
 
Alkylated naphthalene (AN) does not register as oxidation in FTIR. I know that much, but AN also isn't ester. I'm wondering about different types of ester giving different oxidation results. Trimethylolpropane (TMP), neopentylglycol (NPG), pentaerythritol (PE), and so on.
 
Gubkin on here says


ESTER 10 % - oxidation 42-45
ESTER 15 % - oxidation 63-75

Makes sense from what I've seen.
 
If Valvoline Premium Blue Restore indeed is comprised of 50% ester (out of the whole, not just the base oils) as I think it does based on Valvoline's patent, and the VOA below for the oxidation value is correct, its oxidation value per percent ester is 110/50 = 2.2. I seem to recall Tom NJ saying its ester is not a particular polar type, relative to all ester types suitable to be used in motor oils.


You can look at ExxonMobil's various esters and look at the aniline points and Kauri-Butanol Values to compare their polarity/solubility. The different esters have different solubility and within a certain type, the smaller the molecule / lower viscosity, the higher the solubility. Tom NJ said that some of them are unlikely to be used in motor oils.
https://www.exxonmobilchemical.com/en/resources/product-data-sheets/Synthetic-base-stocks/esters

An example of esters suitable for motor oils that are low in polarity relative to other esters are polymer esters. At least part of the reason is they tend to be large molecules. I don't recall if that is also due to molecular structure. Their aniline point is often published by the manufacturer.

Besides esters and alkylated naphthalene, oil-soluble PAGs are another possible way of increasing solubility of the additive package and providing other potential benefits. Ravenol is the only manufacturer that I've seen state that some of their oils use them.

I'm not a chemist, so hopefully Molakule or Tom NJ, or some other chemist will reply and answer questions that are still unanswered.

C08EA640-EC1E-46D7-B194-3EC356E3E631.png
 
Look at the formula for each ester. The greater the number of Ox molecules the greater the oxidation numbers might/could be.

However, there are so many ester-based or esterified additive components I would not equate the oxidation numbers with the amount of ester base oils in a finished lubricant.

It seemed to me the OP's question was about maximum solvency verses the ester with the lowest number of oxygen molecules?
confused2.gif
 
Last edited:
Originally Posted by MolaKule
Look at the formula for each ester. The greater the number of Ox molecules the greater the oxidation numbers might/could be.

However, there are so many ester-based or esterified additive components I would not equate the oxidation numbers with the amount of ester base oils in a finished lubricant.

It seemed to me your question was about maximum solvency verses the ester with the lowest number of oxygen molecules?


Basically, yes. When looking at the VOA of a PAO based engine oil, I like to see an oxidation number >30 as an indication of good ester content for solubility. I'm wondering if a PAO oil shows cm oxidation on a VOA, if it should be a cause for concern in regards to solubility or if there's other esters used for solubility that don't show up in oxidation (or show up in lower amounts).

I'll do some research on various types of ester and their Ox content. That gives me something to go on.
 
Here is an example:

Suppose I use an additive in a synthetic base oil which contains a phosphorilated boron compound in an ester carrier.

That alone will provide a measure of solvency for the rest of the additive package and formulation. Then add to that the other compounds that are in an ester carrier. (don't forget that ZDDP is also an ester)!

My experience is that about 7% TOTAL esters composition in a synthetic formulation will keep everything in solution and provide sufficient seal conditioning as well.

So I am still not quite clear of your question or concern.
 
Last edited:
I get what your saying. That 7% total ester composition would normally show up as >30 abs/cm oxidation. Let's say you have a PAO based oil that shows up as only 10 abs/cm but supposedly has >7% ester. Could certain types of ester not show high oxidation at a >7% concentration? If so, which types.
 
The oxidation value by FTIR does not measure ester base oils per se, it measures carbonyl bonds, C=O. Ester base oils contain C=O bonds, but so do some of the additives. If the oxidation value of an oil is significantly higher than the average conventional oil it usually indicates the presence of some ester base oil content, but how much is difficult to say without knowing which ester is being used.

Ester base oils used in motor oils may contain one, two, three, four, six or more C=O containing ester linkages, so to calibrate the oxidation value against the ester content you need to know which ester(s) are being used and the effect of the additive system. Best you can say is the higher the oxidation value above an average conventional non-ester oil, the higher the ester base oil content is likely to be, but assigning a percentage without composition information and calibration is just a guess.

I agree with Molakule that an ester content of around 5-15% is enough to provide additive solubility and seal conditioning, and more will kick in some cleaning capability and lubricity, but too much can adversely affect seals. Exact numbers depend on which esters and other balancing base oils and additives are used.
 
Originally Posted by Tom NJ
The oxidation value by FTIR does not measure ester base oils per se, it measures carbonyl bonds, C=O. Ester base oils contain C=O bonds, but so do some of the additives. If the oxidation value of an oil is significantly higher than the average conventional oil it usually indicates the presence of some ester base oil content, but how much is difficult to say without knowing which ester is being used.

Ester base oils used in motor oils may contain one, two, three, four, six or more C=O containing ester linkages, so to calibrate the oxidation value against the ester content you need to know which ester(s) are being used and the effect of the additive system. Best you can say is the higher the oxidation value above an average conventional non-ester oil, the higher the ester base oil content is likely to be, but assigning a percentage without composition information and calibration is just a guess.

I agree with Molakule that an ester content of around 5-15% is enough to provide additive solubility and seal conditioning, and more will kick in some cleaning capability and lubricity, but too much can adversely affect seals. Exact numbers depend on which esters and other balancing base oils and additives are used.



Ok, I think I have a good understanding of it now. The oxygen content isn't consistent across all types of ester, and I need to stop overthinking it.
smile.gif


I appreciate the great information in this thread.
 
Mobil 1 ESP 5w30 for example has a virgin oxidation reading of 35. Mobil 1 0w40 - 36. AN's wont' show so that we don't know. All other grades of Mobil 1 show
Of interest is Valvoline Premium Blue which has an oxidation reading of 110 and contains 50% Ester base stock.

Redline VOA's show oxidation to be 95-130 depending on grade and per Dave at RL, they use in the 40% range.

Based on what Tom/Mola said, you can't tell what the % of ester is.
 
Back
Top