Toluene source in diester compressor oil?

Swampdiver,toluene is a clear colorless liquid with a very distinctive smell, it occurs naturally in crude oil and is produced in the process of making gasoline and other fuels from crude oil.Toluene does not stay in the enviroment long or buil up in animals or people.Really i think the answer might be in the unit that was used to produce the air.I would look at the compressor mainly the seperator filter, not sure but sounds dangerous to use a "oil" compressor for this when oiless ones should be available .

Hi Scott,
I have yet to see an oiless compressor used in the commercial scuba or fire compressor world. They all generally are high pressure reciprocating compressors which operate up to 5000 or 6000 psi. Most small dive shops and fire departments have air cooled compressors with small oil sumps using either a petroleum based mineral or diester synthetic oil. I may be wrong but I think the oiless compressors are much more maintenance intensive than the oil lubed ones.

In this particular incident the toluene has been traced to the oil. There was no external source of toluene at the compressor station. Normally these oil vapors would be removed by activated charcoal filtration but in this case the charcoal had become excessively moist and a toluene breakthrough occured.

There seems to be a difference of opinion out there as to the source of the toluene in these synthetic diesters. One chemist said there should be no toluene in a high quality synthetic basestock and it has been added to the basestock to dissolve some of the additives.
He mentioned as an example that the red colour in transmission oils is a dye which is added using a toluene solvent.

I thought the toluene might be a carry over from the actual diester basestock production but he disagreed. If the toluene is not a carry over product and is being added to the basestock then the problem of producing a safer oil for this application should be manageable.

Any thoughts?

Swampdiver,
Perhaps i am missing the point here, toluene is used in making of some products, solvents ,paints lacquers, adhesives as well as being a naturally occuring product in crude oils.My thoughts are what oil would i be willing to breathe?Well none .I find it hard to imagine a dive shop using a compressor regardless of costs that has a chance of oil contamination in a breathing apparatus...disturbing...Some compressors mainly screw drive ones,use a antifoaming atf fluid which could easily have toluene.Diester more than likely does not make there own oil a msds on the oil might help you on determine more on that subject.I sure am not ready to go diving anytime soon

Swampdiver, have you given any thought to the toluene contamination arising from the ambient environment? Toluene vapor in the air pulled through the compressor may concentrate in the oil sump because the toluene is very soluble in the oil.

Was anyone using a toluene containing product in the shop while the compressor was running? Is the inlet of the compressor drawing fresh outdoor air or dirty indoor air? Indoor air pollution is a much worse problem than many know about.

Scott,
I received some more vapor data back today and the diester oils from two different companies have ten times the toluene levels than either a mineral oil or PAO oil which are also used in breathing air compressors, although the PAO rarely.There was very little toluene in the PAO oil. There must something particular to the diesters as a group with regard to their toluene levels?

You are absolutely right in that one would not want to breath any of these vapors and normally the dessicant and activated charcoal when maintained properly should remove these vapors. But when the compressor manager, often trying to save money or not correcting for excessive humidity and temperature stretches the filtration change interval out to far, those vapors breakthrough the charcoal bed endangering the lives of divers. All divers and firemen in North America are at risk but divers moreso as toluene (and lots of other hydrocarbons) act like anesthetics at high pressure. A concentration that on surface may just give you a headache can be lethal at depth with increased pressure.

Do you have the name of this anti foaming agent? Is toluene used as a solvent?

Regrig guy,
Good thought but we are 100 percent certain the toluene is from an internal compressor source and not from entraining toluene via the remote air intake. There was a case of this external contamination about a decade ago where the remote intake was above 45 gallon barrels of toluene solvent.

I still think you may have an external source for the toluene (rubber cement from a wet suit repair?), but here is one other possibilty for you to investigate.

Diesters are manufactured from acid and alcohol, and water is removed as a byproduct of the chemical reaction. The water needs to be removed to allow the reaction to go to completion. Toluene and water form an azeotrope, allowing the water to be easily removed from the reaction mixture by distillation. Toluene and water are easily separated after distillation by decanting the toluene off the top of the water layer allowing the toluene to be recycled back into the reaction mixture.

The toluene could be a residual solvent from the dehydration of the diester during synthesis. I would expect the toluene, if used, to be completely removed from the finished lubricant when the manufacturer of the diester distills off and recovers the excess acid used in the synthesis.

You will need to check with the manufacturer of the diester to see if they use toluene in the reaction process. They may or may not want to share that information, especially because of the California Proposition 66 labeling regulations. PAO and mineral oil would not need any azeotropic dehydration, so would not contain any residual solvent.

The defoamer additive mentioned above is likely a silicone oil, and would be a liquid at room temperature. These silicone oils are not normally diluted with solvent.

Refrig guy,

We now have two separate diester oils brands where the vapor was extracted directly from a new container of oil and both are contaminated with toluene. We are in the process of determining the toluene concentration in the oil itself. This is definitely an internal compressor source problem.

That being said your theory is the best I have heard to date and makes a lot of sense. I suspect the diester basestock manufacturers would try and remove/recover as much toluene as possible but likely some residual remains. For industrial lubrication use I assume this low level of contamination is not a problem, but for breathing air production it most likely is. There are so many applications these oils are used for that I doubt the manufacturer is aware of all the potential problems especially for a small niche market like breathing air production.

One chemist told me that the red dye in auto transmission oil uses toluene as a solvent. There are no dyes in the diesters we have it appears as they are very light in color. Are you aware of any powdered additives which may use toluene as a solvent?

I truly appreciate your help here and will speak with a few diester basestock manufacturers this week regarding your idea. Hopefully I can find the guy who is also a scuba diver and may be more willing to talk

Swampdiver, based on your information I agree you may have a toluene problem in the lubricant. I hope you have success in your conversations with the lubricant manufacturer, as that is your best bet to get the answer as to the source of the toluene.

The only additives you should find in the diester lubricants are antioxidants and possibly anti-wear compounds. The antioxidants are added for shelf life stability, and are normally hindered phenols or amines. One of the most common hindered phenols is BHT (butylated hydroxy toluene), the same compound as used in food products. BHT is a powder at room temperature, and there is a possibility it could be disssolved in solvent prior to addition to the diester lubricant to speed up the final blending of the lubricant. BHT can be readily dissolved in hot lubricant just after final dehydration and acid removal, so solvent is not necessary.

If the lubricant darkens over time to an orange-reddish-brown color when exposed to air, the antioxidant is likely an amine. These are typically liquids and should need no solvent.

The antiwear compounds are typically phosphate esters, things like tricresyl phosphate (TCP). TCP is a viscous liquid at room temperature so should need no solvent.

Just a follow up on this for those interested.

We spoke with the manufacturer and they said no toluene was used in the production of the base stock ester, however one of the phenol antioxidant additives may contain toluene. The toluene may improve the low temperature handling of the additive.

From an industrial lubricant standpoint the toluene concentration is definitely at trace levels, and for these applications does not pose a problem. Unfortunately for breathing air applications such as those found in fire departments and scuba facilities this trace contaminant can be a serious problem if the filtration/purifier system is not properly maintained.

Thanks to all who offered help with this and to any of you who are divers always smell your air prior to jumping in!

I thought only food grade oils were allowed in diving compressors? A synthetic diester oil? Perhaps in my steam turbine EHC system, but not in my dive shops compressor!!

Actually Andy you will find that in North American the bulk of diving and fire hall high pressure recip breathing air compressors are using a synthetic ester or a mineral oil. From what I understand with the small sumps, water, and heat from a straight compressor performance standpoint the ester is still considered the best oil.

The US Navy uses a mineral oil called TEP 2190 in most of its breathing air compressors unless the manufacturer specifies otherwise. I believe it is a steam turbine oil for extreme pressure.

As for food grade that was a bit of a misnomer for breathing air use as this H1 designation was for ingestion of the oil not inhalation of its vapors. Many of the food grade oils (PAO) still contain alkanes and aromatic vapors in trace levels which are not a problem for industrial applications at these concentrations, but breathing these vapors under hyperbaric conditions becomes a problem.

For breathing air use one must not only consider the oil's compressor performance but also the safety of its vapors both native and degradation should the filtration go down.