Safety
of Breathing Air Compressor Fluids
Dr.
James Sandler

Diester compressor fluids have been the products preferred for the lubrication of Breathing Air Compressors. This preference stems from their high level of solvency and lubricity due to the Alcohol and Fatty Acids present in their chemistry. It has been assumed that these Esters are safe for there intended application.

Recent
research into the chemical nature of these diesters has indicated some major issues relating to their safe use in Breathing Air Applications and especially their use in Enriched Oxygen applications.

The
FDA authorizes lubricant usage in food plants where there is the possibility of incidental contact of the lubricant with food stuffs. The approved lubricant is listed as H-1 (H-2 lubricants may be used ill food plants but only where there is no possibility of contact with food stuffs) and meets the requirements of 21 CFR 178.3570. H-1 lubricants are the safest type of lubricants that are
presently
available and may be present in foods stuffs that are approved for Human Consumption. There is no diester approved as an H-1 lubricant.

The
concern on the part of the FDA regarding diester lubricants is because of the toxicity levels of esters in general. In Breathing Air Applications, it is assured that to a lesser or greater degree some lubricant will be consumed.

The toxic effects of esters can be approached on a number of levels.

  1. The chemical formulation of the esters.
  2. The decomposition of esters in high pressure high temperature compressor applications.
  3. The susceptibility of diesters to early oxidation in the presence of enriched oxygen.

The most common esters used in air compressors are Diesters of Diisodecyl and Tridecyl Alcohols and Acids (Fig 1). The alcohols used in the production of esters are normally tri or tetrapropylene, diisobutene, codimers of propylene and n-butenes. These oxo-alcohols are esterified in the form of isomer mixtures. The dicarboxylic acids (fatty acids) are joined with the alcohols in the presence of acidic catalysts (NaHSO4 Phosphoric acid and its salts Trialkyl or Triaryl phosphates, p-toluenesulfonic acid and mineral acids) to make the desired diester. The alcohol groups and in many cases the fatty acids have a level of toxicity that is considered unacceptable for human consumption.

Diesters start to thermally decompose at temperatures as low as 180C (374F). While this may be desirable from the aspect that the decomposition products may leave the compressor and thus have less operational effect. The decomposition products in their natural states are toxic and in thermal degradation there are other undesirable compounds formed such as CO and CO2, This relative thermal instability is one of the most undesirable traits of diesters in Breathing Air Applications.

Diesters are also subject to early oxidation at temperatures over 65C (149F) especially in the presence of metals, especially copper. The presence of higher than normal levels of oxygen enhances this undesirable tendency. The American Society of Testing Materials have a test that establishes the oxidative stability of Oils at 375 F, 175 psig in the presence of pure oxygen and copper and steel catalysts. This ASTM 2272 RBOT test normally shows the best diesters with test a life of approximately I000 minutes. In comparison advance technology stabilized food grade products, such as EZ-1000 can last twice as long in this test environment.

We believe that it is incumbent on industry producing and using consumed by the general public to offer the safest products that are most up to date technology. New technology highly stabilized food grade lubricants are the next step in ensuring that the safest air possible is offered in breathing air applications. These new lubricants have demonstrated constantly lower wear rates and superior oxidative stability in addition to their safer operation.

Follow the links below for more information:

Typical Use and Application Of EZ-1000
Material Safety Data Sheet
Safety of Breathing Air Compressor Fluids
Toxins found in Common High Pressure Compressor Lubricants
Toxicity of Phthalate Esters used to Lubricate Breathing Air Compressors