Tagged: Group IV

Base Oil Groups

Base_oil_groups

Q: How many Groups of Base oils are there?

There are 5 groups of base oils as defined by the American Petroleum Institute (API). However, between 2003-2010, the Association Technique de L’Industrie Européenne des Lubrifiants (ATIEL) (Europe) included Group VI - All polyinternalolefins (PiO).

Groups I-III are typically mineral oils while Groups IV-V are synthetic oils.

  • Group I: Solvent refined
  • Group II: Hydrocracked / Hydrotreated
  • Group III: Hydrocracked / Hydro-isomerized
  • Group IV: PAO Synthetics
  • Group V: All other Synthetics

Here is a table that shows the different groups.

Reference: Lubrication Fundamentals Second Edition, Revised and Expanded. D.M. Pirro, A.A. Wessol, Chapter 2.

 

Group I: <90% Saturates, ≥0.03% Sulphur, Viscosity Index: 80 to 120

These were characteristically the most popular initially since they were relatively inexpensive to produce (solvent refined) and used in non-severe, non-critical applications. This Group has more double bonds (carbon) which allows for an increase in stability of the carbon chain.

 

Group II: ≥90% Saturates, ≤0.03% Sulphur, Viscosity Index: 80 to 120

These are hydrocracked and higher refined. However, due to hydrocracking, the double bonds are reduced greatly which decreases the stability of the carbon chain. (A lot of turbine users would have noticed this change around 2010 when most Group I base oils were replaced by Group II base stock. These users saw increased varnish as the oils did not have the level of solubility that they did before!).

Group II+: (yes, this exists!) These have VIs of 110-120 with improved low temperature and volatility Characteristics.

 

Group III: ≥90% Saturates, ≤0.03% Sulphur, Viscosity Index ≥ 120

There is an argument that this group should be placed in the synthetic category. However, by definition, this group is the severely hydrocracked and highly refined crude oil which can be used in semi-synthetic applications as it has similar properties to that of synthetic oil.  These are also called synthesized hydrocarbons.

Group III+: These have VIs approaching (or in some cases exceeding) those of synthetic PAOs (some even go above 140). They are also very pure with almost non-existent levels of sulphur, nitrogen, aromatics and olefins. Typically, Gas to liquid base oils can be found in this group as it approaches the Group IV categorization.

 

Group IV: Polyalphaolefins – these are very stable, uniformed molecular chains where there is a reduction in the coefficient of friction. Most are formed through oilgomerisation.

 

Group V: Ester and other base stocks not included in Groups I-IV such as silicone, phosphate esters, PAGs, Polyol esters, Biolubes and Naphthenics.

 

References:

  1. Chemistry and Technology of Lubricants 3rd Edition, Chapter 1, R.M. Mortier, M.F. Fox, S.T. Orszulik)
  2. Lubrication Fundamentals Second Edition, Revised and Expanded. D.M. Pirro (Exxon Mobil Corporation Fairfax, Virginia), A.A. Wessol (Lubricant Consultant Manassas, Virginia). 2001.

PAOs vs PAGs

PAO_vs_PAG

Q: What’s the main difference between PAOs & PAGs?

Let’s start off with definitions!

PAO: Polyalphaolefin

PAG: Polyalklene Glycol

While both are synthetic oils they are classified under different Groups of Base oils. PAOs have their own Base oil Group IV while PAGs fall into the Group V (catch all).

PAOs

PAOs are actually hydrogenated oligomers of an α-olefin and there are different methods of oligomerisation. Due to this process, PAOs have very good low temperature properties and the products are wax free! Additionally, their lower volatilities also allow them to operate over a wide temperature range. Usually, they can be used in a lot of versatile applications such as gearboxes, screw compressors, fans, motors and even automotive!

However, PAOs have a low polarity which gives rise to poor solvency of polar compounds and issues with seal performance.1

PAGs

On the other hand, PAGs can differ depending on their structure. For instance, Ethylene is water soluble while Propylene is not, however, neither are oil soluble. Both experience significant chemical reactions producing sludge like deposits when mixed with mineral oil.

Usually, their properties include a wide viscosity range, low pour points, good lubricity, low toxicity and non-flammable in aqueous solutions. PAGs are typically always found in fire-resistant hydraulic fluids as well as industrial gear oils, compressor lubricants, heat transfer liquids and metalworking fluids.1

Compatibility

Both products need to be tested for compatibility with mineral oils before any mixing occurs. Additionally, most lubricant suppliers deem PAOs & PAGS as “filled for life” solutions which last for a longer time compared to mineral oils. Typically, the purchase of these products are more expensive than mineral oils, however if one looks at the cost of waste disposal and reduced downtime (due to decreased shutdowns for oil changes) the overall cost of the lubricant is by far less than that of mineral oil.

 

References:

  1. Chemistry and Technology of Lubricants 3rd Edition, Chapter 2, R.M. Mortier, M.F. Fox, S.T. Orszulik