There is a wide range of performance levels among both readily biodegradable and petroleum-based lubricants. It’s important to know that some EALs provide higher performance results than some petroleum based or other readily biodegradable lubricants. The folk at RSC Bio take a look at the four types of EALs⎯their performance advantages and disadvantages⎯ and they tell Splash readers why EALs should be considered for your lubricant application.
Environmentally Acceptable Lubricants are defined by the EPA as offering these three characteristics. First, they must be “biodegradable” as defined within the VGP⎯biodegrading into carbon dioxide and water by ≥ 60% or more within 28 days (according to OECD 301B or ASTM D7373 methods). Next, they must be “minimally toxic,” causing only a light impact on the aquatic environment (LC50> 100mg/L for lubricants and LC50>1000mg/L). Lastly, they are “not bioaccumulative,” and must have a low propensity to bioaccumulate in organisms in accordance with the specific requirements set forth within the VGP definition of “not bioaccumulative”.
Additionally, the Clean Water Act of 1972 mentions discharges of oil should not exhibit any visible ‘sheen’ on the water’s surface. Otherwise it is considered a pollutant (according to CFR 40 Part 435 A).
Where and When to Use EALs
Under the EPA’s 2013 Vessel General Permit (or VGP), all ships larger than 79 feet must use Environmentally Acceptable Lubricants in oil-to-sea interfaces when operating within the three nautical mile limit of the United States and in the Great Lakes unless technically infeasible.
The EPA VGP requirements can be a useful roadmap for operating in or adjacent to aquatic or other sensitive environments. Use of EALs can reduce overall operating risk, enhance environmental responsibility profile of operators and choice of the right EAL can also enhance a company’s overall sustainability position.
The Four EAL Types
The EPA recognizes four types of EALs:
- Vegetable Oils (HETG)
- Synthetic Esters (HEES)
- Polyalkylene Glycols (HEPG)
- Polyalphaolefins (PAOs) and related hydrocarbon products (HEPR)
Also referred to as Natural Esters, these lubricants are made of vegetable, rapeseed (Canola), sunflower, coconut, palm or soybean oil.
- High viscosity index
- Very good wear properties
- Compatible with most seals and hoses
- More susceptible to oxidation under high temperatures and pressures
- More prone to hydrolysis in the presence of water
- Shorter lifespan than other EAL types
- Typically recommended for use in a wide range of land-based applications with shortest scheduled change out intervals
Synthetic Esters (HEES)
Esters are synthesized by the reaction of an alcohol with an acid to form an ester. This reaction process allows for the flexibility to customize the type of ester used for each application.
- Delivers high performance
- Good thermal and oxidation stability
- Readily separates from water
- Offers good corrosion prevention and hose compatibility
- Extended fluid life
- Prone to hydrolysis in the presence of water
- Typically recommended for use in a wide range of both land and marine applications with scheduled change out intervals. For marine applications, saturated esters are commonly used as they are more stable than unsaturated esters but are still susceptible to hydrolysis of the ester functionality, leading to acid formation and viscosity loss. EALs based on saturated esters can often, but not always, last a full 5 year drydock cycle in service.
Polyalkylene Glycols (HEPG)
Made of synthetic, petroleum-based oil, HEPGs are created by the polymerization of ethylene or propylene oxide and contain hydroxyl groups that make them hydrophilic in nature.
- Designed to be partially or fully water soluble; however, solubility may increase the toxicity
- Excellent high and low temperature viscosity performance
- Fire resistant properties
- Compatibility challenges with seals, hoses, paints and varnishes
- Incompatible with mineral oils and other EALs
- Typically not derived from a renewable resource
- Typically recommended for use in a wide range of both land and marine applications with short to midrange change out intervals of up to 5 years.
Polyalphaolefins (PAOs) and related hydrocarbon products (HEPR)
Often referred to as classic mineral oil-based lubricants, HEPRs are synthesized hydrocarbons historically derived from crude oil meant to provide a low viscosity base oil that is readily biodegradable. However, more recently, HEPR type base stocks from renewable sources have been developed and are being offered by some manufacturers.
- Exceptionally durable and offer extended wear protection
- Extended fluid life
- Broad temperature range performance
- Excellent thermal and hydrolytic stability
- Excellent seal compatibility
- Excellent water separation characteristics
- Good corrosion protection and oxidation stability
- None, since the development of base oils from renewable sources.
- Typically recommended for use in a wide range of both land and marine applications with extended scheduled change out intervals of up to 10 years in some cases.