Lubrication - Environmentally Acceptable Lubricants

                          Environmentally Acceptable Lubricants

Mineral-oil-based lubricating oils, greases, and hydraulic fluids are found in widespread use throughout the industry. These products are usually toxic to plant and marine life with limited degreadability with long lasting effects and cumulative in nature.

Environmental Protection Agency (EPA) and other government regulators have imposed increasingly stringent regulations on the use, containment, and disposal of these materials., with varied regulations , such as no visible sheen close to facilities and point of discharges into water ways not to exceed 10ppm , from all facilities operating within the waterways.

 Grease, hydraulic fluids, and oil leaking from equipment may be carried into the ecosystem and the spills of  these mineral-oilbased materials though limited , the minerals in soluble form tend to accumulate in the organisms causing destruction to ecosystem prevalent in that area, hence reaching human population.The extent of this impact is still under study . Hence to mitigate the concerns, a new class of

environmentally acceptable (EA) materials is becoming available and starting to find increasing use in sensitive locations.

Environmentally acceptable lubricants, in contrast to  mineral-oil-based equivalents, are made out of renewable resources and are easily bio degradable. The cost factor still lingers regarding their usage as to the limited supply and limited regions having  legislation to mandate their usage. With technological advances , and reduced cost will slowly mandate their usage over a wide spectrum of areas , inevitable in near future.

.                  Environmentally Acceptable Guidelines

There are no specific guidelines at  present for EA lubricants. However in order to make them environmentally acceptable, the following broad based guidelines were considered..

Non toxic:. That is, using test method EPA 560/6-82-002, concentrations greater than 1000 ppm of the test material are necessary to kill 50 percent of the test organisms in 96 hours (LC50>1000).

Bio degradeable. That is, using the ASTM test method D 5864, 60 percent ormore of the test material   carbon must be converted to CO2 in 28 days.

Biodegradation

Biodegradation is defined as the chemical breakdown or transformation of a substance caused by organisms or their enzymes.

Primary biodegradation is defined as a modification of a substance by microorganisms that causes a change in some measurable property of the substance.

Ultimate biodegradation is the degradation achieved when a substance is totally utilized by microorganisms resulting in the production of carbon dioxide, methane, water, mineral salts, and new microbial cellular constituents.

. Tests.

The most established test methods used by the lubricant industry for evaluating the biodegradability of their products  to check aerobic aquatic bio-degradation under lab conditions.

Method CEC-L-33-A-94 developed by the Coordinating European Council (CEC); measures the disappearance of the lubricant by analyzing test material at various incubation times through infrared spectroscopy

 Method OECD 301B, the Modified Sturm Test, developed by the Organization for Economic Cooperation and Development (OECD); calculate the rate of conversion of the lubricant to CO2 .

Method EPA 560/6-82-003, number CG-2000, the Shake Flask Test, adapted by the U.S. Environmental Protection Agency (EPA)

ASTM test method D 5864 by US EPA  determines lubricant biodegradation. This test determines the rate and extent of aerobic aquatic biodegradation of lubricants when exposed to an inoculum under laboratory conditions.

The inoculum  is a representative sample of  activated sewage-sludge from a domestic sewage-treatment plant, or it may be derived from soil or natural surface waters, or any combination of the three sources. The degree of biodegradability is measured by calculating the rate of conversion of the lubricant to CO2. A lubricant, hydraulic fluid, or grease is classified as readily biodegradable when 60 percent or more of the test material carbon is converted to CO2 in 28 days, as determined using this test method.

Laboratory tests have shown that the degradation rates may vary widely among the various test methods indicated above.

Toxicity

Toxicity of a substance is evaluated by conducting an acute toxicity test , which involves measurement of mortality percentage in test organisms.

Test methods used by the lubricant industry for evaluating the acute toxicity are EPA 560/6-82-002, Sections EG-9 and ES-6; and OECD 203. These tests determine the concentration of a substance that produces a toxic effect on a specified percentage of test organisms in 96 hours.

The acute toxicity test is normally conducted using rainbow trout. Toxicity is expressed as concentration in parts per million (ppm) of the test material that results in a 50 percent mortality rate after 96 hours (LC50).

 Lubricant is considered acceptable, if a concentration of more than 1000 ppm results in  aquatic toxicity (LC50.)

COMPOSITION AND CONSISTENCY

Base Fluids

a. Vegetable oils.

          Vegetable oils offer excellent lubricating properties, and they are nontoxic and highly biodegradable,relatively inexpensive compared to synthetic fluids, and are made from natural renewable resources. Vegetable oil lubricants, including rapeseed, castor, and sunflower oils, tend to age quickly, due to linoleic and linolenic fatty acid bonds , which were later overcome by genetically modifying  seeds to produce oleic bonds to improve oxidation stability.At high temperatures, they become dense and change composition; at low temperatures, they thicken and Gel (limiting the operating temperature from 32 to 82 deg c) .

Rapeseed oil (RO), or canola oil, excellent lubricity, and high viscosity index and flash point ,extreme pressure and antiwear  properties, passing  the Vickers35VQ25.  The first RO-based hydraulic fluids were commercially available in 1985. Laboratory tests have identified limits to the use of this oil, but extensive practical experience has yielded relatively few problems. It has problems at both high and low temperatures and tends to age rapidly. It offers good corrosion protection for hydraulic systems and does not attack seal materials, varnish, or paint. Mixing with mineral oil is acceptable and has no influence on oil performance. RO is not water soluble and is lighter than water. Escaped oil can be skimmed off the surface of water. Molecular weight is high, indicating low volatility and low evaporation loss.

         

         

b. Synthetic esters (SE).

Synthetic esters are made from modified animal fat and vegetable oil reacted with alcohol.

Esters are more thermally stable and have much higher oxidative stability than veg oils. Synthetic esters with suitable additives can also be nontoxic. They perform well as lubricants.

They have excellent lubrication properties over veg oils

-High viscosity index,

-Thermal stability,

-Low friction characteristics,

-Aging stability and load bearing capacity

This makes  them suitable for severe condition applications.

They suffer from incompatibility with certain paints, finishes and seal materials. They are easily miscible with mineral oils.

The most commonly used synthetic esters are polyol esters;

the most commonly used polyol esters are trimethylolpropane and pentaerithritol.

c. Polyglycols (PG).

Polyglycol hydraulic fluids have been available for several decades and are widely used, particularly in the food-processing industry later into  construction machinery (primarily excavators) and a variety of stationary installations. They were the first biodegradable oils on the market

              The use of polyglycols is declining due to their aquatic toxicity when mixed with lubricating additives and their incompatibility with mineral oils and seal materials.

The rate and degree of biodegradation are controlled by the ratio of propylene to ethylene, and diminishes with increasing molecular weight. Polyglycols are soluble in water, so water must be excluded from the system.

Polyglycols have the greatest stability with a range from -45 to 250 deg C. Polyglycols excel where fire hazard is a concern.

Polyglycols oils are not compatible with mineral oils and may not be compatible with common coatings, linings, seals, and gasket materials. They must be stored in containers free of linings.

d. Water.

Water has been used as hydraulic fluid in specialty applications where leakage contamination and fire hazard are major concerns. New designs and use of highly wear-resistant materials have opened up possibilities for new water hydraulic applications.

The limitations being technical developments and other commercial considerations.

Additives

Base fluids are mixed with additives to form the final products. These additives are necessary because they provide the resulting end product with physical and chemical characteristics such as oxidation stability, foaming, etc., required for successful application. However, most additives currently used for mineral based oil are toxic and no biodegradable.

Physical and chemical properties of EA fluids are quite different than those of mineral oil, EA fluids will require entirely different additives. Several additive manufacturers are working with the lubricant industry to produce environmentally suitable additives for improving the properties of EA base fluids.

 Additives that are more than 80 percent biodegradable (CEC-L33-T82) are available.

Sulfurized fatty materials (animal fat or vegetable oils) are used to formulate extreme pressure/antiwear additives,

Succinic acid derivatives are used to produce ashless (no metal) additives for corrosion protection.

Suppliers are using a variety of base fluids to formulate EA hydraulic fluids, lubricating oils, and greases.

The base fluid may be the same for all three products. For example a biodegradable and nontoxic ester may be used as the base fluid for production of hydraulic fluid, lubricating oil, and grease. The most popular base fluids are vegetable oils, synthetic esters, and polyglycols.

                              Properties of Available EA Products

a. Oxidation stability. One of the most important properties of lubricating oils and hydraulic fluids is their oxidation stability. Oils with low values of oxidation stability will oxidize rapidly in the presence of water at elevated temperatures. When oil oxidizes it will undergo a complex chemical reaction that will produce acid and sludge. Sludge may settle in critical areas of the equipment and interfere with the

lubrication and cooling functions of the fluid. The oxidized oil will also corrode the equipment.

Oxidation stability is normally measured ( ASTM D 943) by Turbine Oil Stability Test (TOST), is used to evaluate the oxidation stability of oils in the presence of oxygen, water, and iron-copper catalyst at an elevated temperature.

TOST life of mineral oil is more than 1000 hours.

Synthetic esters and polyglycols are hydrolytically less stable than mineral oils at elevated temperatures, resulting in lower TOST lives. formulated synthetic esters with proper additives will produce high TOST values.

Vegetable oils, on the other hand, have a TOST life of less than 75 hours.

To improve the TOST life of vegetable oil products,more research must be done on formulating a proper mixture of base oil with a suitable additive package.

Until acceptable commercial formulations are demonstrated, vegetable oils should be confined to applications involving very dry conditions and low temperatures.

b. Lubricity. Lubricity is the degree to which an oil or grease lubricates moving parts and minimizes wear.

Lubricity is usually measured by test method (ASTM D 2266) commonly known as the Four-Ball Method. Laboratory tests have shown that EA lubricants normally produce good wear properties.

c. Pour point. Pour point defines the temperature at which an oil solidifies. When oil solidifies, its performance is greatly compromised.

Pour point is normally evaluated by test method (ASTM D 97.)

The low-temperature fluidity of vegetable-based fluids is poor compared to other fluids .

However, the pour point of vegetable-based hydraulic fluids and lubricants may be acceptable for many applications.

d. Viscosity index. Viscosity index (VI) is a measure of the variation in the kinematic viscosity of oils as the temperature changes. The higher the viscosity index, the less the effect of temperature on its kinematic viscosity. VI is measured by test method (ASTM D 2270) shows, the VI of most

EA fluids meets or exceeds the VI of petroleum-based fluids.

e. Foaming. The tendency of oils to foam can be a serious problem in lubricating and hydraulic systems. The lubrication and hydraulic properties of oils are greatly impeded by excessive foaming.

Foaming characteristics of oils are usually determined by test method (ASTM D 892). Laboratory tests have shown that most formulated fluids do not have foaming problems.

f. Paint compatibility. Some common paints used in fluid systems are incompatible with many EA fluids. When it is anticipated that these fluids may be used in a fluid system, the use of epoxy resin paints should be used to eliminate potential compatibility problems.

g. Elastomeric seal compatibility. Polyurethane seals should not be used with EA fluids. Instead, the use of Viton and Buna N (low to medium nitrile) is recommended. EA fluids are compatible with steel and copper alloys and provide excellent rust protection. The fluid manufacturer must be consulted for

specific compatibility data for each material encountered in the application.

h. Degradability. Since EA fluids are biodegradable they will break down in the presence of water and bacteria. Moisture traps in breather intakes and other equipment modifications which will keep moisture out of the system should be considered. EA fluids should be periodically monitored to insure that biodegradation is not occurring.

        Changing  over issues  from Conventional to EA Lubricants and further

EA fluids are not necessarily equal to one another. It is important to make a thorough assessment of the requirements of the specific application to determine whether a substitution can be made, and whether any compromises in quality or performance will be compatible with the needs of the user. Switching to EA -

products may require special considerations, measures, or adaptations to the system. Depending on the application and the product chosen, these could include the following:

a. Some commercially available synthetic ester and vegetable-oil-based lubricants meet the requirements of nontoxicity and biodegradability. However, the compatibility of these fluids with existing materials encountered in the application, such as paints, filters, and seals, must be considered. The fluid manufacturer must be consulted for specific compatibility data for each material of construction. The

manufacturer of the existing equipment must be consulted, especially when the equipment is still under warranty.

b. Extreme care must be taken when selecting an EA oil or grease for an application. Product availability may be impacted due to the dynamic nature of developing standards and environmental requirements.

c. Accelerated fluid degradation at high temperature, change of performance characteristics at low temperature, and possible new filtration requirements should be investigated carefully. The oxidation rate of vegetable-based EA lubricants increases markedly above 82 deg C and lengthy exposure at the

low temperature can cause some products to gel.

d. On a hydraulic power system, when changing over to EA lubricants, the system should be thoroughly drained of the mineral oil and, if possible, flushed. Flushing is mandatory if diesel engine oil was the previous hydraulic fluid. This will avoid compromising the biodegradability and low toxicity of the EA fluids. Disposal of the used fluids should be in accordance with applicable environmental regulations and procedures.

e. More frequent filter changes may be necesary.

f. Moisture scavengers may be necessary on breather intakes to keep water content in the lubricant low.

g. Temperature controls for both upper and lower extremes may need to be added to the system.

h. Redesign of hydraulic systems to include larger reservoirs may be necessary to deal with foaming problems.

i. The use of stainless steel components to protect against corrosion may be necessary.

j. The number of manufacturers who produce EA hydraulic fluids, lubricating oils, and greases continues to expand. Names of the manufacturers include some well-known companies that have marketed lubricants for many years as well as a large number of smaller companies that appear to specialize in EA products. Some of these companies also market specialty EA products such as gear oils, wire rope lubricants, air tool lubricants and cutting and tapping fluids. EA turbine oils exist; however, till date, none of the oil suppliers has recommended these products for hydroelectric power plants.