how lubricating oil is made

7/28/2019 How Lubricating Oil is Made

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Lubricating Oil

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Background

Since the Roman era, many liquids, including water, have been used as lubricants to minimize

the friction, heat, and wear between mechanical parts in contact with each other. Today,

lubricating oil, or lube oil, is the most commonly used lubricant because of its wide range of

possible applications. The two basic categories of lube oil are mineraland synthetic. Mineral oils

are refined from naturally occurring petroleum, or crude oil. Synthetic oils are manufactured

polyalphaolefins, which are hydrocarbon-based polyglycols or ester oils.

Although there are many types of lube oils to choose from, mineral oils are the most commonly

used because the supply of crude oil has rendered them inexpensive; moreover, a large body of

data on their properties and use already exists. Another advantage of mineral-based lube oils is

that they can be produced in a wide range of viscositiesviscosity refers to the substance's

resistance to flowfor diverse applications. They range from low-viscosity oils, which consist of

hydrogen-carbon chains with molecular weights of around 200 atomic mass units (amu), tohighly viscous lubricants with molecular weights as high as 1000 amu. Mineral-based oils with

different viscosities can even be blended together to improve their performance in a given

application. The common 1OW-30 motor oil, for example, is a blend of low viscous oil (for easy

starting at low temperatures) and highly viscous oil (for better motor protection at normal

running temperatures).

First used in the aerospace industry, synthetic lubricants are usually formulated for a specific

application to which mineral oils are ill-suited. For example,

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synthetics are used where extremely high operating temperatures

are encountered or where the lube oil must be fire resistant. This

article will focus on mineral-based lube oil.

Raw Materials

Lube oils are just one of many fractions, or components, that can be

derived from raw petroleum, which emerges from an oil well as a

yellow-to-black, flammable, liquid mixture of thousands of

hydrocarbons (organic compounds containing only carbon and

hydrogen atoms, these occur in all fossil fuels). Petroleum deposits

were formed by the decomposition of tiny plants and animals that

lived about 400 million years ago. Due to climatic and geographical

changes occurring at that time in the Earth's history, the breakdown

of these organisms varied from region to region.

Because of the different rates at which organic material decomposed

in various places, the nature and percentage of the resulting

hydrocarbons vary widely. Consequently, so do the physical and

chemical characteristics of the crude oils extracted from different

sites. For example, while California crude has a specific gravity of

0.92 grams/milliliter, the lighter Pennsylvania crude has a specific

gravity of 0.81 grams/milliliter. (Specific gravity,which refers to the

ratio of a substance's weight to that of an equal volume of water, is an

important aspect of crude oil.) Overall, the specific gravity of crudes

ranges between 0.80 and 0.97 grams/milliliter.

Depending on the application, chemicals called additives may be mixed with the


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Lubricating oil is refined from crude oil. After undergoing a purifying process colled

sedimentation, the crude oil is heated in huge fractionating towers. The various vaporswhich

can be used to make fuel, waxes, or propane, among other substancesboil off and are collected

at different points in the tower. The lube oil that is collected is filtered, and then additives are

mixed in.

refined oil to give it desired physical properties. Common additives include metals such as lead or

metal sulphide, which enhance lube oil's ability to prevent galling and scoring when metalsurfaces come in contact under extremely high pressures. High-molecular weight polymerics are

another common additive: they improve viscosity, counteracting the tendency of oils to thin at

high temperatures. Nitrosomines are employed as antioxidants and corrosion inhibitors because

they neutralize acids and form protective films on metal surfaces.

The Manufacturing

Process

Lube oil is extracted from crude oil, which undergoes a preliminary purification process(sedimentation) before it is pumped into fractionating towers. A typical high-efficiency

fractionating tower, 25 to 35 feet (7.6 to 10.6 meters) in diameter and up to 400 feet (122

meters) tall, is constructed of high grade steels to resist the corrosive compounds present in

crude oils; inside, it is fitted with an ascending series of condensate collecting trays. Within a

tower, the thousands of hydrocarbons in crude oil are separated from each other by a process

calledfractional distillation.As the vapors rise up through the tower, the various fractions cool,

condense, and return to liquid form at different rates determined by their respective boiling


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points (the lower the boiling point of the fraction, the higher it rises before condensing). Natural

gas reaches its boiling point first, followed by gasoline, kerosene, fuel oil, lubricants, and tars.

Sedimentation

1 The crude oil is transported from the oil well to the refinery by pipeline or tanker ship. At

the refinery, the oil undergoes sedimentation to remove any water and solid contaminants,

such as sand and rock, that maybe suspended in it. During this process, the crude is

pumped into large holding tanks, where the water and oil are allowed to separate and the

contaminants settle out of the oil.

Fractionating

2 Next, the crude oil is heated to about 700 degrees Fahrenheit (371 degrees Celsius). At

this temperature it breaks down into a mixture of hot vapor and liquid that is then pumped

into the bottom of the first of two fractionating towers. Here, the hot hydrocarbon vapors

float upward. As they cool, they condense and are collected in different trays installed at

different levels in the tower. In this tower, normal atmospheric pressure is maintained

continuously, and about 80 percent of the crude oil vaporizes.

3 The remaining 20 percent of the oil is then reheated and pumped into a second tower,

wherein vacuum pressure lowers the residual oil's boiling point so that it can be made to

vaporize at a lower temperature. The heavier compounds with higher boiling points, such

as tar and the inorganic compounds, remain behind for further processing.

Filtering and solvent extraction

4 After further processing to remove unwanted compounds, the lube oil that has been

collected in the two fractionating towers is passed through several ultrafine filters, which

remove remaining impurities. Aromatics, one such contaminant, contain six-carbon rings

that would affect the lube oil's viscosity if they weren't removed in a process called solvent

extraction. Solvent extraction is possible because aromatics are more soluble in the solvent

than the lube oil fraction is. When the lube oil is treated with the solvent, the aromatics

dissolve; later, after the solvent has been removed, the aromatics can be recovered from it.

Additives, inspection, and packaging

5 Finally, the oil is mixed with additives to give it the desired physical properties (such as

the ability to withstand low temperatures). At this point, the lube oil is subjected to a

variety of quality control tests that assess its viscosity , specific gravity , color, flash, and fire

points. Oil that meets quality standards is then packaged for sale and distribution.

Quality Control


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Most applications of lube oils require that they be nonresinous, pale-colored, odorless, and

oxidation-resistant. Over a dozen physical and chemical tests are used to classify and determine

the grade of lubricating oils. Common physical tests include measurements for viscosity, specific

gravity, and color, while typical chemical tests include those for flash and fire points.

Of all the properties, viscosity, a lube oil's resistance to flow at specific temperatures and

pressures, is probably the single most important one. The application and operating temperature

range are key factors in determining the proper viscosity for an oil. For example, if the oil is too

viscous, it offers too much resistance to the metal parts moving against each other. On the other

hand, if it not viscous enough, it will be squeezed out from between the mating surfaces and will

not be able to lubricate them sufficiently. T he Saybolt Standard Universal Viscometer is the

standard instrument for determining viscosity of petroleum lubricants between 70 and 210

degrees Fahrenheit (21 and 99 degrees Celsius). Viscosity is measured in theSay bolt Universal

second,which is the time in seconds required for 50 milliliters of oil to empty out of a Saybolt

viscometer cup through a calibrated tube orifice at a given temperature.

The specific gravity of an oil depends on the refining method and the types of additives present,

such as lead, which gives the lube oil the ability to resist extreme mating surface pressure and

cold temperatures. The lube oil's color indicates the uniformity of a particular grade or brand.

The oil's flash and fire points vary with the crude oil's origin. Theflash pointis the temperature

to which an oil has to be heated until sufficient flammable vapor is driven off so that it will flash

when brought into contact with a flame. Thefire pointis the higher temperature at which the oil

vapor will continue to burn when ignited.

Common engine oils are classified by viscosity and performance according to specifications

established by the Society of Automotive Engineers (SAE). Performance factors include wear

prevention, oil sludge deposit formation, and oil thickening.

The Future

The future of mineral-based lubricating oil is limited, because the natural supplies of petroleum

are both finite and non-renewable. Experts estimate the total recoverable light to medium

petroleum reserves at 1.6 trillion barrels, of which a third has been used. Thus, synthetic-based

oils will probably be increasingly important as natural reserves dwindle. This is true not only for

lubricating oil but also for the other products that result from petroleum refining.

Where To Learn More

Books

Fuels, Lubricants, and Coolants, 7th ed. Deere & Company Service Publications, 1992.


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Malone, L. J.Basic Concepts of Chemistry. John Wiley & Sons, Inc., 1989.

Nadkarni, R. A., ed.Analysis of Petroleum Products & Lubricants.American Society for Testing

& Materials, 1991.

Seal, Shirley C., ed.Fluids, Lubricants & Sealing Devices. National Fluid Power Association,

1989.

Periodicals

Bienkowski, Keith. "Coolants and Lubricants: The Truth."Manufacturing Engineering.March,

1993.

"System Provides Real-Time Lube Oil Blending."Design News. February 26, 1990, p. 39.

O'Lenick, Anthony and Raymond E. Bilbo. "Saturated Liquid Lubricant Withstands Aluminum

Forming."Research & Development. February, 1989, p. 162.

Peterson, Ivars. "Friction Features."Science News.April 30, 1988, p. 283.

Templeton, Fleur. "The Right Lube Job for Superhot Ceramic Engines?"Business Week. May 18,

1992, p. 11 3.

Vogel, Todd, John Rossant, and Sarah Miller. "Oil's Rude Awakening."Business

Week.September 26, 1988, p. 44.

Craig F. Whitlow

how lubricating oil is made

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