Base oil

Base oils are main raw materials in lubricants, in other words, to produce the final oils, the base oil is mixed with additives as the primary base of the product. Different formulations and specifications of the product cause various applications in different industries. In fact, a lubricant contains 70-100% base lubricants and up to 30% different compounds, known as additives.

But the question that arises here is that, how do you know which base oil is the best? Trying to choose between mineral and synthetic oils can be confusing.

Production of base oils

It is worth noting that “crude” oil from different oil wells varies in texture not only from place to place, but even within the same region.

After the crude oil is extracted from the ground, it will sent to the refinery, where its various parts are separated into usable petroleum products.

Base oils are one of the specialized products, which are produced by a refinery. It is important to know that base oils are not fuels, but rather they are compounds that are used to formulate a variety of lubricating oils for use in engines and other machineries.

In oil refineries, crude oil undergoes fractional distillation and a number of other processes, resulting in the production of various types of fuel, base oils, paraffin, bitumen and even some secondary products.

In general, it can be said that the production process of base oils includes the following steps:

1) Distillation:

The process of removing components at very low and very high boiling point and remaining distillation in the lubricant boiling range.

2) Removal of aromatics:

This process makes the lubricating oil with a high proportion of residual saturated hydrocarbons and improves its viscosity index and stability.

3) Deparaffinization:

It separates the paraffins and controls the low temperature properties of the lubricant.

4) Complete:

Removes polar components and improves base oil color and stability.

It is noteworthy that the efficiency of the base oil from the distillation column of the refinery depends on the ratio of the desired components in the range of the lubricant’s boiling point.

The production of base oils is usually very profitable for a refinery. Because it allows the refinery to extract some of the least valuable part of crude oil, vacuum diesel and sell it as a high-value Specialized product. However, base oil production facilities have a relatively high capital cost per barrel, so only a subset of refineries have installed them.

Classification of base oils

Base oils can be classified in different ways, one of the most common classifications based on the constituent base oil is as follows:

1) Mineral base oils:

Mineral oils from crude oil or natural oil obtained from oil wells, a mixture of hydrocarbons, gases and other unwanted components can be produced with a wide range of qualities associated with the oil refining process.

It is noteworthy that, although refining and processing techniques have been technologically developed to produce mineral base oils with very good properties, those produced cannot meet the needs of today’s applications.

Therefore, additives or chemical improvers are added to base mineral oils and increase their physical and chemical characteristics and properties and thus achieve the properties and characteristics of the final product required for each application. This is done in mixing units that can be inside or outside the refinery.

2) Synthetic or vegetable base oils:

Synthetic lubricants first appeared in the early 1930s. Synthetic materials are produced in a number of formulations with unique properties for a specific purpose through a man-made synthesis process. Vegetable base oils, derived from vegetable oils, contain a very small percentage of lubricants and are mainly used for renewable and environmental applications.

Characteristics of synthetic base lubricants:

Better thermal and oxidative stability
Solubility of additives
Less variability in different conditions
Compatibility with elastomers (sealants)
Anti-friction properties
Low pour point
Maintaining viscosity
Low volatility, this means that the lubricant resists evaporation due to high temperatures and therefore does not lose its rheological properties (i.e. viscosity).
There are more expensive choices

Characteristics of base oils

All base oils have characteristics that determine how well they withstand a variety of lubrication challenges. For a mineral oil (which is the target of the refining process), optimizing the final properties to produce a high-performance lubricant is the most important goal. For synthetically produced oils, the purpose of different formulations is to create a lubricant with properties that may not be achievable in a mineral oil.

It is necessary to explain that each base oil, whether based on mineral substances or synthetic substances, is designed in such a way that it has a specific application. Therefore, the choice of lubricant depends entirely on the application for which it is intended.

Some of the most important properties of base oils are:

Viscosity limits and viscosity index
Pour point
Oxidation and thermal stability
Aniline point (measure of base oil solubility compared to other substances, including additives)

. Hydrolytic stability (lubricant resistance against chemical decomposition in the presence of water)

Base oil groups

The 20th century saw improvements in the refining process of mineral oils along with the introduction of synthetic materials.

In the early 1990s, the American Petroleum Institute in the United States classified all base oils into five groups based on their origin (mineral or synthetic), manufacturing process, viscosity index range, and percentage of saturated hydrocarbons. The first three groups were mineral oils and the remaining two groups were mainly synthetic base oils.

Groups one, two and three are all mineral oils, which the intensity of their refining process increases.

Group I base oils are created using solvent extraction or solvent refining technology. This technology has been used since the early days of mineral oil refining with the aim of extracting undesirable components in the oil such as ring structures and aromatics.

Base oils of the second group are produced using hydrogen gas in a process called hydrogenation. The purpose of this process is the same as solvent treatment while it is more effective in converting undesirable components such as aromatics into desirable hydrocarbon structures.

Group III base oils are made almost like Group II mineral oils, with the difference that the hydrogenation process is associated with high temperatures and high pressure, and as a result, almost all the undesirable components in the oil are converted into desirable hydrocarbon structures.

When comparing properties between mineral base oil groups. including those with higher oxidation stability, thermal stability, viscosity index, pour point and operating temperature. And with oils that are highly refined, you’ll see more benefits. It should be explained that with further refining of the oil, some key weaknesses also occur, which can affect additive solubility and biodegradability.

The fourth group is dedicated to a type of synthetic material called Polyalphaolefin, which is the most widely used synthetic base oil. Polyalphaolefins are hydrocarbons that are synthetically produced by growing an olefin formed through a polymerization process involving ethylene gas, which is called a synthetic process. The result is a structure that is very similar to the purest form of mineral oils described in the third group. The advantages of polyalpha olefins compared to mineral oils include higher viscosity index, excellent performance at low and high temperatures, superior oxidation stability and lower volatility. However, these synthetic lubricants can also have deficiencies in additive solubility, lubricity, and film strength.Like mineral oils, polyalphaolefins are widely used for lubricating applications, Because they have very stable structures and very uniform molecular chains and are often the preferred option when higher temperatures are expected.

The fifth group is assigned to all other base oils, especially synthetic oils. Some of the most common oils in this group include diesters, polyesters, polyalkylene glycols, phosphate esters, and silicones as follows.

1) Diester (dibasic acid ester):

A diester is produced through the reaction of a dibasic acid with an alcohol. The resulting properties can be adjusted based on the types of dibasic acid and alcohol used.

The interesting thing about esters is that they are 100% synthetic chemical compounds and many of them with different chemical compositions, due to their excellent lubricity, are used either as additives or as base oils to produce final lubricants. On the other hand, due to their high price, they are used in a small proportion in the formula to improve the stability of the final product.

2) polyester:

Polyester is made from the reaction of a monobasic acid with a polyhydric alcohol. Like diesters, the resulting properties depend on these two types of constituents.

3) polyalkylene glycol:

Polyalkylene glycol is produced through a reaction involving ethylene or propylene oxides and alcohol to form various polymers. A number of products have been developed based on the oxide used, which ultimately affects the solubility of the base oil in water.

4) Phosphate ester and 5) Silicon:

Phosphate ester is formed through the reaction of phosphoric acid and alcohol, whereas silicones are formulated to have a silicon-oxygen structure with organic chains attached.

The noteworthy point is that each of these synthetic materials has specific strengths and weaknesses.

Application of base oils

In general, synthetic materials can offer more advantages when it comes to properties affected by extreme temperatures, including oxidative and thermal stability, which can contribute to a longer useful life. Therefore, when the lubricant encounters cold start-ups or high operating temperatures, synthetic materials such as polyalphaolefins usually perform better than mineral oils.

Polyalphaolefins also exhibit improved characteristics in terms of degradability and hydrolytic stability, which affect the lubricant’s ability to control water pollution.

While polyalphaolefins are ideal for applications such as motor oil, gear oil, bearing oil, and other applications, mineral oil will be choose as the base oil due to its lower cost and reasonable serviceability.

With more than 90% use in industrial and automotive markets, mineral oil has established its position as the most common base oil in most applications.

What you should pay attention to when it comes to base oils!

Not all base oils are the same, because formulas can create unique distinctions Therefore, the properties described for each type of base oil are generalized for the batch as a whole.

Sometimes third group oils are advertised as synthetic oils. It is understood that the refining process has drastically altered the original hydrocarbon, thus synthesizing a much purer product.

When fire resistance is essential and conventional lubricant properties such as viscosity or lubricity are less important, water-based fluids are a suitable alternative.

Care must be taken when changing lubricants, especially when they have different base oils, as they may be incompatible with each other.

Paraffinic mineral oils, which come in groups one, two, and three, have a low specific gravity and contain paraffin, have little or no bitumen. Compared to naphthenic mineral oils, which have a lower pour point and better additive. solubility, these oils can provide a higher viscosity index and a higher flash point.

Although naphthenic oils are mineral-based, they are considered group 5 oils, because they do not meet the requirements of the American Petroleum Institute for groups one, two and three, because they have a high specific gravity and contain bitumen, little or no paraffin. The unique properties of naphthenic mineral oils often make them good lubricants for locomotive engine oils, compressor oils, transformer oils, and process oils. However, paraffinic oils are still the preferred choice for high temperature applications when longer lubricant life is required.

Ester-based synthetic materials, such as diesters and polyesters, have advantages in terms of biodegradability and miscibility with other oils. In fact, it is common for esters and polyesters to be blended with polyalphaolefins during additive compounding to help accept more important additive packages. Diesters and polyesters are often used as base oils for compressor fluids, high temperature grease applications, and even gear oils. Since polyesters perform well at higher temperatures, they are also widely used for jet engine oil.

Compared to other oils, polyalkylene glycols have a much higher viscosity index, detergent properties, lubrication properties, and oxidative and thermal stability properties. Polyalkyne glycols can be formulated as soluble or insoluble in water and do not form deposits or residues under severe operating conditions. Polyalkyne glycols can be used to produce oils such as compressor oil, brake oil, high temperature chain oil, gear oil, metalworking fluid, as well as for food grade, biodegradable or fire-resistant applications.

Phosphate esters are primarily useful for fire retardant applications. They are often used in hydraulic turbines and compressors due to their unique properties including high ignition temperature, oxidation stability and low vapor pressure.

Silicone-based synthetics are rarely used in industrial applications, but can be beneficial at very high temperatures when the lubricant is exposed to chemicals, radiation, or oxygen. These synthetic materials have a very high viscosity index and are among the best options for oxidation and thermal stability due to their chemical neutrality.

Choosing a base oil

Remarkable topic is that, when you choose a base oil, there will be variations in the lubricant properties required for the application.

Optimizing lubricant selection can help minimize opportunities for machine failure. Although synthetics are justifiably more expensive than mineral oils, the cost of equipment failure is usually much higher. So, if cost is a key factor in your decision, be sure to choose wisely.

Re-purification of used lubricants

Used lubricant due to the loss of its original properties, the presence of impurities and other products (including other mineral or synthetic base lubricants, water, fuel, bituminous products, etc.) is unsuitable for lubrication. Re-refining separates the water, oil and asphalt by-products and recovers the lubricating oil through distillation as in the refining process.

The hydrotreating unit refines the lubricant in the presence of selected catalysts to remove undesirable chemical compounds (which make the lubricant unsuitable for use as a base). The result is the conversion of olefins (alkenes) and unsaturated cyclic components in high-quality paraffinic or naphthenic (cyclic) saturated bases, which are much less toxic and more neutral. The base lubricant produced is combined with chemical additives to be produced and used for all purposes, and again at the end of its life cycle, it is collected and refined by the refinery, and thus the life cycle of the lubricant will be beginning again. Recovered lubricants (recycled base oil) currently have a very high added export value for the countries of India, Pakistan and Afghanistan.

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Base oil

Base oil