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Lubricants have evolved from the role of providing mere lubrication and component protection, to a more challenging role. From providing the necessary protection, lubricants are now expected to give longer drain intervals, provide fuel efficiency and to help original equipment manufacturer (OEM’s), meet stringent emission norms. Moreover, to meet the productivity demands, equipment’s today are designed to have more power and have compact designs, making them run faster and hotter than ever. Thus arises the need for lubricants, which can not only provide good protection, but also provide additional benefits like extended drains & lesser consumption. Synthetics lubricants due to their better performance over conventional mineral oils, have hence gained importance and have gradually started to become preferred choice of lubricant of various industries, which require high level of performance.
But as synthetic lubricants offer many benefits, they also have their disadvantages.
Lubricants are made from base oil and additives, wherein base oil forms major portion of a lubricant formulation. Base oil percentage in a lubricant formulation varies with application and can range from 65-80% in Marine engine oils to 98-100% for commonly used industrial oils. Hence it’s the base oil performance which mainly drives the performance of a lubricant. Here comes the choice of the base oil.
Where conventional mineral base oils are derived from crude oil refining, synthetic oils are formulated artificially. They are made by chemical process of breaking down petroleum molecules and then rebuilding them to make higher molecular-weight materials molecules.
These reactions are controlled and as a result we get an oil which contains specific molecules that are tailored with uniform consistency, to provide optimal lubrication properties and better performance. Greater molecular uniformity and stability compared to conventional base oils, provide synthetics advantage of reduced oil burn-off in the presence of extreme heat and oxidation, which results in…
Image Courtesy: www.wolflubes.com
Key benefit of synthetics come from its high oxidation stability. Oxidation of a lubricant will lead to an increase in the oil’s viscosity, formation of acids and will cause deposits of varnish and sludge on components. Synthetic oils are free of impurities and have better oxidation stability than mineral base oils. Hence they provide better life to lubricant and hence longer oil drain intervals can be achieved.
Image: www.machinarylubrication.com
Other key performance benefits that synthetics give than mineral oils are as below:
Higher Flash Points – Improved Fire resistance
Excellent thermal stability – Oil does not degrade or thicken easily at high temperatures
Inherently possesses high viscosity index – Lesser change in lube viscosity with temperature. Gives better energy efficiency.
Disadvantages of Synthetics - Synthetics do have their drawbacks, the most obvious of these being costs. Depending on the type of base stock, the cost for a synthetic lubricant may be three to fifteen times the cost for the equivalent grade of mineral oil.
Source: Machinarylubrication.com
Synthetics do have their drawbacks, the most obvious of these being costs. Depending on the type of base stock, the cost for a synthetic lubricant may be three to fifteen times the cost for the equivalent grade of mineral oil. Lubricant Base Oil Production and Relative Cost Source: Machinarylubrication.com Also, some synthetic lubricants like certain types of phosphate esters are hazardous, requiring special care and attention when handling and disposing. Yet others have a limited ability to dissolve additives, making formulation and additive suspension under less-than-ideal conditions difficult, while yet others are incompatible with petroleum-based products, requiring care and attention when storing, handling and dispensing. And increased solvency is not always a good thing - particularly when a mineral oil has been in use for some time and the removal of deposits can result in seal leaks.
During WWII, due to scarcity and limited access to crude oil, Germany was looking for a product, which would have the inherent properties of mineral oil but was not derived from crude oil. By mid-1940s, Dr. Hermann Zorn of Germany did achieve success in developing variety of such oil products, which were made from different blends of esters, including diesters and polyolesters.
These ester based lubricants were extensively used by both Germany and US during WWII and they noticed that these synthetics oils were performing much better than the conventional crude oil-derived lubricants. Engine starts were much easier in colder climates and they performed better under severe operating conditions.
The first synthetic oil developed for automotive combustion engines and fully recognized by the American Petroleum Institute (API) was produced in 1972. This first API-rated synthetic motor oil meeting API SE/CC specifications was based on a SAE 10W-40 grade Di-ester API Group V formulation.
But the higher cost of synthetic oils (as they need to be processed) and due to their limited availability, kept the attractiveness of synthetic oils low to the general automotive and industrial markets.
Only in the last 20 years, however, have end users throughout industry really recognized the cost benefits of synthetics. Now, more and more uses are being found for these formulations and they are experiencing significantly high growth rates.
American Petroleum Institute (API) base oil groups (see table), and the choice of As earlier pointed out that in a lubricant formulation, base oil is a major determining factor in the quality and performance of the finished product. API classifies base oils into five categories.
Image source: Selectsynthetics.com
Group I-III are conventional mineral base oils, made by refining from crude oil. Process includes various distillation processes, followed by applying either extraction, or hydroprocessing techniques to get the final base oil product.
Group IV base oils are fully synthesized poly-alpha-olefin (PAO) oils, which is made by polymerizing an alpha-olefin molecule like ethylene.
API Group V is for all other base oils not included in Groups I through IV. These include napthenics, diesters, phosphate esters, polyol esters, alkylated benzenes, polyalkylene glycol (PAG), silicones, etc.
In general, the chemical composition and performance properties of the base oil categories improve with advancing group number. As we see in table, Group I base oils have a lower concentration of saturates than Group II base oils, while Group II base oils have a lower concentration of saturates than Group III base oils. Now,the higher the number of Saturates, the higher the molecular bond strength of the oil and therefore the better the resistance to breakdown or loss of viscosity. Similarly, Sulphur content shows the purity and refinement of oil. So lower the Sulphur content, the better the purity and thus lower the corrosiveness in oil.
As Group IV and V base oils are synthesized, hence they are traditionally called as “Synthetics”. However, now even “Group III” can legally be labeled ‘synthetic’. The same will be discussed later in the article.
Interesting to note that the word ‘Synthetic’ is not part of the API Classification. “Synthetic” is a marketing term, not a technical term.
Apart from Polyalphaolefins (PAO), synthetic oils can be of many types like silicone, phosphate ester, polyalkylene glycol (PAG), polyolester, biolubes, etc.
Infact, if it is a synthetic base oil and it is not a PAO, it is a Group V base oil. Each of these oils have their own sets of advantages and disadvantages, mentioned in the table below.
Image Source: Machinarylubrication.com
These base oils are generally not used as base oils themselves, but they may be mixed with other base stocks to enhance their properties.
Polyalphaolefin is by far the most common major synthetic base oil used in industrial and automotive lubricants. It is a synthetic hydrocarbon (SHC) that mimics the best hydrocarbon (branched) structure found in mineral oils. They exhibit certain inherent physical and chemical properties such as lower volatility, higher viscosity index, lower pour point, and better oxidative/thermal stability. PAOs have a much broader temperature range than Group I, II or III base oils and are therefore great for use in extreme cold conditions and high heat applications. These properties combined with superior oxidative stability of PAO, are driving its market for various segments and in a variety of applications like in engine oils, hydraulic oils, transmission oils, and compressor oils.
You might already know that synthetic oils typically outperform conventional oils, but you might not know the difference between synthetic blend oils and full synthetic oils.
As the true synthetics are chemically designed, the word “synthetic” in the lubricants industry has been historically synonymous with polymerised base oils such as polyalphaolefins (PAOs), and other synthetics, such as esters, polyphenylethers, etc.,which are polymerized and made from small molecules.
But that changed a number of years ago when some lubricant manufacturers, developed certain improvised catalytic conversions of crude oil base stocks, which could produce highly refined, impurities free, Group III base oils which were somewhat equivalent in properties to traditional synthetic base oils. Some lubricant manufacturers, specially in Europe and North America, began replacing the Group IV PAOs in their synthetic engine oils with these newly available Group III base oils.
Although made from crude oil, Group III base oils were also claimed as synthetic oils and as being cheaper than synthesized polymerized oils, they soon started capturing the market of conventional synthetic oils. This created a controversy in the lubricant industry, as some synthetic base oil producers argued that polymerised base oils like PAO’s were the only true synthetics. In the late 1990s, a complaint was filed with the National Advertising Division (NAD) in the US, but Group III producers were able to provide enough data to convince NAD, that Group III base oil could legitimately be called synthetic. The NAD ruled in favour of the Group III producer in 1999. So even though these Group III base oils are derived from crude oil, they can now legally, from a marketing standpoint, call them synthetic.
Since then “synthetic” word in lubricant industry has become more of a marketing term, rather than a technical term and hence began the great confusion in “Synthetic oil market”.
Some of the common terms used in the lubricant industry and market are as follows:
Fully synthetic oil- Oils that are made totally from Polyalphaolefins (PAO) base oils. Very costly products but of highest performance levels.
Synthetic Oil – They can be either made from Group III “synthetics” base oil or Group IV (PAO) synthetics. PAO based are costlier than Group III synthetic based formulations.
Synthetic blend oil - It’s a mix of crude refined mineral base oils and synthetic base stocks. Because of the added synthetic base stock, customers will get more performance and protection than you would by using a conventional oil alone.
Semi-synthetic oils - Synthetic blends and semi-synthetic refer to the same thing, i.e an oil that uses a combination of conventional and synthetic base oils in its formulation. They provide some of the benefits of synthetic oil, at a lower price.
Interestingly, there are no industry specifications or regulations that define a minimum amount of synthetic base oil that must be present for a lubricant, so as to be classified as a synthetic blend or semi-synthetic.
This uncertainty creates confusion, as the benefits of synthetic oil is proportional to the quantity of it used in a formulation. But customers don’t know how much a semi-synthetic product, is having actual synthetic oil quantity and benefit.
The 1999 the National Advertising Division (NAD) ruling, did took away the advantage of the marketing term of “Synthetics” from the PAO’s, which has hampered its market growth. But PAO has its own advantages over conventional Group III base oils, which we will discuss in our subsequent articles.
However, in lubricant industry, only Groups IV & V base oils are truly 100% Synthetic. However, in lube market it is still understood, that only Groups IV & V base oils are truly 100% Synthetic.
Also in some European countries (e.g. Germany), unlike in North America, only Groups IV and V based motor oils can actually be labelled “Synthetic”.
Also it is important to understand that the quality and performance of the finished lubricant is not only solely dependent on its base oil source and quality, but also it is the combined effect of total formulation as a whole. So base oil choice can be any type of synthetic but the total lubricant formulation should meet the OEM and customer requirements.
Sunil K Banerjee
Sr. Manager, Technical Services, Lubes
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