All lubricants contain a base oil. It serves as the foundation of the lubricant before it is blended with additives or a thickener in the case of a grease. But how do you know which base oil is best? Trying to choose between mineral oils and synthetics can be confusing. This article will break down the complexity between base oil distillation equipment formulations so you can make the right decision for each application.

Base Oil Categories

Lubricants can be categorized in many different ways. One of the most common classifications is by the constituent base oil: mineral, synthetic or vegetable. Mineral oil, which is derived from crude oil, can be produced to a range of qualities associated with the oil’s refining process. Synthetics are man-made through a synthesizing process and come in a number of formulations with unique properties for their intended purpose. Vegetable base oils, which are derived from plant oils, represent a very small percentage of lubricants and are used primarily for renewable and environmental interests.

All base oils have characteristics that determine how they will hold up against a variety of lubrication challenges. For a mineral oil, the goal of the refining process is to optimize the resulting properties to produce a superior lubricant. For synthetically generated oils, the objective of the various formulations is to create a lubricant with properties that may not be achievable in a mineral oil. Whether mineral-based or synthetic-based, each waste engine oil to base oil machine is designed to have a specific application.

Some of the most important base oil properties include the viscosity limitations and viscosity index, pour point, volatility, oxidation and thermal stability, aniline point (a measure of the base oil’s solvency toward other materials including additives), and hydrolytic stability (the lubricant’s resistance to chemical decomposition in the presence of water).

The 20th century saw a number of improvements in the refining process used for mineral oils along with the introduction of a variety of synthetics. By the early 1990s, the American Petroleum Institute (API) had categorized all base oils into five groups, with the first three groups dedicated to mineral oils and the remaining two groups predominantly synthetic base oils.

Groups I, II and III are all mineral oils with an increasing severity of the refining process. Group I base oils are created using the solvent-extraction or solvent-refining technology. This technology, which has been employed since the early days of mineral oil refining, aims to extract the undesirable components within the oil such as ring structures and aromatics.

Group II base oils are produced using hydrogen gas in a process called hydrogenation or hydrotreating. The goal of this process is the same as for solvent-refining, but it is more effective in converting undesirable components like aromatics into desirable hydrocarbon structures.

Group III base oils are made in much the same way as Group II mineral oils, except the hydrogenation process is coupled with high temperatures and high pressures. As a result, nearly all undesirable components within the oil are converted into desirable hydrocarbon structures.

When comparing properties among the waste motor oil to base oil machine groups, you typically will see greater benefits with those that are more highly refined, including those with enhanced oxidation stability, thermal stability, viscosity index, pour point and higher operating temperatures. Of course, as the oil becomes more refined, some key weaknesses also occur, which can affect additive solubility and biodegradability.

Group IV is dedicated to a single type of synthetic called polyalphaolefin (PAO). It is the most widely used synthetic base oil. PAOs are synthetically generated hydrocarbons with an olefinic tail formed through a polymerization process involving ethylene gas. The result is a structure that looks very much like the purest form of the mineral oils described in Group III. The advantages of PAOs over mineral oil include a higher viscosity index, excellent low- and high-temperature performance, superior oxidation stability, and lower volatility. However, these synthetic lubricants can also have deficiencies when it comes to additive solubility, lubricity, seal shrinkage and film strength. Much like mineral oils, PAOs are widely employed for lubricating applications and are often the preferred option when higher temperatures are expected.

Group V is assigned to all other base oils, particularly synthetics. Some of the most common oils in this group include diesters, polyolesters, polyalkylene glycols, phosphate esters and silicones.

Diester (dibasic acid ester) is manufactured through a reaction of dibasic acid with alcohol. The resulting properties can be adjusted based on the types of dibasic acid and alcohol used.

Polyolester is made through a reaction of monobasic acid with a polyhydric alcohol. Much like diesters, the resulting properties will depend on these two constituent types.

Polyalkylene glycol (PAG) is produced through a reaction involving ethylene or propylene oxides and alcohol to form various polymers. A number of PAG products are developed based on the oxide used, which will ultimately influence the base oil’s water solubility.

Phosphate ester is created through a reaction of phosphoric acid and alcohol, while silicones are formulated to have a silicon-oxygen structure with organic chains attached. Each of these synthetics has specific strengths and weaknesses, as shown in the table above.

In general, synthetics can provide greater benefits when it comes to properties influenced by extreme temperatures, such as oxidative and thermal stability, which can contribute to an extended service life. In situations where the lubricant will encounter cold startups or high operating temperatures, synthetics like PAOs typically will perform better than mineral oils. PAOs also exhibit improved characteristics in relation to demulsibility and hydrolytic stability, which influence the lubricant’s ability to handle water contamination.

While PAOs are ideal for applications like engine oils, gear oils, bearing oils and other applications, mineral oil remains the predominant oil of choice due to its lower cost and reasonable service capabilities. With more than 90 percent usage in the industrial and automotive markets, mineral oil has solidified its place as the most common diesel distillation equipment in the majority of applications.

Paraffinic mineral oil, which is represented in Groups I, II and III, can offer a higher viscosity index and a higher flash point in comparison to naphthenic mineral oils, which have lower pour points and better additive solvency. Even though naphthenic oil is mineral-based, it is considered a Group V oil because it does not satisfy the API’s qualifications for Group I, II and III. The unique characteristics of naphthenic mineral oils have often made them good lubricants for locomotive engine oils, refrigerant oils, compressor oils, transformer oils and process oils. Nevertheless, paraffinic oils continue to be the preferred option for high-temperature applications and when longer lubricant life is required.

Ester-based synthetics, such as diesters and polyolesters, have advantages when it comes to biodegradability and miscibility with other oils. In fact, it is common for diesters and polyolesters to be mixed with PAOs during additive blending to help accept more significant additive packages. Diesters and polyolesters are often deployed as the waste oil filtration equipment for compressor fluids, high-temperature grease applications and even bearing or gear oils. Because they are known to perform well at higher temperatures, polyolesters have also been widely used for jet engine oils.

Compared to other oils, polyalkylene glycols (PAGs) have a much higher viscosity index and good detergency, lubricity, and oxidative and thermal stability characteristics. PAGs can be formulated to be water soluble or insoluble and do not form deposits or residue during extreme operating conditions. PAGs can be employed in a number of applications, such as compressor oil, brake fluid, high-temperature chain oil, worm gear oil and metalworking fluid, as well as for applications with food-grade, biodegradability or fire-resistant requirements.

Phosphate esters are primarily beneficial for fire-resistant applications. They are often utilized in hydraulic turbines and compressors due to their unique properties, including high ignition temperatures, oxidation stability and low vapor pressures.

Silicone-based synthetics are infrequently used in industrial applications, but they can be advantageous in extremely high temperatures, when the lubricant will contact chemicals, or when exposed to radiation or oxygen. These synthetics have a very high viscosity index and are among the best options for oxidation and thermal stability because they are chemically inert.

Selecting a Base Oil

When you are choosing a base oil, there will be tradeoffs in the lubricant properties required for the application. A common example is viscosity. Higher viscosity provides adequate film strength, while lower viscosity offers low-temperature fluidity and lower energy consumption. In some cases, you may prefer to have a balance between the two so there isn’t too much of a compromise on either side. The chart on page 33 shows a comparison of the most essential properties for each base oil.

Although it’s not necessarily important to understand the way in which the oil was manufactured, it is critical to know the available base oil options and the advantages and disadvantages they provide. Optimizing your lubricant selection can help minimize the opportunities for machine failure. While synthetics are justifiably more expensive than mineral oil, the cost of equipment failure is typically much higher. If cost is a key factor in your decision, be sure to choose wisely.

The quality of feedstock used in base oil processing depends on the source of the crude oil. Moreover, the refinery is fed with various blends of crude oil to meet the demand of the refining products. These circumstances have caused changes of quality of the feedstock for the base oil production. Often the feedstock properties deviate from the original properties measured during the process design phase. To recalculate and remodel using first principal approaches requires significant costs due to the detailed material characterizations and several pilot-plant runs requirements. To perform all material characterization and pilot plant runs every time the refinery receives a different blend of crude oil will simply multiply the costs. Due to economic reasons, only selected lab characterizations are performed, and the base oil processing plant is operated reactively based on the feedback of the lab analysis of the turnbine oil filtration machine product. However, this reactive method leads to loss in production for several hours because of the residence time as well as time required to perform the lab analysis. Hence in this paper, an alternative method is studied to minimize the production loss by reacting proactively utilizing machine learning algorithms. Support Vector Regression (SVR), Decision Tree Regression (DTR), Random Forest Regression (RFR) and Extreme Gradient Boosting (XGBoost) models are developed and studied using historical data of the plant to predict the base oil product kinematic viscosity and viscosity index based on the feedstock qualities and the process operating conditions. The XGBoost model shows the most optimal and consistent performance during validation and a 6.5 months plant testing period. Subsequent deployment at our plant facility and product recovery analysis have shown that the prediction model has facilitated in reducing the production recovery period during product transition by 40%. 

Lubrication has been around since the invention of the wheel. Horse-drawn carts with wooden axles used meat greases, pine tar and various forms of animal fat as lubricants. Later, Linseed oil, originally a wood preserver, briefly replaced them as the primary lubrication agent.

The earliest internal combustion engines used a product derived from refined crude oil. This was the beginning of the modern base oil. As IC engines became more complex and operated at higher speeds and temperatures, there was a need for better lubrication that could keep up with modern engines. So, additives were supplemented with the base oils. This combination had improved viscosity and protected the engines from wear, friction and resisted corrosion better. 

In modern cars, the base oil is still the primary catalyst for better engine performance. It forms 75%-80% of the finished product while the additives (10%-20%) and the viscosity index improver, which keeps the viscosity within a threshold at higher temperatures, make up the rest of the engine oil composition along with a variety of inhibitors.

We currently produce base oil by refining crude oil. Less than 1% of the standard 42-gallon barrel of crude oil is used to make lubricants—while the rest becomes gasoline, diesel and kerosene-type jet fuels. 

Base oils are classified by the American Petroleum Institute into five groups labeled I-V based on how the oils are processed.

Group II oils are distinguished from less refined Group I by their higher purity, low levels of sulfur, nitrogen and aromatics, and superior oxidation stability. Pure Group II base oil is actually clear as water – it’s the additives that give finished motor oil its darker color. Group I oils are not suitable for applications requiring premium base oils, and their use is steadily declining. Group II oils can be substituted for many Group I applications.  The base oils in these Groups (I and II) are typically referred to as “mineral conventional base oils.”

Group III and IV base oils are high quality oils intended for use in high performance, low viscosity motor oils (such as 0W-20) in technically advanced automotive engines. Oils made from these base oils are classified as synthetics. They exhibit superior oxidation properties, support improved fuel economy, and may allow for extended drain intervals.  In some parts of the world, Group IV – also known as “poly-alpha olefins” or PAOs – are considered to be the ONLY base oil that is truly synthetic.

Automotive manufacturers and lubricant producers have used Groups I to V base oils depending on the application. Demanding applications, like high temperature performance in turbochargers, extreme cold temperature climates, long drain intervals, or even stop and go traffic conditions require a higher level of performance that can be achieved by selecting the “correct base oil” for the engine oil formulation.

The key takeaway to remember about base oils is that they provide a large part of the performance characteristics of the finished oil formulation.  Selecting the correct base oil type is critical in developing oils that will keep metal parts lubricated and equipment performing at its best. Base oils are only a part of the formulation in oils. Scientists and engineers need to also consider the impact of additive technology as well. The final performance of any lubricant is the combination of base oils, additives, and formulating knowledge for the application.

Lubrication is as old as transportation. The horse-drawn wagons of olden times used leftover meat greases and tallow to lubricate wooden axles. Later, pine tar and hog fat were mixed together for use as a lubricant. Eventually, linseed oil, originally developed as a wood preservative, became the lubricant of choice for coachmen.

Early automotive engines used an oil derived through the refining of crude oil, and the modern base oil was born. As engine technology advanced, intricate, fast-moving parts and high temperatures called for better lubrication. Additives were introduced to reduce friction and wear, increase viscosity and improve resistance to corrosion.

Still, the base oil is the fundamental contributor to the finished product’s performance. In today’s passenger car motor oils, the base oil makes up 75% to 80% of the finished product. The additive package makes up another 10% to 20%. A viscosity index improver, which is added to reduce the degree to which viscosity will decrease due to high temperatures, takes up another 5% to 10%. Various inhibitors make up the remaining less than 1%.

Base oil is produced through the refining of crude oil. A 42-gallon barrel of crude oil can actually yield nearly 45 gallons of petroleum products, but only about .4 gallons or less than 1% goes to making lubricants. The bulk goes to gasoline, diesel fuel and kerosene-type jet fuels.

Base oils are classified by the American Petroleum Institute into five groups labeled I-V based on how the oils are processed.

Group II oils are distinguished from less refined Group I by their higher purity, low levels of sulfur, nitrogen and aromatics, and superior oxidation stability. Pure Group II base oil is actually clear as water – it’s the additives that give finished motor oil its darker color. Group I oils are not suitable for applications requiring premium base oils, and their use is steadily declining. Group II oils can be substituted for many Group I applications.  The base oils in these Groups (I and II) are typically referred to as “mineral conventional base oils.”

Group III and IV base oils are high quality oils intended for use in high performance, low viscosity motor oils (such as 0W-20) in technically advanced automotive engines. Oils made from these base oils are classified as synthetics. They exhibit superior oxidation properties, support improved fuel economy, and may allow for extended drain intervals.  In some parts of the world, Group IV – also known as “poly-alpha olefins” or PAOs – are considered to be the ONLY base oil that is truly synthetic.

Automotive manufacturers and lubricant producers have used Groups I to V base oils depending on the application. Demanding applications, like high temperature performance in turbochargers, extreme cold temperature climates, long drain intervals, or even stop and go traffic conditions require a higher level of performance that can be achieved by selecting the “correct base oil” for the engine oil formulation.