Ester Base Oils, PAG Base Oils, and Hydrocarbon: Key Differences and Industrial Applications
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In lubricant formulations, base oil accounts for approximately 70%-99%. How to select the proper base oils for the lubricants? hydrocarbons, esters, or Polyalkylene Glycols (PAG)? What are the differences between these types of base oils? What are the differences in their applications?
Hydrocarbon base oils
Hydrocarbon base oils are the core skeleton of lubricating oils, accounting for more than 90% of global usage. They are essentially hydrocarbons (such as paraffins and cycloalkanes) extracted from petroleum, which are refined to remove impurities and form a stable lubricating carrier. From automobile engines to industrial gearboxes to air-conditioning compressors, the performance foundation of most lubricating products depends on the viscosity characteristics, temperature adaptability, and durability of such base oils. It can be said that without hydrocarbon base oils, modern lubrication technology will lose its fundamental support.
According to API (American Petroleum Institute), base oils are divided into 5 categories, as the following tables:
| API Group | Type | Sulfur Content | Saturates content | Viscosity Index (Ⅵ) |
| Group l | Solvent-Refined Mineral Oil | ＞0.03% | <90% | 80-120 |
| Group ll | Hydroprocessed Mineral Oil | <0.03% | ≥90% | 80-120 |
| Group III | Severely Hydroisomerized Oil | ≈0% | ≥90% | ＞120 |
| Group Ⅳ | Polyalphaolefin (PAO) | Sulfur-Free | ≈100% | 125-150 |
| Graup Ⅴ | Other Synthetics (e.g, Synthctic Esters, PAGs) | |||
Group III+ base oils
GTL (Gas to Liquid) base oil and CTL (Coal to Liquid) base oil are also referred to as Group III+ base oil by some people in China. For example, the CTL coal-based base oil produced by Lu'an Petrochemical has low nitrogen, no aromatic hydrocarbons, a high viscosity index, low evaporation loss, good low-temperature performance, and a much lower price than PAO. CTL base oil has a wide range of applications in lubricants due to its excellent properties in these years.
Generally, the development of mineral oil (API I/II/III ) is the progress of petrochemical technology. It has gone through roughing (I type) → purification (II type) → reconstruction (III type). It is the evolution of refining technology from "physical separation" to "molecular manipulation".
Poly α Olefin (PAO)
PAO (API Group IV): PAOs are linear polyolefins with super low pour point ( -60℃) and viscosity index (VI>120).
PAO base oil is like an "all-around player" in lubricating oil: it can work in severe climates of -60℃, and also keeps the oil film not too thin at high temperature (viscosity index>135), and is particularly resistant to oxidation. It was originally designed for harsh working conditions, such as aircraft engines and equipment in the polar area.
Nowadays, for a smooth cold-start at low temperatures and extended oil intervals (such as maintenance every 10,000 kilometers), PAO is becoming more and more popular in the high-end full synthetic motor oil market.
Simply put, it is used as a premium base oil, from flight to daily driving in nowadays industrials.
Synthetic esters
What is a synthetic ester?
Synthetic esters are like "high-end customization" of lubricating base oils. It is not simply made from petroleum, but is "man-made" by chemical reactions (esterification) of specific organic acids and organic alcohols (such as neopentyl polyols and fatty acids) under the action of catalysts.
Compared with mineral oils, synthetic esters are born with "high-performance genes":
strong polarity (strong ability to dissolve carbon deposits)
good viscosity characteristics (not easy to thin at high temperatures, easy to flow at low temperatures),
High-temperature resistance and oxidation resistance
biodegradable, esters are easy to be "eaten" by microorganisms
"These advantages enable it to excel in high-tech applications where mineral oils cannot compete, such as in the 'heart' of jet aircraft-aviation engines, as well as high-temperature/high-pressure compressors and precision hydraulic systems."
Synthetic Ester Families and Their Technical Development
There are many members in the synthetic ester family, which are mainly classified according to the raw materials combination method:
- Di-Esters: An early-stage super oil, excelling in low-temperature startup performance and once black technology for aircraft/tank lubrication, though with relatively weaker high-temperature endurance.
- Aromatic Esters: Featuring benzene ring structures, these esters exhibit low volatility, excellent solubility, and good heat resistance, making them widely used in high-temperature applications. e.g., Trimellitate Esters
- Polyol Esters: The Current Mainstream Ester Oils. These esters boast exceptional high-temperature resistance and oxidation stability, with minimal evaporation loss and superior lubricity. It is precisely these properties that meet the increasingly stringent requirements of modern jet engines, enabling them to replace diesters.
- Complex Esters: Notable for their outstanding biodegradability, these esters represent an environmentally friendly solution with special ecological advantages.
The "Green Lubrication Star"
As global environmental regulations tighten and consumer eco-awareness grows, synthetic esters have soared beyond aerospace applications to become a household staple, thanks to their "green, eco-friendly"
The ester oils not only meet the demands of high-end equipment-delivering extended service life (e.g., 8,000 hours performance in compressor oils) and superior low carbon deposit properties (effectively dissolving carbon deposits to reduce malfunctions and accidents)-but they are also the mandated choice for lubricants in environmentally sensitive areas (forests, farmlands, mines, rivers, lakes, and oceans).
With their exceptional performance and eco-friendly attributes, synthetic esters are more and more popular in various lubricating applications.
Chorus supplies high-performance Synthetic Esters for compressors, hydraulic systems, gear oils, and other lubricant applications.
PAG base oil: Special Lubricants.
Polyether base oil (PAG) is a lubricating material synthesized by chemical reaction. The ether bond (-C-O-C-) in its molecular chain gives it unique properties. By adjusting the proportion of raw materials such as ethylene oxide, propylene oxide, and butylene oxide, three types of products can be made: water-soluble PAG, water-insoluble PAG, and oil-soluble PAG.
PAG base oil has 3 major technical advantages:
Wide temperature adaptability: The pour point is as low as -60℃, and the viscosity index is as high as 250, ensuring the stable operation of the equipment at low and high temperatures.
Cleaning characteristics: The oxidation decomposition products of PAG are soluble and do not easily generate sludge and carbon deposits.
Special lubrication mechanism: Water-soluble PAG forms a protective film at high temperature through the cloud point effect (70-90℃) in metal processing, and dissolves again after cooling.
PAG base oils are widely used in modern industrial lubrication due to their unique properties: they reduce friction and save energy in industrial gears, provide long-term clean lubrication at 220°C for high-temperature chains (oxidation residues are soluble and do not coke), and become the excel partner of R134a environmentally friendly refrigerant in refrigeration compressors (perfectly soluble and not easy to absorb water to prevent ice blockage).
Through the cloud point effect (precipitating to form a film at 70-80°C), PAG works smartly to lubricate and provide anti-wear protection in fully synthetic cutting fluids. Meanwhile, in aqueous quenchants, it precisely regulates workpiece cooling rates to prevent deformation and cracking."
Chorus supplies high-performance Polyalkylene Glycol (PAG) base oils ideal for industrial lubricants, compressors, and automotive applications.
Click to know more about our PAG solutions!
