How Many Categories of Base Oils Are There?

[Leanne]

Base oils for engine oil are divided into five categories. The names, compositions, and characteristics of each type are introduced in detail as follows: Group I oils are traditional solvent-refined mineral oils, produced through solvent refining. Their operating temperature range is generally between 0~65°C, and they are the cheapest base oils available on the market. Group II oils are hydrocracked mineral oils, produced through hydroprocessing (hydrocracking). After hydroprocessing, the hydrocarbon molecules become saturated, enhancing their oxidation resistance. They appear clearer and more transparent compared to Group I oils and are slightly more expensive. Both Group I and Group II oils are referred to as mineral oils. Mineral base oils are derived from the residual oil left at the bottom of distillation towers after extracting useful light substances (such as aviation fuel, gasoline, diesel, etc.) during crude oil refining (the remaining residue is asphalt). Essentially, they utilize the inferior components of crude oil. Crude oil contains thousands of different molecular compounds, and even with advanced refining techniques, it is impossible to completely remove impurities and undesirable substances. Group III oils undergo severe hydrocracking and hydroisomerization, resulting in a purer product compared to Group II oils. Because the performance of Group III oils is close to that of synthetic oils, they are sometimes classified as synthetic oils. Group IV oils are polyalphaolefins (PAO), a patented technology by ExxonMobil. They are derived from ethylene and propylene dispersed from crude oil's natural gas or gas, undergoing complex chemical reactions such as polymerization and catalysis to form large-molecule base oils. Essentially, they utilize the superior components of crude oil, chemically processed and artificially controlled to achieve the desired molecular structure. Their molecules are neatly arranged, giving them strong resistance to external variables. Thus, synthetic oils inherently exhibit better thermal stability, oxidation resistance, and viscosity stability compared to mineral oils. Group V oils are other synthetic oils (ester-based synthetic oils), including PAG (polyethylene glycol), phosphate esters, silicone oils, and esters. They are primarily synthesized from fatty acids and alcohols derived from plants and animals. However, their main drawback is their high cost. Additionally, ester-based oils are highly hydrophilic, corrosive when exposed to water, and have poor compatibility with rubber and plastic components, requiring extremely high sealing standards. Esters are inherently oily and possess natural lubricating properties, which other base oils (including PAO) achieve through additives. Moreover, the inherent polarity of esters allows oil film molecules to adhere to metal surfaces, making ester-based oils the most superior in terms of lubricating performance.