What are the properties of mineral base oil?
author: Ann
2024-12-02
Mineral base oil is made from petroleum refining, often vacuum distillation, solvent refining, dewaxed clay refining and hydrogenation. Different degrees of hydrogenation result in different viscosity index, oxidation stability, pour point and volatility index. of base oil. Mineral base oils are mainly composed of alkanes, cycloalkanes, aromatics, naphthenic aromatic hydrocarbons, as well as oxygen-, nitrogen-, and sulfur-containing organic compounds and non-hydrocarbon compounds such as colloids and asphaltenes, with almost no olefins. Mineral base oils are mainly hydrocarbons, so the hydrocarbon structure has a significant impact on the viscosity, viscosity-temperature properties, freezing point and other properties of the lubricating oil.
(1) Effect on viscosity
The viscosity of hydrocarbons is related to their molecular structure, molecular size, number and type of rings. The viscosity of lubricating oil increases with the increase of the relative molecular weight of hydrocarbons; among various hydrocarbons with the same number of carbon atoms, the viscosity of alkanes is small, aromatic hydrocarbons are second smallest, and the viscosity of cycloalkanes is very large, and as the viscosity of cycloalkanes increases, The number increases as the proportion of the number in the molecule increases; in hydrocarbons with the same number of rings, the viscosity increases with the length of the side chain.
The viscosity of hydrocarbons is related to their molecular structure, molecular size, number and type of rings. The viscosity of lubricating oil increases with the increase of the relative molecular weight of hydrocarbons; among various hydrocarbons with the same number of carbon atoms, the viscosity of alkanes is small, aromatic hydrocarbons are second smallest, and the viscosity of cycloalkanes is very large, and as the viscosity of cycloalkanes increases, The number increases as the proportion of the number in the molecule increases; in hydrocarbons with the same number of rings, the viscosity increases with the length of the side chain.
(2) Effect on viscosity-temperature properties
The viscosity index of the hydrocarbons themselves varies greatly. Among the hydrocarbons contained in lubricating oil products, the viscosity index of n-alkanes is very high, reaching more than 180; the viscosity index of isoparaffins is higher than that of the corresponding n-alkanes. It is lower and decreases as the degree of branching increases; followed by monocyclic and bicyclic cycloalkanes with alkyl side chains and monocyclic and bicyclic aromatic hydrocarbons; the worse ones are heavy aromatic hydrocarbons, polycyclic cycloalkanes and naphthenic-aromatic hydrocarbons ; For bicyclic and polycyclic hydrocarbons, the viscosity index increases with the increase in the number and length of side chains, and decreases sharply with the increase in the number of rings; colloids are polycyclic oxygen-containing compounds with worse viscosity-temperature properties.
The viscosity index of the hydrocarbons themselves varies greatly. Among the hydrocarbons contained in lubricating oil products, the viscosity index of n-alkanes is very high, reaching more than 180; the viscosity index of isoparaffins is higher than that of the corresponding n-alkanes. It is lower and decreases as the degree of branching increases; followed by monocyclic and bicyclic cycloalkanes with alkyl side chains and monocyclic and bicyclic aromatic hydrocarbons; the worse ones are heavy aromatic hydrocarbons, polycyclic cycloalkanes and naphthenic-aromatic hydrocarbons ; For bicyclic and polycyclic hydrocarbons, the viscosity index increases with the increase in the number and length of side chains, and decreases sharply with the increase in the number of rings; colloids are polycyclic oxygen-containing compounds with worse viscosity-temperature properties.
(3) Effect on freezing point
The order of the freezing points of various hydrocarbons from large to small is: n-alkanes>iso-alkanes>cycloalkanes>aromatic hydrocarbons. The freezing point of n-alkanes is very high and increases with the number of carbon atoms. For example, the freezing point of n-hexadecane is 18.16°C and that of n-octadecane is 36.7°C; the freezing point of isoparaffins is lower than that of corresponding n-alkanes, and it decreases rapidly as the degree of branching increases; with side chains For cyclic hydrocarbons, the greater the degree of side chain branching, the faster the freezing point decreases. From the influence of molecular structure on some physical properties of lubricating oil, it can be seen that there are limitations in changing the performance of lubricating oil from the structure of hydrocarbon molecules. When changing the molecular structure to improve one performance, it often improves another performance. It becomes worse, and only proper selection can get lubricants with relatively good performance.
The order of the freezing points of various hydrocarbons from large to small is: n-alkanes>iso-alkanes>cycloalkanes>aromatic hydrocarbons. The freezing point of n-alkanes is very high and increases with the number of carbon atoms. For example, the freezing point of n-hexadecane is 18.16°C and that of n-octadecane is 36.7°C; the freezing point of isoparaffins is lower than that of corresponding n-alkanes, and it decreases rapidly as the degree of branching increases; with side chains For cyclic hydrocarbons, the greater the degree of side chain branching, the faster the freezing point decreases. From the influence of molecular structure on some physical properties of lubricating oil, it can be seen that there are limitations in changing the performance of lubricating oil from the structure of hydrocarbon molecules. When changing the molecular structure to improve one performance, it often improves another performance. It becomes worse, and only proper selection can get lubricants with relatively good performance.
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