The color of oil can often reflect its refining degree and stability. For base oil, the higher the refining degree, the cleaner the removal of hydrocarbon oxides and sulfides, and the lighter the color. However, even if the refining conditions are the same, the color and transparency of the base oil produced by different oil sources and base crude oils may be different.
For the new finished lubricating oil, due to the use of additives, color has lost its original significance as an index to judge the refining degree of base oil.
Viscosity reflects the internal friction of an oil product and is an indicator of the oiliness and fluidity of an oil product. Without any functional additives, the higher the viscosity, the higher the oil film strength and the worse the fluidity.
The viscosity index indicates the degree to which the oil viscosity changes with temperature. The higher the viscosity index, the smaller the influence of temperature on the oil viscosity, the better its viscosity temperature performance, and vice versa.
Flash point is an indicator of oil evaporation. The lighter the fraction, the greater the evaporation and the lower the flash point. On the contrary, the heavier the oil fraction, the smaller the evaporation and the higher the flash point. At the same time, the flash point is an indicator of the fire risk of petroleum products. The hazard level of oil products is divided according to the flash point. Flammable products are those whose flash point is below 45 ℃ and flammable products are those whose flash point is above 45 ℃. It is strictly prohibited to heat the oil products to its flash point temperature during the storage and transportation of oil products. Under the same viscosity, the higher the flash point, the better. Therefore, the user should select the lubricating oil according to the service temperature and the working conditions of the lubricating oil. It is generally believed that the flash point is 20 ~ 30 ℃ higher than the service temperature, which can be used safely.
Freezing point and pour point
The solidification of oil products is very different from that of pure compounds. There is no definite solidification temperature for oil products. The so-called "solidification" only loses fluidity as a whole, and not all components become solids.
The freezing point of lubricating oil is an important quality index indicating the low-temperature fluidity of lubricating oil. It is of great significance for production, transportation and use. Lubricating oil with high freezing point cannot be used at low temperature. On the contrary, it is not necessary to use lubricating oil with low freezing point in areas with high temperature. Because the lower the freezing point of lubricating oil, the higher the production cost, resulting in unnecessary waste. Generally speaking, the freezing point of lubricating oil shall be 5 ~ 7 ℃ lower than the low temperature of the service environment. However, it should also be mentioned that when selecting low-temperature lubricating oil, it should be comprehensively considered in combination with the freezing point, low-temperature viscosity and viscosity temperature characteristics of the oil. The low temperature viscosity and viscosity temperature characteristics of oil with low freezing point may also not meet the requirements.
Freezing point and pour point are indicators of low-temperature fluidity of oil products. There is no principle difference between them, but the determination method is slightly different. The pour point and pour point of the same oil are not exactly equal. Generally, the pour point is 2 ~ 3 ℃ higher than the pour point, but there are exceptions.
Acid value is an index indicating that the lubricating oil contains acidic substances, and the unit is mgKOH / g. Acid value is divided into strong acid value and weak acid value, and the combination of the two is the total acid value (tan). What we usually call "acid value" actually refers to "total acid value (tan)".
The alkali value is an index indicating the content of alkaline substances in lubricating oil, and the unit is mgKOH / g.
The base number is also divided into strong base number and weak base number, and the combination of the two is the total base number (TBN). What we usually call "base number" actually refers to "total base number (TBN)".
Neutralization value actually includes total acid value and total base value. However, unless otherwise noted, "neutralization value" generally refers to "total acid value", and its unit is mgKOH / g.
Water content refers to the percentage of water content in lubricating oil, usually by weight. The existence of water in the lubricating oil will destroy the oil film formed by the lubricating oil, worsen the lubrication effect, accelerate the corrosion of organic acids on metals, rust equipment, and make the oil easy to produce sediment. In short, the less water in the lubricating oil, the better.
Mechanical impurities refer to precipitates or colloidal suspensions in lubricating oil that are insoluble in solvents such as gasoline, ethanol and benzene. Most of these impurities are sand and iron filings, as well as some organic metal salts insoluble in solvents brought by additives. Generally, the mechanical impurities of lubricating oil base oil are controlled below 0.005% (mechanical impurities below 0.005% are considered as none).
Sulfuric acid ash
Ash refers to the non combustible substances left after burning under specified conditions. The composition of ash is generally considered to be some metal elements and their salts. Ash has different concepts for different oil products. For base oil or oil products without additives, ash can be used to judge the refining depth of oil products. For oil products (new oil) with metal salt additives, ash has become a means to quantitatively control the amount of additives. Sulfuric acid ash is used to replace ash abroad. The method is to add a small amount of concentrated sulfuric acid after the oil sample is burned and before ashing to convert the metal elements of the additive into sulfate.
Under the specified experimental conditions, the coke black residue formed after heating, evaporation and combustion of oil products is called residual carbon. Carbon residue is an important quality index of lubricating oil base oil, and it is an item specified to judge the nature and refining depth of lubricating oil. The amount of residual carbon in lubricating oil base oil is not only related to its chemical composition, but also related to the refining depth of oil. The main substances forming residual carbon in lubricating oil are gum, asphaltene and polycyclic aromatic hydrocarbons in oil. Under the condition of insufficient air, these substances are decomposed and condensed by strong heat to form residual carbon. The deeper the refining depth of oil, the smaller the carbon residue value. Generally speaking, the smaller the residual carbon value of blank base oil, the better.
As of October 2013, many oil products contain additives of metal, sulfur, phosphorus and nitrogen, and their residual carbon value is very high. Therefore, the residual carbon of additive oil has lost its original significance. Mechanical impurities, moisture, ash and residual carbon are quality indicators reflecting the purity of oil products and the refining degree of lubricating base oil. Production process of lubricating oil
It mainly uses lubricating oil fraction and residue fraction from crude oil distillation unit as raw materials. These fractions contain not only ideal components, but also various impurities and non ideal components. Through processes such as solvent deasphalting, solvent dewaxing, solvent refining, hydrofining or acid-base refining, clay refining (see petroleum product refining), remove or reduce non ideal components such as substances forming free carbon, substances with low viscosity index, substances with poor oxidation stability, paraffin and chemicals affecting the color of product oil, so as to obtain qualified lubricating oil base oil, After blending and adding appropriate additives, it becomes a lubricating oil product.