Why does diesel change color when stored for a long time?

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The darkening of light diesel in storage is caused by the elemental components of petroleum, among which hydrocarbons have the greatest impact; these are generally classified into alkanes, cycloalkanes, aromatic hydrocarbons, and unsaturated hydrocarbons. Hydrocarbon components have poor chemical stability; when exposed to air for long periods, they tend to oxidize and form gums. As a result, the longer diesel is stored, the darker its color becomes. 　　Diesel is a type of oil product obtained from the refining of petroleum. It is composed of a mixture of different hydrocarbons. Its main components are alkanes, cycloalkanes, or aromatics with 9 to 18 carbon atoms. Its chemical and physical properties lie between those of gasoline and heavy oil; its boiling point ranges from 170°C to 390°C, and its specific gravity is 0.82–0.845 kg/l. Diesel can be used as fuel for vehicles such as cars, tanks, airplanes, tractors, and railway vehicles, as well as for other mechanical devices; it can also be used for power generation and heating. 　　The reasons for the discoloration of diesel over time are as follows: 1. Discoloration occurs after long periods of storage: Firstly, the discoloration of diesel depends on its stability. Liquefied natural gas operation license. The stability of diesel refers to its ability to resist oxidation during storage and use. Diesel with good stability shows little change in appearance color during storage and is less prone to the formation of gum. Diesel with poor stability will darken significantly and develop more gum after being stored for a certain period of time. 　　The stability of light diesel is determined mainly by its chemical composition, in addition to storage conditions; diesel produced by straight distillation has a low content of olefins and therefore good stability. Diesel blended from two processed fractions contains a high amount of olefins, has poor stability, is prone to oxidation, and is not suitable for long-term storage. 　　II. Diesel changes color at high temperatures: Diesel changes color due to oxidation reactions between the olefins, aromatics, and unsaturated hydrocarbons present in diesel and the oxygen in the air. As a result of these reactions, large amounts of free radicals are generated; these free radicals then lead to the formation of gums and asphaltenes. The asphaltenes, in turn, produce more unsaturated hydrocarbons, creating a continuous cycle that causes the color of the diesel to become increasingly darker. 　　III. Color changes in diesel under other circumstances: If diesel is not sealed, evaporation can increase its concentration slightly, resulting in a darker color than before. This is related to the quality of the diesel; that is, there is a difference between pure diesel that is \"fresh and uncontaminated\" and mixed diesel that has been mixed together in tanks that have been in use for a long time. The presence of impurities and age-related issues also affect the color of the diesel. 　　IV. Basic principles behind diesel color change: 1. Diesel contains hydrocarbons, dienes, polycyclic aromatic hydrocarbons, and aliphatic aromatic hydrocarbons. 　　2. Sulfides in diesel (such as benzothiol and thiophene) produce insoluble precipitates, and they are important factors in the oxidation of diesel. 　　3. Oxides in diesel, such as dimethylpyrrole and quinoline, also have a significant impact on the formation of insoluble sediments in diesel; sulfides and oxides act synergistically to contribute to the formation of these insoluble sediments. 　　4. Trace amounts of catalyst ash, high-temperature coking impurities, as well as acidic and alkaline components present in diesel are also major factors contributing to discoloration. 　　5. Diesel has poor oxidation stability and tends to oxidize and change color easily. 　　6. It is also related to the raw materials used in device processing, as well as the methods of storing diesel. Antioxidant ingredients are added, along with components that facilitate stable storage. Registration of diesel trading companies.