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The oil products generated by the aforementioned devices are typically not suitable for direct commercial use. To meet industry standards, additional processing is usually necessary beyond blending and adding additives. This includes further refining to eliminate impurities and enhance performance in line with practical requirements. Common impurities found in crude oil include sulfur-, nitrogen-, and oxygen-containing compounds, as well as waxes and gums. These can cause unpleasant odors, dark colors, and damage to machinery, while also making storage difficult. Several methods are employed to remove these impurities, such as acid and alkali refining, deodorization, hydrogenation, solvent refining, white clay treatment, and dewaxing.
Acid refining involves treating the oil with sulfuric acid to remove specific sulfur compounds, nitrogen compounds, and gums. Alkaline refining, on the other hand, uses a caustic soda solution to eliminate oxygenates and sulfides, as well as any residual sulfuric acid from the acid refining process. These two techniques are often combined and referred to as acid-base refining.
Deodorization is used to eliminate foul odors caused by mercaptans in fuels derived from high-sulfur crude oil. When mercaptan levels are high, the oil becomes sticky and hard to store. A catalyst is often used to treat the oil with lye before it is oxidized using air.
Hydrogenation takes place under high pressure (around 1.5 MPa) and at temperatures between 300°C and 425°C, using a catalyst to remove sulfur, nitrogen, and oxygen compounds, as well as metal impurities. This process improves the oil's stability, reduces corrosiveness, and enhances its flammability.
Dewaxing is primarily used in the refining of aviation kerosene and diesel. Waxes in the oil can form crystals at low temperatures, affecting flow properties and potentially clogging pipelines. It is especially critical for aviation oils. Molecular sieves are often used for this purpose, and sometimes dewaxing is required during solvent refining.
White clay refining is typically performed at the end of the refining process. The clay, mainly composed of silica and alumina, adsorbs harmful substances, improving the oil’s quality and appearance.
Lubricating oils are mainly derived from crude oil distillation. Their key properties include viscosity, stability, and lubricity. The production process focuses on removing unwanted components like gums, asphaltenes, sulfur-, nitrogen-, and oxygen-containing compounds, waxes, and polycyclic aromatic hydrocarbons. These impurities affect viscosity, stability, and color. Methods used include solvent refining, dewaxing, deasphalting, hydrogenation, and white clay refining.
Solvent refining involves using solvents such as furfural or phenol to separate different components based on their solubility. This method is widely used in lubricant production and resembles the aromatic hydrocarbon extraction process in reformers.
Solvent dewaxing aims to remove paraffin wax from lubricant base oils, which can crystallize at low temperatures and increase viscosity. A common approach is cold crystallization, often using mixed solvents like toluene and methyl ethyl ketone, hence the term "ketone benzene dewaxing."