Knowledge about crude oil

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1. Definition of crude oil: Crude oil is a flammable, viscous liquid that ranges in color from light yellow to black, and is in a liquid or semi-liquid state; it is extracted from deep underground. It is mainly a mixture of various alkanes, cycloalkanes, and aromatic hydrocarbons. Crude oil is a mixture formed over long periods of evolution by organisms in ancient oceans or lakes, and like coal, it belongs to fossil fuels. 2. Chemical composition of crude oil: The main chemical elements that make up crude oil are carbon, hydrogen, sulfur, nitrogen, and oxygen. Typically, carbon accounts for 83–87%, while hydrogen accounts for 11–14%; together these two elements make up 96–99%. The remaining sulfur, nitrogen, oxygen, and trace elements together constitute only 1–4%. However, some crude oils, such as Mexican crude, have a sulfur content as high as 3.6–5.3%. Most crude oils contain very little nitrogen, in the range of a few parts per thousand to a few parts per ten thousand. However, some crude oils, such as those from Algeria and California in the United States, can have a nitrogen content of around 1.4–2.2%. In addition to the five main elements mentioned above, trace amounts of metallic and non-metallic elements are also found in crude oil. Among metal elements, the most important ones are vanadium (V), nickel (Ni), iron (Fe), copper (Cu), and lead (Pb); in addition, calcium (Ca), titanium (Ti), magnesium (Mg), sodium (Na), cobalt (Co), zinc (Zn), and others have also been identified. Among the non-metallic elements, there are mainly chlorine (Cl), silicon (Si), phosphorus (P), arsenic (As), etc., all of which are present in very small amounts. Based on its elemental composition, it can be seen that the compounds that make up crude oil are primarily hydrocarbons. It has been determined that the hydrocarbons in crude oil are mainly classified into three groups: alkanes, cycloalkanes, and aromatics. As for unsaturated hydrocarbons, they are generally not present in crude oil. Elements such as sulfur, nitrogen, and oxygen are present in crude oil in the form of various sulfur-containing, oxygen-containing, and nitrogen-containing compounds, as well as gelatinous and asphaltic substances that contain all three elements; these are collectively referred to as non-hydrocarbons. 3. Physical properties of crude oil: Crude oil produced around the world varies in properties to varying degrees. In terms of color, the vast majority of crude oils are black, but there are also variations such as dark black, dark green, and dark brown ； Some crude oils are reddish-brown, light yellow, or even colorless. The color of crude oil reflects the amount of resins and asphaltenes it contains; the higher this amount, the darker the color. In terms of specific gravity, the specific gravity of the vast majority of crude oils ranges between 0.8 and 0.98; however, there are exceptions – for instance, a certain type of Iranian crude oil has a specific gravity as high as 1.016, while crude oil from California, USA, can have a specific gravity as low as 0.707. The temperature at which crude oil begins to lose its fluidity under certain test conditions is called the freezing point. The freezing points of various crude oils vary greatly. In some regions of our country, the freezing point of crude oil can reach as high as 36°C, while in Karamay, Xinjiang, the freezing point of crude oil is as low as –50°C. The viscosity of crude oil varies over a wide range. The boiling point range of crude oil is generally from room temperature to over 500°C. Generally, crude oil is soluble in various organic solvents and insoluble in water, but it can form an emulsion with water. Furthermore, many crude oils have a strong odor, which is due to the presence of certain foul-smelling sulfur compounds in them. 4. Classification of crude oil The composition of crude oil is extremely complex, making it difficult to accurately classify it. However, due to practical needs, research in this area is still ongoing. In general, crude oil can be classified from geological, chemical, physical, and industrial perspectives, with a tendency to use its chemical classification. In the chemical classification of crude oil, the most commonly used methods are the characteristic factor classification and the key fraction characteristic classification; in addition, there is also the structural group composition classification. In the industrial classification (product classification), it is categorized based on the sulfur content, resin content, wax content, and specific gravity of crude oil.

5. Uses of crude oil Crude oil has a wide range of uses, and the products obtained through its refining can be roughly divided into four categories: (1) Fuels The main types include gasoline, kerosene, diesel, and boiler fuel oil. They are the source of power for engines, the heat source for boilers, and the fuel used for lighting, heating, and cooking in daily life. In terms of quantity, fuel accounts for a large proportion of all crude oil products and is the most widely used one. (2) Lubricants and greases are used to reduce friction between mechanical parts, protect them, extend their service life, and save energy. Their quantity accounts for about 5% of all crude oil products, but there are a great variety of them. (3) Waxes, asphalts, and crude oil coke are obtained through further processing of by-products generated during the production of fuels and lubricants, with their output accounting for a few percent of the crude oil processed. (4) Crude oil chemical products are important basic raw materials or intermediates in the organic synthesis industry. Some crude oil chemical products can be used directly.