Q&A on Basic Knowledge of Petroleum Products

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1. What is oil? Oil is a viscous, oily, flammable liquid mineral; as early as the beginning of our era, the working people of our country had already discovered it and begun to use it. The colors are mostly black, brown, or dark green, with yellow appearing occasionally as well. Under normal circumstances, oil is lighter than water. The density of oil is mostly between 0.77 and 0.96 grams per cubic centimeter. Oil is a complex mixture composed of various hydrocarbons. In the composition of petroleum, the carbon content is about 84–85%, the hydrogen content is about 12–14%, with small amounts of organic compounds containing sulfur, oxygen, and nitrogen. In addition, trace amounts of elements such as iron, nickel, copper, lead, vanadium, arsenic, magnesium, phosphorus, potassium, silicon, calcium, and manganese have also been found in oil. 2. Into which categories are petroleum products divided? Petroleum products generally refer to various products obtained through processing in refineries. Petroleum products can be classified into the following categories according to their uses: 1) Fuels: gasoline, jet fuel, kerosene, diesel, heavy oil, etc ； 2) Solvent oils: petroleum ether, extraction solvent oil, rubber solvent oil, solvent kerosene, etc ； 3) Lubricants: jet engine lubricants, gasoline engine oils, diesel engine oils, turbine oils, refrigeration machine oils, cylinder oils, mechanical oils, instrument oils, etc ； 4) Oils for electrical equipment: transformer oil, oil for circuit breakers, capacitor oil, etc ； 5) Hydraulic oils: aviation hydraulic oil, spindle oil, etc ； 6) Greases: calcium-based greases, sodium-based greases, aluminum-based greases, barium-based greases, precision instrument greases, etc ； 7) Paraffins: paraffin, high-melting-point paraffin, industrial paraffin, purified paraffin, etc ； 8) Asphalts: road petroleum asphalt, construction petroleum asphalt, special-purpose petroleum asphalt, etc ； 9) Petroleum benzenes: toluene, benzene, xylene, etc ； 10) Other vacuum pump oils, diffusion pump oils, rust inhibitors, petroleum coke, petrolic acid, etc. 3. What are the standards for testing methods of petroleum products? How many levels are there? Standards for test methods of petroleum products are technical specifications regarding instruments, reagents, testing conditions, testing procedures, accuracy, etc., in the analysis methods for petroleum products. It is part of the standardized literature. After being approved and issued by the competent authorities, it serves as a technical standard to be adhered to by production, usage, and research institutions. Currently, the standards for testing methods of petroleum products are divided into three levels: **national standards, ministry standards, and enterprise standards. 1) **Standards: Refer to the petroleum product testing method standards that have been approved and issued by the competent authorities, and are uniform across the country** ； 2) Ministry standards: Refer to the standard test methods for petroleum products that are approved and issued by the competent authorities of the Petroleum and Chemical Industry Ministry, and which serve as unified standards within the national petroleum industry ； 3) Enterprise standards: Refer to the unified testing methods standards for petroleum products within an enterprise, which are formulated by the enterprise itself or among several enterprises and organizations in order to implement national and ministerial standards and to guide production; such standards are approved by the enterprise’s competent authorities. 4. What are the sources and forms of moisture in petroleum products? Water that enters petroleum products during transportation and storage ； 2. Petroleum products have a certain degree of water absorption; they can absorb and dissolve a portion of water from the atmosphere or when in contact with water. Gas and kerosene mix very little with water, but can still dissolve no more than 0.01% water. The main forms in which water exists in petroleum products are as follows: 1) Suspended state: Water is suspended in the oil in the form of water droplets. It occurs frequently in heavy oil with high viscosity ； 2) Floating state: refers to water being evenly dispersed in the oil in the form of extremely small droplets ； 3) Dissolved state: Water exists in a state dissolved in oil. The amount it can dissolve in oil is determined by the chemical composition of the petroleum product and the temperature. Generally, alkanes, cycloalkanes, and olefins have weak abilities to dissolve water, while aromatic hydrocarbons can dissolve more water. The higher the temperature, the more water can dissolve in the oil. 5. What harm can moisture in petroleum products cause? 1) When the moisture in petroleum products evaporates, it absorbs heat, which reduces its calorific value ； 2) Moisture in light oils can deteriorate the combustion process. It can also carry dissolved salts into the cylinder, where they form carbon deposits and increase cylinder wear ； 3) At low temperatures, the water in the fuel will freeze, blocking the fuel lines and filters and interfering with the fuel supply to the engine’s fuel system ； 4) When there is moisture in petroleum products, it accelerates the oxidation and gelation of the oil ； 5) The presence of water in the lubricating oil not only causes corrosion of engine components, but also water in contact with metal parts at temperatures above 100°C generates steam, which destroys the lubricating oil film. 6. How are the terms related to petroleum product distillation interpreted? 1) Gasification: refers to the process in which a substance changes from a liquid state to a gas state by absorbing heat ； 2) Evaporation: refers to the process of gasification that occurs only at the surface of a liquid ； 3) Boiling: refers to the process that occurs at a certain temperature when the vapor pressure of a liquid equals the external pressure, with gas formation taking place not only on the surface of the liquid but also throughout its interior ； 4) Condensation: refers to the process in which a substance changes from a gaseous state to a liquid state by releasing heat ； 5) Cooling: The process in which the temperature of a substance decreases without any change in its state of matter ； 6) Distillation: Based on the evaporation of liquids, it involves heating them to boiling point and then guiding the vapor out to allow it to condense and cool down ； 7) Fractionation: The process of separating fractions with different boiling points from oil products using distillation ； 8) Boiling range: Refers to the temperature range over which a liquid sample boils, expressed as a numerical relationship between its distillation temperature and the amount distilled, as measured using specialized distillation equipment. It is often expressed as the volume percentage of the distillate at a certain distillation temperature, or as the distillation temperature at which a certain volume percentage of the distillate is obtained ； 9) Initial boiling point: The distillation temperature at which the first drop of distillate falls from the end of the condenser after distillation begins ； 10) Final boiling point (dry point): refers to the highest temperature indicated by the thermometer at the end of distillation, when the sample being distilled is about to be completely evaporated and the mercury column of the distillation thermometer stops rising and begins to fall ； 11) Residual amount: refers to the amount of residual oil remaining in the flask after distillation is stopped ； 12) Loss amount: The amount of oil lost during the distillation process due to gas leakage, inadequate cooling, coking, etc. 7. What are water-soluble acids and bases in petroleum products? Water-soluble acids or bases in petroleum products refer to water-soluble mineral acids and bases that enter the petroleum products during processing and storage. Mineral acids are mainly sulfuric acid and its derivatives, including sulfonic acids and acidic sulfates. Water-soluble bases are mainly sodium hydroxide and sodium carbonate. They are mostly formed by the residues left over from incomplete removal during acid-base purification. 8. What are the acidity and acid number of petroleum products? What organic acids are typically present in petroleum products? Both the acidity and acid number of petroleum products are indicators that indicate the presence of acidic substances in the petroleum. The number of milligrams of potassium hydroxide required to neutralize the acidic substances in 100 milliliters of petroleum products is called acidity. The number of milligrams of potassium hydroxide required to neutralize the acidic substances in 1 gram of petroleum products is called the acid value. The measured acidity (value) is the total amount of organic and inorganic acids. But in most cases, there are no inorganic acids present in the oil, so the acidity (value) measured almost always represents organic acids. The organic acids contained in oils are mainly naphthenic acids, which are carboxylic acid derivatives of naphthenes. In addition, there are acidic products formed due to oxidation during storage. Heavy distillates also contain high-molecular-weight organic acids; certain oil products further contain phenols, fatty acids, as well as acidic compounds such as sulfides and asphaltenes. 9. What is the flash point of petroleum products? Under specified conditions, the oil is heated; as the temperature of the oil rises, the concentration of oil vapor in the air (above the liquid surface) increases as well. When the temperature reaches a certain level, the oil vapor content in the mixture of oil vapor and air reaches a flammable concentration. If a flame is brought near this mixture, it will ignite. The lowest temperature at which this phenomenon occurs is referred to as the flash point of the petroleum product. Flash point detectors are divided into closed and open types. The flash point measured using a closed-cup flash point tester is called the closed-cup flash point ； The flash point measured using an open-cup flash point tester is called the open-cup flash point. 10. What is the significance of the flash point of petroleum products for production and application? 1) The flash point of the oil can be used to determine the lightness or heaviness of its distillate composition. The general rule is: the higher the vapor pressure of the oil and the lighter its distillate composition, the lower its flash point. Conversely, oils with a heavier distillate composition have a higher flash point ； 2) The flash point can be used to determine the fire hazard of oils. Because the flash point is the lowest temperature at which a fire hazard arises. The lower the flash point, the easier it is for the fuel to burn, and the greater the fire hazard. Therefore, flammable liquids are also classified according to their flash point. Liquids with a flash point below 45°C are called flammable liquids, while those with a flash point above 45°C are called combustible liquids. The various fire safety measures for its transportation, storage, and use can be determined based on its flash point ； 3) For certain lubricants, simultaneously measuring the closed-cup flash point can serve as an indicator of the presence of low-boiling-point contaminants in the oil, for use in production inspections. Generally, the open flash point is 20–30°C higher than the closed flash point, as some of the oil vapor evaporates during the measurement of the open flash point. However, if the two results differ significantly, it indicates that the oil contains light fractions, or there was cracking during distillation, or the solvent used in purification during dewaxing was not completely separated.