What are the classification and quality requirements of petroleum products?

I. Classification of petroleum products

Usually, petroleum products do not include all petrochemical products synthesized from petroleum. According to GB/T 498-20 14 "Classification Methods and Classification Determination of Petroleum Products and Lubricants", China now divides petroleum products into six categories.

(1) Fuel: including gasoline, diesel, jet fuel (aviation kerosene), kerosene for lamps, fuel oil, etc. Fuel accounts for about 80% of China's petroleum products, of which about 60% is used for various engine fuels.

(2) Lubricant: including lubricating oil and grease, the output accounts for about 2% of the total petroleum products, which is mainly used to reduce the friction between contact parts and prevent wear, so as to reduce energy consumption and prolong the service life of equipment.

(3) Petroleum asphalt: it is used for roads, buildings and waterproofing, and its output accounts for about 3% of the total petroleum products.

(4) Petroleum wax: Petroleum wax is a solid hydrocarbon in petroleum, and its output accounts for about 1% of the total petroleum products. It is used as raw material for light industry, chemical industry and food industry.

(5) Petroleum coke: its output accounts for about 2% of the total petroleum products, and petroleum coke can be used as electrodes for aluminum smelting and steelmaking.

(6) Solvents and chemical raw materials: About 65,438+00% of petroleum products are used as petrochemical raw materials and solvents, including raw materials for preparing ethylene (light oil), petroleum aromatics and various solvent oils.

Second, the quality requirements of petroleum products

(1) gasoline

Gasoline can be used as fuel for ignition engines. The main requirements for using gasoline are: fully evaporating to form combustible mixture; Stable combustion, no knocking; Good storage stability, not easy to gel; No corrosion to engine, less pollutant discharge.

1. Evaporation of gasoline

When gasoline has good evaporation, it can quickly vaporize in the engine cylinder and form a uniform combustible mixture with air. After entering the cylinder, it is completely burned, and the engine can run normally. If the evaporation of gasoline is too poor, it can not be completely vaporized in the cylinder, which will reduce the engine power and make it difficult to start and accelerate. On the other hand, if the evaporation of gasoline is too strong, gasoline has evaporated in the oil guide pipe to form gas resistance, which eventually leads to insufficient oil supply and gas resistance is more likely to occur in summer.

2. Explosion resistance of gasoline

When gasoline burns abnormally in the engine, there will be strong vibration of the engine body and huge metal knocking, which will lead to the decline of engine power, black smoke from the exhaust pipe and serious damage to parts. This phenomenon is called knocking. Knocking is harmful to gasoline engines. There are two main reasons for knocking phenomenon: one is related to the nature of fuel. If the fuel is easy to oxidize, the formed peroxide is not easy to decompose, and the spontaneous combustion point is low, so it is easy to deflagrate. The second is related to the working conditions of the engine. If the engine compression ratio is too high, the cylinder wall temperature is too high, or the operation is improper, it is easy to cause knocking. The characteristic that measures whether the fuel is easy to knock is called antiknock. The antiknock performance of gasoline is expressed by octane number. Octane number is divided into research octane number (ROH) and engine octane number (MON), and research octane number is usually used. The higher the octane number of gasoline, the better its antiknock performance. The octane number of gasoline needs to be determined in a special instrument. The antiknock performance of gasoline depends on its chemical composition. For similar hydrocarbons, the octane number decreases with the increase of relative molecular weight. When the relative molecular weight is similar, the octane number of n-alkanes is the lowest, naphthenes and olefins are higher, and the octane number of highly branched isoparaffins and aromatics is the highest. At present, the main component of motor gasoline in China is catalytic cracking gasoline, which contains more aromatic hydrocarbons, isoparaffins and olefins, so it has good antiknock performance.

3. Stability of gasoline

The stability of gasoline refers to its ability to resist oxidation. The gasoline with poor stability is easy to be oxidized during storage and transportation, resulting in gum, which darkens the color of gasoline and even produces some gum and sediment. The poor stability of gasoline will seriously affect the normal operation of the engine. For example, thick glue is formed in the fuel tank, filter screen and carburetor, which will affect the oil supply in serious cases; The deposition of intake valve and exhaust valve will lead to coking, which will lead to lax valve closure.

The most fundamental reason that affects the safety of gasoline is its chemical composition. Alkanes, cycloalkanes and aromatics in gasoline are not easy to undergo oxidation reaction at room temperature, while various unsaturated hydrocarbons contained in gasoline are easy to undergo oxidation and superposition reaction to form colloid. Therefore, the unsaturated hydrocarbon contained in gasoline is the main reason for its poor stability.

In addition to unsaturated hydrocarbons, sulfur-containing compounds and nitrogen-containing compounds such as thiophenol and mercaptan in gasoline can also promote the formation of gum, which makes the color of gasoline darker when it comes into contact with air, and even forms gum.

Straight-run gasoline fraction contains no unsaturated hydrocarbon and has good stability; However, the gasoline fraction obtained by secondary processing (such as FCC gasoline) has poor stability because it contains a large number of unsaturated hydrocarbons and other non-hydrocarbon compounds.

The deterioration of gasoline is not only related to its chemical composition, but also to many external conditions, such as temperature, the role of metal surface, the size of contact area with air and so on. With the increase of temperature, the oxidation speed of gasoline is accelerated, and the tendency of gum formation is increased; Under the action of metal surface, gasoline is not only easy to turn black, but also accelerates the formation of colloid. The greater the contact area between fuel and air, the greater the tendency of oxidation.

In view of the obvious influence of temperature, light and contact with air on the stability of gasoline, measures such as avoiding light, reducing temperature and reducing contact area with air should be taken when storing gasoline.

4. Corrosiveness of gasoline

The main substances that corrode metals in gasoline are sulfur and sulfur-containing compounds, organic acids and water-soluble acids or bases. Therefore, in the use, storage and transportation of gasoline, the corrosiveness of gasoline and its combustion products to contact metals should be controlled.

5. Varieties and brands of gasoline

Gasoline in China is divided into three types according to composition and use: automobile gasoline, automobile ethanol gasoline and aviation gasoline, and all kinds of gasoline are classified according to octane number.

Motor gasoline (national Ⅲ) and motor gasoline (national Ⅳ) are divided into three grades according to the research octane number: 90, 93 and 97, and motor gasoline (national Ⅴ) is divided into four grades according to the research octane number: 89, 92, 95 and 98. According to the research octane number, ethanol gasoline for vehicles is divided into three grades: 90, 93 and 97. Aviation gasoline is divided into three grades according to the octane number of the engine: 75, 95, 100.

(2) Diesel oil

Diesel oil can be used as fuel for compression ignition engines. Diesel products in China are divided into light diesel oil and heavy diesel oil. Light diesel oil is suitable for high-speed diesel engines, and heavy diesel oil is suitable for medium and low-speed diesel engines. This section mainly introduces light diesel oil, and its application requirements mainly include: good atomization, evaporation and combustibility; Good fluidity ensures that the oil supply system can supply oil normally at low temperature; Good storage stability and thermal stability; It has no corrosion and wear on parts and contains no mechanical impurities.

1. Combustion and evaporation of diesel oil

Good flammability of diesel means that diesel can spontaneously ignite after being injected into the combustion chamber, and completely burn in a short time, forming a homogeneous combustible mixture with high-temperature air. Diesel will also knock in diesel engines, similar to gasoline engines, but the reasons for knocking are different from gasoline engines. Gasoline engine knocks because the fuel is too easy to oxidize and the auto-ignition point is too low. Diesel engine knocks because the fuel is not easy to oxidize and the auto-ignition point is too high. Therefore, gasoline engines need fuel with high autoignition point, while diesel engines need fuel with low autoignition point. The antiknock performance of diesel oil is expressed by cetane number. According to the relevant standards in China, the cetane number of ordinary diesel oil is generally not less than 45.

The ignition and combustion of diesel oil in the cylinder of diesel engine are carried out in gaseous state, so the diesel engine can only start and work normally after vaporizing and forming flammable mixture with air. Therefore, the ignition delay of diesel depends not only on its cetane number, but also on its evaporation. The speed of diesel evaporation depends on the air temperature in the combustion chamber and the composition of diesel fraction. The higher the temperature, the more light fractions and the faster the evaporation rate. The faster the speed of diesel engine, the shorter the time of each working cycle, which requires the faster the evaporation speed of diesel oil and the lighter the fraction used. If the diesel fraction is too heavy and the evaporation rate is too slow, it will lead to incomplete combustion, decreased power, increased oil consumption, diluted lubricating oil and aggravated wear. If the fraction of diesel oil is too light, the cylinder pressure of the engine will rise sharply due to the rapid evaporation rate, which will lead to great fluctuation of the diesel engine.

2. Liquidity of diesel oil

When the viscosity of diesel oil is too small, it is easy to leak from the gap between the plunger and the pump barrel of the high-pressure oil pump, which will reduce the fuel injected into the cylinder and cause the engine power to drop. At the same time, the smaller the viscosity of diesel oil, the smaller the diameter of atomized droplets, and the shorter the range of sprayed oil flow, which can not be evenly mixed with all the air in the cylinder, resulting in incomplete combustion. The viscosity of diesel oil is too high, so it is difficult to supply oil. At the same time, the diameter of sprayed oil droplets is too large and the oil flow range is too long, which reduces the effective evaporation area of oil droplets, slows down the evaporation speed, and also makes the composition of mixed gas uneven and incomplete combustion.

The low-temperature fluidity of diesel oil is not only related to whether the diesel oil supply system can supply oil normally at low temperature, but also closely related to whether diesel oil can be stored and transported normally at low temperature. The low-temperature fluidity of diesel oil is related to its chemical composition. The higher the content of n-alkanes, the worse the low-temperature fluidity. The indexes for evaluating the low-temperature fluidity of diesel oil in China are freezing point (or pour point) and cold filter point.

3. Stability, corrosiveness and cleanliness of diesel oil

The stability of diesel oil is generally evaluated by the total insoluble matter and carbon residue of 10% steam residue. The color of diesel oil with poor stability tends to darken during storage, and even precipitation may occur. In severe cases, it will lead to the blockage of the fuel nozzle and filter, which will lead to the increase of deposits in the cylinder and the aggravation of wear. The stability of diesel depends on its chemical composition. Dienes, polycyclic aromatic hydrocarbons and sulfur-containing and nitrogen-containing compounds are unstable components, which will significantly increase the deposits in the engine. Therefore, these harmful compounds must be removed by various purification methods.

Sulfur compounds in diesel oil have a great influence on the working life of engines, among which active sulfur compounds (such as mercaptan) have corrosive effects on metals. SO2 and SO3 produced by combustion of sulfur-containing compounds in the cylinder will not only seriously corrode parts in high temperature area, but also react with lubricating oil on the cylinder wall to accelerate the formation of paint film and carbon deposit. At the same time, sulfur oxides in diesel engine exhaust gas will also pollute the environment. Therefore, in order to protect the environment and reduce engine corrosion, GB 252-20 1 1 Ordinary Diesel Oil stipulates that the sulfur content of diesel oil should not be greater than 0.035%. With the improvement of environmental protection requirements, the sulfur content of diesel oil will be further reduced.

In order to prevent corrosion, it is also required in the technical requirements that diesel oil contains no water-soluble acid or alkali and has limited acidity.

During storage and transportation, refined diesel oil may be mixed with moisture and mechanical impurities. If there is more water in diesel oil, the calorific value of diesel oil will be reduced, and it will freeze at low temperature, blocking the fuel supply system of diesel engine. The existence of mechanical impurities will not only cause oil blockage, but also aggravate the wear of precision parts in fuel injection pumps and injectors. Therefore, it is stipulated in the quality standard of light diesel oil that the water content is not more than trace (0.03%), and no mechanical impurities are allowed.

4. Diesel brand

According to the freezing point, ordinary diesel oil in China can be divided into seven grades: 10, 5, 0,-10, -20, -35 and -50. Motor diesel oil can be divided into six grades according to its freezing point: No.5, No.0,-10, -20, -35 and -50. For example,-10 means that the freezing point of this brand of diesel oil is not higher than-10℃.

According to the kinematic viscosity of 100℃, residual diesel oil can be divided into F-RMA 10, F-RMB 10, F-RMC 10, F-RMD 15, F-RME25 and f. For example, F-RMA 10 means that the kinematic viscosity of oil at 100℃ is not more than10.0mm2/s.

(3) Lubricating oil

There are many lubricating materials used in mechanical equipment, but lubricating oil and grease obtained from petroleum are widely used, among which lubricating oil is the largest.

The main function of lubricating oil is to reduce the friction resistance of mechanical equipment during operation; Take away the heat generated by friction and wash away the worn metal chips of the equipment; Isolate corrosive substances and protect the metal surface of the equipment.

Lubricating oil has different quality requirements for different mechanical equipment, and there are many varieties, including gasoline engine oil, diesel engine oil, compressor engine oil, refrigeration engine oil, cylinder oil, gear oil, hydraulic oil, mechanical oil and electrical oil. Users choose the appropriate lubricating oil according to actual needs.

Although the performance requirements of various lubricating oils vary according to the service conditions, they are similar:

(1) Suitable viscosity, good viscosity-temperature performance. Viscosity-temperature characteristics refer to the characteristics of oil viscosity changing with temperature. The smaller the change of viscosity with temperature, the better the viscosity-temperature characteristics. For example, gasoline engine oil, if the engine oil becomes too thick at low temperature, it is difficult to start the engine; If the oil is too thin at high temperature, it will not form an oil film, and it is difficult to play the role of lubrication and sealing. Therefore, it is required that the lubricating oil is not thickened at low temperature and not diluted at high temperature.

(2) High oxidation stability. If lubricating oil is used for a long time, the catalysis of various metals will accelerate the oxidation of lubricating oil and produce acidic substances and deposits, thus accelerating the corrosion of parts or bearings, making engine piston rings stick together and blocking filters or oil pipes. After the insulating oil is oxidized, the electrical conductivity increases.

(3) Low freezing point and carbon residue. Lubricating oil with high freezing point will crystallize out at low temperature, which will affect the fluidity of oil products. Carbon residue refers to the mass percentage of coke produced when a certain amount of lubricating oil is heated to high temperature for evaporation and decomposition under the condition of air isolation. Carbon residue is related to the content of gum and asphaltene in oil. The high carbon residue value indicates that lubricating oil is easy to produce film or carbon residue when used at high temperature, resulting in equipment wear and poor sealing performance.

The properties of lubricating oil are related to its composition. Lubricating oil composed of hydrocarbons with few rings and long side chains has high viscosity, good viscosity-temperature performance and high oxidation resistance. On the contrary, the viscosity-temperature properties of lubricants with polycyclic and short side chain components are poor. When the wax content in lubricating oil is high, the freezing point is high and the fluidity at low temperature is poor; When the gum and asphaltene are high, the carbon residue value is high; When it contains sulfide and acidic components, it is very corrosive. These harmful components should be removed when producing lubricating oil.