Blending techniques for gasoline and diesel (Be sure to bookmark this!) ）

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I. What is blending technology? Blending technology is an applied technique that involves using various oil products that meet national standards or are of non-standard specifications, produced by refineries; light hydrocarbons (condensate) generated in oil fields; and chemical products. These materials are refined through specialized treatment units, and with the addition of certain additives, they are combined to produce gasoline and diesel that meet the customer’s requirements. This approach aims to minimize costs and conserve petroleum resources. The blending technology for gasoline and diesel is highly developed in the international oil trade sector; for example, anti-knock agents can be used to convert 90# gasoline into 93# or 97# gasoline, and -5# or 0# diesel into -10# diesel for sale. In our country, hundreds of tons of naphtha products are produced each year. Due to its low octane rating, with a RON of only around 40–60, most of this naphtha can only be sold as a raw material for ethylene production; its price is low and unstable. If we employ blending techniques to remove sulfur from the naphtha through refining, mix it with high-octane components, and then add antiknock agents, we can produce 90# and 93# gasoline. This approach can help save a considerable amount of petroleum resources. It can thus be seen that gasoline and diesel blending technology is an applied technology that serves as an effective means of cutting costs and making efficient use of existing petroleum resources; it should be widely promoted in China. Having said that, some may ask: Is blended fuel usable? Is the quality reliable? To answer this question, we need to start by discussing the production processes in refineries. II. Methods for producing gasoline and diesel in refineries The gasoline and diesel currently in use in China are both derived from petroleum. Unrefined petroleum is commonly referred to as crude oil. To produce gasoline and diesel from crude oil, the following basic processes are involved: 1. First, the crude oil is desalted and dehydrated, after which atmospheric distillation is carried out to separate out the fractions suitable for use as gasoline and diesel. These fractions are known as straight-run fractions, such as naphtha, light diesel, and heavy diesel. 2. Using heavy oils produced during the refining process, such as atmospheric and vacuum heavy oils, as raw materials, secondary processing methods such as thermal cracking, catalytic cracking, hydrocracking, and delayed coking are employed to crack the high-boiling-point fractions into low-molecular-weight hydrocarbons suitable as fuels. Through distillation, the components suitable for gasoline and diesel are obtained through thermal cracking, catalytic cracking, and coking processes. If high-octane gasoline is to be produced, methods such as catalytic reforming and alkylation are also required to obtain reformate components and light alkylated oils. 3. The straight-run distillate oils and those obtained through secondary processing methods were separately subjected to electrochemical refining, hydrorefining, desulfurization, and dewaxing in order to remove harmful substances and improve the quality of the oils. 4. Finally, in accordance with the quality requirements for gasoline and diesel of different grades, these various distillate oils are used as components, mixed in the required proportions along with appropriate amounts of various additives, thereby producing gasoline and diesel whose quality meets **the standards. The typical gasoline blending schemes in refineries in our country: Percentage of components used for blending gasoline grades %. Catalytic gasoline, reformated gasoline, alkylated oil, MTBE: 90# – 100; 93# – 70~72, 20~15, 10~13; 93# – 70~72, 20~15, 10~13; 93# – 68~70, 32~30; 93# – 60~64, 40~36; 95# – 58~60, 30~26, 12~14; 95# – 38~41, 32~35, 34~24; 95# – 53~56, 35~30, 12~14; 97# – 28~33, 58~55, 12~14; 97# – 39~44, 33~35, 10~12, 12~14. It can be seen that refineries first produce various components, which are then blended to form the final gasoline products. It’s just that refineries can produce various types of oil components as needed, while blending technology involves using various non-standard oils and chemical raw materials; after refining them, the desired finished oils are produced. The two processes are similar, except that oil produced through blending technology does not generate smoke in the refinery. III. Raw materials used for modifying gasoline and diesel. Raw materials that can be used to modify gasoline include straight-run gasoline (naphtha, petroleum ether), light naphtha, condensate oil (light hydrocarbons), refined C5, C9, C10 chemical oils, aromatics 150# and 200#, mixed aromatics, formaldehyde resins, MTBE, DMC, high-carbon alcohols, etc. Raw materials that can be used to modify diesel include heavy diesel, wax oil, coker wax oil, solvents with a grade of 200# or higher, heavy aromatics, C8, C9, C10, C11, C12, C13, C14, C15, and products from aviation refining. Kerosene for lamps, regular-grade oil, reduced-grade oil, aromatic solvent oils of 200#, 230#, and 270#, #3 mineral oil, domestically produced diesel, pyrolyzed diesel, coking diesel, etc. The aforementioned raw materials undergo preliminary decolorization, deodorization, and refining/stabilization processes. Subsequently, modifying additives are added to form a composite. Finally, after quality testing, once they meet or nearly meet the **standards, they can be sold. Properties of gasoline fractions obtained by atmospheric distillation: Crude oils from Daqing, Shengli, Liaohe, North China, Xinjiang, and Central China – Octane number (RON): 47, 65, 60, 51, 62, 65. Basic properties of materials used for blending gasoline: Material name, relative density, boiling range, octane number range, main components, appearance, boiling point, flash point. Naphtha (crude gasoline): 0.68–0.71, boiling range 70–145°C; Light naphtha: 70–180°C; Heavy naphtha: 40–60°C; C5–C9 hydrocarbons, colorless or light yellow, boiling range 20–160°C, flash point –2°C. Petroleum ether: 0.64–0.66; Pentane and hexane, colorless and transparent liquids with a kerosene-like odor, boiling range 30–120°C, flash point –20°C (closed container). Condensate oil: boiling range 20°C–200°C, octane number 60–70; C5–C8 hydrocarbons. Refined C5: 0.66, boiling range 36°C–41°C, octane number 85–95; C5 is a colorless and transparent liquid, boiling range 36–50°C. Refined C9: 0.88–0.90, boiling range 150°C–190°C, octane number 110–105; Aromatic C9, colorless and transparent liquid. Refined C10: 0.89–0.92, boiling range 180°C–210°C, octane number 105–110; Aromatic C10, colorless and transparent liquid. Aromatic 150#: 0.88–0.90, boiling range 150°C–190°C, octane number 105–115; Mixed aromatics, colorless and transparent liquid. IV. Additives used in the formulation of gasoline and diesel: (I) Anti-knock properties of gasoline: 1. Anti-knock properties of gasoline: The normal combustion of gasoline in the combustion chamber occurs when a combustible mixture is ignited by an electric spark. The flame propagates forward at a speed of 20–50 m/s, causing the temperature and pressure inside the cylinder to rise uniformly until the combustion is complete. This not only enables the engine to deliver its full power output but also ensures smooth and steady operation, allowing the vehicle to move normally. But sometimes abnormal combustion can occur. In this process, once the combustible mixture is ignited in the engine cylinder, a portion of the unburned mixture experiences a sudden increase in temperature and pressure due to the compression and thermal radiation from the normal flame. This leads to intensified chemical reactions that produce many unstable peroxides. Before the normal flame can reach that area, these peroxides decompose violently and catch fire on their own, resulting in explosive combustion that generates strong shock waves. These shock waves cause the engine to vibrate and produce metallic knocking sounds, thereby reducing the engine’s performance. The exhaust emits black smoke and fuel consumption increases. We call this phenomenon knocking. Then, the property of gasoline that resists knocking when burning in an engine is called its anti-knock quality. The anti-knock properties of various hydrocarbons contained in gasoline directly determine the overall anti-knock performance of the gasoline. From a large amount of experimental data, the following rules can be summarized: The anti-knock properties of hydrocarbons can generally be ranked in the following order. Aromatic hydrocarbons > Isoparaffins > Naphthenes > Paraffins > Normal paraffins. In terms of oils and fuels, the anti-knock property of hydrocarbons tends to decrease as the molecular weight increases. Therefore, among petroleum products made from the same crude oil, those with lighter fractions have better anti-knock properties than those with heavier fractions. In terms of processing, catalytic cracking and reforming are superior to thermal cracking or coking, while thermal cracking and coking are better than products from straight distillation. 2. Evaluation criteria for gasoline anti-knock properties: The anti-knock properties of gasoline are represented by the octane number. The so-called octane number is numerically equal to the volume percentage of isooctane contained in a standard fuel with comparable anti-knock properties. Standard fuel consists of octane with extremely high anti-knock properties, namely 2,2,4-trimethylpentane (for which the octane rating is set at 100), and heptane with lower anti-knock properties, GH16 (for which the octane rating is set at 0). The two substances are mixed together in different volume ratios to be synthesized. Among them, the volume percentage of isooctane in the standard fuel is the octane number of that standard fuel. If standard fuel is composed of 90% octane and 10% heptane (by volume), then the octane rating of the standard fuel is 90. When determining the octane number of gasoline, the oil being tested and a selected standard fuel are placed under strictly defined conditions in an octane tester. If their anti-knock properties are exactly the same, it indicates that the octane number of the tested oil is equal to that of the standard fuel. Currently, the main methods used around the world to determine the octane rating of gasoline are the research method (RON), the motor method (MON), and the anti-knock index. Research octane number: The research octane number (RON) is the octane number measured using a laboratory standard engine under moderate demanding conditions, with a lower air-fuel mixture temperature (usually without heating) and a lower engine speed (usually 800 revolutions per minute). Motor Octane Number: The Motor Octane Number (MON) is the octane number measured under severe conditions, at higher mixture temperatures (typically heated to 149°C) and higher engine speeds (usually up to 900 rpm). The equipment used in MON is basically the same as that in RON. But their test conditions are different. MON indicates the anti-knock capacity of gasoline when the engine is operating at high speeds under heavy load conditions, while the research octane number represents the anti-knock capacity of gasoline when the engine is operating at low speeds under normal acceleration conditions. The RON of the same fuel gas is 5~10 units higher than that of MON. Since neither RON nor MON can fully reflect the anti-knock performance of fuel during vehicle operation. Therefore, the index of blast resistance was introduced. Explosion resistance index: Explosion resistance index = (RON + MON) / 2. Since the octane rating testers specified by national standards are ASTM devices imported from the United States and are quite expensive, some simpler instruments can be used for testing. Shanghai-made single-cylinder dielectric constant tester/far-infrared mixing device. Gasoline anti-knock additives. Gasoline is one of the important fuels crucial to the national economy and people’s livelihoods. With the rapid development of China’s national economy and the swift increase in the number of vehicles, the demand for gasoline as a fuel is growing ever greater. Octane rating is the most important quality indicator for automotive gasoline; it reflects the overall level of the refining industry as well as the design standards of vehicles. Therefore, since the early 20th century, people have been seeking effective ways to increase octane ratings, and after nearly a century of effort, the relevant technologies have become increasingly sophisticated. Currently, there are two ways to increase the octane rating of gasoline: one is to achieve this improvement through various processing techniques, such as catalytic cracking and reforming, alkylation, and isomerization; the other is by adding anti-knock agents to gasoline (such as tetraethyl lead, which is now banned) or by incorporating components with high octane ratings (such as MTBE to increase the amount of aromatics). Although the processing method is the main approach to increasing gasoline octane number, it has issues such as high investment costs and changes in the gasoline boiling range; as a result, it is often difficult to achieve an optimal production combination and lacks sufficient flexibility. Numerous practices at home and abroad have proven that the use of anti-knock agents is the most effective method for increasing the octane rating of automotive gasoline. Gasoline anti-knock agents can be divided into ash-containing types (such as metal-containing compounds like methylcyclopentadienyltrimanganese and tetraethyllead) and ash-free types (such as pure organic compounds like methyl tert-butyl ether). There are ash-forming gasoline anti-knock agents. Commonly used ash-forming additives include: tetraethyl lead, ferrocene, and MMT (methylcyclopentadienyl manganese tricarbonyl). Due to the toxicity of tetraethyl lead, the presence of ferrocene causes ignition problems in spark plugs. Our country has banned the use of tetraethyl lead and ferrocene. MMT was introduced by Ethyl Corporation in 1959. It exhibits good anti-knock properties and gasoline compatibility; at a manganese mass concentration of 9–18 mg/L, it can increase the Research Octane Number (RON) of gasoline by 1.7 to 3 units. Its impact on automotive exhaust control systems and its environmental pollution effects are the main points of contention regarding MMT. Studies have found that only a small amount of MMT is emitted after combustion, with most remaining inside the exhaust system and coating the surfaces of components such as engine spark plugs and catalysts, which can lead to ignition problems in the spark plugs. Countries hold different views on the use of MMT. The United States banned the use of MMT in 1978, but reinstated it in October 1995 as a gasoline anti-knock agent. The Environmental Protection Agency and the Association of Automobile Manufacturers (AAMA) are quite opposed to this; the \"Global Fuel Specifications\" established by organizations such as the European Association of Automobile Manufacturers and the Japanese Association of Automobile Manufacturers prohibit the addition of Mn to gasoline used in vehicles. In China, there is no explicit ban on the use of manganese-based anti-knock agents. But a limited amount is allowed to be added. The standards for automotive gasoline (II) specify a limit of no more than 18 mg Mn/L, those for automotive gasoline (III) set the limit at no more than 16 mg Mn/L, while the Beijing standards require a limit of no more than 6 mg Mn/L. The requirements are becoming increasingly strict. However, as the refined oil market gradually opens up to the outside world, European standards have become the universal standard for gasoline worldwide, and domestic refineries must consider alternatives to MMT as soon as possible. Antiknock agents for unleaded gasoline: Organic, ash-free antiknock agents can prevent the automatic acceleration of reactions, limiting the speed of fuel combustion to within normal ranges. This ensures that the antiknock agents added do not cause poisoning of the catalysts, do not increase pollutant emissions, and provide excellent antiknock performance. Because there is currently a lot of research on such blast inhibitors. Common ashless anti-knock agents include ethers, esters, and amines. Ethers: MTBE is widely used worldwide as a gasoline additive. It not only effectively increases the octane number of gasoline—raising its research octane number by 2 to 3 units when the additive concentration is between 3% and 7%—but also improves engine combustion performance, reduces the CO content in exhaust gases, and lowers the production cost of gasoline. Since its introduction, the demand for MTBE has remained on a high growth trajectory. Its production technology is also becoming increasingly mature. But recently, California in the United States banned the use of MTBE on the grounds of contamination of groundwater quality, and the U.S. **environmental protection agency has taken similar actions. This indicates that the United States has begun to restrict the production and application of MTBE. Now the EU and Japan prefer another more easily degradable antiknock agent, ethyl tert-butyl ether (ETBE). Its performance is just as excellent as that of MTBE. The following are the MTBE parameters: Density (kg/m3, 20°C): 740.6; Critical temperature (°C): 223.9; Specific heat capacity (°C): 2.135; Vaporization heat (J/(g·K)): 30.10; Heat of combustion (MJ/kg): 38.21; Red vapor pressure (bar): 0.55; Critical pressure (KPC): 223.9; Refractive index (20 °C): 1.3689; Ignition point (°C): 480; Upper limit for explosion in air (%V): 1.65 ； Lower limit: 8.4. Research method octane number: 117; Motor method octane number: 101. Solubility of water in MTBE (20°C, g/100g): 1.5. Solubility of MTBE in water (20°C, g/100g): 4.3. Ethyl tert-butyl ether (ETBE). Like other ethers, ETBE can be used as an anti-knock agent to increase the octane rating of gasoline. Its RON and MON are 119 and 103 respectively, and its saturated vapor pressures are 27.56 kPa each, which is much lower than that of MTBE. ETBE has a relatively high boiling point and is soluble in gasoline without forming an azeotic mixture; as a result, it can reduce gas resistance inside the engine as well as minimize vapor loss from gasoline. Therefore, using ETBE as an anti-knock agent results in better gasoline economy and safety performance compared to adding MTBE; thus, it has great application prospects. However, the high production cost of ETBE, along with its expensive price, is the biggest obstacle to its widespread adoption. Diisopropyl ether (DIPE). The chemical composition, density, and heat of vaporization among other physical properties of DIPE are similar to those of MTBE, ETBE, and TAME. Its RON value is 107–110, while its anti-knock index ranges from 102 to 106. The saturated vapor pressure is 33.78 kPa. It is produced using propylene and water, which are readily available and have stable prices, and it is not subject to the fluctuations in the ethanol market. Luoyang Petrochemical Engineering Company has developed a one-step hydration-etherification process for producing DIPE from propylene. The active β-zeolite catalyst developed by the company exhibits high conversion rates and DIPE selectivity in the hydration-etherification reaction of propylene; moreover, it demonstrates good activity and stability. The price competitiveness of DIPE could make it a substitute ether component for MTBE following its ban. tert-Butyl methyl ether (TAME). The RON and MON of TAME are 12 and 99 respectively, with a saturated vapor pressure of 20.67 kPa, which is much lower than that of MTBE; its anti-knock performance is slightly better than that of MTBE. TAME uses methanol and isoprene as raw materials, resulting in a lower price. Furthermore, TAME has not yet shown similar environmental and safety issues associated with MTBE, so its potential for market application is quite high. Several research institutions in our country are currently studying the TAME production technology. A catalytic distillation process for the synthesis of TAME has now been successfully developed, and an industrial pilot plant with a capacity of 2,000 tons per year was built at Shanghai Petrochemical Corporation. Meanwhile, the R&D institute of Qilu Petrochemical Corporation has developed a C4/C5 mixed etherification technology that allows for the simultaneous production of MTBE and TAME in the same catalytic distillation unit, thereby increasing the scale of the etherification facility and enhancing economic efficiency. Due to its excellent combustion properties, methylal is used as an additive in petroleum products. Its addition significantly improves combustion performance and reduces the emission of harmful gases. It is also regarded by many companies today as a new type of environmentally friendly fuel. Molecular formula: CH30-CH2-OCH2 Molecular weight: 76.09 Boiling point: 42.3°C Flash point: -17.8°C Density: d15/15 0.866, d20/20 0.861 Melting point: -104.8°C Appearance: Colorless transparent liquid with a chloroform-like odor Esters: Among them, dimethyl carbonate (DMC) attracts the most attention; it is considered one of the most promising octane number improvers. Furthermore, studies have shown that the addition of DMC has little effect on the saturated vapor pressure, freezing point, and water solubility of gasoline. Compared to MTBE, DMC has a higher oxygen content. To achieve the same oxygen content in gasoline, the volume of DMC required is only about 40% of that needed for MTBE. It has a similar blending effect on catalyzed gasoline, but for straight-run gasoline, DMC is less sensitive than MTBE. When the addition volumes were classified as 3% DMC and MTBE, the base octane numbers of straight-run gasoline increased from 51.0 to 52.5 and 53.1 respectively; this shows that DMC is more suitable for blending gasoline with a base octane number greater than 80. At room temperature, dimethyl carbonate is a colorless and transparent liquid with a slight sweet taste; its melting point is 4°C and its boiling point is 90.11°C. It is poorly soluble in water, but it can mix with alcohols, ethers, and almost all other organic solvents. The molecular structure of DMC contains functional groups such as CH=O, CO, and COOCH3, granting it good chemical reactivity. DMC has very low toxicity; it is an environmentally friendly organic chemical raw material that meets the requirements of modern “clean processes”, and serves as an important intermediate in organic synthesis. The molecular formula of sec-butyl acetate is C6H12O2 ； CH3COOCH(CH3)CH2CH3: Appearance and properties: Colorless liquid with a fruity aroma. Molecular weight: 116.16. Vapor pressure: 2.00 kPa at 25°C. Flash point: 19°C. Melting point: -98.9°C. Boiling point: 112.3°C. Solubility: Insoluble in water; soluble in ethanol, ether, and most other organic solvents. Density: Relative density (water = 1): 0.86 ； Relative density (air=1): 4.00 Stability: Stable. Hazard label: 7 (flammable liquid with medium flash point). Amines; the representative example is N-**amine. According to available information, research on amine compounds as anti-knock agents for gasoline began abroad in the early 1970s; their commercial name abroad is MmA. The reason for their not being widely adopted is the nitrogen content in the amine groups. Studies abroad have shown that in order to control the level of NOX emissions from vehicle exhaust, the amount of amine compounds in gasoline should be kept at no more than 17 g/L. Within this range, amine compounds can generally increase the octane rating by 1.2 to 2 units. Therefore, reducing the content of amine compounds in anti-knock agents to enable them to exert maximum effectiveness within environmental constraints is a challenge for the widespread use of such anti-knock agents. Therefore, countries around the world are accelerating research on gasoline anti-knock agents, with pollution-free anti-knock agents representing the direction for future development. (II) Gasoline desulfurization technology: In recent years, with the increase in the number of motor vehicles, vehicle exhaust has become a major source of air pollution, leading to more frequent acid rain, which severely damages buildings, soil, and the living environment of humans. Therefore, countries around the world have set higher standards for oil quality, further restricting the sulfur, olefin, and benzene content in oils in order to better protect the living environment for humans. With the increase in the processing of sulfur-containing crude oil and the widespread use of catalytic cracking of heavy oil, problems such as excessive sulfur content in petroleum products and poor stability are becoming increasingly severe. Due to the constraints in terms of funding and hydrogen supply for hydrodesulfurization, it is of great significance for small and medium-sized refineries to conduct research on non-hydrodesulfurized refining. 1. The main forms of sulfur presence and its distribution in fuel oil. There are hundreds of sulfur-containing hydrocarbons in crude oil, of which more than 200 have had their structures verified and determined. These sulfur-containing hydrocarbons are distributed to varying degrees in various fractions during the crude oil processing process. Sulfur in fuel oil exists mainly in two forms: ； Sulfides that generally cannot react directly with metals are called \"active sulfur,\" including elemental sulfur, hydrogen sulfide, and thiol compounds. Sulfides that can react directly with metals are called \"inactive sulfur,\" including sulfides, disulfides, thiophenes, etc. For gasoline fractions, sulfur-containing hydrocarbons are mainly thiols, sulfides, and monocyclic thiophenes, which primarily originate from catalytic cracking (abbreviated as FCC) gasoline. Therefore, to make gasoline meet the specifications for low-sulfur gasoline, it is necessary to pre-treat the FCC gasoline feedstock or post-treat the FCC gasoline product. The sulfur-containing hydrocarbons in diesel fractions include thiols, sulfides, thiophenes, benzothiophenes, and dibenzothiophenes. In the case of dibenzothiophenes, the presence of alkyl groups at the 4,6 positions makes desulfurization very difficult due to the steric effect of these alkyl groups. Moreover, as the boiling point of petroleum fractions increases, the structure of sulfur-containing compounds becomes increasingly complex. 2. Methods for producing low-sulfur fuel oil 2.1 Acid-base refining Acid-base refining is a traditional method that is still used by some refineries today. Since the acid and alkali residues resulting from acid-base purification are difficult to handle and cause significant losses of oil, this technology will inevitably be phased out in the long run. 2.2 Catalytic methods In the phthalocyanine catalyst method, the catalysts that are widely used in industry at present are polyphthalocyanine cobalt (CoPPC) and sulfonated phthalocyanine cobalt (CoSPc) catalysts. This catalyst is used to treat oils in alkaline solutions, allowing for the removal of thiols from them. 2.3 Solvent extraction method: By selecting an appropriate solvent, sulfides in oils can be effectively removed through extraction. Generally speaking, the extraction method can effectively extract thiols from oils, and then the extraction solvent and the thiols can be separated through distillation to yield thiol by-products with high added value, while the solvent can be reused. 2.4 Catalytic Adsorption Method The catalytic adsorption desulfurization technique involves the use of solid adsorbents with good adsorption selectivity and renewability, to reduce the sulfur content in petroleum products through chemical adsorption. It is a newly developed method that can effectively remove sulfides from FCC gasoline. Compared with conventional gasoline hydrodesulfurization, its investment cost and operating expenses can be reduced by more than half, and it can effectively remove impurities such as sulfur, nitrogen, and oxides from the oil; the desulfurization rate can reach over 90%, making it highly suitable for the current conditions of domestic refining companies. Since adsorption desulfurization does not affect the octane rating or yield of gasoline, this technology has attracted significant attention both domestically and internationally. Catalytic adsorption desulfurization technology can effectively remove sulfides from oils without affecting their quality, and its capital and operating costs are much lower than those of other desulfurization methods (such as hydrorefining, solvent extraction, catalytic oxidation, etc.). Therefore, studying catalytic adsorption desulfurization technology is of great significance. 2.5 Chelation method: Treating sulfur-containing oils with a DMF solution of metal chlorides enables electron pair interactions between organic sulfides and metal chlorides, resulting in the formation of water-soluble chelates that can be removed. There are many metal ions that can form complexes with organic sulfides, among which CdCl2 yields the best results. Since the complexation method cannot remove the acidic components in oils, a combination of complexation extraction and alkaline washing for purification is often used in practice. This approach yields very significant desulfurization results; the resulting oil has good stability, offering favorable economic benefits. 2.6 Biological Desulfurization Technology Biological desulfurization, also known as biocatalytic desulfurization (abbreviated as BDS), is a new technology that utilizes aerobic and anaerobic bacteria to remove sulfur bound in sulfur-containing heterocyclic compounds in petroleum under normal temperature and pressure conditions. 3. Negative effects of low sulfur content: The low sulfur content in gasoline and diesel **reduces environmental pollution, and there is a consensus among countries regarding policies to reduce sulfur content in fuel oils. However, during the process of reducing the sulfur content in fuel oil, unforeseen negative effects emerged, mainly manifested as: (1) a decline in lubrication properties and increased wear on equipment. In 1991, Sweden found that when using diesel with a sulfur content of 0.00%, the caking and wear caused by the fuel pumps were even worse than those caused by regular diesel. Japan also conducted bench tests on diesel fuels with different sulfur contents, and the results confirmed the issue of reduced lubricating performance of the diesel. The main reason is that the natural polar compounds with lubricating properties present in the oil are removed simultaneously during desulfurization, which leads to a decline in lubricating performance and increased equipment wear. (2) Diesel stability deteriorates, and the color of the fuel worsens. When the sulfur content in diesel drops below 0.05%, the increase in peroxides accelerates the formation of gums and precipitates, affecting the proper operation of the equipment and leading to degraded exhaust emissions. The main reason is that the natural antioxidant components originally present in diesel are also removed during desulfurization. At the same time, as the sulfur content in diesel decreases, the color of the oil deepens, giving off an unpleasant appearance. 4. Conclusions and Recommendations Given the widespread use of petroleum products in production and daily life, it is very important to remove the harmful sulfur from them. The non-hydrodesulfurization methods currently used in industry include acid-base refining, solvent extraction, and adsorption desulfurization, all of which have their own defects and limitations. Among them, acid-base purification generates large amounts of waste acid and waste alkali solutions, causing severe environmental pollution ； The solvent extraction desulfurization process is energy-intensive and results in a low yield of oil products ； In the adsorption method, the adsorbent has a low capacity for adsorption and requires frequent regeneration. Other non-hydrodesulfurization technologies are still in the experimental stage, among which biological desulfurization, oxidative desulfurization, and desulfurization using light and plasma show great promise as effective methods for producing clean fuel oils in the future. Since reducing the sulfur content in fuel oil and minimizing air pollution is a complex process, various factors must be taken into account during implementation to enhance the reliability of the technology, thereby achieving the best economic and environmental benefits. (III) Diesel flow improvers (dew point depressants) There are three ways to improve the low-temperature flow properties of diesel: dewaxing, adding secondary processed fractions such as kerosene (cracked kerosene), and adding flow improvers (i.e., dew point depressants). Dewaxing requires additional equipment and reduces the yield of diesel; adding secondary cracked fractions is a simpler method – generally, 10–20% kerosene added to 0# diesel can lower its freezing point, changing it from 0# to –10#. If too much of these secondary cracked fractions is used, it can affect the cetane number, flash point, and lubricity of the diesel. Adding flow improvers to diesel is currently the most commonly used method both domestically and internationally. I. Mechanism of action of flow improvers The mechanism by which diesel flow improvers work at low temperatures is that they adsorb onto the paraffin crystals that form in diesel at low temperatures, creating a barrier layer on the surface of these crystals. This prevents the crystals from bonding together, thereby reducing the freezing point of the diesel. Additionally, these improvers can form co-crystals with the paraffin, inhibiting its growth and causing it to form into smaller crystals, which in turn lowers the freezing point. Diesel flow improvers generally cannot alter the precipitation of wax in diesel; they neither change the cloud point of diesel nor the amount of wax that precipitates at a certain temperature. Instead, they can only modify the shape and size of the crystals and prevent the formation of network structures. Therefore, the impact of paraffin on the low-temperature flow properties of diesel cannot be eliminated fundamentally; only its low-temperature flow properties can be improved. II. What is the role of flow improvers? There are dozens of types of compounds that have been studied as flow improvers both domestically and internationally. The main types used in industrial production are low-molecular-weight ethylene-vinyl acetate and ethylene-acrylate vinyl acetate copolymers. The recommended dosage of diesel antifreeze agents is 0.01–0.1%, while the actual dosage used abroad is around 0.03%. Diesel antifreeze agents are highly sensitive to the chemical composition of diesel; therefore, oil adjustment tests must be conducted before adding such agents. The effectiveness of these antifreeze agents is often influenced by various factors, including the type of crude oil used in diesel production, the processing techniques, the oil adjustment formulas, and the composition of the different fractions in the diesel. In terms of crude oils, naphthenic crude oils yield the best results, intermediate base oils come next, while paraffinic crude oils give the worst results. From the perspective of processing techniques, catalytic diesel, molecular sieve dewaxing, and urea dewaxed oil combined with antifreeze agents yield good results; hydrocracking and thermal cracking of diesel give moderate results, while straight-run diesel and coker diesel produce the worst results. In terms of blending methods, diesel blended with a high proportion of components, as well as diesel containing a high amount of kerosene fractions, generally yields better results. In terms of fractions, the wider the fraction range, the better the effect. Therefore, to achieve good results, the following methods should be employed: Mixing oils from different manufacturers yields better results; adding a certain amount of -10# diesel also improves the effect. Adding kerosene along with additives also proves effective. Incorporating 3–10% aromatic hydrocarbons #200 into the mixture is also beneficial. Additionally, adding anti-wax deposition agents can enhance the pour point depression effect. Since wax deposition is a common issue during the storage and transportation of additive-treated diesel, leading to uneven distribution of the cold filter plugging point and thus affecting its usability, using anti-wax deposition agents in conjunction with pour point depressants can effectively prevent such wax buildup. (IV) Diesel cetane number improvers: The combustibility of diesel, also known as its ignition property, indicates its ability to ignite spontaneously. As can be understood from the working principle of diesel engines. At the end of compression in a diesel engine, the cylinder temperature is not less than 500–600°C, which is far higher than the auto-ignition temperature of diesel (which is 200–270°C). However, time is required for the physicochemical preparation prior to combustion; therefore, diesel injected into the cylinder does not ignite immediately. That is, after entering the cylinder, diesel goes through a delay period before burning, which usually lasts between 0.0007 and 0.0035 seconds. If the ignition delay period of diesel is short, it burns quickly after being injected into the cylinder, thereby enabling the engine to perform normally. If the ignition delay period is too long, once ignition occurs, more fuel will participate in combustion, causing the pressure to rise rapidly at the beginning of combustion and resulting in rough operation of the diesel engine. The results are the same as those of gasoline engine knock: reduced power, increased fuel consumption, and increased noise. ? The flammability of diesel is expressed by the cetane number. The so-called cetane number is the volume percentage of n-hexadecane in the standard fuel, under specified engine test conditions, when the test fuel has the same ignition property as the standard fuel. Standard fuel is composed of n-hexadecane (for which the cetane number is arbitrarily set at 100) and α-methylnaphthalene (for which the cetane number is arbitrarily set at 0), blended in various proportions. Diesel with a high cetane number has a lower auto-ignition point and a shorter ignition delay period, which prevents rough combustion during operation. Additionally, diesel with a high cetane number reduces the load on the engine bearings and improves starting performance, ensuring smooth engine startup. National standards stipulate that the cetane number of light diesel oil must be >45. Light diesel for vehicles: +10#, +5#, 0#, -10# >49; -20# >46; -35#, -50# >35. There are two methods to increase the cetane number: one is to remove aromatics from the oil, and the other is to add a cetane number improver. The commonly used additive is alkyl *ao ester. Such as *ao octyl ester and *ao pentyl ester, adding 1–3‰ can increase the value by 2–9 units. (5) Oil deacidifiers: Straight-run diesel contains a certain amount of organic acids. When preparing diesel, these organic acids must be removed so that the acidity level reaches 7 mg KOH/100 ml in order to meet national standards. The common methods for acid removal include: hydrogenation, refining, alkali washing, and using acid scavengers; these scavengers can be mixed with diesel in a certain ratio. (VI) Decolorizing and deodorizing agents: 1. Sulfuric acid + titanium cobalt sulfonate; 2. Neutralizing agents: ethanol : ethylenediamine : dimethylamide = 5:2:5; 3. Adsorbents. V. Methods of adjustment: 1. For gasoline: ① Using standard-grade oil as the base – 90# gasoline can be used to produce 93# gasoline, and 97# gasoline can be produced from 93# gasoline; 90# gasoline can also be formulated by mixing it with naphtha and antiknock agents, while 93# gasoline can be made by mixing 93# gasoline with naphtha and antiknock agents. ② Using non-standard-grade oil as the base – naphtha (20-60%) + mixed aromatics (5-25%) (by weight) + substances with a sulfur content of no more than 14% + 90# gasoline (0-20%) + C5 (5-15%) + antiknock agents; light hydrocarbons (or light naphtha) (20-60%) + mixed aromatics (20-40%) (light grade) + MTBE (no more than 14%) + C5 (5-15%) + antiknock agents. Note: The first method of formulating gasoline is based on the fact that some manufacturers use 90# gasoline as a starting material; in this case, the mixed aromatics used can have a relatively higher density, as quality requirements are not very high. The second method does not use gasoline as a starting material; in this case, higher standards are applied to the mixed aromatics, requiring them to have a low density and low sulfur content. Light hydrocarbons, light naphtha, or vacuum distillate oils of better quality are typically used in this approach. Both oil blending methods have their advantages and disadvantages, and most oil blenders decide based on the market conditions of raw materials. 2. Diesel: ① Yangtze River Delta: 10% kerosene + 20% catalyzed diesel + 70% standard diesel; ② Pearl River Delta: 10% kerosene + 20% first-tier oil + 70% standard diesel; ③ Bohai Bay region: 10% kerosene + 20% first-tier oil + 70% standard diesel. Based on the proportions of the most commonly used raw materials in the market, standard diesel accounts for at least 70% of the total mixture, catalyzed diesel makes up around 20%, and kerosene constitutes a maximum of 10%. Based on the current prices of raw materials in the market, the cost of blended diesel in the Yangtze River Delta is 8,000 yuan per ton. Although this is 100 yuan per ton higher than the local market price according to national standards, blended diesel trading remains rare. Furthermore, industry experts say that since kerosene is used as a raw material primarily to lower the freezing point, it can generally be omitted from the mixture unless very high temperature requirements exist. Furthermore, since the price of C9 is currently very high, formulators rarely include it in their products; once the price drops to a level that is acceptable for them, the likelihood of using C9 is expected to increase. 3. Mixing method: Spraying mixing: Spraying mixing involves loading the component oils into the transport tank in proportion and in fixed quantities, with the mixing taking place during the tank-filling process. Apart from requiring auxiliary loading devices and measuring instruments, this method does not need any other special equipment; it was a commonly used method abroad in the 1980s. Circulating stirring mixing refers to the use of a circulation pump within the mixing tank to ensure uniform stirring, thereby allowing all components to mix evenly through this circulation process. This method is currently the main one used domestically. Pipeline blending refers to the process of blending component oils through static mixing in pipelines, using computers and blending control equipment. The mixing ratio in this method is controlled by a computer or pre-set equipment, ensuring high precision and facilitating management. VI. Testing standards: National Standard II and III for gasoline, the new Beijing standard (draft for approval); National Standards III, IV, and V (recommendatory standards); additional testing parameters for oil purchased from Sinopec outside its own operations