[E-book] Chapter 2: Fuel and Petroleum Product Additives (Sections 1 and 2)

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This post was last edited by 103388716 on 2017-6-18 14:53. Section 1: Types of additives for petroleum fuel products. Based on their functions, they can generally be classified into the following categories (the product types for which each additive is suitable are indicated in parentheses): 1. Antiknock agents； (Automotive gasoline and aviation gasoline) 2. Octane number improvers ； (Diesel) 3. Combustion improvers (anti-erosion agents) ； (Jet fuel) 4. Surface combustion inhibitor ； (Gasoline for vehicles) 5. Antioxidant and anti-gumming agent ； (Petrol, diesel, jet fuel) 6. Metal passivators ； (Petrol, diesel, jet fuel) 7. Cleaners ； (Automobile gasoline) 8. Anticorrosive agents ； (Petrol, diesel, jet fuel) 9. Antifreeze ； (Aviation gasoline, jet fuel) 10. Flowability improvers ； (Diesel) 11. Anti-static additives ； (Jet fuel) 12. Heavy oil additives ； (Fuel oil) 13. Antifoaming, antimicrobial, etc. (Fuel oil, jet fuel) Section 2: Antiknock Additives I. Overview of Gasoline Antiknock Additives 1. Gasoline antiknock additives (also known as octane number improvers) are additives that can enhance the antiknock properties (octane number) of gasoline used in vehicles and aircraft. The anti-knock property of gasoline is expressed by octane number (ON) and anti-knock index, with the octane number further divided into motor octane number (MON) and research octane number (RON). Octane rating is a numerical indicator that measures a gasoline’s resistance to knocking during combustion in the cylinder; higher octane ratings indicate better resistance to knocking (i.e., better combustion quality or higher quality gasoline). Octane number determination: Isooctane (with an octane number of 100) and n-heptane (with an octane number of 0) are commonly used as reference fuels. By mixing these two reference fuels in different volume ratios, mixtures with various anti-knock properties can be obtained. Using an octane rating machine, under the same engine operating conditions, the sample is tested and compared with a standard mixture; the volume percentage of isooctane in the standard mixture that has the same anti-knock property as the sample is referred to as the octane rating of that sample. In fact, the octane rating of gasoline is the sum of the products of the octane ratings of the various hydrocarbon components it contains and their volume percentages. (ON=∑ViXion) Main types of gasoline antiknock agents: ① Metal-organic compounds (metal-based antiknock agents): Contain metals such as lead, manganese, iron, and nickel; bonded to them are hydrocarbons, alkyl compounds, and carbonyl groups. ② Non-metallic organic compounds (organic ash-free anti-knock agents): Nitrogen-containing compounds: such as aromatic amine compounds ； Oxides: such as methanol, ethanol, isopropanol, tert-butanol, ethers, etc. 2. Methods to increase the octane number of gasoline: ① Change the composition of gasoline, that is, increase the proportion of hydrocarbons with high ON in gasoline. Its main processing methods include: catalytic cracking, hydrocracking, catalytic reforming, alkylation, alkylation, etherification, and blending, which involves adding high-octane components. ② Use additives that increase ON (antiknock agents). For a considerable length of time, the most widely used substances both domestically and internationally were lead-containing organic compounds, such as tetraethyl lead (code T1101); currently, lead-free anti-knock agents are primarily used. 3. History of the application of anti-knock agents In 1882, automotive engineers discovered the phenomenon of knocking. Since then, humanity has been searching for an efficient and effective anti-knock agent to eliminate or mitigate knocking. Subsequently, it was found that iodine and ethanol can serve as anti-knock agents to increase the octane rating of gasoline. In 1921, the American chemist Thomas Midgley, Jr., discovered the highly effective anti-knock agent tetraethyl lead (TEL) ； Production began in the United States in 1922 ； Leaded gasoline was sold as early as 1923 ； For 36 years until 1959, tetraethyl lead was the only antiknock agent used ； Production of tetramethyl lead began in 1960, and it was used alongside tetraethyl lead. Severe environmental pollution was discovered after 1970, leading to research on its prohibition ； Ban began in 1990, with a complete ban implemented in 2000. Research on the production and use of non-lead antiknock agents such as manganese has begun anew. II. Alkyl lead antiknock agents 1. Types, structures, molecular formulas, and properties of alkyl leads There are four types of commercial alkyl leads: (1) Tetraethyl lead (TEL) (2) Tetramethyl lead (TML) (3) PM: A physical mixture of TEL and TML with molar ratios of 25:75, 50:50, and 75:25 (4) GM: A chemical mixture of TEL and TML, also known as “lead liquor” or “ethyl liquid”; alkyl leads are combined with dyes, antioxidants, extractants, and solvents to form products for commercial use. The TEL content in automotive gasoline is generally 1 g/kg ； The TEL content in aviation gasoline is generally 3.3 g/kg. 2. Methods for manufacturing alkyl lead (1) TEL: Industrial production of TEL began in 1922 in the United States; it involves a batch process in which a sodium-lead alloy reacts with ethyl chloride: 4PbNa + (C2H5)Cl → (C2H5)4Pb + 4HCl. The lead-sodium alloy is formed by combining molten metals Pb and Na ； C2H5CL is produced by the reaction of C2H4 with liquid HCl at low temperatures in the presence of a catalyst. At first glance, the reaction seems simple, but it is actually quite difficult; it is a reaction between free radicals. (2) TML Grignard electrolysis method, using Pb as the cathode to electrolyze a solution of methylmagnesium chloride along with excess chloromethane; the reaction is as follows: Advantages: high efficiency, no need for lead recycling. Disadvantages: Magnesium, which is more expensive than sodium, requires more precise process control using alloying methods. 3) Synthesis of GM cat: Lewis acids such as MgCl2, BF3, etc. 3. Mechanism of action of alkyl lead – The phenomenon of \"knocking\" in gasoline engines. The mechanism of action of alkyl lead is closely related to the operating process of gasoline engines and the phenomenon of knocking. Before gasoline ignites and burns in a gasoline engine, the hydrocarbons undergo oxidation reactions under the influence of high temperature and oxygen, resulting in the formation of peroxides. Since certain hydrocarbons in gasoline are prone to oxidation, peroxides are formed at an excessive rate, leading to an overaccumulation of peroxides in the fuel mixture ； Furthermore, due to the low auto-ignition temperature of peroxides, when their concentration reaches this level, they will ignite on their own before any external ignition is necessary, which causes the gasoline engine to malfunction. This results in what is known as \"knocking combustion,\" or simply \"knocking,\" and is commonly referred to as engine damage in gasoline engines. Mechanism of action: Alkyl lead can decompose the peroxides formed as a result of the oxidation of hydrocarbons in gasoline, reducing their concentration to levels below those required for spontaneous combustion. This prevents detonation combustion in gasoline engines and enhances the anti-knock properties of gasoline. Taking TEL as an example, the specific analysis is as follows: (C2H5)4Pb can decompose in engines at temperatures of 200–300°C to produce elemental lead. Lead then reacts with oxygen in the air to form lead dioxide, which in turn reacts with peroxides generated in the unburned mixture to produce chemically inert organic oxides and lead oxide. It reduces the peroxides in the unburned mixture, preventing them from reaching the concentration required for spontaneous ignition, thereby eliminating knock. (C2H5)4Pb → ·Pb + ·(C2H5)4Pb; Pb + O2 → PbO2. R-CH3 + O2 → RCH2OOH; RCH2OOH + PbO2 → RCHO + H2O + 1/2 O2 + PbO. Lead oxide can react with oxygen to form lead dioxide, and by reusing lead dioxide, adding a certain amount of tetraethyl lead no longer results in any further increase in the octane rating of gasoline. Function of TEL: Inside the engine, (C2H5)4Pb decomposes and oxidizes at 200–300°C to produce PbO2 and PbO. 4. Alkyl lead and environmental pollution: This concept was first proposed in January 1970 by Manager Kohler at General Motors (GM) in the United States. Following the lead poisoning incident in Shinjuku Ward, Tokyo, Japan in 1970, lead pollution caused by lead antiknock agents attracted widespread attention. In December 1972, the United States announced a phased phase-out of leaded gasoline, and by January 1, 1996, it had completely banned leaded gasoline. Since the 1980s, many advanced countries around the world, including those in Europe and the United States, have begun to gradually ban the use of lead anti-knock agents. They strive to make gasoline lead-free or low in lead, and seek alternatives to alkyl lead or other methods. Japan made regular gasoline lead-free in 1985. Automobile manufacturers such as those in the United States and Japan have proposed allowing the addition of 0.053 to 0.132 g Pb/L to vehicle gasoline until this issue is resolved. \"Leaded gasoline\" has now faded from history. Since 1990, China has first started using lead-free gasoline in a few large cities such as Beijing, Shanghai, and Guangzhou ； In 1997, the addition of TEL (tetraethyl lead) to gasoline was officially banned. In 1999, new standards for automotive gasoline were established (GB17930-1999), and on July 1, 2000, the new standards for controlling emissions from vehicles came into effect (GB14761-1999). These standards stipulated that, starting from July 1, 2000, the production, use, and sale of lead-containing gasoline should be halted across the country. New standard clean gasoline refers to lead-free gasoline for use in vehicles that meets the quality requirements specified in the standard GB17930—2006 for automotive gasoline. The standard has now been upgraded to GB17930-2011; lead-free gasoline for use in vehicles refers to gasoline with a lead content of 0.005 g/Pb/L in grades 90, 93, and 97. III. Lead-free anti-knock agents 1. Metal-based anti-knock agents (1) Manganese-containing anti-knock agents Common types: Methyl cyclopentadienyl manganese tricarbonyl (MnCH3C5H4(CO)3), (Methyl Cyclopentadienyl Manganese Tricarbonyl, MMT); trade name: AK—33X (1959) ； Hitee3000 (1990), cyclopentadienyltricarbonylmanganese (MnC5H5(CO)3, NMT), pentacarbonylmanganese (Mn(CO)5). MMT, abbreviated as C9H7MnO3 or C5H4(CH3)Mn(CO)3, is an organometallic compound that can increase the octane rating of gasoline. It belongs to the category of metal-based anti-knock agents, and it exhibits good anti-knock properties as well as a favorable compatibility with gasoline. It was introduced in 1959 by the American company Ethyl (now renamed Affton) as a synergist or auxiliary anti-knock agent for tetraethyl lead. It is currently the ideal alternative to TEL, and it is the only anti-knock additive permitted under current **gasoline standards. ① The main advantages of MMT: For high-octane (RON) gasoline, its anti-knock effect is twice that of TEL ； For low octane number (MON) gasoline, the effect is similar to that of TEL ； Most effective against paraffin-based gasoline (high-paraffin hydrocarbon gasoline) ； It has little effect on gasoline containing mainly aromatic hydrocarbons ； Adding it to gasoline that already contains the maximum amount of TEL has a supplementary effect ； At an addition of 9 mg Mn/L, its contribution to octane number is equivalent to that of 5% (V) MTBE ； When added at 9–18 mg Mn/L, it can increase RON by 1.7–2.3 units ； Adding up to a maximum of 18 mg Mn/L can increase RON by nearly 3 units, and it exhibits good compatibility with oxygen-containing blending components ； It can improve refinery operations, reduce the complexity of refining processes (by decreasing the operational demands on reforming units), and lower the aromatic content in gasoline ； It can work in conjunction with a vehicle’s exhaust emission control system to improve the catalytic converter and reduce the vehicle’s emissions of NOX, CO, and CO2; it poses no harm to oxygen sensors ； Reduces collapse of the cylinder exhaust valve seat and helps keep the intake valve clean ； Using MMT results in the lowest costs compared to the process method and the blending method. It is easy to use, requires a small amount, does not increase the content of aromatics and olefins in gasoline, has a low cost, helps save fuel, improves gasoline exhaust emissions, and is non-toxic. ② Mechanism of action: Similar to TEL, manganese-based compounds decompose at high temperatures to produce particles of the active metal MnO2. Due to the effects on their surface, these particles disrupt the chain-breaking reactions involved in combustion, converting them into oxidation intermediates with very low reactivity. As a result, the concentration of peroxides in the pre-flame region decreases, and both the length and number of reaction chains are reduced. This selective suppression of the free radicals in certain organic peroxides prolongs the ignition delay period, expands the cold flame zone, hinders ignition, and reduces the rate at which energy is released; thereby improving the fuel’s resistance to detonation. Introduction to NMT: At room temperature, it appears as yellow or golden-yellow solid particles that crystallize; it sublimes easily in air and has an irritating odor. The product should be stored in a dark place after adding light stabilizers. It is similar to MMT in terms of its effectiveness in increasing octane rating; however, it has a higher freezing point than MMT and remains solid at room temperature, requiring it to be formulated into a solution before it can be used. NMT is a highly efficient and low-toxicity additive. Compared to MMT, it has lower production costs, higher stability, and can be used under milder conditions. It is also an economical and effective additive for improving the anti-knock properties of gasoline and for producing high-octane lead-free gasoline. A brief overview of the application history of manganese-containing anti-knock agents: Developed by Ethyl Corporation (Afton Chemical) in the United States in 1953, it was introduced in 1959 and utilized from 1974 to 1977. However, in 1977 it became controversial: it was believed that deposits formed in the cylinders, reducing the lifespan of spark plugs, increasing hydrocarbon emissions, and damaging the exhaust emission system. In 1978, the U.S. Congress decided to stop using it. In 1978, Ethyl Company appealed to the Federal Court, and based on a large number of tests, it overturned the negative decision by the U.S. Environmental Protection Agency (EPA). On July 11, 1995, the U.S. Environmental Protection Agency approved MMT for use in lead-free gasoline, but it is still not widely used in the United States to date. In Canada, 88–90% of gasoline contains MMT; it has been in use in Russia for many years, while its use is just beginning in the Middle East, Southeast Asia, and Africa. Currently, the product market is largely dominated by the American company Ethyl. The application of manganese-based anti-knock agents in our country (started late): Research, production, and application of manganese-based anti-knock agents in China began at a late stage. Research and development status: The School of Chemical Engineering at Shanghai Jiao Tong University has been working on the development of MMT production technology since 1999, and has now developed a simple and practical process route with a yield of 65% ； Nankai University has made successful efforts in the development of NMT, using as main raw materials the inexpensive coal tar distillate, which is abundant in China, and cyclopentadiene obtained from the C5 fraction of ethylene by-products. This process features mild reaction conditions, low investment costs, high efficiency, ease of operation, and automation of the key steps. Divalent manganese is widely available and inexpensive; the C5 raw materials are easily obtainable, resulting in low production costs. Research institutions such as the Petrochemical Research Institutes of CNPC and Sinopec, as well as various manufacturers, are involved in this research. Production status: Since MMT was introduced to Chinese refineries in 1997, the American company Affton essentially held all of the domestic market share at that time. Production began domestically in 2005, and it showed a rapid growth trend: the output was only about 100 tons in 2005, 900 tons in 2007, 1,300 tons in 2008, and 1,600 tons in 2009. The output increased by 16 times in less than five years. The market share of domestic MMT also increased from 8.7% in 2005 to over 50% at present. Jiangxi Xilinke Co., Ltd. is currently the largest MMT producer in China and the second-largest in the world, with an annual production capacity of 1,000 tons of MMT. In 2009, the MMT produced underwent a 80,000-kilometer driving test, and it became the only domestic anti-knock agent on China’s gasoline market that met the National IV standards, aside from Yafudun; it was also the only domestic MMT product approved by Sinopec. At the 2011 **Science and Technology Awards Ceremony, the MMT development and application project won the second prize for scientific and technological progress.** The MMT produced by Xilinke has a purity of up to 98%, and the company is capable of producing all the key raw materials for MMT on its own – a feature that is unique in the world. This has also changed the situation in which China was dependent on others for MTT supply. In just a few years, the price of imported MMT has dropped from 330,000 yuan per ton to 280,000 yuan per ton. Usage: Since 1998, MMT has been used in domestic gasoline. Currently, more than 50 large and medium-sized refineries in China are using the manganese-containing anti-knock agent MMT. As the domestic automobile industry grows, automobile production increases significantly, consumers’ purchasing power rises, the number of vehicles in use keeps rising, gasoline consumption increases, and there is a demand for higher-grade (higher quality) gasoline, all of these factors drive up the demand for manganese-based anti-knock agents. In China, demand reached 1,200 tons in 2005, 1,600 tons in 2008, and by 2010, approximately 3,000 tons of MMT, both imported and domestically produced, were used. The imported MMT came mainly from the American company Yafulton. MMT is mainly used in the following situations: a. When refineries are unable to produce 90# gasoline by adding catalytic gasoline to it ； b. 93# gasoline is produced by adding 90# catalytic gasoline from the refinery ； c. After blending a certain amount of straight-run gasoline into catalytic gasoline (up to 15% of straight-run gasoline can be added), an anti-knock agent of 0.018 g of manganese per liter is added to produce 90# gasoline; this helps to utilize part of the straight-run gasoline and reduces the sulfur and olefin content in the gasoline ； d. Add 0.018 g of manganese per liter of 93# reformated gasoline as an anti-knock agent to produce 97# gasoline; or mix MTBE with 90# gasoline and then add such an anti-knock agent to produce 97# gasoline ； e. In addition to refineries, local oil companies can also use MMT to increase the octane rating of gasoline in order to earn more profits. After the octane rating of treasury gasoline was raised from 90# to 93#, a price difference of around 280 yuan can be earned per ton. The cost of adding manganese-based anti-knock agents is 30–40 yuan, while the cost of using MTBE for blending is over 80 yuan. f. Domestically produced manganese-based gasoline anti-knock agents are mainly used by oil refineries with limited processing capacity in their reforming units, or where the catalytic gasoline fails to meet the 90# standard. Reasons for the widespread use of MMT in China: In the composition of China’s refining facilities, the proportion of alkylation, isomerization, and reforming units is low, resulting in a shortage of high-octane components used in gasoline. For example, in 2009, China’s gasoline production was 71.948 million tons, of which catalytic cracking gasoline accounted for about 80%. The volume fraction of olefins in this type of gasoline ranges from 45% to 50%. Adding MTBE is currently the most economical method in China for raising the octane rating of catalytic cracking gasoline, and it represents a way to address the issue of insufficient octane ratings in gasoline used for vehicles. Application standard: The \"Standard for Controlling Hazardous Substances in Automotive Gasoline\" established in 1999 for National II gasoline allowed a maximum of 18 milligrams of MMT per liter of gasoline, which is more than three times the standard set by the EU in 2009. In 2006, the content of National III gasoline was reduced to 16 milligrams per liter of gasoline ； The levels in developed countries are all below 6 milligrams, while China’s level is two to three times that of developed countries. The new standards issued in 2011 stipulated that, starting from July 1, 2013, National IV and National V emission standards would be implemented nationwide in China. According to the \"Standards for Controlling Hazardous Substances in Automotive Gasoline (Sections 4 and 5)\) established by the Ministry of Environment, the allowable manganese content in gasoline is limited to 8 milligrams per liter and 2 milligrams per liter, respectively. 2 milligrams was also the EU standard in 2014, which meant that its addition was not allowed, as adding 2 milligrams is completely ineffective. Local standards in many major cities in China have been aligned with international standards. For example, in Beijing and Shanghai, the manganese content in vehicle gasoline is specified to be no more than 6 milligrams per liter ； The local standards to be implemented in Guangdong Province stipulate that the manganese content in gasoline shall not exceed 8 milligrams per liter ； Su Guo IV, which is set to be implemented in Jiangsu Province, also stipulates a limit of no more than 6 milligrams per liter. Problems with MMT: MMT itself is a technological substitute for leaded gasoline; however, it also brings about new problems. One is the direct damage to cars, and the other is air pollution. Debates about MMT emerged as early as 1977, and these controversies have continued for 40 years. It has been proven that increasing the level of heavy metals in the atmosphere harms the environment and directly damages the three-way catalytic converters used in cars to filter exhaust gases. Research by the Automobile Manufacturers Association has found that although MMT containing manganese is inexpensive, it increases fuel consumption and carbon dioxide emissions. It forms deposits on the inner surfaces of the engine combustion chamber, reducing the lifespan of spark plugs. Moreover, when a vehicle is driving at high speeds, MMT accelerates the corrosion of certain catalytic converters. Damage the vehicle’s emission control system. Two cases: 1. At an international seminar held in November 2005, Volkswagen of Germany joined forces with other multinational automakers in China such as Ford, Toyota, and Honda to challenge Yafoton, the global manufacturer of MMTs. Two technical leaders from the German Volkswagen Group presented on site the analysis results of 62 faulty catalytic converters from Shanghai Volkswagen service centers; 54 of these converters failed due to blockages, with MMT being the main culprit. 2. In mid-March 2010, thousands of vehicles experiencing the same malfunction were reported at numerous brand-specific 4S stores in Anyang, Jiaozuo, Xinxiang, and other places in Henan Province. The technical expert group conducted sampling tests on oil samples from the malfunctioning vehicle and the oil at the bottom of the storage tanks at the gas station, determining that the solvent-washable gum and manganese content in this batch of oil exceeded the **specified standards. The excessive manganese content stems from MMT, an additive in gasoline. In recent years, the international industry has generally reached a consensus that it is an inevitable trend to gradually reduce the amount of MMT added to gasoline and to improve its anti-knock properties by advancing refining technologies. In recent years, China’s automotive industry has consistently opposed the addition of MMT to gasoline. MMT is a 100% transitional product, with an expected lifespan of another 15 to 20 years. The new standards stipulate that for gasoline produced after July 2013, the manganese content must be reduced to 6 milligrams per liter. Thus, based on the estimate by the Economic and Technological Research Institute of Sinopec that China’s production of motor gasoline in 2013 was 105.67 million tons, the market demand for MMT is approximately 2,000 tons. After the implementation of the National Standard IV for Motor Gasoline in 2015, the maximum capacity for MMT usage is expected to be around 3,600 tons. At present, catalytic cracking is the main secondary processing method in China’s oil refineries, while the utilization rate of catalytic reforming remains low. This results in a shortage of high-octane components in gasoline. This situation serves as the foundation for the widespread use of high-octane additives, and it is unlikely to change in the short term. Experts in the automotive industry also believe that the development of the automobile sector leads to a continuous increase in gasoline consumption, and at the same time requires an increasing proportion of higher-octane gasoline. These two factors, which drive up MMT usage, will persist in the long term. Iron-containing anti-knock agents mainly include: cyclopentadienyl iron (ferrocene) (C5H5)2Fe, diisobutenylcarbonyl iron [Fe(CO)5]3(C8H16), thiocarbonyl iron [Fe2(CO)6S(C2H5)]2, and pentacarbonyl iron Fe(CO)5. Ferrocene, polyisobutyrenediamide, and barium polyisobutyrate are used to create lead-free gasoline anti-knock agents that are anti-knock, non-toxic, and stable. Explosion resistance effect: Studies show that it has a significant effect on enhancing the ON performance of gasoline. For example, adding five ten-thousandths to 75# gasoline can increase it by 5.1 units, resulting in a MON of 80.1. Ferrocene was originally used as a combustion enhancer in rocket fuel. In recent years, it has attracted considerable attention. However, it also presents several problems: after prolonged use, iron oxide produced during combustion cannot be expelled from the cylinder due to its high melting point. This leads to increased engine wear, short-circuiting and damage of spark plugs, failure to ignite, and ultimately accidents ； No suitable iron oxide expeller has been found (lead expellers include dibromoethane and dichloroethane, etc.) to convert it into a volatile iron compound with a low melting point. Improvement method: Synthesis of modified ferrocene – The hydrogen atoms on the two cyclopentadienyl groups of ferrocene are replaced by certain substituents; these substituents can react with iron during high-temperature combustion to form volatile iron-containing compounds, thereby allowing the metallic iron to be expelled from the cylinder. Synthesis of ferrocene: Electrolysis of cyclopentadiene (in ethanol solution) → (C5H5)2Fe. Iron compounds. Organic ash-free anti-knock agents: Ethers: MTBE (methyl tert-butyl ether), ETBE (ethyl tert-butyl ether), TAME (methyl tert-amyl ether), DIPE (diisobutyl ether). Alcohols: Methanol, ethanol, isopropanol, isobutanol, tert-butanol (TBA). Esters: Dimethyl carbonate (DMC), trimethylsilyl tert-butyl ester, polyoxyethylene ether dicarboxylate. Methylenecyclopentadienes: 2-methyl ester, 6-(dimethylamino)methylenecyclopentadiene ； 2,3-Dimethylenyl-6-(dimethylamino)methylenecyclopentadiene; Aromatic amines: aniline, toluene diamine, dimethylaniline. 1) Oxygen-containing organic compounds: Oxygen-containing organic compounds (ethers, alcohols, esters, etc.), when added to gasoline, enable more complete combustion and reduce emissions such as CO. Explosion-resistant mechanism of oxygen-containing organic compounds: During combustion, they undergo chemical reactions with the unsaturated hydrocarbons in gasoline to form epoxides, which reduces the concentration of peroxides generated throughout the combustion process. This prevents the formation of multiple flame centers and weakens the spread of active combustion cores to unburned areas. Ether compounds: Methyl tert-butyl ether (MTBE, methyl tert-butyl ether) is a representative ether compound. Basic properties: Molecular formula: C5H12O; Structural formula: CH3OC(CH3)3; Relative molecular weight: 88.18. It is a colorless and transparent liquid with an ether-like odor. The purity ranges from 97% to 99.6%, with an oxygen content of 18% (by mass). Physical properties: Boiling point (°C): 55.2°C; Freezing point (°C): -109°C; Density (kg/m3 at 20°C): 740.6; Critical temperature (°C): 223.9; Specific heat capacity (°C): 2.135; Heat of vaporization (J/g·K): 30.10; Heat of combustion (MJ/kg): 38.21; Vapor pressure at 37°C (bar): 0.55; Critical pressure (MPa): 3.37; Refractive index (at 20°C): 1.3689; Ignition point (°C): 480; Flammability range (%V): Upper limit of 15.1% ； Lower limit: 1.6. Solubility of water in MTBE (20°C, g/100g): 1.5. Solubility of MTBE in water (20°C, g/100g): 4.3. Chemical properties: It exhibits good chemical stability (a very important property). Due to the presence of tertiary carbon atoms and methyl groups in its chemical structure, it is relatively stable and has strong resistance to auto-oxidation; peroxides do not form easily in air. Does not easily form peroxides. Used as a blending component for high-octane gasoline. Good miscibility with gasoline: MTBE is a product of the reaction between methanol and isobutylene, and it can mix with gasoline components in any proportion without separation occurring. It can also be used as a solvent for paraffin, fragrances, alkaloids, resins, and rubber, as well as in organic synthesis reactions. Safety: MTBE is an organic ether with an oxygen content of 18.2%. Its vapor is heavier than air and can spread along the ground; it is flammable and poses a risk of explosive combustion in the presence of sparks, heat sources, or strong oxidizing agents. Explosion resistance: RON=118, MON=100; it is a high-octane liquid. It is an excellent high-octane additive and anti-knock agent for gasoline, and an ideal component for producing lead-free, high-octane, oxygenated gasoline. Adding a small amount of MTBE to gasoline (gasoline products containing 2% MTBE can have their octane rating increased by 7%) can result in a significant rise in the octane rating of the gasoline. It is widely used. It has a good blending effect; it is effective for blending various types of gasoline such as straight-run gasoline, alkylated gasoline, catalytic cracking gasoline, and catalytic reforming gasoline, resulting in a high blended octane number. The blending ratio of MTBE to gasoline is generally 1~15%. MTBE has a relatively high oxygen content, which enables more complete combustion of gasoline. It also helps to significantly improve vehicle performance and reduce exhaust emissions – CO emissions are reduced by 30%, while the emission of other harmful substances such as ozone, benzene, and butadiene is also decreased, thereby lowering the production costs of gasoline. Synthesis principle and process: It is synthesized using methanol and isobutylene as raw materials, through an addition reaction facilitated by an acidic catalyst. The most commonly used catalyst in industry is resin ； Different synthetic routes have been developed depending on the source of isobutylene. Source of isobutylene: C4 fraction produced as a by-product of ethylene synthesis via cracking. – C4 fraction produced as a by-product of the catalytic cracking unit in refineries. – Produced from n-butane through isomerization and dehydrogenation. Catalysts for the synthesis of MTBE: – Styrene-based cation exchange resins – Molecular sieves – Heteropoly acids and their salts – Hydrofluoric acid – Solid acids – Sulfuric acid. The reaction for synthesizing MTBE is a selective addition reaction; the tertiary carbon atom in the alkene forms a carbocation in the presence of an acidic catalyst, which then combines with methanol to form an ether. Its reaction is a reversible exothermic reaction. Process principle: In industrial installations, the catalytic etherification reaction takes place in a fixed-bed or fluidized-bed reactor, with the reactants being in liquid form. In the stream after the reaction, in addition to the product MTBE, there is also unreacted methanol as well as other C4 components other than isobutylene. Since both methanol and C4 or MTBE form azeotropes, there are various options available for product separation. Taking Jihua Company’s organic synthesis plant as an example, the process principles and flow are introduced, including the following aspects: – Process flow diagram – Sources of raw materials and preprocessing – Principle of etherification reaction – Principle of catalytic distillation – Principle of product separation – Principle of methanol recovery. Process flow (taking Jihua Company’s organic synthesis plant as an example): Process flow (actual plant flow diagram): Sources of raw materials: – C4: The C4 fraction obtained from liquefied gas produced by catalytic cracking units, after the C3 components have been removed using a gas separation unit. －Methanol: purchased externally －Catalyst: acidic ion exchange resin. The catalyst must be stored in an aqueous state, with a moisture content of generally (50±2%)%. Its main function is to promote an etherification reaction between isobutylene and methanol in C4 to produce MTBE. Purity requirements for MTBE products: The purity of the product depends on its intended use: – When used to increase the octane rating of gasoline, the required purity is ≥95%. – Used to produce high-purity isobutylene, which requires a purity level of >99%. Raw material pretreatment: The mixed C4 is fed into the dealkalization tank (V-409), where amines, bases, and alkali metal ions contained in the free water of the mixed C4 are removed. After that, it is thoroughly mixed with the methanol raw material coming from the storage area, and then fed into the purifier (R-402A/B) to remove harmful substances from the raw material. Principle of the etherification reaction: Isobutylene and methanol in mixed C4 undergo a synthetic reaction to produce MTBE under the action of a strongly acidic styrene-based macroporous cation exchange resin catalyst. Side reactions: (1) Hydration of isobutylene to produce tert-butanol (TBA); (2) Dimerization of isobutylene to produce diisobutylene (DIB); (3) Dehydration of methanol to produce dimethyl ether and water. The main factors affecting the MTBE synthesis reaction are: alcohol-to-olefin ratio: the molar ratio of methanol to isobutylene, which should generally be maintained between 1.0 and 1.05; values too high or too low are not favorable. An excessive amount can increase the isobutylene conversion rate, but excess methanol not only increases the separation difficulty in the reactive distillation column but also increases the load on the methanol recovery column. If it is too small, isobutylene polymerization will occur, releasing a large amount of heat that can cause the reactor to overheat and damage the catalyst. Reaction temperature: Generally, 50–70°C is appropriate; when the temperature exceeds 80°C, side reactions increase and the catalyst’s lifespan is shortened ； The catalyst becomes inactive when the temperature exceeds 120°C. The reaction temperature not only affects the conversion rate of isobutylene, but also influences the selectivity of MTBE, the catalyst life, and the reaction rate. Principle of catalytic distillation: The reaction and distillation take place in the same column; the heat released by the reaction is used to vaporize the material being distilled, thereby ensuring that the reaction occurs at a constant temperature. Product separation principle: Utilizing the property that C4 and methanol form a minimum boiling azeotrope, azotropic distillation is employed to separate MTBE from methanol and C4. The principle of methanol recovery involves utilizing the difference in solubility of C4 and methanol in water; water is used as an extractant to separate methanol from C4, after which distillation is employed to separate methanol from water. Description of the MTBE production process: The raw materials, methanol and isobutylene, undergo an enol etherification reaction in a pre-reactor at a molar ratio of 1.0~1.05; an optimal reaction temperature is 50~70°C. The material after the reaction enters the catalytic distillation tower, where the reaction continues with additional methanol added. The generated MTBE and the unreacted feedstock react and separate within the catalytic distillation tower, with the product MTBE being obtained at the bottom of the tower. At the top of the tower, an azeotrope of C4 and methanol is obtained; part of this mixture is recycled while the rest is taken out and sent to the bottom of the wash tower. The extractant water enters the wash tower from the top, and thanks to the difference in their solubility in water, C4 and methanol are separated. A water solution of methanol is obtained at the bottom of the tower, while C4 is obtained at the top. The methanol-water solution coming out of the bottom of the wash tower enters the methanol recovery tower, where methanol and water are separated using conventional distillation methods. The separated water is sent back to the wash tower to be reused as an extractant, while the separated methanol is recycled as a reaction material. Main problems of the device and solutions: Severe corrosion in the alcohol recovery system: The corrosion in the methanol recovery system is mainly acid corrosion, with the acids coming from residual acids carried by the catalysts and formic acid introduced by methanol. Solution: Installing an anion exchange bed or an alkali washing tank before the C4 stream after ether enters the extraction tower can effectively mitigate corrosion. Additionally, regularly replacing the extraction water can also serve as a solution. High exhaust emissions: As designed, the facility is not supposed to produce any exhaust gases; however, due to the C3 content in the raw materials being much higher than the specified value, the facility is forced to emit exhaust gases. Solution: Currently, the exhaust gas can only be discharged into a flare. Technical renovation of Jihua’s MTBE plant: Original design – 27,500 tons of MTBE per year; designed operating time – 7,200 hours. It was China’s first industrial-scale plant with a production capacity of 10,000 tons, developed by Jihua Research Institute, designed by Jihua Design Institute, and installed by Jihua Construction Company ； Construction began in 1984, production started on October 24, 1986, and qualified MTBE products were produced on the 27th ； The original design process utilized the two-reactor two-tower technology ； In 1996, the facility was upgraded using thermal integration technology to increase its production capacity, which was raised to 55,000 tons per year ； In August 2003, the catalytic distillation technology from Qilu Petrochemical Research Institute was introduced, enabling the implementation of a one-tower one-vessel process, which **reduced energy consumption. The history of MTBE production and application: MTBE came to attention in the 1970s. Since 1978, when the Italian company SNVM built the world’s first MTBE production plant with an annual capacity of 100,000 tons. By the end of the 20th century, the global total production had reached 23 million tons, making it one of the fastest-growing types of petrochemical products. Currently, about 90% of MTBE is used as an octane booster and an oxygenate in gasoline, with 90% of gasoline containing MTBE. The SNVM process first dehydrogenates isobutane using specific catalysts and equipment to obtain an isobutylene mixture with high yield. This process is not limited by the amount of isobutylene feedstock, and it extends to methods for producing butadiene from butane and propylene from propane. The Air Clean Act Amendment of 1990 enacted in the United States (CAA-1990) required new formulations of gasoline to contain oxygenates such as MTBE in order to reduce vehicle pollution. A brief overview of the development of MTBE in China: Research on MTBE technology began in China in the late 1970s. In recent years, MTBE production capacity has grown rapidly. In 1983, the Rubber Plant of Qilu Petrochemical built China’s first set of industrial testing equipment. In 1986, Jilin Chemical Industry Company built China’s first 10,000-ton industrial facility. In 1999, China launched the \"National Air Purification Project – Clean Vehicles Initiative\", beginning to encourage the use of gasoline containing MTBE. In 2003, there were nearly 40 production units across the country, with a production capacity of around 1.6 million tons per year. In 2005, there were over 40 production units nationwide, with a total production capacity of 2.07 million t/a. In 2009, there were over 50 production units across the country, with a total capacity of 3.194 million tons per year. CNPC has 13 plants with a capacity of over 30,000 t/a, resulting in an overall production capacity of 933,000 t/a ； Sinopec has a total of 19 production units, with an aggregate capacity of 1.229 million tons per year ； Local enterprises' installations have a total production capacity of 1.032 million tons per year. There are a total of 6 large-scale MTBE production units in China with an annual capacity of 100,000 tons or more. By June 2010, there were 128 units in the country, with a total production capacity of 6.01 million tons per year. CNPC, Sinopec, and CNOOC possess 60 production units with a total capacity of 3.347 million tons per year, accounting for 55% of the country’s total production capacity ； Local refineries have 68 units with a total capacity of 2.6715 million tons per year, accounting for 45%. As of June 2012, China’s MTBE production capacity was as high as 7.296 million tons per year. It is expected that within the next 3 years, China’s new production capacity will exceed 2.8 million tons. The MTBE projects currently under construction include: Xinjiang China-Kazakhstan Energy with an annual production capacity of 1 million tons, Sinochem Quanzhou with an annual output of 140,000 tons, Daqing Petrochemical with an annual production of 80,000 tons, CNOOC Dongfang with an annual output of 80,000 tons, Heyang Petrochemical with an annual production of 80,000 tons, and the new project of Yanchang Petroleum Group’s refining and chemical company with an annual production capacity of 90,000 tons. There are also facilities in Shanghai Petrochemical, Jilin Petrochemical, and Qingdao Petrochemical that together have a total production capacity of 230,000 tons. In addition, there are more than 20 other projects planned for construction. At present, the scale of refineries in our country is relatively small, and the isobutylene resources are scattered, making it difficult to utilize them on a centralized basis. As a result, the scale of MTBE production facilities in our country is modest, with most of them having a capacity of tens of thousands of tons. Compared to MTBE plants abroad, which are typically on the order of hundreds of thousands of tons in capacity, they have higher energy consumption and costs, resulting in lower overall competitiveness. It is an urgent task to increase the production capacity of a single unit or to expand the manufacturer’s overall production capacity. Since 2010, new technologies for producing MTBE from isobutylene have been developed and widely applied, namely by constructing isomerization units and isobutane dehydrogenation units to convert n-butylene and isobutane contained in liquefied petroleum gas (LPG) into isobutylene. It paved the way for the large-scale production of MTBE, contributing to a significant increase in domestic MTBE production. Currently, the LPG produced as a by-product of fluid catalytic cracking (FCC) technology used in domestic refineries to manufacture gasoline and diesel contains 30%–40% n-butylene and 30% isobutane. In the old process, only 12% to 15% of the isobutylene in LPG can be used to produce MTBE. With new technologies, the annual production capacity of a single MTBE plant can reach up to 740,000 tons, resulting in a significant increase in output. Our country has successively developed a series of new technologies for producing MTBE for industrial use, such as tube reactor technology, adiabatic external circulation reaction technology, mixed-phase bed reaction technology, catalytic distillation technology, and mixed-phase reactive distillation technology – a total of five generations of such technologies. Among them, catalytic distillation and mixed-phase catalytic distillation technologies have reached world-class levels. In 2015, China will experience net exports of MTBE. According to the China Chemical Industry News (August 19, 2013), new technologies for producing MTBE allow for a significant increase in its annual production capacity. As a result, China’s imports of MTBE were significantly reduced, with the proportion of imports in total domestic consumption falling from 14.7% in 2010 to 2.6% in 2012. Data shows that China’s MTBE production will increase to 7.4 million tons in 2015, a significant 32% rise compared to the estimated 5.6 million tons in 2013. By then, China could become a net exporter of MTBE, with the opportunity to export large quantities to countries such as South Korea and Singapore. In the chemical industry, about 10% of China’s MTBE consumption is used as a raw material for producing isobutylene or in solvent applications. The pyrolysis of MTBE to produce isobutylene is an important source of high-purity isobutylene ； Through further processing, butyl rubber, methacrylates, polyisobutylene, and others can be produced. As China’s C4 resources continue to increase, the demand for MTBE as a key downstream chemical product will rise significantly. Antioxidants such as tert-butyl amine, polyisobutylene amine, and tert-butyl phenol derivatives made from high-purity isobutylene all have relatively optimistic market prospects. Problems in the production and application of MTBE: In terms of production: Dependence on improved gasoline quality standards ； Structural adjustment of refining units ； There is an ample supply of raw material methanol ； Isobutylene resources need to be integrated ； Key issue: The market share of high-purity, low-sulfur MTBE is small. **After the widespread adoption of National IV gasoline, the quantity of this quality of MTBE falls far short of market demand, and a shortage of high-quality MTBE resources will become a serious problem. Only a few domestic MTBE manufacturers, such as Qiwanda, Yuhuang, and Linzi Petrochemical, have a purity of over 99% and contain virtually no sulfur ； The products from Sinopec and CNPC plants such as Qilu Petrochemical, Yangzi Petrochemical, and Dushanzi Petrochemical can meet Beijing standards and are suitable for use in oil blending as well as as pharmaceutical intermediates; however, most of them are used internally or supplied to contracted clients, with only a small amount being sold externally. The market share of MTBE with a purity below 95% and a sulfur content above 300PPM will gradually shrink, and it may even disappear from the market over time. The hazards and restrictions of MTBE: The hazards of MTBE lie in its high solubility in water, which leads to groundwater contamination ； (Passes through the soil into underground drinking water systems, is difficult to degrade, and causes the water to have an unpleasant odor) ； It may cause certain degree of harm to the human respiratory tract, eyes, gastrointestinal tract, liver, kidneys, central nervous system, as well as the ecological environment. Due to leaks from underground and above-ground gasoline tanks, MTBE has been found increasingly in underground drinking water sources in the United States. Entering the 21st century, the U.S. Environmental Protection Agency has listed MTBE as a possible human carcinogen. Status and trends regarding the restriction of MTBE: Due to MTBE’s impact on water quality, California, USA, passed a law in March 1999 to ban its use starting from January 1, 2003 (later postponed to 2004), and established standards for limiting the amount of MTBE in drinking water. This action undermined MTBE’s status as a key high-octane additive in gasoline in the United States. By May 2006, 25 states in the United States had banned it ； By April 2007, 26 states in the United States had banned it. The use of MTBE in the United States is on a downward trend year by year. In 2002, 3.65% of total gasoline consumption in the United States was MTBE, and MTBE was used as an oxygenate in approximately 87% of gasoline formulations with new recipes. After 2006, MTBE production in the United States continued to decline, with an average production level of around 131,000 barrels per day (5.63 million tons per year) ； At the beginning of 2007, it was further reduced to 23,000 barrels per day (990,000 tons per year) ； It decreased from 12.9 million tons in 2001 to 3.44 million tons in 2010. Australia has also decided to ban MTBE starting in 2004. In Europe, the European Commission has completed a risk assessment of MTBE, concluding that this substance poses no threat to health. Gas storage tanks in Europe are mainly above ground, so there are no leakage issues. Although Spain, France, Germany, and Italy also show similar trends, so far there are no clear signs of a ban in Europe. After Europe introduced new gasoline standards in 2005, requiring the aromatic content in gasoline to be reduced from 42% to 35%, this move further stimulated the increase in demand for MTBE. There are currently no signs in countries across Asia and Africa of a ban on MTBE. Since the most pressing task facing Asia is addressing urban air pollution, MTBE will serve as a key component of clean fuels for a certain period of time. In particular, there is a significant increase in the demand for gasoline, which requires an increase in its octane rating. Due to the ban on lead and strict restrictions on aromatics, olefins, and sulfur in gasoline, more MTBE is required. It is expected that demand for MTBE will continue to grow to a certain extent in regions such as the Asia-Pacific in the future. Our country regards the addition of MTBE to increase octane rating as the most effective method for raising gasoline standards. On the one hand, it is necessary to address the urgent issue of insufficient octane rating in current gasoline, allowing it to be sold on the market; on the other hand, it is also important to find a use for the C4 by-products. Especially after the completion of the West-East Gas Transmission Project, C4 (liquefied gas) produced as a by-product of FCC processes must find new outlets. Substitution for MTBE: In the United States, after 2006, ethanol will replace MTBE in formulations of high-octane gasoline (RPG). The use of renewable fuels has led to a reduction in MTBE production, with the extent of this reduction depending on the speed at which refiners convert their existing MTBE production facilities to other uses. Europe is accelerating the transition of MTBE plants to produce ETBE (ethyl tert-butyl ether). Between 2005 and 2006, several more MTBE plants in Europe switched to producing ETBE. Europe is also partially replacing it with ETBE; the increase is expected to be significant, but it will not exceed the decline in usage in the United States. Warning: World oil product standards show a trend toward convergence, generally following U.S. standards. Therefore, with the ban on MTBE in the United States now a certainty, we should also strengthen research on adapting to the situation following its ban or restriction.