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Chapter 6 Basic knowledge of MTBE device 1. MTBE (methyl tert-butyl ether) is the English abbreviation of methyl tert-butyl ether. It is a high-octane number (research octane number 115) gasoline additive. The chemical oxygen content is much lower than that of methanol. It is good for warming the car and saving fuel. It has low latent heat of evaporation and is good for cold starting. It is often used in the blending of unleaded gasoline and low-lead oil. It can also be re-cracked into isobutylene and used as a raw material for rubber and other chemical products. 1. 2. Physical and chemical properties of MTBE Methyl tert-butyl ether, abbreviated as MTBE (methyl tert-butyl ether), has a melting point of -109°C and a boiling point of 55.2°C. It is a colorless, transparent, high-octane liquid with an ether-like odor. It is an ideal blending component for the production of lead-free, high-octane, and oxygenated gasoline. It has been commonly used as a gasoline additive throughout the world. It can not only effectively increase the octane number of gasoline, but also improve vehicle performance, reduce CO content in exhaust gas, and reduce gasoline production costs. In addition, MTBE is also an important chemical raw material. For example, high-purity isobutylene can be produced through cracking. MTBE is an organic ether with an oxygen content of 18.2%. Its vapor is heavier than air, can spread along the ground, and can burn when coexisting with strong oxidants. The purity of MTBE is about 97%~99.5%, and its molecular formula is: CH3OC(CH3)3, relative molecular weight: 88.15. 3. Physical properties of MTBE l Density (kg/m3, 20℃): 740.6l critical temperature (°C): 223.9l Specific heat capacity (°C): 2.135l heat of evaporation (J/(g·K)): 30.10l heat of combustion (MJ/kg): 38.21l Reid vapor pressure (bar): 0.55l critical pressure (MPa): 3.37l refractive index (20°C): 1.3689l ignition point (°C): 480l explosion limit in air (%V): Upper limit 15.1 ； Lower limit: 1.6l research method octane number: 117l motor octane number: Solubility of 101l water in MTBE (20℃, g/100g): Solubility of 1.5l MTBE in water (20℃, g/100g): 4.3 IV. Application of MTBE Methyl tert-butyl ether is the current substitute product for tetraethyl lead. It is made from isobutylene and methanol in cracked C4 as raw materials, generated under the catalysis of macroporous sulfonic acid cation exchange resin, and refined. Product performance: This product has an odor similar to camphor, is colorless and transparent, and is completely miscible with alcohols, ethers, aliphatic hydrocarbons, aromatic hydrocarbons, halogenated solvents, etc. at room temperature. Like other methyl tertiary alkyl ethers, this product has another very important property, that is, it has strong resistance to auto-oxidation and is not likely to generate peroxide. It is mainly used as a blending agent for high-octane gasoline in refineries, and can also be used as a solvent for paraffin, oils, spices, alkaloids, resins, and rubber, and as a reagent for organic synthesis. It is flammable and volatile, and may explode when exposed to fire or heat sources. In the 1970s, MTBE began to attract attention as a gasoline blending component to increase the octane number of gasoline. MTBE can increase the octane number of gasoline and is chemically stable. Adding MTBE to gasoline can also improve the driving performance of the car and reduce the carbon monoxide content in the exhaust. It also has high combustion efficiency and can inhibit the generation of ozone. It can replace tetraethyl lead as an anti-riot agent to produce unleaded gasoline. About 95% of MTBE is now used as an octane increaser and oxygenating agent in gasoline. MTBE is also an important raw material for producing polymer-grade isobutylene. Also used in the production of methacrolein and methacrylic acid. In 1973, Italy developed the world's first MTBE industrial device. The Clean Air Act Amendments (CAA-1990) enacted in the United States in 1990 requires the addition of oxygenated compounds (such as MTBE) to reformulated gasoline to reduce vehicle pollution. China began research on MTBE technology in the late 1970s and early 1980s. In 1983, the rubber plant of Qilu Petrochemical Company built China's first MTBE industrial test device, and in 1986, Jilin Chemical Company built China's first 10,000-ton MTBE industrial device. In 1999, China launched the "National Air Purification Project-Clean Car Action" and began to encourage the use of gasoline containing MTBE. As an octane improver for gasoline, MTBE can not only increase the oxygen content of gasoline, but also promote clean combustion and reduce harmful vehicle emissions. MTBE has some solubility in water, so MTBE is increasingly found in underground drinking water bodies in the United States, primarily due to leaks from underground and above-ground gasoline storage tanks. MTBE can cause foul odor in water even at very low concentrations. The U.S. Environmental Protection Agency has classified MTBE as a possible human carcinogen. 5. Main uses of MTBE MTBE has excellent performance as a gasoline additive. It not only has a high net octane number, but also has a good blending effect on various gasolines such as straight-run gasoline, alkylated gasoline, catalytically cracked gasoline, and catalytically reformed gasoline, and has a high blending octane number. Adding a small amount of MTBE to gasoline can greatly increase the octane number of gasoline. The blending ratio of MTBE and gasoline is generally 1~15%. 6. Carbon 4 (C4), the raw material of MTBE: The C4 component is obtained after the C3 component is removed from the liquefied gas produced by the catalytic cracking unit through the gas separation device. Methanol: outsourcing. catalyst: The catalyst is acidic ion exchange resin. This catalyst must be stored in a water-containing state, and the water content is generally (50±2)%. The main function is to promote the etherification reaction between isobutylene and methanol in C4 to generate MTBE. 7. MTBE product purity requirements The purity of MTBE products depends on the purpose of use.: (1) As a blended gasoline to increase the octane number of gasoline, the purity requirements are relatively low, generally ≥95% can meet the requirements. (2) Used to produce high-purity isobutylene, its purity requirement is >99%. 8. Process Principle of MTBE l The raw material is pretreated and mixed C4 enters the dealkali tank (V-409) to remove amines, alkali, alkali metal ions, etc. contained in the free water of the mixed C4. Then it is fully mixed with the raw material methanol from the tank area and then enters the purifier (R-402A/B) to remove harmful substances in the raw material. l Principle of etherification reaction: Mixing isobutylene and methanol in C4 undergoes a synthesis reaction under the action of a strongly acidic styrene-based macroporous cation exchange resin catalyst to generate MTBE. side effects: (1) Isobutylene is hydrated to produce tert-butyl alcohol (TBA) (2) Isobutylene is dimerized to produce diisobutylene (DIB) (3) Methanol is dehydrated to produce dimethyl ether and water. Principle of catalytic distillation The reaction and distillation are carried out in the same tower, and the heat released by the reaction is used to vaporize the distillation material to ensure that the reaction is carried out at a constant temperature. l The product separation principle uses the property of C4 and methanol to form the lowest azeotrope, and uses azeotropic distillation method to separate MTBE from methanol and C4. l The principle of methanol recovery uses the difference in solubility of C4 and methanol in water, uses water as the extraction agent to separate methanol and C4, and then uses distillation to separate methanol and water. 9. Main influencing factors of MTBE reaction l Alcohol-dilute ratio, alcohol-ene ratio: The molar ratio of methanol to isobutylene is generally controlled to be 1.0~1.05. Alcohol-to-ene ratio is too large: It can increase the conversion rate of isobutylene, but the excess methanol not only increases the separation difficulty of the reactive distillation tower but also increases the load of the methanol recovery tower. Alcohol-to-ene ratio is too small: The isobutylene polymerization reaction occurs and a large amount of heat is released, causing the reactor to overheat and burn out the catalyst. l Reaction temperature The reaction temperature not only affects the conversion rate of isobutylene, but also affects the selectivity of MTBE, the service life of the catalyst and the reaction speed. l The production temperature is generally 50~70℃. If the temperature exceeds 80℃, side reactions will increase and the catalyst life will be shortened. If the temperature exceeds 120℃, the catalyst will become deactivated. 10. The process flow of MTBE describes that the raw material methanol and the raw material C4 are used to carry out the etherification reaction of enol in the etherification reactor at a molar ratio of 1.0 to 1.05. The reaction temperature is 50 to 70°C. The reacted material enters the catalytic distillation tower, and the reaction continues under the condition of adding methanol. The generated MTBE and unreacted raw materials are in the catalytic distillation tower. Inside, the product is separated while reacting. The product MTBE is obtained at the bottom of the tower, and the azeotrope of C4 and methanol is obtained at the top of the tower. Part of it is refluxed, and the other part is taken out and enters the bottom of the methanol extraction tower. The extraction agent water enters the extraction tower from the top of the tower. According to the difference in solubility of methanol and C4 in water, C4 is separated from methanol. An aqueous solution of methanol is obtained at the bottom of the tower, and C4 is obtained at the top of the tower. ； The methanol aqueous solution coming out of the bottom of the water washing tower enters the methanol recovery tower, and ordinary distillation is used to separate methanol and water. The separated water is pumped to the water washing tower for extraction agent recycling, and the separated methanol is recycled as a reaction raw material.