MTBE production from C4 after etherification

The MTBE/1-butene plant consists of two units: the MTBE unit and the 1-butene unit. It mainly includes four process systems: (1) the etherification reaction system, which includes a cylindrical external circulation reactor. (2) Catalytic distillation system, including: catalytic distillation column. (3) Methanol washing and recovery system, including: methanol washing tower and methanol recovery tower. (4) Butene-1 distillation system, comprising: two sets of columns, namely the first distillation column (light-end removal column) and the second distillation column (heavy-end removal column). 1.3 The main product is methyl tert-butyl ether, abbreviated as MTBE. The reaction equation is as follows: The main by-products include isobutylene dimers, dimethyl ether, tert-butanol, 2-butene, methyl sec-butyl ether, etc. The reaction equations are as follows: (CH3)2-C=CH2 + (CH3)2-C=CH2 → [(CH3)2-CH-CH2-]2 (dimerization reaction); CH3OH + CH3OH → CH3OCH3 + H2O (dehydration reaction); (CH3)2-C=CH2 + H2O → (CH3)3-C-OH (hydration reaction); CH2=CHCH2CH3 ↔ CH3CH=CHCH3 (isomerization reaction); CH2=CHCH2CH3 + CH3OH → CH3CH2C(CH3)-O-CH3 (TAME formation). Methanol molecules first adsorb onto the active sites of the catalyst, while isobutane molecules form a carbocation, after which MTBE is produced. If the catalyst sites are filled with water, methanol molecules cannot be adsorbed; therefore, it is necessary to remove the water from the catalyst. 1.5 The process technology employed: The MTBE unit uses etherification reactions combined with catalytic distillation. The etherification reaction unit employs series reactor technology and is designed as three fixed-bed reactors, which are fixed-bed cylindrical reactors for external circulation cooling and heat extraction ； Online catalyst replacement is enabled, ensuring high activity and high conversion rate of the etherification reaction catalyst. The reactive distillation unit employs azeotropic distillation technology and catalytic reactive distillation technology. Catalytic distillation is a technique that combines catalytic reaction and distillation separation within a single column. Under the action of the catalyst in the reaction section, MTBE is produced and separated out promptly, disrupting the equilibrium of the reaction and thereby increasing the driving force for the MTBE synthesis. In this way, reaction and separation proceed simultaneously until the reaction is complete. The key to catalytic distillation technology is the catalyst packing structure, which adopts a bundled catalyst packing design. Through reactive distillation for deep etherification, the isobutylene conversion rate is ensured to be over 99.8%, with the purity of the MTBE product exceeding 98.2%. The butene-1 unit employs precision distillation technology. Since butene-1 is in the middle fraction of mixed C4 hydrocarbons, two separation steps are required to obtain butene-1 product. This process follows a sequence of first removing the fractions lighter than butene-1, such as C3 and isobutane, and then removing the fractions heavier than butene-1, such as n-butane and cis/trans-butene-2. Since the boiling points of butene-1 and its adjacent components differ by very little, both distillation columns are relatively tall; therefore, it is necessary to construct and install each of these two distillation columns in two sections. The tray type used is a conventional floating valve tray. 2.1 Etherification unit: The raffinate tetrahydrocarbon obtained from the butadiene plant is mixed with methanol in a alcohol-to-olefin ratio of 1.02:1 (molar ratio of methanol to isobutylene). On the beds of strongly acidic cationic resin catalysts in three etherification reactors, the isobutylene present in the raffinate tetrahydrocarbon reacts with methanol to produce methyl tert-butyl ether (MTBE). After passing through the three etherification reactors, the conversion rate of isobutylene is required to be over 93%. 2.2 Catalytic Distillation Unit: The unreacted isobutylene from the etherification reactor enters the mixed-phase reaction section of the reactive distillation column; at the same time, a certain amount of methanol is added to the column, with an alcohol-to-olefin ratio maintained at 2.50:1. There, it continues to undergo etherification reactions with methanol in each catalyst bed. Meanwhile, conventional distillation methods are used to separate the MTBE produced as a result of these reactions from the other C4 fractions and methanol, thereby facilitating the progress of the etherification reactions in the desired direction. The heat of reaction is absorbed by the vaporization of some of the material, thereby preventing overheating of the catalyst bed. The carbon tetrafluoride after the reaction forms an azeotrope with methanol and is distilled out from the top of the tower. The bottom of the tower yields qualified MTBE product. After catalytic distillation, the conversion rate of isobutylene is required to be over 99.8%. The etherification reaction is a reversible exothermic reaction, and the strongly acidic cationic resin catalyst exhibits high selectivity. The by-products mainly include isobutylene dimers, dimethyl ether, tert-butanol, 2-butene, methyl sec-butyl ether, etc. The aforementioned side products have a high octane rating, and a small amount remaining in the MTBE product does not affect its suitability as a gasoline additive. 2.3 Methanol washing and recovery unit: Methanol washing is based on the principle of liquid-liquid extraction. Water, acting as the extractant, is introduced from the top of the tower, while ether-treated tetrahydrocarbons (the components remaining after isobutylene is removed through etherification) serve as the dispersed phase and are introduced from the bottom of the tower. This allows the ether-treated tetrahydrocarbons and water to come into counter-current contact on the tray surfaces. Utilizing the difference in solubility of methanol and tetrahydrocarbons in water, methanol dissolves in the water, while the tetrahydrocarbons and methanol-water mixture settle apart due to differences in density, thereby removing methanol from the ether-treated tetrahydrocarbons. Methanol-water mixture enters the recovery tower, and by taking advantage of the difference in boiling points between methanol and water, they are separated using conventional distillation methods, thereby achieving the recovery of methanol. 2.4 Butene-1 refining unit: The refinement of 1-butene is based on the principles of conventional pressure distillation. That is, in the de-lightening tower, the carbon four fraction after etherification has its light components such as carbon three and isobutane removed, and water is removed through azeotropic distillation ； In the degassing tower, heavy components such as cis-2-butene, trans-2-butene, and n-butane are removed to obtain polymer-grade 1-butene. Since the boiling points of butene-1 and its adjacent components differ by very little, both distillation columns are relatively tall; these two columns are further divided into upper and lower sections each. The raffinate C4 fraction from the butadiene extraction unit is used as the feedstock for this unit

Actually, heterogenization imagination isn’t that difficult; just like those older people in our facility before, they all wanted to use the heterogenization device. Heterogenization is the simplest: 2 compressors, a degassing tower, and a reactor. The catalyst is produced in the United States, and the price is quoted per KG. Our device is used for C4 after etherification. I don’t know the specifics of the isomerization process either; I wasn’t assigned to the isomerization unit.

Reply to 3# k68315404: It seems we have something similar to the structure you mentioned here. Where are you from? Could you share more relevant experience?