Maleic anhydride-maleic anhydride (Maleic anhydride-maleic anhydride)

It is used as raw materials for producing 1,4-butanediol, γ-butyrolactone, Tetrahydrofuran, succinic acid, unsaturated polyester resin, alkyd resin, etc. It is also used for medicine and pesticide; It acts as collector in metal mineral processing; used for organic synthesis, also used as synthetic fiber Intermediate; Maleic anhydride also known as maleic anhydride, horse..

1. The main production methods of maleic anhydride include benzene oxidation, butene oxidation and n-butane oxidation, but benzene oxidation is still the main method. 1. Benzene oxidation benzene oxidation under the action of V-Mo-P catalyst, oxidation reaction occurs in fiexed bed, generating maleic anhydride, the reaction temperature is 365 ℃ (the reaction bed can also be used boiling bed, but the consumption is high). Then, it is absorbed with water to generate maleic acid, and then it is dehydrated and rectified by azeotropic, and the finished product is obtained doctor blade. 2. Butane (or butene) oxidation butane (or butene) oxidation under the action of V-Mo catalyst, through air or oxygen oxidation to generate maleic anhydride, reaction temperature 350-400 ℃. Then it is absorbed by water, dehydrated and refined to obtain the finished product. (1) the benzene oxidation reactor oxidizes into maleic anhydride by air in the presence of V, MO, Ti and P catalysts, absorbs water into maleic acid aqueous solution, and then uses xylene for azeotropic distillation to dehydrate maleic anhydride, finally, the finished product is obtained by vacuum distillation. 1. The oxidation reactor is a boiling bed with a diameter of 1500mm and a total height of 17500mm, and is loaded into the micro spherical vanadium-molybdenum catalyst 2000kg. Before driving, heat the catalyst layer in the boiling bed to 350℃ with hot air for several hours. Then the cold air is sprayed into the catalyst layer at a flow rate of 150kg per hour, the reaction temperature is controlled to about 360℃, and the reaction gas is separated from the catalyst through the top of the boiling bed and then transported to the absorption system. The oxidation rate is about 45%. 2. Water absorption the reaction gas is cooled by spraying water Venturi, and then enters the water ball spray absorber with a diameter of 1400mm and a height of 7000mm. The maleic anhydride vapor in the reaction gas is absorbed by water, it becomes a maleic acid solution with a content of about 30%. 3. Azeotropic dehydration and distillation in the tower kettle of azeotropic dehydration tower, add 3000kg mixed xylylene to heat it to a temperature higher than 136 ℃, and the dimethylbenzene boiling in the kettle, at this time, 30% of the maleic acid solution is sent from the middle of the tower, and the flow rate per hour is about 350kg. The water in the acid solution and the dimethylbenzene form an azeotrope to steam out from the top, and the maleic acid is dissolved in dimethylbenzene after losing water to anhydride, flow down to the tower kettle. When the total amount of acid liquid to be fed reaches 6000kg, the content of maleic anhydride in the dimethylbenzene in the kettle is about 30%. The solution is transported to the vacuum distillation kettle, and the kettle temperature is 100℃, the tower top temperature is 110℃, under the condition of vacuum degree of 93.3kpa, industrial distillation produces maleic anhydride. The yield of water absorption to distillation is 90% partial yield 40%. The method consumes 2000kg of benzene and 140kg of xylene per ton of maleic anhydride. (2) the mixture of benzene and air preheated by benzene oxidation-combined method is sent to the tubular fiexed bed reactor and contacted with the catalyst for reaction. The reaction gas is cooled to about 150℃ through two gas cooler, then, the part of the condenser is cooled by water to a temperature slightly higher than the melting point of maleic anhydride (60℃), and about 50%-60% of maleic anhydride is condensed into liquid state, the remaining 40%-50% maleic anhydride is absorbed into 40% maleic acid solution with dilute maleic acid solution. Dehydrated into 100% maleic acid solution through thin film evaporator, then into dehydrater dehydrated into crude anhydride, and finally refined through continuous vacuum distillation column to obtain maleic anhydride finished product. (3)C4 olefin method this method uses N-butene, butadiene and other effective components in the mixed C4 fraction as raw materials, and air (or oxygen) maleic anhydride is generated by gas phase oxidation reaction under the action of V2O5-P2O5 series catalyst, in which n-Butene is first hydrogenated to butadiene during the reaction, and then oxidized to maleic anhydride. The process is as follows: the C4 fraction is mixed with air and enters the fluidized bed oxidation reactor, contacting with the catalyst in the reactor to generate maleic anhydride. The heat of reaction is removed from the cooling coil through water and generates high-pressure steam. The temperature is 400-500 ℃. After the reaction, maleic anhydride in the gas is obtained from maleic acid solution through absorption tower, then concentrated and dehydrated, and finally the product is obtained by simple distillation. (4) n-butane oxidation n-butane oxidation process takes n-butane as raw material and generates maleic anhydride by gas phase oxidation reaction under the action of V2O5-P2O5 series catalyst. In addition to carbon monoxide, carbon dioxide and water, side reactions also generate aldehyde, ketone, acid and other compounds. According to the technology published in the public, it is also divided into fiexed bed method and fluidized bed method. The process of fiexed bed method (such as Halcon/SD method) is as follows: air is filtered through a filter and compressed to the required reaction pressure; Butane is vaporized in carburetor, after heating, it is mixed with compressed air, sent to the reactor together, and the reaction heat is removed by circulating molten salt. The reaction gas is cooled to heat exchange with soft water, and cooled to above the melting point of maleic anhydride. About 50% of maleic anhydride condenses and precipitates, enters the refined anhydride storage tank, and then pumps it into the refining process for refining. The tail gas from the top of the separator is washed, and all the uncondensed maleic anhydride is converted into maleic acid. After the storage tank, it is sent to the dehydration tower for dehydration, and finally it is sent to the refining tower for refining to obtain the product maleic anhydride. (5) when phthalic anhydride by-product method produces phthalic anhydride from O-xylene, a certain amount of maleic anhydride products can be obtained by-product, and its output is about 5% of that of phthalic anhydride. In the production of phthalic anhydride, the reaction tail gas is discharged into the atmosphere after removing organic matter by washing tower. Washing liquid is maleic anhydride and a small amount of impurities such as benzoic acid and phthalic acid. After concentration refining and heating dehydration, maleic anhydride product is obtained. 4. Dehydrate malic acid to maleic anhydride, and then refine with trichloromethane: