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1. Introduction to maleic anhydride
Maleic anhydride, also known as MAH, is the anhydride of maleic acid. It is a colorless or white solid with acid taste at room temperature, and its molecular formula is C4H2O3. In the early stage, maleic anhydride was prepared by catalytic oxidation of benzene. But in order to reduce the production cost, it is prepared by n-butane oxidation. And maleic anhydride applications are very extensive.

2. Synthesis of maleic anhydride synthesis
Benzene oxidation process
Under the action of catalyst with V2O5 MnO3 as active component and α-Al2O3 as carrier, benzene vapor reacts with air (or oxygen) to form maleic anhydride. Benzene oxidation process is a traditional production method for maleic anhydride, and its technology is mature and reliable. The main technologies include USA SD process, alusuisle / UCB process and catalytic chemical process in Japan, among which SD process is the most widely used.

C4 olefin process
With butene and butadiene as raw materials, maleic anhydride is produced by gas oxidation reaction with air (or oxygen) under the action of V2O5－P2O5 catalyst. During the reaction, n-butene is dehydrogenated to butadiene, and then oxidized to maleic anhydride. In the reaction process, besides the main products, carbon monoxide, carbon dioxide, water and a small amount of acetaldehyde, acetic acid, acrolein and furan are also produced as by-products. The unit consumption of raw materials is high and the efficiency is low. This method has been gradually eliminated.

By-produce process of maleic anhydride production from benzene
When phthalic anhydride is produced from o-xylene, a certain amount of maleic anhydride can be obtained as by-product, and its yield is about 5% of that of phthalic anhydride. In the production of phthalic anhydride, the reaction tail gas is discharged into the atmosphere after the organic matter is removed by the washing tower. The washing liquid is maleic anhydride and a small amount of benzoic acid, phthalic acid and other impurities. After concentration and purification and heating dehydration, the maleic anhydride product is obtained.

N-butane oxidation process
In the process of n-butane oxidation, n-butane is used as raw material to produce maleic anhydride by gas-phase oxidation reaction in the presence of V2O5-P2O5 catalyst. Since its industrialization by Monsanto Company in 1974, the process has been developed rapidly due to the low price of raw materials, less environmental pollution and abundant n-butane resources, which represents the development trend of maleic anhydride production process.

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