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1. Production process of Tianjin Zhonghe Chemical Plant Maleic anhydride is an important intermediate in chemical products, widely used in the production of unsaturated polyester resins, 1,4-succinic acid, tetrahydrofuran, fumaric acid, tartaric acid, etc. The main production methods of succinic acid include benzene oxidation, butene oxidation, and n-butane oxidation, but benzene oxidation is still the main method. Using benzene as raw material, the solidification point of cis acid is 52 degrees, and benzene vaporizes at 80 degrees. Xylene is a colorless and transparent oily liquid that is insoluble in water at room temperature. It can form azeotropes with water at a certain temperature. The oxidation of this substance is a combination of parallel and serial reactions, and maleic anhydride is prone to further oxidation, requiring the selection of a good catalyst. The commonly used catalysts are metal oxides, V2O5 (vanadium pentoxide), MO2O3 (molybdenum trioxide), which are coated on the reaction support to exert their effects. An exothermic medium, namely molten salt, is also required to participate in the reaction process. Its main components are nitrates (KNO3 and NaNO2), which are white flakes with a melting point of 140 degrees and a boiling point of 480 degrees. It is a low melting point mixture and an excellent high-temperature heat carrier. Special attention should be paid to prevent the molten salt from overheating and decomposing during the reaction process to avoid explosion. 1. Reaction 2. Absorption 3. Constant boiling dehydration 4. Intermittent distillation (1) Reaction: The benzene in the benzene tank is measured by a rotary flow meter and pumped to the benzene vaporizer by a benzene pump to vaporize the benzene into benzene vapor. At the same time, the air is pressurized by a centrifugal fan and exchanges heat with the high-temperature gas discharged from the reaction in the preheater. After reaching a certain temperature, it is mixed with benzene vapor to achieve a benzene content of 1% -2% in the air. The mixed gas is introduced from the top into a fixed bed reactor with thousands of tubes filled with vanadium molybdenum catalyst. Due to the strong exothermic nature of the reaction, a portion of the heat is transferred using molten salt circulating in the reactor. The molten salt is cooled in the molten salt heat exchanger, and the discharged water vapor is passed to the steam storage tank for unified use in the factory. （2） The absorbed product is carefully discharged from the bottom of the reactor, heated in the preheater cover, and then passed to a partial condenser for partial condensation with warm water. When maleic anhydride cools to dew point, it becomes liquid and flows into the crude anhydride tank for distillation through anhydride gas separation. The remaining product still contains a large amount of maleic anhydride. At this time, the material can be passed to the absorption tower for water absorption. When the concentration of cis acid in the absorption tower reaches saturation (30%), the material can be discharged. Transfer the acid to the concentrated acid tank for subsequent processes. At this point, the exhaust gas only contains carbon dioxide, water, and nitrogen, so it can be directly discharged into the air. （3） The concentrated acid produced by constant boiling dehydration is pumped into the acid water evaporator for concentration. Through a gas-liquid separation device, the separated water va

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