Method and device for preparing maleic anhydride by oxidizing n-butane

Abstract

The invention discloses a method and a device for preparing maleic anhydride by oxidizing n-butane, and relates to the technical field of maleic anhydride synthesis. According to the method, n-butane and oxygen-containing gas are subjected to catalytic oxidation in a pressurized reactor, and the reaction temperature is reduced and the reaction space velocity is increased, so that the selectivity of generating maleic anhydride through oxidation of n-butane is improved, and the generation of by-products such as carbon monoxide and carbon dioxide is reduced; maleic anhydride rich oil and maleic anhydride tail gas are obtained after maleic anhydride material flow obtained through reaction is cooled and absorbed, the maleic anhydride tail gas is divided into two gas flows to be recycled, one gas flow is pressurized and then serves as raw material gas to be returned to a pressurization reactor for reaction, and the other gas flow enters a conventional reactor for catalytic oxidation; the utilization rate of n-butane and the total conversion rate of the reaction can be obviously improved, and gases such as carbon dioxide and carbon monoxide in the system are not accumulated in the pressurized reaction system; the maleic anhydride and the maleic anhydride tail gas are separated by adopting a two-stage pressurized absorption method, so that the water content in the separated maleic anhydride product is lower than 0.2%.

Description

Technical Field

[0001] The present invention relates to the technical field of maleic anhydride synthesis, and more specifically, to a method and apparatus for preparing maleic anhydride by oxidizing n-butane. Background Art

[0002] Maleic anhydride, also known as cis-butenedioic anhydride or maleic anhydride, is an important organic chemical raw material and is currently the world's third largest anhydride after phthalic anhydride and acetic anhydride. Maleic anhydride is widely used in industries such as petrochemicals, food processing, pharmaceuticals, and building materials, and is an important raw material for producing a variety of chemical products, such as unsaturated polyester resins, alkyd resins, maleic acid, fumaric acid, γ-butyrolactone, 1,4-butanediol, and tetrahydrofuran.

[0003] Currently, according to the different reaction raw materials, the industrial production routes of maleic anhydride can be mainly divided into the n-butane oxidation method, the benzene oxidation method, the C4 olefin method, and the phthalic anhydride by-product method. Among them, the benzene oxidation method is the most widely used. However, due to the limited benzene resources, the technologies for producing maleic anhydride using C4 olefins and n-butane as raw materials have been widely studied. In recent years, due to the advantages of low price of n-butane raw materials and high product yield, the n-butane oxidation method has occupied a dominant position in maleic anhydride production.

[0004] The n-butane oxidation method uses n-butane as the raw material and undergoes a gas-phase oxidation reaction under the action of a vanadium phosphorus oxygen catalyst to produce maleic anhydride. The main reactions are as follows:

[0005] C4H 10 +3.5O2→C4H2O3+4H2O; ΔΗ=-1261kJ / mol;

[0006] At the same time, other side reactions also occur during the reaction, producing by-products such as carbon monoxide, carbon dioxide, acetic acid, and acrylic acid:

[0007] C4H 10 +4.5O2→4CO+5H2O; ΔΗ=-1525kJ / mol;

[0008] C4H 10 +6.5O2→4CO2+5H2O; ΔΗ=-2654kJ / mol;

[0009] C4H 10 +2.5O2→2CH3COOH+H2O; ΔΗ=-992kJ / mol;

[0010] C4H 10 +2.5O2→4 / 3CH2CHCOOH+7 / 3H2O; ΔΗ=-887kJ / mol;

[0011] It can be seen that the oxidation of n-butane to maleic anhydride is a strongly exothermic reaction, and a large amount of heat is also released in side reactions. The heat released by the oxidation of n-butane in a fixed-bed tubular reactor is usually removed from the reactor by a circulating coolant (usually molten salt) and steam is generated by a molten salt cooler.

[0012] The conversion rate, selectivity and yield of the n-butane oxidation reaction are related to the catalyst and process conditions of the reaction. Among them, the reaction process conditions with greater influence include reaction temperature, pressure, n-butane feed concentration, space velocity, etc. The reaction conversion rate and selectivity often cannot be improved simultaneously. When the reaction temperature is increased, the reaction conversion rate can be improved, but the reaction selectivity is greatly reduced; when the reaction temperature is decreased, the selectivity can be improved, but the reaction conversion rate is decreased due to the decrease in temperature. Similarly, the reaction space velocity also has an opposite effect on the conversion rate and selectivity. Since flammable gases such as n-butane are prone to explosion when mixed with air, the n-butane feed concentration often needs to be controlled outside the explosion limit range and cannot exceed the lower limit of the explosion limit, which greatly limits the degree of increasing the n-butane feed concentration to improve the reaction conversion rate. At present, under appropriate reaction temperature, pressure, space velocity and n-butane feed concentration, the reaction conversion rate can generally reach 80-85 mol%, the selectivity can reach 67-70 mol%, and the maleic anhydride yield is about 60%. There is still a large room for improvement in the conversion rate, selectivity and yield of the n-butane oxidation reaction.

[0013] Due to the limitation of the conversion rate, the maleic anhydride tail gas contains 15-20% unreacted n-butane. In order to improve the utilization rate of n-butane and the maleic anhydride yield, the prior art generally considers recycling the maleic anhydride tail gas back to the reactor. Although the existing tail gas recycling methods improve the utilization rate of n-butane and slightly increase the total conversion rate and yield of n-butane, there are still problems such as low maleic anhydride selectivity and many reaction by-products. In addition, the tail gas recycling ratio is still too low during tail gas recycling, and most of the tail gas containing unreacted n-butane is directly burned in the incinerator, and there are still problems such as serious waste of raw materials, large incinerator load and large carbon dioxide emissions.

[0014] Therefore, there is an urgent need to develop a new process for the oxidation of n-butane to maleic anhydride to improve the selectivity and conversion rate of the reaction simultaneously.

[0015] In view of this, the present invention is specifically proposed. Summary of the Invention

[0016] The purpose of the present invention is to provide a method and device for preparing maleic anhydride by oxidizing n-butane, aiming to improve the reaction selectivity and conversion rate simultaneously.

[0017] The present invention is implemented as follows:

[0018] In a first aspect, the present invention provides a method for preparing maleic anhydride by the oxidation of n-butane, comprising: catalytically oxidizing n-butane and an oxygen-containing gas in a pressurized reactor to obtain a maleic anhydride stream;

[0019] After cooling and absorption of the maleic anhydride stream, maleic anhydride-rich oil and maleic anhydride tail gas are obtained;

[0020] The maleic anhydride tail gas is divided into two gas streams. One gas stream is pressurized and returned as a raw material gas to the pressurized reactor for reaction, and the other gas stream enters a conventional reactor to carry out catalytic oxidation with an oxygen-containing gas and n-butane;

[0021] Among them, the reaction temperature of the pressurized reactor is 320 °C - 450 °C, the reaction space velocity is 1500 h -1 -2500 h -1 , and the reaction pressure is 300 kPaA - 600 kPaA; the reaction pressure of the conventional reactor is 200 kPaA - 300 kPaA.

[0022] In an alternative embodiment, the reaction temperature of the pressurized reactor is 340 °C - 370 °C, the reaction space velocity is 1700 h -1 -2000 h -1 , and the reaction pressure is 450 kPaA - 550 kPaA;

[0023] Preferably, the flow rate ratio of the maleic anhydride tail gas returned to the pressurized reactor to the gas stream entering the conventional reactor is (3 - 8):1; more preferably (4 - 7):1.

[0024] In an alternative embodiment, in the mixed raw materials entering the pressurized reactor, the volume fraction of n-butane in the mixed raw materials is controlled to be 1.0% - 1.8%, the volume fraction of carbon monoxide is 0% - 5%, and the volume fraction of oxygen in the mixed raw materials is 13% - 23%;

[0025] Preferably, the oxygen-containing gas introduced into the pressurized reactor is oxygen-enriched air, and the volume fraction of oxygen is 30% - 90%; the flow rate ratio of the maleic anhydride tail gas returned to the pressurized reactor to the introduced oxygen-containing gas is (3 - 5):1;

[0026] More preferably, the preparation process of the oxygen-enriched air includes: membrane separation or pressure swing adsorption separation of air.

[0027] In an alternative embodiment, part of the maleic anhydride tail gas is mixed with an oxygen-containing gas and a raw material gas containing n-butane to form a mixed raw material and enter the conventional reactor for reaction, and the reaction temperature is controlled to be 410 °C - 480 °C, and the reaction pressure is 200 kPaA - 300 kPaA;

[0028] Preferably, in the mixed raw materials entering the conventional reactor, the volume fraction of n-butane is 1.0%-2.0%, and the volume fraction of oxygen is 13%-23%;

[0029] Preferably, the oxygen-containing gas introduced into the conventional reactor is enriched air and / or air, and the volume fraction of oxygen in the enriched air is 30%-90%.

[0030] In an alternative embodiment, both the pressurized reactor and the conventional reactor are filled with an oxidation catalyst, and the oxidation catalyst is a vanadium phosphorus oxygen catalyst.

[0031] In an alternative embodiment, after the maleic anhydride stream is cooled down, it is treated in a two-stage absorption tower. The unabsorbed maleic anhydride tail gas is output from the top of the second-stage absorption tower, and the maleic anhydride tail gas is washed with water and then divided into two gas streams;

[0032] Preferably, after the maleic anhydride stream is cooled down, it is subjected to primary pressurized absorption to obtain primary rich oil and primary absorption tail gas, and the primary absorption tail gas is subjected to secondary pressurized absorption to obtain secondary rich oil and maleic anhydride tail gas; wherein, both the primary pressurized absorption and the secondary pressurized absorption are in countercurrent contact with the absorbent in the absorption tower;

[0033] More preferably, the operating temperature of the primary pressurized absorption is 80°C - 120°C, the operating pressure is 300 kPaA - 400 kPaA, and the mass fraction of water in the primary rich oil is controlled to be less than 0.2%;

[0034] More preferably, the operating temperature of the secondary pressurized absorption is 60°C - 100°C, and the operating pressure is 200 kPaA - 300 kPaA;

[0035] More preferably, the absorbents used in the processes of primary pressurized absorption and secondary pressurized absorption are each independently selected from at least one of dibutyl phthalate, diisobutyl hexahydrophthalate, diisopropyl phthalate, and water; further preferably dibutyl phthalate.

[0036] In an alternative embodiment, the primary rich oil is subjected to primary flash evaporation to obtain primary flash evaporation tail gas and primary flash evaporation rich oil; the secondary rich oil is subjected to secondary flash evaporation to obtain secondary flash evaporation tail gas and secondary flash evaporation rich oil;

[0037] Preferably, the primary flash evaporation tail gas and the secondary flash evaporation tail gas enter the tail gas scrubbing tower and are scrubbed with the absorbent to obtain scrubbing tower rich oil; the scrubbing tower rich oil is recycled to the primary pressurized absorption stage;

[0038] Preferably, the primary flash evaporation rich oil is divided into two parts, one part is withdrawn, and the other part is recycled to the primary pressurized absorption stage;

[0039] Preferably, the secondary flash-rich oil is divided into two parts, one part is recycled back to the first-stage pressurized absorption stage, and the other part is recycled back to the second-stage pressurized absorption stage.

[0040] In a second aspect, the present invention provides an apparatus for implementing the method according to any one of the foregoing embodiments, comprising:

[0041] A pressurized reactor, on which a feed port is provided, the feed port is communicated with a n-butane raw material gas pipeline and an oxygen-containing gas pipeline, and the pressurized reactor is filled with an oxidation catalyst;

[0042] A post-treatment unit for the pressurized reactor, the post-treatment unit for the pressurized reactor includes an absorption tower and a washing tower, the discharge port of the pressurized reactor is communicated with the absorption tower, an absorbent pipeline is connected to the absorption tower, and the top of the absorption tower is communicated with the washing tower; the gas flow output from the top of the washing tower is divided into two paths, one path of the gas flow is communicated with the pressurized reactor after passing through a booster;

[0043] A conventional reactor, the other path of the gas flow output from the top of the washing tower is communicated with the feed port of the conventional reactor, and the feed port on the conventional reactor is also connected with an oxygen-containing gas pipeline and a n-butane raw material gas pipeline, and the conventional reactor is filled with an oxidation catalyst.

[0044] In an alternative embodiment, the absorption tower in the post-treatment unit for the pressurized reactor includes a first-stage pressurized absorption tower and a second-stage pressurized absorption tower;

[0045] The discharge port of the pressurized reactor is communicated with the bottom feed port of the first-stage pressurized absorption tower, the top of the first-stage pressurized absorption tower is connected with an absorbent pipeline to make the maleic anhydride stream and the absorbent contact countercurrently in the first-stage pressurized absorption tower; the top of the first-stage pressurized absorption tower is communicated with the bottom of the second-stage pressurized absorption tower, the top of the second-stage pressurized absorption tower is connected with an absorbent pipeline, and the top of the second-stage pressurized absorption tower is communicated with the washing tower, and a detergent pipeline is also connected to the washing tower;

[0046] The discharge port of the conventional reactor is communicated with the bottom of another absorption tower, and an absorbent pipeline and a gas discharge pipeline are also connected to the other absorption tower.

[0047] In an alternative embodiment, the post-treatment unit for the pressurized reactor further includes a first-stage flash tower, a second-stage flash tower and a flash tail gas washing tower, the bottom of the first-stage pressurized absorption tower is communicated with the first-stage flash tower, the bottom of the first-stage flash tower obtains the first-stage flash-rich oil and the top of the first-stage flash tower obtains the first-stage flash tail gas; the bottom of the second-stage pressurized absorption tower is communicated with the second-stage flash tower, the bottom of the second-stage flash tower obtains the second-stage flash-rich oil and the top of the second-stage flash tower obtains the second-stage flash tail gas;

[0048] The tops of both the first-stage flash tower and the second-stage flash tower are connected to the bottom of the tail gas scrubbing tower. The top of the tail gas scrubbing tower is also connected to an absorbent delivery pipeline, and the bottom of the tail gas scrubbing tower is connected to the first-stage pressurized absorption tower;

[0049] The bottom of the first-stage flash tower is divided into two paths. One path is connected to the product pipeline, and the other path is connected to the first-stage pressurized absorption tower. The bottom of the second-stage flash tower is divided into three paths. The first path is connected to the second-stage pressurized absorption tower, the second path is connected to the middle part of the first-stage pressurized absorption tower, and the third path is connected to the upper part of the first-stage pressurized absorption tower.

[0050] The present invention has the following beneficial effects: Catalytic oxidation of n-butane and oxygen-containing gas is carried out in a pressurized reactor. By reducing the reaction temperature of the pressurized reactor and increasing the reaction space velocity, the selectivity of n-butane oxidation to maleic anhydride is improved, and the generation of by-products such as carbon monoxide and carbon dioxide is reduced. The maleic anhydride stream obtained from the reaction of the pressurized reactor is cooled and absorbed to obtain maleic anhydride-rich oil and maleic anhydride tail gas. The maleic anhydride tail gas is divided into two gas streams for recycling. One gas stream is pressurized and returned to the pressurized reactor as a raw material gas for reaction, and the other gas stream enters a conventional reactor for catalytic oxidation with oxygen-containing gas and n-butane, which can significantly improve the utilization rate of n-butane and the total conversion rate of the reaction, ensure that gases such as carbon dioxide and carbon monoxide in the system do not accumulate in the pressurized reaction system, and greatly reduce the load of the incinerator and the VOCs emissions. Therefore, the method provided by the present invention can improve the selectivity and conversion rate of the reaction simultaneously and has a very good application prospect. Brief Description of the Drawings

[0051] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0052] Figure 1 It is a process flow diagram for preparing maleic anhydride by oxidizing n-butane provided by the present invention.

[0053] Icons: a - Pressurized oxidation reactor; b - First-stage pressurized absorption tower; c - First-stage flash tower; d - Second-stage pressurized absorption tower; e - Second-stage flash tower; f - Tail gas scrubbing tower; g - Water washing tower; h - Circulation booster; i - Conventional reactor; j - Absorption tower;

[0054] 1 - n-butane feed gas pipeline; 2 - oxygen-containing gas pipeline; 3 - mixed feedstock; 4 - maleic anhydride stream; 5 - primary tower absorbent; 6 - primary absorption tail gas; 7 - primary rich oil; 8 - primary flash tail gas; 9 - rich oil; 10 - circulating solvent for primary pressurized absorption tower; 11 - secondary tower absorbent; 12 - maleic anhydride tail gas; 13 - secondary rich oil; 14 - secondary flash tail gas; 15 - secondary flash rich oil; 16 - circulating solvent for secondary pressurized absorption tower; 17 - absorbent for scrubbing tower; 18 - rich oil in scrubbing tower; 19 - water for water washing; 20 - tail gas after water washing; 21 - wastewater discharge from water washing; 22 - inlet of circulating booster; 23 - outlet of circulating booster; 24 - pressurized tail gas; 25 - oxygen-containing gas pipeline; 26 - n-butane feed gas pipeline; 27 - mixed feedstock; 28 - discharge from conventional reactor; 29 - absorbent; 30 - absorption tail gas; 31 - rich oil; 32 - make-up solvent for primary pressurized absorption tower. Detailed implementation manners

[0055] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. For those not specified in the embodiments, the conventional conditions or the conditions recommended by the manufacturer are followed. The reagents or instruments not specified by the manufacturer are all conventional products that can be obtained through commercial purchase.

[0056] Please refer to Figure 1 , an embodiment of the present invention provides a method for preparing maleic anhydride by oxidizing n-butane. Catalytic oxidation is carried out using a pressurized reactor a, and the generated tail gas is divided into two parts. One part is recycled to the pressurized reactor a for reaction, and the other part is recycled to a conventional reactor i for reaction. The specific steps are as follows:

[0057] S1. Pressurized reaction stage

[0058] Catalytic oxidation of n-butane and oxygen-containing gas is carried out in a pressurized reactor a. Except for the initial start-up stage, a part of the recycled tail gas is also introduced into the pressurized reactor a. Therefore, the feed gas input to the pressurized reactor a includes n-butane feed gas (which can be high-purity n-butane), oxygen-containing gas (which can be oxygen-enriched air) and a part of the recycled tail gas, that is, the mixed feedstock 3.

[0059] In some embodiments, the reaction temperature of the pressurized reactor a is 320°C - 450°C, the reaction space velocity is 1500h -1 -2500h -1 , and the reaction pressure is 300 kPaA - 600 kPaA; preferably, the reaction temperature of the pressurized reactor is 340°C - 370°C, and the reaction space velocity is 1700h -1 -2000h -1, the reaction pressure is 450 kPaA - 550 kPaA. By reducing the reaction temperature of the pressurized reactor a and increasing the space velocity, the selectivity of n-butane oxidation to maleic anhydride is improved, and the generation of by-products such as carbon monoxide and carbon dioxide is reduced. By increasing the reaction pressure of the pressurized reactor a, the absolute amount of n-butane in the mixed feed of the pressurized reactor a is increased. Within the explosion limit range, the reaction efficiency and production capacity of a single reactor are greatly improved, the production efficiency is increased, and the production cost is reduced.

[0060] Specifically, the reaction temperature of the pressurized reactor a can be 320 °C, 330 °C, 340 °C, 350 °C, 360 °C, 370 °C, 380 °C, 390 °C, 400 °C, 410 °C, 420 °C, 430 °C, 440 °C, 450 °C, etc., or any value between adjacent above-mentioned values; the reaction space velocity can be 1500 h -1 , 1600 h -1 , 1700 h -1 , 1800 h -1 , 1900 h -1 , 2000 h -1 , 2100 h -1 , 2200 h -1 , 2300 h -1 , 2400 h -1 , 2500 h -1 etc., or any value between adjacent above-mentioned values; the reaction pressure can be 300 kPaA, 350 kPaA, 400 kPaA, 450 kPaA, 500 kPaA, 550 kPaA, 600 kPaA, etc., or any value between adjacent above-mentioned values. Compared with the prior art, in the embodiment of the present invention, the reaction pressure of n-butane is increased by 1 - 2 times. By compressing and boosting the reaction raw material gas, the absolute amount of n-butane in the raw material gas is increased by 1 - 2 times, so that within the explosion limit range of the pressurized reactor, the reaction efficiency of a single reactor is also increased by 1 - 2 times, and the production capacity of the original device is increased by 1 - 2 times, greatly improving the production efficiency.

[0061] Furthermore, in the mixed raw materials entering the pressurized reactor a, the volume fraction of n-butane in the mixed raw materials is controlled to be 1.0% - 1.8%, the volume fraction of oxygen in the mixed raw materials is 13% - 23%, and the volume content of carbon monoxide is 0% - 5%. It is appropriate to control the ratio of the raw materials within the above range to control the combustible gas within the explosion limit range and increase the process operation stability.

[0062] Specifically, the mixed raw material consists of n-butane, oxygen-containing gas, and recycled tail gas. The volume fraction of n-butane in the entire mixed raw material can be 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, etc., or any value between the adjacent values above; the volume fraction of oxygen in the entire mixed raw material can be 18%, 19%, 20%, 21%, 22%, 23%, etc., or any value between the adjacent values above; the volume fraction of carbon monoxide can be 0%, 1%, 2%, 3%, 4%, 5%, etc., or any value between the adjacent values above.

[0063] Further, the oxygen-containing gas introduced into the pressure reactor a can be oxygen-enriched air, and the volume fraction of oxygen can be 30% - 90%, such as 30%, 40%, 50%, 60%, 70%, 80%, 90%, etc., or any value between the adjacent values above. The flow ratio of the maleic anhydride tail gas returned to the pressure reactor a to the introduced oxygen-containing gas can be (3 - 5):1, such as 3:1, 4:1, 5:1, etc., or any value between the adjacent values above. Since the oxygen content in the pressurized recycled tail gas is relatively low, in order to ensure the oxygen content of the feed in the pressure reactor a, a certain concentration of oxygen-enriched air is supplemented at the inlet of the pressure reactor a, so that the oxidation reaction efficiency of n-butane is higher, and ultimately the unreacted n-butane in the maleic anhydride tail gas can be recycled, thereby improving the total conversion rate of the reaction.

[0064] In some embodiments, the source of the oxygen-enriched air is not limited and can be obtained by membrane separation or pressure swing adsorption separation of air.

[0065] The type of oxidation catalyst filled in the pressure reactor is not limited and can be a catalyst for producing maleic anhydride from n-butane with more catalyst active sites and stronger strength. In some embodiments, the oxidation catalyst is a vanadium phosphorus oxygen type catalyst, and this type of catalyst can further improve the reaction rate and conversion rate.

[0066] S2. Post-treatment stage of the pressurized reaction

[0067] The maleic anhydride stream 4 generated by the pressure reactor a is cooled and absorbed to obtain maleic anhydride-rich oil and maleic anhydride tail gas. The maleic anhydride tail gas is divided into two gas streams. One gas stream is pressurized and returned to the pressure reactor a as a raw material gas for reaction, and the other gas stream enters the conventional reactor i to carry out catalytic oxidation with oxygen-containing gas and n-butane. After the small amount of n-butane contained in the recycled maleic anhydride tail gas in the conventional reactor i is further oxidized, it is sent to the incinerator for incineration and then discharged, ensuring that gases such as carbon dioxide and carbon monoxide do not accumulate in the pressurized reaction system, while greatly reducing the maleic anhydride tail gas emissions, reducing the load of the incinerator, and reducing VOCs emissions.

[0068] It should be noted that the inventor has improved the circulation mode of maleic anhydride tail gas, so that a part of the maleic anhydride tail gas returns to the pressurized reactor a after pressurization, and the other part enters the conventional reactor i for reaction, which can improve the utilization rate of n-butane and the total conversion rate of the reaction. The conventional reactor i can be a conventional reaction system. After discharging part of the tail gas to the conventional reaction system and continuously converting the unreacted n-butane, it can be sent to the incinerator for combustion and then discharged, ensuring that gases such as carbon dioxide and carbon monoxide do not accumulate in the pressurized reaction system, and greatly reducing the load of the incinerator and the VOCs emissions.

[0069] In some embodiments, the flow rate ratio of the maleic anhydride tail gas returning to the pressurized reactor to the flow rate of the gas entering the conventional reactor i is controlled to be (3 - 8):1; more preferably (4 - 7):1. By further controlling the flow rate ratio of the two gas streams, while improving the reaction conversion rate, it is possible to avoid excessive accumulation of carbon monoxide and carbon dioxide in the high-pressure reaction system, increasing the safety of the process operation. Specifically, the flow rate ratio of the maleic anhydride tail gas returning to the pressurized reactor to the gas entering the conventional reactor can be 4:1, 5:1, 6:1, 7:1, 8:1, etc., or any value between the adjacent values above. By regulating the flow rate ratio of the two gas streams in combination with the reaction condition control, the volume content of carbon monoxide in the mixed feed recycled back to the pressurized reactor a can be controlled to be 0% - 5%.

[0070] Furthermore, part of the maleic anhydride tail gas is mixed with an oxygen-containing gas and a raw material gas containing n-butane to form a mixed raw material and enter the conventional reactor i for reaction. In the mixed raw material entering the conventional reactor, the volume fraction of n-butane is 1.0% - 2.0%, and the volume fraction of oxygen is 13% - 23%; the reaction temperature is controlled to be 410°C - 480°C, and the reaction pressure is 200 kPaA - 300 kPaA. By optimizing the operating conditions of the conventional reactor, the n-butane can be utilized more fully, improving the utilization rate of the raw materials.

[0071] Specifically, in the mixed raw material entering the conventional reactor i, the volume fraction of n-butane can be 1.0%, 1.3%, 1.5%, 1.8%, 2.0%, etc., or any value between the adjacent values above; the volume fraction of oxygen can be 18%, 19%, 20%, 21%, 22%, 23%, etc., or any value between the adjacent values above. The reaction temperature of the conventional reactor can be 410°C, 420°C, 430°C, 440°C, 450°C, 460°C, 470°C, 480°C, etc., or any value between the adjacent values above; the reaction pressure can be 200 kPaA, 230 kPaA, 250 kPaA, 280 kPaA, 300 kPaA, etc., or any value between the adjacent values above.

[0072] In some embodiments, the oxygen-containing gas introduced into the conventional reactor i is enriched oxygen air and / or air. The volume fraction of oxygen in the enriched oxygen air is 30%-90%, such as 30%, 40%, 50%, 60%, 70%, 80%, 90%, etc., or any value between adjacent above values. The source of the enriched oxygen air is not limited. It can be obtained by membrane separation or pressure swing adsorption separation of air, or it can be a commercially available product.

[0073] The type of the oxidation catalyst filled in the conventional reactor i is not limited, and it can be a commonly used catalyst for producing maleic anhydride from n-butane. In some embodiments, the oxidation catalyst is a vanadium phosphorus oxygen type catalyst, and this type of catalyst can further improve the reaction rate and conversion rate.

[0074] Furthermore, the maleic anhydride stream contains maleic anhydride, unreacted inert gas, oxygen, n-butane, and by-products generated during the reaction, such as carbon dioxide, carbon monoxide, water vapor, volatile organic compounds acrylic acid and acetic acid, etc. After cooling down the maleic anhydride stream, it is treated in a two-stage absorption tower. The unabsorbed maleic anhydride tail gas is output at the top of the second-stage absorption tower. After washing the maleic anhydride tail gas with water, it is divided into two air streams. By using the two-stage absorption process, the maleic anhydride in the product is fully absorbed, avoiding the recycling of maleic anhydride back to the reactor.

[0075] In a preferred embodiment, the two-stage absorption process may include two stages: primary pressurized absorption and secondary pressurized absorption. The primary pressurized absorption is carried out in the primary pressurized absorption tower b, and the secondary pressurized absorption is carried out in the secondary pressurized absorption tower d. Specifically, after cooling down the maleic anhydride stream 4 (the cooler is not shown in the figure), the primary pressurized absorption is first carried out in the primary pressurized absorption tower b to obtain the primary rich oil 7 and the primary absorption tail gas 6. The primary absorption tail gas 6 is then subjected to secondary pressurized absorption in the secondary pressurized absorption tower d to obtain the secondary rich oil 13 and the maleic anhydride tail gas 12. To improve the absorption effect, both the primary pressurized absorption and the secondary pressurized absorption are in countercurrent contact with the absorbent in the absorption tower. The material flow to be treated enters from the bottom of the tower. The absorbent 5 of the primary tower enters the primary pressurized absorption tower b from the top (or the upper part of the tower), and the absorbent 11 of the secondary tower enters the secondary pressurized absorption tower d from the top (or the upper part of the tower).

[0076] Furthermore, the operating temperature of the primary pressurized absorption is 80°C - 120°C, and the operating pressure is 300 kPaA - 400 kPaA; the operating temperature of the secondary pressurized absorption is 60°C - 100°C, and the operating pressure is 200 kPaA - 300 kPaA; the mass fraction of water in the primary rich oil 7 is controlled to be less than 0.2%; by using the two-stage pressurized absorption method to separate maleic anhydride and the maleic anhydride tail gas, the water content in the separated maleic anhydride product is ensured to be lower than 0.2%.

[0077] It should be noted that after the pressure of the absorption tower increases, the water content carried away in the gas phase decreases, and the water content in the maleic anhydride rich oil increases, which will cause the water content of the separated maleic anhydride product to be unqualified. Therefore, in the embodiment of the present invention, a two-stage pressurized absorption system is used to separate the maleic anhydride logistics of the pressurized reactor. First, the maleic anhydride logistics after the reaction of the pressurized reactor a is cooled and then sent to the two-stage pressurized absorption system for absorption and separation. In the two-stage pressurized absorption system, the cooled maleic anhydride logistics is sent to the first-stage pressurized absorption tower b for absorption and separation, and then the tail gas after absorption in the first-stage pressurized absorption tower b is sent to the second-stage pressurized absorption tower d for further absorption and separation, and flash dehydration is combined with the flash evaporation tower, so that the water content of the finally separated maleic anhydride is lower than 0.2%.

[0078] Specifically, the operating temperature of the first-stage pressurized absorption can be 80°C, 90°C, 100°C, 110°C, 120°C, etc., or any value between the adjacent values above; the operating pressure can be 300 kPaA, 350 kPaA, 400 kPaA, etc., or any value between the adjacent values above; the operating temperature of the second-stage pressurized absorption can be 60°C, 70°C, 80°C, 90°C, 100°C, etc., or any value between the adjacent values above; the operating pressure can be 200 kPaA, 250 kPaA, 300 kPaA, etc., or any value between the adjacent values above.

[0079] Furthermore, the absorbents used in the processes of the first-stage pressurized absorption and the second-stage pressurized absorption are each independently selected from at least one of dibutyl phthalate, diisobutyl hexahydrophthalate, diisopropyl phthalate, and water, and can be any one or several of the above. Preferably, the absorbent is dibutyl phthalate to better absorb the maleic anhydride product.

[0080] Further, the primary rich oil 7 is subjected to primary flash evaporation in the primary flash evaporation tower c to obtain primary flash evaporation tail gas 8 and primary flash evaporation rich oil 9; the secondary rich oil 13 is subjected to secondary flash evaporation in the secondary flash evaporation tower e to obtain secondary flash evaporation tail gas 14 and secondary flash evaporation rich oil 15. The flash evaporation tail gas and the flash evaporation rich oil also need to be further processed. The primary flash evaporation tail gas 8 and the secondary flash evaporation tail gas 14 enter the tail gas scrubbing tower f and are scrubbed using the scrubbing tower absorbent 17 to obtain scrubbing tower rich oil 18, and the gas at the top of the scrubbing tower is discharged; the scrubbing tower rich oil 18 is recycled to the primary pressurized absorption stage (i.e., the primary pressurized absorption tower b). The primary flash evaporation rich oil 9 is divided into two parts, one part is withdrawn, and the other part is recycled to the primary pressurized absorption stage; the secondary flash evaporation rich oil 15 is divided into two parts, one part is recycled back to the primary pressurized absorption stage, and the other part is recycled back to the secondary pressurized absorption stage (i.e., the secondary pressurized absorption tower d). That is to say, part of the primary flash evaporation rich oil 9, the scrubbing tower rich oil 18, and part of the secondary flash evaporation rich oil 15 are mixed to form the primary pressurized absorption tower circulating solvent 10 and enter the primary pressurized absorption tower b; part of the secondary flash evaporation rich oil 15 forms the secondary pressurized absorption tower circulating solvent 16 and enters the secondary pressurized absorption tower d.

[0081] As Figure 1 shown, the secondary flash evaporation rich oil 15 output from the bottom of the secondary flash evaporation tower e is divided into three paths. The first path is connected to the secondary pressurized absorption tower d and enters the secondary pressurized absorption tower d as the secondary pressurized absorption tower circulating solvent 16; the second path is connected to the middle part of the primary pressurized absorption tower b and enters the primary pressurized absorption tower b as the primary pressurized absorption tower circulating solvent 10; the third path is connected to the upper part of the primary pressurized absorption tower b and enters the primary pressurized absorption tower b through the primary pressurized absorption tower make-up solvent 32.

[0082] Further, the maleic anhydride tail gas 12 enters the bottom of the water scrubbing tower g, and the water for water scrubbing 19 is input from the top of the water scrubbing tower g. They contact countercurrently in the water scrubbing tower g to absorb the acidic gas, and the water scrubbing water drain 21 is discharged from the system; the tail gas 20 after water scrubbing is divided into two airflows. One airflow enters the circulating booster h as the circulating booster inlet air 22 and is pressurized to obtain the circulating booster exhaust gas 23 and enters the pressurized oxidation reactor a, and the other airflow enters the conventional reactor i as the pressurized tail gas 24.

[0083] The embodiment of the present invention also provides a device for preparing maleic anhydride by oxidizing n-butane for implementing the above method, including a pressurized reactor a, a post-treatment unit after the pressurized reactor, and a conventional reactor i.

[0084] Specifically, a feed port is provided on the pressurized reactor a. The feed port is connected to the n-butane raw gas transmission pipeline 1 and the oxygen-containing gas transmission pipeline 2. The raw gas entering the pressurized reactor a also includes the circulating booster exhaust gas 23, and the pressurized reactor a is filled with an oxidation catalyst;

[0085] Specifically, for the post-treatment unit of the pressurized reactor, the post-treatment unit of the pressurized reactor includes an absorption tower and a washing tower (which can be a water washing tower g). The discharge port of the pressurized reactor a is communicated with the absorption tower. An absorbent delivery pipeline is connected to the absorption tower, and the top of the absorption tower is communicated with the washing tower. The gas flow output from the top of the washing tower is divided into two paths. One path of the gas flow is communicated with the pressurized reactor after passing through a recycle booster h. The other path of the gas flow output from the top of the washing tower is communicated with the feed port of a conventional reactor i. An oxygen-containing gas delivery pipeline 25 and a n-butane raw gas delivery pipeline 26 are also connected to the feed port of the conventional reactor i. After the oxygen-containing gas, n-butane, and pressurized tail gas 24 are mixed, a mixed raw material 27 is obtained and enters the conventional reactor i filled with an oxidation catalyst.

[0086] In some embodiments, the absorption tower in the post-treatment unit of the pressurized reactor includes a primary pressurized absorption tower b and a secondary pressurized absorption tower d. The discharge port of the pressurized reactor a is communicated with the bottom feed port of the primary pressurized absorption tower b. An absorbent delivery pipeline (for delivering the absorbent 5 of the primary tower) is connected to the top of the primary pressurized absorption tower b to enable countercurrent contact between the maleic anhydride stream and the absorbent in the primary pressurized absorption tower b. The top of the primary pressurized absorption tower b is communicated with the bottom of the secondary pressurized absorption tower d. An absorbent delivery pipeline (for delivering the absorbent 11 of the secondary tower) is connected to the top of the secondary pressurized absorption tower d. The top of the secondary pressurized absorption tower d is communicated with the bottom of the water washing tower g. A detergent delivery pipeline for delivering the washing water 19 is connected to the top of the water washing tower.

[0087] In some embodiments, the conventional reactor discharge 28 output from the conventional reactor i is communicated with the bottom of another absorption tower j. An absorbent delivery pipeline (for inputting the absorbent 29) and a gas discharge pipeline (for outputting the absorption tail gas 30) are connected to the top of the absorption tower j, and rich oil 31 is obtained at the bottom.

[0088] In an alternative embodiment, the post-treatment unit of the pressurized reactor further includes a primary flash tower c, a secondary flash tower e, and a flash tail gas washing tower f. For the specific connection method, refer to the above content in the specification, and it will not be repeated here.

[0089] The features and performance of the present invention will be further described in detail below in conjunction with embodiments.

[0090] Example 1

[0091] This example provides a method for preparing maleic anhydride by oxidizing n-butane. The overall process flow is shown in Figure 1 , and the main steps and parameters are as follows:

[0092] After mixing n-butane, oxygen-rich air, and recycled pressurized tail gas in a reaction feed mixer, they enter from the bottom feed port of the pressurized oxidation reactor a and undergo a catalytic oxidation reaction in the pressurized oxidation reactor a. The generated maleic anhydride stream is withdrawn from the maleic anhydride outlet at the top of the pressurized oxidation reactor. The reaction temperature of the pressurized reactor is 350 °C, and the reaction space velocity is 1770 h -1 , and the operating pressure of the pressurized reactor is 500 KpaA.

[0093] The maleic anhydride stream enters from the lower inlet of the first-stage pressurized absorption tower b, and the absorbent enters from the upper inlet of the first-stage pressurized absorption tower b. In the first-stage pressurized absorption tower b, the absorbent and the maleic anhydride stream are in countercurrent contact. The unabsorbed gas is discharged from the top of the first-stage pressurized absorption tower as the tail gas of the first-stage pressurized absorption tower, and the rich oil containing maleic anhydride is withdrawn from the bottom of the first-stage pressurized absorption tower b and enters the first-stage flash evaporation tower c for vacuum flash evaporation to remove water. The top of the first-stage flash evaporation tower c is connected to the tail gas scrubbing tower f to generate a vacuum. A part of the bottom material of the first-stage flash evaporation tower c is withdrawn, and a part, together with the bottom materials of the second-stage flash evaporation tower e and the tail gas scrubbing tower f, is recycled back to the first-stage pressurized absorption tower b. The tail gas of the first-stage pressurized absorption tower b enters the second-stage pressurized absorption tower d from the lower inlet of the second-stage pressurized absorption tower d, and the absorbent enters from the upper inlet of the second-stage pressurized absorption tower d. In the second-stage pressurized absorption tower d, the absorbent and the maleic anhydride stream are in countercurrent contact. The unabsorbed gas is discharged from the top of the second-stage pressurized absorption tower as the tail gas of the second-stage pressurized absorption tower, and the rich oil containing maleic anhydride is withdrawn from the bottom of the second-stage pressurized absorption tower d and enters the second-stage flash evaporation tower e for vacuum flash evaporation to remove water. The top of the second-stage flash evaporation tower e is connected to the tail gas scrubbing tower f to generate a vacuum. The bottom material of the second-stage flash evaporation tower e is divided into three parts. The first part is cooled and recycled back to the second-stage pressurized absorption tower d, the second part is withdrawn and sent to the middle of the first-stage pressurized absorption tower b, and the third part is withdrawn and sent to the upper part of the first-stage pressurized absorption tower b. The gas phases of the first-stage flash evaporation tower c and the second-stage flash evaporation tower e enter the tail gas scrubbing tower f from the lower part, the solvent (water) is added from the upper part, and the bottom material is withdrawn and sent to the first-stage pressurized absorption tower b. The operating temperature of the first-stage pressurized absorption is 99 °C, and the operating pressure is 320 kPaA; the operating temperature of the second-stage pressurized absorption is 78 °C, and the operating pressure is 210 kPaA.

[0094] The tail gas of the second-stage pressurized absorption tower d enters the water scrubbing tower from the tail gas inlet at the lower part of the water scrubbing g and undergoes countercurrent contact water scrubbing with the solvent (water) entering from the upper part. The scrubbed tail gas is withdrawn from the top outlet of the water scrubbing tower g.

[0095] The tail gas after water washing is divided into two streams. A part of the tail gas is compressed to the reaction pressure of the pressurized oxidation reactor a by the recycle booster h and recycled to the inlet of the pressurized oxidation reactor a. The other part of the tail gas is discharged to the conventional reactor i, mixed with oxygen-enriched air, air and n-butane, and fed into the bottom feed port of the conventional reactor i. A catalytic oxidation reaction occurs in the conventional reactor i, and the maleic anhydride stream generated is withdrawn from the maleic anhydride outlet at the top of the conventional reactor i. The maleic anhydride stream enters the absorption tower j from the lower part. The absorbent is added to the upper part of the absorption tower j. The tail gas after absorption is discharged from the top, and the rich oil containing maleic anhydride is discharged from the bottom. Among them, the flow rate of the maleic anhydride tail gas returned to the pressurized reactor is 1300 t / h, the flow rate of the maleic anhydride tail gas returned to the conventional reactor is 266 t / h, and the flow rate ratio of the maleic anhydride tail gas returned to the pressurized reactor to the conventional reactor is 4.88.

[0096] Example 2

[0097] The process is the same as that of Example 1, except that: the reaction space velocity of the pressurized reactor is 1987 h -1 , the flow rate of the maleic anhydride tail gas returned to the pressurized reactor is 1440 t / h, the flow rate of the maleic anhydride tail gas returned to the conventional reactor is 321 t / h, and the flow rate ratio of the maleic anhydride tail gas returned to the pressurized reactor to the conventional reactor is 4.49. Specific parameters are shown in Table 1 and Table 2.

[0098] Example 3

[0099] The process is the same as that of Example 1, except that: the reaction temperature of the pressurized reactor is 400 °C, and the reaction space velocity is 2135 h -1 , the flow rate of the maleic anhydride tail gas returned to the pressurized reactor is 1440 t / h, the flow rate of the maleic anhydride tail gas returned to the conventional reactor is 317 t / h, and the flow rate ratio of the maleic anhydride tail gas returned to the pressurized reactor to the conventional reactor is 4.54. Specific parameters are shown in Table 1 and Table 2.

[0100] Example 4

[0101] The process is the same as that of Example 1, except that: the reaction temperature of the pressurized reactor is 320 °C, and the reaction space velocity is 1628 h -1 , the flow rate of the maleic anhydride tail gas returned to the pressurized reactor is 1200 t / h, the flow rate of the maleic anhydride tail gas returned to the conventional reactor is 320 t / h, and the flow rate ratio of the maleic anhydride tail gas returned to the pressurized reactor to the conventional reactor is 3.75. Specific parameters are shown in Table 1 and Table 2.

[0102] Example 5

[0103] The process is the same as that of Example 1, except that: the reaction space velocity is 1712 h -1, the oxygen-enriched concentration supplemented to the pressurized reactor is 39%, the flow rate of maleic anhydride tail gas returned to the pressurized reactor is 1300 t / h, the flow rate of maleic anhydride tail gas returned to the conventional reactor is 214 t / h, and the ratio of the flow rate of maleic anhydride tail gas returned to the pressurized reactor to that returned to the conventional reactor is 6.08. Specific parameters are shown in Table 1 and Table 2.

[0104] Comparative Example 1

[0105] This comparative example is the existing process flow, and only one conventional reactor is used for the reaction, corresponding to the conventional reactor in the examples. Specific parameters are shown in Table 1 and Table 2.

[0106] Table 1 Process parameters of reactors in examples and comparative examples

[0107]

[0108]

[0109] Table 2 Feeding and production of reactors in examples and comparative examples

[0110]

[0111]

[0112] It can be seen from Example 1 and Example 5 that under the conditions of basically the same reaction space velocity and reaction feed oxygen concentration, as the oxygen-enriched concentration supplemented to the pressurized reactor decreases, the oxygen-enriched amount supplemented to the pressurized reactor increases, the flow rate of maleic anhydride tail gas returned to the pressurized reactor decreases, the flow rate of maleic anhydride tail gas discharged to the conventional reactor increases, and the CO content in the feed of the pressurized reactor decreases.

[0113] It can be seen from Example 2 and Comparative Example 1 that under the condition of basically the same maleic anhydride production, in Example 2, with the pressurized reactor in series with the conventional reactor with circulation, the butane feed amount is: 39.38 + 12.63 = 52.01 t / h, and the overall maleic anhydride yield = 65.00 / 98 / (52.01 / 58) = 73.97 mol%; in Comparative Example 1, there is only a conventional reactor without circulation, the butane feed amount is 67.06 t / h, and the overall maleic anhydride yield = 65.01 / 98 / (67.06 / 58) = 57.37 mol%. It can be seen that with the pressurized reactor in series with the conventional reactor with circulation, the overall conversion rate of n-butane is increased. Due to the reduction of the reaction temperature, side reactions are reduced, the selectivity of maleic anhydride is increased, and the maleic anhydride yield is significantly increased.

[0114] As can be seen from Example 2 and Example 3, the reaction temperature of the pressurized reactor in Example 2 is 350°C, which is lower than the reaction temperature of the pressurized reactor in Example 3 (400°C). By reducing the reaction temperature of the pressurized reactor, the selectivity of maleic anhydride in the pressurized reactor increases. When the maleic anhydride production is the same, the maleic anhydride yield (75.14%) at a reaction temperature of 350°C in the pressurized reactor is higher than the maleic anhydride yield (68.89%) in the pressurized reactor of Example 3.

[0115] As can be seen from Example 3 and Comparative Example 1, under the condition of controlling the reactor space velocity and maleic anhydride production to be basically the same, when the pressurized reactor is in series with a conventional reactor with circulation, the tail gas emission is 410 t / h. Compared with only a conventional reactor without circulation, where the tail gas emission is 1806 t / h, the tail gas emission of maleic anhydride is significantly reduced, thus greatly reducing the load on the incinerator and reducing VOC emissions.

[0116] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, various modifications and changes can be made to the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing maleic anhydride by oxidizing n-butane, characterized in that, Comprising: Catalytically oxidizing n-butane and an oxygen-containing gas in a pressurized reactor to obtain a maleic anhydride stream; Cooling and absorbing the maleic anhydride stream to obtain maleic anhydride-rich oil and maleic anhydride tail gas; Dividing the maleic anhydride tail gas into two gas streams, one gas stream is pressurized and returned to the pressurized reactor as a raw material gas for reaction, and the other gas stream enters a conventional reactor to carry out catalytic oxidation with an oxygen-containing gas and n-butane; Among them, the reaction temperature of the pressurized reactor is 320°C - 450°C, the reaction space velocity is 1500 h -1 -2500 h -1 , and the reaction pressure is 300 kPaA - 600 kPaA.

2. The method according to claim 1, wherein The reaction temperature of the pressurized reactor is 340°C - 370°C, and the reaction space velocity is 1700 h -1 -2000 h -1 , and the reaction pressure is 450 kPaA - 550 kPaA; Preferably, the flow rate ratio of the gas stream of the maleic anhydride tail gas returned to the pressurized reactor to the gas stream entering the conventional reactor is (3-8):1; more preferably (4-7):

1.

3. The method according to claim 2, characterized in that, In the mixed raw material entering the pressurized reactor, control the volume fraction of n-butane in the mixed raw material to be 1.0%-1.8%, the volume fraction of carbon monoxide to be 0%-5%, and the volume fraction of oxygen in the mixed raw material to be 13%-23%; Preferably, the oxygen-containing gas introduced into the pressurized reactor is oxygen-enriched air with an oxygen volume fraction of 30%-90%; the flow rate ratio of the maleic anhydride tail gas returned to the pressurized reactor to the introduced oxygen-containing gas is (3-5):1; More preferably, the preparation process of the oxygen-enriched air includes: membrane separation or pressure swing adsorption separation of air.

4. The method according to claim 1, wherein Mix a part of the maleic anhydride tail gas with an oxygen-containing gas and a raw material gas containing n-butane to form a mixed raw material and enter the conventional reactor for reaction, control the reaction temperature to be 410°C-480°C, and the reaction pressure to be 200 kPaA-300 kPaA; Preferably, in the mixed raw material entering the conventional reactor, the volume fraction of n-butane is 1.0%-2.0%, and the volume fraction of oxygen is 13%-23%; Preferably, the oxygen-containing gas introduced into the conventional reactor is oxygen-enriched air and / or air, and the oxygen volume fraction in the oxygen-enriched air is 30%-90%.

5. The method according to any one of claims 1-4, characterized in that, Both the pressurized reactor and the conventional reactor are filled with an oxidation catalyst, and the oxidation catalyst is a vanadium phosphorus oxygen-based catalyst.

6. The method according to claim 1, characterized in that, After cooling and reducing the temperature of the maleic anhydride stream, it is treated in a two-stage absorption tower, and the unabsorbed maleic anhydride tail gas is output at the top of the second-stage absorption tower, and the maleic anhydride tail gas is washed with water and divided into two gas streams; Preferably, after cooling and reducing the temperature of the maleic anhydride stream, it is subjected to primary pressurized absorption to obtain primary rich oil and primary absorption tail gas, and the primary absorption tail gas is subjected to secondary pressurized absorption to obtain secondary rich oil and the maleic anhydride tail gas; wherein, both the primary pressurized absorption and the secondary pressurized absorption are in countercurrent contact with the absorbent in the absorption tower; More preferably, the operating temperature of the primary pressurized absorption is 80°C-120°C, the operating pressure is 300 kPaA-400 kPaA, and control the mass fraction of water in the primary rich oil to be less than 0.2%; More preferably, the operating temperature of the secondary pressurized absorption is 60°C-100°C, and the operating pressure is 200 kPaA-300 kPaA; More preferably, the absorbents used in the first-stage pressurized absorption and the second-stage pressurized absorption are each independently selected from at least one of dibutyl phthalate, diisobutyl hexahydrophthalate, diisopropyl phthalate, and water; more preferably dibutyl phthalate.

7. The method according to claim 6, characterized in that, The first-stage rich oil is subjected to first-stage flash evaporation to obtain first-stage flash evaporation tail gas and first-stage flash evaporation rich oil; the second-stage rich oil is subjected to second-stage flash evaporation to obtain second-stage flash evaporation tail gas and second-stage flash evaporation rich oil. Preferably, the first-stage flash evaporation tail gas and the second-stage flash evaporation tail gas enter a tail gas scrubbing tower and are scrubbed with an absorbent to obtain scrubbing tower rich oil; the scrubbing tower rich oil is recycled to the first-stage pressurized absorption stage. Preferably, the first-stage flash evaporation rich oil is divided into two parts, one part is withdrawn, and the other part is recycled to the first-stage pressurized absorption stage. Preferably, the second-stage flash evaporation rich oil is divided into two parts, one part is recycled back to the first-stage pressurized absorption stage, and the other part is recycled back to the second-stage pressurized absorption stage.

8. An apparatus for implementing the method according to any one of claims 1-7, characterized in that, Including: A pressurized reactor, which is provided with a feed port. The feed port is connected to a n-butane raw material gas pipeline and an oxygen-containing gas pipeline. The pressurized reactor is filled with an oxidation catalyst. A post-treatment unit for the pressurized reactor, which includes an absorption tower and a scrubbing tower. The outlet of the pressurized reactor is connected to the absorption tower. The absorption tower is connected with an absorbent pipeline. The top of the absorption tower is connected to the scrubbing tower; the gas flow output from the top of the scrubbing tower is divided into two paths. One path of the gas flow is connected to the pressurized reactor after passing through a booster. A conventional reactor, the other path of the gas flow output from the top of the scrubbing tower is connected to the feed port of the conventional reactor. The feed port on the conventional reactor is also connected to an oxygen-containing gas pipeline and a n-butane raw material gas pipeline. The conventional reactor is filled with an oxidation catalyst.

9. The device according to claim 8, characterized in that, The absorption tower in the post-treatment unit of the pressurized reactor includes a first-stage pressurized absorption tower and a second-stage pressurized absorption tower. The outlet of the pressurized reactor is connected to the bottom feed port of the first-stage pressurized absorption tower. The top of the first-stage pressurized absorption tower is connected with an absorbent pipeline to make the maleic anhydride stream and the absorbent contact countercurrently in the first-stage pressurized absorption tower; the top of the first-stage pressurized absorption tower is connected to the bottom of the second-stage pressurized absorption tower. The top of the second-stage pressurized absorption tower is connected with an absorbent pipeline. The top of the second-stage pressurized absorption tower is connected to the scrubbing tower. The scrubbing tower is also connected with a detergent pipeline. The outlet of the conventional reactor is connected to the bottom of another absorption tower. Another absorption tower is also connected with an absorbent pipeline and a gas discharge pipeline.

10. The device according to claim 9, wherein, The post-treatment unit of the pressurized reactor further includes a first-stage flash evaporation tower, a second-stage flash evaporation tower, and a flash evaporation tail gas scrubbing tower. The bottom of the first-stage pressurized absorption tower is connected to the first-stage flash evaporation tower. The bottom of the first-stage flash evaporation tower obtains first-stage flash evaporation rich oil, and the top of the first-stage flash evaporation tower obtains first-stage flash evaporation tail gas; the bottom of the second-stage pressurized absorption tower is connected to the second-stage flash evaporation tower. The bottom of the second-stage flash evaporation tower obtains second-stage flash evaporation rich oil, and the top of the second-stage flash evaporation tower obtains second-stage flash evaporation tail gas. The tops of the first-stage flash tower and the second-stage flash tower are both connected to the bottom of the tail gas scrubbing tower. The top of the tail gas scrubbing tower is also connected to an absorbent delivery pipeline, and the bottom of the tail gas scrubbing tower is connected to the first-stage pressurized absorption tower; The bottom of the first-stage flash tower is divided into two paths. One path is connected to a product pipeline, and the other path is connected to the first-stage pressurized absorption tower. The bottom of the second-stage flash tower is divided into three paths. The first path is connected to the second-stage pressurized absorption tower, the second path is connected to the middle of the first-stage pressurized absorption tower, and the third path is connected to the upper part of the first-stage pressurized absorption tower.

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