System for preparing maleic anhydride

Abstract

The utility model discloses a system for preparing maleic anhydride. The system for preparing maleic anhydride comprises an n-butane source, an air source, a water vapor source, a mixer and a reactor, wherein the number of the mixers and the number of the reactors are both n, n is larger than or equal to 2, the first mixer is connected with the first reactor in sequence, the second mixer is connected with the second reactor in sequence, and the nth mixer is connected with the nth reactor in sequence; the n-butane source is divided into n paths which are respectively connected with n-butane inlets of the n mixers, the air source is divided into n paths which are respectively connected with air inlets of the n mixers, and the pipeline, connected with each mixer, of the air source is also respectively provided with a branch which is connected with the water vapor source; a moisture detector is arranged on a pipeline through which the air source is connected with each mixer. According to the difference of the running states of different reactors and the difference of reaction conversion rates, selectivity and hot spots, the running states of the different reactors are optimized through fine adjustment of the humidifying amount of each reactor, and a positive effect is achieved on production lean operation.

Description

Technical Field

[0001] This utility model relates to the field of maleic anhydride preparation technology, specifically to a system for preparing maleic anhydride. Background Technology

[0002] In existing technologies, maleic anhydride is mainly prepared by reacting n-butane with oxygen. The oxidation reaction is carried out under the action of a catalyst, and the main chemical reactions are as follows:

[0003] C4H 10 +3.5O2------>C4H2O3+4H2O

[0004] The reaction takes place in a catalyst-filled reactor. n-Butane is vaporized, superheated, and then mixed sequentially with compressed air before entering the oxidation reaction system. The oxidation reaction system has multiple parallel production lines, with the mixed gas continuously entering the reactor's tube side, where it undergoes an oxidation reaction under the action of the catalyst.

[0005] In maleic anhydride reaction systems, a small amount of steam is typically added during air feeding to adjust catalyst performance and improve reaction yield. Currently, steam is directly injected into the air feed manifold. However, due to varying air humidity levels in different seasons and slight differences in humidity requirements among different catalyst brands, direct steam injection into the air feed manifold cannot meet the requirements for precise control.

[0006] Therefore, there is an urgent need for a maleic anhydride production system that can precisely control the steam feed rate in the reactor. Summary of the Invention

[0007] To address the problems existing in the prior art, this invention provides a system for preparing maleic anhydride. This invention employs a segmented steam injection method and installs a moisture detector on each air pipeline, allowing for adjustable humidity within each reactor and enhancing the uniform distribution of steam, thus making the reaction more stable.

[0008] One objective of this invention is to provide a system for preparing maleic anhydride, comprising a n-butane source, an air source, a steam source, a mixer, and a reactor; wherein the number of mixers and reactors is n, n≥2, and the first mixer is sequentially connected to the first reactor, the second mixer is sequentially connected to the second reactor, and so on, with the nth mixer being sequentially connected to the nth reactor; the n-butane source is divided into n paths that are respectively connected to the n-butane inlets of the n mixers, the air source is divided into n paths that are respectively connected to the air inlets of the n mixers, and the air source is further divided into n paths that are respectively connected to the air inlets of the n mixers, with a branch path connected to the steam source on the air source connecting to each mixer, and a moisture detector is installed on the air source connecting to each mixer.

[0009] In a preferred embodiment of this utility model,

[0010] The n = 2-4; and / or,

[0011] The reactor is a fixed-bed vertical shell-and-tube reactor. The fixed-bed vertical shell-and-tube reactor is a conventional reactor in this field, and no special limitations are imposed in this invention.

[0012] In a preferred embodiment of this utility model,

[0013] A steam distributor is installed on each branch of the steam source connecting to each air source feed pipe; preferably, the steam distributor is installed in the branch pipe at the junction of the steam source and each air source feed pipe. The steam distributor is a conventional gas distributor in the art, and no special limitation is imposed in this utility model.

[0014] In a preferred embodiment of this utility model,

[0015] Each air source is equipped with an air heater on the pipe connecting it to each mixer; preferably,

[0016] The air heater is located after the junction of the steam source and each air source feed pipe; and / or,

[0017] The air heater is positioned before or after the moisture detector. The moisture detector is a conventional moisture detection device in the art, and no special limitations are imposed in this invention.

[0018] In a preferred embodiment of this utility model,

[0019] Each branch of the steam source connecting to the air source feed pipe is also equipped with a steam pressure control valve.

[0020] In this invention, the steam required for the reactor reaction is not directly injected through the main air feed pipe. Instead, a segmented injection method is adopted, with a steam distributor (such as a first steam distributor, a second steam distributor, and a third steam distributor) installed on each steam inlet pipeline. Steam is injected into each maleic anhydride reactor's air feed line through the steam distributor. Simultaneously, a moisture detector (such as a first moisture detector, a second moisture detector, and a third moisture detector) is installed on each air feed pipeline to strictly control the humidity within each reactor. The humidity within the reactor can be adjusted according to changes in ambient air humidity and the humidity requirements of different brands of catalysts. The steam distributors on each line enhance the uniformity of steam distribution, ensuring that moisture mixes evenly with air before entering the reactor, resulting in a more stable oxidation reaction and preventing localized reaction anomalies and catalyst damage within the reactor.

[0021] In a preferred embodiment of this utility model,

[0022] Each reactor is further connected to a molten salt collection tank. Preferably, the molten salt outlet of the molten salt collection tank is connected to the molten salt inlet of the shell side of the reactor, and the molten salt inlet of the molten salt collection tank is connected to the molten salt outlet of the shell side of the reactor.

[0023] The n-butane oxidation reaction is carried out in a temperature range of approximately 400°C to maintain the desired n-butane conversion. Molten salt is stored in a molten salt collection tank and pumped to the reactor shell side for circulation. The molten salt passes through the shell side of a salt cooler, where excess exothermic reaction heat is removed by generating high-pressure steam.

[0024] In a preferred embodiment of this utility model,

[0025] The system also includes a nitrogen source, which is connected to each molten salt collection tank via pipelines.

[0026] In a preferred embodiment of this utility model,

[0027] The pipeline connecting the nitrogen source to each molten salt collection tank is also equipped with a nitrogen inlet pressure control valve; and / or,

[0028] Each molten salt collection tank is equipped with a venting pipeline, and a venting pressure control valve is installed on the venting pipeline.

[0029] In a preferred embodiment of this utility model,

[0030] The nitrogen inlet pressure control valve and the vent pressure control valve connected to each molten salt collection tank are respectively connected to a pressure transmitter.

[0031] Molten salt, as a heat carrier in the maleic anhydride reaction, serves to remove heat generated during the reaction or replenish the heat required for the reaction. In existing processes, the molten salt collection tank is an atmospheric pressure tank connected to the atmosphere. Molten salt is easily oxidized by oxygen in the air, altering its composition and causing changes in its physicochemical properties, especially increasing its freezing point after oxidation, which significantly impacts its usability and necessitates regular replenishment of fresh molten salt. This invention incorporates a nitrogen seal into the molten salt collection tank to maintain a slight positive pressure inside. Pressure control valves are installed on both the nitrogen and vent lines, and a pressure transmitter on the tank top controls these two valves in a split-range manner to maintain the slight positive pressure inside the tank. The control scheme is as follows: when the pressure is below the set point, the nitrogen control valve is opened to replenish pressure; when the pressure is above the set point, the vent control valve is opened to release pressure. The molten salt stored in the tank is isolated from air, preventing oxidation and maintaining relatively stable physicochemical properties. This reduces the need for regular replenishment of fresh molten salt, prevents molten salt deterioration, and lowers molten salt consumption.

[0032] In a preferred embodiment of this utility model,

[0033] Each reactor is also equipped with a reaction gas outlet, which is connected to the subsequent maleic anhydride absorption and distillation section.

[0034] The subsequent maleic anhydride absorption and distillation section includes any conventional maleic anhydride absorption and distillation device in the art, and no special limitations are imposed in this utility model.

[0035] The system of this invention is applied in the process of preparing maleic anhydride. The process parameters for preparing maleic anhydride can be the process parameters commonly used in the prior art for preparing maleic anhydride. The catalyst filled in the reactor is also a conventional catalyst for preparing maleic anhydride, such as a vanadium-phosphorus-oxygen catalyst.

[0036] Specifically, in the process of preparing maleic anhydride, the mass flow ratio of air to water vapor introduced into each reactor in this invention's system may be the same or different, independently being (50-80):1; and / or,

[0037] The mass flow ratio of air to n-butane introduced into each reactor may be the same or different, independently being (20–30):1; and / or,

[0038] The operating conditions of each reactor may be the same or different, and each reactor independently includes: a reaction temperature of 380–420°C, and / or a reaction pressure of 160–220 kPaG, and / or a space velocity of 1700–1800 h⁻¹. -1 ; and / or,

[0039] The moisture detection standard range is 0-7% of the water content in the air, preferably 3-5%. When the water content of a certain moisture detection channel is higher or lower than the normal value, the flow rate is adjusted by injecting water vapor into the pipeline.

[0040] The pressure in the molten salt collection tank is 95-105 kPa. The pressure in the molten salt collection tank is maintained at atmospheric pressure, and changes slightly after the molten salt is pumped out and molten salt is input. After nitrogen sealing, the pressure is controlled between 95 kPa and 105 kPa.

[0041] The beneficial effects of this utility model are:

[0042] 1. In actual production, this utility model optimizes the operating state of different reactors by finely adjusting the humidification amount of each reactor based on the differences in reaction conversion rate, selectivity and hot spots, and plays a positive role in lean production operation.

[0043] 2. This utility model, by adding nitrogen sealing to the molten salt collection tank, can effectively reduce molten salt deterioration and reduce losses. Attached Figure Description

[0044] Figure 1This is a simplified diagram of the maleic anhydride preparation system of this invention.

[0045] Explanation of reference numerals in the attached figures:

[0046] S is the air source, P1 is steam feed 1, P2 is steam feed 2, P3 is steam feed 3, 1-1 is the first steam distributor, 1-2 is the second steam distributor, 1-3 is the third steam distributor, 2-1 is the first air heater, 2-2 is the second air heater, 2-3 is the third air heater, 3-1 is the first moisture detector, 3-2 is the second moisture detector, 3-3 is the third moisture detector, Q1 is n-butane feed 1, Q2 is n-butane feed 2, Q3 is n-butane feed 3, 4 -1 is the first mixer, 4-2 is the second mixer, 4-3 is the third mixer, 5-1 is the first reactor, 5-1 is the second reactor, 5-1 is the third reactor, T1 is the reaction gas outlet 1, T2 is the reaction gas outlet 2, T3 is the reaction gas outlet 3, 6-1 is the first molten salt collection tank, 6-2 is the second molten salt collection tank, 6-3 is the third molten salt collection tank, N1 is nitrogen 1, N2 is nitrogen 2, N3 is nitrogen 3, F1 is venting air 1, F2 is venting air 2, F3 is venting air 3. Detailed Implementation

[0047] The present invention will now be described in detail with reference to specific embodiments and accompanying drawings. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0048] It should also be noted that the various specific technical features described in the following embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, this utility model will not describe the various possible combinations separately.

[0049] Furthermore, various different embodiments of this utility model can be combined arbitrarily, as long as they do not violate the spirit of this utility model. The resulting technical solutions are part of the original disclosure of this specification and also fall within the protection scope of this utility model.

[0050] Unless otherwise specified, the raw materials used in the examples and comparative examples are all disclosed in the prior art, such as those that can be directly purchased or prepared according to the preparation methods disclosed in the prior art.

[0051] Example 1

[0052] like Figure 1The system shown includes a n-butane source (omitted in the figure), an air source S, a water vapor source (omitted in the figure), a first mixer 4-1, a second mixer 4-2, a third mixer 4-3, a first reactor 5-1, a second reactor 5-2, and a third reactor 5-3; wherein, the first mixer 4-1 is sequentially connected to the first reactor 5-1, the second mixer 4-2 is sequentially connected to the second reactor 5-2, and the third mixer 4-3 is sequentially connected to the third reactor 5-3; the n-butane source is divided into three paths, each connected to the n-butane inlet of one of the three mixers, and the air source is divided into three paths, each connected to the air inlet of one of the three mixers. The air source S is connected to each mixer via a branch line that connects to the steam source. A steam distributor is installed on each branch line connecting the steam source to the air source feed line. A first air heater 2-1 and a first moisture detector 3-1 are sequentially installed on the air source S connecting to the first mixer 4-1. A second air heater 2-2 and a second moisture detector 3-2 are sequentially installed on the air source S connecting to the second mixer 4-2. A third air heater 2-3 and a third moisture detector 3-3 are sequentially installed on the air source S connecting to the third mixer 4-3.

[0053] Each reactor is also equipped with a reaction gas outlet, which is connected to the subsequent maleic anhydride absorption and distillation section.

[0054] In this embodiment, the steam required for the reactor reaction is not directly injected through the air feed main pipe, but is injected in stages. A steam distributor is installed on each steam inlet pipe, and the steam is injected into each maleic anhydride reactor air feed line through the steam distributor. At the same time, a moisture detector is installed on each air inlet pipe to strictly control the humidity in each reactor. The humidity in the reactor can be adjusted according to changes in ambient air humidity and the humidity requirements of different brands of catalysts. After long-term operation, the reaction conversion rate can be effectively improved.

[0055] Example 2

[0056] like Figure 1The system shown includes a n-butane source (omitted in the figure), an air source S, a water vapor source (omitted in the figure), a first mixer 4-1, a second mixer 4-2, a third mixer 4-3, a first reactor 5-1, a second reactor 5-2, and a third reactor 5-3; wherein, the first mixer 4-1 is sequentially connected to the first reactor 5-1, the second mixer 4-2 is sequentially connected to the second reactor 5-2, and the third mixer 4-3 is sequentially connected to the third reactor 5-3; the n-butane source is divided into three paths, each connected to the n-butane inlet of one of the three mixers, and the air source is divided into three paths, each connected to the air inlet of one of the three mixers. The air source S is connected to each mixer via a branch line that connects to the steam source. A steam distributor is installed on each branch line connecting the steam source to the air source feed line. A first air heater 2-1 and a first moisture detector 3-1 are sequentially installed on the air source S connecting to the first mixer 4-1. A second air heater 2-2 and a second moisture detector 3-2 are sequentially installed on the air source S connecting to the second mixer 4-2. A third air heater 2-3 and a third moisture detector 3-3 are sequentially installed on the air source S connecting to the third mixer 4-3.

[0057] A first molten salt collection tank 6-1 is connected after the first reactor 5-1. The molten salt outlet of the first molten salt collection tank 6-1 is connected to the molten salt inlet of the shell side of the first reactor 5-1, and the molten salt inlet of the first molten salt collection tank 6-1 is connected to the molten salt outlet of the shell side of the first reactor 5-1. A second molten salt collection tank 6-2 is connected after the second reactor 5-2. The molten salt outlet of the second molten salt collection tank 6-2 is connected to the molten salt inlet of the shell side of the second reactor 5-2, and the molten salt inlet of the second molten salt collection tank 6-2 is connected to the molten salt outlet of the shell side of the second reactor 5-2. A third molten salt collection tank 6-3 is connected after the third reactor 5-3. The molten salt outlet of the third molten salt collection tank 6-3 is connected to the molten salt inlet of the shell side of the third reactor 5-3, and the molten salt inlet of the third molten salt collection tank 6-3 is connected to the molten salt outlet of the shell side of the third reactor 5-3.

[0058] The system also includes a nitrogen source (omitted in the figure), which is connected to each molten salt collection tank via pipelines; each pipeline connecting the nitrogen source to each molten salt collection tank is also equipped with a nitrogen inlet pressure control valve; each molten salt collection tank is equipped with a venting pipeline, and each venting pipeline is equipped with a venting pressure control valve; the nitrogen inlet pressure control valve and the venting pressure control valve connected to each molten salt collection tank are respectively connected to a pressure transmitter.

[0059] Each reactor is also equipped with a reaction gas outlet, which is connected to the subsequent maleic anhydride absorption and distillation section.

[0060] In this embodiment, a nitrogen-sealed molten salt collection tank is connected after the reactor. When the pressure is lower than the set pressure, the nitrogen inlet pressure control valve is opened to replenish the pressure; when the pressure is higher than the set pressure, the venting pressure control valve is opened to release the pressure. The molten salt stored in the tank is isolated from air, preventing oxidation and maintaining stable physicochemical properties. This significantly reduces the need for regular replenishment of fresh molten salt, effectively preventing molten salt deterioration and reducing molten salt consumption.

[0061] Comparative Example 1

[0062] Injecting steam directly into the air feed manifold ensures that the air entering each reactor has the same water content. However, due to differences in catalyst manufacturers and batches in each reactor, there are slight variations in humidity requirements. Directly injecting steam into the air feed manifold cannot meet the requirement of precise control over the steam entering each reactor. After long-term operation, the reaction conversion rate is affected, and compared with the segmented steam injection method, the reaction conversion rate is significantly reduced.

[0063] The present invention has been described in detail above with reference to specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the present invention. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and implementation methods of the present invention without departing from the spirit and scope of the present invention, and all such modifications and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the appended claims.

[0064] All publications, patent applications, patents, and other references mentioned in this specification are incorporated herein by reference. Unless otherwise defined, all technical and scientific terms used in this specification have the meanings commonly understood by those skilled in the art. In case of conflict, the definitions in this specification shall prevail.

[0065] When this specification uses the prefixes “known to those skilled in the art,” “prior art,” or similar terms to derive materials, substances, methods, steps, apparatus, or components, the objects derived from such prefixes cover those commonly used in the art at the time of this application, but also include those that are not currently commonly used but will become generally recognized in the art as suitable for similar purposes.

[0066] In the context of this specification, except where expressly stated otherwise, any matters or issues not mentioned shall apply directly to those known in the art without any modification.

Claims

1. A system for preparing maleic anhydride, comprising a n-butane source, an air source, a steam source, a mixer, and a reactor; wherein, The number of mixers and reactors is n, where n≥2, and the first mixer is connected to the first reactor in sequence, the second mixer is connected to the second reactor in sequence, and so on, with the nth mixer connected to the nth reactor in sequence. The n-butane source is divided into n paths that are connected to the n-butane inlets of the n mixers respectively. The air source is divided into n paths that are connected to the air inlets of the n mixers respectively. Each air source connecting to each mixer also has a branch path that connects to the water vapor source. A moisture detector is installed on each air source connecting to each mixer.

2. The system as described in claim 1, characterized in that: The n = 2-4; and / or, The reactor is a fixed-bed vertical shell-and-tube reactor.

3. The system as described in claim 1, characterized in that: A steam distributor is installed on each branch of the steam source connecting to each air source feed pipe; the steam distributor is installed in the branch pipe at the junction of the steam source connecting to each air source feed pipe.

4. The system as described in claim 1, characterized in that: Each air source is equipped with an air heater on the pipe connecting to each mixer. The air heater is located after the junction of the steam source and each air source feed pipe; and / or, The air heater is positioned before or after the moisture detector.

5. The system as described in claim 1, characterized in that: Each reactor is also connected to a molten salt collection tank.

6. The system as described in claim 5, characterized in that: The molten salt outlet of the molten salt collection tank is connected to the molten salt inlet of the shell side of the reactor, and the molten salt inlet of the molten salt collection tank is connected to the molten salt outlet of the shell side of the reactor.

7. The system as described in claim 5, characterized in that: The system also includes a nitrogen source, which is connected to each molten salt collection tank via pipelines.

8. The system as described in claim 7, characterized in that: The pipeline connecting the nitrogen source to each molten salt collection tank is also equipped with a nitrogen inlet pressure control valve; and / or, Each molten salt collection tank is equipped with a venting pipeline, and each venting pipeline is equipped with a venting pressure control valve.

9. The system as described in claim 8, characterized in that: The nitrogen inlet pressure control valve and the vent pressure control valve connected to each molten salt collection tank are respectively connected to a pressure transmitter.

10. The system according to any one of claims 1-9, characterized in that: Each reactor is also provided with a reaction gas outlet, which is connected to the subsequent maleic anhydride absorption and distillation section.

Images