System and method for preparing maleic anhydride and phthalic anhydride by oxidizing n-pentane

Abstract

The invention belongs to the field of C5 alkane utilization, and discloses a system and a method for preparing maleic anhydride and phthalic anhydride through n-pentane oxidation. The system comprises a reaction subsystem, a solvent absorption subsystem, a solvent desorption subsystem, a product refining subsystem and a solvent refining subsystem. According to the system and the method, acid-containing impurities of the maleic anhydride product and the phthalic anhydride product can be reduced, the product purity is improved, and sustainable utilization of the solvent is realized.

Description

Technical Field

[0001] The invention belongs to the field of C5 alkane utilization, and more specifically, relates to a system and method for preparing maleic anhydride and phthalic anhydride by oxidation of n-pentane. Background Art

[0002] my country is rich in C5 resources, but the utilization rate is insufficient, far lower than that of developed countries. With the development of isopentane normalization technology, normal pentane can achieve a stable and large supply; with the restrictions on the production, sales and use of plastic products, degradable plastics have been promoted and applied, and maleic anhydride is an important part of the production of degradable plastics; the traditional naphthalene method and o-xylene method used in phthalic anhydride production technology have problems such as high raw material prices and high energy consumption. In summary, the production of maleic anhydride and phthalic anhydride by oxidation of C5 resources can solve the above problems at the same time and realize the full utilization of resources.

[0003] At present, there are few patent reports on the preparation of maleic anhydride by oxidation of n-pentane. Patent CN112079799A provides a process for preparing maleic anhydride and phthalic anhydride by oxidation of n-pentane, and patent CN112661734A provides a process for preparing phthalic anhydride and maleic anhydride by selective oxidation of n-pentane. However, both processes do not take into account the influence of complex acidic impurities produced by the reaction on the process flow and products. The two patents separate the reaction products and other impurities through azeotropic distillation and flash evaporation systems respectively, and the separation effect is limited. The purity of the product can be improved. Since the azeotropic agent introduced is usually xylene, the device is highly toxic. Therefore, it is urgent to propose a system and method for preparing maleic anhydride and phthalic anhydride by oxidation of n-pentane. Summary of the invention

[0004] The purpose of the present invention is to address the deficiencies of the prior art and to provide a system and method for preparing maleic anhydride and phthalic anhydride by oxidation of n-pentane. The system and method of the present invention can reduce acid impurities in maleic anhydride and phthalic anhydride products, improve product purity, and achieve sustainable utilization of solvents.

[0005] In order to achieve the above-mentioned object, the present invention provides a system for preparing maleic anhydride and phthalic anhydride by oxidation of n-pentane, the system comprising a reaction subsystem, a solvent absorption subsystem, a solvent desorption subsystem, a product refining subsystem and a solvent refining subsystem;

[0006] The inlet of the reaction subsystem is connected to a n-pentane feed pipeline and a pressurized air feed pipeline; the outlet of the reaction subsystem is connected to the middle and lower inlet of the solvent absorption subsystem;

[0007] The upper inlet of the solvent absorption subsystem is connected to a fresh solvent feed pipeline and a refined solvent feed pipeline; the lower inlet of the solvent absorption subsystem is connected to a stripping gas feed pipeline;

[0008] The bottom outlet of the solvent absorption subsystem is connected to the middle inlet of the solvent desorption subsystem; the top outlet of the solvent absorption subsystem and the top outlet of the solvent desorption subsystem are both connected to tail gas discharge pipelines;

[0009] The bottom outlet of the solvent desorption subsystem is connected to the refined solvent feed pipeline through the solvent refining subsystem; the upper product outlet of the solvent desorption subsystem is connected to the inlet of the product refining subsystem;

[0010] The top outlet of the product refining subsystem is connected to a maleic anhydride product discharge pipeline;

[0011] The bottom outlet of the product refining subsystem is connected with a phthalic anhydride product discharge pipeline.

[0012] According to the present invention, preferably, the reaction subsystem is a tube-in-tube fixed bed and / or a fluidized bed, preferably a tube-in-tube fixed bed.

[0013] According to the present invention, preferably, the solvent absorption subsystem is an absorption tower with 20-45 plates.

[0014] According to the present invention, preferably, the solvent desorption subsystem is a packed tower with a packing height of 4 to 10 m.

[0015] According to the present invention, preferably, the product refining subsystem is a refining tower with 15-25 plates.

[0016] According to the present invention, preferably, the exhaust gas exhaust pipeline is connected to the outside.

[0017] According to the present invention, preferably, the solvent refining subsystem comprises an alkali washing mixing device, an alkali washing settling device, a water washing mixing device and a water washing settling device connected in sequence;

[0018] According to the present invention, preferably, the inlet of the alkali washing mixing device is connected to an alkali solution feeding pipeline; the inlet of the water washing mixing device is connected to a washing water feeding pipeline.

[0019] According to the present invention, preferably, the alkali washing mixing device, the alkali washing sedimentation device, the water washing mixing device and the water washing sedimentation device are each independently at least one set, preferably, the water washing mixing device and the water washing sedimentation device are two sets, and the alkali washing mixing device, the alkali washing sedimentation device, the first water washing mixing device, the first water washing sedimentation device, the second water washing mixing device and the second water washing sedimentation device are connected in sequence.

[0020] Another aspect of the present invention provides a method for preparing maleic anhydride and phthalic anhydride by oxidation of n-pentane, wherein the method adopts the system and comprises the following steps:

[0021] S1: sending n-pentane and pressurized air into the reaction subsystem to perform an oxidation reaction to obtain a reaction product;

[0022] S2: For the solvent absorption subsystem, the reaction product is introduced into the middle and lower inlet of the solvent absorption subsystem, the solvent is introduced into the upper inlet, and the stripping gas is introduced into the lower inlet; an absorption mixed liquid is obtained at the bottom of the solvent absorption subsystem, and tail gas is obtained at the top;

[0023] S3: For the solvent desorption subsystem, the absorption mixed liquid is introduced into the middle of the solvent desorption subsystem; the desorbed solvent is obtained at the bottom outlet of the solvent desorption subsystem, the tail gas is obtained at the top, and the mixed product is obtained at the upper part;

[0024] S4: sending the desorbed solvent to the solvent refining subsystem for treatment to obtain a refined solvent and use it as part or all of the solvent in step S2; sending the mixed product to the product refining subsystem to obtain a maleic anhydride product at the top outlet of the product refining subsystem and a phthalic anhydride product at the bottom outlet.

[0025] According to the present invention, preferably, the method further comprises sending the tail gas obtained in steps S2 and S3 out of the boundary.

[0026] According to the present invention, preferably, in step S1,

[0027] The stripping gas is at least one of air, nitrogen, CO and CO2;

[0028] The heat removal medium for the oxidation reaction in the reaction subsystem is at least one of molten salt, heat transfer oil and water;

[0029] The molar ratio of n-pentane to pressurized air is 1:(20-30);

[0030] The pressurized air is air pressurized by a compressor;

[0031] The purity of the n-pentane is 98.99-99.99 wt %.

[0032] According to the present invention, preferably, in step S2,

[0033] The solvent is a fresh solvent and / or a refined solvent;

[0034] The fresh solvent is at least one of dibutyl phthalate, diisobutyl hexahydrophthalate, dioctyl phthalate and diisobutyl phthalate;

[0035] The ratio of the molar amount of the solvent to the total molar amount of maleic anhydride and phthalic anhydride in the reaction product is (5-10):1.

[0036] According to the present invention, preferably, in step S4,

[0037] The desorbed solvent is sent to the solvent refining subsystem, and sequentially treated with alkali washing and mixing, alkali washing and settling, water washing and mixing, and water washing and mixing to obtain a refined solvent and use it as part or all of the solvent in step S2; the acid content of the refined solvent is less than 1000 ppm;

[0038] The mass ratio of the maleic anhydride product to the phthalic anhydride product is (1.5-2):1;

[0039] The purity of the maleic anhydride product is 99.5-99.9%;

[0040] The purity of the phthalic anhydride product is 99.5-99.9%.

[0041] According to the present invention, preferably, the operating conditions of the reaction subsystem include: temperature 320-450°C, pressure 0.1-5 MPaG, space velocity 1000-1800 h -1 Preferably, the operating conditions of the reaction subsystem include: temperature 350-400°C, pressure 0.1-0.3 MPaG, space velocity 1200-1500 h -1 .

[0042] According to the present invention, preferably, the operating conditions of the solvent absorption subsystem include: temperature 60-160° C., pressure -30-50 kPaG.

[0043] According to the present invention, preferably, the operating conditions of the solvent desorption subsystem include: temperature 60-200° C., pressure -80-10 kPaG.

[0044] According to the present invention, preferably, the operating conditions of the product refining subsystem include: temperature 100-280° C., pressure 1-10 kPaA.

[0045] According to the present invention, preferably, the operating conditions of the solvent refining subsystem include: temperature 40-80° C., pressure 0.1-0.5 MPaG.

[0046] The beneficial effects of the technical solution of the present invention are as follows:

[0047] 1) The system and method of the present invention can reduce the acid impurities in maleic anhydride products and phthalic anhydride products through the settings of absorption and desorption, thereby improving the purity of the products;

[0048] 2) The system and method of the present invention can recycle solvents through solvent refining, thereby improving system economy and operating cycle;

[0049] 3) The system and method of the present invention adopts vacuum negative pressure operation (such as the operating conditions of each subsystem), and the operating conditions are mild.

[0050] 4) The solvent absorption subsystem of the present invention can effectively reduce the enrichment of the acidic medium and improve the system operation cycle through stripping with stripping gas.

[0051] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] The above and other objects, features and advantages of the present invention will become more apparent through a more detailed description of exemplary embodiments of the present invention in conjunction with the accompanying drawings, wherein like reference numerals generally represent like components throughout the exemplary embodiments of the present invention.

[0053] Figure 1 A schematic diagram of a system for preparing maleic anhydride and phthalic anhydride by oxidation of n-pentane provided in Example 1 of the present invention is shown.

[0054] The following are the descriptions of the reference numerals:

[0055] Reaction subsystem 1, solvent absorption subsystem 2, solvent analysis subsystem 3, product refining subsystem 4, alkali washing mixing device 5, alkali washing settling device 6, water washing mixing device 7, water washing settling device 8, refined solvent feed pipeline 9, n-pentane feed pipeline 11, boosted air feed pipeline 12, fresh solvent feed pipeline 13, stripping gas feed pipeline 14, tail gas discharge pipeline 15, maleic anhydride product discharge pipeline 16, phthalic anhydride product discharge pipeline 17, alkali solution feed pipeline 18, water washing water feed pipeline 19. DETAILED DESCRIPTION

[0056] The preferred embodiments of the present invention will be described in more detail below. Although the preferred embodiments of the present invention are described below, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to make the present invention more thorough and complete, and to fully convey the scope of the present invention to those skilled in the art.

[0057] Example 1

[0058] This embodiment provides a system for preparing maleic anhydride and phthalic anhydride by oxidation of n-pentane, such as Figure 1 As shown, the system includes a reaction subsystem 1, a solvent absorption subsystem 2, a solvent desorption subsystem 3, a product refining subsystem 4 and a solvent refining subsystem;

[0059] The reaction subsystem 1 is a tube-in-tube fixed bed;

[0060] The inlet of the reaction subsystem 1 is connected to a n-pentane feed pipeline 11 and a pressurized air feed pipeline 12; the outlet of the reaction subsystem 1 is connected to the middle and lower inlet of the solvent absorption subsystem 2;

[0061] The upper inlet of the solvent absorption subsystem 2 is connected to a fresh solvent feed pipeline 13 and a refined solvent feed pipeline 9; the lower inlet of the solvent absorption subsystem 2 is connected to a stripping gas feed pipeline 14;

[0062] The bottom outlet of the solvent absorption subsystem 2 is connected to the middle inlet of the solvent desorption subsystem 3; the top outlet of the solvent absorption subsystem 2 and the top outlet of the solvent desorption subsystem 3 are both connected to an exhaust gas discharge pipeline 15, and the exhaust gas discharge pipeline 15 is connected to the outside;

[0063] The bottom outlet of the solvent desorption subsystem 3 is connected to the refined solvent feed pipeline 9 through the solvent refining subsystem; the upper product outlet of the solvent desorption subsystem 3 is connected to the inlet of the product refining subsystem 4;

[0064] The top outlet of the product refining subsystem 4 is connected to a maleic anhydride product discharge pipeline 16;

[0065] The bottom outlet of the product refining subsystem 4 is connected to a phthalic anhydride product discharge pipeline 17 .

[0066] The solvent absorption subsystem 2 is an absorption tower with 35 plates;

[0067] The solvent desorption subsystem 3 is a packed tower with a packing height of 5.5 m;

[0068] The product refining subsystem 4 is a refining tower with 20 plates;

[0069] The solvent refining subsystem includes an alkali washing mixing device 5, an alkali washing settling device 6, a water washing mixing device 7 and a water washing settling device 8 which are connected in sequence; the inlet of the alkali washing mixing device 5 is connected to an alkali liquid feed pipeline 18; the inlet of the water washing mixing device 7 is connected to a water washing water feed pipeline 19.

[0070] This embodiment also provides a method for preparing maleic anhydride and phthalic anhydride by oxidation of n-pentane, wherein the method adopts the above-mentioned system and comprises the following steps:

[0071] S1: n-pentane (100,000 tons / year processing capacity, 99.0 wt% content) and pressurized air (pressurized by a compressor) (molar ratio of 1:25) are fed into a tube-in-tube fixed bed for oxidation reaction (temperature 380°C, pressure 0.2 MPaG, space velocity 1500 h -1 , the heat removal medium is molten salt, and the temperature at the outlet of the tube-in-tube fixed bed can be reduced to 200°C through drum heat exchange to obtain the reaction product;

[0072] S2: For the solvent absorption subsystem 2, the (tower top / tower bottom) temperature is 70 / 160° C. and the pressure is 10 / 35 kPaG. The reaction product is introduced into the middle and lower inlet of the solvent absorption subsystem 2, the solvent (dioctyl phthalate, the solvent / (maleic anhydride+phthalic anhydride) molar ratio is 8) is introduced into the upper inlet, and the stripping gas (air) is introduced into the lower inlet; the absorption mixed liquid is obtained at the bottom of the solvent absorption subsystem 2, and the tail gas is obtained at the top;

[0073] S3: For the solvent desorption subsystem 3, the (tower top / tower bottom) temperature is 90 / 190°C, the pressure is 2 / 5kPaA, and the reflux molar ratio is 5, so that the absorption mixed liquid enters the middle part of the solvent desorption subsystem 3; the desorbed solvent is obtained at the bottom outlet of the solvent desorption subsystem 3, the tail gas is obtained at the top, and the mixed product is obtained at the upper part; the tail gas obtained in the steps S2 and S3 is sent out of the boundary;

[0074] S4: sending the desorbed solvent to the solvent refining subsystem, with a (tower top / tower bottom) temperature of 120 / 280°C, a pressure of 10 / 25 kPaG, a reflux molar ratio of 5, and sequentially undergoing alkali washing and mixing (5% NaOH aqueous solution), alkali washing and sedimentation, water washing and mixing, and water washing and mixing treatment (the temperature of the treatment process is 40°C and the pressure is 0.1 MPaG) to obtain a refined solvent (with an acid content of less than 1000 ppm) and use it as part or all of the solvent in step S2; sending the mixed product to the product refining subsystem 4, obtaining a maleic anhydride product at the top outlet of the product refining subsystem 4, and a phthalic anhydride product at the bottom, wherein the mass ratio of maleic anhydride to phthalic anhydride is 1.88:1, the maleic anhydride purity is 99.6%, and the phthalic anhydride purity is 99.8%.

[0075] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A system for preparing maleic anhydride and phthalic anhydride by oxidation of n-pentane, characterized in that: The system comprises a reaction subsystem, a solvent absorption subsystem, a solvent desorption subsystem, a product refining subsystem and a solvent refining subsystem; The inlet of the reaction subsystem is connected to a n-pentane feed pipeline and a pressurized air feed pipeline; the outlet of the reaction subsystem is connected to the middle and lower inlet of the solvent absorption subsystem; The upper inlet of the solvent absorption subsystem is connected to a fresh solvent feed pipeline and a refined solvent feed pipeline; the lower inlet of the solvent absorption subsystem is connected to a stripping gas feed pipeline; The bottom outlet of the solvent absorption subsystem is connected to the middle inlet of the solvent desorption subsystem; the top outlet of the solvent absorption subsystem and the top outlet of the solvent desorption subsystem are both connected to tail gas discharge pipelines; The bottom outlet of the solvent desorption subsystem is connected to the refined solvent feed pipeline through the solvent refining subsystem; the upper product outlet of the solvent desorption subsystem is connected to the inlet of the product refining subsystem; The top outlet of the product refining subsystem is connected to a maleic anhydride product discharge pipeline; The bottom outlet of the product refining subsystem is connected with a phthalic anhydride product discharge pipeline.

2. The system for preparing maleic anhydride and phthalic anhydride by oxidation of n-pentane according to claim 1, wherein: The reaction subsystem is a tube-in-tube fixed bed and / or a fluidized bed, preferably a tube-in-tube fixed bed; The solvent absorption subsystem is an absorption tower with 20 to 45 plates; The solvent desorption subsystem is a packed tower with a packing height of 4 to 10 m; The product refining subsystem is a refining tower with 15 to 25 plates.

3. The system for preparing maleic anhydride and phthalic anhydride by oxidation of n-pentane according to claim 1, wherein: The tail gas discharge pipeline is connected to the outside; The solvent refining subsystem comprises an alkali washing mixing device, an alkali washing settling device, a water washing mixing device and a water washing settling device connected in sequence; The inlet of the alkali washing mixing device is connected to an alkali solution feeding pipeline; the inlet of the water washing mixing device is connected to a washing water feeding pipeline.

4. The system for preparing maleic anhydride and phthalic anhydride by oxidation of n-pentane according to claim 3, wherein: The alkali washing mixing device, alkali washing sedimentation device, water washing mixing device and water washing sedimentation device are each independent of each other and are at least one set. Preferably, the water washing mixing device and water washing sedimentation device are each two sets, and the alkali washing mixing device, alkali washing sedimentation device, the first water washing mixing device, the first water washing sedimentation device, the second water washing mixing device and the second water washing sedimentation device are connected in sequence.

5. A method for preparing maleic anhydride and phthalic anhydride by oxidation of n-pentane, characterized in that: The method adopts the system according to any one of claims 1 to 4, comprising the following steps: S1: sending n-pentane and pressurized air into the reaction subsystem to perform an oxidation reaction to obtain a reaction product; S2: For the solvent absorption subsystem, the reaction product is introduced into the middle and lower inlet of the solvent absorption subsystem, the solvent is introduced into the upper inlet, and the stripping gas is introduced into the lower inlet; an absorption mixed liquid is obtained at the bottom of the solvent absorption subsystem, and tail gas is obtained at the top; S3: For the solvent desorption subsystem, the absorption mixed liquid is introduced into the middle of the solvent desorption subsystem; the desorbed solvent is obtained at the bottom outlet of the solvent desorption subsystem, the tail gas is obtained at the top, and the mixed product is obtained at the upper part; S4: sending the desorbed solvent to the solvent refining subsystem for treatment to obtain a refined solvent and use it as part or all of the solvent in step S2; sending the mixed product to the product refining subsystem to obtain a maleic anhydride product at the top outlet of the product refining subsystem and a phthalic anhydride product at the bottom outlet.

6. The method for preparing maleic anhydride and phthalic anhydride by oxidation of n-pentane according to claim 5, wherein: The method further comprises sending the tail gas obtained in steps S2 and S3 out of the boundary.

7. The method for preparing maleic anhydride and phthalic anhydride by oxidation of n-pentane according to claim 5, wherein: In step S1, The stripping gas is at least one of air, nitrogen, CO and CO2; The heat removal medium for the oxidation reaction in the reaction subsystem is at least one of molten salt, heat transfer oil and water; The molar ratio of n-pentane to pressurized air is 1:(20-30); The pressurized air is air pressurized by a compressor; The purity of the n-pentane is 98.99-99.99 wt %.

8. The method for preparing maleic anhydride and phthalic anhydride by oxidation of n-pentane according to claim 5, wherein: In step S2, The solvent is a fresh solvent and / or a refined solvent; The fresh solvent is at least one of dibutyl phthalate, diisobutyl hexahydrophthalate, dioctyl phthalate and diisobutyl phthalate; The ratio of the molar amount of the solvent to the total molar amount of maleic anhydride and phthalic anhydride in the reaction product is (5-10):

1.

9. The method for preparing maleic anhydride and phthalic anhydride by oxidation of n-pentane according to claim 5, wherein: In step S4, The desorbed solvent is sent to the solvent refining subsystem, and sequentially treated with alkali washing and mixing, alkali washing and settling, water washing and mixing, and water washing and mixing to obtain a refined solvent and use it as part or all of the solvent in step S2; the acid content of the refined solvent is less than 1000 ppm; The mass ratio of the maleic anhydride product to the phthalic anhydride product is (1.5-2):1; The purity of the maleic anhydride product is 99.5-99.9%; The purity of the phthalic anhydride product is 99.5-99.9%.

10. The method for preparing maleic anhydride and phthalic anhydride by oxidation of n-pentane according to claim 5, wherein: The operating conditions of the reaction subsystem include: temperature 320-450°C, pressure 0.1-5 MPaG, space velocity 1000-1800 h -1 Preferably, the operating conditions of the reaction subsystem include: temperature 350-400°C, pressure 0.1-0.3 MPaG, space velocity 1200-1500 h -1 ; The operating conditions of the solvent absorption subsystem include: temperature 60-160°C, pressure -30-50kPaG; The operating conditions of the solvent desorption subsystem include: temperature 60 to 200°C, pressure -80 to 10 kPaG; The operating conditions of the product refining subsystem include: temperature 100-280°C, pressure 1-10 kPaA; The operating conditions of the solvent refining subsystem include: temperature 40-80° C., pressure 0.1-0.5 MPaG.

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