N-butane fixed bed oxidation and DBP solvent absorption system, molecular sieve membrane and preparation method

Abstract

The invention relates to the technical field of maleic anhydride production, in particular to an n-butane fixed bed oxidation and DBP solvent absorption system, a molecular sieve membrane and a preparation method, the system comprises an air pretreatment unit, an oxidation unit and an absorption unit; the oxidation unit comprises an n-butane evaporation tank, an air-butane mixer, an oxidation reactor, a fused salt cooler, a gas cooler and a switching cooler; a molecular sieve filter body is arranged at a bottom outlet of the switching cooler; the absorption unit comprises an absorption tower, and the absorption tower is used for absorbing crude maleic anhydride in the reaction generated gas passing through the molecular sieve filter body; the molecular sieve filtering body is provided with an inlet for the reaction generated gas to enter, an outlet for the reaction generated gas to release and an internal cavity for communicating the inlet and the outlet, and after the reaction generated gas in the cavity is released through the outlet, part of water is filtered. The system can be used for efficiently adsorbing and removing moisture in the butane oxidation generated gas, and coking of equipment is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of maleic anhydride production, and specifically to a system, a molecular sieve membrane and a preparation method for n-butane fixed-bed oxidation and DBP solvent absorption. Background Art

[0002] As the dominant method for maleic anhydride production, n-butane fixed-bed oxidation uses n-butane as the raw material, and under the action of a catalyst, a gas containing maleic anhydride is generated through a gas-phase oxidation reaction. In the reaction process, n-butane is first dehydrogenated to form butadiene, and then oxidized to form maleic anhydride. Due to reasons such as the low price of the raw material (compared with the benzene method) and less environmental pollution, this method has developed rapidly and currently accounts for about 80% of the total global maleic anhydride production capacity.

[0003] The maleic anhydride generating gas generated by the oxidation reaction also needs to go through unit operations such as DBP solvent absorption, desorption, and refining before the product can be obtained. The specific production process is as follows: First, the maleic anhydride in the gas generated by the oxidation reaction is absorbed by the solvent DBP in the absorption system, and then the maleic anhydride is desorbed from the DBP in the desorption system. The waste gas at the absorption tower top is sent to the tail gas treatment unit for incineration treatment. The crude maleic anhydride produced by desorption enters the refining system for further refining to meet the specifications of the finished product. A part of the lean DBP solvent desorbed enters the solvent treatment system, where it is first stirred and mixed with desalted water in a certain proportion and then enters a disc centrifuge to remove impurities such as fumaric acid and tar in the lean solvent (when the impurity concentration is high, it will cause blockage of the system). The treated solvent returns to the absorption system. The process of producing maleic anhydride by n-butane fixed-bed oxidation and DBP solvent absorption mainly involves absorbing the maleic anhydride-containing gas generated by the oxidation of n-butane and air with the DBP solvent, and then obtaining a purer maleic anhydride product through desorption and refining.

[0004] Since the maleic anhydride reaction generating gas contains more than 5 wt% of water, reactions will occur after entering the DBP absorption and desorption systems. The following is the reaction mechanism of maleic anhydride and water and the isomerization mechanism of maleic acid.

[0005]

[0006]

[0007] In the maleic anhydride production process, due to the presence of water in the reaction generating gas, after the above reactions, coking occurs in the equipment after running for a period of time, and the equipment has to be stopped for cleaning. A higher water content may not only cause side effects of chemical reactions but also lead to poor stability and inconsistent performance of the final product. Therefore, reducing the water content in the maleic anhydride reaction generating gas has become the key to extending the stable operation time of the equipment. Common water removal methods include condensation, adsorption, and drying, etc., but these methods often have disadvantages such as high energy consumption, low efficiency, and complex operation.

[0008] In view of the above challenges, it is particularly important to adopt an efficient and accurate method to remove moisture from the reaction-generated gas. Summary of the Invention

[0009] To solve the above technical problems existing in the prior art, the present invention discloses a system for the oxidation of n-butane in a fixed bed and the absorption of DBP solvent, a molecular sieve membrane and a preparation method thereof. The molecular sieve filter body provided at the bottom of the switching cooler can effectively reduce the moisture in the maleic anhydride reaction-generated gas, reduce the side reactions in the DBP absorption and desorption process, reduce the coking of the equipment, and extend the continuous operation time of the equipment.

[0010] One of the purposes of the present invention is to provide a system for the oxidation of n-butane in a fixed bed and the absorption of DBP solvent, which includes an air pretreatment unit, an oxidation unit and an absorption unit; the air pretreatment unit includes an air filter, an air compressor, a humidifying mixer and an air heater connected in sequence; the oxidation unit includes an n-butane evaporation tank, an air-butane mixer, an oxidation reactor, a molten salt cooler, a gas cooler and a switching cooler; A molecular sieve filter body is provided at the bottom outlet of the switching cooler; the absorption unit includes an absorption tower, and the absorption tower is used to absorb the crude maleic anhydride in the reaction-generated gas after passing through the molecular sieve filter body; The molecular sieve filter body has an inlet for the reaction-generated gas to enter, an outlet for the reaction-generated gas to be released, and an internal cavity connecting the inlet and the outlet. After the reaction-generated gas in the cavity is released through the outlet, part of the moisture is filtered.

[0011] Further, the molecular sieve filter body includes a support body, and the inlet and the outlet are provided on the support body; the outlet is covered with a molecular sieve membrane.

[0012] Further, after the reaction-generated gas passes through the molecular sieve filter body, the moisture content is reduced to 0.42 - 0.49 wt%.

[0013] The present invention also discloses a molecular sieve membrane for the system for the oxidation of n-butane in a fixed bed and the absorption of DBP solvent.

[0014] The present invention also discloses a preparation method of a molecular sieve membrane for the system for the oxidation of n-butane in a fixed bed and the absorption of DBP solvent, which includes the following steps: S1. Mix tetraethoxysilane, tetrapropylammonium hydroxide and deionized water, and carry out hydrothermal synthesis; S2. Recover the hydrothermal synthesis product in S1 by ultracentrifugation, wash and calcine it to obtain the required nanocrystal seeds; S3. Then add SiO 2 , Al 2 O 3 , Na2 O, NaF, H 2 Mix O and NaF, H for aging by stirring to obtain a sol; S4. Then insert the α-Al tubular support coated with nanoseeds 2 O 3 into the reaction kettle containing the sol; perform secondary hydrothermal synthesis in a blast drying oven to obtain ZSM-5 membrane; S5. Finally, take out the α-Al tubular support with the formed membrane 2 O 3 from the stainless steel reaction kettle, repeatedly boil it with ultrapure water until the moisture on the membrane surface reaches neutrality, and place it in a blast drying oven for drying to obtain the molecular sieve.

[0015] Further, in step S1, the molar ratio of tetraethoxysilane, tetrapropylammonium hydroxide and deionized water is 5:(0.5~1.5):(90~100).

[0016] Further, in step S1, the temperature of the hydrothermal synthesis reaction is 90~100 °C, and the reaction time is 42~54 h.

[0017] Further, in step S2, the nanoseeds are washed until neutral.

[0018] Further, in step S3, SiO 2 , Al 2 O 3 , Na 2 O, NaF, H 2 O are mixed according to the molar ratio of 100:(3~6):(18~25):(95~105):(4800~5200); In step S3, the stirring temperature is 25~40 °C; the aging time is 2~5 h.

[0019] Furthermore, in step S4, the temperature of the blast drying oven is 145 °C~175 °C; the secondary hydrothermal reaction time is 12~48 h.

[0020] The beneficial effects of the present invention are: In the system for the oxidation of n-butane in a fixed bed and the absorption of DBP by a solvent according to the present invention, the molecular sieve filter is disposed at the bottom outlet of the switching cooler. This design enables the reaction product gas to be efficiently dried by passing through the molecular sieve filter before entering the absorption tower, significantly reducing the water content in the reaction product gas. In this way, the molecular sieve filter not only reduces the hydration reaction and isomerization reaction during the absorption and desorption of DBP, but also effectively prevents coking of the equipment and extends the continuous operation time of the equipment. Through experimental verification, the system using the molecular sieve filter of the present invention can reduce the water content in the reaction product gas from 5.49 wt% to 0.42 - 0.49 wt%, significantly improving the stability and operation efficiency of the system, and the stable operation time of production can reach more than 8600 hours.

[0021] The molecular sieve membrane preparation process of the present invention realizes the efficient preparation of ZSM-5 molecular sieve membranes through carefully designed steps and precisely controlled process parameters.

[0022] Specifically: 1) By controlling the molar ratios of TEOS, TPAOH, and deionized water, as well as the temperature and time of hydrothermal synthesis, a precursor gel with a good structure is formed, laying the foundation for subsequent synthesis; 2) By subjecting the hydrothermal synthesis product to ultracentrifugation recovery, washing to neutrality, and calcination, nanocrystalline seeds are prepared. As the "seeds" for inducing crystal growth, they help control the crystal morphology and size of the molecular sieve; 3) Mix SiO 2 , Al 2 O 3 , Na 2 O, NaF, H 2 O in specific molar ratios and stir and age to obtain a sol, providing a uniform reaction medium for secondary hydrothermal synthesis; 4) Insert the α-Al 2 O 3 tubular support coated with nanocrystalline seeds into the sol, and conduct secondary hydrothermal synthesis at appropriate temperature and time to obtain ZSM-5 membranes. The use of the α-Al 2 O 3 tubular support ensures the mechanical strength and thermal stability of the molecular sieve membrane; 5) Boil with ultrapure water to neutrality and dry to remove impurities and excess water to obtain a molecular sieve with excellent performance.

[0023] In summary, the present invention not only improves the efficiency and quality of maleic anhydride production, but also significantly reduces the equipment maintenance cost and downtime, and has important industrial application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1Application diagram of molecular sieve membrane in the system of n-butane fixed bed oxidation and DBP solvent absorption.

[0025] In the figure: 1. Air filter; 2. Air compressor; 3. Humidifying mixer; 4. Air heater; 5. n-Butane evaporation tank; 6. Air-butane mixer; 7. Oxidation reactor; 8. Molten salt cooler; 9. Gas cooler; 10. Switching cooler; 11. Molecular sieve filter body; 12. Absorption tower. Specific implementation mode

[0026] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention; obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0027] Embodiment 1 This embodiment discloses a method for preparing a molecular sieve membrane for a system of n-butane fixed bed oxidation and DBP solvent absorption, including the following steps: S1. Mix tetraethoxysilane (TEOS), tetrapropylammonium hydroxide (TPAOH) and deionized water in a molar ratio of 5:1:96, and perform hydrothermal synthesis at 95 °C for 48 hours; S2. Recover the hydrothermal synthesis product in S1 by ultracentrifugation and wash it until the pH is about 7, and calcine it at 480 °C for 4 hours to remove the organic template to obtain the required nanoseeds; S3. Mix SiO 2 , Al 2 O 3 , Na 2 O, NaF, H 2 O in a molar ratio of 100:3:20:99:5000, stir at 25 °C, and age for 2 h to prepare a sol; S4. Transfer the sol prepared in S3 to a stainless steel autoclave, and insert an α-Al 2 O 3 tubular support with a pore size of 200 nm, a diameter of 12 mm, a wall thickness of 2 mm, a length of 60 mm and coated with nanoseeds vertically into the autoclave; place the autoclave in a forced air oven and perform hydrothermal reaction at 165 °C for 24 hours to obtain a ZSM-5 membrane synthesized by washing with deionized water; S5. Take out the ZSM-5 membrane from the autoclave, wash the membrane surface repeatedly with boiling water until it is neutral, and place it in an oven at 60 °C to dry to obtain a molecular sieve membrane.

[0028] Embodiment 2 This embodiment discloses a method for preparing a molecular sieve membrane for a system of n-butane fixed-bed oxidation and DBP solvent absorption, comprising the following steps: S1. Mix tetraethyl orthosilicate (TEOS), tetrapropylammonium hydroxide (TPAOH) and deionized water in a molar ratio of 5:1:96, and conduct hydrothermal synthesis at 95 °C for 48 hours; S2. Recover the hydrothermal synthesis product in S1 by ultracentrifugation and wash it until the pH is about 7, and calcine it at 480 °C for 4 hours to remove the organic template to obtain the required nanocrystalline seeds; S3. Mix SiO 2 , Al 2 O 3 , Na 2 O, NaF, H 2 O in a molar ratio of 100:6:25:105:5000, stir at 27 °C, and age for 5 h to prepare a sol; S4. Transfer the sol prepared in S3 to a stainless-steel autoclave, and vertically insert an α-Al 2 O 3 tubular support with a pore diameter of 200 nm, a diameter of 12 mm, a wall thickness of 2 mm, a length of 60 mm and coated with seeds into the autoclave; place the autoclave in a forced-air oven and conduct hydrothermal reaction at 165 °C for 48 hours to obtain a ZSM-5 membrane synthesized by washing with deionized water; S5. Take out the ZSM-5 membrane from the autoclave, repeatedly wash the membrane surface with boiling water until it is neutral, and place it in an oven at 60 °C to dry to obtain a molecular sieve membrane.

[0029] Example 3 This embodiment discloses a method for preparing a molecular sieve membrane for a system of n-butane fixed-bed oxidation and DBP solvent absorption, comprising the following steps: S1. Mix tetraethyl orthosilicate (TEOS), tetrapropylammonium hydroxide (TPAOH) and deionized water in a molar ratio of 5:1:96, and conduct hydrothermal synthesis at 95 °C for 48 hours; S2. Recover the hydrothermal synthesis product in S1 by ultracentrifugation and wash it until the pH is about 7, and calcine it at 480 °C for 4 hours to remove the organic template to obtain the required nanocrystalline seeds; S3. Mix SiO 2 , Al 2 O 3 , Na 2 O, NaF, H 2 O in a molar ratio of 100:5:25:100:4900, stir at 25 °C, and age for 3 h to prepare a sol; S4. Transfer the sol prepared in S3 into a stainless-steel autoclave, and vertically insert an α-Al tubular support with a pore size of 200 nm, a diameter of 12 mm, a wall thickness of 2 mm, a length of 60 mm and coated with nanoseeds into the autoclave; place the autoclave in a forced-air oven and carry out hydrothermal reaction at 165 °C for 12 hours to obtain a synthesized ZSM-5 membrane washed with deionized water; 2 O 3 S5. Take out the ZSM-5 membrane from the autoclave, repeatedly wash the membrane surface with boiling water until it is neutral, and place it in an oven at 60 °C for drying to obtain a molecular sieve membrane.

[0030] Comparative Example This comparative example discloses a preparation process of a molecular sieve membrane, including the following steps: S1. Mix tetraethyl orthosilicate (TEOS), tetrapropylammonium hydroxide (TPAOH) and deionized water in a molar ratio of 5:1:96, and carry out hydrothermal synthesis at 95 °C for 48 hours; S2. Recover the hydrothermal synthesis product in S1 by ultracentrifugation and wash it until the pH is about 7, and calcine it at 480 °C for 4 hours to remove the organic template to obtain the required nanoseeds; S3. Mix SiO 2 , Al 2 O 3 , Na 2 O, NaF, H 2 O in a molar ratio of 100:7:15:90:4700, stir at 30 °C and age for 12 h to prepare a sol; S4. Transfer the sol prepared in S3 into a stainless-steel autoclave, and vertically insert the α-Al tubular support coated with the nanoseeds into the autoclave. The pore size of the α-Al support is 200 nm, the diameter is 12 mm, the wall thickness is 2 mm, and the length is 60 mm; place the autoclave in a forced-air oven and carry out hydrothermal reaction at 165 °C for 12 hours to obtain a synthesized ZSM-5 membrane washed with deionized water; 2 O 3 2 O 3 S5. Take out the ZSM-5 membrane from the autoclave, repeatedly wash the membrane surface with boiling water until it is neutral, and place it in an oven at 60 °C for drying to obtain a molecular sieve membrane.

[0031] ​​​In the laboratory, after the simulated gas generated from the oxidation of butane passes through the adsorption column equipped with the molecular sieve membrane, the water content can be reduced from 5% to 0.5%, showing excellent dehydration effect. The data of the reaction-generated gas before and after passing through different molecular sieve membranes and the corresponding production time are shown in Table 1.

[0032] Table 1

[0033] As can be seen from the data in Table 1, the molecular sieves prepared in Examples 1 to 3 can reduce the water content in the reaction-generated gas passing through water to less than 0.5 wt%, reduce the side reactions in the DBP absorption and desorption process, reduce the coking of equipment, and extend the continuous operation time of the equipment.

[0034] Based on the above experimental results, the present invention proposes that the molecular sieve membrane can be applied to the maleic anhydride production technology field and a supporting process flow be developed.

[0035] Application Example This application example discloses a system containing the molecular sieve membrane described in Examples 1 to 3 and used for the oxidation of n-butane in a fixed bed and the absorption of DBP solvent. The system includes an air pretreatment unit, an oxidation unit, and an absorption unit; The air pretreatment unit includes an air filter 1, an air compressor 2, a humidifying mixer 3, and an air heater 4 connected in sequence; ambient air, as the raw material for the oxidation reaction, is filtered, compressed, humidified, and heated by the air pretreatment unit and then transported to the oxidation unit.

[0036] The oxidation unit includes an n-butane evaporation tank 5, an air-butane mixer 6, an oxidation reactor 7, a molten salt cooler 8, a gas cooler 9, and a switching cooler 10; high-purity liquefied n-butane enters the n-butane evaporation tank, vaporizes and superheats to a specific temperature, mixes with the humidified air to form a mixed gas with a certain concentration, and enters the oxidation reactor; under the action of a catalyst and high-temperature conditions, a gas-solid catalytic oxidation reaction occurs to generate maleic anhydride, and the heat released by the reaction is removed by molten salt. Part of the molten salt exchanges heat with boiler water in the shell side of the molten salt cooler to generate steam, while cooling the molten salt; the temperature of the molten salt in the shell side of the reactor is controlled by adjusting the flow rate of the molten salt flowing through the molten salt cooler; the gas after the oxidation reaction is cooled by the cooler and then sent to the absorption tower of the absorption unit. The boiler water in the shell sides of the gas cooler and the switching cooler is heated and partially vaporized, separated from the steam generated by the molten salt cooler in the steam drum, and high-pressure saturated steam is produced. A small part is sent to the desorption system as a heating medium, and the rest is sent to the tail gas treatment unit. The generated high-pressure superheated steam is all used to drive the back-pressure steam turbine supporting the air compressor, and the superheated steam after back-pressure is supplied to the maleic anhydride unit after being desuperheated and depressurized.

[0037] The molecular sieves of Examples 1 to 3 and the comparative example were respectively made into molecular sieve filter bodies 11, which were arranged at the bottom outlet of the switching cooler 10; it should be noted that the molecular sieve filter body 11 has an inlet for the reaction product gas to enter, an outlet for the reaction product gas to be released, and the molecular sieve filter body includes a support body, on which the inlet, the outlet and an internal cavity connecting the inlet and the outlet are provided; a molecular sieve membrane is covered at the outlet. After the reaction product gas in the cavity is released through the outlet, a part of the moisture is filtered. When the moisture content in the molecular sieve filter body reaches a certain level, it is replaced during the cleaning of the switching cooler.

[0038] The absorption unit includes an absorption tower 12; the crude maleic anhydride in the reaction product gas discharged from the oxidation unit switching cooler and passing through the molecular sieve filter body is absorbed by a large amount of rich solvent circulated in the absorption tower and a small amount of lean solvent supplemented at the top of the tower. The rich solvent at the bottom of the absorption tower after absorption is transported to the desorption tower, and the tail gas containing a small amount of organic matter is transported to the tail gas treatment unit.

[0039] Although the present invention has been described above with reference to the embodiments, various improvements can be made to it and its components can be replaced with equivalents without departing from the scope of the present invention. In particular, as long as there is no structural conflict, the various features in the embodiments disclosed in the present invention can be combined with each other in any way, and the exhaustive description of these combinations is omitted in this specification only for the consideration of saving space and resources. Therefore, the present invention is not limited to the specific embodiments disclosed in the text, but includes all technical solutions falling within the scope of the claims.

Claims

1. A system for n-butane fixed bed oxidation and DBP solvent absorption, comprising an air pretreatment unit, an oxidation unit and an absorption unit; the air pretreatment unit comprises an air filter, an air compressor, a humidifying mixer and an air heater connected in sequence; the oxidation unit comprises an n-butane evaporator, an air butane mixer, an oxidation reactor, a molten salt cooler, a gas cooler and a switching cooler; characterized in that: A molecular sieve filter is provided at the bottom outlet of the switching cooler; the absorption unit comprises an absorption tower, which is used to absorb the crude maleic anhydride in the reaction product gas after passing through the molecular sieve filter; The molecular sieve filter body has an inlet for the reaction product gas to enter, an outlet for the reaction product gas to release, and an internal cavity connecting the inlet and the outlet. After the reaction product gas in the cavity is released through the outlet, a part of the water is filtered.

2. The system for n-butane fixed bed oxidation and DBP solvent absorption according to claim 1, characterized in that: The molecular sieve filter body comprises a support body, on which the inlet and outlet are arranged; the outlet is covered with a molecular sieve membrane.

3. The system for n-butane fixed bed oxidation and DBP solvent absorption according to claim 1, characterized in that: After the reaction generated gas passes through the molecular sieve filter, the moisture content is reduced to 0.42-0.49wt%.

4. A molecular sieve membrane used in the system for n-butane fixed bed oxidation and DBP solvent absorption as claimed in claim 1.

5. A method for preparing a molecular sieve membrane for a system for n-butane fixed bed oxidation and DBP solvent absorption as claimed in claim 4, characterized in that: The steps include: S1, mixing tetraethoxysilane, tetrapropylammonium hydroxide and deionized water for hydrothermal synthesis; S2, recovering the hydrothermal synthesis product in S1 by ultracentrifugation, washing and calcining to obtain the desired nanocrystalline seeds; S3, mixing SiO2, Al2O3, Na2O, NaF and H2O and stirring them for aging to obtain a sol; S4, then inserting the α-Al2O3 tubular support coated with nanocrystalline seeds into a reaction kettle containing sol; performing secondary hydrothermal synthesis in a blast drying oven to obtain a ZSM-5 membrane; S5. Finally, the formed α-Al2O3 tubular support is taken out from the stainless steel reactor, and is repeatedly boiled with ultrapure water until the moisture on the membrane surface reaches neutrality. The support is then placed in a forced air drying oven for drying to obtain a molecular sieve.

6. The method for preparing a molecular sieve membrane for a system for n-butane fixed bed oxidation and DBP solvent absorption according to claim 5, characterized in that: In step S1, the molar ratio of tetraethoxysilane, tetrapropylammonium hydroxide and deionized water is 5:(0.5-1.5):(90-100).

7. The method for preparing a molecular sieve membrane for a system for n-butane fixed bed oxidation and DBP solvent absorption according to claim 5, characterized in that: The temperature of the hydrothermal synthesis reaction in step S1 is 90-100° C., and the reaction time is 42-54 h.

8. The method for preparing a molecular sieve membrane for a system for n-butane fixed bed oxidation and DBP solvent absorption according to claim 5, characterized in that: In step S2, the nanocrystal seeds are cleaned to be neutral.

9. The method for preparing a molecular sieve membrane for a system for n-butane fixed bed oxidation and DBP solvent absorption according to claim 5, characterized in that: In step S3, SiO2, Al2O3, Na2O, NaF, and H2O are mixed in a molar ratio of 100:(3-6):(18-25):(95-105):(4800-5200); the stirring temperature is 25-40°C; and the aging time is 2-5h.

10. The method for preparing a molecular sieve membrane for a system for fixed-bed oxidation of n-butane and absorption of DBP solvents as claimed in claim 5, wherein the temperature of the blast oven in step S4 is 145°C to 175°C; and the secondary hydrothermal reaction time is 12 to 48 hours.

Images