Method for preparing tetrahydrofuran through dehydration of 1, 4-butanediol in air atmosphere

Abstract

The invention belongs to the technical field of chemical engineering, and particularly relates to a method for preparing tetrahydrofuran through dehydration of 1, 4-butanediol in an air atmosphere, which comprises the following steps: (1) adding 1, 4-butanediol and water into a glass kettle, and stirring until the 1, 4-butanediol is completely dissolved to obtain a homogeneous phase mixed solution of the 1, 4-butanediol and the water; (2) preheating a homogeneous-phase mixed solution of 1, 4-butanediol and water by a preheater, conveying the preheated homogeneous-phase mixed solution to a fixed bed reactor by a liquid inlet pump, carrying out a reaction, filling a reaction section of the fixed bed reactor with a catalyst, filling quartz sand at two ends of the catalyst respectively, and introducing air into the fixed bed reactor; (3) condensing the reaction product obtained in the step (2) by a condenser, flowing into a crude product tank, and conveying to a THF rectifying tower for purification; (4) condensing components separated from the tower top of the THF rectifying tower through a condenser II, and storing the condensed components into a THF finished product tank; the fixed bed reactor is adopted, operation is relatively simple, and reaction conditions are easy to control.

Description

Technical Field

[0001] The present application belongs to the field of chemical technology, and specifically relates to a method for preparing tetrahydrofuran by dehydrating 1,4-butanediol under air atmosphere. Background Art

[0002] Tetrahydrofuran (THF) is an important organic chemical and fine chemical raw material. It is colorless, volatile, and miscible with water and a variety of organic solvents. THF's excellent solvent properties make it known as a "universal solvent". THF is widely used to dissolve natural and synthetic resins (such as polyvinyl chloride, rubber, etc.), and as a reaction solvent, it participates in the synthesis of Grignard reagents, alkyl alkali metal compounds, aryl alkali metal compounds, and high molecular polymers. In addition, THF is a key monomer for the synthesis of polytetramethylene ether glycol (PTMEG), which is an important raw material for the manufacture of spandex, polyurethane elastomers, and high-performance fibers. In the fields of medicine, electronics, coatings, etc., THF also plays an important role as an intermediate or solvent.

[0003] At present, the production methods of THF mainly include furfural method, maleic anhydride hydrogenation method and 1,4-butanediol (BDO) dehydration method. The furfural method has the problems of high raw material consumption, many by-products and serious environmental pollution; the maleic anhydride hydrogenation method is limited by raw material supply and difficult to promote on a large scale. In contrast, the 1,4-butanediol dehydration method has become the current mainstream process due to its simple process, low equipment investment and high product selectivity (the by-product is only water).

[0004] The dehydration of 1,4-butanediol is usually carried out under the action of acid catalysts. Among them, inorganic acid catalysts (such as sulfuric acid and phosphoric acid), metal salts (such as sulfates, phosphates or metal salts of halides) and ionic liquids (such as [HO-EtMIm][OTf]) have high activity and mild reaction conditions, but there are problems such as difficulty in product separation, strong equipment corrosion, and environmental pollution, which significantly increase the cost of equipment and post-processing; metal oxides (such as γ-Al2O3, ZrO2), supported catalysts (such as CuO / ZSM-5), heteropoly acids and their salts (such as Y2P2W 18 O 62 、La2P2W 18 O 62Although heterogeneous catalysts such as ·nH2O / MWCNTs), resins (such as sulfonic acid resins) and molecular sieves (such as modified silica-alumina molecular sieves) are recyclable and have low corrosiveness, they still require inert gas protection and face technical bottlenecks such as low reaction rate, unsatisfactory THF yield, large or expensive catalyst dosage, and difficulty in catalyst regeneration. In addition, green processes (such as high-temperature liquid water / CO2 systems) are environmentally friendly and have good reaction effects, but the reaction conditions are relatively harsh and have high requirements for equipment (Catalysis Communications 68 (2015) 6-10). Although reactive distillation technology can improve reaction conversion and selectivity, it has problems such as complex processes and high energy consumption.

[0005] The above technical defects seriously restrict the economic and sustainable development of THF production, and it is urgent to develop an efficient and stable catalytic system and supporting processes. Summary of the invention

[0006] In order to solve the problems of the prior art, the present application provides a method for preparing tetrahydrofuran by dehydrating 1,4-butanediol under air atmosphere, which is achieved by the following scheme: A method for preparing tetrahydrofuran by dehydrating 1,4-butanediol in an air atmosphere, the preparation steps are as follows: (1) adding 1,4-butanediol and water into a glass kettle, stirring until 1,4-butanediol is completely dissolved, thereby obtaining a homogeneous mixed solution of 1,4-butanediol and water; (2) preheating the homogeneous mixed solution of 1,4-butanediol and water in a preheater and then conveying it to a fixed bed reactor by a liquid inlet pump for reaction, wherein a catalyst is loaded in a reaction section of the fixed bed reactor, quartz sand is loaded at both ends of the catalyst, and air is introduced into the fixed bed reactor; (3) the reaction obtained in step (2) is heated to 400 ℃ and then heated to 800 ℃; The product is condensed in a condenser and flows into a crude product tank, and then transported to a THF distillation tower for purification; (4) The components separated from the top of the THF distillation tower are condensed in a second condenser and stored in a THF finished product tank. The components separated from the bottom of the THF distillation tower pass through a reboiler, and a part of them is heated and vaporized and then sent back to the THF distillation tower to provide a certain amount of continuously rising steam flow for the distillation operation. The unvaporized part is discharged into a water distillation tower for separation; (5) The water component separated from the top of the water distillation tower is condensed in a condenser and refluxed to step (1) for repeated use, and the components at the bottom of the tower are transported to a waste liquid tank for temporary storage.

[0007] Furthermore, in step (1), the mass ratio of 1,4-butanediol to water is 1-2:1-4.

[0008] Furthermore, in step (2), the temperature in the reaction zone is 180-220° C., the gas hourly space velocity of air is 300 h-1, and the pressure is normal pressure.

[0009] Furthermore, in the step (2), the volume ratio of the amount of quartz sand loaded above the catalyst to the amount of quartz sand loaded below the catalyst in the reaction section is 1:1.

[0010] Furthermore, the total loading amount of the catalyst and quartz sand in the reaction section of step (2) is 100-200 mL, the volume ratio of the loading amount of the catalyst to the quartz sand is 1:9, and the particle size of the quartz sand is smaller than that of the catalyst.

[0011] Furthermore, the catalyst in step (2) is a metal-doped modified metal oxide catalyst; the metal-doped modified metal oxide catalyst is metal-doped modified Al2O3, wherein the doped metal is one or more of Mg, Cu, and Co.

[0012] Furthermore, the molar ratio of Co, Cu, Mg and Al is 8-10:2-4:1.1-1.3:45-55.

[0013] Furthermore, the molar ratio of Co, Cu, Mg and Al is 9:3:1.2:50.

[0014] Furthermore, in step (4), the temperature of the THF distillation tower is 60-80°C; the temperature in the reboiler in step (4) is not lower than the temperature in the THF distillation tower; and the temperature in the water distillation tower in step (5) is 100-120°C.

[0015] Beneficial effects: This application uses a metal oxide solid acid catalyst to achieve liquid phase dehydration of 1,4-butanediol to prepare tetrahydrofuran (THF) in a fixed bed reactor under normal pressure air atmosphere. Compared with the prior art, this application has the following innovative advantages: (1) Outstanding catalyst performance: The solid acid catalyst or metal oxide catalyst or metal-doped modified metal oxide catalyst used has both high mechanical strength and thermal stability. Through the synergistic effect of high specific surface area, strong adsorption and high-density acid sites, it can achieve a 1,4-butanediol conversion rate of ≥99% and a THF selectivity of ≥98%; (2) The process is economical: the solid acid catalyst and the water solvent are less corrosive to the equipment, and the reaction does not require inert gas protection, which reduces the production cost; the existing preparation of tetrahydrofuran is carried out under an inert atmosphere, while the present application carries out the reaction under an air atmosphere, which saves costs. In addition, the process uses a fixed bed reactor, which is relatively simple to operate and the reaction conditions are easy to control; this makes it possible to achieve continuous production and further improves production efficiency; (3) Environmentally friendly features: The catalyst is insoluble in water and organic solvents, and is easy to separate, recycle, and recycle. The 1,4-butanediol dehydration process uses deionized water as a solvent, and the only by-product is water, which effectively reduces the discharge of three wastes and is environmentally friendly. Therefore, this application is more suitable for large-scale industrial production and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for the description of the embodiments are briefly introduced below. Obviously, the drawings described below are only some of the preferred embodiments of the present application, not all of the embodiments. For the preferred embodiments in the present application, for ordinary technicians in this field, other embodiments and drawings can be obtained based on these embodiments and drawings without creative work, and they all belong to the protection scope of the present application.

[0017] Figure 1 This is a schematic diagram of the device structure of an embodiment of the present application; In the figure: 1. glass kettle, 2. preheater, 3. reactor, 4. condenser, 5. crude product tank, 6. THF distillation tower, 7. condenser II, 8. finished product tank, 9. reboiler, 10. water distillation tower, 11. waste liquid tank, 12. water intermediate tank, 13. water raw material tank. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solutions and advantages of the present application clearer, the embodiments of the present application will be further described in detail below. It should be understood that the orientation or position relationship indicated by the terms "upper", "lower", "top", "bottom", "inside", "outside", etc. is based on the orientation or position relationship shown in the accompanying drawings. The above definitions are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the structure referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application.

[0019] Example 1 A method for preparing tetrahydrofuran by dehydrating 1,4-butanediol in an air atmosphere, the preparation steps are as follows: (1) adding 1,4-butanediol and water into a glass kettle, stirring until 1,4-butanediol is completely dissolved, thereby obtaining a homogeneous mixed solution of 1,4-butanediol and water; (2) preheating the homogeneous mixed solution of 1,4-butanediol and water in a preheater and then conveying it to a fixed bed reactor by a liquid inlet pump for reaction, wherein a catalyst is loaded in a reaction section of the fixed bed reactor, quartz sand is loaded at both ends of the catalyst, and air is introduced into the fixed bed reactor; (3) the reaction obtained in step (2) is heated to 400 ℃ and then heated to 800 ℃; The product is condensed in a condenser and flows into a crude product tank, and then transported to a THF distillation tower for purification; (4) The components separated from the top of the THF distillation tower are condensed in a second condenser and stored in a THF finished product tank. The components separated from the bottom of the THF distillation tower pass through a reboiler, and a part of them is heated and vaporized and then sent back to the THF distillation tower to provide a certain amount of continuously rising steam flow for the distillation operation. The unvaporized part is discharged into a water distillation tower for separation; (5) The water component separated from the top of the water distillation tower is condensed in a condenser and refluxed to step (1) for repeated use, and the components at the bottom of the tower are transported to a waste liquid tank for temporary storage.

[0020] Preferably, the solvent in step (1) is deionized water; Furthermore, in step (1), the mass ratio of 1,4-butanediol to deionized water is 1:4; Furthermore, in step (2), the temperature in the reaction zone is 200°C, the atmosphere selected is air, the gas hourly space velocity of the air is 300h-1, and the pressure is normal pressure; Furthermore, in step (2), the volume ratio of the amount of quartz sand loaded above the catalyst to the amount of quartz sand loaded below the catalyst in the reaction section is 1:1; Furthermore, the total loading amount of the catalyst and quartz sand in the reaction section of step (2) is 150 mL, the volume ratio of the loading amount of the catalyst to the quartz sand is 1:9, the particle size of the quartz sand is smaller than the particle size of the catalyst, and the loading amount of the mixture of the catalyst and the quartz sand is 150 mL.

[0021] Furthermore, in step (2), the catalyst is a metal-doped and modified metal oxide catalyst; Furthermore, in step (2), the catalyst is an Al2O3 catalyst doped with metal Cu and Mg, wherein the molar ratio of element Cu, element Mg and element Al is 0.03:0.012:0.5.

[0022] Furthermore, in step (4), the temperature of the THF distillation tower is 75° C.; the temperature in the reboiler in step (4) is not lower than the temperature in the distillation tower; and the temperature in the water distillation tower in step (5) is 110° C.

[0023] Example 2 Compared with Example 1, the difference is that the temperature in the reaction zone in step (2) is 220°C. The results are shown in the table below.

[0024] Example 3 Compared with Example 1, the difference is that the mass ratio of 1,4-butanediol to water is 1:1. The results are shown in the table below.

[0025] Example 4 Compared with Example 1, the difference is that the mass ratio of 1,4-butanediol to water is 1:1, and the temperature in the reaction zone in step (2) is 220°C. The results are shown in the table below.

[0026] Example 5 Compared with Example 1, the difference is: The catalyst in step (2) is an Al2O3 catalyst doped with metals Co, Cu and Mg, wherein the molar ratio of element Co, element Cu, element Mg and element Al is 0.09:0.03:0.012:0.5. The results are shown in the table below.

[0027] Example 6 Compared with Example 5, the difference is that the temperature in the reaction zone in step (2) is 220°C. The results are shown in the table below.

[0028] Example 7 Compared with Example 5, the difference is that the mass ratio of 1,4-butanediol to water is 1:1. The reaction results are shown in the table below.

[0029] Example 8 Instance number 1,4-Butanediol conversion rate / % Tetrahydrofuran selectivity / % Instance number 1,4-Butanediol conversion rate / % Tetrahydrofuran selectivity / % 1 100 85.56 5 100 98.35 2 100 90.45 6 100 94.20 3 100 85.02 7 100 95.09 4 100 91.76 8 100 93.56

[0030] Example 9 The equipment used in Examples 1-8 is a device for preparing tetrahydrofuran by dehydrating 1,4-butanediol under an air atmosphere, comprising a glass kettle 1, a preheater 2, a reactor 3, a condenser 4, a crude product tank 5, a THF distillation tower 6, a condenser 2 7, a finished product tank 8, a reboiler 9, a water distillation tower 10, and a waste liquid tank 11, which are sequentially connected through pipelines. The reboiler 9 is connected to the THF distillation tower 6 through a reflux pipe. The device also includes a water raw material tank 13 and a water intermediate tank 12. The water raw material tank 13 is connected to the water intermediate tank 12 through a pipeline, the water intermediate tank 12 is connected to the glass kettle through a pipeline, and the water distillation tower 10 is connected to the water intermediate tank through a reflux pipe.

[0031] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present application and are not intended to limit it. Although the present application has been described in detail with reference to the preferred embodiments, a person of ordinary skill in the art should understand that the technical solution of the present application can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution of the present application, which should be included in the scope of the claims of the present application.

Claims

1. A method for preparing tetrahydrofuran by dehydrating 1,4-butanediol under air atmosphere, characterized in that: The preparation steps are as follows: (1) adding 1,4-butanediol and water into a glass kettle, stirring until 1,4-butanediol is completely dissolved, thereby obtaining a homogeneous mixed solution of 1,4-butanediol and water; (2) preheating the homogeneous mixed solution of 1,4-butanediol and water in a preheater and then conveying it to a fixed bed reactor by a liquid inlet pump for reaction, wherein the reaction section of the fixed bed reactor is filled with a catalyst, and both ends of the catalyst are respectively filled with quartz sand, and air is introduced into the fixed bed reactor; (3) the reaction product obtained in step (2) is condensed in a condenser and then flows into a The crude product tank is then transported to the THF distillation tower for purification; (4) the components separated from the top of the THF distillation tower are condensed in the condenser and stored in the THF finished product tank, and the components separated from the bottom of the THF distillation tower pass through the reboiler, and a part of them is heated and vaporized and then sent back to the THF distillation tower to provide a certain amount of continuously rising steam flow for the distillation operation, and the unvaporized part is discharged into the water distillation tower for separation; (5) the water component separated from the top of the water distillation tower is condensed in the condenser and refluxed to step (1) for repeated use, and the bottom component is transported to the waste liquid tank for temporary storage.

2. The method for preparing tetrahydrofuran by dehydrating 1,4-butanediol under air atmosphere as claimed in claim 1, characterized in that: In the step (1), the mass ratio of 1,4-butanediol to water is 1-2:1-4.

3. The method for preparing tetrahydrofuran by dehydrating 1,4-butanediol under air atmosphere as claimed in claim 1, characterized in that: In the step (2), the temperature in the reaction zone is 180-220° C., the gas hourly space velocity of air is 300 h-1, and the pressure is normal pressure.

4. The method for preparing tetrahydrofuran by dehydrating 1,4-butanediol under air atmosphere as claimed in claim 1, characterized in that: In the step (2), the volume ratio of the amount of quartz sand loaded above the catalyst to the amount of quartz sand loaded below the catalyst in the reaction section is 1:

1.

5. The method for preparing tetrahydrofuran by dehydrating 1,4-butanediol under air atmosphere as claimed in claim 4, characterized in that: The total loading amount of the catalyst and quartz sand in the reaction section of step (2) is 100-200 mL, the volume ratio of the loading amount of the catalyst to the quartz sand is 1:9, and the particle size of the quartz sand is smaller than that of the catalyst.

6. The method for preparing tetrahydrofuran by dehydrating 1,4-butanediol under air atmosphere as claimed in claim 1, characterized in that: The catalyst in step (2) is a metal-doped modified metal oxide catalyst; the metal-doped modified metal oxide catalyst is metal-doped modified Al2O3, wherein the doped metal is one or more of Mg, Cu, and Co.

7. The method for preparing tetrahydrofuran by dehydrating 1,4-butanediol under air atmosphere as claimed in claim 6, characterized in that: The molar ratio of Co, Cu, Mg and Al is 8-10:2-4:1.1-1.3:45-55.

8. The method for preparing tetrahydrofuran by dehydrating 1,4-butanediol under air atmosphere as claimed in claim 7, characterized in that: The molar ratio of Co, Cu, Mg and Al is 9:3:1.2:

50.

9. The method for preparing tetrahydrofuran by dehydrating 1,4-butanediol under air atmosphere as claimed in claim 1, characterized in that: The temperature of the THF distillation tower in step (4) is 60-80°C; the temperature in the reboiler in step (4) is not lower than the temperature in the THF distillation tower; and the temperature of the water distillation tower in step (5) is 100-120°C.

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