Device and method for preparing adiponitrile by electrolytic dimerization of acrylonitrile

Abstract

The present invention belongs to the technical field of preparation of adiponitrile, and specifically relates to a device and method for preparing adiponitrile by integrating electrolytic reaction of acrylonitrile into a reaction distillation tower. The reaction distillation tower is composed of a distillation section, a reaction section and a stripping section. Condensers are arranged at the top of the tower, the reaction section and the distillation section, a reboiler is arranged at the bottom of the tower, and an array of positive and negative electrodes is arranged in the reaction section. After acrylonitrile, a supporting electrolyte, water and other auxiliary components are introduced into the reaction distillation tower, acrylonitrile is highly selectively generated into adiponitrile at the cathode, and water is oxidized at the anode to generate oxygen. Finally, oxygen is discharged through the top of the tower, and heavy components adiponitrile, water, salt and a small amount of by-products are extracted from the bottom of the tower. The present invention integrates the electrolytic dimerization reaction of acrylonitrile into the reaction distillation tower, solves the problems of low single-pass conversion rate and poor selectivity of acrylonitrile in ordinary parallel plate electrolyzers, and the volume expansion of the reactant flow caused by oxygen evolution at the anode, and the acrylonitrile conversion rate can be as high as 99%, and the adiponitrile selectivity obtained is greater than 95%.

Description

Technical Field

[0001] The invention belongs to the technical field of preparation of adiponitrile, and particularly relates to a method for preparing adiponitrile by integrating an electrolysis device into a reaction distillation tower. Background Art

[0002] Adiponitrile (ADN), also known as 1,4-dicyanobutane, is an important chemical raw material. It is mainly used to prepare hexamethylenediamine, an intermediate of polyamide nylon 6,6. It can also be used to prepare rubber additives, pesticides and fungicides, polymer materials, and can also be used as a plasticizer, textile additive, solvent and extractant, etc. It has a wide range of uses.

[0003] At present, adiponitrile (ADN) is mainly prepared industrially through the thermochemical catalytic cyanation reaction of 1,3-butadiene or the electrochemical dimerization reaction of acrylonitrile (AN). Among them, the electrochemical dimerization method is less toxic, more environmentally friendly, and only requires one step of reaction compared to the traditional butadiene method, so it will be more sustainable and competitive in the future.

[0004] The electrolytic dimerization process of acrylonitrile (AN) was first developed by Monsanto Company in the United States in the 1960s and has great practical significance. Many methods for carrying out the reaction have been developed, such as electrolysis in an electrolytic cell separated by a diaphragm or in an unseparated electrolytic cell. Among them, patents US3193475, US3193481, US3616319, and US3335162 disclose methods for electrolyzing AN dimerization in an electrolytic cell separated by a diaphragm. The method has enough appeal to be used in industry for a long time, but the required electrolysis energy consumption is high, the electrolytic cell structure is usually complicated, and the diaphragm needs to be replaced regularly. Compared with the electrolytic cell separated by a diaphragm, the unseparated electrolytic cell is simple in design, has a low cell voltage, and is easy to operate in industry, and is a direct electrosynthesis process. For example, patents US3898140 and US3689382 disclose a method for preparing adiponitrile by electrolyzing AN aqueous solution in a membrane-free electrolytic cell. Later, patent US4789442 further improved the reaction efficiency by electrolyzing an emulsion composed of an aqueous phase and an organic phase on a lead or lead alloy cathode. BASF of Germany also used a special capillary gap electrolyzer (patent US3616320) to establish a membrane-free electrolysis device, which reduced the ohmic pressure drop and energy consumption of the solution by reducing the electrode gap to form a capillary gap reactor of a thin-film electrolyte, but like other electrolytic processes, the electrochemical reduction or oxidation reaction can only occur on the parallel plate cathode or anode wall respectively, and the electrode area corresponding to the unit reaction liquid volume is very small, so the single-pass AN conversion rate is not high, and the outlet liquid needs to be recycled to the electrolytic cell through a large number of separation operations, which increases the difficulty and cost of operation. If the conversion rate is simply increased by increasing the current density or electrode area, the by-products will increase due to the decrease in AN concentration in the later stage of the reaction, which will reduce the process performance. In addition, for every 1 mol of ADN generated at the cathode, half a mol of oxygen is produced at the anode. When the conversion rate is high, this will cause a significant expansion of the volume of the reactant flow between the electrode plates, which not only reduces the local residence time, but also hinders the contact between the electrolyte solution and the electrodes, making it difficult to operate.

[0005] In order to overcome the shortcomings of traditional electrolytic cells in the ADN electrolytic synthesis process, further improve the conversion rate of AN, reduce the separation procedures and the occurrence of by-products, and continuously remove the gaseous oxygen in the emulsion, it is necessary to seek a new process for electrolyzing AN to prepare ADN. Summary of the invention

[0006] The object of the present invention is to provide a device and method for preparing adiponitrile (ADN) by integrating electrolytic reaction into a reactive distillation tower, so as to overcome the shortcomings of the current electrolytic dimerization process of acrylonitrile (AN), provide a process for preparing adiponitrile by integrating electrolytic reaction and phase separation, reduce costs, improve the conversion rate of acrylonitrile (AN), and obtain a highly selective adiponitrile (ADN) product.

[0007] A device and method for preparing adiponitrile by electrolytic dimerization of acrylonitrile comprises: a reaction distillation tower R001 consisting of a distillation section, a reaction section and a stripping section, a condenser D001 is arranged at the top of the tower, a reboiler E001 is arranged at the bottom of the tower, and a plurality of positive and negative electrodes are arranged in the reaction section; one or more streams containing acrylonitrile, a supporting electrolyte, water and other auxiliary components are introduced into the reaction distillation tower R001, acrylonitrile is highly selectively generated into adiponitrile at the cathode, and water is oxidized to generate oxygen at the anode; finally, the oxygen is discharged through the tower top condenser D001, and the heavy component adiponitrile, water, salt and a small amount of by-products are extracted from the tower bottom reboiler E001.

[0008] The reaction section and the distillation section of the reaction distillation tower are provided with a plurality of intermediate condensers C001-C005.

[0009] The mass fraction of acrylonitrile in the feed stream is 1% to 90%, the mass fraction of supporting electrolyte is 1% to 20%, and the mass fraction of water is 10% to 95%.

[0010] The reaction distillation tower R001 has a pressure of 0.5 to 10 atm, a top temperature of -20 to 20°C, a bottom temperature of 90 to 250°C, and a bottom reboiling ratio of 0.5 to 3.

[0011] The reactive distillation tower R001 has 30-100 theoretical plates, wherein the distillation section has 5-50 theoretical plates, and the feed plate is located at the 10th-21st theoretical plate.

[0012] The total cathode surface area corresponding to the unit acrylonitrile feed flow rate (1 kg / h) in the reactive distillation tower R001 is 200-1000 m 2 , current density is 10~10000A / m 2 .

[0013] The cathode is a mesh material composed of one or more of lead, cadmium and their alloys, and the anode material is a mesh material composed of stainless steel, Ti\RuO2, Ti\IrO2 and the like.

[0014] The cathode and the anode are installed in the liquid phase flow area of ​​the reaction distillation tower R001.

[0015] The tower top condenser D001 is a partial condenser, and the purity of the tower top oxygen is 90-100%.

[0016] The supporting electrolyte is one or more of phosphate and hydrogen phosphate, preferably dipotassium hydrogen phosphate and sodium phosphate.

[0017] Beneficial Effects

[0018] The advantages of the present invention are

[0019] By integrating the electrolytic dimerization reaction of acrylonitrile into the reactive distillation tower, the gaseous oxygen in the emulsion can be removed while reacting, solving the problems of low single-pass conversion rate of acrylonitrile in ordinary parallel plate electrolyzers and reactor volume expansion caused by the anode oxygen evolution reaction. Compared with the traditional electrolytic dimerization process of acrylonitrile, the conversion rate of acrylonitrile is increased to 99%, and the selectivity of the obtained adiponitrile product is greater than 95%, which reduces the difficulty and cost of separation operation. The introduction of several intermediate condensers in the reactive distillation tower not only reduces the load of the top condenser and saves costs, but also the change of the gas-liquid flow rate in the reaction zone can be kept within a narrow range, which is conducive to the design and operation of the distillation tower and the uniform occurrence of the electrolytic reaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The present invention is a schematic diagram of a reaction device for preparing adiponitrile by electrolytic dimerization of acrylonitrile. DETAILED DESCRIPTION

[0021] The object of the present invention is to provide a novel device and method for preparing adiponitrile by electrolyzing acrylonitrile dimerization. The present invention is described in detail below in conjunction with examples and drawings. It should be understood that the embodiments and drawings are only used for illustrative description of the present invention and cannot constitute any limitation on the protection scope of the present invention. All reasonable changes and combinations included in the scope of the invention spirit of the present invention fall within the protection scope of the present invention.

[0022] like Figure 1 As shown, R001 is a reaction distillation tower, D001 is a condenser, E001 is a reboiler, and C001-C005 are intermediate condensers. The reaction distillation tower R001 consists of a distillation section, a reaction section and a stripping section. The reaction section is provided with an array of positive and negative electrodes, and 5 intermediate condensers are provided in the reaction section and the distillation section. Acrylonitrile, supporting electrolyte and aqueous solution are introduced into the reaction distillation tower R001 from the feed plate. Acrylonitrile dimerization at the cathode is highly selective to generate adiponitrile, and water oxidation at the anode generates oxygen; oxygen is discharged after being cooled by the top condenser D001, and the heavy components adiponitrile, water, salt and a small amount of by-products are extracted from the tower kettle reboiler E001. The intermediate condensers C001-C005 are mainly used to remove the heat brought by the input electric energy, reduce the load of the top condenser D001 and maintain the change of the gas-liquid flow rate in the reaction zone within a narrow range.

[0023] Example 1

[0024] Acrylonitrile (AN) and potassium dihydrogen phosphate aqueous solution are introduced into the reaction distillation tower through the feed plate above the reaction zone, respectively. The total feed amount is 11 kg / hr, of which AN is 5 kg / hr, potassium dihydrogen phosphate is 1 kg / hr, and water is 5 kg / hr. The feed temperature of the reaction distillation tower is 60 °C, the tower operating pressure is 1.5 atm, the tower top temperature is 77.63 °C, the tower bottom temperature is 110 °C, the boiling ratio is fixed at 1, the theoretical number of plates is 45, the feed plate is the 10th plate above the reaction zone, and the reaction residence time is 5 s. The cathode and anode plates are made of lead and Ti\RuO2 materials, respectively, and are installed in the 11th to 35th theoretical plate area. The cathode area per unit plate is 24.5 m 2 , the cathode potential is fixed at -3.0V vs SCE; 5 intermediate condensers are set in the reaction section and the distillation section of the reaction distillation tower, respectively located at the 5th, 10th, 15th, 20th, 25th, and 30th theoretical plates (C001-C005), the load of C001 is -3.25kW, and the load of C002-C005 is -2kW. After the reaction distillation, the oxygen produced by the anode is discharged through the top condenser, and the molar concentration reaches 99%. After the tower bottom material is heated by the reboiler, the heavy component adiponitrile (ADN), water, salt and a small amount of by-products are extracted from the tower bottom, and the AN with a medium boiling point is retained in the reaction distillation tower until it is completely converted, and the AN conversion rate is 98.21%.

[0025] Example 2

[0026] Acrylonitrile (AN) and potassium dihydrogen phosphate aqueous solution are introduced into the reaction distillation tower through the feed plate above the reaction zone, respectively. The total feed amount is 11 kg / hr, of which AN is 5 kg / hr, potassium dihydrogen phosphate is 1 kg / hr, and water is 5 kg / hr. The feed temperature of the reaction distillation tower is 30 °C, the tower operating pressure is 1.5 atm, the tower top temperature is 78.27 °C, the tower bottom temperature is 107.01 °C, the boiling ratio is fixed at 0.8, the theoretical number of plates is 45, the feed plate is the 10th plate above the reaction zone, and the reaction residence time is 5 s. The cathode and anode plates are made of lead and Ti\RuO2 materials, respectively, and are installed in the 11th to 35th theoretical plate area, and the cathode area per unit plate is 30 m 2, the cathode potential is fixed at -3.0V vs SCE; 5 intermediate condensers are set in the reaction section and the distillation section of the reaction distillation tower, respectively located at the 5th, 10th, 15th, 20th, 25th, and 30th theoretical plates (C001-C005), the load of C001 is -3.25kW, and the load of C002-C005 is -2kW. After the reaction distillation, the oxygen produced by the anode is discharged through the top condenser, and the molar concentration reaches 98%. After the tower bottom material is heated by the reboiler, the heavy component adiponitrile (ADN), water, salt and a small amount of by-products are extracted from the tower bottom, and the AN with a medium boiling point is retained in the reaction distillation tower until it is completely converted, and the AN conversion rate is 99.3%.

[0027] Example 3

[0028] Acrylonitrile (AN) and potassium dihydrogen phosphate aqueous solution are introduced into the reaction distillation tower through the feed plate above the reaction zone, respectively. The total feed amount is 22 kg / hr, of which AN is 8 kg / hr, potassium dihydrogen phosphate is 3 kg / hr, and water is 11 kg / hr. The feed temperature of the reaction distillation tower is 60 °C, the tower operating pressure is 1 atm, the tower top temperature is 69.8 °C, the tower bottom temperature is 118.3 °C, the boiling ratio is fixed at 1, the theoretical number of plates is 45, the feed plate is the 11th plate, and the reaction residence time is 5 s. The cathode and anode plates are made of lead and Ti\RuO2 materials, respectively, and are installed in the 11th to 35th theoretical plate area. The cathode area per unit plate is 24.5 m 2 , the cathode potential is fixed at -3.0V vs SCE; 5 intermediate condensers are set in the reaction section and the distillation section of the reactive distillation tower, respectively located at the 5th, 10th, 15th, 20th, 25th, and 30th theoretical plates (C001-C005), the load of C001 is -3.25kW, and the load of C002-C005 is -2kW. After reactive distillation, the oxygen produced by the anode is discharged through the top condenser, and the bottom material of the tower is heated by the reboiler, and the heavy component adiponitrile (ADN), water, salt and a small amount of by-products are taken out of the bottom of the tower, and AN with a medium boiling point is retained in the reactive distillation tower until it is completely converted, and the AN conversion rate is 90.2%.

[0029] Example 4

[0030] Acrylonitrile (AN) and potassium dihydrogen phosphate aqueous solution are introduced into the reaction distillation tower through the feed plate above the reaction zone, respectively. The total feed amount is 11 kg / hr, of which AN is 5 kg / hr, potassium dihydrogen phosphate is 1 kg / hr, and water is 5 kg / hr. The feed temperature of the reaction distillation tower is 60 °C, the tower operating pressure is 1.5 atm, the tower top temperature is 76.1 °C, the tower bottom temperature is 114 °C, the boiling ratio is fixed at 1, the theoretical number of plates is 55, the feed plate is the 15th plate, and the reaction residence time is 5 s. The cathode and anode plates are made of lead and Ti\RuO2 materials, respectively, and are installed in the 16th to 40th theoretical plate area. The cathode area per unit plate is 30 m 2 , the cathode potential is fixed at -3.0V vs SCE; 5 intermediate condensers are set in the reaction section and the distillation section of the reactive distillation tower, respectively located at the 5th, 10th, 15th, 20th, 25th, and 30th theoretical plates (C001-C005), the load of C001 is -3.25kW, and the load of C002-C005 is -2kW. After reactive distillation, the oxygen produced by the anode is discharged through the top condenser, and the bottom material of the tower is heated by the reboiler, and the heavy component adiponitrile (ADN), water, salt and a small amount of by-products are taken out of the bottom of the tower, and AN with a medium boiling point is retained in the reactive distillation tower until it is completely converted, and the AN conversion rate is 98.27%.

[0031] Example 5

[0032] Acrylonitrile (AN) and sodium phosphate aqueous solution are introduced into the reaction distillation tower through the feed plate above the reaction zone, respectively. The total feed amount is 11 kg / hr, of which AN is 5 kg / hr, sodium phosphate is 1 kg / hr, and water is 5 kg / hr. The feed temperature of the reaction distillation tower is 60 °C, the tower operating pressure is 1.5 atm, the tower top temperature is 73.52 °C, the tower bottom temperature is 116.7 °C, the boiling ratio is fixed at 1.5, the theoretical number of plates is 45, the feed plate is the 10th plate, and the reaction residence time is 5 s. The cathode and anode plates are made of lead and Ti\RuO2 materials, respectively, and are installed in the 10th to 40th theoretical plate area. The cathode area per unit plate is 24.5 m 2 , the cathode potential is fixed at -3.0V vs SCE; 5 intermediate condensers are set in the reaction section and the distillation section of the reactive distillation tower, respectively located at the 5th, 10th, 15th, 20th, 25th, and 30th theoretical plates (C001-C005), the load of C001 is -3.25kW, and the load of C002-C005 is -2kW. After reactive distillation, the oxygen produced by the anode is discharged through the top condenser, and the bottom material of the tower is heated by the reboiler, and the heavy component adiponitrile (ADN), water, salt and a small amount of by-products are taken out of the bottom of the tower, and AN with a medium boiling point is retained in the reactive distillation tower until it is completely converted, and the AN conversion rate is 97.89%.

[0033] For the convenience of comparison and explanation, the material feeding conditions in each embodiment are listed in Table 1, the reaction distillation tower conditions are listed in Table 2, and the reaction distillation results are listed in Table 3.

[0034] Table 1

[0035]

[0036] Table 2

[0037]

[0038] Table 3

[0039]

Claims

1. A method for preparing adiponitrile by electrolytic dimerization of acrylonitrile, characterized in that: The method comprises: introducing one or more streams containing acrylonitrile, supporting electrolyte, water and other auxiliary components into a reactive distillation tower (R001), generating adiponitrile with high selectivity from acrylonitrile at the cathode, and simultaneously generating oxygen through water oxidation at the anode; finally, the oxygen is discharged through a tower top condenser (D001), and heavy components adiponitrile, water, salt and a small amount of by-products are extracted from a tower bottom reboiler (E001); The reactive distillation tower is composed of a distillation section, a reaction section and a stripping section. A condenser (D001) is arranged at the top of the tower, a reboiler (E001) is arranged at the bottom of the tower, a plurality of anode and cathode electrodes and a plurality of intermediate condensers are arranged in the reaction section, and a plurality of intermediate condensers are arranged in the stripping section. The reactive distillation tower (R001) includes 45-100 theoretical plates, wherein the distillation section has 5-50 theoretical plates, the feed plate is located at the 10th to 21st theoretical plates, and the cathode and anode plates are installed in the 16th to 40th theoretical plate area.

2. The method according to claim 1, characterized in that The cathode in the positive and negative electrodes is a mesh material composed of one or more of lead, cadmium and their alloys, and the anode is a mesh material composed of one or more of stainless steel, Ti\RuO2, Ti\IrO2.

3. The method according to claim 1, characterized in that The positive and negative electrodes are installed in the liquid phase flow area of ​​the reaction distillation tower.

4. The method according to claim 1, characterized in that: The tower top condenser (D001) is a partial condenser.

5. The method according to claim 1, characterized in that In the logistics introduced into the reactive distillation tower (R001), the mass fraction of acrylonitrile is 1% to 90%, the mass fraction of supporting electrolyte is 1% to 20%, and the mass fraction of water is 10% to 95%.

6. The method according to claim 1, characterized in that The reaction distillation tower (R001) has a pressure of 0.5 to 10 atm, a top temperature of -20 to 20°C, a bottom temperature of 90 to 250°C, and a bottom reboiling ratio of 0.5 to 3.

7. The method according to claim 6, characterized in that The unit acrylonitrile feed flow rate in the reactive distillation tower (R001) is 1 kg / h, and the total cathode surface area corresponding to each unit acrylonitrile feed flow rate is 200-1000 m 2 , current density is 10~10000A / m 2 .

8. The method according to claim 1, characterized in that The purity of oxygen extracted from the tower top is 90-100%.

9. The method according to claim 1, characterized in that: The supporting electrolyte is one or more of phosphate and hydrogen phosphate.

10. The method according to claim 9, characterized in that The supporting electrolytes are dipotassium hydrogen phosphate and sodium phosphate.

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