Preparation method of iron-based composite anode and application of iron-based composite anode in electrochemical synthesis of adiponitrile

Abstract

The invention discloses a preparation method of an iron-based composite anode for electrochemical synthesis of adiponitrile, the iron-based composite anode comprises an iron base material, the iron base material can be pure iron, carbon steel, 304, 316L, 904L, 2204 and the like, and a tungsten carbide bottom layer and a doped active layer are sequentially arranged on the surface of the iron base material from inside to outside. A tungsten carbide bottom layer is sprayed on the surface of an iron base material, and a doped active layer is prepared on the tungsten carbide bottom layer. During electrochemical synthesis of adiponitrile, the iron-based composite anode is applied as an anode. According to the iron-based composite anode, the binding force of the doped active layer and the substrate is improved, the conductivity is improved, and the corrosion resistance is improved; in electrochemical synthesis of adiponitrile, the defect that the anode is easy to corrode in electrolysis is overcome, the service life is prolonged, and meanwhile, the yield of adiponitrile and the electrolytic current efficiency are improved.

Description

Technical Field

[0001] The invention relates to a method for preparing an iron-based composite anode and application thereof in electrochemical synthesis of adiponitrile, belonging to the technical field of chemical industry. Technical Background

[0002] Adiponitrile (ADN) is a very important organic chemical raw material. About 90% of the adiponitrile produced in the world each year is used to synthesize hexamethylenediamine by hydrogenation of adiponitrile, and then used in the production of nylon 66 salt, which is the most important industrial use of adiponitrile so far. In addition, 1,6-hexamethylenediisocyanate (HDI) can be generated by the photochemical reaction of hexamethylenediamine. HDI is an important raw material for the production of high-end environmentally friendly coatings. Resins and adhesives made from HDI have good yellowing resistance. Therefore, it is of great significance to study the method of synthesizing adiponitrile.

[0003] The current production processes of adiponitrile mainly include butadiene hydrocyanation, acrylonitrile electrolytic dimerization and adipic acid ammoniation dehydration. The acrylonitrile electrolysis method is one of the three main methods for synthesizing adiponitrile. The process route of this method is simple, and adiponitrile can be obtained in one step. It is relatively easy to overcome technically. The raw material acrylonitrile used is less toxic than the raw material hydrocyanic acid used in the butadiene method, and the safety risks faced are relatively small. However, there are also some problems in the synthesis of adiponitrile by acrylonitrile electrolysis, such as severe anode corrosion, large electrolyte resistivity, and high energy consumption.

[0004] In view of the shortcomings of the above-mentioned process, it is urgent to develop a new type of anode material for synthesizing adiponitrile to overcome the problems existing in current production, such as easy corrosion of the anode, hydrogen evolution at the cathode caused by anode dissolution, and poor product quality. Summary of the invention

[0005] The object of the present invention is to provide an iron-based composite anode and a preparation method thereof, which can be used as an anode for electrochemical synthesis of adiponitrile. By adding a tungsten carbide bottom layer, the bonding force between the Fe3O4 coating and the substrate is improved, the conductivity is improved, the working tank pressure of the anode is reduced, and the service life is increased.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] An iron-based composite anode comprises an iron substrate, on the surface of which a tungsten carbide bottom layer and a doped active layer are arranged from the inside to the outside;

[0008] The iron substrate can be pure iron, carbon steel, 304, 316L, 904L, 2204, etc.

[0009] Preferably, the doped active layer is manganese ferrite doped with ferroferric oxide (Fe3O4-MnFe2O4); preferably, the thickness of the doped active layer is 1-5 μm;

[0010] Preferably, the tungsten carbide bottom layer has a thickness of 10-50 μm.

[0011] The present invention also provides a method for preparing the above-mentioned iron-based composite anode, comprising the following steps:

[0012] 1) Optionally, performing surface treatment on the iron substrate;

[0013] 2) Spray tungsten carbide primer on the surface of the iron substrate;

[0014] 3) The iron substrate prepared in step 2) is used as an anode and a carbon steel plate is used as a cathode, and an anodic oxidation electrodeposition method is used in a nitric acid deposition solution system containing MnFe2O4 to prepare a doped active layer.

[0015] Preferably, in step 1), the iron substrate is surface treated by an electrochemical method, and the surface of the iron substrate is polished with sandpaper to make it uniform and free of oxide scale; in a specific embodiment, the electrochemical method is, for example: 1L of water is added to a plastic box, then 110g of NaHCO3, stirred evenly, a carbon rod is used as the anode, an iron plate is clamped by the cathode, the cathode and the anode are immersed in water without contact, 1-5A of electricity is applied, the voltage is 12-36V, and the time is 3-8h.

[0016] Preferably, in step 2), the tungsten carbide bottom layer is prepared by spraying, and the spraying method is flame spraying. In some specific embodiments, the flame spraying process is: drying the tungsten carbide powder for spraying in an oven at 80-100°C for 1-2 hours, and then flame spraying, with a flame temperature of 2000-3000°C.

[0017] Preferably, the operation of the step 3) anodizing electrodeposition method comprises: using a nitric acid deposition liquid system containing MnFe2O4 as an electrolyte, using the iron substrate prepared in step 2) as an anode and a carbon steel plate as a cathode at a temperature of 30 to 70°C, and electro-depositing for 2 to 8 hours under ultrasound (e.g., 40kHz), and the electrodeposition current density is 150 to 300A / m 2 ;

[0018] The nitric acid deposition liquid system containing MnFe2O4 is a mixed solution of ferrous acetate and titanium nitrate containing MnFe2O4. Preferably, the nitric acid deposition liquid system containing MnFe2O4 is prepared with deionized water, wherein the nitric acid deposition liquid system contains 140-180 g / L Fe 2 + , 15~30g / L Ti 2+ , 4-10g / L MnFe2O4.

[0019] The invention also provides the use of the iron-based composite anode as an anode in the electrochemical synthesis of adiponitrile.

[0020] Preferably, when the iron-based composite anode is used as the anode for electrochemical synthesis of adiponitrile, the carbon steel cadmium-plated plate is used as the cathode, and the current density of the electrochemical synthesis of adiponitrile is 1000-2000A / m 2 ;

[0021] Preferably, in the electrochemical synthesis of adiponitrile system, the electrolyte contains 1-5% acrylonitrile, 7%-20% dipotassium hydrogen phosphate as supporting electrolyte, 0.5-3% EDTA sodium salt as buffer for the pH value of the electrolyte, 1-3% borax, 0.5%-6% quaternary ammonium salt as guiding ion sources, and the rest is water, and phosphoric acid or strong alkali is used to adjust the pH value of the electrolyte to a range of 7-10; the concentration of each substance in the electrolyte is a mass percentage concentration;

[0022] The quaternary ammonium salt can be tetrabutylammonium hydroxide, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tributylmonomethylammonium hydroxide, tetrabutylammonium hydrogen sulfate, tetrabutylammonium dihydrogen phosphate, and the like.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The iron-based composite anode of the present invention which can be used for electrochemical synthesis of adiponitrile comprises, from inside to outside, an iron substrate (Fe), a tungsten carbide bottom layer (WC), and a doped active layer (Fe3O4-MnFe2O4), wherein the tungsten carbide bottom layer has two main functions: first, excellent electrical conductivity, and second, improving bonding strength and preventing corrosion and passivation of the iron substrate; the doped active layer is mainly for improving the oxygen evolution activity of the anode active layer, thereby reducing the anode working cell pressure.

[0025] The iron-based composite anode improves the conductivity and service life of the anode product.

[0026] The electrochemical method is used to treat the oxide scale of the iron substrate, replacing the traditional sandblasting and pickling process. The process is simple and practical; the WC bottom layer is prepared by flame spraying in the electrode, which greatly improves the conductivity. The prepared iron-based composite anode is used in the electrochemical synthesis of adiponitrile, which solves the problem of easy corrosion of the anode in electrolysis, improves the service life, and at the same time improves the yield of adiponitrile and the electrolysis current efficiency. DETAILED DESCRIPTION

[0027] The present invention is further described in detail with reference to the following examples, but the scope of the present invention is not limited to these examples.

[0028] Preparation of MnFe2O4: According to Mn 2+ / Fe 3+ =1:2 molar ratio of MnSO4·H2O and FeCl3·6H2O were weighed and dissolved in deionized water to prepare a mixed solution. Stir the mixed solution and slowly add 3 mol·L-1 100% NaOH was added to adjust the pH value to 11. After stirring evenly, the mixture was transferred to a polytetrafluoroethylene-lined autoclave (filling degree 75%) and heated at 200°C for 12 hours. It was washed with deionized water and anhydrous ethanol for several times to neutrality, placed in an electric thermostatic blower at a constant temperature of 80°C for drying, and sintered at 400°C for 5 hours.

[0029] Example 1

[0030] The method for preparing an iron-based composite anode comprises the following steps:

[0031] 1) The surface of the carbon steel substrate was treated by electrochemical method (1L of deionized water was added to a plastic box, and then 110g of NaHCO3 was added, stirred and dissolved, the anode was inserted into the water with a carbon rod, and the cathode clamped the carbon steel and immersed below the liquid surface to ensure that the positive and negative electrodes did not touch, the voltage was 12V, the current was 1.5A, and the power-on time was 3h) to remove the surface oxide scale and polish it with 200-mesh sandpaper to make the surface of the carbon steel substrate uniform.

[0032] 2) The carbon steel substrate treated by electrochemical method in step 1) is flame sprayed to prepare a tungsten carbide bottom layer: the tungsten carbide powder is dried in an oven at 80°C for 2 hours, and then flame sprayed at a flame temperature of 2500°C to prepare a WC bottom layer with a thickness of 10 μm.

[0033] 3) The carbon steel substrate prepared in step 2) is used as the anode and the carbon steel plate is used as the cathode, and an anodic oxidation electrodeposition method is used in a nitric acid deposition solution system containing MnFe2O4 to prepare a doped active layer (Fe3O4-MnFe2O4):

[0034] The nitric acid deposition solution system containing MnFe2O4 is prepared in an electrolytic cell with a mixed solution of ferrous acetate and titanium nitrate containing MnFe2O4, wherein the solution contains 180 g / L Fe 2+ , 20g / L Ti 2+ , 6g / L MnFe2O4, and heat to 30℃, stir evenly;

[0035] Then, the carbon steel substrate anode and the carbon steel plate cathode prepared in step 2) were fixed in the electrolytic cell respectively, and ultrasonic electroplating was performed for 3 hours at a current density of 200 A / m 2 A Fe3O4-MnFe2O4 doped active layer with a thickness of 2 μm is formed on the carbon steel substrate prepared in step 2).

[0036] The iron-based composite anode (Fe / WC / Fe3O4-MnFe2O4) prepared in the above steps 1) to 3) is used to prepare electrochemical synthesis of adiponitrile. Specific operation method:

[0037] The iron-based composite anode and the carbon steel cadmium-plated cathode were fixed in the electrolytic cell respectively, and the power was turned on. The electrochemical synthesis current density was 1500A / m 2 ;

[0038] The electrolyte in the electrochemical synthesis of adiponitrile system contains: 3% acrylonitrile, 10% dipotassium hydrogen phosphate, 1% EDTA sodium salt, 3% borax, 0.5% tetrabutylammonium hydroxide, and the rest is water. The pH value of the electrolyte is 7.

[0039] After running for 3000 hours, the Fe ion content in the water phase was 186 ppm, the yield of adiponitrile was over 90%, and the current efficiency was over 80%.

[0040] The Fe / WC / Fe3O4-MnFe2O4 anode is used to electrochemically synthesize adiponitrile, which solves the problem of easy corrosion of the anode during electrolysis and prolongs the service life by 1 time.

[0041] Example 2

[0042] The method for preparing an iron-based composite anode comprises the following steps:

[0043] 1) The surface of the carbon steel substrate was treated by the same electrochemical method as in Example 1 to remove the surface oxide scale, and then polished with 200-mesh sandpaper to make the surface of the iron substrate uniform.

[0044] 2) The carbon steel substrate treated by electrochemical method in step 1) is flame sprayed to prepare a tungsten carbide bottom layer: the tungsten carbide powder is dried in an oven at 100°C for 1 hour, and then flame sprayed at a flame temperature of 2000°C to prepare a WC bottom layer with a thickness of 15 μm.

[0045] 3) The carbon steel substrate prepared in step 2) is used as an anode and the carbon steel plate is used as a cathode, and an active layer is electrodeposited in a nitric acid deposition solution system containing MnFe2O4 to prepare an iron-based composite anode (Fe3O4-MnFe2O4):

[0046] The nitric acid deposition solution system containing MnFe2O4 is prepared in an electrolytic cell with a mixed solution of ferrous acetate and titanium nitrate containing MnFe2O4, wherein the solution contains 180 g / L Fe 2+ , 30g / L Ti 2+ , 6g / L MnFe2O4, and heat to 30℃, stir evenly;

[0047] Then, the carbon steel substrate anode and the carbon steel plate cathode prepared in step 2) were fixed in the electrolytic cell respectively, and ultrasonic electroplating was performed for 4 hours, and the electroplating current density was 250A / m 2 A Fe3O4-MnFe2O4 doped active layer with a thickness of 3 μm was formed on the carbon steel substrate.

[0048] The carbon steel-based composite anode prepared in the above steps 1) to 3) is used to prepare electrochemical synthesis of adiponitrile. Specific operation method:

[0049] The carbon steel-based composite anode and the carbon steel cadmium-plated plate cathode were fixed in the electrolytic cell respectively, and the power was turned on. The electrochemical synthesis current density was 1200A / m 2 ;

[0050] The electrolyte in the electrochemical synthesis of adiponitrile system contains: 2% acrylonitrile, 10% dipotassium hydrogen phosphate, 1.5% EDTA sodium salt, 3% borax, 2% tetraethylammonium hydroxide, and the rest is water, and the pH value of the electrolyte is 7.5.

[0051] After running for 2000 h, the Fe ion content in the water phase was 200 ppm, the yield of adiponitrile was over 88%, and the current efficiency was over 80%.

[0052] The Fe / WC / Fe3O4-MnFe2O4 anode is used to electrochemically synthesize adiponitrile, which solves the disadvantage that the anode is easily corroded during electrolysis.

[0053] Example 3

[0054] The method for preparing an iron-based composite anode comprises the following steps:

[0055] 1) The surface of the iron substrate was treated by the same electrochemical method as in Example 1 to remove the surface oxide scale, and then the surface was polished with 200-mesh sandpaper to make the surface of the iron substrate uniform.

[0056] 2) The iron substrate treated by electrochemical method in step 1) is flame sprayed to prepare a tungsten carbide bottom layer: the tungsten carbide powder is dried in an oven at 90°C for 1 hour, and then flame sprayed at a flame temperature of 2000°C to prepare a WC bottom layer with a thickness of 30 μm.

[0057] 3) The iron substrate prepared in step 2) is used as an anode and a carbon steel plate is used as a cathode, and an active layer is electrodeposited in a nitric acid deposition solution system containing MnFe2O4 to prepare an iron-based composite anode (Fe3O4-MnFe2O4):

[0058] The nitric acid deposition solution system containing MnFe2O4 is prepared in an electrolytic cell with a mixed solution of ferrous acetate and titanium nitrate containing MnFe2O4, wherein the solution contains 140 g / L Fe 2+ , 20g / L Ti 2+ , 5g / L MnFe2O4, and heat to 40℃, stir evenly;

[0059] Then, the iron substrate anode and the carbon steel plate cathode prepared in step 2) were fixed in the electrolytic cell respectively, and ultrasonic electroplating was performed for 2 hours. The electroplating current density was 300A / m 2A Fe3O4-MnFe2O4 doped active layer with a thickness of 1 μm was formed on the iron substrate.

[0060] The iron-based composite anode prepared in the above steps 1) to 3) is used to prepare electrochemical synthesis of adiponitrile. Specific operation method:

[0061] The iron-based composite anode and the carbon steel cadmium-plated plate cathode were fixed in the electrolytic cell respectively, and the power was turned on. The electrochemical synthesis current density was 1800A / m 2 ;

[0062] The electrolyte in the electrochemical synthesis of adiponitrile system contains: 5% acrylonitrile, 20% dipotassium hydrogen phosphate, 3% EDTA sodium salt, 2% borax, 3% tetramethylammonium hydroxide, and the rest is water. The pH value of the electrolyte is 8.

[0063] After running for 1000 hours, the Fe ion content in the water phase was 80 ppm, the yield of adiponitrile was over 85%, and the current efficiency was over 82%.

[0064] The Fe / WC / Fe3O4-MnFe2O4 anode is used to electrochemically synthesize adiponitrile, which solves the disadvantage that the anode is easily corroded during electrolysis.

[0065] Comparative Example 1

[0066] The carbon steel anode and the carbon steel cadmium-plated cathode were fixed in the electrolytic cell respectively, and the power was turned on. The electrochemical synthesis current density was 1500A / m 2 ;

[0067] The electrolyte in the electrochemical synthesis of adiponitrile system contains: 3% acrylonitrile, 10% dipotassium hydrogen phosphate, 1% EDTA sodium salt, 3% borax, 0.5% tetrabutylammonium hydroxide, and the rest is water. The pH value of the electrolyte is 7.

[0068] After running for 1000 h, the Fe ion content in the water phase was 800 ppm, the yield of adiponitrile was 83%, and the current efficiency was 74%.

[0069] Compared with the iron-based composite anode, directly using carbon steel as the anode causes severe corrosion, and the cathode hydrogen evolution causes a decrease in yield and current selectivity.

[0070] The iron-based composite anode of the present invention improves the conductivity and the bonding strength between the Fe3O4 coating and the substrate by adding a WC bottom layer, while preventing the substrate from being corroded and passivated; the doping active layer is mainly to improve the oxygen evolution activity of the anode active layer, thereby reducing the anode working tank pressure. Therefore, the iron-based composite anode has good conductivity and a long service life.

Claims

1. An iron-based composite anode, characterized in that: It comprises an iron substrate, on the surface of which there are a tungsten carbide bottom layer and a doped active layer from inside to outside, wherein the doped active layer is manganese ferrite doped with ferrosoferric oxide; preferably, the thickness of the doped active layer is 1-5 μm.

2. The iron-based composite anode according to claim 1, characterized in that: The thickness of the tungsten carbide bottom layer is 10-50 μm.

3. The method for preparing the iron-based composite anode according to claim 1 or 2, comprising the following steps: 1) Optionally, performing surface treatment on the iron substrate; 2) Spray tungsten carbide primer on the surface of the iron substrate; 3) The iron substrate prepared in step 2) is used as an anode and a carbon steel plate is used as a cathode, and an anodic oxidation electrodeposition method is used in a nitric acid deposition solution system containing MnFe2O4 to prepare a doped active layer.

4. The method according to claim 3, characterized in that The operation of step 3) includes: using a nitric acid deposition liquid system containing MnFe2O4 as an electrolyte, using the iron substrate prepared in step 2) as an anode and a carbon steel plate as a cathode, and electro-depositing under ultrasound at a temperature of 30 to 70°C; preferably, the electrodeposition current density is 150 to 300 A / m 2 .

5. The method according to claim 4, characterized in that The nitric acid deposition solution system containing MnFe2O4 is a mixed solution of ferrous acetate and titanium nitrate containing MnFe2O4, preferably containing 140-180 g / LFe 2+ , 15~30g / L Ti 2 + , 4~10g / L MnFe2O4.

6. Use of the iron-based composite anode according to claim 1 or 2 as an anode in electrochemical synthesis of adiponitrile.

7. A method for electrochemically synthesizing adiponitrile, using the iron-based composite anode according to claim 1 or 2 as an anode, a carbon steel cadmium-plated plate as a cathode, and a current density of 1000 to 2000 A / m 2 .

8. The method according to claim 7, wherein: The electrolyte contains 1-5% acrylonitrile, 7%-20% dipotassium hydrogen phosphate, 0.5-3% EDTA sodium salt, 1-3% borax, 0.5%-6% quaternary ammonium salt, and the pH value is within the range of 7-10; the concentration of each substance in the electrolyte is mass percentage concentration.

9. The method according to claim 8, wherein: The quaternary ammonium salt is selected from tetrabutylammonium hydroxide, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tributylmonomethylammonium hydroxide, tetrabutylammonium hydrogen sulfate, and tetrabutylammonium dihydrogen phosphate.