A Raney nickel catalyst for the production of reduced indigo and a production method of reduced indigo

Abstract

The present invention discloses a Raney nickel catalyst for producing reduced indigo and a production method of reduced indigo. The Raney nickel is prepared according to the following steps: (1) Mix nickel powder and molybdenum powder evenly, soak them with dilute acid, then wash them with deionized water until neutral, and then dry them under vacuum; (2) Take aluminum powder and mix it with the dried molybdenum powder and nickel powder, and put them into a planetary ball mill for ball milling; (3) Place the ball-milled mixed powder in a muffle furnace, set the temperature to 250-300 °C, and carry out tempering treatment to further stabilize the crystal phase; (4) Reflux and activate the alloy powder after the tempering treatment with sodium hydroxide solution, remove the upper layer of lye and wash it with clear water until neutral to obtain the activated Raney nickel catalyst. The preparation process of the Raney nickel catalyst is simple, with low energy consumption. The prepared Raney nickel can enhance the hydrogen adsorption behavior, thereby enhancing the catalytic effect and having good cycling performance.

Description

Technical Field

[0001] The present invention relates to the field of fine chemicals, and particularly relates to a Raney nickel catalyst for producing indigo carmine and a production method of indigo carmine. Background Art

[0002] At present, indigo in China is mainly sold as a powder commodity and is dyed by using a chemical reduction method to prepare a dye bath before printing and dyeing. Its disadvantages are that the particles are coarse, the particle size distribution range is wide, a large amount of dust is generated during the production process, the reduction rate is slow and uneven during use, and when in use, it must be reduced with sodium dithionite (or other reducing agents) to prepare a dye bath, which is easy to cause uneven dyeing, affecting the printing and dyeing quality. A large amount of dye-containing wastewater is generated during the printing and dyeing process, and the treatment cost is high.

[0003] Since indigo is insoluble in water, the indigo leuco body salt is usually used to dye the warp and then oxidized to make it develop color. At present, the main technical routes for the reduction of indigo include: bacterial reduction method, chemical reduction method, catalytic hydrogenation reduction method, and electrochemical reduction method.

[0004] Bacterial reduction method: Before the invention of the chemical reduction method, indigo was usually reduced through a fermentation process, which completely relied on the action of bacteria. Therefore, it requires a long reduction time and relatively harsh environmental conditions, and due to the involvement of biological processes, the consistency of reduction cannot be guaranteed.

[0005] Chemical reduction method: Sodium dithionite is the most commonly used chemical reducing agent in the indigo industry at present, but since it will generate more difficult-to-treat sewage, it has deficiencies in environmental protection. At the same time, some newly developed reducing agents have also been applied to the indigo reduction industry, such as α-hydroxy ketone, thiourea, glucose, etc. Similarly, these reducing agents also have many unavoidable deficiencies, thus limiting the application of the chemical reduction method in green chemical industry.

[0006] Electrochemical reduction method: By dispersing indigo in a suitable solution, the reduction of indigo can be achieved by direct or indirect methods, and the active hydrogen generated during the electrolysis of water can also be used to reduce indigo. However, in order to achieve the large-scale production of liquid indigo carmine, it is necessary to increase the current density by increasing the electrode area and raising the current, which undoubtedly increases a large amount of energy consumption and reduces the economy.

[0007] Catalytic hydrogenation reduction method: The product of catalytic hydrogenation is generally water and no other by-products are generated, which has good atom economy. And the process conditions for the catalytic hydrogenation of indigo are mild, with low energy consumption, and have the prospect of development and application.

[0008] At present, the catalytic hydrogenation catalysts for pre-reduced liquid indigo can be divided into noble metal catalysts and Raney nickel catalysts. For noble metal catalysts, the patent "Method for Preparing Indigo White by Fluidized Bed Catalytic Hydrogenation" (CN 114644585A) indicates that through the fluidized bed process, the circulation times of the noble metal supported catalyst can reach 50 times. However, the noble metal catalyst still has the problem of high cost. During the circulation, additional noble metal supported catalyst needs to be added, further increasing the cost. It is estimated that according to this method, about 360 g of catalyst is required for each ton of 40% liquid indigo product, and the cost exceeds 3000 yuan / ton of product.

[0009] CN 102516817 B discloses an environmentally friendly preparation method of indigo white solution, which uses Raney nickel for catalytic hydrogenation. A relatively high hydrogen pressure is required to achieve good reaction results, and the pressure range is 1.5 MPa - 5.5 Mpa, which poses a safety hazard.

[0010] That is to say, although noble metal catalysts have high circulation performance, their cost is still high. While Raney nickel is relatively cheap, it requires a relatively high pressure and has poor circulation performance. Therefore, we hope to prepare a Raney nickel catalyst with good reduction performance, high safety and good circulation performance through the modification of Raney nickel.

[0011] CN 103480394 A discloses a preparation method of a novel modified Raney nickel catalyst, which prepares Raney nickel by the impregnation method. From the XRD pattern of the catalyst prepared by this method, the peak of molybdenum is not obvious, which may be due to only a small amount of molybdenum adhering to the surface of the catalyst, so it cannot achieve good catalytic effects.

[0012] CN 104056641 B discloses a preparation method and application of a Raney nickel catalyst resistant to sulfur in a slurry bed. The specific steps of the present invention are as follows: (1) Pretreatment: Mix nickel powder and molybdenum powder evenly, soak them in a dilute acid solution for 5 - 60 min, then soak them in absolute ethanol for 5 - 30 min, and then wash them with deionized water 2 - 4 times, and dry them at 50 - 110 °C for 1 - 8 hours for standby; Soak aluminum powder in an organic solvent for 5 - 30 minutes, then wash it with deionized water 2 - 4 times, and dry it at 50 - 110 °C for 1 - 8 hours for standby; (2) Preparation of nickel-molybdenum-aluminum alloy powder: Mix nickel powder, molybdenum powder and aluminum powder evenly, fuse them in a high-temperature furnace with an external magnetic field, cool them to room temperature under the protection of an inert gas, and grind the nickel-molybdenum-aluminum alloy powder into particles with a mesh size of 80 - 200 for standby; (3) Preparation of Raney nickel catalyst: Place a stainless-steel container filled with NaOH solution in an ultrasonic constant-temperature water bath, adjust the temperature of the constant-temperature water bath and the ultrasonic intensity, add the prepared nickel-molybdenum-aluminum alloy powder to the above NaOH solution while stirring, and then stir at a constant temperature of 0 - 70 °C for 3 - 12 h. After the reaction is completed, remove the upper-layer alkali solution, repeatedly rinse it with deionized water until it is neutral, and then rinse it with absolute ethanol 2 - 4 times to obtain the Raney nickel catalyst. The Raney nickel prepared by this method is used in the slurry-bed methanation reaction, and can exhibit good sulfur resistance. When the sulfur content in the syngas is between 300 - 6000 ppm, it has good catalytic activity and selectivity. Summary of the Invention

[0013] To solve the above technical problems, the first object of the present invention is to provide a Raney nickel catalyst for the production of reduced indigo. The second object is to provide a production method of reduced indigo. The preparation process of the Raney nickel catalyst is simple, with low energy consumption. The prepared Raney nickel can enhance the hydrogen adsorption behavior, thereby enhancing the catalytic effect and having good recycling performance.

[0014] To achieve the above first object, the present invention provides the following technical solution: A Raney nickel catalyst for the production of reduced indigo, characterized in that it is prepared according to the following steps:

[0015] (1) Mix nickel powder and molybdenum powder evenly, soak them in dilute acid for 10 - 15 min, and then wash them with deionized water until neutral, and then dry them to constant weight in a vacuum dryer.

[0016] (2) Take aluminum powder and mix it with the dried molybdenum powder and nickel powder, and put them into a planetary ball mill for ball milling. The rotation speed of the ball mill is 500 - 1000 rpm, and ball milling is carried out for 30 - 40 min.

[0017] (3) Place the ball-milled mixed powder in a muffle furnace, set the temperature to 250 - 300 °C, and carry out tempering treatment to further stabilize the crystal phase.

[0018] (4) The alloy powder after tempering treatment is reflux-activated with sodium hydroxide solution, the upper-layer alkali solution is removed and washed with clear water until neutral to obtain the activated Raney nickel catalyst.

[0019] In the above solution: in the Raney nickel catalyst, the mass percentage content of molybdenum is 3-6%, the mass percentage content of nickel is 50%, and the balance is aluminum.

[0020] In the above solution: after ball milling, the powder particle size is 0.1-1 μm.

[0021] In the above solution: the dilute acid is one of dilute hydrochloric acid, dilute sulfuric acid, and dilute nitric acid.

[0022] In the above solution: in step (4), the mass concentration of the sodium hydroxide solution is 20-25%, and the reflux time is 45-60 min.

[0023] When ball milling in the present invention, the metal powder undergoes severe deformation under the collision of the steel balls in the ball mill and is cold-welded to form a lamellar structure alloy. As the ball milling collision continues, the lamellar structure becomes finer and finer. Due to the existence of a large number of crystal defects introduced by deformation, a large number of interfaces introduced by cold welding, and the temperature rise caused by the ball milling collision, the diffusion ability of the components is greatly enhanced. The generation of crystal defects can enhance the hydrogen adsorption behavior, thereby enhancing the catalytic effect.

[0024] It can be seen from XRD that both the catalysts prepared by the impregnation method and the method of the present invention have relatively obvious nickel metal peaks, but only the catalyst prepared by the alloy method of the present invention has a relatively obvious molybdenum metal peak, which indicates that molybdenum exists in the catalyst in the form of a solid solution; while the molybdenum peak in the impregnation method catalyst is not obvious, indicating that only a small amount of molybdenum adheres to the catalyst surface by impregnation. The Raney nickel prepared by the present invention has a different structure from the Raney nickel prepared by the impregnation method.

[0025] The second object of the present invention is achieved as follows: A production method of reducing indigo, characterized in that it is produced according to the following method:

[0026] (1) Weigh indigo powder, sodium hydroxide, potassium hydroxide, and a dispersant, put them into water or a pre-reduced indigo solution to prepare a dispersion, put the dispersion into a high-pressure reaction kettle, and add the prepared Raney nickel catalyst and an antifoaming agent;

[0027] (2) After the high-pressure reaction kettle is completely sealed, the air in the kettle is pumped out with a vacuum pump and nitrogen is introduced until the air in the kettle is completely replaced;

[0028] (3) Hydrogen is introduced into the high-pressure kettle until the pressure is 0.2-0.8 MPa, stirred, heated, after complete reaction, the catalyst is separated and recovered through a magnetic separator, and the pre-reduced indigo is pressed into a container for storage;

[0029] (4) After washing the magnetically separated catalyst with water and then washing it with N,N-dimethylformamide, it is put into step 1 for recycling.

[0030] The dispersant can be a non-ionic surfactant or an amphoteric surfactant, and the addition amount is generally 1-5% of the mass of indigo powder.

[0031] In the above scheme: the addition amount of sodium hydroxide is 15-28% of the mass of indigo; the addition amount of potassium hydroxide is 3-10% of the mass of indigo; the addition amount of water is 150-350% of the mass of indigo; the addition amount of Raney nickel catalyst is 3-10% of the mass of indigo; the defoamer is one or more of silicone-based, polyether-based, and polyether-modified polysiloxane defoamers, and the addition amount is 0.1-0.5% of the mass of indigo.

[0032] In the above scheme: in step (3), the stirring speed should be 500-1500 rpm, the reaction temperature is 80-90 °C, and the reaction time is 2-5 hours.

[0033] In the above scheme: in step (4), a new Raney nickel catalyst with an amount of 0.2-1% of the mass of indigo is replenished every two cycles.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] (1) The reaction pressure can be reduced to 0.2-0.8 MPa at the lowest, greatly reducing the requirements for equipment and production risks.

[0036] (2) In the present invention, N,N-dimethylformamide can dissolve and elute the indigo attached in the pores of the catalyst, greatly prolonging the service life of the catalyst. In the experiment, more than 20 cycles can be carried out, thereby reducing the catalyst cost per ton of product to less than 20% of that of the noble metal-supported catalyst.

[0037] (3) For the Raney nickel catalyst of the present invention, molybdenum metal in the alloy will not be etched by sodium hydroxide like aluminum, but will enter the nickel lattice. The addition of molybdenum changes the catalytic lattice structure, increasing the number of active sites of Raney nickel and its hydrogen adsorption capacity.

[0038] (4) Under pure sodium hydroxide conditions, a large amount of foam will be generated due to vigorous stirring, affecting the contact between the catalyst and the indigo dispersion, thus hindering the further progress of the reaction; the addition of potassium hydroxide and hydroxy silicone oil defoamer can avoid the generation of foam in the reaction.

[0039] By partially replacing sodium hydroxide with potassium hydroxide, the crystallization of indigo salt can also be avoided at low temperatures. When the addition amount is less than 3%, after the product is placed in an environment of 0 °C for 24 hours, the product will become solid; while when the addition amount of potassium hydroxide is higher than 3%, this phenomenon will not occur. In addition, in order to control costs, the addition amount of potassium hydroxide should not be too high. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 XRD patterns of the Raney nickel prepared in Example 1 of the present invention and by the impregnation method. DETAILED DESCRIPTION OF THE INVENTION

[0041] The present invention will be further described below with reference to the drawings and embodiments.

[0042] Example 1

[0043] Preparation of Raney nickel catalyst:

[0044] (1) Mix nickel powder and molybdenum powder evenly, soak them in dilute hydrochloric acid for 10 - 15 minutes, then wash them with deionized water until neutral, and dry them to constant weight in a vacuum dryer. The mass percentage content of molybdenum is 3%, the mass percentage content of nickel is 50%, and the rest is aluminum.

[0045] (2) Take aluminum powder and mix it with the dried molybdenum powder and nickel powder, put them into a planetary ball mill for ball milling, the rotational speed of the ball mill is 500 - 1000 rpm, and ball mill for 30 - 40 minutes. After ball milling, the particle size of the powder is 0.1 - 1 μm.

[0046] (3) Place the ball-milled mixed powder in a muffle furnace, set the temperature to 250 °C, and carry out tempering treatment for 20 - 40 minutes to further stabilize the crystal phase.

[0047] (4) Activate the alloy powder after tempering treatment with a sodium hydroxide solution with a mass concentration of 21% by refluxing for 45 - 60 minutes, remove the upper layer of alkali solution and wash it with water until neutral to obtain the activated Raney nickel catalyst.

[0048] Example 2

[0049] Weigh 200 g of indigo powder, 56 g of sodium hydroxide, 6 g of potassium hydroxide, 4 g of dispersant NNO, put them into 400 g of water and mix them into a liquid, then add it to a 2 L high-pressure reactor, add 0.2 g of organosilicon defoamer and 9 g of the Raney nickel catalyst of Example 1.

[0050] After completely sealing the high-pressure reactor, evacuate the air inside the reactor with a vacuum pump and introduce nitrogen. Repeat this cycle 3 times until the air inside the reactor is completely replaced. After introducing 0.8 MPa of hydrogen, close the inlet valve, adjust the stirring speed to 900 rpm, and then raise the temperature to 85 °C. When the temperature inside the reactor reaches 85 °C, record the reaction time, rotation speed, temperature, and pressure changes. After the pressure stops changing, stop the reaction. The recorded reaction time is 2.5 hours, and the pressure drops to 0.1 MPa.

[0051] After pressing the materials inside the reactor into the magnetic separator, a pre-reduced liquid indigo product and a catalyst are obtained. The catalyst is washed with water and N,N-dimethylformamide respectively and then recycled.

[0052] The obtained pre-reduced indigo is a red-brown liquid with a concentration of 29.5% and a reduction rate of 97.7%.

[0053] Example 3

[0054] Weigh 200 g of indigo powder, 30 g of sodium hydroxide, 20 g of potassium hydroxide, and 2 g of dispersant NNO. Put them into 400 g of water and mix into a liquid, then add it to a 2 L high-pressure reactor. Add 1 g of defoamer and 6 g of the Raney nickel catalyst from Example 1.

[0055] After completely sealing the high-pressure reactor, evacuate the air inside the reactor with a vacuum pump and introduce nitrogen. Repeat this cycle 3 times until the air inside the reactor is completely replaced. After introducing 0.2 MPa of hydrogen, close the inlet valve, adjust the stirring speed to 500 rpm, and then raise the temperature to 85 °C. When the temperature inside the reactor reaches 85 °C, supplement the hydrogen pressure to 0.3 MPa and keep the valve open for continuous ventilation. Record the reaction time, rotation speed, temperature, and changes. After reacting for 3 - 4 hours, stop the reaction.

[0056] After pressing the materials inside the reactor into the magnetic separator, a pre-reduced liquid indigo product and a catalyst are obtained. The catalyst is washed with water and N,N-dimethylformamide respectively and then recycled.

[0057] The obtained pre-reduced indigo is a clear red-brown liquid with a concentration of 29.4% and a reduction rate of 97.3%.

[0058] Example 4

[0059] To obtain a pre-reduced liquid indigo with a higher concentration and further reduce transportation costs, the two-stage feeding method can be used to increase the product concentration. First, take 200 g of indigo powder, 56 g of sodium hydroxide, 6 g of potassium hydroxide, and 4 g of dispersant NNO, add them to 400 g of water, mix them into a liquid, then add the mixture to a 2 L high-pressure reactor, and add 0.2 g of defoamer and 9 g of the Raney nickel catalyst of Example 1. After completely sealing the high-pressure reactor, use a vacuum pump to evacuate the air in the reactor and introduce nitrogen, and repeat this process 3 times until the air in the reactor is completely replaced. After introducing 0.8 MPa of hydrogen, close the inlet valve, adjust the stirring speed to 900 rpm, and then raise the temperature to 85 °C. When the temperature in the reactor reaches 85 °C, record the reaction time, rotation speed, temperature, and pressure changes. After the pressure no longer changes, stop the reaction.

[0060] Open the reactor and add another 160 g of indigo powder, 35 g of sodium hydroxide, 5 g of potassium hydroxide, and 3 g of dispersant NNO. Then, after completely sealing the high-pressure reactor, use a vacuum pump to evacuate the air in the reactor and introduce nitrogen, and repeat this process 3 times until the air in the reactor is completely replaced. After introducing 0.8 MPa of hydrogen, close the inlet valve, adjust the stirring speed to 900 rpm, and then raise the temperature to 85 °C. When the temperature in the reactor reaches 85 °C, record the reaction time, rotation speed, temperature, and pressure changes. After the pressure no longer changes, stop the reaction.

[0061] Press the materials in the reactor into a magnetic separator to obtain the pre-reduced liquid indigo product and the catalyst. The catalyst is washed with water and N,N-dimethylformamide respectively and then recycled.

[0062] The obtained pre-reduced indigo is a clear reddish-brown liquid with a concentration of 40.5% and a reduction rate of 98.3%.

[0063] Example 5 is a repeated application test of Example 2. Table 1 lists the relationship between the number of cycles and the catalyst cost per ton of product. As the number of cycles increases continuously, the average catalyst consumption per cycle decreases monotonically. Add a new Raney nickel catalyst with a mass of 0.2 - 1% of the indigo every two cycles.

[0064] Based on the average catalyst consumption per ton of product and combined with the unit price of the Raney nickel catalyst of 200 to 250 yuan per kilogram, the average catalyst cost per ton of product is calculated.

[0065]

[0066]

[0067] Example 6

[0068] Weigh 200 g of indigo powder, 50 g of sodium hydroxide, 10 g of potassium hydroxide, and 10 g of dispersant NNO. Put them into 700 g of water and mix into a liquid. Then add it to a 2 L high-pressure reactor, and add 0.6 g of silicone defoamer and 20 g of the Raney nickel catalyst of Example 1.

[0069] After completely sealing the high-pressure reactor, use a vacuum pump to evacuate the air in the reactor and introduce nitrogen. Repeat this process 3 times until the air in the reactor is completely replaced. After introducing 0.5 MPa of hydrogen, close the inlet valve. Adjust the stirring speed to 1500 rpm and then raise the temperature to 90 °C. When the temperature in the reactor reaches 90 °C, record the reaction time, rotation speed, temperature, and pressure changes. After the pressure stops changing, stop the reaction. The recorded reaction time is 2 hours.

[0070] Press the materials in the reactor into a magnetic separator to obtain the pre-reduced liquid indigo product and the catalyst. The catalyst is washed with water and N,N-dimethylformamide respectively and then recovered.

[0071] The pre-reduced indigo is a red-brown liquid with a concentration of 20.6% and a reduction rate of 97.4%.

[0072] Example 7

[0073] Weigh 200 g of indigo powder, 40 g of sodium hydroxide, 20 g of potassium hydroxide, and 5 g of dispersant NNO. Put them into 350 g of water and mix into a liquid. Then add it to a 2 L high-pressure reactor, and add 0.6 g of silicone defoamer and 9 g of the Raney nickel catalyst of Example 1.

[0074] After completely sealing the high-pressure reactor, use a vacuum pump to evacuate the air in the reactor and introduce nitrogen. Repeat this process 3 times until the air in the reactor is completely replaced. After introducing 0.8 MPa of hydrogen, close the inlet valve. Adjust the stirring speed to 900 rpm and then raise the temperature to 80 °C. When the temperature in the reactor reaches 80 °C, record the reaction time, rotation speed, temperature, and pressure changes. After the pressure stops changing, stop the reaction. The recorded reaction time is 5 hours.

[0075] Press the materials in the reactor into a magnetic separator to obtain the pre-reduced liquid indigo product and the catalyst. The catalyst is washed with water and N,N-dimethylformamide respectively and then recovered.

[0076] The pre-reduced indigo is a red-brown liquid with a concentration of 32.5% and a reduction rate of 98.1%.

[0077] Example 8

[0078] Preparation of Raney nickel catalyst:

[0079] (1) Mix nickel powder and molybdenum powder evenly, soak them in dilute sulfuric acid for 10 - 15 min, then wash with deionized water until neutral, and dry to constant weight in vacuum drying. The mass percentage content of molybdenum is 6%, the mass percentage content of nickel is 50%, and the rest is aluminum.

[0080] (2) Take aluminum powder and mix it with the dried molybdenum powder and nickel powder, and put them into a planetary ball mill for ball milling. The rotational speed of the ball mill is 500 - 1000 rpm, and ball milling is carried out for 30 - 40 min. After ball milling, the particle size of the powder is 0.1 - 1 μm.

[0081] (3) Place the ball - milled mixed powder in a muffle furnace, set the temperature to 300 °C, and carry out tempering treatment for 20 - 40 min to further stabilize the crystal phase.

[0082] (4) Activate the alloy powder after tempering treatment by refluxing with a sodium hydroxide solution with a mass concentration of 21% for 45 - 60 min, remove the upper - layer alkali solution and wash with clear water until neutral to obtain an activated Raney nickel catalyst.

[0083] Weigh 200 g of indigo powder, 56 g of sodium hydroxide, 6 g of potassium hydroxide, 4 g of dispersant NNO, put them into 400 g of water and mix into a liquid, then add it to a 2 L high - pressure reactor, and add 0.2 g of organosilicon defoamer and 9 g of the Raney nickel catalyst of this example.

[0084] After completely sealing the high - pressure reactor, use a vacuum pump to evacuate the air in the reactor and introduce nitrogen, and cycle 3 times like this until the air in the reactor is completely replaced. After introducing 0.8 MPa of hydrogen, close the inlet valve, adjust the stirring speed to 900 rpm, and then raise the temperature to 85 °C. When the temperature in the reactor reaches 85 °C, record the reaction time, rotational speed, temperature, and pressure changes. After the pressure no longer changes, stop the reaction, and the recorded reaction time is 2 hours.

[0085] Press the materials in the reactor into a magnetic separator to obtain a pre - reduced liquid indigo product and the catalyst. The catalyst is washed with water and N,N - dimethylformamide respectively and then recycled.

[0086] The obtained pre - reduced indigo is a reddish - brown liquid, its concentration is 30.0%, and the reduction rate is 98.2%.

[0087] Comparative Example 1

[0088] Weigh 200 g of indigo powder, 62 g of sodium hydroxide, 4 g of dispersant NNO, put them into 400 g of water and mix into a liquid, then add it to a 2 L high - pressure reactor, and add 9 g of the Raney nickel catalyst of Example 1.

[0089] After completely sealing the high-pressure reactor, evacuate the air inside the reactor with a vacuum pump and introduce nitrogen. Repeat this cycle 3 times until the air inside the reactor is completely replaced. After introducing 0.8 MPa of hydrogen, close the inlet valve, adjust the stirring speed to 900 rpm, and then raise the temperature to 85 °C. When the temperature inside the reactor reaches 85 °C, record the reaction time, rotation speed, temperature, and pressure changes. After the pressure stops changing, stop the reaction. The recorded reaction time is 7 hours.

[0090] After pressing the materials inside the reactor into the magnetic separator, a pre-reduced liquid indigo sodium salt product is obtained.

[0091] In the experiment of Comparative Example 1, after the reaction ended, opening the high-pressure reactor revealed a large amount of foam. The product was a slightly viscous liquid with a reduction rate of 90.2%. Further, taking the products of Comparative Example 1 and Example 2 and placing them in a refrigerator at -10 °C for 24 hours, the product of Comparative Example 1 became solid and lost fluidity, while the product of Example 1 remained in a liquid state with good fluidity.

[0092] Comparative Example 2

[0093] Weigh 200 g of indigo powder, 56 g of sodium hydroxide, 6 g of potassium hydroxide, and 4 g of dispersant NNO. Add them to 400 g of water to mix into a liquid, then add it to a 2 L high-pressure reactor, and add 9 g of the Raney nickel catalyst of Example 1.

[0094] After completely sealing the high-pressure reactor, evacuate the air inside the reactor with a vacuum pump and introduce nitrogen. Repeat this cycle 3 times until the air inside the reactor is completely replaced. After introducing 0.8 MPa of hydrogen, close the inlet valve, adjust the stirring speed to 900 rpm, and then raise the temperature to 85 °C. When the temperature inside the reactor reaches 85 °C, record the reaction time, rotation speed, temperature, and pressure changes. After the pressure stops changing, stop the reaction. The recorded reaction time is 6 hours.

[0095] After pressing the materials inside the reactor into the magnetic separator, a pre-reduced liquid indigo sodium-potassium salt product is obtained.

[0096] In the experiment of Comparative Example 2, after the reaction ended, opening the high-pressure reactor revealed a small amount of foam floating on the surface of the product and adhering to the stirring rod. After placing it in a refrigerator at -10 °C for 24 hours, the product remained in a liquid state with good fluidity.

[0097] The obtained pre-reduced indigo is a reddish-brown liquid with a concentration of 30.0% and a reduction rate of 96.5%.

[0098] Comparative Example 3

[0099] Weigh 200 g of indigo powder, 62 g of sodium hydroxide, 0.2 g of defoamer, and 4 g of dispersant NNO. After mixing them in 400 g of water to form a liquid, add it to a 2 L high-pressure reactor, and then add 9 g of the Raney nickel catalyst of Example 1.

[0100] After completely sealing the high-pressure reactor, use a vacuum pump to evacuate the air inside the reactor and then introduce nitrogen. Repeat this cycle 3 times until the air inside the reactor is completely replaced. After introducing 0.8 MPa of hydrogen, close the inlet valve. Adjust the stirring speed to 900 rpm and then raise the temperature to 85 °C. When the temperature inside the reactor reaches 85 °C, record the reaction time, rotation speed, temperature, and pressure changes. After the pressure stops changing, stop the reaction. The recorded reaction time is 6.5 hours.

[0101] Press the materials inside the reactor into a magnetic separator to obtain the pre-reduced liquid indigo sodium salt product.

[0102] In the experiment of Comparative Example 3, after the reaction ended, opening the high-pressure reactor revealed that foam adhered to the stirring rod. The obtained pre-reduced indigo was a reddish-brown liquid with a concentration of 30.0% and a reduction rate of 96.8%. Further, after placing it in a refrigerator at -10 °C for 24 h, the product became solid and lost its fluidity.

[0103] Comparative Example 4

[0104] Weigh 200 g of indigo powder, 56 g of sodium hydroxide, 4 g of potassium hydroxide, and 2 g of dispersant NNO. After mixing them in 400 g of water to form a liquid, add it to a 2 L high-pressure reactor, and then add 1 g of defoamer and 6 g of the Raney nickel catalyst of Example 1.

[0105] After completely sealing the high-pressure reactor, use a vacuum pump to evacuate the air inside the reactor and then introduce nitrogen. Repeat this cycle 3 times until the air inside the reactor is completely replaced. After introducing 0.2 MPa of hydrogen, close the inlet valve. Adjust the stirring speed to 500 rpm and then raise the temperature to 85 °C. When the temperature inside the reactor reaches 85 °C, supplement the hydrogen pressure to 0.3 MPa and keep the valve open for continuous ventilation. Record the reaction time, rotation speed, temperature, and changes. After reacting for 5 hours, stop the reaction.

[0106] Press the materials inside the reactor into a magnetic separator to obtain the pre-reduced liquid indigo product and the catalyst. The catalyst is washed with water and N,N-dimethylformamide respectively and then recovered.

[0107] The obtained pre-reduced indigo was a clear reddish-brown liquid with a concentration of 30.2% and a reduction rate of 96.9%. Further, after placing it in a refrigerator at -10 °C for 24 h, the product became solid and lost its fluidity.

[0108] Comparative Example 5

[0109] Weigh 200 g of indigo powder, 56 g of sodium hydroxide, 6 g of potassium hydroxide, and 4 g of dispersant NNO. After mixing them in 400 g of water to form a liquid, add the mixture to a 2 L high-pressure reactor. Then add 0.2 g of silicone defoamer and 9 g of Raney nickel catalyst prepared by the impregnation method disclosed in CN 103480394A.

[0110] After completely sealing the high-pressure reactor, use a vacuum pump to evacuate the air inside the reactor and then introduce nitrogen. Repeat this process 3 times until the air inside the reactor is completely replaced. After introducing 0.8 MPa of hydrogen, close the inlet valve. Adjust the stirring speed to 900 rpm and then raise the temperature to 85 °C. When the temperature inside the reactor reaches 85 °C, record the reaction time, rotation speed, temperature, and pressure changes. After the pressure stops changing, stop the reaction. The recorded reaction time is 7 hours, and the pressure drops to 0.5 MPa.

[0111] Press the materials inside the reactor into a magnetic separator to obtain a pre-reduced liquid indigo sodium salt product.

[0112] In the experiment of the comparative example, after the reaction is completed, opening the high-pressure reactor shows that the product is relatively viscous. Further, take the product of comparative example 5 and test its reduction rate to be 60.8%.

[0113] Comparative Example 6

[0114] Weigh 200 g of indigo powder, 56 g of sodium hydroxide, 6 g of potassium hydroxide, and 4 g of dispersant NNO. After mixing them in 400 g of water to form a liquid, add the mixture to a 2 L high-pressure reactor. Then add 0.2 g of silicone defoamer and 9 g of Raney nickel catalyst prepared in Example 1 of CN 104056641B.

[0115] After completely sealing the high-pressure reactor, use a vacuum pump to evacuate the air inside the reactor and then introduce nitrogen. Repeat this process 3 times until the air inside the reactor is completely replaced. After introducing 0.8 MPa of hydrogen, close the inlet valve. Adjust the stirring speed to 900 rpm and then raise the temperature to 85 °C. When the temperature inside the reactor reaches 85 °C, record the reaction time, rotation speed, temperature, and pressure changes. After the pressure stops changing, stop the reaction. The recorded reaction time is 5 hours.

[0116] Press the materials inside the reactor into a magnetic separator to obtain a pre-reduced liquid indigo product.

[0117] In the experiment of the comparative example, after the reaction is completed, opening the high-pressure reactor shows that the product is relatively viscous. Further, take the product of comparative example 6 and test its reduction rate to be 81.2%.

[0118] The present invention should not be limited to the embodiments. For example, the concentration of sodium hydroxide used for activation can be appropriately adjusted to 20% - 25%.

Claims

1. A method for producing reduced indigo, characterized in that: Produced as follows: (1) Weigh indigo powder, sodium hydroxide, potassium hydroxide, and a dispersant, and put them into water or a pre-reduced indigo solution to prepare a dispersion, put the dispersion into a high-pressure reactor, and add a Raney nickel catalyst and a defoaming agent; the Raney nickel catalyst is prepared according to the following steps: (1) nickel powder and molybdenum powder were mixed evenly, soaked in dilute acid for 10-15 min, then washed with deionized water until neutral, and vacuum dried to constant weight; (2) mixing aluminum powder with dried molybdenum powder and nickel powder, and milling the mixture in a planetary ball mill at a speed of 500-1000 rpm for 30-40 min; (3) placing the ball-milled mixed powder in a muffle furnace, setting the temperature to 250-300° C., and performing a tempering treatment for 20-40 min to further stabilize the crystal phase; (4) refluxing the tempered alloy powder with a sodium hydroxide solution to activate it, removing the upper alkali solution and washing with clean water until it is neutral to obtain an activated Raney nickel catalyst; the reflux time is 45-60 min; In the Raney nickel catalyst, the mass percentage of molybdenum is 3-6%, the mass percentage of nickel is 50%, and the rest is aluminum; after ball milling, the powder particle size is 0.1-1μm; (2) After the autoclave is completely sealed, the air in the autoclave is evacuated with a vacuum pump and nitrogen is introduced until the air in the autoclave is completely replaced; (3) introducing hydrogen into the autoclave to a pressure of 0.2-0.8 MPa, stirring, heating, and after the reaction is complete, separating the material through a magnetic separator to recover the catalyst, and pressing the pre-reduced indigo into a container for storage; the stirring speed should be 500-1500 rpm, the reaction temperature is 80-95° C., and the reaction time is 2-5 hours; (4) washing the magnetically separated catalyst with water, washing it with N,N-dimethylformamide, and then putting it into step 1 for recycling; The amount of sodium hydroxide added is 15-28% of the mass of indigo; the amount of potassium hydroxide added is 3-10% of the mass of indigo; the amount of water added is 150-350% of the mass of indigo; the amount of Raney nickel catalyst added is 3-10% of the mass of indigo; the defoamer is one or more of silicone, polyether, and polyether-modified polysiloxane defoamers, and the amount added is 0.1-0.5% of the mass of indigo.

2. The method for producing reduced indigo according to claim 1, characterized in that: The dilute acid is one of dilute hydrochloric acid, dilute sulfuric acid, and dilute nitric acid.

3. The method for producing reduced indigo according to claim 2, characterized in that: In step (4), after every two cycles, new Raney nickel catalyst with a mass percentage of 0.2-1% of indigo is added.

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