A reducing dye dispersant, its application and a preparation method of a liquid pre-reduced reducing dye

Abstract

The present invention discloses a reducing dye dispersant, its application and a preparation method of a reducing dye. The reducing dye dispersant is an aqueous solution of a copolymer and an alkali. The copolymer is one or more of an ethylene-maleic anhydride alternating copolymer, a propylene-maleic anhydride alternating copolymer, and an isobutylene-maleic anhydride alternating copolymer. Different from a graft copolymer, this copolymer is an alternating copolymer, and the ethylene, propylene, and isobutylene groups and the maleic anhydride groups in its structural units alternate. Since the basic unit of the olefin-maleic anhydride alternating copolymer is a hydrophobic olefin unit and a hydrophilic maleic group after being dissolved by an alkali, the molecule has amphiphilicity. Different from a small molecule dispersant, this dispersant can form a self-assembled structure in the reducing dye dispersion liquid, better wrap the reducing dye colloidal particles, and thus exhibit better dispersion performance. This dispersant only contains three elements of carbon, hydrogen, and oxygen, does not contain elements such as N and S, and has high environmental friendliness.

Description

Technical Field

[0001] The present invention relates to the field of fine chemicals, and specifically relates to a reducing dye dispersant, its application, and a preparation method of a liquid pre-reduced reducing dye. Background Art

[0002] Since reducing dyes are insoluble in water, they are usually dyed on yarns using reduced leuco salt and then oxidized to make them develop color. Therefore, in the printing and dyeing industry, a dispersant is always needed to be added to the dye bath to improve the uniformity of the dye. Currently, the common reduction technical routes of reducing dyes include: chemical reduction method, catalytic hydrogenation reduction method, and electrochemical reduction method. Among them, the catalytic hydrogenation reduction method and the electrochemical reduction method are more environmentally friendly and have good application prospects. However, taking indigo as an example, since indigo is insoluble in water and the indigo particles will swell in water, and completely lose fluidity and become solid (paste) after the concentration reaches more than 25%. This greatly limits the continuation of the reduction reaction. Therefore, in practice, the fluidity of the indigo dispersion is usually maintained by adding a dispersant.

[0003] For example, in the patent: Method for Preparing Indigo White by Fluidized Bed Catalytic Hydrogenation (CN 114644585 A), by adding a dispersant, the concentration of the reaction solution is increased to more than 25% (the calculation of the concentration is: the mass of indigo / (the mass of indigo + the mass of water + sodium hydroxide + potassium hydroxide), the same below), and it still has good fluidity and reactivity. However, in order to further reduce the storage and transportation costs, the industry hopes that the pre-reduced reducing dye solution has a higher effective concentration. Therefore, currently in patents and literature, the effective concentration is often increased to more than 30% by secondary feeding or distillation methods. However, this undoubtedly increases the complexity of the process and raises the production cost.

[0004] Most of the currently commercially available dispersants for the dye industry are sulfonates, sulfate esters, polyacrylamide, etc. Specifically, such as dispersant NNO, dispersant 5027, dispersant MF, etc. On the one hand, most of these catalysts contain elements such as N and S, posing certain environmental protection risks; on the other hand, the dispersing ability of these dispersants is slightly insufficient. Summary of the Invention

[0005] In order to solve the above technical problems, the first object of the present invention is to provide a reducing dye dispersant, the second object is to provide the application of this dispersant in the preparation of reducing dyes, and the third object is to provide a preparation method of a liquid pre-reduced reducing dye. This dispersant has good dispersing performance, no N and S elements, and reduces environmental pollution. It can maintain its fluidity when the concentration of the dye is lower than 40%.

[0006] To achieve the above first object, the present invention provides the following technical solution: A vat dye dispersant, characterized in that: it is an aqueous solution of a copolymer and an alkali, and the copolymer is one or more of an ethylene-maleic anhydride alternating copolymer, a propylene-maleic anhydride alternating copolymer, and an isobutylene-maleic anhydride alternating copolymer.

[0007] In the above solution: the alkali is one or both of sodium hydroxide and potassium hydroxide.

[0008] In the above solution: the addition amount of the alkali is 28%-35% of the mass of the copolymer, and the addition amount of water is 0.8-1.2 times the mass of the copolymer.

[0009] In the above solution: the molecular weight of the copolymer is 10-40k.

[0010] Different from graft copolymers, this copolymer is an alternating copolymer, and ethylene, propylene, isobutylene groups and maleic anhydride groups in its structural units alternate. Since the basic unit of the olefin-maleic anhydride alternating copolymer is a hydrophobic olefin unit and a hydrophilic maleic acid group after being dissolved by an alkali, the molecule has amphiphilicity. Different from small molecule dispersants, this dispersant can form a self-assembled structure in the dye dispersion liquid, better wrap the dye colloidal particles, and thus exhibit better dispersion performance. This dispersant only contains three elements of carbon, hydrogen and oxygen, does not contain elements such as N and S, and has high environmental protection.

[0011] The second object of the present invention is achieved as follows: The application of the above-mentioned vat dye dispersant in the dye reduction reaction.

[0012] The dye is one of vat dyes such as indigo or vat pink.

[0013] The addition amount of the dispersant is 1%-2.5% of the mass of the dye.

[0014] This dispersant can still maintain its fluidity when the dye concentration is 35%. In processes such as dye hydrogenation reduction, the concentration of vat dye can be increased to 40% without secondary feeding. And it can achieve hydrogenation reaction at a lower reaction temperature and maintain good fluidity at a lower reaction temperature. It reduces the reaction temperature. Improves the safety of the reaction and reduces the energy consumption of the reaction.

[0015] The third object of the present invention is achieved as follows: A method for preparing a liquid pre-reduced vat dye, characterized in that it is prepared according to the following steps:

[0016] (1) Weigh dye powder, sodium hydroxide, potassium hydroxide, and dispersant, put them into water to make a dispersion liquid, put the dispersion liquid into a high-pressure reaction kettle, and add a catalyst and an antifoaming agent;

[0017] (2) After completely sealing the high-pressure reactor, evacuate the air inside the reactor with a vacuum pump and introduce nitrogen until the air inside the reactor is completely replaced;

[0018] (3) Introduce hydrogen into the autoclave until the pressure reaches 0.2 - 0.8 MPa, stir, heat to 50 - 60 °C. After complete reaction, separate and recover the catalyst, and the reduced dye solution is then pressed into a container for storage.

[0019] In the above solution: The catalyst is a self-made Raney nickel catalyst, which is prepared according to the following steps:

[0020] (1) Mix nickel powder and molybdenum powder evenly, soak them in dilute acid for 10 - 15 min, then wash them with deionized water until neutral, and dry them in vacuum until constant weight;

[0021] (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 min;

[0022] (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;

[0023] (4) Reflux and activate the alloy powder after 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.

[0024] 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.

[0025] After ball milling, the particle size of the powder is 0.1 - 1 μm. The dilute acid is one of dilute hydrochloric acid, dilute sulfuric acid, and dilute nitric acid. In step (4), the mass concentration of the sodium hydroxide solution is 20 - 25%, and the reflux time is 45 - 60 min.

[0026] When the Raney nickel catalyst prepared by the present invention is ball milled, the metal powder undergoes severe deformation under the collision of the steel balls in the ball mill and cold welds to form a lamellar structure alloy. With the continuous progress of ball milling collision, the lamellar structure becomes finer and finer. Due to the existence of a large number of crystal defects introduced by deformation and a large number of interfaces introduced by cold welding, as well as the temperature rise caused by ball milling collision, the diffusion ability of the components is greatly enhanced. And the generation of crystal defects can enhance the adsorption behavior of hydrogen, thereby enhancing the catalytic effect.

[0027] It can be seen from XRD that both the catalysts prepared by the impregnation method and the method of the present invention have obvious nickel metal peaks. However, only the catalyst prepared by the alloy method of the present invention has an obvious molybdenum metal peak, indicating 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.

[0028] The catalyst of the present invention is separated and recovered by a magnetic separator. After the magnetically separated catalyst is washed with water, it is washed with N,N-dimethylformamide and then put into step 1 for recycling. After every two cycles, a new Raney nickel catalyst with a mass of 0.2-1% of indigo is added.

[0029] In the method for preparing liquid pre-reduced vat dyes: the addition amount of sodium hydroxide is 15-28% of the mass of the dye; the addition amount of potassium hydroxide is 3-10% of the mass of the dye; the addition amount of Raney nickel catalyst is 3-10% of the mass of the dye; the defoaming agent is one or more of silicone-based, polyether-based, and polyether-modified polysiloxane-based defoaming agents, and the addition amount is 0.1-0.5% of the mass of the dye.

[0030] In the preparation method of the present invention, the reaction pressure can be reduced to as low as 0.2-0.8 MPa at the lowest, and the reaction temperature is reduced to 50-60 °C. The reaction time is 2.5-5 h. This greatly reduces the requirements for equipment and production risks. In 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 and the hydrogen adsorption capacity of Raney nickel. 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 liquid, thus hindering the further progress of the reaction; the addition of potassium hydroxide and hydroxy silicone oil defoaming agent can avoid the generation of foam in the reaction.

[0031] By partially replacing sodium hydroxide with potassium hydroxide, the crystallization of reduced indigo salt at low temperature can also be avoided. When the addition amount is less than 3%, after the product is placed in an environment of 0 °C for 24 h, 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. Description of the Drawings

[0032] Figure 1 It is the XRD pattern of the Raney nickel prepared by the present invention and the impregnation method. Detailed Embodiments

[0033] The present invention will be further described below with reference to the drawings and embodiments.

[0034] Example 1

[0035] Preparation of Raney nickel catalyst:

[0036] (1) Mix nickel powder and molybdenum powder evenly, soak in dilute hydrochloric 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 3%, the mass percentage content of nickel is 50%, and the rest is aluminum.

[0037] (2) Take aluminum powder and mix it with the dried molybdenum powder and nickel powder, put it 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 powder particle size is 0.1 - 1 μm.

[0038] (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 min to further stabilize the crystal phase.

[0039] (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 the activated Raney nickel catalyst.

[0040] Example 2

[0041] Weigh 10 g of ethylene - maleic anhydride alternating copolymer (molecular weight 15k), 3 g of sodium hydroxide, and 8 g of water, and mix and stir well to dissolve.

[0042] Weigh 100 g of indigo powder and mix it with 180 g of water to obtain an indigo paste, add 1 g of copolymer solution and stir, and the mixture restores fluidity.

[0043] Example 3

[0044] Weigh 10 g of ethylene - maleic anhydride alternating copolymer (molecular weight 15k), 3.5 g of sodium hydroxide, and 12 g of water, and mix and stir well to dissolve.

[0045] Weigh 250 g of indigo powder, 55 g of sodium hydroxide, 7.5 g of potassium hydroxide, 4 g of copolymer solution, put it into 400 g of water and mix into a liquid, then add it to a 2 L high - pressure reaction kettle, add 1 g of defoamer and 12 g of the Raney nickel catalyst prepared in Example 1.

[0046] 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 55 °C. Stop the reaction after the pressure no longer drops. The reaction time is 3 h, and then cool down. 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 recycled.

[0047] The pre-reduced indigo obtained by the above method is a red-brown liquid with a concentration of 35% and a reduction rate of 98.3%.

[0048] Example 4

[0049] Weigh 10 g of the alternating copolymer of propylene-maleic anhydride (molecular weight 20 k), 2.8 g of sodium hydroxide, and 8 g of water, and mix and stir them thoroughly to dissolve.

[0050] Weigh 250 g of reduced pink powder, 45.7 g of sodium hydroxide, 12.5 g of potassium hydroxide, and 6.25 g of the copolymer solution. Put them into 400 g of water and mix into a liquid, then add it to a 2 L high-pressure reactor, add 1.25 g of defoamer and 12 g of the Raney nickel catalyst of Example 1.

[0051] 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 60 °C. Stop the reaction after the pressure no longer drops. The reaction time is 2.5 h, and then cool down. Press the materials inside the reactor into a magnetic separator to obtain the pre-reduced liquid pink product and the catalyst. The catalyst is washed with water and N,N-dimethylformamide respectively and then recycled.

[0052] The pre-reduced pink obtained by the above method is a red-brown liquid with a concentration of 35% and a reduction rate of 97.9%.

[0053] Example 5

[0054] Weigh 10 g of the alternating copolymer of ethylene-maleic anhydride (molecular weight 40 k), 3 g of sodium hydroxide, and 12 g of water, and mix and stir them thoroughly to dissolve.

[0055] Weigh 250 g of indigo powder, 56 g of sodium hydroxide, 7.5 g of potassium hydroxide, and 2.5 g of the copolymer solution. Put them into 340 g of water and mix into a liquid, then add it to a 2 L high-pressure reactor, add 1 g of defoamer and 10 g of the Raney nickel catalyst of Example 1.

[0056] 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 50 °C for reaction. Stop the reaction after the pressure no longer drops. The reaction time is 3 h, and then cool down. Separate the catalyst. The pre-reduced indigo obtained by the above method is a reddish-brown liquid with a concentration of 38% and a reduction rate of 97.3%.

[0057] Example 6

[0058] Weigh 10 g of isobutene-maleic anhydride alternating copolymer (molecular weight 15k), 3.5 g of sodium hydroxide, and 12 g of water, and mix and stir them thoroughly to dissolve.

[0059] Weigh 250 g of indigo powder, 53 g of sodium hydroxide, 7.5 g of potassium hydroxide, 4 g of copolymer solution, 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 defoaming agent and 12 g of Raney nickel catalyst prepared in Example 1.

[0060] 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 900 rpm, and then raise the temperature to 60 °C. Stop the reaction after the pressure no longer drops. The reaction time is 5 h, and then cool down. 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.

[0061] The pre-reduced indigo obtained by the above method is a reddish-brown liquid with a concentration of 35% and a reduction rate of 95.5%.

[0062] Example 7

[0063] The preparation of the Raney nickel catalyst is the same as that in Example 1. The difference is that the mass percentage content of molybdenum is 6%, the mass percentage content of nickel is 50%, and the balance is aluminum.

[0064] Weigh 10 g of ethylene-maleic anhydride alternating copolymer (molecular weight 40k), 3 g of sodium hydroxide, and 12 g of water, and mix and stir them thoroughly to dissolve.

[0065] Weigh 250 g of indigo powder, 56 g of sodium hydroxide, 7.5 g of potassium hydroxide, 2.5 g of copolymer solution, put them into 340 g of water and mix into a liquid, then add it to a 2 L high-pressure reactor, add 1 g of defoaming agent and 10 g of Raney nickel catalyst prepared in this example.

[0066] After completely sealing the high-pressure reactor, evacuate the air inside the reactor with a vacuum pump and introduce nitrogen gas. Repeat this cycle 3 times until the air inside the reactor is completely replaced. After introducing 0.8 MPa of hydrogen gas, close the inlet valve, adjust the stirring speed to 900 rpm, and then raise the temperature to 60 °C for the reaction. Stop the reaction after the pressure no longer drops. The reaction time is 2.5 h, and then cool down. Separate the catalyst. The pre-reduced indigo obtained by the above method is a red-brown liquid with a concentration of 38% and a reduction rate of 98.2%.

[0067] After placing the products of Examples 3-7 of the present invention in a refrigerator at -10 °C for 24 h, the products still remain in a liquid state and have good fluidity.

[0068] Comparative Example 1

[0069] Weigh 200 g of indigo powder, 56 g of sodium hydroxide, and 6.4 g of potassium hydroxide, and put them into 400 g of water. After mixing, the mixture loses its fluidity and cannot undergo a hydrogenation reaction.

[0070] Comparative Example 2

[0071] Weigh 250 g of indigo powder, 55 g of sodium hydroxide, 7.5 g of potassium hydroxide, and 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. After adding 1 g of defoamer, add 12 g of the Raney nickel catalyst of Example 1. After completely sealing the high-pressure reactor, evacuate the air inside the reactor with a vacuum pump and introduce nitrogen gas. Repeat this cycle 3 times until the air inside the reactor is completely replaced. After introducing 0.8 MPa of hydrogen gas, close the inlet valve, adjust the stirring speed to 900 rpm, and then raise the temperature to 85 °C. Stop the reaction after the pressure no longer drops, and then cool down.

[0072] The pre-reduced indigo obtained by the above method is a viscous asphalt-like semi-fluid with a concentration of 35% and a reduction rate of 2.3%, and it is basically impossible to undergo a hydrogenation reaction.

[0073] Comparative Example 3

[0074] Weigh 190 g of indigo powder, 56 g of sodium hydroxide, 6.4 g of potassium hydroxide, and 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. After adding 1 g of defoamer and 9 g of the Raney nickel catalyst of Example 1. After completely sealing the high-pressure reactor, evacuate the air inside the reactor with a vacuum pump and introduce nitrogen gas. Repeat this cycle 3 times until the air inside the reactor is completely replaced. After introducing 0.8 MPa of hydrogen gas, close the inlet valve, adjust the stirring speed to 900 rpm, and then raise the temperature to 85 °C. Stop the reaction after the pressure no longer drops, and then cool down.

[0075] The pre-reduced pink obtained by the above method is a red-brown liquid with a concentration of 28.9% and a reduction rate of 96.9%.

[0076] Comparative Example 4

[0077] Weigh 200 g of indigo powder, 30 g of sodium hydroxide, 20 g of potassium hydroxide, and 2 g of dispersant NNO. After putting them into 400 g of water and mixing into a liquid, add them 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.

[0078] After completely sealing the high-pressure reactor, use a vacuum pump to evacuate the air in the reactor and then introduce nitrogen. Repeat this cycle 3 times until the air in the reactor is completely replaced. After introducing 0.2 MPa of hydrogen, close the inlet valve. After adjusting the stirring speed to 500 rpm, raise the temperature to 85 °C. When the temperature in 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 their changes. After reacting for 3 - 4 hours, stop the reaction.

[0079] After pressing the materials in the reactor into a 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 recovered.

[0080] The obtained pre-reduced indigo is a clear reddish-brown liquid with a concentration of 29.4% and a reduction rate of 97.3%.

[0081] Comparative Example 5

[0082] Weigh 200 g of indigo powder, 62 g of sodium hydroxide, 4 g of dispersant NNO. After putting them into 400 g of water and mixing into a liquid, add them to a 2 L high-pressure reactor, and then add 9 g of the Raney nickel catalyst of Example 1.

[0083] After completely sealing the high-pressure reactor, use a vacuum pump to evacuate the air in the reactor and then introduce nitrogen. Repeat this cycle 3 times until the air in the reactor is completely replaced. After introducing 0.8 MPa of hydrogen, close the inlet valve. After adjusting the stirring speed to 900 rpm, 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, and the recorded reaction time is 7 hours.

[0084] After pressing the materials in the reactor into a magnetic separator, a pre-reduced liquid indigo sodium salt product is obtained.

[0085] In the experiment of Comparative Example 5, after the reaction is completed, opening the high-pressure reactor can observe a large amount of foam. The product is a slightly viscous liquid with a reduction rate of 90.2%. Further, after taking the product of Comparative Example 5 and placing it in a refrigerator at -10 °C for 24 h, the product of Comparative Example 5 becomes solid and loses fluidity.

[0086] Comparative Example 6

[0087] Weigh 10 g of the alternating copolymer of propylene and maleic anhydride (molecular weight 20 k), 2.8 g of sodium hydroxide, and 8 g of water, and mix and stir well until dissolved.

[0088] Weigh 250 g of reduced pink lake powder, 45.7 g of sodium hydroxide, 12.5 g of potassium hydroxide, and 6.25 g of copolymer solution. Add them to 400 g of water, mix into a liquid, then add it to a 2 L high-pressure reactor, and add 12 g of the Raney nickel catalyst of Example 1.

[0089] After completely sealing the high-pressure reactor, use a vacuum pump to evacuate the air in the reactor and then 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 60 °C. Stop the reaction after the pressure no longer drops. The reaction time is 4 h, and then cool down. When opening the high-pressure reactor, it can be observed that a small amount of foam floats on the surface of the product and adheres to the stirring rod. Press the materials in the reactor into a magnetic separator to obtain the pre-reduced liquid pink lake product and the catalyst. The catalyst is washed with water and N,N-dimethylformamide respectively and then recovered.

[0090] The pre-reduced pink lake obtained by the above method is a reddish-brown liquid with a concentration of 35% and a reduction rate of 96.5%. After being placed in a refrigerator at -10 °C for 24 h, the product still remains in a liquid state and has good fluidity.

[0091] Comparative Example 7

[0092] Weigh 10 g of the alternating copolymer of propylene and maleic anhydride (molecular weight 20 k), 2.8 g of sodium hydroxide, and 8 g of water, and mix and stir well until dissolved.

[0093] Weigh 250 g of reduced pink lake powder, 58.2 g of sodium hydroxide, 6.25 g of copolymer solution. Add them to 400 g of water, mix into a liquid, then add it to a 2 L high-pressure reactor, and add 1 g of defoamer and 12 g of the Raney nickel catalyst of Example 1.

[0094] After completely sealing the high-pressure reactor, use a vacuum pump to evacuate the air in the reactor and then 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 60 °C. Stop the reaction after the pressure no longer drops. The reaction time is 7 h, and then cool down. When opening the high-pressure reactor, it can be observed that a small amount of foam floats on the surface of the product and adheres to the stirring rod. Press the materials in the reactor into a magnetic separator to obtain the pre-reduced liquid pink lake product and the catalyst. The catalyst is washed with water and N,N-dimethylformamide respectively and then recovered.

[0095] The pre-reduced pink obtained by the above method is a red-brown liquid with a concentration of 35% and a reduction rate of 96.3%. After being placed in a refrigerator at -10°C for 24 hours, the product becomes solid and loses its fluidity.

[0096] When the addition amount of potassium hydroxide is less than 3% of the dye, the product will become solid and lose its fluidity at low temperature.

[0097] Comparative Example 8

[0098] Weigh 10 g of ethylene-maleic anhydride alternating copolymer (molecular weight 15k), 3.5 g of sodium hydroxide, and 12 g of water, and mix and stir them thoroughly to dissolve.

[0099] Weigh 250 g of indigo powder, 55 g of sodium hydroxide, 7.5 g of potassium hydroxide, and 4 g of copolymer solution, put them into 400 g of water, mix them into a liquid, then add them to a 2 L high-pressure reactor, add 1 g of defoamer and 12 g of Raney nickel catalyst prepared by the impregnation method disclosed in CN 103480394A.

[0100] 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 55°C. Stop the reaction after the pressure no longer drops, with a reaction time of 6 hours, and then cool down. 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. The measured reduction rate is 64.8%.

[0101] Comparative Example 9

[0102] The rest is the same as Comparative Example 8, except that 12 g of Raney nickel catalyst prepared in Example 1 of CN 104056641 B is added. The measured reduction rate is 83.3%.

[0103] Comparative Example 10

[0104] Weigh 10 g of styrene-maleic anhydride alternating copolymer (molecular weight 15k), 3.5 g of sodium hydroxide, and 12 g of water, and mix and stir them thoroughly to dissolve.

[0105] Weigh 250 g of indigo powder, 55 g of sodium hydroxide, 7.5 g of potassium hydroxide, and 4 g of copolymer solution, put them into 400 g of water, mix them into a liquid, then add them to a 2 L high-pressure reactor, add 1 g of defoamer and 12 g of Raney nickel catalyst prepared in Example 1.

[0106] 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 55 °C. Stop the reaction after the pressure no longer drops. The reaction time is 3 h, and then cool down.

[0107] The pre-reduced indigo obtained by the above method is an asphalt-like fluid with a concentration of 35% and a reduction rate of 8.3%.

[0108] The present invention is not limited to the embodiments. In the preparation method of vat dyes: the addition amount of sodium hydroxide is 15 - 28% of the mass of the dye; the addition amount of potassium hydroxide is 3 - 10% of the mass of the dye; the addition amount of Raney nickel catalyst is 3 - 10% of the mass of the dye; the defoamer is one or more of silicone-based, polyether-based, and polyether-modified polysiloxane-based defoamers, and the addition amount is 0.1 - 0.5% of the mass of the dye.

Claims

1. A method for preparing a liquid pre-reduced vat dye, characterized in that: Prepare according to the following steps: (1) Weighing dye powder, sodium hydroxide, potassium hydroxide, and a dispersant, adding them into water to prepare a dispersion, adding the dispersion into a high-pressure reactor, and adding a catalyst and a defoamer; the dispersant is an aqueous solution of a copolymer and an alkali, and the copolymer is one or more of ethylene-maleic anhydride alternating copolymer, propylene-maleic anhydride alternating copolymer, and isobutylene-maleic anhydride alternating copolymer; the amount of sodium hydroxide added is 15-28% of the mass of the dye; the amount of potassium hydroxide added is 3-10% of the mass of the dye; the dye is one of indigo or vat pink; (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, and heating to 50-60° C. After the reaction is complete, separating and recovering the catalyst, and pressing the pre-reduced dye solution into a container for storage; The catalyst is a homemade Raney nickel catalyst, which 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 and setting the temperature to 250-300° C. for tempering to further stabilize the crystal phase; (4) refluxing and activating the alloy powder after the tempering treatment with a sodium hydroxide solution, removing the upper alkali solution and washing with clean water until neutral, thereby obtaining an activated Raney nickel catalyst; 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.

2. The method for preparing a liquid pre-reduced vat dye according to claim 1, characterized in that: The alkali is one or both of sodium hydroxide and potassium hydroxide.

3. The method for preparing a liquid pre-reduced vat dye according to claim 1 or 2, characterized in that: The added amount of the alkali is 28%-35% of the mass of the copolymer, and the added amount of the water is 0.8-1.2 times of the mass of the copolymer.

4. The method for preparing a liquid pre-reduced vat dye according to claim 3, characterized in that: The molecular weight of the copolymer is 10-40k.

5. The method for preparing a liquid pre-reduced vat dye according to claim 4, characterized in that: The added amount of the dispersant is 1%-2.5% of the dye mass.

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