A method for microwave-assisted preparation of a lignosulfonate dye dispersant

Abstract

The application discloses a microwave-assisted preparation method of a lignin sulfonate dye dispersant, and belongs to the technical field of dye dispersants. The preparation steps are as follows: purified lignin is prepared by taking papermaking black liquor as raw material; the purified lignin is dispersed in water, the pH value is adjusted to 10-12, and then the purified lignin is transferred to a microwave reaction kettle; formaldehyde and sodium sulfite are added, and a microwave-assisted heating mode is adopted to perform reaction, so that sulfonated lignin is prepared; the sulfonated lignin is added into water, the pH value is adjusted to 5, and under the protection of nitrogen, acrylic acid is added, sodium bisulfite solution is added dropwise, and ammonium persulfate solution is added dropwise; under the protection of nitrogen, the reaction is performed under light shielding and heating, so that an LS-AA grafting product is obtained; the LS-AA grafting product and polyethylene glycol diglycidyl ether are used as raw materials, a microwave heating mode is adopted to perform crosslinking reaction, and the lignin sulfonate dye dispersant is prepared. The application can improve the heat-resistant stability and dispersing force of the dispersant product, reduces the staining property, and achieves the resource recycling and product upgrading targets.

Description

Technical Field

[0001] This invention relates to the field of dye dispersant technology, and more specifically, to a microwave-assisted preparation method for a lignin sulfonate dye dispersant. Background Technology

[0002] Currently, lignin sulfonate dye dispersants are typically prepared from papermaking black liquor through sulfonation and formaldehyde reaction. However, products prepared by this method suffer from poor heat resistance, insufficient dispersibility, and significant staining, making it difficult to meet the requirements of high-temperature (above 130℃) dyeing processes. The root cause of these defects lies in the complex and heterogeneous structure of lignin in papermaking black liquor. Conventional sulfonation reactions struggle to achieve uniform substitution, resulting in low sulfonation degrees and disordered molecular weight distribution. Conventional formaldehyde reaction easily leads to excessive or insufficient cross-linking, causing an imbalance between the rigidity and flexibility of the molecular chains, which in turn affects heat resistance and dispersibility. Furthermore, residual impurities exacerbate staining problems. Therefore, developing a superior method for preparing lignin sulfonate dye dispersants to achieve both resource recovery and product quality improvement has become an urgent technical challenge. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a microwave-assisted preparation method for lignin sulfonate dye dispersants.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A microwave-assisted preparation method for a lignin sulfonate dye dispersant includes the following steps:

[0006] (a) Purified lignin was obtained by using black liquor from papermaking as raw material, through static filtration, flocculation precipitation, membrane concentration and acid precipitation.

[0007] (b) The purified lignin was dispersed in deionized water, the pH of the system was adjusted to 10-12, the mixture was transferred to a microwave reactor, formaldehyde and sodium sulfite were added, and the reaction was carried out by microwave-assisted heating to obtain sulfonated lignin;

[0008] (c) Sulfonated lignin was added to deionized water, the pH was adjusted to 5, acrylic acid was added under nitrogen protection, sodium bisulfite solution was added dropwise first, then ammonium persulfate solution was added dropwise, and then the reaction was carried out under nitrogen protection and in the dark to obtain LS-AA grafted product.

[0009] (d) Using LS-AA grafted product and polyethylene glycol diglycidyl ether as raw materials, a cross-linking reaction was carried out by microwave heating to obtain lignin sulfonate dye dispersant.

[0010] The present invention is further configured such that, in step (b), the mass ratio of lignin to sodium sulfite is 1:(0.7-1), and the molar ratio of sodium sulfite to formaldehyde is 1:(1-2).

[0011] The present invention is further configured such that, in step (b), the microwave power is 700-800W, the reaction temperature is 80-90℃, and the reaction time is 2-3h.

[0012] The present invention is further configured such that, in step (c), the amount of acrylic acid is 15-20% of the sulfonated lignin content, the amount of APS is 0.8-1.5% of the sulfonated lignin content, and the molar ratio of NaHSO3 to APS is (0.9-1.2):(4-6).

[0013] The present invention is further configured such that step (d) specifically involves: adding the LS-AA graft product to water, purging with nitrogen to remove oxygen, adding polyethylene glycol diglycidyl ether, adjusting the pH to 10, and then transferring the mixture to a microwave reactor. The first stage reaction is carried out by microwave heating at 220-250W, 55-65℃ and under nitrogen protection, and the second stage reaction is carried out by microwave heating at 380-420W, 70-80℃ and under nitrogen protection to obtain the lignin sulfonate dye dispersant.

[0014] The present invention is further configured such that, in step (d), the mass ratio of LS-AA graft product to polyethylene glycol diglycidyl ether is (3-5):(1-2).

[0015] The present invention is further configured such that, in step (d), the reaction time of the first stage is 20-30 min and the reaction time of the second stage is 30-40 min.

[0016] In summary, the present invention has the following beneficial effects:

[0017] This invention obtains high-purity lignin through filtration, flocculation, membrane concentration, and acid precipitation purification of papermaking black liquor. Then, it prepares lignin sulfonate dye dispersants through microwave-assisted sulfonation, acrylic acid grafting, and microwave crosslinking of polyethylene glycol diglycidyl ether. This significantly improves the uniformity and efficiency of each reaction step, enhances the heat resistance and dispersing power of the product, reduces staining, and achieves the dual goals of resource recovery and product quality improvement, thus possessing both economic benefits and environmental value. Detailed Implementation

[0018] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0019] The microwave-assisted preparation method of the lignin sulfonate dye dispersant of the present invention includes the following steps:

[0020] (a) Purified lignin was obtained by using black liquor from papermaking as raw material, through static filtration, flocculation precipitation, membrane concentration and acid precipitation.

[0021] (b) Disperse purified lignin in deionized water, adjust the pH of the system to 10-12, transfer the mixture to a microwave reactor, add formaldehyde and sodium sulfite, and react using microwave-assisted heating to obtain sulfonated lignin; wherein the mass ratio of lignin to sodium sulfite is 1:(0.7-1), and the molar ratio of sodium sulfite to formaldehyde is 1:(1-2); the microwave power is 700-800W, the reaction temperature is 80-90℃, and the reaction time is 2-3h;

[0022] (c) Sulfonated lignin is added to deionized water, the pH is adjusted to 5, acrylic acid is added under nitrogen protection, sodium bisulfite solution is added dropwise first, followed by ammonium persulfate solution, and the reaction is carried out under nitrogen protection in the dark to obtain LS-AA grafted product; wherein the amount of acrylic acid is 15-20% of the mass of sulfonated lignin, the amount of APS is 0.8-1.5% of the mass of sulfonated lignin, and the molar ratio of NaHSO3 to APS is (0.9-1.2):(4-6);

[0023] (d) A lignin sulfonate dye dispersant was prepared by crosslinking LS-AA graft product and polyethylene glycol diglycidyl ether using microwave heating. Specifically, LS-AA graft product was added to water, and after deoxygenation by purging with nitrogen, polyethylene glycol diglycidyl ether was added. The mass ratio of LS-AA graft product to polyethylene glycol diglycidyl ether was (3-5):(1-2). After adjusting the pH to 10, the mixture was transferred to a microwave reactor. The first stage reaction was carried out for 20-30 min by microwave heating at 220-250 W, 55-65 °C and nitrogen protection. The second stage reaction was carried out for 30-40 min by microwave heating at 380-420 W, 70-80 °C and nitrogen protection to obtain the lignin sulfonate dye dispersant.

[0024] Example 1

[0025] (a) After the black liquor of papermaking was allowed to stand for 24 hours, it was filtered to remove large particulate suspended matter. Polyacrylamide was added to the filtrate for flocculation and precipitation. The filtrate was filtered again and concentrated by membrane treatment to retain crude lignin with a relative molecular weight of 10,000-30,000. The solid content of the concentrate was controlled to be 25%. The concentrate was acid-precipitated with 15wt% sulfuric acid at 50°C for 2 hours (the pH value of the acid precipitation system was 3). After acid precipitation, plate and frame filter was used to obtain purified lignin.

[0026] (b) The purified lignin was dispersed in deionized water (lignin to deionized water mass ratio of 1:10), and the pH of the system was adjusted to 10 with NaOH solution. The mixture was transferred to a microwave reactor, and formaldehyde and sodium sulfite were added (lignin to sodium sulfite mass ratio of 1:0.7, sodium sulfite to formaldehyde molar ratio of 1:1.2). The reaction was carried out by microwave-assisted heating (microwave power of 800W, reaction temperature of 85℃, reaction time of 2h). After the reaction, the microwave device was turned off, the reaction solution was cooled to room temperature, and dilute sulfuric acid was added to the reaction solution to adjust the pH of the system to 2.5 to precipitate the precipitate. The precipitate was collected by centrifugation, washed with water until neutral, and dried to obtain sulfonated lignin.

[0027] (c) Sulfonated lignin was added to deionized water (the mass ratio of sulfonated lignin to deionized water was 1:7), the pH was adjusted to 5 with HCl solution, and nitrogen was purged for 30 minutes to remove oxygen. Acrylic acid (the amount of acrylic acid was 15% of the mass of sulfonated lignin) was added under nitrogen protection. First, 3wt% sodium bisulfite (NaHSO3) solution was added dropwise, followed by 5wt% ammonium persulfate (APS) solution (the amount of APS was 1% of the mass of sulfonated lignin, and the molar ratio of NaHSO3 to APS was 1:5). The ammonium persulfate solution and sodium bisulfite solution were added dropwise within 20 minutes. Then, the reaction was carried out at 50°C in the dark for 4 hours under nitrogen protection. After the reaction, the system was cooled to room temperature, the pH was adjusted to neutral with NaOH solution, and 4 times the volume of 95% ethanol was added to precipitate the precipitate. The precipitate was collected by centrifugation and dried to obtain the LS-AA graft product.

[0028] (d) The LS-AA graft product was added to water (LS-AA graft product to water mass ratio of 1:10), and nitrogen gas was purged for 30 minutes to remove oxygen. Polyethylene glycol diglycidyl ether (Mw≈600, mass ratio of LS-AA graft product to polyethylene glycol diglycidyl ether of 4:1.34) was added and stirred evenly. The pH was adjusted to 10 with NaOH solution. The mixture was then transferred to a microwave reactor and reacted for 20 minutes under microwave heating at 250W, 60℃ and nitrogen protection. The reaction was then carried out for 35 minutes under microwave heating at 400W, 70℃ and nitrogen protection. After the reaction, the mixture was cooled to room temperature, and dilute hydrochloric acid was added to adjust the system to neutral. Eight times the volume of cold acetone was added to precipitate the precipitate. The precipitate was collected by centrifugation and dried to obtain lignin sulfonate dye dispersant.

[0029] Comparative Example 1

[0030] The lignin sulfonate dye dispersant was prepared according to the method in Example 1, except that step (b) was not microwave heating reaction, but water bath heating reaction at 85°C for 2 hours.

[0031] Comparative Example 2

[0032] Prepared according to the method of Example 1 but without performing step (d), and use the LS-AA graft product obtained in step (c) as a dye dispersant.

[0033] Comparative Example 3

[0034] The lignin sulfonate dye dispersant was prepared according to the method in Example 1, except that step (d) was not microwave heating reaction, but segmented water bath heating, that is, the mixture was heated in a water bath at 60°C for 30 min, and then heated to 70°C in a water bath for 20 min.

[0035] The dispersants prepared in Example 1 and Comparative Examples 1-3 were subjected to performance tests, and the test results are shown in the table below:

[0036]

[0037] Heat resistance, staining, and dispersing power were tested according to the industry standard "HGT-3507-2008-Sodium Lignosulfonate Dispersant".

[0038] The room temperature dispersibility was tested using a double-layer filter paper filtration method: 2g of Disperse Red 3B, 0.5g of the test dispersant, and 200mL of deionized water were added to a beaker and ultrasonically dispersed at 500W for 3 minutes to prepare a dye dispersion. A Buchner funnel was installed on a suction flask, and a sheet of rapid qualitative filter paper was placed at the bottom of the funnel, followed by a sheet of medium-speed qualitative filter paper (with the smooth sides of both filter papers facing upwards; the rapid and medium-speed qualitative filter papers are those described in GB / T1914-2017). For the 101 and 102 superior grades, wet the filter paper with a small amount of deionized water and make it stick tightly to the bottom of the funnel. Turn on the vacuum pump and adjust the vacuum degree to -0.08MPa. Quickly pour all the dye dispersion into the Buchner funnel for filtration. Start timing at the same moment when the dye liquid contacts the filter paper and begins to drip. Stop timing when the last drop of filtrate drips from the outlet and record the total time used for filtration. Perform three parallel experiments on the same sample and calculate the average value as the room temperature dispersion time.

[0039] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A microwave-assisted preparation method for a lignin sulfonate dye dispersant, characterized in that, Includes the following steps: (a) Purified lignin was obtained by using black liquor from papermaking as raw material, followed by static filtration, flocculation precipitation, membrane concentration, and acid precipitation. (b) The purified lignin was dispersed in deionized water, the pH of the system was adjusted to 10-12, the mixture was transferred to a microwave reactor, formaldehyde and sodium sulfite were added, and the reaction was carried out by microwave-assisted heating to obtain sulfonated lignin; (c) Sulfonated lignin was added to deionized water, the pH was adjusted to 5, acrylic acid was added under nitrogen protection, sodium bisulfite solution was added dropwise first, then ammonium persulfate solution was added dropwise, and then the reaction was carried out under nitrogen protection and in the dark to obtain LS-AA grafted product. (d) Using LS-AA grafted product and polyethylene glycol diglycidyl ether as raw materials, a cross-linking reaction was carried out by microwave heating to obtain lignin sulfonate dye dispersant.

2. The microwave-assisted preparation method of a lignin sulfonate dye dispersant according to claim 1, characterized in that, In step (b), the mass ratio of lignin to sodium sulfite is 1:(0.7-1), and the molar ratio of sodium sulfite to formaldehyde is 1:(1-2).

3. The microwave-assisted preparation method of a lignin sulfonate dye dispersant according to claim 1, characterized in that, In step (b), the microwave power is 700-800W, the reaction temperature is 80-90℃, and the reaction time is 2-3h.

4. The microwave-assisted preparation method of a lignin sulfonate dye dispersant according to claim 1, characterized in that, In step (c), the amount of acrylic acid is 15-20% of the sulfonated lignin content, the amount of APS is 0.8-1.5% of the sulfonated lignin content, and the molar ratio of NaHSO3 to APS is (0.9-1.2):(4-6).

5. The microwave-assisted preparation method of a lignin sulfonate dye dispersant according to claim 1, characterized in that, Step (d) is as follows: LS-AA graft product is added to water, nitrogen is passed through to remove oxygen, polyethylene glycol diglycidyl ether is added, the pH is adjusted to 10, and the mixture is transferred to a microwave reactor. The first stage reaction is carried out by microwave heating at 220-250W, 55-65℃ and nitrogen protection, and the second stage reaction is carried out by microwave heating at 380-420W, 70-80℃ and nitrogen protection to obtain lignin sulfonate dye dispersant.

6. The microwave-assisted preparation method of a lignin sulfonate dye dispersant according to claim 1, characterized in that, In step (d), the mass ratio of LS-AA graft product to polyethylene glycol diglycidyl ether is (3-5):(1-2).

7. The microwave-assisted preparation method of a lignin sulfonate dye dispersant according to claim 6, characterized in that, In step (d), the reaction time for the first stage is 20-30 min, and the reaction time for the second stage is 30-40 min.

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