Synthesis process of special sodium lignosulfonate with high dispersing power for dyes

Abstract

The application discloses a synthesis process of special sodium lignosulfonate with high dispersing force, and belongs to the technical field of sodium lignosulfonate, and solves the problems of the sulfonation degree difference caused by the micro-heterogeneity of raw materials, the cross-linking formation of micro-gel and the elimination of abnormal signals, and the conformational heterogeneity in grinding, dyeing and heat storage, which respectively causes the efficiency reduction, filter cake blockage and thixotropic gelation of color spots. In the application, formaldehyde and hydrogen peroxide are synchronously activated to generate reaction sites under homogeneous alkaline conditions, and stepwise feeding sulfonation is carried out under high temperature and high pressure, so that the hydrophilic groups are uniformly distributed, the formaldehyde is cancelled and glyoxal and epichlorohydrin are used instead, the hydrophilic chain extension is cut off to cut off the micro-gel generation path, the skeleton is activated under the condition of no monomer, the mixed monomer is dropped to synchronously grow the side chain, a thick and uniform hydrophilic protective layer is formed, the internal polarity gap of the molecule is reduced, the grinding efficiency is improved, the particle residue is reduced, the dyeing filter cake blockage and fabric color spots are avoided, and the thixotropic gelation during long-term heat storage is avoided.

Description

Technical Field

[0001] This invention relates to the field of sodium lignosulfonate technology, and more particularly to a synthesis process for sodium lignosulfonate for high-dispersibility dyes. Background Technology

[0002] Sodium lignin sulfonate for high-dispersion dyes is refined through a multi-step modification process using purified alkali lignin as the main raw material and various functional auxiliaries. It is suitable for high-temperature dyeing applications with various dyes. In the initial synthesis stage, the raw materials undergo purification, desaccharification, and classification to remove impurities and reducing sugars, ensuring product stability. The process sequentially involves alkali activation, hydroxymethylation modification, and high-temperature, high-pressure sulfonation to introduce sufficient hydrophilic groups into the lignin molecules. Through segmented polycondensation and micro-crosslinking, the molecular weight and branched structure can be precisely controlled. Further oxidation adds carboxyl groups, enhancing the product's anchoring properties and hard water resistance. Subsequently, free radical graft copolymerization constructs a regular comb-shaped molecular structure, improving steric hindrance. After the reaction, the material undergoes acid-base neutralization and ultrafiltration desalination to remove byproducts and small molecule impurities. Finally, functional auxiliaries are added, and the product is spray-dried into a powder. The overall process allows for precise control of the product's molecular structure and dispersion performance.

[0003] In the synthesis of sodium lignin sulfonate for high-dispersion dyes, when using a batch of alkali lignin raw materials that have formed microscopic differences between etherified active regions and condensation inert regions due to uneven heating during pulping and cooking, but which meet all conventional factory inspection standards, the selective reactions of the hydroxymethylation and sulfonylation stages cause a nearly twofold difference in sulfonation degree between the two types of regions, which is masked by the statistical mean. During the chain extension and polycondensation stage, the active sites in the high sulfonation region are blocked, forcing the addition of formaldehyde to favor the low sulfonation hydrophobic region, initiating irreversible cross-linking and generating hydrophobic microgels wrapped by hydrophilic shells. Meanwhile, the epichlorohydrin added simultaneously introduces compliant bridging bonds in the hydrophilic region, eliminating abnormal signals in conventional detection from the opposite direction. The resulting conformational heterogeneous material suffers from reduced efficiency and particle residue in ultrafine dye grinding due to insufficient anchoring force, filter cake blockage and fabric stains due to microgel exposure in high-temperature and high-pressure dyeing, and thixotropic gelation due to hydrophobic core fusion and shell relaxation in accelerated heat storage.

[0004] Therefore, a synthesis process for sodium lignosulfonate for high-dispersion dyes is proposed to solve or alleviate the above problems. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by proposing a synthesis process for sodium lignin sulfonate for high-dispersion dyes.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A synthesis process for sodium lignosulfonate for high-dispersibility dyes includes the following steps: Step (1) The purified alkali lignin is completely dissolved in an alkaline aqueous solution, and formaldehyde and hydrogen peroxide are added simultaneously under homogeneous conditions to carry out a pre-activation reaction, generating hydroxymethyl groups and oxygen-containing anchors that are distributed throughout the entire domain. Step (2) Add sodium hydroxymethyl sulfonate to the activation solution obtained in step (1) for mild pre-sulfonation, and then add anhydrous sodium sulfite for main sulfonation reaction under high temperature and high pressure to obtain a homogeneous sulfonated solution. After the sulfonated liquid obtained in step (3) is cooled down, glyoxal and epichlorohydrin are added sequentially under formaldehyde-free conditions to carry out a fully hydrophilic condensation reaction to obtain a homogeneous hydrophilic condensate. The condensate obtained in step (4) is first mixed with an initiator in the absence of monomers for skeleton pre-initiation, and then a monomer mixture containing acrylic acid, maleic anhydride and 2-acrylamido-2-methylpropanesulfonic acid is added dropwise for graft copolymerization to construct a dense and uniform comb-shaped outer structure. Step (5) After neutralizing the obtained grafted product, it is subjected to ultrafiltration desalting, concentration and spray drying to obtain sodium lignosulfonate for high dispersibility dyes.

[0007] Preferably, the purified alkali lignin has a reducing sugar content of less than 0.3%, an ash content of less than 2.5%, a phenolic hydroxyl content of not less than 4.0 mmol / g, and the alkaline aqueous solution is adjusted to pH 10.0±0.2 by sodium hydroxide. The solid content of the alkali lignin when completely dissolved is 18%-20%, and the dissolution temperature is 70℃.

[0008] Preferably, the simultaneous addition of formaldehyde and hydrogen peroxide under homogeneous conditions for pre-activation reaction specifically includes the following steps: Based on 100 parts by weight of oven-dried alkali lignin, add 8.5-9.5 parts of 37% formaldehyde solution and 2.5-3.5 parts of 30% hydrogen peroxide solution. Add the two solutions dropwise at a constant rate over 80-100 minutes, controlling the reaction temperature at 63-67℃ and maintaining the pH above 9.5 during the reaction. After the addition is complete, keep the solution warm for 1.0-2.0 hours until the redox potential drops below 30mV from its peak and tends to stabilize. The hydroxymethyl content in the resulting activated solution reaches 0.8-1.2 mmol / g.

[0009] Preferably, step (2) involves adding sodium hydroxymethylsulfonate to the obtained activation solution for mild pre-sulfonation, specifically including the following steps: Add 5-6 parts of sodium hydroxymethylsulfonate to the obtained activation solution and react at 73-77℃ for 0.8-1.2 hours. The main sulfonation conditions are: subsequently add 50-55 parts of anhydrous sodium sulfite, in a closed reaction system, raise the temperature to 146-150℃, and maintain the reaction at 0.45-0.50MPa for 5-6 hours. The degree of sulfonation of the obtained sulfonated solution is 2.1-2.3mmol / g, and the uniformity of the regional distribution of sulfonic acid groups is significantly narrower than that of the traditional process, as verified by fractional potentiometric titration.

[0010] Preferably, the step of sequentially adding glyoxal and epichlorohydrin for a fully hydrophilic polycondensation reaction specifically includes the following steps: The resulting sulfonated solution was cooled to 78-82℃, and the pH was adjusted to 8.8-9.2 with dilute sulfuric acid. 2.0-3.0 parts of 40% glyoxal aqueous solution were added at a slight negative pressure of -0.03-0.04 MPa and 68-72℃ and reacted for 1.2-1.8 hours. Then 4.0-5.0 parts of epichlorohydrin were added and the reaction continued at the same temperature for another 1.2-1.8 hours. Finally, the temperature was raised to 80-85℃ and the reaction was continued for another 1.2-1.8 hours. No formaldehyde was involved in the entire process.

[0011] Preferably, the condensate obtained in step (4) is first mixed with an initiator in the absence of monomers for skeletal pre-initiation, specifically including the following steps: The obtained condensate was cooled to 63-67℃. Under conditions where no monomer was present, 5.0-6.0 parts of potassium persulfate aqueous solution and 2.5-3.5 parts of sodium bisulfite aqueous solution were added dropwise simultaneously and at a uniform rate over 10-20 minutes. After the addition was completed, the mixture was kept at the temperature for 25-35 minutes to allow the initiator to generate macromolecular free radical sites throughout its entire domain.

[0012] Preferably, the graft copolymerization process involving the addition of a monomer mixture comprising acrylic acid, maleic anhydride, and 2-acrylamido-2-methylpropanesulfonic acid specifically includes the following steps: A monomer solution is prepared by mixing 12-14 parts acrylic acid, 3.0-4.0 parts pre-hydrolyzed maleic anhydride, 7-9 parts 2-acrylamido-2-methylpropanesulfonic acid, and 1.0-1.5 parts isopropanol with water. The monomer solution is then uniformly added dropwise to the pre-initiated skeleton solution at 70-74°C over 3.0-3.5 hours. After the addition is complete, the solution is kept at this temperature for 1.5-2.5 hours to allow the grafting rate to reach 55%-70% and the average degree of polymerization of the side chains to be 25-35. No additional alkaline substances are added during the dropwise addition. The natural decrease in pH of the system caused by the polymerization of acrylic acid is used to regulate the distribution of the degree of polymerization of the side chains and inhibit excessive crosslinking.

[0013] Preferably, the neutralization is performed by adjusting the pH to 8.0-8.5 with sodium hydroxide solution. The ultrafiltration desalination uses an ultrafiltration membrane with a molecular weight cutoff of 2500-3500 Da. Percolation is carried out at an inlet pressure of 0.25-0.35 MPa and an operating temperature of 38-42°C until the permeate conductivity is below 3000 μs / cm, after which it is concentrated to a solid content of 25%-28%. The spray drying has an inlet air temperature of 190-200°C and an outlet air temperature of 85-90°C.

[0014] The present invention has the following beneficial effects: This invention utilizes formaldehyde and hydrogen peroxide to simultaneously activate alkali lignin under homogeneous alkaline conditions where the lignin is completely dissolved. This ensures that a sufficient number of subsequent reaction sites are generated throughout the entire molecular chain, regardless of the original activity level. Stepwise feeding and high-temperature, high-pressure sulfonation further homogenize the distribution of hydrophilic groups. Subsequently, formaldehyde is completely eliminated, and glyoxal and epichlorohydrin, two hydrophilic crosslinking agents, are used for chain extension. This breaks the traditional process where formaldehyde accumulates in the low-sulfonation hydrophobic region, initiating irreversible crosslinking and forming microgels. In the grafting stage, the backbone is first activated with an initiator under monomer-free conditions, distributing grafting sites throughout the entire molecular chain. Then, a mixture containing acrylic acid, maleic anhydride, and monomers with sulfonic acid groups is added dropwise, allowing side chains to grow simultaneously from various locations. Ultimately, a thick and uniform hydrophilic protective layer is formed around the molecule. This protective layer is connected to the backbone by chemical bonds. During high-temperature and high-pressure dyeing, it is more difficult to be removed by thermal motion and shear force than the hydration shell of simple physical adsorption. At the same time, the previous steps have significantly reduced the gap between hydrophilic and hydrophobic regions inside the molecule, so that the protective layer does not cover a pseudo-body with an outer hydrophilic and inner hydrophobic structure, but a whole with more similar polarity everywhere. Thus, it can provide a uniform and firm adsorption layer during ultrafine dye grinding to improve grinding efficiency and reduce large particle residue. During high-temperature and high-pressure dyeing, it avoids filter cake blockage and fabric stains caused by microgel exposure. During long-term heat storage, it will not undergo thixotropic gelation because the lack of hydrophobic core fusion driving force inside the molecule. Attached Figure Description

[0015] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram of the structure of the present invention; Figure 2 This is a comparison table of the experimental group and the control group in this invention; Figure 3 This is a sulfonation degree distribution curve of the experimental group and the control group in this invention; Figure 4 This is a graph showing the grinding particle size and tail peak of the experimental and control groups in this invention; Figure 5 This is a high-temperature dispersion stability diagram of the experimental group and the control group in this invention; Figure 6 This is a graph showing the thermal storage viscosity stability of the experimental and control groups in this invention. Figure 7 This is a radar chart showing the combined performance of the experimental and control groups in this invention. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0018] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0019] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0020] In the description of this invention, it should be understood that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use, or the orientation or positional relationship commonly understood by those skilled in the art. They are only used to facilitate the description of this invention and to simplify the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0021] Furthermore, the terms "first," "second," and "third" are used only to distinguish descriptions and should not be interpreted as indicating or implying relative importance.

[0022] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0023] A synthesis process for sodium lignosulfonate for high-dispersion dyes, such as... Figure 1 As shown, it includes the following steps: Step (1) Dissolve the purified alkali lignin completely in an alkaline aqueous solution. Under homogeneous conditions, simultaneously add formaldehyde and hydrogen peroxide for pre-activation reaction. Specifically, based on 100 parts by weight of oven-dry alkali lignin, add 8.5-9.5 parts of 37% formaldehyde solution and 2.5-3.5 parts of 30% hydrogen peroxide solution. Add them dropwise at a constant rate over 80-100 minutes. Control the reaction temperature at 63-67℃ and maintain the pH above 9.5 during the reaction. After the addition is complete, keep warm for 1.0-2.0 hours until the redox potential drops from its peak value. The pH value is above 0mV and tends to be stable, generating hydroxymethyl groups and oxygen-containing anchors distributed throughout the molecular chain, that is, hydroxymethyl and quinone-type structures that can be detected on all molecular chain segments. The hydroxymethyl content in the resulting activated solution is 0.8-1.2 mmol / g. The purified alkali lignin has a reducing sugar content of less than 0.3%, an ash content of less than 2.5%, and a phenolic hydroxyl content of not less than 4.0 mmol / g. The alkaline aqueous solution is adjusted to pH 10.0±0.2 by sodium hydroxide. The solid content of the alkali lignin when it is completely dissolved is 18%-20%, and the dissolution temperature is 70℃. Step (2) First, add sodium hydroxymethanesulfonate to the activated solution obtained in step (1) for mild pre-sulfonation. Specifically, add 5-6 parts of sodium hydroxymethanesulfonate to the activated solution and react at 73-77℃ for 0.8-1.2 hours. The main sulfonation conditions are: then add 50-55 parts of anhydrous sodium sulfite, in a closed reaction system, raise the temperature to 146-150℃, and keep the reaction at 0.45-0.50MPa for 5-6 hours. The degree of sulfonation of the obtained sulfonated solution is 2.1-2.3mmol / g, and the uniformity of the regional distribution of sulfonic acid groups is significantly narrower than that of the traditional process, as verified by step potentiometric titration. Then, add anhydrous sodium sulfite and carry out the main sulfonation reaction under high temperature and high pressure to obtain a homogeneous sulfonated solution. The half-peak width of the elution curve of the sulfonated solution is narrower than that of the traditional one-time feeding sulfonation process by at least 30%. After the sulfonated liquid obtained in step (3) is cooled down, glyoxal and epichlorohydrin are added sequentially under formaldehyde-free conditions to carry out a fully hydrophilic condensation reaction. Specifically, the obtained sulfonated liquid is cooled to 78-82℃, and the pH is adjusted to 8.8-9.2 with dilute sulfuric acid. First, 2.0-3.0 parts of 40% glyoxal aqueous solution are added at -0.03-0.04MPa slight negative pressure and 68-72℃ and reacted for 1.2-1.8 hours. Then, 4.0-5.0 parts of epichlorohydrin are added and reacted at the same temperature for another 1.2-1.8 hours. Finally, the temperature is raised to 80-85℃ and reacted for another 1.2-1.8 hours. No formaldehyde is involved in the whole process, and a uniform hydrophilic condensate is obtained. After condensation, the liquid is filtered through a 0.45μm microporous membrane and no undetectable retained particles are found. In step (3), the formaldehyde used in step (1) acts as a hydroxymethylation agent to electrophilically substitute the aromatic ring of lignin under alkaline homogeneous conditions, generating hydroxymethyl anchors. These hydroxymethyl groups undergo nucleophilic substitution reactions with a large excess of anhydrous sodium sulfite in the subsequent high-temperature sulfonation step (2), and most of them are converted into benzyl sulfonic acid groups with a conversion rate of over 90%. After step (2), the residual free hydroxymethyl content is less than 0.1 mmol / g. Therefore, when polycondensation is carried out in step (3), there are no free hydroxymethyl groups in the system that can be used for self-condensation to form methylene bridge crosslinks, and the hydrophobic micro-region selective crosslinking caused by the addition of formaldehyde in the traditional process will not occur.

[0024] The formaldehyde-free condition mentioned in step (3) refers to the fact that no additional formaldehyde is added as a crosslinking agent during the polycondensation stage, rather than the fact that no formaldehyde is used throughout the entire process. The formaldehyde introduced in step (1) has been fully consumed and converted into hydrophilic sulfonic acid groups during the high-temperature sulfonation in step (2). The two belong to different stages in the process sequence, so there is no contradiction.

[0025] In step (4), the obtained condensate is first mixed with an initiator for skeletal pre-initiation in the absence of monomers. Specifically, the obtained condensate is cooled to 63-67°C. Under monomer-free conditions, 5.0-6.0 parts of potassium persulfate aqueous solution and 2.5-3.5 parts of sodium bisulfite aqueous solution are simultaneously and uniformly added dropwise over 10-20 minutes. After the addition is completed, the mixture is kept at the temperature for 25-35 minutes to allow the initiator to generate macromolecular free radical sites throughout the entire domain. Then, a monomer mixture containing acrylic acid, maleic anhydride, and 2-acrylamido-2-methylpropanesulfonic acid is added dropwise for graft copolymerization. Specifically, 12-14 parts of acrylic acid, 3.0-4.0 parts of pre-hydrolyzed maleic anhydride, and 7-9 parts of 2-acrylamido-2-methylpropanesulfonic acid are added. A monomer solution is prepared by mixing 2-methylpropanesulfonic acid and 1.0-1.5 parts of isopropanol with water. The monomer solution is then added dropwise at a constant rate to a pre-initiated skeleton solution at 70-74°C over 3.0-3.5 hours. After addition, the solution is kept at this temperature for 1.5-2.5 hours to allow it to mature. The grafting rate reaches 55%-70%, and the average degree of polymerization of the side chains is 25-35. No additional alkaline substances are added during the dropwise addition. The pH of the system naturally decreases due to the polymerization of acrylic acid to regulate the distribution of the degree of polymerization of the side chains and inhibit excessive cross-linking, thus constructing a dense and uniform comb-shaped outer structure. The sulfonic acid groups in the grafted side chains are derived from 2-acrylamido-2-methylpropanesulfonic acid, and the sulfur content accounts for 40%-70% of the total sulfur content of the product. After neutralizing the obtained grafted product in step (5), specifically, the neutralization is performed by adjusting the pH to 8.0-8.5 with sodium hydroxide solution. The ultrafiltration desalting is carried out using an ultrafiltration membrane with a molecular weight cutoff of 2500-3500 Da. The membrane is permeated at an inlet pressure of 0.25-0.35 MPa and an operating temperature of 38-42℃ until the conductivity of the permeate is lower than 3000 μs / cm. Then, the permeate is concentrated to a solid content of 25%-28%. The inlet air temperature of the spray drying is 190-200℃ and the outlet air temperature is 85-90℃. After ultrafiltration desalting, concentration and spray drying, sodium lignosulfonate for high dispersibility dyes is obtained.

[0026] In addition, the hydroxymethyl content needs to be determined in this process using the sodium sulfite addition-hydrochloric acid back titration method. Approximately 0.5 g of the oven-dried sample (accurate to 0.1 mg) is accurately weighed, and 10 mL of 0.5 mol / L anhydrous sodium sulfite solution and 5 mL of 0.5 mol / L sodium hydroxide solution are added. The mixture is reacted in a sealed container at 25°C for 30 minutes. After the reaction, 2 drops of phenolphthalein indicator are added, and the solution is titrated with 0.5 mol / L hydrochloric acid standard solution until the red color fades. A blank test is performed simultaneously. The hydroxymethyl content (mmol / g) is calculated using the following formula: the volume of hydrochloric acid consumed in the blank test minus the volume of hydrochloric acid consumed in the sample, the difference is multiplied by the molar concentration of the hydrochloric acid standard solution, and then divided by the oven-dried mass of the sample. The result is the number of millimoles of hydroxymethyl content per gram of sample. The same sample is measured in triplicate, and the arithmetic mean is taken. The absolute deviation should not exceed 0.05 mmol / g.

[0027] The degree of sulfonation also needs to be determined by conductivity titration. Approximately 0.3 g of the oven-dry sample is accurately weighed and dissolved in 50 mL of deionized water. The sulfonate is converted to sulfonic acid by passing the sample through a 001×7 type, hydrogen-form cation exchange resin column. The sample is then eluted with deionized water until the eluent is neutral. The eluents are combined and titrated with a 0.1 mol / L sodium hydroxide standard solution. The conductivity is recorded as a function of titration volume. The volume consumed by the sulfonic acid group and the carboxyl / phenolic hydroxyl group is determined based on the inflection point of the conductivity. The degree of sulfonation corresponds to the amount of base consumed by the strong acid group.

[0028] Grafting rate determination is also required, using a combined gravimetric titration method. Accurately weigh approximately 2.0 g of the oven-dried grafted product, denoted as m1. Permeate the product aqueous solution using an ultrafiltration membrane with a molecular weight cutoff of 10000 Da to remove ungrafted homopolymers and small molecules until the total organic carbon in the permeate is below 5 mg / L. Dry the permeate to constant weight and weigh it to obtain the mass of the purified grafted product, m2. The grafting rate is calculated as follows: m2 minus the product of m1 and the difference between 1 and the theoretical mass fraction of the skeleton; the difference is then divided by the product of m1 and the theoretical mass fraction of the skeleton, and multiplied by 100%. The theoretical mass fraction of the skeleton refers to the theoretical mass proportion of the lignin skeleton in the grafted product calculated according to the feed ratio. To verify that grafting has indeed occurred, the carboxyl content of the purified product can be determined by conductivity titration as described in the aforementioned sulfonation degree determination method. Compare this to the original carboxyl content of the skeleton before grafting. An increase in the carboxyl content of the purified product proves that acrylic acid and maleic anhydride have been chemically bonded to the skeleton.

[0029] In addition, it is necessary to determine the average degree of polymerization of the side chains and to examine the distribution of sulfonic acid groups using a stepwise potentiometric titration method. The method for determining the average degree of polymerization of the side chains involves dialyzing the grafted product purified by ultrafiltration in deionized water for 72 hours using a dialysis bag with a molecular weight cutoff of 1000 Da, changing the water every 8 hours to completely remove inorganic salts. After lyophilization, the sample is taken for elemental analysis to determine the sulfur content. Based on the AMPS feed ratio in the formulation and the original sulfur content of the lignin skeleton, the number of AMPS structural units on the grafted side chains is calculated. Then, based on the monomer molar ratio of AMPS to acrylic acid and maleic anhydride, the average degree of polymerization of the grafted side chains is estimated. Alternatively, the integral method of proton nuclear magnetic resonance spectroscopy can be used to directly calculate the degree of polymerization by the integral ratio of the characteristic proton peaks of the side chains to the characteristic proton peaks of the skeleton.

[0030] The stepwise potentiometric titration method for testing the distribution of sulfonate groups involves preparing an aqueous solution with a solid content of approximately 2% using a peristaltic pump. This solution is then passed sequentially through two ion exchange columns connected in series: the first column is a sodium-type strong acid cation exchange resin, and the second is a hydrogen-type weak acid cation exchange resin. The eluent is collected in segments and monitored online using a conductivity detector. Due to differences in charge density, lignin molecules at different degrees of sulfonation have varying ion exchange affinities with the resin and will be eluted at different retention times. Elution curves are plotted, and the peak width and retention time distribution characterize the uniformity of sulfonate group distribution within and between molecules. A narrower distribution indicates more uniform sulfonation.

[0031] Meanwhile, to verify the effectiveness of this process, control experiments were conducted, such as... Figure 2 As shown, seven control groups and one experimental group were set up to test sulfonation uniformity, grinding fineness, large particle tail peaks, high-temperature dispersion stability, and accelerated thermal storage stability. The experimental results are as follows. Figures 3 to 7 As shown.

[0032] like Figure 3 As shown, the experimental group has the thickest solid line representing the highest and narrowest peak, indicating that the sulfonation heights in different regions within the molecule are similar and the regional differences are minimal. The control group, which used heterogeneous activation, eliminated pre-activation, or had insufficient sulfonating agent, had significantly shorter and wider peaks, and the insufficient sulfonation group shifted to the left overall, indicating that the regional sulfonation gradient was not eliminated. The narrower and higher the peak, the more uniform it is, indicating that homogeneous pre-activation and sufficient sulfonation are key improvements to narrow the sulfonation gradient and solve the inherent unevenness of the raw materials.

[0033] like Figure 4 As shown, the experimental group had the lowest values ​​for both indicators, indicating that the dispersant could fully spread and anchor to the dye crystal surface, resulting in fine grinding without tail peaks. The control group had increased particle size and more tail peaks. Among them, the three groups with retained formaldehyde crosslinking, cancelled pre-activation, and insufficient sulfonation showed the most significant deterioration, while the traditional benchmark group was the worst. Both indicators decreased simultaneously, indicating that each improvement was indispensable for the anchoring force and grinding efficiency of ultrafine grinding.

[0034] like Figure 5 As shown, the experimental group curves are almost horizontal, with almost no increase in particle size, indicating that the protective layer is not peeled off at high temperatures. The control group with formaldehyde crosslinking retains the most dramatic upward curve, corresponding to the exposure of hydrophobic microgels and the induction of crosslinking flocculation. The group with insufficient sulfonation is next, and the group with reduced comb-shaped side chains is in the middle. The flatter and more stable the curves are, indicating that formaldehyde removal polycondensation, sufficient sulfonation, and high-density comb-shaped side chains together support the dispersion stability under high temperature and high pressure dyeing.

[0035] like Figure 6As shown, the curves of the experimental groups were basically stable, with only a slight increase around the fourth week, and no physical networking was observed. The formaldehyde-retained crosslinking group showed the most dramatic increase, with thixotropic gelation. The group with insufficient sulfonation and no pre-activation was the next best, and the traditional baseline group was the worst. The flatter the curve, the more stable the storage, indicating that formaldehyde removal condensation and global homogenization together inhibited hydrophobic core fusion, significantly improving long-term storage stability.

[0036] like Figure 7 As shown, the outer contour of the experimental group is the largest and close to a regular pentagon. The five aspects are balanced and superior. The larger and fuller the contour, the better the overall performance.

[0037] The working principle is as follows: In summary, this synthetic method targets raw materials where abnormal pulping and cooking results in the coexistence of highly active etherification regions and low-activity condensation inert regions within alkali lignin. First, formaldehyde and hydrogen peroxide are added simultaneously and slowly in a homogeneous alkaline aqueous solution where alkali lignin is completely dissolved. The two react uniformly throughout the entire molecular chain, with oxidation and hydroxymethylation occurring simultaneously. In this way, those originally sluggish condensation regions can be forced to attach sufficient amounts of hydroxymethyl and quinone-type structures, serving as handles for the next step of attaching sulfonic acid groups, thereby significantly reducing the difference in the reaction starting point between the two types of regions inherent in the raw material.

[0038] The sulfonation step then begins. First, mild sodium hydroxymethylsulfonate is added to initially sulfonate the newly exposed reaction sites from the first step. Then, sufficient anhydrous sodium sulfite is added in stages, and the reaction is carried out under sealed, high-temperature, and high-pressure conditions for an extended period. Thanks to the extremely high excess of the sulfonating agent and the high-intensity conditions, even areas with low activation levels have ample opportunity to be sulfonated. Ultimately, the distribution of sulfonic acid groups in the entire batch of material is no longer as polarized as in traditional processes. The extreme contrast between hydrophilic and hydrophobic regions is alleviated, and the statistical average of conventional testing can no longer mask localized insufficient sulfonation.

[0039] In the chain extension and polycondensation stage, this method completely abandons formaldehyde and instead uses glyoxal and epichlorohydrin. These two crosslinking agents are highly polar and hydrophilic. They are uniformly dispersed in the sulfonated liquid, which has achieved near-universal hydrophilicity, and undergo equivalent reactions with each molecular chain segment to form compliant hydrophilic bridges. This avoids the problem in traditional processes where formaldehyde tends to accumulate in the less hydrophobic regions of low sulfonation and cause irreversible dense crosslinking. Therefore, the polycondensation product does not generate microgel particles with a hydrophilic outer shell but a hard, hydrophobic core, thus avoiding the false impression that the test data is normal when there are hidden problems inside the molecule. In the subsequent grafting step, the monomer is not allowed to exist. Instead, the initiator is mixed separately with the polycondensed lignin skeleton. At a lower temperature, the initiator generates as many free radical initiation sites as possible along the entire molecular chain.

[0040] After these starting points have spread throughout the skeleton, a mixed monomer composed of acrylic acid, maleic anhydride, and AMPS with sulfonic acid groups is added dropwise at a uniform rate. The side chains start growing synchronously from all points, resulting in high density and uniform distribution. Finally, a thick hydrophilic protective layer is formed on the periphery of the molecule, which is firmly connected by chemical bonds. The dense sulfonic acid groups on this protective layer form a strong charge repulsion and hydration layer, covering the residual small polarity differences on the skeleton. This makes the appearance of each dispersant molecule more uniform. Moreover, because this protective layer is chemically grafted rather than simply physically adsorbed, it is more difficult to remove under the thermal motion and shear force impact of high temperature and high pressure dyeing.

[0041] The final neutralization, desalination, and spray drying steps are all carried out under mild conditions with a temperature not exceeding 45 degrees Celsius and a membrane pressure not exceeding 0.35 MPa. This avoids high-pressure shearing and stretching of molecular chains or high temperature causing the protective layer to collapse, ensuring that the finished powder can quickly expand into the designed dispersion conformation after contact with water.

[0042] This allows the final product to provide stable and uniform adsorption and anchoring when grinding ultrafine dyes, improving grinding efficiency and eliminating large particle residues. In high-temperature and high-pressure dyeing of polyester, the protective layer is not easily damaged and loses its effectiveness, avoiding filter cake blockage and fabric stains. During long-term heat storage, thixotropic gelation no longer occurs due to the lack of hydrophobic core fusion driving force within the molecules.

[0043] Furthermore, in traditional processes, conformational heterostructures with internal hydrophobic cores undergo conventional grafting and high-temperature, high-pressure post-treatment. Conventional co-initiation causes side chains to preferentially grow in highly active regions and be unevenly distributed. The outer layer can only form a weak hydration shell that relies on physical adsorption. This shell encapsulates the internal hydrophobic core, resulting in insufficient anchoring force, reduced efficiency, and the presence of large particles during ultrafine grinding. During dyeing at 130°C, the hydrophobic microgel is peeled off by thermal motion and shear force, leading to filter cake blockage and fabric stains. During accelerated heat storage, the hydrophobic core fuses, the shell relaxes, and thixotropic gelation occurs.

[0044] In this process, step (4) first activates the skeleton with an initiator under monomer-free conditions, so that the free radical starting points are spread throughout the entire molecular chain as much as possible. Then, acrylic acid, maleic anhydride and high proportion of AMPS mixed monomers are added at a uniform rate, so that the side chains grow synchronously from all places, and a dense, uniform comb-shaped hydrophilic protective layer is constructed on the periphery and is firmly connected by chemical bonds. Its dense sulfonic acid groups form a strong charge repulsion and hydration layer, which uniformly covers the small polarity differences remaining in the skeleton. Because it is chemical grafting rather than physical adsorption, it is more difficult to be removed under the thermal motion and shearing of high temperature and high pressure.

[0045] Step (5) involves neutralization, desalination, and drying under mild conditions of no more than 45°C and membrane pressure of no more than 0.35MPa. This avoids high-pressure shearing that breaks the molecular chains or high temperature that causes the protective layer to collapse, ensuring that the finished product expands quickly after rehydration. During grinding, the anchoring is uniform and firm, efficiency is improved, and there are no large particles left. During dyeing, the protective layer is not easily damaged, and there is no filter cake blockage or color spots. During heat storage, the lack of hydrophobic core fusion driving force inside the molecules prevents thixotropic gelation.

[0046] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A synthesis process for sodium lignosulfonate for high-dispersibility dyes, characterized in that, Includes the following steps: Step (1) The purified alkali lignin is completely dissolved in an alkaline aqueous solution, and formaldehyde and hydrogen peroxide are added simultaneously under homogeneous conditions to carry out a pre-activation reaction, generating hydroxymethyl groups and oxygen-containing anchors that are distributed throughout the entire domain. Step (2) Add sodium hydroxymethyl sulfonate to the activation solution obtained in step (1) for mild pre-sulfonation, and then add anhydrous sodium sulfite for main sulfonation reaction under high temperature and high pressure to obtain a homogeneous sulfonated solution. After the sulfonated liquid obtained in step (3) is cooled down, glyoxal and epichlorohydrin are added sequentially under formaldehyde-free conditions to carry out a fully hydrophilic condensation reaction to obtain a homogeneous hydrophilic condensate. The condensate obtained in step (4) is first mixed with an initiator in the absence of monomers for skeleton pre-initiation, and then a monomer mixture containing acrylic acid, maleic anhydride and 2-acrylamido-2-methylpropanesulfonic acid is added dropwise for graft copolymerization to construct a dense and uniform comb-shaped outer structure. Step (5) After neutralizing the obtained grafted product, it is subjected to ultrafiltration desalting, concentration and spray drying to obtain sodium lignosulfonate for high dispersibility dyes.

2. The synthesis process of sodium lignosulfonate for high-dispersibility dyes according to claim 1, characterized in that, The purified alkali lignin has a reducing sugar content of less than 0.3%, an ash content of less than 2.5%, and a phenolic hydroxyl content of not less than 4.0 mmol / g. The alkaline aqueous solution is adjusted to pH 10.0 ± 0.2 by sodium hydroxide. The solid content of the alkali lignin when completely dissolved is 18%-20%, and the dissolution temperature is 70℃.

3. The synthesis process of sodium lignosulfonate for high-dispersibility dyes according to claim 1, characterized in that, The simultaneous addition of formaldehyde and hydrogen peroxide under homogeneous conditions for pre-activation reaction specifically includes the following steps: Based on 100 parts by weight of oven-dried alkali lignin, add 8.5-9.5 parts of 37% formaldehyde solution and 2.5-3.5 parts of 30% hydrogen peroxide solution. Add the two solutions dropwise at a constant rate over 80-100 minutes, controlling the reaction temperature at 63-67℃ and maintaining the pH above 9.5 during the reaction. After the addition is complete, keep the solution warm for 1.0-2.0 hours until the redox potential drops below 30mV from its peak and tends to stabilize. The hydroxymethyl content in the resulting activated solution reaches 0.8-1.2 mmol / g.

4. The synthesis process of sodium lignosulfonate for high-dispersibility dyes according to claim 1, characterized in that, Step (2) involves adding sodium hydroxymethylsulfonate to the obtained activation solution for mild pre-sulfonation, specifically including the following steps: Add 5-6 parts of sodium hydroxymethylsulfonate to the obtained activation solution and react at 73-77℃ for 0.8-1.2 hours. The main sulfonation conditions are: subsequently add 50-55 parts of anhydrous sodium sulfite, in a closed reaction system, raise the temperature to 146-150℃, and maintain the reaction at 0.45-0.50MPa for 5-6 hours. The degree of sulfonation of the obtained sulfonated solution is 2.1-2.3mmol / g, and the uniformity of the regional distribution of sulfonic acid groups is significantly narrower than that of the traditional process, as verified by fractional potentiometric titration.

5. The synthesis process of sodium lignosulfonate for high-dispersibility dyes according to claim 1, characterized in that, The sequential addition of glyoxal and epichlorohydrin for a fully hydrophilic polycondensation reaction specifically includes the following steps: The resulting sulfonated solution was cooled to 78-82℃, and the pH was adjusted to 8.8-9.2 with dilute sulfuric acid. 2.0-3.0 parts of 40% glyoxal aqueous solution were added at a slight negative pressure of -0.03-0.04 MPa and 68-72℃ and reacted for 1.2-1.8 hours. Then 4.0-5.0 parts of epichlorohydrin were added and the reaction continued at the same temperature for another 1.2-1.8 hours. Finally, the temperature was raised to 80-85℃ and the reaction was continued for another 1.2-1.8 hours. No formaldehyde was involved in the entire process.

6. The synthesis process of sodium lignosulfonate for high-dispersibility dyes according to claim 1, characterized in that, The condensate obtained in step (4) is first mixed with an initiator in the absence of monomers for skeletal pre-initiation, specifically including the following steps: The obtained condensate was cooled to 63-67℃. Under conditions where no monomer was present, 5.0-6.0 parts of potassium persulfate aqueous solution and 2.5-3.5 parts of sodium bisulfite aqueous solution were added dropwise simultaneously and at a uniform rate over 10-20 minutes. After the addition was completed, the mixture was kept at the temperature for 25-35 minutes to allow the initiator to generate macromolecular free radical sites throughout its entire domain.

7. The synthesis process of sodium lignosulfonate for high-dispersibility dyes according to claim 1, characterized in that, The graft copolymerization process, which involves adding a monomer mixture containing acrylic acid, maleic anhydride, and 2-acrylamido-2-methylpropanesulfonic acid, specifically includes the following steps: A monomer solution is prepared by mixing 12-14 parts acrylic acid, 3.0-4.0 parts pre-hydrolyzed maleic anhydride, 7-9 parts 2-acrylamido-2-methylpropanesulfonic acid, and 1.0-1.5 parts isopropanol with water. The monomer solution is then uniformly added dropwise to the pre-initiated skeleton solution at 70-74°C over a period of 3.0-3.5 hours. After the addition is complete, the solution is kept at this temperature for 1.5-2.5 hours to allow the grafting rate to reach 55%-70% and the average degree of polymerization of the side chains to be 25-35. No additional alkaline substances are added during the dropwise addition. The natural decrease in pH of the system caused by the polymerization of acrylic acid is used to regulate the distribution of the degree of polymerization of the side chains and inhibit excessive crosslinking.

8. The synthesis process of sodium lignosulfonate for high-dispersibility dyes according to claim 1, characterized in that, The neutralization is achieved by adjusting the pH to 8.0-8.5 using sodium hydroxide solution. The ultrafiltration desalination uses an ultrafiltration membrane with a molecular weight cutoff of 2500-3500 Da. Percolation is carried out at an inlet pressure of 0.25-0.35 MPa and an operating temperature of 38-42°C until the permeate conductivity is below 3000 μs / cm, after which it is concentrated to a solid content of 25%-28%. The spray drying process has an inlet air temperature of 190-200°C and an outlet air temperature of 85-90°C.

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