Method for preparing water reducing agent through oxidation-sulfomethylation of enzymatic hydrolysis lignin and water reducing agent

Abstract

The invention provides a method for preparing a water reducing agent through oxidation-sulfomethylation of enzymatic hydrolysis lignin and the water reducing agent. The method comprises the following steps: adding water and an oxidizing agent into enzymatic hydrolysis lignin, and carrying out oxidation reaction to obtain a first solution; adjusting the pH value of the first solution to 10-12, and then adding a sulfonating agent and a formaldehyde solution to perform sulfomethylation reaction to obtain the water reducing agent. According to the method disclosed by the invention, by utilizing the characteristic that the enzymatic hydrolysis lignin is close to original lignin and has relatively high activity, the enzymatic hydrolysis lignin is firstly oxidized and then subjected to sulfomethylation by adopting a hydrothermal method, and efficient utilization and efficient conversion of the enzymatic hydrolysis lignin are realized by optimizing a process flow, so that a lignosulfonate product with relatively high purity, sulfonation degree and water reducing performance is obtained; the water reducing agent has more excellent water reducing performance, has a certain retarding effect, and can improve the compressive strength of concrete.

Description

Technical Field

[0001] This invention relates to the field of water-reducing agent technology, and more specifically, to a method for preparing a water-reducing agent using enzymatic hydrolysis of lignin oxidation-sulfonylation, and a water-reducing agent. Background Technology

[0002] Currently, China's comprehensive timber utilization rate is approximately 65%, which is significantly lower than the over 80% utilization rate in developed countries, indicating considerable room for improvement. As the main component of timber, lignocellulose's effective utilization is crucial for enhancing the overall timber utilization rate. Lignocellulose is primarily composed of lignin, cellulose, and hemicellulose. Currently, the main resource utilization pathway for lignocellulose involves hydrolyzing cellulose and hemicellulose to convert them into sugar alcohol products, while lignin remains in the biomass residue.

[0003] Lignin is generally considered to be a three-dimensional network polymer composed of three phenylpropane units linked by ether bonds and carbon-carbon double bonds. It includes guaiacol-based propane monomer (G type), syringylpropane (S type), and p-hydroxyphenylpropane (H type) structural units, containing aromatic skeletons, phenolic hydroxyl groups, methoxy groups, aldehyde groups, and carboxylic acid groups.

[0004] Lignin is often cross-linked with cellulose and hemicellulose to form the plant skeleton. While enzymatic methods can be used to separate lignin from cellulose and hemicellulose, the complex spatial structure, uneven molecular weight distribution, and high methoxy content of enzymatically hydrolyzed lignin limit its application. Modifications such as sulfonation, amination, oxidation, alkylation, and graft copolymerization are effective means to realize the resource utilization of enzymatically hydrolyzed lignin.

[0005] Lignosulfonates, obtained by enzymatic hydrolysis and sulfonation modification of lignin, can be used as cement water-reducing agents. When added to cement paste, they adsorb onto the surface of cement particles, forming an interfacial adsorption layer. Through electrostatic repulsion, the cement particles are dispersed. Sodium lignosulfonate is widely used as a water-reducing agent and is currently one of the most widely applied water-reducing agents in construction engineering. However, its low water-reducing rate (typically 8-10% in concrete) and its ability to reduce concrete strength limit its application in concrete engineering.

[0006] Chinese patents CN111704725A, CN102001841B, CN111087190A, CN109503859B, CN103497342A, CN111218489A, CN101921639A, CN102585247A, and CN115896204A disclose methods for preparing lignin sulfonates using enzymatic hydrolysis. However, these methods have low conversion rates of enzymatically hydrolyzed lignin, and the yield and purity of the lignin sulfonate products obtained after sulfonation are also low. The preparation process requires the use of alkalis that can destroy the original structure of lignin, or the introduction of chloride ions that can corrode building materials. The products suffer from problems such as low degree of sulfonation, low water-reducing performance, and significant environmental pollution, which are not conducive to the full utilization of lignin and the improvement of the strength of building materials, especially concrete. Summary of the Invention

[0007] The main objective of this invention is to provide a method and a water-reducing agent for preparing water-reducing agents by enzymatic hydrolysis of lignin oxidation-sulfonylation, in order to solve the problems of low lignin utilization rate, poor water-reducing performance, and low compressive strength of concrete caused by lignin sulfonate water-reducing agents in the prior art.

[0008] To achieve the above objectives, according to one aspect of the present invention, a method for preparing a water-reducing agent using enzymatic hydrolysis of lignin oxidation-sulfonyl methylation is provided, comprising the following steps: Step S1, adding water and an oxidizing agent to enzymatically hydrolyzed lignin to carry out an oxidation reaction to obtain a first solution; Step S2, adjusting the pH of the first solution to 10-12, and then adding a sulfonating agent and a formaldehyde solution to carry out a sulfonyl methylation reaction to obtain a water-reducing agent.

[0009] Further, the solid-liquid ratio of enzymatically hydrolyzed lignin to water is (10-15g):(150-250mL); and / or the oxidant includes one or more of hydrogen peroxide, potassium permanganate, persulfate, potassium persulfate and ozone; and / or the weight ratio of enzymatically hydrolyzed lignin to oxidant is (10-15):(1-4).

[0010] Furthermore, the oxidation reaction is carried out at a temperature of 80–120°C for a time of 0.5–2 hours.

[0011] Further, step S1 also includes adding water, an oxidant and a reducing agent to the enzymatically hydrolyzed lignin to carry out an oxidation reaction; preferably, the reducing agent includes one or more of ferrous sulfate, hydroxylamine hydrochloride and ascorbic acid; and / or the weight ratio of enzymatically hydrolyzed lignin to reducing agent is (10-15):(0.05-0.15).

[0012] Further, the sulfonating agent includes one or more of sodium sulfite, calcium sulfite, magnesium sulfite, 1,4-butyrosulactone and 1,3-propanesulfonactone; and / or the weight ratio of enzymatically hydrolyzed lignin to sulfonating agent is (10-15):(2-6); and / or the mass concentration of formaldehyde solution is 37-40%, and the solid-liquid ratio of enzymatically hydrolyzed lignin to formaldehyde solution is (10-15g):(1-5mL).

[0013] Furthermore, the sulfonation reaction is carried out at a temperature of 150–180 °C for a time of 10–14 h.

[0014] Further, step S2 also includes centrifuging the material after the sulfonation reaction to obtain a supernatant; drying and grinding the supernatant, or spray drying it to obtain a water-reducing agent; preferably, the drying temperature is 100-110°C and the time is 6-14 hours; and / or the inlet air temperature of the spray drying is 110-180°C and the outlet air temperature is 70-110°C; preferably, the water content of the water-reducing agent is 2-10%.

[0015] Further, by weight percentage, the enzymatically hydrolyzed lignin contains 35-45% lignin, 2-4% hemicellulose, 30-40% cellulose, 35-45% carbon, 4-6% hydrogen, 0.2-0.4% nitrogen, and 0.1-0.2% sulfur. Preferably, the enzymatically hydrolyzed lignin is prepared by enzymatically hydrolyzing straw and / or bagasse using cellulase and hemicellulase to obtain enzymatically hydrolyzed residue, i.e., enzymatically hydrolyzed lignin.

[0016] According to another aspect of the present invention, a water-reducing agent is provided, which is obtained by the method described above for preparing a water-reducing agent by enzymatic hydrolysis of lignin oxidation-sulfonylation.

[0017] Furthermore, the enzymatic hydrolysis lignin utilization rate of the water-reducing agent is 60-85%, the sulfonation degree is 1.3-1.8 mmol / g; and / or the cement paste fluidity of the water-reducing agent is 140-170 mm / 0.6%, and the compressive strength of C30 concrete is 36-42 MPa.

[0018] By applying the technical solution of this invention, and utilizing the high activity of enzymatically hydrolyzed lignin due to its near-original lignin, a hydrothermal method is employed to first oxidize and then sulfonate the enzymatically hydrolyzed lignin. Through optimized process flow, efficient utilization and conversion of enzymatically hydrolyzed lignin are achieved, yielding lignin sulfonate products with high purity, high sulfonation degree, and high water-reducing properties. Compared to traditional lignin sulfonate water-reducing agents, the high-efficiency water-reducing agent prepared by this invention exhibits superior water-reducing performance and a certain retarding effect, which can improve the compressive strength of concrete. Detailed Implementation

[0019] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0020] Terminology Explanation:

[0021] Enzymatic hydrolysis of lignin: A lignin preparation obtained by enzymatic hydrolysis of plant raw materials to remove sugars (carbohydrates).

[0022] Sulfonation: A reaction in which hydrogen atoms in aromatic hydrocarbons such as benzene are replaced by sulfonic acid groups in sulfuric acid molecules. Sulfonation is a process of introducing sulfonic acid or sulfonyl chloride groups into an organic molecule. Direct sulfonation occurs when a sulfonic acid group replaces a hydrogen atom on a carbon atom; indirect sulfonation occurs when a sulfonic acid group replaces a halogen or nitro group on a carbon atom.

[0023] Sulfonation: A reaction in which a hydrogen atom in a molecule is replaced by an alkali metal sulfonyl group.

[0024] Water-reducing agent: It is a concrete admixture that can reduce the amount of water used in mixing while maintaining the slump of concrete. Most of them are anionic surfactants. After being added to the concrete mixture, they have a dispersing effect on cement particles, which can improve its workability, reduce the amount of water used per unit, improve the fluidity of the concrete mixture, and save cement.

[0025] High-efficiency water-reducing agent: A water-reducing agent that can reduce the amount of mixing water by more than 15% under the condition that the slump of concrete is basically the same.

[0026] Retarder: An additive that reduces the hydration rate and heat of hydration of cement or gypsum, and prolongs the setting time.

[0027] Hydrothermal method: This is a method for preparing materials by dissolving and recrystallizing powders in a sealed pressure vessel using water as a solvent. Compared to other powder preparation methods, powders prepared by the hydrothermal method have advantages such as well-developed crystals, small particle size, uniform distribution, less particle agglomeration, the ability to use relatively inexpensive raw materials, and the ease of obtaining suitable stoichiometry and crystal form.

[0028] Infrared absorption spectroscopy (IR spectroscopy for short) is a method of molecular analysis. When infrared light of a certain frequency (energy) irradiates a molecule, if the vibrational frequency of a certain group in the molecule matches the frequency of the external infrared radiation, the energy of the light is transferred to the molecule through the change in the molecular dipole moment. This group absorbs the infrared light of that frequency, resulting in a vibrational transition. Recording the absorption of infrared light by the molecule yields the infrared absorption spectrum of the sample. The wavelength, intensity, and shape of the absorption peaks in the spectrum are used to identify the functional groups within the molecule, enabling structural analysis.

[0029] Ultraviolet-visible spectrophotometry, also known as ultraviolet-visible absorption spectroscopy, is a method that uses the continuous electromagnetic spectrum in the ultraviolet-visible region (typically 200–800 nm) as a light source to illuminate a sample and study the relative intensity of light absorption by molecules. When molecules or groups in a substance absorb the energy of incident ultraviolet-visible light, the resulting energy level transitions between electrons produce characteristic ultraviolet-visible spectra, which can be used to determine the structure of compounds and characterize their properties.

[0030] As described in the background section of this invention, existing technologies suffer from problems such as low lignin utilization rate, poor water-reducing performance, and low concrete compressive strength when used in the construction field. To address these issues, in a typical embodiment of this invention, a method for preparing a water-reducing agent using enzymatic hydrolysis of lignin oxidation-sulfonylation is provided, comprising the following steps: Step S1, adding water and an oxidizing agent to enzymatically hydrolyzed lignin to conduct an oxidation reaction, obtaining a first solution; Step S2, adjusting the pH of the first solution to 10-12, then adding a sulfonating agent and formaldehyde solution to conduct a sulfonylation reaction, obtaining the water-reducing agent.

[0031] The inventors unexpectedly discovered during their research that the sulfonic acid group is the dominant functional group in lignin sulfonate water-reducing agents, possessing a high electrical potential and exhibiting a significant dispersing and water-reducing effect. Therefore, introducing sulfonic acid groups and increasing their content to improve the degree of sulfonation can effectively enhance the surface activity and dispersing water-reducing properties of lignin sulfonates. Because enzymatic hydrolysis of lignin contains many guaiac structures and has few reactive sites, oxidation can increase the reactivity of lignin sulfonates, thus facilitating the sulfonation reaction.

[0032] Specifically, this invention first adds water and an oxidant to enzymatically hydrolyzed lignin to carry out an oxidation reaction under hydrothermal conditions. During this process, the oxidant degrades lignin into smaller molecular fragments, reducing the degree of lignin condensation and methoxy content, while increasing the active sites for lignin sulfonation, which is beneficial for improving the degree of sulfonation in subsequent sulfonylation reactions. After the oxidation reaction, a first solution is obtained. The pH of the first solution is adjusted to 10-12, and then a sulfonating agent and formaldehyde solution are added to carry out a sulfonylation reaction. Under alkaline conditions, lignin first reacts with formaldehyde to undergo hydroxymethylation, and then reacts with the sulfonating agent to undergo sulfonylation, thereby obtaining a lignin sulfonate high-efficiency water-reducing agent.

[0033] This invention utilizes the high activity of enzymatically hydrolyzed lignin, which closely resembles the original lignin. A hydrothermal method is employed to first oxidize and then sulfonate the enzymatically hydrolyzed lignin. By optimizing the process flow, efficient utilization and conversion of the enzymatically hydrolyzed lignin are achieved, yielding lignin sulfonate products with high purity, high sulfonation degree, and high water-reducing properties. Furthermore, due to its high sulfonation degree, it overcomes the shortcomings of existing lignin sulfonate water-reducing agents, such as low water reduction rate and reduced concrete strength, achieving the standard of a high-efficiency water-reducing agent. In addition, because the raw materials contain a large amount of sugars, the synthesized water-reducing agent also has a better retarding effect, which is beneficial for concrete pumping. Simultaneously, because the high-efficiency water-reducing agent can reduce the water-cement ratio during application, it can effectively improve the compressive strength of concrete.

[0034] Furthermore, while ensuring product performance, this invention minimizes the addition of environmentally polluting components and avoids introducing components that corrode building materials. The lignin sulfonate water-reducing agent prepared by this invention has a molecular weight approximately three times that of enzymatically hydrolyzed lignin and a uniform molecular weight distribution. In addition to being used as a water-reducing agent, it is also suitable for preparing various lignin derivatives that can be used for polymer modification, and can replace some petrochemical products, thus having broad prospects for industrial application.

[0035] In a preferred embodiment, the solid-liquid ratio of enzymatically hydrolyzed lignin to water is (10-15 g):(150-250 mL); and / or the oxidant includes one or more of hydrogen peroxide, potassium permanganate, persulfate, potassium peroxymonosulfonate, and ozone; and / or the weight ratio of enzymatically hydrolyzed lignin to oxidant is (10-15):(1-4). Under these conditions, the degradation of lignin by the oxidant is more favorable, promoting a more complete oxidation reaction. This also increases the number of active sites for sulfonation and enhances the reactivity of enzymatically hydrolyzed lignin, thereby further improving the utilization rate and degree of sulfonation of enzymatically hydrolyzed lignin in the subsequent sulfonation methylation process, and ultimately improving the water-reducing properties of lignin sulfonates and the compressive strength of concrete.

[0036] For similar reasons, in a preferred embodiment, the oxidation reaction is carried out at a temperature of 80–120°C for a time of 0.5–2 hours. This invention employs relatively mild process conditions and can better preserve the activity of natural lignin.

[0037] To make fuller use of the high-value C=O bonds in lignin, in a preferred embodiment, step S1 further includes adding water, an oxidant, and a reducing agent to the enzymatically hydrolyzed lignin to carry out an oxidation reaction; preferably, the reducing agent includes one or more of ferrous sulfate, hydroxylamine hydrochloride, and ascorbic acid; and / or the weight ratio of enzymatically hydrolyzed lignin to reducing agent is (10-15):(0.05-0.15).

[0038] In a preferred embodiment, the sulfonating agent includes one or more of sodium sulfite, calcium sulfite, magnesium sulfite, 1,4-butyrosulactone, and 1,3-propanesulfonactone; and / or the weight ratio of enzymatically hydrolyzed lignin to the sulfonating agent is (10-15):(2-6); and / or the mass concentration of the formaldehyde solution is 37-40%, and the solid-liquid ratio of enzymatically hydrolyzed lignin to the formaldehyde solution is (10-15g):(1-5mL). Under the above conditions, the forward sulfonation reaction can be further promoted, thereby further improving the utilization rate of enzymatically hydrolyzed lignin and resulting in better overall product performance.

[0039] For similar reasons, in a preferred embodiment, the sulfonation reaction is carried out at a temperature of 150–180°C for 10–14 hours. These conditions are more conducive to the reaction, further increasing the degree of sulfonation and improving the water-reducing properties of the product.

[0040] To facilitate the transportation and storage of lignin sulfonate water-reducing agents and thus their practical application, in a preferred embodiment, step S2 further includes centrifuging the material after sulfonation reaction to obtain a supernatant; for convenient product transportation, the supernatant is dried and then ground, or spray-dried to obtain the water-reducing agent; preferably, the drying temperature is 100-110°C and the time is 6-14 hours; and / or the inlet air temperature of the spray drying is 110-180°C and the outlet air temperature is 70-110°C; preferably, the water content of the water-reducing agent is 2-10%.

[0041] In a preferred embodiment, the enzymatically hydrolyzed lignin, by weight percentage, contains 35-45% lignin, 2-4% hemicellulose, 30-40% cellulose, 35-45% carbon, 4-6% hydrogen, 0.2-0.4% nitrogen, and 0.1-0.2% sulfur. Preferably, the enzymatically hydrolyzed lignin is prepared by enzymatically hydrolyzing straw and / or bagasse using cellulase and hemicellulase to obtain enzymatically hydrolyzed residue, i.e., enzymatically hydrolyzed lignin. The raw material used in this invention is lignin obtained from the enzymatic hydrolysis of waste straw or bagasse. Its molecular structure contains a large number of active functional groups such as phenolic hydroxyl groups, aliphatic hydroxyl groups, methoxy groups, benzene rings, ether bonds, and carbonyl groups, which is beneficial for its sulfonation and conversion into high-value products. This has significant practical implications for the resource utilization of waste biomass energy and the implementation of carbon emission reduction.

[0042] As described above, the method of the present invention can prepare a lignin sulfonate water-reducing agent with high lignin utilization, good water-reducing performance, and the ability to improve the compressive strength of concrete. In another typical embodiment of the present invention, a water-reducing agent is also provided, which is obtained by the method of preparing water-reducing agent by enzymatic hydrolysis of lignin oxidation-sulfonylation described above.

[0043] Specifically, in a preferred embodiment, the enzymatic hydrolysis lignin utilization rate of the water-reducing agent is 60-85%, the sulfonation degree is 1.3-1.8 mmol / g; and / or the cement paste fluidity of the water-reducing agent is 140-170 mm / 0.6%, the water reduction rate is 14-19%, and the compressive strength of C30 concrete is 36-42 MPa.

[0044] Typical, but not limiting, when the weight of enzymatically hydrolyzed lignin is 10–15 g, the weight of the oxidant is 1 g, 1.5 g, 2 g, 2.5 g, 3 g, 3.5 g, 4 g, or any two of these values; the weight of the reducing agent is 0.05 g, 0.06 g, 0.08 g, 0.1 g, 0.02 g, 0.14 g, 0.15 g, or any two of these values; the weight of the sulfonating agent is 2 g, 3 g, 4 g, 5 g, 6 g, or any two of these values; and the volume of the formaldehyde solution is 1 mL, 2 mL, 3 mL, 4 mL, 5 mL, or any two of these values.

[0045] Typically, but not limitingly, in step S1, the temperature of the oxidation reaction is 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, 120°C or any two of these values, and the time is 0.5h, 1h, 1.5h, 2h or any two of these values.

[0046] Typical, but not limiting, step S2, the sulfonylation reaction temperature is 150°C, 155°C, 160°C, 165°C, 170°C, 175°C, 180°C or any two of these values, and the time is 10h, 11h, 12h, 13h, 14h or any two of these values.

[0047] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0048] Unless otherwise specified, the enzymatically hydrolyzed lignin used in the following examples and comparative examples are enzymatically hydrolyzed residues obtained by enzymatically hydrolyzing straw and bagasse using cellulase and hemicellulase, wherein the lignin content is 41%, the hemicellulose content is 3.1%, the cellulose content is 34%, the carbon content is 40.2%, the hydrogen content is 4.701%, the nitrogen content is 0.28%, and the sulfur content is 0.128%.

[0049] Example 1

[0050] Step S1: Place 10g of enzymatically hydrolyzed lignin in a PPL reactor (polymerization reactor), add 250mL of water, 5mL of hydrogen peroxide (30% aqueous solution) and 0.1g of ferrous sulfate heptahydrate, and stir thoroughly. After the above solution is stirred evenly, place the reactor in an oven at 100℃ for 1h to obtain the first solution.

[0051] Step S2: Adjust the pH of the first solution to 12 with 1 mol / L NaOH, then add 5 g sodium sulfite and 5 mL formaldehyde aqueous solution (38%), and stir thoroughly to dissolve it. Finally, place the reaction vessel in an oven at a reaction temperature of 180℃ for 12 h.

[0052] Step S3: After the reaction, the solution is removed and centrifuged. The precipitate and supernatant are dried at 105℃ for 14 hours and weighed separately. The product after drying the supernatant is ground into powder to obtain lignin sulfonate water-reducing agent, which is then stored in a dry environment.

[0053] Example 2

[0054] Step S1: Place 10g of enzymatically hydrolyzed lignin in a PPL reactor, add 150mL of water, 10mL of hydrogen peroxide (30% aqueous solution) and 0.1g of ferrous sulfate heptahydrate, and stir thoroughly. After the above solution is stirred evenly, place the reactor in an oven at 100℃ for 1h to obtain the first solution.

[0055] Step S2: Adjust the pH of the first solution to 12 with 1 mol / L NaOH, then add 2 g sodium sulfite and 1 mL formaldehyde aqueous solution (38%), and stir thoroughly to dissolve it. Finally, place the reaction vessel in an oven at a reaction temperature of 180℃ for 12 h.

[0056] Step S3: Remove the reacted solution and centrifuge. Dry the precipitate and supernatant at 105℃ for 10 hours, and weigh them separately. Grind the dried supernatant into powder to obtain lignin sulfonate water-reducing agent, and store it in a dry environment.

[0057] Example 3

[0058] Step S1: Place 10g of enzymatically hydrolyzed lignin in a PPL reactor, add 150mL of water, 10mL of hydrogen peroxide (30% aqueous solution) and 0.1g of ferrous sulfate heptahydrate, and stir thoroughly. After the above solution is stirred evenly, place the reactor in an oven at 100℃ for 1h to obtain the first solution.

[0059] Step S2: Adjust the pH of the first solution to 12 with 1 mol / L NaOH, then add 4 g sodium sulfite and 1 mL formaldehyde aqueous solution (38%), and stir thoroughly to dissolve it. Finally, place the reaction vessel in an oven at a reaction temperature of 180℃ for 12 h.

[0060] Step S3: Remove the reacted solution and centrifuge. Dry the precipitate and supernatant at 105℃ for 6 hours, and weigh them separately. Grind the dried supernatant into powder to obtain lignin sulfonate water-reducing agent, and store it in a dry environment.

[0061] Example 4

[0062] Step S1: Place 10g of enzymatically hydrolyzed lignin in a PPL reactor, add 150mL of water, 10mL of hydrogen peroxide (30% aqueous solution) and 0.1g of ferrous sulfate heptahydrate, and stir thoroughly. After the above solution is stirred evenly, place the reactor in an oven at 100℃ for 1h to obtain the first solution.

[0063] Step S2: Adjust the pH of the first solution to 12 with 1 mol / L NaOH, then add 2 g sodium sulfite and 5 mL formaldehyde aqueous solution (38%), and stir thoroughly to dissolve it. Finally, place the reaction vessel in an oven at 180℃ for 12 h.

[0064] Step S3: After the reaction, the solution is removed and centrifuged. The precipitate and supernatant are dried at 105℃ for 14 hours and weighed separately. The product after drying the supernatant is ground into powder to obtain lignin sulfonate water-reducing agent, which is then stored in a dry environment.

[0065] Example 5

[0066] Step S1: Place 10g of enzymatically hydrolyzed lignin in a PPL reactor, add 150mL of water, 5mL of hydrogen peroxide (30% aqueous solution) and 0.1g of ferrous sulfate heptahydrate, and stir thoroughly. After the above solution is stirred evenly, place the reactor in an oven at 100℃ for 1h to obtain the first solution.

[0067] Step S2: Adjust the pH of the first solution to 12 with 1 mol / L NaOH, then add 2 g sodium sulfite and 1 mL formaldehyde aqueous solution (38%), and stir thoroughly to dissolve it. Finally, place the reaction vessel in an oven at a reaction temperature of 180℃ for 12 h.

[0068] Step S3: Remove the reacted solution and centrifuge. Dry the precipitate and supernatant at 105℃ for 8 hours, and weigh them separately. Grind the dried supernatant into powder to obtain lignin sulfonate water-reducing agent, and store it in a dry environment.

[0069] Example 6

[0070] Step S1: Place 10g of enzymatically hydrolyzed lignin in a PPL reactor, add 250mL of water, 10mL of hydrogen peroxide (30% aqueous solution) and 0.1g of ascorbic acid, and stir thoroughly. After the above solution is stirred evenly, place the reactor in an oven at 100℃ for 1h to obtain the first solution.

[0071] Step S2: Adjust the pH of the first solution to 12 with 1 mol / L NaOH, then add 2 g sodium sulfite and 1 mL formaldehyde aqueous solution (38%), and stir thoroughly to dissolve it. Finally, place the reaction vessel in an oven at a reaction temperature of 180℃ for 12 h.

[0072] Step S3: Remove the reacted solution and centrifuge. Dry the precipitate and supernatant at 105℃ for 6 hours, and weigh them separately. Grind the dried supernatant into powder to obtain lignin sulfonate water-reducing agent, and store it in a dry environment.

[0073] Example 7

[0074] Step S1: Place 10g of enzymatically hydrolyzed lignin in a PPL reactor, add 250mL of water, 10mL of potassium peroxymonosulfonate (5%) and 0.1g of hydroxylamine hydrochloride, and stir thoroughly. After the above solution is stirred evenly, place the reactor in an oven at 100℃ for 1h to obtain the first solution.

[0075] Step S2: Adjust the pH of the first solution to 12 with 1 mol / L NaOH, then add 2 g sodium sulfite and 1 mL formaldehyde aqueous solution (38%), and stir thoroughly to dissolve it. Finally, place the reaction vessel in an oven at a reaction temperature of 180℃ for 12 h.

[0076] Step S3: Remove the reacted solution and centrifuge. Dry the precipitate and supernatant at 105℃ for 6 hours, and weigh them separately. Grind the dried supernatant into powder to obtain lignin sulfonate water-reducing agent, and store it in a dry environment.

[0077] Example 8

[0078] Step S1: Place 10g of enzymatically hydrolyzed lignin in a PPL reactor, add 150mL of water, 5mL of hydrogen peroxide (20% aqueous solution) and 0.05g of ferrous sulfate heptahydrate, and stir thoroughly. After the above solution is stirred evenly, place the reactor in an oven at 80℃ for 2 hours to obtain the first solution.

[0079] Step S2: Adjust the pH of the first solution to 11 with 1 mol / L NaOH, then add 4 g sodium sulfite and 3 mL formaldehyde aqueous solution (38%), and stir thoroughly to dissolve it. Finally, place the reaction vessel in an oven at a reaction temperature of 160℃ for 12 h.

[0080] Step S3: Remove the reacted solution and centrifuge. Dry the precipitate and supernatant at 100℃ for 14 hours, and weigh them separately. Grind the dried supernatant into powder to obtain lignin sulfonate water-reducing agent, and store it in a dry environment.

[0081] Example 9

[0082] Step S1: Place 15g of enzymatically hydrolyzed lignin in a PPL reactor, add 250mL of water, 10mL of hydrogen peroxide (40% aqueous solution) and 0.15g of ferrous sulfate heptahydrate, and stir thoroughly. After the above solution is stirred evenly, place the reactor in an oven at 120℃ for 0.5h to obtain the first solution.

[0083] Step S2: Adjust the pH of the first solution to 11 with 1 mol / L NaOH, then add 4 g sodium sulfite and 3 mL formaldehyde aqueous solution (38%), and stir thoroughly to dissolve it. Finally, place the reaction vessel in an oven at a reaction temperature of 160℃ for 12 h.

[0084] Step S3: Remove the reacted solution and centrifuge. Dry the precipitate and supernatant at 110℃ for 6 hours, and weigh them separately. Grind the dried supernatant into powder to obtain lignin sulfonate water-reducing agent, and store it in a dry environment.

[0085] Example 10

[0086] In the enzymatic hydrolysis of lignin, the lignin content is 35%, the hemicellulose content is 2%, and the cellulose content is 40%; the carbon content is 35%, the hydrogen content is 4%, the nitrogen content is 0.2%, and the sulfur content is 0.1%.

[0087] Step S1: Place 12g of enzymatically hydrolyzed lignin in a PPL reactor, add 200mL of water, 8mL of hydrogen peroxide (30% aqueous solution) and 0.1g of ferrous sulfate heptahydrate, and stir thoroughly. After the above solution is stirred evenly, place the reactor in an oven at 100℃ for 1h to obtain the first solution.

[0088] Step S2: Adjust the pH of the first solution to 10 with 1 mol / L NaOH, then add 2 g magnesium sulfite and 1 mL formaldehyde aqueous solution (40%), and stir thoroughly to dissolve it. Finally, place the reaction vessel in an oven at a reaction temperature of 150℃ for 14 h.

[0089] Step S3: Take out the solution after reaction, centrifuge, and spray dry it. The inlet air temperature is 110℃ and the outlet air temperature is 70℃ to obtain lignin sulfonate water-reducing agent, which is then stored in a dry environment.

[0090] Example 11

[0091] In the enzymatic hydrolysis of lignin, the lignin content is 45%, the hemicellulose content is 4%, and the cellulose content is 30%; the carbon content is 45%, the hydrogen content is 6%, the nitrogen content is 0.4%, and the sulfur content is 0.2%.

[0092] Step S1: Place 12g of enzymatically hydrolyzed lignin in a PPL reactor, add 200mL of water, 8mL of hydrogen peroxide (30% aqueous solution) and 0.1g of ferrous sulfate heptahydrate, and stir thoroughly. After the above solution is stirred evenly, place the reactor in an oven at 100℃ for 1h to obtain the first solution.

[0093] Step S2: Adjust the pH of the first solution to 12 with 1 mol / L NaOH, then add 6 g of 1,4-butyric acid lactone and 5 mL of formaldehyde aqueous solution (37%), and stir thoroughly to dissolve it. Finally, place the reaction vessel in an oven at a reaction temperature of 180℃ for 10 h.

[0094] Step S3: Take out the solution after reaction, centrifuge, and spray dry it. The inlet air temperature is 180℃ and the outlet air temperature is 110℃ to obtain lignin sulfonate water-reducing agent, which is then stored in a dry environment.

[0095] Comparative Example 1

[0096] Step S1: Place 10g of enzymatically hydrolyzed lignin into a PPL reactor (polymerization reactor), add 250mL of water and stir thoroughly. After the above solution is stirred evenly, place the reactor in an oven at 100℃ for 1h to obtain the first solution.

[0097] Step S2: Adjust the pH of the first solution to 12 with 1 mol / L NaOH, then add 5 g sodium sulfite and 5 mL formaldehyde aqueous solution (38%), and stir thoroughly to dissolve it. Finally, place the reaction vessel in an oven at a reaction temperature of 180℃ for 12 h.

[0098] Step S3: Remove the reacted solution and centrifuge it. Dry the precipitate and supernatant at 105℃ for 10 hours, and weigh them separately. Grind the dried supernatant into powder to obtain the water-reducing agent, and store it in a dry environment.

[0099] Comparative Example 2

[0100] Step S1: Place 5g of enzymatically hydrolyzed lignin in a PPL reactor, add 300mL of water, 3mL of hydrogen peroxide (15% aqueous solution) and 0.01g of ferrous sulfate heptahydrate, and stir thoroughly. After the above solution is stirred evenly, place the reactor in an oven at 60℃ for 0.4h to obtain the first solution.

[0101] In step S2, the pH of the first solution is adjusted to 9 with 1 mol / L NaOH, then 1 g of sodium sulfite and 0.5 mL of formaldehyde aqueous solution (35%) are added and stirred thoroughly to dissolve them. Finally, the reaction vessel is placed in an oven at a reaction temperature of 120°C for 8 hours.

[0102] Step S3: Remove the reacted solution and centrifuge it. Dry the precipitate and supernatant at 105℃ for 10 hours, and weigh them separately. Grind the dried supernatant into powder to obtain the water-reducing agent, and store it in a dry environment.

[0103] Comparative Example 3

[0104] Step S1: Place 20g of enzymatically hydrolyzed lignin in a PPL reactor, add 200mL of water, 15mL of hydrogen peroxide (50% aqueous solution) and 0.2g of ferrous sulfate heptahydrate, and stir thoroughly. After the above solution is stirred evenly, place the reactor in an oven at 130℃ for 3h to obtain the first solution.

[0105] Step S2: Adjust the pH of the first solution to 13 with 1 mol / L NaOH, then add 8 g of sodium sulfite and 8 mL of formaldehyde aqueous solution (43%), and stir thoroughly to dissolve it. Finally, place the reaction vessel in an oven at a reaction temperature of 200℃ for 16 h.

[0106] Step S3: Remove the reacted solution and centrifuge it. Dry the precipitate and supernatant at 105℃ for 10 hours, and weigh them separately. Grind the dried supernatant into powder to obtain the water-reducing agent, and store it in a dry environment.

[0107] The water-reducing agents prepared in the above examples and comparative examples were tested, and the results are shown in Table 1.

[0108] Performance testing:

[0109] Moisture content: After washing and drying the crucible to constant weight, a certain mass of enzymatically hydrolyzed lignin was weighed and placed in the crucible, and its mass was recorded as m1. Next, the crucible containing the enzymatically hydrolyzed lignin was placed in a forced-air drying oven and dried at a temperature of 105℃. During the drying process, the mass of the crucible containing the enzymatically hydrolyzed lignin was weighed every 1 hour until constant weight was achieved, and the mass after constant weight was recorded as m2. The moisture content (W) of the enzymatically hydrolyzed lignin can be expressed as: Moisture content (W) of enzymatically hydrolyzed lignin = (m1 - m2) / m1 × 100%.

[0110] Purity: First, prepare a standard solution of a specific concentration using sodium lignosulfonate as a standard reference, measure its absorption wavelength at 280 nm, and plot a standard curve for sodium lignosulfonate. Select one of the concentration values ​​within the measurement range of the standard curve as a reference, denoted as C1. Prepare a solution of sodium lignosulfonate to be tested with a reference concentration of C1, and measure its absorbance at 280 nm, denoted as A. Then, substitute the absorbance value A into the standard curve to calculate its effective concentration C2. The purity (P) of sodium lignosulfonate can be expressed as: Purity (P) of sodium lignosulfonate = C2 / C1 × 100%.

[0111] Enzymatic lignin utilization rate: Powdered enzymatically hydrolyzed lignin with a mass of m1 is weighed and converted into hydrophilic sodium lignin sulfonate through a sulfonation reaction. However, some components of the enzymatically hydrolyzed lignin cannot be effectively utilized and precipitate out, denoted as m2. The mass of the effectively utilized enzymatically hydrolyzed lignin is m1 - m2. Therefore, the utilization rate (L) of enzymatically hydrolyzed lignin can be expressed as: Utilization rate (L) of enzymatically hydrolyzed lignin = (m1 - m2) / m1 × 100%.

[0112] Sulfonation degree: Prepare a 1 g / L (or 2 g / L) sodium lignosulfonate solution and adjust the pH of the solution to 5.5; simultaneously prepare a 0.01 mol / L CTAB (cetyltrimethylammonium bromide) solution. Accurately transfer 10 mL of the lignosulfonate solution into a 25 mL volumetric flask, and sequentially add 0.5–2.5 mL (volume intervals of 0.2 mL, adjusted according to actual conditions) of CTAB solution to the volumetric flask. Shake well and let stand for 10 min. Take 8 mL of the mixture into a centrifuge tube, centrifuge at 5000 rpm for 5 min, and take 2 mL of the supernatant. Measure the absorbance using a UV spectrophotometer. Determine a titration curve by comparing the absorbance at 280 nm with the amount of CTAB used. The amount of CTAB used corresponding to the minimum absorbance is the sulfonation degree of the sample.

[0113] Cement paste fluidity at a 0.6% admixture ratio: (1) Place the glass plate horizontally and wipe the glass plate, truncated cone mold, mixer, and mixing pot with a damp cloth to make the surface wet but without water stains. Place the truncated cone mold in the center of the glass plate and cover it with a damp cloth for later use. (2) Weigh 300g of cement and pour it into the mixing pot. Add the recommended amount of admixture and 87g or 105g of water, and stir immediately (slow speed 120s, stop for 15s, fast speed 120s). (3) Quickly pour the mixed paste into the truncated cone mold, smooth it with a scraper, lift the truncated cone mold vertically, and let the cement paste flow on the glass plate. Use a ruler to measure the maximum diameter of the flowing part in two mutually perpendicular directions. The total time from the start of adding water to the end of the measurement should not exceed 6 minutes. Take the average value as the cement paste fluidity.

[0114] Water reduction rate, bleeding rate, slump, and compressive strength of concrete: GB8076-2008, GB50081-2002.

[0115] Table 1

[0116]

[0117]

[0118] As can be seen from the above, compared with the comparative examples, the embodiments of the present invention utilize the characteristic that enzymatically hydrolyzed lignin is close to that of original lignin and therefore has high activity. A hydrothermal method is used to first oxidize and then sulfonate the enzymatically hydrolyzed lignin. Through optimized process flow, efficient utilization and conversion of enzymatically hydrolyzed lignin are achieved, resulting in lignin sulfonate products with high purity, high sulfonation degree, and high water-reducing properties. Compared with traditional lignin sulfonate water-reducing agents, the high-efficiency water-reducing agent prepared by the present invention has superior water-reducing performance and a certain retarding effect, which can improve the compressive strength of concrete.

[0119] Furthermore, it can be seen that the overall effect is better when all process parameters are within the preferred range of the present invention.

[0120] 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 method for preparing a water-reducing agent using enzymatic hydrolysis, lignin oxidation, and sulfonylation, characterized in that, Includes the following steps: Step S1: Water and oxidant are added to the enzymatically hydrolyzed lignin to carry out an oxidation reaction and obtain the first solution; Step S2: Adjust the pH of the first solution to 10-12, and then add sulfonating agent and formaldehyde solution to carry out sulfonylation reaction to obtain the water-reducing agent.

2. The method according to claim 1, characterized in that, The solid-liquid ratio of the enzymatically hydrolyzed lignin to water is (10-15g):(150-250mL); and / or The oxidant includes one or more of hydrogen peroxide, potassium permanganate, persulfate, potassium peroxymonosulfonate, and ozone; and / or the weight ratio of the enzymatically hydrolyzed lignin to the oxidant is (10-15):(1-4).

3. The method according to claim 1 or 2, characterized in that, The oxidation reaction is carried out at a temperature of 80–120°C for a time of 0.5–2 hours.

4. The method according to any one of claims 1 to 3, characterized in that, Step S1 further includes adding water, the oxidant, and the reducing agent to the enzymatically hydrolyzed lignin to carry out the oxidation reaction; Preferably, the reducing agent includes one or more of ferrous sulfate, hydroxylamine hydrochloride and ascorbic acid; and / or the weight ratio of the enzymatically hydrolyzed lignin to the reducing agent is (10-15):(0.05-0.15).

5. The method according to any one of claims 1 to 4, characterized in that, The sulfonating agent includes one or more of sodium sulfite, calcium sulfite, magnesium sulfite, 1,4-butyronitrile and 1,3-propanesulfonate; and / or the weight ratio of the enzymatically hydrolyzed lignin to the sulfonating agent is (10-15):(2-6); and / or The formaldehyde solution has a mass concentration of 37-40%, and the solid-liquid ratio of the enzymatically hydrolyzed lignin to the formaldehyde solution is (10-15g):(1-5mL).

6. The method according to any one of claims 1 to 5, characterized in that, The sulfonylation reaction is carried out at a temperature of 150–180°C for 10–14 hours.

7. The method according to any one of claims 1 to 6, characterized in that, Step S2 further includes centrifuging the material that has undergone the sulfonation reaction to obtain a supernatant; drying and grinding the supernatant, or spray drying it, to obtain the water-reducing agent; Preferably, the drying temperature is 100-110°C and the time is 6-14 hours; and / or the inlet air temperature of the spray drying is 110-180°C and the outlet air temperature is 70-110°C. Preferably, the water-reducing agent has a water content of 2-10%.

8. The method according to any one of claims 1 to 7, characterized in that, By weight percentage, the enzymatically hydrolyzed lignin contains 35-45% lignin, 2-4% hemicellulose, 30-40% cellulose, 35-45% carbon, 4-6% hydrogen, 0.2-0.4% nitrogen, and 0.1-0.2% sulfur. Preferably, the enzymatically hydrolyzed lignin is prepared by enzymatically hydrolyzing straw and / or bagasse using cellulase and hemicellulase to obtain enzymatically hydrolyzed residue, i.e., the enzymatically hydrolyzed lignin.

9. A water-reducing agent, characterized in that, The water-reducing agent is prepared by any one of claims 1 to 8 using the enzymatic hydrolysis of lignin oxidation-sulfonylation.

10. The water-reducing agent according to claim 9, characterized in that, The water-reducing agent has an enzymatic lignin utilization rate of 60-85% and a sulfonation degree of 1.3-1.8 mmol / g; and / or the water-reducing agent has a cement paste fluidity of 140-170 mm / 0.6% and a C30 concrete compressive strength of 36-42 MPa.

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