Phosphate-modified polycarboxylic acid water-reducing agent and application thereof in desulfurized gypsum

Abstract

The application discloses a phosphate-modified polycarboxylic water reducing agent and application thereof in desulfurization gypsum, and belongs to the technical field of water reducing agents. The preparation raw materials of the phosphate-modified polycarboxylic water reducing agent comprise the following components in parts by mass: polyether macromonomer (TPEG): 90-110 parts; unsaturated carboxylic acid monomer: 5.0-12.0 parts; unsaturated phosphate ester monomer: 1.5-9.0 parts; oxidant (initiator): 0.4-0.8 parts; reducing agent: 0.1-0.4 parts; chain transfer agent: 0.2-0.6 parts; and water: 150-200 parts. The phosphate group (-PO3H2) has stronger chemical complexing capacity for calcium ions, so that the phosphate group has an advantage in competitive adsorption, and thus the initial dispersion capacity of the water reducing agent in a complex desulfurization gypsum system is remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of water-reducing agent technology, specifically relating to a phosphate ester modified polycarboxylate water-reducing agent and its application in desulfurized gypsum. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Desulfurization gypsum, a major industrial byproduct of flue gas desulfurization in coal-fired power plants, is of great significance for resource utilization. However, desulfurization gypsum differs significantly from natural gypsum in composition, containing high concentrations of soluble salts, especially abundant sulfate ions (SO42-). 2- This has become a bottleneck restricting its large-scale application in the field of high-performance building materials.

[0004] Currently, polycarboxylate superplasticizers (PCE) widely used in the construction industry mainly achieve dispersion through the electrostatic anchoring of carboxyl groups (-COO-) on the main chain to the surface of gypsum particles, combined with the steric hindrance effect provided by the long side chains. However, in desulfurized gypsum systems, this mechanism faces severe challenges. On the one hand, there is the competitive adsorption effect, and on the other hand, the large amount of SO4 in the system... 2- It preferentially occupies the active sites on the surface of gypsum dihydrate crystals. Due to the limited electronegativity and complexation strength of the carboxyl groups, SO4 2- The resulting intense competitive adsorption leads to PCE molecules being unable to anchor effectively, resulting in a sharp reduction in adsorption. On the other hand, there is the problem of dispersion failure. With the failure of anchoring groups, PCE cannot build sufficient spatial repulsive potential energy between gypsum particles, directly resulting in extremely poor initial fluidity of desulfurized gypsum slurry, which cannot meet the requirements of modern construction for high fluidity and high water reduction. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a phosphate-modified polycarboxylate superplasticizer and its application in desulfurized gypsum. This invention addresses the problem of poor dispersibility of traditional polycarboxylate superplasticizers in desulfurized gypsum due to sulfate competitive adsorption, by providing a modified polycarboxylate superplasticizer incorporating phosphate groups. This invention utilizes the stronger chemical complexation ability of the phosphate group (-PO3H2) for calcium ions, giving it an advantage in competitive adsorption and thus significantly improving the initial dispersion ability of the superplasticizer in complex desulfurized gypsum systems.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: In a first aspect, the present invention provides a phosphate ester modified polycarboxylate superplasticizer, the raw materials for which are prepared include the following components in parts by mass: Polyether macromonomer (TPEG): 90~110 parts; Unsaturated carboxylic acid monomers: 5.0 ~ 12.0 parts; Unsaturated phosphorylated monomer: 1.5~9.0 parts; Oxidizing agent (initiator): 0.4 ~ 0.8 parts; Reducing agent: 0.1 ~ 0.4 parts; Chain transfer agent: 0.2 ~ 0.6 parts; Deionized water: 150-200 parts.

[0007] Secondly, the present invention provides a method for preparing the above-mentioned phosphate ester modified polycarboxylate superplasticizer, comprising the following steps: Preparation of Solution A: Dissolve the unsaturated carboxylic acid monomer (such as acrylic acid) and the phosphorylated monomer in water and stir until homogeneous; Preparation of solution B: Dissolve the reducing agent and chain transfer agent in water and stir until homogeneous; Preparation and reaction of the base solution: Dissolve the polyether macromonomer and oxidant in water and heat to a certain temperature; Dropping and heat preservation: Add solution A and solution B dropwise at a constant rate and simultaneously under constant temperature. After the dropwise addition is completed, continue to maintain the constant temperature. Neutralization and compounding: Cool to room temperature, add pH adjuster to adjust the pH value of the system to 6.0~7.0, and add water to adjust the solid content to the standard value, thus obtaining the water-reducing agent.

[0008] Thirdly, the present invention provides an application of the above-mentioned phosphate ester modified polycarboxylate superplasticizer in building material systems with high sulfate content, preferably for water reduction and dispersion of desulfurization gypsum in coal-fired power plants.

[0009] One or more of the above technical solutions have the following advantages or beneficial effects: Overcoming physical steric hindrance limitations to achieve strong chemical anchoring and anti-competitive adsorption: Traditional polycarboxylate superplasticizers rely heavily on long side chains to provide steric hindrance, but in desulfurization gypsum systems with high sulfate concentrations, sulfate (SO4)... 2- The phosphate group competes with the carboxyl group (-COO-) of the main chain for calcium sites, leading to a significant decrease in the effective adsorption capacity of the polycarboxylate superplasticizer, thus preventing the superplasticizer from achieving its intended dispersion effect. Although the introduction of phosphate groups in this invention results in a shorter copolymer main chain and a regular decrease in weight-average molecular weight (from approximately 96,000 in the traditional unmodified form to approximately 55,000-76,000), the phosphate group (-PO3H2) competes with the carboxyl group (-COO-) of the main chain for calcium sites, resulting in a significant decrease in the effective adsorption capacity of the polycarboxylate superplasticizer, thus preventing the superplasticizer from achieving its intended dispersion effect. 2+The chelation constant of the phosphate group is much higher than that of sulfate and carboxyl groups, and its initial fluidity in desulfurized gypsum is significantly higher without causing serious retardation side effects. This fully demonstrates that the phosphate group (-PO3H2) introduced in this invention has an extremely strong chemical complexation and anchoring effect on calcium ions on the surface of desulfurized gypsum, successfully reversing the steric hindrance disadvantage caused by the decrease in molecular weight, and fundamentally resisting the competitive adsorption of sulfate.

[0010] The highly concentrated molecular chain length distribution and extremely stable synthesis process: This invention employs an optimized 45℃ low-temperature aqueous phase redox initiation system, effectively matching the polymerization competition rates between highly reactive phosphate ester monomers and polyether macromonomers, achieving highly uniform copolymerization between monomers. Gel permeation chromatography (GPC) tests show that the series of modified water-reducing agents prepared by this invention all have monomer conversion rates exceeding 97%, with almost no macromonomer residue, and the polydispersity index (PDI) of the polymer is controlled within the range of 1.5~1.8. This extremely high monomer conversion rate and extremely narrow molecular weight distribution fully demonstrate the strong controllability and excellent batch stability of this synthesis process. Simultaneously, the high purity and highly concentrated molecular chain length of the product eliminates the competition for adsorption sites by ineffective small molecule oligomers from the source, ensuring not only the high consistency of the final water-reducing agent product's performance and excellent dispersibility, but also laying a solid foundation for subsequent large-scale, standardized industrial production.

[0011] The process is green and environmentally friendly with low energy consumption: it adopts low-temperature aqueous phase synthesis at 40~50℃, which has low energy consumption and no organic solvent volatilization, meeting the requirements of green chemical industry. Attached Figure Description

[0012] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0013] Figure 1 shows the Fourier transform infrared (FTIR) spectra of the polymers prepared in the embodiments and comparative examples of the present invention. Figure 2 This is a superimposed graph of the molecular weight distribution of polymers prepared by gel permeation chromatography (GPC) in the embodiments and comparative examples of the present invention; Figure 3 The fluidity of desulfurized gypsum slurry prepared with polymers from different embodiments and comparative examples; Figure 4 The setting time of desulfurized gypsum prepared with polymers from different embodiments and comparative examples is given. Detailed Implementation

[0014] Terminology Explanation: PCE: Polycarboxylate Superplasticizer.

[0015] Desulfurization gypsum: Industrial by-product gypsum produced during the desulfurization process of flue gas from coal-fired power plants. Its main component is calcium sulfate dihydrate, and it often contains soluble sulfate impurities.

[0016] GPC: Gel permeation chromatography, used to determine the relative molecular mass and distribution of polymers.

[0017] In response to the persistent problems of traditional water-reducing agents such as "poor adsorption and susceptibility to interference", it is particularly urgent to develop a new type of modified polycarboxylate water-reducing agent with strong anchoring properties.

[0018] A leap from "physical occupancy" to "chemical anchoring": This invention, through molecular design, introduces SO4 into the PCE backbone. 2- Phosphate ester groups possess extremely strong affinity. Utilizing the higher chelation constant of phosphate groups compared to carboxyl and sulfate groups, they achieve "preemptive occupation" and "strong anchoring" in complex ionic environments.

[0019] The scientific balance of synergistic effects: The core necessity of this study lies in precisely controlling the molar ratio of phosphate ester monomers to polyether macromonomers. By appropriately sacrificing molecular weight (reducing physical steric hindrance) and achieving a significant improvement in chemical anchoring ability, the negative impact of high-intensity ionic interference on dispersion performance was successfully reversed. This technical approach of "compensating for physical steric hindrance with chemical anchoring" not only solves the initial flowability problem of desulfurized gypsum but also effectively avoids the excessive retardation side effects easily caused by conventional phosphate modification, providing crucial chemical admixture support for the high-value utilization of industrial solid waste.

[0020] This invention aims to solve the problem of low dispersion efficiency of existing polycarboxylate superplasticizers in high ionic strength systems such as desulfurized gypsum due to competitive adsorption of sulfate ions. Simultaneously, it provides a room-temperature, low-energy-consumption preparation process that enhances the chemical anchoring ability of molecules on the surface of dihydrate gypsum crystals by introducing side-chain phosphate ester functional monomers.

[0021] In one typical embodiment, the present invention provides a phosphate ester modified polycarboxylate superplasticizer, the raw materials for which are prepared include the following components by mass parts: Polyether macromonomer (TPEG): 90~110 parts; Unsaturated carboxylic acid monomers: 5.0 ~ 12.0 parts; Unsaturated phosphorylated monomer: 1.5 ~ 9.0 parts; Oxidizing agent (initiator): 0.4 ~ 0.8 parts; Reducing agent: 0.1 ~ 0.4 parts; Chain transfer agent: 0.2 ~ 0.6 parts; Deionized water: 150-200 parts.

[0022] The unsaturated monomers are composed of unsaturated carboxylic acid monomers and unsaturated phosphorylation monomers, and the total molar ratio of the polyether macromonomer to the unsaturated monomers is controlled within the range of 1:(3.0~5.0). Specifically, it can be 1:3, 1:3.2, 1:3.5, 1:3.6, 1:3.7, 1:3.8, 1:3.9, 1:4.0, 1:4.2, 1:4.5, 1:4.6, 1:4.8, 1:5.0, etc., preferably 1:(3.5~4.5).

[0023] In one or more embodiments, the unsaturated carboxylic acid monomer includes acrylic acid (AA).

[0024] In one or more embodiments, the unsaturated phosphorylation monomer includes a phosphorylation monomer (HEMAP). The mass fraction of the unsaturated phosphorylation monomer is 1.5 to 9.0 parts, specifically 1.5, 1.75, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.25, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 8.75, 9, etc.

[0025] In the preliminary experimental stage of this invention, APS was 0.4-0.5% of the total monomer mass, VC was 0.2-0.3% of the total monomer mass, and chain transfer agent MPA was 0.2-0.3% of the total monomer mass. The core inventive point and main variable of this invention focus on the effect of different proportions of phosphate ester monomers on the anti-competitive adsorption performance of desulfurized gypsum.

[0026] Different modified groups lead to fundamental changes in the microscopic adsorption mechanism of water-reducing agents. The superior technical effect of this invention is highly dependent on the unique chemical properties of the phosphate ester group, and its irreplaceable nature is only achieved through modification with this group.

[0027] Conventional carboxyl groups are prone to desorption. Specifically, carboxyl-based water-reducing agents mainly rely on weak complexation with calcium ions and hydrogen bonding. In the high-ionic environment of desulfurized gypsum containing a large amount of sulfate, carboxyl groups with weak adsorption capacity are easily replaced from the gypsum surface by high-concentration sulfate ions through competitive adsorption, resulting in loss of steric hindrance and failure of water reduction.

[0028] Sulfonic acid groups are susceptible to electrostatic shielding. While existing technologies disclose that sulfonic acid groups in hemihydrate gypsum exhibit good anti-interference capabilities, their core dispersion mechanism still heavily relies on electrostatic adsorption and surface charge repulsion. In real industrial desulfurization gypsum, not only sulfate ions are present, but also calcium sulfite, unreacted calcium carbonate, and extremely high concentrations of alkali metal salts. In this extremely high-salt environment, the electric double layer is severely compressed (i.e., a strong electrostatic shielding effect occurs), leading to a significant decrease in the performance of sulfonic acid-based water-reducing agents that rely solely on electrostatic repulsion.

[0029] The phosphate ester group used in this invention possesses strong chemical specificity. The reason for using phosphate ester groups and their derivatives is that the interaction between them and calcium ions on the gypsum surface is not a simple electrostatic adsorption or hydrogen bonding, but an extremely robust multidentate chemical chelation. The calcium complexation constant of the phosphate group is much higher than that of the carboxyl and sulfate groups. No matter how harsh the external environment or how high the sulfate concentration, the phosphate ester group can remain firmly anchored to the gypsum crystal surface. This chemical specificity is unmatched by other groups.

[0030] In one or more embodiments, the weight-average molecular weight M of the water-reducing agent w The range is 50,000-80,000, and the multi-dispersion index (PDI) is 1.5-1.8.

[0031] In this application, by precisely controlling the amount of chain transfer agent used during synthesis, the weight-average molecular weight of the product is significantly increased and controlled within the range of 50,000 to 80,000. Simultaneously, a specific process involving placing the initiator (APS) in the base solution (at 45°C) ensures a stable global free radical concentration, resulting in an extremely narrow polydispersity index (PDI) for the high molecular weight polymer. This synergistic process of "specific chain transfer control + base solution initiation" constitutes the core competitive advantage of this application.

[0032] In the phosphate ester-modified polycarboxylate superplasticizer synthesis system of this invention, the chain transfer agent (preferably mercaptopropionic acid, etc.) is the core key to precisely controlling the polymer weight-average molecular weight (Mw) and its distribution. Its control mechanism and the resulting technical effects are as follows: During free radical copolymerization, the chain transfer agent mainly functions through a "chain transfer reaction." It can transfer active hydrogen atoms to the growing active long polymer chain, thereby "terminating" the continued growth of that long chain; simultaneously, the chain transfer agent itself, having lost hydrogen atoms, transforms into a new primary free radical, which in turn "initiates" the generation of a completely new short chain. This mechanism can effectively cut off excessively long polymer chains without reducing the overall monomer conversion rate of the system, significantly reducing the degree of polymerization of the macromolecules and making the molecular weight distribution more concentrated.

[0033] In actual synthesis, the weight-average molecular weight of the water-reducing agent is significantly inversely proportional to the amount of chain transfer agent. By precisely adjusting the mass percentage of chain transfer agent to the total monomer, the weight-average molecular weight of the phosphate-modified polycarboxylate water-reducing agent of this invention can be anchored within the optimal performance range.

[0034] In one or more embodiments, the oxidant (initiator) includes ammonium persulfate (APS). The reducing agent includes vitamin C. The chain transfer agent includes mercaptopropionic acid.

[0035] In one typical embodiment, the present invention provides a method for preparing the above-mentioned phosphate ester modified polycarboxylate superplasticizer, comprising the following steps: Preparation of Solution A: Dissolve the unsaturated carboxylic acid monomer (such as acrylic acid) and the phosphorylated monomer in water and stir until homogeneous; Preparation of solution B: Dissolve the reducing agent and chain transfer agent in water and stir until homogeneous; Preparation and reaction of the base solution: Dissolve the polyether macromonomer and oxidant in water and heat to a certain temperature; Dropping and heat preservation: Add solution A and solution B dropwise at a constant rate and simultaneously under constant temperature. After the dropwise addition is completed, continue to maintain the constant temperature. Neutralization and compounding: Cool to room temperature, add pH adjuster to adjust the pH value of the system to 6.0~7.0, and add water to adjust the solid content to the standard value, thus obtaining the water-reducing agent.

[0036] In one or more embodiments, during the preparation of the base solution and the reaction process, the temperature is raised to a constant 40°C to 50°C, specifically 40°C, 41°C, 42°C, 43°C, 44°C, 45°C, 46°C, 47°C, 48°C, 49°C, 50°C, etc., preferably 43°C to 47°C, and most preferably 45°C. 60°C to 80°C is the thermal initiation system, usually using APS (ammonium persulfate) as the thermal initiator. This invention uses 45°C because it employs a redox system of ammonium persulfate (APS) + VC. The presence of VC greatly reduces the activation energy of APS, allowing for stable and continuous generation of free radicals at a low temperature of 45°C. The reactivity of the phosphate ester monomer (HEMAP) differs significantly from other monomers; at high temperatures above 60°C, it readily undergoes homopolymerization or block polymerization, resulting in uneven distribution of effective groups and a significant reduction in anchoring ability. 45°C is the optimal "sweet spot temperature" for matching the reactivity ratio of the highly reactive phosphate ester monomer and the polyether macromonomer, ensuring highly uniform random copolymerization of each monomer.

[0037] In one or more embodiments, during the uniform and synchronous dropwise addition of solution A and solution B at a constant temperature, the dropwise addition time of solution A is 2.0~3.0 hours, and the dropwise addition time of solution B is 2.5~3.5 hours, wherein the dropwise addition time of solution B is longer than that of solution A. It is emphasized that the dropwise addition time of solution B (reducing agent side) is longer than that of solution A, which is a key process for synthesizing polymers with high conversion rates and narrow distribution.

[0038] Regarding the dripping rate, it is generally calculated based on the volume of liquid A and liquid B and the total dripping time after they are prepared.

[0039] In one or more embodiments, after the addition is complete, the temperature is maintained for another 1.0 to 2.0 hours. The entire addition process is carried out under a nitrogen atmosphere.

[0040] In one or more embodiments, water is added to adjust the solid content to a calibrated value of 30-50%, such as 40%. The solid content of polycarboxylate superplasticizers is generally 30-50%. In the formulation of this invention, the ratio of macromonomers, small monomers, and the total water volume of the system determines that the solid content of the original solution after the reaction is naturally around 40%. Adding water to fine-tune it to 40% is the most economical and best suited operation for this process.

[0041] In one or more embodiments, the pH adjuster is not limited to sodium hydroxide (or conventional liquid alkali), but may also be selected from at least one of potassium hydroxide and ammonia water.

[0042] In one or more embodiments, the mass ratio of polyether macromonomer to water in the base solution is (90~110):(60~80). In solution A, the mass ratio of unsaturated carboxylic acid monomer to water is (5.0~12.0):(40~50). In solution B, the mass ratio of chain transfer agent to water is (0.2~0.6):(45~55).

[0043] As a preferred embodiment, the preparation method of the above-mentioned phosphate ester modified polycarboxylate superplasticizer includes the following steps: (1) Preparation of solution A: Dissolve acrylic acid and phosphoric acid esterified monomer in deionized water and stir until homogeneous; (2) Preparation of solution B: Dissolve the reducing agent and chain transfer agent in deionized water and stir until homogeneous; (3) Preparation and reaction of the base liquid: Add polyether macromonomer, oxidant and some deionized water to a reaction vessel equipped with a stirrer and thermometer, and heat to 40℃~50℃ and keep at a constant temperature; (4) Dropping and Heating: Solution A and solution B are added dropwise at a constant temperature and at a uniform rate. The dropping time for solution A is 2.0~3.0 hours, and the dropping time for solution B is 2.5~3.5 hours (the dropping time for solution B is longer than that for solution A). After the dropping is completed, the solution is kept at a constant temperature for 1.0~2.0 hours. The entire process is carried out under a nitrogen atmosphere. (5) Neutralization and compounding: Cool to room temperature, add pH adjuster to adjust the pH value of the system to 6.0~7.0, and add water to adjust the solid content to the standard value (e.g. 40%), and the water-reducing agent is obtained.

[0044] In one typical embodiment, the present invention provides the application of the above-mentioned phosphate ester modified polycarboxylate superplasticizer in building material systems with high sulfate content, preferably for water reduction and dispersion of desulfurization gypsum in coal-fired power plants.

[0045] The "building material system with high sulfate content" described in this invention refers to a system in which the liquid phase of the mixture contains a high concentration of soluble sulfate ions, which can lead to severe competitive adsorption of conventional polycarboxylate superplasticizers, resulting in deterioration of their dispersion performance.

[0046] Specifically, in this invention, high sulfate content refers to a soluble sulfate ion concentration in the liquid phase of the mixture being greater than or equal to 0.1 mol / L; preferably greater than or equal to 0.15 mol / L; more preferably greater than or equal to 0.2 mol / L.

[0047] Alternatively, based on solid mass, the high sulfate content refers to a percentage of soluble sulfate ions in the total mass of the cementitious material that is greater than or equal to 0.4%; preferably greater than or equal to 0.6%; more preferably greater than or equal to 0.8%. Typical high sulfate building material systems in this invention are desulfurized gypsum systems from coal-fired power plants or high-alkali sulfate cement systems.

[0048] The phosphate superplasticizer specifically synthesized in this application has excellent compatibility in the harsh environment of desulfurized gypsum, and its initial flowability can reach 310 mm at the standard thickening water content.

[0049] Different types of gypsum result in fundamental differences in hydration and impurity environments. This invention is limited to desulfurized gypsum and possesses extremely strong targeting specificity.

[0050] Desulfurized gypsum is an industrial solid waste product from flue gas of coal-fired power plants. The system naturally contains a large amount of free impurities, which fluctuate dramatically from batch to batch (such as unreacted limestone / calcium carbonate, highly destructive calcium sulfite, fly ash, and extremely high concentrations of soluble sulfates). In this system, sulfate ions compete fiercely with water-reducing agents, causing conventional products to fail. Phosphate groups, however, have a much stronger chemical anchoring ability with calcium ions than sulfate ions, thus exhibiting superior performance in this extreme environment.

[0051] Natural gypsum has an extremely low concentration of free ions, resulting in a lack of ion competition. If applied here, the strong anchoring advantage of this invention will not only fail to be highlighted, but will also lead to a significant increase in gypsum setting time due to excessive adsorption, causing excessively slow setting.

[0052] The phosphogypsum system contains a large amount of free inorganic phosphorus (phosphate, dihydrogen phosphate) and fluorides. In this system, inorganic phosphate groups are homologous to "phosphate ester groups," and their competitive ability is much stronger than that of sulfate groups. Phosphate ester water-reducing agents will have their adsorption sites occupied due to intense homologous competition in this environment, making it extremely difficult for them to achieve their intended water-reducing effect.

[0053] Performance testing methods: The methods for determining initial fluidity, setting time (initial setting / final setting), etc., refer to GB / T17669.4-1999 Determination of physical properties of building gypsum slurry.

[0054] In this invention, unless otherwise specified, all other test materials and instruments are conventional test materials in the field and can be purchased through commercial channels.

[0055] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0056] Comparative Example 1 (Unmodified polycarboxylate superplasticizer, PCE-2) Add 100g of polyether macromonomer (TPEG), 0.54g of ammonium persulfate (APS), and 70g of deionized water to a four-necked flask and heat to 45°C. Dissolve 10.8g of acrylic acid (AA) in 42.2g of water to prepare solution A; dissolve 0.26g of vitamin C and 0.28g of mercaptopropionic acid in 53.3g of water to prepare solution B. Simultaneously add solutions A and B at 45°C, with solution A added over 2.5 hours and solution B over 3 hours. After the addition is complete, maintain the temperature for 1 hour, then cool down and adjust the pH to approximately 7 with 30% NaOH solution. Add water to adjust the solid content to 40%.

[0057] According to GPC analysis, the weight-average molecular weight M of this unmodified water-reducing agent is... w The value is 96,529, and the multiplicity index (PDI) is 1.786.

[0058] Example 1 (Low phosphate ester modified water-reducing agent, PCE-4) The preparation was carried out using the same process steps as Comparative Example 1. The only difference was that the formulation of solution A was adjusted to: 11.4 g of acrylic acid and 1.75 g of phosphate-esterified monomer (HEMAP) dissolved in 46.8 g of deionized water. Specifically: Add 100g of polyether macromonomer (TPEG), 0.54g of ammonium persulfate (APS), and 70g of deionized water to a four-necked flask and heat to 45°C. Dissolve 11.4g of acrylic acid and 1.75g ​​of phosphate-modified monomer (HEMAP) in 46.8g of deionized water to prepare solution A; dissolve 0.26g of vitamin C and 0.28g of mercaptopropionic acid in 53.3g of water to prepare solution B. Simultaneously add solutions A and B at 45°C, with solution A added over 2.5 hours and solution B over 3 hours. After the addition is complete, maintain the temperature for 1 hour, then cool down and adjust the pH to approximately 7 with 30% NaOH solution. Add water to adjust the solid content to 40%.

[0059] According to GPC analysis, the weight-average molecular weight M of this modified water-reducing agent is... w The value is 76,123, and the multi-dispersion index (PDI) is 1.771.

[0060] Example 2 (Low phosphate ester modified water-reducing agent, PCE-5) The preparation was carried out using the same process steps as Comparative Example 1. The only difference was that the formulation of solution A was adjusted to: 10.8 g of acrylic acid and 3.5 g of phosphate-esterified monomer (HEMAP) dissolved in 45.7 g of deionized water. Specifically: Add 100g of polyether macromonomer (TPEG), 0.54g of ammonium persulfate (APS), and 70g of deionized water to a four-necked flask and heat to 45°C. Dissolve 10.8g of acrylic acid and 3.5g of phosphate-modified monomer (HEMAP) in 45.7g of deionized water to prepare solution A; dissolve 0.26g of vitamin C and 0.28g of mercaptopropionic acid in 53.3g of water to prepare solution B. Simultaneously add solutions A and B at 45°C, with solution A added over 2.5 hours and solution B over 3 hours. After the addition is complete, maintain the temperature for 1 hour, then cool down and adjust the pH to approximately 7 with 30% NaOH solution. Add water to adjust the solid content to 40%.

[0061] According to GPC analysis, the weight-average molecular weight M of this modified water-reducing agent is... w The value is 72,123, and the multivariate index (PDI) is 1.731.

[0062] Example 3 (Medium phosphate modified water-reducing agent, PCE-6) The preparation was carried out using the same process steps as Comparative Example 1. The only difference was that the formulation of solution A was adjusted to: 10.2 g of acrylic acid and 5.25 g of phosphate-esterified monomer (HEMAP) dissolved in 44.6 g of deionized water. Specifically: Add 100g of polyether macromonomer (TPEG), 0.54g of ammonium persulfate (APS), and 70g of deionized water to a four-necked flask and heat to 45°C. Dissolve 10.2g of acrylic acid and 5.25g of phosphate-modified monomer (HEMAP) in 44.6g of deionized water to prepare solution A; dissolve 0.26g of vitamin C and 0.28g of mercaptopropionic acid in 53.3g of water to prepare solution B. Simultaneously add solutions A and B dropwise at 45°C, with solution A added over 2.5 hours and solution B over 3 hours. After the addition is complete, maintain the temperature for 1 hour, then cool down and adjust the pH to approximately 7 with 30% NaOH solution. Add water to adjust the solid content to 40%.

[0063] According to GPC analysis, the weight-average molecular weight M of this modified water-reducing agent is... w The value is 69,305, and the multi-dispersion index (PDI) is 1.671.

[0064] Example 4 (Medium phosphate modified water-reducing agent, PCE-7) The preparation was carried out using the same process steps as Comparative Example 1. The only difference was that the formulation of solution A was adjusted to: 9.6 g of acrylic acid and 7.0 g of phosphate-esterified monomer (HEMAP) dissolved in 43.4 g of deionized water. Specifically: Add 100g of polyether macromonomer (TPEG), 0.54g of ammonium persulfate (APS), and 70g of deionized water to a four-necked flask and heat to 45°C. Dissolve 9.6g of acrylic acid and 7.0g of phosphate-modified monomer (HEMAP) in 43.4g of deionized water to prepare solution A; dissolve 0.26g of vitamin C and 0.28g of mercaptopropionic acid in 53.3g of water to prepare solution B. Simultaneously add solutions A and B at 45°C, with solution A added over 2.5 hours and solution B over 3 hours. After the addition is complete, maintain the temperature for 1 hour, then cool down and adjust the pH to approximately 7 with 30% NaOH solution. Add water to adjust the solid content to 40%.

[0065] According to GPC analysis, the weight-average molecular weight M of this modified water-reducing agent is... w The value is 66,905, and the multiplicity index (PDI) is 1.597.

[0066] Example 5 (High phosphate modified water-reducing agent, PCE-8) The preparation was carried out using the same process steps as Comparative Example 1. The only difference was that the formulation of solution A was adjusted to: 9g of acrylic acid and 8.75g of phosphate-esterified monomer (HEMAP) dissolved in 42.3g of deionized water. Specifically: Add 100g of polyether macromonomer (TPEG), 0.54g of ammonium persulfate (APS), and 70g of deionized water to a four-necked flask and heat to 45°C. Dissolve 9g of acrylic acid and 8.75g of phosphate-modified monomer (HEMAP) in 42.3g of deionized water to prepare solution A; dissolve 0.26g of vitamin C and 0.28g of mercaptopropionic acid in 53.3g of water to prepare solution B. Simultaneously add solutions A and B at 45°C, with solution A added over 2.5 hours and solution B over 3 hours. After the addition is complete, maintain the temperature for 1 hour, then cool down and adjust the pH to approximately 7 with 30% NaOH solution. Add water to adjust the solid content to 40%.

[0067] According to GPC analysis, the weight-average molecular weight M of this modified water-reducing agent is... w The value is 54,980, and the multiplicity index (PDI) is 1.527.

[0068] The monomer conversion rates are as follows: PCE-2: 99.01%, PCE-4: 98.33%, PCE-5: 98.13%, PCE-6: 97.98%, PCE-7: 97.85%, and PCE-8: 97.42%. Therefore, the series of modified water-reducing agents prepared in this invention all have monomer conversion rates exceeding 97%, with almost no macromonomer residue. The monomer conversion rate was calculated using gel permeation chromatography (GPC) area normalization, i.e., the percentage of the polymer peak integral area to the total integral area of ​​the polymer and unreacted macromonomer peaks.

[0069] Combination Figures 1 to 4 The anti-competitive adsorption mechanism and excellent performance of this invention have been conclusively verified: Microstructure confirmation, such as Figure 1 and Figure 2 As shown in Figure 1, the infrared spectra of all modified embodiments and the unmodified comparative example (PCE-2) of this invention exhibit the typical characteristic absorption peaks of polycarboxylate superplasticizers. At 1112 cm⁻¹... -1 There is an extremely strong COC ether bond stretching vibration peak nearby (originating from the side chain of the polyether macromonomer), at 1727 cm⁻¹. -1 The C=O carbonyl stretching vibration peak (originating from monomers such as acrylic acid) is present nearby, and is located at 1630 cm⁻¹. -1 The characteristic peaks of the nearby C=C double bonds have essentially disappeared. This confirms that the aqueous redox initiation system used in this invention has extremely high catalytic efficiency, successfully promoting the free radical copolymerization of the monomers and synthesizing the target polycarboxylic acid polymer backbone. Furthermore, as... Figure 2As shown in the GPC molecular weight distribution overlay diagram, with the increase of phosphate ester monomer content, the polymer molecular weight distribution curve shifts regularly towards lower molecular weight. This confirms that after introducing large-volume phosphate groups into copolymerization, the copolymer backbone becomes shorter, and the "physical steric hindrance" effect traditionally provided by high molecular weight is objectively weakened.

[0070] Improvements in macroscopic dispersion performance, such as Figure 3 As shown, specifically: Figure 3 As shown in the flow trend chart, although Figure 2 It was confirmed that the molecular weight and physical steric hindrance of the example group were lower than those of the unmodified group, but its initial fluidity in desulfurized gypsum showed a significant reversal. With the deepening of modification, the introduced phosphate groups provided a strong chemical anchoring effect, successfully overcoming the competitive adsorption of high-concentration sulfate ions, which greatly increased the effective adsorption of water-reducing agent and the fluidity was significantly improved. However, when the modification ratio was too high, the polymer backbone was excessively shortened, which greatly weakened the steric hindrance effect provided by the molecular chain and the dispersion performance declined reasonably. Figure 2 and Figure 3 The stark contrast fully demonstrates that the phosphate groups introduced in this invention produce an extremely strong chemical complexation and anchoring effect on the surface of desulfurized gypsum. The phosphate groups act like "anchors," gripping the gypsum surface, while the sulfate ions act like "interference waves," being deflected. This strong chemical anchoring successfully overcomes the competitive adsorption of calcium ions by the high concentration of sulfate ions in desulfurized gypsum, completely compensating for and surpassing the physical disadvantages caused by the decrease in molecular weight, fundamentally achieving a leapfrog improvement in the dispersion performance of the water-reducing agent.

[0071] Excellent engineering adaptability, such as Figure 4 As shown, specifically: the conventional introduction of strongly adsorbing groups (such as phosphate groups) often easily leads to severe retardation side effects, limiting its engineering applications. However, as... Figure 4 As shown in the comparison chart of setting times, the embodiments of the present invention at each gradient not only significantly improved the initial dispersibility, but also maintained the initial and final setting times within a similar and reasonable range to the comparative examples, without excessive retardation. This confirms that the specific molecular structure and monomer ratio defined in the present invention, while achieving strong anti-competitive adsorption, perfectly takes into account the setting process required for normal hydration of desulfurized gypsum, and possesses extremely high industrial practical value.

[0072] Performance test comparison: The water-reducing agents obtained in Examples 1-5 and Comparative Example 1 were uniformly adjusted to a solid content of 40%, and the fluidity and setting time of the desulfurized gypsum slurry were tested under the same dosage (specifically, 0.3% of the mass of desulfurized gypsum) and the same water-to-gypsum ratio (0.65). The test results are shown in Table 1.

[0073] Table 1 Performance Test Table for Each Group

[0074] As can be clearly seen from the test results in Table 1, with the increase of the amount of phosphate-modified monomer (HEMAP), the initial fluidity of the modified water-reducing agent in desulfurized gypsum exhibits a parabolic pattern of first significantly increasing and then slightly decreasing. However, the overall dispersion performance of Examples 1-5 is comprehensive and significantly better than that of the unmodified Comparative Example 1. Combined with the GPC test results of Examples 1-5 (the molecular weight decreases with increasing modification degree), it is confirmed that the present invention fundamentally changes the action mode of the water-reducing agent by introducing large-volume phosphate groups. Relying on strong chemical anchoring, it successfully overcomes the competitive adsorption of high-concentration sulfate ions, effectively improving the dispersion performance of the water-reducing agent while reducing steric hindrance dependence, and the setting time is kept within a reasonable range.

[0075] 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 phosphate ester modified polycarboxylate superplasticizer, characterized in that, The raw materials used in its preparation include the following components by mass: Polyether macromonomer: 90~110 parts; Unsaturated carboxylic acid monomers: 5.0 ~ 12.0 parts; Unsaturated phosphorylated monomer: 1.5 ~ 9.0 parts; Oxidizing agent: 0.4 ~ 0.8 parts; Reducing agent: 0.1 ~ 0.4 parts; Chain transfer agent: 0.2 ~ 0.6 parts; Water: 150-200 parts.

2. The phosphate-modified polycarboxylate superplasticizer according to claim 1, characterized in that, The unsaturated monomer is composed of unsaturated carboxylic acid monomer and unsaturated phosphorylation monomer, and the total molar ratio of the polyether macromonomer to the unsaturated monomer is 1:(3.0~5.0), preferably 1:(3.5~4.5).

3. The phosphate-modified polycarboxylate superplasticizer according to claim 1, characterized in that, Unsaturated carboxylic acid monomers include acrylic acid; Preferably, the unsaturated phosphorylation monomer includes a phosphorylation monomer.

4. The phosphate-modified polycarboxylate superplasticizer according to claim 1, characterized in that, The weight-average molecular weight M of the water-reducing agent w The range is 50,000-80,000, and the multi-dispersion index (PDI) is 1.5-1.

8.

5. The phosphate-modified polycarboxylate superplasticizer according to claim 1, characterized in that, Oxidizing agents include ammonium persulfate; Preferably, the reducing agent includes vitamin C; Preferably, the chain transfer agent includes mercaptopropionic acid.

6. A method for preparing the phosphate ester modified polycarboxylate superplasticizer according to any one of claims 1 to 5, characterized in that, Includes the following steps: Preparation of solution A: Dissolve the unsaturated carboxylic acid monomer and the phosphorylated monomer in water and stir until homogeneous; Preparation of solution B: Dissolve the reducing agent and chain transfer agent in water and stir until homogeneous; Preparation and reaction of the base solution: Dissolve the polyether macromonomer and oxidant in water and heat to a certain temperature; Dropping and heat preservation: Add solution A and solution B dropwise at a constant rate and simultaneously under constant temperature. After the dropwise addition is completed, continue to maintain the constant temperature. Neutralization and compounding: Cool to room temperature, add pH adjuster to adjust the pH value of the system to 6.0~7.0, and add water to adjust the solid content to the standard value, thus obtaining the water-reducing agent.

7. The preparation method according to claim 6, characterized in that, During the preparation and reaction of the base liquid, the temperature is raised to 40℃~50℃ and kept constant.

8. The preparation method according to claim 6, characterized in that, During the process of adding solution A and solution B at a constant temperature and uniform rate, the addition time of solution A is 2.0~3.0 hours and the addition time of solution B is 2.5~3.5 hours, with the addition time of solution B being longer than that of solution A. Preferably, after the dripping is complete, the temperature is kept constant for 1.0 to 2.0 hours.

9. The preparation method according to claim 6, characterized in that, The pH adjuster includes an alkali, preferably, the alkali includes at least one of sodium hydroxide, potassium hydroxide, and ammonia.

10. The application of the phosphate-modified polycarboxylate superplasticizer according to any one of claims 1 to 5 or the phosphate-modified polycarboxylate superplasticizer prepared by the preparation method according to any one of claims 6 to 9 in a building material system with high sulfate content, preferably in desulfurized gypsum.

Images