Solid polycarboxylate superplasticizer as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of water reducing agents, and discloses a solid polycarboxylic acid water reducing agent and a preparation method and application thereof.The preparation method comprises the steps that a polycarboxylic acid compound and a saturated polyether monomer are mixed and sequentially subjected to decompression dehydration and decompression esterification reaction under the action of an acid catalyst, a product is directly synthesized through a one-pot method, and the solid polycarboxylic acid water reducing agent is obtained. Esterification balance is broken through a decompression environment, the polycondensation process is accurately controlled, no extra solvent or secondary drying is needed, the solid content of the solid polycarboxylic acid water reducer is larger than or equal to 99%, meanwhile, molecular weight distribution is narrow, the defects that a liquid water reducer is high in transportation cost and prone to hydrolysis, and thermal degradation of a polymer is prone to being caused by a traditional spray drying method are overcome, and the solid polycarboxylic acid water reducer is suitable for large-scale production. And the method has important industrial application value.

Description

Technical Field

[0001] This invention belongs to the field of water-reducing agents, specifically relating to a solid polycarboxylate water-reducing agent, its preparation method, and its application. Background Technology

[0002] Polycarboxylate superplasticizers are characterized by simple synthesis processes and low costs, and can be polymerized under ambient or low-temperature conditions. They are currently the world's most widely used and best-performing superplasticizers. Liquid polycarboxylate superplasticizers are easy to produce, so most polycarboxylate superplasticizer products are currently supplied and used in 10-20% solution form. However, this liquid supply form has significant limitations in practical applications: First, the high moisture content during long-distance transportation leads to a significant increase in packaging, logistics, and warehousing costs; second, liquid products generally contain easily hydrolyzed side chain groups, which are prone to hydrolysis during long-term storage, leading to performance degradation; furthermore, liquid admixtures are difficult to directly apply to dry-mixed mortars or grouting materials and other dry powder building materials. Solid polycarboxylate superplasticizers can effectively improve these problems; therefore, developing high-performance and highly stable solid polycarboxylate superplasticizers has become a core demand in the industry.

[0003] Currently, the common methods for preparing solid polycarboxylate superplasticizers in the industry mainly include spray drying or bulk polymerization. Spray drying involves atomizing and dehydrating the polycarboxylate solution with high-temperature hot air. However, because polycarboxylate molecules contain a large number of hydrophilic polyethylene glycol (PEG) segments, they are highly hygroscopic and extremely difficult to dehydrate. Furthermore, they are prone to chain transfer reactions or thermal degradation under high-temperature conditions, leading to product agglomeration or impaired water-reducing properties. Bulk polymerization involves direct polymerization in an anhydrous system, but the reaction system has extremely high viscosity and uneven heat dissipation, resulting in products with wide molecular weight distribution and poor performance consistency.

[0004] Therefore, it can be seen that the production of solid polycarboxylate superplasticizers still faces significant challenges. Developing a simple, efficient, and low-cost production process for solid polycarboxylate superplasticizers is of great significance to the development of the industry. Summary of the Invention

[0005] The purpose of this invention is to provide a solid polycarboxylate superplasticizer and its preparation method. The preparation method uses polycarboxylate compounds and saturated polyether monomers as raw materials, and directly prepares the solid polycarboxylate superplasticizer in a one-pot process through vacuum dehydration and vacuum esterification reaction, which solves the technical problem of complex preparation process of existing solid polycarboxylate superplasticizers.

[0006] Another objective of this invention is to provide an application of a solid polycarboxylate superplasticizer in concrete.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] This invention provides a method for preparing a solid polycarboxylate superplasticizer, the method comprising the following steps:

[0009] 1) The polycarboxylic acid compound is dispersed in deionized water to obtain an aqueous solution of the polycarboxylic acid compound;

[0010] 2) The aqueous solution of the polycarboxylic acid compound, the catalyst and the polyether monomer are mixed evenly and placed in a reaction vessel for dehydration under reduced pressure. Then, a reduced pressure esterification reaction is carried out. The product is cooled and sliced ​​to obtain the solid polycarboxylic acid water-reducing agent.

[0011] The polycarboxylic acid compound mentioned in step 1) is one or more of polyacrylic acid or polymethacrylic acid, and the molecular weight of the polycarboxylic acid compound is 2000~12000.

[0012] The mass fraction of the polycarboxylic acid compound in the aqueous solution of the polycarboxylic acid compound in step 1) is 10-30%.

[0013] The polyether monomer mentioned in step 2) is one or more of polyethylene glycol monomethyl ether or polyethylene glycol monoethyl ether, and the molecular weight of the polyether monomer is 200~5000.

[0014] The catalyst mentioned in step 2) is one or more of p-toluenesulfonic acid or solid acid catalyst, and the amount of catalyst used is 0.1 to 5.0% of the mass of the polyether monomer.

[0015] The preparation method of the solid acid catalyst includes the following steps:

[0016] a. Dissolve ZrOCl2 in distilled water, then add 25 wt% ammonia water dropwise while stirring to adjust the pH of the solution to 8-9. The precipitate is then washed and dried in air to obtain the dried product.

[0017] b. Soak the dried product in a 0.5-1 mol / L sulfuric acid aqueous solution for 5-10 h. After soaking, vacuum dry the product and calcine it at 450-650℃ for 2-4 h to obtain the solid acid catalyst.

[0018] The molar ratio of the carboxyl group in the polycarboxylic acid compound described in step 1) to the hydroxyl group in the polyether monomer described in step 2) is 1~7:1.

[0019] In step 2), the absolute pressure of the dehydration process is ≤10 kPa, the dehydration temperature is room temperature, and the dehydration time is 1~3h.

[0020] The absolute pressure of the reduced pressure esterification reaction described in step 2) is ≤10 kPa, the reaction temperature is 120~200 ℃, and the reaction time is 1~4 h.

[0021] This invention provides a solid polycarboxylate superplasticizer prepared using the above-described preparation method.

[0022] The molecular weight of the solid polycarboxylate superplasticizer is 10,000 to 50,000.

[0023] The solid polycarboxylate superplasticizer has a solid content of ≥99.0%.

[0024] This invention provides an application of the solid polycarboxylate superplasticizer described herein in concrete.

[0025] This invention utilizes an esterification reaction to prepare a solid polycarboxylate superplasticizer. The core reaction is a reversible esterification reaction between the carboxyl groups in the polycarboxylate compound and the hydroxyl groups in the polyether monomer under the action of an acid catalyst. The reaction equation is as follows:

[0026] R-COOH + HO-R' ⇌ R-COO-R' + H2O;

[0027] This esterification reaction is a typical reversible equilibrium reaction. When a large amount of water is present in the system, the equilibrium shifts significantly to the left. Continuously removing the water generated in the reaction can cause the equilibrium to shift continuously to the right, thereby increasing the conversion rate. During the reaction, it is a step-condensation polymerization reaction, rather than a traditional chain-growing free radical polymerization. The reaction rate is relatively mild and controllable. The polyether monomer itself is liquid or fusible and is in a low-viscosity melt state at the reaction temperature. Therefore, it also acts as a reaction medium and a solvent, enabling the polycarboxylic acid compound and the polyether monomer to achieve uniform mixing and full contact. The system always maintains good fluidity and thermal conductivity, avoiding the problems of wide molecular weight distribution and poor performance consistency that often result from bulk polymerization.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] 1. The preparation of the solid polycarboxylate superplasticizer of the present invention does not require additional organic solvents or spray drying equipment steps. The entire preparation process is completed in one pot. The whole process has low energy consumption and no wastewater or waste solvent discharge, which significantly reduces production costs.

[0030] 2. The solid polycarboxylate superplasticizer of the present invention has a solid content of ≥99.0%, and can be cooled and sliced ​​to obtain a solid product in solid powder form without secondary curing or drying. It is not easy to stick together or absorb moisture, and at the same time, it completely avoids the high cost of long-distance transportation caused by the water content of liquid polycarboxylate superplasticizer.

[0031] 3. Unlike solid polycarboxylate superplasticizers prepared by traditional bulk polymerization, this invention uses esterification grafting instead of free radical chain growth polymerization, which avoids problems such as gelation effect, uneven heat dissipation and local overheating. The reaction is mild, the viscosity rises slowly and the batch repeatability is high. The product has a narrow molecular weight distribution and stable and consistent performance, which is convenient for industrial scale-up and quality control.

[0032] 4. The performance of the synthesized water-reducing agent can be adjusted by changing the molecular weight of the polyether monomer. When using a low molecular weight polyether monomer with a molecular weight (Mn) < 1000, the viscosity-reducing effect of the water-reducing agent can be enhanced; while when using a high molecular weight polyether monomer with a molecular weight (Mn > 3000), the early strength effect of the water-reducing agent can be enhanced. Attached Figure Description

[0033] Figure 1 The image shows the GPC spectrum of the solid polycarboxylate superplasticizer prepared in Example 2. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] Unless otherwise specified, all test materials and reagents used in the following examples are commercially available.

[0036] The solid acid catalysts used in each embodiment are prepared by the following methods:

[0037] A method for preparing a solid acid catalyst specifically includes the following steps:

[0038] a. Dissolve 100g ZrOCl2 in distilled water, then add 25wt% ammonia water dropwise while stirring to adjust the pH of the solution to 8-9. Wash the hydroxide with deionized water and then dry it in air at 100℃ for 24h to obtain the dried product.

[0039] b. The dried product was soaked in a 0.8 mol / L sulfuric acid solution for 8 h to adsorb sulfate onto the dried ZrO2 sample. Then, it was vacuum dried at 100 °C for 24 h and then transferred to a muffle furnace for calcination at 550 °C for 3 h to obtain the solid acid catalyst.

[0040] Example 1

[0041] A method for preparing a solid polycarboxylate superplasticizer specifically includes the following steps:

[0042] 1) Polyacrylic acid with a molecular weight of 2000 was dispersed in deionized water to obtain a polyacrylic acid aqueous solution with a total mass of 14.4g and a mass fraction of 30wt%.

[0043] 2) 30g of polyethylene glycol monomethyl ether with a molecular weight of 3000, the polyacrylic acid aqueous solution obtained in step 1), and 0.15g of solid acid catalyst were placed in a reaction vessel and mixed evenly. The mixture was dehydrated under reduced pressure at 5kPa for 2 hours at room temperature. The pressure inside the vessel was kept at 5kPa. The temperature was raised to 120℃ and the reaction was carried out under reduced pressure for 2 hours. After cooling and slicing, the solid polycarboxylate superplasticizer was obtained.

[0044] Example 2

[0045] A method for preparing a solid polycarboxylate superplasticizer specifically includes the following steps:

[0046] 1) Polyacrylic acid with a molecular weight of 5000 was dispersed in deionized water to obtain a polyacrylic acid aqueous solution with a total mass of 10.08g and a mass fraction of 30wt%.

[0047] 2) 18g of polyethylene glycol monomethyl ether with a molecular weight of 3000, the polyacrylic acid aqueous solution obtained in step 1), and 0.018g of p-toluenesulfonic acid were placed in a reaction vessel and mixed evenly. The mixture was dehydrated under reduced pressure at 10 kPa for 2 hours at room temperature. The pressure inside the vessel was kept at 10 kPa. The temperature was raised to 160 °C and the mixture was subjected to reduced pressure esterification reaction for 3 hours. After cooling and slicing, the solid polycarboxylate superplasticizer was obtained.

[0048] Example 3

[0049] A method for preparing a solid polycarboxylate superplasticizer specifically includes the following steps:

[0050] 1) Polymethacrylic acid with a molecular weight of 8000 was dispersed in deionized water to obtain a polymethacrylic acid aqueous solution with a total mass of 14.62g and a mass fraction of 30wt%;

[0051] 2) 36g of polyethylene glycol monoethyl ether with a molecular weight of 3000, the polymethyl methacrylate aqueous solution obtained in step 1), and 0.72g of p-toluenesulfonic acid were placed together in a reaction vessel and mixed evenly. The mixture was dehydrated under reduced pressure at room temperature and 8kPa for 2 hours. The pressure inside the vessel was kept at 8kPa. The temperature was raised to 180℃ and the mixture was subjected to reduced pressure esterification reaction for 3 hours. After cooling and slicing, the solid polycarboxylate superplasticizer was obtained.

[0052] Example 4

[0053] A method for preparing a solid polycarboxylate superplasticizer specifically includes the following steps:

[0054] 1) Polymethacrylic acid with a molecular weight of 6000 was dispersed in deionized water to obtain a polymethacrylic acid aqueous solution with a total mass of 51.6g and a mass fraction of 30wt%;

[0055] 2) 12g of polyethylene glycol monoethyl ether with a molecular weight of 200, the polymethyl methacrylate aqueous solution obtained in step 1), and 0.36g of solid acid catalyst were placed in a reaction vessel and mixed evenly. The mixture was dehydrated under reduced pressure at 6kPa for 2 hours at room temperature. The pressure inside the vessel was kept at 6kPa. The temperature was raised to 120℃ and the reaction was carried out under reduced pressure for 1 hour. After cooling and slicing, the solid polycarboxylate superplasticizer was obtained.

[0056] Example 5

[0057] A method for preparing a solid polycarboxylate superplasticizer specifically includes the following steps:

[0058] 1) Polyacrylic acid with a molecular weight of 6000 was dispersed in deionized water to obtain a polyacrylic acid aqueous solution with a total mass of 7.20g and a mass fraction of 30wt%;

[0059] 2) 15g of polyethylene glycol monoethyl ether with a molecular weight of 1000, the polyacrylic acid aqueous solution obtained in step 1), and 0.6g of p-toluenesulfonic acid were placed together in a reaction vessel and mixed evenly. The mixture was dehydrated under reduced pressure at 10 kPa for 2 hours at room temperature. The pressure inside the vessel was kept at 10 kPa. The temperature was raised to 200 °C and the mixture was subjected to reduced pressure esterification reaction for 3 hours. After cooling and slicing, the solid polycarboxylate superplasticizer was obtained.

[0060] Example 6

[0061] A method for preparing a solid polycarboxylate superplasticizer specifically includes the following steps:

[0062] 1) Polyacrylic acid with a molecular weight of 6000 was dispersed in deionized water to obtain a polyacrylic acid aqueous solution with a total mass of 1.44g and a mass fraction of 30wt%.

[0063] 2) 30g of polyethylene glycol monoethyl ether with a molecular weight of 5000, the polyacrylic acid aqueous solution obtained in step 1), and 1.5g of solid acid catalyst were put into a reaction vessel and mixed evenly. The mixture was dehydrated under reduced pressure at 10kPa for 2 hours at room temperature. The pressure inside the vessel was kept at 10kPa. The temperature was raised to 200℃ and the esterification reaction was carried out under reduced pressure for 3 hours. After cooling and slicing, the solid polycarboxylate superplasticizer was obtained.

[0064] Comparative Example 1

[0065] The comparative example used was the commercially available solid polycarboxylate superplasticizer, Focke & Fitch GB180.

[0066] Comparative Example 2

[0067] A method for preparing solid polycarboxylate superplasticizer using spray drying, the method comprising the following steps:

[0068] 1) Dissolve 30g of polyethylene glycol monomethyl ether macromonomer with a molecular weight of 5000 in 100mL of deionized water and label it as component A; dissolve 0.8g of sodium persulfate in 2.7mL of deionized water and label it as component B; dissolve 2.60g of polyacrylic acid and 0.15g of mercaptopropionic acid in 8.7mL of deionized water and label it as component C.

[0069] 2) Components A, B and C were added dropwise into the reactor at 80 ℃ and 60 rpm to carry out the polymerization reaction. The dropwise reaction lasted for 3 hours, and the temperature was maintained for 1.5 hours after the dropwise reaction was completed.

[0070] 3) The polymerization product from step 2) is dried by a spray dryer with an inlet temperature of 140°C and an outlet temperature of 70°C, and then pulverized by a high-speed pulverizer to obtain solid polycarboxylate superplasticizer.

[0071] Comparative Example 3

[0072] A method for preparing solid polycarboxylate superplasticizer using bulk polymerization, the method comprising the following steps:

[0073] 1) Mix 4.32g of acrylic acid, 0.4g of ammonium persulfate and 0.11g of mercaptoethanol to obtain a mixed solution;

[0074] 2) Add 30g of polyethylene glycol monomethyl ether macromonomer with a molecular weight of 3000 to the reactor, heat to 80 ℃ to gradually melt it, and keep at 80 ℃ to dropwise add the mixed solution into the reactor for polymerization reaction for 2h. After the addition is completed, keep the temperature and continue the polymerization reaction for 1.5h. After the reaction is completed, cool the product and then crush it with a high-speed pulverizer to obtain solid polycarboxylate superplasticizer.

[0075] Test case

[0076] Molecular weight distribution and solid content testing

[0077] The solid content of each embodiment and comparative example was tested according to GB / T 8077-2012 "Test Method for Homogeneity of Concrete Admixtures".

[0078] The molecular weight and PDI of the polycarboxylate superplasticizers prepared in each example and comparative examples 2-3 were tested using gel permeation chromatography. The test results are shown in Table 1.

[0079] Table 1 Solid content and GPC test data

[0080]

[0081] As shown in Table 1, the solid content of the products obtained in Examples 1-6 of this invention all reached over 99.0%. The solid polycarboxylate superplasticizer prepared by the preparation method of this invention has a high solid content and does not require secondary spray drying. At the same time, the PDI value of each example is stable between 1.44 and 1.52, which is significantly better than that of Comparative Example 2 and Comparative Example 3. This indicates that this invention effectively solves the problems of thermal degradation caused by high temperature during spray drying and excessive polydispersity caused by uncontrolled reaction in bulk polymerization by macromolecular esterification grafting under reduced pressure. It ensures the high uniformity and controllability of the superplasticizer molecular structure while achieving efficient curing.

[0082] Concrete performance testing

[0083] The solid polycarboxylate superplasticizers prepared in Examples 1-6 were compared with Comparative Example 1 according to GB / T8076-2008. The performance of the polycarboxylate superplasticizers was tested at a solid content of 0.20%, and the test results are shown in Table 2.

[0084] Table 2 Performance Comparison Data

[0085]

[0086] As shown in Table 2, in Examples 1-3, polyether monomers with a molecular weight of 3000 were used as branched-chain synthesized solid polycarboxylate superplasticizers. Their water reduction rate was comparable to that of Comparative Example 1, but their strength was slightly improved. In Examples 4-5, polyether monomers with smaller molecular weights of 200 and 1000 were used as side chains to synthesize solid polycarboxylate superplasticizers. These superplasticizers had a long main chain and short side chain structure. Their water reduction rate was lower than that of Comparative Example 1, but their collapse time was significantly reduced. This reduced the viscosity of concrete, improved its workability, and did not affect the later strength. In Example 6, polyethers with longer side chains were used, which significantly improved the early strength and later strength of concrete. Therefore, the invention method of this patent can improve the viscosity reduction or early strength performance of solid polycarboxylate superplasticizers by adjusting the molecular weight of the main chain and side chains.

[0087] It should be noted that the above embodiments are merely some preferred embodiments of the present invention, and not all embodiments. Obviously, based on the above embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0088] The above description of the embodiments is intended to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for preparing a solid polycarboxylate superplasticizer, characterized in that, The preparation method includes the following steps: 1) The polycarboxylic acid compound is dispersed in deionized water to obtain an aqueous solution of the polycarboxylic acid compound; 2) The aqueous solution of the polycarboxylic acid compound, the catalyst and the polyether monomer are mixed evenly and placed in a reaction vessel for dehydration under reduced pressure. Then, a reduced pressure esterification reaction is carried out. The product is cooled and sliced ​​to obtain the solid polycarboxylic acid water-reducing agent.

2. The preparation method according to claim 1, characterized in that, The polycarboxylic acid compound mentioned in step 1) is one or more of polyacrylic acid or polymethacrylic acid, and the molecular weight of the polycarboxylic acid compound is 2000~12000.

3. The preparation method according to claim 1, characterized in that, The polyether monomer mentioned in step 2) is one or more of polyethylene glycol monomethyl ether or polyethylene glycol monoethyl ether, and the molecular weight of the polyether monomer is 200~5000.

4. The preparation method according to claim 1, characterized in that, The catalyst mentioned in step 2) is one or more of p-toluenesulfonic acid or solid acid catalyst, and the amount of catalyst used is 0.1 to 5.0% of the mass of the polyether monomer.

5. The preparation method according to claim 4, characterized in that, The preparation method of the solid acid catalyst includes the following steps: a. Dissolve ZrOCl2 in distilled water, then add 25 wt% ammonia water dropwise while stirring to adjust the pH of the solution to 8-9. The precipitate is then washed and dried in air to obtain the dried product. b. Soak the dried product in a 0.5-1 mol / L sulfuric acid aqueous solution for 5-10 h. After soaking, vacuum dry the product and calcine it at 450-650℃ for 2-4 h to obtain the solid acid catalyst.

6. The preparation method according to claim 1, 2 or 3, characterized in that, The molar ratio of the carboxyl group in the polycarboxylic acid compound described in step 1) to the hydroxyl group in the polyether monomer described in step 2) is 1~7:

1.

7. The preparation method according to claim 1, characterized in that, In step 2), the absolute pressure of the dehydration process is ≤10 kPa, the dehydration temperature is room temperature, and the dehydration time is 1~3 h.

8. The preparation method according to claim 1, characterized in that, The absolute pressure of the reduced pressure esterification reaction described in step 2) is ≤10 kPa, the reaction temperature is 120~200 ℃, and the reaction time is 1~4 h.

9. A solid polycarboxylate superplasticizer prepared by the preparation method according to any one of claims 1-8.

10. The application of a solid polycarboxylate superplasticizer as described in claim 9 in concrete.

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