A solid polycarboxylate superplasticizer and its preparation method

Abstract

This invention provides a solid polycarboxylate superplasticizer and its preparation method. First, a polyether macromonomer, water, an activator, and an oxidant are mixed as a base material. Then, an unsaturated carboxylic acid monomer is used as component A, and an aqueous solution of a chain transfer agent and a reducing agent is used as component B. Under heating conditions, components A and B are simultaneously added dropwise to the base material. After the addition is complete, the reaction is maintained at a constant temperature, and caustic soda is added for neutralization, yielding a polycarboxylate superplasticizer mother liquor. The mother liquor is then transferred to a primary devolatilization unit for devolatilization under heating conditions. Next, it is transferred to a secondary mixing unit, where a desiccant is added. Finally, it is transferred to a slicing unit to obtain the finished solid polycarboxylate superplasticizer with a moisture content <3% and a solid content >97%. Compared with existing technologies, this invention has a simple preparation method, lower production energy consumption, and superior product performance.

Description

Technical Field

[0001] This invention belongs to the field of concrete admixtures, specifically relating to a solid polycarboxylate superplasticizer and its preparation method. Background Technology

[0002] Solid polycarboxylate superplasticizer (SPC) is a commonly used admixture in dry-mix mortar, cement-based grouting materials, and shotcrete. It can be directly mixed and packaged with various powder materials. Before use, SPC is in a physically mixed state, and its performance is effectively released upon adding water. Furthermore, traditional polycarboxylate superplasticizer mother liquor contains 40%-50% solids, resulting in high transportation costs over long distances. Transporting it in SPC form can significantly reduce transportation costs.

[0003] Literature and patent reports indicate that spray drying is currently the main method for producing and applying solid polycarboxylate superplasticizers. This process requires preparing a 20%-30% aqueous solution of the polycarboxylate superplasticizer, then adding 5%-10% of an anti-blocking agent (generally inorganic powders with particle sizes of 5-20 μm, such as calcium carbonate, fumed silica, alumina, calcium oxide, and talc). After thorough mixing, the mixture is atomized and dried using a spray drying device at an inlet air temperature of 180-200℃ to obtain powdered polycarboxylate superplasticizer. This process not only has high energy consumption during the drying process (requiring the removal of approximately 70% of the moisture), but also results in a lower effective content of the polycarboxylate superplasticizer due to the anti-blocking agent, with a water reduction rate only about 85%-90% of that of liquid polycarboxylate superplasticizers.

[0004] Chinese patents CN111362615A, CN107652402A, and CN109535340A introduce rigid benzene ring structures into polycarboxylate superplasticizers, increasing the softening point of the final product and reducing the amount of anti-caking agent required. This improves the problems of clumping and low effective content in powdered polycarboxylate superplasticizers. Furthermore, traditional aqueous free radical polymerization methods are used to ensure the conversion rate of polyether monomers, preventing excessive unconverted polyether monomers from hindering the spray drying process and hindering the powder drying of the polycarboxylate superplasticizer. However, the spray drying process still requires the removal of a large amount of moisture, resulting in high energy consumption.

[0005] Another widely studied method for preparing solid polycarboxylate superplasticizers is bulk polymerization, which avoids the use of existing aqueous free radical polymerization. Bulk polymerization involves a high reaction temperature, where the polyether macromonomer becomes liquid after reaching its melting point. Azobisisobutyronitrile (AIB) or benzoyl peroxide is used as a free radical initiator. Unsaturated carboxylic acid and chain transfer agent solutions are added dropwise to the reaction system, either separately or in combination. The resulting polycarboxylate superplasticizer is then directly sliced ​​to obtain powdered polycarboxylate superplasticizer. Chinese patents CN 110240676A, CN 108084362 A, CN 114685729 A, and CN 108821633A all report bulk polymerization methods for polycarboxylate superplasticizers. Bulk polymerization offers advantages such as convenient production processes and significant energy savings; however, the viscosity is high in the later stages of bulk polymerization, which negatively impacts mass and heat transfer. Furthermore, the monomer conversion rate of polycarboxylate superplasticizers synthesized by bulk polymerization is relatively low, generally between 80% and 90%, making it difficult to achieve the polymerization effect of traditional aqueous free radical polymerization.

[0006] In summary, solid polycarboxylate superplasticizers have certain advantages in terms of saving transportation costs, packaging, and product application range, and are one of the development directions of polycarboxylate superplasticizers. Currently, the spray drying method and bulk polymerization method, which are more widely studied and applied, have defects such as high energy consumption, low effective content, and insufficient monomer conversion rate, which increase the production cost of solid polycarboxylate superplasticizers and make it difficult to promote and apply them on a large scale. Summary of the Invention

[0007] The purpose of this invention is to provide a solid polycarboxylate superplasticizer and its preparation method, which has a simple preparation process, low production energy consumption, and excellent product performance.

[0008] The specific technical solution of this invention is as follows:

[0009] A method for preparing a solid polycarboxylate superplasticizer includes the following steps:

[0010] 1) Mix polyether macromonomers, water, active activator and oxidant as base material; then unsaturated carboxylic acid monomers as material A, and aqueous solution of chain transfer agent and reducing agent as material B. Under heating conditions, material A and material B are added dropwise to the base material at the same time. After the addition is completed, keep the reaction at the temperature and add caustic soda flakes to neutralize, and obtain polycarboxylic acid water-reducing agent mother liquor.

[0011] 2) The polycarboxylate superplasticizer mother liquor is transferred to the first-stage devolatilization unit and devolatilized under heating conditions; then it is transferred to the second-stage mixing unit and a desiccant is added; finally, it is transferred to the slicing unit to obtain the solid polycarboxylate superplasticizer finished product.

[0012] In step 1), the polyether macromonomer is a commercially available polyether macromonomer product, including commonly used HPEG, TPEG, EPEG, and VPEG product grades, with a number average molecular weight (M). n The molecular structure of polyether macromonomers in the range of 2000-6000 is shown in the following formula:

[0013] R is H, -CH 3 X is one of -CH2-, -CH2-CH2-, -O-CH2-CH2-, -O-CH2-CH2-O-CH2-CH2-, -O-CH2-CH2-CH2-CH2-, and -O-CH2-CH(CH3)-CH2-.

[0014] In step 1), the water is ordinary process water, and the amount used is 10%-20% of the mass of the polyether macromonomer.

[0015] In step 1), the activation agent is used to ensure the polymerization activity of each monomer in a high-solids-content system and to improve the conversion rate of the polyether macromonomer. This invention uses a ferrous salt as the activation agent, which is selected from ferrous sulfate, ferrous chloride, and ferrous nitrate. Preferably, the activation agent is prepared as a 0.01% (w / w) aqueous solution of the ferrous salt, and the amount of the ferrous salt aqueous solution is 0.05%-0.1% of the mass of the polyether macromonomer.

[0016] In step 1), considering the polymerization reaction temperature, hydrogen peroxide, which is easily decomposed and volatile, is not used as the oxidant. Preferably, the oxidant used in this invention is a persulfate, preferably one of ammonium persulfate or sodium persulfate; the amount of the oxidant is 0.2%-1.0% of the mass of the polyether macromonomer.

[0017] In step 1), component A is an unsaturated carboxylic acid monomer, including one or more monomers such as maleic anhydride, acrylic acid, itaconic acid, itaconic anhydride, methacrylic acid, hydroxyethyl acrylate, and hydroxypropyl acrylate. Maleic anhydride, itaconic anhydride, itaconic acid, and methacrylic acid, which are solid unsaturated carboxylic acid monomers at room temperature, are added directly to the base solution; the amount of the unsaturated carboxylic acid monomer used is 10%-15% of the mass of the polyether macromonomer.

[0018] In step 1), material B is a mixed aqueous solution of a chain transfer agent and a reducing agent; the chain transfer agent is one of mercaptoethanol, mercaptopropionic acid, and mercaptoacetic acid; the amount of the chain transfer agent is 0.4%-0.8% of the mass of the polyether macromonomer; the reducing agent is one of L-ascorbic acid (hereinafter referred to as Vc), sodium formaldehyde sulfoxylate, and sodium metabisulfite; the amount of the reducing agent is 0.2%-0.5% of the mass of the polyether macromonomer.

[0019] In step 1), the chain transfer agent and reducing agent are dissolved in water at 10% of the mass of the polyether macromonomer.

[0020] In step 1), the heating conditions refer to the following: the reaction temperature should reach above the melting point of the polyether macromonomer, between 50-65℃, and materials A and B should be added dropwise simultaneously. The dropwise addition time of material A is 1.0-3.0h, and the dropwise addition time of material B is 0.5h longer than that of material A.

[0021] The heat preservation reaction described in step 1) has a reaction time of 60±5 min.

[0022] In step 1), the caustic soda tablets are sodium hydroxide tablets, and the amount used is the same as the molar amount of carboxylic acid groups in the unsaturated carboxylic acid monomers.

[0023] In step 1), the prepared polycarboxylate superplasticizer mother liquor has an effective solid content between 80% and 90%, and a weight-average molecular weight (M). w The values ​​are between 25,000 and 45,000, the polyether macromonomer conversion rate is ≥90%, and the pH value is between 8 and 10.

[0024] In step 2), the primary devolatilization device is a commercially available twin-screw extruder equipped with electric heating and vacuum devolatilization devices. The twin screws in a twin-screw extruder provide better material conveying, mixing, and heat transfer during the rotation and meshing process. The increased material viscosity has a much smaller impact on devolatilization efficiency compared to a stirred tank reactor, resulting in higher moisture removal efficiency. All twin-screw extruder equipment is commercially available and purchased from a twin-screw extruder manufacturer. Its structural schematic diagram is shown below. Figure 1 As shown.

[0025] The reaction temperature of the primary devolatilization unit is between 150-250℃, the reaction pressure is -0.1MPa, and the residence time of the material in the unit is 3-10min.

[0026] The devolatilization effect of the primary devolatilization device is that the effective solid content of the polycarboxylate superplasticizer mother liquor after passing through the primary devolatilization device is ≥97%.

[0027] The secondary mixing unit is a conventional commercially available twin-screw extruder. During the rotation and meshing process of the twin screws, the materials are thoroughly mixed and conveyed. Its structural schematic diagram is as follows. Figure 2 As shown.

[0028] In step 2), the desiccant is an inorganic or organic desiccant, and the amount of desiccant used is 0.05% to 0.25% of the mass of the polycarboxylate superplasticizer mother liquor.

[0029] The inorganic desiccant is one of sodium thiosulfate, sodium sulfate, sodium carbonate, ferrous sulfate, zinc sulfate, magnesium sulfate, alum, calcium chloride, calcium nitrate, calcium oxide, copper sulfate, etc. Considering the influence of color, chloride ion content, and its impact on the performance of polycarboxylate superplasticizers, preferably, the inorganic desiccant of the present invention is one of sodium thiosulfate, sodium sulfate, sodium carbonate, or calcium oxide, etc.

[0030] The organic desiccant is a commercially available water-absorbing resin, whose main components are sodium polyacrylate or sodium polymethacrylate, with a weight-average molecular weight between 1 million and 2 million. The water-absorbing resin can not only be used as a desiccant for solid polycarboxylate superplasticizers, but also has a thickening and water-retaining effect after being dissolved in water, further improving the performance of polycarboxylate superplasticizers.

[0031] The secondary mixing device has a material mixing temperature between 100-150℃ and a material residence time of 3-10 minutes.

[0032] In step 2), the slicing device is a common commercially available drum slicer for slicing polyether macromonomers.

[0033] The present invention provides a solid polycarboxylate superplasticizer, which is prepared by the above method and is in brown flakes and powder form with a moisture content of <3% and a solid content of >97%.

[0034] This invention provides a method for preparing a solid polycarboxylate superplasticizer that is simple to manufacture, has low energy consumption, and produces a product with excellent performance. Specifically, the method for preparing the solid polycarboxylate superplasticizer provided by this invention has the following advantages:

[0035] 1. This invention prepares a high-solids-content polycarboxylate superplasticizer mother liquor via aqueous-phase free radical polymerization. The use of an active activator ensures the conversion rate of the polyether macromonomer and the water-reducing effect, while reducing dehydration energy consumption. Compared to bulk polymerization, this method improves the conversion rate of the polyether macromonomer and the water-reducing effect; compared to spray drying, the solids content of the polycarboxylate superplasticizer is increased from 20%-30% to 80%-90%, saving 50%-70% of dehydration energy consumption.

[0036] 2. In this invention, caustic soda is used to completely neutralize the carboxylic acid groups in the polycarboxylate superplasticizer to sodium carboxylate groups. On the one hand, this helps to further increase the solid content of the polycarboxylate superplasticizer mother liquor and reduce the energy consumption of devolatilization. On the other hand, it helps to avoid the dehydration esterification reaction between the main chain carboxylic acid groups and the terminal hydroxyl groups of the polyether side chain during high-temperature drying, which would form a high molecular weight cross-linked polymer that would affect the solubility and water-reducing performance of the subsequent solid polycarboxylate superplasticizer.

[0037] 3. This invention employs a two-stage twin-screw extruder as both a devolatilization and mixing device for high-solids-content polycarboxylate superplasticizer mother liquor. It leverages the advantages of twin-screw extruders in devolatilization and mixing high-viscosity materials, thereby improving mass and heat transfer efficiency. This invention efficiently completes the dehydration and mixing processes of the polycarboxylate superplasticizer mother liquor, further reducing the energy consumption of solid polycarboxylate superplasticizers.

[0038] 4. This invention uses a desiccant instead of an anti-adhesion agent as an additive in solid polycarboxylate superplasticizers. During processing, the desiccant acts as a filler and an anti-adhesion agent. In the finished solid polycarboxylate superplasticizer, it absorbs moisture, preventing deliquescence and clumping. Furthermore, the organic desiccant, after dissolving in concrete, can be used as a thickener or water-retaining agent, further improving the workability of the polycarboxylate superplasticizer.

[0039] Compared with existing technologies, this invention prepares a polycarboxylate superplasticizer mother liquor with a solid content of 70-80% through aqueous phase free radical polymerization. An equimolar amount of caustic soda is used to completely neutralize the carboxylic acid groups, further increasing the solid content to 80-90%, thus reducing dehydration energy consumption. The mother liquor uses inorganic salts capable of forming water of crystallization, or high-molecular-weight sodium polyacrylate or sodium polymethacrylate with excellent water absorption properties as a desiccant, replacing anti-adhesion agents in smaller quantities. A twin-screw extruder is used as the dehydration and mixing device for high-viscosity materials, improving efficiency and reducing energy consumption. This invention utilizes the water-retaining effect of high-molecular-weight sodium polyacrylate to improve the working performance of the final superplasticizer. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the first-stage devolatilization unit.

[0041] Figure 2 This is a schematic diagram of the two-stage mixing unit. Detailed Implementation

[0042] The present invention is described in detail below through examples. These examples are merely illustrative and do not limit the scope of the invention. Based on the disclosure herein, those skilled in the art can make changes to the chemical reagents, processes, and reaction equipment within the scope of the present invention. All equivalent changes or modifications made according to the spirit and essence of the present invention should be covered within the protection scope of the present invention.

[0043] In this embodiment of the invention, the weight-average molecular weight, molecular weight distribution (PDI), and monomer conversion rate of the polycarboxylate superplasticizer mother liquor were determined using a Wyatt Technology Corporation gel permeation chromatography system. The test parameters were as follows: mobile phase: 0.1 mol / L NaNO3 aqueous solution; mobile phase velocity: 1 ml / min; injection volume: 20 μl; sample concentration: 0.5% (sample g / mobile phase g); detector: Shodex RI-71 differential refractive index detector; standard: polyethylene glycol GPC standard (Sigma-Aldrich, molecular weight 1010000, 478000, 263000, 118000, 44700, 18600, 6690, 1960, 628, 232). Solid content was determined using a rapid moisture analyzer, and moisture content was determined using the Karl Fischer method.

[0044] The examples are divided into two parts: first, the preparation of the high-solids-content polycarboxylate superplasticizer mother liquor, and then the preparation of the solid polycarboxylate superplasticizer. In the examples, "parts" specifically refers to parts by mass; the amounts of other materials added are all converted to parts by mass.

[0045] I. Preparation of mother liquor for high-solids polycarboxylate superplasticizers in Examples 1-7:

[0046] 1. The molecular structures, initiators, and codes of the polyether macromonomers used are shown in Table 1.

[0047] Table 1 lists the molecular structures, initiators, and codes of the polyether macromonomers used.

[0048]

[0049]

[0050] 2. The molecular structures and codes of the unsaturated carboxylic acid monomers used are shown in Table 2.

[0051] Table 2 lists the molecular structures and codes of the unsaturated carboxylic acid monomers used.

[0052]

[0053] 3. Using the above raw materials, a high solids content polycarboxylate superplasticizer mother liquor was prepared. The aqueous phase free radical polymerization method was adopted, and by adjusting the polymerization process conditions, a high solids content polycarboxylate superplasticizer mother liquor with a solids content of 80-90% was prepared. The material ratio table for the synthesis of polycarboxylate superplasticizer is shown in Table 3.

[0054] Table 3. Raw materials and dosage for preparing high-solids-content polycarboxylate superplasticizer mother liquor (all dosages are parts by weight).

[0055]

[0056]

[0057] 4. The preparation method of the high solids content polycarboxylate superplasticizer mother liquor in Examples 1-7 above is as follows:

[0058] According to the raw material ratio in Table 3, weigh the prescribed amounts of polyether macromonomer and water into a reaction vessel, heat to 50-65℃, and stir thoroughly until completely dissolved to obtain the base solution. Weigh the unsaturated acrylic monomers and name them dropwise solution A. Maleic anhydride, itaconic anhydride, itaconic acid, methacrylic acid, and other unsaturated carboxylic acid monomers that are solids at room temperature are directly added to the base solution (in Example 1, maleic anhydride is a solid and is directly added to the base solution without dropwise addition solution A). Weigh the reducing agent and chain transfer agent, and dissolve them in water at 10% of the mass of the polyether macromonomer until a clear solution is obtained, which is named dropwise solution B. Weigh out the active activator and oxidant sequentially and add them to the reactor as a base (as bottom material). After the oxidant has been thoroughly stirred and dissolved for 5-10 minutes, maintain the reactor temperature at 50-65℃. Set the dropping times for solutions A and B: solution A should be added for 2.5 hours, and solution B for 30 minutes longer than solution A. After the dropping is complete, maintain the reaction temperature for 1.0 hour. After the reaction is complete, add caustic soda flakes for neutralization, using the same amount as the molar amount of carboxylic acid groups in the unsaturated carboxylic acid monomers. This yields a high-solids-content polycarboxylate superplasticizer mother liquor, named PCE-1 to PCE-7 in sequence.

[0059] 5. The high solids content polycarboxylate superplasticizer mother liquors PCE-1 to PCE-7 prepared in Examples 1 to 7 above were tested according to the prescribed method. The test results are shown in Table 4.

[0060] Table 4 Test data of high solids content polycarboxylate superplasticizer mother liquor

[0061]

[0062]

[0063] II. Preparation of solid polycarboxylate superplasticizer using the high-solids-content polycarboxylate superplasticizer mother liquor prepared in Examples 1-7 above:

[0064] 1. Prepare raw materials: The dosage of high solids content polycarboxylate superplasticizer mother liquor and desiccant is shown in Table 5.

[0065] Table 5. Raw materials and dosage of solid polycarboxylate superplasticizer (all dosages are parts by weight).

[0066]

[0067] 2. The specific preparation method is as follows: The high-solids-content polycarboxylate superplasticizer mother liquor prepared in Examples 1-7 is transferred to a primary devolatilization device for devolatilization under certain temperature and pressure conditions; then it is transferred to a secondary mixing device, where a desiccant is added in a certain proportion; finally, it is transferred to a slicing device to obtain the solid polycarboxylate superplasticizer product. The process parameters for each device are set as shown in Table 6.

[0068] Table 6 Production process parameters of solid polycarboxylate superplasticizer

[0069]

[0070] 3. Product performance testing: The finished solid polycarboxylate superplasticizer was tested according to the prescribed method, and the test results are shown in Table 7.

[0071] Table 7 Test data of solid polycarboxylate superplasticizer finished products

[0072]

[0073]

[0074] The results of the two GPC tests indicate that dehydration did not cause the polycarboxylate superplasticizer to undergo a cross-linking side reaction.

[0075] Application Experiment 1:

[0076] The flowability test of cement paste was conducted according to GB / T8077-2012 standard. The solid polycarboxylate superplasticizers prepared in Examples 1-7 of this invention were first dissolved into a finished product with a solid content of 10%. Conch PO 42.5 cement was used, with a water-cement ratio of 0.29 and the admixture dosage (converted to solids) of 0.12% of the cement weight. The flowability of the cement paste was measured on a flat glass plate. Commercially available solid polycarboxylate superplasticizers were purchased and named GPCE-1 and GPCE-2 as control samples. Among them, GPEG-1 contained 88.0% effective polycarboxylate superplasticizer, 11.0% 5-20μm calcium carbonate (anti-blocking agent), and 1.0% water content; GPEG-2 contained 85.0% effective polycarboxylate superplasticizer, 14% fumed silica (anti-blocking agent), and 1.5% water content. The test results of cement paste are shown in Table 8.

[0077] Table 8 Cement Paste Flowability Test

[0078]

[0079]

[0080] The data in the table show that the solid polycarboxylate superplasticizer prepared using the method described in this invention has significant advantages over commercially available samples in terms of initial water reduction and slump retention. Furthermore, Examples 2-4 all contain unsaturated carboxylic acid ester structures, resulting in solid superplasticizers with even better slump retention performance.

[0081] Application Experiment 2:

[0082] The performance of the solid polycarboxylate superplasticizer described in this invention was tested using concrete tests. The tests were conducted in accordance with the national standard GB / T 8076-2008 "Concrete Admixtures". The cement used was Conch PO 42.5 cement, and the fly ash was grade II; the sand was medium sand with a fineness modulus Mx = 2.6 and a moisture content of 5%; the aggregate was continuously graded crushed stone with a particle size of 5–20 mm and a moisture content of 2%. The superplasticizer dosage was 0.16% (converted to solids). The unit weight of C30 strength grade concrete was 2317 kg / m³. 3 The raw material mix for the concrete test is shown in Table 9.

[0083] Table 9 Concrete Raw Material Proportioning Table

[0084]

[0085] The concrete test data of the solid polycarboxylate superplasticizer are shown in Table 10.

[0086] Table 10 Concrete Tests for Solid Polycarboxylate Superplasticizers

[0087]

[0088]

[0089] The data in the table show that the solid polycarboxylate superplasticizer prepared using the method described in this invention has significant advantages over commercially available samples in terms of initial spread and slump retention in concrete. Furthermore, in Examples 5-7, sodium polyacrylate or sodium polymethacrylate was used as a desiccant, resulting in a larger slump while maintaining similar concrete spread, thus exhibiting better workability during concrete application.

Claims

1. A method for preparing a solid polycarboxylate superplasticizer, characterized in that, The preparation method includes the following steps: 1) Mix polyether macromonomers, water, active activator and oxidant as base material; then unsaturated carboxylic acid monomers as material A, and aqueous solution of chain transfer agent and reducing agent as material B. Under heating conditions, material A and material B are added dropwise to the base material at the same time. After the addition is completed, keep the reaction at the temperature and add caustic soda flakes to neutralize, and obtain polycarboxylic acid water-reducing agent mother liquor. 2) The polycarboxylate superplasticizer mother liquor is transferred to the first-stage devolatilization unit and devolatilized under heating conditions; then it is transferred to the second-stage mixing unit and a desiccant is added; finally, it is transferred to the slicing unit to obtain the solid polycarboxylate superplasticizer finished product. In step 1), the amount of water used is 10%-20% of the mass of the polyether macromonomer; the active activator is: a ferrous salt aqueous solution with a mass concentration of 0.01% is prepared, and the amount of ferrous salt aqueous solution used is 0.05%-0.1% of the mass of the polyether macromonomer.

2. The preparation method according to claim 1, characterized in that, In step 1), the amount of oxidant used is 0.2%-1.0% of the mass of the polyether macromonomer, and the oxidant is persulfate.

3. The preparation method according to claim 1, characterized in that, In step 1), the amount of the unsaturated carboxylic acid monomer used is 10%-15% of the mass of the polyether macromonomer.

4. The preparation method according to claim 1, characterized in that, In step 1), the amount of chain transfer agent used is 0.4%-0.8% of the mass of the polyether macromonomer; the amount of reducing agent used is 0.2%-0.5% of the mass of the polyether macromonomer.

5. The preparation method according to claim 1, characterized in that, In step 1), the prepared polycarboxylate superplasticizer mother liquor has an effective solid content between 80% and 90%, a weight-average molecular weight between 25,000 and 45,000, a polyether macromonomer conversion rate ≥90%, and a pH value between 8 and 10.

6. The preparation method according to claim 1, characterized in that, The reaction temperature of the primary devolatilization device is between 150-250℃, the reaction pressure is -0.1 MPa, and the residence time of the material in the device is 3-10 min.

7. The preparation method according to claim 1 or 6, characterized in that, The secondary mixing device has a material mixing temperature of 100-150℃ and a material residence time of 3-10 minutes.

8. The preparation method according to claim 1, characterized in that, In step 2), the amount of desiccant used is 0.05% to 0.25% of the mass of the polycarboxylate superplasticizer mother liquor.

9. A solid polycarboxylate superplasticizer prepared by the preparation method according to any one of claims 1-8, characterized in that, The solid polycarboxylate superplasticizer has a moisture content of <3% and a solid content of >97%.

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