Polycarboxylate water reducing agent, preparation method thereof, fixed bed reaction device and preparation system

Abstract

The application discloses a polycarboxylic acid water reducing agent and a preparation method and a fixed bed reaction device and a preparation system thereof. The fixed bed reaction device comprises a first feeding channel, a multi-layer plate structure and a discharging channel arranged in sequence along a specified direction, and the first feeding channel is used for conveying reaction monomers to the multi-layer plate structure; and a plurality of second feeding channels are further arranged and used for conveying reaction aids to the overflow surface of the laminar flow plate, wherein the reaction aids comprise an initiator and a chain transfer agent. The fixed bed reaction device, the system and the preparation method provided by the application avoid the polymerization explosion phenomenon in the preparation reaction process of the polycarboxylic acid water reducing agent by the specific feeding arrangement of the reaction aids, avoid the axial back mixing while retaining the beneficial effect of the radial mass transfer, and thus can improve the preparation efficiency of the polycarboxylic acid water reducing agent, save energy, and maintain the excellent use performance of the polycarboxylic acid water reducing agent.

Description

Technical Field

[0001] This invention relates to the field of concrete admixtures, and in particular to a polycarboxylate superplasticizer and its preparation method, fixed-bed reaction apparatus, and preparation system. Background Technology

[0002] In actual construction projects, admixtures are usually added to concrete to ensure its overall quality. High-performance water-reducing agents, as a commonly used admixture, can reduce the amount of mixing water used under flowing concrete conditions, improve the workability of aggregates such as cement, and enhance the strength and lifespan of concrete.

[0003] New high-performance water-reducing agents, represented by polycarboxylate superplasticizers, have the advantages of low dosage, high water reduction, green environmental protection, controllable molecular structure, good dispersibility, high slump retention and low shrinkage of hardened concrete compared with traditional water-reducing agents. Therefore, they are widely used in the construction of infrastructure such as railways, highways and bridges.

[0004] However, fluctuations in the quality of concrete raw materials present challenges in transportation and plasticity maintenance during construction. These issues can be mitigated by altering the type and quantity of monomers. Adding monomers with phosphate groups to synthesize polycarboxylate superplasticizers can promote the interaction between cement particles and the superplasticizer, while simultaneously improving the water retention of the cement paste.

[0005] Traditionally, the production of polycarboxylate superplasticizers has primarily been carried out in batch reactors. These reactors typically require mechanical stirring to ensure sufficient material exchange, resulting in high energy consumption. Furthermore, backmixing caused by stirring occurs in such reactors, leading to uneven reaction rate distribution and reduced conversion rate. This backmixing also negatively impacts the reaction process and ultimately affects the performance of the polycarboxylate superplasticizer.

[0006] In contrast, fixed-bed reactors have less backmixing and higher production efficiency, and have great potential in the field of high-efficiency polycarboxylate production. However, the inventors of this invention have found that there are two obstacles to the application of this reactor in the production reaction of polycarboxylate superplasticizers. Specifically: (1) If the fixed-bed reactor adopts the conventional fixed-bed reaction method, it is easy to produce explosive polymerization; (2) Although axial backmixing is not good for the reaction, radial mass transfer is very important for free radical polymerization reactions with initiators. However, the conventional fixed-bed reactor in the prior art is difficult to meet this condition.

[0007] Therefore, it is of great significance and necessity to design and develop a dedicated fixed-bed reactor for polycarboxylate superplasticizers, based on their reaction characteristics, to achieve efficient production and preparation of polycarboxylate superplasticizers, and at the same time improve their performance. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the present invention aims to provide a polycarboxylate superplasticizer, its preparation method, a fixed-bed reaction apparatus, and a preparation system.

[0009] To achieve the aforementioned objectives, the technical solution adopted by this invention includes:

[0010] In a first aspect, the present invention provides a fixed-bed reaction apparatus for preparing polycarboxylate superplasticizer, comprising: a first feed channel, a multilayer plate structure, and a discharge channel arranged sequentially along a specified direction, wherein the first feed channel is used to feed the reaction monomers to the multilayer plate structure, and the multilayer plate structure includes a plurality of laminar flow plates arranged along the specified direction;

[0011] It also includes multiple second feed channels for conveying reaction aids to the overflow surface of the laminar flow plate, the reaction aids including initiators and chain transfer agents.

[0012] In a second aspect, the present invention also provides a reaction system for preparing polycarboxylate superplasticizer, comprising a first feeding device, a second feeding device, the above-mentioned fixed-bed reaction device, and a discharge device;

[0013] The first feeding device is connected to the first feeding channel of the fixed bed reactor and is used to feed the reactants into the first feeding channel.

[0014] The second feeding device is connected to the second feeding channel of the fixed bed reactor and is used to feed the reaction aid into the second feeding channel;

[0015] The discharge device is connected to the discharge channel of the fixed-bed reactor and is used to output the polycarboxylate superplasticizer produced by the reaction.

[0016] Thirdly, the present invention also provides a method for preparing a polycarboxylate superplasticizer, which is carried out using the above-mentioned fixed-bed reactor, the preparation method comprising:

[0017] The reactants are made to flow sequentially through multiple laminar flow plates in a multi-layer plate structure from the first feed channel in a specified direction to form multiple reaction liquid layers.

[0018] The reaction aids are fed into multiple reaction liquid layers through multiple second feed channels to form a continuous reaction system and continuously carry out the polymerization reaction to obtain polycarboxylate superplasticizer.

[0019] Fourthly, the present invention also provides a polycarboxylate superplasticizer product prepared by the above preparation method.

[0020] Based on the above technical solution, compared with the prior art, the beneficial effects of the present invention include:

[0021] The fixed-bed reaction apparatus, system, and preparation method provided by this invention avoid the explosive polymerization phenomenon in the conventional fixed-bed polycarboxylate superplasticizer preparation process by using specific reaction aid feeding settings. While avoiding axial backmixing, it retains the beneficial effect of radial mass transfer. Thus, on the one hand, it can improve the preparation efficiency of polycarboxylate superplasticizer and save energy, and on the other hand, it maintains the excellent performance of the obtained polycarboxylate superplasticizer.

[0022] The above description is merely an overview of the technical solution of the present invention. In order to enable those skilled in the art to better understand the technical means of this application and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described below in conjunction with detailed drawings. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the reaction system for preparing polycarboxylate superplasticizer provided in a typical embodiment of the present invention;

[0024] Explanation of reference numerals in the attached drawings: 1. Stirred vessel; 2. Interleaved valve; 3. Feed pump; 4. First feed channel; 5. Fixed bed shell; 6. Second feed channel; 7. Flow meter; 8. Valve; 9. Initiator storage tank; 10. Chain transfer agent storage tank; 11. Laminar flow plate; 12. Discharge channel; 13. Neutralization reactor; 14. Product storage tank. Detailed Implementation

[0025] In view of the shortcomings of the prior art, the inventors of this invention, through long-term research and extensive practice, have proposed the technical solution of this invention. The following will further explain and illustrate this technical solution, its implementation process, and its principles.

[0026] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0027] Moreover, relational terms such as “first” and “second” are used merely to distinguish one component or method step from another that has the same name, and do not necessarily require or imply any such actual relationship or order between these components or method steps.

[0028] See Figure 1This invention provides a fixed-bed reaction apparatus for preparing polycarboxylate superplasticizers, comprising: a first feed channel 4, a multilayer plate structure, and a discharge channel 12 arranged sequentially along a specified direction. The first feed channel 4 is used to feed reaction monomers into the multilayer plate structure, which includes a plurality of laminar flow plates 11 arranged along the specified direction. The apparatus also includes a plurality of second feed channels 6, which are used to feed reaction aids into the overflow surface of the laminar flow plates 11. The reaction aids include initiators and chain transfer agents.

[0029] The specified direction is usually the overall direction of material movement during use, that is, from the first feed channel 4 to the discharge channel 12. However, in actual use, the specified direction is usually perpendicular to the ground and downwards. However, due to differences in manufacturing, transportation, maintenance and debugging, the specified direction of the fixed bed reactor may change, for example, it may be placed horizontally or at an angle.

[0030] The second material channel 6 can be equipped with separate pipelines for the initiator and the chain transfer agent, allowing for independent feeding to achieve optimal control. Alternatively, the materials can be fed through a single main pipeline, achieving the same technical effect.

[0031] The main principle of the reaction apparatus and corresponding preparation method provided by the present invention is to controllably and dispersedly pump reaction aids into different reaction stages on multiple laminar flow plates 11 through the second feed channel 6, thereby controlling the reaction process in a fixed bed. This avoids the disadvantages of axial backmixing while retaining the beneficial effect of radial mass transfer, thus forming an efficient, stable and controllable reaction system, thereby achieving high efficiency in preparation and excellent performance of the product.

[0032] The axial backmixing refers to the mixing phenomenon caused by uneven reaction rates in a continuous process. This effect affects the material concentration distribution and residence time distribution of the reaction system. The radial mass transfer refers to the mass transfer process that occurs radially due to uneven substance concentration. This phenomenon affects the radial convection and diffusion process of the fluid, thereby increasing the radial concentration distribution of reactants and thus benefiting the efficiency, stability, and controllability of the reaction.

[0033] In some embodiments, the outlet of the second feed channel 6 may be located in the middle of the laminar flow plate 11; the middle part is, for example, a portion within half of the radial diameter, or an equivalent portion of that region, so that the pumped reaction aid can diffuse in all directions within the laminar flow plate 11.

[0034] In some implementations, the outlet of the second feed channel 6 may be located on the axis of the fixed bed reactor.

[0035] In some implementations, the edge of the laminar flow plate 11 is provided with an overflow weir, the height of which can be 40-60mm.

[0036] In some embodiments, the radial width of the fixed-bed reactor can be 25-30 cm and the height can be 25-50 cm.

[0037] In some implementations, the number of laminar flow plates 11 in the multilayer plate structure can be 10-20.

[0038] Of course, the dimensions and numbers mentioned above are merely convenient choices adopted by this invention for facilitating experiments and verification. In this field, the reaction equipment used naturally increases progressively from small-scale to pilot-scale to mass production. Clearly, the key technical means provided by this invention lies in the specific reactor structure, rather than being limited to the reactor dimensions and other parameters of the specific disclosed examples. Based on the above structure, those skilled in the art, using existing knowledge in the chemical industry, can adaptively increase the reactor size to obtain greater production capacity; this is a conventional technical approach and will not significantly affect the reaction results.

[0039] See also Figure 1 This invention also provides a reaction system for preparing polycarboxylate superplasticizer, including a first feeding device, a second feeding device, a fixed-bed reactor provided in any of the above embodiments, and a discharge device; the first feeding device is connected to the first feeding channel 4 of the fixed-bed reactor and is used to feed the reaction monomer into the first feeding channel 4; the second feeding device is connected to the second feeding channel 6 of the fixed-bed reactor and is used to feed the reaction aid into the second feeding channel 6; the discharge device is connected to the discharge channel 12 of the fixed-bed reactor and is used to output the polycarboxylate superplasticizer obtained by the reaction.

[0040] In some embodiments, the discharge device may include a neutralization reactor 13, which is connected to the discharge channel 12 and is used to terminate the chain growth reaction.

[0041] This invention also provides a method for preparing a polycarboxylate superplasticizer, which is carried out using the fixed-bed reactor provided in any of the above embodiments. The preparation method includes:

[0042] The reactant monomers flow sequentially through multiple laminar flow plates 11 in the multilayer plate structure along the first feed channel 4 in a specified direction to form multiple reaction liquid layers.

[0043] The reaction aids are fed from multiple second feed channels 6 to multiple reaction liquid layers to form a continuous reaction system and continuously carry out the polymerization reaction to obtain polycarboxylate superplasticizer.

[0044] In some implementations, the preparation method may specifically include:

[0045] After the polymerization reaction, a copolymer solution is obtained, and after chain termination treatment, the polycarboxylate superplasticizer is obtained.

[0046] In some implementations, the chain termination process is carried out by acid-base neutralization.

[0047] As some typical application examples of the above technical solutions, specific implementation cases of the present invention provide a fixed-bed reaction device and process for producing polycarboxylate superplasticizers, which can realize the rapid and continuous production of high-performance polycarboxylate superplasticizers.

[0048] Continue as Figure 1 As shown, the fixed-bed reactor and process described herein have the following flow and steps:

[0049] 1) First, the polyether macromonomer, phosphate monomer, and small molecule monomer are mixed in a stirred tank 1. Then, the mixed solution is pumped into the fixed bed from the first feed channel 4 at the top of the fixed bed reactor through a flow valve 2 and a feed pump 3. 2) The initiator and chain transfer agent are pumped into the laminar flow plate 11 from the second feed channel 6 on the side of the fixed bed. 3) The monomers, initiator, and chain transfer agent remain on the laminar flow plate 11 at a specified reaction temperature for a certain time, undergoing radial diffusion and mass transfer. The liquid flows horizontally across the laminar flow plate 11 and flows into the next laminar flow plate 11 through a downcomer. The copolymer solution of the monomers is obtained at the discharge channel 12 at the bottom of the reactor. 4) An alkaline solution is added for neutralization to terminate chain growth, resulting in a polycarboxylate superplasticizer for concrete pouring. To achieve continuous processing, the specific implementation of this invention adopts the "one-use, two-standby" principle, such as... Figure 1 As shown, when the monomer solution is pumped into the fixed-bed reactor from the first stirred tank 1, the monomers in the other two stirred tanks 1 are mixed. Since the monomer concentration decreases as the laminar flow plate 11 increases (from top to bottom) during the polymerization reaction in the fixed bed, the feed rate of the additive is controlled by a valve to prevent the polymerization reaction from being caused by excessively high additive concentration. In order to achieve continuous reaction process and reduce operating errors, two neutralization reactors 13 are placed in the discharge channel 12 in this invention.

[0050] Of course, it is understandable that the structure of the above-mentioned fixed-bed reactor can be set in the fixed-bed shell 5 like a conventional reactor. Each second feed channel is equipped with flow meters 7 and 8 to control the pumping flow rate of each layer. The initiator and chain transfer agent can be stored in the initiator storage tank 9 and the chain transfer agent storage tank 10 respectively, or they can be directly mixed and stored in a single storage tank. The final product obtained can be directly transported to other equipment or containers, or it can be temporarily stored in the product storage tank 14. These specific embodiments are all conventional choices in the art, and even if not fully described herein, these details should not limit the scope of protection of the present invention.

[0051] Specifically, in the fixed-bed reactor of the process steps, the liquid overflow method in the plate-type fixed bed can be one of U-shaped flow, single overflow, and double overflow, and the height of the overflow weir can be 40-60mm. The diameter of the fixed-bed reactor can be 25-30cm. The height of the fixed-bed reactor can be 25-50cm.

[0052] In some very specific and preferred embodiments, the overflow method can be, for example, a single overflow with an overflow weir height of 50 mm; and preferably, the reactor has a diameter of 30 cm and a height of 50 cm.

[0053] The polyether monomer in step 2) can be one or more of polyethylene glycol monomethyl ether, allyl polyoxyethylene ether, and methyl alkenyl polyoxyethylene ether, and the phosphate monomer includes one or more of dicalcium phosphate, tricalcium phosphate, and hydroxyethyl methyl propionate phosphate.

[0054] In some very specific and preferred embodiments, the polyether monomer is one of polyethylene glycol monomethyl ether, allyl polyoxyethylene ether, and methyl alkenyl polyoxyethylene ether, and the phosphate monomer is one of dicalcium phosphate, tricalcium phosphate, and hydroxyethyl methyl propionate phosphate.

[0055] The reaction temperature in step 3) is 50-70℃ and the material residence time is 20-50min; in some very specific and preferred embodiments, the reaction temperature is set at 50-55℃ and the material residence time is 20-40min.

[0056] The alkaline solution in step 4) is one of NaOH, KOH, Ca(OH)2, sodium alkoxide, or potassium alkoxide solution, with an alkaline solution concentration of 20%-30%, and the pH value of the neutralized solution is between 5.0 and 8.0.

[0057] In some very specific and preferred embodiments, the alkaline solution can be one of NaOH, KOH, sodium alkoxide, or potassium alkoxide solution; the concentration of the alkaline solution can be 20%-25%; and the final pH value of the neutralized polycarboxylate superplasticizer can be between 6.0 and 7.5.

[0058] It should be noted that the above-mentioned termination reaction method is only one of the more convenient methods selected in the specific embodiments of the present invention. For similar reactions, many existing technologies have been disclosed in the field. The various chain termination reaction methods and selectable ripening treatment methods and principles disclosed therein can all be applied to the preparation process of the present invention. The above-mentioned preferred termination method is only one of the methods selected in order to maintain the integrity of the technical solution of the present invention.

[0059] Therefore, it can be concluded that in some implementation schemes, the reactive monomers include polyether monomers, small molecule monomers, and optionally phosphate monomers.

[0060] In some embodiments, the polyether monomer includes any one or a combination of two or more of polyethylene glycol monomethyl ether, allyl polyoxyethylene ether, and methyl allyl polyoxyethylene ether.

[0061] In some embodiments, the phosphate monomer includes any one or a combination of two or more of dicalcium phosphate, tricalcium phosphate, and hydroxyethyl methacrylate phosphate.

[0062] In some embodiments, the hydroxyethyl acrylate, hydroxypropyl acrylate, and acrylic acid are any one or a combination of two or more of them.

[0063] It should be noted that the main inventive concept of this invention lies in the influence of a specially designed fixed-bed reaction device on the synthesis process of polycarboxylate superplasticizer. The specific raw materials involved are commonly found in various existing technologies and are not limited to the material selections in the specific examples above. Any method for preparing polycarboxylate superplasticizer based on the same or similar reactants / reaction principles, as long as it uses the overall concept of the device structure and preparation method provided by this invention, including at least the distributed addition of reaction aids, can achieve the corresponding technical effects and is also within the protection scope of this invention.

[0064] In some embodiments, the polymerization reaction is carried out at a temperature of 50-70°C, preferably 50-55°C, for a time of 20-50 min, preferably 20-40 min.

[0065] In some embodiments, the polymerization reaction is preferably carried out at a temperature of 50-55°C and for a time of 20-40 minutes.

[0066] In some embodiments, the flow rate ratio of the reactant to the reaction auxiliaries is 100:5-15.

[0067] In some embodiments, the flow rate of the reaction aid corresponding to each of the reaction liquid layers has a decreasing trend along the specified direction.

[0068] In some embodiments, the flow rate of the reaction aid corresponding to each reaction liquid layer decreases by 1-10%.

[0069] Through long-term practice, the inventors of this invention have discovered that the reaction environment of each laminar flow plate 11 is different. Along the specified direction from top to bottom, the concentration of monomer gradually decreases. Therefore, in order to prevent excessive polymerization caused by excessive concentration of additives in the polymerization reaction and to obtain a suitable reaction environment, the pumping amount of initiator and chain transfer agent should preferably be adaptively adjusted. Thus, through long-term practice and experimental summary, the inventors of this invention were able to propose the above-mentioned empirical rules.

[0070] However, this does not mean that one must rely on the above empirical rules to test the technical effects of the present invention. The above empirical rules are further improvements based on achieving the technical effects of the present invention. Even with a uniform pump flow rate of the reaction aid, the technical means provided by the present invention can still achieve better preparation efficiency and obtain polycarboxylate superplasticizer with higher performance.

[0071] This invention also provides a polycarboxylate superplasticizer product prepared by the preparation method provided in any of the above embodiments.

[0072] In some embodiments, the sustained-release time of the polycarboxylate superplasticizer is 1.5-3 hours.

[0073] The technical solution of the present invention will be further described in detail below through several embodiments and in conjunction with the accompanying drawings. However, the selected embodiments are only for illustrating the present invention and do not limit the scope of the present invention.

[0074] Example 1

[0075] This embodiment illustrates the process of preparing polycarboxylate superplasticizer and the fixed-bed reactor used, as detailed below:

[0076] This embodiment uses the fixed-bed reactor described in this invention for preparation, and its structure is as follows: Figure 1 As shown in the preferred embodiment above, its diameter is 30cm, its height is 50cm, the spacing between the laminar flow plates 11 is 4cm, there are a total of 10 layers, and the overflow weir height of the laminar flow plates 11 is 50mm.

[0077] Prepare a total of 20 kg of polyether monomer (methyl allyl polyoxyethylene ether 2400), phosphate monomer (hydroxyethyl methacrylate phosphate), and small molecule monomer (acrylic acid), including 16 kg of polyether monomer, 2 kg of phosphate monomer, 2 kg of small molecule monomer, 1.5 kg of initiator (hydrogen peroxide, vitamin) and 0.09 kg of chain transfer agent (mercaptoethanol), 25 kg of water, and 1 kg of alkaline solution.

[0078] The preparation process is as follows: The pre-mixed monomers are pumped into the fixed bed reactor through the first feed channel 4 at the top. The temperature inside the fixed bed reactor is maintained at 50°C. After stabilization, the pre-prepared initiator and chain transfer agent are pumped into the fixed bed laminar flow plate 11 through the second feed channel 6 on the side. The monomer flow rate is controlled so that the reaction time in the reactor is 40 minutes. The concentration of each material and the flow rate after mixing are configured according to the above mass ratio. The copolymerized solution is released from the discharge channel 12 at the bottom of the reactor and matured for 30 minutes. Then, an alkaline solution is added for neutralization. After stabilization, a slow-release polycarboxylate superplasticizer product is obtained.

[0079] Example 2

[0080] This embodiment illustrates the process of preparing polycarboxylate superplasticizer and the fixed-bed reactor used, as detailed below:

[0081] Using the same fixed-bed reactor as in Example 1 described in this invention, 20 kg of polyether monomer (methyl allyl polyoxyethylene ether 2400) and small molecule monomer (acrylic acid) were prepared, including 18 kg of polyether monomer, 2 kg of small molecule monomer, 1.5 kg of initiator (hydrogen peroxide and vitamin) and 0.09 kg of chain transfer agent (mercaptoethanol), 25 kg of water, and 1 kg of alkaline solution.

[0082] The preparation process is as follows: The pre-mixed monomers are pumped into the fixed bed reactor from the top feed port. The temperature inside the fixed bed reactor is maintained at 50°C. After stabilization, the pre-prepared initiator and chain transfer agent are pumped into the fixed bed laminar flow plate 11 from the side feed port. The reaction time is 40 minutes. The concentration of each material and the flow rate after mixing are configured according to the above mass ratio. The copolymerized solution is released from the discharge channel 12 at the bottom of the reactor and matured for 30 minutes. Then, an alkaline solution is added for neutralization. After stabilization, a slow-release polycarboxylate superplasticizer is obtained.

[0083] Example 3

[0084] This embodiment illustrates the process of preparing polycarboxylate superplasticizer and the fixed-bed reactor used, as detailed below:

[0085] Using the same fixed-bed reactor as in Example 1, a total of 20 kg of polyether monomer (methyl allyl polyoxyethylene ether 2400), phosphate monomer (hydroxyethyl methacrylate phosphate), and small molecule monomer (acrylic acid) was prepared, including 16 kg of polyether monomer, 2 kg of phosphate monomer, 2 kg of small molecule monomer, 1.5 kg of initiator (hydrogen peroxide and vitamin) and 0.09 kg of chain transfer agent (mercaptoethanol), 25 kg of water, and 1 kg of alkaline solution.

[0086] The preparation process is as follows: The pre-mixed monomers are pumped into the fixed bed reactor from the top feed port. The temperature inside the fixed bed reactor is maintained at 50°C. After stabilization, the pre-prepared initiator and chain transfer agent are pumped into the fixed bed laminar flow plate 11 from the side feed port. The reaction time is 20 minutes. The concentration of each material and the flow rate after mixing are configured according to the above mass ratio. The copolymerized solution is released from the discharge channel 12 at the bottom of the reactor and matured for 30 minutes. Then, an alkaline solution is added for neutralization. After stabilization, a slow-release polycarboxylate superplasticizer is obtained.

[0087] Example 4

[0088] Using the fixed-bed reactor described in this invention, a total of 20 kg of polyether monomer (methyl allyl polyoxyethylene ether 2400), phosphate monomer (hydroxyethyl methacrylate phosphate), and small molecule monomer (acrylic acid) were prepared, including 16 kg of polyether monomer, 2 kg of phosphate monomer, 2 kg of small molecule monomer, 1.5 kg of initiator (hydrogen peroxide and vitamin) and 0.09 kg of chain transfer agent (mercaptoethanol), 25 kg of water, and 1 kg of alkaline solution.

[0089] The preparation process is as follows: The pre-mixed monomers are pumped into the fixed bed reactor from the top feed port. The temperature inside the fixed bed reactor is maintained at 50°C. After stabilization, the pre-prepared initiator and chain transfer agent are pumped into the fixed bed laminar flow plate 11 from the side feed port. The reaction time is 30 minutes. The concentration of each material and the flow rate after mixing are configured according to the above mass ratio. The copolymerized solution is released from the discharge channel 12 at the bottom of the reactor and matured for 30 minutes. Then, an alkaline solution is added for neutralization. After stabilization, a slow-release polycarboxylate superplasticizer is obtained.

[0090] Example 5

[0091] The process for preparing polycarboxylate superplasticizer and the fixed-bed reactor used in Example 1 of this embodiment are largely the same as those in Example 2, with the only difference being:

[0092] Unlike Examples 1-4, where the flow rate of the initiator and chain transfer agent mixture was consistent for each layer, in this example, the pumping rate of the initiator and chain transfer agent mixture decreased from top to bottom for each layer, with a decrease rate of 5%.

[0093] Using the same preparation process and equipment with identical raw materials and reaction conditions, a slow-release polycarboxylate superplasticizer was finally obtained.

[0094] Example 6

[0095] The process for preparing polycarboxylate superplasticizer and the fixed-bed reactor used in Example 1 of this embodiment are largely the same as those in Example 5, with the only difference being:

[0096] The macromonomer used in this experiment is polyethylene glycol monomethyl ether, with a molecular weight of 2000.

[0097] Using the same preparation process and equipment with identical raw materials and reaction conditions, a slow-release polycarboxylate superplasticizer was finally obtained.

[0098] Example 7

[0099] The process for preparing polycarboxylate superplasticizer and the fixed-bed reactor used in Example 1 of this embodiment are largely the same as those in Example 5, with the only difference being:

[0100] The small molecule monomer used in this experiment is hydroxyethyl acrylate.

[0101] Using the same preparation process and equipment with identical raw materials and reaction conditions, a slow-release polycarboxylate superplasticizer was finally obtained.

[0102] Comparative Example 1

[0103] The preparation process of a traditional polycarboxylate superplasticizer in this comparative example is shown below:

[0104] Using a conventional batch reactor, prepare the same polyether monomer, phosphate monomer, and small molecule monomer as in Example 1, totaling 20 kg, including 16 kg of polyether monomer, 2 kg of phosphate monomer, 2 kg of small molecule monomer, 1.5 kg of initiator and 0.09 kg of chain transfer agent, 25 kg of water, and 1 kg of alkaline solution.

[0105] The preparation process is as follows: The monomer is added into the kettle to dissolve and stir, and the temperature is raised to 50°C. After stabilization, the pre-prepared initiator and chain transfer agent are added dropwise. The dropwise addition time is controlled at a uniform rate of 2.5h. After the dropwise addition is completed, it is cured for 1h to obtain the slow-release polycarboxylate superplasticizer.

[0106] Comparative Example 2

[0107] The preparation process of a traditional polycarboxylate superplasticizer in this comparative example is shown below:

[0108] Using a conventional batch reactor, 20 kg of the same polyether monomer and small molecule monomer as in Example 2 were prepared, including 18 kg of polyether monomer, 2 kg of small molecule monomer, 1.5 kg of initiator and 0.09 kg of chain transfer agent, 25 kg of water, and 1 kg of alkaline solution.

[0109] The preparation process is as follows: The monomer is added into the kettle to dissolve and stir, and the temperature is raised to 50°C. After stabilization, the pre-prepared initiator and chain transfer agent are added dropwise. The dropwise addition time is controlled at a uniform rate of 2.5h. After the dropwise addition is completed, it is cured for 1h to obtain the slow-release polycarboxylate superplasticizer.

[0110] Comparative Example 3

[0111] This comparative example demonstrates the preparation process of polycarboxylate superplasticizer using an existing fixed-bed reactor, as detailed below:

[0112] Similar to Example 1, except that equal amounts of monomer, initiator and chain transfer agent are directly mixed evenly in stirred tank 1 before being introduced into a fixed-bed reactor with the same structure.

[0113] During the above preparation process, explosive polymerization is very likely to occur, which manifests as a rapid increase in temperature inside the reaction device that is difficult to control, ultimately leading to preparation failure and the inability to obtain a suitable product.

[0114] Comparative Example 4

[0115] This comparative example demonstrates the preparation process of polycarboxylate superplasticizer using an existing fixed-bed reactor, as detailed below:

[0116] Similar to Example 1, except that the mixture of initiator and chain transfer agent is introduced into the uppermost laminar flow plate 11 at the same total flow rate as in Example 1, and the other laminar flow plates 11 receive the reaction liquid flowing down from the upper laminar flow plate 11.

[0117] Although this implementation method does not mix the monomer and reaction aid in the initial stage as in Comparative Example 3, the concentration of the reaction aid in each layer is still much higher than in the implementation method of Example 1.

[0118] During the above preparation process, explosive polymerization is still prone to occur, which manifests as a significant increase in temperature within the reaction device that cannot be controlled within a reasonable range, ultimately leading to preparation failure and the inability to obtain a suitable product.

[0119] The polycarboxylate superplasticizers obtained in the above-mentioned embodiments and comparative examples were tested for their performance in use, specifically as follows:

[0120] The cement paste test was conducted in accordance with the national standard GB / T 8077-2000 "Test Method for Homogeneity of Concrete Admixtures". The test used Conch P·042.5 cement, polycarboxylate superplasticizer prepared in the comparative example, 300g cement and 87g water. The superplasticizer used in the experiment was added in equal amounts.

[0121] The cement concrete test was conducted according to GB / T50080-2002 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures". The concrete used was Conch P·042.5 cement; crushed stone particle size 5-25mm; river sand: fineness modulus 2.7; manufactured sand: mud content 5%; fly ash: Grade II. The polycarboxylate superplasticizer products in the comparative examples were tested using a concrete mixer. The concrete mix proportions used were: cement: river sand: manufactured sand: large aggregate: fly ash: water: superplasticizer = 220:360:360:1050:100:160:4

[0122] The experimental data obtained are as follows:

[0123] Table 1 Comparison of the results of polycarboxylate superplasticizer paste under different test parameters

[0124]

[0125]

[0126] Table 2 Comparison of concrete test results for polycarboxylate superplasticizer under different test conditions

[0127]

[0128] As can be seen from Tables 1 and 2, under the same preparation conditions, the addition of phosphate monomer can effectively improve the slow-release performance of polycarboxylate superplasticizer, giving the superplasticizer a slower release rate, and the concrete still has good fluidity after 3 hours.

[0129] Under the same conditions of reactants and reaction parameters, the fixed-bed reactor has a shorter reaction time and is easier to operate than the traditional batch reactor. Moreover, within a suitable reaction time, the polycarboxylate superplasticizer obtained by the fixed-bed reactor can have the same structural function as that prepared by the traditional method, which can greatly improve production efficiency, reduce production costs, and, due to fewer side reactions, the compressive strength of the concrete obtained will be slightly better.

[0130] Furthermore, the reaction apparatus, system, and preparation method provided by this invention overcome the problem that existing fixed-bed reaction apparatuses cannot be directly applied to the preparation of polycarboxylate superplasticizer products.

[0131] Furthermore, in a more optimized implementation, by setting the flow rate of the reaction aid to decrease proportionally, specifically, for example, around 5%, or even 4-6%, a better sustained-release performance is achieved. This is likely due to the effect of adapting the amount of reaction aid introduced into each layer to the changes in the reaction environment within each layer.

[0132] It should be understood that the above embodiments are merely illustrative of the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a polycarboxylate superplasticizer, characterized in that, The preparation is carried out using a fixed-bed reactor, which includes: a first feed channel, a multilayer plate structure, and a discharge channel arranged sequentially along a specified direction. The first feed channel is used to feed the reactant monomers into the multilayer plate structure. The multilayer plate structure includes multiple laminar flow plates arranged along the specified direction and also includes multiple second feed channels. The second feed channels are used to feed reaction aids into the overflow surface of the laminar flow plates. The reaction aids include initiators and chain transfer agents. The preparation method includes: The reactive monomers flow sequentially through multiple laminar flow plates in a multilayer plate structure along a designated direction from the first feed channel to form multiple reaction liquid layers. The reactive monomers include polyether monomers, monomer A, and monomer B. The polyether monomers include any one or a combination of two or more of polyethylene glycol monomethyl ether, allyl polyoxyethylene ether, and methyl alkenyl polyoxyethylene ether. Monomer A is any one or a combination of two or more of hydroxyethyl acrylate, hydroxypropyl acrylate, and acrylic acid. Monomer B is any one or a combination of two or more of dicalcium phosphate, tricalcium phosphate, and hydroxyethyl methacrylate phosphate. The reaction aids are fed into multiple reaction liquid layers through multiple second feed channels to form a continuous reaction system and continuously carry out the polymerization reaction to obtain polycarboxylate superplasticizer.

2. The preparation method according to claim 1, characterized in that, The outlet of the second feed channel is located in the middle of the laminar flow plate and on the axis of the fixed bed reactor.

3. The preparation method according to claim 1, characterized in that, An overflow weir is provided at the edge of the laminar flow plate, and the height of the overflow weir is 40-60 mm; And / or, the radial width of the fixed-bed reactor is 25-30 cm and the height is 25-50 cm; And / or, the number of laminar flow plates in the multilayer plate structure is 10-20.

4. The preparation method according to claim 1, characterized in that, The fixed-bed reactor also includes a first feeding device, a second feeding device, and a discharge device; The first feeding device is connected to the first feeding channel and is used to feed the reaction monomer into the first feeding channel; The second feeding device is connected to the second feeding channel and is used to feed the reaction aid into the second feeding channel; The discharge device is connected to the discharge channel and is used to output the polycarboxylate superplasticizer produced by the reaction.

5. The preparation method according to claim 4, characterized in that, The discharge device includes a neutralization reactor, which is connected to the discharge channel and is used to terminate the chain growth reaction.

6. The preparation method according to claim 1, characterized in that, Specifically, it includes: After the polymerization reaction, a copolymer solution is obtained. The copolymer solution is then subjected to chain termination treatment to obtain the polycarboxylate superplasticizer. The chain termination treatment is carried out by acid-base neutralization.

7. The preparation method according to claim 1, characterized in that, The polymerization reaction is carried out at a temperature of 50-70℃ for a time of 20-50 min. The mass flow ratio of the reactant to the reaction auxiliaries is 100:5-15.

8. The preparation method according to claim 7, characterized in that, The polymerization reaction is carried out at a temperature of 50-55℃ for a time of 20-40 min.

9. The preparation method according to claim 1, characterized in that, The flow rate of the reaction aid corresponding to each reaction liquid layer has a decreasing trend along the specified direction, with a decreasing ratio of 1-10%.

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