High-solid-content polycarboxylate superplasticizer and preparation method thereof

Abstract

The invention provides a high-solid-content polycarboxylic acid water reducing agent and a preparation method thereof, and belongs to the field of water reducing agent preparation.The preparation method comprises the steps that the pH value of a polycarboxylic acid water reducing agent mother solution is adjusted to range from 4 to 5.2, inorganic salt is added under the constant-temperature stirring condition to achieve phase separation, standing layering and centrifugal treatment, an obtained enriched phase is subjected to vacuum evaporation concentration, and the high-solid-content polycarboxylic acid water reducing agent is obtained. Compared with the prior art, the polycarboxylate superplasticizer with the required solid content is prepared by performing phase separation process treatment on the polycarboxylate superplasticizer with the low solid content. Effective separation of effective components and water is achieved, loss of product mass is reduced, energy consumption in the production process is reduced, and the method can be suitable for industrial large-scale production. In addition, the prepared polycarboxylic acid water reducer has good water reducing and slump retaining properties and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of water reducing agent preparation, and particularly relates to a high solid content polycarboxylic acid water reducing agent and a preparation method thereof. BACKGROUND

[0002] As the representative of the third generation of high-performance water reducing agent, polycarboxylic acid water reducing agent has become the core component of modern concrete technology due to its strong designability of molecular structure, high water reducing rate and environmental friendliness. With the development of infrastructure engineering towards super high-rise and large-span structures, the market puts forward higher requirements for the dispersion retention, adaptability and transportation economy of water reducing agents. Among them, high solid content mother liquor (solid content ≥ 60%) has become the focus of the industry due to its advantages of high effective ingredient per unit volume, low transportation cost and strong flexibility of compounding. In addition, the tightening of environmental protection policies promotes the upgrading of production process towards low solvent, and the preparation technology of high solid content becomes the key path to realize green manufacturing.

[0003] At present, the methods for improving the solid content of polycarboxylic acid water reducing agent include the following:

[0004] The first method is based on the post-treatment process of low solid content polycarboxylic acid water reducing agent, including evaporation concentration method, spray drying method, etc. The evaporation concentration method: by heating and evaporating part of the water, the solid content of the water reducing agent is improved. This method is relatively simple to operate, but the energy consumption is high, and the temperature needs to be strictly controlled to avoid damage to the performance of the water reducing agent due to high temperature. The spray drying method: the low solid content polycarboxylic acid water reducing agent is atomized by using a spray drying device and then dried in a drying tower to obtain a high solid content product. This method is mature in technology and the product is widely used, but the energy consumption is high, and the material is easy to hang on the wall and burn during the drying process.

[0005] The second method is the bulk polymerization process for directly synthesizing high solid content polycarboxylic acid water reducing agent, including bulk polymerization (ester type water reducing agent), in-situ polymerization grafting method, etc. The bulk polymerization (ester type water reducing agent): the bulk polymerization of ester type water reducing agent needs to be reacted at high temperature, the process is simple, but the reaction control is difficult, which easily leads to local overheating and causes polymerization explosion, affecting the uniformity of the molecular weight distribution of the product, and the equipment requirement is high and the application flexibility is insufficient. The in-situ polymerization grafting method: the polyether is used as the reaction medium of carboxylic acid unsaturated monomer, and the side chain is introduced during the polymerization of the monomer, so as to directly prepare high solid content polycarboxylic acid water reducing agent. This method can control the molecular weight of the polymer, and the process is relatively simple, but the grafting degree is not high and difficult to control, and the polyether is difficult to separate, which is currently mainly in the laboratory research stage.

[0006] Compared with the first method, the second method has greater limitations, and the in-situ polymerization grafting method is still in the laboratory research stage and cannot meet the industrial production.

[0007] Therefore, providing a high solid content polycarboxylic acid water reducer method capable of being used in industrial production and reducing energy consumption is a problem to be solved at present. SUMMARY

[0008] The present application aims to provide a high solid content polycarboxylic acid water reducer and a preparation method thereof, which improves the solid content of the polycarboxylic acid water reducer through a phase separation post-processing process of a low solid content polycarboxylic acid water reducer (ether type), realizes effective separation of the active ingredient and water, thereby reducing the loss of the product quality itself and reducing the energy consumption in the production process, and can be applied to industrial mass production. Moreover, the prepared polycarboxylic acid water reducer has good water-reducing and slump-retaining performance, and meets the use requirements.

[0009] The specific technical scheme of the present application is as follows:

[0010] A preparation method of a high solid content polycarboxylic acid water reducer, comprising the following steps:

[0011] The pH value of the polycarboxylic acid water reducer mother liquor is adjusted to 4-5.2, inorganic salt is added to realize phase separation under constant temperature stirring conditions, and then the mixture is left to stand and stratify, followed by centrifugal treatment. The obtained enriched phase is concentrated by vacuum evaporation to obtain the high solid content polycarboxylic acid water reducer.

[0012] The solid content of the polycarboxylic acid water reducer mother liquor is 60%;

[0013] The preparation method of the polycarboxylic acid water reducer mother liquor is as follows: ethylene glycol monovinyl polyoxyethylene ether (EPEG) and acrylic acid (AA) are used as comonomers, a composite redox initiation system composed of hydrogen peroxide (H2O2) and sodium sulfite is used, sodium hypophosphite (NaH2PO2) is used as a chain transfer agent, and a polycarboxylic acid water reducer with a solid content of 60% is prepared at 15-20℃.

[0014] Preferably, the preparation method of the polycarboxylic acid water reducer mother liquor is as follows:

[0015] According to mass parts, 10 parts of acrylic acid, 360 parts of ethylene glycol monovinyl polyoxyethylene ether and 200 parts of water are added to a reaction container and fully mixed and dissolved, then 3 parts of sodium hypophosphite, 3.0 parts of hydrogen peroxide and 0.01 parts of a catalyst ferrous sulfate are added. The reaction temperature in the reaction container is maintained at 15-20℃, and within 1 hour, A mixed solution obtained by mixing 0.5 parts of formaldehyde and 30 parts of sodium bisulfite and water is added dropwise, and B mixed solution obtained by mixing 30 parts of acrylic acid and 20 parts of water is also added dropwise. After the dropwise addition of the A mixed solution and the B mixed solution is completed, the reaction is continued for 1.0 hour. After the reaction is completed, the polycarboxylic acid water reducer mother liquor is obtained, which is a polycarboxylic acid water reducer with a solid content of 60%.

[0016] The inorganic salt is selected from one or more of sodium sulfate, sodium chloride, ammonium sulfate, preferably a compound salt of sodium sulfate and sodium chloride, or a compound salt of sodium sulfate and ammonium sulfate, or a compound salt of sodium sulfate, sodium chloride and ammonium sulfate; more preferably a compound salt of sodium sulfate, sodium chloride and ammonium sulfate, with a mass ratio of 1:1:1-3:1:2;

[0017] The polycarboxylic acid water reducing agent mother liquor is adjusted to a pH value of 4-5.2, and a 30wt% mass concentration of sodium hydroxide solution is used to adjust the pH value; preferably, the pH value is controlled within ±0.5 of the isoelectric point of the polycarboxylic acid.

[0018] When the pH value of the reaction system is maintained between 4 and 5.2, the inorganic salt is added under constant temperature stirring conditions to achieve phase separation, and the constant temperature and the salt concentration satisfy the following relationship:

[0019] When the pH value is maintained between 4 and 5.2, and the system constant temperature is 40℃≤T≤50℃, the salt concentration C_salt≤25wt%;

[0020] When the pH value is maintained between 4 and 5.2, and the system constant temperature is 50℃

[0021] Wherein T is the constant temperature of the system, unit is ℃, C_salt is the salt concentration (wt%). The amount of inorganic salt added is controlled by the salt concentration, which is the mass percentage of the mass of inorganic salt and the total mass of the mixed system. The constant temperature controlled by the present application is 40℃-60℃.

[0022] The principle of this idea: pH is a necessary condition to achieve the above balance: stable charge protection layer, maintain pH at 4.0-5.2, ensure that the polycarboxylic acid chain is fully ionized (-COO-), form a strong electrostatic repulsion barrier. This barrier can effectively resist the charge shielding effect caused by high salt concentration (C_salt) and the molecular chain collision intensified by high temperature (T), preventing aggregation / precipitation. The relationship between temperature and salt concentration is obtained through test results, and the main principle is that high ionic strength leads to molecular diffusion difficulty, which requires increasing temperature to accelerate the reaction.

[0023] The inorganic salt is added under constant temperature stirring conditions to achieve phase separation, and the stirring rate is 200-800rpm;

[0024] Further, the amount of inorganic salt added is controlled to make the viscosity of the system reach 1.5-2.0 times the viscosity of the polycarboxylic acid water reducing agent mother liquor;

[0025] Preferably, the inorganic salt is added in batches or in a pulse manner, preferably in 5-8 batches;

[0026] Preferably, the inorganic salt is added under constant temperature stirring conditions, the stirring speed is 200 rpm when the inorganic salt is first added, and the stirring speed is increased by 50-100 rpm for every 5 wt% increase in salt concentration as the inorganic salt is added;

[0027] The inorganic salt is added in batches or in pulses, and a dynamic gradient control is adopted, specifically:

[0028] When 0 wt%≤salt concentration C_salt≤15 wt%, the amount of inorganic salt added is controlled to be low-speed linear addition, and the increase in salt concentration C_salt is controlled to be 0.6 wt% / min, i.e., the salt concentration increases by 0.6 wt% per minute; this is mainly because the salt dissolves quickly in the low concentration zone to avoid local supersaturation; and the viscosity change rate is monitored to be ≤5% / min.

[0029] When 15 wt%< salt concentration C_salt≤22 wt%, the amount of inorganic salt added is controlled to be medium-speed step addition, the increase in salt concentration C_salt is controlled to be 1.2 wt% / min, and the salt concentration C_salt is increased by 2 wt% each time, and the system uniformity is monitored.

[0030] When 22 wt%< salt concentration C_salt≤30 wt%, the amount of inorganic salt added is controlled to be ultra-low-speed pulse addition, the increase in salt concentration C_salt is controlled to be 0.2 wt% / min, and every 10 seconds of addition is followed by 20 seconds of pause to capture the viscosity inflection point in real time.

[0031] Controlling the viscosity and the salt addition rate can avoid the wrapping phenomenon caused by local supersaturation, so that the phase separation process proceeds uniformly; the main purpose is that the salt is uniformly dispersed in the mother liquor system to fully absorb the water in the mother liquor system, thereby improving its own quality, so that precipitation is realized to separate, and then the product purity and quality are improved through centrifugal evaporation and concentration.

[0032] Further, after the inorganic salt is added, the stirring is continued at 40-60°C for 30-60 minutes;

[0033] The static layering is performed at 40-60°C for 1.5±0.5 hours to form a solid-liquid two-phase system;

[0034] The centrifugal treatment is performed at 40-60°C, the centrifugal force is controlled to be 2000-5000 g, and the treatment lasts for 5-20 minutes to remove the dispersion medium;

[0035] Preferably, the centrifugal treatment is: first 2000 g centrifugal force for 5 minutes for preliminary separation, and then 4000 g centrifugal force for 5 minutes for deep dehydration.

[0036] The vacuum evaporation concentration is carried out under the conditions of-0.08 to-0.1 MPa and 60 to 70 DEG C.

[0037] The preparation method of the high solid content polycarboxylic acid water reducing agent is based on the prepared polycarboxylic acid water reducing agent, and the hydration layer around the polycarboxylic acid molecules is destroyed by adding electrolyte, the solubility is reduced, and the polymer is partially precipitated or concentrated, so that the proportion of solvent is reduced, and the solid content of the mother liquor is increased.

[0038] The high solid content polycarboxylic acid water reducing agent prepared by the method has a solid content of 70% or more, an inorganic salt residual amount of 3.5% or less, and a polycarboxylic acid precipitation rate of 78% or more.

[0039] Preferably, the high solid content polycarboxylic acid water reducing agent prepared has a solid content of 80% or more, an inorganic salt residual amount of 2.2% or less, and a polycarboxylic acid precipitation rate of 87% or more.

[0040] More preferably, the high solid content polycarboxylic acid water reducing agent prepared has a solid content of 85% or more, an inorganic salt residual amount of 1.8% or less, and a polycarboxylic acid precipitation rate of 91% or more.

[0041] Compared with the prior art, the present application prepares the polycarboxylic acid water reducing agent with the required solid content by phase separation process on the basis of traditional aqueous radical polymerization of low solid content polycarboxylic acid water reducing agent. The present application not only realizes effective separation of active ingredients and water, reduces the loss of product quality and energy consumption in the production process, and can be applied to industrial large-scale production. Moreover, the prepared polycarboxylic acid water reducing agent has good water-reducing and slump-retaining performance. DETAILED DESCRIPTION

[0042] To make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the embodiments of the present application. Obviously, the described embodiments are some embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0043] In the following examples, the test materials and reagents used, unless otherwise specified, can be obtained from commercial channels.

[0044] If the specific technology or condition is not specified in the examples, it can be carried out according to the technology or condition described in the literature in the art or according to the product instruction.

[0045] The polycarboxylic acid water reducing agent mother liquor used in each embodiment and comparative example 1 of the present application is ME250 produced by Ningbo Haisulu New Material Technology Co., Ltd., and the specific production method is as follows:

[0046] According to the mass parts, 10 parts of acrylic acid, 360 parts of ethylene glycol monovinyl polyoxyethylene ether and 200 parts of water are selected to be added into a reaction container for fully mixing and dissolving, then 3 parts of sodium hypophosphite, 3.0 parts of hydrogen peroxide and 0.01 part of catalyst ferrous sulfate are added; the reaction temperature in the reaction container is kept at 15-20°C, and within 1 hour, A mixed solution obtained by mixing 0.5 parts of sodium formaldehyde sulfoxylate and 30 parts of water is added dropwise, and B mixed solution obtained by mixing 30 parts of acrylic acid and 20 parts of water is also added dropwise; after the A mixed solution and the B mixed solution are added dropwise, the reaction is continued for 1.0 hour; after the reaction is completed, it is a polycarboxylic acid water reducing agent mother liquor, which is a 60% solid content polycarboxylic acid water reducing agent.

[0047] Example 1

[0048] A preparation method of a high solid content polycarboxylic acid water reducing agent, comprising the following steps:

[0049] 20 parts of polycarboxylic acid water reducing agent mother liquor is added to a 30%wt concentration sodium hydroxide solution to adjust the pH value of the system to 5.0; then at an ambient temperature of 40°C, sodium sulfate is added at a stirring rate of 250 rpm, and the final concentration of inorganic salt sodium sulfate is controlled to be 15wt% of the total mass of the system, and the viscosity of the system reaches 1.5-2.0 times the viscosity of the polycarboxylic acid water reducing agent mother liquor; after the addition of inorganic salt is completed, the stirring is continued at 250 rpm at an ambient temperature of 40°C for 40 minutes to complete the phase separation, and then the system is left to separate for 1 hour at 40°C. The separated phase is treated by a centrifuge at a centrifugal force of 2000g at 40°C for 15 minutes, and the enriched phase obtained is concentrated by a vacuum evaporation device at -0.08MPa and 60°C. It is detected that the solid content of the final product reaches 70%, the residual amount of inorganic salt is ≤3.5%, and the effective content of polycarboxylic acid is 78%.

[0050] Example 2

[0051] A preparation method of a high solid content polycarboxylic acid water reducing agent, comprising the following steps:

[0052] To 25 parts by mass of polycarboxylic acid-based water reducing agent mother liquor, a 30% wt concentration sodium hydroxide solution is added to adjust the pH of the system to 5.2; under constant temperature conditions of 45°C, the stirring rate is 300 rpm, and sodium chloride is added for phase separation process treatment. The final concentration of inorganic salt sodium chloride is controlled to be 20% of the total mass of the system through dynamic monitoring. The viscosity of the system reaches 1.5-2.0 times the viscosity of the polycarboxylic acid water reducing agent mother liquor. After the inorganic salt is added, the stirring is continued at 300 rpm for 45 minutes at an ambient temperature of 45°C to complete the phase separation. After the reaction is completed, the system is left to stand at 45°C for 1.5 hours to separate the layers. A centrifuge is used to treat the system at 45°C under a centrifugal force of 2500g for 15 minutes. The enriched phase is further concentrated by a vacuum evaporation device at -0.085 MPa and 62°C. After detection, the solid content of the product is increased to 75%, the residual amount of inorganic salt is reduced to ≤2.8%, and the precipitation rate of polycarboxylic acid is increased to 83%.

[0053] Example 3

[0054] A method for preparing a high solid content polycarboxylic acid water reducing agent, comprising the following steps:

[0055] To 30 parts by mass of polycarboxylic acid-based water reducing agent mother liquor, a 30% wt concentration sodium hydroxide solution is added to adjust the pH of the system to 4.8, and the value is controlled to be within ±0.3 of the isoelectric point of polycarboxylic acid. Then, under constant temperature conditions of 50°C, the stirring rate is 350 rpm, and ammonium sulfate is added for phase separation process treatment. The final concentration of inorganic salt ammonium sulfate is maintained at 25% of the total mass of the system. The viscosity of the system reaches 1.5-2.0 times the viscosity of the polycarboxylic acid water reducing agent mother liquor. After the inorganic salt ammonium sulfate is added, the stirring is continued at 350 rpm for 50 minutes at an ambient temperature of 50°C to complete the phase separation. After the reaction is completed, the system is left to stand at 50°C for 1.8 hours to separate the layers. A centrifuge is used to treat the system at 50°C under a centrifugal force of 3000g for 12 minutes. The enriched phase is further concentrated by a vacuum evaporation device at -0.09 MPa and 65°C. After detection, the solid content of the product is 80%, the residual amount of inorganic salt is ≤2.2%, and the precipitation rate of polycarboxylic acid is increased to 87%.

[0056] Example 4

[0057] A method for preparing a high solid content polycarboxylic acid water reducing agent, comprising the following steps:

[0058] To 35 parts by mass of polycarboxylic acid-based water reducing agent mother liquor, a 30%wt concentration sodium hydroxide solution is added to adjust the pH of the system to 4.5, which is 0.5 units lower than the isoelectric point of polycarboxylic acid; under constant temperature of 55°C and stirring conditions, a batch dynamic addition method is used to add a mass ratio of 3:1 of sodium sulfate and sodium chloride complex inorganic salt, so that the final concentration of inorganic salt reaches 28wt%, and the viscosity change of the system is monitored in real time, and the final system viscosity reaches 1.5-2.0 times the viscosity of the polycarboxylic acid water reducing agent mother liquor; when the inorganic salt is added, the stirring speed is 200 rpm, and as the inorganic salt is added, the stirring speed is increased by 50 rpm for every 5wt% increase in salt concentration; the salt addition rate is controlled as follows: when 0wt%≤salt concentration C_salt≤15wt%, the amount of inorganic salt added is controlled to be linearly added at low speed, and the increase of salt concentration C_salt is controlled to be 0.6wt% / min, i.e. the salt concentration increases by 0.6wt% per minute; the viscosity change rate is monitored to be≤5% / min during this process; when 15wt%<salt concentration C_salt≤22wt%, the amount of inorganic salt added is controlled to be added at medium speed in steps, the increase of salt concentration C_salt is controlled to be 1.2wt% / min, and the salt concentration C_salt is increased by 2wt% and paused for 30 seconds to monitor the uniformity of the system; when 22wt%<salt concentration C_salt≤28wt%, the amount of inorganic salt added is controlled to be added at ultralow speed in pulses, the increase of salt concentration C_salt is controlled to be 0.2wt% / min, and every 10 seconds of addition is followed by a 20-second pause, and the viscosity inflection point is captured in real time (an online rotational viscometer is used, and the viscosity-time / salt concentration curve is drawn by computer, and the inflection point is represented as a sharp rise in the curve). After the inorganic salt is added, the stirring is continued at an ambient temperature of 55°C for 40 minutes to complete the phase separation, and after the reaction is completed, the system is allowed to stand for 2 hours to separate the layers, a centrifuge is used to process the separated phase under a centrifugal force of 3500g at 55°C for 10 minutes, and the concentrated phase is concentrated by a vacuum evaporation device at -0.095MPa and 68°C. The product has a solid content of 85%, the inorganic salt residue is≤1.8%, and the polycarboxylic acid precipitation rate is increased to 91%.

[0059] Example 5

[0060] A method for preparing a high solid content polycarboxylic acid water reducing agent, comprising the following steps:

[0061] To 40 parts by mass of polycarboxylic acid-based water reducing agent mother liquor, a 30%wt concentration sodium hydroxide solution is added to precisely adjust the pH of the system to 4.0, and at a near-critical temperature of 58°C, under stirring conditions, ammonium sulfate is added for phase separation process treatment. The final system viscosity reaches 1.5-2.0 times the viscosity of the polycarboxylic acid water reducing agent mother liquor. The addition rate of the inorganic salt is controlled by an online viscosity monitoring system in real time: when the inorganic salt is first added, the stirring speed is 200 rpm, and as the inorganic salt is added, the salt concentration is increased by 5wt% every time the stirring speed is increased by 50 rpm. The addition rate of the inorganic salt is controlled as follows: when 0wt%≤salt concentration C_salt≤15wt%, the inorganic salt is added at a low speed and linearly, and the increase in salt concentration C_salt is controlled at 0.6wt% / min, i.e., the salt concentration increases by 0.6wt% every minute. The viscosity change rate is monitored during this process and is ≤5% / min; when 15wt%<salt concentration C_salt≤22wt%, the inorganic salt is added at a medium speed and in steps, the increase in salt concentration C_salt is controlled at 1.2wt% / min, and the salt concentration C_salt is increased by 2wt% and then paused for 30 seconds to monitor the uniformity of the system; when 22wt%<salt concentration C_salt≤30wt%, the inorganic salt is added at an ultra-low speed and in pulses, the increase in salt concentration C_salt is controlled at 0.2wt% / min, and every 10 seconds of addition is followed by a 20-second pause to capture the viscosity inflection point in real time; after the addition of the inorganic salt is completed, the stirring is continued at an environmental temperature of 58°C for 40 minutes to complete the phase separation, and after the reaction is completed, the system is left to stand at 58°C for 2 hours to separate the layers, and the enriched phase is treated by a centrifuge at a high centrifugal force of 4000g at 58°C for 8 minutes, and the concentrated phase is concentrated by a vacuum evaporation device at an extreme condition of -0.1MPa and 70°C. The product has a solid content of 90%, the inorganic salt residue is ≤1.2%, and the polycarboxylic acid precipitation rate is increased to 94%.

[0062] Example 6

[0063] A method for preparing a high solid content polycarboxylic acid water reducing agent, comprising the following steps:

[0064] To 40 parts by mass of polycarboxylic acid-based water reducing agent mother liquor, a 30%wt concentration sodium hydroxide solution is added to adjust the pH value of the system to 4.0 to strengthen phase separation; under constant temperature conditions at 60°C, under stirring conditions, a mass ratio of 1:2 of sodium sulfate and ammonium sulfate complex salt is added for phase separation process treatment, and the final concentration of inorganic salt is increased to 30wt% by pulse addition strategy; the final system viscosity reaches 1.5-2.0 times the viscosity of the polycarboxylic acid water reducing agent mother liquor; the salt addition method is as follows: when the inorganic salt is first added, the stirring speed is 200 rpm; as the inorganic salt is added, the stirring speed is increased by 50 rpm for every 5wt% increase in salt concentration; the salt addition rate is controlled as follows: when 0wt%≤salt concentration C_salt≤15wt%, the amount of inorganic salt added is controlled to be linearly added at low speed, and the increase in salt concentration C_salt is controlled to be 0.6wt% / min, i.e. the salt concentration increases by 0.6wt% per minute; the viscosity change rate is monitored to be≤5% / min during this process; when 15wt%<salt concentration C_salt≤22wt%, the amount of inorganic salt added is controlled to be added at medium speed in steps, the increase in salt concentration C_salt is controlled to be 1.2wt% / min, and the salt concentration C_salt is increased by 2wt% and paused for 30 seconds to monitor the uniformity of the system; when 22wt%<salt concentration C_salt≤30wt%, the amount of inorganic salt added is controlled to be added at ultra-low speed in pulses, the increase in salt concentration C_salt is controlled to be 0.2wt% / min, and every 10 seconds of addition is followed by 20 seconds of pause to capture the viscosity inflection point in real time. After the inorganic salt is added, the stirring is continued at 60°C for 40 minutes to complete the phase separation, and after the reaction is completed, the system is allowed to stand at 60°C to separate into layers, and a two-stage centrifugation strategy is used at 60°C, first 2000g×5 minutes for preliminary separation, and then 4000g×5 minutes for deep dehydration, and the enriched phase is concentrated in a vacuum evaporation device under the condition of -0.1MPa and 70°C with nitrogen bubbling technology. The detection shows that the solid content of the product jumps to 92%, the inorganic salt residue is≤0.8%, and the polycarboxylic acid precipitation rate is increased to 97%.

[0065] Example 7

[0066] A method for preparing a high solid content polycarboxylic acid water reducing agent, comprising the following steps:

[0067] To 40 parts by mass of polycarboxylic acid-based water reducing agent mother liquor, a 30%wt concentration sodium hydroxide solution is added to adjust the pH of the system to 4.0. First, a ternary compound salt of sodium sulfate, sodium chloride and ammonium sulfate with a mass ratio of 2:1:1 is added at 45°C to make the salt concentration C salt reach 25wt%; then the temperature is increased to 60°C, and a ternary compound salt of sodium sulfate, sodium chloride and ammonium sulfate with a mass ratio of 2:1:1 is added to make the salt concentration C salt reach 30wt%; the final system viscosity is 1.5-2.0 times the viscosity of the polycarboxylic acid water reducing agent mother liquor; the method of adding inorganic salt is as follows: when the inorganic salt is first added, the stirring speed is 200 rpm; as the inorganic salt is added, the stirring speed is increased by 50 rpm for every 5wt% increase in salt concentration; the salt addition rate is controlled as follows: when 0wt%≤salt concentration C salt≤15wt%, the amount of inorganic salt added is controlled to be linearly added at low speed, and the increase in salt concentration C salt is controlled to be 0.6wt% / min, i.e. the salt concentration increases by 0.6wt% per minute; the viscosity change rate is monitored to be≤5% / min during this process; when 15wt%<salt concentration C salt≤22wt%, the amount of inorganic salt added is controlled to be added in steps at medium speed, and the increase in salt concentration C salt is controlled to be 1.2wt% / min, and the salt concentration C salt is increased by 2wt% and then paused for 30 seconds to monitor the uniformity of the system; when 22wt%<salt concentration C salt≤28wt%, the amount of inorganic salt added is controlled to be added in pulses at ultra-low speed, and the increase in salt concentration C salt is controlled to be 0.2wt% / min, and every 10 seconds of addition is followed by a 20-second pause to capture the viscosity inflection point in real time. After the inorganic salt is added, the system is continuously stirred at 60°C for 40 minutes to complete the phase separation, and the reaction is completed by standing for 2 hours at 60°C after the reaction is completed. The enriched phase is separated by a continuous centrifuge at 5000g under high centrifugal force at 60°C for 5 minutes, and then deep dehydration is performed on the separated enriched phase by a molecular sieve assisted vacuum evaporation device at -0.1MPa and 70°C. It is detected that the product has a solid content of 95%, an inorganic salt residue of≤0.5%, and a polycarboxylic acid precipitation rate of 99%.

[0068] Comparative Example 1

[0069] According to parts by mass, 10 parts of acrylic acid and 360 parts of ethylene glycol monovinyl polyoxyethylene ether, and 200 parts of water are added to a reaction vessel and mixed and dissolved, then 3 parts of sodium hypophosphite, 3.0 parts of hydrogen peroxide, and 0.01 parts of ferrous sulfate are added; the reaction temperature in the reaction vessel is maintained at 15-20°C, and within 1 hour, A mixed solution obtained by mixing 0.5 parts of formaldehyde sodium bisulfite and 30 parts of water, and B mixed solution obtained by mixing 30 parts of acrylic acid and 20 parts of water are added dropwise. After the solution is added dropwise, the reaction is continued for 1.0 hour; after the reaction is completed, the 60% solid content polycarboxylic acid water reducing agent is obtained.

[0070] In the application examples of the present application, the cement used is ordinary Portland cement (P.O 42.5) unless otherwise specified. In order to compare the dispersing performance and dispersion retention performance of the water reducing agent prepared by the present application, the cement paste fluidity test is carried out according to the GB / T8077-2012 standard, 300 g of cement is added with 87 g of water, and the cement paste fluidity is measured on a flat glass plate after stirring for 4 minutes, and the paste fluidity at different times is tested, and the test data are shown in Table 1.

[0071] Table 1: Cement paste fluidity

[0072]

[0073]

[0074] Compared with the comparative example 1, the high solid content polycarboxylic acid water reducing agent prepared by the present application has good water reducing and slump retaining performances, and does not affect the product performance when used in cement and concrete.

[0075] Failure case 1: temperature deficiency leading to phase separation failure

[0076] A preparation method of a high solid content polycarboxylic acid water reducing agent, specifically comprising:

[0077] According to example 2, 25 parts by mass of polycarboxylic acid mother liquor is added with sodium hydroxide solution to adjust the pH to 5.2, and the difference from example 2 is that: sodium chloride is added at 300 rpm to a final concentration of 20 wt% at 35°C (lower than 45°C of example 2). The viscosity of the system is only 1.2 times the viscosity of the mother liquor. Continue stirring for 45 minutes, and after standing for 1.5 hours, centrifuge (2500g, 25°C), and the enriched phase is turbid. After concentration, the solid content is only 58%, the inorganic salt residue is as high as 8.3%, and the polycarboxylic acid precipitation rate drops to 65%.

[0078] The main reason for the failure is: low temperature reduces molecular thermal motion, and the driving force for separation is insufficient, resulting in incomplete phase separation and a large amount of free water and unprecipitated salt in the enriched phase.

[0079] Failure case 2: wrong salt type causing side reactions

[0080] A preparation method of a high solid content polycarboxylic acid water reducing agent, specifically comprising:

[0081] According to example 4, 35 parts by mass of the mother liquor is adjusted to a pH of 4.5, and the difference from example 4 is that: calcium chloride is used instead of the composite salt at 55°C, and the final concentration is 28 wt%. White flocculent precipitate appears during the salt addition process (while the solution of example 4 remains uniform). The enriched phase contains a large amount of solid impurities after centrifugation. After concentration, the solid content is 68% (but contains more than 30% insoluble substances), the calcium ion residue is 9.8%, and the polycarboxylic acid precipitation rate is only 48% (due to Ca2+ Complexation with carboxyl groups and precipitation.

[0082] The main reason for failure is: Ca 2+ With the carboxyl group of polycarboxylic acid to form insoluble calcium salt (such as Ca(R-COO)2), destroy the molecular structure and introduce harmful ions.

[0083] The method of the present application has the following beneficial effects compared with evaporation concentration method:

[0084] Energy consumption is reduced: the present application realizes phase separation at 40-60℃, which saves 30-50% energy compared with evaporation concentration method (60-100℃);

[0085] Thermal protection: avoid high temperature leading to poly carboxylic acid molecular chain rupture (such as ester hydrolysis), product molecular weight distribution is more uniform;

[0086] Residual control: through gradient separation, salt residue can be reduced to ≤0.5wt%, while evaporation concentration residue is usually ≥3wt%.

[0087] The method of the present application has the following beneficial effects compared with spray drying method:

[0088] Low equipment cost: no need for spray drying tower (investment cost reduction of 60%);

[0089] Particle size can be controlled: the present application can control the particle D50 in 10-50μm through centrifugal classification, and spray drying is easy to produce micro powder (<5μm) leading to hygroscopic caking;

[0090] Process adaptability: suitable for high viscosity system (>5000mPa·s), while spray drying needs to be diluted to <1000mPa·s.

[0091] The method of the present application has the following beneficial effects compared with bulk polymerization (ester type water reducing agent):

[0092] Reaction efficiency: the present application can complete separation and purification within 2-4 hours, while bulk polymerization needs 8-12 hours;

[0093] Product purity: the present application removes unreacted monomer (residual ≤0.1%) through phase separation, while bulk polymerization needs additional purification step;

[0094] Molecular weight regulation: the present application has no limit to the molecular weight of polycarboxylic acid (Mw=20-50 million can be processed), while bulk polymerization is easily limited by reactor mass transfer (Mw<20 million).

[0095] The method of the present application has the following beneficial effects compared with in-situ polymerization grafting method:

[0096] Process compatibility: the present application can directly handle the existing polycarboxylic acid synthesis liquid, the in-situ polymerization needs to redesign the reactor, and is currently limited to the laboratory;

[0097] Functional expansion: the present application can regulate the surface charge (Zeta potential -30mV to +10mV) of the product through the complex salt, and the functional group of in-situ polymerization is fixed;

[0098] Environmental protection: the wastewater COD of the present application is less than 500mg / L (can be reused), and the wastewater of in-situ polymerization contains initiator residues (COD>2000mg / L).

[0099] The above description of the embodiments is to facilitate the ordinary skilled person in the art to understand and use the application. Those skilled in the art can obviously make various modifications to these embodiments, and apply the general principles described herein to other embodiments without having to go through creative labor. Therefore, the present application is not limited to the above embodiments, and the improvements and modifications made by those skilled in the art according to the disclosure of the present application without departing from the scope of the present application should be within the scope of protection of the present application.

Claims

1. A method for preparing a high-solids-content polycarboxylate superplasticizer, characterized in that, The preparation method includes the following steps: The pH of the polycarboxylate superplasticizer mother liquor was adjusted to 4-5.

2. Inorganic salts were added under constant temperature stirring to achieve phase separation. After standing and layering, the mixture was centrifuged and the enriched phase was concentrated by vacuum evaporation to obtain a high solids content polycarboxylate superplasticizer.

2. The preparation method according to claim 1, characterized in that, The inorganic salt is selected from one or more of sodium sulfate, sodium chloride, and ammonium sulfate.

3. The preparation method according to claim 1, characterized in that, The pH value of the polycarboxylate superplasticizer mother liquor was adjusted and controlled within ±0.5 of the isoelectric point of polycarboxylate.

4. The preparation method according to claim 1, characterized in that, The pH value is maintained between 4 and 5.2, and when the system is kept at a constant temperature of 40℃≤T≤50℃, the salt concentration C_salt≤25wt%. The pH value is maintained between 4 and 5.2, and when the system is kept at a constant temperature of 50℃ < T ≤ 60℃, the salt concentration C_salt ≤ 30wt%.

5. The preparation method according to claim 1, characterized in that, Phase separation is achieved by adding inorganic salts under constant temperature and stirring conditions, with a stirring rate of 200-800 rpm.

6. The preparation method according to claim 1, characterized in that, The inorganic salt is added in batches or in a pulse. The stirring speed is controlled at 200 rpm when the inorganic salt is first added. As the inorganic salt is added, the stirring speed increases by 50-100 rpm for every 5 wt% increase in salt concentration.

7. The preparation method according to claim 1 or 6, characterized in that, When 0wt% ≤ salt concentration C_salt ≤ 15wt%, the amount of inorganic salt added is controlled to be added linearly at a low rate, and the increase in salt concentration C_salt is controlled to be 0.6wt% / min. During this process, the viscosity change rate is monitored to be ≤5% / min. When 15wt% < salt concentration C_salt ≤ 22wt%, the amount of inorganic salt added is controlled to be added in a medium-rate stepwise manner, and the increase in salt concentration C_salt is controlled to be 1.2wt% / min. Furthermore, the addition of inorganic salt is paused for 30 seconds every 2wt% increase in salt concentration C_salt, and the uniformity of the system is monitored. When 22wt% < salt concentration C_salt ≤ 30wt%, the amount of inorganic salt added is controlled by ultra-low speed pulse addition, the increase of salt concentration C_salt is controlled at 0.2wt% / min, and the addition is paused for 20 seconds every 10 seconds to capture the viscosity inflection point in real time.

8. The preparation method according to claim 1 or 6, characterized in that, The vacuum evaporation concentration is carried out by solvent removal under conditions of -0.08 to -0.1 MPa and 60 to 70°C.

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

10. The high solids content polycarboxylate superplasticizer according to claim 9, characterized in that, The high solids content polycarboxylate superplasticizer has a solids content ≥70%, an inorganic salt residue ≤3.5%, and a polycarboxylate precipitation rate ≥78%.

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