Ammonium polyacrylate emulsion, process for its preparation and use thereof

Abstract

The application belongs to the technical field of emulsion synthesis, and particularly relates to a kind of polyacrylammonium emulsion and its preparation method and application, the preparation method includes: in the pH value of 7-8 ammonium acrylate aqueous solution is added amino polycarboxylic acid chelating agent and inorganic hypophosphite chain transfer agent, then with organic phase solution is mixed homogeneously;The emulsion after homogenization is heated to 25-35 DEG C, and azo initiator I is added to carry out reaction I to obtain reaction product I;Reaction product I is heated to 40-50 DEG C, and azo initiator II is added to carry out reaction II.Organic phase solution contains white oil and surfactant, azo initiator I contains azo dimethoxy isopropyl cyanide, and azo initiator II contains azo diisobutyl imidazoline hydrochloride.The method can be safe, stable, efficient reaction, and is conducive to reducing cost.

Description

Technical Field

[0001] This invention belongs to the field of emulsion synthesis technology, and in particular relates to ammonium polyacrylate emulsions, their preparation methods, and applications. Background Technology

[0002] In the alumina production process, polyammonium acrylate (PAA-NH4) reverse emulsion is often used for red mud settling as a dispersant or anti-flocculation agent to improve solid-liquid separation efficiency, reduce red mud liquid loss, and lower alkali consumption.

[0003] Existing ammonium polyacrylate emulsions generally employ redox catalytic systems. The drawback of this system is that free radicals are generated extremely rapidly at low temperatures, easily leading to a violently exothermic reaction. Strict temperature control is required; otherwise, gelation or chain termination may occur. Furthermore, metal ions (such as Fe) are often introduced. 2+ Catalysis can be performed using metal ions or inorganic salts (such as persulfates and sulfites). Residual metal ions or inorganic salts may affect the conductivity, toxicity, or subsequent applications of PAM. Rapid free radical generation in redox systems can lead to increased chain transfer, a wider molecular weight distribution at low temperatures, poor stability, and difficulty in storage and transportation. Furthermore, reducing agents such as sulfites are easily consumed by oxygen, requiring strict deoxygenation to ensure initiation efficiency; they may also generate sulfur-containing wastewater, requiring additional treatment; and their settling effect in red mud sedimentation needs further improvement.

[0004] Furthermore, azo initiators are typically added directly to initiator catalytic systems. However, the products prepared by this system have a relatively wide molecular weight distribution and relatively poor stability, making them difficult to store and transport. Their effectiveness in red mud sedimentation needs further improvement.

[0005] Furthermore, the methods described above have relatively low conversion rates, and the reaction time for industrial production is relatively long, generally 6-12 hours, resulting in relatively high raw material and time costs. The prepared emulsion also requires the addition of a demulsifier to dissolve in alkaline solution, which is complex industrially, and the amount of demulsifier is difficult to control precisely. Summary of the Invention

[0006] The purpose of this invention is to provide a polyammonium acrylate emulsion, its preparation method, and its application. The emulsion prepared by this method has a suitable viscosity, high stability, and good settling effect in red mud sedimentation. This method can effectively improve the conversion rate of acrylic acid to polyammonium acrylate.

[0007] The first aspect of this invention provides a method for preparing an ammonium polyacrylate emulsion, the method comprising the following steps: (1) Add amino polycarboxylic acid chelating agents and inorganic hypophosphite chain transfer agents to the aqueous phase solution, and then mix and homogenize with the organic phase solution; (2) Heat the homogenized emulsion to the first temperature, add azo initiator I to carry out reaction I, and the reaction time of reaction I is 0.5-3 hours to obtain reaction product I; (3) Heat the reaction product I to a second temperature, add azo initiator II to carry out reaction II, and the reaction time of reaction II is 1-5 hours; The aqueous phase solution contains ammonium acrylate and the pH value of the aqueous phase solution is 7-8. The organic phase solution contains white oil and surfactant. The azo initiator I contains azodimethoxyisoheptanenitrile and the azo initiator II contains azodiisobutylimidazoline hydrochloride. The first temperature is 25-35℃ and the second temperature is 40-50℃.

[0008] Furthermore, based on the total mass of the final obtained ammonium polyacrylate emulsion, the content of ammonium acrylate is 34-40 wt%, the amount of white oil is 23-27 wt%, and the amount of surfactant is 2-4 wt%.

[0009] Furthermore, the mass ratio of the aqueous phase solution to the organic phase solution is 2.2-2.8:1.

[0010] Furthermore, the organic phase solution also contains a phase stabilizer, which is a C6-C25 saturated fatty acid and / or a C6-C25 unsaturated fatty acid.

[0011] Furthermore, the phase stabilizer is a C14-C25 unsaturated fatty acid.

[0012] Furthermore, the phase stabilizer is a C16-C20 monounsaturated fatty acid.

[0013] Preferably, the amount of phase stabilizer is 2-3 wt% based on the total mass of the final obtained ammonium polyacrylate emulsion.

[0014] Furthermore, the aminopolycarboxylic acid chelating agent is diethylenetriaminepentaacetic acid pentasodium, and the inorganic hypophosphite chain transfer agent is sodium hypophosphite.

[0015] Furthermore, based on the total mass of the final obtained ammonium polyacrylate emulsion, the amount of the amino polycarboxylic acid chelating agent added is 20-60 ppm, and the amount of the inorganic hypophosphite chain transfer agent added is 10-60 ppm.

[0016] Furthermore, based on the total mass of the final obtained ammonium polyacrylate emulsion, the amount of azo initiator I is 30-45 ppm, and the amount of azo initiator II is 15-30 ppm.

[0017] Furthermore, the azo initiator I also contains azobisisobutyrazoline hydrochloride; in the azo initiator I, the mass ratio of azobismethoxyisoheptanenitrile to azobisisobutyrazoline hydrochloride is 10-45:1.

[0018] Furthermore, in step (1), the viscosity of the emulsion obtained by homogenization is 1000-2000 mPa·s (i.e., centipoise).

[0019] Furthermore, the homogenization conditions include a shear rate of 15,000-20,000 rpm and a time of 30-90 seconds.

[0020] A second aspect of the present invention provides an ammonium polyacrylate emulsion, which is prepared by the above-described preparation method.

[0021] Preferably, the viscosity of the emulsion at 25°C is 1200-1600 mPa·s, and the viscosity of the ammonium polyacrylate emulsion at 25°C in a 1 wt% sodium hydroxide solution is 120-250 mPa·s.

[0022] A third aspect of the present invention provides an application of the above-mentioned ammonium polyacrylate emulsion in the flocculation and sedimentation of solid suspensions, preferably in the separation and sedimentation or washing and sedimentation of red mud.

[0023] The beneficial effects of this invention are: 1. The preparation method provided by this invention does not employ a redox catalytic system. Instead, it uses an azo initiation system composed of azodimethoxyisoheptanenitrile and azodiisobutylimidazoline hydrochloride. In the initial low-temperature stage of the reaction, azodimethoxyisoheptanenitrile preferentially decomposes to generate free radicals to initiate polymerization. Subsequently, azodiisobutylimidazoline hydrochloride continues to decompose during the heating stage, maintaining reaction activity. This avoids incomplete reactions caused by temperature fluctuations due to single initiators or direct mixing. It also optimizes the free radical generation rate, precisely controls the free radical concentration, and achieves more stable free radical release, which is beneficial for improving conversion rate and reaction efficiency. Simultaneously, it improves mixing uniformity, resulting in an emulsion product with suitable viscosity, good uniformity, good stability, and high viscosity in alkaline solutions. When applied to red mud settling, this product exhibits a faster settling rate, shorter settling time, and smaller red mud compression volume. This method is stable, less prone to local overheating or explosive polymerization, and ensures safe and stable industrial production. Moreover, the emulsion prepared by the above method will not produce toxic byproducts, metal or inorganic salt residues, and the product is purer and more in line with the requirements of green chemistry.

[0024] 2. The method provided by this invention utilizes the low-temperature initiation capability of azodimethoxyisoheptanenitrile to advance the reaction, while the subsequent action of azodiisobutylimidazoline hydrochloride ensures sufficient consumption of the monomer, especially effective for high-concentration or high-viscosity systems. This effectively reduces the amount of residual monomer, improves the conversion rate, and enhances the purity and application performance of the final product. Simultaneously, it effectively reduces the total amount of initiator used, which is beneficial for cost control.

[0025] 3. By controlling the temperature stepwise and limiting the reaction time, this invention effectively controls the generation rate of free radicals and the monomer conversion rate at each stage, thereby obtaining a high molecular weight, high conversion rate emulsion in a short time.

[0026] 4. The method provided by this invention uses azobis(dimethoxy)isoheptanenitrile as the main component and a trace amount of azobis(isobutylazoline) hydrochloride as an auxiliary component in the low-temperature initiation stage. By utilizing the weak and continuous decomposition of the trace amount of high-activation-energy initiator at low temperature, a more stable supply of free radicals, a shorter induction period, and a milder reaction initiation are achieved in the early stage. After heating, azobis(isobutylazoline) hydrochloride is added to form a free radical release curve that matches the entire process, which significantly improves the polymerization conversion rate and reaction uniformity, effectively inhibits explosive polymerization and gel formation, makes the polyacrylamide emulsion more stable, and increases its viscosity in 1% sodium hydroxide solution, which greatly improves the flocculation and sedimentation separation effect in red mud sedimentation.

[0027] 5. The specific viscosity range (1200-1600 mPa·s) and high viscosity in alkaline solutions of the polyammonium acrylate emulsion prepared by this invention are key physical characteristics that ensure its excellent flocculation performance and high solid-liquid separation efficiency in red mud sedimentation applications.

[0028] 6. The method provided by this invention adds a specific phase stabilizer to the organic phase solution to further improve the stability of the emulsion. Moreover, it does not require the addition of a demulsifier when dissolved in alkaline solution. It is simple to use and more environmentally friendly.

[0029] 7. Traditional phase inversion agents (such as alcohols or high HLB surfactants) function to regulate the hydrophilic-hydrophobic balance. This invention adds C16-C20 monounsaturated fatty acids to the original emulsion system. Under the premise of ensuring product stability, the product is converted into water-soluble soap in situ under alkaline conditions during application, dynamically adjusting the HLB value of the system to achieve spontaneous phase inversion. This avoids the use of synthetic phase inversion agents, conforms to the trend of green chemistry, and further reduces product costs. Detailed Implementation

[0030] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this document.

[0031] As mentioned above, the first aspect of the present invention provides a method for preparing an ammonium polyacrylate emulsion, the method comprising the following steps: (1) Add an amino polycarboxylic acid chelating agent and an inorganic hypophosphite to the aqueous phase solution and then mix and homogenize with the organic phase solution; (2) Heat the homogenized emulsion to the first temperature, add azo initiator I to carry out reaction I, and the reaction time of reaction I is 0.5-3 hours to obtain reaction product I; (3) Heat the reaction product I to a second temperature, add azo initiator II to carry out reaction II, and the reaction time of reaction II is 1-5 hours; The aqueous phase solution contains ammonium acrylate and the pH value of the aqueous phase solution is 7-8. The organic phase solution contains white oil and surfactant. The azo initiator I contains azodimethoxyisoheptanenitrile and the azo initiator II contains azodiisobutylimidazoline hydrochloride. The first temperature is 25-35℃ and the second temperature is 40-50℃.

[0032] During their research, the inventors discovered that mixing an aqueous solution containing ammonium acrylate (pH 7-8) with an organic solution containing white oil and surfactants, and then using an azodicarbonamide (dimethoxyisoheptanenitrile) in the initial low-temperature stage of the emulsion polymerization reaction, preferentially decomposes into free radicals to initiate polymerization. Subsequently, azodiisobutylimidazoline hydrochloride is used to continuously decompose during the heating stage, maintaining reactivity and avoiding incomplete reactions caused by temperature fluctuations when using a single initiator or direct mixing. This also optimizes the free radical generation rate, precisely controls the free radical concentration, and achieves more stable free radical release, which is beneficial for improving conversion rate and reaction efficiency. Simultaneously, it improves mixing uniformity, resulting in an emulsion product with suitable viscosity, high solid content, good uniformity, good stability, and high viscosity in alkaline solutions. When applied to red mud settling, this product exhibits a faster settling rate, shorter settling time, and smaller red mud compression volume. Furthermore, this method ensures that the final product does not produce toxic byproducts, metal or inorganic salt residues, resulting in a purer product that better meets green chemistry requirements.

[0033] The method provided by this invention utilizes the low-temperature initiation capability of azodimethoxyisoheptanenitrile to advance the reaction, while the subsequent action of azodiisobutylimidazoline hydrochloride ensures sufficient consumption of the monomer, especially effective for high-concentration or high-viscosity systems. This effectively reduces the amount of residual monomer, improving the purity and application performance of the final product. Simultaneously, it effectively reduces the total amount of initiator used, thus controlling costs.

[0034] Preferably, based on the total mass of the final obtained ammonium polyacrylate emulsion, the content of ammonium acrylate is 34-40 wt%, the amount of white oil is 23-27 wt%, and the amount of surfactant is 2-4 wt%. An ammonium polyacrylate emulsion prepared by controlling the content or amount of the above substances within the above ranges has a more suitable viscosity.

[0035] Preferably, the mass ratio of the aqueous solution to the organic solution is 2.2-2.8:1. The ammonium polyacrylate emulsion prepared by mixing the aqueous and organic solutions at the above mass ratio exhibits better uniformity and stability.

[0036] In order to further improve the stability and uniformity of the prepared emulsion, preferably, the surfactant is Span 60 and Tween 60, and the mass ratio of Span 60 to Tween 60 is 1:1.8-2.1.

[0037] Preferably, the organic phase solution further contains a phase stabilizer, which is a C6-C25 saturated fatty acid and / or a C6-C25 unsaturated fatty acid. Using the above-mentioned phase stabilizer can further improve the stability of the emulsion. According to the present invention, the C6-C25 saturated fatty acids can be caprylic acid, nonanoic acid, capric acid, dodecyl acid, or hexadecyl acid, and the C6-C25 unsaturated fatty acids can be C6-C25 monounsaturated fatty acids and / or C6-C25 polyunsaturated fatty acids. Exemplarily, the C6-C25 unsaturated fatty acids can be myristoleic acid (C14:1, cis-9), palmitoleic acid (C16:1, cis-9), oleic acid (C18:1, cis-9), trans oleic acid (C18:1, trans-9), ricinoleic acid (C18:1, cis-9), erucic acid (C22:1, cis-13), linoleic acid, α-linolenic acid, γ-linolenic acid, arachidonic acid, docosahexaenoic acid, or eicosapentaenoic acid. More preferably, the phase stabilizer is a C14-C22 unsaturated fatty acid. Using this phase stabilizer not only further enhances the stability of the emulsion, but also eliminates the need for additional demulsifiers when dissolved in alkaline solutions, making it simple to use and more environmentally friendly. To further improve the stability and solubility of the emulsion in alkaline solutions, more preferably, the phase stabilizer is a C16-C20 monounsaturated fatty acid. Even more preferably, the phase stabilizer is a plant-derived C16-C20 monounsaturated fatty acid. Preferably, the phase stabilizer is oleic acid and / or palmitoleic acid.

[0038] Preferably, the amount of phase stabilizer is 2-3 wt% based on the total mass of the final obtained ammonium polyacrylate emulsion.

[0039] To further improve the yield and purity of ammonium polyacrylate emulsion, preferably, the aminopolycarboxylic acid chelating agent is pentasodium diethylenetriaminepentaacetate, and the inorganic hypophosphite chain transfer agent is sodium hypophosphite. Preferably, based on the total mass of the final ammonium polyacrylate emulsion, the amount of the aminopolycarboxylic acid chelating agent added is 20-60 ppm, and the amount of the chain transfer agent added is 10-60 ppm. Controlling the amounts of the aminopolycarboxylic acid chelating agent and the inorganic hypophosphite chain transfer agent within the above ranges can further improve the yield and purity of the ammonium polyacrylate emulsion while controlling costs, and simultaneously enhance its application effect in red mud sedimentation.

[0040] Preferably, based on the total mass of the final obtained ammonium polyacrylate emulsion, the amount of azo initiator I is 30-45 ppm, and the amount of azo initiator II is 15-30 ppm. Controlling the amounts of azo initiator I and azo initiator II within the above ranges can further improve the uniformity and stability of the ammonium polyacrylate emulsion, while also increasing its yield and purity. Further preferably, considering the ability to further improve the uniformity and stability of the obtained ammonium polyacrylate emulsion, the azo initiator I also contains azobisisobutyrazoline hydrochloride, wherein the mass ratio of azobismethoxyisoheptanenitrile to azobisisobutyrazoline hydrochloride in the azo initiator I is 10-45:1. More preferably, it is 20-45:1, further preferably 20-35:1, and even more preferably 20-30:1.

[0041] Preferably, in step (1), the viscosity of the homogenized emulsion is 1000-2000 mPa·s. Controlling the viscosity of the homogenized emulsion within this range can further improve the uniformity and stability of the subsequently obtained ammonium polyacrylate emulsion. Preferably, the homogenization conditions include a shear rate of 15000-20000 rpm and a time of 30-90 seconds. By controlling the shear rate and time of homogenization within the above range, the viscosity of the homogenized emulsion can be controlled to be 1000-2000 mPa·s.

[0042] Preferably, the preparation method further includes: introducing nitrogen gas into the reaction solution when adding azo catalyst I; stopping the introduction of nitrogen gas into the reaction solution when the temperature of the reaction solution rises by 0.1-0.3°C, switching to top nitrogen sealing, and simultaneously slowly opening the cooling water valve. Introducing nitrogen gas into the reaction solution when adding azo catalyst I can remove oxygen from the reaction solution and shorten the reaction induction time. Stopping the introduction of nitrogen gas into the reaction solution when the temperature of the reaction solution rises by 0.1-0.3°C, switching to top nitrogen sealing, and simultaneously slowly opening the cooling water valve can both ensure the solution heating rate and achieve the purpose of isolating oxygen, preventing the air-cooling effect of nitrogen itself from negatively affecting the rise of the reaction temperature.

[0043] Furthermore, the present invention also provides a polyammonium acrylate emulsion prepared by the above-described preparation method. Based on the above description, this polyammonium acrylate emulsion has a suitable viscosity, high uniformity, and stability. When applied to red mud settling, it exhibits a faster settling rate, shorter settling time, and smaller red mud compression volume.

[0044] Preferably, the polyacrylamide emulsion has a viscosity of 1200-1600 mPa·s at 25°C, and the polyacrylamide emulsion has a viscosity of 120-250 mPa·s at 25°C in a 1 wt% sodium hydroxide solution.

[0045] More preferably, the viscosity of the ammonium polyacrylate emulsion in a 1wt% sodium hydroxide solution at 25°C is 120-200 mPa·s, more preferably 120-150 mPa·s.

[0046] This invention provides an application of the aforementioned ammonium polyacrylate emulsion in the flocculation and sedimentation of solid suspensions. The aforementioned ammonium polyacrylate emulsion exhibits a faster sedimentation rate, shorter sedimentation time, and smaller red mud compression volume when applied to the flocculation and sedimentation of solid suspensions (especially for the analytical sedimentation and washing sedimentation of red mud), resulting in better application performance.

[0047] In a relatively preferred embodiment of the present invention, a method for preparing an ammonium polyacrylate emulsion is provided, comprising the following steps: (1) Preparation of aqueous solution: Mix 130-180g of deionized water, 280-320g of 99.5% acrylic acid and 235-270g of 28% ammonia water, stir evenly to obtain an aqueous solution with a pH of 7-8; (2) Preparation of oil phase solution: Based on the total mass of the final obtained ammonium polyacrylate emulsion, mix 240-270 g of white oil, 20-40 g of surfactant and 20-30 g of phase stabilizer, and stir evenly to obtain oil phase solution; Based on the total mass of the final emulsion, the white oil content is 24-27 wt%, the surfactant content is 2-4 wt%, and the phase stabilizer content is 2-3 wt%. (3) Addition of aqueous catalyst: Add 0.02-0.06 g of DTPA 5Na and 0.01-0.06 g of sodium hypophosphite to the aqueous solution of step (1) and stir until homogeneous; (4) Homogenization of aqueous and oil phases: After stirring the aqueous solution in step (3) for 10-20 minutes, add the oil solution in step (2) for homogenization. The homogenization time is 30-90 seconds. The content of the ammonium polyacrylate in the resulting emulsion is 34-40 wt%. (5) Initial temperature setting and azo initiator preparation steps: Heat the homogenized emulsion from step (4) to 25-35℃ and maintain this temperature, while preparing azo catalyst I and azo catalyst II; (6) Reaction start-up steps: Add the prepared azo catalyst I to the emulsion and start recording the time and temperature, and introduce nitrogen gas into the reaction solution; (7) Reaction control steps: Monitor temperature changes. When the temperature rises by 0.1-0.3℃, stop introducing nitrogen into the reaction solution and switch to top nitrogen sealing. Slowly open the cooling water valve and start controlling the reaction temperature. When the temperature is maintained between 40-50℃, add azo initiator II and pay close attention to temperature changes. The main reaction temperature is controlled between 44-50℃ and maintained within this temperature range. When the temperature gradually decreases, reduce the cooling water flow until it is completely shut off. The reaction ends when the temperature does not rise. Based on the total mass of the aqueous solution and the organic solution, the amount of azo initiator I is 30-45 ppm, the amount of azo initiator II is 15-30 ppm, azo initiator I is azodimethoxyisoheptanenitrile or a mixture of azodimethoxyisoheptanenitrile and azodiisobutylimidazoline hydrochloride, and azo initiator II is azodiisobutylimidazoline hydrochloride. When azo initiator I is a mixture of azodimethoxyisoheptanenitrile and azodiisobutylimidazoline hydrochloride, the mass ratio of azodimethoxyisoheptanenitrile to azodiisobutylimidazoline hydrochloride is 10-45:1. (8) Reaction retention step: After the reaction is basically completed, control the temperature at 45 to 50°C and maintain it for 30 to 60 minutes; (9) Cooling and unloading steps: Cool the emulsion to the unloading temperature of 22-27℃ and filter it with a 300-micron filter screen.

[0048] The polyammonium acrylate emulsion prepared by the above preferred embodiment has a suitable viscosity, a high viscosity in alkaline solution, and high uniformity and stability. When applied to red mud settling, it exhibits a fast settling rate, a shorter settling time, and a smaller red mud compression volume.

[0049] The present invention will be further described below with reference to embodiments and comparative examples.

[0050] In the following examples, the concentration is a mass percentage concentration.

[0051] Example 1: A method for preparing an ammonium polyacrylate emulsion includes the following steps: Step 1: Prepare the aqueous phase solution. Weigh 170g of deionized water, 290g of 99.5% acrylic acid and 240g of 28% ammonia water to prepare the aqueous phase solution. Adjust the pH of the aqueous phase solution to 7.6 with ammonia water and stir the aqueous phase solution for 30 minutes. Step 2: Prepare the oil phase solution. Weigh 255g of white oil, 8g of Span 60, 17g of Tween 60 and 20g of vegetable oleic acid, prepare the oil phase solution, and stir the oil phase solution evenly for 20 minutes. Step 3: Weigh 0.03 g of DTPA 5Na and 0.02 g of sodium hypophosphite, add them to the aqueous solution prepared in Step 1, and stir until homogeneous; Step 4: After stirring the aqueous solution for 15 minutes, add the oil solution and mix. Then homogenize for 40 seconds to achieve a homogenization viscosity of 1400 mPa·s. Step 5: Heat the homogenized emulsion to 28.5°C and maintain this temperature. Add 0.035 g of azodimethoxyisoheptanenitrile to the emulsion all at once, and start recording the time and temperature. Pour nitrogen gas into the reaction solution. Step 6: Monitor the temperature change. When the temperature rises by 0.2℃, stop introducing nitrogen into the reaction solution, switch to top nitrogen sealing, and then slowly open the cooling water valve to start controlling the reaction temperature. Step 7: Maintain the main reaction temperature at 41℃. Add 0.03 g of azobisisobutyrazoline hydrochloride at once and monitor the temperature change constantly. Maintain the main reaction temperature at 43±1℃ and keep it at this temperature. When the temperature gradually decreases, reduce the cooling water flow until it is completely shut off. The reaction ends when the temperature does not rise. Step 8: After the reaction is basically complete, control the temperature at 47.5±0.5℃ and maintain it for 45 minutes; Step 9: After the retention time is over, take a sample and send it to the laboratory for analysis, and record the product's volumetric viscosity; Step 10: Cool to the unloading temperature of 23°C and filter using a 300-micron filter screen.

[0052] Example 2: A method for preparing an ammonium polyacrylate emulsion includes the following steps: Step 1: Prepare the aqueous phase solution. Weigh 139g of deionized water, 305g of 99.5% acrylic acid and 256g of 28% ammonia water to prepare the aqueous phase solution. Adjust the pH of the aqueous phase solution to 7.5 with ammonia water and stir the aqueous phase solution for 30 minutes. Step 2: Prepare the oil phase solution. Weigh 249g of white oil, 10g of Span 60, 18g of Tween 60 and 23g of vegetable oleic acid, prepare the oil phase solution, and stir the oil phase solution evenly for 30 minutes. Step 3: Weigh 0.04 g of DTPA 5Na and 0.03 g of sodium hypophosphite, add them to the aqueous solution prepared in Step 1, and stir until homogeneous; Step 4: After stirring the aqueous solution for 15 minutes, add the oil solution and mix. Then homogenize for 1 minute and the homogenized viscosity is 1500 mPa·s. Step 5: Heat the homogenized emulsion to 28°C and maintain this temperature. Add 0.035 g of azodimethoxyisoheptanenitrile and 0.0008 g of azodiisobutylimidazoline hydrochloride to the emulsion at once, and start recording the time and temperature. Pour nitrogen gas into the reaction solution. Step 6: Monitor the temperature change. When the temperature rises by 0.2℃, stop introducing nitrogen into the reaction solution, switch to top nitrogen sealing, and then slowly open the cooling water valve to start controlling the reaction temperature. Step 7: Slowly raise the main reaction temperature to 42℃, add 0.0292 g of azobisisobutyrazoline hydrochloride at once, and keep a close eye on the temperature change. Control the main reaction temperature at 43±1℃ and maintain this temperature. When the temperature gradually decreases, reduce the flow of cooling water until it is completely turned off. The reaction ends when the temperature does not rise. Step 8: After the reaction is basically complete, control the temperature at 46.5±0.5℃ and maintain it for 45 minutes; Step 9: After the retention time is over, take a sample and send it to the laboratory for analysis, and record the product's volumetric viscosity; Step 10: Cool to the unloading temperature of 25°C and filter using a 300-micron filter screen.

[0053] Example 3: A method for preparing an ammonium polyacrylate emulsion includes the following steps: Step 1: Prepare an aqueous solution. Weigh 130g of deionized water, 310g of 99.5% acrylic acid and 260g of 28% ammonia water, and prepare an aqueous solution. Adjust the pH of the aqueous solution to 7.4 with ammonia water and stir the aqueous solution for 30 minutes. Step 2: Prepare the oil phase solution. Weigh 246g of white oil, 10g of Span 60, 20g of Tween 60 and 24g of vegetable oleic acid, prepare the oil phase solution, and stir the oil phase solution evenly for 35 minutes. Step 3: Weigh 0.05 g of DTPA 5Na and 0.04 g of sodium hypophosphite, add them to the aqueous solution prepared in Step 1, and stir until homogeneous; Step 4: After stirring the aqueous solution for 15 minutes, add the oil solution and mix. Then homogenize for 70 seconds to achieve a homogenization viscosity of 1600 mPa·s. Step 5: Heat the homogenized emulsion to 29°C and maintain this temperature. Add 0.03 g of azodimethoxyisoheptanenitrile and 0.0015 g of azodiisobutylimidazoline hydrochloride to the emulsion at once, and start recording the time and temperature. Pour nitrogen gas into the reaction solution. Step 6: Monitor the temperature change. When the temperature rises by 0.3℃, stop introducing nitrogen into the reaction solution, switch to top nitrogen sealing, and then open the cooling water valve to start controlling the reaction temperature. Step 7: Control the main reaction temperature at 41℃, add 0.0285 g of azobisisobutyrazoline hydrochloride at once, and keep a close eye on the temperature change. Control the main reaction temperature at 43±1℃ and maintain this temperature. When the temperature gradually decreases, reduce the cooling water flow until it is completely shut off. The reaction ends when the temperature does not rise. Step 8: After the reaction is basically complete, control the temperature at 47.5±0.5℃ and maintain it for 50 minutes; Step 9: After the retention time is over, take a sample and send it to the laboratory for analysis, and record the product's volumetric viscosity; Step 10: Cool to the unloading temperature of 26°C and filter using a 300-micron filter screen.

[0054] Example 4: A method for preparing an ammonium polyacrylate emulsion includes the following steps: Step 1: Prepare the aqueous phase solution. Weigh 136g of deionized water, 307g of 99.5% acrylic acid and 257g of 28% ammonia water to prepare the aqueous phase solution. Adjust the pH of the aqueous phase solution to 7.5 with ammonia water and stir the aqueous phase solution for 30 minutes. Step 2: Prepare the oil phase solution. Weigh 249g of white oil, 10g of Span 60, 18g of Tween 60 and 23g of vegetable oleic acid, prepare the oil phase solution, and stir the oil phase solution evenly for 30 minutes. Step 3: Weigh 0.04 g of DTPA 5Na and 0.03 g of sodium hypophosphite, add them to the aqueous solution prepared in Step 1, and stir until homogeneous; Step 4: After stirring the aqueous solution for 15 minutes, add the oil solution and mix. Then homogenize for 60 seconds to achieve a homogenization viscosity of 1550 mPa·s. Step 5: Heat the homogenized emulsion to 29.5°C and maintain this temperature. Add 0.03 g of azodimethoxyisoheptanenitrile and 0.001 g of azodiisobutyrazoline hydrochloride to the emulsion at once, and start recording the time and temperature. Pour nitrogen gas into the reaction solution. Step 6: Monitor the temperature change. When the temperature rises by 0.2℃, stop introducing nitrogen into the reaction solution, switch to top nitrogen sealing, and then open the cooling water valve to start controlling the reaction temperature. Step 7: Maintain the main reaction temperature at 41℃. Add 0.019 g of azobisisobutyrazoline hydrochloride at once and monitor the temperature change constantly. Maintain the main reaction temperature at 44±1℃ and keep it at this temperature. When the temperature gradually decreases, reduce the cooling water flow until it is completely shut off. The reaction ends when the temperature does not rise. Step 8: After the reaction is basically complete, control the temperature at 47.5±0.5℃ and maintain it for 45 minutes; Step 9: After the retention time is over, take a sample and send it to the laboratory for analysis, and record the product's volumetric viscosity; Step 10: Cool to the unloading temperature of 25°C and filter using a 300-micron filter screen.

[0055] Example 5: A method for preparing an ammonium polyacrylate emulsion includes the following steps: Step 1: Prepare the aqueous phase solution. Weigh 140g of deionized water, 305g of 99.5% acrylic acid and 255g of 28% ammonia water to prepare the aqueous phase solution. Adjust the pH of the aqueous phase solution to 7.3 with ammonia water and stir the aqueous phase solution for 30 minutes. Step 2: Prepare the oil phase solution. Weigh 249g of white oil, 10g of Span 60, 18g of Tween 60 and 23g of vegetable oleic acid, prepare the oil phase solution, and stir the oil phase solution evenly for 30 minutes. Step 3: Weigh 0.04 g of DTPA 5Na and 0.03 g of sodium hypophosphite, add them to the aqueous solution prepared in Step 1, and stir until homogeneous; Step 4: After stirring the aqueous solution for 15 minutes, add the oil solution and mix. Then homogenize for 60 seconds to achieve a homogenization viscosity of 1550 mPa·s. Step 5: Heat the homogenized emulsion to 28.5°C and maintain this temperature. Add 0.03 g of azodimethoxyisoheptanenitrile and 0.002 g of azodiisobutylimidazoline hydrochloride to the emulsion at once, and start recording the time and temperature. Pour nitrogen gas into the reaction solution. Step 6: Monitor the temperature change. When the temperature rises by 0.2℃, stop introducing nitrogen into the reaction solution, switch to top nitrogen sealing, and then open the cooling water valve to start controlling the reaction temperature. Step 7: Maintain the main reaction temperature at 41.5℃. Add 0.018 g of azobisisobutyrazoline hydrochloride at once and monitor the temperature change constantly. Maintain the main reaction temperature at 44±1℃ and keep it at this temperature. When the temperature gradually decreases, reduce the cooling water flow until it is completely turned off. The reaction ends when the temperature does not rise. Step 8: After the reaction is basically complete, control the temperature at 47.5±0.5℃ and maintain it for 45 minutes; Step 9: After the retention time is over, take a sample and send it to the laboratory for analysis, and record the product's volumetric viscosity; Step 10: Cool to the unloading temperature of 25°C and filter using a 300-micron filter screen.

[0056] Comparative Example 1:

[0057] Step 1: Prepare the aqueous phase solution. Weigh 125g of deionized water, 309g of 99.5% acrylic acid and 261g of 28% ammonia water to prepare the aqueous phase solution. Adjust the pH of the aqueous phase solution to 7.0 with ammonia water and stir the aqueous phase solution for 30 minutes. Step 2: Prepare the oil phase solution. Weigh 233g of white oil, 23g of Span 60, and 9g of Tween 60, prepare the oil phase solution, and stir the oil phase solution evenly for 20 minutes. Step 3: Weigh 0.031 g of DTPA 5Na, 0.015 g of sodium formate and 0.085 g of sodium persulfate, add them to the aqueous solution prepared in Step 1, and stir until homogeneous; Step 4: After stirring the aqueous solution for 15 minutes, add the oil solution and mix. Then homogenize for 60 seconds to achieve a homogenization viscosity of 1720 mPa·s. Step 5: Blow nitrogen into the homogenized emulsion from the bottom for 30 minutes to maintain a slight positive pressure; Step 6: After nitrogen blowing is completed, maintain the emulsion temperature at 20 degrees Celsius and slowly add 1 mL of 1% sodium metabisulfite solution at a flow rate of 5 mL / h. Step 7: After the reaction starts, open the cooling water valve, control the main reaction temperature at 45℃ and maintain this temperature. When the temperature gradually decreases, reduce the cooling water flow until it is completely closed. The reaction ends when the temperature does not rise. Step 8: After the reaction is basically complete, maintain the temperature at 48℃ for 45 minutes. Step 9: After the retention time is over, add 5 grams of 40% sodium bisulfite solution and maintain at the current temperature for 30 minutes. Step 10: Weigh 35 grams of nonylphenol polyoxyethylene ether and add it while the emulsion is being stirred. Stir for 15 minutes after the emulsion is completed. Step 11: Take a sample and send it to the laboratory for analysis, and record the product's volumetric viscosity; Step 12: Cool to the unloading temperature of 25°C and filter using a 300-micron filter screen.

[0058] Comparative Example 2: Step 1: Prepare the aqueous phase solution. Weigh 135g of deionized water, 307g of 99.5% acrylic acid and 258g of 28% ammonia water, and prepare the aqueous phase solution. Adjust the pH of the aqueous phase solution to 7.6 with ammonia water and stir the aqueous phase solution for 30 minutes. Step 2: Prepare the oil phase solution. Weigh 248g of white oil, 10g of Span 60, 18g of Tween 60 and 24g of vegetable oleic acid, prepare the oil phase solution, and stir the oil phase solution evenly for 30 minutes. Step 3: Weigh 0.037 g of DTPA 5Na and 0.028 g of sodium hypophosphite, add them to the aqueous solution prepared in Step 1, and stir until homogeneous; Step 4: After stirring the aqueous solution for 15 minutes, add the oil solution and mix. Then homogenize for 60 seconds to achieve a homogenization viscosity of 1520 mPa·s. Step 5: Heat the homogenized emulsion to 28.8°C and maintain this temperature. Add 0.03 g of azodimethoxyisoheptanenitrile and 0.02 g of azodiisobutylimidazoline hydrochloride at once. Start recording the time and temperature. Pour nitrogen gas into the reaction solution. Step 6: Monitor temperature changes. When the temperature rises by 0.2℃, switch to top nitrogen sealing and slowly open the cooling water valve. Step 7: The main reaction temperature is controlled at 31℃. The temperature naturally rises to 32.5±0.5℃ and stabilizes. Maintain this temperature and gradually reduce the cooling water flow as the temperature decreases until it is completely shut off. The reaction ends when the temperature does not rise. Step 8: After the reaction is basically complete, maintain the temperature at 37°C for 45 minutes. Step 9: After the retention time is over, take a sample and send it to the laboratory for analysis, and record the product's volumetric viscosity; Step 10: Cool to the unloading temperature of 25°C and filter using a 300-micron filter screen.

[0059] Comparative Example 3: Step 1: Prepare the aqueous phase solution. Weigh 141g of deionized water, 304g of 99.5% acrylic acid, and 255g of 28% ammonia solution to prepare the aqueous phase solution. Adjust the pH of the aqueous phase solution to 7.5 with ammonia solution. Stir the aqueous phase solution evenly for 30 minutes. Step 2: Prepare the oil phase solution. Weigh 249g of white oil, 10g of Span 60, 18g of Tween 60 and 23g of vegetable oleic acid, and prepare the oil phase solution. Stir the oil phase solution evenly for 30 minutes. Step 3: Weigh 0.04 g of DTPA 5Na and 0.03 g of sodium hypophosphite, add them to the aqueous solution prepared in Step 1, and stir until homogeneous; Step 4: After stirring the aqueous solution for 15 minutes, add the oil solution and mix. Then homogenize for 60 seconds to achieve a homogenization viscosity of 1500 mPa·s. Step 5: Heat the homogenized emulsion to 43°C and maintain this temperature. Add 0.03 g of azodimethoxyisoheptanenitrile and 0.02 g of azodiisobutylimidazoline hydrochloride to the emulsion at once, and start recording the time and temperature. Pour nitrogen gas into the reaction solution. Step 6: Monitor temperature changes. Once the temperature rises by 0.2℃, switch to top nitrogen sealing and slowly open the cooling water valve. Step 7: Control the main reaction temperature at 46-48℃ and maintain this temperature. As the temperature gradually decreases, reduce the cooling water flow until it is completely shut off. The reaction ends when the temperature does not rise. Step 8: After the reaction is basically complete, maintain the temperature at 49℃ for 45 minutes. Step 9: After the retention time is over, take a sample and send it to the laboratory for analysis, and record the product's volumetric viscosity; Step 10: Cool to the unloading temperature of 25°C and filter using a 300-micron filter screen.

[0060] Comparative Example 4: Step 1: Prepare the aqueous phase solution. Weigh 131g of deionized water, 307g of 99.5% acrylic acid and 259g of 28% ammonia water to prepare the aqueous phase solution. Adjust the pH of the aqueous phase solution to 7.0 with ammonia water and stir the aqueous phase solution for 30 minutes. Step 2: Prepare the oil phase solution. Weigh 238g of white oil, 21g of Span 60, and 8g of Tween 60 to prepare the oil phase solution. Add 0.3g of azobisisobutyronitrile and stir the oil phase solution evenly for 20 minutes. Step 3: Weigh 0.032 g of DTPA 5Na, 0.011 g of sodium hypophosphite and 0.0075 g of tert-butyl hydroperoxide, add them to the aqueous solution prepared in Step 1, and stir until homogeneous; Step 4: After stirring the aqueous solution for 15 minutes, add the oil solution and mix. Then homogenize for 60 seconds to achieve a homogenization viscosity of 1540 mPa·s. Step 5: Blow nitrogen into the homogenized emulsion from the bottom for 30 minutes to maintain a slight positive pressure; Step 6: After nitrogen blowing is completed, maintain the emulsion temperature at 20 degrees Celsius and slowly add 1 mL of 1% sodium metabisulfite solution at a flow rate of 5 mL / h. Step 7: After the reaction starts, open the cooling water valve. The cooling water temperature is 15℃. The main reaction temperature is controlled at 43±1℃ and maintained at this temperature. When the temperature gradually decreases, reduce the cooling water flow until it is completely shut off. The reaction ends when the temperature does not rise. Step 8: After the reaction is basically complete, maintain the temperature at 44℃ for 45 minutes. Step 9: After the retention time is over, add 4 grams of 40% sodium bisulfite solution and maintain at the current temperature for 30 minutes. Step 10: Weigh 32 grams of nonylphenol polyoxyethylene ether and add it while stirring the emulsion. Stir for 15 minutes after completion. Step 11: Take a sample and send it to the laboratory for analysis, and record the product's volumetric viscosity; Step 12: Cool to the unloading temperature of 25°C and filter using a 300-micron filter screen.

[0061] Comparative Example 5: Step 1: Prepare the aqueous phase solution. Weigh 140g of deionized water, 305g of 99.5% acrylic acid and 255g of 28% ammonia water to prepare the aqueous phase solution. Adjust the pH of the aqueous phase solution to 7.3 with ammonia water and stir the aqueous phase solution for 30 minutes. Step 2: Prepare the oil phase solution. Weigh 249g of white oil, 10g of Span 60, 18g of Tween 60 and 23g of vegetable oleic acid, prepare the oil phase solution, and stir the oil phase solution evenly for 30 minutes. Step 3: Weigh 0.04 g of DTPA 5Na and 0.03 g of sodium hypophosphite, add them to the aqueous solution prepared in Step 1, and stir until homogeneous; Step 4: After stirring the aqueous solution for 15 minutes, add the oil solution and mix. Then homogenize for 60 seconds to achieve a homogenization viscosity of 1550 mPa·s. Step 5: Heat the homogenized emulsion to 30°C and maintain this temperature. Add 0.03 g of azobis(methoxy)isoheptanenitrile and 0.002 g of azobis(isobutylamidine) hydrochloride to the emulsion at once, and start recording the time and temperature. Pour nitrogen gas into the reaction solution. Step 6: Monitor the temperature change. When the temperature rises by 0.2℃, stop introducing nitrogen into the reaction solution, switch to top nitrogen sealing, and then open the cooling water valve to start controlling the reaction temperature. Step 7: Maintain the main reaction temperature at 55℃. Add 0.018 g of azobisisobutylamidine hydrochloride at once and monitor the temperature change at all times. Maintain the main reaction temperature at 56±1℃ and keep it at this temperature. When the temperature gradually decreases, reduce the cooling water flow until it is completely turned off. The reaction ends when the temperature does not rise. Step 8: After the reaction is basically complete, control the temperature at 57.5±0.5℃ and maintain it for 45 minutes; Step 9: After the retention time is over, take a sample and send it to the laboratory for analysis, and record the product's volumetric viscosity; Step 10: Cool to the unloading temperature of 25°C and filter using a 300-micron filter screen.

[0062] Table 1 below compares the reaction process and product indicators of the examples and comparative examples.

[0063]

[0064] As can be seen from the data in Table 1, compared with Comparative Examples 1-5, Examples 1-5 have higher conversion rates and higher viscosity in alkaline solutions. Compared with Comparative Example 1, Examples 1-5 have lower reaction times, lower viscosity, and higher stability. Compared with Comparative Example 2, Examples 1-5 have lower reaction times and lower viscosity. Compared with Comparative Example 3, Examples 1-5 have lower gelation rates, higher viscosity, and higher stability. Compared with Comparative Example 4, Examples 1-5 have lower viscosity and higher stability. This indicates that the emulsion prepared by the present invention performs excellently in terms of conversion rate, selectivity, and stability-related indicators, has a suitable apparent viscosity, and exhibits high conversion rate and emulsion stability, showing significant advantages compared with the comparative examples.

[0065] In summary, the outstanding contribution of this invention compared to the prior art lies in the discovery of a synergistic effect between a specific combination of azo initiators (azodimethoxyisoheptanenitrile and azodiisobutylimidazoline hydrochloride) and a specific stepwise temperature control program (reacting first at 25-35°C, then increasing the temperature to 40-50°C), which is the key to achieving the aforementioned excellent effect.

[0066] Comparative Example 2 attempted a one-step reaction using the same composite azo initiation system as the present invention within the low-temperature range (25-35℃) defined in this invention. The results showed that the monomer conversion rate of this method was only 82.3% (see Table 1), with a large amount of monomer residue, resulting in low reaction efficiency and failing to meet the economic and product purity requirements for industrial production. This demonstrates that if the initiation is limited to the low-temperature stage, the initiator with a higher decomposition temperature of azobisisobutyrazoline hydrochloride cannot be effectively activated, leading to insufficient free radical supply and incomplete polymerization.

[0067] Comparative Example 3 attempted to apply the same composite azo initiator system directly to a conventional high-temperature range (40-50℃) for a one-step reaction. The results showed that although the total reaction time was short (150 minutes), this method resulted in a 15% gelation rate, and the product emulsion stability was less than 3 months. This demonstrates that if the two initiators are directly mixed at high temperatures, the low-temperature initiator azodimethoxyisoheptanenitrile will instantly generate a large number of free radicals, leading to localized violent reactions, thermal runaway, and explosive polymerization, severely affecting product quality and process safety.

[0068] Comparative Example 4 attempted a combination of initiator and redox system, but the resulting emulsion had low stability and relatively low emulsion conversion efficiency.

[0069] Comparative Example 5 experimented with other combinations of azo initiators, but the resulting emulsions also had lower viscosity in alkaline solutions, resulting in relatively lower conversion rates.

[0070] As the above comparison shows, neither a single low-temperature domain nor a high-temperature domain can achieve the high-quality product with high conversion rate, suitable viscosity, and high stability obtained using the composite azo initiation system of this invention. The core of this invention lies in the organic coupling of a "specific initiator combination" with a "stepwise temperature ramping program": first, at a relatively mild first temperature (25-35℃), the low-temperature decomposition characteristics of azodimethoxyisoheptanenitrile are utilized to smoothly and controllably initiate polymerization and establish the initial molecular chain; then, the temperature is raised to a second temperature (40-50℃) to activate azodiisobutylimidazoline hydrochloride, allowing it to continuously and smoothly release free radicals, driving the efficient conversion of residual monomers into polymers and completing chain growth. The selection of temperature windows, the matching of initiator types, and the timing of addition in these two steps together constitute a precise and synergistic initiation-temperature control system, resulting in a comprehensive leap in conversion rate, product uniformity, and process safety. This effect is unpredictable by existing one-step methods or single initiator systems.

[0071] Example 6: Step 1: Prepare the aqueous phase solution. Weigh 140g of deionized water, 305g of 99.5% acrylic acid, and 255g of 28% ammonia solution to prepare the aqueous phase solution. Adjust the pH of the aqueous phase solution to 7.5 with ammonia solution. Stir the aqueous phase solution evenly for 30 minutes. Step 2: Prepare the oil phase solution. Weigh 250g of white oil, 10g of Span 60, 18g of Tween 60 and 22g of octanoic acid, and prepare the oil phase solution. Stir the oil phase solution evenly for 30 minutes. Step 3: Weigh 0.04 g of DTPA 5Na and 0.03 g of sodium hypophosphite, add them to the aqueous solution prepared in Step 1, and stir until homogeneous; Step 4: After stirring the aqueous solution for 15 minutes, add the oil solution and mix. Then homogenize for 60 seconds and the homogenized viscosity is 1200 mPa·s. Step 5: Heat the homogenized emulsion to 30°C and maintain this temperature. Add 0.03 g of azodimethoxyisoheptanenitrile and 0.001 g of azodiisobutylimidazoline hydrochloride to the emulsion at once, and start recording the time and temperature. Pour nitrogen gas into the reaction solution. Step 6: Monitor the temperature change. When the temperature rises by 0.2℃, stop introducing nitrogen into the reaction solution, switch to top nitrogen sealing, and then slowly open the cooling water valve to start controlling the reaction temperature. Step 7: Maintain the main reaction temperature at 43℃. Add 0.019 g of azobisisobutyrazoline hydrochloride at once and monitor the temperature change constantly. Maintain the main reaction temperature at 46±1℃ and keep it within this temperature range. When the temperature gradually decreases, reduce the cooling water flow until it is completely shut off. The reaction ends when the temperature does not rise. Step 8: After the reaction is basically complete, control the temperature at 46.5±0.5℃ and maintain it for 45 minutes; Step 9: After the retention time has expired, take samples and send them to the laboratory for analysis; Step 10: Cool to the unloading temperature of 27°C and filter using a 300-micron filter screen.

[0072] Example 7: Step 1: Prepare the aqueous phase solution. Weigh 140g of deionized water, 305g of 99.5% acrylic acid, and 255g of 28% ammonia solution to prepare the aqueous phase solution. Adjust the pH of the aqueous phase solution to 7.2 with ammonia solution. Stir the aqueous phase solution evenly for 30 minutes. Step 2: Prepare the oil phase solution. Weigh 239 grams of white oil, 21 grams of Span 60 and 10 grams of Tween 60, and prepare the oil phase solution. Stir the oil phase solution evenly for 30 minutes. Step 3: Weigh 0.04 g of DTPA 5Na and 0.03 g of sodium hypophosphite, add them to the aqueous solution prepared in Step 1, and stir until homogeneous; Step 4: After stirring the aqueous solution for 15 minutes, add the oil solution and mix. Then homogenize for 60 seconds to achieve a homogenization viscosity of 1550 mPa·s. Step 5: Heat the homogenized emulsion to 30°C and maintain this temperature. Add 0.03 g of azodimethoxyisoheptanenitrile and 0.001 g of azodiisobutylimidazoline hydrochloride to the emulsion at once, and start recording the time and temperature. Pour nitrogen gas into the reaction solution. Step 6: Monitor the temperature change. When the temperature rises by 0.2℃, stop introducing nitrogen into the reaction solution, switch to top nitrogen sealing, and then slowly open the cooling water valve to start controlling the reaction temperature. Step 7: Maintain the main reaction temperature at 43℃. Add 0.019 g of azobisisobutyrazoline hydrochloride at once and monitor the temperature change constantly. Maintain the main reaction temperature at 46±1℃ and keep it within this temperature range. When the temperature gradually decreases, reduce the cooling water flow until it is completely shut off. The reaction ends when the temperature does not rise. Step 8: After the reaction is basically complete, control the temperature at 46.5±0.5℃ and maintain it for 45 minutes; Step 9: After the retention time is over, add 30 grams of nonylphenol polyoxyethylene ether, stir for 15 minutes, and then send a sample to the laboratory for analysis. Step 10: Cool to the unloading temperature of 25°C and filter using a 300-micron filter screen.

[0073] Example 8: Step 1: Prepare the aqueous phase solution. Weigh 140g of deionized water, 305g of 99.5% acrylic acid, and 255g of 28% ammonia solution to prepare the aqueous phase solution. Adjust the pH of the aqueous phase solution to 7.5 with ammonia solution. Stir the aqueous phase solution evenly for 30 minutes. Step 2: Prepare the oil phase solution by weighing 250g of white oil, 10g of Span 60, 18g of Tween 60 and 23g of palmitoleic acid, and preparing the oil phase solution; stir the oil phase solution evenly for 30 minutes. Step 3: Weigh 0.04 g of DTPA 5Na and 0.03 g of sodium hypophosphite, add them to the aqueous solution prepared in Step 1, and stir until homogeneous; Step 4: After stirring the aqueous solution for 15 minutes, add the oil solution and mix. Then homogenize for 60 seconds and the homogenized viscosity is 1200 mPa·s. Step 5: Heat the homogenized emulsion to 30°C and maintain this temperature. Add 0.03 g of azodimethoxyisoheptanenitrile and 0.001 g of azodiisobutylimidazoline hydrochloride to the emulsion at once, and start recording the time and temperature. Pour nitrogen gas into the reaction solution. Step 6: Monitor the temperature change. When the temperature rises by 0.2℃, stop introducing nitrogen into the reaction solution, switch to top nitrogen sealing, and then slowly open the cooling water valve to start controlling the reaction temperature. Step 7: Maintain the main reaction temperature at 43℃. Add 0.019 g of azobisisobutyrazoline hydrochloride at once and monitor the temperature change constantly. Maintain the main reaction temperature at 46±1℃ and keep it within this temperature range. When the temperature gradually decreases, reduce the cooling water flow until it is completely shut off. The reaction ends when the temperature does not rise. Step 8: After the reaction is basically complete, control the temperature at 46.5±0.5℃ and maintain it for 45 minutes; Step 9: After the retention time has expired, take samples and send them to the laboratory for analysis; Step 10: Cool to the unloading temperature of 27°C and filter using a 300-micron filter screen.

[0074] Table 2 below compares the emulsion stability and solubility of the emulsions provided in Examples 4, 6, 7 and 8.

[0075]

[0076] As shown in Table 2, Examples 4 and 8, using oleic acid / palmitoic acid as phase stabilizers, exhibited excellent solubility in 1% sodium hydroxide solution and good centrifugal stability, requiring no additional demulsifier for application, resulting in the best overall performance. Example 6 used short-chain octanoic acid, which, while possessing some solubility, failed to form a stable interfacial film due to its short hydrophobic segments, leading to a significant decrease in centrifugal stability. Example 7, without any phase stabilizer, resulted in poor emulsion stability and difficulty in dissolving in alkaline solutions, necessitating the addition of a demulsifier for application, increasing process complexity and cost. In summary, this invention, by introducing oleic acid / palmitoic acid as a phase stabilizer, ensures emulsion storage stability while utilizing its dynamic transformation mechanism of in-situ water-soluble soap formation under alkaline conditions, achieving spontaneous and uniform dissolution during product application. This avoids the use of traditional demulsifiers, truly achieving simple usage and environmental friendliness.

[0077] Application effect evaluation: Based on the above embodiments and comparative examples, Embodiment 1, Embodiment 4, Embodiment 5, Embodiment 7, Comparative Example 1, Comparative Example 2, and Comparative Example 3 were selected for product application performance evaluation.

[0078] The testing method is as follows: 1. The test site was the No. 2 settling line at the Bayer aluminum plant. The solid content of the red mud slurry was 82 g / L, the organic matter content was 3 g / L, of which the organic oxalic acid content was 1.5 g / L. Each batch of red mud slurry was 1 liter. The laboratory phase analysis of the red mud used in the test was as follows: dry basis mass fraction: sodium silicate slag 10.32%, quartz 0.64%, goethite 33.93%, hematite 29.81%, rutile 3.77%, anatase 5.99%, and gibbsite below the detection limit. The solid phase contained almost no coarse particles larger than 0.841 mm; particles larger than 0.177 mm accounted for 37.55% of the total solid phase, particles larger than 0.147 mm accounted for 41.95%, particles larger than 0.125 mm accounted for 45.21%, and fine particles smaller than 0.125 mm accounted for 54.79%.

[0079] 2. Before testing, dissolve the emulsion in a 1.0% sodium hydroxide solution to prepare a 3.3% solution.

[0080] 3. The test was divided into 4 groups, with corresponding addition amounts of 11mL, 10mL, 9mL and 8mL, respectively. The differences in settling time, settling speed and compression volume of red mud were observed.

[0081] Product application test 1: The volume of 3.3% solution added was 11 mL. The test results are shown in Table 3 below.

[0082]

[0083] Product application test 2: The volume of 3.3% solution added was 10 mL. The test results are shown in Table 4.

[0084]

[0085] Product application test 3: The volume of 3.3% solution added was 9 mL. The test results are shown in Table 5.

[0086]

[0087] Product application test 4: The volume of 3.3% solution added was 8 mL. The test results are shown in Table 6.

[0088]

[0089] As shown in Tables 3 to 6, the emulsion provided in the examples has a shorter settling time and a higher settling rate than the emulsion provided in the comparative examples. The compressed volume of the red mud after settling is also smaller than that in the comparative examples, indicating that the emulsion provided by this invention has a better effect on red mud settling. The data from Example 4 are superior to those from Examples 1, 5, and 7, indicating that adding azodimethoxyisoheptanenitrile and a portion of azodiisobutylimidazoline hydrochloride first during the initiator addition process at a low temperature of 25-35℃, followed by adding the remaining azodiisobutylimidazoline hydrochloride at a high temperature of 40-50℃, and strictly controlling the mass ratio of the first added azodimethoxyisoheptanenitrile to azodiisobutylimidazoline hydrochloride to 10-45:1, can further improve the effect of the prepared emulsion on red mud settling.

[0090] By comparing the reaction process and product indicators, we found that using azodimethoxyisoheptanenitrile in the initial low-temperature stage of the reaction preferentially decomposes to generate free radicals to initiate polymerization. Subsequently, azodiisobutylimidazoline hydrochloride is used to continuously decompose during the heating stage, maintaining reaction activity and avoiding incomplete reactions caused by temperature fluctuations due to single initiators or direct mixing. This also optimizes the free radical generation rate, precisely controls the free radical concentration, and achieves more stable free radical release, which is beneficial to improving conversion rate and reaction efficiency. Simultaneously, it improves mixing uniformity, resulting in an emulsion product with suitable viscosity, good uniformity, good stability, and high viscosity in alkaline solutions. When applied to red mud settling, this product exhibits a faster settling rate, shorter settling time, and smaller red mud compression volume. The introduction of oleic acid / palmitoic acid improves the emulsion's solubility and stability, aligning with the trend of green and environmentally friendly development. In practical applications, the new composite azodicarbonyl segmented addition method, along with the addition of oleic acid / palmitoic acid, significantly enhances the overall performance of the emulsion product.

[0091] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, including combining the various technical features in any other suitable manner. These simple modifications and combinations should also be regarded as the contents disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A process for the preparation of an ammonium polyacrylate emulsion, characterized in that: The preparation method includes the following steps: (1) Add amino polycarboxylic acid chelating agents and inorganic hypophosphite chain transfer agents to the aqueous phase solution, and then mix and homogenize with the organic phase solution; (2) Heat the homogenized emulsion to the first temperature, add azo initiator I to carry out reaction I, and the reaction time of reaction I is 0.5-3 hours to obtain reaction product I; (3) Heat the reaction product I to a second temperature, add azo initiator II to carry out reaction II, and the reaction time of reaction II is 1-5 hours to obtain ammonium polyacrylate emulsion; The aqueous phase solution contains ammonium acrylate and the pH value of the aqueous phase solution is 7-8. The organic phase solution contains white oil and surfactant. The azo initiator I contains azodimethoxyisoheptanenitrile and the azo initiator II contains azodiisobutylimidazoline hydrochloride. The first temperature is 25-35℃ and the second temperature is 40-50℃.

2. The production method according to claim 1, characterized by, Based on the total mass of the final obtained ammonium polyacrylate emulsion, the content of ammonium acrylate is 34-40 wt%, the amount of white oil is 23-27 wt%, and the amount of surfactant is 2-4 wt%.

3. The production method according to claim 2, characterized by, The mass ratio of the aqueous phase solution to the organic phase solution is 2.2-2.8:

1.

4. The production method according to any one of claims 1 to 3, characterized by, The organic phase solution further contains a phase stabilizer, which is a C6-C25 saturated fatty acid and / or a C6-C25 unsaturated fatty acid, preferably a C14-C25 unsaturated fatty acid, and more preferably a C16-C20 monounsaturated fatty acid.

5. The preparation method according to claim 4, characterized in that, The amount of phase stabilizer used is 2-3 wt% based on the total mass of the final obtained ammonium polyacrylate emulsion.

6. The preparation method according to claim 1, characterized in that, The aminopolycarboxylic acid chelating agent is diethylenetriaminepentaacetic acid pentasodium, and the inorganic hypophosphite chain transfer agent is sodium hypophosphite. Preferably, based on the total mass of the final obtained ammonium polyacrylate emulsion, the amount of the amino polycarboxylic acid chelating agent added is 20-60 ppm, and the amount of the inorganic hypophosphite chain transfer agent added is 10-60 ppm.

7. The preparation method according to any one of claims 1 to 3, characterized in that, Based on the total mass of the final obtained ammonium polyacrylate emulsion, the amount of azo initiator I is 30-45 ppm; the amount of azo initiator II is 15-30 ppm. Preferably, the azo initiator I further contains azobisisobutyrazoline hydrochloride; in the azo initiator I, the mass ratio of azobismethoxyisoheptanenitrile to azobisisobutyrazoline hydrochloride is 10-45:

1.

8. The preparation method according to any one of claims 1 to 3, characterized in that, In step (1), the viscosity of the emulsion obtained by homogenization is 1000-2000 mPa·s; Preferably, the homogenization conditions include a shear rate of 15,000-20,000 rpm and a time of 30-90 seconds.

9. The ammonium polyacrylate emulsion prepared by the preparation method according to any one of claims 1 to 8; Preferably, the viscosity of the ammonium polyacrylate emulsion at 25°C is 1200-1600 mPa·s, and the viscosity of the ammonium polyacrylate emulsion at 25°C in a 1 wt% sodium hydroxide solution is 120-250 mPa·s.

10. The application of the polyammonium acrylate emulsion according to claim 9 in the flocculation and sedimentation of solid suspensions, preferably in the separation and sedimentation or washing and sedimentation of red mud.

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