Synthesis of a Thiol-Modified Hydrophobic Polyacrylamide and Its Application in the Purification Process of Dilute Phosphoric Acid

Abstract

The present invention relates to a synthesis method of a mercapto-modified hydrophobic polyacrylamide, belonging to the field of polymer material synthesis. According to the synthesis method provided by the present invention, first, the reaction monomers are stirred and mixed evenly with water to obtain a mixed solution, the pH value of the mixed solution is adjusted to 5.0 - 7.0, and then a dispersant is added and stirred to form an emulsion. When adding the dispersant, the temperature is raised. When the temperature is raised to 50 - 70 °C, an initiator is added to start the polymerization reaction until the viscosity of the reaction system remains unchanged and the polymerization reaction ends; wherein, the addition amount of the dispersant is 5% - 10% of the total mass of the monomers; the addition amount of the initiator is 0.1% - 0.5% of the total mass of the monomers. The synthesis method of the hydrophobic modified polyacrylamide provided by the present invention reduces the viscosity of the system during the synthesis process without reducing the product effect, which is beneficial to realizing industrial production.

Description

Technical Field

[0001] The invention belongs to the field of functional macromolecular polymers and relates to a synthesis method of a thiol-modified hydrophobic polyacrylamide and application of the thiol-modified hydrophobic polyacrylamide in a wet-process phosphoric acid purification process. Background Art

[0002] Phosphate fertilizer is an indispensable production material in agricultural production, and phosphoric acid, one of the main raw materials of phosphate fertilizer, is also a very important chemical. Wet-process phosphoric acid is one of the main methods for industrial production of phosphoric acid. It is the most widely used low-cost phosphoric acid production method. Because it contains more fluoride ions and heavy metal impurities, it is necessary to purify and remove impurities from wet-process phosphoric acid for environmental protection and food safety considerations. At present, the more common wet-process phosphoric acid purification technologies are: chemical precipitation method, gas phase method, solvent precipitation method and solvent extraction method. Among them, the chemical precipitation method is the simplest, easy to operate and cost-controllable. However, the defluorination efficiency is low, and due to its high viscosity, the iron, aluminum and other elements contained in the low-grade phosphate ore in the entire purification production process will form iron aluminum fluoride salts that are difficult to precipitate with fluoride ions, which greatly reduces the application effect of the chemical precipitation method. And because the hydrogen fluoride content in dilute phosphoric acid is low, the defluorination effect of the gas phase method is also not ideal. Although the solvent extraction method has a good purification effect on wet-process phosphoric acid, it requires a large investment in multi-stage reactors and stripping equipment, and the cost performance is relatively low. Therefore, there is an urgent need for a high-efficiency and cost-effective wet-process phosphoric acid defluorination method.

[0003] Chinese patent CN105085802B (Xu Jie, Fei Dejun, etc.) has conducted detailed research on the modification and production process of polyacrylamide, and has also improved the synthesis process of polyacrylamide, making it more suitable for industrial production and application in the wet-process phosphoric acid industry. However, it has not completely broken away from the framework of traditional polyacrylamide, making the function of polyacrylamide relatively single, and the gain for the entire phosphoric acid purification process is not very obvious. Therefore, it is necessary to further optimize and modify polyacrylamide to give it more functions.

[0004] The present invention shows that the affinity of polyacrylamide to heavy metal ions, heavy metal particles and flocs can be improved by modifying polyacrylamide to a certain extent, which helps to improve the auxiliary removal effect of polyacrylamide on heavy metals.

[0005] At the same time, by using alcohol dispersants, on the one hand, the emission of toxic gases in the production process can be reduced, and on the other hand, the use of alcohol dispersants can improve the emulsification effect of monomers and water. Therefore, starting from the monomer, the present invention improves and optimizes the hydrophobic polyacrylamide by adjusting the dispersion system, and optimizes its synthesis process, thereby improving the use effect of the final product in the defluorination of dilute phosphoric acid. Summary of the invention

[0006] In view of the above deficiencies, the present invention provides a new method for synthesizing polyacrylamide emulsion products. By modifying some monomers with mercapto groups, polyacrylamide with higher affinity for heavy metal ions is prepared, and the entire production process is made safer and more reliable by adjusting the additives used in the synthesis.

[0007] Specifically, the present invention provides a method for synthesizing mercapto-modified hydrophobic polyacrylamide, comprising:

[0008] S1: Customize three monomers, namely a hydrophobic monomer, a mercapto-modified monomer, and the main monomer acrylamide, and the three monomers are obtained through customization from Nanjing Pharmaceutical Stone Technology Co., Ltd.

[0009] S2: Mix the three monomers, water, and a dispersant described in step S1 to obtain a mixed solution, and use an alkaline solution to adjust the pH value of the mixed solution to 5.0 - 7.0.

[0010] S3: Introduce an inert gas to remove the dissolved oxygen in the mixed solution.

[0011] S4: Heat the mixed solution to 50°C - 70°C, add an initiator to initiate the polymerization reaction, and stop the polymerization until the viscosity of the reaction system no longer changes. Age for 10 - 12 hours to obtain a mercapto-modified hydrophobic polyacrylamide solution.

[0012] Further, in step S2, the volume ratio of the dispersant to water in the mixed solution is 1:(9 - 49).

[0013] Further, the mass concentration of the monomers in the mixed solution is 5% - 30%, preferably 10% - 20%.

[0014] Further, in step S4, the mass percentage of the initiator in the total mass of the three monomers is 0.1% - 0.5%, preferably 0.1% - 0.3%.

[0015] Further, the mass ratio of the main monomer acrylamide, the hydrophobic monomer, and the mercapto-modified monomer is 1:(0.5 - 0.9):(0.1 - 0.5).

[0016] Further, the hydrophobic monomer is n-heptyl acrylate, isoheptyl acrylate, n-octyl acrylate, isooctyl acrylate, n-nonyl acrylate, isononyl acrylate; the mercapto monomer is at least one of ethylenedithiol acrylate mercaptan, 1,3-propanedithiol acrylate mercaptan, 1,4-butanedithiol acrylate mercaptan, 1,5-pentanedithiol acrylate mercaptan, 1,6-hexanedithiol acrylate mercaptan, 1,8-octanedithiol acrylate mercaptan, 3,6-dioxa-1,8-octanedithiol acrylate mercaptan.

[0017] Further, the dispersant is at least one of n-butanol, isobutanol, n-pentanol, isopentanol, and isopentanediol.

[0018] Further, the alkaline solution is a soluble alkali solution, specifically at least one of sodium hydroxide, sodium carbonate, and sodium bicarbonate solutions;

[0019] Further, the inert gas is at least one of helium, neon, argon, krypton, xenon, and radon.

[0020] Further, during the reaction process, the mass percentage of the initiator in the total mass of the reaction system is 0.1% - 0.3%.

[0021] Further, the initiator is a persulfate-sodium bisulfite mixed system, and the mass ratio of persulfate to sodium bisulfite is (1.0 - 1.2):1, where the persulfate includes potassium persulfate, ammonium persulfate, and sodium persulfate.

[0022] Further, the thiol-modified hydrophobic polyacrylamide is used as a co-precipitant for purifying dilute phosphoric acid during the chemical precipitation process, and the chemical precipitation process is a fluorosilicate precipitation process.

[0023] Further, the defluorinating agent used is an alkali metal salt or an alkaline earth metal salt, including but not limited to sodium chloride, sodium sulfate, potassium sulfate, sodium carbonate, calcium chloride, calcium carbonate, potassium carbonate, potassium chloride, and a 1:1 mixture of sodium chloride and potassium chloride, preferably sodium chloride, potassium chloride, and a mixture of sodium chloride and potassium chloride with a mass ratio of 1:1.

[0024] Further, the inorganic salt used is at least one of a sodium salt and a potassium salt, and the silicate used is at least one of silica white, silica dioxide, and silica gel.

[0025] In the present invention, the use of polyacrylamide is as a precipitation aid in the chemical precipitation method, which is used to improve the precipitation efficiency and filtration rate.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] (1) The present invention adopts a modified monomer and an improved synthesis process to prepare a quick-dissolving hydrophobic modified polyacrylamide emulsion product with appropriate viscosity and good stability, which greatly promotes the industrial production of new polyacrylamide-based additives. This polyacrylamide-based additive can be applied to the phosphoric acid production process and has good economic and social benefits.

[0028] (2) Starting from monomers, based on the main monomer acrylamide, the present invention introduces the strong coordination group mercapto group of heavy metal ions into the molecular structure through chemical synthesis methods for mercapto modification to form a mercapto-modified monomer, and prepares a mercapto-modified polyacrylamide with higher affinity for heavy metal ions. As a new type of heavy metal chelating flocculant, it has both chelating and flocculating dual functions, improving its affinity for heavy metal ions, heavy metal particles, and flocs, and improving the auxiliary removal effect of heavy metals. Therefore, this mercapto-modified polyacrylamide can be directly applied to the treatment of heavy metal wastewater.

[0029] (3) In the method of the present invention, a hydrophobic monomer is introduced. The introduction of the hydrophobic monomer can not only increase the dilution viscosity of the emulsion, but also shorten the nucleation period of the polymer during the polymerization process, making it easier for the reactants to enter the polymer particles through the solvent channels for polymerization reaction, thereby increasing the viscosity-average relative molecular weight of the polymer emulsion.

[0030] (4) In the method of the present invention, a mercapto-modified monomer is introduced. The structure of this monomer contains dithiocarboxyl group, which can chelate and precipitate with most heavy metal ions. Using the mercapto-modified hydrophobic polyacrylamide as a co-precipitant for purifying dilute phosphoric acid during the chemical precipitation process can improve the precipitation efficiency and filtration speed.

[0031] (5) The present invention uses an alcohol dispersant. On the one hand, it can reduce the emission of toxic gases during the production process, making the entire production process safer and more reliable by adjusting the additives used in the synthesis; on the other hand, it can improve the emulsification effect of the above monomers and water, improve and optimize the hydrophobic polyacrylamide in the dispersion system, and optimize its synthesis process, enhancing the use effect of the final product polyacrylamide in defluorination of dilute phosphoric acid. Description of the Drawings

[0032] Figure 1 : From left to right are the sample diagrams provided in Examples 1-6 of the present application. Detailed Embodiments

[0033] To make the purpose, technical solutions and advantages of the present application clearer and more understandable, the present application will be further described in detail below. However, it should be understood that the description herein is only used to explain the present application and is not used to limit the scope of the present application.

[0034] Unless otherwise defined, all technical terms and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present application belongs. The terms used in the description of the present application herein are only for the purpose of describing specific embodiments and are not intended to limit the present application. The reagents and instruments used herein are all commercially available, and the characterization means involved can be referred to the relevant descriptions in the prior art and will not be elaborated herein.

[0035] To further understand the present application, the following provides a more detailed description of the present application in conjunction with the best embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0036] In the first aspect, the present invention provides a method for synthesizing a new mercapto-modified hydrophobic polyacrylamide, and the method includes the following steps:

[0037] 1) Customize and purchase three monomers from Nanjing Pharmaceutical Stone Technology Co., Ltd., namely a hydrophobic monomer, a mercapto-modified monomer, and the main monomer acrylamide;

[0038] 2) Stir and dissolve the main monomer acrylamide, the hydrophobic monomer, the mercapto-modified monomer, water, and a dispersant evenly and then add them to a polymerization reaction kettle;

[0039] 3) Use a high and low temperature circulating pump to control the system temperature to be stable at about 50-70°C (such as 50°C, 51°C, 52°C, 53°C, 54°C, 55°C, 56°C, 57°C, 58°C, 59°C, 60°C, 61°C, 62°C, 63°C, 64°C, 65°C, 66°C, 67°C, 68°C, 69°C, or 70°C), preferably 60°C; control the stirring speed at 100-150 rpm (such as 100 rpm, 110 rpm, 120 rpm, 130 rpm, 140 rpm, or 150 rpm), ensure that the reaction system is in an emulsion state without separation, and add an alkali solution to adjust the pH to 6.0-7.0 (such as 6.0, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, or 7.0);

[0040] 4) Introduce the inert gas nitrogen from the bottom of the kettle, keep stirring for 30 minutes, then add an initiator to initiate the polymerization reaction. Sample and detect the system viscosity every 30 minutes. After the viscosity no longer changes, continue to stir for 30-60 minutes (such as 30, 40, 50, or 60 min) and then the reaction ends.

[0041] In the above step 2), the main monomer is acrylamide; the hydrophobic monomer is n-heptyl acrylate, iso-heptyl acrylate, n-octyl acrylate, iso-octyl acrylate, n-nonyl acrylate, iso-nonyl acrylate; the mercapto monomer is one or more of ethylenedithiol acrylate mercaptan, 1,3-propanedithiol acrylate mercaptan, 1,4-butanedithiol acrylate mercaptan, 1,5-pentanedithiol acrylate mercaptan, 1,6-hexanedithiol acrylate mercaptan, 1,8-octanedithiol acrylate mercaptan, 3,6-dioxa-1,8-octanedithiol acrylate mercaptan; the dispersant is one or more of n-butanol, isobutanol, n-pentanol, isopentanol, isopentylene glycol;

[0042] In the above step 2), the volume ratio of the dispersant to water is 1:(9 - 49), preferably 1:20.

[0043] In the above step 2), the mass ratio of the main monomer, the hydrophobic monomer to the mercapto-modified monomer is 1:(0.5 - 0.9):(0.1 - 0.5), preferably 2:1:1.

[0044] In the above step 2), the total mass concentration of the three monomers in the reaction system is 5% - 30% (such as 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29% or 30%), preferably 10% - 20% (such as 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19% or 20%).

[0045] In the above step 3), the lye is sodium hydroxide, sodium carbonate or sodium bicarbonate solution, preferably sodium carbonate.

[0046] In the above step 4), the inert gas is nitrogen and carbon dioxide, preferably nitrogen; the duration of passing the inert gas is greater than or equal to 30 minutes (such as 30, 40, 50, 60, 70, 80 or 90 minutes), preferably 60 minutes; the initiator is a persulfate-sodium bisulfite system, and the persulfate includes potassium persulfate, ammonium persulfate, sodium persulfate; the addition amount of the initiator is 0.1% - 0.5% (such as 0.1%, 0.2%, 0.3%, 0.4% or 0.5%) of the total mass of the three monomers, preferably 0.1% - 0.3%, more preferably 0.2%.

[0047] The present invention in another aspect provides the application of the mercapto-modified hydrophobic polyacrylamide prepared above in the purification process of dilute phosphoric acid.

[0048] The dilute phosphoric acid purification process described in the present invention is mainly a process for purifying dilute phosphoric acid using a chemical precipitation method.

[0049] The chemical precipitation method described in the present invention is a fluorosilicate precipitation method.

[0050] The thiol-modified hydrophobic polyacrylamide of the present invention is used as a precipitation auxiliary agent in a chemical precipitation method to improve the precipitation efficiency and the filtration speed.

[0051] In the present invention, a hydrophobic monomer is introduced. The introduction of the hydrophobic monomer can not only increase the dilution viscosity of the emulsion, but also shorten the polymer nucleation period during the polymerization process, and the reactants can more easily enter the polymer particles through the solvent channel to carry out the polymerization reaction, thereby increasing the viscosity-average relative molecular weight of the polymer emulsion.

[0052] According to some preferred embodiments, the amount of each raw material is: 10 parts by weight of the main monomer acrylamide, 5 parts by weight of the hydrophobic monomer, 5 parts by weight of the thiol-modified monomer, 0.04 parts by weight of the initiator, and 10 parts by weight of the dispersant.

[0053] According to some preferred embodiments, the defluorinating agent used is an alkali metal salt or an alkaline earth metal salt, including but not limited to sodium chloride, sodium sulfate, potassium sulfate, sodium carbonate, calcium chloride, calcium carbonate, potassium carbonate, potassium chloride and a mixture of sodium chloride and potassium chloride in a mass ratio of 1:1; preferably sodium chloride, potassium chloride and a mixture of sodium chloride and potassium chloride in a mass ratio of 1:1.

[0054] In the present invention, the three monomers are preferably added in three times, so that the distribution of the three monomers is more uniform compared to adding them all at once. Adding the three monomers all at once will result in uneven local concentration distribution of the monomers, thus resulting in poor heavy metal removal effect.

[0055]

[0056] Example 1

[0057] This example provides a method for synthesizing thiol-modified hydrophobic polyacrylamide. Specifically, 1000 g of acrylamide, 500 g of n-heptyl acrylate, and 500 g of 1,3-propanedithiol acrylate thiol are dissolved in 9000 g of distilled water and 1000 g of n-butanol by stirring, and then added to a 20 L polymerization reactor. Stir to fully dissolve and disperse them. After the temperature of the system rises to room temperature, the pH of the system is adjusted to 5.0 with a dilute sodium hydroxide (NaOH) solution. N2 is introduced from the bottom of the polymerization reactor to remove oxygen for 60 min, and the solution is slowly stirred at 100 rpm and then slowly heated from room temperature to 50 °C, during which the stirring speed is adjusted to 200 rpm. 18 g of potassium persulfate and 18 g of sodium bisulfite are taken and dissolved in 100 g of distilled water to prepare an initiator solution. After the polymerization reactor is heated to the required temperature, the initiator solution is added. Samples are taken every 10 - 30 min to measure the viscosity change of the system. When the viscosity no longer changes, the polymerization reaction ends, and the solution is aged for 10 hours to obtain thiol-modified hydrophobic polyacrylamide.

[0058] Example 2

[0059] This example provides a method for synthesizing thiol-modified hydrophobic polyacrylamide. 1000 g of acrylamide, 500 g of n-octyl acrylate, and 500 g of 3,6-dioxa-1,8-octanedithiol acrylate thiol are dissolved in 9000 g of distilled water and 1000 g of n-pentanol by stirring, and then added to a 20 L polymerization reactor. Stir to fully dissolve and disperse them. After the temperature of the system rises to room temperature, the pH of the system is adjusted to 7.0 with a dilute sodium hydroxide (NaOH) solution. N2 is introduced from the bottom of the polymerization reactor to remove oxygen for 60 min, and the solution is slowly stirred at 100 rpm. Then it is slowly heated from room temperature to 60 °C, during which the stirring speed is adjusted to 200 rpm. 1.5 g of potassium persulfate and 1.5 g of sodium bisulfite are taken and dissolved in 100 g of distilled water to prepare an initiator solution. After the polymerization reactor is heated to the required temperature, the initiator solution is added. Samples are taken every 10 - 30 min to measure the viscosity change of the system. When the viscosity no longer changes, the polymerization reaction ends, and the solution is aged for 11 hours to obtain thiol-modified hydrophobic polyacrylamide.

[0060] Example 3

[0061] This example provides a method for synthesizing mercapto-modified hydrophobic polyacrylamide. After dissolving 1000 g of acrylamide, 500 g of n-nonyl acrylate, and 500 g of 1,4-butanedithiol acrylate mercaptan in 9000 g of distilled water and 1000 g of isobutanol, it is added to a 20 L polymerization reactor. Stir to make it fully dissolved and dispersed. After the system temperature rises to room temperature, adjust the pH of the system to 6.5 with a dilute sodium hydroxide (NaOH) solution. Pass N2 from the bottom of the polymerization reactor to remove oxygen for 60 min, and slowly stir the solution at 100 rpm. Then start to slowly heat up from room temperature to 70 °C, and adjust the stirring speed to 200 rpm during this process. Take 1.5 g of ammonium persulfate and 1.5 g of sodium bisulfite, dissolve them in 100 g of distilled water to prepare an initiator solution. After the polymerization reactor finishes heating up, start adding the initiator solution. Sample and measure the viscosity change of the system every 10 - 30 min. When the viscosity no longer changes, it can be considered that the polymerization reaction is over. Age the solution for 12 hours to obtain a polyacrylamide solution.

[0062] Example 4

[0063] This example provides a method for synthesizing mercapto-modified hydrophobic polyacrylamide. After dissolving 1000 g of acrylamide, 500 g of isoheptyl acrylate, and 500 g of 3,6-dioxa-1,8-octanedithiol acrylate mercaptan in 9000 g of distilled water and 1000 g of isoamyl alcohol, it is added to a 20 L polymerization reactor. Stir to make it fully dissolved and dispersed. After the system temperature rises to room temperature, adjust the pH of the system to 5.5 with a dilute sodium hydroxide (NaOH) solution. Pass N2 from the bottom of the polymerization reactor to remove oxygen for 60 min, and slowly stir the solution at 100 rpm. Then start to slowly heat up from room temperature to 55 °C, and adjust the stirring speed to 200 rpm during this process. Take 1.5 g of ammonium persulfate and 1.5 g of sodium bisulfite, dissolve them in 100 g of distilled water to prepare an initiator solution. After the polymerization reactor finishes heating up, start adding the initiator solution. Sample and measure the viscosity change of the system every 10 - 30 min. When the viscosity no longer changes, it can be considered that the polymerization reaction is over. Age the solution for 10 hours to obtain a polyacrylamide solution.

[0064] Example 5

[0065] This embodiment provides a method for synthesizing a mercapto-modified hydrophobic polyacrylamide. After dissolving 1000 g of acrylamide, 500 g of isononyl acrylate, and 500 g of 1,5-pentanedithiol acrylate mercaptan in 9000 g of distilled water and 1000 g of isopentyl glycol, it is added to a 20 L polymerization reactor. Stir to fully dissolve and disperse it. After the system temperature rises to room temperature, adjust the pH of the system to 6.0 with a dilute sodium hydroxide (NaOH) solution. Pass N2 from the bottom of the polymerization reactor to remove oxygen for 60 min, and slowly stir the solution at 100 rpm. Then start to slowly heat up from room temperature to 65 °C, and adjust the stirring speed to 200 rpm during this process. Take 1.5 g of ammonium persulfate and 1.5 g of sodium bisulfite, dissolve them in 100 g of distilled water to prepare an initiator solution. After the polymerization kettle finishes heating up, start adding the initiator solution. Take samples every 10 - 30 min to measure the viscosity change of the system. When the viscosity no longer changes, it can be considered that the polymerization reaction is over. Age the solution for 12 hours to obtain a polyacrylamide solution.

[0066] Example 6

[0067] This embodiment provides a method for synthesizing a mercapto-modified hydrophobic polyacrylamide. After dissolving 1000 g of acrylamide, 500 g of isooctyl acrylate, and 500 g of 1,8-octanedithiol acrylate mercaptan in 9000 g of distilled water and 1000 g of n-butanol, it is added to a 20 L polymerization reactor. Stir to fully dissolve and disperse it. After the system temperature rises to room temperature, adjust the pH of the system to 5.0 with a dilute sodium hydroxide (NaOH) solution. Pass N2 from the bottom of the polymerization reactor to remove oxygen for 60 min, and slowly stir the solution at 100 rpm. Then start to slowly heat up from room temperature to 70 °C, and adjust the stirring speed to 200 rpm during this process. Take 1.5 g of ammonium persulfate and 1.5 g of sodium bisulfite, dissolve them in 100 g of distilled water to prepare an initiator solution. After the polymerization kettle finishes heating up, start adding the initiator solution. Take samples every 10 - 30 min to measure the viscosity change of the system. When the viscosity no longer changes, it can be considered that the polymerization reaction is over. Age the solution for 11 hours to obtain a polyacrylamide solution.

[0068] Comparative Example 1

[0069] After dissolving 17 g of acrylamide by stirring with 150 g of distilled water, mix it evenly with 7.28 g of octylphenol polyoxyethylene acrylate (AOP-10) and add it to the polymerization reactor. After the temperature of the system rises to room temperature, adjust the pH of the system to 5.5 with a dilute NaOH solution, record the mass of the added NaOH solution, and add distilled water after adjustment to make the monomer solid content 20%. Purge oxygen with N2 from the bottom of the polymerization reactor for 45 min, and slowly stir the solution at 100 rpm. Slowly heat up from room temperature to 60 °C, and adjust the stirring speed to 200 rpm during this process. Take 0.0456 g of potassium persulfate and 0.042 g of sodium thiosulfate pentahydrate, dissolve them in 50 g of distilled water to prepare the initiator solution. After the polymerization kettle finishes heating up, start adding the initiator solution, sample and measure the viscosity change of the system every 10 - 30 min. When the viscosity no longer changes, the polymerization reaction can be considered to end. Take samples for analysis and test its filter aid effect and heavy metal removal effect.

[0070] The main difference in operation from Examples 1 - 6 is the difference in the monomers used. The monomer of this Comparative Example 1 does not contain a mercapto group, while the monomers of the Examples contain a mercapto monomer. By comparing with the products obtained in the Examples, it is proved that the introduction of the mercapto monomer can greatly improve its heavy metal removal ability.

[0071] This comparative example does not introduce a dispersant, while the above examples introduce a dispersant. The introduction of the dispersant helps to improve the hydrophobicity of polyacrylamide.

[0072] Comparative Example 2

[0073] After dissolving 17 g of acrylamide by stirring with 150 g of distilled water, mix it evenly with 7.28 g of n-heptyl acrylate and add it to the polymerization reactor. After the temperature of the system rises to room temperature, adjust the pH of the system to 5.5 with a dilute NaOH solution, record the mass of the added NaOH solution, and add distilled water after adjustment to make the monomer solid content 20%. Purge oxygen with N2 from the bottom of the polymerization reactor for 45 min, and slowly stir the solution at 100 rpm. Slowly heat up from room temperature to 60 °C, and adjust the stirring speed to 200 rpm during this process. Take 0.0456 g of potassium persulfate and 0.042 g of sodium thiosulfate pentahydrate, dissolve them in 50 g of distilled water to prepare the initiator solution. After the polymerization kettle finishes heating up, start adding the initiator solution, sample and measure the viscosity change of the system every 10 - 30 min. When the viscosity no longer changes, the polymerization reaction can be considered to end. Take samples for analysis and test its filter aid effect and heavy metal removal effect.

[0074] The main difference in operation from Examples 1 - 6 is still that mercapto monomers and dispersants are not used.

[0075] Comparative Example 3

[0076] After dissolving 17 g of acrylamide in 150 g of distilled water with stirring, it was mixed evenly with 7.28 g of isooctyl acrylate added, and then added to the polymerization reactor. After the temperature of the system rose to room temperature, the pH of the system was adjusted to 5.5 with a dilute NaOH solution, the mass of the added NaOH solution was recorded, and distilled water was added after adjustment to make the monomer solid content 20%. N2 was introduced from the bottom of the polymerization reactor to remove oxygen for 45 min, and the solution was slowly stirred at 100 rpm. The temperature was slowly raised from room temperature to 60 °C, and the stirring speed was adjusted to 200 rpm during this process. 0.0456 g of potassium persulfate and 0.042 g of sodium thiosulfate pentahydrate were taken and dissolved in 50 g of distilled water to prepare an initiator solution. After the polymerization kettle was heated up, the initiator solution was added. Samples were taken every 10 - 30 min to measure the viscosity change of the system. When the viscosity no longer changed, the polymerization reaction was considered to be over. Sampling and analysis were carried out to test its filter aid effect and heavy metal removal effect.

[0077] The main difference in operation from Examples 1 - 6 was still that no mercapto monomer and dispersant were used.

[0078] Performance test: Heavy metal removal and filtration effect test

[0079] 15 L of wet-process phosphoric acid from Hubei Xiangyun Group was placed in a 20 L reactor and stirred at 75 °C and 150 rpm for 10 min; 1% potassium sulfate and 0.5% silica gel were added and reacted for 4 h, and then 150 g of a 5% mercapto polyacrylamide solution or the solution in which PAM obtained in Comparative Example 1 was dissolved was added respectively, and stirred for 10 min; then constant-temperature vacuum filtration was carried out under a vacuum of 0.05 MPa, the time when the filtrate reached a certain volume was recorded, and then the supernatant was taken to measure the heavy metal residue in the solution; the specific results are shown in Table 1.

[0080]

[0081] The comprehensive experimental results showed that: The mercapto polyacrylamide solutions prepared in Examples 1 - 6 were far superior to traditional hydrophobic polyacrylamides in terms of filter aid speed, and had obvious removal effects on common heavy metal impurities such as iron, aluminum, arsenic, and lead in phosphoric acid.

[0082] The results showed that by carrying out certain mercapto modification on polyacrylamide, its affinity for heavy metal ions, heavy metal particles, and flocs could be improved, thereby enhancing its auxiliary heavy metal removal effect. At the same time, using an alcohol dispersant could, on the one hand, reduce the emission of toxic gases during the production process, and on the other hand, using an alcohol dispersant could improve the emulsification effect of the monomer and water.

[0083] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention; any person skilled in the art can, without departing from the scope of the technical solution of the present invention, make many possible changes and modifications to the technical solution of the present invention by using the methods and technical contents disclosed above, or modify it into equivalent embodiments with equivalent changes. Therefore, any simple modification, equivalent replacement, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A synthesis method of mercapto-modified hydrophobic polyacrylamide, characterized in that, the method comprises: S1: Prepare monomers, the monomers include hydrophobic monomers, mercapto-modified monomers and the main monomer acrylamide; S2: Mix the three monomers described in step S1 with water and a dispersant to obtain a mixed solution, and adjust the pH value of the mixed solution to 5.0 - 7.0 using an alkaline solution; S3: Remove the dissolved oxygen in the mixed solution; S4: Heat the mixed solution to 50°C - 70°C, add an initiator to initiate the polymerization reaction, and stop the polymerization until the viscosity of the reaction system no longer changes, and age for 10 - 12 hours to obtain a mercapto-modified hydrophobic polyacrylamide solution; The hydrophobic monomers are n-heptyl acrylate, isoheptyl acrylate, n-octyl acrylate, isooctyl acrylate, n-nonyl acrylate, isononyl acrylate; The mercapto-modified monomers are at least one of ethylenedithiol acrylate mercaptan, 1,3-propanedithiol acrylate mercaptan, 1,4-butanedithiol acrylate mercaptan, 1,5-pentanedithiol acrylate mercaptan, 1,6-hexanedithiol acrylate mercaptan, 1,8-octanedithiol acrylate mercaptan, 3,6-dioxa-1,8-octanedithiol acrylate mercaptan; The dispersant is at least one of n-butanol, isobutanol, n-pentanol, isopentanol, isopentanediol; The mass ratio of the main monomer acrylamide, hydrophobic monomer and mercapto-modified monomer is 1:(0.5 - 0.9):(0.1 - 0.5); In step S2, the volume ratio of the dispersant to water in the mixed solution is 1:(9 - 49); the mass concentration of the monomers in the mixed solution is 5% - 30%.

2. The synthesis method of mercapto-modified hydrophobic polyacrylamide according to claim 1, characterized in that, in step S4, the mass percentage of the initiator in the total mass of the three monomers is 0.1% - 0.5%.

3. The synthesis method of mercapto-modified hydrophobic polyacrylamide according to claim 1, characterized in that, the alkaline solution is a soluble alkali solution, including at least one of sodium hydroxide, sodium carbonate and sodium bicarbonate solutions; the inert gas is at least one of helium, neon, argon, krypton, xenon and radon.

4. The synthesis method of mercapto-modified hydrophobic polyacrylamide according to any one of claims 1 - 3, characterized in that, the total mass percentage of the three monomers in the reaction system during the reaction process is 10% - 20%.

5. The synthesis method of mercapto-modified hydrophobic polyacrylamide according to claim 1, characterized in that, the mass percentage of the initiator in the reaction system during the reaction process is 0.1% - 0.3%.

6. The synthesis method of mercapto-modified hydrophobic polyacrylamide according to any one of claims 1 - 3, characterized in that, the initiator is a persulfate-sodium bisulfite mixed system, and the mass ratio of persulfate to sodium bisulfite is (1.0 - 1.2):1, where the persulfate is potassium persulfate, ammonium persulfate and sodium persulfate.

7. Use of the thiol-modified hydrophobic polyacrylamide synthesized by the method according to any one of claims 1-3 in the purification process of dilute phosphoric acid, characterized in that, the thiol-modified hydrophobic polyacrylamide is used as a co-precipitant for purifying dilute phosphoric acid in the chemical precipitation process, and the chemical precipitation process is a fluorosilicate precipitation process, wherein the defluorinating agent used is sodium chloride, sodium sulfate, potassium sulfate, sodium carbonate, calcium chloride, calcium carbonate, potassium carbonate, potassium chloride, and a mixture of sodium chloride and potassium chloride with a mass ratio of 1:1.

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