A process for the preparation of MA / AA

Abstract

The application discloses a preparation process of MA / AA, and belongs to the technical field of water treatment. The process comprises the following steps: (a) adding a sodium hydroxide solution into a maleic acid aqueous solution to stir, so as to obtain a sodium maleate solution as a reaction bottom material; (b) heating the bottom material to 95-105 DEG C, while dropping an acrylic acid and a hydrogen peroxide solution, dropping for 4-6 hours, and then performing first-stage polymerization by keeping warm for 1-3 hours; (c) adjusting the pH of the system to 4.8-5.2, dropping an ammonium persulfate aqueous solution, dropping for 0.5-1 hour, and then performing second-stage polymerization by keeping warm for 1-2 hours, so as to obtain a MA / AA copolymer product. The two-stage segmented initiation process of "hydrogen peroxide initiation polymerization -> pH adjustment -> ammonium persulfate secondary initiation" is adopted, no metal catalyst and chain transfer agent are added, the residual monomer content can be reduced to 0.8%-1.0% while maintaining a high MA proportion, the molecular weight Mw can reach 4000-5200, and the process is simple and easy to implement in industrialization.

Description

Technical Field

[0001] This invention belongs to the field of water treatment technology, specifically relating to a preparation process of MA / AA. Background Technology

[0002] MA / AA, or maleic acid-acrylic acid copolymer, is a low molecular weight polyelectrolyte and a highly efficient water treatment chemical. It has many properties such as high scale inhibition, excellent corrosion inhibition, chemical stability, thermal stability, environmental friendliness, economy, and compatibility. It is widely used in many fields such as cooling water systems, boiler water systems, reverse osmosis systems, industrial circulating water systems, textile industry, and petrochemical industry.

[0003] The properties of MA / AA polymers vary depending on the ratio of MA to AA. A higher MA ratio results in higher thermal stability, stronger chelating ability, and better inhibition of calcium carbonate and calcium sulfate formation. A higher AA ratio leads to higher polymerization activity, larger molecular weight and viscosity, and better dispersion. Conversely, a higher MA ratio results in lower polymerization activity and lower feed conversion rates during polymer synthesis. Therefore, preparing MA / AA polymers with a high MA ratio while increasing molecular weight and reducing residual monomers has been a research hotspot in this field.

[0004] Currently, the industrial production of MA / AA mainly employs aqueous free radical polymerization, using maleic acid (usually obtained from the hydrolysis of maleic anhydride) and acrylic acid as raw materials, and polymerizing in an aqueous medium. Various initiation systems for the preparation of MA / AA have been reported in existing technologies. For example, studies have shown the synthesis of acrylic acid-maleic anhydride copolymers using potassium persulfate as an initiator and sodium bisulfite as a chain transfer agent; other literature has reported the synthesis of maleic anhydride-acrylic acid copolymers using aqueous polymerization with sodium persulfate as an initiator and sodium bisulfite as a reducing agent. Furthermore, there are reports of using ammonium persulfate as an initiator to react maleic anhydride, acrylic acid, and sodium hypophosphite to synthesize phospho-maleic acid-acrylic acid copolymers. Schemes using hydrogen peroxide as an initiator have also been reported, such as the semi-continuous aqueous copolymerization of acrylic acid and maleic anhydride at 120°C, or the preparation of complexing dispersants by initiating copolymerization with hydrogen peroxide. In addition, studies have also used redox initiation systems such as persulfate-sodium bisulfite for aqueous polymerization. However, the above-mentioned existing technologies still have the following shortcomings: First, maleic acid (MA) has a low conversion rate and a high residual monomer content. Due to the presence of conjugated double bonds and two carboxyl groups in its molecular structure, the free radical polymerization activity of MA monomer is much lower than that of AA. In polymerization systems with a high proportion of MA, the conversion rate of MA is usually low, resulting in a high residual MA monomer content in the final product. The presence of residual monomer not only affects the purity and performance of the product but may also pose environmental and safety risks. Although CN119285836A reports that using a composite catalyst and azo initiators can reduce residual maleic acid monomer to below 30 ppm, its system is quite complex, involving a composite catalyst of copper sulfate pentahydrate and ferrous sulfate heptahydrate, as well as various auxiliaries such as azo initiators, increasing production costs and operational difficulty.

[0005] Secondly, it is difficult to balance a high MA ratio with a high molecular weight. A higher MA ratio results in lower polymerization activity, making it more difficult to increase the polymer molecular weight. Conversely, an excessively low molecular weight can negatively impact the product's dispersion performance and scale inhibition. How to maintain a high MA ratio while achieving a relatively high molecular weight has long been a challenging problem for those skilled in the art.

[0006] Third, existing processes rely on a single initiation method and lack segmented control over the polymerization process. Most reported methods for preparing MA / AA employ a one-stage initiation process, meaning the initiator is added all at once or continuously added dropwise over a period of time with a single initiator (or a combination of initiators). For example, while CN109970911A mentions several optional initiators such as hydrogen peroxide and ammonium persulfate, it still uses a conventional one-stage dropwise addition process. This single initiation method makes it difficult to segmentally control the polymerization process, hindering the simultaneous achievement of high conversion rates and ideal molecular weight distribution.

[0007] Fourth, some improvement solutions involve complex processes and high costs. In recent years, although some researchers have tried to improve product quality by adding composite catalysts, azo initiators, or multiple auxiliaries, these solutions often involve multiple auxiliaries and complex process control, which increases production costs and operational difficulty, hindering industrial-scale promotion.

[0008] In view of the shortcomings of the existing technology, the present invention is proposed. Summary of the Invention

[0009] To address the shortcomings of the existing technology, this invention provides a process for preparing MA / AA. This invention does not add metal catalysts or chain transfer agents. It employs a two-stage initiation process of "hydrogen peroxide-initiated polymerization → pH adjustment → ammonium persulfate secondary initiation," effectively reducing the residual monomer content while maintaining a high MA ratio, resulting in a high molecular weight MA / AA polymer product. Furthermore, the process is simple, requires no complex additives, and is easy to implement industrially.

[0010] To achieve the above objectives, the present invention adopts the following technical solution: A process for preparing MA / AA, the process comprising the following steps: (a) Slowly add sodium hydroxide solution to maleic acid aqueous solution and stir for 10-30 min to obtain sodium maleate solution, which is used as the reaction substrate; (b) Heat the reaction substrate to a certain temperature, and then simultaneously add acrylic acid and hydrogen peroxide solution to the reaction substrate. The addition is completed in 4-6 hours. After the addition is completed, keep it at a certain temperature for a certain time to carry out the first stage polymerization reaction. (c) After the first stage of polymerization is completed, the pH of the system is adjusted to 4.8-5.2 with sodium hydroxide solution. Then, ammonium persulfate aqueous solution is added dropwise to the system at a certain temperature. The addition is completed in 0.5-1h. The system is kept warm for 1-2h to carry out the second stage of polymerization, and the MA / AA copolymer product is obtained.

[0011] Further, in step (a), the mass concentration of the maleic acid aqueous solution is 60-80%, the mass concentration of the sodium hydroxide solution is 40-60%, and the molar ratio of maleic acid to sodium hydroxide is 1:1.

[0012] Further, in step (b), the temperature of the reaction substrate and the temperature of the first-stage polymerization reaction are 95~105℃, and the holding time of the first-stage polymerization reaction is 1~3h.

[0013] Further, in step (b), the amount of acrylic acid added is 0.6 to 1.0 times the mass of maleic acid.

[0014] Furthermore, in step (b), the mass concentration of the hydrogen peroxide solution is 27.5%.

[0015] Further, in step (b), the amount of hydrogen peroxide solution added (calculated as H2O2) is 0.1 to 0.3 times the total mass of maleic acid and acrylic acid.

[0016] Further, in step (c), the mass concentration of the sodium hydroxide solution used to adjust the pH is 40-60%.

[0017] Further, in step (c), the mass concentration of the ammonium persulfate aqueous solution is 50%.

[0018] Further, in step (c), the amount of ammonium persulfate aqueous solution added (calculated as ammonium persulfate) is 0.05 to 0.15 times the total mass of maleic acid and acrylic acid.

[0019] Furthermore, in step (c), the temperature of the second stage polymerization reaction is 95~105℃.

[0020] This invention employs a two-stage initiation process. At the end of polymerization, unreacted MA and AA monomers remain in the system, primarily MA monomers, as free radicals have been largely consumed during the main reaction stage. By adjusting the pH to a weakly acidic level of 5.0 and adding ammonium persulfate, the thermal decomposition of persulfate ions continuously generates primary sulfate free radicals. These free radicals attack the double bonds of free monomers, re-initiating chain growth and incorporating small monomer molecules into the polymer chain. Simultaneously, some macromolecular chains are activated, generating new free radicals that further capture residual monomers, thereby reducing the free monomer content in the system. Maintaining the pH to 5.0 controls the initiator decomposition rate and reduces side reactions such as polymer oxidative chain scission.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention adopts a two-stage segmented initiation process—first, hydrogen peroxide is used to initiate polymerization, and after adjusting the pH, ammonium persulfate is used for secondary initiation. This achieves segmented control of the polymerization reaction and overcomes the shortcomings of the existing one-stage initiation process, which makes it difficult to achieve both high conversion rate and suitable molecular weight.

[0022] 2. The present invention can effectively reduce the residual monomer content in MA / AA copolymers. The data from the examples show that the residual monomer (calculated as maleic acid) can be as low as 0.8%, which is significantly better than the comparative scheme without secondary initiation (3.2% residual monomer).

[0023] 3. The process of this invention is simple, requiring no addition of metal salt catalysts or chain transfer agents. High-quality MA / AA copolymers can be prepared using only two conventional initiators: hydrogen peroxide and ammonium persulfate. It has a high safety factor and is easy to implement industrially.

[0024] 4. Under the condition of maintaining a high MA ratio (MA / AA=3:2), the present invention can obtain an MA / AA copolymer product with a molecular weight of about 5000 Mw, which has good thermal stability, chelating ability and dispersion performance. Detailed Implementation

[0025] The technical solution and effects of the present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto. Example 1

[0026] The process for preparing MA / AA in this embodiment is as follows: Step 1: Dissolve 300g of maleic acid in 100g of pure water to prepare a maleic acid aqueous solution; slowly add 207g of 50% sodium hydroxide solution to the maleic acid aqueous solution and stir for 30 minutes as the reaction substrate.

[0027] Step 2: Heat the reaction substrate to 100±2℃, and then simultaneously add 200g of acrylic acid and 200g of hydrogen peroxide solution (27.5wt%) to the reaction substrate. The addition is completed in 5 hours. After the addition is completed, keep the temperature at 100±2℃ for 1 hour to carry out the first stage polymerization reaction.

[0028] Step 3: After the first stage of polymerization is completed, adjust the pH of the system to 5.0±0.02 with sodium hydroxide solution, and then add 100g of ammonium persulfate aqueous solution (50wt%) dropwise to the system at 100±2℃. The addition is completed in 1 hour, and the system is kept at the temperature for 2 hours to carry out the second stage of polymerization, thus obtaining the MA / AA copolymer product.

[0029] In this embodiment, the residual monomer (calculated as maleic acid) is 0.82%, and the molecular weight Mw is 5126. Example 2

[0030] The process for preparing MA / AA in this embodiment is as follows: Step 1: Dissolve 300g of maleic acid in 100g of pure water to prepare a maleic acid aqueous solution; slowly add 207g of 50% sodium hydroxide solution to the maleic acid aqueous solution and stir for 30 minutes as the reaction substrate.

[0031] Step 2: Heat the reaction substrate to 100±2℃, and then simultaneously add 240g of acrylic acid and 240g of hydrogen peroxide solution (27.5wt%) to the reaction substrate. The addition is completed in 5 hours, and the first stage polymerization reaction is carried out by keeping the temperature at 100±2℃ for 2 hours.

[0032] Step 3: After the first stage of polymerization is completed, adjust the pH of the system to 5.0±0.02 with sodium hydroxide solution, and then add 80g of ammonium persulfate aqueous solution (50wt%) dropwise to the system at 100±2℃. The addition is completed in 1 hour, and the system is kept at the temperature for 2 hours to carry out the second stage of polymerization, thus obtaining the MA / AA copolymer product.

[0033] In this embodiment, the residual monomer (calculated as maleic acid) is 0.8%, and the molecular weight Mw is 5212. Example 3

[0034] The process for preparing MA / AA in this embodiment is as follows: Step 1: Dissolve 300g of maleic acid in 100g of pure water to prepare a maleic acid aqueous solution; slowly add 207g of 50% sodium hydroxide solution to the maleic acid aqueous solution and stir for 30 minutes as the reaction substrate.

[0035] Step 2: Heat the reaction substrate to 100±2℃, then simultaneously add 180g of acrylic acid and 220g of hydrogen peroxide solution (27.5wt%) to the reaction substrate. The addition is completed in 5 hours, and the substrate is kept at 100±2℃ for 1.5 hours to carry out the first stage polymerization reaction.

[0036] Step 3: After the first stage of polymerization is completed, adjust the pH of the system to 5.0±0.02 with sodium hydroxide solution, and then add 120g of ammonium persulfate aqueous solution dropwise to the system at 100±2℃. The addition is completed in 0.5 hours. Keep the temperature for 2 hours to carry out the second stage of polymerization, and the MA / AA copolymer product is obtained.

[0037] In this embodiment, the residual monomer (calculated as maleic acid) is 1.0%, and the molecular weight Mw is 4256. Comparative Example 1 (using a combined initiation system with simultaneous addition of hydrogen peroxide and ammonium persulfate)

[0038] The process for preparing MA / AA in this comparative example is as follows: Step 1: Dissolve 300g of maleic acid in 100g of pure water to prepare a maleic acid aqueous solution; slowly add 207g of 50% sodium hydroxide solution to the maleic acid aqueous solution and stir for 30 minutes as the reaction substrate.

[0039] Step 2: Heat the reaction substrate to 100±2℃, and then simultaneously add 200g of acrylic acid, 200g of hydrogen peroxide solution (27.5wt%), and 20g of ammonium persulfate solution (50wt%) to the reaction substrate. The addition is completed in 5 hours. After the addition is completed, keep the temperature at 100±2℃ for 2 hours to carry out the polymerization reaction.

[0040] The residual monomer in this comparative example (calculated as maleic acid) is 2.8%, and the molecular weight Mw is 5100. Comparative Example 2 (without the second stage initiated by ammonium persulfate)

[0041] The process for preparing MA / AA in this comparative example is as follows: Step 1: Dissolve 300g of maleic acid in 100g of pure water to prepare a maleic acid aqueous solution; slowly add 207g of 50% sodium hydroxide solution to the maleic acid aqueous solution and stir for 30 minutes as the reaction substrate.

[0042] Step 2: Heat the reaction substrate to 100±2℃, and then simultaneously add 200g of acrylic acid and 200g of hydrogen peroxide solution (27.5wt%) to the reaction substrate. The addition is completed in 5 hours. After the addition is completed, keep the temperature at 100±2℃ for 1 hour to carry out the first stage polymerization reaction, and the MA / AA copolymer product is obtained.

[0043] The residual monomer in this comparative example (calculated as maleic acid) is 3.2%, and the molecular weight Mw is 5214. Comparative Example 3 (Preparation of MA / AA using a metal catalyst in a hydrogen peroxide initiation system)

[0044] The process for preparing MA / AA in this comparative example is as follows: Step 1: Dissolve 300g of maleic acid in 100g of pure water to prepare a maleic acid aqueous solution, and add 0.03g of ferrous ammonium sulfate; slowly add 207g of 50% sodium hydroxide solution to the maleic acid aqueous solution and stir for 30min as the reaction substrate.

[0045] Step 2: Heat the reaction substrate to 100±2℃, and then simultaneously add 200g of acrylic acid and 200g of hydrogen peroxide solution (27.5wt%) to the reaction substrate. The addition is completed in 5 hours. After the addition is completed, keep the temperature at 100±2℃ for 1 hour to carry out the first stage polymerization reaction, and the MA / AA copolymer product is obtained.

[0046] The residual monomer in this comparative example (calculated as maleic acid) is 2.4%, and the molecular weight Mw is 2528. Comparative Example 4 (Adjusting the type of initiator in the second stage)

[0047] The process for preparing MA / AA in this comparative example is as follows: Step 1: Dissolve 300g of maleic acid in 100g of pure water to prepare a maleic acid aqueous solution; slowly add 207g of 50% sodium hydroxide solution to the maleic acid aqueous solution and stir for 30 minutes as the reaction substrate.

[0048] Step 2: Heat the reaction substrate to 100±2℃, and then simultaneously add 200g of acrylic acid and 200g of hydrogen peroxide solution (27.5wt%) to the reaction substrate. The addition is completed in 5 hours. After the addition is completed, keep the temperature at 100±2℃ for 1 hour to carry out the first stage polymerization reaction.

[0049] Step 3: After the first stage of polymerization is completed, adjust the pH of the system to 5.0±0.02 with sodium hydroxide solution, and then add 100g of hydrogen peroxide dropwise to the system at 100±2℃. The addition is completed in 1 hour, and the system is kept at this temperature for 2 hours to carry out the second stage of polymerization, thus obtaining the MA / AA copolymer product.

[0050] The residual monomer in this comparative example (calculated as maleic acid) is 2.2%, and the molecular weight Mw is 4986. Comparative Example 5 (the initiator in the first stage was changed to ammonium persulfate, and the initiator in the second stage was hydrogen peroxide).

[0051] The process for preparing MA / AA in this comparative example is as follows: Step 1: Dissolve 300g of maleic acid in 100g of pure water to prepare a maleic acid aqueous solution; slowly add 207g of 50% sodium hydroxide solution to the maleic acid aqueous solution and stir for 30 minutes as the reaction substrate.

[0052] Step 2: Heat the reaction substrate to 100±2℃, and then simultaneously add 200g of acrylic acid and 100g of ammonium persulfate aqueous solution (50wt%) to the reaction substrate. The addition is completed in 5 hours. After the addition is completed, keep the temperature at 100±2℃ for 2 hours to carry out the first stage polymerization reaction.

[0053] Step 3: After the first stage of polymerization is completed, adjust the pH of the system to 5.0±0.02 with sodium hydroxide solution, and then add 100g of hydrogen peroxide solution (27.5wt%) dropwise to the system at 100±2℃. The addition is completed in 1 hour, and the system is kept at this temperature for 1 hour to carry out the second stage of polymerization, thus obtaining the MA / AA copolymer product.

[0054] The residual monomer (calculated as maleic acid) in this comparative example was 5.0%, mainly due to incomplete polymerization.

[0055] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A preparation process for MA / AA, characterized in that, The preparation process includes the following steps: (a) Slowly add sodium hydroxide solution to maleic acid aqueous solution and stir for 10-30 min to obtain sodium maleate solution, which is used as the reaction substrate; (b) Heat the reaction substrate to a certain temperature, and then simultaneously add acrylic acid and hydrogen peroxide solution to the reaction substrate. The addition is completed in 4-6 hours. After the addition is completed, keep it at a certain temperature for a certain time to carry out the first stage polymerization reaction. (c) After the first stage of polymerization is completed, the pH of the system is adjusted to 4.8-5.2 with sodium hydroxide solution. Then, ammonium persulfate aqueous solution is added dropwise to the system at a certain temperature. The addition is completed in 0.5-1h. The system is kept warm for 1-2h to carry out the second stage of polymerization, and the MA / AA copolymer product is obtained.

2. The preparation process according to claim 1, characterized in that, In step (a), the mass concentration of the maleic acid aqueous solution is 60-80%, the mass concentration of the sodium hydroxide solution is 40-60%, and the molar ratio of maleic acid to sodium hydroxide is 1:

1.

3. The preparation process according to claim 1, characterized in that, In step (b), the temperature of the reaction substrate and the temperature of the first stage polymerization reaction are 95~105℃, and the holding time of the first stage polymerization reaction is 1~3h.

4. The preparation process according to claim 1 or 3, characterized in that, In step (b), the amount of acrylic acid added is 0.6 to 1.0 times the mass of maleic acid.

5. The preparation process according to claim 1, characterized in that, In step (b), the mass concentration of the hydrogen peroxide solution is 27.5%.

6. The preparation process according to claim 1 or 5, characterized in that, In step (b), the amount of hydrogen peroxide solution added (calculated as H2O2) is 0.1 to 0.3 times the total mass of maleic acid and acrylic acid.

7. The preparation process according to claim 1, characterized in that, In step (c), the mass concentration of the sodium hydroxide solution used to adjust the pH is 40-60%.

8. The preparation process according to claim 1, characterized in that, In step (c), the mass concentration of the ammonium persulfate aqueous solution is 50%.

9. The preparation process according to claim 1 or 8, characterized in that, In step (c), the amount of ammonium persulfate aqueous solution added (based on ammonium persulfate) is 0.05 to 0.15 times the total mass of maleic acid and acrylic acid.

10. The preparation process according to claim 1, characterized in that, In step (c), the temperature of the second stage polymerization reaction is 95~105℃.