A method for preparing low-color polymaleic anhydride

Abstract

This invention relates to a method for preparing low-color polymaleic anhydride, belonging to the field of fine chemical technology. The method involves polymerizing maleic anhydride monomers in an aqueous solution using hydrogen peroxide as an initiator and a composite catalyst. Specifically, the method includes the following steps: Step (1) mixing ferrous ammonium sulfate, vanadium pentoxide, and 95wt% concentrated sulfuric acid to prepare a composite catalyst; Step (2) adding pure water and maleic anhydride to a reaction vessel, then adding the composite catalyst, purging with nitrogen for protection, heating to 90℃, starting stirring, and adding hydrogen peroxide dropwise, controlling the temperature at 90-95℃ during the dropwise addition; Step (3) after the dropwise addition is complete, maintaining the temperature for 1 hour, and then cooling to obtain an aqueous solution of polymaleic anhydride. This method effectively reduces the color of polymaleic anhydride, and the entire process is simple to operate and generates no waste, making it environmentally friendly. Simultaneously, this method ensures the scale inhibition and dispersion performance of polymaleic anhydride while maintaining its molecular weight.

Description

Technical Field

[0001] This invention belongs to the field of fine chemical technology, and specifically relates to a method for preparing low-color polymaleic anhydride. Background Technology

[0002] Hydrolyzed polymaleic anhydride (HPMA) is a water-soluble, highly efficient scale inhibitor and dispersant, particularly effective at inhibiting calcium carbonate and calcium sulfate scale under challenging conditions such as high temperature, high pH, ​​and high strength. It exhibits excellent temperature resistance, with a decomposition temperature above 300℃, surpassing that of typical polyacrylic acid polymers. Furthermore, due to its low toxicity and harmlessness to humans, it is frequently used as a water treatment agent for circulating cooling water and low-pressure boiler boiler water, as well as for scale inhibition and prevention in oilfield water injection and crude oil dehydration systems. HPMA is an organic fatty acid polymer with good thermal and chemical stability. There are two synthesis methods for hydrolyzed polymaleic anhydride: aqueous synthesis and solvent synthesis. Since the solvent method uses toxic and harmful solvents that are difficult to remove completely, and the process is complex and costly, aqueous synthesis is generally preferred. Hydrolyzed HPMA typically has a molecular weight of 400-800, with higher molecular weight generally indicating better performance. In addition, regardless of whether polymaleic anhydride is synthesized by solvent method or hydrolysis, the color is basically a brownish-red transparent liquid. Due to its inherent color, polymaleic anhydride cannot be used in special fields, and a polymaleic anhydride with low color intensity is needed as a substitute. Summary of the Invention

[0003] The purpose of this invention is to provide a method for preparing low-color polymaleic anhydride. This method can effectively reduce the color of polymaleic anhydride, and the entire process is simple to operate and generates no waste, making it environmentally friendly. At the same time, this method can also ensure the scale inhibition and dispersion performance of polymaleic anhydride while maintaining its molecular weight.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] A method for preparing low-color polymaleic anhydride, comprising the following steps: polymerization of maleic anhydride monomers in an aqueous solution using hydrogen peroxide as an initiator and a composite catalyst.

[0006] Step (1) involves mixing ferrous ammonium sulfate, vanadium pentoxide, and 95 wt% concentrated sulfuric acid to prepare a composite catalyst;

[0007] Step (2): Add pure water and maleic anhydride into the reactor, then add the composite catalyst, purge with nitrogen for protection, heat to 90°C, start stirring, and add hydrogen peroxide dropwise, controlling the temperature at 90-95°C during the dropwise process.

[0008] Step (3): After the addition is complete, keep warm for 1 hour, then cool down to obtain polymaleic anhydride aqueous solution.

[0009] Furthermore, the mass fraction ratio of ferrous ammonium sulfate, vanadium pentoxide, and 95wt% concentrated sulfuric acid in the composite catalyst is 5:3:12, calculated as maleic anhydride.

[0010] Furthermore, in step (2), the molar ratio of maleic anhydride: composite catalyst: hydrogen peroxide is 1:0.0005-0.0015:0.4-0.7.

[0011] Furthermore, the mass of the pure water in step (2) is 45-55% of the mass of maleic anhydride.

[0012] Furthermore, the mass fraction of hydrogen peroxide in step (2) is 25%.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0014] 1. This invention uses a hydrolysis method for synthesis, with 25wt% hydrogen peroxide as the initiator, a composite catalyst added, and maleic anhydride as the monomer for water-soluble polymerization. The entire reaction is simple to operate and produces no waste, making it green and environmentally friendly.

[0015] Synthetic route of water-soluble polymaleic anhydride:

[0016]

[0017] 2. Ordinary polymaleic anhydride requires a production temperature of around 100-115℃ to achieve a molecular weight of around 700. In contrast, light-colored polymaleic anhydride requires a temperature of 85-90℃, resulting in a reduction in energy consumption.

[0018] 3. The selection of composite catalysts plays a crucial role in reducing the color of maleic anhydride, lowering the reaction system temperature, and reducing the bromine value. Ferrous ammonium sulfate, a conventional catalyst, was chosen as one of the composite catalysts primarily to ensure its molecular weight reaches the appropriate level while simultaneously reducing the bromine value. Vanadium pentoxide, as a composite catalyst, has been recommended in many literatures; however, in our experience, it effectively lowers the overall reaction temperature, ensuring the rapid reaction of the initiator hydrogen peroxide, while also reducing the bromine value. Concentrated sulfuric acid, as another composite catalyst, primarily helps maintain pH stability during the reaction and also contributes to reducing the bromine value.

[0019] 4. Compared with single catalysts, composite catalysts can effectively control costs while achieving the same performance. Detailed Implementation

[0020] 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.

[0021] Example 1

[0022] The preparation method of low-chroma polymaleic anhydride in this embodiment includes the following steps:

[0023] Step 1: Mix ferrous ammonium sulfate, vanadium pentoxide and concentrated sulfuric acid (95%) in a ratio of 5:3:12 (based on maleic anhydride) to prepare 0.5g of composite catalyst;

[0024] Step 2: Add 140g of pure water and 300g of maleic anhydride to a four-necked round-bottom flask, then add 0.5g of composite catalyst. After heating to 85℃, start stirring and add 210g of hydrogen peroxide dropwise at a flow rate of 52.5g / h. During this process, maintain the temperature at 85-90℃. The reaction is completed in 4 hours.

[0025] Step 3: After the addition is complete, keep warm for 1 hour, cool down, and filter to obtain a light-colored polymaleic anhydride aqueous solution with a mass fraction of about 50%.

[0026] The product was tested and found to have the following molecular weight (Mw): 720, bromine value: 35mg / g, and color code: 9 (50% polymaleic anhydride stock solution).

[0027] Comparative Example 1

[0028] The comparative method for preparing polymaleic anhydride includes the following steps:

[0029] Step 1: Mix ferrous ammonium sulfate and concentrated sulfuric acid (95%) in a ratio of 8:12 (based on maleic anhydride) to prepare 0.5g of composite catalyst;

[0030] Step 2: Add 140g of pure water and 300g of maleic anhydride to a four-necked round-bottom flask, then add the composite catalyst. After heating to 95℃, start stirring and add 210g of hydrogen peroxide dropwise at a flow rate of 52.5g / h. During this process, maintain the temperature at 95-105℃. The reaction is completed in 4 hours.

[0031] Step 3: After the addition is complete, keep warm for 1 hour, cool down, and filter to obtain a 50% mass fraction of polymaleic anhydride aqueous solution.

[0032] The product was tested and found to have a molecular weight of 688, a bromine value of 80 mg / g, and a color code of 15 (50% polymaleic anhydride stock solution).

[0033] Comparative Example 2

[0034] The comparative method for preparing polymaleic anhydride includes the following steps:

[0035] Step 1: Mix ferrous ammonium sulfate, vanadium pentoxide, and concentrated sulfuric acid (95%) to prepare 0.5g of composite catalyst according to the specified ratio;

[0036] Step 2: Add 140g of pure water and 300g of maleic anhydride to a four-necked round-bottom flask, then add the composite catalyst. After heating to 95℃, start stirring and add 210g of hydrogen peroxide dropwise at a flow rate of 52.5g / h. During this process, maintain the temperature at 95-105℃. The reaction is completed in 4 hours.

[0037] Step 3: After the addition is complete, keep warm for 1 hour, cool down, and filter to obtain a 50% mass fraction of polymaleic anhydride aqueous solution.

[0038] The product was tested and found to have a molecular weight of 698, a bromine value of 80 mg / g, and a color code of 14 (50% polymaleic anhydride stock solution).

[0039] Comparative Example 3

[0040] The comparative method for preparing polymaleic anhydride includes the following steps:

[0041] Step 1: Mix ferrous ammonium sulfate, vanadium pentoxide, and concentrated sulfuric acid (95%) to prepare a composite catalyst of 0.5g in the specified proportions.

[0042] Step 2: Add 140g of pure water and 300g of maleic anhydride to a four-necked round-bottom flask, then add the composite catalyst. After heating to 80℃, start stirring and add 210g of hydrogen peroxide dropwise at a flow rate of 52.5g / h. During this process, maintain the temperature at 80-85℃. The reaction is completed in 4 hours.

[0043] Step 3: After the addition is complete, keep warm for 1 hour, cool down, and filter to obtain a 50% mass fraction of polymaleic anhydride aqueous solution.

[0044] The product was tested and found to have a molecular weight of 335, a bromine value of 200 mg / g, and a color code of 9 (for 50% polymaleic anhydride stock solution). Polymaleic anhydride monomers were precipitated after the reaction was completed.

[0045] Comparative Example 4

[0046] The comparative method for preparing polymaleic anhydride includes the following steps:

[0047] Step 1: Mix vanadium pentoxide and concentrated sulfuric acid (95%) in a ratio of 8:12 (based on maleic anhydride) to prepare 0.5g of composite catalyst;

[0048] Step 2: Add 140g of pure water and 300g of maleic anhydride to a four-necked round-bottom flask, then add the composite catalyst. After heating to 80℃, start stirring and add 210g of hydrogen peroxide dropwise at a flow rate of 52.5g / h. During this process, maintain the temperature at 85-90℃. The reaction is completed in 4 hours.

[0049] Step 3: After the addition is complete, keep warm for 1 hour, cool down, and filter to obtain a 50% mass fraction of polymaleic anhydride aqueous solution.

[0050] The product was tested and found to have a molecular weight of 660, a bromine value of 58 mg / g, and a color code of 9 (for 50% polymaleic anhydride stock solution). 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. The application of a composite catalyst in reducing the color and bromine value of polymaleic anhydride, characterized in that: The composite catalyst is a mixture of ferrous ammonium sulfate, vanadium pentoxide, and 95 wt% concentrated sulfuric acid in a mass ratio of 5:3:12; wherein, Ferrous ammonium sulfate ensures the molecular weight of polymaleic anhydride and reduces the bromine value; vanadium pentoxide lowers the reaction temperature of the entire system, ensuring the initiator reacts quickly and reducing the bromine value; 95wt% concentrated sulfuric acid maintains pH stability during the reaction and reduces the bromine value. This application involves the polymerization of maleic anhydride monomers in an aqueous solution using hydrogen peroxide as an initiator and a composite catalyst. The specific steps include: Step 1: Prepare 0.5g of composite catalyst based on maleic anhydride; Step 2: Add 140g of pure water and 300g of maleic anhydride to a four-necked round-bottom flask, then add 0.5g of composite catalyst, purge with nitrogen for protection, and wait until the temperature reaches 85℃. Start stirring and add 210g of 25% hydrogen peroxide dropwise at a flow rate of 52.5g / h. Maintain the temperature at 85-90℃ during the process. The reaction is completed in 4 hours. Step 3: After the addition is complete, keep warm for 1 hour, cool down, and filter to obtain a light-colored polymaleic anhydride aqueous solution with a mass fraction of about 50%. The prepared polymaleic anhydride aqueous solution has a molecular weight (Mw) of 720, a bromine value of 35 mg / g, and a color code of 9.

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