A method for removing a polymerization inhibitor from an olefinic monomer

Abstract

This invention discloses a method for removing polymerization inhibitors from olefin monomers. The method involves ultrasonic gradient alkaline extraction of olefin monomers, followed by thorough stirring and mixing. After standing and separating the layers, the upper layer of alkaline-washed olefin monomers is collected. Lignite activated carbon is added, and the mixture is stirred and filtered to obtain olefin monomers free of activated carbon. This purified monomer is then mixed with molecular sieves and sealed for later use. This method achieves highly efficient removal of organic polymerization inhibitors through the synergistic effect of gradient alkaline extraction and lignite activated carbon. The gradient alkaline extraction process is conducted under mild reaction conditions, and ultrasonic-assisted alkaline extraction helps enhance mass transfer between different parts of the sample, improving the uniformity of extraction. Simultaneously, the oxygen-containing functional groups in the lignite activated carbon enhance the adsorption effect. After treatment using this method, the content of polymerization inhibitors in the olefin monomers is reduced to as low as 4.85 ppm. Furthermore, this method is simple, efficient, and widely applicable, suitable for large-scale industrial production.

Description

Technical Field

[0001] This invention relates to a method for removing polymerization inhibitors, specifically a method for removing polymerization inhibitors from olefin monomers. Background Technology

[0002] Alkene monomers are important raw materials widely used in the chemical industry, such as ethylene and propylene. In the production of alkene monomers, polymerization inhibitors are usually added to prevent premature polymerization and ensure the produced monomers have the required purity and stability. However, the residue of these inhibitors in the product can adversely affect downstream processing and applications. For example, glycidyl methacrylate contains the structure of acrylic acid: CH2=CH-COOH, which contains chemically active carboxyl and vinyl groups, making it highly prone to self-polymerization. Therefore, to prevent self-polymerization during transportation and storage, 4-methoxyphenol (MEHQ) polymerization inhibitor is usually added, with a typical content of 100±5 ppm. However, in production, to obtain a superior product, the polymerization inhibitor in glycidyl methacrylate must be removed, and its content controlled to 10±5 ppm.

[0003] Methods for removing polymerization inhibitors typically include alkaline washing, distillation, and ion exchange resin adsorption. However, these methods all have drawbacks and cannot effectively remove polymerization inhibitors from olefin monomers. For example, alkaline washing is simple to operate, but it does not remove the polymerization inhibitor completely; distillation can separate the polymerization inhibitor from the olefin monomer by heating and distillation, but this method is suitable for situations where there is a large difference in boiling points between the polymerization inhibitor and the olefin monomer, and glycidyl methacrylate can undergo self-polymerization during high-temperature distillation; ion exchange resin adsorption requires regeneration of the resin after use, which may introduce other residual substances into the glycidyl methacrylate, affecting purity and production applications. Summary of the Invention

[0004] Purpose of the invention: The purpose of this invention is to provide an efficient and convenient method for removing polymerization inhibitors from olefin monomers. The method involves removing the polymerization inhibitor 4-methoxyphenol from glycidyl methacrylate by alkaline washing combined with activated carbon adsorption, thereby controlling its content to 10±5ppm.

[0005] Technical solution: The method for removing polymerization inhibitors from olefin monomers according to the present invention includes the following steps:

[0006] (1) Take alkene monomers, use ultrasonic gradient alkali washing extraction, stir and mix thoroughly, let stand to separate layers and remove the lower alkali solution to obtain the upper alkali washed alkene monomers.

[0007] (2) Add lignite activated carbon to the alkaline washed olefin monomer, stir, filter to obtain olefin monomer without activated carbon, mix with molecular sieve and seal for later use, thus obtaining olefin monomer without polymerization inhibitor.

[0008] The olefinic monomer is one or more selected from ethylene, propylene, styrene, acrylic acid, methacrylate, or glycidyl methacrylate, and the polymerization inhibitor is a phenolic polymerization inhibitor selected from one or more selected from 4-methoxyphenol, p-tert-butylcatechol, 2,5-di-tert-pentylhydroquinone, bisphenol A, or hydroquinone.

[0009] In step (1), the alkaline washing uses an alkaline solution with a mass ratio of 0.5 to 1.0:1 to the alkali monomer, and the alkaline solution is an aqueous sodium hydroxide solution with a concentration of 5 to 15%.

[0010] In step (1), the gradient alkaline washing is either linear extraction or nonlinear extraction. For linear extraction, sodium hydroxide aqueous solution is added at a linear increase of 5%-15% or a linear decrease of 15%-5%. For nonlinear extraction, a 5% sodium hydroxide aqueous solution is used for extraction, followed by separation and then a second extraction with a 15% sodium hydroxide aqueous solution, or a 15% sodium hydroxide aqueous solution is used for extraction, followed by separation and then a second extraction with a 5% sodium hydroxide aqueous solution.

[0011] The preferred method is to perform alkaline extraction by linearly increasing the concentration from low to high. The low-concentration alkaline washing at the beginning stage results in milder conditions, reduces the risk of side reactions, and helps maintain the stability of the product. The use of low-concentration alkaline solution makes it easier to control the pH value in the reaction solution, which helps to carry out the reaction within the ideal range. The high-concentration alkaline solution in the later stage has stronger deprotonation properties, which helps to neutralize the polymerization inhibitor more effectively.

[0012] In step (2), the mass ratio of the olefin monomer to the lignite activated carbon is 1:0.05-0.1; the mass ratio of the olefin monomer to the molecular sieve is 1:0.05-0.1; the molecular sieve is 4A molecular sieve, and the lignite activated carbon is 40-80 mesh.

[0013] In step (2), the pH is adjusted to 3-6 after adding lignite activated carbon.

[0014] Invention Principle: This invention relates to a method for removing polymerization inhibitors from olefin monomers. It achieves highly efficient removal of the polymerization inhibitor 4-methoxyphenol through the synergistic effect of ultrasonic gradient alkaline washing and lignite activated carbon adsorption. The gradient alkaline washing extraction process utilizes mild reaction conditions, while ultrasonic-assisted alkaline extraction enhances mass transfer between different parts of the sample, improving the uniformity and repeatability of the extraction. In the gradient alkaline solution, ultrasound accelerates the process of 4-methoxyphenol combining with hydroxide ions in the alkaline solution to form ion pairs, which facilitates the dissolution and extraction of 4-methoxyphenol.

[0015] Furthermore, compared to other activated carbons, lignite activated carbon has more pores and its surface is rich in various functional groups, mainly phenolic hydroxyl groups, exhibiting high reactivity and short activation time. 4-Methoxyphenol, on the other hand, contains methoxy functional groups and a benzene ring structure. Therefore, this invention specifically selects lignite activated carbon rich in oxygen-containing functional groups, which is more conducive to interaction with the target substance 4-methoxyphenol, thereby improving the adsorption effect.

[0016] Furthermore, lignite activated carbon with medium pore size is more suitable for adsorbing medium-sized 4-methoxyphenol, with 40-80 mesh being the preferred lignite activated carbon.

[0017] Furthermore, under low pH conditions, lignite activated carbon may have some cationic surface functional groups on its surface, which have a good adsorption capacity for organic matter in acidic solutions. This helps to adsorb negatively charged 4-methoxyphenol molecules. It is preferable to use lignite activated carbon at pH 3-6 to remove 4-methoxyphenol from glycidyl methacrylate, as this pH range is more conducive to improving the adsorption effect of lignite activated carbon.

[0018] Beneficial effects: Compared with the prior art, the present invention has the following advantages: (1) After being treated by the method of the present invention, the content of polymerization inhibitor in olefin monomers can be controlled at 10±5ppm, with a minimum of only 4.85ppm; (2) The method is simple and efficient, has a wide range of applications, and can be applied to large-scale industrial production. Attached Figure Description

[0019] Figure 1 The HPLC chromatogram of glycidyl methacrylate without the polymerization inhibitor is shown.

[0020] Figure 2 Microscopic image of glycidyl methacrylate synthesized into microspheres after treatment with polymerization inhibitor in Comparative Example 1;

[0021] Figure 3 The HPLC chromatogram of glycidyl methacrylate after treatment with the polymerization inhibitor in Example 2 is shown below.

[0022] Figure 4 This is a microscope image of glycidyl methacrylate synthesized into microspheres after treatment with the polymerization inhibitor in Example 2. Detailed Implementation

[0023] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0024] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0025] Among them, glycidyl methacrylate was purchased from Alfa in the United States, with the product number L11133-50g; sodium hydroxide aqueous solution A: 15.0g of sodium hydroxide solid was weighed and added to 100.0g of purified water and stirred until dissolved; sodium hydroxide aqueous solution B: 5.0g of sodium hydroxide solid was weighed and added to 100.0g of purified water and stirred until dissolved.

[0026] Example 1

[0027] (1) Weigh 100.0g of glycidyl methacrylate into a beaker, use nonlinear extraction, add 50g of sodium hydroxide aqueous solution A, maintain 20-25℃ and sonicate (35kHz, 400w) for 30min at a stirring speed of 300r / min, transfer it into a 500mL separatory funnel and let it stand and separate into layers, then separate the lower layer liquid; then transfer the upper layer liquid into a 500mL beaker, add 50g of sodium hydroxide aqueous solution B, sonicate (35kHz, 400w) at room temperature for 30min at a stirring speed of 200r / min, then transfer it into a 500mL separatory funnel and let it stand and separate into layers, then separate the lower layer liquid;

[0028] (2) Transfer the upper layer of glycidyl methacrylate in the separatory funnel into a 500mL reaction flask, add 5.0g of lignite activated carbon (Naqu, 60 mesh), and sonicate (35kHz, 400w) at 25-30℃ for 1h at a stirring speed of 100r / min. Filter the mixture, put the filtrate into a 250mL single-necked glass bottle, add 5.0g of 4A molecular sieve, seal, and set aside for later use.

[0029] Example 2

[0030] (1) Weigh 50.0g of glycidyl methacrylate into a beaker, use nonlinear extraction, add 25g of sodium hydroxide aqueous solution B, maintain 20-25℃ and sonicate (35kHz, 400w) for 30min at a stirring speed of 200r / min, transfer it into a 500mL separatory funnel and let it stand and separate into layers, then separate the lower layer liquid; then transfer the upper layer liquid into a 500mL beaker, add 25g of sodium hydroxide aqueous solution A, sonicate (35kHz, 400w) at room temperature for 30min at a stirring speed of 300r / min, then transfer it into a 500mL separatory funnel and let it stand and separate into layers, then separate the lower layer liquid;

[0031] (2) Transfer the upper layer of glycidyl methacrylate in the separatory funnel into a 500mL reaction flask, add 5.0g of lignite activated carbon (Naqu, 40 mesh), and sonicate (35kHz, 400w) at 25-30℃ for 1h at a stirring speed of 100r / min. Filter the mixture, put the filtrate into a 250mL single-necked glass bottle, add 5.0g of 4A molecular sieve, seal, and set aside for later use.

[0032] Example 3

[0033] (1) Weigh 100.0g of glycidyl methacrylate into a beaker and use linear extraction. Add sodium hydroxide aqueous solution in a linear increment of 5%-15% using an automatic titrator, for a total of 50g. Titrate for 30min. During the addition process, stir ultrasonically (35kHz, 400w) at a stirring speed of 200r / min. Then transfer it into a 500mL separatory funnel and let it stand and separate into layers. Separate the lower layer liquid. Repeat the above linear extraction steps with the upper layer liquid to obtain glycidyl methacrylate after secondary extraction.

[0034] (2) Transfer the upper layer of glycidyl methacrylate in the separatory funnel into a 500mL reaction flask, add 5.0g of lignite activated carbon (Naqu, 60 mesh), and sonicate (35kHz, 400w) at 25-30℃ for 1h at a stirring speed of 100r / min. Filter the mixture, put the filtrate into a 250mL single-necked glass bottle, add 5.0g of 4A molecular sieve, seal, and set aside for later use.

[0035] Example 4

[0036] (1) Weigh 100.0g of glycidyl methacrylate into a beaker and use linear extraction. Add sodium hydroxide aqueous solution in a linear increment of 5%-15% using an automatic titrator, for a total of 50g. Titrate for 30min. During the addition process, stir ultrasonically (35kHz, 400w) at a stirring speed of 200r / min. Then transfer it into a 500mL separatory funnel and let it stand and separate into layers. Separate the lower layer liquid. Repeat the above linear extraction steps with the upper layer liquid to obtain glycidyl methacrylate after secondary extraction.

[0037] (2) Transfer the upper layer of glycidyl methacrylate in the separatory funnel to a 500mL reaction flask, add 5.0g of lignite activated carbon (Naqu, 60 mesh), adjust the pH to 3 with 0.1mol / L dilute hydrochloric acid, sonicate (35kHz, 400w) at 25-30℃ for 1h at a stirring speed of 100r / min, filter, transfer the filtrate to a 500mL separatory funnel to stand and separate the layers, separate the lower layer liquid, and put the upper layer liquid into a 250mL single-necked glass bottle, add 5.0g of 4A molecular sieve, seal, and set aside for later use.

[0038] Example 5

[0039] (1) Weigh 100.0g of glycidyl methacrylate into a beaker and use linear extraction. Add sodium hydroxide aqueous solution in a linear increment of 5%-15% using an automatic titrator, for a total of 50g. Titrate for 30min. During the addition process, stir ultrasonically (35kHz, 400w) at a stirring speed of 200r / min. Then transfer it into a 500mL separatory funnel and let it stand and separate into layers. Separate the lower layer liquid. Repeat the above linear extraction steps with the upper layer liquid to obtain glycidyl methacrylate after secondary extraction.

[0040] (2) Transfer the upper layer of glycidyl methacrylate in the separatory funnel to a 500mL reaction flask, add 5.0g of lignite activated carbon (Naqu, 80 mesh), adjust the pH to 6 with 0.1mol / L dilute hydrochloric acid, sonicate (35kHz, 400w) at 25-30℃ for 1h at a stirring speed of 100r / min, filter, transfer the filtrate to a 500mL separatory funnel to stand and separate the layers, separate the lower layer liquid, and put the upper layer liquid into a 250mL single-necked glass bottle, add 5.0g of 4A molecular sieve, seal, and set aside for later use.

[0041] Comparative Example 1

[0042] (1) Weigh 50.0g of glycidyl methacrylate, add 25g of sodium hydroxide aqueous solution B, maintain 20-25℃ and sonicate (35kHz, 400w) for 30min at a stirring speed of 200r / min, transfer it into a 500mL separatory funnel and let it stand and separate into layers, then separate the lower layer liquid; then transfer the upper layer liquid into a 500mL beaker, add 25g of sodium hydroxide aqueous solution A, sonicate (35kHz, 400w) at room temperature for 30min at a stirring speed of 300r / min, then transfer it into a 500mL separatory funnel and let it stand and separate into layers, then separate the lower layer liquid;

[0043] (2) Pour the upper liquid into a 250mL single-necked glass bottle, add 5.0g of 4A molecular sieve, seal, and set aside.

[0044] Comparative Example 2

[0045] (1) Weigh 100.0g of glycidyl methacrylate, transfer it to a 500mL reaction flask, add 5.0g of lignite activated carbon (Naqu, 40 mesh), and sonicate (35kHz, 400w) at 25-30℃ for 1h at a stirring speed of 100r / min. Filter the mixture, put the filtrate into a 250mL single-necked glass bottle, add 5.0g of 4A molecular sieve, seal, and set aside for later use.

[0046] Comparative Example 3

[0047] The difference between Comparative Example 3 and Example 2 is that isocratic alkaline extraction was used, and an aqueous sodium hydroxide solution C was prepared: 10.0 g of solid sodium hydroxide was weighed and added to 100.0 g of purified water, and stirred until dissolved to obtain aqueous sodium hydroxide solution C:

[0048] (1) Weigh 50.0g of glycidyl methacrylate, add 25g of sodium hydroxide aqueous solution C, maintain 20-25℃ and sonicate (35kHz, 400w) for 30min at a stirring speed of 200r / min, transfer it into a 500mL separatory funnel and let it stand and separate into layers, then separate the lower layer liquid; then transfer the upper layer liquid into a 500mL beaker, add 25g of sodium hydroxide aqueous solution C, sonicate (35kHz, 400w) at room temperature for 30min at a stirring speed of 200r / min, then transfer it into a 500mL separatory funnel and let it stand and separate into layers, then separate the lower layer liquid;

[0049] (2) Transfer the upper layer of glycidyl methacrylate in the separatory funnel into a 500mL reaction flask, add 5.0g of lignite activated carbon (Naqu, 40 mesh), and sonicate (35kHz, 400w) at 25-30℃ for 1h at a stirring speed of 100r / min. Filter the mixture, put the filtrate into a 250mL single-necked glass bottle, add 5.0g of 4A molecular sieve, seal, and set aside for later use.

[0050] Comparative Example 4

[0051] The difference between Comparative Example 4 and Example 2 is that the lignite activated carbon was replaced with ordinary wood-based activated carbon (Macklin, 40 mesh), while all other aspects remained the same.

[0052] The content of polymerization inhibitors was detected in the olefin monomers obtained after treatment in the examples and comparative examples:

[0053] The content of polymerization inhibitor in glycidyl methacrylate in the original sample and the treated sample was determined by HPLC. The HPLC detection conditions are as follows:

[0054] Instrument: High-performance liquid chromatograph (Shimadzu LC-20A)

[0055] Sample solution preparation: Weigh approximately 5.00 g of sample into a 50 mL volumetric flask, add methanol to dissolve, then dilute to volume and shake well before use.

[0056] Chromatographic conditions: C18 reverse-phase column, mobile phase: methanol:water = 50:50, flow rate 1.0 mL / min, column temperature: room temperature, UV detector wavelength: 275 nm.

[0057] Combination Figure 1 Analysis of the polymerization inhibitor content in the original sample:

[0058] 10.043mg / L*50.0mL / 5.079g=98.88ppm;

[0059] Combination Figure 3 Analysis of the polymerization inhibitor content in the sample treated in Example 2:

[0060] 0.780mg / L*50.0mL / 5.5045g=7.09ppm.

[0061] Table 1. Polymer inhibitor content in samples treated in the examples and comparative examples.

[0062] sample Polymer inhibitor content (ppm) As is 98.88 Example 1 10.24 Example 2 7.09 Example 3 6.67 Example 4 4.85 Example 5 5.57 Comparative Example 1 33.56 Comparative Example 2 41.32 Comparative Example 3 21.02 Comparative Example 4 19.98

[0063] As shown in Table 1, the highest content of polymerization inhibitor in the samples treated in the examples was 10.24 ppm, and the lowest was only 4.85 ppm, while the content in the comparative examples was much higher than that after treatment by the method in the examples. Using a combination of low-concentration alkali extraction and high-concentration alkali extraction can reduce the 4-methoxyphenol polymerization inhibitor content in glycidyl methacrylate to about 7 ppm, as in Examples 2 and 3. The gradient extraction with a linear increase in alkali concentration showed the best effect. Furthermore, by optimizing the pH value after adding lignite activated carbon (Examples 4 and 5), adjusting the pH to 3-6, the lignite activated carbon exhibited superior performance under acidic conditions, more efficiently improving the adsorption and removal of polymerization inhibitors, and further reducing the 4-methoxyphenol polymerization inhibitor content in glycidyl methacrylate.

[0064] Using glycidyl methacrylate treated in Comparative Example 1 and Glycidyl methacrylate treated in Example 2 as monomers, AIBN as an initiator and PVP as a dispersant, anhydrous ethanol and water were added, and the reaction was heated. The effect of the polymerization inhibitor content on the subsequent pelleting reaction was tested. The specific reaction conditions are referenced in: Zhang Jianping et al. "Preparation and characterization of Glycidyl methacrylate GMA monodisperse microspheres." Journal of Hebei University of Science and Technology 28.2(2014):5.

[0065] like Figure 2 As shown, glycidyl methacrylate treated in Comparative Example 1 was used to form microspheres. The polymerized microspheres agglomerated, exhibiting clustered agglomeration with a highly uneven particle size distribution. The cause of agglomeration was a high content of polymerization inhibitor, which hindered the reaction process. Under heated and oxygen-rich conditions, the polymerization inhibitor was consumed, leading to explosive polymerization of the microspheres and resulting in agglomeration.

[0066] like Figure 4As shown, after the spheroidizing reaction, the glycidyl methacrylate treated in Example 2 did not spheroidize. The particles were dispersed individually and did not stick together, presenting a uniform spherical shape. This indicates that the polymerization inhibitor of the glycidyl methacrylate treated in Example 2 was removed, and no polymerization effect was generated that would cause spheroidizing problems.

Claims

1. A method for removing polymerization inhibitors from olefin monomers, characterized in that, Includes the following steps: (1) Take alkene monomers, use ultrasonic gradient alkaline washing extraction, stir and mix thoroughly, let stand to separate layers and remove the lower alkaline solution to obtain the upper alkaline washed alkene monomers. The gradient alkaline washing is linear extraction or nonlinear extraction. For linear extraction, sodium hydroxide aqueous solution is added at a linear increase of 5%-15% or a linear decrease of 15%-5%. For nonlinear extraction, 5% sodium hydroxide aqueous solution is used for extraction, separation of layers and liquids, and then a second extraction with 15% sodium hydroxide aqueous solution, or 15% sodium hydroxide aqueous solution is used for extraction, separation of layers and liquids, and then a second extraction with 5% sodium hydroxide aqueous solution. (2) Add lignite activated carbon to the alkaline washed olefin monomers. After adding lignite activated carbon, adjust the pH to 3-6 and stir. Filter to obtain olefin monomers without activated carbon. Mix with molecular sieve and seal for later use to obtain olefin monomers without polymerization inhibitor.

2. The method according to claim 1, characterized in that, The olefinic monomer is one or more selected from ethylene, propylene, styrene, acrylic acid, methacrylate, or glycidyl methacrylate, and the polymerization inhibitor is a phenolic polymerization inhibitor selected from one or more selected from 4-methoxyphenol, p-tert-butylcatechol, 2,5-di-tert-pentylhydroquinone, bisphenol A, or hydroquinone.

3. The method according to claim 1, characterized in that, In step (1), the alkaline washing uses an alkaline solution with a mass ratio of 0.5 to 1.0:1 to the alkali monomer, and the alkaline solution is an aqueous sodium hydroxide solution with a concentration of 5 to 15%.

4. The method according to claim 1, characterized in that, The mass ratio of the olefin monomer to the lignite activated carbon is 1:0.05~0.

1.

5. The method according to claim 1, characterized in that, The mass ratio of the olefin monomer to the molecular sieve is 1:0.05~0.

1.

6. The method according to claim 1, characterized in that, In step (2), the molecular sieve is 4A molecular sieve and the lignite activated carbon is 40-80 mesh.

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