Composite polymerization inhibitor for vinyl acetate production process and application thereof

Abstract

The invention provides a composite polymerization inhibitor for a vinyl acetate production process, especially a rectification process, the polymerization inhibitor comprises a component A and a component B, the component A is a nitroxide free radical compound, and the component B is styrene. The composite polymerization inhibitor provided by the invention fully utilizes the synergistic effect of the two polymerization inhibitors, overcomes the defect of short high-temperature polymerization inhibition validity period of a nitroxide free radical type polymerization inhibitor, remarkably improves the polymerization inhibition effect of the polymerization inhibitor, can effectively prevent self-polymerization of vinyl acetate in the production process of vinyl acetate, and improves the production efficiency of vinyl acetate. And the continuity of the production process is ensured.

Description

Technical Field

[0001] The present invention belongs to the field of chemical industry, and in particular relates to a composite polymerization inhibitor for inhibiting the self-polymerization of vinyl acetate in a production process, and an application and use method thereof. Background Art

[0002] Vinyl acetate is a very important organic chemical raw material, primarily used as a monomer in the production of polyvinyl acetate (PVAc) emulsions, polyvinyl alcohol (PVA), vinyl acetate-ethylene copolymer emulsions (VAE), copolymer resins (EVA), vinyl acetate-vinyl chloride copolymers (EVC), and derivatives such as acetal resins. However, during the production of vinyl acetate, particularly during processes such as degassing, extraction, and distillation, the unsaturated double bonds in the vinyl acetate molecule can easily cause self-polymerization, resulting in polymer blockage in equipment and raw material loss. Furthermore, if uncontrolled, this can lead to implosion, requiring plant shutdown and even explosions in severe cases. Therefore, the addition of appropriate inhibitors to suppress self-polymerization during vinyl acetate production is a critical step in its industrial production.

[0003] There are generally four types of polymerization inhibitors that can be used in the vinyl acetate production process: free radicals, phenolic compounds (such as hydroquinone and tert-butylhydroquinone), quinone compounds (such as p-benzoquinone), and amines (such as phenthazine and diphenylamine). It is important to note that since the temperature of vinyl acetate distillation towers is generally in the range of 60-100°C, the polymerization inhibitors used in the vinyl acetate distillation process are different from those added to the vinyl acetate product (during storage and transportation). They are required to have a good polymerization inhibition effect at high temperatures (e.g., 80-95°C).

[0004] At present, the commonly used inhibitors in the production of vinyl acetate are para-benzoquinone (PBQ), hydroquinone (HQ), amines, etc. These inhibitors have certain effects in the production process of vinyl acetate (including the distillation process), but they also have obvious disadvantages such as low inhibition efficiency (short maintenance time, need for continuous addition), high toxicity, and poor heat resistance.

[0005] In the prior art, a combination of various polymerization inhibitors is usually used to obtain better effects.

[0006] For example, US Patent No. 8691994B discloses a composition for inhibiting the polymerization of ethylenically unsaturated monomers and a method for using the composition. The composition is prepared by reacting a nitroxyl-stabilized free radical with a dialkyl / aryl hydroxylamine, reducing it to its corresponding hydroxylamine. A polymerization-inhibiting component targeting the ethylenically unsaturated monomer is then added, selected from phenolic antioxidants, phenylenediamine, and phenylenediamine derivatives. This technology is preferably applicable to vinyl aromatic compounds such as styrene, methylstyrene, vinyltoluene, divinylbenzene, or vinyl aliphatic compounds.

[0007] Chinese invention patent application CN111100001A discloses a composite polymerization inhibitor for vinyl acetate distillation and its use method. The inhibitor is composed of three components: 4-hydroxy-2,2,6,6-tetramethylpiperidinylnitroxide, N,N-diphenyl-p-phenylenediamine, and 2,4-dimethyl-6-sec-butylphenol, compounded in a specific ratio. This composite polymerization inhibitor cleverly utilizes the synergistic effect between its components, overcoming the shortcomings of both retarders and true inhibitors, resulting in significantly improved polymerization inhibition compared to the individual components. Furthermore, the inhibitor is highly efficient and has low toxicity, effectively improving the yield of vinyl acetate distillation.

[0008] U.S. patent application US2015152053A1 discloses a polymerization inhibitor composition. The polymerization inhibitor composition may include at least one hydroxylamine nitroxide and at least one phenylenediamine. A method for inhibiting the unwanted polymerization of a monomer is also provided. The method comprises adding the polymerization inhibitor composition to a fluid containing a monomer. The monomer may be an ethylenically unsaturated monomer, such as acrylic acid, methacrylic acid, acrylonitrile, methacrylonitrile, acrolein, methacrolein, acrylates, methacrylates, acrylamide, methacrylamide, vinyl acetate, butadiene, ethylene, propylene, and styrene.

[0009] The composite polymerization inhibitors mentioned in the above documents all include components such as phenylenediamine polymerization inhibitors, which are relatively costly and toxic, and they do not fundamentally solve the problem of low inhibition efficiency (short maintenance time and need for continuous addition). Summary of the Invention

[0010] To solve the above technical problems, the present invention provides a composite polymerization inhibitor for use in the vinyl acetate production process, especially the distillation process. The polymerization inhibitor comprises component A and component B, wherein component A is a nitroxide free radical compound and component B is styrene.

[0011] Preferably, the A component nitroxide free radical compound is selected from one or more of 2,2,6,6-tetramethylpiperidinyl nitroxide free radical (TEMPO), 2,2,6,6-tetramethyl-4-hydroxypiperidinyl nitroxide free radical (4-OH-TEMPO), phosphite-3-(2,2,6,6-tetramethyl-4-hydroxypiperidinyl nitroxide free radical), di-tert-butyl nitroxide free radical and 4,4'-dinitrodiphenyl nitroxide free radical.

[0012] Preferably, in the composite polymerization inhibitor of the present invention, the mass ratio of the nitroxide free radical polymerization inhibitor of component A to the styrene of component B is 1:9-5:5, preferably the mass ratio of the two is 3:7-5:5.

[0013] The present invention also provides a method for inhibiting the self-polymerization of vinyl acetate monomer in the vinyl acetate production process: relative to the mass of vinyl acetate monomer, the vinyl acetate production inhibitor is added to the vinyl acetate production system in an amount of 1-100 ppm, preferably 3-50 ppm.

[0014] Furthermore, the polymerization inhibitor of the present invention is soluble in vinyl acetate at room temperature and can be directly added to the vinyl acetate production system by a pump, such as from the middle or top of a distillation tower, or from the feed point of a storage tank.

[0015] The beneficial effects of the present invention are:

[0016] Compared with the existing polymerization inhibitors used in the vinyl acetate production process, the present invention has at least the following advantages:

[0017] The purpose of the present invention is to prevent vinyl acetate from self-polymerizing during the production process (such as degassing, extraction, distillation, etc.), causing blockage and scaling of production equipment such as distillation towers, pipelines, and storage tanks, thereby affecting production and product quality.

[0018] The polymerization inhibitor provided by the present invention is prepared by compounding a nitroxide free radical compound and styrene, which is rarely used as a polymerization inhibitor, in a certain proportion. It fully utilizes the characteristics of the two polymerization inhibitors to produce a synergistic effect in the polymerization inhibition process; its high-temperature polymerization inhibition lasts for a long period of time and has high inhibition efficiency.

[0019] The composite polymerization inhibitor provided by the present invention fully utilizes the synergistic effect between the two polymerization inhibitors, overcomes the disadvantage of the short effective period of high-temperature polymerization inhibition of the nitroxide free radical type polymerization inhibitor, significantly improves the polymerization inhibition effect of the polymerization inhibitor, and is used in the vinyl acetate production process to effectively prevent the self-polymerization of vinyl acetate and ensure the continuity of the production process.

[0020] Compared with the polymerization inhibitor p-benzoquinone currently used in industry, the polymerization inhibitor provided by the present invention reduces the amount of highly toxic substances used, reduces toxicity, and significantly reduces the health hazards to production operators. DETAILED DESCRIPTION

[0021] The embodiments listed in the present invention are merely for the purpose of better illustrating the contents of the present invention, and the contents of the present invention are not limited to the listed embodiments. A person skilled in the art may make non-essential improvements and adjustments to the following embodiments based on the above-mentioned invention, which do not deviate from the spirit of the present invention, and which still fall within the scope of protection of the present invention. Specifically, the scope of protection of the present invention shall be based on the contents of the claims of the present invention.

[0022] Compounds that react with chain free radicals to generate non-radicals or low-activity free radicals that cannot initiate monomer polymerization, thereby completely halting the polymerization reaction, are called polymerization inhibitors; compounds that slow the polymerization reaction rate are called retarders. When an inhibitor is present in the system, polymerization cannot be initiated immediately after the polymerization reaction begins (the initiator begins to decompose). The polymerization reaction will not proceed normally until all the inhibitor in the system is consumed. In other words, there is a time interval between the start of initiator decomposition and the beginning of monomer conversion, which is called the induction period. Inhibitors cause an induction period in the polymerization reaction, but after the induction period, they do not change the polymerization rate. A longer induction period can delay the onset of polymerization. The longer the induction period, the longer the interval between replenishing the inhibitor, which is important in preventing monomer self-polymerization.

[0023] Piperidine nitroxides are a new class of stable free radical polymerization inhibitors discovered after the 1960s. Representative compounds include 2,2,6,6-tetramethylpiperidinyl nitroxide (TEMPO) and 2,2,6,6-tetramethyl-4-hydroxypiperidinyl nitroxide (4-OH-TEMPO). These compounds are broad-spectrum, highly effective polymerization inhibitors with excellent polymerization inhibition effects on olefins. Piperidine nitroxides offer advantages such as fast inhibition reaction speed and the absence of oxygen, but their sustained effectiveness is poor. By combining them with other inhibitors, the drawbacks of their individual use can be eliminated, resulting in new, more efficient, less toxic, and environmentally friendly polymerization inhibitors. Related research reports on composite polymerization inhibitors have been conducted both domestically and internationally. Zhang Ziyi et al. proposed the inhibitory effect of a composite polymerization inhibition system of TMHPO and benzoquinone on acrylic acid [Zhang Ziyi and Wei Xiuying, Highly Effective Inhibition of Acrylic Acid by 2,2,6,6-Tetramethyl-4-Hydroxy-Piperidinyloxy Free Radical, Journal of Chemistry in Higher Education Institutions, Vol. 4, No. 2, pp. 244-246 (1983)]. The free radical polymerization inhibitor used in the present invention is selected from 2,2,6,6-tetramethyl-4-hydroxypiperidinyl nitroxide free radical compound (codename ZJ-701) and 3-(2,2,6,6-tetramethyl-4-hydroxypiperidinyl nitroxide free radical) phosphite (codename ZJ-705).

[0024] Examples 1-6

[0025] A certain amount of purified vinyl acetate was added to a three-necked flask equipped with a thermometer, a reflux condenser, and a stirrer. An initiator (0.05% by weight of the vinyl acetate) and a composite polymerization inhibitor (30 ppm) were then added. After nitrogen displacement for 10 minutes, the reaction was heated and stirred at 65°C. Bubbles were continuously observed in the reaction system. The appearance of bubbles indicated the end of the induction period and the start of polymerization. The respective polymerization induction period times were recorded. The composite polymerization inhibitor was a complex of 2,2,6,6-tetramethyl-4-hydroxypiperidinyl nitroxide (ZJ-701) or 3-(2,2,6,6-tetramethyl-4-hydroxypiperidinyl nitroxide) phosphite (ZJ-705) with styrene (SM).

[0026] Table 1 Inhibition effect of different composite inhibitors

[0027]

[0028] Examples 7-16

[0029] Examples 7-16 were used as comparative examples. Experimental conditions were the same as in Example 1 to compare the inhibitory effects of other polymerization inhibitors. These experiments were conducted using either 2,2,6,6-tetramethyl-4-hydroxypiperidinyl nitroxide (ZJ-701), 3-(2,2,6,6-tetramethyl-4-hydroxypiperidinyl nitroxide) phosphite (ZJ-705), or styrene (SM) in combination with phenols (hydroquinone (HQ) or tert-butylhydroquinone (TBHQ)). The results are shown in Table 2.

[0030] Table 2 Comparison of the inhibitory effects of the inhibitors

[0031]

[0032]

[0033] As shown in Table 2, the induction periods for the self-polymerization of vinyl acetate monomers produced by various polymerization inhibitors, either alone or in combination, were significantly shorter than those of the compound polymerization inhibitor of the present invention. Under the same experimental conditions as in Example 1, the induction periods produced by the other polymerization inhibitors, either alone or in combination, ranged from a maximum of 240 minutes to a minimum of 80 minutes, significantly shorter than the 345 minutes of the compound polymerization inhibitor of Example 1 of the present invention.

[0034] Examples 17-26

[0035] Examples 17-26 show the actual results of polymerization inhibition experiments in the production process of vinyl acetate. The composite polymerization inhibitor is prepared into a certain concentration with vinyl acetate and continuously added from the top of the vinyl acetate distillation tower. The addition amount is 1-100ppm of the distillation system flow. Under constant process conditions, the pressure difference at each part of the distillation tower is basically fixed. If a significant pressure difference changes, it indicates that the polymer has blocked the tower plate. After 10 consecutive days of operation, the pressure at the top and bottom of the distillation tower is recorded with a pressure gauge and the pressure difference change is calculated. A larger pressure difference indicates that polymer has formed and blocked the tower plate. The composite polymerization inhibitor composition is 35% ZJ-705 and 75% SM. The experimental results are shown in Table 3.

[0036] Table 3 Experimental effects of different addition amounts of composite polymerization inhibitor

[0037]

[0038]

[0039] As shown in Table 3, the composite polymerization inhibitor of the present invention can effectively reduce autopolymerization in a vinyl acetate system at a dosage of 1-100 ppm. The greater the amount of inhibitor added, the better the inhibition effect. At a dosage of 100 ppm, almost no pressure difference changes. However, considering cost, the preferred dosage is 3-50 ppm.

[0040] The above is only an embodiment of the present invention. The commonly known technical common sense in the scheme is not described in detail here. Those of ordinary skill in the art are aware of all the common technical knowledge in the technical field to which the invention belongs before the application date, can obtain all the existing technologies in the field, and have the ability to apply conventional experimental means before that date. Those of ordinary skill in the art can improve and implement this scheme in combination with their own abilities under the enlightenment given by this application. Some typical commonly known technologies should not become obstacles for those of ordinary skill in the art to implement this application. It should be pointed out that for those skilled in the art, without departing from the structure of the present invention, several adjustments and improvements can be made, which should also be regarded as the scope of protection of the present invention. These will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A composite polymerization inhibitor for use in the production process of vinyl acetate, characterized in that: The polymerization inhibitor comprises component A and component B, wherein component A is a nitroxide free radical compound and component B is styrene.

2. The composite polymerization inhibitor according to claim 1, characterized in that The A component nitroxide free radical compound is selected from one or more of 2,2,6,6-tetramethylpiperidinyl nitroxide free radical (TEMPO), 2,2,6,6-tetramethyl-4-hydroxypiperidinyl nitroxide free radical (4-OH-TEMPO), 3-(2,2,6,6-tetramethyl-4-hydroxypiperidinyl nitroxide free radical) phosphite, di-tert-butyl nitroxide free radical and 4,4'-dinitrodiphenyl nitroxide free radical.

3. The composite polymerization inhibitor according to claim 1, characterized in that The mass ratio of the nitroxide free radical compound of component A to the styrene of component B is 1:9-5:

5.

4. The composite polymerization inhibitor according to claim 3, characterized in that The mass ratio of the nitroxide free radical compound of component A to the styrene of component B is 3:7-5:

5.

5. A use of the composite polymerization inhibitor according to any one of claims 1 to 4, characterized in that: Used in vinyl acetate production to inhibit the self-polymerization of vinyl acetate monomer.

6. The use according to claim 5, characterized in that Used in the distillation process of vinyl acetate production to inhibit the self-polymerization of vinyl acetate monomer.

7. A method for inhibiting the self-polymerization of vinyl acetate monomer in a vinyl acetate production process, characterized in that: The polymerization inhibition is carried out using the composite polymerization inhibitor according to any one of claims 1 to 4.

8. The method according to claim 7, characterized in that The amount of the composite polymerization inhibitor added to the vinyl acetate system is 1-100 ppm relative to the weight of vinyl acetate.

9. The method according to claim 8, characterized in that The amount of the composite polymerization inhibitor added to the vinyl acetate system is 3-50 ppm relative to the weight of vinyl acetate.

10. The method according to claim 8, characterized in that The composite polymerization inhibitor is added into the system through the middle or top of the distillation tower or through the feed point.

Images