Polymerization inhibitor

Abstract

The present invention relates to a mixture comprising at least one substituted hydroxypyrazole and at least one polymerizable compound.

Description

[0001] The present invention relates to a mixture containing at least one substituted 5-hydroxypyrazole and at least one polymerizable compound.

[0002] Compounds containing one or more vinyl unsaturated groups exhibit a strong tendency for free radical polymerization. Therefore, in the following text, these compounds are also referred to as polymerizable compounds. Due to their tendency for free radical polymerization, these compounds can be used as monomers in polymer production. However, this strong tendency for free radical polymerization is also disadvantageous, as unwanted, spontaneous free radical polymerization can occur during storage and transportation, as well as during chemical and / or physical processing (e.g., distillation or rectification), particularly under the influence of energy (e.g., heat and / or light). This uncontrolled polymerization can lead to the gradual formation of polymer deposits on surfaces such as heated surfaces, requiring the removal of these deposits and often resulting in shortened run times. This uncontrolled polymerization can even lead to explosions.

[0003] Therefore, it is common practice to add a compound to vinyl unsaturated compounds, or mixtures containing such compounds, that are prone to free radical polymerization during storage and transportation, as well as during chemical and / or physical processing, to prevent or at least slow down undesirable spontaneous free radical polymerization. Such substances are called polymerization inhibitors.

[0004] Polymerization inhibitors can be used as single compounds or as mixtures of compounds. Depending on the application area, certain requirements are imposed on the polymerization inhibitor. For a polymerization inhibitor to be suitable as a stabilizer for the transport and / or storage of vinyl unsaturated compounds, its efficiency (i.e., the degree of polymerization inhibition) must be adjustable. Under the storage and / or transport conditions of the vinyl unsaturated compound, the polymerization inhibitor should be able to sufficiently prevent or slow down unwanted spontaneous free radical polymerization; while under appropriate polymerization conditions, the vinyl unsaturated compound should be able to undergo the desired free radical polymerization without prior separation of the polymerization inhibitor used during storage and / or transport. If the stabilizer used during storage and / or transport is not separated before polymerization, it is important that the stabilizer does not adversely affect the polymerization (e.g., unintentionally act as a regulator).

[0005] In terms of global production, acrylic acid is undoubtedly one of the most important vinyl unsaturated compounds. By standard, acrylic acid is stabilized during storage and / or transportation using 0.018% to 0.022% by weight of p-hydroxyanisole (MEHQ), based on the amount of acrylic acid used, to prevent undesirable spontaneous free radical polymerization. For acrylic acid to be sufficiently stabilized with MEHQ to prevent undesirable spontaneous free radical polymerization, a sufficient amount of oxygen must be dissolved in the acrylic acid. Typically, sufficient oxygen is dissolved in acrylic acid when stored and / or transported in an atmospheric environment with an oxygen content of 5% to 21% by volume. Reducing the dissolved oxygen content in acrylic acid before polymerization reduces the polymerization inhibition efficiency of MEHQ, allowing acrylic acid to polymerize in the presence of MEHQ.

[0006] In addition to its use as a polymerization inhibitor in the storage and / or transport of acrylic acid, MEHQ can also be used as a polymerization inhibitor in the storage and / or transport of methacrylic acid, acrylates and / or methacrylates, or mixtures containing one or more of the above compounds.

[0007] Due to its wide range of applications, MEHQ is one of the most important storage and / or transport stabilizers for polymerizable compounds, particularly acrylic acid, methacrylic acid, acrylates and methacrylates.

[0008] Polymerizable compounds are stored in suitable fixed bundles, such as storage tanks or containers (see, for example, Acrylic Acid, Safety and Handling Summary, 4th Edition, 2013, 7 Bulk Storage Facilities and Accessories). Preferably, during storage, the polymerizable compound is present in the corresponding bundle for at least one minute, particularly preferably at least 10 minutes, and very particularly preferably at least 60 minutes. Although theoretically the storage time is unlimited under suitable conditions, for economic reasons, the storage time is usually minimized as much as possible. Preferably, during storage, the polymerizable compound is present in the corresponding bundle for a maximum of 180 days, particularly preferably a maximum of 90 days, and very particularly preferably a maximum of 30 days. The best range is any combination of the lower and upper limits mentioned above.

[0009] The transport of polymerizable compounds is typically carried out in suitable transportable bundles, such as tanks or containers by ship, railcar, and / or truck (see, for example, Acrylic Acid, Safety and Handling Summary, 4th Edition, 2013, p. 9, Safe Transport of Acrylic Acid). Of course, the transportable bundles can also be securely mounted to the appropriate means of transport, such as ship tanks or railcars. Naturally, the bundles can also be stored at one location for a period of time before being transported to another location. The transport of polymerizable compounds can also be carried out via pipes or hoses, for example, after the polymerizable compound has been purified into a storage tank, during loading from the storage tank into the transportable bundle, and / or during loading from one transportable bundle into another. Preferably, during transport, the polymerizable compound is present in the respective bundle for at least 10 seconds, preferably at least 1 minute, particularly preferably at least 10 minutes, and very particularly preferably at least 60 minutes. While theoretically the storage time is unlimited under suitable conditions, it is generally preferred to minimize the storage time for economic and safety reasons. Preferably, during transport, the polymerizable compound remains in the corresponding bundle for a maximum of 180 days, particularly preferably a maximum of 90 days, and very particularly preferably a maximum of 30 days. The best range is any combination of the lower and upper limits mentioned above.

[0010] The object of this invention is to provide mixtures containing: at least one polymerizable compound, particularly acrylic acid, methacrylic acid, acrylates, and / or methacrylates; and at least one polymerization inhibitor. The polymerization inhibitor is intended to ensure sufficient stability of the polymerizable compound, prevent undesirable free radical polymerization, and provide an alternative to MEHQ. However, in cases where free radical polymerization is desired, the polymerization inhibitor should not need to be separated from the mixture prior to polymerization. Therefore, the polymerization inhibitor should not act as a polymerization regulator and / or polymerization inhibitor in the event of free radical polymerization.

[0011] This objective is achieved by mixtures containing at least one compound of general formula (I).

[0012] (I)

[0013] in

[0014] R 1 H, methyl or ethyl, preferably methyl or ethyl,

[0015] R 2 It is H, methyl, or ethyl, preferably methyl or ethyl, and

[0016] R 3 It is H, methyl or ethyl, preferably H;

[0017] And at least one compound capable of polymerization.

[0018] Suitable compounds of general formula (I) include, for example: 5-hydroxypyrazole, 1-methyl-5-hydroxypyrazole, 3-methyl-5-hydroxypyrazole, 4-methyl-5-hydroxypyrazole, 1-ethyl-5-hydroxypyrazole, 3-ethyl-5-hydroxypyrazole, 4-ethyl-5-hydroxypyrazole, 1,3-dimethyl-5-hydroxypyrazole, 1,4-dimethyl-5-hydroxypyrazole, 3,4-dimethyl-5-hydroxypyrazole, 1,3-diethyl-5-hydroxypyrazole, 1,4-diethyl-5-hydroxypyrazole, 3,4-diethyl-5-hydroxypyrazole, 1,3,4-trimethyl-5-hydroxypyrazole, 1,3,4-triethyl-5-hydroxypyrazole, 1- Methyl-3-ethyl-5-hydroxypyrazole, 1-methyl-4-ethyl-5-hydroxypyrazole, 1-ethyl-3-methyl-5-hydroxypyrazole, 1-ethyl-4-methyl-5-hydroxypyrazole, 3-methyl-4-ethyl-5-hydroxypyrazole, 3-ethyl-4-methyl-5-hydroxypyrazole, 1-methyl-3,4-diethyl-5-hydroxypyrazole, 1,3-dimethyl-4-ethyl-5-hydroxypyrazole, 1,4-dimethyl-3-ethyl-5-hydroxypyrazole, 1-ethyl-3,4-dimethyl-5-hydroxypyrazole, 1,3-diethyl-4-methyl-5-hydroxypyrazole and 1,4-diethyl-3-methyl-5-hydroxypyrazole.

[0019] Compounds of general formula (I) exist in solution in equilibrium with their keto form (tautomerism). For example, 1,3-dimethyl-5-pyrazolone is the keto form of 1,3-dimethyl-5-hydroxypyrazole. The tautomerism equilibria of compounds of general formula (I) are generally described below. Within the scope of this invention, when referring to one tautomer of a compound of general formula (I), other tautomers conforming to the equilibrium below should also be included in each case. This also applies particularly to the description of quantities. In this context, for mixtures according to the invention, one of these tautomers or any mixture of two or three of the tautomers shown may be used, wherein an equilibrium is established.

[0020]

[0021] The compound of general formula (I) is particularly preferably 1,3-dimethyl-5-hydroxypyrazole or its keto form 1,3-dimethyl-5-pyrazole.

[0022] The tautomerism equilibria of 1,3-dimethyl-5-hydroxypyrazole are illustrated below. The compounds are in the following order: 1,3-dimethyl-1H-pyrazole-5-ol, 2,5-dimethyl-2,4-dihydro-3H-pyrazole-3-one, and 2,5-dimethyl-1,2-dihydro-3H-pyrazole-3-one (synonymous nomenclature).

[0023]

[0024] In the mixture, the total amount of the compound of general formula (I) is preferably from 0.0001 wt% to 0.1000 wt%, more preferably from 0.0002 wt% to 0.0750 wt%, particularly preferably from 0.0005 wt% to 0.0500 wt%, very particularly preferably from 0.0007 wt% to 0.0250 wt%, especially preferably from 0.0008 wt% to 0.0100 wt%, very particularly preferably from 0.0009 wt% to 0.0050 wt%, particularly preferably from 0.0010 wt% to 0.0025 wt%, in each case based on the total amount of the compound capable of polymerization.

[0025] In each case, based on the total weight of the mixture, the total amount of polymerizable compound in the mixture is preferably at least 5% by weight, preferably at least 50% by weight, particularly preferably at least 80% by weight, very particularly preferably at least 98% by weight, and especially preferably at least 99% by weight.

[0026] The polymerizable compounds are preferably mono-, di-, or triethylene-unsaturated C3 to C8 carboxylic acids, mono-, di-, or triethylene-unsaturated C3 to C8 aldehydes, mono-, di-, or triethylene-unsaturated C3 to C8 carboxylic acid esters having 1 to 20 carbon atoms in the ester group, mono-, di-, or triethylene-unsaturated C3 to C8 carboxylic acid amides, mono-, di-, or triethylene-unsaturated C3 to C8 nitriles, mono-, di-, or triethylene-unsaturated C3 to C8 carboxylic acid anhydrides, and saturated C2 to C8 carboxylic acid anhydrides. 20 Vinyl esters of carboxylic acids, saturated C1 to C2 10 Vinyl ethers of alcohols, vinyl aromatics, vinyl heteroaromatics, vinyl lactams having 3 to 10 carbon atoms in the ring, open-chain N-vinylamides and N-vinylamines, vinyl halides, aliphatic optional halogenated hydrocarbons having 2 to 8 carbon atoms and 1 or 2 ethylene double bonds, vinylidenes, or any mixture of two or more of the foregoing compounds.

[0027] Particularly preferred are mono-, di-, or triethylene-unsaturated C3 to C8 carboxylic acids, such as acrylic acid, methacrylic acid, dimethacrylic acid, ethylacrylic acid, citric acid, methylene malonic acid, crotonic acid, fumaric acid, medaconic acid, itaconic acid, and maleic acid, specifically mono-, di-, or triethylene-unsaturated C3 to C8 carboxylic acid esters having 1 to 20 carbon atoms in the ester group, for example, having C1 to C2 carbon atoms in the ester group. 20 Alkyl acrylates, having C1 to C 20 Alkyl methacrylates, having C1 to C 20 Alkyl dimethacrylates, having C1 to C1 20 Alkyl ethyl acrylate, having C1 to C 20 Alkyl citrates, having C1 to C 20Alkyl methylene malonate, having C1 to C2 20 Alkyl crotonate, having C1 to C 20 Alkyl fumarates, having C1 to C2 20 Alkyl esters, having C1 to C2 20 Alkyl itaconic acid esters and those having C1 to C2 20 Alkyl maleate esters, mono-, di-, or triethylene unsaturated C3 to C8 carboxylic amides, such as acrylamide, methacrylamide, dimethacrylamide, ethylacrylamide, citamide, methylenemalonamide, crotonamide, fumaramide, zearalenone, itacamide, and maleamide; mono-, di-, or triethylene unsaturated C3 to C8 nitriles, such as acrylonitrile and methacrylonitrile; and mono-, di-, or triethylene unsaturated C3 to C8 carboxylic anhydrides, such as acrylic anhydride, methacrylic anhydride, itaconic anhydride, and maleic anhydride.

[0028] Very particularly preferred are acrylic acid, methacrylic acid, acrylates containing C1 to C8 alkyl groups (e.g., methyl acrylate, ethyl acrylate, n-butyl acrylate and 2-ethylhexyl acrylate), and methacrylates containing C1 to C8 alkyl groups (e.g., methyl methacrylate).

[0029] Other suitable polymerizable compounds include dipropylene glycol diacrylate, tripropylene glycol diacrylate, polyethylene glycol diacrylate, glyceryl triacrylate, ethoxylated glyceryl triacrylate, trimethylolpropane triacrylate, ethoxylated trimethylolpropane triacrylate, butanediol monoacrylate, dicyclopentadiene acrylate, 2-dimethylaminoethyl acrylate, 2-hydroxyethyl acrylate, and 2-hydroxypropyl acrylate.

[0030] The present invention also provides the use of at least one compound of general formula (I) as described above for inhibiting the polymerization of at least one polymerizable compound.

[0031] The present invention also provides a method for storing and / or transporting a mixture comprising at least one compound of general formula (I) as described above and at least one polymerizable compound.

[0032] The mixture is typically stored and / or transported in an oxygen-containing atmosphere.

[0033] The mixture is preferably stored in a container under an oxygen-containing atmosphere with an oxygen content of 5% to 10% by volume, and the mixture is circulated in the container periodically, for example by completely pumping the contents of the container at least once a week. The relatively low oxygen content prevents the formation of flammable gas mixtures within the container. Circulating the liquid replaces the dissolved oxygen consumed in the polymer compound. Example

[0034] Preparation of 1,3-dimethyl-5-hydroxypyrazole

[0035] 1,3-Dimethyl-5-hydroxypyrazolone is provided as described in Fakhraian, H., Nafari, Y; Preparative, mechanistic and tautomeric investigation of 1-phenyl and 1-methyl derivative of 3-methyl-5-pyrazolone; J Chem Sci 133, 40 (2021) (DOI: https: / / doi.org / 10.1007 / s12039-021-01902-9).

[0036] Polymerization inhibition experiment

[0037] The monomer used is distilled twice to remove the polymerization inhibitor MEHQ. In each case, a specified amount of the polymerization inhibitor is added to the resulting monomer.

[0038] Inject each 0.5 ml of the mixture into 1.8 ml ampoules and store in an air-circulating drying cabinet at the preset temperature.

[0039] In each test series, each mixture was tested in three ampoules, and the average time required for the complete polymerization reaction was visually recorded.

[0040] Relative effectiveness was calculated by dividing the polymerization time of the sample containing the test polymerization inhibitor by the polymerization time of the sample containing MEHQ. Therefore, the effectiveness of MEHQ itself is 100%.

[0041] The results are summarized in Tables 1 and 2:

[0042] Table 1: Mixtures with acrylic acid

[0043] MEHQ*) 10 80 8.3 100% MEHQ*) 20 80 15.5 100% DMHP 10 80 13.5 163% DMHP 20 80 19.3 125% TBHP*) 20 80 5.3 34% TMHP*) 20 80 3.1 20% MHP*) 20 80 3.1 20% IMHP*) 20 80 5.6 36%

[0044] MEHQ: Hydroquinone Monomethyl Ether

[0045] DMHP: 1,3-Dimethyl-1H-pyrazole-5-ol

[0046] TBHP: 3-(tert-butyl)-1-methyl-1H-pyrazole-5-ol

[0047] TMHP: 1,3,4-Trimethyl-1H-pyrazole-5-ol

[0048] MHP: 1-Methyl-1H-pyrazole-5-ol

[0049] IMHP: 1-Isopropyl-3-methyl-1H-pyrazole-5-ol

[0050] *)contrast

[0051] Compared with MEHQ and non-inventory derivatives, the polymerization inhibitor according to the present invention has improved effectiveness.

[0052] Polymerization reaction experiment

[0053] Under nitrogen atmosphere, 450g of water was placed in the reaction vessel. The provided reaction mixture was heated to 95°C while stirring. Once the temperature reached 95°C, the three liquid streams were added quantitatively while continuing stirring and maintaining the temperature.

[0054] Liquid flow rate 1: 5-hour quantitative addition, 500g acrylic acid

[0055] Liquid flow 2: Quantitative addition over 4.75 hours, 15g sodium hypophosphite added to 35g deionized water.

[0056] Liquid flow 3: Quantitative addition over 5.25 hours, 5g sodium persulfate added to 66.4g deionized water.

[0057] After adding the three liquid streams, the reaction mixture was stirred at 95°C for one hour. The reaction mixture was then cooled to room temperature and 80 g of water was added.

[0058] The acrylic acid used in flow 1 was stabilized with 200 ppm by weight of 1,3-dimethyl-5-hydroxypyrazole or 200 ppm by weight of MEHQ.

[0059] The obtained polymers were analyzed using GPC (gel permeation chromatography) (calibrated with Na-PAA standard, the eluent was 0.01 mol / L phosphate buffer, pH=7.4 in distilled water with 0.01 M NaN3 added).

[0060] Table 2: Polymerization reaction of acrylic acid

[0061] MEHQ*) 0.020% by weight 10400 DMHP 0.020% by weight 10200

[0062] MEHQ: Hydroquinone Monomethyl Ether

[0063] DMHP: 1,3-Dimethyl-5-hydroxypyrazole

[0064] *)contrast

[0065] The polymerization inhibitor according to the present invention produces polyacrylic acid with comparable molecular weight.

Claims

1. A mixture comprising: at least one compound of general formula (I), (I) in R 1 It is H, methyl or ethyl. R 2 It is H, methyl, or ethyl, and R 3 It is H, methyl or ethyl. And at least one compound capable of polymerization.

2. The mixture according to claim 1, wherein R 1 It is methyl or ethyl, R 2 It is methyl or ethyl and R 3 For H.

3. The mixture according to claim 1, wherein, The compound of general formula (I) is 1,3-dimethyl-5-hydroxypyrazole.

4. The mixture according to any one of claims 1 to 3, wherein, Based on the total amount of polymerizable compounds, the total amount of the compounds of general formula (I) in the mixture is from 0.0001% by weight to 0.1000% by weight.

5. The mixture according to any one of claims 1 to 3, wherein, Based on the total amount of polymerizable compounds, the total amount of the compounds of general formula (I) in the mixture is from 0.0008% by weight to 0.0100% by weight.

6. The mixture according to any one of claims 1 to 5, wherein, Based on the total weight of the mixture, the total amount of the polymerizable compound is at least 5% by weight.

7. The mixture according to any one of claims 1 to 5, wherein, Based on the total weight of the mixture, the total amount of the polymerizable compound is at least 98% by weight.

8. The mixture according to any one of claims 1 to 7, wherein, The polymerizable compound is acrylic acid and / or methacrylic acid.

9. Use of at least one compound of general formula (I) according to any one of claims 1 to 3 for inhibiting the polymerization of at least one polymerizable compound.

10. A method for storing and / or transporting a mixture according to any one of claims 1 to 8.

11. The method according to claim 10, wherein, The mixture is stored and / or transported in an oxygen-containing atmosphere.

12. The method according to claim 11, wherein, The mixture is stored in a container in an oxygen-containing atmosphere with an oxygen content of 5% to 10% by volume, and the mixture in the container is periodically circulated.

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