Storage and / or transportation of ethylenically unsaturated compounds

Abstract

The present invention relates to a method for storing and / or transporting ethylenically unsaturated compounds, which are protected from undesired free radical polymerization using sterically hindered N-oxyls.

Description

[Technical field]

[0001] The present invention relates to a method for storing and / or transporting ethylenically unsaturated compounds, which are protected from undesired free radical polymerization using sterically hindered N-oxyls. [Background technology]

[0002] Compounds having one or more ethylenically unsaturated groups have a pronounced tendency towards free radical polymerization. Such compounds are therefore also called polymerizable compounds. The tendency of these compounds towards free radical polymerization means that they are used as monomers for producing polymers. However, the pronounced tendency of these compounds towards free radical polymerization is also a drawback. This is because during storage and transportation, as well as during chemical and / or physical processing, for example during distillation or rectification, undesirable spontaneous free radical polymerization may occur, especially under the action of energy such as heat and / or light. As a result of such uncontrolled polymerization, for example on heated surfaces, polymer deposits may gradually form, which makes it necessary to remove the polymer deposits and therefore often reduces the operating time. Uncontrolled polymerization may even proceed explosively.

[0003] It is therefore customary to add compounds that prevent or at least retard undesired spontaneous free radical polymerization during storage and transportation, as well as during chemical and / or physical processing, of ethylenically unsaturated compounds prone to free radical polymerization, or mixtures containing such compounds. Such substances are called polymerization inhibitors.

[0004] Polymerization inhibitors can be used as individual compounds or as mixtures of compounds. Depending on the field of use, specific requirements are imposed on the polymerization inhibitor. For a polymerization inhibitor to be suitable as a transport and / or storage stabilizer for ethylenically unsaturated compounds, it is important that the efficiency of the polymerization inhibitor, i.e. the degree of inhibition of polymerization, is controllable. Under the conditions of storage and / or transportation of ethylenically unsaturated compounds, the polymerization inhibitor should sufficiently prevent or retard undesired spontaneous free radical polymerization, but under suitable polymerization conditions, the desired free radical polymerization of ethylenically unsaturated compounds should be possible without the need to first isolate the polymerization inhibitor used during storage and / or transportation. If the stabilizer used during storage and / or transportation is not isolated for the desired polymerization, it is important that this stabilizer does not have a negative effect on the desired polymerization, e.g. does not act unintentionally as a chain transfer agent.

[0005] In terms of worldwide production, acrylic acid is undoubtedly one of the most important ethylenically unsaturated compounds. Acrylic acid is usually stabilized against undesired spontaneous free radical polymerization during storage and / or transportation with 0.018% to 0.022% by weight of hydroquinone monomethyl ether (MEHQ), based on the amount of acrylic acid. In order to adequately stabilize acrylic acid against undesired spontaneous free radical polymerization using MEHQ, it is necessary that a sufficient amount of oxygen is dissolved in the acrylic acid. If acrylic acid is stored and / or transported under an atmosphere having 5% to 21% by volume of oxygen, generally, a sufficient amount of oxygen dissolves in the acrylic acid. In the desired polymerization of acrylic acid, the content of dissolved oxygen in the acrylic acid decreases, thereby reducing the efficiency of MEHQ as a polymerization inhibitor sufficiently for acrylic acid to undergo polymerization in the presence of MEHQ.

[0006] In addition to its use as a polymerization inhibitor for the storage and / or transport of acrylic acid, MEHQ is also used as a polymerization inhibitor for the storage and / or transport of methacrylic acid, acrylic acid esters, and / or methacrylic acid esters, or mixtures containing one or more of said compounds.

[0007] MEHQ is widely used and has become one of the most important storage and / or transport stabilizers for ethylenically unsaturated compounds, especially acrylic acid, methacrylic acid, acrylic acid esters, and methacrylic acid esters.

[0008] The ethylenically unsaturated compounds are stored in suitable permanently installed containers, such as storage tanks (see, for example, Acrylic Acid, A Summary of Safety and Handling, 4th edition 2013, 7 Bulk Storage Facilities and Accessories). Preferably, the storage of the ethylenically unsaturated compounds in each container lasts for at least 1 hour, more preferably at least 10 hours, and most preferably at least 100 hours. Although the storage period under suitable conditions is theoretically unlimited, for economic reasons, the storage period is generally reduced to a minimum. Preferably, the storage of the ethylenically unsaturated compounds in each container lasts for no more than 180 days, more preferably no more than 90 days, and most preferably no more than 30 days. Particularly preferred ranges result from any combination of the above lower and upper limits.

[0009] The ethylenically unsaturated compounds are typically transported in suitable transportable containers, such as tanks or drums, by ship, rail, and / or truck (see, for example, Acrylic Acid, A Summary of Safety and Handling, 4th edition 2013, 9 Safe Transport of Acrylic Acid). The transportable containers may of course be permanently installed in the corresponding means of transport, such as a tanker ship or a railroad tank car. Of course, it is also possible to store the containers at a specific location for a certain time before transporting them to another location. The ethylenically unsaturated compounds may also be transported, for example, by pipeline or hose to a storage tank, after purification of the ethylenically unsaturated compounds, when they are transferred from a storage tank to a transportable container and / or when they are transferred from one transportable container to another transportable container. Preferably, the transport of the ethylenically unsaturated compounds in each container lasts for at least 1 hour, more preferably at least 10 hours, and most preferably at least 100 hours. Although the period under suitable conditions is theoretically unlimited, for economic and safety reasons, the period is generally reduced to a minimum. Preferably, the transport of the ethylenically unsaturated compound in each container is for a period of not more than 180 days, more preferably not more than 90 days, and most preferably not more than 30 days. Particularly preferred ranges result from any combination of the above lower and upper limits.

[0010] EP 0 685 447 and JP 2002-234858 disclose mixtures of polymerization inhibitors of (meth)acrylic acid and its esters, which contain N-oxyl.

[0011] WO 2001 / 040149 and WO 2001 / 040319 disclose mixtures of polymerization inhibitors for ethylenically unsaturated monomers, which also contain N-oxyls. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] European Patent No. 0685447 [Patent Document 2] JP 2002-234858 A [Patent Document 3] International Publication No. 2001 / 040149 Brochure [Patent Document 4] International Publication No. 2001 / 040319 Brochure [Non-patent literature]

[0013] [Non-Patent Document 1] Acrylic Acid,A Summary of Safety and Handling,4th edition 2013 Summary of the Invention [Problem to be solved by the invention]

[0014] The object of the present invention was to provide a method for storing and / or transporting ethylenically unsaturated compounds. The polymerization inhibitor ensures sufficient stabilization of the ethylenically unsaturated compounds against undesired free radical polymerization. However, in the desired free radical polymerization, it is not necessary to separate the polymerization inhibitor from the mixture before polymerization. Thus, the polymerization inhibitor does not act as a polymerization chain transfer agent and / or polymerization inhibitor in the desired free radical polymerization. [Means for solving the problem]

[0015] This object is achieved by a method for storing and / or transporting an ethylenically unsaturated compound, in which the ethylenically unsaturated compound has a purity of at least 90% by weight, the mass of the ethylenically unsaturated compound to be stored and / or transported is at least 100 kg, the temperature during storage and / or transport of the ethylenically unsaturated compound is below 50° C., the ethylenically unsaturated compound is a carboxylic acid or a carboxylic acid ester, and the ethylenically unsaturated compound contains 0.00001% by weight to 0.00050% by weight (0.1 to 5 ppm) of sterically hindered N-oxyl, based on the total amount of the ethylenically unsaturated compound.

[0016] A sterically hindered N-oxyl has an NO group with a free electron on the oxygen atom and a completely substituted carbon atom apart from the NO group.

[0017] Suitable sterically hindered N-oxyls include 1-oxyl-2,2,6,6-tetramethylpiperidine, 1-oxyl-2,2,6,6-tetramethylpiperidin-4-ol (HTEMPO), 1-oxyl-2,2,6,6-tetramethylpiperidin-4-one, 1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl acetate, 1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl 2-ethylhexanoate, 1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl Stearate, 1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl benzoate, 1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl (4-tert-butyl)benzoate, bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) succinate, bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) adipate, bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) sebacate, bis(1-oxyl -2,2,6,6-tetramethylpiperidin-4-yl) n-butyl malonate, bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) phthalate, bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) isophthalate, bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) terephthalate, bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) hexahydroterephthalate, N,N'-bis(1-oxyl- 2,2,6,6-tetramethylpiperidin-4-yl)adipamide, N-(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)caprolactam, N-(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)dodecylsuccinimide, 2,4,6-tris[N-butyl-N-(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl]-s-triazine and tris(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)phosphite.

[0018] The purity of the ethylenically unsaturated compounds is preferably at least 95% by weight, more preferably at least 98% by weight, and most preferably at least 99% by weight.

[0019] The mass of the ethylenically unsaturated compound to be stored and / or transported is preferably at least 200 kg, more preferably at least 500 kg, and most preferably at least 1000 kg. The mass of the ethylenically unsaturated compound to be stored and / or transported is typically less than 10 million kg.

[0020] The ethylenically unsaturated compounds preferably have a temperature during storage and / or transportation of less than 45° C., more preferably less than 40° C., and most preferably less than 35° C. In the case of acrylic acid, the temperature during storage and / or transportation should be at least 15° C.

[0021] The ethylenically unsaturated compounds preferably contain less than 0.0001% by weight each of manganese salts, copper salts, non-N-oxyl 2,2,6,6-tetramethylpiperidine compounds, and nitroso compounds, based on the total amount of ethylenically unsaturated compounds.

[0022] In a preferred embodiment of the invention, a sterically hindered N-oxyl is used essentially as the sole polymerization inhibitor.

[0023] The ethylenically unsaturated compound is preferably contained in an amount of 0.00005% by weight to 0.00045% by weight (0.5 to 4.5 ppm), more preferably 0.00010% by weight to 0.00040% by weight (1 to 4 ppm), and most preferably 0.00015% by weight to 0.00035% by weight (1.5 to 3.5 ppm) based on the total amount of the ethylenically unsaturated compounds in any case.

[0024] The ethylenically unsaturated compound is preferably a mono-, di-, or triethylenically unsaturated C3-C8 carboxylic acid, a mono-, di-, or triethylenically unsaturated C3-C8 carboxylic acid ester having 1 to 20 carbon atoms in the ester group.

[0025] Mono-, di-, or triethylenically unsaturated C3-C6 carboxylic acids, such as acrylic acid, methacrylic acid, dimethacrylic acid, ethacrylic acid, citraconic acid, methylenemalonic acid, crotonic acid, fumaric acid, mesaconic acid, itaconic acid, and maleic acid; mono-, di-, or triethylenically unsaturated C3-C6 carboxylic acid esters having 1 to 12 carbon atoms in the ester group, such as C1-C 12 Alkyl-containing acrylic esters, C1-C 12 Methacrylic acid esters with alkyl groups, C1-C 12 Dimethacrylate esters with alkyl groups, C1-C 12 Ethacrylic acid esters with alkyl groups, C1-C 12 Citraconic acid esters with alkyl groups, C1-C 12 Methylenemalonate esters with alkyl groups, C1-C 12 Alkyl crotonates, C1-C 12 Alkyl fumarate esters, C1-C 12 Mesaconic acid esters with alkyl groups, C1-C 12 Itaconic acid esters with alkyl groups, and C1-C 12 Alkyl-containing maleates are particularly preferred.

[0026] Acrylic acid, methacrylic acid, acrylic acid esters having C1-C8 alkyl groups such as methyl acrylate, ethyl acrylate, n-butyl acrylate, and 2-ethylhexyl acrylate, and methacrylic acid esters having C1-C8 alkyl groups such as methyl methacrylate are most preferred.

[0027] Further suitable ethylenically unsaturated compounds are dipropylene glycol diacrylate, tripropylene glycol diacrylate, polyethylene glycol diacrylate, glycerol triacrylate, ethoxylated glycerol triacrylate, trimethylolpropane triacrylate, ethoxylated trimethylolpropane triacrylate, butanediol monoacrylate, dicyclopentadienyl acrylate, 2-dimethylaminoethyl acrylate, 2-hydroxyethyl acrylate, and 2-hydroxypropyl acrylate.

[0028] Acrylic acid and / or methacrylic acid are typically stored and / or transported in stainless steel containers. Suitable stainless steels contain 16.5% to 19.5% by weight chromium and 8.0% to 13.5% by weight nickel.

[0029] Ethylenically unsaturated compounds are typically stored and / or transported under an oxygen-containing atmosphere.

[0030] The ethylenically unsaturated compound is preferably stored in a container under an oxygen-containing atmosphere having an oxygen content of 5% to 10% by volume, and the mixture in the container is periodically recirculated at least once a week, for example by pumping recirculation of the entire tank contents. This relatively low oxygen content prevents the formation of an ignitable gas mixture in the container. Recirculation replenishes the dissolved oxygen consumed in the liquid ethylenically unsaturated compound.

[0031] The present invention further provides a method of free radical polymerization in which at least one of the above ethylenically unsaturated compounds is polymerized by a polymerization initiator, and the use of one of the above ethylenically unsaturated compounds for free radical polymerization by a polymerization initiator.

[0032] The free radical polymerization of the present invention can provide, for example, water-soluble and water-swellable polyacrylic acid and its sodium salt.

[0033] Free radical polymerization itself is common knowledge and is typically carried out in solution. Suitable polymerization initiators are all compounds that can decompose into free radicals under the selected reaction conditions, such as thermal initiators, redox initiators, photoinitiators. Suitable thermal initiators are peroxo mono- and disulfates, as well as peroxo mono- and diphosphates. Suitable redox initiators are sodium peroxodisulfate / ascorbic acid, hydrogen peroxide / ascorbic acid, sodium peroxodisulfate / sodium hypophosphite, sodium peroxodisulfate / sodium bisulfite, and hydrogen peroxide / sodium bisulfite. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS EXAMPLES

[0034] Polymerization inhibition experiment The ethylenically unsaturated compounds used were distilled twice to remove the hydroquinone monomethyl ether (MEHQ) polymerization inhibitor. Defined amounts of the indicated polymerization inhibitors were added to the resulting ethylenically unsaturated compounds in each case. MEHQ and 4-hydroxy-2,2,6,6-tetramethylpiperidine N-oxyl (HTEMPO) were used.

[0035] 0.5 ml of each mixture was transferred into 1.8 ml ampoules and stored in an air circulating oven at the specified temperature.

[0036] In each test series, in each case three ampoules were filled with each mixture and tested, and the average time for complete polymerization was determined by visual inspection.

[0037] [Table 1]

[0038] [Table 2]

[0039] [Table 3]

[0040] [Table 4]

[0041] [Table 5]

[0042] [Table 6]

[0043] 4-Hydroxy-2,2,6,6-tetramethylpiperidine N-oxyl (HTEMPO) has an inhibitory effect comparable to that of MEHQ, even at significantly lower concentrations.

[0044] Polymerization experiments The reaction vessel was initially charged with 450 g of water under a nitrogen atmosphere. The initial charge reaction mixture was heated with stirring to 95° C. Once a temperature of 95° C. was reached, the three streams were metered in with stirring while maintaining the temperature. Flow 1: 500 g of acrylic acid metered in over 5 hours Stream 2: 15 g sodium hypophosphite in 35 g deionized water, metered in over 4.75 hours Stream 3: 5 g sodium peroxodisulfate in 66.4 g deionized water, metered in over 5.25 hours

[0045] After the three streams were added, the reaction mixture was stirred for an additional hour at 95° C. The reaction mixture was then cooled to room temperature and 80 g of water was added.

[0046] The acrylic acid used in stream 1 was stabilized with MEHQ or 4-hydroxy-2,2,6,6-tetramethylpiperidine N-oxyl (HTEMPO).

[0047] The obtained polymer was analyzed by GPC (calibration with Na-PAA standards, eluent: 0.01 mol / l phosphate buffer in distilled water containing 0.01 M NaN3, pH=7.4).

[0048] [Table 7]

[0049] The concentrations of 4-hydroxy-2,2,6,6-tetramethylpiperidine N-oxyl (HTEMPO) tested lead to polyacrylic acid with molar masses comparable to those obtained using the standard concentration of MEHQ.

Claims

1. 1. A method for storing and / or transporting an ethylenically unsaturated compound, wherein the ethylenically unsaturated compound has a purity of at least 90% by weight, the mass of the ethylenically unsaturated compound stored and / or transported is at least 100 kg, the temperature during storage and / or transportation of the ethylenically unsaturated compound is below 50° C., the ethylenically unsaturated compound is a carboxylic acid or a carboxylic acid ester, and the ethylenically unsaturated compound comprises 0.00001% to 0.00050% by weight of sterically hindered N-oxyl, based on the total amount of ethylenically unsaturated compound.

2. 2. The method of claim 1, wherein the ethylenically unsaturated compounds comprise less than 0.0001% by weight each of manganese salts, copper salts, 2,2,6,6-tetramethylpiperidine compounds that are not N-oxyl, and nitroso compounds, in each case based on the total amount of ethylenically unsaturated compounds.

3. The method of claim 1, wherein the sterically hindered N-oxyl is used essentially as the only polymerization inhibitor.

4. 4. The process according to any one of claims 1 to 3, wherein 1-oxyl-2,2,6,6-tetramethylpiperidin-4-ol is the sterically hindered N-oxyl used.

5. 5. The method of claim 1, wherein the storing and / or transporting of the ethylenically unsaturated compound is carried out for a period of at least 10 hours.

6. 6. The method of any one of claims 1 to 5, wherein the ethylenically unsaturated compounds comprise from 0.00005% to 0.00045% by weight of sterically hindered N-oxyl, based on the total amount of ethylenically unsaturated compounds.

7. 7. The method of any one of claims 1 to 6, wherein the ethylenically unsaturated compounds comprise from 0.00010% to 0.00040% by weight of sterically hindered N-oxyl, based on the total amount of ethylenically unsaturated compounds.

8. 8. The method of any one of claims 1 to 7, wherein the ethylenically unsaturated compounds comprise from 0.00015% to 0.00035% by weight of sterically hindered N-oxyl, based on the total amount of ethylenically unsaturated compounds.

9. 8. The method according to any one of claims 1 to 7, wherein the ethylenically unsaturated compound is acrylic acid, methacrylic acid, methyl acrylate, methyl methacrylate, ethyl acrylate, n-butyl acrylate and / or 2-ethylhexyl acrylate.

10. 10. The method of claim 1, wherein the ethylenically unsaturated compound is stored and / or transported under an oxygen-containing atmosphere.

11. 10. The method according to claim 1, wherein the ethylenically unsaturated compound is stored in a container under an oxygen-containing atmosphere having an oxygen content of 5% to 10% by volume, and the ethylenically unsaturated compound in the container is periodically recirculated.

12. 1. A method for free radical polymerization, wherein at least one ethylenically unsaturated compound is polymerized by a polymerization initiator, said ethylenically unsaturated compound being a carboxylic acid or a carboxylic acid ester, said ethylenically unsaturated compound used has a purity of at least 90% by weight, and said ethylenically unsaturated compound comprises 0.00001% to 0.00050% by weight of sterically hindered N-oxyl, based on said total amount of ethylenically unsaturated compounds.

13. The method of claim 12, wherein the sterically hindered N-oxyl is used essentially as the sole polymerization inhibitor.

14. 1. Use of an ethylenically unsaturated carbonyl compound for free radical polymerization with a polymerization initiator, wherein the ethylenically unsaturated compound is a carboxylic acid or a carboxylic acid ester, the ethylenically unsaturated compound has a purity of at least 90% by weight, and the ethylenically unsaturated compound contains 0.00001% to 0.00050% by weight of a sterically hindered N-oxyl, based on the total amount of ethylenically unsaturated compounds.

15. The use according to claim 14, wherein the sterically hindered N-oxyl is used essentially as the sole polymerization inhibitor.

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