Storage and / or transportation of ethylenically unsaturated carboxylic acids

Abstract

The present invention relates to a method for storing and / or transporting ethylenically unsaturated carboxylic acids, which are protected from unwanted radical polymerization by manganese(II) ions.

Description

Technical Field

[0001] The present invention relates to a method for storing and / or transporting ethylenically unsaturated carboxylic acids, which are protected from unwanted free radical polymerization by manganese(II) ions.

Background Art

[0002] Compounds having one or more ethylenically unsaturated groups have a marked tendency to undergo free radical polymerization. Therefore, such compounds are also referred to hereinafter as polymerizable compounds. The fact that these compounds have a tendency to undergo free radical polymerization means that they are used as monomers for producing polymers. However, the marked tendency of these compounds to undergo 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, unwanted spontaneous free radical polymerization can occur, especially under the action of energy such as heat and / or light. As a result of such uncontrolled polymerization, for example, polymer deposits may gradually form on a heated surface, which requires the removal of the polymer deposits and thus often results in a shortening of the operating time. Uncontrolled polymerization can even proceed explosively.

[0003] Therefore, during the storage and transportation of ethylenically unsaturated compounds having a tendency to undergo free radical polymerization, or mixtures containing such compounds, as well as during chemical and / or physical processing, it is common practice to add a compound that prevents or at least delays unwanted spontaneous free radical polymerization. Such substances are referred to as polymerization inhibitors.

[0004] The polymerization inhibitor can be used as an individual compound or as a mixture of compounds. Specific requirements are imposed on the polymerization inhibitor depending on its field of use. For the 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 transport of ethylenically unsaturated compounds, the polymerization inhibitor should sufficiently prevent or delay unwanted spontaneous free radical polymerization, but under appropriate polymerization conditions, the desired free radical polymerization of the ethylenically unsaturated compound should be possible without first separating the polymerization inhibitor used during storage and / or transport. If the stabilizer used during storage and / or transport is not separated for the desired polymerization, it is important that this stabilizer does not adversely affect the desired polymerization, for example, does not act unintentionally as a chain transfer agent.

[0005] From the perspective of global production volume, acrylic acid is undoubtedly one of the most important ethylenically unsaturated compounds. Acrylic acid is usually stabilized against unwanted spontaneous free radical polymerization using 0.018% to 0.022% by mass of hydroquinone monomethyl ether (MEHQ) relative to the amount of acrylic acid during storage and / or transport. For MEHQ to sufficiently stabilize acrylic acid against unwanted spontaneous free radical polymerization, it is necessary that a sufficient amount of oxygen is dissolved in the acrylic acid. When acrylic acid is stored and / or transported in an atmosphere having 5% to 21% by volume of oxygen, generally, a sufficient amount of oxygen is dissolved 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 such that acrylic acid polymerizes in the presence of MEHQ.

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

[0007] Due to its wide use, MEHQ has become one of the most important storage and / or transportation stabilizers for ethylenically unsaturated compounds, especially acrylic acid, methacrylic acid, acrylic acid esters, and methacrylic acid esters.

[0008] Ethylenically unsaturated compounds are stored in permanently installed containers suitable for the purpose, 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 compound in each container preferably lasts for at least 1 hour, more preferably at least 10 hours, and most preferably at least 100 hours. The storage period under appropriate conditions is theoretically unlimited, but for economic reasons, the storage period is generally minimized. Preferably, the storage of the ethylenically unsaturated compound in each container lasts for 180 days or less, more preferably 90 days or less, and most preferably 30 days or less. Particularly preferred ranges result from the free combination of the above lower and upper limits.

[0009] Ethylenically unsaturated compounds are typically transported by ship, rail, and / or truck in suitable transportable containers, such as tanks or drums (see, e.g., 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 corresponding transport means, such as tanker ships or railroad tank cars. Of course, it is also possible to store the containers at a particular location for a certain period of time before transporting them to another location. Ethylenically unsaturated compounds may also be transported by pipeline or hose, e.g., to a storage tank, after purification of the ethylenically unsaturated compound, when transferred from a storage tank to a transportable container and / or when transferred from one transportable container to another transportable container. Preferably, the transport of the ethylenically unsaturated compound in each container preferably takes place over at least 1 hour, more preferably at least 10 hours, and most preferably at least 100 hours. The period under suitable conditions is theoretically unlimited, but for economic and safety reasons, the period is generally minimized. Preferably, the transport of the ethylenically unsaturated compound in each container takes place over 180 days or less, more preferably 90 days or less, and most preferably 30 days or less. Particularly preferred ranges result from any free combination of the above lower and upper limits.

[0010] European Patent Application Publication No. 0 398 633 discloses a method for inhibiting the polymerization of acidic monomers using a source of manganese and a source of phenylenediamine containing an NH group.

[0011] Japanese Patent No. 5140027 discloses the use of a mixture of a) phenols such as phenol, hydroquinone, p-methoxyphenol, cresol, and catechol, b) manganese salts, and c) sterically hindered phenols such as 2,5-di-tert-butylhydroquinone, 2,6-di-tert-butylphenol, 6-tert-butyl-m-cresol; 2,6-di-tert-butyl-p-cresol, 4-tert-butylcatechol, 2,4-dimethyl-6-tert-butylphenol, 2-tert-butylhydroquinone, and 2-tert-butyl-4-methoxyphenol for the stabilization of acrylic acid, methacrylic acid, and their esters.

[0012] U.S. Patent No. 6,207,859 discloses a method for the storage and transportation of α,β-unsaturated carboxylic acids. The α,β-unsaturated carboxylic acids are stabilized against unwanted free radical polymerization using phenols and at least divalent metal cations. This at least divalent metal cation is removed again after storage and transportation.

Prior Art Documents

Patent Documents

[0013]

Patent Document 1

Patent Document 2

Patent Document 3

Non-Patent Documents

[0014]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0015] An object of the present invention was to provide a method for storing and / or transporting ethylenically unsaturated carboxylic acids. The polymerization inhibitor surely and sufficiently stabilizes the ethylenically unsaturated carboxylic acid against unwanted free radical polymerization. However, in the desired free radical polymerization, it is not necessary to separate the polymerization inhibitor from the mixture before polymerization. Therefore, the polymerization inhibitor does not act as a polymerization chain transfer agent and / or a polymerization inhibitor in the desired free radical polymerization. Furthermore, the polymerization inhibitor should not cause unwanted discoloration during polymerization.

Means for Solving the Problems

[0016] This object is achieved by a method for storing and / or transporting an ethylenically unsaturated carboxylic acid, wherein the purity of the ethylenically unsaturated carboxylic acid is at least 90% by mass, the mass of the ethylenically unsaturated carboxylic acid to be stored and / or transported is at least 100 kg, the temperature during storage and / or transportation of the ethylenically unsaturated carboxylic acid is less than 50°C, and the ethylenically unsaturated carboxylic acid contains 0.000002% to 0.00005% by mass (20 to 500 ppb) of manganese (II) ions based on the total amount of the ethylenically unsaturated carboxylic acid.

Modes for Carrying Out the Invention

[0017] The purity of the ethylenically unsaturated carboxylic acid is preferably at least 95% by mass, more preferably at least 98% by mass, and most preferably at least 99% by mass.

[0018] The mass of the ethylenically unsaturated carboxylic acid 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 carboxylic acid to be stored and / or transported is typically less than 10000000 kg.

[0019] The temperature during storage and / or transportation of the ethylenically unsaturated carboxylic acid is preferably 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 must be at least 15 °C.

[0020] The ethylenically unsaturated carboxylic acid preferably contains less than 0.01% by mass (100 ppm), preferably less than 0.001% by mass (10 ppm), more preferably less than 0.0002% by mass (2 ppm), and most preferably less than 0.0001% by mass (1 ppm) of phenol, in each case based on the total amount of the ethylenically unsaturated carboxylic acid.

[0021] The ethylenically unsaturated carboxylic acid preferably contains essentially no phenol and / or essentially no phenylenediamine.

[0022] The ethylenically unsaturated carboxylic acid preferably contains from 0.000002% to 0.00005% by mass (20 to 500 ppb), preferably from 0.000005% to 0.000045% by mass (50 to 450 ppb), more preferably from 0.00001% to 0.00004% by mass (100 to 400 ppb), and most preferably from 0.000015% to 0.000035% by mass (150 to 350 ppb) of manganese(II) ions, in each case based on the total amount of the ethylenically unsaturated carboxylic acid.

[0023] The ethylenically unsaturated carboxylic acid is preferably a mono-, di-, or triethylenically unsaturated C3 - C8 carboxylic acid.

[0024] Acrylic acid, methacrylic acid, dimethacrylic acid, ethacrylic acid, citraconic acid, methylenemalonic acid, crotonic acid, fumaric acid, mesaconic acid, itaconic acid, and maleic acid, or any desired mixture of two or more of the above ethylenically unsaturated carboxylic acids are particularly preferred.

[0025] Acrylic acid and methacrylic acid are most particularly preferred.

[0026] The ethylenically unsaturated carboxylic acids are typically stored and / or transported in a stainless steel container. Suitable stainless steel contains 16.5% to 19.5% by mass of chromium and 8.0% to 13.5% by mass of nickel.

[0027] The ethylenically unsaturated carboxylic acids are typically stored and / or transported in an oxygen-containing atmosphere.

[0028] The ethylenically unsaturated carboxylic acids are preferably stored in a container in 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 pump recirculation of the entire tank contents. This relatively low oxygen content prevents the formation of a flammable gas mixture in the container. Recirculation replenishes the consumed dissolved oxygen in the liquid ethylenically unsaturated carboxylic acid.

[0029] The present invention further provides a method of free radical polymerization in which at least one of the above ethylenically unsaturated carboxylic acids is polymerized by a polymerization initiator, and the use of one of the above ethylenically unsaturated carboxylic acids for free radical polymerization by a polymerization initiator.

[0030] By the free radical polymerization of the present invention, for example, water-soluble and water-swellable polyacrylic acid and its sodium salt can be obtained.

[0031] Free radical polymerization itself is common general knowledge and is typically carried out in solution. Suitable polymerization initiators are all carboxylic acids that can decompose into free radicals under the selected reaction conditions, such as thermal initiators, redox initiators, and photoinitiators. Suitable thermal initiators are peroxomonopersulfates and disulfates, as well as peroxomonophosphates 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.

Example

[0032] <Test for polymerization inhibition> The ethylenically unsaturated carboxylic acid used was distilled twice to remove the hydroquinone monomethyl ether (MEHQ) polymerization inhibitor. A specified amount of the designated polymerization inhibitor was added to the obtained ethylenically unsaturated carboxylic acid in each case. MEHQ and manganese(II) acetate were used.

[0033] 0.5 ml of each mixture was transferred to a 1.8 ml ampoule and stored at the specified temperature in an air-circulating oven.

[0034] In each of a series of tests, in each case three ampoules were filled with each mixture and tested, and the average time taken for complete polymerization was measured by visual inspection.

[0035]

Table 1

[0036] Manganese(II) ions have an effect comparable to that of MEHQ even at a concentration of one thousandth.

[0037] <Polymerization test> 450 g of water was initially charged into the reaction vessel under a nitrogen atmosphere. The initially charged reaction mixture was heated to 95 °C with stirring. Once the temperature reached 95 °C, while maintaining the temperature, three streams were metered in with stirring. Stream 1: 500 g of acrylic acid metered in over 5 hours Stream 2: A 35 g solution of 15 g of sodium hypophosphite in deionized water metered in over 4.75 hours Stream 3: A 66.4 g solution of 5 g of sodium peroxodisulfate in deionized water metered in over 5.25 hours

[0038] After adding these three streams, the reaction mixture was stirred at 95 °C for an additional 1 hour. The reaction mixture was then cooled to room temperature and 80 g of water was added.

[0039] The acrylic acid used in Stream 1 was stabilized with MEHQ or manganese(II) acetate.

[0040] The resulting polymer was analyzed by GPC (calibration with Na-PAA standard, eluent: 0.01 mol / l phosphate buffer in distilled water containing 0.01 M NaN3, pH = 7.4).

[0041]

Table 2

[0042] Manganese(II) ions at the tested concentrations result in polyacrylic acid having a molar mass comparable to that obtained using standard concentrations of MEHQ.

[0043] <Polymerization of sodium acrylate or sodium methacrylate> Under a nitrogen atmosphere, 52 g of deionized water and 60 g of an aqueous solution of sodium acrylate or an aqueous solution of sodium methacrylate (in both cases the concentration is 37.2% by mass and is stabilized with 0.01% by mass of MeHQ or 0.0000057% by mass of manganese(II) acetate) were first charged into the reaction vessel. Then, 0.4 g of sodium peroxydisulfate dissolved in 10 g of deionized water was added, and the mixture was heated to 80 °C while stirring. The reaction mixture was stirred at 80 °C for 4 hours and then cooled to ambient temperature.

[0044] In all tests using MEHQ, the solution changed color during heating (at about 60 °C).

Claims

**Claim 1** A method for storing and / or transporting an ethylenically unsaturated carboxylic acid, wherein the purity of the ethylenically unsaturated carboxylic acid is at least 90% by mass, the mass of the ethylenically unsaturated carboxylic acid to be stored and / or transported is at least 100 kg, the temperature during the storage and / or transportation of the ethylenically unsaturated carboxylic acid is less than 50 °C, and the ethylenically unsaturated carboxylic acid contains 0.000002% to 0.00005% by mass of manganese(II) ions based on the total amount of the ethylenically unsaturated carboxylic acid. **Claim 2** The method according to claim 1, wherein the ethylenically unsaturated carboxylic acid contains less than 0.0001% by mass of phenol based on the total amount of the ethylenically unsaturated carboxylic acid. **Claim 3** The method according to claim 1, wherein the ethylenically unsaturated carboxylic acid is essentially free of phenol and / or essentially free of phenylenediamine. **Claim 4** The method according to any one of claims 1 to 3, wherein the ethylenically unsaturated carboxylic acid contains 0.000005% to 0.000045% by mass of manganese(II) ions based on the total amount of the ethylenically unsaturated carboxylic acid. **Claim 5** The method according to any one of claims 1 to 3, wherein the ethylenically unsaturated carboxylic acid contains 0.00001% to 0.00004% by mass of manganese(II) ions based on the total amount of the ethylenically unsaturated carboxylic acid. **Claim 6** The method according to any one of claims 1 to 3, wherein the ethylenically unsaturated carboxylic acid contains 0.000015% to 0.000035% by mass of manganese(II) ions based on the total amount of the ethylenically unsaturated carboxylic acid. **Claim 7** The method according to any one of claims 1 to 6, wherein the storage and / or transportation of the ethylenically unsaturated carboxylic acid is carried out over a period of at least 10 hours. **Claim 8** The method according to any one of claims 1 to 7, wherein the ethylenically unsaturated carboxylic acid is acrylic acid and / or methacrylic acid. **Claim 9** The method according to any one of claims 1 to 8, wherein the ethylenically unsaturated carboxylic acid is stored and / or transported in a steel container, and the steel contains 16.5% to 19.5% by mass of chromium and 8.0% to 13.5% by mass of nickel. **Claim 10** The method according to any one of claims 1 to 9, wherein the ethylenically unsaturated carboxylic acid is stored and / or transported in an oxygen-containing atmosphere.

11. The method according to any one of claims 1 to 10, wherein the ethylenically unsaturated carboxylic acid is stored in a container in an oxygen-containing atmosphere having an oxygen content of 5% to 10% by volume, and the ethylenically unsaturated carboxylic acid in the container is periodically recycled.

12. A method of free radical polymerization, wherein at least one ethylenically unsaturated carboxylic acid is polymerized by a polymerization initiator, and the ethylenically unsaturated carboxylic acid used contains 0.000002% to 0.00005% by mass of manganese (II) ions based on the total amount of the ethylenically unsaturated carboxylic acid.

13. The method according to claim 12, wherein the ethylenically unsaturated carboxylic acid contains 0.000015% to 0.000035% by mass of manganese (II) ions based on the total amount of the ethylenically unsaturated carboxylic acid.

14. Use of an ethylenically unsaturated carboxylic acid for free radical polymerization by a polymerization initiator, wherein the ethylenically unsaturated carboxylic acid used contains 0.000002% to 0.00005% by mass of manganese (II) ions based on the total amount of the ethylenically unsaturated carboxylic acid.

15. The use according to claim 14, wherein the ethylenically unsaturated carboxylic acid contains 0.000015% to 0.000035% by mass of manganese (II) ions based on the total amount of the ethylenically unsaturated carboxylic acid.

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