Storage and / or transportation of vinyl unsaturated carboxylic acids

Abstract

The invention relates to a method for the storage and / or transportation of vinyl unsaturated carboxylic acids, in which the vinyl unsaturated carboxylic acids are protected by divalent manganese ions in order to avoid undesirable free radical polymerization.

Description

[0001] The present invention relates to a method for storing and / or transporting ethylenically unsaturated carboxylic acids, wherein the ethylenically unsaturated carboxylic acids are protected by divalent manganese ions to avoid undesired free radical polymerization.

[0002] Compounds containing one or more ethylenically unsaturated groups have a pronounced tendency to free radical polymerization. Therefore, in the following text, such compounds are also referred to as polymerizable compounds. Due to their tendency to free radical polymerization, these compounds can be used as monomers in the production of polymers. However, the pronounced tendency of these compounds to free radical polymerization is also disadvantageous, because during storage and transportation, as well as during chemical and / or physical processing (such as distillation or rectification), in particular under the influence of energy (such as heat and / or light), undesirable, spontaneous free radical polymerization may occur. This uncontrolled polymerization may lead to the gradual formation of polymer deposits on, for example, heated surfaces, which requires the removal of the polymer deposits, and thus often leads to shortened operating times. This uncontrolled polymerization may even produce explosions.

[0003] It is therefore common practice to add a compound to ethylenically unsaturated compounds having a tendency to free-radical polymerization, or to mixtures containing such compounds, in order to avoid or at least slow down the undesired spontaneous free-radical polymerization during storage and transport and during chemical and / or physical processing. Such substances are known as polymerization inhibitors.

[0004] Polymerization inhibitors can be used as individual compounds or as mixtures of compounds. Depending on the field of application of the polymerization inhibitors, certain requirements are imposed on them. In order for the polymerization inhibitors to be suitable as stabilizers for the transport and / or storage of ethylenically unsaturated compounds, it must be possible to adjust the efficiency of the polymerization inhibitor, i.e. the degree of polymerization inhibition. Under the storage and / or transport conditions of the ethylenically unsaturated compounds, the polymerization inhibitor should be able to sufficiently avoid or slow down undesirable, spontaneous free-radical polymerization; and under appropriate polymerization conditions, the ethylenically unsaturated compounds should be able to undergo the desired free-radical polymerization without the need for previous separation of the polymerization inhibitor used during storage and / or transportation. If the stabilizer used during storage and / or transportation is not separated off when the polymerization is to be carried out, it is important that the stabilizer does not have an adverse effect on the polymerization when the polymerization is to be carried out (e.g. inadvertently play a regulating role).

[0005] Acrylic acid is undoubtedly one of the most important ethylenically unsaturated compounds in terms of global production. According to the standard, acrylic acid is stabilized by using 0.018wt% to 0.022wt% (weight percentage) of p-hydroxyanisole (MEHQ) based on the amount of acrylic acid used during storage and / or transportation to avoid undesirable spontaneous free radical polymerization. In order to make acrylic acid fully stabilized with the help of MEHQ to avoid undesirable spontaneous free radical polymerization, a sufficient amount of oxygen must be dissolved in the acrylic acid. Generally, when acrylic acid is stored and / or transported in an atmosphere with an oxygen content of 5vol% to 21vol%, sufficient oxygen will be dissolved in the acrylic acid. When acrylic acid is about to polymerize, the oxygen content dissolved in the acrylic acid is reduced, thereby reducing the polymerization inhibition efficiency of MEHQ, so that acrylic acid can be polymerized in the presence of MEHQ.

[0006] In addition to being used as a polymerization inhibitor during storage and / or transportation of acrylic acid, MEHQ can also be used as a polymerization inhibitor during storage and / or transportation of methacrylic acid, acrylic acid esters and / or methacrylic acid esters, or mixtures containing one or more of the foregoing compounds.

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

[0008] Ethylenically unsaturated compounds are stored in matching fixed containers, such as storage tanks (for examples, see "Acrylic Acid, Summary of Safety and Handling Methods", 4th edition, 2013, 7 Bulk Storage Facilities and Accessories). When storing, ethylenically unsaturated compounds are preferably stored in their respective containers for at least 1 hour, preferably for at least 10 hours, and preferably for at least 100 hours. Although theoretically the storage time is unlimited under appropriate conditions, for economic reasons, the storage time is usually shortened as much as possible. The storage time of ethylenically unsaturated compounds in their respective containers should not exceed 180 days, preferably not exceed 90 days, and preferably not exceed 30 days. The best range interval is any combination of the above lower limit and upper limit values.

[0009] Ethylenically unsaturated compounds are usually transported in suitable transportable containers such as tanks or drums by ship, freight train and / or truck (for example, see Acrylic Acid, Summary of Safety and Handling Methods, 4th edition, 2013, 9 Safe Transport of Acrylic Acid). Of course, the transportable containers can also be fixedly installed on the corresponding means of transportation, such as tank ships or rail tank cars. Of course, these containers can also be stored for a period of time at a specific location before being transported to another location. The transportation of ethylenically unsaturated compounds can also be carried out in pipelines or hoses, for example, when the ethylenically unsaturated compounds are purified in a storage tank and then loaded from the storage tank into a transport container and / or from one transport container to another. During transportation, the ethylenically unsaturated compounds are preferably stored in the corresponding containers for at least 1 hour, preferably for at least 10 hours, and most preferably for at least 100 hours. Although theoretically the storage time is unlimited under appropriate conditions, for economic and safety reasons, the storage time is usually shortened as much as possible. During transportation, the storage time of the ethylenically unsaturated compounds in their respective containers should preferably not exceed 180 days, more preferably not exceed 90 days, and most preferably not exceed 30 days. The best range interval is any combination of the above lower limit and upper limit.

[0010] EP 0 398 633 A1 discloses a process for inhibiting the polymerization of acidic monomers using a manganese source and a phenylenediamine containing NH groups.

[0011] JP 5140027 discloses the use of a mixture of a) phenols (such as phenol, hydroquinone, p-methoxyphenol, cresol and catechol), b) manganese salts and c) 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-butyl-catechol, 2,4-dimethyl-6-tert-butylphenol, 2-tert-butylhydroquinone and 2-tert-butyl-4-methoxyphenol) for stabilizing acrylic acid, methacrylic acid and their esters.

[0012] US 6,207,859 discloses a method for storing and transporting α, β unsaturated carboxylic acids. Phenol and at least divalent metal cations are used to stabilize the α, β unsaturated carboxylic acids to avoid unfavorable free radical polymerization. The at least divalent metal cations are removed again after storage and transport.

[0013] The object of the present invention is to provide a method for storing and / or transporting ethylenically unsaturated carboxylic acids. The polymerization inhibitor should ensure that the ethylenically unsaturated carboxylic acids have sufficient stability to avoid unnecessary free radical polymerization. However, in the case where free radical polymerization is desired, the polymerization inhibitor should not need to be separated from the mixture before polymerization. Therefore, when free radical polymerization is to be carried out, the polymerization inhibitor should not play the role of polymerization regulator and / or polymerization inhibitor. In addition, the polymerization inhibitor should not cause undesirable discoloration during the polymerization process.

[0014] The object is solved by a method for storing and / or transporting ethylenically unsaturated carboxylic acids, wherein the purity of the ethylenically unsaturated carboxylic acids is at least 90 wt %, the mass of the ethylenically unsaturated carboxylic acids to be stored and / or transported is at least 100 kg, and the temperature of the ethylenically unsaturated carboxylic acids during storage and / or transportation is required to be lower than 50° C., characterized in that the ethylenically unsaturated carboxylic acids contain 0.000002 wt % to 0.00005 wt % (20 ppb to 500 ppb) of divalent manganese ions, calculated based on the total amount of the ethylenically unsaturated carboxylic acids.

[0015] The purity of the ethylenically unsaturated carboxylic acid is preferably at least 95 wt%, more preferably at least 98 wt%, and most preferably at least 99 wt%.

[0016] 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, most preferably at least 1000 kg. The mass of the ethylenically unsaturated carboxylic acid to be stored and / or transported is usually less than 10,000,000 kg.

[0017] The temperature of the ethylenically unsaturated carboxylic acid during storage and / or transportation is preferably below 45°C, more preferably below 40°C, most preferably below 35°C. In the case of acrylic acid, the temperature during storage and / or transportation should be at least 15°C.

[0018] Calculated based on the total amount of the ethylenically unsaturated carboxylic acid, the phenol content of the ethylenically unsaturated carboxylic acid is preferably less than 0.01wt% (100ppm), more preferably less than 0.001wt% (10ppm), further preferably less than 0.0002wt% (2ppm), particularly preferably less than 0.0001wt% (1ppm).

[0019] Preferably, the ethylenically unsaturated carboxylic acid is substantially free of phenol and / or substantially free of phenylenediamine.

[0020] The ethylenically unsaturated carboxylic acid advantageously contains 0.000002 wt-% to 0.00005 wt-% (20 ppb to 500 ppb), more preferably 0.000005 wt-% to 0.000045 wt-% (50 ppb to 450 ppb), further preferably 0.00001 wt-% to 0.00004 wt-% (100 ppb to 400 ppb), particularly preferably 0.000015 wt-% to 0.000035 wt-% (150 ppb to 350 ppb), based on the total amount of the ethylenically unsaturated carboxylic acid.

[0021] The ethylenically unsaturated carboxylic acid is preferably a mono-, di- or tri-ethylenically unsaturated C3 to C8 carboxylic acid.

[0022] Particularly preferred are acrylic acid, methacrylic acid, dimethacrylic acid, ethacrylic acid, citraconic acid, methylmalonic acid, crotonic acid, fumaric acid, mesaconic acid, itaconic acid and maleic acid, or any mixtures of two or more of the abovementioned vinyl unsaturated carboxylic acids.

[0023] Acrylic acid and methacrylic acid are particularly preferred.

[0024] Ethylene unsaturated carboxylic acids are usually stored and / or transported in stainless steel containers. Suitable stainless steel should contain 16.5 wt% to 19.5 wt% chromium and 8.0 wt% to 13.5 wt% nickel.

[0025] The ethylenically unsaturated carboxylic acid is usually stored and / or transported in an oxygen-containing environment.

[0026] The ethylenically unsaturated carboxylic acid is preferably stored in a container in an oxygen-containing environment having an oxygen content of 5 vol% to 10 vol% (volume percentage), and the mixture in the container is circulated regularly, such as by using a pump to thoroughly recirculate the tank contents at least once a week. The relatively low oxygen content can avoid the formation of a flammable mixture in the container. By circulating, the dissolved oxygen consumed in the liquid ethylenically unsaturated carboxylic acid is replaced.

[0027] A further object of the present invention is a method for free radical polymerization, in which at least one of the above-mentioned ethylenically unsaturated carboxylic acids is polymerized with the aid of a polymerization initiator; and the use of one of the above-mentioned ethylenically unsaturated carboxylic acids for free radical polymerization with the aid of a polymerization initiator.

[0028] For example, according to the present invention, water-soluble and water-swellable polyacrylic acid and its sodium salt can be obtained by free radical polymerization.

[0029] Free radical polymerizations are known per se and are usually carried out in solution. All carboxylic acids which decompose into free radicals under the chosen reaction conditions are suitable as polymerization initiators, for example thermal initiators, redox initiators and photoinitiators. Suitable thermal initiators are peroxymonosulfates and peroxydisulfates, and peroxymonophosphates and peroxydiphosphates. 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

[0030] Polymerization inhibition experiment

[0031] The ethylenically unsaturated carboxylic acid used was distilled twice to remove the polymerization inhibitor p-hydroxyanisole (MEHQ). The obtained ethylenically unsaturated carboxylic acid was mixed with a specified amount of polymerization inhibitor. MEHQ and manganese diacetate were used.

[0032] 0.5 ml of each mixture was filled into 1.8 ml ampoules and stored in an air-circulating drying cabinet at a preset temperature.

[0033] In each test series, three ampoules of each mixture were tested and the average value of the time required for complete polymerization was recorded visually.

[0034] Table 1: Mixtures with acrylic acid

[0035] Polymerization inhibitors quantity temperature Aggregation time none*) 80℃ 3.6 hours MEHQ*) 0.002wt% 80℃ 11.1 hours MEHQ*) 0.004wt% 80℃ 14.6 hours MEHQ*) 0.006wt% 80℃ 21.6 hours <![CDATA[Mn 2+ ]]> 0.000002wt% 80℃ 12.0 hours <![CDATA[Mn 2+ ]]> 0.000005wt% 80℃ 19.8 hours <![CDATA[Mn 2+ ]]> 0.00001wt% 80℃ 37.9 hours <![CDATA[Mn 2+ ]]> 0.00002wt% 80℃ >46 hours

[0036] *)contrast

[0037] At concentrations a thousand times lower, divalent manganese ions already have an effect comparable to that of MEHQ.

[0038] Polymerization reaction experiment

[0039] Under nitrogen atmosphere, 450 g of water was placed in the reaction vessel. The reaction mixture was heated to 95° C. while stirring. When the temperature reached 95° C., three streams were quantitatively added while continuing to stir and maintain the temperature.

[0040] Liquid flow 1: quantitative addition of 500g acrylic acid over 5 hours

[0041] Stream 2: 4.75 hours of quantitative addition, 15g sodium hypophosphite added to 35g deionized water

[0042] Stream 3: 5.25 hours of quantitative addition, 5 g of sodium persulfate was added to 66.4 g of deionized water

[0043] After the three streams had been added, the reaction mixture was stirred for a further hour at 95° C. The reaction mixture was then cooled to room temperature and 80 g of water were added.

[0044] The acrylic acid injected into stream 1 is stabilized with MEHQ or manganese diacetate.

[0045] The polymer obtained was analyzed by GPC technique (gel permeation chromatography) (calibration with Na-PAA standards, eluent 0.01 mol / l phosphate buffer, pH=7.4 in distilled water, with addition of 0.01 M sodium azide).

[0046] Table 2: Polymerization of acrylic acid

[0047] Polymerization inhibitors quantity Average value Mn Average weight Mw Dispersion Mw / Mn MEHQ*) 0.020wt% 3240g / mol 11100g / mol 3.4 <![CDATA[Mn 2+ ]]> 0.0000001wt% 3550g / mol 11200g / mol 3.2 <![CDATA[Mn 2+ ]]> 0.000002wt% 3620g / mol 11600g / mol 3.2 <![CDATA[Mn 2+ ]]> 0.000005wt% 3170g / mol 10500g / mol 3.3 <![CDATA[Mn 2+ ]]> 0.00001wt% 3450g / mol 12100g / mol 3.5 <![CDATA[Mn 2+ ]]> 0.00002wt% 3510g / mol 10600g / mol 3.0 <![CDATA[Mn 2+ ]]> 0.00004wt% 3510g / mol 12100g / mol 3.4

[0048] *)contrast

[0049] The molecular weight of polyacrylic acid generated by divalent manganese ions is comparable to that when using standard concentration of MEHQ.

[0050] Polymerization of sodium acrylate or sodium methacrylate

[0051] In a nitrogen atmosphere, 52 g of deionized water and 60 g of an aqueous sodium acrylate solution or an aqueous sodium methacrylate solution (each in a weight ratio of 37.2 wt%, stabilized by 0.01 wt% of MEHQ or 0.0000057 wt% of manganese diacetate) were placed in a reaction vessel. Subsequently, 0.4 g of sodium persulfate dissolved in 10 g of deionized water was added and heated to 80° C. with stirring. The reaction mixture was stirred at 80° C. for 4 hours and then cooled to ambient temperature.

[0052] In all experiments using MEHQ, the solution changed color during heating (about 60 °C).

Claims

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 wt %, the mass of the ethylenically unsaturated carboxylic acid to be stored and / or transported is at least 100 kg, and the temperature of the ethylenically unsaturated carboxylic acid during storage and / or transportation is required to be lower than 50° C., characterized in that, based on the total amount of the ethylenically unsaturated carboxylic acid, the ethylenically unsaturated carboxylic acid contains 0.000002 wt % to 0.00005 wt % of divalent manganese ions.

2. The method according to claim 1, characterized in that The phenol content of the ethylenically unsaturated carboxylic acid is less than 0.0001 wt % calculated based on the total amount of the ethylenically unsaturated carboxylic acid.

3. The method according to claim 1, characterized in that: The ethylenically unsaturated carboxylic acid is substantially free of phenol and / or substantially free of phenylenediamine.

4. The method according to any one of claims 1 to 3, characterized in that The ethylenically unsaturated carboxylic acid contains 0.000005 wt % to 0.000045 wt % of divalent manganese ions, calculated based on the total amount of the ethylenically unsaturated carboxylic acid.

5. The method according to any one of claims 1 to 3, characterized in that The ethylenically unsaturated carboxylic acid contains 0.00001 wt % to 0.00004 wt % of divalent manganese ions, based on the total amount of the ethylenically unsaturated carboxylic acid.

6. The method according to any one of claims 1 to 3, characterized in that The ethylenically unsaturated carboxylic acid contains 0.000015 wt % to 0.000035 wt % of divalent manganese ions, based on the total amount of the ethylenically unsaturated carboxylic acid.

7. The method according to any one of claims 1 to 6, characterized in that The storage and / or transportation of the ethylenically unsaturated carboxylic acid lasts for at least 10 hours.

8. The method according to any one of claims 1 to 7, characterized in that The vinyl unsaturated carboxylic acid is acrylic acid and / or methacrylic acid.

9. The method according to any one of claims 1 to 8, characterized in that The ethylenically unsaturated carboxylic acid is stored and / or transported in a stainless steel container, and the steel contains 16.5 wt % to 19.5 wt% chromium and 8.0 wt% to 13.5 wt% nickel.

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 environment.

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 environment having an oxygen content of 5 vol% to 10 vol%, and the ethylenically unsaturated carboxylic acid in the container is periodically circulated.

12. A free radical polymerization method, wherein: At least one ethylenically unsaturated carboxylic acid is polymerized with the aid of a polymerization initiator, characterized in that the ethylenically unsaturated carboxylic acid used contains 0.000002 wt % to 0.00005 wt % of divalent manganese ions, calculated on the total amount of the ethylenically unsaturated carboxylic acid.

13. The method according to claim 12, characterized in that The ethylenically unsaturated carboxylic acid contains 0.000015 wt % to 0.000035 wt % of divalent manganese ions, based on the total amount of the ethylenically unsaturated carboxylic acid.

14. Use of an ethylenically unsaturated carboxylic acid for free radical polymerization with the aid of a polymerization initiator, characterized in that: The ethylenically unsaturated carboxylic acid used contains 0.000002 wt % to 0.00005 wt % of divalent manganese ions, calculated based on the total amount of the ethylenically unsaturated carboxylic acid.

15. The method according to claim 14, characterized in that The ethylenically unsaturated carboxylic acid contains 0.000015 wt % to 0.000035 wt % of divalent manganese ions, based on the total amount of the ethylenically unsaturated carboxylic acid.