Container and method for storing saturated aliphatic C6-C12 carboxylic acids

Abstract

Saturated aliphatic C 6-12 A container and method for decomposition-stable storage and transport of a liquid containing a carboxylic acid, wherein the liquid is covered with an oxygen-free or at least significantly oxygen-depleted inert gas phase atmosphere.

Description

Technical Field

[0001] The present invention relates to a container with an internal volume of 0.05 to 10,000 m 6-12 for storing and transporting a liquid containing a saturated aliphatic C 3 carboxylic acid or a mixture thereof, wherein the liquid has a saturated aliphatic C 6-12 carboxylic acid content of 99 to 100 wt.-% (weight %), while the liquid occupies 1 to 99% of the internal volume of the container and a gas phase is present above the liquid.

[0002] Furthermore, the present invention also relates to a method for storing and transporting such a liquid in such a container, wherein the liquid is filled into the container to occupy 1 to 99% of the internal volume of the container, is covered by a gas phase, and is held therein for more than 1 hour.

Background Art

[0003] Saturated aliphatic carboxylic acids are globally important intermediates with a wide range of applications. They can be used as such, but are typically further processed into metal salts, esters, amides, anhydrides, acid chlorides, and other derivatives. Generally, they are important intermediates for the production of a wide range of compounds, such as metal salts and metal soaps, fragrances, flavorings, pharmaceutical and agrochemical ingredients, cosmetic ingredients, plasticizers, paints, coating additives, coolants, lubricants, or catalysts for polymer processing. C 6~12 A very important representative of saturated aliphatic carboxylic acids is 2-ethylhexanoic acid. This is mainly used in the form of its derivatives, such as its metal salts or esters, for its use as a thickener and dryer for alkyd resins and paints, as a catalyst in the production of polyurethane foams, as a stabilizer and / or plasticizer for PVC, or as a corrosion inhibitor and anti-wear agent for lubricants. C 6~12 Esters of saturated aliphatic carboxylic acids, such as n-heptanoic acid, n-octanoic acid, 2-ethylhexanoic acid, n-nonanoic acid, or 3,5,5-trimethylhexanoic acid, are also often used as lubricants.

[0004] Saturated aliphatic C 6~12 An important method widely used for the production of carboxylic acids is the oxidation of the corresponding aldehyde with molecular oxygen (oxygen molecules) in the liquid phase, with or without a catalyst or any additives. This general synthetic route is described, for example, in "Carboxylic acids, aliphatic" in J. Kubitschke et al., Ullmann's Encyclopedia of Industrial Chemistry, 2014, Wiley-VCH Verlag GmbH & Co. KGaA, DOI: 10.1002 / 14356007.a05_235.pub2, Chapter 4.2.1 "Aldehyde oxidation" and Chapter 7 "Commercially important aliphatic carboxylic acids". The resulting C 6-12 Carboxylic acids are usually purified by distillation to obtain C in preferably pure form 6-12 Carboxylic acids. However, before the C 6-12 Carboxylic acids are further processed into their derivatives or used otherwise, the C 6-12 Carboxylic acids are usually stored in fixed containers of different sizes or in mobile containers and, if necessary, transported therein to other locations for their further use. Since most aliphatic carboxylic acids are flammable and corrosive, J. Kubitschke et al. teach storing and transporting them in corrosion-resistant containers in Chapter 6 "Storage and transportation" of the above-mentioned paper. This implies that they can be easily handled in stainless steel containers or acid-resistant plastic containers without any further specific measures and without paying specific attention to the above-mentioned flammability.

[0005] J. Kubitschke et al. have described the flammability of aliphatic carboxylic acids, but based on the data available in the European Chemicals Agency (ECHA) database, a publicly available electronic database of chemicals provided by the European Union, various saturated aliphatic C6-12 An overview of carboxylic acids reveals typical flash points above 100 °C at atmospheric pressure. For example, for C6, hexanoic acid has a flash point of 104 °C, for C7, heptanoic acid has a flash point of 117 °C, for C8, octanoic acid has a flash point of 132 °C, 2-ethylhexanoic acid has a flash point of 118 °C, for C9, nonanoic acid has a flash point of 137 °C, 3,5,5-trimethylhexanoic acid has a flash point of 117 °C, C 10 for C10, decanoic acid has a flash point of 147 °C, and C 12 for C11, 2-butyl octanoic acid has a flash point of 154 °C are as follows.

[0006] Flash points above 100 °C are relatively high, but are not inherently released from explosion prevention measures, such as keeping aliphatic carboxylic acids under an inert gas atmosphere. N. Allen, in his paper "Hazards of high flash point liquids in relation to the ATEX 137 directive" in Hazards XXI, Symposium Series No. 155, IChemE 2009, pages 271 - 276, states that liquids with flash points below 40 °C usually require explosion prevention measures, but liquids with flash points above 40 °C may also require such measures if the liquid is intentionally or unintentionally heated above its flash point, forming vapors and aerosols, chemical reactions or decompositions occur, or the liquid is contaminated or mixed with low flash point components. The flash points of saturated aliphatic C 6-12 carboxylic acids are well above any temperature that can reasonably be expected during storage or transportation, and since none of the other exceptions mentioned above apply either, N. Allen 6-12 has confirmed that the storage and transportation of saturated aliphatic C

[0007] In summary, the paper by J. Kubitschke et al. and N. Allen, saturated aliphatic C 6-12 the absence of an oxygen-sensitive C=C double bond in carboxylic acids, saturated aliphatic C 6-12 the fact that saturated aliphatic carboxylic acids are neither explosive nor highly flammable, saturated aliphatic C 6-12 the finding that saturated aliphatic carboxylic acids are usually prepared by the oxidation of each aldehyde with molecular oxygen, even when using excess molecular oxygen, and the widespread recognition in the literature that carboxylic acids are quite resistant to oxidation show that saturated aliphatic C 6-12 carboxylic acids can be easily handled, stored, and transported in the atmosphere, which is clearly shown to those skilled in the art.

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0008] EP application number 20191855.4 deals with the preparation of saturated aliphatic C 6-12 carboxylic acids with color stability, but does not describe how to store or transport them.

[0009] However, according to the present invention, it has been recognized that saturated aliphatic C 6-12 carboxylic acids tend to decompose over time even when stored or transported under the conditions described or shown in the prior art, even when they are prepared under the specific color stability promoting method characteristics described in EP20191855.4.

[0010] Therefore, an object of the present invention is to prevent or at least significantly reduce the discoloration of products derived from saturated aliphatic C 6-12 carboxylic acids even when stored or transported for a long time, for example, for several months, and / or saturated aliphatic C 6-12 carboxylic acids, and / or saturated aliphatic C 6-12A method in which carboxylic acids do not or only slightly impair their color stability under heat stress, to improve the storage and transportation of saturated aliphatic C 6-12 carboxylic acids. The improved storage and transportation should preferably be easily carried out in readily available standard containers, and the saturated aliphatic C 6-12 carboxylic acids should not be contaminated with harmful compounds. This objective involves finding methods and containers that meet the requirements.

Means for Solving the Problem

[0011] Surprisingly, the inventors have found that a container with an internal volume of 0.05 to 10,000 m 3 which contains a) a liquid containing a saturated aliphatic C 6-12 carboxylic acid or a mixture thereof, wherein the liquid has a saturated aliphatic C 6-12 carboxylic acid content of 99 to 100 wt.-% and occupies 1 to 99% of the internal volume of the container, and b) a gas phase above the liquid wherein c) the container is a metal container and d) the gas phase above the liquid is an inert gas phase containing nitrogen, helium, neon, argon, krypton, xenon, hydrogen, carbon dioxide, carbon monoxide or a mixture thereof having a molecular oxygen content of 0 to 100 vol.-ppm (volume ppm). The inventors have found such a container.

[0012] In EP20191855.4, it has been found that even the presence of a small amount of molecular oxygen immediately causes saturated aliphatic C 6-12 carboxylic acids to form a small amount of highly oxidizable components under distillation conditions. Through a more detailed study of the nature of these highly oxidizable components, it has been found that they are mainly of the general formula (1)

[0013]

Chemical Formula

[0014] Components with high oxidation potential are usually characterized as so-called "active oxygen", which is a quantitative measure of the amount of reactive oxygen. The term "active oxygen" is already known and used in the current state of the art, for example, described in "Peroxy Compounds, Organic" in A. Uhl et al., Ullmann's Encyclopedia of Industrial Chemistry, 2017, Wiley-VCH Verlag GmbH & Co. KGaA, DOI: 10.1002 / 14356007.a19_199.pub2, Chapter 10 "Analytical Determination". The amount of active oxygen in a sample is generally determined by adding a certain amount of an easily oxidizable compound, such as an iodide (1-) or an iron (II) salt, to a certain amount of the sample. The reactive oxygen present oxidizes the oxidizable compound, and the amount of the oxidized oxidizable compound is then determined by titration.

[0015] To be more accurate regarding the information value of the amount of reactive oxygen species, the measurement method will be described in more detail. According to the present invention, the determination of reactive oxygen species is preferably carried out by the oxidation of iodide (I-). This analytical method is called iodometric titration and is well known to those skilled in the art. However, it will be outlined below.

[0016] In iodometric titration, an aqueous potassium iodide solution in a certain amount of acetic acid is added to a certain amount of sample at room temperature and stirred to oxidize iodide (I-) to elemental iodine. The amount of potassium iodide added is related to the predicted amount of reactive oxygen species and can be estimated by preliminary measurement. For iodometric titration measurement, the amount of iodide (I-) added must be slightly more than the amount oxidized to elemental iodine. The elemental iodine is then titrated with sodium thiosulfate to determine the amount of elemental iodine formed by the previous oxidation. Starch is typically used as an indicator, which is purple as long as elemental iodine is present and becomes colorless when all the elemental iodine is reduced to iodide. Alternatively, a platinum electrode can also be used. Based on the amount of potassium iodide added and the amount of elemental iodine formed by oxidation, the amount of oxidized iodide (I-) can be calculated. Formal equations

[0017]

Chemical formula

[0018]

Chemical formula

[0019] Assuming that the active oxygen is bonded alone in the carboxylic acid as hydroperoxide, it can be easily converted to an equal content of peroxide compound. The conversion can be carried out by multiplying the measured active oxygen content by the ratio of the molar mass of the hydroperoxy acid to the molar mass of the oxygen atom. For example, in the case of 2-ethylhexanoic acid, the magnification is 176.2 / 16.0 = 11.0125. 6~12 For the sake of completeness, it is also mentioned that the amount of active oxygen in the carboxylic acid-containing sample can basically be determined by physical methods, such as

[0020] C-NMR. 13 However, in the present invention, active oxygen is understood as the mass of oxygen present in the sample that can oxidize iodide (I-) to elemental iodine in an aqueous acetic acid medium at room temperature and atmospheric pressure.

[0021] In EP20191855.4, it was further found that active oxygen compounds such as alkyl hydroperoxides can cause darkening of saturated aliphatic carboxylic acids during storage over time, when exposed to thermal stress and / or in products derived therefrom.

[0022] Regarding the preparation by oxidation of the corresponding aldehyde of saturated aliphatic C 6-12 carboxylic acid, EP20191855.4 teaches that as a countermeasure against such decomposition tendency, before isolating the purified saturated aliphatic C 6-12 carboxylic acid, molecular oxygen is removed from the crude liquid obtained by the oxidation step to a content of 10 wt.-ppm or less. Therefore, such purified saturated aliphatic C 6-12Carboxylic acids have a very low content of molecular oxygen and a very low content of reactive oxygen, and show only a very low tendency to darken when exposed to heat stress (i.e., when heated in the absence of molecular oxygen) and / or in products in which they are normally applied.

[0023] Molecular oxygen and reactive oxygen are two different types of compounds. While reactive oxygen is a type of component with high oxidizing potential, as already mentioned above, molecular oxygen is simply dissolved O2. Molecular oxygen can be easily measured using a molecular oxygen-sensitive device, such as an optical sensor often used in the analysis of water. A specific example is an optical fluorescence sensor. Optical fluorescence sensors are at the state of the art, and those skilled in the art know how to calibrate and use them. Such sensors are very specific to oxygen and very sensitive to oxygen. They can even measure very low concentrations down to 0.01 wt.-ppm. Since such optical fluorescence sensors have a certain degree of heat resistance and pressure resistance, they can also be used for in-line measurement.

[0024] Molecular oxygen and reactive oxygen are not only two different types of compounds but can also be measured separately. A molecular oxygen-sensitive device measures only molecular oxygen and not reactive oxygen, and vice versa, reactive oxygen does not include molecular oxygen. Molecular oxygen reacts very slowly under iodometric titration conditions, and furthermore, since it is excellent practice to perform iodometric titration under an inert gas to minimize any interference from molecular oxygen, only reactive oxygen is measured by iodometric titration. As a beneficial result, reactive oxygen and molecular oxygen can be determined and evaluated separately.

[0025] Saturated aliphatic C 6-12Carboxylic acids are known as stable and insensitive compounds that can be easily handled, especially at atmospheric pressure and ambient (atmospheric) temperature, and are therefore stored and transported under the atmosphere (air). Surprisingly, however, such treatment has been found to cause some decomposition, impair the color stability under heat stress, or cause discoloration of the products derived therefrom. This also applies to the storage and transportation of carboxylic acids having a very low content of only molecular oxygen and active oxygen, such as can be obtained by the method described in EP20191855.4, and very pure saturated aliphatic C 6-12 also applies to the storage and transportation of carboxylic acids.

[0026] Then, according to the present invention, surprisingly, a strict measure to exclude the intrusion of molecular oxygen into a liquid containing saturated aliphatic C 6-12 carboxylic acid is such that the saturated aliphatic C 6-12 carboxylic acid is much more color-stable under heat stress and causes much less discoloration of the products derived therefrom, and it has been found that such decomposition can be avoided or at least significantly reduced. One effective measure of the present invention is the application of an inert gas atmosphere above a liquid containing saturated aliphatic C 6-12 carboxylic acid having at least a very low content of molecular oxygen. Another effective measure of the present invention is to prevent the diffusion of molecular oxygen through the walls of the container used. This can be achieved by using a metal container.

Mode for Carrying Out the Invention

[0027] Therefore, the container of the present invention is a metal container having an internal volume of 0.05 to 10000 m 3 The above-mentioned range of the internal volume relates to a technically useful amount. The container in the sense of the present invention can be any vessel (container), tank or any other storage tank that can store or transport a liquid containing saturated aliphatic C 6-12 carboxylic acid covered with a gas phase on top.

[0028] "Made of metal" means that the wall of the container consists only of metal or at least includes a metallic mantle which may be part of a composite material. The composite material can be, for example, a container having a coated metal, such as a painted, varnished, rubberized, or enamelled metal, a non-metallic liner, such as a metal container having a synthetic material, or a plastic container having a metal liner. The connecting holes are, for example, holes for filling and discharging, as well as service holes for pressure balance and supply of the gas phase. Although not counted as walls, they should of course essentially consist of a material resistant to oxygen diffusion. Depending on the overall mechanical stability of the wall and the intended use, the container can be mechanically supported by a stable frame or cage. Furthermore, the container may also have means for its startup, stacking or fixing.

[0029] When the metal is in contact with a saturated aliphatic C 6-12 In the case of a composite material where the metal is not in contact with a carboxylic acid, a non-corrosive metal can also be used provided that the material in contact with the corrosive liquid is chemically stable against the corrosive liquid and durably protects the non-corrosive metal from any contact with the corrosive liquid. Under these conditions, even a thin layer of aluminium with a thickness of 1 mm or less, or even 0.1 mm or less, is sufficient to prevent the intrusion of molecular oxygen through the wall. If the metal barrier is not elastic enough to provide the required mechanical stability of the container, for example in the case of a thin layer of aluminium, the metal barrier needs to be mechanically supported. Such mechanical support can be provided by a mechanically stable wall as part of the composite material and / or by a frame or cage. If the metal barrier consists of a non-corrosive metal with a thickness allowing sufficient mechanical elasticity, for example low alloy steel, the metal barrier can be protected by coating it with a durable corrosion-resistant coating, such as varnish, rubber or enamel, or by using a corrosion-resistant liner, such as a polyethylene bag, etc.

[0030] The material is a saturated aliphatic C 6-12When in contact with a liquid containing carboxylic acid, it is necessary to be chemically resistant to corrosive liquids. Such corrosion-resistant metals are, for example, zirconium or tantalum, alloys of precious metals such as titanium / palladium, or alloy steels such as stainless steel. Stainless steel is preferred. Stainless steel with a PREN value of 17 or more is particularly preferred. PREN represents the "pitting resistance equivalent number" and is a predictive measurement of the resistance of stainless steel to local pitting based on its chemical composition. As a general rule, as the PREN value increases, the resistance of stainless steel to local pitting increases. Such high PREN values can also be obtained by some ferritic steels, such as 1.4113, 1.4526 or 1.4521, the numbers of which refer to European standard steel grades, but austenitic steels and duplex steels are more preferred, and austenitic steels are particularly preferred. Examples of such particularly preferred austenitic steels are 1.4306, 1.4401, 1.4436, 1.4404, 1.4435, 1.4432, 1.4541 and 1.4571.

[0031] The internal volume of the container is 0.05 to 10000 m 3 This includes movable containers that can be manually moved, placed by forklift, or transported by truck, railway vehicle, ship or airplane, and containers fixed to a tank storage. Fixed containers are also often simply called storage tanks, but are typically larger in size and usually have an internal volume of 20 to 10000 m 3 including. They are usually cylindrical or spherical in shape, whereby cylindrical tanks are typically arranged either upright or horizontally and may have a domed or flat roof. Movable containers are characterized by physical dimensions that allow their transportation on land, water or in the air. Except for specific ship tanks that can have a container with an internal volume of 1000 m 3 or more, movable containers typically have an internal volume of 0.05 to 120 m 3It has an internal volume. Examples of mobile containers that are technically noteworthy include drums, barrels, IBC tank containers, tank lorries, ISO tank containers, BASF classification tank containers, and railway tank cars. Drums and barrels typically have an internal volume of 0.05 - 0.25 m 3 characterized by an internal volume of. IBC tank containers (intermediate bulk containers) typically have an internal volume of 0.5 - 3 m 3 and preferably about 1 m 3 and are reusable multi-purpose industrial-grade containers designed for the handling, transportation, and storage of liquids. They can be easily moved by forklifts. Tank lorries typically have an internal volume of 5 - 45 m 3 characterized by an internal volume of, and preferably 10 - 35 m 3 ISO tank containers are based on ISO standards and are attached to frames. They are designed for the handling, transportation, and storage of liquids and typically have an internal volume of about 15 - 30 m 3 and have the advantage of being easily lifted from one standardized transport medium to another and stacked on top of each other. A relatively new type of transport container is the BASF classification tank container. They were developed for fully automated handling and their transportation by automated guided vehicles, but their transportation by trucks, railway vehicles, or ships is also possible. Their typical internal volume ranges from 53 - 73.5 m 3 The internal volume of railway tank cars typically ranges from about 10 - 120 m 3 within the range of.

[0032] The term internal volume belongs to the freely available volume inside the container. Potential internal parts (for mechanical or hydrodynamic reasons) and connecting pipes (for example, for inlets, outlets, or recirculation lines) are not part of the internal volume.

[0033] The container of the present invention contains a liquid containing a saturated aliphatic C 6-12 carboxylic acid or a mixture thereof, and a gas phase above the liquid, where C 6-12 represents 6 - 12 carbon atoms.

[0034] Saturated aliphatic C 6-12 carboxylic acids may be linear (straight-chain) or branched and may be substituted or unsubstituted. Substituted saturated aliphatic C 6-12 carboxylic acids contain one or more heteroatoms in addition to carbon and hydrogen, examples of which include halogen. Unsubstituted saturated aliphatic C 6-12 carboxylic acids are preferred. Preferred examples grouped by their number of carbon atoms are For C6, hexanoic acid, 2-methylpentanoic acid, 3-methylpentanoic acid, 4-methylpentanoic acid, 2,3-dimethylbutanoic acid and 3,3-dimethylbutanoic acid, For C7, heptanoic acid and 2-methylhexanoic acid, For C8, octanoic acid, 2-methylheptanoic acid, 2-ethylhexanoic acid, 2-ethyl-4-methylpentanoic acid and 2-propylpentanoic acid, For C9, nonanoic acid, 7-methyloctanoic acid and 3,5,5-trimethylhexanoic acid, C 10 For, decanoic acid, 2-propylheptanoic acid and 2-propyl-4-methylhexanoic acid, C 11 For, undecanoic acid and 2-methyldecanoic acid, and C 12 For, dodecanoic acid and 2-butyloctanoic acid are.

[0035] Among the above lists, hexanoic acid, 2-methylpentanoic acid, heptanoic acid, octanoic acid, 2-ethylhexanoic acid, nonanoic acid, 3,5,5-trimethylhexanoic acid, decanoic acid, 2-propylheptanoic acid and dodecanoic acid are more preferred. Saturated aliphatic C 8-12 carboxylic acids, among which octanoic acid, 2-ethylhexanoic acid, nonanoic acid, 3,5,5-trimethylhexanoic acid, decanoic acid, 2-propylheptanoic acid and dodecanoic acid are particularly preferred. 2-Ethylhexanoic acid is very particularly preferred.

[0036] Saturated aliphatic C 6-12The liquid containing carboxylic acid can also be a mixture of different saturated aliphatic C 6-12 carboxylic acids. Examples of technically relevant mixtures include a mixture of mainly 3,5,5-trimethylhexanoic acid and the other isomeric saturated nonanoic acid, which is technically produced and traded as isononanoic acid.

[0037] Saturated aliphatic C 6-12 The liquid containing carboxylic acid is characterized by a high content of saturated aliphatic C carboxylic acid of 99 - 100 wt.-% based on the liquid. 6-12 For a mixture of different saturated aliphatic C carboxylic acids, the above range refers to the mixture. Preferably, the total content of saturated aliphatic C carboxylic acid is 99.3 wt.-% or more, more preferably 99.5 wt.-% or more, particularly preferably 99.8 wt.-% or more, and very particularly preferably 99.9 wt.-% or more. 6-12 6-12

[0038] Saturated aliphatic C 6-12 carboxylic acid may contain a small amount of impurities and by-products to make up a possible gap to 100 wt.-%. Typical impurities and by-products are water, other isomers of saturated aliphatic C carboxylic acids containing fewer carbon atoms, esters of saturated aliphatic C carboxylic acids with the corresponding alcohol or a shorter-chain alcohol, alkyl-substituted lactones, or α,β-unsaturated aliphatic C carboxylic acids and their derivatives. The amount and nature of the impurities and by-products usually depend on the saturated aliphatic C 6-12 carboxylic acid. 6-12 6-12 carboxylic acids and their derivatives. The amount and nature of the impurities and by-products usually depend on the saturated aliphatic C 6-12 ​​​It depends on the properties of the carboxylic acids, especially whether they are linear or branched, their manufacturing methods, and their purification procedures. In order to support the effort to maintain a low decomposition tendency during storage and transportation of the container, the liquid preferably has an active oxygen content of 0 to 100 wt.-ppm, more preferably 50 wt.-ppm or less, and particularly preferably 10 wt.-ppm or less. The liquid typically has an active oxygen content of 1 wt.-ppm or more. In addition, it is advantageous for the liquid to also have a low molecular oxygen content dissolved therein, and thus a range of 0 to 10 wt.-ppm is preferred. More preferably, the liquid contains molecular oxygen of 5 wt.-ppm or less, and particularly preferably 2 wt.-ppm or less.

[0039] Saturated aliphatic C 6-12 Many carboxylic acids, especially many of the branched ones, generally have a low melting point, so many of them already exist as liquids at ambient temperature. However, some linear ones have melting points even exceeding 0 °C, as can be seen in the following list of melting points of carboxylic acids. 6-12 As can be seen in the following list of melting points of carboxylic acids, some have melting points even exceeding 0 °C. -70 °C 3,5,5-Trimethylhexanoic acid -59 °C 2-Ethylhexanoic acid -10 °C Heptanoic acid -4 °C Hexanoic acid 12 - 15 °C Nonanoic acid 17 °C Octanoic acid 31 °C Decanoic acid 44 °C Dodecanoic acid

[0040] Depending on the location and season, and thus the expected temperature conditions during storage and transportation, which can range from 20 ± 30 °C, the container can be separated or heated by trace heating as necessary to keep the saturated aliphatic C 6-12 carboxylic acid in a liquid state.

[0041] The containers of the present invention allow a very wide range of filling levels such that the degree of filling can vary from only 1 to 99% based on the internal volume of the container. In particular, the above-described stringent measures regarding the presence of an inert gas atmosphere having a very low molecular oxygen content and the use of a metal container that prevents the diffusion of molecular oxygen through the walls enable this high degree of adaptability in the degree of filling. Such excellent adaptability is particularly advantageous for containers in which saturated aliphatic C 6-12 carboxylic acids are withdrawn gradually over a longer period of time, or for storage tanks in which saturated aliphatic C 6-12 carboxylic acids are withdrawn irregularly and replenished. Nevertheless, in the case of mere storage or transportation, it is usually advantageous to apply a higher filling level. In a preferred embodiment, the liquid occupies 90 to 99% of the internal volume of the container, more preferably 95% or more, particularly preferably 98% or more.

[0042] In addition to the use of a metal container that prevents the diffusion of molecular oxygen through the walls, another effective measure of the present invention is the application of an inert gas phase over the liquid. The term "inert" means chemically inert with respect to each saturated aliphatic C 6-12 carboxylic acid. The inert gas phase contains nitrogen (N2), helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), hydrogen (H2), carbon dioxide (CO2), carbon monoxide (CO) or a mixture thereof, and is characterized by a molecular oxygen content of 0 to 100 vol.-ppm. Preferably, the inert gas phase contains nitrogen, helium, neon, argon, krypton, xenon, carbon dioxide or a mixture thereof. In addition to the above-described inert components, the inert gas phase also contains a small amount of saturated aliphatic C 6-12 carboxylic acid(s) that have evaporated according to their vapor pressure. Their concentration in the gas phase depends quite strongly on the nature of the saturated aliphatic C 6-12 carboxylic acid and the temperature present. However, even for saturated aliphatic C 6-12 carboxylic acids with the highest vapor pressure and a temperature of 50 °C, their concentration in the gas phase is well below 0.4 vol.-%.

[0043] Generally, as the content of molecular oxygen in the gas phase decreases, the prevention of the decomposition of saturated aliphatic C 6-12 carboxylic acids in the liquid becomes better. Therefore, the content of molecular oxygen in the inert gas phase is preferably 50 vol.-ppm or less, more preferably 20 vol.-ppm or less, particularly preferably 10 vol.-ppm or less, very particularly preferably 5 vol.-ppm or less, especially 2 vol.-ppm or less. In addition to a small amount of molecular oxygen, the inert gas phase may also contain typical impurities of a small amount of each gas, such as water vapor, lower hydrocarbons, or noble gases in the case of nitrogen, and also trace amounts of carbon monoxide in the case of carbon dioxide. Depending on the applied purity of the inert gas mentioned, the inert gas phase is calculated based on subtracting the vapor of the saturated aliphatic C 6-12 carboxylic acid evaporated from the liquid and setting the remaining gas phase to 100 vol.-%, and contains preferably 99.5 vol.-% or more, more preferably 99.8 vol.-% or more, particularly preferably 99.9 vol.-% or more, very particularly preferably 99.99 vol.-% or more of these gases. The plural "acids" also includes the singular "acid" when the liquid contains only one saturated aliphatic C 6-12 carboxylic acid. By this subtraction, it is possible to provide a percentage value for the purity of the inert gas independent of the properties of the saturated aliphatic C 6-12 carboxylic acid and the temperature of the container.

[0044] Due to the excellent availability of nitrogen as a technical standard inert gas, nitrogen is preferred. In a particularly preferred embodiment, the inert gas phase contains 99.9 vol.-% or more of nitrogen calculated based on subtracting the vapor of the saturated aliphatic C 6-12 carboxylic acid evaporated from the liquid and setting the remaining gas phase to 100 vol.-%.

[0045] Saturated aliphatic C 6-12A possible alternative for the present invention regarding the inert gas phase above the liquid containing carboxylic acid is that there is no gas phase. Since the liquid would then be completely surrounded by the metal-containing walls, at least one wall needs to be flexible or movable in order to compensate for thermal expansion and contraction and allow filling and discharging. Such an ability is provided by so-called floating roof tanks in which an upper cover floats on the filling liquid. To protect the upper cover from the weather, the floating roof tank can further have a top fixed to the upper end. Such a tank is called an internal floating roof tank and can optionally contain an inert gas atmosphere in the internal space between the floating roof and the fixed top.

[0046] In the containers of the present invention, typically saturated aliphatic C 6-12 Since it is intended to store and transport carboxylic acids, typically it is handled at a temperature of 20 ± 30 °C, or even up to -30 to +50 °C, depending on the location and season. As already mentioned above, the container can be thermally separated or heated if necessary, i.e., if each liquid has a melting point below the expected ambient temperature. The temperature of the liquid is preferably maintained at -20 °C or higher, more preferably -10 °C or higher, particularly preferably 0 °C or higher, and preferably 40 °C or lower, more preferably 35 °C or lower.

[0047] Regarding pressure, the inert gas phase can be maintained within the range of 0.09 to 0.6 MPa abs, which relates from a very small underpressure to a low excess pressure. When the lid or seal is not tightly closed, even a very small underpressure may cause some intrusion of ambient air. Therefore, it is preferable to apply at least a pressure substantially equal to or slightly above ambient atmospheric pressure, i.e., 0.1 MPa abs or more, preferably 0.102 MPa abs or more. On the other hand, as the excess pressure increases, filling becomes more complex and the risk of undesirable cases becomes higher. Therefore, it is preferable to apply only a low excess pressure resulting in an overall pressure of 0.2 MPa abs or less, more preferably 0.15 MPa abs or less, particularly preferably 0.12 MPa abs or less, and very particularly preferably 0.11 MPa abs or less.

[0048] A further aspect of the present invention is a method for storing and transporting a liquid containing a saturated aliphatic C 6-12 carboxylic acid or a mixture thereof, wherein the liquid has a saturated aliphatic C 6-12 carboxylic acid content of 99 to 100 wt.-%, and the liquid is filled into a container having an internal volume of 0.05 to 10,000 m 3 such that the liquid occupies an amount of 1 to 99% of the internal volume of the container, where the liquid is held therein for more than 1 hour, and further a) the container is a metal container, and b) the gas phase in the container is inactivated with an inert gas containing nitrogen, helium, neon, argon, krypton, xenon, hydrogen, carbon dioxide, carbon monoxide or a mixture thereof, having a molecular oxygen content of 0 to 100 vol.-ppm. It has surprisingly been found that the method.

[0049] The descriptions and preferences of terms, expressions, lists, and values that have already been used and described above in connection with the description of the container also apply mutatis mutandis to the terms, expressions, lists, and values of the method. In case of differences, the descriptions and preferences explicitly disclosed with respect to the method shall take precedence over the method.

[0050] In the method of the present invention, a liquid containing a saturated aliphatic C 6-12 carboxylic acid or a mixture thereof is filled into a metal container in an amount that occupies 1 to 99% of the internal volume of the container. As already described above in connection with the description of the container, the container has an internal volume of 0.05 to 10,000 m 3 and can be a mobile container or a fixed container that has a metal-only wall or at least includes a metal covering that may be part of a composite material. It would be possible to first fill the liquid into an un-inactivated container, for example, a container containing a gas phase with a molecular oxygen content exceeding 100 vol.-ppm, but it is advantageous if the gas phase of the container already contains nitrogen, helium, neon, argon, krypton, xenon, hydrogen, carbon dioxide, carbon monoxide, or a mixture thereof and has been inactivated with an inert gas with a molecular oxygen content of 0 to 100 vol.-ppm, preferably 50 vol.-ppm or less, more preferably 20 vol.-ppm or less, particularly preferably 10 vol.-ppm or less, very particularly preferably 5 vol.-ppm or less, especially 2 vol.-ppm or less. This also applies to the equipment required for filling in direct contact with the liquid, such as pipes, valves, or accessories. If the container contains a gas phase with a molecular oxygen content exceeding the intended value during the filling procedure, the gas phase is at least subsequently exchanged or at least changed with an inert gas to be adjusted to the intended inert gas quality.

[0051] As already described above in connection with the description of the container, a higher filling level is advantageous because the gas storage tank above the liquid becomes smaller. In a preferred method, the liquid occupies 90 to 99% of the internal volume of the container, more preferably 95% or more, particularly preferably 98% or more.

[0052] The container filled with liquid may already contain some liquid, which is common, for example, in the storage tanks of tank storage facilities, or it may be empty or almost empty, which may be common, for example, in transport containers that move back and forth between a filling position and a discharge position.

[0053] If it is necessary to cover the connection part with a lid after filling, this is the case before the transportation of the movable container, but it is necessary to ensure that the inert gas phase above the liquid maintains the intended quality.

[0054] Next, the filled container can be held for storage or transported. Storage means holding the container in the same place, while transportation means moving the container to another place. To be complete, movable containers can also be used for storage, which is mentioned in the case where the movable container is, for example, before or after its transportation, or usually held in a fixed place. Transportation can be carried out on land, water or in the air.

[0055] The method of the present invention is preferably carried out by using a movable container with an internal volume of 0.05 to 120 m 3 Such a movable container enables high adaptability for storing and transporting saturated aliphatic C 6-12 carboxylic acids. Technically notable movable containers of such sizes are, for example, drums, barrels, IBC tank containers, truck tanks, ISO tank containers, BASF classification tank containers or railway tank cars.

[0056] The inert gas phase in the container is usually maintained at a pressure in the range of 0.09 to 0.6 MPa abs, preferably not less than 0.102 MPa abs and preferably not more than 0.2 MPa abs, depending on the location and season, and is typically handled at a temperature of 20 ± 30 °C, or -30 to +50 °C, while the preferences already described in connection with the description of the container are applied as appropriate. The container may be thermally insulated or heated as required.

[0057] Once a liquid containing saturated aliphatic C 6-12 carboxylic acid is filled, the liquid is held under inert conditions for more than 1 hour, preferably for more than 1 day, more preferably for more than 1 week, and particularly preferably for more than 4 weeks. There is no upper limit on the time. Even when the liquid is stored for more than 1 year under the conditions of the present invention, its decomposition will be significantly lower than when the liquid is stored in an oxygen-permeable container and / or under a gas phase having a significant content of molecular oxygen.

[0058] Nevertheless, in addition to the use of an oxygen-impermeable metal container and the supply of an inert gas phase over the liquid, it is further advantageous for the liquid to already have a low content of dissolved molecular oxygen therein to prevent the decomposition of saturated aliphatic C 6-12 carboxylic acid, where molecular oxygen in the range of 0 to 10 wt.-ppm is preferred, 5 wt.-ppm or less is more preferred, and 2 wt.-ppm or less is particularly preferred.

[0059] Furthermore, to support the effort to maintain a low decomposition tendency during storage and transportation of the container, the liquid preferably has an active oxygen content of 0 to 100 wt.-ppm, more preferably 50 wt.-ppm or less, particularly preferably 10 wt.-ppm or less, and preferably 1 wt.-ppm or more.

[0060] Similar to the filling of the container, the release of the liquid containing saturated aliphatic C 6-12 carboxylic acid is also advantageously carried out by avoiding direct contact of the liquid with an oxygen-containing gas phase having an oxygen content exceeding 100 vol.-ppm. Therefore, the equipment required for the release in direct contact with the liquid, such as pipes, valves or accessories, should preferably be inactivated.

[0061] Furthermore, as already mentioned in connection with the description of the container, nitrogen is preferred as the inert gas due to its excellent availability as a technical standard inert gas. In a particularly preferred method, the inert gas phase contains 99.9 vol.-% or more of nitrogen.

[0062] Saturated aliphatic C 6-12 As the carboxylic acid, hexanoic acid, 2-methylpentanoic acid, heptanoic acid, octanoic acid, 2-ethylhexanoic acid, nonanoic acid, 3,5,5-trimethylhexanoic acid, decanoic acid, 2-propylheptanoic acid, and dodecanoic acid are more preferable. Saturated aliphatic C 8-12 carboxylic acid, among which octanoic acid, 2-ethylhexanoic acid, nonanoic acid, 3,5,5-trimethylhexanoic acid, decanoic acid, 2-propylheptanoic acid, and dodecanoic acid are particularly preferable. 2-Ethylhexanoic acid is very particularly preferable.

[0063] A further aspect of the present invention is the use of nitrogen as an inerting gas for supplying an inerting gas phase having a molecular oxygen content of 0 to 100 vol.-ppm into a metal container having an internal volume of 0.05 to 10,000 m 3 wherein a liquid containing a saturated aliphatic C 6-12 carboxylic acid having a saturated aliphatic C 6-12 carboxylic acid content of 99 to 100 wt.-% or a mixture thereof occupies 1 to 99% of the internal volume of the container and is stored or transported for more than 1 hour.

[0064] In a general embodiment, 2-ethylhexanoic acid is filled in a 1 m 3 metal IBC tank container pre-inerted with nitrogen having a molecular oxygen content of 5 vol.-ppm or less in an amount occupying 98% of the internal volume. The container is tightly closed at a nitrogen gas pressure of 0.1 to 0.11 MPa abs and then stored and / or transported.

[0065] In another general embodiment, a mixture of 3,5,5-trimethylhexanoic acid and other saturated aliphatic branched C9 carboxylic acids is filled in a 26 m 3 ISO tank container pre-inerted with nitrogen having a molecular oxygen content of 10 vol.-ppm or less in an amount occupying 95% of the internal volume. The container is tightly closed at a nitrogen gas pressure of 0.1 to 0.15 MPa abs and then transported by truck, railway vehicle, and / or container ship.

[0066] A more general embodiment relates to the storage of 2-ethylhexanoic acid in a tank storage facility. 2-Ethylhexanoic acid is continuously manufactured and purified at a manufacturing plant and is continuously pumped through a fully filled pipeline into a fixed 2000 m 3 tank. The tank contains an inert gas phase with a nitrogen content of 99.9 vol.-% or more and a molecular oxygen content of 5 wt.-ppm or less. Depending on the use and demand for the stored 2-ethylhexanoic acid, it is released either continuously or irregularly. Thus, the filling level varies depending on the supply and release amounts of 2-ethylhexanoic acid and can be in the range of 1 to 99%.

[0067] The containers and methods of the present invention prevent or at least considerably reduce discoloration of products derived from saturated aliphatic C 6-12 carboxylic acids even when the saturated aliphatic C 6-12 carboxylic acids are stored or transported for a long time, for example, for several months, and / or the saturated aliphatic C 6-12 carboxylic acids do not lose or only slightly lose their color stability under thermal stress, and enable the storage and transportation of saturated aliphatic C 6-12 carboxylic acids. The improved storage and transportation can be easily carried out in available standard containers without contaminating the saturated aliphatic C 6-12 carboxylic acids with harmful compounds.

Examples

[0068] Measurement of Active Oxygen by Iodometric Titration The content of active oxygen in 2-ethylhexanoic acid was measured by iodometric titration. A general description of how the measurement was carried out is shown below.

[0069] Weigh approximately 5 g of the sample to the nearest 0.1 mg, place it in a reaction vial, flash it with argon, and add 40 ml of a 1:1 acetic acid / chloroform mixture to dissolve the sample. Equip the reaction vial with a condenser and place it in a stirring heating block that has already been preheated to 80 °C. Pass a weak argon stream through the condenser to prevent air intrusion. After the temperature reaches equilibrium, add 5.0 mL of a saturated potassium iodide solution (approximately 60.0 g of potassium iodide dissolved in 100 mL of deionized water) through the condenser and boil the mixture under reflux for 10 minutes. In the next step, add 40.0 mL of deionized water and titrate the sample solution with a 0.01 M thiosulfate solution while using a platinum electrode as the end point detector.

[0070] Measurement of molecular oxygen The content of molecular oxygen in 2-ethylhexanoic acid was measured by a highly accurate and highly O2-sensitive optical fluorescence sensor suitable for measuring molecular oxygen in carboxylic acids. In the example, an optical sensor named WTW's FDO® 925 was used. The measurement data was verified by further measurements using a galvanic cell oxygen analyzer, also known as a Hersch cell.

[0071] Measurement of APHA color number The APHA color number of the sample was measured by a colorimeter pre-calibrated against distilled water. In the example, a colorimeter named Hach's Lico® 620 was used together with a 10 mL cuvette.

[0072] Description of the esterification test A 4-liter stirred tank reactor was charged under nitrogen (molecular oxygen content 100 ppm or less) with 520 g (5 mol) of neopentyl glycol, 1469 g (10.2 mol) of 2-ethylhexanoic acid, and 0.75 g of powdered tin oxide as a catalyst. The mixture was then heated to 180 - 190 °C under ambient pressure to form a diester between neopentyl glycol and 2-ethylhexanoic acid, and the water formed was distilled off. The reaction was terminated when no more water was formed. The mixture was then cooled to about 60 °C, a specified amount of activated carbon was added, and it was held for 30 minutes with stirring. The suspension was then filtered and the APHA color number was determined.

[0073] Example 1 (comparative) In a technical plant having a production capacity of about 3.75 tons of 2-ethylhexanoic acid per hour, 2-ethylhexanal was continuously oxidized with pure oxygen at a temperature of 30 - 60 °C and a pressure of 0.25 MPa abs in the presence of 0.4 wt.-% potassium ions in the reaction mixture to produce 2-ethylhexanoic acid. The technical plant included three reactors connected in series, and the addition of oxygen supply was divided among these three reactors. 2-Ethylhexanal and a potassium salt were added to the first reactor. The resulting crude 2-ethylhexanoic acid was stripped with a nitrogen stream (molecular oxygen content 100 ppm or less) until the content of dissolved molecular oxygen was only 2 wt.-ppm, and then distilled in a distillation column, and purified 2-ethylhexanoic acid was withdrawn as a side stream. The purified 2-ethylhexanoic acid had a 2-ethylhexanoic acid content of 99.85 wt.-% as analyzed by gas chromatography, contained 2 wt.-ppm of active oxygen and less than 1 wt.-ppm of dissolved molecular oxygen, and showed an APHA color number of 0.

[0074] The purified liquid 2-ethylhexanoic acid was then filled in an un-inactivated polyethylene IBC container containing air to an amount occupying about 95% of the internal volume. The IBC container was then tightly closed and stored and transported at a pressure of 0.12 MPa abs and a temperature in the range of 0 - 40 °C for about 3 weeks. 3

[0075] After storage and transportation, a sample of 2-ethylhexanoic acid was taken out under an inert nitrogen atmosphere and esterified as described in the esterification test to determine the amount of activated carbon required to obtain an APHA color number of less than 10. The required amount of activated carbon was 8.4 g per kg of the applied extract (neopentyl glycol + 2-ethylhexanoic acid).

[0076] Example 2 (according to the present invention) 2-Ethylhexanoic acid was produced under the same conditions in the same technical plant as described in Example 1. Analysis by gas chromatography showed that it had a 2-ethylhexanoic acid content of 99.85 wt.-%, contained 2 wt.-ppm of active oxygen and less than 1 wt.-ppm of dissolved molecular oxygen, and showed an APHA color number of 0.

[0077] Next, the purified liquid 2-ethylhexanoic acid was filled in a stainless steel IBC container inactivated with 1 m 3 of nitrogen (molecular oxygen content 100 vol.-ppm or less) in an amount occupying about 95% of the internal volume. Then, the IBC container was tightly closed and stored and transported for about 3 weeks at a pressure of 0.12 MPa abs and a temperature in the range of 0 to 40 °C.

[0078] After storage and transportation, a sample of 2-ethylhexanoic acid was taken out under an inert nitrogen atmosphere and esterified as described in the esterification test to determine the amount of activated carbon required to obtain an APHA color number of less than 10. The required amount of activated carbon was only 1.4 g per kg of the applied extract (neopentyl glycol + 2-ethylhexanoic acid).

[0079] Examples 1 and 2 are identical in the production and properties of purified 2-ethylhexanoic acid, the period of storage and transportation, the applied pressure and temperature, and the conduct of the esterification test, differing only in the material of the container used for storage and transportation and the properties of the gas atmosphere above the 2-ethylhexanoic acid. In Example 1, 2-ethylhexanoic acid was stored and transported in a typical polyethylene container under an air (0.12 MPa abs) atmosphere, while in Example 2, 2-ethylhexanoic acid was stored and transported in an oxygen-impermeable stainless steel container under a nitrogen inert gas (0.12 MPa abs) atmosphere. Due to these two differences, as a result, the amount of activated carbon required to decolorize the diester formed in the esterification test to less than 10 APHA color number is reduced by a very large factor of one-sixth between 8.4 g per kg of the extract applied in Example 1 and 1.4 g in Example 2.

[0080] The measures of the present invention as applied in Example 2 prevent or at least considerably reduce the oxygen-induced decomposition of 2-ethylhexanoic acid during storage and transportation, and thus prevent or at least considerably reduce the discoloration of the resulting product.

Claims

1. The container has an internal volume of 0.05 to 10,000 m 3 and is a container such that a) Non-replaced saturated aliphatic C 6-12 A liquid containing carboxylic acid or a mixture thereof, wherein the liquid has a saturated aliphatic C 6-12 carboxylic acid content of 99 to 100 wt.-% and occupies 1 to 99% of the internal volume of the container, and b) a gas phase above the liquid and wherein c) the container is a metal container and d) the gas phase above the liquid is an inert gas phase containing nitrogen, helium, neon, argon, krypton, xenon, hydrogen, carbon dioxide, carbon monoxide or a mixture thereof and having a molecular oxygen content of 0 to 100 vol.-ppm, a container.

2. The container according to claim 1, which is a stainless steel container.

3. The internal volume is 0.05 to 120 m 3 The container according to claim 1 or 2, which is a movable container.

4. The non-replaceable saturated aliphatic C 6-12 The carboxylic acid is octanoic acid, 2-ethylhexanoic acid, nonanoic acid, 3,5,5-trimethylhexanoic acid, decanoic acid, 2-propylheptanoic acid or dodecanoic acid, or a mixture thereof. The container according to any one of claims 1 to 3.

5. Non-replaceable saturated aliphatic C 6-12 The container according to claim 4, wherein the carboxylic acid is 2-ethylhexanoic acid.

6. The container according to any one of claims 1 to 5, wherein the liquid has an active oxygen content of 0 to 100 wt.-ppm.

7. The container according to any one of claims 1 to 6, wherein the liquid occupies 90 to 99% of the internal volume of the container.

8. The container according to any one of claims 1 to 7, wherein the inert gas phase has a molecular oxygen content of 10 vol.-ppm or less.

9. The inert gas phase is saturated aliphatic C evaporated from the liquid 6-12 The container according to any one of claims 1 to 8, containing 99.9 vol.-% or more of nitrogen, calculated based on subtracting the vapor of the carboxylic acid and setting the remaining gas phase to 100 vol.-%.

10. A method for storing and transporting a liquid containing a non-substituted saturated aliphatic C 6-12 carboxylic acid or a mixture thereof, wherein the liquid has a non-substituted saturated aliphatic C 6-12 carboxylic acid content of 99 to 100 wt.-%, and the liquid is filled into a container having an internal volume of 0.05 to 10,000 m 3 such that the liquid occupies an amount of 1 to 99% of the internal volume of the container, wherein the liquid is held therein for more than 1 hour, and further, a) the container is a metal container and b) the gas phase in the container is inactivated with an inert gas containing nitrogen, helium, neon, argon, krypton, xenon, hydrogen, carbon dioxide, carbon monoxide or a mixture thereof and having a molecular oxygen content of 0 to 100 vol.-ppm, characterized in that.

11. The container is a movable container with an internal volume of 0.05 to 120 m 3 The method according to claim 10, wherein the container is a movable container having an internal volume of 0.05 to 120 m

12. The method according to claim 10 or 11, wherein the liquid is held therein for at least one week.

13. The method according to any one of claims 10 to 12, wherein the liquid has an active oxygen content of 0 to 100 wt.-ppm.

14. The method according to any one of claims 10 to 13, wherein the inert gas phase contains 99.9 vol.-% or more of nitrogen.

15. Non-replaceable saturated aliphatic C 6-12 The method according to any one of claims 10 to 14, wherein the carboxylic acid is 2-ethylhexanoic acid.

Images