CONTAINER AND PROCESS FOR THE STORAGE OF A SATURATED ALIPHATIC C6-C12 CARBOXYLIC ACID

Abstract

A container and a process for the degradation stable storage and transport of a liquid comprising a saturated aliphatic C.sub.6-12 carboxylic acid in which the liquid is covered with an oxygen free or at least heavily oxygen depleted inert gas phase atmosphere above the liquid.

Claims

1.-15. (canceled)

16. A container with an inner volume of 0.05 to 10000 m.sup.3 comprising: a) a liquid comprising a non-substituted saturated aliphatic C.sub.6-12 carboxylic acid or a mixture thereof, whereas the liquid has a saturated aliphatic C.sub.6-12 carboxylic acid content of 99 to 100 wt.-% and occupies 1 to 99% of the inner volume of the container, and b) a gas phase above the liquid, wherein c) the container is a metallic 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.

17. The container of claim 16, wherein the container is a stainless steel container.

18. The container of claim 16, wherein the container is a mobile container with an inner volume of 0.05 to 120 m.sup.3.

19. The container of claim 16, wherein the non-substituted saturated aliphatic C.sub.6-12 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.

20. The container of claim 19, wherein the non-substituted saturated aliphatic C.sub.6-12 carboxylic acid is 2-ethylhexanoic acid.

21. The container of claim 16, wherein the liquid has an active oxygen content of 0 to 100 wt.-ppm.

22. The container of claim 16, wherein the liquid occupies 90 to 99% of the inner volume of the container.

23. The container of claim 16, wherein the inert gas phase has a molecular oxygen content of ≤10 vol.-ppm.

24. The container of claim 16, wherein the inert gas phase contains ≥99.9 vol.-% nitrogen, calculated on a basis, in which the vapor of the saturated aliphatic C.sub.6-12 carboxylic acids vaporized from the liquid was deducted and the remaining gas phase set to 100 vol.-%.

25. A process for the storage and transport of a liquid comprising a non-substituted saturated aliphatic C.sub.6-12 carboxylic acid or a mixture thereof, whereas the liquid has a non-substituted saturated aliphatic C.sub.6-12 carboxylic acid content of 99 to 100 wt.-%, by filling the liquid into a container with an inner volume of 0.05 to 10000 m.sup.3 in an amount that the liquid occupies 1 to 99% of the inner volume of the container, wherein the liquid is kept therein for more than 1 hour, characterized in that: a) the container is a metallic container, and b) the gas phase in the container is inertized 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.

26. The process of claim 25, wherein the container is a mobile container with an inner volume of 0.05 to 120 m.sup.3.

27. The process of claim 25, wherein liquid is kept therein for ≥1 week.

28. The process of claim 25, wherein the liquid has an active oxygen content of 0 to 100 wt.-ppm.

29. The process of claim 25, wherein the inert gas phase contains ≥99.9 vol.-% nitrogen.

30. The process of claim 25, wherein the non-substituted saturated aliphatic C.sub.6-12 carboxylic acid is 2-ethylhexanoic acid.

Description

EXAMPLES

Determination of Active Oxygen by Iodometry

[0099] The content of active oxygen in 2-ethylhexanoic acid was determined by iodometry. The following gives a general description on how the determination was performed.

[0100] Approximately 5 g of the sample, weighed to the nearest 0.1 mg, are placed in a reaction vial, flushed with argon, and 40 ml of a 1:1 acetic acid/chloroform mixture added to dissolve the sample. The reaction vial is provided with a cooler and placed in a stirring heating block, that is already preheated to 80° C. A weak argon flow is passed through the cooler to prevent the ingress of air. After the temperature has equilibrated, 5.0 mL of a saturated potassium iodide solution (ca. 60.0 g potassium iodide dissolved in 100 mL deionized water) are added through the cooler and the mixture is boiled under reflux for 10 min. In the next step, 40.0 mL deionized water are added, and the sample solution is titrated with a 0.01 M thiosulfate solution while using a platinum electrode as end point indicator.

Determination of Molecular Oxygen

[0101] The content of molecular oxygen in 2-ethylhexanoic acid was determined by a high precision and highly O.sub.2 sensitive optical fluorescence sensor, which was suitable to measure molecular oxygen in carboxylic acids. In the examples, an optical sensor named FDO® 925 from WTW was used.

[0102] The measured data were cross-checked by additional measurements using a galvanic cell oxygen analyzer, which is also known as a Hersch cell.

Determination of the APHA Color Number

[0103] The APHA color number of the samples was determined by a colorimeter which was in advance calibrated against distilled water. In the examples, a colorimeter named Lico® 620 from Hach with a 10 mL cuvette was used.

Description of the Esterification Test

[0104] A 4 liter stirred tank reactor was filled under nitrogen (molecular oxygen content≤100 ppm) with 520 g (5 mol) of neopentyl glycol and 1469 g (10.2 mol) of 2-ethylhexanoic acid and 0.75 g of powdered tin oxide as catalyst. The mixture is then heated to 180-190° C. under ambient pressure to form the diester between neopentyl glycol and 2-ethylhexanoic acid, and the formed water allowed to distill off. The reaction is finished when no more water is formed. The mixture is then cooled to approximately 60° C., a defined amount of active charcoal added and kept for 30 minutes under stirring. The suspension was then filtered and the APHA color number determined.

Example 1 (Comparative)

[0105] 2-Ethylhexanoic acid was produced in a technical plant with a production capacity of around 3.75 tons 2-ethylhexanoic acid per hour by continuously oxidizing 2-ethylhexanal with pure oxygen at a temperature of 30 to 60° C. and a pressure of 0.25 MPa abs and in the presence of 0.4 wt.-% of potassium ions in the reaction mixture. The technical plant contained three reactors connected in series and the addition of the oxygen feed was divided between these three reactors. The 2-ethylhexanal and the potassium salt were added to the first reactor. The obtained crude 2-ethylhexanoic acid was stripped with a stream of nitrogen (molecular oxygen content≤100 ppm) until the content of the dissolved molecular oxygen was only 2 wt.-ppm, subsequently distilled in a distillation column and purified 2-ethylhexanoic acid withdrawn as a side stream. The purified 2-ethylhexanoic acid had a 2-ethylhexanoic acid content of 99.85 wt.-%, analyzed by gas chromatography, contained 2 wt.-ppm active oxygen, <1 wt.-ppm dissolved molecular oxygen and showed an APHA color number of 0.

[0106] The purified liquid 2-ethylhexanoic acid was then filled in a non-inertized, air containing 1 m.sup.3 polyethylene IBC-container in an amount occupying around 95% of the inner volume. The IBC-container was then closed tightly and stored and transported for around three weeks at a pressure of 0.12 MPa abs and a temperature in the range of 0 to 40° C.

[0107] After storage and transport, samples of the 2-ethylhexanoic acid have been taken under an inert nitrogen atmosphere and esterified as described by the esterification test to determine the amount of active charcoal required for attaining an APHA color number of <10. The required amount of active charcoal was 8.4 g per kg of the applied educts (neopentyl glycol plus 2-ethylhexanoic acid).

Example 2 (According to the Invention)

[0108] 2-Ethylhexanoic acid was produced in the same technical plant and under the same conditions as described in example 1. It had a 2-ethylhexanoic acid content of 99.85 wt.-%, analyzed by gas chromatography, contained 2 wt.-ppm active oxygen, <1 wt.-ppm dissolved molecular oxygen and showed an APHA color number of 0.

[0109] The purified liquid 2-ethylhexanoic acid was then filled in a 1 m.sup.3 nitrogen inertized (molecular oxygen content≤100 vol.-ppm) stainless steel IBC-container in an amount occupying around 95% of the inner volume. The IBC-container was then closed tightly and stored and transported for around three weeks at a pressure of 0.12 MPa abs and a temperature in the range of 0 to 40° C.

[0110] After storage and transport, samples of the 2-ethylhexanoic acid have been taken under an inert nitrogen atmosphere and esterified as described by the esterification test to determine the amount of active charcoal required for attaining an APHA color number of <10. The required amount of active charcoal was only 1.4 g per kg of the applied educts (neopentyl glycol plus 2-ethylhexanoic acid).

[0111] Examples 1 and 2 are identical in the production and nature of the purified 2-ethylhexanoic acid, in the storage and transport period, in the applied pressure and temperature, as well as in the performance of the esterification test, and only differ in the material of the container used for storage and transport and in the nature of the gas atmosphere above the 2-ethylhexanoic acid. Whereas in example 1, the 2-ethylhexanoic acid was stored and transported in a typical polyethylene container under an atmosphere of air (0.12 MPa abs), the 2-ethylhexanoic acid in example 2 was stored and transported in an oxygen-impermeable stainless steel container under an atmosphere of nitrogen inert gas (0.12 MPa abs). These two differences result in a very strong decrease of the amount of active charcoal required for decolorizing the diester formed in the esterification test to an APHA color number of <10 by a factor of 6 between 8.4 g per kg of the applied educts in example 1 and 1.4 g in example 2.

[0112] The inventive measures as applied in example 2 prevent, or at least strongly reduce the oxygen induced degradation of the 2-ethylhexanoic acid during storage and transport and thus prevent from, or at least strongly reduce the discoloration of the products derived therefrom.