JP2002505246A - Method for producing hydroxylammonium salt - Google Patents

Abstract

  (57) [Summary] In a process for producing a hydroxylammonium salt by catalytic reduction of nitric oxide with hydrogen in the presence of an acid and a hydrogenation catalyst, prior to said catalytic reduction, a porous oxide or activated carbon based on silicon and / or aluminum is used. Purifying the nitric oxide by treating at least once with the method.

Description

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a method for producing a hydroxylammonium salt by catalytically reducing nitric oxide with hydrogen in the presence of an acid and a hydrogenation catalyst.

[0002] Hydroxylamines are widely used, especially for the production of caprolactam. Today it is produced on an industrial scale, in particular by reducing nitric oxide with hydrogen.
This nitric oxide is obtained by reacting ammonia and oxygen by the Ostwald process, which is used directly for the synthesis of hydroxylamine. Here, nitric oxide is purified with a scrubber, and using a suitable noble metal supported catalyst in a sulfuric acid suspension,
Reacts with hydrogen below 50 ° C. to convert to hydroxylamine. in this way,
Small amounts of ammonium sulfate and nitrous oxide (laughter) are formed as by-products. In general, platinum-supported catalysts can be used in which the selectivity for hydroxylamine is maximized by partial toxic effects.

[0003] DE-A 956038 discloses a process for producing hydroxylammonium salts in which nitric oxide is reduced over a platinum / graphite catalyst. This catalyst is obtained by reductively precipitating platinum on a suspended graphite support and adding a catalyst poison such as sulfur, selenium, arsenic or tellurium compound as appropriate. This catalyst has the disadvantage that its reactivity and selectivity are immediately reduced after prolonged use.

[0004] DE-A 402 2851 discloses platinum / graphite catalysts for the hydrogenation of nitric oxide in which the selectivity is related to the apparent density, the compressive strength and the porosity of the graphite support.

[0005] DE-A 40 22 853 describes that the graphite support has a specific particle size distribution of 1 to 5.
A platinum / graphite catalyst that is 600 μm is disclosed. When using this catalyst, the selectivity for hydroxylamine formation during hydrogenation of nitric oxide can be increased.

In known processes for producing hydroxylamine, selectivity for nitric oxide formation, space-time yield and working life of the catalyst can be improved.

[0007] Nitric oxide obtained by combustion of ammonia can be converted to other NOx compounds (for example,
NO ₂ , N ₂ 0), as well as a number of impurities in the ppm range (most importantly, H ₂ S, CO ₂ , CO, CH ₄ and other hydrocarbons). DE-A 15 42 628 describes:
A method for selectively removing nitrogen dioxide and / or molecular oxygen by catalytic reduction with a reducing gas using a catalyst containing silver and optionally manganese in the form of an oxide compound as an active ingredient has already been disclosed. However, this method is too complicated for industrial use. This is because an additional hydrogenation step and a catalyst are required. Furthermore, the removal of NO ₂ is insufficient, and the concentration of nitrous oxide is increased.

Accordingly, it is an object of the present invention to provide an improved process by which the production of hydroxylammonium salts by reducing NO with hydrogen is technically simple and which results in high selectivity and space-time yield. To provide. Furthermore, the working life of this catalyst has to be relatively long.

The present inventors have found that the purity of the nitric oxide used influences the parameters mentioned above, so that the object of the present invention is to provide a porous oxide based on silicon or aluminum or It has been found that by treating with activated carbon, this can be achieved by purifying nitric oxide by a simple method.

The present invention relates to a method for producing a hydroxylammonium salt by catalytically reducing nitric oxide with hydrogen in the presence of an acid and a hydrogenation catalyst, wherein silicon and / or aluminum are converted before the catalytic reduction. It is an object of the present invention to provide a production method characterized in that the nitric oxide is purified by treating it at least once with a base porous oxide or activated carbon.

[0011] Porous oxides that can be used are, in particular, silicon dioxide (eg, silica gel) and molecular sieves. Molecular sieves include known natural or synthetic zeolites, ie, alkali metal cations or alkaline earth metal cations, and have the following formula:

[0012]

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Wherein M represents an alkali metal or an alkaline earth metal, n is the valency of a cation, and x is 2 or more. The pore size of this molecular sieve is often on the order of Angstroms (0.1 × 10 ⁻⁹ m), ie the molecular sieve designated as 3A has a pore size of 3
It has an opening of Angstrom (0.3 nm) pores. According to the invention, molecular sieves 5A and especially molecular sieves 4A are preferred.

[0014] Oxides, especially molecular sieves, are often used in a state containing a small amount of water or in a substantially anhydrous state.

The activated carbon that can be used is a commercially available activated carbon, such as Degusorb, Contarbon BA, Supersorbon K or Desorex A.

According to the present invention, it has been found to be particularly effective to dry the nitric oxide before purification. For this purpose, conventional materials can be used, but it is particularly useful to use any of the porous oxides mentioned above, in particular silica gel, in the drying step. Thus, in a particularly preferred embodiment, the nitric oxide is first treated with silica gel for drying (and first purification) and then with molecular sieves for further purification.

Both drying and refining can be performed in one or more stages using one or more drying or refining agents. Generally, drying and purification are carried out in a usual apparatus, but it is effective to carry out in a column having an appropriate size.

To purify about 10 standard L (liter) / hour of NO, usually 1000
1500 ml of purifying agent and about the same amount of desiccant can be used. Generally, after operating for about 8 to 12 hours, the purification tower is regenerated by baking completely. About 30
After operating for 0-400 hours, the drying tower is completely baked.

Both the temperature and the pressure during the purification and drying of the nitric oxide can be varied within wide limits. In general, drying and / or purification is carried out at 20-500 ° C., especially 2
It is carried out at a temperature of from 0 to 150 ° C. and a pressure of from 100 mbar to 100 bar, in particular from 800 mbar to 2 bar, the pressure being most conveniently at about atmospheric pressure for convenience.

Analysis of carbon monoxide before and after purification reveals, among other things, other nitric oxides (eg N 2 _Two O and NO_Two) Content and H_TwoIt can be seen that the content of S in ppm is greatly reduced. This can be seen in Table 3 of Example 3.

The hydrogenation following the purification step is carried out in a manner known per se. Preferably, hydrogen and nitric oxide are reacted in a molar ratio in the range of 1.5: 1 to 6: 1. Good results are obtained when the molar ratio of hydrogen to nitric oxide in the reaction zone is kept in the range 3.5: 1 to 5: 1.

The hydrogenation catalysts used are those customarily used for this purpose. DE
Preference is given to using platinum catalysts coated on graphite as disclosed in A4022853. In particular, the catalyst is treated before hydrogenation in an acid solution, preferably with the acid in which the hydrogenation takes place. Thereby, the catalyst is activated.

The hydrogenation may be carried out with an acid, preferably a strong mineral acid such as nitric acid, sulfuric acid or phosphoric acid, or C ₁ ~ C_FiveAliphatic monocarboxylic acids such as formic acid, acetic acid, propionic acid, butyric acid or
It is carried out in the presence of valeric acid, preferably formic acid or acetic acid. Ammonium hydrogen sulfate
Acid salts, such as potassium, are also suitable. Generally, a 4-6N aqueous acid solution is used, and
Care is taken that the acid concentration does not drop below 0.2 N during the hydrogenation. If necessary,
Add more acid.

[0024] The ratio of acid to catalyst is very dependent on the catalyst used. Generally, the catalyst is in the range of 1 to 150 g per liter of the mineral acid. In the case of the above-mentioned platinum catalysts disclosed in DE-A 40 22 853, the catalyst is preferably in the range of 1 to 100 g, especially 20 to 80 g, per liter of mineral acid.

The hydrogenation is generally carried out at a temperature between 30 and 80 ° C., preferably between 35 and 60 ° C.
The pressure during the hydrogenation is usually chosen to be between 1 and 30 bar, preferably between 1 and 20 bar (absolute).

The process of the present invention for producing hydroxylammonium salts results in very high selectivity for hydroxylammonium and low selectivity for nitrous oxide. Furthermore, the space-time yield of the catalyst exposed to nitric oxide purified by the method of the present invention is significantly increased compared to using untreated nitric oxide. In addition, the working life of the catalyst used is also increased. As a result, catalysts that improve the economics of the process are recovered less frequently.

The following examples illustrate the invention in detail, but do not limit the invention.

[0028]

【Example】

Example 1 a) 40 g of Asbury graphite having a particle size of 2 to 50 μm and 0 g
. 3.87 ml of 5310 g of hexachloroplatinic acid (IV) hexahydrate
And stirred at 80 ° C. overnight in an aqueous solution containing concentrated hydrochloric acid and 0.87 ml of concentrated nitric acid. Sodium carbonate was added to the resulting suspension until the pH reached 2.75. continue,
2.5 g of sodium acetate was added as a buffer. Two minutes after the addition of 5 mg of elemental sulfur, the resulting suspension was diluted with a 40% by mass aqueous solution of sodium formate (8%).
(3 mmol) and stirred at 80 ° C. for 4 hours. After this, platinum was no longer detectable by hydrazine hydrate (this gives a black precipitate in alkaline solution in the presence of platinum).

[0029] The catalyst thus obtained was separated from the reaction mixture by filtration through a glass frit and washed with distilled water. This washing was performed until the pH of the washing became out of the acidic range. The dried catalyst contained 0.5% by weight of platinum.

B) 3.6 g of the catalyst obtained in a) are suspended in 120 ml of 4.3N sulfuric acid,
At 40 ° C. with vigorous stirring (3500 rpm), a drying tower packed with 35% by volume of nitric oxide ｛800 ml of silica gel was then filled with 1200 ml of molecular sieve 4A (from Carl Roth GmbH, Karlsruhe). 7.75 L / h of a mixture consisting of｝ and 65% by volume of hydrogen previously passed through the purified column were passed through the suspension. After 4 hours, the catalyst was separated off and the liquid phase was analyzed. Subsequently, the separated catalyst was mixed with 120 ml of 4.3N sulfuric acid and the reaction was continued. This process is repeated every four hours and is called a batch. The catalyst was tested until the hydroxylamine synthesis changed from batch to batch (activated phase) by less than 0.5%. This required 20 batches of catalytic time.
In the twenty-first batch, unpurified NO was then used; in the twenty-second batch, purified NO as in the preceding batch was used again. In this case, the liquid phase was analyzed. Table 1 shows the selectivities obtained in these batches.

[0031]

[Table 1]

From Table 1, it was found that the use of unpurified NO resulted in a substantial increase in the selectivity of NO ₂ , mainly due to the loss of hydroxylamine selectivity. If the purified N 2 O is used again for the next batch, the values of the previous batch are obtained again.

Example 2 Passage of NO through a drying tower 3.6 g of the catalyst obtained in example 1a) are suspended in 120 ml of 4.3N sulfuric acid and, at the same time, vigorously stirred at 40 ° C. (3500 rpm) 7.75 L / h of a mixture consisting of 35% by volume of nitric oxide {previously passed through a drying tower packed with 800 ml of silica gel} and 65% by volume of hydrogen were passed through the suspension. After 4 hours, the catalyst was separated off and the liquid phase was analyzed. Subsequently, the separated catalyst was mixed with 120 ml of 4.3N sulfuric acid and the reaction was continued. This process was repeated every 4 hours. 5% selectivity to nitrous oxide is the upper limit
If exceeded, the reaction was stopped. The experimental values are shown in Table 2.

Example 3 Passage of NO by a drying tower and a purification tower 3.6 g of the catalyst obtained in Example 1a) was suspended in 120 ml of 4.3N sulfuric acid and stirred vigorously at 40 ° C. (3500 rpm) ) At the same time, it is passed beforehand through a drying tower filled with 35% by volume of nitric oxide @ 800 ml of silica gel and then through a purification tower filled with 1200 ml of molecular sieve 4A (from Carl Roth GmbH, Karlsruhe). 7.75 L of a mixture consisting of copper and 65% by volume of hydrogen
/ H was passed through this suspension. After 4 hours, the catalyst was separated off and the liquid phase was analyzed. Subsequently, the separated catalyst was mixed with 120 ml of 4.3N sulfuric acid and the reaction was continued. This process was repeated every 4 hours. After 50 batches, the reaction was stopped. At this point, the selectivity to nitrous oxide was 0.41%. Table 2 shows the obtained results.

[0035]

[Table 2]

From Table 2 above, the catalyst previously exposed to NO previously passed only through the drying tower was:
It can be seen that the working life is short with comparable hydroxylamine selectivity and space-time yield. Thus, it is clear that the molecular sieve does not contain NO, an additional impurity that promotes catalyst aging. In order to clearly show the effect of purification, unpurified NO
Table 3 shows the impurity content in NO and in NO purified by different methods (silica gel or drying tower with molecular sieve 4A).

[0037]

[Table 3]

The values in the table were obtained in columns of the type indicated below or by separating the NO analyzed in the manner described above.

Molecular sieve 5A; 50 m; 0.32 mm; (inert gas) activated carbon; 2 m; 4 mm; (hydrogen) Polaplot Q; 50 m; 0.53 mm; (carbon dioxide) Al ₂ O ₃ / KCl; 100 m; 0.53 mm; (hydrocarbon) GC atomic emission method (H ₂ S) IR spectroscopy (N ₂ O, NO ₂ )

[Procedural Amendment] Submission of translation of Article 34 Amendment of the Patent Cooperation Treaty

[Submission date] November 17, 1999 (November 17, 1999)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Tome, Alfred Germany, D-67346, Speyer, Garbriel-Biel-Strasse, 4 (72) Inventor Achhammer, Gunter Germany, D-68309, Mannheim, Kirch Platz, 17 (72) Inventor Müller, Ulrich Germany, D-67434, Neustadt, Birkenweg, 16 (72) Inventor Hofstadt, Otto Germany, D-67122, Altrip, Ziegereistrasse, 12

Claims (9)

[Claims] 1. A process for producing a hydroxylammonium salt by catalytically reducing nitric oxide with hydrogen in the presence of an acid and a hydrogenation catalyst, comprising the steps of: Purifying the nitric oxide by at least one treatment with a porous oxide or activated carbon. 2. The method according to claim 1, wherein a molecular sieve or silica gel is used as the porous oxide. 3. The method according to claim 1, wherein the nitric oxide is introduced into a drying step before purification. 4. The process according to claim 2, wherein the nitric oxide is first passed through silica gel and then through a molecular sieve, in particular a molecular sieve having a pore size of 0.4 nm. 5. The method according to claim 1, wherein the purification is carried out at 20 to 500 ° C., especially at 20 to 150 ° C. 6. The process according to claim 1, wherein said purification is in the range from 100 mbar to 100 bar, in particular 8 mbar.
A method according to any of claims 1 to 5, which is carried out in the range from 00 mbar to 2 bar. 7. The process according to claim 1, wherein the catalytic reduction is carried out at a temperature in the range from 30 to 80 ° C. and a pressure in the range from 1 to 30 bar. 8. The process according to claim 1, wherein the hydrogenation is carried out in a molar ratio of hydrogen to nitric oxide in the range of 3.5: 1 to 5: 1. 9. The method according to claim 1, wherein sulfuric acid, nitric acid or phosphoric acid is used as the acid.
9. The method according to any one of items 8.