EP0828707A1

EP0828707A1 - Process for producing cyclohexanonoxim and caprolactam

Info

Publication number: EP0828707A1
Application number: EP96917419A
Authority: EP
Inventors: Franz-Josef Weiss; Hugo Fuchs; Eberhard Fuchs; Tom Witzel
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 1995-06-02
Filing date: 1996-05-24
Publication date: 1998-03-18
Also published as: MX9708928A; PL323676A1; EA199700443A1; CN1186484A; AU6000196A; WO1996038407A1; CZ359197A3; JPH11506440A; KR19990022175A; BR9608960A; TW342383B; DE19520271A1

Abstract

The production of cyclohexanonoxim by the reaction of cyclohexanone with a hydroxyl ammonium salt, i.e. hydroxyl ammonium formiate, and the production of caprolactam by the Beckmann rearrangement of cyclohexanonoxim in a C1-C4 carboxylic acid.

Description

Process for the preparation of cyclohexanone oxime and caprolactam

description

The present invention relates to a process for the preparation of cyclohexanone oxime by reacting cyclohexanone with a hydroxylammonium salt.

The invention further relates to a process for the production of caprolactam.

DE-C 14 93 198 describes, according to claim, the preparation of cyclohexanone oxime by reacting cyclohexanone with an aqueous solution of a hydroxylamine salt of an inorganic or organic acid, wherein a residual solution containing aqueous acid obtained after the removal of the oxy is obtained Performs salt / acid separation, uses the separated amount of acid to prepare the hydroxylamine salt starting solution. A disadvantage of this process is the great expenditure on equipment and the use of sulfuric acid and ammonia in the workup of the acid / salt mixture when a carboxylic acid, in particular acetic acid, is used, so that ammonium sulfate or a phosphate - in smaller amounts than previously - but still has to be disposed of.

EP-A 620 042 describes the preparation of hydroxylammonium salts by reduction of nitrogen monoxide with hydrogen in the presence of a hydrogenation catalyst in strong mineral acids or aliphatic Ci-Cs monocarboxylic acids such as formic and acetic acid, the hydrogenation catalyst being obtainable by treatment a platinum metal salt with finely divided sulfur and subsequent reduction of the platinum metal salt to metallic platinum metal. However, neither the explicit production of hydroxylammonium formate nor the production of cyclohexanone oxime and caprolactam is described.

It was therefore an object of the present invention to provide a process for the preparation of cyclohexanone oxime in which less than no ammonium sulfate or any other salt to be disposed of is obtained even less than in the prior art. Furthermore, a process for the production of caprolactam from the cyclohexanone oxime thus obtained should be made available, in which the accumulation of ammonium sulfate should also be avoided or at least minimized. Accordingly, a process for the preparation of cyclohexanone oxime by reacting cyclohexanone with a hydroxylaπimonium salt has been found by using hydroxylammonium formate as the hydroxylammonium salt.

Furthermore, a process for the preparation of cyclohexanone oxime by reacting cyclohexanone with hydroxylammonoformate was found, and also a process for the production of caprolactam.

According to the invention, cyclohexanone oxime is prepared by reacting cyclohexanone with hydroxylammonium formate in aqueous formic acid.

The molar ratio of hydroxylammonium formate to cyclohexanone is usually chosen in the range from 1.3: 1 to 1: 1, preferably from 1.2: 1 to 1: 1.

Furthermore, according to the invention, the hydroxylammonium formate is converted into aqueous formic acid, the concentration increasing

Hydroxylammonium formate is generally selected in the range from 10 to 16, preferably from 12 to 14,% by weight. The concentration on

Formic acid in the aqueous formic acid solution is in the

Rule 10 to 15, preferably from 12 to 14 wt .-%.

The temperature is generally chosen in the range from 70 to 90, preferably from 75 to 80 ° C.

The pressure is generally selected in the range from 90 to 120, preferably from 100 to 120, particularly preferably from 105 to 110 kPa.

The pH is usually selected in the range from 0.5 to 2.5, preferably from 1.2 to 1.8. The pH value is generally set by the buffering action of the ammonium formate / formic acid system itself, if one uses, preferably, hydroxylammonium formate solutions which come directly from the hydroxylammonium formate synthesis without further work-up.

The reaction can be carried out batchwise or continuously, in one or more stages, preferably in two stages, particularly preferably continuously and in two stages.

In a preferred embodiment, which is carried out in two stages and continuously, the residence time is usually 1.5 to 3 hours per stage. According to previous observations, the yields are generally in the range from 94 to 98, based on the cyclohexanone used.

In a preferred embodiment, hydroxylammonium formate is used, which is obtained by reducing nitrogen monoxide with hydrogen in the presence of a hydrogenation catalyst in aqueous formic acid.

10 The preparation of hydroxylammonium formate is usually carried out by suspending the hydrogenation catalyst in aqueous formic acid and introducing a mixture of nitrogen monoxide and hydrogen into the suspension.

In the preparation of hydroxylammonium formate, a molar ratio of hydrogen to nitrogen monoxide of 1.5: 1 to 6: 1, particularly preferably from 3: 1 to 5: 1, is preferably maintained.

The formic acid content is generally chosen in the range from 20 50 to 500, preferably from 100 to 250 g of formic acid per liter of formic acid / water mixture. According to previous observations, hydrogenation at concentrations of more than 60% by weight of formic acid is no longer possible.

25 The hydrogenation of nitrogen monoxide is generally carried out at a temperature in the range from 30 to 80, preferably from 35 to 60 ° C. Furthermore, the pressure during the hydrogenation is usually chosen in the range from 100 to 3000, preferably from 150 to 2000 kPa.

30

The ratio of formic acid to catalyst is usually chosen in the range from 10 to 100, preferably from 30 to 80, g of platinum-graphite catalyst per liter of the aqueous formic acid. In a preferred embodiment, catalyst is treated

35 before hydrogenation in acidic solution, suitably in formic acid, with hydrogen ("activation").

The usual hydrogenation catalysts known for the preparation of hydroxylammonium salts can be used as the catalyst.

40 zen. A hydrogenation catalyst is particularly preferred, produced by the process described in DE-A 4,311,420. According to this process, platinum is treated with finely divided sulfur and then the platinum thus treated is reduced to metallic platinum.

45 Suitable platinum salts are, in particular, the water-soluble salts such as the halides, nitrates and sulfates. Examples include:

- Platinum (IV) compounds such as hexachloroplatinic acid and its alkali metal and ammonium salts, tetrachloroplatinate or tetrachlorodihydroxyplatinic acid; and

Platinum (II) compounds such as tetrachloroplatinic acid and its alkali metal salts or plati (II) chloride;

In principle, mixtures of essentially salts with other metal salts, for example arsenic, antimony, selenium or tellurium salts, can also be used.

According to this preferred method, finely divided sulfur, for example the commercially available "sulfur bloom", is used as the sulfur used for partial poisoning. It is preferred to use sulfur with a particle size of less than 500 μm, preferably less than 50 μm, particularly preferably one

Particle size distribution in which 20% of the particles are smaller than 1 μm, 50% of the particles are smaller than 5 μm and 90% of the particles are smaller than 10 μm. Suitable sulfur is commercially available, for example, as "Kumulus WG®" network sulfur (BASF) or using methods known per se, in particular sieves, from, for example, sulfur bloom or finely ground sulfur.

As a rule, the platinum salt is treated with the finely divided sulfur in aqueous solution by bringing the aqueous platinum salt solution into contact with the finely divided sulfur. The sulfur can also be used as a colloidal sulfur solution. The sulfur is preferably added in the form of an aqueous suspension.

In principle, other solvents can be used instead of the preferred solvent water, or water can be added to the water. The sulfur can also be added to the solution of the platinum metal salt as a dry powder.

Furthermore, substances which improve the solubility or dispersibility of the starting compounds can be added to the reaction mixture. According to previous observations, all common surfactants are particularly suitable for this purpose in order to improve the solubility and wetting of the sulfur. Suitable surfactants, which are also referred to as dispersants, can be found, for example, in Ullmann's Encyclopedia of Industrial Chemistry, 4th edition, volume 23, Verlag Chemie, Weinheim, 1983, pp. 31-39. Examples include:

Polyacrylates, polyvinyl sulfonates, polyvinyl pyrrolidone, TAMOL ^® (BASF), Schaeffer salt and lignin sulfonates.

In a particularly preferred embodiment, the surfactant used is lignin sulfonates (known, for example, from Ulimann, Encyclopedia of Industrial Chemistry, 4th edition, vol. 16, pp. 253 ff., Verlag Chemie, 1978), preferably alkali metal lignosulfonates such as sodium and potassium lignin sulfonate , since they can be easily removed with the washing water when washing the finished catalyst and because of their easy degradability they do not represent an environmental burden.

The surfactants are generally added to the reaction mixture before the sulfur is added to the platinum salt or advantageously to the aqueous sulfur suspension.

The weight ratio of surfactant to sulfur is generally chosen in the range from 0.1 to 50, preferably from 1 to 15,% by weight.

The temperature during the treatment of the platinum salt with the finely divided sulfur is usually chosen in the range from 20 to 95 ° C., preferably from 40 to 95 ° C., particularly preferably from 50 to 85 ° C.

The pH during the treatment of the platinum salt with the finely divided sulfur is generally chosen in the range from 1.5 to 11.5, preferably from 2.5 to 8.5, particularly preferably 4.5 to 8.5 , very particularly preferably from 7.0 to 7.5.

The duration of treatment of the platinum salt with the finely divided sulfur, i.e. the period from the addition of the finely divided sulfur to the addition of the reducing agent is generally chosen in the range from 0.5 to 60 min, preferably from 2 to 15 min.

The molar ratio of platinum to sulfur is generally selected in the range from 90 to 10, preferably from 75 to 35, mol%. Following the partial poisoning with sulfur, the platinum salt is reduced to metallic platinum by expediently adding a reducing agent to the reaction mixture obtained after treating the platinum salt with finely divided sulfur.

Suitable reducing agents are usually all known reducing agents for platinum salts to platinum, e.g. Hydrazine, formaldehyde, formic acid or an alkali metal or alkaline earth metal formate such as. Sodium, potassium and calcium formate, particularly preferably formic acid.

The molar ratio of platinum to reducing agent is generally chosen in the range from 0.5 to 100, preferably from 5 to 85 mol%.

The temperature during the reduction is usually chosen in the range from 20 to 95 ° C., preferably from 40 to 95 ° C., particularly preferably from 50 to 85 ° C.

The pH during the reduction essentially depends on the amount and type of reducing agent. For example, when using formic acid, the pH is generally selected in the range from 0.5 to 3.5, preferably from 1.0 to 2.5.

When the reduction has ended, the catalyst is generally worked up in the customary manner, for example by filtering it off from the reaction mixture and washing it appropriately with water.

In a preferred embodiment, the reduction and, if desired, the treatment with finely divided sulfur is carried out in the presence of a catalyst support such as graphite or activated carbon, preferably graphite. The platinum salt is particularly preferably mixed with finely divided graphite before the treatment with finely divided sulfur, generally with a particle size in the range from 0.1 to 1000, preferably from 0.1 to 300 μm, particularly preferably from 5 to 100 μm.

The molar ratio of carbon (or graphite or activated carbon) to platinum is generally chosen in the range from 99.99 to 10 mol%, preferably 99.99 to 30 mol%, especially if it is platinum, preferably 99, 99 to 90 mol%, particularly preferably from 99.98 to 95.0 mol%.

In a further preferred embodiment, the formic acid used and released in the preparation of cyclohexanone oxime is separated from the reaction mixture obtained. The separated formic acid can then be used again in the production of hydroxylammonium formate and cyclohexanone oxime. Especially preferred is a procedure in which the formic acid is esterified by

(a) the cyclohexanone oxime is separated off from the reaction mixture obtained to obtain a mixture A, essentially comprising water and formic acid, and

(b) the mixture A is mixed with a C 1 -C ₄ -alkanol and an esterification of the formic acid to an formic acid ester is carried out under the usual conditions to obtain a mixture B,

(c) separating the formic acid ester obtained in step (b) from mixture B by distillation,

(d) the formic acid ester obtained from step (c) is saponified in a manner known per se to obtain a mixture C comprising essentially formic acid and the corresponding alcohol used in step (a),

(e) the formic acid from stage (d) is separated from the mixture and used to prepare hydroxylammonium formate and / or cyclohexanone oxime.

The cyclohexanone oxime is usually obtained by phase separation processes, for example in a phase separator at 70 to 75 ° C. in the upper phase, from the reaction mixture obtained in the preparation of the cyclohexanone oxime. In addition, a mixture A is obtained which essentially consists of water, formic acid and, if appropriate, impurities such as ammonium formate and traces of hydroxylammonium formate.

According to the invention, this mixture A is mixed with a C 1 -C 4 -alkanol such as methanol, ethanol, n-, i-propanol, n-, i-, sec.- and tert. Butanol, the alkanol usually being used in an excess of 10 to 40, preferably 20 to 40,% by weight, based on the formic acid.

Formic acid is particularly preferably esterified with methanol, since methyl formate can be easily separated off because of its low boiling point (31.8 ° C. at 100 kPa).

The esterification is carried out according to methods known per se, for example by heating the mixture A to which the alkanol has been added to a temperature in the range from 40 to 80 ° C. and by maintaining a pressure in the range from 150 to 500 kPa. Esterification produces a mixture B containing the formic acid ester. The formic acid ester is removed by distillation from mixture B. In a preferred embodiment, the formic acid ester formed is removed continuously during the esterification.

In general, the esterification is carried out acid-catalyzed by using up to 2% by weight, based on formic acid, of an acid, preferably a mineral acid such as sulfuric acid, hydrochloric acid or phosphoric acid.

This procedure is preferably carried out in a stirred tank reactor with a distillation column attached, the C 1 -C ₄ -alkyl formate formed being continuously separated off by distillation.

It is also possible to use a strongly acidic ion exchanger such as Amberlite ^® or Duolite ^® instead of an acid. In this case, the reaction will generally be carried out in a tubular reactor, the C 1 -C ₄ -alkyl formate formed being continuously separated off by distillation.

The pH is usually in the range of 0.5 to 2.5.

The formic acid ester, C 1 -C ₄ -alkyl formate, is usually saponified in a manner known per se, ie cleaved into formic acid and C ₄ -C ₄ -alkanol. The saponification can be carried out in an acidic as well as in a basic environment.

In a preferred embodiment, the saponification can be carried out in a stirred tank, with either acid or base catalysis being carried out in a manner known per se.

In a further preferred embodiment, the saponification can be carried out in a fixed bed reactor which contains a basic ion exchanger.

In both preferred embodiments, the reactors used preferably contain a rectification attachment in order to separate the system H ₂ θ / HCOOH / Cι-C ₄ alkanol / formic acid ester.

After the hydrolysis, the formic acid is separated off from the reaction mixture by customary methods, for example by distilling off the lower-boiling constituents of the reaction mixture. The separated formic acid, preferably in the form of an aqueous solution, is preferably used for the synthesis of hydro- xylammonium formate and / or for the synthesis of cyclohexanone oxime, so that formic acid is circulated.

In a particularly preferred embodiment, methanol is used in the esterification and is obtained in the saponification

(Temperature range: 40 to 80 ° C, pressure range: 100 to 500 kPa, pH range: 8 to 11) accordingly methanol back and methyl formate as ester. In this procedure, methyl formate, which has a very low boiling point, can be distilled off overhead, methanol removed as a side stream, while the aqueous formic acid remains in the bottom and can preferably be recycled for the synthesis of hydroxylamine.

This process has the advantage that the recovered formic acid is free of by-products, especially of other organic impurities ("TOC" total organic carbon). Since the by-products are removed, the accumulation of undesired by-products is avoided in a circular manner.

According to the invention, caprolactam is prepared by Beckmann rearrangement of cyclohexanone oxime in the presence of a Cχ-C ₄ -carboxylic acid such as formic acid, acetic acid, propionic acid or butyric acid, preferably formic acid and acetic acid, particularly preferably formic acid.

The molar ratio of cyclohexanone oxime to carboxylic acid is preferably selected in the range from 1: 1 to 1:30, preferably from 1: 1 to 1:10.

The cyclohexanone oxime is usually used as a C ₄ -C ₄ carboxylic acid solution, the concentration of the generally aqueous carboxylic acid solution generally being in the range from 10 to 70% by weight, preferably from 15 to 50% by weight. The same carboxylic acid which is used as the solvent for the rearrangement is particularly preferably used, formic acid being particularly preferred.

The temperature is generally chosen in the range from 50 to 150, preferably from 70 to 120 ° C.

The pressure is generally selected in the range from 100 to 1000, preferably from 100 to 200 kPa.

According to previous observations, the pH value is freely established; the use of buffers is usually not necessary. The rearrangement can otherwise be carried out according to methods known per se, ie optionally continuously or discontinuously, in one or more stages, preferably in multiple stages.

The residence time is generally 2 to 10, preferably 3 to 6 hours.

In a preferred embodiment, use is made of cyclohexanone oxime which has been prepared by one of the processes according to the invention described above and is documented in the subclaims.

In a preferred embodiment, after the rearrangement to caprolactam, the C 1 -C ₄ -carboxylic acid used at the beginning of the rearrangement is distilled off from the reaction mixture, and it is preferably used again for the rearrangement of the cyclohexanone oxime.

The caprolactam produced according to the invention can be worked up by methods known per se, such as extraction of the crude lactam with a solvent, for example by the processes described in the following documents: EP-B 22,261, DE-A 37 35 054, US 28 13 858, EP-B 411 455.

The caprolactam produced according to the invention serves as a starting material for the production of polycaprolactam and corresponding copolymers.

The process according to the invention for the preparation of cyclohexanone oxime has the advantage that it works without the accumulation of salt. Furthermore, the carboxylic acids used can be circulated. A further advantage lies in the rearrangement of the oxime with a carboxylic acid, since the disposal of ammonium sulfate, as in the usual processes of the prior art, is also avoided.

Examples

Example 1 - Preparation of hydroxylammonium formate

640 g (calculated as dry matter) of a finely divided graphite support (0.1 to 300 μm) were suspended in 500 ml of water and 100 ml of king's water, 0.5% by weight of platinum as hexachloroplatinic acid-hexahydrate were added and over Stirred at 80 ° C overnight. The next day the suspension was diluted with 400 ml of water, cooled to 30 ° C. and then adjusted to a pH of 7.5 with soda. 150 mg of finely divided elemental sulfur suspended in 50 ml of water (particle size distribution: 20% <1 μm; 50% <5 μm; 90% <10 μm) were then added to the reaction mixture. After 10 minutes, 100 ml of 99 wt. -% Formic acid added to the reaction mixtures.

50 g of the catalyst thus treated were 25 wt. In 1250 ml. -% formic acid suspended and treated with H ₂ at 40 ° C (so-called "activation").

100 l / h of a mixture of 70% by volume H ₂ (99.95% pure) and 30% by volume NO (99.5% pure) were then passed into the suspension.

After a total of 300 l of the gas mixture had been introduced, 1320 ml of a solution of the following composition were obtained:

145.3 g / 1 HCOOH 51.2 g / 1 NH ₂ OH (as NH ₂ OH-HCOOH) 4.8 g / 1 NH ₃ (as HCOONH ₄ )

The total amount of exhaust gas was 99.8 l.

Selectivities:

65.3% to NH ₂ OH (as NH ₂ OH-HCOOH) 10.7% to NH ₃ (as HCOONH ₄ ) 24.0% to N ₂ 0

Space-time yields:

0.84 MOI / I _{RR f} i. • h, based on NO sales

0.55 MOI / I _{RR f} i. • h, based on the NH ₂ OH formed.

Example 2 - Preparation of cyclohexanone oxime

Cyclohexanone and hydroxylamine were mixed in a 2 liter stirred tank reactor. Hydroxylamine was added as a hydroxylammonium formate solution.

The following conditions were met:

Stirring speed: 100 rpm

Temperature: 80 ° C pressure: normal pressure

Residence time: 2 hours. The reaction was carried out by first adding excess NH ₂ OH (20 mol%) to the cyclohexanone in order to implement it completely. After the cyclohexanone oxime formed had been separated off (as the upper phase in a phase separator), the lower phase (with the unreacted NH ₂ OH) was fed back into the stirred tank reactor together with fresh hydroxylammonium formate solution.

Yield: approx. 92%, based on cyclohexanone.

Example 3 - Preparation of Caprolactam

A 20% by weight solution of cyclohexanone oxime (from Example 2) in formic acid (100% by weight A. acid) was heated under reflux at a temperature of 105 ° C. for 5 hours. The formic acid was then distilled off and reused for rearrangement, and the crude lactam obtained in liquid form was fed for further processing (according to the prior art: extraction with a solvent, distillation).

Claims

claims

1. A process for the preparation of cyclohexanone oxime by reacting cyclohexanone with a hydroxylammonium salt, characterized in that hydroxylammonium salt is used as hydroxylammonium formate.

2. A process for the preparation of cyclohexanone oxime according to claim 1, characterized in that the hydroxylammonium formate is obtained by reducing nitrogen monoxide with hydrogen in the presence of a hydrogenation catalyst in aqueous formic acid.

3. The method according to claim 2, characterized in that the hydrogenation catalyst is obtainable by essentially the following steps:

(a) treating a platinum metal salt with finely divided sulfur and

(b) subsequent reduction of the platinum metal salt to metallic platinum metal.

4. The method according to claims 1 to 3, characterized gekennzeich¬ net that one

(a) separating the cyclohexanone oxime from the reaction mixture obtained to obtain a mixture A, essentially comprising water and formic acid, and

(b) the mixture A is mixed with a C 1 -C ₄ -alkanol and an esterification of the formic acid to an formic acid ester is carried out under the usual conditions while maintaining a mixture B,

(d) the formic acid ester obtained from step (c) is saponified in a manner known per se to obtain a mixture C comprising essentially formic acid and the corresponding alcohol used in step (a), (e) the formic acid from stage (d) is separated from the mixture and used to prepare hydroxylammonium formate and / or cyclohexanone oxime.

5. Process for the production of caprolactam by Beckmann rearrangement of cyclohexanone oxime, characterized in that the rearrangement is carried out in the presence of a C 1 -C ₄ carboxylic acid as solvent.

6. The method according to claim 5, characterized in that the cyclohexanone oxime is obtained by reacting cyclohexanone with hy droxylammonium formate.

7. The method according to claim 6, characterized in that the hydroxylammonium formate is obtained by reducing nitrogen monoxide with hydrogen in the presence of a hydrogenation catalyst in aqueous formic acid.

8. The method according to claim 7, characterized in that the hydrogenation catalyst is obtainable by essentially the following steps:

(a) treating a platinum metal salt with finely divided sulfur and

(b) subsequent reduction of the platinum metal salt to metallic platinum metal.

9. The method according to claims 6 to 8, characterized in that one

(a) the cyclohexanone oxime is separated from the reaction mixture obtained in the preparation of the cyclohexane oxime to obtain a mixture A, essentially comprising water and formic acid, and

(c) separating the formic acid ester obtained in step (b) by distillation from mixture B, (d) the formic acid ester obtained from step (c) is saponified in a manner known per se to obtain a mixture C comprising essentially formic acid and the corresponding alcohol used in step (a),

5

10. The method according to claims 5 to 9, characterized gekennzeich¬ net that from the reaction mixture obtained after the cyclization of the cyclohexanone oxime, the C 1 -C ₄ carboxylic acid used at the beginning of the rearrangement is separated off by distillation.

15 11. The method according to claim 10, characterized in that one uses the separated -CC 4 carboxylic acid for the rearrangement of cyclo-hexanone oxime.

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