DE1814489C3 - Process for the production of lactams - Google Patents

Description

The invention relates to a process for the preparation of lactams by passing cyclic ones over them Ketoxime in the gas phase in the presence of steam, optionally mixed with a Inert gas, over a boron oxide rearrangement catalyst.

It is known that cyclic ketoximes, in particular cyclohexanone, at 200 - 400 ⁰ C can rearrange in the gas phase over solid catalysts in the corresponding lactams. Catalysts made from boric acid or boron oxide on supports have proven to be particularly effective. For the rearrangement into the lactams, the oxime vapors are passed over these catalysts with or without a carrier gas at elevated temperature and normal, over or underpressure. It is also known that hydrous oxime can be used for the rearrangement or that water vapor can be passed as a carrier gas with the vaporized oxime over the catalyst. The presence of water vapor increases the rearrangement performance of the catalysts considerably. The addition of steam, which is indispensable for the economic viability of the catalytic rearrangement process, is bought at the cost of a decisive disadvantage, namely the increased volatility of the boric acid from contact. It is known that both boric acid and boron oxide are volatilized by water vapor at an elevated temperature. Therefore, the B2O3 content of the contacts drops to such low values within a short time that the catalysts become ineffective and have to be replaced by fresh contact.

According to an older proposal of our own, the B ₂ O ₃ -VeHuSt is repeatedly supplemented by pyrolysis of an orthoboric acid alkyl ester at regular intervals, especially during the reactivation treatment necessary to burn off the carbon-containing deposits from the contact. With this type of regeneration, the boron oxide is reapplied in a separate process step in which the boric acid ester is fed to the catalyst, which is fluidized by means of an inert gas, at a temperature between 200 ° and 800 ° C. The alcoholic component of the ester is converted into cracking products that cannot be used any further.

The invention relates to a process for the preparation of lactams by passing cyclic ketoximes in the gas phase in the presence of water vapor, optionally mixed with an inert gas, over a boron oxide relocation catalyst, which is characterized in that the water vapor is added either alone or in a mixture with oxime vapor 280 to 45O ⁰ C before the transfer over the rearrangement catalyst, optionally together with an inert gas, passes over the X-ray crystalline modification of the boron oxide, with sole transfer

processing of the water vapor this after the transfer in the range of the rearrangement temperature mixes with the oxime vapor and then passes the vapor mixture over the catalyst.
This process offers a simple way of _{keeping the B 2} O ₃ content of the catalysts at a constant level even during the rearrangement. In the process according to the invention, the catalyst can be used both in a fixed bed and in a fluidized bed. The temperature of the crystalline

ίο Boron oxide can be the same as the temperature of the catalyst, but can also be higher or lower. The process can be carried out at atmospheric pressure, but also at higher or lower pressure.

Investigations of the water vapor volatility of the

Boron oxide at the temperatures required for the rearrangement of the ketoximes to the lactams of 200 to 450 ° C have shown that volatility increases with increasing temperature. The transported The amount of boric acid is also dependent on the

the water vapor partial pressure dependent in the sense that the transported amount increases with increasing partial pressure. Under the given rearrangement conditions, the gas stream on the catalyst is saturated with a defined amount of boric acid. Evaporation of the boron oxide at the contact could be avoided if the incoming gas stream already contains the saturation amount of boric acid. But that means that you have to pass the gas stream over B ₂ O ₃ of essentially the same temperature as that of the catalyst to the

To achieve saturation of the gas stream with boric acid before it reaches the catalyst. The difficulty lies in the fact that the normally available softened B ₂ O 3 modification, the so-called glassy boric oxide, at temperatures above 25O ⁰ C slowly and is present already largely melted at 27O ⁰ C. For a technical application, vitreous B ₂ O ₃ is therefore only poorly suited for saturating the gas stream, since one would have to use extremely large containers _{to achieve a sufficiently large B 2 O3 surface.} By using an inert carrier material, the boron oxide could be prevented from melting together, but this would in principle make the production of a catalyst necessary, which one wants to avoid, since with the catalysts in question it is less the raw material costs than the production costs for their price are responsible. In addition, the use of boron oxide on a carrier in the technical implementation would be made more difficult by the fact that the carrier material remains after the boron oxide has volatilized and has to be removed before a new charge.

The inventive method therefore uses the X-ray crystalline modification of boron oxide, in which the disadvantages described do not occur, since their melting point is 450-470 ° C and below the Melting point no softening or sintering occurs. In addition, vaporized X-ray leaves behind

Gene crystalline boron oxide leaves no residue, so that the evaporated portion can be supplemented by simply adding fresh, X-ray crystalline boron oxide. The saturation of the water vapor required for the rearrangement with boric acid can therefore be carried out in a conventional manner without difficulty, for example a tower-shaped saturator heated to the desired temperature can be filled with lumpy, X-ray crystalline B ₂ O ₃ and the water vapor stream or the mixture of oxime vapor and water vapor pass through. But you can also make the saturation in the fluidized bed. If the rearrangement of the oxime is to be carried out in the presence of inert gas, such as nitrogen or carbon dioxide, it is also possible to pass the inert gas partially or completely together with the water vapor or with the oxime-water-vapor mixture over the X-ray crystalline boron oxide.

The amount of water vapor is not particularly critical and can vary within wide limits; however, the proportion of water vapor, based on the oxime used, is preferably between 1 and 30% by weight. The X-ray crystalline modification of B ₂ O ₃ is known. X-ray crystalline B ₂ O ₃ can be obtained _{from H 3} BO ₃ in accordance with the instructions in the “Handbook of Preparative Inorganic Chemistry”, editor G. Brauer, 2nd edition, Stuttgart 1960, page 699. Once one has X-ray crystalline B ₂ O ₃ to the jointing, the further manufacture takes place in einfachster manner by inoculating a H ₃ BOJ melt at 225-250 ⁰ C with a small amount of X-ray crystalline B ₂ O _3. The melt solidifies after a short time to the desired X-ray crystalline modification of the boron oxide, which is identified on the basis of its melting point or its characteristic X-ray diagram (crystalline B ₂ O ₃ belongs to the trigonal crystal system with a = 4.325 A and c = 8.317 A as the edge lengths of the unit cell) can be.

When carrying out the process according to the invention, care must be taken to ensure that no temperature drops occur between the saturator and the catalyst, since here some of the boric acid contained in the water vapor-containing gas stream would be deposited again in accordance with the equilibrium of the low temperature. The consequence would be that the gas stream would become saturated again with boric acid at the catalyst, which would be equivalent to a B ₂ O ₃ loss from the catalyst. In a specific embodiment of the method according to the invention passes the water vapor at a temperature of 280-450 ⁰ C on an X-ray crystalline modification of the boron oxide, this water vapor mixed in the rearrangement temperature with the Oximdampf and then brings the vapor mixture with the catalyst in contact. Both water vapor and the oxime vapor can be mixed with inert gas, for example nitrogen or carbon dioxide. The gaseous oxime introduced upstream of the catalyst zone can be essentially anhydrous. In this case, the temperature of the X-ray crystalline boron oxide in the saturator is essentially that of the catalyst. However, if the oxime still contains z. B. small amounts of water from its production, the temperature of the X-ray crystalline boron oxide should be so far above the temperature of the catalyst that the amount of boron oxide transported by the oxime-free, water-vapor-containing gas stream corresponds to that after mixing with the oxime vapor containing small amounts of water vapor in the Temperature of the catalyst can be transported.

In another preferred procedure, the water vapor is not passed alone, but S together with the oxime vapor, optionally mixed with inert gas, via X-ray crystalline boron oxide and then over the catalyst. In this case you only have to make sure that in the Catalyst layer and in the layer of X-ray crystalline boron oxide are essentially the same temperatures to rule. If in this simple way of performing the method according to the invention X-ray crystalline boron oxide decreases in its effectiveness because there are coking products on it separate, they can be eliminated by burning them off. But the burning down is at temperatures below the melting temperature of the X-ray crystal boron oxide.

A suitable method is e.g. B. the slow burning with nitrogen oxides. Assuming the burning in a fluidized bed before, so one can to the swirling, 150-450 ⁰ C hot B ₂ O spray ₃ particles nitric acid by the evaporating liquid droplets over-temperature, and thus a-melting, ₃ zen of B ₂ O slightly is to be avoided.

Production of the X-ray crystalline modification of boron oxide:

250 g of crystallized boric acid (H ₃ BO ₃ ) were placed in a 500 ml flat porcelain dish

jo heated oven for fourteen days at 230 to 24O ⁰ C, the porcelain dish was covered by a loose overlying glass plate. This gave 140 g of a solid, white product which, on the basis of its characteristic X-ray diagram, was identified _{as an X-ray crystalline modification of B 2} O _3. Its melting point was determined to be 455 ° C.

The further preparation was carried out in such a way that after the crystallized boric acid had melted, which was carried out as described above, X-ray crystalline B ₂ O ₃ in an amount of 10%, based on the amount of boric acid used, was added as seed crystals. Crystallization then occurred within about 12 to 24 hours.

example 1

a) Without saturator: Over the course of 12 hours, over 30 g of a catalyst which was fixedly arranged in a tube furnace and consisted of 12.9% B ₂ O ₃ on titanium dioxide as a support, 245.6 g of cyclohexanone oxime and 50.0 g of water were added 40 Torr and a catalyst temperature of 340 ⁰ C passed. The quantitative determination of the B ₂ O ₃ content in the catalyst then resulted in a value of only 8.3%.

$ 5 b) With saturator: The experiment was carried out as described under a), but the water vapor was passed through a tube filled with granular, X-ray crystalline boron oxide and heated to the temperature of the catalyst as a saturator. In this experiment, 248.5 g of cyclohexanone oxime and 54.0 g of water were passed over the catalyst over the course of 11 hours. The quantitative determination of the B ₂ O ₃ content then showed that it had increased slightly from 12.9% in fresh contact to 13.7%.

Example 2

a) Without saturator: In the course of 18 hours, more than 30 g of 12.9% B ₂ O _{3 were converted} to titanium dioxide

existing catalyst at 40 Torr and 34O ⁰ C passed 376.6 g of cyclohexanone oxime and 76.3 g of water as steam. The catalyst was then ^{freed from carbon deposits by heating to 700 °} C. in air for one hour and reused for the rearrangement. A further 132.1 g of oxime and 2.5.0 g of water were passed in vapor form over the catalyst over the course of 5 hours, but the activity of the catalyst had dropped to such an extent that the experiment had to be terminated. Dip quantitative determination of the B2O3 content in the catalyst only resulted in a value of 2.2%.

b) With saturator: In the course of 16 hours, 369.1 g of cyclohexanone oxime were passed over 30 g of the same catalyst and under the same pressure and temperature conditions as in a). At the same time 71.9 g of water vapor were at this time a heated to 34O ⁰ C tower, which was filled with granular, X-ray crystalline boron oxide, and sent mixed immediately before the catalyst zone with the Oximdampf. The catalyst was then freed from carbon deposits by heating to 700 ^° C. in air for one hour and reused for the rearrangement. In the course of a further 17 hours, 378.5 g of cyclohexanone oxime and 75.3 g of water vapor saturated with boron oxide were passed over the contact in the manner described. In contrast to the procedure without prior saturation of the water vapor with boron oxide, there were no signs of a decrease in the rearrangement effectiveness of the catalyst. The quantitative determination of the I ^ Or content in the catalyst showed 13.0% B-1O3, a virtually unchanged chlorine oxide content compared to the initial value of 12.9%.

Example 3

35

a) Without saturator: In the course of 20.7 hours, at atmospheric pressure and 340 ⁰ C over 20 g of a 7.0% B2O3 on titanium dioxide catalyst consisting total of 642.8 g of cyclohexanone oxime supplied as vapor, nitrogen in an amount of 15 Nl / h served as a carrier gas for the oxime. Upstream of the catalyst zone, a stream of nitrogen, likewise 15 Nl / h, which had been moistened with water at 25 ° C. by passing through a wash bottle, was mixed into this gas stream. In this way, in the course of the rearrangement, 8.9 g of water were passed over the catalyst together with the oxime (corresponding to 1.39% based on the amount of oxime). During the rearrangement, the catalyst was freed from carbon deposits ^{four times by heating to 600 ° C. in air for one hour.} After the rearrangement, only a value of 4.8% was found in the quantitative determination of the B2O3 content.

b) With saturator: were within 22.9 hours over 20 g of a 7.0% B ₂ O ₃ existing on titania catalyst at normal pressure and 340 ⁰ C. 648.7 g of cyclohexanone oxime together with a carrier gas flow of 15 Nl / h of nitrogen directed. Simultaneously, a second nitrogen flow of 15 Nl was / h with water vapor at 25 ° C loaded on a heated to 34O ⁰ C tower which was filled with granular, X-ray crystalline B2OJ sent ,, mixed immediately before Katalysatorzonc with the oxime-containing gas stream and together passed over the catalyst. In this way, 9.4 g of water (corresponding to 1.4! 5%, based on the amount of oxime) were passed over the catalyst in the course of the rearrangement. As described under a), the catalyst was burned off four times. After the rearrangement had ended, the quantitative analysis showed a B2O3 content of 6.6% compared to 4.8% without a saturator.

Example 4

In a 2 cm wide reaction tube, a layer of 10 g of catalyst and a layer of 40 g X-ray crystalline boron oxide arranged so that the two layers are only separated from each other by a sieve was.

The catalyst consisted of 18% boron oxide on titanium dioxide as support material and had a grain size of 0.6-1 mm. The X-ray crystalline boron oxide upstream of the catalyst layer had a grain size of 1-5 mm. To carry out the rearrangement reaction, the gas mixture of cyclohexanone oxime vapor (22 g / h), water vapor (2.3 g / h) and nitrogen (50 l / h) was initially added. passed through the layer of X-ray crystalline boron oxide and then through the catalyst layer, the two layers 320 - 35O ⁰ C were maintained.

The catalyst on which the oxime rearrangement took place was at time intervals of 12 hours by burning at 600 - 700 ⁰ C regenerated.

In the first 6 hours when the catalyst was still new the oxime conversion was 82%. After the catalyst had been in operation for 36 hours and for the third time had been regenerated, the oxyme conversion was 84% in the following 6 hours.

In a comparative experiment in which no X-ray crystalline boron oxide was placed in front of the catalyst layer was, the oxyme rate was already after the 2nd regeneration, i. H. so after 24 hours, below 10%.

Claims (1)

Claim: Process for the production of lactams by passing cyclic ketoximes in the gas phase into Presence of steam, optionally mixed with an inert gas, over a boron oxide rearrangement catalyst, characterized, that the water vapor either alone or in a mixture with oxime vapor at 280 to 450 "C before the transfer over the rearrangement catalyst, optionally together with an inert gas, via the X-ray crystalline modification of the boron oxide conducts, with the sole transfer of water vapor this after the Transition in the range of the rearrangement temperature mixes with the oxime vapor and then the Steam mixture passes over the rearrangement catalyst.