GB1581788A - Process for preparing lactams from cyclic oximes - Google Patents

Abstract

A process is described for preparing lactams from cyclic oximes by rearrangement of the oxime in a liquid medium, wherein a circulating reaction mixture is forced through a vortex chamber in which it passes through a fast cyclone flow and into which the oxime is fed in, or in the vicinity of, the axis of the cyclone flow via a metering tube. The metering tube is formed in such a way that the oxime can leave the latter at least partially in a direction which forms an angle with the axis of the cyclone flow.

Description

(54) PROCESS FOR PREPARING LACTAMS FROM CYCLIC OXIMES (71) We, STAMICARBON B.V., a Netherlands Limited Liability Company of P.O. Box 10, Geleen, the Netherlands, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a process for the preparation of a lactam by the conversion of a cyclic oxime in a reaction vessel (e.g. in the presence of oleum by the so-called Beckmann Rearrangement) wherein a recycle stream of reaction product (optionally with a reaction component) to the said reaction vessel is passed through a rotation chamber wherein it undergoes a cyclonic motion and oxime feedstock is introduced into the stream undergoing cyclonic motion within the said rotation vessel through a feed pipe, and particularly relates to an improvement in such a process whereby a final product of enhanced purity may be obtained.

A process of this type is described for example in United States Patent specification 2,769,000. By such a process lactam e.g. E-caprolactam, of high quality may be produced containing only a small proportion of impurities which may result from undesired secondary reactions e.g. the decomposition of lactam that has already formed and of oxime that has not yet been converted. When use is made of a rotation chamber for mixing the oxime and the circulating reaction mixture according to the known process, the production of such impurities is limited. but nevetheless the current quality demands for lactams used in the chemical industry are very high. and the object of the invention is so to effect an improvement on such process whereby lactams of enhanced purity may be obtained Whereas in the known process the oxime is introduced to the reaction mixture in the rotation chamber along the axis of the cyclone flow through a feed pipe with one central outflow opening, the desired improvement may be obtained according to the invention by introducing the oxime at an angle to the cyclonic flow.

Thus the invention provides a process for the preparation of a lactam by the conversion of a cyclic oxime in a reaction vessel (e.g. in the presence of oleum by the so-called Beckmann Rearrangement) wherein a recycle stream of reaction product (optionally with a reaction component) to the said reaction vessel is passed through a rotation chamber wherein it undergoes a cyclonic motion and oxime feedstock is introduced into the said stream undergoing cyclonic motion within the said rotation vessel through a feed pipe, characterized in that at least a portion of the said oxime feedstock is introduced through the said feedpipe into the said stream undergoing cyclonic motion in the said rotation vessel at an angle to the axis of the cyclonic flow of the rotating stream.

Use is preferably made of a feed pipe so mounted that an angle of more than 45 , in particular from 80" to 100 , is included between the outflow direction and the axis of the cyclone flow.

A particularly suitable type of feedpipe is one which has a plurality of apertures in the pipe wall for delivering a stream of oxime to the stream undergoing cyclonic motion within the rotation vessel, preferably arranged rotation-symmetically with respect to the axis of the cyclone flow.

The invention is hereinafter particularly described and illustrated in the accompanying drawings, of which Figure 1 is a schematic representation of an installation for the preparation of Ecaprolactam from cyclohexanone oxime according to one embodiment of the invention; Figure 2 is a diagrammatical axial section through the rotation chamber shown in Figure 1, and Figure 3 shows a detail of the axial feedpipe of the rotation chamber of Figure 2.

Referring to Figure 1, a reaction vessel 1 containing a process liquid consisting substantially of a mixture of oleum (concentrated sulphuric acid with free SO) Ecaprolactam and cyclohexanone oxime that has not yet been converted. A rotation chamber 2 is disposed under the liquid level in reaction vessel 1. A circulating pump 5 draws process liquid from reaction vessel 1 through lines 3 and 4. Part of the liquid drawn off is passed to heat exchanger 7 by way of. three-way valve 6 and is cooled therein by cooling water supplied to heat exchanger 7 through line 8 and valve 9, which is always open during normal operation. The cooling water is discharged through line 10. The cooled process liquid is recycled through line 11 and fed tangentially to rotation chamber 2 wherein it undergoes cyclonic motion. Another part of the liquid drawn off by pump 5 is fed uncooled to line 11 by way of three-way valve 6 and line 12.

The ratio between the uncooled and the cooled part is adjusted by a temperature controller 13 that controls three-way valve 6. The controller 13 is provided with a sensor measuring the temperature of the liquid in line 3.

Cyclohexanone oxime is fed through line 14 to an insulated and heated buffer vessel 15. Cyclohexanone oxime is fed axially to rotation chamber 2 through lines 18 and 19 by means of a pump 16 that is driven by a motor 17 and is mounted under the liquid level in buffer vessel 15. A flow meter 20, a control valve 21 and a non-return valve 22 are provided in line 18. Control valve 21 is controlled by a flow controller 23.

Oleum is fed to the process liquid in line 4 through line 24 in which a filter 25. a flow meter 26 and a control valve 27 are incorporated. Control valve 27 is controlled by a ratio controller 28, which receives signals from both the oxime flow meter 20 and the oleum flow meter 26 and which controls the oleum flow in a constant ratio to the oxime flow.

The composition of the oleum can be controlled by means of an analyzer 29.

Through line 30 a flow of process liquid containing caprolactam and correspondirlg to the feed of oxime and oleum is continuously discharged to an installation for further processing (neutralization and purification). A sample for analysis may be drawn from line 30 through sampling line 31 and valve 32.

Line 11 is equipped with a pressure gauge 33 and a temperature meter 34. each provided with an alarm that is actuated by too high and/or too low a pressure or temperature. When the supply of oleum and/or oxime is interrupted, the circulating process liquid can be kept at the required temperature by feeding hot water, instead of cooling water, to the heat exchanger 7 through line 35 which incorporates a valve 36 that is closed under normal operating conditions.

Valve 9 must then be closed and valve 36 opened.

Referring to Figure 2, the rotation chamber 2 has a conical part 41 with a discharge opening 49 and a cylindrical part 42 with a cover 43. Feed line 44 is connected tangentially to the cylindrical part to introduce the mixture of oleum recycled reaction product from line 11 (Figure 1) into the rotation chamber. An axial feedpipe 45 passes through cover 43 into the rotation chamber, through which the oxime feedstock is fed from line 19 (Figure 1). The end 46 of this feedpipe is closed. Near the end 46 a plurality of radical apertures 47 (e.g. six) are present in the feedpipe wall, through which the oxime feedstock is introduced into the stream undergoing cyclonic motion in rotation chamber 2.

The bottom part of feedpipe 45 is shown on a larger scale in Figure 3. The end of feedpipe 45 is closed by a cap 48 that is fitted to pipe 45, e.g. by pressing or shrinking.

The apertures 47 pass radially through cap 48.

The following practical Example is provided.

The process according to the invention is carried out in an installation of the type hereinbefore particularly described and illustrated in the drawings.

The internal diameter of the cylindrical part 42 (as shown in the drawing) of the rotation chamber was 100 mm, the respective internal diameters of the tangential feed 44, feedpipe 45 and discharge opening 49 were 32 mm, 7 mm, and 23 mm, respectively. The feedpipe was closed near the end 46 and provided with six radial bores, each of 1 mm in diameter. The amount of cyclohexanone oxime supplied through line 18 was 1.3 m3 per hour, the amount of oleum (with about 26% by weight of SO3) supplied through line 24 was 0.8 m3 per hour.

The amount of process liquid recycled through line 11 was 43 m3 per hour. The temperature of the process liquid fed to the rotation chamber 2 through line 11 was 95.3"C., the temperature of the liquid flowing from reactor vessel 1 through line 3 was 1300C.

A sample for analysis was drawn from discharge line 30 at regular intervals by way of sampling conduit 31. Each sample was neutralized with ammonia water (14% by weight) and then extracted with benzene, so that a benzene-caprolactam solution was obtained, which also contained the impurities. This solution was always examined for the caprolactam content, and by means of a spectrophotometer, for the extinction at a wave length of 290 nanometers with the use of a cell with a 1 cm thick liquid layer.

A 20% by weight solution of pure caprolactam in benzene was used to adjust the spectrophotometer to 100% transmission.

The measured value was recalculated to a caprolactam content of 50% by weight. The extinction determined in this way was fully caused by the impurities.

In all 34 samples were drawn and examined at regular intervals in a period of 11 days. The average extinction was 1.0, with a standard deviation of 0.2. None of the samples showed an extinction of over 1.3.

For comparison, a similar series of analyses was carried out under exactly the same processing conditions, but using a feedpipe of known type having an axial outflow opening. Here again 34 samples were examined. In these runs however, the average extinction was 1.7 with a standard deviation of 0.6. Three samples showed an extinction of between 2.8 and 3.0.

Not only is the average extinction, which is proportional to the content of impurities, considerably higher than that of the samples drawn in the process according to the invention, but also the variation of the extinction is greater. This indicates that the product obtained was less constant in quality than in the process according to the invention.

WHAT WE CLAIM IS: 1. A process for the preparation of a lactam by the conversion of a cyclic oxime in a reaction vessel wherein a recycle stream of reaction product (optionally with a reaction component) to the said reaction vessel is passed through a rotation chamber wherein it undergoes a cyclonic motion and oxime feedstock is introduced into the said stream undergoing cyclonic motion within the said rotation vessel through a feedpipe char acterized in that at least a portion of the said oxime feedstock is introduced through the said feedpipe into the said stream undergoing cyclonic motion in the said rotation vessel at an angle to the axis of the cyclonic flow of the rotating stream.

2. A process according to Claim 1, wherein the said angle included between the outflow direction of the oxime stream and the said axis of cyclonic flow, is more than 450 3. A process according to Claim 2, wherein the said angle is from 80" to 100 .

4. A process according to any of Claims 1 to 3, wherein the said feedpipe has a plurality of apertures for the passage of oxime streams therethrough.

5. A process according to Claim 4, wherein the said apertures are disposed in the wall of the said feedpipe so that they are rotation-symmetrical with respect to the axis of the cyclonic motion within the rotation vessel.

6. A process according to any of Claims 1 to 5, wherein the said oxime is converted to a lactam by the Beckmann Rearrangement process, and a mixture of reaction product and oleum is recycled to the said reaction vessel.

7. A process as claimed in Claim 1, substantially as hereinbefore described.

8. A purified lactam when obtained by a process according to any of Claims 1 to 7.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. that a benzene-caprolactam solution was obtained, which also contained the impurities. This solution was always examined for the caprolactam content, and by means of a spectrophotometer, for the extinction at a wave length of 290 nanometers with the use of a cell with a 1 cm thick liquid layer. A 20% by weight solution of pure caprolactam in benzene was used to adjust the spectrophotometer to 100% transmission. The measured value was recalculated to a caprolactam content of 50% by weight. The extinction determined in this way was fully caused by the impurities. In all 34 samples were drawn and examined at regular intervals in a period of 11 days. The average extinction was 1.0, with a standard deviation of 0.2. None of the samples showed an extinction of over 1.3. For comparison, a similar series of analyses was carried out under exactly the same processing conditions, but using a feedpipe of known type having an axial outflow opening. Here again 34 samples were examined. In these runs however, the average extinction was 1.7 with a standard deviation of 0.6. Three samples showed an extinction of between 2.8 and 3.0. Not only is the average extinction, which is proportional to the content of impurities, considerably higher than that of the samples drawn in the process according to the invention, but also the variation of the extinction is greater. This indicates that the product obtained was less constant in quality than in the process according to the invention. WHAT WE CLAIM IS:

1. A process for the preparation of a lactam by the conversion of a cyclic oxime in a reaction vessel wherein a recycle stream of reaction product (optionally with a reaction component) to the said reaction vessel is passed through a rotation chamber wherein it undergoes a cyclonic motion and oxime feedstock is introduced into the said stream undergoing cyclonic motion within the said rotation vessel through a feedpipe char acterized in that at least a portion of the said oxime feedstock is introduced through the said feedpipe into the said stream undergoing cyclonic motion in the said rotation vessel at an angle to the axis of the cyclonic flow of the rotating stream.

2. A process according to Claim 1, wherein the said angle included between the outflow direction of the oxime stream and the said axis of cyclonic flow, is more than 450

3. A process according to Claim 2, wherein the said angle is from 80" to 100 .

4. A process according to any of Claims 1 to 3, wherein the said feedpipe has a plurality of apertures for the passage of oxime streams therethrough.

5. A process according to Claim 4, wherein the said apertures are disposed in the wall of the said feedpipe so that they are rotation-symmetrical with respect to the axis of the cyclonic motion within the rotation vessel.

6. A process according to any of Claims 1 to 5, wherein the said oxime is converted to a lactam by the Beckmann Rearrangement process, and a mixture of reaction product and oleum is recycled to the said reaction vessel.

7. A process as claimed in Claim 1, substantially as hereinbefore described.

8. A purified lactam when obtained by a process according to any of Claims 1 to 7.