The method of evaporation aminonitriles

 

(57) Abstract:

The invention relates to a method of evaporation aminonitriles and water in the synthesis of lactam by the reaction between aminonitriles and water in the vapor phase in the presence of a catalyst is aluminum hydroxide. The method consists in the fact that enter in contact aminonitriles in the liquid state and water vapor to evaporate aminonitriles by contact of the liquid/vapor, and the resulting mixture aminonitriles/water vapor quickly bring in the heat exchanger to a temperature at which there is complete evaporation of the mixture. The method allows to reduce the formation of heavy by-products and to increase the service life of the catalyst. 11 C.p. f-crystals.

The present invention relates to the evaporation of aminonitriles and water conditions that limit or eliminate the formation of heavy by-products, especially oligomers aminocarbonyl acid.

The reaction between aminonitriles and water leads to the formation of lactam, in particular caprolactam in the case of 6-aminocaproate.

This reaction can be carried out in the liquid phase temperature and at high pressure. It can also be carried out in the vapor phase. For atacadista examples of the implementation of the hydrolysis of aminonitriles in the vapor phase can be referenced, in particular, the patent application EP-A-0659741 and international application WO-A-96/22974.

The choice of vaporization aminonitriles and water is not trivial.

Indeed, one can propose obtaining a liquid mixture of water/aminonitriles, then heating the mixture to a temperature sufficient for evaporation of both components. In this note the formation of heavy compounds with amide function or carboxyl function (oligomers). These compounds are able to gain a foothold, at least in part on the catalyst and thus reduce its service life. On the other hand, they are deposited in the equipment and clog it. This requires periodic cleaning of these instruments, and therefore, relatively frequent stops installation with all the attendant economic consequences.

Another possible way would be to separate the evaporation flows aminonitriles and water. It was noted by the applicant that at the temperatures required for vaporization aminonitriles, it decomposes in a considerable number with the formation of compounds of type amidine or polyamidine (condensation few molecules of aminonitriles with the removal of ammonia).

To address these various naanee serves as a carrier gas for this evaporation.

Decomposition of aminonitriles temperature dependent evaporation and exposure time of the liquid during its evaporation. Thus, in the method according to the invention, the exposure time of the fluid is minimized through technology evaporator, and water in the vapor state reduces the partial pressure of aminonitriles that lowers the temperature of evaporation.

The molar ratio of water/aminonitriles may vary within very wide limits in the method according to the invention. It mainly depends on how cyclization hydrolysis, which uses reagents. This molar ratio between the participating water and aminonitriles is usually from 0.5 to 100, and preferably from 1 to 20. A higher value of this ratio is not critical for the invention, however, higher values have no meaning for the reaction of hydrolysis for economic reasons.

In General, water vapor has a temperature of from 120 to 600 S), and preferably from 200 to S.

Aminonitriles is typically used at a temperature of from 20 to 300C. Preferably the temperature is from 100 to S.

The mixture aminonitriles/water vapor quickly brought into a heat exchanger to a temperature at which IMI, where is the reaction between aminonitriles and water. This reaction temperature is usually from 200 to 450C, and preferably from 250 to 400C.

The absolute pressure at which the evaporation of aminonitriles, is usually from 0.1 to 3 bar.

Used in the method according to the invention aminonitriles is, in particular, aliphatic linear or branched aminonitriles containing from 3 to 12 carbon atoms.

As examples one can cite, in particular, aliphatic aminonitriles obtained from hydrogenation to the function of a primary amine of one of the two nitrile functions dinitriles, such as adiponitrile, methylglutaronitrile, ethyl succinonitrile, dimethylaminomethyl, malononitrile, succinonitrile, glutaronitrile, dodecyldimethyl.

The most important aminonitriles is 6-amino-cupronickel cyclisme, the hydrolysis of which leads to the formation of caprolactam, the polymerization of which results in a polyamide-6.

For convenience in the following description, it is possible to refer, in particular, 6-amino-cupronickel (or DCA).

The method is carried out using the system without detention liquid.

There are two types of technologies ptx2">

- evaporation film of aminonitriles on a heating surface,

- the evaporation of fog at least partially liquid aminonitriles in overheated water vapour; in this case, the contact liquid/heated wall are replaced by contact of the gas/liquid droplets.

In the case of evaporation film on the heated surface of the heat required for evaporation is supplied, on the one hand, from the heat of the heating steam and aminonitriles, and on the other hand, the heat transfer through surface evaporation. Evaporating device refers to the type evaporator with the flowing film.

The distribution of liquid to the evaporator tubes can be carried out through distribution systems commonly used in this type of technology:

by submitting at least partially liquid aminonitriles on a tubular manifold, then the distribution of this aminonitriles in each tube, or by feeding the at least partially liquid aminonitriles in each tube by spraying in the form of a mist over the tubular collector, this technology compared with the previous has the advantage that further reduces the exposure time of aminonitriles in the liquid phase at high temperature; RA is both liquid and water vapor.

In the case of evaporation in the fog through the contact gas/liquid droplets heat fully paid due to the heat of the heating of both components, aminonitriles at least partially in the liquid phase and water in the vapor phase.

The temperature of the water vapor and temperature aminonitriles at least partially in the liquid phase are selected so that the resulting mist had a temperature equal to or above the dew point of the mixture water/aminonitriles, forming fog. The dew point depends on the relationship of water/aminonitriles and easily determined for the selected relationship.

So, as an example, at atmospheric pressure dew point is 180C for molar ratio of water/6-amino-cupronickel (DCA), is equal to 4, 100C for the molar ratio of water/DCA, equal to 56, C for the molar ratio of water/DCA equal to 1, and 230S for pure DCA.

This evaporation in the fog through the contact gas/liquid droplets can be single-stage or multistage. In the case when the single-stage evaporation temperature aminonitriles and water vapor is such that evaporation of the liquid may be full or partial. If the multi-stage evaporation, the flow of aminonitriles, pre-heated to the 230S, for example, NYM steam at 300C, for example, in such a way as to evaporate all of the liquid, the temperature of the mixture at the same time is reduced to approximately the dew point due to evaporation. The mixture in the form of steam is then superheated, for example, to 300C, and then mixed with the second part of the liquid, which, in turn, is evaporated, the process is repeated as many times as necessary to achieve complete evaporation of liquid. In this way the fog fluid is created at each step through raspylyayushchikh nozzle, the mixture then get sufficient to ensure the complete evaporation of the liquid.

The evaporation system of aminonitriles is selected preferably so that the presence of liquid aminonitriles in the system, including pre-heating the named aminonitriles was less than or equal to one minute, preferably less than or equal to 5 seconds.

The following examples illustrate the present invention.

Example 1

200 g/h 6-amino-cupronickel (DCA), pre-heated to the 230S, and 129 g/h of steam at 300C pump through a nozzle 1 mm

So produced mist evaporated and then superheated to 300C with utilizator, moreover, in the above reactor, keep the temperature of 300C.

For more than 400 hours of work did not notice any contamination of the reactor, no decrease in catalytic activity (measured through the coefficient of conversion of DCA with a constant flow equal to 99%).

Comparative test 1

329 g/h of a mixture of DCA/water from 61 wt.% DCA is served in the evaporation apparatus with a capacity of 200 ml, heated to 300C.

The gaseous mixture emerging from the evaporator is sent to a hydrolysis, containing 162 g of aluminum hydroxide, and in the said reactor keep the temperature 300C.

The test is stopped after 172 hours. During this period, the conversion factor AKH decreases from 99% to 95%.

After dismantling of the equipment note the presence of solids (polyamide 6) inside the evaporator, and the outlet of the hydrolysis reactor (harden 25% of the height of the contents of the named reactor).

1. The method of evaporation aminonitriles and water in the synthesis of lactam by the reaction between aminonitriles and water in the vapor phase in the presence of a catalyst of aluminum hydroxide, characterized in that enter in contact aminonitriles liquid and steam for you the tro bring in the heat exchanger to a temperature in which there is complete evaporation of the mixture.

2. The method according to p. 1, characterized in that water vapor is used at a temperature of from 120 to 600C and preferably from 200 to S.

3. The method according to p. 1 or 2, characterized in that aminonitriles is used at a temperature of from 20 to 300C and preferably from 100 to S.

4. The method according to any of paragraphs.1-3, wherein the produced mixture of aminonitriles in water vapour is heated to the reaction temperature between aminonitriles and water, preferably to a temperature of from 200 to 450C and even more preferably from 250 to 400C.

5. The method according to any of paragraphs.1-4, characterized in that aminonitriles is an aliphatic linear or branched aminonitriles containing from 3 to 12 carbon atoms.

6. The method according to any of paragraphs.1-5, characterized in that use aminonitriles with the primary amino group obtained by partial hydrogenation of one of the two nitrile groups dinitrile selected from adiponitrile, methylglutaronitrile, ethylsuccinate, dimethylbenzonitrile, malononitrile, succinonitrile, glutaronitrile, dodecanediol, preferably 6-aminocaproate.

7. The method according to any of paragraphs.1-6, otlichalosb on any of the PP.1-7, characterized in that it is carried out with the system of detention without liquid.

9. The method according to p. 8, characterized in that use one of the following technologies: evaporation film aminonitriles on the heated surface in the evaporation apparatus of the type with flowing film or evaporation fog, at least partially liquid aminonitriles in overheated water vapour.

10. The method according to p. 9, characterized in that the distribution of aminonitriles through tubes that contain evaporating device with flowing film by filing an at least partially liquid aminonitriles on a tubular manifold, then feed this aminonitriles to each tube, or by applying at least partially liquid aminonitriles in each tube by spraying the latter in the form of a mist over the tubular manifold.

11. The method according to p. 9, characterized in that the evaporation of the mist, at least partially liquid aminonitriles in overheated water vapour is a single-stage or multistage.

12. The method according to any of paragraphs.1-11, characterized in that the evaporation system of aminonitriles is selected so that the presence of liquid aminonitriles was not the Sabbath.

 

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EFFECT: improved preparing method.

5 cl, 2 ex

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