DE1271119B - Process for the preparation of hexamethylenetetramine - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. α .:

C07d

German class: 12 ρ - 10/10

Number:
File number:
Registration date:
Display day:

P 12 71 119.2-44
March 4, 1963
June 27, 1968

The invention relates to an improved process for the preparation of hexamethylenetetramine.

The production of hexamethylenetetramine by exothermic reaction of ammonia and formaldehyde is preferably carried out in an aqueous, generally saturated solution of hexamethylenetetramine. Attempts to carry out this reaction in the gaseous phase have shown that the reaction is not complete and over is also very violent, with the dissipation of the heat released leads to difficulties.

There are already many variations of this reaction in the liquid phase under different pressure and pressure Temperature conditions have been described. So you can immediately see the respondents in introduce an aqueous solution of hexamethylenetetramine or place it at the bottom of a column introduce, which is traversed by a saturated aqueous solution of hexamethylenetetramine, the is introduced ao in finely divided form at the top of the column.

However, these different methods have different disadvantages. So they often require Working under a strong vacuum or the use of external coolants, or it eras difficulties arise in the removal of water (water of reaction and the water entrained with the reactants), which in general leads to increased energy losses.

The invention relates to a process for the preparation of hexamethylenetetramine by continuously introducing anhydrous ammonia and a gaseous mixture of formaldehyde with inert gases, which has been obtained by catalytic oxidation of methanol, at about atmospheric pressure in a saturated aqueous solution of hexamethylenetetramine, continuously withdrawing one Part of the saturated solution and introduction of this part of the solution into a crystallization zone and then into a device for separating the hexamethylenetetramine crystals from the mother liquor, which is characterized in that a constant reaction temperature of 62 to 66 ° C is maintained by the liquid level of the reaction mixture kept constant by washing the gas mixture escaping from the reaction medium, which essentially contains the inert gases supplied with the formaldehyde, with the dilute hexamethylenetetramine mother liquor, the dilution of the The amount of water supplied to mother liquor together with the amount of water produced in the reaction is the same as the water method for production
of hexamethylenetetramine

Applicant:

Societe Beige de l'Azote et des Produits
Chimiques du Marly, Soci6t6 Anonyme,
Liege (Belgium)

Representative:

Dr. W. Schalk, Dipl.-Ing. P. Wirth,

Dipl.-Ing. G. Dannenberg

and Dr. V. Schmied-Kowarzik, patent attorneys,

6000 Frankfurt, Große Eschenheimer Str. 39

Named as inventor:
Andre Lefebvre, Liege;
Roger Englebert, Angleur;
Arthur Geukenne, Brussels (Belgium)

Claimed priority:

Great Britain March 5, 1962 (8475)

amount that is entrained by the gas mixture escaping from the reaction medium.

By keeping the liquid level constant in the reaction vessel in the manner indicated, the temperature stabilizes itself a, which was not possible in this form with the known methods. In particular, can be based on the use no special coolants are used; Working under a strong vacuum is just as impossible necessary.

The washing of the gas mixture escaping from the reaction medium can take various forms be made. So you can the gas mixture with a dilute hexamethylenetetramine solution, the mother liquor obtained by diluting the separated hexamethylenetetramine crystals has been obtained, wash, or one uses the concentrated mother liquor and leads above their point of introduction into the system is pure water. The only thing that matters is that through the Amount of liquid supplied, the liquid level in the reaction system at a constant level is held.

809 567/539

Factors that influence the amount of water to be fed are in particular the temperature of the Formaldehyde-containing gas, the temperature of the ammonia (e.g. gaseous or liquid) and the Quantity of the gas containing ammonia and formaldehyde fed to the reaction system. This amount is of course also dependent on the size of the reaction vessel; the capacity of the reaction vessel is known to the person skilled in the art, and therefore it will not be introduced at extreme speeds Select.

The drawing illustrates one useful for carrying out the method according to the invention Contraption.

It consists of a column 1 with a frustoconical bottom, which directly through the lower Part is connected to a crystallization zone 2. The lines 3 and 4 are used to introduce the Reactants below the level of a saturated hexamethylenetetramine solution. The upper part of the Column is with trays 5, z. B. dome bottoms, provided, around the unreacted gas and the liquid phase used to scrub this gas in To bring touch.

The mixture of mother liquor and crystals dispersed therein is withdrawn from crystallization zone 2 through line 6, and the mixture is separated in the spinner 7. The hexamethylenetetramine crystals are obtained through line 8, while the mother liquor by adding water introduced through line 9, is diluted; the aqueous, unsaturated hexamethylenetetramine solution thus obtained becomes uniform given on the top of the floors 5. The column 1 also has an opening 10 for the outlet of inert gases and a device (not shown) for regulating the liquid level in the Reaction zone.

By using an unsaturated hexamethylene tetramine solution, i.e. H. a solution that doesn't have any Contains crystallization nuclei, passes over the floors, these are kept clean without premature crystallization can occur. The crystal formation only begins in the reaction zone and is in the crystallization zone completed. Furthermore, the reaction takes place at a temperature below the boiling point of the solution, whereby the formation of side reactions is greatly reduced and expediently in the presence a slight excess of ammonia. When using such a device, the Hexamethylenetetramine obtained in the form of beautiful crystals.

Since there is practically no reaction between the gases on the floors above the reaction zone contained ammonia and formaldehyde takes place, one can also with only a small number of Work floors or omit them completely if you z. B. an atomizer for that Wash water used.

The formaldehyde-containing gas obtained from the catalytic synthesis of methanol consists essentially of nitrogen, oxygen, carbon oxide, water vapor and usually about 6 % formaldehyde. This gas becomes saturated with water vapor at the reaction temperature in the reaction medium or during subsequent washing with the dilute Haxamethylenetetramine solution, and this water vapor is lost from the system. This amount is essentially dependent on the temperature of the reaction system, since the subsequent washing only leads to a practically negligible change in temperature. (The column is usually short and the volume of gas is relatively large compared to the amount of wash water supplied.) The gas leaving the reaction system, saturated with water vapor, no longer contains formaldehyde.

The following experiments show the various interdependence of reaction variables, where such amounts of reactants were introduced that 200 kg of hexamethylenetetramine per Hour were gained.

1. If z. B. introduced the formaldehyde-containing gas at a temperature of 135 ° C, used gaseous ammonia at a temperature of 10 to 50 ° C and a mixture of solid hexamethylenetetramine to mother liquor of 50:50 withdrawn, the reaction temperature is about 66 ⁰ C, and about 400 kg of water must be introduced per hour.

2. Proceed as in 1, but the formaldehyde-containing gas with a temperature introduced from 110 ° C, the reaction temperature is about 65 ° C and that to be fed Amount of water about 350 kg per hour.

3. Proceed as in 1, but a mixture of solid hexamethylenetetramine for Mother liquor of 20:80 withdrawn, the values are about 64 ° C reaction temperature and about 31Okg per hour of water.

4. If you proceed as in 2, but use liquid ammonia, the values are approximately 63 to 64 ° C reaction temperature and about 290 kg of water per hour.

5. If you proceed as in 3, but use liquid ammonia, the values are 62 ° C Reaction temperature and about 200 kg of water per hour.

From these values it can be seen that z. B. a change in temperature of the supplied gas of 25 ° C only has an effect of 1 ° C difference in the reaction temperature. The new procedure is thus very insensitive to fluctuations in the reaction conditions, and the control of the reaction temperature from 62 to 66 ° C. is extremely easy by keeping the liquid level in the reaction system constant.

One would at a temperature of 60 ° C work, the amount of water supplied to the floors and the reaction system should be greater than that Amount that can be carried by the gases. This would mean that the level of the reaction medium in the reaction vessel would have to overflow rise. If, on the other hand, one were to work at 70 ° C, the opposite would occur and the level of the Falling reaction medium in the reaction vessel. The regulation of the liquid level is thus automatic a stable system.

Compared to the known process for the production of hexamethylenetetramine, in which ammonia and formaldehyde are reacted in the gas phase, with water being injected at the same time, result There are several advantages in the method according to the invention. So this is done in the liquid phase The method according to the invention is significantly less sensitive to temperature fluctuations and therefore

easier to control (see the experiments above). Furthermore, it can be carried out at lower temperatures and is therefore more economical. Finally, the hexamethylenetetramine obtained by the process according to the invention is extremely pure and free from amines, so that further purification is not necessary. In contrast, the reactions carried out in the gas phase at higher temperatures still give rise to small amounts of amines as a result of side reactions, and these have to be removed in all cases in which an unobjectionable odor plays a role.
The following examples illustrate the invention.

example 1

In the device shown in the drawing, 13 kg or 235 m ^{3 of} a 6.1% formaldehyde-containing gas at a temperature of 110 ° C. were introduced through line 4 into a saturated hexamethylenetetramine solution every hour. The gas still contained nitrogen as the main component, as well as small amounts of oxygen, carbon monoxide and water vapor. At the same time, 5 kg of ammonia at a temperature of 20 ° C. were introduced per hour through line 3.

The reaction between formaldehyde and ammonia to form hexamethylenetetramine took place at atmospheric pressure and 64.5 ° C.

Part of the saturated hexamethylenetetramine solution was continuously fed into the crystallization zone 2, where part of the mixture of crystals and mother liquor continuously withdrawn through line 6 and into the centrifugal device 7 was sent. After the crystals had been separated off, mother liquor containing 24 l / hour was obtained of 27.5 percent by weight hexamethylenetetramine. This mother liquor was pure at 12.5 l / hour, water introduced through line 9, and the solution thus diluted at a temperature around 20 ° C passed to the top of the reaction vessel 1. The downward flowing solution met the rising gas stream leaving the reaction zone, which followed the washing by means of this solution escaped through the opening 10. The effectiveness of this washing can be increased by adding three floors 5 in the upper part of the reaction vessel 1. The reaction temperature remained constant at 64.5 ° C, and under these conditions the amount of water entrained by the gases leaving the reaction zone was equal to the sum of the amount of water introduced as washing solution and that resulting from the reaction Amount of water.

The level of the reaction medium remained constant, indicating that the reaction was proceeding normally.

Large crystals of hexamethylenetetramine were obtained in a yield of 99.8% based on the imported one Formaldehyde, and of 98.5% based on ammonia consumed.

Example 2

As indicated in Example 1, 220 m ^s / hour of gas with a formaldehyde content of 5.84% and 4.47 kg of anhydrous liquid ammonia were introduced into a saturated hexamethylenetetramine solution, the temperature of which was a constant 64.5 ° C.

A portion of the saturated solution was continuously drawn off and yielded after passage through the crystallization zone and the centrifugal device 7 19.5 l / hour mother liquor with a hexamethylene tetramine content of 29%. This mother liquor was returned below the lower tray 5, while in the upper part of the reaction vessel 11.2 l / hour of pure water was introduced. For better contact between the gaseous phase and the water, three trays 5 were used.

Investigations showed that the amount of hexamethylenetetramine in the aqueous solutions on the different soils varied as follows (average values):

Upper bottom 0.28 percent by weight

Average soil 3.9 percent by weight

Lower bottom 4.7 percent by weight

The yield of hexametlylenetetramine was 99.7%, calculated on the formaldehyde introduced, and 98.5% based on ammonia consumed.

Claims (2)

Patent claims: 1. Process for the preparation of hexamethylenetetramine by continuous introduction of anhydrous ammonia and a gaseous mixture of formaldehyde with inert ones Gases obtained by the catalytic oxidation of methanol at about atmospheric Pressure into a saturated aqueous solution of hexamethylenetetramine, continuous Withdrawing part of the saturated solution and introducing this part of the solution into a Crystallization zone and then into a device for separating the hexamethylenetetramine crystals from the mother liquor, characterized that a constant reaction temperature of 62 to 66 ° C is maintained by the liquid level of the reaction mixture is kept constant by the fact that the from the Gas mixture escaping from the reaction medium, which is essentially that with the formaldehyde supplied inert gases contains, with the dilute hexamethylenetetramine mother liquor washes, the amount of water supplied by the dilution of the mother liquor together with the amount of water formed in the reaction is equal to the amount of water that is produced by the gas mixture escaping from the reaction medium is entrained. 2. The method according to claim 1, characterized in that there is anhydrous liquid Uses ammonia. Considered publications:
German Auslegeschrift F11872 Hb / 12p (published on February 23, 1956). 1 sheet of drawings 809 567/539 6.68 © Bundesdruckerei Berlin