DE2149998A1 - PROCESS FOR THE PRODUCTION OF AROMATIC POLYAMINES - Google Patents

Description

Process for the preparation of aromatic polyamines

The present invention relates to a process for the preparation of aromatic polyamines by condensation of aromatic amines with formaldehyde in the presence of acidic catalysts.

The acid condensation of aromatic amines with E ⁿ ormaldehyd is an exothermic reaction. It is generally carried out in such a way that formaldehyde is added to a cooled mixture of amine and acidic catalyst and the heat of reaction which is released is dissipated by external cooling of the reactor. This heat dissipation can become a problem in large production plants and especially in boiler equipment, since the larger the boiler size, the smaller the surface-to-volume ratio. However, since the heat dissipation of the boiler surface as a cooling surface is directly proportional and also limited by the heat transfer coefficient of the boiler material used, the throughput per unit of time is drastically reduced when a strongly exothermic reaction is to be carried out at low temperatures. This problem arises in the acidic condensation of aromatic amines with formaldehyde, because the exothermic formation of precondensation products must take place at temperatures of not more than 40 ° C. in order to deliver a perfect end product.

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It has now been found that the heat dissipation is designed in a simple manner without any problems even at high throughputs can be if you run the reaction of amine catalyst with formaldehyde under reduced pressure leaves. Then namely depending on the level of the negative pressure set in the reaction mixture, the temperature of the prevailing saturation vapor pressure of the vaporizable substance present, usually water. The for the evaporation energy required is withdrawn from the reaction mixture, which is no longer possible is to heat up more than desired by the exothermic heat of reaction.

The present invention thus provides a process for the preparation of aromatic polyamines by condensation of aromatic amines with formaldehyde in the presence of acidic catalysts; characterized in that a 0 ° to 6O ⁰ C mixture of aromatic amine and acidic catalyst is used

Reacts formaldehyde in the presence of water and / or another vaporizable solvent under reduced pressure and thereby adjusts the negative pressure so that the temperature of the reaction mixture does not ^{rise above 40 °} C. due to evaporation cold, after an average residence time of at least three minutes the resultant mixture brings out precondensation products and excess amine in a heated on at least 8O ⁰ C residence reactor, in which under atmospheric pressure or superatmospheric pressure the rearrangement to polyamine salts are prepared and then alkaline worked up in a conventional manner.

It is preferred that the reaction mixture remains at least 5 minutes at a maximum of 40 ° C and then transferred to a reaction zone of at least 8O ⁰ C and remains there between 0.1 and 6 hours. Possible negative pressures 0.1 - 700 Torr, preferably * 0 - 200 Torr, IeA 14 004 - 2 -

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In the drawing, an apparatus is shown with which the process according to the invention can be carried out continuously. The measured and regulated currents of amine from container (1) and catalyst from container (2) are brought together at point (A). The heat of reaction developed can, if desired, be wholly or partially discharged in the heat exchanger (4). However, this is generally the case not mandatory. The amine-catalyst mixture thus obtained is mixed with formaldehyde from container (3) at point (B) and fed into the reactor (5). The loading the reactor (5) with amine catalyst and formaldehyde can also be carried out through separate lines. Of the The reactor (5) is connected to the vacuum pump (9) via the cooler (8), which maintains a vacuum of up to 10 Torr can. The condensate formed in the cooler (8) is led into the foot container (10) and again via the siphon Reactor (5) fed. It can also be fed to the reactor (7). Then it must, since this is usually barometric is closed, the barometric height of the condensed liquid is set between the cooler (8) and the foot tank (10) which must be increased if the reactor (7) operates under increased pressure. The one produced in the reactor (5) Product is pumped into the heated reactor (7) by means of the pump (6) to terminate the reaction. The overflow leads to alkaline work-up. The process can also be carried out batchwise.

The method according to the invention offers the following advantages over known methods:

1) Favorable space-time yield by eliminating the usual Problems with heat dissipation.

2) The heat of neutralization of the amine-catalyst mixture does not need to be dissipated. This results in savings and savings in cooling energy and investment costs by eliminating the need for a cooler. . .., .- Le A 14 004 - 3 -

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3) By eliminating the cooled reactor walls, there are no deposits, even with my amine / formaldehyde ratio on the reactor walls.

4) During the expansion of the mixture of amine catalyst and Formalin (as formaldehyde supplier) in the vacuum of the Reactor (5) a spontaneous atomization takes place, the rapid (and also necessary) mixing of the freshly flowing Product with the existing product. The effect guaranteed when using primary Amines have a content of sec. Nitrogen functions that can result from undesired side reactions are close to zero.

5) During the cooling process under reduced pressure, vapor bubbles are distributed over the entire reaction mixture, which strive to the surface and support the action of the stirrer by increasing the turbulence. As known and Already indicated above is high turbulence when formaldehyde is mixed with amine catalyst or with amine catalyst precondensation product Requirement for a usable end product.

If formalin is used as an aqueous-methanolic solution of formaldehyde, this can be done in the subsequent process stage disturbing methanol can easily be removed via the foot container (10). Likewise, there can be other volatile at the same point Substances such as chlorobenzene, phenols, etc., which are brought into the system with the components used, are discharged will.

The process according to the invention can be applied particularly favorably to anhydrous processes which, as is known, are used when the isomer distribution is to be shifted in favor of 2,4'-diamino-diaryl-methanes and at the expense of 4,4'-diaminodiaryl-methanes. Water introduced and water of condensation can be ^{conveniently distilled off below 40 °} C. in vacuo. That dehydrated at low temperature

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Precondensation gas can, as there are no more low boilers are present, are heated to the boiling point of the aromatic amine used for the rearrangement without a pressure vessel. Pie post-condensation time is shortened considerably in this way. In addition, it emerges as essential The advantage of this procedure is that an anhydrous product has a higher 2,4 '/ 4,4'-isomer ratio at an elevated rearrangement temperature delivers as a water-containing (or also anhydrous) product at a lower rearrangement temperature.

Aromatic amines with hydrolysis-sensitive functions, such as e.g. esters, conveniently condense in an aqueous medium with formaldehyde in the presence of acidic catalysts. Through the As already mentioned, the procedure under reduced pressure makes the precondensation more vaporizable by means of evaporative cooling Substances carried out at low temperature and thus suppressed hydrolysis. If after the precondensation completely removed all water including the condensation water in the vacuum, the rearrangement that can only runs at elevated temperature without the risk of hydrolysis. The rearrangement temperature can be increased so far that, when using hydrochloric acid as the acid catalyst, the decomposition temperature of the Aaino-Hydrochloride is achieved using hydrogen chloride gas is released and escapes quantitatively. In this way, the subsequent alkalization that is otherwise necessary becomes There is no need for the polyamines to be released and the risk of hydrolysis that occurs again during alkalization is eliminated.

Not only homogeneous but also heterogeneous polyamines, ie those polyamines which are formed from two or more starting amines, can be produced by the process according to the invention. For this purpose, either both (or also several) amines are passed together after mixing with the catalyst into the reactor (5) and then into the reactor (7) or one A 1 $ QO ^ .- 5 -

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passes an amine with a catalyst according to (5) and the other (the others) with or without a catalyst according to (7). The division recommends amines or amine-catalyst mixtures when it comes to increasing the proportion of unbalanced connections.

In the process according to the invention, any aromatic amines can be used, such as aniline, o-, m-, p-chloroaniline, o-, m-, p-bromoaniline, o-, m-, p-anisidine, o-, m-, p-phenetidine, o-, m-, p-toluidine, o-, m-, p-ethylaniline, o-, m-, p-isopropylaniline, o-, m-, p-xylidines, C- and ß-naphthylamine, o-, m-, p-benzylaniline, 2,6-dimethyl-, -Diethyl-, -diisopropyl-aniline, 2,4- and 2,6-diaminotoluene, o-, m-, p-diaminobenzene, anthranilic acid and its esters, N-methyl, N-ethyl, N-propyl, N-butyl, N-oxethyl, N-chloroethyl aniline, o-, m-, p-methyl-N-methylaniline, o-, m-, p-methyl-N-ethy! aniline, o-, m-, p-chloro-N-methylaniline, o-, m-, p-chloro-N-ethylaniline, and any mixtures of the aforementioned Amines and mixtures of the aforementioned amines with their formaldehyde condensation products of the diarylmethane type. In the process according to the invention, preference is given to aniline, o-toluidine, N-methylaniline or the aromatic amine N-ethylaniline or any mixtures thereof are used. It is also preferred to use as the amine anthranilic acid alkyl ester, e.g. to use the Cj-Cg alkyl esters.

The formaldehyde used in the process according to the invention can be in the form of aqueous or aqueous-methanolic Solution or in the form of formaldehyde-releasing compounds, such as methylal, trioxane or paraformaldehyde can be used. In general, organic vaporizable solvents, e.g. alcohols such as Methanol, ethanol or isopropanol, esters or ketones can be used.

An aqueous formaldehyde solution is preferably used in the process according to the invention.

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Any acidic catalysts can be used in the process according to the invention, such as hydrochloric acid, Sulfuric acid, hydrobromic acid, gaseous Hydrogen chloride, acetic acid, etc. In the process according to the invention, preference is given to using aqueous hydrochloric acid or acetic acid used as catalysts.

The primary polyamines obtainable by the process according to the invention are valuable starting materials for production the corresponding polyisocyanates by phosgenation of the polyamines according to the known methods of the prior Technology. The N-substituted amines obtained when using or also using N-substituted aromatic amines Process products can, for example, as well as the primary polyamines for the production of polyureas find use by reaction with isocyanates.

The process according to the invention is illustrated by the following examples. The hydrochloric acid and formalin used are both 30 # aqueous solutions.

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Example 1:

2 parts by volume of aniline from container (1) and 1 part by volume of hydrochloric acid from container (2) are mixed at the mixing point (A), 1 part by volume of formalin from container (3) is added at the mixing point (B) and fed into the reactor (5) , in which a pressure of 45 Torr is maintained by means of the vacuum pump (9). The reaction temperature adjusts to 36-38 ^{° C.} The evaporating water-aniline azeotrope is precipitated in the cooler (8) and flows back into the reactor (5) via the base vessel (10). After a mean residence time of 30 minutes, the pre-reacted product via the pump (6) flows to the reactor (7), which is maintained at boiling temperature of about 105 ⁰ C. From there, after a dwell time of about one hour, it passes to the alkaline work-up, where it is made alkaline with sodium hydroxide solution in a manner known per se. After phase separation, the organic phase is freed from adhering water and excess aniline by distillation. A polyamine of the following specification is obtained:

Diamond salary $ 61

Triamine content 25%

Content of tetramines 10 f

Content of pentamines 3 i °

Viscosity at 8O ⁰ Q 62 cP

Yield 88 % based on the aniline used

The diamines are divided into $ 58.7 4,4'-diamino-diphenylmethane and $ 2.3>2,4'-diamino-diphenyl-methane.

Example 2;

The procedure is analogous to Example 1, but the formalin used is mixed beforehand with 40 % of its volume of methanol. A polyamine of the following specification is obtained:

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Diamine content 65 %

Triamine content 25 # ■

Content of tetramines 7% Content of pentamines 3%

Viscosity at 80 ^° C. 60 cP

Yield $ 86, based on the aniline used

The diamines are divided into 62.6 $ 4,4'-diamino-diphenylmethane and 2.2% 2,4'-diamino-diphenylmethane.

A completely analogous product is obtained if methanol is replaced by chlorobenzene, which is added to the aniline used will.

Example 3;

The procedure is analogous to Example 1 and a solution of 1 mol of hydrochloric acid in 20 mol of aniline is reacted with 7 »2 mol of formalin. The reactor (5) is heated from the outside in such a way that, at a pressure of 12 torr, the reaction mixture ^{assumes a temperature of 40 °} C. and all of the water is removed via the cooler (8). The overflow of the siphon (10) is not fed to the reactors (5) or (7). The pre-reacted in the reactor (5) and dehydrated product is heated for one hour at 10O ⁰ C in the reactor (7) and then worked up alkaline. A polyamine of the following specification is obtained:

Diamine content 67%

Triamine salary $ 18

Tetramine content 7%

Petnamine salary $ 3

Viscosity at 80 ^° C. 74 cP

Yield $ 73> based on the aniline used

The diamines are divided into 59.1 % 4 »4'-diamino-diphenylmethane, 6.9 ^ 2,4'-diamino-diphenyl-methane. and 0.7 1 » 2,2'-diamino-diphenyl-methane.

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Example 4:

The procedure is analogous to Example 3, but the product in the reactor (7) is heated to boiling (200 ^° C.). A polyamine of the following specification is obtained:

Diamond content $ 63>

Triamine content 21 #

Content of tetramines 10%

Pentamine content 6%

Viscosity at 80 ^° C. 104 cP

Yield $ 69, based on the aniline used

The diamines are divided into 48.0 $> 4.4 ^l diamino-diphenyl methane ~, 13.8% of 2,4'-Diamino-diphenyl methane and 1.1 fo 2,2'-Diamino-diphenyl methane.

Example 5:

5 moles of 2-ethyl-n-hexyl ethereal acid are dissolved in 10 moles of 2-ethylhexanol- (1), and 1 mole of hydrochloric acid is added. Evacuating the system and give ^t% at 25 ° C 2 moles of formalin into the clear solution. All of the water is removed in vacuo. When the solvent begins to distill on heating in vacuo (75 ° C. in a water jet vacuum), the system is ventilated and heated to boiling temperature at normal pressure while passing in nitrogen. From 160 ^° C., a noticeable evolution of HCl gas begins, which ^{becomes very strong at 180 °} C. and is essentially complete after 15 minutes. The heating is continued up to 200.degree. C. and is held for a further 30 minutes, some of the solvent being distilled off. The remaining solvent is removed in vacuo, as is the unreacted anti-anil ester. The bottom product remaining at 250 ^° C. and 12 Torr is the desired methylenebis-anthranilate. It is a red-brown oil at room temperature.
Yield: 94 # of theory.

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Claims (8)

Patent claims: \1__. / A process for the preparation of aromatic polyamines by condensation of aromatic amines with formaldehyde in the presence of acid catalysts, characterized in that a 0 ° to 60 ⁰ C mixture comprising of an aromatic amine and an acid catalyst with formaldehyde in the presence of water and / or brings another vaporizable solvent to reaction under reduced pressure and "adjusts the negative pressure so that the temperature of the reaction mixture does not ^{rise above 40 0} C due to evaporation cold, after an average residence time of at least three minutes as the resulting mixture of precondensation products and excess amine brings in a heated to at least 80 ⁰ C residence reactor, in which under atmospheric pressure or superatmospheric pressure the rearrangement to polyamine salts are prepared and then alkaline worked up in a conventional manner. 2. The method according to claim 1, characterized in that the reaction mixture remains at least 5 minutes at a maximum of 40 ⁰ C and is then transferred to a reaction zone of at least 80 ⁰ C and remains there between 0.1 and 6 hours. 3. Process according to Claim ] and 2, characterized in that the polyamines with alkali hydroxide are set free from the acidic product obtained and, after phase separation, the organic product is freed from water, solvent and excess amine. 4. The method according to claim 1 and 2, characterized in that the product flowing to the reactor (7) is anhydrous. 5) Process according to claim 1 to 4, characterized in that hydrochloric acid is used as the acidic catalyst. Le A 14 004 - 11 - 309815/1224 2H9998 6. The method according to claim 1, 2, 4 and 5, characterized in that that the acidic catalyst is removed by thermal decomposition of the amine hydrochloride . 7. The method according to claims 1 to 6, characterized in that that the aromatic amine is aniline, o-toluidine, N-methylaniline or N-ethylaniline or any mixtures thereof are used. 8. The method according to claim 1 to 2 and 4 to 6, characterized in that the aromatic amine is anthranilic acid alkyl ester used. Le A 14 004 - 12 - 309815/1224