FR2605002A1 - Process for the synthesis of primary amines from esters - Google Patents

Abstract

The invention relates to a process for the synthesis of long-chain primary amines by reaction of ammonia, hydrogen and carboxylic acid esters. The reaction is carried out in the presence of specific catalysts consisting of an oxide of titanium and of active metals, copper or copper and chromium, in combination with cobalt, under pressures of 50 to 100 bars.

Description

The invention relates to a process for direct synthesis of primary aliphatic amines from fatty acid esters by the action of ammonia and hydrogen in the presence of metal catalysts.

The most widely used industrial processes for the production of long-chain primary amines, that is to say the molecule containing from 10 to about 24 carbon atoms, are still largely based on the conventional reaction of preparation of the nitrile by reaction of ammonia on the fatty acid and dehydration, and subsequent hydrogenation of the nitrile thus formed
But there are also known processes for obtaining in a single step, which involve the reaction of hydrogen and ammonia in the presence of metal catalysts, especially zinc-chromium or zinc-aluminum (French Patent No. 1 549,655), nickel with various cocatalysts (see, for example, East German Patent No. 110,487), or based on metal sulfides (British Patent No. 1,135,915).

Also described in the prior art are processes for producing primary amines using triglycerides as starting materials (German Patent No. 1,288,595).

The one-step processes that are based on the acid or on the glyceride, are obviously of a better industrial interest than the traditional processes which require two distinct stages and two distinct catalysts, one for the dehydration in nitrile, the other for its hydrogenation, and an intermediate product transfer. But they also recognize the disadvantages of being rather selective, and operate only at pressures of 200 to 250 bar.

The present invention is a process for synthesizing primary amines in one step from carboxylic acid esters, and more particularly from long chain acids comprising from 10 to 24 carbon atoms, by reaction with ammonia and hydrogen, the reaction operating through the use of advanced catalysts based on copper.

The reaction is carried out under advantageously much lower pressure conditions than those of the prior art, and which are between 20 and 150 bar, and preferably between 50 and 100 bar.

It is also an advantage of the invention to offer excellent yields, and especially a very good selectivity, that is to say a very good percentage of primary amine relative to the ester consumed, which is particularly reflected by the presence of a very small amount of amide or nitrile, annoying and troublesome pests products to remove the crude amine. The invention makes use of carboxylic acid esters.

long chain, and more particularly to methyl esters, which have become accessible by methanolysis of fats, and which are generally liquid, are of a maneuvering much appreciated at the level of industrial units.

Catalysts useful for the present invention are dehydration-hydrogenation catalysts resulting from the combination of a metal and an acid-base oxide additionally acting as a support. Many catalysts of this type are known, combinations of noble metals, nic
Kel, cobalt, etc. and alumina, zinc oxide, chromium oxide ...

The Applicant has found in the combination of titanium oxide with copper and cobalt, or copper, chromium and cobalt, a highly active and highly selective catalyst for the conversion of long-chain methylesters to amine corresponding primary.

The catalysts according to the invention contain from 2 to 80% by weight of metals; however, levels of between 10 and 40% by weight are preferred.

Cobalt is present for 2 to 30% of the total active metal, the preferred contents being of the order of 10%. In ternary systems that contain chromium, this metal can be present in a highly variable proportion that can range from 2 to 50% of the metal part; in practice, we will stick to levels of the order of 5.

These catalysts are obtained by impregnation, precipitation or coprecipitation on the support of the metal taken in the form of a water-soluble salt.

In the precipitation preparation mode, the titanium oxide is suspended in water, and the metal salt is added as such or in the form of an aqueous solution. The slurry is completely evaporated, and the collected powder is air-dried at approximately 100-150 ° C. and then calcined, also in the air, at about 3500 C. The result is the "precatalyst", which is the storable form of the product, which must be activated, to be carried out within the reactor. In the precipitation process, a titanium oxide slip containing the salts of the catalytically active metals, the hydroxide of which is precipitated by ammonia, is prepared as previously, operating at a temperature of about 60.degree.-800.degree. a maximum pH of about 7 to 8. The solid is recovered by filtration, then dried and calcined as in the method of preparation described above.

The invention is described below in its laboratory implementation, transposable on an industrial scale without other developments than those that are customary in the field.

In all the examples which follow, there will be found a certain number of common elements, which relate to the activation of the catalyst and the reactor operation for the actual synthesis. They are described below.

The implementation is carried out in a fixed bed reactor, of about 200 ml capacity, which can operate under pressure and continuously. After introduction of the precatalyst, a nitrogen purge is carried out at a rate of 50 l / h at atmospheric pressure and at room temperature.

The nitrogen is then replaced by hydrogen, and then the temperature is gradually raised, at a rate of about 4 ° C./min, until the desired reaction temperature is reached.These temperature conditions are maintained for about 12 hours. hours.

The temperature is then adjusted to the desired value (depending on the reaction, between 250 and 3500 C), and the pressure increased to a value of the order of 50 bars.

The ester and the liquid ammonia are then introduced through two diaphragm pumps, controlling the flow rates so that the ester / ammonia / hydrogen ratio is, under standard conditions, 1/10/100. , and that the space velocity of the reaction mixture (milliliters per milliliter of catalyst and per hour) is about 1/3 h 1. These conditions set only orders of magnitude, adjustable in fairly large proportions to take account of particular conditions of the reactions.

The gas-liquid mixture leaving the reactor is fractionated, the liquid fraction being recovered, the gases being either rejected or recycled.

The composition of the reaction products is obtained by vapor phase chromatographic analysis. The best conditions are - column loaded with chromosorb WAW (Johns Manville Corp.) impregnated with
Carbowax 20 M (Johns Manville Corp.) and potash (2%), - nitrogen carrier gas (30 ml / min), - equilibrium oven temperature of 2250 C.

Calibrations and reaction balances are performed using aniline as an internal standard.

The invention will be better understood from the following examples which describe syntheses of dodecylamine from methyl dodecanoate.

Examples 1 to 4 describe reactions carried out on catalysts according to the prior art, the following examples illustrate the synthesis under the conditions of the invention.

Example 1
The catalyst consists of the Cu / TiO 2 system, 9/91 X, obtained by impregnation of titanium oxide with cupric nitrate. The reaction is carried out at a temperature of 3000 ° C., the chosen ester / ammonia / hydrogen molar ratio is 1/10/100, and the reagent space velocity 0.33 h -1.

The composition of the liquid fraction from the reactor is:
Dodecylamine .................. 71.0%
N-methylidodecylamine .......... 6.3%
N, N-dimethyldodecylamine ..... 1.4%
Dodecylamide .................. 13.0 X
Dodecylnitrile ................ 8.3%
The conversion of the ester is almost complete, but the selectivity is poor.

Example 2
The synthesis is carried out under the same conditions as in Example 1, but the catalyst has the composition Cu / Al 2 O 3, 9.1 / 90.9%.

The conversion is complete, but the selectivity is poor, as shown by the composition balance of the liquid effluents
Dodecylamine ................... 72.0 X
N-Methyldodecylamine ........... 16.0 X
N, N-dimethylidodecylamine ...... 2.5 X
Dodecylnitrile ................. 1.0%
Other ......................... 0,5%
Example 3
The synthesis is carried out under the same conditions as in Example 1 except for the catalyst which has the composition. Cu / Cr203, 40/60, and the temperature which is 300 - 3500 C.The balance of composition of the part of the effluents corresponding to the ester actually converted is the following

<tb> Temperature <SEP> 3000 <SEP> C <SEP> 350 C <SEP> C
<tb> Dodecylamine <SEP> 67.0 <SEP> X <SEP> 74.0 <SEP> X <SEP>
<tb> N-Methyldodecylamine <SEP> 3.4 <SEP>% <SEP> 4.3 <SEP> X
<tb> N, <SEP> N-dimethyldodecylamine <SEP> 15.4 <SEP>% <SEP> 14.5 <SEP>% <SEP>
<tb> Dodecylamide <SEP> 9.7 <SEP>% <SEP> 1.0 <SEP>% <SEP>
<tb> Dodecylnitrile <SEP> 3.6 <SEP> X <SEP> 4.7 <SEP>%. <September>
<Tb>

Other <SEP> Amines <SEP> 0.9 <SEP>% <SEP> | <SEP> 1.5 <SEP>% <SEP>
<Tb>
In both cases, the selectivity is poor or very poor, although the conversion rates are respectively 95 X and 100 X.

Example 4
The synthesis is carried out under the conditions of Example 1, on Cu / ZnO catalyst, 9/91. The ester is converted at a rate of 90%, and the converted fraction has the composition
Dodecylamine ................... 75.0%
N-Methyldodecylamine ........... 6.7%
N, N-dimethyldodecylamine ...... 1.5%
Dodecylamide .................. 14.0 X
Dodecylnitrile ................. 2,5 X
Other amines .................. 0.3 X
Example 5
The reaction is carried out on a Cu / Cr / TiO 2 catalyst, 21.6 / 1.5 / 76.9; prepared by coimprégnation, and the temperature is 250 C. We obtain:
Dodecylamine ................. 80.0 X
N-Methyldodecylamine ......... 12.0%
N, N-dimethyldodecylamine .... 0.5 X
Dodecylamine ................. Neant
Dodecylnitrile ............... None
Dodecane ..................... None
Other amines ................ 7,5%
Example 6
The reaction is carried out in the presence of a co-impregnated catalyst and a Cu / Co / TiO 2, 20 / 2.5 / 77.5 composition and the reaction temperature is 2500 ° C. All other operating conditions are identical to those of example 1. We get
Dodecylamine .................. 86.2% N-Methyldodecylamine .......... 2.1%
N, N-dimethyldodecylamine ..... 0.9%
Dodecylamide .................. Not measurable
Dodecylnitrile ................ Not measurable
Dodecane ...................... 1,7%
Other amines ................. 9.1%
Example 7
The reaction is carried out using a Cu / Cr / Co / TiO2 mixed catalyst, obtained by coimprolining titanium oxide, and having a composition of 20 / 1.5 / 1.5n7, the reaction temperature being 2500 C. all other conditions are those of example 1.On
Dodecylamine ................... 83.0 X
N-Methyldodecylamine ........... 4.1%
0.5% N, N-dimethyldodecylamine
Dodecylamide ................... 1.0 X
Dodecylnitrile ................. 0.7 X
Dodecane ....................... 8.0%
Other amines .................. 2.7%
Example 8
The reaction is carried out at a temperature of 2500 ° C., on a catalyst
Cu / Cr / Co / TiO2, 15.1 / 1.1 / 2.6 / 81.2 weight composition, prepared by mechanical mixing of Co / TiO2 and Cu / Cr / TiO2 impregnation catalysts.

The liquid effluent has the following composition
Dodecylamine .................. 74.5% N-Methyldodecylamine 1.0 h%
N, N-dimethyldodecylamine ..... 1.0%
Dodecylamide .................. 1.0%
Dodecylnitrile ................ 1.0%
Dodecane 16.4 16.4
Other 5.1%
It can be seen from these three examples using catalysts according to the invention that the combination of titanium oxide with copper-cobalt or copper-chromium-cobalt metal compositions makes it possible to obtain a virtually total conversion of the ester, and the long-chain alkylamine formed contains very few methylated homologs. Hydrocarbons can be a significant part of the by-products of the reaction; they are not generally troublesome in the subsequent applications of the primary amine, and in any case, are easily separable.

They come from an excess of cobalt in the catalyst and can be reduced by a slight decrease of this metal in the composition of the active metal component.

Claims (7)

1. Improved process for the preparation of primary amines of formula  general R - NH2> where R is a saturated or unsaturated hydrocarbon chain  containing from 10 to 24 carbon atoms, by reaction, in the presence  mixed catalysts of the oxide-metal, ammonia and hydrogen type  long-chain carboxylic acid esters, characterized in that  that the catalyst consists, on the one hand, of titanium oxide, and  on the other hand, copper or copper and chromium associated with cobalt. 2. Method according to claim 1, characterized in that the catalyst  contains from 2 to 80% and preferably from 10 to 40% by weight of metals. 3. Method according to claims 1 and 2, characterized in that the  cobalt represents from 2 to 30% of the weight of the metals contained in the  catalyst. 4. Process according to claim 1, characterized in that the acid ester  Long chain carboxylic acid is a methyl ester. 5. Method according to claim 1, characterized in that the reaction  proceeds under pressures between 20 and 150 bars, and pre  between 50 and 100 bar. 6. Process according to claims 1 and 2, characterized in that the cata  The lyser is obtained by reduction of a precatalyst itself obtained by  drying and calcination of titanium oxide impregnated with copper salts and  cobalt, or salts of copper, chromium and cobalt. 7. Method according to claims 1 and 2, characterized in that the cata  lyseur is obtained by reducing a précatlyseur, itself obtained by  drying and calcination of titanium oxide on which co-precipitated  hydroxides of copper and cobalt or hydroxides of copper,  chrome and cobalt.