EP1212290A1

EP1212290A1 - Method for producing fatty acid amides

Info

Publication number: EP1212290A1
Application number: EP00974367A
Authority: EP
Inventors: Bernhard Gutsche; Christophe Sicre; Rene Armengaud; Jean Rigal; Gerhard Wollmann
Original assignee: Cognis Deutschland GmbH and Co KG
Current assignee: BASF Personal Care and Nutrition GmbH
Priority date: 1999-09-16
Filing date: 2000-09-07
Publication date: 2002-06-12
Also published as: KR20020029131A; WO2001019781A1; JP2003509402A; DE19944418A1

Abstract

The invention relates to a method for producing fatty acid amides from fatty acid alkyl esters and ammonia in the presence of a catalyst. According to this method, substantially water and fatty acid-free esters are used and the catalyst is a compound of tetravalent tin that is soluble in the reaction mixture. The method is carried out at low pressure, with short reaction times and to a large extent, without the formation of by-products.

Description

Process for the preparation of fatty acid amides

The invention relates to a process for producing fatty acid amides from fatty acid alkyl esters and ammonia in the presence of a catalyst.

Primary fatty acid amides, e.g. B. stearic acid amide, oleic acid amide, erucic acid amide, can be used as lubricants and antiblocking agents (slip agents) in the plastics industry, as intermediates for organic syntheses and as foam stabilizers in detergents and cleaning agents.

For a better understanding, the reaction equations are given in a simplified form below. The following reactions take place in the methods according to the prior art: The main reaction is

Fatty acid + ammonia = fatty acid amide + water.

At the same time find the back reaction

Fatty acid amide + water = fatty acid + ammonia

as well as the reaction

Fatty acid amide = water + fatty acid nitrile

instead of. If fatty acid methyl esters are used in the prior art, the reaction is always carried out in the presence of fatty acid or water. The following reactions take place:

Fatty acid methyl ester + ammonia = fatty acid amide + methanol (main reaction)

Fatty acid methyl ester + water = fatty acid + methanol.

The fatty acid then reacts with ammonia to form fatty acid amide, as indicated above. If, on the other hand, additional fatty acid is added, the water formed during the reaction of fatty acid with ammonia (see above) is used to split methyl fatty acid and thus to produce further fatty acid, which in turn is reacted with ammonia. The simultaneous presence of methanol (or another corresponding lower alcohol) and ammonia is harmful because of the reaction

Methanol + ammonia = n-methylamide + water.

Because n-methylamide continues to react with fatty acid methyl ester:

Fatty acid methyl ester + n-methylamide = fatty acid methylamide + methanol.

The fatty acid contained in the reaction mixture reacts in a corresponding manner with n-methylamide:

Fatty acid + n-methylamide = fatty acid-methylamide + water.

The production of fatty acid amides by reacting the free carboxylic acids with ammonia gas is known (German patent DE 20 26 832 C3). Water is formed as a by-product. In technical production processes, the fatty acid is heated to the reaction temperature in discontinuously operated stirred tanks. During the reaction, ammonia gas strips the water of reaction from the reaction mixture. When the ammonia is recirculated, it is freed of the water which has formed during the reaction and is carried along from the reaction mixture before being recycled.

It is known that fatty acid amides can be produced in yields of 90 to 96% from the corresponding methyl or ethyl esters and ammonia, 0.8 to 5% of the fatty acid being added (book "Fatty Amides", by Arthur L. McKenna, edited by Humko Chemical Division and Witco Chemical Corporation, 1982, pages 12 to 14). Typical reaction conditions are 10 to 18 hours at 150 ° C and 500 to 1000 psig, the equivalent of about 35 to 70 bar. This relatively high overpressure is disadvantageous in the technical production of fatty acid amides. Powdered iron, lead and lead oxides, calcium nitrate, ethylene glycol and others are given as known catalysts. Further catalysts can be found in DE 20 26 832 C3. There, compounds of titanium, zirconium or tantalum which are soluble in the reaction mixture are proposed as catalysts. However, examples of the reaction of fatty acid esters with ammonia to produce fatty acid amides are not found in this document. The proportion of fatty acid in the end product, which has to be separated in a complex manner, is particularly disadvantageous. For this purpose, sodium hydroxide solution is added, for example, and the amide, as a low boiler, is separated from the soap formed by distillation by means of molecular distillation.

Another method for producing fatty acid amides is known from US Pat. No. 3,253,006. Here, for example, one starts from fatty acid esters, which are converted to fatty acid amides with ammonia in the presence of water. The proportion of water is 50 to 200% by weight based on the amount of water required to saturate the equilibrium reaction mixture. The reaction is carried out at temperatures from about 160 ° C. to about 290 ° C., that is to say at relatively high temperatures. The converted reaction pressure is about 70 to 140 bar.

The presence of water in the reaction mixture is typical of the prior art reaction processes. This can also be achieved by adding fatty acid, the fatty acid producing fatty acid amide and water by reaction with ammonia.

The invention is therefore based on the object of developing a process for producing fatty acid amides of the type mentioned at the outset, secondary and reverse reactions being largely avoided. The crude product should contain practically no fatty acid and only very little nitrile. The process should also be able to be carried out on a technical scale with considerably lower pressure and considerably shorter reaction times than in the prior art.

This object is achieved according to the invention in the process of the type mentioned at the outset by starting from esters which are essentially free of water and fatty acids and using a compound of tetravalent tin which is soluble in the reaction mixture as the catalyst.

According to the invention, neither fatty acid nor water is added to the reaction mixture. The methanol is continuously removed to shift the reaction equilibrium towards the end product fatty acid amide. Therefore, the above-mentioned undesirable reactions for the formation of n-methylamide, fatty acid, fatty acid-methylamide do not occur or only to an extremely small extent. The main reaction in the process according to the invention is:

Fatty acid methyl ester + ammonia = fatty acid amide + methanol, the methanol is continuously removed. Instead of a fatty acid methyl ester, other fatty acid alkyl esters, e.g. B. fatty acid ethyl ester, but fatty acid methyl ester has the advantage that the by-product methanol has a very low boiling point and can therefore be removed particularly easily from the reaction mixture, in particular by continuously or temporarily reducing the reaction pressure.

Surprisingly, it has been found that high conversions in the process according to the invention with very small amounts of nitrile and fatty acid in the end product at pressures of at most 20 bar, in particular at most about 2 to 6 bar, and reaction times of significantly less than 10 hours. The practically non-existent proportion of fatty acid in the end product is particularly advantageous. A possible formation of nitrile is accepted because it is easy to separate.

Since there is no fatty acid in the end product, a generally complex removal of this disruptive constituent is not necessary according to the invention.

In particular, it is surprising that the process according to the invention leads to high yields of fatty acid amide at only moderate reaction pressure and moderate reaction temperatures and with short reaction times even without the presence of fatty acid or water in the reaction mixture.

The catalyst used in the process according to the invention can be in solid or liquid form. It is only essential that this is a compound of tetravalent tin which is soluble, in particular organic, in the reaction mixture, that is to say in the fatty acid ester.

It is also surprising that the titanium catalyst typical of the production of fatty acid amide from free fatty acid, e.g. B. "TYZOR LA" (trade name of Du Pont de Nemours), in the production of fatty acid amides from fatty acid esters only provides significantly lower sales compared to the catalyst used according to the invention, as shown in Example 1 below.

To further improve the economics of the process, it is advantageous to carry out the reaction at a slight excess pressure. It is therefore proposed that the reaction be carried out at an excess pressure of at least 3 bar and in particular at an excess pressure of 3 to 6 bar. Even the low pressure of only 3 to 6 bar compared to the prior art leads to a significant further improvement in the economy of the process. It is also proposed that the reaction be carried out at temperatures of 140 to 200 ° C and in particular at temperatures of 150 to 180 ° C. The proposed reaction temperatures are therefore significantly lower than the values known from the prior art, whereby a further improvement in the economy of the process according to the invention is achieved.

The process according to the invention can be carried out batchwise or continuously, the latter variant being preferred. On the one hand, it is proposed that the process be carried out batchwise and the pressure reduced from time to time to remove the lower alcohol formed during the reaction. As a result of the ongoing removal of the lower alcohol, the reaction equilibrium shifts towards the desired fatty acid amides. In addition, the undesirable formation of alkyl amide and water by reaction of the lower alcohol with ammonia is largely avoided.

Alternatively, it is proposed that the process be carried out continuously, in particular in a reaction column, and the gaseous lower alcohol formed under the reaction conditions is continuously removed. The advantages have already been mentioned.

In the continuous process, it is also advantageous if the liquid fatty acid ester together with the catalyst is passed in countercurrent to the gaseous ammonia within the reaction column. The countercurrent procedure increases the yield and shortens the reaction time. To further improve the economy, it is also advantageous if the ammonia is circulated through the reactor, the lower alcohol being separated off before recycling.

In a continuously operating plant for carrying out the process according to the invention, it is preferred to operate the reactor part under excess pressure and the remaining part without pressure or with only low pressure. It is therefore proposed that the by-products formed be separated off under a pressure lower than the reaction pressure. This ensures, among other things, that a very high or practically all of the lower alcohol is separated from the ammonia gas to be recycled.

It is particularly advantageous if fatty acid methyl esters are used, which are inexpensive and available in large quantities. On the other hand arises as By-product methanol, which is particularly easy and completely removable due to its very low boiling point.

Finally, it is proposed that dibutyltin oxide be used as the catalyst. When using this catalyst, it was surprisingly found that the reaction product contained no proportion of fatty acid at all. Another particularly suitable catalyst is dibutyltin dilaurate.

For working up, it is proposed that the fatty acid ester contained therein and any fatty acid nitrile which may be formed be separated off from the reaction product, in particular by distillation. The nitrile and fatty acid ester can be separated off overhead.

It is also advantageous if the catalyst is also separated off from the reaction product. For this purpose, it is proposed to remove the catalyst by distilling the amide overhead.

Exemplary embodiments of the invention and comparative examples are described in more detail below, partly with reference to drawings. Show it

1 shows a plant for batchwise implementation of the invention

Procedure and

Figure 2 shows a plant for the continuous implementation of the method.

Examples 1 and 2

Experiments were carried out with a system corresponding to Figure 1, which works in batches. Fatty acid methyl ester was placed in a reactor 1. The reactor 1 designed as a stirred tank is surrounded by a jacket 2 with an electric heater. The outlet of the reactor is connected via a 3-way valve 3 and a pressure reducing and regulating valve 4 to an ammonia source 5, namely an ammonia bottle under 6 bar. The temperature inside the reactor and at its inlet and outlet was recorded by appropriate measuring devices 6.

In the experiments explained below, a stainless steel reactor 1 with a capacity of 1 liter and an electrical jacket heater were used to generate temperatures up to 350 ° C. The test conditions and results are summarized in Tables 1 and 2. Table 1: Test conditions

Table 2: Results

The percentages are percentages by weight.

In example 1 (comparative example), a test was carried out with the liquid catalyst "TYZOR LA" (product from Du Pont de Nemours). These are diammonium dihydroxybis (lactato (2 -) - 01, 02) titanate (2-).

In Example 2, an experiment according to the invention was carried out with the catalyst "TEGOKAT 248" (product from Goldschmidt France) in solid form. It is amorphous dibutyltin oxide (C4 Hg ^ SnO.

In the "depressions" listed in the table, the ammonia pressure was reduced to normal pressure and then increased again to the maximum pressure. The very low content of fatty acid in the reaction product, which was even below the detection limit, is remarkable.

Examples 3 and 4

It is particularly advantageous to carry out the process according to the invention in a continuous procedure with a reaction column. A corresponding system is shown as an example in FIG. 2. The reaction takes place in a reaction column 7 built-in floors 8 under increased pressure. Gaseous ammonia is fed in at the bottom of the column and fatty acid methyl ester is fed in at the top of the column together with the catalyst used according to the invention. The liquid methyl ester with the catalyst dissolved therein flows down over the trays 8. The gaseous ammonia flows from bottom to top and leaves the reaction area via a pressure reducing valve 9. From here on, work is carried out without overpressure or with only very slight overpressure. The gaseous ammonia together with the likewise gaseous methanol is fed to the ammonia regeneration 10, where methanol is separated off and the cleaned ammonia gas is fed back into the reaction column 7 via a return line 11 and a compressor 12. At the bottom of the column, the liquid product is discharged via a further pressure reducing valve 13 to a separation device 14, in which the gaseous methanol and ammonia are separated off after the pressure reduction. These gases also end up in ammonia regeneration 10. The crude product, which contains fatty acid methyl ester in addition to fatty acid amide, is worked up by distillation, with methyl ester and nitrile being separated off overhead as a first step. If desired, the catalyst can also be separated off by crystallization in a solvent.

According to FIG. 2, fatty acid methyl ester was converted into fatty acid amide in a reaction column with 17 trays. The tallow acid methyl ester "Edenor METi 05" (product from Henkel KGaA) was used with a throughput of about 0.5 l / h. A NH3 throughput of 117 g / h in Example 3 and 134 g / h in Example 4 was used. In example 3 "TEGOKAT 218" (product from Goldschmidt France), namely a dibutyltin dilaurate (C4Hc)) Sn (OOC-R) 2 present in liquid form, was used as the catalyst. The catalyst in Example 4 was the "TEGOKAT 248" already mentioned above. The other test conditions and the results are listed in Tables 3 and 4.

Table 3

Table 4

LIST OF REFERENCE NUMBERS

Reactor (stirred reactor)

coat

Three-way valve

Valve

ammonia source

A temperature measuring device

reaction column

ground

Valve

Ammonia regeneration

Return line

compressor

Valve

separator

Claims

claims

1. A process for the preparation of fatty acid amides from fatty acid alkyl esters and ammonia in the presence of a catalyst, characterized in that one starts from esters essentially free of water and fatty acid and uses a compound of tetravalent tin which is soluble in the reaction mixture as catalyst.

2. The method according to claim 1, characterized in that one carries out the reaction at an excess pressure of at least 3 bar and in particular at an excess pressure of 3 to 6 bar.

3. The method according to any one of the preceding claims, characterized in that one carries out the reaction at temperatures from 140 to 200 ° C and in particular at temperatures from 150 to 180 ° C.

4. The method according to any one of the preceding claims, characterized in that the process is carried out batchwise and the pressure is reduced from time to time to remove the lower alcohol formed during the reaction.

5. The method according to any one of claims 1 to 3, characterized in that the process is carried out continuously, in particular in a reaction column, and the gaseous lower alcohol formed under the reaction conditions is continuously removed.

6. The method according to the preceding claim, characterized in that one leads the liquid fatty acid ester together with the catalyst in countercurrent to the gaseous ammonia within the reaction column.

, Process according to Claim 5 or 6, characterized in that the ammonia is circulated through the reactor, the lower alcohol being separated off before the return.

8. The method according to the preceding claim, characterized in that one carries out the separation of the by-products formed under a lower pressure than the reaction pressure.

9. The method according to any one of the preceding claims, characterized in that fatty acid methyl ester is used.

10. The method according to any one of the preceding claims, characterized in that dibutyltin oxide is used as the catalyst.

11. The method according to any one of the preceding claims, characterized in that from the reaction product, the fatty acid ester contained therein and any fatty acid nitrile formed, in particular by distillation, is removed overhead.

12. The method according to the preceding claim, characterized in that the catalyst is also separated from the reaction product, in particular by overhead distillation of the amide.