US2061314A - Process of preparing nitriles - Google Patents

Description

Nov. 17, 1936. A. w. RALSTON ET AL 2,061,314

PROCESS OF PREPARING NITRILES Filed Dec. 9, 1935 HEATING COIL warm woman NE CATALYST CONDENSER 3, 5, -75

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Patented Nov. 17, 1936 UNITED STATES PROCESS OF PATENT OFFICE PREPARING NITRILES Anderson W. Balaton, William 0. Pool, and James Harw ood, Chicago, 111., aaaignors to Armour and Company, Chicago, 111., a corporation of Illinois Application December 9, 1935, Serial No. 53,650

'16 Claims. (01. zoo-ease) This invention relates to processes of preparingpounds. For example, they can be hydrogenated to amines which can in turn be used in organic syntheses. Commercial methods of preparing the nitriles are therefor of considerable technical interest.

Many ways of preparing nitriles have been proposed. Most of the prior art methods are, however, of only academic interest. For example, the nitriles can be prepared by heating an alkyl iodide with an alcoholic solution of potassium cyanide. In other cases, ammonia salts of the higher fatty acids are distilled, this resulting in the decomposition of the salt to yield an amide. The amide can then be converted to the nitrile by treatment with a dehydrating agent such as phosphorous pentoxide. Neither of these methods are of commercial importance, however, because of various technical difficulties.

More recently it has been suggested to treat fatty acids or their esters in the vapor phase'with ammonia in the presence of certain dehydrating catalysts. satisfactory but in many instances it is diflicult to vaporize the higher fatty acids without decomposition. ;At temperatures above the boiling point of the acid decomposition may occur quite rapidly and this in an inherent disadvantage which requires special procedures to overcome.

We have now discovered ways of preparing nitriles of the class specified which avoid the many disadvantages commonly encountered hitherto. We have discovered that nitriles can be prepared from fatty acids while in liquid This at once avoids the necessity for vaporizing the fatty acids and hence substantially avoids any possibility of decomposition in the fatty acid starting material.

We have discovered that fatty acids of six or more carbon atoms can be made 'to react with ammonia to give nitriles by simply passing gaseous ammonia into contact with such fatty acids while in liquid condition a d at elevated p This vapor phase reaction is generally atures provided water formed during the course of the reaction is continuously removed. We need not use dehydrating agents or catalysts, although such can be present in admixture with the liquefled fatty acids if desired. But ordinarily we find no necessity for using catalysts and this is an important step forward in the art. Hitherto catalysts or dehydrating agents have always been considerednecessary elements in the reaction between ammonia and fatty acids or caters to give nitriles.

In broadest aspects our invention comprises contacting gaseous ammonia with fatty acids of at least six carbon atoms while in liquid phase at Y an elevated temperature and under conditions such that the water formed during the action is continuously vaporized from the reaction mix ture. Thus, for example, we heat, in a suitable vessel a body of stearic acid to a temperature of a about 330C. During the course of the heating ammonia vapor is led into the body of molten fatty acid, and water formed during the reaction is continuously distilled or vaporized from the reaction mixture. We believe that the course of the reaction is as follows: The ammonia probably reacts with the fatty acid to form first an ammonium soap. The ammonium soap then probably breaks down to liberate one molecule of water and one molecule of stearamide. The stearamide then breaks down to liberate a second molecule of .water and forms the nitrile. If conditions are such that the water liberatedin the decomposition of the ammonium soap is not immediately removed, the reaction appears to stop at the amide stage. We believe, however, that there are other contributing factors. We so operate our process that an excess of ammonia is bubbled up through the mass of liquefied fatty acids and this ammonia may in part act to carry away some of the water developed. In other words, the ammonia may help in the rapid removal of water formed in the reaction. We need not always operate with a large excess of ammonia, however. We can use gas and liquid contact apparatus in which a down-flowing stream of liquefied fatty acids. at reaction temperature, meets an ascending current of ammonia. Under these conditions great opportunity is given for the immediate vaporization and removal of water. We find it generally better, however, to use excess ammonia and recycle the excess ammonia back to the body of liquiiled fatty acid undergoing treatment.

On the appended single sheet of drawing we have indicated in general diagrammatic form a suitable flow sheet of our process.

Referring to the drawing, the mass of fatty acid, or aliphatic esters thereof, to be converted to nitriles is maintained in reaction vessel I which is provided with a heating coil 2 and a charge inlet 3. Gaseous ammonia is introduced into the system by way of pipe I and pipe 5. The lower end of pipe 5 terminates at the bottom of the reaction vessel and its outlet is, advantageously provided with a distributing nozzle to.

divide the incoming ammonia vapor into a plurality of small streams which can bubble up through the body of fatty acid. At the top of reaction vessel we advantageously provide an air cooled reflux condenser 6. This can take the form of a fairly long upwardly extending pipe. The condenser functions to return any vaporized acids to the reaction vessel.

In many instances the raw fatty acid material used may contain small amounts of lower fatty acids which have boiling points somewhat less than the average boiling point of the mass of fatty acid taken as a whole. Since we operate our process at temperatures very close to, but slightly below, the normal boiling point of the bulk of the fatty acids, any lower boiling point fatty acids present may vaporize to some extent and these do not always condense in the air cooled condenser and reflux back. In order to prevent any clogging of the system by soaps formed from such fatty acids as may distill during the heating treatment, we find it advantageous to provide a catalyst chamber 1 containing a dehydrating catalyst such as alumina 9. The catalyst is heated by heating coil 8. Should small quantities of fatty acids, or ammonium soaps, vaporize from reaction vessel I and pass through the air condenser 6, they will be decomposed to nitriles, in vapor phase, by catalyst 9. In this way we avoid any possibility of contaminating or clogging the ammonia recycle system by any ammonium soaps or acids which might possibly escape through the air condenser. Other ways of freeing the vapors leaving the reaction vessel through condenser 6 from any fatty acid or soaps can of course be used. At the top of catalyst chamber 1 we provide an outlet pipe I which leads to a water cooled condenser II and terminates in a water receiver I2 having a draw-off outlet I3. Partially dried ammonia vapor leaves receiver I2 by way of line I4 and is conducted through a brine cooled condenser I5. The purpose of condenser II and I5 is to dry the ammonia vapors so that they can be returned to reaction vessel I for reuse. The water cooled condenser I I condenses any traces of nitriles and most of the water and brine cooled condenser I 5 removes practically all of the moisture in the ammonia gas.

The ammonia is recycled back to reaction vessel I by way of line I6, pump I1 and line I8. A pressure gage is provided at I9 and a vent for the system at 20. 4

Although, as stated, we can simply bubble gaseous ammonia through a mass of fatty acids maintained in the reaction vessel at a temperature high enough to facilitate the reaction and to vaporize water as soon as formed, we find it better to provide the ammonia recycle system shown on the drawing. Of course it is understood that as the ammonia is consumed in the reaction Vessel more ammonia is admitted to the system through inlet 4.

We generally prefer to operate the system at pressures slightly above atmospheric, We find that pressures of from 5 to 30'pounds are desirable since this prevents any introduction of air through leakage. Air is undesirable since it may aid in the decomposition of the fatty acids, a thing which we wish to avoid. Moreover, operating under a moderately elevated pressure also increases the observed boiling point of the fatty acids somewhat and thus enables us to operate at somewhat higher reaction temperatures without undesirable vaporization of free fatty acids. We do not wish to be limited to any particular pressure, however, since we can operate at atmospheric pressure, at pressures slightly above, and even at reduced pressures, but with no particular advantage.

We shall now describe our invention in more specific detail. We can use our process for the preparation of n triles corresponding to any fatty acid having six or more carbon atoms. Thus, we can use caproic, caprylic, capric, laurio, myristic, palmitic, stearic, oleic, linoleic, and other fatty acids. In many instances we use as starting materials crude fatty acids obtained by splitting fats. These acids may contain three or more different fatty acids. When starting with a mixture of crude fatty acid the product flowing from the outlet 2| of reaction vessel I will of course consist of a mixture of nitriles corresponding to the fatty acid starting materials. These nitriles can be separated by fractional distillation as has been described in our copending application, Serial Number 47,716 filed August 31, 1935. The present process offers an excellent way of initially preparing a mixture of nitriles from a mixture of fatty acids for the purpose of separating the individual fatty acids from said mixture as described in the copending application.

When we wish to make stearonitrile we charge the reaction vessel I with 1,000 parts by weight of commercial stearic acid. The contents of the vessel is then heated at a temperature of about 330 C. and ammonia is passed in continuously during a heating period of six hours. The water generated during the reaction is continuously vaporized from the molten mass in the vessel I. The system is maintained under a pressure of 5 pounds per square inch and the ammonia recycled as shown in the flow sheet. The catalyst chamber 1 is advantageously maintained at a temperature of about 400 C. During the reaction excess ammonia and water together with extremely small amounts of soaps and fatty acids leave the air condenser G and pass through the catalyst. The soaps are broken up by the catalyst and the nitriles formed therefrom are either returned to the reaction vessel or pass by way of line I0 and collect in the water receiver I2. The gaseous ammonia and its content of water pass through line I0 and condenser I I and most of the water collects in I2. The residual moisture is condensed in condenser I5, and substantially dried ammonia gas is recycled back to the reaction vessel through line I6, pump I1 and line I8.

After the period of heating specified the reaction product in vessel I is allowed to cool and is then withdrawn through outlet 2|. It consists of 920 parts by weight of stearonitrile containing less than 1.5 percent of stearic acid and much smaller amounts of amides.

Under the conditions of our process we find that substantially no decomposition products of fatty acids are formed. Although we are operating at relatively high temperatures, of the order of 250 to 350 C. in the reaction vessel deaoensm composition of the fatty acids does not occur and we endeavor to explain this in part by the protective action of ammonia. Apparently, in the presence of large quantities of ammonia, fatty acids do not decompose to nearly as great an extent. On the other hand, we have found that under similar temperature conditions, and in the presence of nitrogen, the fatty acids decompose appreciably. We note these facts in order to show the peculiar action of ammonia in preventing fatty acid decomposition at temperatures approaching the boiling point of the fatty acid.

In another example, we charge the reaction vessel with about 1,000 parts by weight of lauric acid obtained from coconut oil. We maintain the reaction vessel at a temperature of about 300 C. and treat the acid with ammonia for seven hours as described above. The reaction product consists of approximately 900 parts by weight of lauryl nitrile containing about 3 percent of unreacted lauric acid.

In another commercial embodiment of our invention we start with 1000 parts by weight of the mixture of fatty acids obtained by splitting garbage grease. After six hours treatment with ammonia at a temperature of 310 C. and under a pressure of about 25 pounds per square inch we obtain a product containing a mixture of nitriles and less than 3 percent of fatty acids. Lard fatty acids are also desirable starting materials.

Our invention is also applicable to the treatment'of unsaturated fatty acids. Forexample, we react 1000 parts by weight of oleic acid with ammonia at a temperature of about 330 C. for a period of about six hours and obtain oleic nitrile containing less than 1 percent of free fatty acid.

Our invention is also applicable to the treatment of synthetic fatty acids obtained by the oxidation of petroleum.

Although for most purposes it is unnecessary to free the final product of the last traces of acids, it is of course apparent that continued treatment will convert all of the free fatty acid present to nitriles.

The temperatures which we have specified in.

present therein. with the lower members of the series, such as capric, we operate at somewhat lower temperatures but, as stated, the temperature in the reaction vessel should be correlated with the character of the fatty acids being used. Capric acid, for example, boils at 27 H when using this acid we would heat reaction vessel l to a temperature of about 250 C. As noted above, we can increase the temperature somewhat and thus increase the rate of reaction, by operating under moderately elevated pressures since pressure increases the observed boiling point of the acid. The heating times given are, of course, dependent upon the quantity of starting material and capacity of apparatus and we are not to be limited to any particular times.

Although we have referred more particularly to the treatment of free fatty acids such as stearic, lauric, and oleic, we can also use as starting materials simple aliryl esters of the acids and also their ordinary glycerides. For practical reasons we prefer to'start with the fatty acid since this gives us as final products nitriles through outlet in and water through outlet l3. When we startwithjglycerideswe find that the final product is contaminated with glycerine and also considerable glycerine collects in the water receiver II. 'There may also be some decomposition of the glycerine at the elevated temperatures used in the catalyst chamber. But we refer to the use of esters of the fatty acids to show the generic scope of our invention so that we are not to be limited to the treatment of the free fatty acids only.

The catalyst chamber 1 is advantageously maintained at a temperature of about 400 C. This is below the decomposition point or cracking temperature of any nitriles which may be formed therein.

We are aware that others have prepared nitriles from abietic acid by reaction of the acid in vapor phase with ammonia in the presence of dehydrating catalyst. We are also aware that oleic acid has been mentioned as a diluent for that reaction. But that prior process has no reference to the process of the present invention since we are herein dealing with a substantial .liquid phase conversion in the absence of any added dehydrating agents. As stated above, we can include a catalytic material such as aluminum oxide in admixture with the fatty acids undergoing conversion but we find that the catalyst contributes no appreciable advantages and we prefer to operate without it.

Having thus described our invention, what we claim is:

1. The process of preparing aliphatic nitriles which comprises reacting a fatty substance chosen from the group consisting of fatty acids of at least six carbon atoms and esters there of while in liquid phase with gaseous ammonia and continuously vaporizing water formed in said reaction from the reaction mixture.

2. The process of preparing aliphatic nitriles which comprises reacting a fatty acid of at least six carbon atoms while inliquid phase with gaseous ammonia and continuously vaporizing water formed in said reaction from the reaction mixture.

3. The process of preparing aliphatic nitriles which comprises heating a fatty acid of at least six carbon atoms to a temperature of about 250 C. to 350 C. but not exceeding the boiling point of the acid, treating the heated acid with gaseous ammonia to form nitriles and water and driving off the water from the reaction mixture.

4. The process of preparing aliphatic nitriles which comprisesheating a mixture of fatty acids of at least six carbon atoms to a temperature of about 250 C. to 350 C. but not exceeding the boiling point of the bulk of the fatty acids present, treating the heated acids with gaseous ammonia. to form nitriles and water, and driving off the water from the reaction mixture.

5. The process as in claim 2 wherein the fatty acid is stearic.

6. The process as in claim 3 wherein the fatty acid is stearic.

'z. The process as in claim 4 whe'reinthe fatty acid mixture comprises lard fatty acids.

8. The process as in claim 4 wherein the fatty acid mixture comprises fatty acids.

9. The process of preparing aliphatic nitriles which comprises reacting a fatty acid of at least six carbon atoms while in liquid phase with an excess of gaseous ammonia to form nitriles and water, continuously vaporizing the water from the reaction mixture to give an eflluent vapor of unreacted ammonia and water, removing water from said vapor and returning the ammonia in said vapor to the reaction mixture.

10. The process as in claim 9 wherein the fatty acid is stearic.

11. The process as in claim 9 wherein the fatty acid is lard fatty acids.

12. The process as in claim 9 wherein the fatty acid is garbage grease fatty acids.

13. The process of preparing aliphatic nitriles which comprises reacting afatty acid of at least garbage grQse six carbon atoms while in liquid phase with an excess of gaseous ammonia to form nitriles and water, continuously vaporizing the water from the reaction mixture to give an eiiluent vapor containing unreacted ammonia and water, contacting the eiiiuent vapor with a dehydrating catalyst to convert any traces of vaporized fatty

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