US2748175A - Process for reducing alkyl esters of fatty acids - Google Patents

Description

PROCESS FGR REDUCING ALKYL ESTERS F FATTY ACIDS Glenn R. Wilson, Detroit, Mich, assignor to Ethyl Corporation, New York, N. Y., a corporation or Bel-aware No Drawing. Application July 28, 1952, Serial No. 301,387

4 Claims. (Cl. 260-638) The present invention relates to the reduction of vegetable and animal fats and oils, and more particularly to an improved process for effecting the reduction of the lower alkyl esters of the fatty acids occurring in these materials.

It has been shown that the naturally occuring animal and vegetable fats and oils represent an extremely valuable source of high molecular weight fatty alcohols. In their natural state these oils and fats consist largely of glycerol esters of fatty acids. Alcohols are prepared from these materials by reducing the esters with an alkali metal such as sodium, in the presence of a reducing alcohol, followed by hydrolysis to form the corresponding fatty alcohols.

The overall economics of such a process depends in large part upon the recovery of glycerol as a byproduct. There are, in general, two ways of approaching this problem of glycerol recovery. The first consists of reducing the oil, i. e. the glycerides, as such and recovering the glycerol after the hydrolysisstep. This expedient, however, is unattractive from the commercial standpoint since upon hydrolysis the glycerol goes into a caustic layer, and it is extremely difficult, if not impossible, to economically recover glycerol from this mixture. The second expedient, and the one which offers the most promise for commercial success, consists of recovering the glycerol from the oil or fat prior to reduction. This is accomplished by treating the oil with an aliphatic alcohol so as to effect what is known as a transesterification or ester exchange. In this process the alkyl radical of the alcohol displaces the glycerol radical so as to permit recovery of glycerol and form the alkyl ester of the fatty acids. It has been found that this transesterification proceeds most readily using the lower aliphatic alcohols such as methanol and ethanol. While this process does permit the efiicient recovery of glycerol as a valuable byproduct, it introduces an additional complication to the overall reduction process. It has been found that these lower alkyl esters of fatty acids are difiicult to reduce since upon reduction the reaction mass sets-up to a semi-solid immobile mass which cannot be stirred or mixed satisfactorily by conventional processing equipment.

Attempts have been made to solve this problem by carrying out the reduction with alkali metal in an inert solvent medium using solvents such as benzene, toluene, xylene, and the like. Although the alkyl esters themselves are soluble in such solvents, the reduction mixture tends to gel and solidify, even in the presence of such solvents. The precise reason for this is not known, but it is postulated that one of the intermediates formed during the reduction is responsible for this difliculty. The obvious solution is" to employ a solvent in which this unknown intermediate will dissolve, but attempts in that direction have been unsuccessful. The problem has also been approached from the standpoint of using extremely high solvent-to-ester ratios, i. e. ratios of the order of to 1. This latter expedient, in addition to compliatent eating the over-all process by the presence of so large a volume of materials, does not solve the problem since the reduction mixture still sets-up to an immobile mass. This is true even though the ester is added to the reduction mixture at a very slow rate. It is apparent that both of these expedients; that is, the use of high solventto-ester ratios and slow addition of ester to the reaction mixture, necessarily add cost to the final product.

It is therefore an object of my invention to overcome these disadvantages of the prior art and provide a new and improved process for economically effecting the reduction of alkyl esters of fatty acids. A further object of my invention is to provide an improved process for reducing such esters with an alkali metal in the presence of a reducing alcohol. A still further object is to provide an efficient process for preparing high molecular weight fatty alcohols from fats and oils. These and other objects of my invention will become apparent from the following discussion.

The above and other objects of my invention are accomplished by carrying out the reduction of alkyl esters of fatty acids with alkali metal in the presence of minor amounts of a pyridine. I have found that the presence of a pyridine in the reaction mixture is highly effective in preventing the mixture from gelling or solidifying. Furthermore, when carrying out the reduction in accordance with my invention, the extremely high solvent-to-ester ratios previously thought necessary need not be employed. Another advantage which my invention offers is that the alkyl ester to be reduced can be added to the reduction mixture at a reasonably rapid rate so as to materially decrease the time required for the overall reaction. It is apparent that these advantages result in considerable economic savings.

The pyridines which I employ in my process consist of pyridine itself as well as the various. substituted pyridines. Typical examples of the substituted pyridines which can be used include dimethyl pyridine, Z-methyl pyridine, 3-methyl pyridine, 4-methyl pyridine, 2-ethyl pyridine, 3-ethyl pyridine, 4-ethyl pyridine, ethylmethyl pyridines (such as ,B-collidine, 'yc0llidine, and aldehydine), 2-isopropyl pyridine, 4-isopropyl pyridine, 2,4,6- trimethyl pyridine, tetramethyl pyridine, quinoline, acridine, and the like. Still other pyridines can be employed, the above list merely representing those most commonly known. The amount of the pyridinethat I employ in my process is not especially critical, although I have found that best results are obtained when using between 2 to 20 percent by weight of the alkyl ester being reduced.

A better understanding of my invention can be obtained from a consideration of the following description of the overall process for reducing the alkyl esters of fatty acids. As previously mentioned, prior to reduction the glycerol is recovered from the fat or oil by treating the oil with a lower aliphatic alcohol so as to form the corresponding alkyl esters of the fatty acids and simultaneously recover the glycerol. Ethanol or methanol are preferably employed in this transesterification or ester exchange step. The alkyl ester of the fatty acid is then dissolved in a suitable solvent such as benzene, toluene, or xylene. In accordance with my invention, the solventto-ester ratio generally need not exceed 5 to 1, and ratios as low as 2 to 1 can be successfully employed. A reducing alcohol is added to this mixture. The reducing alcohols employed are generally well known in the art and can be any of the lower, secondary, or tertiary aliphatic alcohols such as t-butyl alcohol, sec-butyl alcohol, t-amyl alcohol, methyl isobutyl carbinol, and the like. The amount of reducing alcohol generally employed in reduction processes of this nature is about 5 per cent in excess of the stoichiometric amount.

The alkali metal which is employed as a reducing agent can be used in the form of lumps or bricks, but it has been found that the reduction reaction proceeds more smoothly if the alkali metal be used in dispersed form. Such alkali metal dispersions are well known in the art, and are generally prepared by fusing the metal in the presence of inert liquid medium and subjecting the mixture to vigorous agitation. Any inert liquid can be employed as the dispersing medium, although for use in my process, it is preferred that the liquid chosen as the dispersing medium be the same as that used for the ester solvent. Thus, aromatic hydrocarbons such as toluene and xylene are well suited for this purpose, although still other inert liquids can be used. The amount of alkali metal present in such dispersions can vary, and dispersions having metal concentrations from trace amounts up to 60 per cent by weight are common. For use in my process, however, it is preferred that the dispersion have a metal concentration of between 20 and 50 per cent. The amount of alkali metal employed in reducing the esters is generally between 5 and per cent in excess of that stoichiometri'cally required.

The reduction reaction itself is carried out in accordance with my invention by adding a pyridine to such a dispersion and thereafter heating the dispersion so as to obtain a vigorous reflux. The ester solution containing the reducing alcohol is then added to the dispersion at a rate so as to maintain reflux. After all of the ester has been added, the reaction mixture is cooked for a period of about one hour at reflux temperature and thereafter hydrolyzed so as to convert the alcoholates formed to the corresponding alcohols. Upon hydrolysis, the alcohols, together with the solvent and reducing alcohol, separate into a separate phase, and the product alcohol is recovered by distillation.

To illustrate the advantages of my invention over the prior art, the following two examples are given. In Example I a conventional reduction is carried out in which no pyridine is employed in the reduction mixture. Example II is identical to Example I with the exception that a pyridine is present in the reaction mixture. The material chosen for reduction in these examples was the methyl ester of coconut oil fatty acids since these particular esters have been found to present the most difiicult problems with respect to maintaining a mobile reduction mixture. All percentages and parts are on weight basis.

Example I One hundred parts methyl esters of coconut oil fatty acids was dissolved in 346 parts toluene, and 102 parts methyl isobutyl carbinol was added to this mixture. Forty-four parts sodium was dispersed in 174 parts toluene and the dispersion heated so as to establish a vigorous reflux. The ester mixture was then slowly added to the dispersion while maintaining a vigorous reflux. This addition was made slowly so as to attempt to avoid solidification or gelling of the reaction mixture. After five hours only one-half of the ester mixture had been added, and the reaction solution was so viscous that it could not be stirred and consequently could not be hydrolyzed. It was necessary to discard the entire reaction mixture.

Example II A reduction was carried out using the same quantities of materials as described in Example I with the exception that 9.8 parts of pyridine was added to the dispersion before the addition of the ester mixture. After bringing the dispersion to vigorous reflux the ester mixture was added, and within 40 minutes the entire amount had been added, and no thickening of the reaction solution occurred. The mixture was refluxed for a period of 30 minutes and thereafter hydrolyzed with 383 parts water. The product alcohol, along with the solvent and reducing alcohol, separated into a separate phase from which the product alcohol was recovered by distillation. Seventyeight parts of coconut oil alcohols, representing a yield of 86.7 per cent of theoretical, was obtained.

Example III The reduction was carried out using the same quantities of materials as described in Example I with the exception that 5 parts pyridine was added to the dispersion prior to carrying out the reaction. As in Example II, the ester mixture was added at a very rapid rate with no thickening of the reduction solution. This addition was complete after 30 minutes. The reaction mixture was refluxed for one hour, after which the mixture was hydrolyzed and the product alcohol recovered as in Example II. The yield of coconut oil alcohols obtained was 90.7 per cent of theoretical.

The above examples clearly demonstrate the advantages of my process over the prior art. Example I demonstrates what generally occurs in trying to reduce alkyl esters of fatty acids by conventional means using an alkali metal as a reducing agent. The reduction mixture rapidly set-up to an immobile mass and actually made it impossible to go forward with the reaction. In contrast to this, in Examples 11 and III wherein minor amounts of a pyridine were present in the reaction mixture, this solidification and gelling did not occur, thus permitting rapid addition of the ester to the reaction mixture. In the case of Examples II and III, the addition was substantially complete at the end of 30 to 40 minutes, whereas in the case of Example I, after five hours only one-half of the ester solution had been added and still the reaction mixture gelled.

As indicated above, the methyl esters of coconut oil fatty acids were chosen for these examples since they appear to present the most difl'icu'lt problem. It is apparent, however, that my invention can be applied with equal success to the alkyl esters of other fatty acids such as those contained in cottonseed oil, rape seed oil, linseed oil, palm oil, peanut oil, tallow, okra seed oil, safllower seed oil, sunflower seed oil, rice bran oil, castor oil, soybean oil, olive oil, and the like. Also it is to be understood that any of the substituted pyridines can be used in place of pyridine as in the above examples. Thus, equally good results are obtained using dimethyl pyridine, 2-rnethyl pyridine, Z-ethyl pyridine, ethylmethyl pyridine, 4-isopropyl pyridine, 3,4,6-trimethyl pyridine, quinoline, and the like.

It is also apparent that alkali metals other than sodium can be used as reducing agent. For example, potassium or lithium or any of the other alkali metals can be employed with equally good results. Similarly, other secondary and tertiary alcohols can be employed as reducing alcohol such as t-butyl alcohol, t-amyl alcohol, methyl cyclohexanol, and the like.

It is to be understood that the above examples are given only for the purpose of illustrating specific embodiments, and I intend by the appended claims to cover all modifications falling within the spirit and scope of my invention.

I claim:

1. A process for reducing an alkyl ester of a fatty acid, comprising reacting said ester with an alkali metal and reducing alcohol in the presence of an essentially inert hydrocarbon solvent and in the further presence of about 2 to 20% of a pyridine based on the weight of the ester.

2. A process for reducing the methyl esters of fatty acids, comprising reacting said esters with an alkali metal and reducing alcohol in the presence of an essentially inert aromatic hydrocarbon solvent and in the further presence of about 2 to 20% of a pyridine based on the weight of the ester.

3. A process for reducing the methyl esters of coconut oil fatty acids, comprising reacting said esters with an alkali metal and a reducing alcohol in the presence of an essentially inert aromatic hydrocarbon solvent and in 5 the further presence of about 2 to 20% of pyridine based on the weight of the ester.

4. In a process which comprises reducing about 100 parts by weight of methyl esters of coconut oil fatty acid esters with about 44 parts by weight sodium and 6 about 102 parts by weight methylisobutyl carbinol in the presence of about 520 parts by weight of toluene, the improvement which comprises conducting said process in the further presence of 5 parts by weight of pyridine.

References Cited in the file of this patent UNITED STATES PATENTS Bouveault Oct. 15, 1907 Scott Oct. 29, 1935 Hansley Oct. 24, 1939 Blinotf Feb. 8, 1949

Claims (1)

1. A PROCESS FOR REDUCING AN ALKYL ESTER OF A FATTY ACID, COMPRISING REACTING SAID ESTER WITH AN ALKALI METAL AND REDUCING ALCOHOL IN THE PRESENCE OF AN ESSENTIALLY INERT HYDROCARBON SOLVENT AND IN THE FURTHER PRESENCE OF ABOUT 2 TO 20% OF A PYRIDINE BASED ON THE WEIGHT OF THE ESTER.