US2727049A - Process for the alcoholysis of oils, fats, and waxes - Google Patents

Description

Patented Dec. 13, 1955 This invention relates to an alcoholysis process of oils,

fats or Waxes, applied particularly in such fashion that the alcoholic compound of one ester is replaced with another alcohol, through methods known as transesterification.

As it is known, oils and fats (triglycerides of higher fatty acids, whether saturated or not, containing from 6 to 24 carbon atoms), and waxes (esters of higher fatty acids and of higher fatty alcohols) may, through treatment with lower fatty alcohols, preferably containing from 1 to 6 carbon atoms be converted to esters of lower fatty acids and alcohols, While the alcohols initially combined with the fatty acids, are liberated (glycerin, in the case of oils and fats, and higher alcohols than the alcohol originally combined with the acid, in the case of waxes).

These alcoholysis processes are of considerable interest to the industry, inasmuch as they permit to obtain, on the one hand, glycerol or higher alcohols, and on the other hand the higher fatty acids of the oils, fats and waxes, in the form of esters, which lend themselves to divers uses, such as mainly their easier transformation, by catalytic hydrogenation, into the corresponding higher fatty alcohols.

In accordance with the current technique, the alcoholysis of fatty substances and waxes may be performed in various ways, one of such methods consisting, in the treatment of the fat or oil with an excess of alcohol, such as methanol, in the presence of an acid catalyst, such as for example, hydrochloric, sulfuric or sulfonic acids, etc., according to e. g., Haller (C. R. 143, pp. 657 and 803, of 1906, and 144, p. 462, of 1907) and Chavanne (Belgian Patent 422,877 of 1937). At this time, generally, preference is given as against this method, to the treatment of the substances with an excess of alcohol, in the presence of an alkaline catalyst, such as e. g., soda or caustic potash, alkaline carbonates, pyridine, lime, etc. This process, which is considerably faster, nevertheless, is still handicapped by several deficiencies, in that the alkaline catalyst produces formation of soaps mainly when fatty substances of a lower quality are used which are not neutral but contain free fatty acids and/or moisture, and if an alcohol is employed which is not strictly anhydrous. Because of this circumstance, the subsequent separation of reagents is usually ditficult to achieve, as the formed soaps must be destroyed by the addition of an acid, and the products contain fatty acids, which are a troublesome impurity.

In accoruance with other methods, in order to reduce the excess of alcohol which is otherwise necessary, the process is performed under pressure, with or without alkaline catalysts. Without a catalyst, as e. g., according to the process of U. S. Patent No. 2,177,407 of E. I. du Pont de Nemours & Co., the duration of the reaction is nevertheless still excessively long, and with an alkaline catalyst, e. g., in accordance with the processes of British Patents 587,532 and 587,533 of Colgate-Palmolive-Peet Company, the reaction time is considerably decreased, and better results are obtained, at a lower temperature and pressure. However, the inconvenience of having formation of soaps is not avoided but, on the contrary, increased.

The acid as well as the alkaline catalysts, employed In these reactions of a homogeneous catalysis, furthermore, have the common defect in that their action is not solely catalytic. In fact, by their nature, they are susceptible to combine under the operating conditions of fractionation with one or the other of the starting materials, not only in an intermediary manner, i. e., as a catalyst, but permanently which results in the progressive disappearance of the catalyst from the reactive medium, and weakens or even completely destroys the catalytic action by introducing into the medium undesirable impurities, such as, e. g., salts and alkyl chlorides (methyl chloride) in the case of hydrochloric catalysts, or soaps (or fatty acids) and salts in the case of an alkaline catalyst.

In order to avoid the inconveniences of the various previous processes as they were described above, this invention resorts simultaneously to the use of a relatively high pressure with a rating of about 100 atmospheres (1500 p. s. i.) in the case of the methanolysis, and to the heterogeneous catalysis by means of a fixed catalyst, which does not tend to combine permanently with the substances that participate in the esterification.

It has been actually established that an increase of the temperature, and consequently, of the pressure, may largely substitute the alkaline g'catalysts, which are usually employed in alcoholysis as the most active catalysts. However, at high temperatures of approximately from 275 to 280 C. (from 527 to 536 deg. F), corresponding to pressures of about 100 atm. (1500 p. s. i.), at which yields of the alcoholysis process are obtained which are acceptable from an industrial point of view, the freed glycerol is already subjected to considerable decomposition through the action of the pyrolysis, decomposition which may attain and even exceed 25%. it is, therefore, very desirable to have the temperature reduced by using an appropriate catalyst which, evidently, should be neither acid nor alkaline, and should be mainly such as would not tend to form soaps, and preferably active in a heterogeneous environment. Through the works of E. Fischer (Ben'chte 53, B, 1920, pp. 1634-44) it has become known that, among others, tin, cadmium, lead, zinc, and certain compounds of these metals may be used for the heterogeneous fractionation catalysis.

The principle of employing fixed catalysts in alcoholysis has been applied partially in practice in the processes of British Patent No. 634,411 and U. S. Patent No. 2,521,742 of Lever Bros, 8 Unilever Ltd, for the treatment of low-grade fatty substances (such as tallow and raw fats) containing free fatty acids. In effect, these processes adapted the method of having the fatty material traversed by a stream of alcohol vapors containing, up to 6 carbon atoms per molecule, in the presence of a catalyst selected from among the insoluble oxides of elements in groups 111 to VIII of the periodic system of elements, such as, e. g., aluminum, silicon, tungsten or zirconium oxides, used either separately, or in admixture. This treatment, having mainly the object of the esterification of free fatty acids, may nevertheless be carried sufli ciently far, and so result in the alcoholysis, by trans esterification, of a portion of the glycerides. Moreover, in accordance with these procedures, in order to complete the transesterification, the heterogeneous catalytic alcoholysis must still be followed by an alkaline homogeneous catalytic alcoholysis, which shows that the operating conditions, and particularly the recommended catalysts do not allow the complete splitting up of the fatty substances into fatty acids and glycerol.

Furthermore, the catalyzing force of substances which are likely to favor the heterogeneous catalysts of the alcoholysis process has proven to be very specific and quite variable from one catalyst to another, and therefore, practically a rather limited number of substances only can be relied on as catalysts which are suitable for use industrially. Among these, zinc silicate particularly has been found to be the most appropriate catalyst for the alcoholysis of oils, fats and waxes.

The process of alcoholysis, employing zinc silicate in a heterogeneous catalysis, may be carried out as follows:

The oil and alcohol (such as, e. g., methanol, or some other alcohol, preferably with not more than 12 atoms of carbon) are thoroughly mixed, for instance by dissolution or emulsification, and first forced under pressure (e."g., of 100 atm./approx. 1500 p. s. i. in the case of methanol) into a preheater (for example, of the pipestill type), where the mixture is heated to the required temperature (275280 C./527-536 deg. F. when using methanol), and thereafter passed into a reaction chamber, e. g., of the tubular kind, which is provided with a zinc silicate catalyst placed between baflie platesjthis reaction chamber being maintained, over the whole extent thereof, at a constant temperature of about 280 C. (536 deg. F.), for example by means of an electric heating system on the outside, and through heat insulation.

After the reaction, the mixture of esters, e. g., methylesters as well as glycerol, unconverted oils and excess alcohol, for example methanol, is cooled, expanded and injected at the foot of a wash tower, which, e. g., is equipped with Raschig rings and is caused to flow in countercurrent with water moving in a downward direction. The water carries along ,,the glycerol and the excess alcohol, which are afterwards separated by distillation and evaporation, whereas the esters and oils, being lighter than water and remaining undissolved therein, pass through the water layer in an upward direction, so as to be evacuated at the head of the wash column.

In accordance with an advantageous modification of the process, the products of the alcoholysis may be also separated from the excess alcohol by continuous distillation, immediately after the reaction mixture leaves the catalyzing tube, the distillation being, e. g., carried out by flashing, by means of the sensible heat of the mix ture, this operation owing to the elimination of the alcohol, acting in the reaction mixture as a third solvent, produces the decantation of esters and glycerol in two layers which are easy to separate, without necessitating a useless and burdensome dilution by the washing water.

In order to increase the rate of transesterification, it may be of advantage, in the treatment of glycerides, to perform the alcoholysis in two stages. To this end, the esterification products, after leaving the first reactor, are sent, after the excess of the used alcohol is separated, into a heated decanter from which the decanted glycerol is continuously drawn oif, whereas the incompletely converted mixture of esters and glycerides, is sent with the alcohol into a second reactor where it is subjected to another transesterification. Owing to this id termediary elimination of glycerol, the rate of esterification may thus be still increased.

The invention will be illustrated by the following examples, which relate to the alcoholysis of coconut oil by means of various alcohols, the first example relating more particularly to the separation of the products of the alcoholysis by washing with water and by distillation, and the other examples to separation by decantation, after first eliminating the excess alcohol by flashing.

EXAMPLE 1 A mixture of coconut oil with a mixture of 50% octanol and 50% decanol, in the gravimetric proportion of 1:1, preheated to 250 C. (482 deg. F.) under a pressure of 40 atm. (approx. 600 p. s. i.) was caused to flow, at the volumetric speed of 1 liter of mixture per 1 liter of catalyst per hour, into a transesterification kiln heated to 250 C. (482 deg. F.) and provided with a zinc silicate 4 catalyst. The reaction products, after being cooled to 60 C. (140 deg. F.) and expanded, were washed with warm water in a column in order to eliminate glycerol. The conversion of coconut oil into octanol and decanol esters resulted in a yield of EXAMPLE 2 A mixture of coconut oil and of methanol, with 33% (by weight) of methanol, preheated under a pressure of 100 atm. (1500 p. s. i.) to from 240 to 280 C. (464-536 deg. F), was caused to flow, at the volumetric speed of 1 liter of mixture per 1 liter of catalyst per hour, into a catalyzing kiln, which was provided with zinc silicate and heated to 250 C. (482 deg. F.). The reaction products of the transesterification process were expanded (by flashing) and conducted into a tower equipped with Raschig rings. The methanol, vaporized in this process was condensed in a reflux condenser, so that at the foot of the tower a mixture of methyl esters and glycerol were drawn off and separated by decantation; the glycerol dissolved in the esters, was thereafter recovered by means of scrubbing with water. This transesterification process yielded an output of EXAMPLE 3 The same procedure was applied as in Example 2, however, after flashing out the methanol and decanting the glycerol, the methyl esters were subjected to further alcoholysis, drawn off at the foot of the tower, and again charged with incompletely converted glycerides; this procedure yielded a transesterification output of 93%.

EXAMPLE 4 A mixture of coconut oil and butanol (N), at the gravimetric ratio of 1:1, was caused to flow at the volumetric speed of 0.6 liter of mixture for each liter of zinc silicate catalyst into a reaction kiln, maintained at a temperature of 250 C. (482 deg. F.), under a pressure of 50 atm. (750 p. s. i.).

After the reaction, the excess butyl alcohol was eliminated by flashing, and the butyl esters, scrubbed with warm water, resulting in a transesterification yield of 85% The Zinc silicate catalyst, used for the alcoholysis process in accordance with the invention, may be prepared in the following manner:

Example of the preparation of granulated zinc silicate catalyst A zinc acetate solution, obtained by treating 43 kg. of zinc oxide, at a temperature of from 70 to 80 C. (158-176 deg. F.) with 70 kgs. of an 80% concentration of acetic acid is poured, while it is vigorously stirred, into astainless steel vat filled with 200 liters of sodium silicate having a gravity of 36 deg. B. and diluted to 2000 liters. This mixture is filled up to 3,000 liters, agitated, and the formed precipitate is left to settle, the clear liquid floating to the surface is siphoned off, and theprecipitate is washed by successive agitations, decantations and removals of the clear liquid, until all soluble salts are eliminated. Then the washed paste is centrifuged, extruded into cylindrical pellets and the pellets are preliminarily dried at a temperature of from 40 to 50 C. (104-122 deg. F.) until they attain a consistency sufiicient to permit the transportation thereof into a drier, where they are dried at a temperature of 130 C. (266 deg. F.). By this operation, to kgs. of catalyst are obtained.

In comparison with other catalysts, such as tin hydrate in pellets, permitting a greater volumetric speed, the extruded zinc silicate is considerably less expensive, while it is sutficiently active for use in industrial operations. it is a catalyst having great resistance and little susceptibility of being contaminated, it can function as a kind of purifying body by retaining the organic sulphur and the metals of the products which are subjected to the trans esterification process. The period of its applicability, under the conditions as described in the above examples, exceeds one thousand hours.

In methanolysis with a heterogeneous catalyst of zinc silicate, the optimum pressure is about 100 atm. (1500 p. s. i.), i. e., slightly above the critical pressure (78 atm./ 1170 p. s. i.) of methanol and an increase of the pressure, even if it is quite substantial, e. g., to 800 atm. (12,000 p. s. i.) will be practically inoperative. Owing to this combination of a moderate pressure with the heterogeneous catalysis with zinc silicate acting as the catalyst, the process in accordance with the invention, even though it requires complicated equipment of a more delicate construction, is particularly difierent from the customary processes employing alkaline catalysis, by the following advantages among others.

The reaction which is simple and fast, operates continuously with a catalyst having a very long period of applicability. The products obtained in the reaction are comparatively pure, above all, not contaminated by soaps or by impurities resulting from the decomposition of soaps by a mineral acid, i. e., by fatty acids and mineral salts. Therefore, all the products of the alcoholysis process, which are of value, can be easily separated from each other, and are obtained, without difiiculty, in a pure state. This is notably so in the case of glycerol which, without any other purifying process, is recovered directly in a marketable state of saponification glycerol, and is void of mineral salts, as Well as excess alcohol (methanol) which, being recovered without additional expense by flashing, may be reused directly in the process, and consequently, this excess alcohol is a favorable feature in the execution of the alcoholysis process itself.

Nevertheless, in order to avoid the partial hydrolysis of fatty substances, which would produce free fatty acids, it is recommended that the alcoholysis be accomplished with anhydrous alcohol (methanol).

In relation to the previous alcoholysis processes by means of the heterogeneous catalysis (British Patent No. 643,411 and U. S. Patent No. 2,521,742), it is pointed out that in these processes the reaction, which moreover is efiectuated according to a difierent operative procedure, does not succeed in the complete splitting of the glycerides and must be followed up by an alkaline alcoholysis, which causes operating difliculties and produces impurities in the products which difiiculties have been successfully avoided in the process according to this invention.

What we claim and desire to protect by Letters Patent l. A process for the alcoholysis of a substance selected from the group consisting of oils, fats and waxes, which comprises passing a mixture of said substance and an excess of an aliphatic monovalent alcohol over a fixed catalyst for heterogeneous catalysis consisting essentially of zinc silicate at a pressure approximating the critical pressure of said alcohol and separating the resulting products from each other.

2. Process according to claim 1, in which the pressure employed is above the critical pressure of said alcohol.

3. Process according to claim 1, in which the alcohol contains from 1 to 12 straight chain carbon atoms.

4. Process according to claim 1, in which the said substance is a triglyceride of a carboxylic acid containing 6 to 24 carbon atoms and said alcohol is methanol.

5. Process according to claim 1, in which the zinc silicate catalyst is obtained by the precipitation of an aqeous solution of an alkaline silicate by means of an aqueous solution of a zinc salt, the separation and centrifuging of said silicate, the extrusion thereof into cylindrical pellets and the drying of the formed pellets.

6. Process according to claim 5, in which the alkaline silicate is sodium silicate and the zinc salt is zinc acetate.

7. A process for the alcoholysis of a substance selected from the group consisting of oil, fats and waxes, which comprises passing a mixture of said substance and an excess of an aliphatic monovalent alcohol over a fixed catalyst for heterogeneous catalysis consisting essentially of zinc silicate at a pressure approximating the critical pressure of said alcohol, adding water to the reaction mixture comprising esters, liberated alcohol and said monovalent aliphatic alcohol, separating the esters from the aqueous extract so formed, and separating the liberated alcohol from said monovalent aliphatic alcohol by frac tional distillation.

8. A process for the alcoholysis of a substance selected from the group consisting of oils, fats and waxes, which comprises passing a mixture of said substances and an excess of an aliphatic monovalent alcohol over a fixed catalyst for heterogeneous catalysis consisting essentially of zinc silicate at a pressure approximating but not inferior to the critical pressure of said alcohol, to form a mixture of esters, liberated alcohols and unreacted monovalent aliphatic alcohol, separating the unreacted alco hol from said mixture by distillation and separating said esters from the liberated alcohols by decantation.

9. A process for the alcoholysis of a triglyceride of a carboxylic acid containing 6 to 24 carbon atoms which comprises passing a mixture of said triglyceride of a carboxylic acid and an aliphatic monovalent alcohol over a fixed catalyst for heterogeneous catalysis consisting essentially of zinc silicate at a pressure in the vicinity of the critical pressure of said alcohol, to form a mixture of esters, glycerol, incompletely converted glycerides, and unreacted alcohol, separating the unreacted alcohol from said mixture by distillation, separating the glycerol by decantation and subjecting said esters and incompletely converted glycerides to further alcoholysis.

No references cited.

Claims (1)

1. A PROCESS FOR THE ALCOHOLYSIS OF A SUBSTANCE SELECTED FROM THE GROUP CONSISTING OF OILS, FATS AND WAXES WHICH COMPRISES PASSING A MIXTURE OF SAID SUBSTANCE AND AN EXCESS OF AN ALIPHATIC MONOVALENT ALCOHOL OVER A FIXED CATALYST FOR HETEROGENOUS CATALYSIS CONSISTING ESSENTIALLY OF ZINC SILICATE AT A PRESSURE APPROXIMATING THE CRITICAL PRESSURE OF SAID ALCOHOL AND SEPARATING THE RESULTING PRODUCTS FROM EACH OTHER.