US3413324A - Process for alkali refining of glyceride oils and fatty acid esters - Google Patents

Description

NOV. 26, 1968 P, P 3,413,324

PROCESS FOR ALKALI REFINING OF GLYCERIDE OILS AND FATTY ACID ESTERS Filed March 14, 1966 INVENTOR.

PAULUS JOHANNES SEIP BY'EMWL, 4m,

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his ATTORNEYS United States Patent 3,413,324 PROCESS FOR ALKALI REFINING OF GLYCERIDE OILS AND FATTY ACID ESTERS Paulus Johannes Seip, Zwijndrecht, Netherlands, assignor to Lever Brothers Company, New York, N.Y., a corporation of Maine Filed Mar. 14, 1966, Ser. No. 541,436 Claims priority, application Luxembourg, Mar. 19, 1965, 48,221; Dec. 20, 1965, 50,100 12 Claims. (Cl. 260-425) ABSTRACT OF THE DISCLOSURE A process for the alkali refining of glyceride oils and other fatty acid esters containing free fatty acid which gives unexpectedly low refining losses comprises mixing the ester with an ester (of the same or different chemical constitution) containing a lower percentage of free fatty acid in such proportions that the percentage of free fatty acid in the mixture is not greater than 4% and substantially less than in the first-mentioned esters, and the free fatty acid in the mixture is then substantially neutralized by the action of aqueous alkali thereon. Continuous methods for carrying out the invention are described, in one of which part of the neutralized oil issuing from a reaction space in which neutralization has been effected is recirculated to that space.

The invention relates to improvements in the treatment of fatty acid derivatives and especially to the alkali re fining of glyceride oils and other functional fatty acid derivatives, containing free fatty acids and other impurities.

The term glyceride oils will be used throughout this specification to include animal and vegetable glyceride oils which .are normally solid, as well as those which are normally liquid.

In alkali refining the refining losses tend to increase with increasing free fatty acid content of the glyceride oils or other materials. It is known that, if the crude oil to be refined contains considerable amounts of free fatty acids, say above 4%, the refining losses per kg. of fatty acid present are higher than in the case of glyceride oils of the same kind with a much lower free fatty acid content. It has further been found that the type of free fatty acid present in the crude oil or other material plays a role and thus oils containing, for instance, predominant amounts of free fatty acids with a chain length of 16 carbon atoms or more give less satisfactory results in alkali refining than oils containing predominantly'free fatty acids with a chain length below 16 carton atoms.

According to the present invention a method is provided for the alkali refining of crude glyceride oils and other functional derivaties of fatty acids, containing free fatty acids and other impurities, especially those having a relatively high initial free fatty acid content, in which to the oils or derivatives before the alkali treatment oils or derivatives are added having a lower free fatty acid content than said crude oils and derivatives.

It has surprisingly been found that by carrying out the process according to the invention a considerable reduction in the refining losses is obtained, which is greater than that to be expected from the interpolation of the results of separate refining treatments.

The process of the invention is suitably carried out by mixing oils and other functional derivatives of fatty acids of the same type. In view of the aforesaid synergistic effect even an oil or derivative may be added which has already been alkali-refined.

In treating crude oils containing substantial amounts of free fatty acids, either saturated or unsaturated, with a chain length of 16 carbon atoms or more, which generally tend to give higher refining losses than those oils containing free fatty acids with a chain length below 16 carbon atoms, it is advisable to mix them prior to the alkali refining with oils of the lauric acid class, such as coconut oil and palmkernel oil. When oils are treated which contain predominantly saturated free fatty acids with a chain length of 16 carbon atoms or more, such as cocoa butter, beef tallow, lard, mutton tallo, Borneo tallow, as well as hardened fats, these may also be mixed with oils containing predominantly unsaturated free fatty acids with a chain length of 16 carbon atoms or more, such as vegetable liquid oils of the kind of cottonseed oil, soybean oil, olive oil, sunflower oil and groundnut oil, so as to obtain a reduction in refining losses.

Although the free fatty acid content in the oil mixture to be treated may differ appreciably for each particular oil if good results are to be obtained, it can be broadly indicated that this content is in the range of 14%, with preference for 25%.

The process may be carried out batchwise or continuously; in the latter case oil with a lower free fatty acid content is mixed with the crude oil prior to the alkali treatment. In a continuous process, however, it is preferred to separate during refining part of the treated oil from the aqueous phase and recirculate and add it to the crude oil to be treated. Thus, according to this modification, it is now possible in a continuous process to obtain in one step a neutral oil with a satisfactory low content of free fatty acids with only a small refining loss. The amount of oil to be added to the crude oil orin the continuous processto be recirculated is dependent on the kind of crude oil treated, the amount and type of free fatty acids present in the crude oil, and on other process conditions, like temperature and concentration of the alkali. In the continuous process the amount of oil to be recirculated must not be chosen too high in order not to reduce the throughput more than necessary, nor too low lest the process be ineffective. In general the amount must be so chosen that the free fatty acid content of the mixture obtained, which has to be refined, is in the range which is advantageous for the particular oil to be treated. Apart from the already indicated condition it can be stated that the reduction of the free fatty acid content of the oil coming into contact with the aqueous alkaline solution must be so that the soap content of the refined oil is generally not more than about 0.1% by weight. For instance, for palmoil with an initial free fatty acid content of about 6%, the preferred recirculation ratio is about 0.5. The recirculation ratio is defined as the amount of oil which is recirculated in proportion to the amount of crude oil which is introduced into the refining apparatus. The concentration of the aqueous alkali used usually lies in the range of 0.05 N to 2 N.

The method of the present invention may be carried out in a variety of ways. The oil may, for instance, be neutralized in the still frequently used stirred cylindrical kettle having a cone-shaped bottom, the alkali being sprayed onto the oil. Or, as in a more recently described method, the oil in the form of droplets may be caused to rise through a static body of aqueous alkali. Another advantageous method of carrying out the invention is the one described in my co-pending application No. 366,240, filed May 11, 1964, where the oil and the aqueous solution are caused to flow in the same or opposite direction through a succession of treating regions in each of which the oil flows smoothly, horizontally or upwards at a small angle, on a surface of the aqueous solution, and transfer between each such region and the next is effected in such a way that any layer of aqueous soap solution that has formed immediately below the oil layer is displaced to bring the oil into direct contact with aqueous alkaline solution containing less soap and more unreacted alkali than is present in such a layer, substantial intermixture of the aqueous and oil phases being avoided throughout.

Another advantageous process is that in which the alkali refining process is effected continuously in a bed of chemically inert packing material by causing the glyceride oil and the alkaline liquid to make random contacts with each other while flowing along tortuous paths through said bed and subsequently separating the oil and aqueous liquids by virtue of their different specific gravities. This process may be carried out at temperatures from 60-100 C., but also temperatures above 100 C. are suitable, in which case the refining process has generally to be carried out at superatmospheric pressures to avoid evaporation of the aqueous phase. Such a process is described in my co-pending application, Ser. No. 441,378, filed Mar. 19, 1965.

The process of the present invention may also be carried out continuously with the aid of centrifuges.

The improved method is also applicable to functional derivatives of fatty acids other than glyceride oils, which, for instance owing to their way of preparation or by other circumstances, contain appreciable amounts of free carboxylic acids, in particular free fatty acids. Among such derivatives can be mentioned esters, amides and the like, which, owing to their way of preparation or as a result of hydrolysis, thermal decomposition or other causes contain free carboxylic acids, in particular free fatty acids.

Compounds like partial or complete esters, amides which may be substituted and possibly nitriles which can be treated according to the process of the invention can be schematically indicated according to the composition of the carboxylic acid from which they are derived, viz.:

(a) A compound derived from substituted or not substituted fatty acids with 2-28 carbon atoms, saturated as well as unsaturated, either epoxidized or not;

(b) Compounds derived from polycarboxylic acids which may be substituted, such as, e.g., the aliphatic dicarboxylic acids (adipic acid, azelaic acid, succinic acid), aromatic dicarboxylic acids (phthalic acid, tercphthalic acid, etc.), polymerized fatty acids and other polycarboxylic acids, such as, e.'g., citric acid. The polycarboxylic acids maybe epoxidized.

The esters can be prepared from the above acids with as an alcohol component one or more of the alcohols belonging to the following classes:

(a) Aliphatic or aromatic monovalent alcohols, like methanol, ethanol, octanol, benzylalcohol, laurylalcohol, stearylalcohol, which may be substituted;

(b) Aliphatic or aromatic polyvalent alcohols, like propyleneglycol, triethyleneglycol, butanediol, neopentylglycol, glycerol, trimethylolpropane, trimethyolbutane, pentaerythritol, polypentaerythritol, allylalcohol, etc., which may be substituted.

The process is also applicable to mixtures of glyceride oils or mixtures of other fatty acid derivatives.

In the accompanying figure a flow sheet of the modification of the process according to the invention is indicated, in which a glyceride oil is continuously refined with an aqueous alkaline solution and part of the refined oil is recirculated. The oil is stored in the vessel 1 and is after heating introduced into a neutralizing column 2 via pipe 3. The neutralizing vessel may be one as described in our British patent application No. 11,861/ 64, but the figure is applicable to a variety of continuously refining processes. The oil is introduced at the bottom of the column in the figure, but of course it can be introduced at any other place if desired, depending on the P evailing process conditions. The alkali stored in another vessel 4 is after heating introduced into the column by pipe 5, but it can be introduced at any other place, if necessary. The oil separated from the alkali leaves the column through pipe 6 and is collected in a vessel 7. The pent alkali leaves the column through an outlet 8 and is transported to a collecting vessel 9. Part of the refined oil is recirculated by means of pipe 10 and introduced into the stream of crude oil. In starting up the process it is advisable to mix initially the crude oil to be refined with another oil, which may be of a different kind, but which has a sufiiciently low free fatty'acid content to 'bring the free fatty acid content of the crude oil to the desired low level. In the figure this is indicated by conduit 11. After some time when equilibrium conditions are obtained, the supply of this oil with a low free fatty acid content is stopped, for instance by switching valve 12 and part of the neutralized oil is recirculated in the desired amount.

The following examples illustrate the invention:

Example I Tallow was neutralized in an apparatus of the kind as described in British patent application No. 19,008/ 63. The apparatus consisted of 36 zig-zag mounted guide plates having a length of 18 cm. and a width of 5 cm., placed in a slope of 5 in a housing having a length of 18 cm., a width of 5 cm. and a height of 100 cm. In each plate a pipe was mounted in the middle of the plate at a distance of 1 cm. from the end of the plate. The pipe ha d to carry the alkaline solution downward through the oil layer onto the plate below. The alkaline solution had a strength of 0.1 N to which 1% salt was added. This solution was dosed in an excess of 25%. The temperature during neutralization was C. After this treatment the neutralized oil was post-treated with a 10 volume percent solution of 0.1 N caustic soda solution and subsequently washed with 10 volume percent (based on the amount of oil) of water to remove the soap.

To illustrate the influence in mixing two batches of an oil, either of which has different amounts of free fatty acids, a tallow with about 1, 2, 3, 4, 5 and 6% of free fatty acids respectively was neutralized in the apparatus as described.

From the figures obtained it may be seen that the arithmetical average of the ultimate free fatty acid content of two samples of tallow, either of which has a different initial free fatty acid content, is always higher than the ultimate free fatty acid content of a neutralized tallow having an initial free fatty acid content that is the arithmetical average of the initial free fatty acid content of said two samples, when refined in the same way.

The results were as follows:

Neutralized oil Crude oil, Neutralizing Percent LLa. F.t.a., Moisture, Soap, factor Percent Percent Percent 0. 46 0. 24 0. 004 1. 6 0.59 0. 17 0.005 1. 5 0. 55 I. I6 0. 004 1. 6 0. 63 O. 36 0.010 1. 7 1. 12 1 34 0. 053 2. l 1. 14 2. 1

v From the neutralizing factor it follows that kg. of tallow with 1.12% initial free fatty acid loses of neutral oil during the neutralization treatment.

The 4.93% free fatty acid containing tallow has lost (2.11) 4.93:5.43 kg. of neutral oil per 100 kg. when treated, so that the total loss is 5.43+0.67=6.1 kg. of neutral oil per 200 kg. of tallow.

If these oils were mixed before neutralization, a batch of 200 kg of tallow having an initial free fatty acid content of 3.03% should be obtained. This oil neutralized in the same way gives a neutralizing factor of 1.6. The total loss in neutral oil is consequently:

2 3.03 0.6=3.6 kg. per 200 kg. of tallow This shows the considerable improvement obtained (41% less refining loss) when the oils to be neutralized are mixed before the treatment.

Example 2 (1) Palm oil was alkali-refined in a column of stainless steel with a height of 125 cm. and a diameter of cm. of the kind as described in British patent application No. 11,861/ 64. In the column a bed of inert fillings was present which had a height of 90 cm. and consisted of stainless Raschig rings of 8 by 8 by 0.5 mm. The column was closed to the atmosphere and the refining effected under a pressure of about 6.5 atm., the atmosphere being composed of introgen saturated with water vapour. The alkaline solution flowed countercurrently to the dispersed oil phase, the oil being introduced in the column just below the bed. The initial free fatty acid content of the crude oil was 6.1% and the water content 0.02%. The alkaline solution has a concentration of 0.3 N and was present in an excess of The temperature during the neutralization was kept at 140 C.

In a first trial the crude palm oil was treated without any recirculation and it appeared that a small through put had to be maintained to obtain a neutral oil with a satisfactory low soap content. At higher throughputs it was impossible to obtain a neutral oil with a low soap content.

In a second trial a portion of the refined palm oil was recirculated into the crude oil stream in such an amount that the recirculation ratio was about 0.5. The throughput of the crude oil amounted to 3 tons/m. /hr. A neutral oil was obtained which had a free fatty acid content of 0.06, a water content of 1.3 and a soap content of 0.08%. The refining factor was estimated at 1.3.

The refining factor was determined as follows:

weight free fatty acid in crude oil weight free fatty acid in neutral 011 Example 3 Crude palm oil with a free fatty acid content of 12.8% was alkali refined using the same apparatus as described in Example 2. The alkali had a concentration of 0.4 N and was present in an excess of 25%. The temperature was 140 C. In a first trial the palm oil was refined with a throughput of 1.8 tons/m. /hr. without recirculation. A neutral oil was obtained with a rather high soap content (about 1% of soap and 10% of water). In a second trial part of the refined palm oil was recirculated with a ratio of 2. The neutral oil had a final fatty acid content of 0.10, a water content of 1.4 and a soap content of 0.08%. The refining factor was estimated at 1.3. In a third trial in which the throughput of the crude oil was increased to 2.5 tons/m. /hr., the recirculation ratio being 1.5, the final free fatty acid content was 0.09, the water content 1.8 and the soap content 0.12.

Example 4 Illipe butter was treated in the apparatus as described in Example 2, the initial free fatty acid content being 24.4%. The alkali had a concentration of 0.4 N and was present in an excess of 25%, the temperature was adjusted at 140 C. The crude oil throughput amounted to 1.2 tons/mF/hr. In a first trial without any recirculation the neutral oil contained a high amount of soap (about 20% of water and 2.0% of soap). In a second trial a portion of the refined oil was recirculated (the recirculation ratio being 3) and good results were obtained. The final free fatty acid content was 0.12%, the water content 1.3 and the soap content 0.07%. The refining factor was estimated at 1.3.

Example 5 Fish oil was treated in the apparatus as described in Example 2. The free fatty acid content of the fish oil was about 3%. It has to be observed that fish oildepending on the source where it comes fromis often difficult to refine, even if the free fatty acid content is in the range which gives no difficulties for other oils. In a first trial 3.9 tons/m. /hr. of fish oil was refined at a temperature of C. with an alkaline concentration of 0.4 N present in an excess of 50%. The final free fatty acid content was 0.11, the water content 2.5 and the soap content 0.17. In a second trial 2.2 tons/m. /hr. oil was recirculated, maintaining the throughput of crude oil on 3.9. The final free fatty acid content was 0.12, the water content 1.3 and the soap content 0.05. From these figures it appears that the water and soap content of the neutral oil was appreciably reduced. In another trial under the same conditions an excess of alkali was used of 25% instead of 50%. In this case the results were as follows:

Neutral oil without recirculation:

Free fatty acid content 0.14

Water content 7.5

Soap content 0.5

And with recirculation:

Free fatty acid content 0.17

Water content 1.4

Soap content 0.06

This again stresses the considerable reduction in water and soap content of the final oil.

Example 6 Stearyl stearate was treated in the apparatus as described in Example 2, the initial free fatty acid content being 10%. The alkali had a concentration of 0.4 N and was present in an exces of 25 The temperature was kept at C. and the throughput amounted to 1.4 tons/m. /hr. In a first trial without any recirculation the ester contained a relatively high amount of water (about 12%) and soap (about 1.5% In a second trial a portion of ester treated was recirculated, the recirculation ratio being 2, and good results were obtained.

The final free fatty acid content was 0.1% and the soap content 0.02%.

What is claimed is:

1. Process for alkali-refining fatty acid esters contaminated with free fatty acid, wherein said esters are mixed with fatty acid esters containing lower percentages of free fatty acid in such proportions that the percentage of free fatty acid in the mixture is not greater than 4% by weight and substantially lower than in the first-mentioned esters, and the free fatty acid in the mixture is then substantially neutralized by the action of aqueous alkali thereon.

2. Process for alkali-refining glyceride oils contaminated with free fatty acid, wherein said oils are mixed with glyceride oils containing lower percentages of free fatty acid in such proportions that the percentage of free fatty acid in the mixture is not greater than 4% by weight and substantially lower than in the first-mentioned esters, and the free fatty acid in the mixture is then substantially neutralized by the action of aqueous alkali thereon.

3. Process according to claim 1, characterized in that the process is carried out continuously and during refining part of the treated material is sepaarted from the aqueous phase, recirculated and added to the crude material to be treated in such proportions that the percentage of free fatty acid in the mixture is not greater than 4% by weight and substantially lower than in the initial ester.

4. Process according to claim 2 which comprises feeding continuously into a reaction space at a temperature above 60 C. aqueous alkali of concentration 0.05 N to 2 N, the said oil and an oil of lower free fatty acid content, in such proportions that the percentage of free fatty acid in the mixture is not greater than 4% and substantially lower than in the first-mentioned oil, allowing the mixture to travel through said reaction space at a temperature above 60 C. until the free fatty acid is substantially neutralized, stopping the flow of said oil of lower free fatty acid content and instead continuously feeding back into the reaction space a proportion of the neutralized oil said proportion being such as to maintain the initial free fatty acid content of the mixture substantially unchanged.

5. Process according to claim 1 which comprises feeding continuously into a reaction space at a temperature above 60 C. aqueous alkali of concentration 0.05 N to 2 N, the said ester and an ester of lower free fatty acid content, in such proportions that the percentage of free fatty acid in the mixture is not greater than 4% and substantially lower than in the first-mentioned ester, allowing the mixture to travel through said reaction space at a temperature above 60 C. until the free fatty acid is substantially neutralized, stopping the flow of said ester of lower free fatty acid content and insttead continuously feeding back into the reaction space a proportion of the neutralized ester said proportion being such as to maintain the initial free fatty acid content of the mixture substantially unchanged.

6. Process according to claim 2, characterized in that the alkali-refining process is effected continuously in a bed of chemically inert packing material by causing the glyceride oil or other functional derivative of fatty acids and the alkaline liquid to make random contacts with each other While flowing along tortuous paths through said bed at a temperature above 100 under superatmos pheric pressure and subsequently separating the oil or derivative and aqueous liquids by virtue of their different specific gravitie's.

7. Process according to claim 2 characterized in that the amount of material added is so chosen that the free fatty acid content of the mixture to be treated is in the range of 2-5 by weight.

8. Process according to claim 2 characterized in that the process is carried out continuously and during refining, part of the treated material is separated from the aqueous phase, recirculated and added to the crude material to be treated in such proportions that the percentage of free fatty acid in the mixture is not greater than 4% by weight and substantially lower than in the initial oil.

9. Process according to claim 2, characterized in that oils and derivatives of the same kind are mixed, differing only in free fatty acid content.

10. Process according to claim 2 characterized in that the oil or derivative to be treated is one of which a predominant amount of the free fatty acids present has a chain length of 16 carbon atoms or more.

11. Process according to claim 2, characterized in that an oil or derivative is added which has already been alkali-refined.

12. Process according to claim 2, characterized in that the alkali-refining process is effected continuously in a bed of chemically inert packing material by causing the glyceride oil or other functional derivative of fatty acids and the alkaline liquid to make random contacts with each other while flowing along tortuous paths through said bed and subsequently separating the oil or derivative and aqueous liquids by virtue of their different specific gravities.

References Cited Bailey, A. E.: Industrial Oil and Fat Products, Interscience Publishers, Inc., New York, 1945, pp. 502-513 relied on.

NICHOLAS S. RIZZO, Primary Examiner.

A. M. TIGHE, Assistant Examiner.

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