US2463015A - Method of treating animal and vegetable oils - Google Patents

Description

Patented Mar. 1, 1949 METHOD OF TREATING ANIMAL AND VEGETABLE OILS Frederick C. Bersworth, Verona, N. J.

No Drawing. Application March 17, 1948, Serial No. 15,515

11 Claims.

This invention relates to chemistry, and more particularly to organic chemistry, and-has for its object the provision of a method of treating animal and vegetable oils to remove therefrom associated inorganic impurities and freefatty' acids and to recover the fatty acid and glycerine contents thereof in a high state of purity.

Another object is to provide a method of producing fatty acid glycerine compounds substantially free of associated inorganic impurities and of free fatty acids.

Still another object is to provide an improved process for forming substantially pure free fatty acids.

Other objects will be apparent as the invention is more fully hereinafter disclosed.

It is well known in the art that animal and vegetable oils contain various inorganic impurities, and free fatty acids, the amount and kind thereof varying widely depending upon the origin and history of the oil and the extent to which the oil has been refined and purified as well as the care with which the oil has been refined, shipped and handled. No process is known today by which the inorganic impurities contained in the oil can be substantially completely removed from such oils, particularly those not susceptible to separation by such physical means as distillation and filtering. The present invention aims to provide such a process.

I have discovered that by treating such oils with an aqueous solution containing the di-alkali metal salt of ethylene diamine tetraacetic acid, the major portion of the basic inorganic compounds present in the oil are solubilized as poly-metallic salts and complexes of this amino acid and that these poly-metallic salts are highly reactive in their ionized state in aqueous solution as sequestering agents for other neutral inorganic salts present in the oil forming water soluble complexes therewith of unknown composition.

Most animal and vegetable oils consist mainly of fatty acid glyceride compounds. Some oils,

however, either originally or following one or.

more refining steps contain some free fatty acids which in contact with metal surfaces or with basic metal compounds react therewith to form metallic soap compounds which are miscible or soluble in the fatty acid glycerides. Further, some oils are subjected to refining operations in which metallic catalysts are employed with the result that certain amounts of this catalyst contaminate the oil either in the form of submicroscopic suspended particles or as metallo-organic compounds dissolved in the glycerides.

The di-alkali metal salt of ethylene diamine tetraacetic acid, in aqueous solution has an alkaline pH of about 8 but due tothe presence therein of two acid carboxylic groups the salt reacts chemicall in such alkaline pH solutions as a strong acid towards metals and basic metal compounds, such as oxides, hydroxides and carbonates, forming poly-metallic tetra salts which are highly soluble in water.

In the treatment of animal and vegetable oils with the di-alkali metal salt of ethylene diamine tetra-acetic acid to remove therefrom the associated inorganic impurities, the practice may be modified widely without essential departure from the invention depending upon Whether the purified oil only is desired or the purified, fatty acidfree oil is desired, or upon whether it is desired to decompose the oil into fatty acid and glycerine components, each being substantially free from associated inorganic impurities.

As one specific example of the present invention the practice of removing the associated inorganic impurities only will first be described. In this process the oil is agitated with an aqueous solution containing from 2% to 10% of the dialkali metal salt of ethylene diamine tetra-acetic acid, for example, the di-sodium salt of this amino acid. The relative volumes of oil and solution may be varied widely without essential departure from the invention as long as the disodium salt content of the solution is sufiicient in amount to react with the metallic and basic compounds present in the oil to form poly-metal tetra salts therewith. In the absence of such basic metal compounds and in the presence of associated non-basic inorganic salts, such as chlorides, sulfates, etc., it is sometimes advantageous to add to the agitated oil-water solution a sufficient amount of some basic compound such as alkaline earth metal oxide, hydroxide or carbonate to form at least a small amount of the poly-metal tetra salt by reaction of the alkaline earth metal oxide with the (ii-alkali metal salt thereby to sequester these electrolytes in aqueous solution as Water soluble complexes.

Generally, a volume ratio of /2' to 1 of aqueous di-alkali metal salt solution to oil is adequate with good agitation to obtain a good dispersion of the oil in water or vice versa, and to remove from the oil the associated inorganic impurities, where the concentration of the di-alkali metal amino acid salt in the solution is as low as 5%. Heating of the agitated oil-water mixture facilitates the chemical reactions involved but temperatures in excess of the vaporizing temperature of either component of the mixture should. be avoided.

After thorough agitation of the oil-aqueous solution mixture for an extended time interval effective to complete the chemical reactions involved and to attain chemical equilibrium conditions, the mixture is allowed to cool and settle into water and oil fractions which are separated from each other in any convenient manner.

The aqueous solution fraction after being evaporated to a volume providing a concentrated solution of the poly-metallic salt of ethylene diamine tetra-acetic acid is acidified with a strong mineral acid (HCl or H2SO4) to a pH of about 1.2 to precipitate out the insoluble tetraacetic amino acid which is recovered and redissolved in caustic alkali solution for re-use as the di-alkali metal salt in the treatment of additional quantities of oil. The filtrate from the acid precipitation step normally is discarded.

Many tests have shown that the animal and Vegetable oil fraction obtained is substantially completely free of associated inorganic impurities, and that the only metallic or metalloid constituents remaining therein are those bound chemically in non-reactive organic groups present in the oil which normally cannot be expected to be removed under the reaction conditions involved.

In this invention the di-alkali metal salt of ethylene diamine tetra-acetic acid may be comprised of any one of the alkali metals, sodium, potassium, lithium or caesium. The di-sodium salt is the least expensive and most economically practical salt to employ, although for certain purposes some of the other di-alkali metal salts are better reactants.

Animal and vegetable oils treated in accordance with the first example may contain some free fatty acids or metallic fatty acid soap compounds which are non-reactive with the di-alkali metal ethylene diamine tetra-acetic acid under the conditions given in the example. The addition of free alkali to the agitated oil-amino acid salt solution mixture of the first example in an amount calculated to be approximately sufficient to neutralize the free fatty acid content of the oil and. to decompose by base exchange reaction the metallic soap compounds present in the oil, will efiectively remove these two undesired impurities from the oil leaving on settling separation substantially pure fatty acid glycerides with the alkali metal-fatty acid soap compounds dissolved along with the amino acid salts in the aqueous fraction.

Alternatively, the alkali metal hydroxide solution may be added first to the agitated oil and the free fatty acids present therein saponified to fatty acid soap compounds prior to the addition of the di-alkali metal amino acid salt solution. A third alternative is to form an aqueous solution of the di-alkali metal salt and an alkali metal hydroxide in which the alkali metal hydroxide approximates one molar weight per molar weight of the di-alkali metal salt. In such a solution the amino acid salt present consists essentially of the tri-alkali metal mono-acid salt. In such an amino acid salt the third alkali metal ion which neutralizes one of the secondary carboxylic acid groups is available for base exchange reaction with the free fatty acids and with the metallic soap compounds of the oil. The alkali metal ions neutralizing the primary carboxylic groups are not open to base exchange reaction.

The fatty acid soap compounds thus formed in the oil are soluble in the aqueous solution and may be recovered therefrom after separation of the oil and water fractions by acidification to a pH at which the fatty acid soaps are decomposed generally at a pH of about 4.5, freeing the fatty acid from alkali metal combination. The insoluble fatty acid is separated from the acid aqueous solution and on further acidification of the solution to a pH of 1.2 the amino acid is precipitated and recovered, as hereinabove disclosed.

Where, as in the third modification of this invention, it is desired to convert the oil into fatty acid soap compounds and glycerine directly without first removing the assosciated inorganic impurities or metallic fatty acid soaps as above described, the oil may be saponified in accordance with prior art practices using a caustic alkali solution such as NaOH in which is dissolved ethylene diamine tetra-acetic acid, the amount of said solution used being limited to that which provides approximately enough alkali metal ions to neutralize the fatty acids present in a known quantity of the oil plus not less than 2 and not more than 3 molar weights of caustic alkali per molar weight of ethylene diamine present in the solution. By so limiting the quantities of reactants during saponification a final saponified reaction product is obtained which on attaining chemical equilibrium contains sufficient di-alkali metal salt of ethylene diamine tetra-acetic acid to react with substantially all basic metallic compounds set free during the saponification reaction to form poly-metal tetra salt compounds of ethylene diamine tetra-acetic acid which are active as sequestering agents for neutral inorganic salts and compounds present therein.

The precise amount of ethylene diamine tetraacetic acid to any given volume of caustic alkali solution in this modification may vary widely without essential departure from the invention as long as the ratios of alkali metal hydroxide to amino acid expressed above are maintained in the saponification reaction. An amount of the tetra-acid approximating 5% generally has been found to be adequate. Any amino acid in excess of that required for reaction with basic metal compounds is recoverable subsequently for re-use in the process as hereinabove indicated. A slight excess of caustic alkali over that required for saponification normally is desirable.

In the practice of this modification, an alterna tive practice is to saponify the oil with an aqueous solution containing ethylene diamine tetra-acetic acid and alkali metal hydroxide in the ratio of 1 molar weight of the diamine to three molar weights of the hydroxide which provides an aqueous solution of the tri-alkali metal salt of ethylene diamine tetra-acetic acid. This salt, per se, is a strong sanopifying agent for fatty acid glycerides giving up to the fatty acid the alkali metal ion neutralizing one of the secondary carboxylic groups present therein and forming the di-alkali metal salt of the tetra-amino acid.

The tetra alkali metal salt of ethylene diamine tetra-acetic acid also is, per se, a saponifying agent for fatty acid glyceride compounds giving up to the fatty acid both alkali metal ions neutralizing the two secondary carboxylic groups present therein being converted thereby into the di-alkali metal salt of the tetra-amino acid.

Whereas, the triand tetra-alkali metal salts of ethylene diamine tetra-acetic acid may be used as a saponifying agent by employing an aqueous solution of the salts containing one molar weight of the salt for each oneand each two molar Weights, respectively, of fatty acids present in the oil, the use of a caustic alkali solution containing caustic alkali and about ethylene diamine tetra-acetic acid (as the tetra-alkali metal salt) in the approximate amount providing upon saponification of the oil an alkali metal hydroxide content not in excess of about two molar weights per molar weight of the diamine of that required to neutralize all of the fatty acids present in the oil, is preferred for economic reasons and for the subsequent ease in processing the aqueous solution for the recovery of the amino acid content thereof as the free amino acid for re-use in the process.

Following saponification of the oil for the complete conversion of the fatty acid content thereof to fatty acid soap compounds, the fatty acid-soap compounds obtained are dissolved in hot water and sodium chloride in an amount sufficient to insolubilize the soap compounds is added to the soap solution. The insolubilized soap compounds are separated from the aqueous solution and the water of the solution is removed by evaporation to a concentration effective to precipitate the major portion and substantially all of the sodium chloride from the concentrated solution.

The sodium chloride-free aqueous solution remaining is separated from the precipitated chloride and is acidified, preferably with HCl, to a pH of about 1.2 to precipitate the ethylene diamine tetra-acetic acid content thereof which is recovered by filtration and the acid solution remaining is neutralized, preferably by caustic alkali, the glycerine content of the solution being recovered therefrom by distillation methods, well known in the art.

As will be recognized, it is preferable to employ the lowest practical amount of ethylene diamine tetra-acetic acid effective to remove the associated metallic impurities in the practice of this modification of the present invention in order to economize and to facilitate the recovery of the same as the free amino acid during processing of the solutions after saponification.

Where it is desired to produce free fatty acids from the fatty acid soap compounds produced in accordance with the above disclosures, the fatty acid soap compounds after separation from the aqueous solution, as above described, are redissolved in water and the soap solution obtained is neutralized with a strong mineral acid to a pH of about 4.5 to insolubilize the free fatty acids. Only those fatty acids which are insoluble in water may be recovered in this manner.

It is believed apparent from the above disclosure that the invention may be widely modified without essential departure therefrom and all such modifications and departures are contemplated as may fall within the scope of the following claims,

What I claim is:

1. The method of treating animal and vegetable oils to free the same from metallic impurities which comprises agitating the said oil with an aqueous solution containing-an alkali metal salt of ethylene diamine tetra-acetic acid having at least two and not over three of its carboxylic groups neutralized by an alkali metal ion.

2. The method of claim 1, wherein the said salt is the di-alkali metal salt of ethylene diamine tetra-acetic acid and the amount thereof is approximately that providing from about 2 to'10% of the salt in the aqueous solution.

3. The method of claim 1, wherein the said aqueous solution contains alkali metal hydroxide and ethylene diamine tetra-acetic acid in the rela- Q weights per molar weight of ethylene diamine tetra-acetic acid present therein.

4. The method of claim 1, wherein aqueous solution contains an alkali metal hydroxide and ethylene diamine tetra-acetic acid, each in such relative amounts providing an'amount of alkali metal hydroxide substantially sufficient to saponify the entire fatty acid content of a known volume of said oil and an amount of alkali metal hydroxide in excess thereof substantially equivalent to two molar weights per molar weight of ethylene diamine tetra-acetic acid present therein. 5. The method of claim 1, wherein said aqueous solution contains an alkali metal hydroxide and ethylene diamine tetra-acetic acid in the relative proportions of at least two molar weights of the hydroxide'to each molar weight of the tetra-acid and up to a maximum of not over 2 molar weights of the hydroxide per molar weight of the tetraacid in excess of that molar weight empirically required to substantially completely neutralize the fatty acid content of a known quantity of the said oil.

6. The method of treating animal and vegetable oils to remove therefrom associated metallic and basic metal compounds and inorganic salt impurities which comprises agitating a known volume of the oil with an aqueous solution containing from 2 to 10% of a di-alkali metal salt of ethylene diamine tetra-acetic acid, the relative volumes of the oil and water being that providing good emulsification of one into the other.

7. The method. of treating animal and vegetable oils to remove therefrom the free fatty acid content thereof and associated inorganic impurities which comprises agitating a. known volume of the oil with an aqueous solution containing an alkali metal hydroxide and ethylene diamine tetra-acetic acid, the amount of said hydroxide in the solution being that empirically sufiicient to react with the fatty acid content of the oil and with not less than two and not over three carboxylic groups of the known quantity of tetra acid present in the solution, the said aqueous solution containing about 5% of said tetra acid.

8. A treating agent for animal and vegetable oils, said agent consisting of an aqueous solution containing an alkali metal hydroxide and ethylene diamine tetra-acetic acid in the relative amounts providing a. minimum ratio of two molar weights of the hydroxide for each molar weight of the tetra acid up to a maximum ratio providing an amount of said hydroxide in excess of this minimum amount sufiicient to substantially completely saponify the fatty acid content of a known volume of the oil.

9. The method of processing animal and vegetable oils to recover therefrom the fatty acid glyceride content substantially free of free fatty acids and associated inorganic impurities which comprises agitating the oil while in its liquid phase with an aqueous solution containing an alkali metal hydroxide and ethylene diamine tetraacetic acid, the hydroxide content of said solution being substantially that providing an amount of hydroxide empirically equivalent to the free fatty acid content of the said oil, plus an amount approximating two molar weights per molar maaeaozis weighttof tetra acid present in the solution and the amount of the tetra acid present being within the range of 2% to 10% based on the volume of the said solution, and separating the oil and water mixture obtained to recover the glycericle compounds therefrom.

10. The method of processing animal and vege table oils which comprises saponifying the oil with an aqueous solution containing an alkaline metal hydroxide and ethylene diamine tetra-acetic acid,

the amount of hydroxide present in the solution being approximately that providing an excess over that required to substantially completely saponify the fatty acid content of a known volume of the oil which is not less than two molar weights and not over three molar Weights equivalent to the known amount of ethylene diamine tetra-acetic acid present therein, dissolving the fatty acid soap compounds formed in watenvadding sodium chloride to the resultant solution to insolubilize the fatty acid soap compounds present therein and separating the same from the solution, removing the water from the solution down to the point where the major portion of the sodium; chloride precipitates therefrom and separating said chloride from the solution,

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,164,012 'Hund et al. June 27, 1939