US2732388A

US2732388A - Treatment of fatty oils

Info

Publication number: US2732388A
Authority: US
Publication date: 1956-01-24
Anticipated expiration: 1973-01-24

Description

United States Patent TREATMENT or FATTY orrs Fred S. Sadler, Savannah, Ga, assignor to The Sharples Corporation, a corporation of Beiaware N0 Drawing. Application May 14, 1953, Serial No. 355,179

9 Claims. (Ci. 25l-425) This. invention relates to a process for purifying animal, marine, and vegetable oils, including the fats and greases, and commonly classified under the general term of fatty oils, i. e., oils from animal, vegetable and marine sources and consisting chiefly of glycerides and esters of fatty acids. It particularly relates to a process for conditioning fatty oils for refining to remove various impurities and otherwise prepare the fatty oil for various uses. More specifically the invention relates to the refining of fatty oils such as those obtained from cottonseed, sesame seed, sunflower seed, corn, soybean, cocoanut, palm, peanut, whale, various fish, and fish livers, and fatty oils such as lard and tallow.

Undesirable constituents of crude fatty oils, which constituents are herein termed impurities, and which may render the oils inedible or less desirable as a food or other product, include free fatty acids, gums and/or coloring matter. The term gums, as used herein, is intended to broadly cover resins, phosphatides, mucines, certain carbohydrates, and the like, which normally occur in crude fatty oils. These gums are either in solution in the oil or are in colloidal suspension, or both, or dispersed in some other way throughout the fatty oil.

In common practice, the impurities are removed from the oil by the addition of an aqueous alkaline refining reagent such as aqueous caustic soda solution. This alkaline reagent reacts with the free fatty acids, forming soap which can be separated as soapstock from the oil, such as by gravity or by centrifugal force. An excess of alkali beyond that required to neutralize the free fatty acids is ordinarily used so as to improve the color, and a portion of this excess normally becomes associated with the gums, agglomerating them so that they can be removed with the soapstock.

The losses of neutral oil thatoccur during the removal of impurities from fatty oils result from:

(1) Neutral oil entrained in the precipitated gums.

(2) Neutral oil entrained in the soap formed during the treatment.

v(3) Neutral oil saponified into soap because of an excess of refining reagent used. This action is autocatalytic, since any soap produced dissolves oil which can react with the unused saponifying reagent already present in the soap to produce more soap.

(4) Neutral oil emulsified with the soap formed during the treatment.

Various methods have been tried in an attempt to reduce these losses of neutral oil. One methodis to treat the crude oil with suificient water to hydrate and precipitate a part of the gums, then to separate the gums that have-been precipitated from the oil, and subsequently to refine the oil'with a refining reagent. By first separately removing a part of the gums, it is possible to refine with a smaller excess of alkali beyond that required to neutralize the free fatty acids, since none of this alkali will be taken up by the gums that have been removed. The reduction in the alkali excess makes it possible to refine with less saponification of neutral oil. Also the soapstock formed by an alkali treat of so-called degumrned oil is less massive (since gums are an agglomerating agent) and, therefore, entrains less oil. In some cases the combined losses from the degumming and the refining steps are less than if the oil were refined without previous degumming, but in any case the gums themselves absorb from 30 to 40 per cent of their weight of oil, and this oil is not ordinarily recoverable.

An object of the present invention is to condition gum-containing fatty oils for refining by treating the gums contained therein so that they will release their natural complement of contained oil.

In accordance with the present invention a small amount of an aqueous solution of sodium hydrosulphite (NazSzOr) is added to the crude fatty oil. Commercial sodium hydrosulphite (hydrosulphite concentrate) is very satisfactory in preparing the solution. In the presence of this treating agent the oil can be refined in any desired manner, with or without using an excess of alkali, and with a resultant surprisingly high yield, the oil content in the gums apparently being released, and, therefore, not being lost. The amount of water in the added aqueous solution should preferably represent 0.2% to 2.0% by weight of the oil.

It has been found that increase in the amount of sodium hydrosulphite used in this process increases the effect produced. The determination of the amount to be used, therefore, is usually governed by the relation between the cost of sodium hydrosulphite and the value of the additional oil recovered. Since both sodium hydrosulphite and water are added to the oil, it is convenient to control the amount of sodium hydrosulphite through its percentage solution in the water. In this connection aqueous solutions of sodium hydrosulphite in concentrations of from 10 per cent to 50 per cent by weight are highly useful. The percentage of sodium hydrosulphite based on crude oil by weight should be at least 0.01%, and usually does not exceed 0.2%, although larger amounts may be used if desired. A particularly good operating range is between 0.05% and 0.125%.

In the presence of sodium hydrosulphite the oil may be refined in any desired way, although it is preferred to use aqueous caustic soda, and particularly aqueous caustic soda of relatively high Baum, for example 20 to 40 36., and to use approximately only the amount of caustic soda necessary to neutralize the free fatty acid, e. g., 0.9 to 1.1 times the stoichiometric quantity. Temperatures between F. and 160 F. are quite satisfactory.

The soapstock may be removed from the refined oil by gravity settling, although it is preferred to use a centrifugal separator to take the soapstock out of the oil, since in this manner better yields are obtainable.

The-following examples illustrate the operation of the process and the results obtained.

Example 1 Two samples of crude soybean oil having a F. F. A. (free fatty acid) content of 0.5% were refined as follows: Sample A was heated with agitation to P. whereupon sufficient caustic soda of 30 Be. was added to neu- Percent Percent Sample Residual Refining F. F. A. Loss Ditferences in refining loss of the nature illustrated are of particular significance, in view of the highly developed nature of the art.

Example 2 To demonstrate the effect of varying amounts of sodium hydrosulphite on the basis of the crude oil, three samples of crude corn oil having a F. F. A. content of 2.3% were refined in the following manner:

Sample A was heated with agitation to 140 F. whereupon a 15.1% concentration of an aqueous solution of sodium hydrosulphite was added, the amount of sodium hydrosulphite in the solution representing 0.05% of the oil by weight. Sufficient caustic soda of 30 B. was added to exactly neutralize (by calculation) the F. F. A. present. This was followed by separation of soapstock by centrifuging.

To sample B a quantity of an aqueous solution of sodium hydrosulphite of 26.2% concentration was added, the amount of sodium hydrosulphite representing 0.10% of the oil by weight. This was followed by refining with caustic soda in the same manner as in the case of sample A.

To sample C a quantity of an aqueous solution of sodium hydrosulphite of 34.8% concentration Was added, the amount of sodium hydrosulphite representing 0.15% of the oil by weight. This was followed by refining with caustic soda in the same manner as in the case of sample A.

The results are shown in the following table:

Percent Percent Percent Sample Residual Refining 333: F. F. A. Loss sulphite Example 3 Percent; Percent; Sample Residual Refining F. F. A. Loss Example 4 Crude cottonseed oil containing 5.3% F. F. A. was refined in a continuous process as follows:

The crude oil was pumped at a rate of 4000 pounds per hour through the system. To this oil, which was at a temperature of 92 F., was continuously added .5% of an 13.6% solution of sodium hydrosulphite. The mixture of sodium hydrosulphite solution and crude oil was then continuously heated to F. and 30 B. caustic soda was then continuously added to the flowing stream in an amount calculated to neutralize exactly the F. F. A. The mixture was then promptly fed into a centrifuge having an inside rotor diameter of 4 /8 rotating at 15,000 R. P. M., and refined oil and separated soapstock were continuously discharged. The refined oil was continuously delivered from the centrifuge to a second centrifuge, and in the flowing stream to the second centrifuge was added 2.5% of 20 B. caustic soda to act as a refining reagent to reduce the color and the F. F. A. The re-refined oil was continuously treated with 10% wash water and again centrifuged, after which it was continuously fed to a vacuum drier. The oil discharging from the first refining centrifuge contained 04% of F. F. A. and the finished oil contained .03% F. F. A. The overall loss of the whole process, including both refining steps, water washing, and vacuum drying, was 10.3%. For cottonseed oil containing originally 5.3% F. F. A. this refining loss is remarkably low as compared to losses which may be anywhere up to 15% when this invention is not employed.

With proper agitation the aqueous sodium hydrosulphite can be dispersed into the crude oil in 30 seconds or less, and a longer agitation time is not disadvantageous. Its benefit is independent of the temperature of the oil when the treating agent is introduced, or subsequent temperatures used before or after the addition of the refining reagent.

In the presence of the sodium hydrosulphite, the oil may be refined by the batch kettle process, or by a continuous centrifugal process or otherwise. Caustic soda or other refining reagent may be used; the oil may be agitated and conditioned after the caustic soda addition or it may be promptly centrifuged without delay; the refining reagent treat may be merely the amount calculated as necessary to neutralize the free fatty acids or less or more; the oil may be heated before or after the addition of the refining reagent, or refined without the addition of heat; color may be removed by a single refining with an excess of refining reagent, or by a re-refining step. These variations in refining procedure may show definite differences in refining loss. However, the savings due to the use of this invention are independent of these variations.

Having particularly described the invention, it is to be understood that this is by a way of illustration and not of limitation. Accordingly it is intended that the patent shall cover by suitable expression in the claims, the various features of patentable novelty that reside in the invention.

I claim:

1. A process for treating a gum-containing crude fatty oil to condition said oil for refining which comprises admixing with said oil sodium hydrosulphite to condition said gums for said refining, the amount of said sodium hydrosulphite admixed with said oil being at least 0.01% by weight of said oil.

2. The process of claim 1 wherein the amount of said sodium hydrosulphite admixed with the oil is between 0.05% and 0.125% by weight of said oil.

3. The process of claim 2 wherein the sodium hydrosulphite is added to the crude fatty oil in aqueous solution and said addition is followed by treatment of said oil with an alkaline refining reagent.

4. The process of claim 3 wherein the refining reagent is caustic soda of at least 20 B. concentration.

5. The process of claim 4 wherein the amount of caustic soda employed is approximately just sutficient to neutralize the free fatty acid content of the oil.

6. The process of claim 3 wherein the steps as defined are followed by an additional refining treatment with caustic soda of at least 20 B. concentration.

7. The process of claim 2 wherein the oil is a vegetable oil.

8. The process of claim 1 wherein the crude fatty oil is vegetable oil, wherein the amount of sodium hy- 6 hydrosulfite is admixed with said oil while in aqueous solution.

9. The process of claim 8 wherein the amount of water added to said oil is between 0.2% and 2% by drosulfite admixed with said oil is between 0.01% and 5 Weight of Said 0.2% by weight of said oil, and wherein said sodium No references cited.