US2741643A - Process of concentrating carotene and tocopherol in palm oil by thermal difusion - Google Patents

Description

United States Patent C PROCESS 6F CONCENTRATHIG CAROTENE AND ggzHEROL 1N PALE i OIL BY THERMAL DIF- Arthur Letcher dones, Lyndhurst, and Ernest C. Milherger, Maple Heights, Ohio, assignors to The Standard Oil Company, Cleveland, Ghio, a corporation of Ghio No Drawing. Application October 31, 1952, Serial No. 318,086

4 Claims. (Cl. 269-666) The present invention relates to a method of concentrating, by liquid thermal difiusion, carotene in palm oil and particularly in resolving palm oil into two fractions, one of which is enriched in carotene, contains a lower percentage of fatty acids than contained in the initial palm oil and has increased stability against oxidation, and the other of which is lighter in color.

Among the various vegetable oils that are available, palm oil is unique in containing an amount of carotene that is relatively large as compared with the carotene content of other vegetable oils. The concentration of carotene in palm oil usually varies between about 0.05 and 0.20% and it is this relatively large amount of carotene that is believed to be responsible for the deep orange-red coloring of crude palm oil.

Carotene, which term is intended herein to include alpha-, beta, and gamma carotene, is a provitamin. A, being converted into vitamin A by a splitting of the carotene molecule.

Palm oil contains traces of tocopherols, also known as vitamin E. it is believed that the tocopherols in palm oil act as antioxidants and as such inhibit to a certain extent the oxidation of the carotene and other ingredients. Depending upon the geographical origin of the palm fruits from which it is extracted and the procedure used in extraction, palm oil contains as little as 3% and as much as 45% free fatty acids. The presence of free fatty acids in palm oil is objectionable because of their relative instability to heat and oxidation.

At present the extraction of carotene from palm. oil is carried out by saponifying the crude palm oil withsodium hydroxide or potassium hydroxide and then extracting the resulting soap with ethylene dichloride. While approximately 95% carotene recovery is obtained by this method, the extremely large amounts of bulk palm oil that must be processed to obtain a small amount of carotene, e. g., approximately a thousand pounds of palm oil must be handled and separated from the solvent by centrifuges to obtain a pound of carotene, makes the present method an extremely expensive one and results in a correspondingly high price for concentrated carotene. In addition the oil is useless for food and other purposes for which the oil is desirable. It is recoverable only as the soap which greatly limits the use of the bulk of the oil.

It has now been found that a preliminary concentration of the carotene in palm oil can be obtained by subjecting the crude palm oil to liquid thermal diffusion and that, surprisingly, in effecting such concentration the desirable tocopherols are retained with the carotene-enriched fraction and the concentration of the undesirable free fatty acids is considerably reduced.

It will be apparent that the method of this invention has a number of important advantages, among which are a considerable reduction in the bulk of oil that must he handle to extract carotene by the conventional solvent extraction method, a corresponding increase in the capacity of existing solvent extraction equipment, and in an increased stability against oxidation of the oil subjected 2,741,643 Patented Apr. 10, 19.56

lighter colored oils is reflected in the market by the higher prices of the light colored oils as compared with those at which the darker oils are quoted.

Inasmuch as the present invention is concerned primarily with the concentration of carotene, it is of advantage to utilize the lower grades of darker colored palm oils as source material for carotene. An important ancillary advantage of the method of the invention is that the carotene-impoverished fraction obtainable by this method is lighter in color than the initial oil and possesses all of the qualifications of the lighter crude palm oils that command higher prices in the market. Thus, the method of the invention is useful not only in the concentration of the carotene contentin palm oil, but also but. also in converting the palm oil into a lighter colored. oil, for which there is greater demand in. the market than the initial and. comparatively dark palm oil.

It is also to be understood thatthe carotene enriched productobtainable by the method of this invention is suitable for use in purposes other than the conventional solvent extraction methods utilized in obtaining highly concentrated carotene. Thus, for example, the carotene enriched fractionv is particularly useful as a natural vegetable coloring for addition to butter, margarine and the like, while. at the same time increasing the vitamin A content of such products.

Liquid thermal diffusion, as is kell-known in the art, consists essentially in forming a thin film of liquid confined by closely-spaced, mutually parallel and opposed surfaces. of heat-conductive material that. is inert to the liquid and its components, heating one of the surfaces to maintain a temperature gradient across the film and accumulating and Withdrawing from the film two dissimilar fractions, one fraction being concentrated by thermal diffusion adjacent the cooler of the two surfaces and the other fraction being concentrated by thermal diffusion adjacent the hotter of the two surfaces.

Inasmuch as ithas been found that a fraction enriched in carotene and impoverished infree fatty acids becomes concentrated adjacent the cooler surfaces. by thermal diffusion, the method of this invention in essence comprises the steps of forming a thin film of palm oil confined. by closely-spaced, mutually parallel and opposed surfaces of heat-conductive, inert material, such as glass, stainless steel, aluminum or the like, maintaining a temperature gradient across the film so formed, and accumulating and withdrawing from the film a carotene-enriched fraction concentrated by thermal diffusion adjacent the cooler surface.

The thermal diffusion of palm oil may be carried out in a number of Ways. One such way is to fill a vertical slit formed by closely-spaced, mutually parallel and opposed surfaces with the crude palm oil, maintaining a temperature gradient across the slit until the liquid has separated into an upper light colored fraction and a lower darker fraction and then removing the lower fraction which is enriched in carotene and impoverished in fatty acids.

Another method is substantially similar except that the crude palm oil is more or less continuously introduced into the slit at any point therein and light and dark colored fractions are more or less continuously removed from the top and the bottom, respectively, of the slit.

A third method is to introduce the crude liquid palm oil continuously or intermittently at one point or area in a thermal difiusion slit, the hot surface being above the cold surface if the slit is other than vertical, and continuously or intermittently removing, at points or areas remote from the point or area of introduction, light and dark colored fractions from adjacent the hot and cold surfaces, respectively, or alternatively, removing the dark fraction at one end of the slit from adjacent the cold jacent the hot surfaceat the other end of the slit.

These modifications all have in common the step of V the hot and cold surfaces and the further step of ,ac-

cumulating and then withdrawing the fractions so concentrated. For optimum results, it is desirable either or both to add an inert and easily separable material, such as chlorobenzene, for reducing the viscosity of the liquid in the slit and to dehydrate the palm oil before subjecting it to thermal difiusion.

The temperature of the hot and cold walls may vary widely so long as that of the hot wall is not so high as to equal the temperature at which carotene decomposes under the conditions of thermal diffusion, bearing in mind the residence time of the palm oil and its components and presence of a residual anti-oxidant such as tocopherol, or of an added anti-oxidant, and the temperature of the cold wall is not so low as to equal the congealing temperature of the oil or cause an appreciable increase in its viscosity. Hot wall temperatures as high as about 300 F. and cold wall temperatures as low as about 105 F. are preferred. Higher hot wall temperatures may be employed .if anti-oxidant is present in amounts sufficient to avoid oxidation of the carotene at such higher temperatures, especially if the residence time of the carotene in the apparatus is relatively short. The extent of separation within the permissible range is a 7 function of the temperature gradient.

The film must be thin enough to permit the thermal diffusive forces to efiect the separation, and the temperature gradient and withdrawal rates must be related to the film dimensions to permit the desired degree of separation. Film'thicknesses of the order of about 0.01 to 0.15 inch, preferably between about 0.01 and 0.06 inch, are desirable from the standpoint of being thin enough to make etfective use of the thermal difiusive forces and thick enough to make possible the accumulation of the separated fractions in different portions of the slit..

It is advantageous, in order to obtain a carotene-enriched fraction of maximum concentration, to reduce the rate of withdrawal of said fraction to a small percentage of the rate of withdrawal of the carotene-impoverished.

fraction. 'This may be accomplished in apparatus wherein the crude palm oil is introduced at a point or area between the ends of the column and the two fractions are withdrawn at opposite ends and is particularly effective in countercurrent and concurrent end feed methods, i. e.,

where the palm oil is introduced at one point or area in the column and the carotene'enriched fraction is withdrawn at a considerably lower rate, at a remote point or area from adjacent the cold wall. The ratio of withdrawal rates may desirably be as low' as 5 or even lower and if desired the larger volume of carotene-impoverished fraction may be resubjected to continuous thermal difiusion in one or more subsequent thermal difiusion columns.

Inasmuch as crude palm oil frequently contains some water, usually less than 1%, and the presence of such' water reduces the eficiency of the process, it is desirable to dry the palm oil before it is subjected to thermal diffusion. It is necessary, when operating the method of the invention in a continuous manner, to introduce the crude palm oil into the thermal difiusion apparatus in a fluid and not too viscous condition. To this end, it may be necessary to preheat the palm oil to a temperature of the order of about 110 F., the exact temperature depending upon the congealing temperature of the particular palm oil. The advantages and utility of the invention will become further apparent from the following examples:

Example 1 An annular slit having a volume of approximatelySO cc., a slit width of 0.043 inch and a height of 8 feet, formed by two concentric glass tubes, was filled with crude palm oil. One surface of the slit was maintained at a temperature of approximately 212 F. by means of steam at atmospheric pressure, continually passed through the inner tube. The other surface of the slit, formed by the inner surface of the outer tube, was maintained at a temperature of 110 F. by the continuous circulation of top water through a jacket surrounding the outer tube. After three nights and two days, or approximately 60 hours, it was observed that the liquid in the upper portion of the slit was colored light orange and that the liquid in the lower portion of the slit was a dark red orange. These differently colored portions of the liquid were separately withdrawn and analyzed. The results are tabulated in the table immediately below:

Percent Refractive Percent Stream Fatty Index Carotene Acids This type of operation is indicative of the extent of the separation that is possible with the equipment and under the conditions described. It is to be noted that most of the carotene can be separated by the process. 7

Example 2 Percent Percent Stream Carotene Fatty Acids Volume The top products obtained in Examples 1 and 2 were allowed to stand for approximately one month while being exposedto air. It was observed that the products turned from a light orange to a yellow color.

This change is believed to result from oxidation and to indicate that the natural anti-oxidants, i. e., the tocopherols, had concentrated in the lower fraction enriched in carotene.

Example 3 A number of separations were carried out in a vertical aluminum plate column having an effective height of six feet and a breadth of 19 inches. The crude palm oil was preheated to F., introduced into the column midway between the ends of the slit, and the hot and cold fractions were withdrawn from the top and bottom of the column, respectively. The temperatures of the hot and cold walls and the slit width of the column, the rate of tene in the bottom fractions and the feed are listed in the table below:

Percent Carotene Ratio of Temperature Concentration Carotene Ratio of Slit Feed Cone. in with Width, Rate, Bottom drawal Remarks Inches in Bot- Fraction Hot Cold in Feed tom and Rates W311 W311 Fraction Feed 303 126 030 480 0893 0938 1 50/50 CF-CIIB. 293 134 .029 660 .0413 .329 8 0 /1 GF-CIB. 297 130 029 440 113 201 1. 74 10/1 EF. 289 126 029 440 0968 254 2. 62 10/1 EFdried. 297 133 029 660 0733 217 2. 96 10/1 EF-drled. 294 136 044 194 057 0936 1 64 7. 4/1 EF-drled. 283 155 019 218 076 1042 1. 37 9. 5/1 EF-dried. 293 126 030 214 0542 133 2. 46 10/1 EF-dried. 293 127 030 228 077 175 3. 02 9. 6/1 CF-drled. 292 126 030 440 0513 183 3. 57 10/1 OF-dried. 293 133 030 224 0914 190 2. 08 10. 7/1 CF-RBE. 294 135 030 414 0932 404 4. 34 9.7/1 OF-RBE.

feed and carotene concentration of the crude palm oil fed to the column, the ratio of withdrawal rates at the top and bottom of the column, and the concentration of carotene in the bottom fraction are listed in the table immediaely below:

. Carotene Cold Feed Carotene Ratio E 9 Wan Wall gg Rate, Gone. in of Withfigg S Temp., m1./ Feed, drawal Fraction F. hour Percent Rates Percent The temperatures of the hot and cold walls were measured by thermocouples at various locations in each of the opposed aluminum plates. The reason for the spread in cold wall temperatures is believed due to ineflicient circulation of the cooling water.

The higher concentrations of carotene in the fraction withdrawn at the bottom of the column are believed to be surprising in view of the initial low concentrations thereof in the crude palm oil subjected to thermal diffusion. Since the degree of separation obtainable by thermal diffusion is a function of the temperature gradient, it is evident that separations of even superior quality are possible with more uniform and adequate cooling of the cold wall to a temperature of the order of about to F.

Example 4 A number of separations were carried out in the vertical aluminum plate column described in Example 3. In some of the separations, as noted in the last column of the table, a miscible third component such as 15% by volume chlorobenzene (ClB) or 0.5% by Weight rice bran extract (RBE) was added to the feed and in some of these separations and others, the palm oil was dehydrated before being introduced into the thermal diffusion column. Crude palm oil was preheated to 110 F., introduced into the column at the top adjacent the cold wall of the slit or at the center (as indicated by EF and CF," respectively, under Remarks), a carotene-enriched fraction was withdrawn from adjacent the cold wall or at the bottom of the column and a carotene-impoverished fraction was withdrawn from adjacent the hot wall or the top of the column. The average hot and cold wall temperatures, the slit width, the rate of feed of crude palm oil, the concentrations of carotene in the feed and in the bottom fraction, the ratios of rates of withdrawal of the top and bottom fractions, and the ratios of concentration of caro- The results show that higher efficiencies of separation are obtained with higher feed rates and lower ratios of product withdrawal, and that at a suitably high feed rate and low ratio of product withdrawal it is possible to obtain a carotene-enriched fraction that is valuable for further processing to produce concentrated carotene as well as a carotene-impoverished fraction useful as a byproduct because of its lighter color. The data in the table further indicate that even superior results are obtainable by (a) dehydrating the palm oil before subjecting it to thermal diffusion, ([1) adding to the feed a material, such as chlorobenzene, that has a lower specific heat and viscosity and a higher density than palm oil, and (0) adding to the feed an anti-oxidant such as rice bran extract.

It is apparent that modifications and changes in the method described will occur readily to those skilled in the art upon reading this description. All such modifications and changes are intended to come within the scope of the appended claims.

We claim:

1. Method of concentrating carotene in palm oil which comprises forming a thin film of palm oil confined by opposed surfaces of heat-conductive inert material, said surfaces being closely and substantially uniformly spaced apart between 0.01 and 0.15 inch, heating one of said opposed surfaces to a higher temperature than the temperature of the other surface to maintain a temperature gradient across the film of oil, the temperature of the hotter surface being not over about 300 F. and the temperature of the cooler surface being not under about 105 F., withdrawing from the film a carotene and tocopherol-emiched fraction concentrated by thermal diffusion adjacent the cooler surface, and withdrawing from the film a lighter-colored, carotene and tocopherol-improverished, fatty acid-enriched fraction concentrated by thermal difiusion adjacent the hotter surface.

2. Method defined in claim 1 wherein the ratio of the rate of withdrawal of the carotene-enriched fraction to the rate of withdrawal of the carotene-impoverished fraction is below about 1 to 10.

3. Method defined in claim 1 wherein the palm oil is dehydrated before being subjected to thermal diffusion.

4. Method defined in claim 1 wherein an inert, viscosityreducing agent is added to the palm oil before the palm oil is subjected to thermal difiusion.

References Cited in the file of this patent UNITED STATES PATENTS 2,313,747 Buxton May 11, 1943 2,482,635 Petering et al. Sept. 20, 1949 2,541,069 Jones et al. Feb. 13, 1951 2,562,970 Thompson Aug. 7, 1951 2,615,927 Passino et al. Oct. 28, 1952

Claims (1)

1. METHOD OF CONCENTRATING CAROTENE IN PALM OIL WHICH COMPRISES FORMING A THIN FILM OF PALM OIL CONFINED BY OPPOSED SURFACES OF HEAT-CONDUCTIVE INERT MATERIAL, SAID SURFACES BEING CLOSELY AND SUBSTANTIALLY UNIFORMLY SPACED APART BETWEEN 0.01 AND 0.15 INCH, HEATING ONE OF SAID OPPOSED SURFACES TO A HIGHER TEMPERATURE THAN THE TEMPERATURE OF THE OTHER SURFACE TO MAINTAIN A TEMPERATURE GRADIENT ACROSS THE FILM OF OIL, THE TEMPERATURE OF THE HOTTER SURFACE BEING NOT OVER ABOUT 300* F. AND THE TEMPERATURE OF THE COOLER SURFACE BEING NOT UNDER ABOUT 105* F., WITHDRAWING FROM THE FILM A CAROTENE AND TOCOPHEROL-ENRICHED FRACTION CONCENTRATED BY THERMAL DIFFUSION ADJACENT THE COOLER SURFACE, AND WITHDRAWING FROM THE FILM A LIGHTER-COLORED, CAROTENE AND TOCOPHEROL-IMPROVERISHED, FATTY ACID-ENRICHED FRACTION CONCENTRACTED BY THERMAL DIFFUSION ADJACENT THE HOTTER SURFACE.