US3382262A - Process for neutralizing free fatty acids in oils - Google Patents

Description

y 7, 1968 J. J. HEPBURNY 3,382,262

PROCESS FOR NEUTRALIZING FREE FATTY ACIDS IN OILS Filed Feb. 25, 1965 4 Sheets-Sheet l y 7, 1968 J. J. HEPBURN 3,382,262

PROCESS FOR NEUTRALIZING FREE FATTY ACIDS IN OILS "Filed Feb. 25, 1965 4 Sheets-Sheet 2 May 7, 1968 J. J. HEPBURN PROCESS FOR NEUTRALIZING FREE FATTY ACIDS IN OILS 4 Sheets-Sheet 5 Filed Feb. 25,

May 7, 1968 J J. HEPBURN 3,332,262

PROCESS FOR NEUTRALIZING FREE FATTY ACIDS IN OILS Filed Feb. 25, 1965 4 Sheets-Sheet 4 United States Patent 3,382,262 PROCESS FOR NEUTRALIZING FREE FATTY ACIDS IN OILS John James Hepburn, Harpenden, England, assignor to Lever Brothers Company, New York, N.Y., a corporation of Maine Filed Feb. 25, 1965, Ser. No. 435,256 Claims priority, application Great Britain, Feb. 25, 1964, 7,832/ 64 4 Claims. (Cl. 260-425) ABSTRACT OF THE DISCLOSURE A process for neutralizing the free fatty acid in a fatty oil by the passage on a carrier surface of a film thereof through an aqueous alkaline bath and an apparatus therefor comprising a movable carrier having film-forming and film-removing means operative therewith.

This invention relates to a process for improving fatty oils by subjection to treatment with liquid oil-immiscible liquids and especially for the alkali refining of glyceride oils.

In this specification the term fatty oils is used to include fats and glyceride oils generally (whether solid or liquid).

It is known to subject fatty oils to treatment with oilimmiscible liquids, for instance to remove therefrom const tuents present in minor proportions and unwanted in the final products either because their presence therein is deleterious or because they are valuable and worth recovery. Such constituents include colouring agents, gums, resins, proteins, phosphatides and especially free fatty acids and such treatments include extraction with aqueous and non-aqueous oil-immiscible liquids and treatment with aqueous solutions of substances, for example, alkalis, that react with substances to be removed to form water soluble substances that go into solution in the treating liquid. The most important of such treatments is the alkali refining of fatty oils and the invention will be described with particular reference thereto.

The present invention provides a novel process for subjecting a fatty oil to treatment with a liquid, oil-immiscible treating agent, wherein the oil is continuously supplied to a moving carrier surface, each point on which follows a closed path, is carried as a film by said surface through a body of the liquid and continuously removed from the surface.

Preferably the film of treated oil is continuously removed from a carrier surface and fed to a pool of treated oil partly covering the surface of the treating liquid and treated oil is continuously withdrawn from said pool.

The process of the invention is of particular advantage when applied to the carrying out of treatments of such a nature that there is a tendency for emulsification of the oil to occur, as when for instance the treatment is one involving the production of a certain proportion of soap as by-product. The alkali refining of fatty oils is a process of this nature. In such processes the tendency towards emulsification is in general greater when the oil is treated in finely divided form. In the process of the invention, however, the oil is exposed to the treating agent in the form of a film adhering to the carrier surface, andthis film should remain continuous until stripped in the treated form from the carrier surface and the maintenance of such a continuous film, while providing adequate surface for the treatment to be effected, reduces the tendency to- Wards emulsification.

Fatty oils obtained by extraction of pressing or other methods from vegetable or animal raw material always contain a greater or smaller amount of free fatty acids. Before these oils can be used in the preparation of foodstuffs, the free fatty acids and other impurities must be substantially removed. The oldest and best-known deacidification process is alkali-refining-a treatment comprising subjecting the oil to the action of an alkaline liquid which neutralizes the free fatty acid in the oil while effecting little or no saponification. This process has the advantage that at the same time a purification of the oil is brought about by absorption in the soap formed of a number of the undesirable substances present in the crude oil. This purifying effect obtained in alkali-refining has a great influence on the results obtained in subsequent processes such as bleaching, hardening and deodorizing. In de-acidification methods in which caustic soda solutions are used, however, it is difficult to prevent some saponification of glycerides. Moreover, one always finds neutral oil in the soap solution formed. This leads to an increase in the amount of neutral oil in the acid oil which is obtained when the soap is later split by acid hydrolysis and to reduction in the yield of refined oil. In general acid oils containing 30 to 40% or more of neutral oil are still quite usual. It is possible to recover neutral oil of a fair quality from the soap solution, but this is rather expensive and therefore industrially unsatisfactory. In the literature several methods have been proposed to reduce the losses inherent in alkali-refining. It has, for example, been proposed to use dilute caustic soda in neutralization, but this increases the tendency of the soap solution to form emulsions. Further, it has been proposed to use less alkaline compounds, such as soda ash and ammonia, and to de-acidify with the help of centrifuges, using very short contact times between oil and alkaline solution. Although these proposed methods give some improvement, the oil losses still remain considerable.

In general tie-acidification may be regarded as a liquidliquidextraction process, but there are certain features that make this process complicated. The fatty acids are not extracted with the aid of a selective solvent, but are taken up into the alkaline solution while forming soap. However, in addition to this desirable action of the alkaline solution, undesirable side reactions may occur. An example of such side reactions is saponification of the oil by the alkaline solution. Further, the refining process is strongly affected by what happens at the oil-lye interface.

In view of all the complications referred to above it has been difficult to devise a satisfactory method of carrying out the alkali refining of fatty oils. It has now been found, however, that satisfactory results can be obtained when the alkali treatment is carried out by the novel process referred to above, or when at least one stage of that treatment is so carried out. The invention includes apparatus for carrying the process into effect.

The carrier surface is preferably that of a rotating drum, mounted on a horizontal axis, but other carrier surfaces such, for example, as a rotating disc and an endless driven belt, may also be used. When using a rotating drum it is mounted on a horizontal axis so as to dip into a bath of the alkaline solution and the oil is fed to a descending part of the surface of the drum along a horizontal line above the level of the solution, is carried in the form of a thin layer or film through the solution by the rotating drum and is removed therefrom, for instance to form a layer or pool covering part of the surface of the bath from which pool refined oil can continuously be drawn off. In a similar arrangement the drum is re placed by an endless driven belt of steel or other impermeable alkali-resistant material. Instead of a drum a disc or discs rotatably mounted on a horizontal shaft may provide the carrier surface the oil film being carried on the face of the disc in a film extending from the edge inwards for about one third to one quarter of the diameter.

It is desirable that the body of alkaline solution should be stirred to facilitate removal of spent alkali from contact with the oil but care must be taken not to stir so vigorously as to disrupt the oil film on the carrier surface.

In order to obtain an adequate neutralization the oil layer should have a thickness of not more than a few millimetres, preferably between about 0.05 and 0.5 mm., as a thin layer can be neutralized to a lower free fatty acid content and will result in a glyceride oil with a lighter colour than a thicker layer. The thickness of the layer is governed by two factors, one being the speed of the moving surface the other the feed rate of the oil.

Each oil behaves dilfcrently and requires special conditions for the best results. In general in the refined oil the soap content tends to be higher drum speed and the free fatty acid content tends to decrease with decreasing thickness of the oil film. The molecular weights of the free fatty acids present in the unrefined oil influence the neutralizing process in that this tends to become more difficult with increasing molecular weight of the free fatty acids, since the soaps of fatty acids with higher molecular weights need a longer period to dissolve in the alkaline solution.

In order to obtain satisfactory results it is desirable that the oil is preheated to and during the process kept at a temperature at which it is completely molten. In general temperatures between 80 C. and 95 C. are preferred, but for low melting oils lower temperatures may be used.

The process of the invention is broadly applicable to the treatment of unrefined oils. For those having a very high free fatty acid content it has been found advantageous to make the moving surface lipophilic, for example, by treatment with aluminium stearate or other substantially water insoluble soap, to ensure that a stable uniform film is maintained during the process.

The presence of a small proportion of soap in the aqueous alkaline solution has been found to facilitate the neutralization and with this in view soap and/or other wetting agent such as, for example, dodecylbenzene sulphonate may be added to the fresh lye. Small proportions of sodium chloride or like electrolytes may also be added. It is of advantage to use sodium hydroxide as the alkali, but other alkaline agents are also applicable. In general an alkaline solution with a concentration of 0.05 to 1.5 N is applied, the range of 0.1 to 0.8 N being preferred.

Apparatus according to the invention may comprise: a vessel for containing the alkaline solution, an outlet from said vessel for the alkaline solution near the bottom of the vessel, an inlet for said solution above the outlet, an outlet for the refined oil above that for the alkaline solution, carrier means providing a carrier surface for oil, said means being so constructed and mounted as to provide an endless carrier surface, preferably such that each point thereon describes a smooth path of the same length, said path passing downwards from the space in said vessel above the level of the oil outlet into, through and out of the space below said level and means for continuously applying the unrefined oil to a descent part of the carrier surface above the level of the oil outlet, so as to form a layer on said surface.

In a preferred form of the apparatus the carrier means comprises a rotatable cylindrical drum which is mounted on a horizontal axis.

Two embodiments of the invention will now be described with reference to the accompanying drawings, in which:

FIG. 1 is a diagram depicting one form of apparatus for carrying out the process of the invention, in sectional side elevation.

FIG. 2 is a diagram depicting an alternative form of apparatus for carrying out the process of the invention, in sectional side elevation.

FIG. 3 is a plan view of the apparatus depicted in FIG. 2.

FIG. 4 is a side elevation of FIG. 3, with part of the side wall of a tank broken away to show internal details.

FIG. 5 is a sectional view on the line 55 of FIG. 4.

Referring to the drawings, FIG. 1 shows in sectional side elevation, and diagrammatically, an arrangement in which a horizontally mounted drum 10 is employed for carrying on its periphery an oil layer which the drum transports through an aqueous alkaline solution in a storage tank 11. An outlet pipe 12 near the base of the tank 11 leads the aqueous alkaline solution from the tank to a motor-driven pump indicated at 13, from Which the solution is fed to a heat-exchanger indicated at 14, and thence to an inlet pipe 15 through which the aqueous alkaline solution is returned to the tank 11 after heating or re-heating in the heat-exchanger 14. Steam may be used as the heating fluid in the heat-exchanger 14. Beyond the motor-driven pump 13, the pipe to the heatexchanger 14 is joined by a branch pipe 16 through which the tank 11 can be pumped empty, when desired, via a valve 17 in the branch pipe 16. The inlet pipe 15 is also joined by a branch pipe 18, through which fresh aqueous alkaline solution can be supplied to the tank 11, when desired, via an inlet valve 19.

The drum 10 is driven to rotate about its mounting shaft 20 in the direction of the arrow.

A pipe 21, fitted with a flow control valve 22, feeds unrefined oil to the periphery of the drum 10, into a trough defined between the periphery of the drum, an adjustable radial blade member 23, and flexible end plates which define the end of the trough, and one of which is indicated at 24- in contact with the end of the drum 10. A screw adjusting mechanism for the blade 23 is indicated at 26, and it will be apparent that the rate at which oil flows from the pool 25 on to the periphery of the drum 10, to form a layer 27, depends upon the spacing of the tip of the blade member 23 from the periphery of the drum 10, and since this spacing is adjustable the rate of oil flow is also adjustable.

Approximately diametrically opposite the blade member 23 in FIG. 1, is shown a scraper blade 28 having its tip in contact with the periphery of the drum 10 across its full width, and this blade 28 is formed with holes at least in the region immediately behind its tip, so that liquid can pass freely through the blades. An auxiliary scraper blade is indicated at 29, spaced from the blade 28 in the direction of rotation .of the drum 10.

The aqueous alkaline solution in the tank 11 can be stirred continuously, while the drum 10 is rotating, by means of a stirrer 30 carried by a shaft 31 of an electric driving motor 32.

In operation, unrefined oil from a convenient source of supply is fed through the pipe 21 to produce the pool 25 and continuously replenish the pool. The unrefined oil is kept at a selected temperature at which it is completely molten, as by heating it during its passage through the pipe 2 1 in any convenient and Well-known manner. The drum 10 is rotated at constant speed, so that an even layer 27 of oil is deposited on the periphery of the drum from the pool 25, and the layer 27 is transported through the hot aqueous alkaline solution in the tank 1 1. The layer 27 of oil, neutralized by its passage through the hot aqueous alkaline solution, is removed from the periphery of the drum by the scraper blade 28, and forms a pool 33 between the periphery of the drum 11 and the adjacent end and side wall of the tank 11. As previously mentioned the scraper blade 28 is formed with holes, so that it does not interfere with the formation of the pool 33. The auxiliary scraper 29 removes any residue of oil not previously removed by the scraper blade 28.

The aqueous alkaline solution in the tank 11 is temperature-adjusted to be at about the same temperature as the oil, and the solution is agitated by the stirrer 30, sufliciently gently so that the agitation does not break down the oil layer 27 on the drum 10.

Refined oil collected in the pool 33 can be drawn 011 via a pipe 34 provided with a flow control valve 35, the upper level of the pool 33 of neutralized oil being sufficiently above the level of the pipe 34 to prevent any soap, floating on the neutralized oil, to be entrained when neutralized oil is removed from the pool through the pipe 34. Scraper blade 28 is located to be approximately at the interface of the aqueous alkaline solution in the tank 11 and the pool 33 of neutralized oil.

The following examples illustrate the invention.

EXAMPLE I The apparatus was as shown in FIG. 1, but without the auxiliary scraping blade 29. The horizontal drum 10 had a length of 20 cm. and a diameter of 15 cm., rotating with half its volume submerged in a bath of 0.8 N sodium hydroxide solution containing 0.25% by weight of sodium chloride.

The oil treated was unrefined palm kernel oil containing 5.7% by weight of free fatty acid, dried under vacuum at 90 C. and stirred with 0.1% by weight of phosphoric acid. The temperature of the oil and the alkaline solution was kept at about 90 C. A series of trials was carried out with varying feed rates and drum speeds. The results are shown in Table 1. In the table the feed rate of the oil is expressed in kg. per hour, and the speed to the drum is expressed in rotations per minute. The percentages of free fatty acid (F.F.A.) and of soap are based on weight of refined oil obtained.

The process was carried out as in Example I except that the oil was unrefined coconut oil containing 2.9% by weight of free fatty acids.

TABLE II Drum Refined oil speed (r.p.n1.)

soap

Percent Percent;

F F.A.

Feed rate oil, kg /hour- 0.04 Nil 0.88. o. 05 N11 1.94. 15 0. 04 N11 2.7 000 N11 2.72"- 0.03 Nil 1.75.--" 0.03 0.03 2.4 0.02 Nil EXAMPLE III The apparatus was as shown in FIG. 1, that is, including the auxiliary scraper blade (29). Unrefined groundnut oil containing 1.06% by weight of free fatty acids was treated in said apparatus under conditions identical to those described in Example I, but for the temperature and the concentration of the alkaline solution. These variables and the results are given in Table III below.

The apparatus was the same as used in Example III. Unrefined soya bean oil containing 1.25% by weight of free fatty acid was treated in said apparatus under conditions identical to those described in Example I, but for the concentration of the alkaline solution. This variable and the results are given in Table IV below.

TABLE IV Refined oil Drum Nor malspeed ity of Percent Percent (r.p.m.) NaOH I .F.A. soap 5 0. 85 0.01 Nil 10 0.85 0.08 Nil 15 0.90 0.05 0.11 20 0.60 0.05 0.09 25 0. 55 0. 04 0. 19

EXAMPLE V The apparatus was the same as used in Example III. Unrefined rapeseed oil containing 2.23% by weight of free fatty acid was treated in said apparatus under conditions identical to those described in Example I, but for the concentration of the alkaline solution. This variable and the results are given in Table V below.

TAB LE V Refined oil Drum N ormalspced ity of Percent Percent (r.p.m.) NaOH F.F.A. soap Feed rate 011, kg./hour:

EXAMPLE VI The apparatus was the same as used in Example III. Unrefined cottonseed oil containing 0.45% by weight of free fatty acid was treated in said apparatus under conditions identical to those described in Example I, but for the temperature and the concentration of the alkaline solution. These variables and the results are given in Table VI below.

Referring to FIGS. 2 to 5 of the drawings, FIG. 2 shows in sectional side elevation, and diagrammatically, an arrangement in which a vertically disposed disc 36 is rotated about the axis of a horizontal shaft 37, in the direction of the arrow, the disc 36 being employed for carrying on each of its vertical faces an oil layer or film which the disc transports through an aqueous alkaline solution in a storage tank 38. An outlet pipe 39 near the base of the tank 38 leads the aqueous alkaline solution from the tank to a motor-driven pump indicated at 40, from which the solution is fed to a heat-exchanger indi cated at 41, and thence to an inlet pipe 42 through which the aqueous alkaline solution is returned to the tank 38 after heating or re-heating in the heat-exchanger 41. Steam may be used as the heating fluid in the heat-exchanger 41. Beyond the motor-driven pump 40, the pipe to the heat exchanger 41 is joined by a branch pipe 43 through which the tank 38 can be pumped empty, when desired, via a valve 44 in the branch pipe 43. The inlet pipe 42 is also joined by a branch pipe 45, through which fresh aqueous alkaline solution can be supplied to the tank 38, when desired, via an inlet valve 46.

Two pipes 47, only one of which is seen in FIG. 2 and shown as including a flow-control valve 48, feed unrefi ed oil to the respective vertical faces of the disc 36. Each feed pipe 47 supplies unrefined oil to a feed trough assembly designated generally by the T. Only one feed trough assembly T can be seen in FIG. 2, but these feed assemblies are shown in greater detail and to an enlarged scale in FIGS. 3 to 5, and will be further described later.

Still referring to FIG. 2, approximately diametrically opposite each feed trough assembly T, is a scraper blade assembly designated by the S. Only one scraper blade assembly S can be seen in FIG. 2, but .both of these scraper blade assemblies can be seen in FIGS. 3 to 5, in greater detail and to an enlarged scale, and will be further described later. Both the feed trough assembly T and the scraper blade assembly S are mounted on a common cross-member 49 which bridges the tank 38.

The aqueous alkaline solution in the tank 38 can be stirred continuously, while the disc 36 is rotating, by means of a stirrer 50 carried by a shaft 51 of an electric driving motor 52.

In operation, unrefined oil from a convenient source of supply is fed through the pipes 47 to produce an oil pool in each of the feed trough assemblies T and continuously replenish the pools. The unrefined oil is kept at a selected temperature at which it is completely molten, as by heating it during its passage through the pipe 47 in any convenient and well known manner. The disc 36 is rotated at constant speed, so that on each vertical face of the disc 36 is deposited an even layer of oil, indicated at 53 in FIG. 2, in the form of an annular band extending inwardly from the edge of the disc 36.

The layers 53 of oil, neutralized by passage through the hot aqueous alkaline solution in the tank 38, are each removed from the faces of the disc 36 by a scraper blade assembly S, and the oil scraped off by the scraper blade assembly forms a pool 54 between the adjacent end wall and the side wall portions of the tank 38, and flexible sealing wall members, one of which is seen at 55 in FIG.

upper level of the pool 54 of neutralized oil being sufficiently above the level of the pipe 56 to prevent any soap, floating on the neutralized oil, being entrained when neutralized oil is removed from the pool through the pipe 56.:

Referring now to FIGURES 3, 4 and 5 of the drawing, like parts to those in FIGURE 2 bear like reference numerals, and while the oil feed pipes 47 are indicated in FIG. 5, detail of the circulation system for the aqueous alkaline solution, the stirrer, and the oil drain-off pipe 56 has not been inserted in FIGS. 3 to 5.

Particularly in FIG. 5, details of construction of the feed trough assemblies T are clearly shown. Unrefined oil from each feed pipe 47 is fed into a trough defined by an L-shaped plate 58 carrying flexible end plates 59, and the confronting face of the disc 36. The edge of the horizontal limb of the L-shaped plate 59 is spaced from the face of the disc 36, so that unrefined oil can flow from the trough to form layers 53 on the faces of the disc 36. The L-shaped plates 58 are adjustably supported on the cross-members 49, for adjustment towards or away from the disc 36, by means of screw adjusting mechanisms 60, whereby the thicknesses of the layers of oil 53 deposited on the faces of the disc 36 can be varied.

Each scraper blade assembly S comprises an elongated blade 61, secured to a carrier bar 62 to be inclined with the tip of the blade bearing against the face of the disc 36. Each carrier bar 62 is provided with two carrier rods 63, and these rods pass s'lidably through sleeves 64, in which they are lockable by means of screws 65, whereby the blade 61 is adjustable to some degree to ensure that its blade edge bears evenly against the face of the disc 36.

The sleeves 63 are carried by a bracket 66, and the latter is pivotal about a hinge pin 67 carried by a pair of pillars 68 mounted on the cross member 49.

A tail portion 69 of the bracket 66 is engaged by a screw-adjusting mechanism 70, by means of which the scraper blade assembly S can be pivotally adjusted about the pivot pin 67 to vary the degree of pressure with which the blade 61 bears against the face of the disc 36.

EXAMPLE VII The apparatus was as shown in FIGS. 2 to 5 of the drawings. The disc 36 was approximately 46 cm. in diameter, rotating half-submerged in a bath of sodium hydroxide solution, and the oil layers 53 extended from the outer edge of the disc 36 for a distance of approximately 15.2 cm. The oil treated was crude coconut oil containing 2.24% by weight of free fatty acid. The percentages of free fatty acid (F.F.A.) and of soap are based on the weight of refined oil obtained. The variables and results obtained are given in Table VII below.

TABLE VIII.OPERATING CONDITIONS Disc Normal- Temp. of Temp. of Speed ity of NaOlI crude oil Refined Oil (r.p.rn.) NaOH in C. in C.

Percent Percent.

F.F.A. soap Feed rate oil, kg./l1our:

3. 0 3 0. I5 80 0. 22 0. 04 6. 0 3 0. 15 76 G8 0. 51 0. 03 2. 5 3 1. 00 76 58 0. 0B O. 07 4.5 3 0. 925 76 65 0. l4 0. 0l 4. 5. r 4 1.02 74 60 0.20 0. C0 4. 5 5 I. 02 60 0. 26 0. 05

2, extending between each face of the disc 36 and the ad- I claim:

jacent side wall of the tank 38.

The aqueous alkaline solution in the tank 38 is temperature-adjusted to be at about the same temperature as the oil, and the solution is agitated by the stirrer 50, sufliciently gentle so that the agitation does not break down the oil layer 53 on the disc 36.

Refined oil collected in the pool 54 can be drawn off -1. Process for neutralizing the free fatty acid in a fatty oil, comprising the steps of continuously forming a film of the fatty oil on a moving carrier surface moving in an endless path, transporting said film of fatty oil through a bath of aqueous alkaline liquid by means of said carrier surface to effect said neutralizing, and continuously removing said film of neutralized oil from said carrier via a pipe 56 provided with a flow control valve 57, the 75 surface after transportation through said bath.

9 10 2. Process according to claim 1 where-in the bath of of the bath, and continuously withdrawing oil from said aqueous alkaline liquid is composed essentially of caustic pool. soda of normality 0.1 to 0.8. References Cited 3. Process according to claim 1, and including the further steps of forming from the continuously removed UNITED STATES PATENTS film oif neutralized oil a pool partly covering the surface 2,895,799 7/1959 Baron et a1 23--286 of the bath, and continuously withdrawing oil from said 3,226,407 12/1965 Bergman 260425 pool.

4. Process according to claim 2, and including the fur- NICHOLAS S. RIZZO, Primary Examiner.

ther steps of forming from the continuously removed 10 R BOYD A M TIGHE Assistant Examiners film of neutralized oil a pool partly covering the surface

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