US3590059A - Process for the purification of edible oils - Google Patents

Abstract

IN A PROCESS FOR THE PURIFICATION OF VEGETABLE AND ANIMAL OILS COMPRISING THE SUCCESSIVE OPERATIONS OF BLEACHING BY MEANS OF BLEACHING EARTH AND CARRYING OFF THE FATTY ACIDS CONTAINED IN THE OIL BY MEANS OF STEAM UNDER VACUUM, THE IMPROVEMENT WHICH CONSISTS, BEFORE BLEACHING THE OIL, IN TREATING THE OIL WITH A SMALL AMOUNT OF ACID, MORE PARTICULARLY OF AN ORGANIC NATURE, AT A TEMPERATURE OF THE ORDER OF 50 TO 80*C. AND ADJUSTING THE MOISTURE LEVEL OF THE OIL AT A VALUE RANGING BETWEEN 0.1 AND 0.5%; OPTIONALLY, THE ABOVE-MENTIONED ACID TREATMENT MAY BE PRECEDED BY TREATMENT OF THE CRUDE OIL WITH A SMALL AMOUNT OF AN ALKALINE AGENT AND CENTRIFUGING WITH THE OBJECT OF ELIMINATING THE ALKALIZED IMPURITIES.

Description

29, 1971 I VELAN v 3,590,059

PROCESS FOR THE PURIFICATION OF EDIBLE OILS or'i inammd Aug. 31. 1967 s Sheets-Sheet 1 mp2 1 7} 10 Y Y m MAURICE EUGENE VELAN M. E. VELAN 3,590,059

:5 Sheets-Sheet a A a M a H l 2 m c? H HI m H x F U CL June 29, 1971 PROCESS FOR THE PURIFICATION OF EDIBLB OILS Original Filed Aug. 31, 1967 June 29 1971 E, VELAN I 3,590,059

raocsss FOR THE PURIFICATION OF EDIBLE OILS Original Filed Aug. 31, 1967 3 Sheets-Sheet I MAURICE EUGENE VELAN United States Patent Ofiice 3,590,059 Patented June 29, 1971 Int. Cl. Cllb 3/04 US. Cl. 260-.423 14 Claims ABSTRACT OF THE DISCLOSURE In a process for the purification of vegetable and animal oils comprising the successive operations of bleaching by means of bleaching earth and carrying off the fatty acids contained in the oil by means of steam under vacuum, the improvement which consists, before bleaching the oil, in treating the oil with a small amount of acid, more particularly of an organic nature, at a temperature of the order of 50 to 80 C. and adjusting the moisture level of the oil at a value ranging between 0.1 and 0.5 option ally, the above-mentioned acid treatment may be preceded by treatment of the crude oil with a small amount of an alkaline agent and centrifuging with the object of eliminating the alkalized impurities.

This application is a continuation of application Ser. No. 664,725, filed Aug. 31, 1967, now abandoned.

The invention relates to an improved process for the purification of vegetable and animal oils.

The process most generally used for refining edible oils consists:

In neutralizing the fatty acids contained in the oil by means of an alkaline base such as caustic soda;

In bleaching the oil by means of activated or nonactivated bleaching earth; and

In eliminating the volatile substances present in the oil so as to deodorize it.

This process has the drawbacks of requiring separation of the soaps formed by action of the caustic soda on the fatty acids and of entailing a considerable loss of neutral oil which may vary between half the weight and the full weight of soap formed, according to the nature and the acidity of the initial oil.

There are also refining processes which permit elimination of the fatty acids not by alkaline neutralization, but by entrainment by means of steam under a high vacuum. These processes of so-called physical refinement have the advantage of effecting the deodorization of the oil simultaneously, the volatile substances being eliminated at the same time as the fatty acids.

This'refining process is almost always preceded by two operations of purification of the crude oil, namely:

Washing of the oil, or removal of the mucilages therefrom; and

Bleaching of the oil.

The washing may be effected either in a tank by agitation, or by large-flow circulation through a chamber, with quantities of water varying between 1 and of the weight of the oil, and either continuously or intermittently, according to the methods used. This washing is always followed by a centrifuging designed to separate the washed oil from the aqueous phase containing the impurities.

The bleaching is carried out on the washed oil, this having been advantageously dehydrated beforehand. The operation is performed by stirring oil together with bleaching earths at a temperature ranging between about 70 and 130 C., with or without subjection to vacuum. The bleaching earth is separated from the oil by filtration after a period of contact which may vary between a few minutes and one hour, according to circumstances. The purified oil obtained in this way is then subjected to the entrainment with steam under vacuum.

These processes therefore seem to be economically superior to the process of refinement by alkaline neutralization, inasmuch as the fatty acids are merely separated from the oil without any loss of neutral oil.

In fact, the use of these processes of so-called physical refinement reveals the following defects:

(1) The gain of neutral oil is off-set by an increased consumption of bleaching earth due to the fact that, as the bleaching is carried out on acid oil, it requires more earth than in the alkaline process, in which it is performed on neutral oil, because oils neutralized by an alkaline agent lose part of their coloured pigments and, above all, the major part of the foam-inhibiting substances and foam-inhibiting substances and foam-producing substances, and foam-producing substances, such as the carbohydrates, the nitrogenous or protein complexes, the sucroglcerides, the resins, the traces of phosphatides, etc.

As the presence of these foams on a refined oil is an impediment to its commercialization, it is necessary to eliminate them by more bleaching earth and this reduces the advantage of processes of this kind.

(2) The treatment of an oil with an activated bleaching earth generally results in spectral changes in the ultraviolet of the oil. An unbleached crude oil always has a distinctly higher coefficient of extinction at 232 m than at 268 m The first wave length corresponds to the diene compounds contained in the oil, while the second wave length corresponds to the more oxidation-sensitive conjugated triene compounds contained in the oil. A crude oil, for example peanut oil: which is dried and bleached even with as small amounts of activated earth as 0.5% by weight, with respect to the oil, undergoes a considerable spectral change. The extinction at 232 m decreases, whereas that at 268 III/L increases considerably. This is due to the conversion of dienes into trienes, this conversion being catalyzed by the activated earth. This conversion takes place both in the free air and under vacuum. This spectral reversal is less sharp if natural earths are used. It can be considered that with the latter it appears for amounts of the order of 0.8 to 1.5% by weight with respect to the oil. The spectral change is more or less considerable according to the nature of the oil; it is particularly marked in the case of peanut oil, with regard to which the following figures can be given:

Peanut oil bleached with 0 5% by weight of activated earth Peanut oil bleached with 1.5% of natural earth.

(3) After the oil treated by a physical refining process has been subjected to an entrainment with steam, the object of which is to neutralize it, it is cooled and filtered in the same manner as an oil which has just been subjected to the deodorizing operation after alkaline refining. In the case of the physical refining process, inferior characteristics in relation to alkaline refining are found at this stage, namely:

The filtration rate is slower,

The sparkle of the oil obtained after filtration is not as good or, if this sparkle seems good after filtration, a slight clouding may appear after several days, so that it is then necessary to effect a second filtration if it is not desired to have an oil of unattractive appearance.

The magnitude of the defect is dependent upon the nature of the oil. It is found especially in peanut oil.

The present invention has for its object a special treatment process which makes it possible: either to remedy the three above-mentioned defects as a whole, or to remedy the first defect, which is a major one since it is linked directly with the refining efficiency, in the case where the second and third defects have little effect 011 the quality of the oil.

The treatment process according to the invention moreover enables the refined oil obtained by this process to be given a good stability. This stability, measured by the variation of the peroxide index in time, is very much superior to that of oil which has undergone normal physical refining and, in the majority of cases, to that of oils treated by a conventional alkaline refining process.

The process according to the invention comprises the following operations:

(1) The incorporation in the crude oil (or in this oil after being degummed) of a small amount of an alkaline agent so as to increase the pH of the oil and preferably bring it to a value of about 8 to 9;

(2) The addition, immediately after or during this alkaline treatment, of a small amount of water of the order of 1 to by weight with respect to the oil;

(3) The separation of the oil from the aqueous phase containing the alkalized mucilages by centrifuging;

(4) The treatment of the oil with an amount of acid, more particularly of an organic nature, less than 0.3%, and preferably ranging between 0.1 and 0.2%, of the weight of the oil to be treated, at a temperature ranging between about 50 and 80 C. and for a time which may vary from a few minutes to one hour and preferably ranging between and minutes;

(5) The adjustment of the moisture level of the oil at a value ranging between 0.1 and 0.5% according to the quality and the source of the oil. If necessary, this adjustment may be effected before the acid treatment;

(6) The bleaching of the oil by means of an amount of activated or natural bleaching earth which is less by 1 to 3% than that which would be used on the same oil in a conventional physical refining process.

After these operations, the fatty acids contained in the oil are carried off by means of steam.

The process as defined above enables the three defects mentioned to be remedied as a whole. When it is desired to remedy only the first defect, it is possible to omit the operation (1) and only subject the oil to conventional washing followed by separation.

It is to be noted that the amount of alkaline agent is very much less than that which would be necessary to neutralize the acidity of the oil completely, contrary to what is done in the refining processes emplying alkaline neutralisation.

In certain special cases concerning crude oils containing a large amount of phosphatides, or phosphatides which are ditficult to eliminate, it is necessary to apply the process to oils which have been degummed beforehand in conventional manner by means of, for example, phosphoric acid. In this case, the prior degumming and the alkaline treatment may be effected in a single operation and in the following manner: the oil is treated with the usual amount of phosphoric acid by known methods. After contact, the alkaline agent is added in such manner that it allows a surplus alkalinity to subsist which permits the pH to be brought to a preferred value of 8 to 9. The series of operations is then resumed from the second stage hereinbefore described.

The process is preferably carried out continuously. The time of contact between the alkaline agent and the oil must be relatively short, for example of the order of one minute, and the bringing into contact is advantageously effected at a temperature close to 80 C. The time of contact between the water and the alkalized oil is advantageously equal to the duration of the centrifuging operation. The alkaline agent used is preferably a mixture of alkaline base (caustic soda, potash, etc.), or

alkaline carbonate, and mineral or organic salts with the same cation as the base employed, As examples of salts which can be used, there may be mentioned the phosphates, preferably the complex phosphates such as the tripolyphosphates and the pyrophosphates; the silicates; the sulphates, the chlorides; the nitrates; the acetates; the oxalates; the citrates, etc. As a variant, instead of the salt, it is possible to add a mineral or organic acid before, at the same time as, or after the alkaline base, in order to form the salt in situ by reaction with a part of the alkaline base.

When caustic soda is employed as alkaline base, the amount to be used is of the order of 0.01 to 0.05% by weight respect to the crude oil.

This alkaline treatment makes it possible to obtain:

A selective alkaline destruction of certain minor organic compounds and certain colouring substances contained in the oil;

A good coagulation of the phosphatides;

An effective subsequent separation of the alkalized mucilages by centrifuging.

The centrifuged oil must then undergo the acid treatment operation (4). It is important to note that in this stage the main purpose of the acid treatment is not the destruction of the traces of soap contained in the oil as a result of the preceding alkaline treatment, since the amount of acid used is from 5 to 10* times greater than that which is necessary to eliminate these traces of soap. This point is of prime importance, because the acid treatment is the only treatment of the invention which remains when the preservation of the initial chemical characteristics of the oils and the obtainment of an oil of attractive appearance (satisfactory and stable sparkle or brilliance) are not sought or when the defects which have been pointed out are of little importance. In this particular case, in fact, the acid treatment is carried out on an oil which has not undergone any alkaline treatment and therefore in the absence of soap. The main purpose of the acid treatment of the invention is to perfect the coagulation of the traces of phosphatides, destroy certain inconvenient minor constituents assumed to the lipoprotein complexes, carbohydrates and other foam-producing compounds and subsequently permit substantial savings of bleaching earths.

The acid treatment is advantageously efiected with an organic acid such as formic, acetic, oxalic, latic, citric, tartaric, succinic acid, etc, and mixture thereof in solution in water or in a solvent, but their nature and number are not restricted by the foregoing. As a variant, the anhydrides of these acids may be used.

It is also possible to use mineral acids, but their action on the oil may be prejudicial to the quality of the oil in some cases.

Likewise, certain mineral or organic salts could be employed and we may mention the tartrates, the aicd phos phates, etc.

Generally speaking, it is advantageous to choose a volatile acid or an acid which can be decomposed into volatile constituents or constituents which can be absorbed by the bleaching earth, so that practically speaking none of its subsists in the oil after bleaching and the entrainment with steam.

As hereinbefore described, a certain moisture level must remain in the oil after the acid treatment with an eye to the bleaching operation. The moisture level preferably adjusted between about 0.1 and 0.5 either by partial drying or by complete drying and rehumidification of the oil obtained after the acid treatment or, if necessary, before this treatment. The effect of the acid treatment and the residual moisture enables only very small amounts of bleaching earth to be used, and in particular of non-activated natural bleaching earth, which has less tendency than activated bleaching earth to cause a spectral inversion of the oil in the ultra-violet. It is to be pointed out that the moisture in the oil can be adjusted during the bleaching operation by effecting the latter under a partial vacuum which does not permit an elimination of water greater than that desired; of course, if the moisture is suitable after the acid treatment, the oil can be used as it is for continuing the operations.

It is obvious that if it is not desired to bleach the oil, it is possible to be satisfied with filtering it by means of a suitable apparatus.

It is to be noted that several acid treatments have already been recommended in the past for eliminating or reducing certain drawbacks of the physical refining processes. The following may be mentioned: acid treatments in the stage of the mucilage-removal and washing operation, which enable the phosphatides to be coagulated better and the oils to be washed more satisfactorily; the additions of traces of acid in the course of the bleaching by means of the bleaching earth. which facilitates this operation in the case of oils neutralized by caustic soda by eliminating the residual traces of soaps.

All these processes, however, have given poor results as regards the problems of bleaching and of elimination of the foaming substances from the unneutralized oils.

The applicant desires to point out that the acid treatment operation according to the invention is different from previous acid treatments both in its nature and in its effects. In fact, previous acid treatment processes have given poor results as regards the problems of bleaching and of elimination of the foaming substances from the unneutralized oils, whereas the special acid treatment operation according to the invention furnishes a solution to these problems, thus giving afresh to physical refining an economic advantage which seemed to be forfeited.

The process of the invention may be performed continuously or intermittently.

The process of the invention can be applied to all vegetable and animal oils, such as peanut, sunflower seed, colza, soybean, olive, corn, grape pip oil, etc., as well as tallow oil, lard oil, horse fat oil, etc.

The description which follows with reference to the accompanying drawing, which is given by way of non-limitative example, will make it clearly understood how the invention can be carried into effect, the details appearing both from the drawing and from the text forming, of course, part of the said invention.

FIG. 1 is a diagram showing an installation enabling the simplified process of the invention to be carried into effect;

FIG. 2 is a diagram showing another installation enabling the amplified process of the invention to be carried into effect;

FIG. 3 is a diagram showing an installation enabling both the acid treatment of the invention and the bleaching operation to be effected;

FIG. 4 is a diagram showing an installation enabling the complete process of the invention to be carried into effect;

FIG. 5 is a diagram illustrating a simplified construction form of the installation of FIG. 4;

FIG. 6 is a diagram illustrating a modified form of FIGS. 4 and 5;

FIG. 7 is a diagram illustrating a modified form of the installation of FIG. 6.

In FIG. 1, a peanut oil previously washed in an installation such as that described in French Pat. No. 1,313,003 filed on J an. 31, 1962 is centrifuged and then delivered at a rate of 3000 kg./h. through the conduit 3 to a contact tank 1 equipped with a stirrer 2. At the same time, an amount of citric acid in 50% solution which is equal to 9 kg./h., that is 0.15% by weight with respect to the oil, is injected through the conduit 4 with the aid of a metering pump 5. The volume of the tank is such that the duration of contact is of the order of 30 minutes. The oil overflowing from this tank is delivered through the conduit 6 to a bleaching installation of the type described in French Pat. No. 1,160,353 filed on July 24, 1956. The obtainment of a properly bleached oil from the oil treated in this way requires a portion of about 0.6% of activated bleaching earth with respect to the weight of oil. By way of comparison, the proportions of bleaching clay used for oils not treated by the process of the invention have been:

3 for a peanut oil washed with water;

3% for a peanut oil washed in the presence of 0.15 of citric acid by a conventional technique and then centrifuged;

3% for a peanut oil washed with water, centrifuged and then bleached in the presence of a mixture of clay and 0.15 of citric acid.

The process of the invention therefore enables the amount of bleaching earth employed to be reduced by a coefiicient of 5.

In FIG. 2, after passing through a flow meter 8 and heating to 50 C. in an exchanger 7, 1000 kg./h. of crude or previously washed peanut oil are introduced into a tank 9 provided with an outlet conduit 10, the orifice 10a of which serves as a level regulator. Tartaric acid in solution is injected simultaneously into this tank at the rate of 1 kg./h. (that is, 0.1% by weight with respect to the oil) through the conduit 11 with the aid of the pump 12. The mixture formed in this way arrives at 13 and circulates at a high rate of flow through the vessel 14. by means of the pump 15, which ensures satisfactory stirring of the mixture. This vessel 14 has a discharge conduit 17a connected to a pump 17 which enables the treated oil to be withdrawn at the rate of 1000 kg./h. This oil is then introduced into a bleaching installation similar to that mentioned in the example of FIG. 1 or else it is stored for this subsequent operation. Moreover, the tanks 9 and 14 are kept under vacuum by means of the vane pump 16.

The obtainment of a properly bleached oil from the oil treated in this way requires a proportion of about 0.2% of activated bleaching earth with respect to the weight of the oil.

By way of comparison, the proportions of bleaching earth used for oils not treated by the process of the invention have been 2.5% in the following three cases:

Peanut oil washed with water before bleaching;

Peanut oil washed in the presence of 0.1% of tartaric acid;

Peanut oil washed with water and bleached by a mixture of clay and 0.1% of tartaric acid.

FIG. 3 shows a method of carrying the present invention into effect which enables the acid treatment and the bleaching to be effected in the same apparatus. 1000 kg./ h. of sunflower seed oil which has been previously washed and heated to 6070 C. are introduced through the conduit 18 into a drying chamber 19, adjusted to a moisture level equal to 0.2%, reheated to C. by means of the exchanger 20 and then mixed at 21 with lactic acid in solution arriving at the rate of 2 kg/h. through the conduit 22 by means of the pump 23. The mixture formed in this way enters the lower part of the column 24, where it is suitably agitated by means of the stirrer 25. The treated oil then escapes into the upper part 27 of the column 24 through the orifice 26a formed in the partition 26 and, through the medium of the pump 29, receives from the tank 28 a stream of bleaching earth in concentrated suspension in the same oil at the rate of 4 kg. of earth per hour, that is 0.4% by weight with respect to the oil.

The bleaching is effected in the zone 30 of the column 24, the different constituents of the mixture being brought into contact either by stirring, or by circulation, or by pulsation (not shown). The mixture of bleached oil and earth is then withdrawn by the pump 31 and passed through filter 32. The column 24 and the drying chamber 19 are kept under vacuum by means of the vane pump 33. Of course, the apparatus hereinbefore described could be modified by applying the upper part of the column 24 to the acid treatment and the lower part of the said column to thebleaching. By way of comparison, the proportions of bleaching earth used for oils not treated by the process of the invention have been 2.7% in the following three cases:

Sunflower seed oil washed with water before bleaching;

Sunflower seed oil washed in the presence of 0.2% of lactic acid;

Sunflower seed oil washed with water and bleached by a mixture of earth and 0.2% of lactic acid.

FIG. 4 shows an installation enabling the complete process of the invention to be carried into effect. In this installation, the crude oil H is sucked up by a centifugal pump 34 and is delivered to the conduit 35 and passes through a flow meter 36 and a heater 37. At 38, the oil receives through the conduit 39 an alkaline solution A-l prepared in the tank 40 and metered by the pump 41. The mixture enters a continuous mixer 42 and leaves it through the conduit 43. Water E, the supply of which is measured by a flow meter 45, is added to the mixture at 44. The whole mixture reaches the centrifuge 46, where it is separated into alkalized impurities in which are discharged through the conduit 47 and purified oil which leaves through the conduit 48. The latters opens into a tank 49 equipped with a stirrer 50. In this tank, a certain amount of organic acid Ac from the tank 51 is added to the oil after passing through a metering pump 52. The oil treated with the acid and overflowing from the tank 49 is con- 'veyed through the conduit 53 into 'a tank 54 equipped with a stirrer 55, where it continuously receives bleaching earth stored in a silo 56 equipped with a discharge screw 57. The mixture of oil and earth is drawn into the conduit 58 by means of the pump 59, which delivers it to the conduit 60. The oil is kept at a constant level in the tank 54 by means of a float 61, which controls the opening of the conduit 60. From the conduit 60 the mixture passes into a heater 62 and is then atomized in a'drier 63 connected to a suitable source of vacuum 64 such as an ejector-condenser. At this stage, two possibilities are offered. If it is desired to perform the bleaching under vacuum, the following circuit is used: the mixture, the humidity or moisture level of which is controlled by the temperature of the heater 62 and the vacuum of the drier 63, flows into the tank 65, which is also under vacuum, the valve 66 being open. Contact between the oil and the earth is ensured in the tank 65 by means of a stirrer 67, the mixture being brought to the desired temperature by a heating coil 68. The vacuum can be controlled in the tank 65 so that the loss of moisture in the oil is insignificant. The oil and the earth are withdrawn from the tank 65 through the conduit 69 by means of the vacuum extraction pump 70, which deliver them to the conduits 71 and 72, the level in the tank 65 being controlled by means of the float 73, which controls the opening of the conduit 71. The mixture then enters the intermediate storage tank 74, which is connected through the medium of the conduit 75, the pump 76 and the conduit 77 to a filter press 78 from which the purified, bleached and filtered oil issues at 79. If, on the other hand, it is desired to perform the bleaching in the free air, the mixture of oil and earth is withdrawn from the drier 63 through the conduit 80 by means of the pump 70, which delivers it to the tank 65 through the conduits 71 and 81, the float 73 being by-passed in this case. After bleaching contact in the tank 65, the overflowing mixture flows into the tank 74 through the conduit 82. In this case, the valve 66 is closed. Of course, the installation comprises the valves 83, 84, 85, 86, 87 and 88 required for establishing one or the other of the above-described circuits.

1000 kg./h. of crude peanut oil were treated in this installation with a solution supplying to the oil 0.03% of caustic soda and 0.06% of sodium tripolyphosphate, these amounts being calculated with respect to the amount of oil. The rate of flow of water at 44 was litres/hour, while 2 litres/hour of a 50% citric acid solution were supplied to the tank 49. The residual moisture level after the mixture had passed through the drier 63 was 0.03% by weight. The temperature of contact in the tank 65 Coefiicient of extinction Crude oil 7. 3 1. 2 Refined oil 7. 2 1. 3

The sparkle of the oil is perfect on storage after the filtration which follows the refining. The interfacial tension of the oil measured with respect to distilled water is 14 dynes/sq. cm. The ageing stability of the oil is excellent, the peroxide index only reaching the figure of 0.8 after the oil has remained for 96 hours in an oven at 60 C.

By way of comparison, the same crude oil treated by a conventional physical refining process needed 2% of activated bleaching earth. The values of the coefficient of spectral extinction of the refined oil at 232 m and 268 Ill/.6 were 5.5 and 8.4, respectively, and therefore very much changed with respect to those of the crude oil. The refined and filtered oil showed a cloudiness after a week. The interfacial tension in comparison with water was 8.5 dynes/sq. cm. The peroxide index reached the figure of 5 after 96 hours at 60 C. This demonstrates the very distinct advantage of the process of the invention in all respects.

FIG. 5 shows a simplified constructional form of the installation of FIG. 4. In this embodiment, the oil treated in the tank 49 is pumped by a pump 93 towards the heater 62 and the drier 63. The level of the oil in the tank 49 is kept constant by a float 94, Which controls the opening of the conduit 95 connecting the pump 93 and the heater 62. The oil may not be dried or dried to a given degree in the drier 63. From the drier, the oil flows into a bleaching tank 96 equipped with a stirrer 97 and a heating coil 98 through a column 99, the length of which corresponds to the barometric height, so that it is not necessary to use a vacuum extraction pump. Bleaching earth stored in a silo 56 equipped with a discharge screw 57 is added continuously to the oil. The mixture of oil and earth that overflows passes from the tank 96 towards the tank 74 of the installation of FIG. 4. The vacuum in the drier 63 is ensured by the ejectorcondenser 64.

FIG. 6 illustrates a modified constructional form of the installations of FIGS. 4 and 5. According to this embodiment, the oil is pumped from the acid treatment tank 49 to the heater 62 and the drier 63 by means of a pump 93. The moisture in the oil is adjusted in the drier 63 and the oil then flows by gravity into the barometric column 99. The bleaching earth is mixed with the oil in a tank 103 by means of the silo 56 and the screw 57. The level in the tank 10-3 is kept constant by the float 104. The mixture of oil and earth is then pumped into a bleaching tank 105 equipped with a stirrer 106 by the pump 107 after passing through a heater 108. The bleaching may be effected in the tank 105 with or without vacuum, a valve 109 being provided so that the tank 105 can be placed in communication with the ejector-condenser 110, which also ensures that the drier 63 is placed under vacuum. The mixture of oil and earth flows off into the tank 74 of the installation of FIG. 4 through a barometric column 111. The end of the circuit of the installation of FIG. 4 is then resumed.

In this installation, 1000 kg. of colza oil previously degummed with 0.1% of phosphoric acid in known manner, then brought to pH 8, diluted with water and centri fuged as shown by the diagram of FIG. 4 to enter the tank 49, were treated with 2 liters/hour of a 50% oxalic acid solution. Bleaching required 0.3% by weight of activated bleaching earth with respect to the oil; by way of comparison, the same oil, after conventional washing and without applying the same process, needed an amount of 2% of the same activated bleaching earth to bleach it.

FIG. 7 illustrates a modified constructional form of the installation of FIG. 6. According to this modified embodiment, after the oil has passed through the centrifuge 46, it is delivered to a tank 113 maintained at constant level by a float 114. The oil is then pumped by the pump 115 into a drier 63 and then flows 011? through a barometric column 116 into a tank 117 equipped with a stirrer, where the acid treatment is carried out. The oil overflowing from the tank 117 flows into a tank 118 equipped with a stirrer, where bleaching earth is added to it. The mixture of oil and earth resumes by way of the pump 119 the circuit of the installation of FIG. 6 in the direction of the heater 108.

As will be seen from the examples hereinbefore described, the process of the invention enables substantial savings of bleaching earth to be made.

It is obvious that the embodiments described are only examples and that it would be possible to modify them, in particular by substituting technical equivalents, without thereby departing from the scope of the invention.

It is claimed:

1. A process for purifying vegetable and animal oils containing fatty acids and other impurities, which consists essentially of the steps of 1) washing the crude or degummed oil with a small amount of water comprising from about 1 and percent by weight with respect to the oil; (2) separating the aqueous phase from the resultant mixture; (3) treating the washed oil with an amount of organic acid less than 0.3 percent of the weight of the oil, at a temperature ranging between 50 and 80 C., said acid being selected from the group consisting of formic, acetic, oxalic, lactic, citric, tartaric, succinic acids, the anhydrides of these acids and mixtures of these acids; (4) adjusting the moisture level of the oil at a value ranging between 0.1 and 0.5 percent by weight; (5) bleaching the oil by means of bleaching earths; and (6) submitting the bleached oil to steam distillation under vacuum so as to remove the fatty acids contained in the oil.

2. A process as claimed in claim 1 wherein the amount of acid used ranges between 0.1 and 0.2 percent of the weight of the oil to be treated.

3. A process as claimed in claim 1 wherein the duration of the acid treatment ranges between a few minutes and one hour.

4. A process as claimed in claim 3 wherein said duration ranges between and minutes.

5. A process for purifying vegetable and animal oils containing fatty acids and other impurities, which consists essentially of the steps of (1) treating crude or degummed oil with a small amount of an alkaline agent so as to bring the pH of the oil to a value of about 8 to 9; (2) washing the oil with a small amount of water comprising from about 1 and 5 percent by weight with respect to the oil; (3) separating the aqueous phase from the resultant mixture so as to remove the alkalized impurities from the oil; (4) treating the oil with an amount of organic acid less than 0.3 percent of the weight of the oil, at a temperature ranging between 50 and 80 C., said acid being selected from the groups consisting of formic, acetic, oxalic, lactic, citric, tartaric, succinic acids, the anhydrides of these acids and mixtures of these acids; (5) adjusting the moisture level of the oil at a value ranging between 0.1 and 0.5 percent by weight; (6) bleaching the oils by means of bleaching earths; and (7) submitting the bleached oil to steam distillation so as to remove the fatty acids contained therein.

6. A process as claimed in claim 5 wherein the amount of acid used ranges between 0.1 and 0.2 percent of the weight of the oil to be treated.

7. A process as claimed in claim 5 wherein the duration of the acid treatment ranges from a few minutes to one hour.

8. A process as claimed in claim 7 wherein said duration ranges between 10 and 15 minutes.

9. A process as claimed in claim 5 wherein the time of contact between the alkaline agent and the oil is of the order of one minute.

'10. A process as claimed in claim 5 wherein the alkaline agent and the oil are contacted at a temperature of about C.

11. A process as claimed in claim 5 wherein the alkaline agent is caustic soda and is used in an amount ranging from 0.01 to 0.05 percent by weight with respect to the oil.

12. A process as claimed in claim 5 wherein the alkaline agent is a mixture of an alkaline base or alkaline carbonate with alkaline metal salts having the same cation as the base or carbonate, said salts being selected from the phosphates, silicates, sulphates, chlorides, nitrates, acetates, oxalates, and citrates.

13. A process as claimed in claim 12 wherein said salts are selected from the tripolyphosphates and pyrophosphates.

14. A process as claimed in claim 5 which is performed continuously and wherein the time of contact between the water and the alkalized oil is substantially equal to the duration of the separating step.

References Cited UNITED STATES PATENTS LEWIS GO'ITS, Primary Examiner E. G. LOVE, Assistant Examiner US. Cl. X.R. 260424, 425

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