US3419588A - Process for continuously deacidifying glyceride oils - Google Patents

Description

Dec. 31, 1968 W. DE MAN PROCESS FOR CONTINUOUSLY DEACIDIFYING GLYCERIDE OILS Filed Sept 19, 1966 FIG. 7.

Sheet of 2 WILLEM de MA his INVENTOR.

ATTORNEYS.

31, 1968 w. DE MAN 3,419,588

PROCESS FOR CONTINUOUSLY DEACIDIFYING GLYCERIDE OILS Filed Sept. 19, 1966 Shet 2 of 2 IN VENTOR.

WILLEM deMAN w BY W$WA i ATTORNEYS.

United States Patent Ofi ice 3,419,588 Patented Dec. 31, 1968 3,419,588 PROCESS FOR CONTINUOUSLY DEACIDIFYING GLYCERIDE OILS Willem de Man, Hilversum, Netherlands, assignor to Lever Brothers Company, New York, N.Y., a corporation of Maine Filed Sept. 19, 1966, Ser. No. 580,390 Claims priority, applicatio; Germany, Oct. 30, 1965,

7 Claims. of. 260-425) ABSTRACT OF THE DISCLOSURE The invention relates to deacidification and especially to a continuous process for deacidifying lyceride oils using an alkaline liquid.

The term glyceride oils used in this specification includes both fatty acid glycerides that are normally solid and also those that are liquid at the normal temperature. Glyceride oils obtained by extraction, expression, or other processes from vegetable or animal raw material always contain a larger or smaller proportion of free fatty acids. Before these oils can be used for the preparation of foodstuffs, the free fatty acids and other accompanying impurities, erg. phosphatides, must be removed or separated.

The oldest and best known deacidification processes are those in which the oil is treated with an alkaline liquid with stirring. The free fatty acids react with the alkaline liquid to form soap. After the reaction, the soap solution that has been formed is separated from the oil. In addition to the desired formation of soap from alkaline liquid and fatty acids and a possible reaction of the alkaline liquid with pigments, which may lead to the removal of these substances, however, undesirable effects also occur such as the formation of emulsions and the saponification of neutral oil. These effects always lead to considerable losses of neutral oil. In practice, it is not possible to prevent the losses completely. Thus, for example, it is known that vigorous stirring is necessary to achieve the largest possible surface of contact between oil and alkaline liquid to promote deacidification, but this increases the danger of the formation of emulsions between the soap-containing alkali and oil.

The factors mentioned above lead to the presence of neutral oil in the acid oils that are obtained when the soapstock is split by means of acid, and therefore to a decrease in the yield of refined oil. In general, acid oils with a content of 30-40% or more of neutral oil are still quite usual. It is possible to recover neutral oil of acceptable quality from the soapstock, but this is expensive and therefore industrially unsatisfactory.

Various processes have been proposed for reducing the losses inherent in alkali refining-for example, by using weak alkalis, such as sodium carbonate and ammonia, and by centrifuging, giving very short times of contact between the oil and the alkaline solution. Although a certain improvement can be achieved by this process, the oil losses remain appreciable.

The invention relates to a process for the continuous deacidification of glyceride oils by means of an alkaline liquid in which the losses of neutral oil are reduced to a minimum. In this process, the oil is caused to flow in the form of a thin layer and along its surface or a part of it, it is brought into contact with a mist of the alkaline liquid to bring about the neutralisation of the free fatty acids. During the further flow of the mixture of oil and alkaline liquid, in cocurrent under substantially non-turbulent conditions, neutralisation occurs after which the aqueous phase containing soap and impurities is separated from the neutral oil.

It is essential that the alkaline liquid in finely divided form is brought into contact with a thin layer of oil in order to obtain a large contact area, so that a very short time of neutralisation is achieved and, moreover, the inclusion of oil droplets in larger soap droplets is avoided. The formation of emulsions is almost completely avoided by means of the gentle addition of small droplets of alkaline liquid to the slowly flowing thin layer of oil. Moreover, this process requires only a small excess of alkaline liquid, so that the saponification of neutral oil is reduced in a desirable :manner. The angle of incidence of the drops of alkaline liquid accelerated in the direction of flow of the oil should be as small as possiblenot more than -and the velocity and the kinetic energy of the droplets of alkaline liquid should be so low that, when they meet, the velocities of the oil and the alkaline liquid are as nearly as possible equal and the reaction therefore takes place in cocurrent flow. The cocurrent cont-act of oil and alkaline liquid is advantageous since no shear forces occur between oil and alkaline liquid, so that the use of very fine droplets of alkaline liquid is possible without the danger of the formation of an emulsion. Moreover, the uniform distribution of the droplets of alkaline liquid in the cocurrent contact guarantees that stoichiometric neutralisation conditions prevail throughout the mixture. In this way the saponification of neutral oil caused by local excesses of alkaline liquid and the formation of acid soaps due to local deficiencies of alkaline liquid are avoided.

During the contact between oil and alkaline liquid it is desirable that the mixture moves in substantially nonturbulent flow, preferably at Reynolds numbers between 1000 and 5000. In general, the time of contact between oil and alkaline liquid will be less than 15 seconds. After the brief and gentle cocurrent contact between oil and alkaline liquid, a coalescence of the droplets both of oil and soap occurs.

The mixture of oil and soap is led to a settling vessel where a direct separation of the two phases takes place, since no stable emulsions are present. The thickness of the oil layer must be between certain limits since when the oil layer is too thick the droplets of alkaline liquid are not distributed uniformly in the oil and when the oil layer is too thin the throughput of the unit concerned will be unnecessarily low. In general, the thickness of the oil layer to achieve optimum results is 1 to 3 mm. A suitable process for obtaining a continuously flowing uniform layer of oil consists in passing the oil over downwardly inclined surfaces making a small angle, for example, between 0 and 25, with the horizontal. At larger angles, the uniform and continuous flow of the oil may be disturbed by excessively high rates of flow leading to turbulence which can promote the formation of emulsions.

The droplets of the alkaline liquid that are brought into contact with the slowly flowing layer of oil. should have a diameter of not more than 1.0 mm., i.e., a diameter between 0.01 mm. and 1.0 mm., preferably a mean diameter of 0.1 mm. These droplets, which are obtained, for example, by spraying the alkaline liquid by means of a nozzle, are caused to contact the layer of oil practically without having any residual kinetic energy. When the droplets of alkaline liquid are greater than 1.0 mm., the good contact between oil and droplets of alkaline liquid may be effected. The oil layer need not be uniform or coherent during the whole process. It is only essential that a coherent slowly-flowing thin layer of oil is present where it comes into contact with the finely divided droplets of alkaline liquid. Since the reaction between droplets of alkaline liquid and the free fatty acids in the oil takes place very rapidly, the laminar flow of the mixture need not be maintained longer than necessary, so that almost immediately after the contact between oil and alkaline liquid the mixture can be fed into a decanting vessel. The process according to the invention possesses the advantage that oil and alkaline liquid are brought into contact and the resulting mixtures of oil and soap can be separated immediately without substantial amounts of oil being emulsified in the alkaline liquid or conversely.

It is advantageous to use sodium hydroxide for the alkaline liquid, but other alkaline agents may be used as well provided that they can be sprayed. In general, an alkaline liquid with a concentration of 005-20 N is used, the range from 0.1 N to 1.2 N being preferred. The optimum concentration of the alkaline liquid may be different from each oil and, moreover, different for the same type oil according to the lecithin content of the oil. As is customary, a certain excess of alkaline liquid-for example, l80%--may be used, but this again depends on the oil being treated. Small amounts of electrolytes such as, for example, NaCl may be advantageous in the alkaline liquid.

The temperature during the process is chosen according to the type of oil present but is usually above 80 C., although temperatures higher than 100 are possible and are necessary in certain cases to achieve optimum results. In the latter case, the whole process is carried out in a closed apparatus under pressure and the alkaline liquid is sprayed in inert gases. All steps of the process must then be carried out under a pressure high enough to prevent the boiling of the soap solution. The upper temperature limit is determined by the increasing hydrolysis reactions at these temperatures. In this process, the pressure will in general be in the range up to 6 atm. gauge, under which conditions reaction temperatures up to 160 C. may be used.

The process according to the invention can be used for a large number of crude oils. Even those oils which have a very high content of free fatty acids can be refined until their content of free fatty acids is reduced to less than 0.15%. The process condtions, such as temperature, concentration of alkali, concentration of electro lytes, etc., may be varied so that even oils which are difficult to deacidify because of their high content of mainly C and higher saturated fatty acids can be treated in a satisfactory manner without appreciable emulsification occurring. By way of example reference is made to oils of the lauric acid group, especially coconut and palm kernel oils; of the oleic-linoleic group, especially cottonseed, groundnut, corn oil, sunflower and safflower oil (all containing over 40% of combined linoleic acid and composed substantially of glycerides of C and C fatty acids the latter predominating and more highly unsaturated acids than linoleic being substantially absent, and palm oil (which palmitic and oleic acids predominate, with a much smaller proportion of linoleic); of the linolenic group especially those which contain only small proportions, e.g., 2 to 5 or of this acid with over 40% of linoleic acid and substantially no C to C acids, e.g., soyabean and wheat germ oil; and of the erucic acid group, especially rape seed and mustard oils. The process is also applicable to the neutralisation of tallow.

Finally, the direct separation of the two phases may take place in a settling vessel. If desired, the deacidified oil ca b t e t d f h r in a p cked c l m o s i countercurrent extraction apparatus by washing with water or a dilute alkaline solution to remove traces of soap. A suitable washing column contains packing consisting of spheres, saddles, or rings, the deacidified oil being fed into the device at the bottom below the layer of packing and the washing liquid being fed in above the layer of packing. The washing column may contain several layers of packing. Either the oil ascends in subdivided form in countercurrent to the downward-flowing washing liquid or the oil is brought in the form of a continuous phase into contact with subdivided washing liquid. When it is desired to post-wash in the first stage in the packed column with dilute alkaline solution to lighten the colour or to carry out a post-deacidification, part of the deacidification liquid is bled off and fed into the column via a rotameter. Since the post-deacidification or washing with dilute alkaline solution is carried out in the column below the washing zone, the washing water trickling down from the top serves to dilute the alkaline liquid fed in so that the post-deacidification or alkaline pre-washing processs is combined with the water washing process.

In a preferred embodiment, the mixture of soap and oil is, for example, fed into a centrifugal separator, the neutral oil issuing at the top and the soap at the bottom. A post-deacidification/ washing process may take place in a layer of packing in a packed column following the separator in which the oil is fed in at the bottom and rises in subdivided form in countercurrent to the continuous water phase, which may also contain alkali. The issuing washing liquid, which contains traces of soap, can be fed to the separator or be combined with the soap leaving the separator. After this treatment, the oil can be treated with washing water in a second washing column or in the second part of the same washing column. In this case, the oil phase remains continuous and the wash water, fed in at the top, is finely subdivided.

Instead of an ordinary separator operating under the influence of gravity, a centrifuge can be used as a highoutput separator when care is taken that turbulence and, therefore, the formation of emulsions in the two-phase system is avoided at its entry into the centrifuge. Because no emulsion is present, the centrifuge can separate the mixture satisfactorily.

Various modifications are possible to achieve the desired contact between oil and droplets of alkaline liquid. The oil can be passed over an inclined surface and the alkaline liquid be sprayed onto this layer of oil. This surface may have the form of a funnel, with one or more spray nozzles for the alkaline solution being arranged in such a way that the droplets of alkaline liquid come into contact with the layer of oil uniformly, after which the mixture of oil and soap flows through the central discharge tube into a separating device. The oil may also flow in a thin layer over a plate connected with a hori zontal channel which leads the mixture of oil and soap via a discharge tube to the separating device. The spray nozzles which spray the droplets of alkaline liquid onto the flowing layer of oil can be arranged over the end of the plate where the plate leads into the channel. The oil may be allowed to flow in the form of a layer over a horizontal or slightly inclined surface on which an overflow weir is arranged. A chamber containing the spray nozzles for the alkaline liquid is arranged over the overflow weir. When the oil flows over the weir, which may have either an angular or a wavy edge, the alkaline liquid is sprayed onto the oil, which flows away over the weir. It is not necessary that the oil itself should flow; the layer of oil may be present on a moving surface for example, rollers or plates-which is sprayed with droplets of alkaline liquid and from which the mixture of oil and soap can be scraped off or thrown off by centrifugal force.

Thus, the layer of oil can be put in motion by means of a slowly rotating drum, the droplets. of alkaline liquid being sprayed onto the layer of oil, and the resulting mixture of oil and soap being scraped off.

Moreover, the oil can be fed from below onto a stationary or slowly rotating plate which is horizontal or has a slight downward Slope outwards, so that it spreads out uniformly in all directions. The alkaline liquid is sprayed uniformly on to the thin layer of oil. The resulting mixture of oil and soap runs into a collecting channel arranged round the plate and from this into the separating device.

Other variations are possible which all have in common with one another that droplets of alkaline liquid are sprayed uniformly on to a moving or moved thin layer of oil.

Apparatus suitable for carrying out the process of the invention is described by way of example in the accompanying diagrammatic drawings both of which show in elevation a complete layout, that of FIGURE 2 including means for washing the neutralised oil.

Referring to FIGURE 1, the crude oil is pumped by means of pump 1 to a heating device 2 where it is heated to about 95 C. The heated oil is fed via conduit 5, provided with a Rotarneter 3 into the lower conical part 7 of vessel 4. The oil is distributed in a thin layer along the inner surface of the conical part of the vessel by means of an annular conduit 6 provided at the bottom with small holes. The alkaline solution is pumped from the container 9 through a filter 10 and a heating device 12 by means of pump 11 into the neutralisation vessel 4. In the heating device, the alkaline liquid is heated to a temperature of about 95 C. A rotameter 13 is again provided in the conduit. The alkaline liquid flows into the upper part of the neutralisation vessel through the feed conduit 14 and is sprayed by means of nozzle 15 on to the layer of oil. The nozzle is so directed that the mist comes into contact uniformly with the layer of oil present on the conical part of the neutralisation vessel. The mixture of oil and soap leaves the neutralisation vessel through the discharge pipe 8, which is connected with a separating device 16, for in stance a centrifuge. The discharge pipe 8 has an inspection sight glass 19 below the cone and a sample cock 20. In the device 16, the soaps formed and other impurities of the oil are separated from the oil. The neutral oil is taken ofi through outlet 17 and the soap through outlet 18 (FIG. 1).

When desired, the deacidified oil can 'be washed with a weakly alkaline liquid and/or hot water in a subsequent packed washing column 21 shown in FIGURE 2 in order to remove traces of soap that may still be present. The alkaline liquid is fed into the bottom 21 and the hot water into the top 22 of the washing column. A post-deacidification process can be carried out in the same apparatus, if desired.

The following examples illustrate the invention.

EXAMPLE 1 A crude coconut oil with a free fatty acid content of 15.35% was deacidified at 8085 C. with 0.9 N caustic soda solution in an apparatus as shown in the figures. The throughput of crude oil was 280 kg./hour. The excess of alkali was 5%.

The oil and the alkaline solution or oil and soap were in close contact for approximately 15 seconds, after which the mixture of oil and soap entered the separator.

A sample taken from the sample cock showed that the neutralisation of the free fatty acids in the oil was complete. The mixture of oil and soap of this sample separated after a short time. The analysis of the separated oil showed a free fatty acid content below the prescribed percentage content of free fatty acid for neutral oil namely 0.1%.

In the separator, oil and soap were separated from one another and taken off. A sample of the separated soap was split with sulphuric acid. Analysis gave an acid number of 257.5 and a saponification number of 259. From these figures calculation gave a degree of splitting of 99.4% and a free fatty acid content of the acid oil of 97.9%.

To improve the colour and to remove the traces of soap, the deacidified oil was treated in countercurrent with a 0.1 N solution of caustic soda in the lower part of the washing column at a temperature of 95 C. The column was filled with packing rings with a diameter of 2.5 cm. The oil was washed with hot water litres/hour) at a temperature of 90 C. in the top part of the same apparatus. 3379 kg. of water-free neutral oil was obtained from 3575 kg. of crude coconut oil, the content of free fatty acids being 0.07% and the content of soap 0.03%.

The practical yield was 99.9%, and thus agreed with the theoretical yield.

EXAMPLE 2 Crude coconut oil with a free fatty acid content of 5.3% was deacidified.

The alkali used had a normality of 1.0 N.

The throughput was 300 kg. of crude oil per hour,

The deacidification and separation were carried out in the apparatus described. The separating vessel was followed by a packed column for washing.

The excess of alkali amounted to a total of 5% for deacidification.

100 litres/hour of water was used for washing. The temperatures during the process were:

C. During deacidification During separation 98 During washing 95 The analysis of the neutral oil obtained gave the following average values:

Percent Residual content of free fatty acids 0.07 Residual content of soap 0.036

The analysis of the acid oil obtained by the splitting of the soap produced gave the following figures:

Percent Acid number 257 Saponification number 258 Degree of splitting 99.5 Content of free fatty acids in the acid oil 98.0

In a similar way tallow of free fatty acid content 4.5 can be neutralised with 0.2 N caustic soda at C. and separated and washed at the same temperature and groundnut oil of free fatty acid content 0.8 to 0.9 can be neutralised and washed under the same conditions of temperature and using the same concentration of alkali.

EXAMPLE 3 C. During deacidification 90 During separation 97 During washing The analysis of the neutral oil obtained gave the following average figures:

Percent Residual content of free fatty acid 0.04 Residual content of soap 0.05

The analysis of the acid oil obtained by splitting the soap produced gave the following figures:

Acid number 258 Saponification number 260 Degree of splitting percent 99.3

Content of free fatty acids in the acid oil "percent" 98.4

In a similar way tallow of free fatty acid content 4.5% can be neutralised at 150 C. and separated and washed at 95 C. and palm oil of the same free fatty acid content can be neutralised at 140 C. and separated and washed at 90 C.

EXAMPLE 4 Crude coconut oil with a free fatty acid content of 6.76% was deacidified.

The alkali used had a normality of 1.0 N.

The throughput was 400 kg. of crude oil per hour.

The deacidification and separation took place in the apparatus described. The separating vessel was followed 1 by a packed column for washing.

The excess of alkali mounted to a total of 30%, 20% being used in the deacidification process and 10% in washing.

100 litres of water per hour was used for washing. The temperatures during the process were:

C. During deacidification 92 During separation 99 During washing 95 The analysis of the neutral oil obtained gave the following average figures:

Percent Residual content of free fatty acid 0.09

Residual content of soap 0.039

The analysis of the acid oil obtained by splitting the soap produced gave the following figures:

Acid number 262 saponification number 266 Degree of splitting percent 98.5 Content of free fatty acids in the acid oil percent 97.0

EXAMPLE 5 C. During deacidification 94 During separation 98 During washing 98 The analysis of the neutral oil obtained gave the following average figures:

Percent Residual content of free fatty acid 0.06 Residual content of soap 0.03

The analysis of the acid oil obtained by splitting the soap produced gave the following figures:

Acid number 171 saponification number 199 Degree of splitting percent 86.0 Content of free fatty acid in the acid oil percent 85.7

8 In a similar way a partly refined cottonseed oil of free fatty acid content 0.2 to 0.3 can be neutralised at 130 C. with 0.2 N caustic soda and separated and washed at C.

EXAMPLE 6 Crude soyabean oil with a free fatty acid content of 0.3% was deacidified.

The alkali used had a normality of 0.5 N.

The throughput was 450 kg. of crude oil per hour.

The deacidification and separation were carried out in the apparatus described. The separating vessel was followed by a packed column for washing.

The excess of alkali amounted to a total of 50% for the deacidification process.

100 litres of water per hour were used for washing. The temperatures during the process were:

During deacidification During separation 96 During washing 98 The analysis of the neutral oil obtained gave the following average figures:

Percent Residual content of free fatty acid 0.05 Residual content of soap 0.34

The analysis of the acid oil obtained by splitting the soap produced gave the following figures:

Acid number 195 saponification number 205 Degree of splitting percent 94.5 Content of free fatty acids in the acid oil "percent" 97.5

EXAMPLE 7 Crude soyabean oil with a free fatty acid content of 0.4% was deacidified.

The alkali used had a normality of 0.5 N.

The throughput was 450 kg. of crude oil per hour.

The deacidification and separation were carried out in the apparatus described. The separating vessel was followed by a packed column for washing.

The excess of alkali amounted to a total of 50% for the deacidification process.

100 litres of water per hour were used for washing. The temperatures during the process were:

C. During deacidification 94 During separation 90 During washing 98 The analysis of the neutral oil obtained gave the following average figures:

Percent Residual content of free fatty acid 0.09 Residual content of soap 0.44

The analysis of the acid oil obtained by splitting the soap produced gave the following figures:

Acid number saponification number 203 Degree of splitting Percent 88.8

Content of free fatty acid in the acid oil Percent 89.6

What is claimed is:

1. A process for continuously deacidifying glyceride oil containing free fatty acids and other impurities while avoiding substantial emulsification and saponification which comprises flowing said oil through a contact zone in which the oil in the form of a coherent thin film is contacted with an aqueous alkaline liquid by spraying the film with droplets of the said liquid having an average particle size of from 0.1 to 1 mm. diameter, in a non-disruptive impact, maintaining the resultant substantially non-turbulent mixture in cocurrent flow and subsequently separating the resultant neutral oil from the resultant soap-containing and impurity-containing aqueous phase.

2. A process for continuously deacidifying glyceride oil containing free fatty acids and other impurities while avoiding substantial emulsification and saponification which comprises flowing a thin layer of said oil having a thickness of from about 1 to about 3 millimeters at an incline of from to about 25 from the horizontal, spraying droplets having an average diameter of from about 0.01 to about 1.0 millimeter in a nondisruptive impact of an aqueous alkaline liquid onto said oily layer, maintaining the resultant laminar cocurrent flow of the substantially non-turbulent mixture for a neutralization period of time up to about 15 seconds and thereafter separating the resultant neutral oil from the resultant soap-containing and impurity-containing aqueous phase.

3. The process as defined by claim 1 wherein the alkaline droplets have substantially the same amount of kinetic energy as the oily layer.

4. The process as defined by claim 1 wherein the alkaline liquid has a concentration between about 0.05 N and about 2 N.

5. The process as defined by claim 1 wherein the alkaline droplets and oily layer have a temperature of from about C. to about C. and are at atmospheric pressure.

6. The process as defined by claim 1 wherein the alkaline droplets and oily layer have a temperature of from about 95 C. to about C. and are under a pressure of up to 6 atmospheres gauge.

7. The process as defined by claim 1 wherein, after the separation of the netural oil and soap containing aqueous phases, the neutral oil is washed countercurrently with water.

References Cited UNITED STATES PATENTS 2,327,569 8/1943 Thurman et al. 260-425 2,906,606 9/ 1959 Signer 23-2705 3,226,407 12/1965 Bergman 260-425 NICHOLAS S. RIZZO, Primary Examiner.

20 A. M. TIGHE, Assistant Examiner.

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