US3440253A - Method of refining vegetable and animal oils - Google Patents

Description

United States Patent U.S. Cl. 260425' Claims ABSTRACT OF THE DISCLOSURE The alkali refining of edible oils is carried out in the presence of a concentrated, e.g. 25%30% or 40%, aqueous solution of a salt of a mononuclear aryl or mononuclear alkyl aryl sulphonic acid in which the total number of carbon atoms of the alkyl chains is not greater than 4. The mixture resolves into a refined oil phase and an aqueous phase containing the soapstock. After separation, the soap is split by acidification and the resulting free fatty acids are recovered. The aqueous residue is preferably recycled after crystallising out excess inorganic salts.

The present invention relates to an improved method of refining vegetable, animal and marine oils and is a continuation-in-part of our copending application No. 340,804 filed Jan. 20, 1964 and now abandoned, which is itself a continuation-in-part of application No. 290,935 filed June 27, 1963 and now abandoned.

Such oils are neutral glyceride esters of fatty acids, but during extraction from their naturally occurring state some degradation of the oil occurs and the resulting crude oil contains free fatty acids dissolved in the oil. The conventional method of refining such oils involves treating the crude oil with an aqueous alkaline solution, such as dilute sodium hydroxide or sodium carbonate, followed by several water washes and, if necessary, by an adsorptive bleaching process using activated earths. In some cases, a process of deodorisation is also used in which steam or an inert gas is blown through the oil at an elevated temperature under vacuum. In this alkali refining process, the free fatty acids present in the crue oil are removed as soaps. This method of refining suffers from the inherent disadvantage that the soap forms a micellar solution in water which entrains appreciable quantities of the glyceride oil. Thus, not only is there a loss of the glyceride oil, but also the fatty acids which may be recovered from the soapstock are contaminated with considerable amounts of glyceride oil. Moreover the refining process takes several hours to complete if separation is carried out by the usual gravity method.

Various methods have been proposed to reduce the losses of oil and/ or to improve the purity of the recovered oil and soapstock, e.g., U.S. Patents Nos. 2,225,575, 2,437,075, 2,551,496 and 3,065,249. All of these proposed solutions have been partially or wholly unsatisfactory and oil refiners have to accept that considerable oil losses will occur even with the most advanced of the prior oil refining techniques.

We have now found that the presence of a concentrated aqueous solution of certain benzene or a'lkylbenzene sulphonat salts during the alkali refining of the crude oil enables a much more rapid and complete separation of the oil and soap layers to be achieved, with the result that the amount of oil entrained in the soap layer is greatly reduced. Moreover the presence of the sulphonate salts during refining reduces the time required to secure adequate separation of the oil from the soap layer to a matter of minutes. This is to be contrasted with the hours required to secure a comparable separation when conventional refining techniques are used.

Where the original glyceride oil contains phosphatides, eg in the case of soya bean oil, we have found that these are extracted into the the aqueous layer and can be recovered therefrom by known methods. The phosphatides, e.g. lecithin, may be valuable by-products of the process. Furthermore, other polar bodies such as proteins, aldehydes and colouring matter which are more hydrophilic than the glyceride oils but somewhat less hydrophilic than the soaps, are also removed from the oil phase into the aqueous phase. Because of this the oils obtained by our method are substantially equal in quality to oils obtained by conventional refining methods which involve purification in several stages including alkali refining, adsorptive bleaching and de-odorising. By using our method it may be possible in some cases to reduce the number of refining stages to one.

The sulphonate salts for use in the invention are defined as monouuclear sulphonates of alkyl aryl sulphonates wherein the aromatic nucleus may contain up to three alkyl substituents, and the total number of carbon atoms of all the alkyl substituents does not exceed four. Such sulphonate salts include for example the alkalimetal or ammonium salts of benzene, xylene, toluene, cymene and cumene sulphonic acids. Where the refined olis are intended for use in the preparation of foodstuffs, it is preferred to employ sulphonate salts which are substantially free from sulphone materials. Such sulphonefree sulphonate salts may be readily obtained in known manner by preparing a crude sulphonic acid by the action of sulphur trioxide on the appropriate hydrocarbon, quenching the reaction mixture, neutralising it with a base and subsequently washing the crude sulphonate salt with the hydrocarbon from which it has been derived. Especially preferred sulphone-free hydrotropes for present use are those sodium xylene sulphonates sold by the applicants under the trademark Halvopon Or.

The sulphonate salts for present use do not markedly depress the surface tension of water and are not to be confused with the surface-active sulphonate salts, which contain long chain alkyl substituents. The surface-active sulphonate salts are not suitable for present use since, even when used in minor amounts, they bring about emulsification of the oil and soap layers and render it virtually impossible to recover any oil from the refining mixture.

The concentration of the sulphonate salt during refining required to achieve the clean separation of the oil and soap layers will depend upon the salt employed. As a general guide we have found that a concentration of at least 30% by weight is required with most of the sulphonate salts although cumene sulphonates are effective when used in a concentration as low as 25%. There is no upper limit to the concentration of the aqueous sulphonate solution which is employed and saturated solutions may therefore be used. However, the optimum concentration is less than saturation and is usually within the range 40 to 60%. The concentrations referred to above are based on the total amount of water present in the refining mixture. Since appreciable amounts of water are added with the alkali and since the oil may contain some water, the concentration of the aqueous solution of the sulphonate added to the refining mixture is usually Well in excess of the figures quoted above in order to achieve the desired concentration during refining. In some instances to achieve the desired concentration it may be necessary to add dry sulphonate salt to the refining mixture.

The amount of sulphonate salt, as opposed to the concentration of its aqueous solution, required to bring about a satisfactory separation of the oil and soap layers will depend upon the amount of free fatty acid in the crude oil. The use of 2 to 6 times the weight of the free fatty acid in the crude oil usually provides satisfactory results.

The alkali used in the refining of the crude oil may be any of the saponifying or non-saponifying alkalis in common use. It is preferred to use sodium hydroxide and/or sodium carbonate. The amount of water present is determined by the amount of and concentration required for the sulphonate salt, with the result that the alkali is usually present initially as a dilute aqueous soltion, for example a 20% solution. As indicated above, the water added to the crude oil in the form of the aqueous alkali must be allowed for when calculating the concentration of the sulphonate solution which is to be added. In some cases it may be necessary to use comparatively concentrated aqueous alkali in order to avoid adding excessive amounts of wateuto the refining mixture. Owing to the reduction in the viscosity of the soapstock using the sulphonate salts, it is possible to reduce the excess of alkali used from the conventional 25% excess over that theoretically required to neutralise all the free fatty acids in the crude to 10% or less.

The process of the invention is applicable to the treatment of a large variety of crude oils and has the advantage that it can be used for refining oils which contain more than the normal amount of fatty acids and which would not be worth refining, or would be impossible to refine, by conventional methods owing to the excessive loss of oil or the impossibility of breaking the soap/oil emulsions formed during refining. In particular, tallow oils, which contain as much as 25 fatty acids, can be refined by the method of our invention with very little loss of glyceride oil.

One method of extracting vegetable oils is to digest crushed seeds with a hydrocarbon solvent, for example hexane. We have found that the resulting solution of the oil is excellently suited to the process of the invention, since the separation into the aqueous layer and the oil layer is even quicker than in the case when the oil undissolved in hydrocarbon is used. It is to be understood that in the description of the invention and the claims herein, the term oil includes, where the context permits, solutions of oil in hydrocarbon solvents.

In view of the short time required for separation of the aqueous and solvent phases, the use of hydrocarbon solu tions of the oils lends itself with especial advantage to the operation of the invention as a continuous process, though the invention is also applicable to batch operations.

The refining of the crude oil may be carried out in the normal manner. The oil may be admixed with the alkali and subsequently with the sulphonate salt or in the reverse order. More commonly the sulphonate salt and alkali solutions may be premixed and the mixture then fed to the crude oil.

During the refining of the oil soaps are formed by the action of the alkali on the free fatty acids in the crude oil. After refining has been completed, the refining mixture is allowed to separate into an upper oil layer and a lower aqueous soap layer. The separation of the layers may be aided by, for example, centrifuging or other mechanical means.

If an even higher degree of purity in the oil is req ired, the oil layer, after separation of the aqueous layer,

may be treated with a further small qauntity of sulphonate salt in aqueous solution and the two layers formed allowed to separate. The second aqueous layer is separated off and may be combined with that originally obtained if desired. The oil layer, after a wash with water, is dried under vacuum to obtain substantially pure glyceride oil.

The aqueous layer or layers obtained from the refining of the crude oil comprise a solution of the fatty acid soaps in the sulphonate salt solution. The fatty acid values may be recovered from such a solution by treatment with a mineral acid, such as sulphuric acid. Acidification is preferably carried out to give a pH value of from about 4 to about 5. Often the fatty acids, especially if they are of comparatively low polarity, will separate out after acidification to form an upper fatty acid layer which may be recovered, for example, by decantation but in the case of acids of higher polarity it may be necessary to dilute the sulphonate salt in order to render the acids insoluble. Dilution of the acidified aqueous layer thus offers a simple and convenient method for separating out the liberated fatty acids. It will be appreciated that the use of a sufiiciently dilute mineral acid will achieve both acidification and dilution.

After liberation and recovery of the fatty acids from the aqueous layer, the residual aqueous solution may be discarded or recycled for further use since it contains the sulphonate salt. The recycled aqueous solution also contains appreciable quantities of alkali-metal salts of the mineral acid used to liberate the fatty acids. The presence of excessive quantities of these salts may prove detrimental in the refining process and the amount present in the recycling aqueous solution is preferably main tained at a low level. We have found that the solubility of sodium sulphate in sodium sulphonate solutions is comparatively low and therefore that, upon cooling of the recycling aqueous solution, a major proportion of the sodium sulphate therein crystallises out and can be removed, for example by filtration or centrifuging. The recycling aqueous solution is usually too dilute for direct reuse in the refining of further crude oil and it is then concentrated to approximately the level required for reuse. Conveniently this concentration is carried out before the mineral acid salts are separated. If required, additional quantities of sulphonate salt may be added to the recycling aqueous solution in order to make up any losses which may have occurred during the process. Furthermore, other impurities such as glycerol, or useful byproducts such as phosphatides may accumulate in the recycling aqueous solution and it may be desirable to remove these in known manner, or to discard the recycling solution.

Although the fatty acid mixture obtained by acidification of the aqueous layer derived from the original alkali treatment is comparatively pure, it generally contains a residue of glyceride oil. According to a feature of the invention the process for recovering the fatty acids just described is modified so as to give a fatty acid of improved purity. The aqueous layer derived from the original alkali treatment is boiled with at least sufficient alkali to hydrolyse the glyceride oil therein to give a further quantity of fatty acid soap and glycerol; the mixture is acidified with a mineral acid to hydrolyse the soap; the resulting mixture is allowed to form two layers; and the lower, aqueous layer is removed to leave a fatty acid layer of improved purity. It will be understood that the aqueous layer used as starting material for this process contains the sulphonate salt originally present during the refining of the crude oil. The presence of the sulphonate salt is essential to the success of the process since without it, boiling of the mixture would be a difiicult or impossible task owing to foaming caused by the soap, this foaming being wholly or largely prevented by the sulphonate salt. All the alkali necessary for the process of the invention may be provided by adding a sufiicient excess of aikali in the original treatment of the raw glyceride oil.

Alternatively some or all of the alkali may be provided separately after the initial refining process.

In carrying out this modified process just described, the original oil and acid mixture may first be treated as before, but with approximately twice the amount of alkali required to saponify the acids present, in the presence of the sulphonate salt. The resulting mixture separates into an upper purified oil layer and a lower aqueous layer, which contains the saponified acids, sulphonate salt, excess alkali and some entrained glyceride oil. This aqueous layer is run off and boiled for about one hour. At this temperature and time the alkali present splits the glyceride oil. If necessary, further alkali may be added at this stage in order to give an excess calculated on the glyce-ride which is present. The aqueous layer is then treated as before to liberate the fatty acids, and to recover the sulphonate salt solution, which may be recycled. Hence, the process as a whole lends itself to continuous operation.

As indicated above, it may be necessary to add further sulphonate salt to the recycling aqueous solution in order to make up any losses which may occur in the process. The point at which the additional required sulphonate salt is added to the recycling solution is comparatively unimportant and this addition may in fact be made before or during the acidification of the soap layer to liberate the free fatty acids therefrom.

The process of the invention will now be illustrated by the following Examples, in which all parts are given by weight:-

In order to assess the results of the processes described, we quote the refining factors of these processes, since this is the criterion by which oil refiners judge the value of a refining operation. The refining factor is the proportion of the total weight of substance removed from the oil to the weight of free fatty acid originally present in the oil, and the ideal to be aimed at is a factor of unity.

EXAMPLE 1 100 parts of soya bean oil (acid value 2.2 mgs KOH/ g.) was heated to 95 C. To the hot oil was added 7 parts of sodium xylene sulphonate (SXS) in aqueous solution and an aqueous solution of caustic soda in an amount sufficient to give a excess based on the acid value of the oil. The amount of water in these solutions was enough to give a 40% solution of the SXS. The mixture was stirred and then allowed to settle. After 30 minutes the aqueous layer was separated, the oil was washed a second time with 30% SXS, separated, washed with water and then dried under vacuum at a temperature of 95 C. The combined aqueous layers were treated with sulphuric acid to liberate the fatty acids. After removal of the fatty acids, the sodium sulphate was crystallised out and filtered off to give a solution of SXS for reuse. The experiment was repeated except that the SXS solution was not present during refining. 8 hours were required for the separation. The observed results are shown in Table 1.

XS Based Weight, AcidValue, Saponifica- Percent AcrdValuc,

Neutral mg. KOH/g.

011 Parts in KOI-I g. tion Value, on g mg./KOH/ Oil Eng. trained 7 1.30 160 196 0. 0. 05 Nil 3.16 114 196 1. 32 0.

In this example the refining factor may readily be calculated as follows:

weight of substances recovered from the oil weight of free fatty acids originally present in the oil Refining factor (R.F.)=

The weight of substances removed from the oil when the SXS is present is 1.30 parts and the weight of free fatty acids in the original oil is 1.10 parts (half the acid value of 2.2 mg. KOH/g.).

Where no SXS was used the refining factor is The advantages of the process can also be shown by reference to calculated values of the percentage of neutral oil entrained in the aqueous layer. These figures may be calculated by two methods, as follows:

(i) The extra weight of crude fatty acid obtained i.e. weight of crude fatty acids obtainedweight of fatty acid originally present, per parts of crude oil. This method gives the correct result only if there has been no hydrolysis of the oil during refining.

(ii) Since the acid value of the crude fatty acids is a measure of the actual fatty acid content thereof the ratio acid value (AV) fatty acid saponification value (SV) fatty acids +entrained oil per 100 parts of crude oil. Applying methods (i) and (ii) to the cited example 7% SXS No SXS 1.30-1.l=0.20% 3.16-1.10=2.06%

The coincidence of the results obtained by method (i) and method (ii) in the SXS refining is yet another measure of the superiority of the process. This shows that all of the acid ending up in the crude acid oil was originally present as fatty acid in the oil.

In the conventional refining experiment the two figures are inconsistent, and since method (i) relies on there being no more acid present in the system at the end of the refining procedure than at the start, method (ii), which relies only on measured quantities, applies, and shows that more acid is present at the end, i.e. hydrolysis has occurred during the refining.

Since the refined neutral oil in the conventional process still contains 0.13% fatty acid (the equivalent of an acid value of 0.25 mg. KOH/g.), only 0.85% (Ll-0.25) of the original fatty acid is transferred into the crude fatty acid. Since 3.16% of crude fatty acid is obtained, then 2.31% (3.16-0.85) of oil is entrained, either as acid produced by hydrolysis or as oil. Thus the loss of oil is even greater than at first sight appears, due to the relative inetficiency of the conventional deacidification.

EXAMPLES 2-12 The quantity of oil stated in Table 2 was heated to 90 C. and treated while stirring with a solution of SXS (4X percent FFA) and sodium hydroxide of theory) in water such that the final Halvopon concentration was 40%.

After the times shown, the lower aqueous layer was separated, acidified to pH4 with 70% sulphuric acid and the separated acid oil washed with water and dried.

The neutral oil layer was washed twice with water and vacuum dried.

TABLE 2 Neutral Oil Acid 011 Time of Example Oil Percent Wt. crude Refining Separation F oil Wt. Percent Percent Wt. AV SV Factor (mins) FFA Soap 2 Peruvian Fish. 0. 05 1. 16 40 a 0.2 1.00 45 Fish (Herring) 0.05 1.00 40 5..- Crude Hardened 0. 05 1. 11 35 Fish Oil. 6 Tallow 471 g 230 g 1.1 0.6 1.23 45 Coconut"... 1,170.5 g 1,067 g 056 0. 084 l. 18 30 Sunfiower. 3,267 g. 3,232 g. 0.008 0. 042 1.00 35 Rice Bran 400 g 161 g 1. 27 O. 28 1.16 45 Rape 000g s73 0.14 0. 07 1.25 40 Soya Bean..- 500 g 495 0.07 0. 1.38 40 12 live 1,000 g 886 g 0.12 0.05 1.00 35 EXAMPLE '13 The results are summarised in Table 3.

Crude snufiower seed oil (10,000 kg.) was treated at TABLE 3 50 C. with 60% phosphoric acld (100 kg.), the tem- Neutralon Acid Oil Refining perature ralsed to 90 during 30 minutes with stirring, and Y. m P m v P factor the mixture allowed to separate for 1 hour. The aqueous i r ii (1% g.) A W l r i phase was discarded, the oil washed with water (400 kg),

f 5 000 k h Ontaim A 4,792 0.08 185 75 188 39.8 8.1 and dlVl ed into two portions 0 g. eac c 4,922 Q06 76 166 189 8&0 1.17

ing 1.34% FFA.

Portion- A The degummed oil (5,000 kg.) was neutralised in the conventional manner at 70 C. with sodium hydroxide (67.2 kg. of 15% solution). The mixture was stirred for minutes after alkali addition then allowed to separate for four hours.

The aqueous soapstock layer was removed and the oil washed with water (200 kg.). It was necessary to repeat this operation a further 14 times to bring the soap content of the neutral oil below 0.05%.

The yield of neutral oil after vacuum drying was 4792 kg, thus the refining loss was 208 kg. giving Refining factor= In connection with this example it should be noted that a lower temperature was required when no SXS was present, since in the absence of SX'S there is a greater tendency of the alkali to hydrolyse the oil.

Herring oil (5.65 %FFA) was used in the following examples.

The oil -('100 g.) was stirred at 90 C. with a solution of 34 g. of the sulphonate salt (equivalent to 6 FFA) together with 0.88 g. of sodium hydroxide (equivalent to 110% of theory) in water, (51 g. in Examples 14 and 15, 80 g. in Examples 16 and 17, corresponding to 40% and 30% solutions of sulphonate salt respectively).

After separation (maximum 30 minutes) the neutral oils were separated and analysed. The soapstocks were split with sufficient 70% suphuric acid to give a pH of 4, and the acid oil recovered, washed dried and analysed.

TABLE 4 Neutral Oil Acid Oil Refining Example Sulphonate Salt Factor Weight Percent Percent Weight AV S FFA Soap We claim:

The neutral oil had an FFA content of 0.08%.

The soapstock was acidified to pH4 with 70% sulphuric acid causing a separation of acid oil. The acidic aqueous layer was run off, the acid oil was Washed with water kg.) and dried.

Portion B The degummed oil (5,000 kg.) was heated to 93 C. and treated, with stirring, with a solution of sodium hydroxide, (9.5 kg.) and Halvopon OR (202 kg.) in water (2885 kg). After stirring for 10 minutes the mixture was allowed to separate for 20 minutes.

The lower aqueous phase was run 011 and the neutral oil washed with water (3 X 200 kg.) giving a soap content in the oil of 0.04%.

The oil was vacuum dried and weighed, giving 4922 kg. with an FFA content of 0.06%. The refining factor calculated as for A is 1.17.

The soapstock was treated as in A.

1. In a process for refining crude vegetable, animal and marine oils consisting of neutral glyceride esters of fatty acid containing fatty acid impurities which comprise refining said crude oil at a temperature above the melting point of said crude oil by admixing with said crude oil an aqueous solution of an alkali thereby forming an oil phase and an aqueous soap phase, and separating the aqueous soap phase from said oil phase, the improvement which comprises admixing with said crude oil and said aqueous alkali, a salt of a sulphonic acid selected from the group consisting of mononuclear aryl or alkyl mononuclear aryl sulphonic acids wherein the aromatic nucleus may contain up to three alkyl substituents and the total number of carbon atoms of all the alkyl substituents does not exceed four, the concentration of the sulphonic acid salt being at least 30% by Weight based on the total amount of water present.

2. The process of claim 1 wherein said salt is an alkali metal or ammonium salt of at least one sulphonic acid selected from the group consisting of benzene, xylene, toluene and cumene sulphonic acids, said salt being present in an amount between about 2 and 6 times the weight of the fatty acid present in said crude oil.

3. The process of claim 2 wherein the concentration of said sulphonic acid salt is between 40% and 60% of the weight of the water present.

4. The process of claim 1 wherein the concentration of said sulphonic acid salt is at least 40% by weight based on the total amount of water present.

5. The process of claim 4 wherein said sulphonic acid salt is a salt of an alkali metal.

6. The process of claim 5 wherein said salt is at least one sulphonic acid selected from the group consisting of benzene, xylene, toluene and cumene sulphonic acids, and wherein said sulphonic acid is present in an amount between about 40% and 60% of the weight of the water present.

7. The process of claim 6 wherein said salt is a salt of Xylene sulphonic acid.

8. The process of claim 7 wherein said salt is a sodium salt, and is present in an amount between about 2 and 6 times the weight of free fatty acid in said crude oil.

9. In a process for refining crude vegetable, animal and marine oils consisting of neutral glyceride esters of fatty acid containing fatty acid impurities which comprise refining said crude oil at a temperature above the melting point of said crude oil by admixing with said crude oil an aqueous solution of an alkali thereby forming an oil phase and an aqueous soap phase, and separating the aqueous soa-p phase from said oil phase, the improvement which comprises admixing with said crude oil and said aqueous alkali, a salt of cumene sulfonic acid, the concentration of said salt of cumene sulfonic acid being at least 25% by weight based on the total amount of water present.

10. The process of claim 9 wherein said salt is an alkali metal salt.

References Cited UNITED STATES PATENTS 3,065,249 11/1962 Repapis 260-42'5 ALEX MAZEL, Primary Examiner.

A. M. T. TIGHE, Assistant Examiner.