EP0058712A1

EP0058712A1 - A process in the purification of crude or partially purified vegetable, animal and marine triglyceride oils

Info

Publication number: EP0058712A1
Application number: EP19810902490
Authority: EP
Inventors: Aage Holm Kroman
Original assignee: DANSK SOJAKAGEGABRIK ApS
Current assignee: DANSK SOJAKAGEGABRIK ApS
Priority date: 1980-08-25
Filing date: 1981-08-18
Publication date: 1982-09-01
Also published as: DK364580A; WO1982000657A1

Abstract

Purification d'huiles de triglycerides deshydratees brutes ou partiellement purifiees, en les traitant avec une quantite de Na3PO4, 12H2O solide ou une solution aqueuse hautement concentree de celui-ci, tel que la concentration dans l'eau de ce sel, comprenant l'eau residuelle libre pouvant se trouver dans l'huile, soit au moins egale a 40%. A cause de l'insolubilite du phosphate le traitement doit avoir lieu a au moins 60 et de preference a 80-85 C, et afin d'assurer un contact rapide avec les agents de contamination une homogeneisation est executee de preference pendant ou apres l'adjonction. Par ce traitement les "lecithines", les lipoides residuels et specialement un lipide mucilagineux contenu dans l'huile, ainsi que la partie principale des traces metalliques de pro-oxydation presente, notamment du Fe et du Cu, sont liees. Le traitement permet specialement l'utilisation d'huiles vegetales peu couteuses, par exemple de l'huile de soya, pour la preparation d'huile comestible et de margarine ainsi qu'une utilisation technique plus raffinee, grace a une amelioration du gout et de la qualite de conservation.Purification of crude or partially purified dehydrated triglyceride oils, treating them with an amount of solid Na3PO4, 12H2O or a highly concentrated aqueous solution thereof, such as the concentration in water of this salt, including water free residual which can be found in oil, at least equal to 40%. Because of the insolubility of phosphate the treatment must take place at least 60 and preferably at 80-85 C, and in order to ensure rapid contact with the agents of contamination a homogenization is carried out preferably during or after the addition. By this treatment the "lecithins", the residual lipids and especially a mucilaginous lipid contained in the oil, as well as the main part of the metallic traces of pro-oxidation present, in particular of Fe and Cu, are linked. The treatment allows especially the use of inexpensive vegetable oils, for example soybean oil, for the preparation of edible oil and margarine as well as a more refined technical use, thanks to an improvement in taste and the quality of conservation.

Description

A process in the Purification of Crude or Partially Purified Vegetable, Animal and Marine Triglyceride Oils.

Technical Field

The present invention relates to a process in the purification of crude or partially purified vegetable, animal and marine triglyceride oils by treatment with tri- sodium orthophosphate, optionally as an aqueous solution. The crude oil may be obtained from the primary source by pressing and/or extraction or in any other manner. When using the process for the treatment of crude vegetable oils, particularly crude soybean oil, its use will normally be preceded by a removal of the so-called lecithin fraction by treatment with water.

Background Art All triglyceride oils, both vegetable, animal and marine ones, contain at the crude oil stage, whether the crude oil has been obtained by pressing or extraction or other known manner, besides triglycerides and varying amounts of free fatty acids as well as partial (mono- and di-) glycerol esters also accompanying substances known under the common denomination lipoids; they are sometimes called "the lecithin fraction". When using the oils as animal feed or for cruder technical uses these accompanying substances or contaminations may remain entirely or partly in the oil without causing big damages, but if it is to be used for finer technical purposes or for edibles, especially for preparing margarine grades for the North European, North American or Australian markets or for preparing other refined fat products such as monoglycerides and high grade fatty acids, the said fractions must be entirely or partly removed from the oil because, i.a., they may cause discoloration and disagreeable taste in the ultimate product. The said fractions are a complex mixture and part of of its components has a complicated chemical structure. As a non-exhausting mention of the components of the mixture should be mentioned on one hand phospholipoids, which may be subdivided into phoslipids (phosphatids or lecithin in the narrow sense), acetal phosphatids (plasmologens) and inositol phosphatid; and on the other hand sphingolipoids, which are subdivided into phosphosphingosides (sphingomyelines) and glycolipoids. The latter again may be subdivided into hexose sphingosides which contain glycosidebound glucose and/or galactose; and gangliosides which contain glycoside-bound hexoses, hexosamines or similar "building stones".

Especially vegetable oils, be it pressed or extracted, contain rather big amounts of this lipoid fraction, soybean oil, for instance, after evaporation of extraction agents about 2.5%. It is conventional to separate part of this lipoid material by treatment of the oil with water, but nevertheless there remains not quite small residues which prevent a satisfactory high oil quality for the finer and economically most profitable uses such as in edible oils and margarine. The residues may give after-taste and discoloration of the oils, which for edibles must be pale yellow to colourless. Since, moreover, the residues partly possess both a hydrophobic and a hydrophilic moiety in their molecule, they may give rise to the formation of emulsifiers which prevent or render it difficult to keep the oil limpid, for instance in a subsequent, quite usual alkali treatment of the oil. The emulsions like the lipoid residues in themselves may give trouble when washing with water and in filtrations or centrifugations, and the lipoid residues may also give deposition of carbon in deodorization and destination apparatus and impaired keeping qualities and colour stability in the final product.

A known method for the removal or deactivation of lipoid residues or lecithin residues is a treatment with phosphoric acid ( orthophosphoric acid), usually in a concentration of 86% and with an amount of 0.1-0.3%, calculated on the weight of the crude oil, under vacuum at 70-90°C. Immediately after this the oil as a rule is subjected to a treatment with alkali and/or bleaching earth.

In this treatment with phosphoric acid it has been found to be a drawback, however, that a small part of the acid binds itself very firmly to the oil so that only a very strong subsequent treatment is capable of removing these residues. Moreover, the phosphoric acid has a tendency to form strong and stable emulsifiers with the lipoids, which also impedes the separation. It must be mentioned that part of the lipoid moiety of crude soybean oil and many other vegetable oils, and probably also animal and marine oils, is a mucilaginous lipid belonging to the above-mentioned hexose sphingosides . It consists of a lipid moiety (aglycone) and a mucilage moiety and is saponified in common refining processes while separating the two moieties. The lipid moiety, the nature of which is not really known, follows the oil phase whereas the mucilage moiety is hydrophilic and may cause some trouble of the aforementioned kinds. During the thorough and prolonged steam treatment of the crude oil , which was used in slightly earlier times for the removal of the extraction agent or carried out as a step in the refining process, a separation into the lipid moiety and the mucilaginous moiety took place. These long-lasting processes nowadays are seldom used as they are difficult to fit into a continious process sequence. The mucilaginous residues are not removed by the known treatment with phosphoric acid, at least not in a sufficient extent.

From US patent specification No. 2,115,668 there is known a process for the refining of soybean oil by admixture with a saturated aqueous solution of trisodium phosphate in an amount approximately 50% in excess of the amount necessary to neutralize the free fatty acids present in the oil, and subsequent heating of the mixture to 15-21°C, gradually increasing to 43-60°C. Hereby a selective saponification of the free fatty acids to sodium soap takes place. and at the same time a conversion of the trisodium phosphate to disodium phosphate, which possibly reacts further with free fatty acid while being converted to monosodium phosphate; triglycerides are not attacked in contradistinction to what is the case in the treatment with strong alkali. According to the patent specification it may also happen that some of the colouring matter in the oil is brought into a form as to be readily separated off, but there is not obtained a profound liberation from the "lecithin fraction" or the lipoid fraction, and specifically the afore-mentioned mucilaginous substances remain in the oil. The reason is that the concentration of the trisodium orthophosphate is too low in a saturated aqueous solution at such low temperatures, to wit only about 10%, see Kirk- Othmer, Encyclopedia of Chemical Technology, second edition, Volume 15, pages 236-238. British patent specification No. 661,703 describes the refining of triglyceride oils with alkali in the presence of inorganic phosphorus compounds in order to decrease the refining loss. Predominantly there is used pyrophosphates but Example 6 describes the treatment with a solution, saturated at room temperature, of trisodium phosphate. The treatment of wax and cocoa butter in a similar manner is known from US patent specification No. 1,644,280 and German patent specification No. 565,079, respectively. There is mainly obtained a selective saponification of free fatty acids and removal of some impurities, but not to any appreciable degree of the said mucilaginous substances.

Disclosure of Invention

It is the purpose of the invention to provide a process in which a high degree of purification may be obtained and in which especially the mucilaginous substances mentioned are very extensively removed. According to the invention this is obtained thereby that the oil in anhydrous or approximately anhydrous state at a temperature of at least 60°C is treated with solid or a so highly concentrated aqueous solution of trisodium orthophosphate dodekahydrate (Na₃-PO4,12H₂O; hereinafter also called trisodium phosphate) that the concentration in the oil relative the amount of water, including free water possibly present in the oil, is at least 40%, after which the substances bound by the phosphoric salt are separated off together with the salt itself. Normally there is employed a highly concentrated aqueous solution.

It has been found that the high concentration of trisodium phosphate employed according to the invention, in contradistinction to the far lower concentration empolyed according to US patent specification No. 2,115,668 or GB patent No. 661,703, leads to the desired extensive purification and especially removal of the mucilaginous substances; as the solubility of the salt in water as well as its dispersibility in the oil increases with temperature, the temperature of at least 60°C stated must be employed. According to the invention the temperature is conveniently kept at at least 70°C and preferably 80-85°C.

Detailed Description of the Invention

The amount of trisodium orthophosphate employed depends upon the amount of impurities in the oil to be removed by the phosphate and therefore cannot be stated generally. For soybean oil which has been well de-lecithinated by treatment with water the amount is normally 0.1-0.3% of the weight of the oil, and this order of magnitude will also be typical for other de-lecithinated vegetable oils and for a number of animal and marine oils although both bigger and smaller amounts may be possibilities , bigger amounts notably in the case of bad or no preceding removal of lecithin. It is important to employ the trisodium orthophosphate under such conditions that the concentration compared to all of the water present is at least 40%. in practice a 60% solution will frequently be employed and the oil will have been dried (dehydrated) prior to the addition of the phosphate. When using the process for the purification of extracted or pressed vegetable oils after partial separation of the socalled lecithin fraction by treatment with water and subsequent dehydration, particularly in the purification of soybean oil de-lecithinated with water, it is therefore in accordance with the invention convenient, after drying of the oil to a water-content of at most 0.05% by weight, to treat it with about 0.2% by weight of 60% solution of Na₃PO₄, 12H₂O.

As trisodium orthophosphate there may be used technical or more highly purified grades, if desired also grades which in known manner contain 1/7 or 1/4 mol of NaOH together with 12 mols of water of solvation. However, the phosphate should not contain metals, especially not iron or copper, as they may act as oxidation catalysts, socalled pro-oxidants. Liquid yellow edible oils, for instance soybean oil, rape oil, groundnut oil, corn oil, sunflower oil and olive oil contain C₁₈ fatty acids having one or more double bonds (i.a. oleic, linoleic and linolenic acids with one, two, and three, respectively). Oxygen may attack the double bonds, notably when they are conjugated, and form peroxides which are cleaved to aldehydes and ketones. It seems as if the treatment with trisodium phosphate according to the invention to some degree counteracts the oxidation, presumably by binding pro-oxidants, possibly other pro- oxidants than the said traces of metals. However, this effect will be destroyed if the trisodium phosphate itself contains metal traces and in accordance with the invention it may therefore be convenient that the trisodium phosphate and/or the oil prior to, simultaneously with or immediately after mixing is treated with a chelating agent. Particularly when treating soybean oil this is valuable; soybean oil is inexpensive but contains large amounts of linolenic acid and therefore is rather much in danger of going rancid; in the manner stared there may be obtained an oil grade having satisfactory taste and keeping qualities for use as edible oil and in margarine. As chelating agent there may according to the invention with particular advantage be used ethylenediamine- tetraacetic acid and/or citric acid, which are readily available and comparatively inexpensive. Generally, those chelating agents may be used which are mentioned in Kirk- Othmer, 1.cit., Volume 6, pages 6-8 (1965), besides those mentioned for instance nitrilotriacetic acid, tartaric acid and gluconic acid. In general, the addition of a separate chelating agent will not be needed. The reason for this may be that polyphosphate ions, for instance the tripolyphosphate ion as is known act as a chelating agent and it is conceivable that a part of the anion of the trisodium orthophosphate at the treatment according to the invention condenses while forming polyphosphate ions.

If a chelating agent is employed, the amount is quite small but depends upon the amount of pro-oxydants present, particularly metal traces; the order of magnitude of the amount of chelating agent may be until 0.1% of the amount of oil but will normally be considerably less or not come into use at all.

The very treatment of the oil with the trisodium phosphate, and, if at all, also with the chelating agent in principle takes place by a simple mixing. However, the commencement of the effect may take too long time if there are not taken special precautions against it, and it is therefore convenient according to the invention simultaneously with or immediately after the addition of the trisodium orthophosphate solution to the oil at the treatment temperature to carry out an intensive mixing process, i.e. homogenization of the mixture. The duration of the treatment hereby will be limited to 5-15 minutes and after the mixing it is advantageous to lead the mixture to a holding vessel or column wherein it can be kept for, e.g., 15 minutes in order to be certain of the reaction going to completion.

When the lipoid contaminations and especially the muclaginous substances, and possibly pro-oxidants such as traces of metals and metal compounds, have been bound by the treatment with the trisodium orthophosphate, the salt and the components bound thereby must be removed from the oil. It is most expedient to precipitate these components by treatment with a small amount of water; if about 0.2% of trisodium phosphate has been employed an amount of water of about 1%, calculated on the amount of oil, as a rule will be suitable. The water is admixed into the oil under moderate conditions such as the treatment temperature (preferably 80-85°C) and weak stirring. Conveniently one may after the addition of the water condition the mixture by allowing it to complete the reaction in, for instance, 15 minutes.

The separation of the material bound by the phosphate may hereafter take place by decanting but this will normally be too slow a process and one may speed it up by the addition of a suitably heavy flocculation or precipitation agent, according to the invention for instance bleaching earth or a similar kind of clay. The amount of precipitation or flocculation agent will typically be from 0.1 to 0.3% of the weight of the oil.

Finally one may separate the material, bound in any conventional manner, e.g. by filtration or according to the invention particularly conveniently by centrifugation. The treatment according to the invention hereafter has been concluded and the oil may be used or conducted further to conventional treatment steps such as bleaching, refining, hardening or splitting to fatty acids and glycerol.

Brief Description of Drawing In the drawing

Fig. 1 shows the ultraviolet absorption spectrum of a crude, untreated soybean oil.

Fig. 2 the ultraviolet absorption spectrum of the same oil, treated with phosphoric acid as explained in Experiment 1 below, and

Fig. 3 the ultraviolet absorption spectrum of the same oil, treated with trisodium orthophosphate in accordance with the invention and as explained more fully in said Experiment 1.

Best Mode for Carrying Out the Invention

The best embodiment of the process of the invention known at the present moment consists in heating to 80-85°C a triglyceride oil, e.g. soybean oil, which has been de- lecithinated with water and thereafter dried to a water content of about 0.04% by weight, after which 0.2% by weight of a 60% aqueous solution of trisodium orthophosphate dodekahydrate free of heavy metals are added. The mixture is homogenized and left standing to condition it for 10-15 minutes at the same temperature. Thereafter 1% by weight of water is added at the same temperature and after renewed homogenization and conditioning for 5-10 minutes, still at 80-85°C, 0.15-0.2% by weight of bleaching earth are added. Again an intensive mixing and a few minutes conditioning are carried out whereupon the sludge separated is removed by centrifugation at 80-85°C. Thereafter the oil thus purified is cooled to ambient temperature and is ready for use.

The effect of the process of the invention will be illustrated further in the following by some experiments.

Experiment 1

1000 g of crude soybean oil were heated to 75° and treated with 3 ml of 86% aqueous orthophosphoric acid under rapid propeller agitation for 15 minutes. Thereafter 30 ml of water were added and propeller agitated for 5 minutes. After this the mixture was stood, decanted and filtered by the aid of a paper flocculation agent ("Solka Floe", a paper powder). After the treatment the content in the oil of free fatty acids (% f.f.a.) and its ultraviolet spectrum were determined. Moreover, the socalled splitting value was determined. It was determined by boiling the oil with 1% of sulfuric acid for 18 hours, % f.f.a. being determined before and after the boiling. The splitting number is determined as % f.f.a., i.e. the difference between the contents of free fatty acids (in per cent) before and after the boiling. For comparison 1000 g of the same oil were heated to 75ºC and treated with 5 ml of 40% solution, having the same temperature, of Na₃PO₄, 12H₂O under stirring at 20,000 p.p.m. for 2 minutes. Thereupon there was continued with propeller agitation and addition of 30 ml of water, and thereafter the same treatment and analyses as in the case of the sample treated with phosphoric acid.

The results appear in Table 1 below and of the aforementioned drawing.

Furthermore, the precipitation at standing of the oils treated with phosphoric acid and trisodium orthophosphate, respectively, is assessed visually. In the firstmentioned case the sedimentation was slow and the amount of sediment high, in the lastmentioned the sedimentation rapid and amount of sediment small.

The analyses, especially the splitting values, show that the substances formed by the treatment with phosphoric acid have a high emulsifying effect and yield a turbid and muddy oil, which drawbacks are avoided by treatment with trisodium phosphate.

Experiment 2

In this experiment a soybean oil was treated with orthophosphoric acid (a) and trisodium orthophosphate dodekahydrate (b) in the same manner as in Experiment 1, yet at 80-85°C instead of 75°C. For comparison furthermore two samples (c) were treated with 20% (c-1) and 30% (c-2) solution of sodium tetrapyrophosphate (Na₄P₂0₇) .

After the experiments % f.f.a., splitting value, the content of lecithin in %, the content of Fe in p.p.m. and the ultraviolet data were determined on all of the samples. To improve the results of the treatment with phosphoric acid samples from the treatment with phosphoric acid were washed once or twice with 3% of water, decanted and filtered with "Solka Floe" paper powder. Since the results of this did not differ substantially from the results of the treatment with phosphoric acid, the results have been omitted in Table 2 below, which apart from this does show the analytical results . Sedimentation tests were also carried out; the sample treated with phosphoric acid exhibited a large amount of sediment and slow sedimention, both with and without washing water, whereas treatment both with orthophosphate and pyrophosphate resulted in rapid sedimentation and a small amount of sediment.

These data show the same as Experiment 1 with respect to the effect of phosphoric acid and trisodium orthophosphate on the content of free fatty acids and the splitting value as well as the ultraviolet data, and also that the orthophosphate is far more efficient than phosphoric acid in removing lecithin and iron. They also show that sodium tetrapyrophosphate has some effect on the splitting value and on the ultraviolet data, i.e. yields a less turbid oil than the treatment with phosphoric acid, but that it only is able in a low degree to remove iron and only partly the lecithin fraction, whereas trisodium orthophosphate is far superior in these respects.

The process of the invention will be illustrated in the following by some Examples.

Example 1

Two different crude palm oils (I and II) were treated at 80-85°C with firstly 0.2% and secondly 0.3% trisodium orthophosphate dodekahydrate in 60% solution. After homogenisation, conditioning, addition of about 1% of water, renewed mixing and conditioning, addition of about 0.2% bleaching earth, mixing and conditioning, all at 80-85°C, a sludge containing mucilaginous substances and formed by the phosphate treatment was centrifuged off. The results appear from Table 3 below.

Example 2

Crude coconut oil was treated in the same manner as stated in Example 1 with 0.15% trisodium orthophosphate dodekahydrate. Prior to the treatment the oil contained 6.4% free fatty acids and 1.2 p.p.m. Fe, after the treatment 6.2% free fatty acids and 0.5 p.p.m. Fe. Example 3

Technical lard, meant for splitting, was treated as described in Example 1 with 0.5% of Na₃P0₄, 12H₂O. Prior to the treatment the fat contained 184 p.p.m. Fe, after the treatment 10 p.p.m. Fe.

Example 4

Crude soybean oil was treated at 80-85°C with 60% solution of trisodium phosphate in a total amount of 0.2% Na₃P0₄,12H₂O. The result after further treatment as described in Example 1 appears from Table 4 below.

The socalled foot test consists in treatment of the sample with a solution of zinc chloride consisting of 300 g ZnCl₂ dissolved in 10 ml concentrated sulfuric acid and 90 ml water; 10 ml of the solution are added to 50 ml of oil sample. After shaking for one minute (which causes a colour change) 50 ml of acetone are added and there is shaked anew. The mucilaginous substance is gathered in the transition between the acetone phase and the oil phase and the volume of this border zone is measured.

Industrial Applicability

The process of the invention may be utilized industrially in the refining of vegetable, animal and marine triglyceride oils for a higher degree of purification than normally, especially for the removal of heavy metal residues (Fe and Cu) and the aforementioned mucilaginous lipid fraction whereby comparatively inexpensive oils of a grade unfit for edible purposes, manufacture of margarine or finer technical use may be improved and thereby becomes suitable for such uses at low costs.

Claims

Patent Claims

1. A process in the purification of crude or partially purified vegetable, animal and marine triglyceride oils by treatment with trisodium orthophosphate, c h a r a c t e r i z e d in treating the oil in anhydrous or approximately anhydrous state at a temperature of at least 60ºC with so large an amount of trisodium orthophosphate dodekahydrate (Na₃PO₄, 12H₂O) or a so highly concentrated aqueous solution thereof, that the concentration in the oil relative the amount of water, including free water possibly present in the oil, is at least 40%, after which the substances bound by the phosphoric salt are separated off.

2. A process according to claim 1, c h a r a c t e ri z e d in maintaining the temperature during the treatment at at least 70°C and preferably 80-85°C.

3. A process according to claim 1 or claim 2, c h a r a c t e r i z e d in carrying out an intensive mixing process at the treatment temperature simultaneously with or immidiately after the addition of the trisodium orthophosphate to the oil.

4. A process according to anyone of the preceding claims, c h a r a c t e r i z e d in the separating the substances bound by trisodium orthophosphate, particularly mucilages and mucilaginous substances, from the oil by treatment in arbitrary order or simultaneously with a small amount of water, preferably about 1% of the weight of the oil, and a heavy flocculating or precipitating agent.

5. A process according to claim 4, c h a r a c t e ri z e d in using bleaching earth or a similar kind of clay as the flocculating or precipitating agent.

6. A process according to anyone of the preceding claims for use in the purification of extracted or pressed vegetable oils after the separation of possible organic solvents and partial separation of the socalled lecithin fraction by treatment with water and subsequent dehydration, notably in the purification of soybean oil de-lecithinated with water, c h a r a c t e r i z e d in treating the oil, after drying to a water content of at most 0.05% by weight, with about 0.2% by weight of a 60% solution of Na₃PO₄,12H₂O.

7. A process according to anyone of the preceding claims, notably for use in the purification of soybean oil, c h a r a c t e r i z e d in treating the trisodium phosphate and/or the oil with a chelating agent prior to, simultaneously with or immidiately after mixing them.

8. A process according to claim 8, c h a r a c t e ri z e d in using ethylenediaminetetraacetic acid and/or citric acid as chelatin agent.

9. A process as claimed in anyone of the preceding claims, c h a r a c t e r i z e d in removing the trisodium phosphate with the substances bound thereby by centrifugation or electrofiltration.