EP0473985B1 - Process for degumming - Google Patents

Description

The invention relates to a method for reducing the content of mucilages which can no longer be hydrated with water and at the same time the wax content of vegetable oils.

When raw vegetable oils are obtained, phosphorus-containing compounds, namely phosphorus glycerides and phosphosphyngolipids - collective names of mucilaginous substances or phosphatides - emerge together with oil from the cells of the raw materials and get into the oil.

These compounds play a vital role in the plants, primarily in the formation of lipoprotein cell membranes, photosynthesis, fatty acid metabolism and other processes taking place in the cells.

Depending on the properties of the vegetable raw materials and the technology used to extract the crude oil, the amount of it entering the crude oil fluctuates between 3.0 and 0.5%, based on the oil weight.

Despite their relatively small amount, their composition is complicated. They consist of a variety of compounds, with regard to the main components alone, of at least 10 to 12 compounds, which is not surprising since, as mentioned, they have different functions in the cells and must therefore be diverse.

The majority of these compounds have the characteristic peculiarity that they can be hydrated by water. They form lyotropic phases that swell and can be separated from the oil in gel form.

This precipitating substance causes turbidity and precipitation. It interferes with the further process steps of oil refining and its removal is therefore necessary.

These so-called hydratable mucilages are removed by treatment with water or steam, swelling or hydration with subsequent separation, usually by centrifugation.

This process step is called aqueous degumming.

Among the mucilages, however, there are also compounds which cannot be hydrated under the influence of the water molecules and therefore remain in the oil even after aqueous degumming.

The amount of these so-called non-hydratable mucilages - after the corresponding aqueous degumming - is approx. 0.15 to 0.20%, i.e. 5 to 30% of the mucilages originally present, and their removal requires special methods.

However, even this small amount must be reduced to as little as 0.01% as possible in the course of the further refining of the oils up to the final process step of deodorization, in order to avoid problems in the deodorizing apparatus and with the raffinate quality. Because the mucilages are not thermal sufficiently resistant and therefore polymerize and crack at the usual deodorization temperatures of over 200 ° C. In addition, the degradation and decomposition products of the phosphatides remaining in the raffinate cause a negative change in taste of the finished refined oil.

In classic chemical refining, in which the free fatty acids are neutralized with alkalis and the soaps formed are separated and washed out, the mucilages are simultaneously reduced to approx. 0.015 to 0.03%. The necessary further reduction then takes place in the bleaching before the final deodorization.

With the increasing importance of physical refining, which is increasingly being used and practiced for more and more oils, degumming is followed only by bleaching and finally by deacidification and deodorization by distillation. The necessary reduction in mucilage after degumming can therefore only be achieved with an increased and therefore costly use of bleaching earth. Therefore, the reduction of mucilage is of particular importance in the first step.

Numerous researchers have worked to uncover the structure of this non-hydratable compound (K. Nielsen: dissertation Copenhagen, 1956; B. Braae, U. Brimberg and N. Nyman: J.Am.Oil Chem. Soc., 34, 1957, 293; A. Hvolby: Femte Nordiska Fett Symposiet, Tyringe, 1969, 338-351; CR Scholfield, HJ Dutton et al: J.Am. Oil Chem. Soc., 25, 1948, 368-372, etc.).

The most important findings are: In contrast to the hydratable mucilages, the phosphatides, their Molecules containing a strongly polar portion (choline, ethanolamine, serine, inositol) lack the polar parts of the non-hydratable mucilages, and they mainly consist of the Ca and Mg salts of phosphatidic acid and lysophosphatidic acid. However, it can also be assumed that other cations (Fe, Cu, Al etc.) also participate in the salt formation.

Knowing their structure, several methods have already been developed for their removal. A large part of the compounds that cannot be hydrated with water can also be eliminated using these processes.

One such is the process described in German Offenlegungsschrift 26 09 705, according to which the oil is treated with acid or acid anhydride and subsequently with water.

This process corresponds to US Pat. No. 4,049,686, in which the oil is also treated with acid and then 0.5 to 3% water is added to the oleic acid mixture to wash out the acid and the phosphatides decomposed by the acid.

As also stated in the more recent European publication 0 195 991, these processes do not remove the metallic impurities present in the oil satisfactorily, and when using such processes the removal of the non-hydratable phosphatides also encounters difficulties, even after further experience.

The treatment can be carried out more successfully from both of the above points of view if, after the acid treatment, a lye-like substance - a base - is added to the mixture, so that from the Acid excess fat-soluble salts are formed.

The action of the base also enables the phosphatidic acid or lysophosphatidic acid freed from its cations (calcium, magnesium, iron, etc.) to dissociate, thereby promoting their hydration and excretion from the oil.

Such a process is described in British Patent 1,565,569, European Publication 0 195 991, US Patent 4,698,185 and FR-A-2442882.

However, there are two aspects which the previous procedures do not take sufficiently into account.

The critical aspect of treatment is the question of protection.

The general opinion already today is that the substances used as food - including the oils - should be subjected to as little treatment as possible by chemicals.

Therefore, it should be advisable to look for an optimal technology for the removal of the phosphatides that cannot be hydrated with water, which promises success on the one hand in achieving the goals, but on the other hand requires the least possible exposure to chemicals and heat.

These aspects were not taken into account in the previously known proposals.

The gentle treatment is also from the point of view of economy, the second essential aspect (cost of chemicals and energy) advantageous.

In order to ensure that the process technology is also economical, a simple solution was also sought for the practical implementation, which means that the machines and apparatus required to achieve an excellent result are as low as possible.

Based on previous calculations and experience, an average of 0.20% remains, i.e. 2,000 ppm of non-hydratable phosphatides in the oil after the corresponding aqueous degumming. If this amount of substance consists entirely of the Mg or Ca salts of phosphatidic acid, then this above-mentioned amount contains about 110 ppm calcium - all cations counted as Ca - for the decomposition of which stoichiometric 190 ppm H₃PO₄ or 380 ppm citric acid are required. Based on oil, this is 0.02% and 0.04%, respectively.

According to further investigations, the calcium, magnesium and iron content of the oils hydrated with water is lower than the value mentioned above, so that only a very small amount of acid of approx. 0.04 to 0.08% on oil is required to achieve the corresponding effect calculated, is sufficient.

Surprisingly, the tests carried out with these values led to a fairly good result, even if this small amount of acid was used in dilute - 10 to 15% solution, the temperature was not raised above 70 ° C and the aqueous acid solution was not powerful with the Oil was mixed.

As a result, the use of degumming processes, which are also used in the acid and alkali, was mentioned excessive concentration (concentrated or 50% acid) and a high temperature (95 ° C), as described in British Patent 1,565,569, and the dosage of excessive amounts of acid (more than 0.08%, possibly even 1.2%) in a relatively concentrated form (20 to 50% concentration) and with very vigorous stirring, as described in European publication 0 195 991, can be avoided.

This gentle process requires a somewhat longer time (10 to 15 minutes) than the stirring time according to the known processes. However, since the systems are closed and the temperature is low (approx. 70 ° C), the effect is particularly gentle, which is also confirmed by the fact that the oil's key oxidation figures, e.g. the peroxide value does not deteriorate, or deteriorates only very slightly during the process.

After the treatment with acid, a dilute (1 to 2%) lye solution is also added to the oil in a gentle manner, the oil being cooled to 20 to 40 ° C. before the addition.

As an effect of this treatment, phosphatidic acid and lysophosphatidic acid dissociate. They are hydrated and can be removed from the oil by separation.

The possibility of removal is significantly improved by the low temperature, since the mucilage is thereby separated from the oil in gel form.

At the same time, the low temperature ensures that this phase of the treatment is also gentle. The Oxidation characteristics of the oil do not change unfavorably.

Another advantage of the low temperature is that in the case of oils containing wax and oils which contain triglycerides with a higher melting point, their excretion is also promoted.

Based on practical experience, the elimination and possible crystallization of the higher melting triglycerides and waxes is substantially prevented by the phosphatide compounds present in the oil. Therefore, after the non-hydratable phosphatides have been excreted by swelling, the previously mentioned triglycerides and waxes are surprisingly eliminated from the oil in a short time.

The amount of lye is measured so that it is sufficient to neutralize the acid previously added to the oil.

With such oils - e.g. Sunflower oil - for which a more powerful dewaxing is necessary, the amount of wax excretion can be increased significantly, in addition to a temperature reduction of the oil to 8 to 10 ° C before the addition of the lye solution.

Since experience has shown that the possibility of removing both the phosphatide substances and the wax substances is increased by the absorption effect of soap micelles, the process can be carried out depending on the character of the oil to be degummed in such a way that the diluted lye contains a small part of the oil always present neutralizes free fatty acids, so a small amount of soap is created.

As mentioned, the gentle conditions, including the low temperature, so that the oxidative characteristics of the oil do not increase during the treatment. This fact also promotes the crystallization of the waxes, since it is known that the oxidized fatty acids have crystallization-inhibiting properties.

A so-called "resting time" is required for the elimination of the triglycerides with a higher melting point or the wax substances, but this also promotes the elimination of the phosphatides. That is why oil and lye are left to their own devices for 2 to 3 hours after the lye has been added with very slow stirring or slow flow.

Then, as a third step, the phases are separated by heating the mixture of oil and lye solution in a flash, immediately separating it and washing it with a little condensed water.

The separated mucilages and waxes are also neutral in terms of their pH and can be easily added to the extraction meal or other feed.

By using this method, the amount of mucilages that can no longer be hydrated with water is significantly reduced, but due to the gentle treatment the oxidation characteristics of the oil do not significantly deteriorate, and at the same time the amount of triglycerides with a higher melting point and decreases the wax content of oils so that subsequent dewaxing is not necessary or this process step can be carried out more easily. If the goal is to significantly reduce the wax content in the oil, a very small amount of soap can be made in the oil by using a very small amount of excess liquor to take advantage of the micellar adsorptive effect.

As can be seen from the examples, an almost complete degumming of the oil used is achieved by using the method described above. Therefore, very little bleaching earth is required in the subsequent bleaching stage, which means significant cost savings and thus increased economy.

example 1

Sunflower oil degummed with water was used as the basic material, which has the following characteristic properties: Acid number 1.5 Peroxide number 8.0 Anisidine number 0.9 Phosphorus content 75 ppm Iron content 1.00 ppm Copper content 0.04 ppm UV absorption (232 nm) 3.1 Wax content 0.06%

In a vegetable oil plant, the oil described above was continuously heated to 50 ° C and the 10% citric acid solution was continuously added in a tank provided with a stirrer. Based on solid citric acid, 700 g of citric acid was added to the oil to 1000 kg each. The treated oil was held in a stirring tank for 15 minutes while stirring slowly, then cooled to 30 ° C.

The mixture was then stirred in a tank with a quantity of 4% NaOH solution, which corresponds stoichiometrically to the acid number increase caused by the citric acid, for two hours, then heated to 80 ° C. in a flash and separated with a separator.

The oil phase obtained on separation was washed on another separator with 10% soft water.

The washed oil was dried or placed for further refining or in an apparatus suitable for the production of edible oil.

The characteristic properties of the ultrafine degummed oil thus obtained are as follows: Acid number 1.5 Peroxide number 8.0 Anisidine number 1.0 Phosphorus content 2.5 ppm Iron content 0.1 ppm Copper content 0.01 ppm UV absorption (232 nm) 3.2 Wax content 0.04%

After treatment with 0.1% bleaching earth, the phosphorus content of the vegetable oil can be reduced to a value below 1 ppm and its color complies with the regulations.

Example 2

Sunflower oil degummed with water was used with the following characteristic properties: Acid number 1.2 Peroxide number 7.5 Anisidine number 0.7 Phosphorus content 80 ppm Iron content 0.9 ppm Copper content 0.05 ppm UV absorption (232 nm) 3.5 Wax content 0.05%

In a continuous operation, vegetable oil was stirred at 40 ° C with a 15% citric acid solution. 400 g of solid citric acid in a 15% solution were added to 1000 kg of the oil. After slowly stirring for 15 minutes, the fabric was cooled to 25 ° C. The oil was then slowly stirred in a tank with a 5% strength NaOH solution of 110%, which corresponds stoichiometrically to the acid number increase caused by the citric acid, for two hours, then the material heated to 80 ° C. was separated in a flash onto a separator.

The oil phase obtained during the separation was washed on a new separator with 10% soft water. The washed oil was dried or sent for further refining.

The main properties of the degummed oil obtained are as follows: Acid number 1.0 Peroxide number 6.0 Anisidine number 1.0 Phosphorus content 4.5 ppm Iron content 0.08 ppm Copper content 0.01 ppm UV absorption (at 232nm) 3.5 Wax content 0.03%

Example 3

Pressed sunflower oil was used as a raw material with the following characteristic properties: Acid number 1.3 Peroxide number 6.0 Anisidine number 0.1 Phosphorus content 150 ppm Iron content 5.0 ppm Copper content 0.05 ppm UV absorption (at 232nm) 3.0 Wax content 0.07 g

In a 150 l tank equipped with a stirrer, 1000 kg of oil were gradually heated to 50 ° C, then first with soft water of 0.2% and then with a phosphoric acid solution of 10% (for 1000 kg of oil 700 g of phosphoric acid added) and slowly stirred for a further 20 minutes.

With continued stirring, a 5% NaOH solution was added to the fabric to completely neutralize the given phosphoric acid. At the same time, the mixture was cooled to 30 ° C.

After stirring for a further two hours, the material was heated to 80 ° C. in a flash and placed on a separator.

After separation, the fabric was washed twice on two successive separators with 10% water. The washed oil was dried or sent for further refining.

Characteristic properties of the end product: Acid number 1.3 Peroxide number 7.1 Anisidine number 0.2 Phosphorus content 7.0 ppm Copper content 0.01 ppm Iron content 0.1 ppm UV absorption (at 232nm) 3.0 Wax content 0.07%

Example 4

Rapeseed oil degummed with water was used with the following properties: Acid number 1.5 Peroxide number 8.5 Anisidine number 0.5 Phosphorus content 90 ppm Iron content 0.7 ppm Copper content 0.05 ppm UV absorption (at 232nm) 2.1

1000 kg of the oil described above were gradually heated to 40 ° C. in a 1500 l tank equipped with a stirrer. Then, from a 15% aqueous phosphoric acid solution, 0.05% amount calculated for pure phosphoric acid was added and slowly stirred for 20 minutes. After stirring, the oil was neutralized with 5% NaOH solution in an amount stoichiometrically sufficient with phosphoric acid.

After slowly stirring for one hour, the material was heated to 80 ° C in a flash and placed on a separator. After separation, the fabric was washed twice with 10% soft water.

The washed oil was dried or sent for further refining. Characteristic properties of the end product are: Acid number 1.5 Peroxide number 9.0 Anisidine number 0.5 Phosphorus content 9.0 ppm Iron content 0.5 ppm Copper content 0.01 ppm UV absorption (at 232nm) 3.0

Example 5

Soy oil degummed with water was used with the following properties: Acid number 1.7 Peroxide number 7.1 Anisidine number 0.7 Phosphorus content 100 ppm Iron content 2.0 ppm Copper content 0.05 ppm UV absorption (at 232nm) 3.2

The above oil was heated to 60 ° C in continuous treatment, and 10% citric acid solution was added in a stirrer tank. Based on solid citric acid, 800 g were added to 1000 kg of oil. The fabric was kept in a stirring tank with slow stirring for 15 minutes, then cooled to 30 ° C and then stirred with 4% NaOH solution. An amount was added to the oil from the NaOH solution, which stoichiometrically neutralizes the citric acid. In the tank, the fabric was slowly stirred for two hours, then instantly heated to 80 ° C and separated on a separator.

The oil phase obtained in the separation was washed in another separator with 10% soft water. The washed oil was dried or conveyed for further refining.

Characteristic properties of the end product: Acid number 1.7 Peroxide number 7.8 Anisidine number 0.7 Phosphorus content 6.0 ppm Iron content 0.1 ppm Copper content 0.01 ppm AV absorption (at 232nm) 3.4

Example 6

Sunflower oil degummed with water was used as a starting material with the following characteristic properties: Acid number 1.2 Peroxide number 6.0 Anisidine number 0.9 Phosphorus content 52 ppm Iron content 1.0 ppm Copper content 0.03 ppm UV absorption (at 232nm) 3.0 Wax content 0.06%

The oil was heated to 50 ° C in continuous treatment and 15% citric acid solution was added in a stirrer tank. Based on 1000 kg, 300 g of citric acid were added to the oil. The treated fabric became slow for 15 minutes stirred, then cooled to 20 ° C. The substance was then stirred with an amount of 4% NaOH solution corresponding to the 100% stoichiometric increase in acid number caused by the citric acid for a further two hours, heated to 80 ° C. in a flash and separated in a separator.

Then the separated oil phase was washed with soft water.

The washed oil was dried or sent for further refining.

Characteristic properties of the end product are: Acid number 1.2 Peroxide number 6.0 Anisidine number 0.9 Phosphorus content 3.0 ppm Iron content 0.1 ppm Copper content 0.01 ppm UV absorption (at 232nm) 3.0 Wax content 0.02%

Claims (4)

1. Process for the reduction of glutinous substances no longer hydratable with water and at the same time of the wax contained in vegetable oils, characterised in that

   a) 0.01% to 0.08% of an acid suitable for foodstuffs or an acid anhydride a 5% to 15% solution is added to the oil at a temperature of 20° to 70°C, and the oil and the acid solution are then carefully mixed, the subsequent contact time amounting to more than five minutes while the mixture is slowly stirred,

   b) a 1% to 5% solution of a base is then added to the oil at 10° to 40°C, the quantity of said solution amounting to 40% to 150% of the amount required according to stoichiometric calculation to neutralise the added acid, and a reaction time lasting one to four, preferably two, hours is then adhered to while the mixture is slowly stirred (at 20 to 40 min⁻¹) to extensively flocculate the non-hydratable phosphatides and possibly to reduce the content of high-melting triglycerides or waxes,

   c) before the separated substances and the water are separated from the oil after quick heating, whereupon the oil may be washed with a small quantity of water, if required.
2. Process according to Claim 1, characterised in that a temperature of 8° to 10°C is used for expedience for the reaction time according to b) for a more vigorous dewaxing.
3. Process according to one of Claims 1 or 2, characterised in that to more vigorously reduce the wax content in the oil by adding a very small additional amount of alkaline solution, very little soap of free fatty acids or oil is formed to utilise the absorption properties of the soap micelles for the dewaxing.
4. Process according to one of Claims 1 to 3, characterised in that the process is applied to a raw oil, i.e. one not degummed with water.