EP0041002B1 - Process for treating vegetable oils to improve their stability in the cold state - Google Patents

Description

The subject of the present invention is a process for treating vegetable oils for improving their cold stability. This process makes it possible to clarify (for example by dewaxing, wintering) oils and in particular edible oils, such as for example, sunflower oil, corn oil, or peanut oil.

It is well known that certain edible oils become cloudy due to the presence of compounds with a high melting point such as waxes, partial glycerides, etc. which crystallize. However, the presence of such compounds, if it does not in any way affect the quality of the oil, markedly alters its appearance, and therefore decreases its appeal to the consumer.

Consequently, it is common to subject these oils, before marketing them, to a clarification operation, the aim of which is to achieve the elimination of the crystallized compounds.

To carry out this clarification operation, two conventional methods are usually used.

According to the first of these methods, the oil is cooled for a few hours to an appropriate temperature, making it possible to obtain crystals which can be separated by filtration. Often used as a filter aid (e.g. filter earth).

According to the second of these methods, after precipitation of the crystals as above, a mixture of this oil is centrifuged with an aqueous solution of wetting agent. In this way, the passage of the crystals in the aqueous solution, which separates from the oil by centrifugation, is favored.

However, these methods are not without many drawbacks.

• - la difficulté d'obtenir des cristaux filtrables nécessite des cycles de refroidissement et de maturation de longue durée,
• - la capacité de production est fonction de la teneur en cristaux, elle peut diminuer d'environ 20 à 30 % lorsque la teneur en cristaux double, ce qui est courant dans la pratique industrielle,
• - ce procédé nécessite, en outre, l'emploi de terres filtrantes coûteuses qui en plus donnent des gâteaux de filtration pouvant contenir jusqu'à 60 % d'huile entraînée d'où des pertes importantes en huile raffinée. Ces gâteaux posent un problème de pollution de l'environnement (danger d'une inflammabilité spontanée à la suite de l'oxydation des graisses contenues et pollution de la nappe phréatique par la matière grasse par entraînement de celle-ci dans les eaux pluviales)..

Indeed, for the first process mentioned:

• - the difficulty of obtaining filterable crystals requires long-term cooling and maturation cycles,
• - the production capacity is a function of the crystal content, it can decrease by around 20 to 30% when the crystal content doubles, which is common in industrial practice,
• - This process requires, in addition, the use of expensive filtering earths which in addition give filter cakes which can contain up to 60% of entrained oil hence significant losses in refined oil. These cakes pose a problem of environmental pollution (danger of spontaneous flammability following the oxidation of the fats contained and pollution of the water table by fatty matter by entrainment of the latter in rainwater). .

Furthermore, the second method mentioned requires the use of a large quantity of wetting agent solution (5 to 10%) and the use of an expensive separation material and requiring high maintenance costs.

The object of the present invention is to overcome these drawbacks by proposing a process making it possible to obtain clear oils even from oils having high levels of constituents with a high melting point (waxes, partial glycerides, etc.). without the use of filter earth or centrifugation.

This process is characterized in that, after cooling the oil to be treated to a temperature chosen so as to allow the crystallization of the compounds to be eliminated, at least part of this oil is subjected to a neutral gas pressure of 4 to 10 bars and then an expansion at atmospheric pressure so as to create fine gas bubbles which are fixed on the crystallized compounds so as to produce a foam with a density lower than that of the oil constituted by a crystal-bubble gas complex which rises to the surface of the container, thus making it possible to obtain at the lower part of the latter, after decantation, a clarified oil having a content of less than 30 ppm of crystals and with a yield greater than 90%.

The performance of such a process essentially depends on the formation of crystals of an appropriate size, a sufficient quantity of fine gas bubbles, in the liquid, and on the adhesion of the bubbles to the solid particles.

According to the invention, it was possible to obtain gas bubbles whose quantity and diameter are such that they promote the quantitative formation of a bubble-crystal complex with a density lower than that of the oil.

According to a variant of the process, a small amount of clarification aid is added to the oil to be treated, making it possible to reduce the affinity of the crystals with respect to the oily phase.

According to another characteristic of the invention, the oil to be treated is a neutralized oil containing soaps, the latter fulfilling the function of clarifying adjuvants. In fact, we have noticed that the presence of water and surfactants (soaps) promotes the adhesion of waxes to air bubbles.

Preferably, the gas-oil contact under pressure is carried out with stirring for a period of approximately 30 min.

Furthermore, and according to another characteristic of the invention, the method comprises a step of reprocessing the waxes making it possible to recover the oils which are contained therein.

The process which is the subject of the invention can operate continuously or batchwise and will be described in more detail with reference to the appended figure which is a block diagram of continuous operation.

According to the figure, the oil to be treated is brought according to arrow A in a cooler 1 comprising an agitator 2. In this cooler 1, the oil to be treated is brought to the appropriate temperature, chosen according to the type of oil to be treated . At the outlet of this cooler, the oil is then brought to a ripener 3 where it is kept at the same temperature so as to allow quantitative crystallization of the compounds to be removed, under conditions suitable according to the type of oil. During this maturation stage, the oil is also subjected to agitation by means of an agitator 4.

At the outlet of the ripener 3, the oil is brought along arrow D to the lower part of a decantation container 5 and, it is subjected to the action of fine bubbles of a neutral gas, which attach to the crystals to eliminate so as to produce a gas-crystal complex in the form of a foam with a density lower than that of oil. This complex collects in zone 6 of the container, where it is removed by scraping according to arrow C.

The production of fine bubbles of neutral gas is obtained by taking a fraction E of clarified oil which is brought into a saturator 8, where it is subjected to the action of a neutral gas such as air or nitrogen arriving according to arrow F under a pressure of between 4 and 10 bar, before being expanded to atmospheric pressure, the duration of the gas-oil contact in the saturator 8 being approximately equal to 30 min. Thus, there occurs in fraction E ', leaving the saturator 8, a formation of fine bubbles of air or nitrogen which are released in the container 5 and come to be fixed to the particles of solid suspended in the oil . According to a variant of the process, all of the oil leaving the ripener 3 can be pressurized by passing it through the saturator 8 before introducing it into the lower part of the container 5.

Thus, at the bottom 7 of the container 5, a clarified oil G is recovered, a fraction E of which is recycled to the saturator 8. As indicated above, the flow rate of this fraction can range up to 300% of the flow rate of the oil to be treated leaving the ripener 3.

Furthermore, after destruction of the foams by heating, for example, 1.5 to 5% of oil containing 1% of waxes is recovered.

This oil enriched in waxes can be treated by the method according to the invention or by usual methods (decantation, centrifugation, filtration).

Example 1

The starting raw material is a sunflower oil containing 800 ppm of waxes. We take 3 kg of this oil which has been subjected beforehand to neutralization and contains 0.4% water and 1080 ppm of sodium hydroxide soap, it is introduced into a 5 liter beaker, equipped with an agitator, the whole placed in a refrigerated enclosure at 5 ° C for a period of approximately 10 hours with continuous stirring. This oil is transferred to a 4 liter saturator equipped with an agitator. The saturator is subjected to a pressure of 10 bars.

The contact time is 30 min. under continuous stirring, the oil temperature being maintained at 5 ° C by a coil located inside the reactor. At the end of this operation, the oil is expanded to atmospheric pressure by direct transfer to a 4-liter beaker. After one hour of decantation at + 5 ° C, a separation of two phases is obtained. At the bottom of the container, about 2,850 g of the dewaxed oil are recovered, which now contains only 20 ppm of waxes and 0.1% of water. At the top of the container, about 150 g of foam is recovered, consisting of a wax-fine gas bubble complex.

The dewaxed oil can either be subjected to the following stages of refining, or subjected to a new treatment cycle in order to perfect the dewaxing process.

Example 2

2 kg of dewaxed oil obtained according to example 1 are treated in the same way as for example 1. The oil entering the cycle contained 29 ppm of waxes, 0.1% of water and approximately 50 ppm of soap. After decantation, an oil is obtained, the wax content of which has been reduced to 9 ppm. This oil is subjected to the following stages of refining (washing, drying).

Example 3

The starting raw material is a sunflower oil containing 85 ppm of waxes. We take 3 kg of this oil previously neutralized and containing 0.3% water and 1400 ppm of sodium soap. By applying the method of Example 1, a dewaxed oil is obtained containing 7 ppm of waxes, 0.05% water and 52 ppm of soap. The dewaxed oil yield is 98.4

Example 4

The starting oil is a neutralized and discolored sunflower oil, containing 700 ppm of waxes, less than 0.05% water and less than 2 ppm of sodium. We proceed in the same way as in the example 1. A dewaxed oil is obtained containing approximately 60 ppm of residual waxes with a yield greater than 93% of dewaxed oil.

Example 5

The starting oil is a crude corn oil containing 150 ppm of waxes. The procedure is as indicated in Example 1. A dewaxed oil is obtained containing 50 ppm of residual waxes and from which the suspended materials such as mucilages, solid particles, etc. are at the same time partially removed.

It goes without saying that these examples are not limiting.

Yield

The yield of dewaxed oil after clarification is therefore 95% and can range up to approximately 98.5%.

Cold stability of the oils obtained in Examples 1 to 5

The oils obtained in Examples 1 to 5 are subjected to conventional refining operations as the case may be, up to the stage before deodorization.

The samples thus obtained are stored at + 5 ° C for 24 hours or more.

The results are set out in the table below:

Example 6 Foam treatment

An oil containing 1% of waxes from dewaxing foams obtained by the process according to the invention is cooled to 25-30 ° C overnight and then centrifuged. The heavy phase containing the waxes represents 12% of the oil thus treated. The light fraction represents approximately 88% partially dewaxed oil at 400 ppm of waxes, which can be recycled as a mixture with the oil to be treated.

It can therefore be seen that by additional treatment of the oils originating from the foams, it is possible to improve the dewaxing yield.

Claims (7)

1. A process for the treatment of vegetable oils in order to improve their cold stability, characterised in that the oil for treatment is first cooled to a temperature so selected as to allow crystallization of the compounds which are to be eliminated, and then at least some of said oil is subjected to an inert gas pressure of 4-10 bars and then expansion to atmospheric pressure so as to create fine gas bubbles which are fixed on the crystallized compounds so as to produce a foam having a density below that of the oil in the form of a complex comprising the crystals and gas bubbles, which rises to the surface of the container, to enable a clarified oil having a crystal content less than 30 ppm to be obtained with a yield of above 90 % at the bottom part of the container after decantation.

2. A process according to claim 1, characterised in that a small quantity of clarification additive is added to the oil for treatment to enable the affinity of the crystals for the oily phase to be reduced.

3. A process according to claim 1 or 2, characterised in that the oil for treatment is a neutralized oil containing soaps, the latter acting as the clarification additive.

4. A process according to any one of claims 1 to 3, characterised in that the oil is pressurized for a period of about 30 minutes.

5. A process according to any one of claims 1 to 4, characterised in that the various steps are together carried out at a temperature lying between 0 and 10 °C, and preferably approximately 5°C.

6. A process according to any of claims 1 to 5, characterised in that some of the clarified oil obtained at the bottom of the container is recycled to the treatment stage in which an inert gas is applied at a pressure of 4 to 10 bars.

7. A process according to any one of claims 1 to 6, characterised in that it comprises a wax retreatment stage for recovery of the oils contained therein.

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