EP2166072A1 - Method for continuous crystallisation with seeding for body fat - Google Patents

Abstract

Crystallizing fat material comprises: complete fusion of the fat material; pre-cooling the material to a supersaturation temperature, in a reactor optionally equipped with a cooling system or exchanger; and treatment of the material with ultrasound to cause seeding, where the seeding is continuous seeding of fat material flux, in a small reactor or a pipe "on line", subjected to the action of an ultrasonic transmitter, and in that the fat material is then transferred continuously in an arrangement having a decreasing temperature.

Description

FIELD OF THE INVENTION

The purpose of the fractional crystallization of the fats is to crystallize a fat to separate a solid fraction rich in saturated triglycerides (TG), called stearin, from a liquid fraction with a low melting point called olein. Fractional crystallization, more commonly referred to as dry fractionation, that is to say without solvent or additive, is a technology commonly used for palm, butter and animal fats, partially hydrogenated oils, fish oil and many others. . For dry fractionation, for example, palm fat, semi-solid in tropical countries, is separated into two new higher value-added fractions than the starting fat: stearin used in margarine and olein used as oil table and frying. In the case of butter fat, thanks to dry fractionation, it is possible to produce stearines with the same texture all year long regardless of the seasonal variation of the starting fat and even to produce frigotartinables butters.

In general, the fat is completely melted and heated to remove all the crystals and the memory effect of the crystals. The melted fat is cooled with stirring and controlled cooling for generate the first germs from triglycerides with a high melting point. These seeds grow to form the required size crystals. When the crystallization has progressed sufficiently to allow the crystals to grow and agglomerate, the crystal suspension or stearin is separated from the liquid part, olein.

Traditionally, the separation was done using a vacuum filter, for example the rotating drum filter or the continuous belt filter, but more generally using a membrane filter where after pressure filtration, each stearin cake is compressed using a gas or liquid. These filters, although discontinuous compared to vacuum filters, offer a better yield of olein. Other separation means exist such as super-decanters or centrifuges.

In practice, dry fractionation is complicated by the fact that seed formation depends on the presence of foreign particles, impurities, temperature, super saturation of fat, agitation, triglyceride composition and the quality of the raw material if it has been pre-refined or refined completely. The growth of crystals depends on the number of seeds present and the degree of supersaturation of the fat. Finally, crystal growth also depends on the polymorphism (the property that triglycerides have to crystallize in different crystalline forms of different physical property) and the intersolubility or formation of mixed crystals.

Given all these points, at present industrial dry fractionation is carried out batchwise, in huge tanks equipped with stirrers and different cooling systems because the batch process allows easier control of the important parameters of the crystallization. that is, control of temperature, super saturation of fat, cooling rate, agitation, crystallization time.

Nevertheless, this technique in batch is slow: it requires to keep the fat for several hours, on average 8 to 10 hours, in tanks of 5 to 90 tons because the formation of germs, step-key Successful crystallization requires a lot of time. Currently palm oil reaches an annual world production of 40 million tonnes, much of which is valued by dry fractionation. As a result, industrial facilities are becoming larger and more expensive.

Nucleation or formation of seeds is the most critical step of all crystallization. In order to create the first seeds from high melting TGs, the temperature of the melt is lowered below its melting point (supersaturation). As the nucleation rate increases in proportion to the lowering of the melt temperature, the result is that the crystals formed are smaller and smaller with a large increase in the viscosity of the suspension. Whence to obtain crystals of sufficient size for a good separation, it is necessary to limit the quantity of seeds formed and consequently to reduce the nucleation rate. Industrially this operation is carried out by slow cooling and gentle agitation which is the longest step of crystallization.

PRIOR ART

Ultrasound has already been used for the crystallization of chemicals and in particular fats ( EP 0957 953 A ; US Patent 6630185 ). The method described in this document is characterized in that the batch crystallized liquid is exposed to ultrasound in the absence of cavitation ("transient cavitation"), that is to say using a source of ultrasound of a relatively low intensity. This paper discusses criteria for estimating the presence or absence of the cavitation phenomenon.

The document EP 0765605A1 describes a "Process for accelerating the polymorphic transformation of edible fats using ultrasonication" in which the cocoa butter brought into supercooling of about 4 ° C is subjected to ultrasound for a duration and a frequency capable of inducing nucleation of stable crystals of polymorphism beta. This process is not, however, a fractionation process.

Continuous crystallization was also industrialized (Société Bernardini -Italie) in the 1980s but without success. In the absence of a nucleation step or adequate seeding, this process resulted in spontaneous nucleation leading to a formation of germs on the walls, agitators and pipes and thus complete freezing.

More recently Hartel (Continuous crystallization system with controlled nucleation for milk fat fractionation, October 31,2000 - PCT WO 98/51753 ) has described a continuous crystallization system for butter oil with control of nucleation. The nucleation step consists of supersaturing the oil flow and passing it through a small reactor equipped with a high speed stirrer to create the seeds. Although described on a pilot scale, such a system is difficult to implement industrially and has been abandoned because it relies on the impact, or the energy, provided by the stirrer as a function of the fat, which is a problem. natural product and whose behavior varies from one oil to another.

The present invention provides an advantageous method for continuously crystallizing fat by using ultrasonic radiation for the controlled generation of seed crystals and passage through a series of small size crystallizers as compared to the "batch" method, agitated either mechanically and / or or using a gas.

DETAILED DESCRIPTION OF THE INVENTION

According to the method of the present invention, continuously controlled seeding (nucleation or nucleus formation) is provoked, thereby considerably reducing the time required for the germ formation step. As a result, the cycle of The cooling currently carried out in batches and usually taking from 5 to 6 hours for the rapid process and from 9 to 10 hours for the slow process is reduced to a total time of 2 to 3 hours or to a cycle 2 times or even 3 times shorter. Continuous crystallization comprising the steps of charging, heating, pre-cooling, continuous seeding and crystallization in a series of crystallizers, preferably small crystallizers, in cascade, which allows to obtain a process much faster. Fractionation facilities are also more compact, the investment cost is much lower.

By small crystallizers are meant crystallizers whose dimensions are significantly smaller than the dimensions of crystallizers used in the batch method of the prior art for equivalent production. For example, a capacity of 100 to 2,000 kg can be cited, compared to 1,000 to 60,000 kg in a prior art installation.

• fusion complète de la matière grasse, de préférence au dessus de 70°C,
• pré-refroidissement de celle-ci à une température de supersaturation, dans un réacteur muni d'un système de refroidissement ou échangeur tubulaire, statique ou à plaques,
• ensemencement en continu d'un flux de graisse liquide dans un petit réacteur ou une tuyauterie, soumis à l'action d'un émetteur ultrasons d'une puissance de 20 à 100W et une fréquence de 16 à 100 KHz. Le débit est de de 0 à 100 litres/heure pour l'unité pilote et de 100 litres à 50 m3 / heure pour des unités industrielles.
• transfert en continu de la matière grasse dans un arrangement ou circuit présentant une température décroissante.

According to one aspect of the invention, the process of continuous crystallization of the oils / greases comprises the following steps:

• complete melting of the fat, preferably above 70 ° C,
• pre-cooling thereof to a supersaturation temperature, in a reactor equipped with a static or plate-like cooling system or exchanger,
• continuous seeding of a flow of liquid fat in a small reactor or piping, subject to the action of an ultrasonic transmitter with a power of 20 to 100W and a frequency of 16 to 100 KHz. The flow rate is from 0 to 100 liters / hour for the pilot unit and from 100 liters to 50 m3 / hour for industrial units.
• continuous transfer of the fat into an arrangement or circuit having a decreasing temperature.

The fat is pre-cooled preferably rapidly to its supersaturation zone, e.g., 25 to 35 ° C.

The fat is pre-cooled preferably for 5 to 60 minutes to its supersaturation zone.

The decreasing temperature is advantageously decreasing in stages, for example from 3 to 7 ° C and the residence time in a crystallizer is typically 30 to 60 min.

The arrangement can be small crystallizers placed in series and provided with stirrers and cooling elements. The arrangement can also be constituted by a single crystallizer to proceed in decreasing temperature steps.

In one embodiment, the seeded fat is transferred by gravity into small crystallizers placed in series. The small crystallizers may be vertical cylindrical containers provided with a paddle stirrer, one or more coils and possibly a jacket, or vertical containers provided with a concentric stirrer provided with a a series of U-tubes to stir and cool at the same time.

According to the invention, the small crystallizers may also be cylindrical or cubic containers equipped with gas distribution ramps for agitating the seed or crystallized mass subjected to an injection of any gas but which will preferably be nitrogen.

According to the invention, in general, the grease is heated, pre-cooled by an economizer, then using continuous heat exchangers, to its critical point of supercooling or supersaturation, subjected to induction ultrasonic so as to generate in situ and continuously the crystalline seeds.

The seeded material is either controlled and continuously cooled in tubular or static stirring exchangers or in plates or in a series of small crystallizers equipped with stirrers and cooling adapted to each step.

In the present invention, the supercooled liquid is subjected to ultrasound above the cavitation threshold or in the presence of low cavitation. Sononucleation applied in the metastable zone at a lower supersaturation rate considerably reduces the induction time and leads to crystals whose final size can be perfectly controlled and with better selectivity.
According to the described method, an aliquot portion of the fat may be sonicated and served mixing for seeding.

In the present invention, the nucleation step is indeed much easier because it is possible to precisely control the frequency, the intensity, the induction times, the induction temperature and consequently generate the quantity of germs necessary. For the seeding of the fatty substances, one will use a minimum power so as not to remelt the germs immediately after their formation. It can also be seeded by wave trains or discontinuously so as not to form too many germs. As already mentioned, part of the flow can be sonicated and continuously mixed with the rest of the fat.

• la FIG.1 présentée à titre d'exemple uniquement dans laquelle on illustre schématiquement un mode de réalisation du procédé de l'invention.
• la FIG. 2 ilustre schématiquement un autre mode de réalisation.

The invention will be better understood on examining the figures in which

• the FIG.1 presented by way of example only in which is schematically illustrated an embodiment of the method of the invention.
• the FIG. 2 schematically illustrates another embodiment.

Referring to the FIG. 1 the storage tank 1 is shown with its heating system 11 and an agitator 12. In 2 is a feed pump, in 3 a tubular cooler with static mixer, in 4 the positioning of the ultrasonic cells, in 5, 6 and 7 crystallizers equipped with a jacket 13 and stirrer 14 to blades and 8 a diaphragm filter feed pump or separator not shown.

According to the diagram shown in figure 2 the process may comprise 25, 26 and 27 small crystallizers provided with a jacket or preferably coils or cooling plates. Each small crystallizer is equipped with a nitrogen distribution manifold 55 for agitating the crystalline mass. According to the invention, surprisingly, the combination of ultrasonic seeding and stirring with a gas makes it possible to obtain not only fast cycles but also very regular crystals with better yields.

In general, the crystallization with gaseous stirring, to our unknown knowledge, has an additional advantage over crystallization with mechanical stirring: it significantly reduces the shearing force, shearing, which is one of the major obstacles to crystallization. fatty substances. The invention therefore also relates to the use of a gas agitation for the crystallization of fatty substances, in particular fractional crystallization.

The tank 27 serving as a buffer tank for loading the membrane filters may be gaseous or mechanical stirring. The path of the fat from 25 to 27 can be done from the bottom as well as from the top as indicated in the Fig. 1 & 2 . or using a pump.

The crystallization can also be performed in batch after a step of loading, heating, pre-cooling, continuous seeding. In that case, the seeded material can be crystallized in a single vessel with agitation and batch cooling and called semi-continuous crystallization.

According to the invention, the semi-continuous cycle will be as fast as if it were continuous in the case where the cooling vessel still has the same capacity.

The process of the invention can be applied generally to fats or oils such as triglycerides, fatty acids or esters of fatty acids. The fat may be palm oil, butter fat, palm kernel, coconut oil, fish oil, partially hydrogenated vegetable oils, cocoa fat or any other animal / vegetable fat and any fraction from the mentioned fats. The fat may be refined, semi-refined or raw.

For fats such as coconut fat, palm kernel and palm oil fractions which form a crystalline network leading to a crystalline mass rather than to a suspension of crystals during cooling, unlike the process described in EP 01202906, they will preferably be inoculated continuously and transferred to a crystallizer comprising a series of chambers equipped with a gas distributor and at least one cooling surface. The plates equipped with cooling walls which constitute the chambers are assembled as in a filter press. Seeded and uncrystallized fat is transferred easily in a chamber crystallizer or plate crystallizer where it is rapidly brought to its solidification point with gaseous stirring and gradual cooling. According to the invention, the crystalline mass is preferably maintained for 5 hours at 18 ° C. before being discharged and converted into paste ready to be pumped into a membrane filter press.

The invention will also be better understood on examining the non-limiting examples of embodiments which follow

EXAMPLE 1

Continuous crystallization of an anhydrous butter oil after continuous seeding using an ultrasonic transmitter.

The fat was melted and held for at least one hour at 70 ° C. It was then pumped and cooled from 70 to 32 ° C and treated continuously at a rate of 3 liters per hour, at 32 ° C by ultrasound (26 KHz and 50 Watt) throughout the transfer to a series of small crystallizers put in series. Each small crystallizer is equipped with a double jacket or coils or embossed plates and a multi-blade stirrer or an agitator comprising a set of U tubes going up and down the crystallizer and for cooling and stirring in same time. The sown mass stays for 45 minutes in the first crystallizer whose temperature is maintained at 28 ° C. The crystalline mass is then continuously transferred by gravity from the first crystallizer to the second crystallizer maintained at a temperature below 5 ° C. The crystalline mass can also be transferred using a pump positive. After a residence time of 45 minutes, it is transferred by gravity into a third crystallizer whose temperature is maintained at 18 ° C. The crystalline mass is filtered after a residence time of 40 min. The butter oil is fully crystallized after a total cooling cycle of 130 to 150 min. After filtering on a membrane filter press, a olein of pt is obtained. drop of 21 ° C with 82% yield and a stearin of 42.5 ° C pt. of gout.

EXAMPLE 2

Refined palm oil I.I. 53 (I.I. Iodine number) treated in the same way as the butter oil of Example 1, provided after filtering on a 6 Bar compression membrane filter a I.I. 58 with a yield of 82% and a stearine of 32 I.I. and 52.4 ° C drop point. The total cooling cycle is 140 min.

Example 3

A refined palm oil II 53 and crystallized in the same manner as in the preceding example, the installation however using agitation under nitrogen as indicated in FIG. figure 2 , obtained after filtration on a membrane filter and compression at 6 Bar a olein 58.6 II / with a higher yield of 83.8%. Stearin obtained with 30.2 II has a drop point of 53 ° C. The total cooling time is 160 min.

Example 4

Raw palm kernel fat of 3.5% acidity and 17.5 iodine number is melted at 70 ° C, pre-cooled to 24-25 ° C, seeded in the same way as butter oil of Example 1, and transferred to a crystallizer comprising a series of chambers cooled to 22 ° C and in which the seeded material is rapidly brought to 18 ° C with stirring of nitrogen. After maintaining for 4 to 5 hours at 18 ° C., the chambers are opened and the cakes thus discharged are transformed into paste according to the well-known crashing process. The filter press filter pulp at 28 bar compression provides 37% stearin with an iodine value of 6.8 and an olein with an iodine number of 23.8.

Claims (14)

Process for the crystallization of fat comprising the successive steps: - complete fusion of the fat, pre-cooling thereof to a supersaturation temperature, in a reactor possibly equipped with a cooling system or exchanger, - Ultrasonic treatment to cause seeding, characterized in that the seeding is a continuous seeding of a flow of said fat, in a small reactor or piping "on line", subjected to the action of an ultrasonic transmitter, and in that the fat is then transferred continuously in an arrangement with decreasing temperature. The method of claim 1 wherein the intensity of ultrasound emitted by the emitter is such that a cavitation phenomenon is induced in the fat. The method of claim 1 or 2 wherein the decreasing temperature is decreasing in steps. A process according to claim 1, 2 or 3 wherein the arrangement or circuit is constituted by series crystallizers comprising stirring means and cooling elements. A method according to any one of the preceding claims wherein the arrangement is constituted by a single crystallizer capable of producing decreasing temperature levels. A process according to claim 3, 4 or 5 wherein the decrement is 3 to 7 ° C. The process of claim 4 wherein the residence time in a crystallizer ranges from 30 to 60 minutes. The method of any one of claims 1 to 6 wherein the ultrasonic frequency is 16 to 100 KHz with a preferential area of 20 to 40 KHz. The method of any one of claims 1 to 7 wherein the power of the ultrasonic transmitter is 10 to 3000 W, preferably 20 to 50 W. Method according to any one of the preceding claims wherein the ultrasonic transmitter is placed in line on a pipe. The method of any one of claims 1-4 and 5-10 wherein the seeded fat is gravity-transferred into the small crystallizers in series. A process according to any one of the preceding claims wherein the seeded oil is stirred with a gas, preferably nitrogen to reduce the shear rate. A process according to any one of the preceding claims wherein the flow is from 100 liters to 50 m ³ per hour. The process of any one of claims 1 to 12 wherein the flow is from 1 to 100 liters per hour.

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