EP2253363B1 - Method for producing crop crystals for sugar fabrication and compound for same for use in the production of sugar - Google Patents

Abstract

The method for producing a seed product for sugar fabrication, where the seed product contains complete sucrose seed crystals, comprises producing a mixture of sucrose and water, heating the obtained mixture up to a boiling point by dissolving the sucrose in the water and optionally adjusting the dry substance content of the solution by keeping the solution at the boiling point under the evaporation of the water, cooling the heated solution at 50[deg] C or less under the crystallization of the seed crystals, developing supersaturation in the solution based on cooling. The method for producing a seed product for sugar fabrication, where the seed product contains complete sucrose seed crystals, comprises producing a mixture of sucrose and water, heating the obtained mixture up to a boiling point by dissolving the sucrose in the water and optionally adjusting the dry substance content of the solution by keeping the solution at the boiling point under the evaporation of the water, cooling the heated solution at 50[deg] C or less under the crystallization of the seed crystals, developing supersaturation, which triggers the crystallization of the seed crystals, in the solution based on cooling. The seed product is seed crystal suspension, where the sucrose content of the hot solution is 70 wt.% or more if necessary after adjusting the dry substance content. A viscosity-increasing agent is added to the mixture in a quantity of 5 wt.% related to the mixture of water and sucrose. The cooling step takes place within 1 second or less. The content of sucrose in the seed crystal suspension is reduced by chemically converting the dissolved sucrose. The chemical conversion is an enzymatic or acid-catalyzed inversion of the dissolved sucrose to inverted sugar. The pH value of the seed crystal suspension is adjusted by the addition of acid in the acid range for the acid-catalyzed inversion. The seed crystal suspension is kept for the time period of the inversion in the acid range and the inversion is stopped by neutralizing the solution under the addition of a base. The inversion is carried out so long until the content of sucrose is reduced to 15-25 wt.%. An independent claim is included for a seed crystal suspension.

Description

The present invention relates to a process for the production of seed crystals for the production of sugar, the use of the seed crystals according to the invention in the manufacture of sugar and a composition comprising the seed crystals produced according to the invention.

Table sugar or granulated sugar is chemically considered sucrose, a disaccharide composed of dimers consisting of glucose and fructose. The main sources of sucrose are sugar cane and sugar beet, with sugar beets being grown in temperate latitudes, as in Germany.

For sugar production, these raw materials are crushed and the sucrose in aqueous solution obtained from it. The sugar is then crystallized from the aqueous solution.

Processes for the production of sugar are described in numerous ways. For example, in WO 2009/049391 A1 a process for the production of high-purity granulated sugar, according to this method is based on a raw sugar solution, which has been obtained from sugar cane or sugar beets. This raw sugar solution is added to a crystallizer at a temperature of 78 ° C to 120 ° C, wherein in a first stage by heating the raw sugar solution, a supersaturated solution is prepared. The supersaturated solution is then cooled gradually under crystallization. As a result, pure sugar crystals in a size of 0.3 to 1 mm are obtained. According to one embodiment, a seed crystal suspension may be added to the saturated raw sugar solution in the first stage. However, no information is available on the preparation and composition of this seed crystal suspension.

The U.S. Patent 5,989,351 describes a process for producing brown sugar. Unlike in the production of white sugar is here the molasses contained in the cane sugar or sugar beet juice is not separated.
It should be retained for nutritionally beneficial ingredients of the molasses. However, a taste adjusting treatment is required. For this purpose, according to the US patent, the raw sugar juice is first filtered, the pH adjusted to a value of 5.0 to 6.0 and added to adjust the purity of sugar or liquid sugar. The sugar syrup obtained is then subjected to conventional crystallization, wherein the sugar syrup is first concentrated under heating and then cooled to crystallize.
According to the US patent, the cooling is carried out under the action of shear forces, so as to obtain a sugar granules.
This method also relates to the production of sugar, but not to a process for preparing a seed crystal suspension for sugar production.

In the large-scale crystallization of sucrose, the crystal size can be controlled by adding a certain amount of a so-called "seed". The seed may be in the form of a suspension of seed crystals in a suitable dispersing medium, ie a liquid. The dispersing medium is to be chosen so that it does not dissolve the seed crystals of sucrose on the one hand and on the other hand is suitable for foodstuffs.
By adding the seeds, the average crystal size and the uniformity of the resulting sugar should be controlled. For this it is necessary that the seed crystals in the seed have as uniform a size and shape as possible.

The seed is produced outside the crystallization process of the sugar and added at the seed point to the supersaturated sucrose solution for sugar production. The small crystals of seed then grow through one or more crystallization stages to the desired average final crystal size.

It is known to produce seed in the form of a so-called slurry. In this case, a sugar / isopropanol suspension is wet-ground. For example For wet milling in a ball mill per batch of 1 kg refined sugar with a crystal size of 0.2 to 0.7 mm together with 2.2 I isopropanol milled. The grinding time is set here to 4 hours.
The slurry thus produced has a defined crystal content of 33%. The crystal size is about 10 microns with a relatively broad particle size distribution.

A slurry produced by grinding is a regrind, that is, the small sucrose particles obtained are fragments and crystal chips, but not whole crystals. Due to the broken surfaces, the crystal fragments can easily get caught in each other. These interlocked crystal fragments would lead to unwanted crystal aggregation without further pretreatment in a crystallizer. Therefore, there is a need to subject the slurry to sufficiently high shear before addition to the sucrose solution to reground the contiguous crystal fragments.

On the basis of investigations (Buchholz and Schliephake 1988), a specific agitator capacity of at least 10 kW / m ³ immediately before the addition of the seed to the sucrose solution is necessary in order to be able to reduce the aggregate fraction sufficiently.

Further, to increase the dispersing effect, the addition of viscosity-increasing agents is recommended. Like the dispersing medium, these dispersants, on the one hand, must not dissolve the seed crystals, and on the other hand must be suitable for the food industry. Usually this glycerol is used.
However, glycerol has the disadvantage that it is hygroscopic and untreated contains a high proportion of water that would dissolve the seed crystals. Therefore, before addition of glycerin to the slurry, the water in the glycerol must be saturated with sucrose.

Overall, the method described above is characterized by a high workload and many possibilities for error, which require precise compliance with the processes and their monitoring.

Another marketed on the market under the trade name "Seed Crystal Fondant" slurry also contains crushed crystal fragments. With a size of 7 microns, the crystal fragments obtained therein are considerably smaller than described above and should have a narrower distribution. The dispersion is obviously improved here by the use of special emulsifiers. The lower average crystal size compared to the slurry described above leads to a smaller amount of slurry required according to the d ³ rule, since the number of added seed crystals, but not their mass, is of importance for the inoculation of the sucrose solution. However, this advantage is relativized by the lower crystal content of only 19% in the slurry. The emulsifiers prevent sedimentation of the seed crystals and thus facilitates an exact dosage of the seed to the sucrose solution.

Another method for preparing a slurry is described by Grapka (1989). Here, the wet grinding is carried out with alcohol and then exchanged the alcohol for a vegetable oil. Also, this method has the principal disadvantages of slurry production by wet grinding and has not prevailed in practice.

According to another approach, the seed crystals are obtained from a slightly supersaturated sucrose solution by use of an ultrasonic field (Qui Tai-Quin 1993).
In this method, crystal nuclei are formed by compression in the compression points of the sound field. This method has the advantage that not crystal fragments, but whole crystals are obtained. In addition, the mother solution is highly viscous as a saturated sucrose solution, so that rapid sedimentation of the crystals is prevented. A disadvantage of this method, however, is that it is difficult to control. In addition, the slurry can not be stored for a long period of time because the small crystals in the solution disappear and larger crystals continue to grow. This phenomenon, known as "oswald ripening", leads to significantly less crystals over time but larger crystals in the solution. Larger crystals in the seed have the disadvantage that then according to the d ³ rule also larger amounts of seed at the seed point of the sucrose solution must be added.

The British patent GB 1 221 125 relates to a process for producing a seed crystal suspension for sugar production. In particular, the purpose of the British patent was to avoid the formation of large irregular aggregates of crystal fragments and chips as obtained by the conventional methods. According to the British patent, this object is achieved by providing a seed crystal suspension which consists of whole crystals, that is to say by avoiding the formation of crystal fragments or fragments, the crystals having a size between 5 and 10 μm. This seed crystal suspension of whole crystals is obtained by mixing an aqueous sucrose solution with an aqueous glucose solution, the mixture is thickened by boiling at atmospheric pressure until it has reached a boiling point of 116 ° C, the thickened solution carefully cooled to 60 ° C and then under is quenched vigorous stirring.

It was an object of the present invention to provide a method for the production of seeds for sugar production and a corresponding seed, with which the above-mentioned disadvantages can be overcome.
In particular, it was an object of the present invention to provide such a method, with which a seed can be obtained controllably, which has whole crystals as seed crystals, which have a small average size and narrow particle size distribution.

This object is achieved by a method for producing a seed with whole sucrose seed crystals for sugar production, wherein a mixture of sucrose and water is prepared, the resulting mixture is heated to dissolve the sucrose in the water to the boiling point, optionally the dry matter content of the solution by holding on Boiling point is adjusted with evaporation of water, the heated solution is cooled to crystallize the seed crystals to 50 ° C or less, and wherein due to the cooling in the solution builds a supersaturation, which triggers the crystallization of the seed crystals.

An aqueous sucrose solution boils at over 100 ° C, the boiling point increases with increase in dry matter content due to the evaporation of water.

According to the invention, the production of the small sucrose crystals, which are later used as seed crystals, takes place by means of a cooling crystallization, the supersaturation occurring due to the cooling in the solution, which is reduced by spontaneous nucleation.

The sucrose content of the heated solution, optionally after adjusting the dry matter content, should be 70% by weight or more, preferably between 75 and 85% by weight.

The sucrose content of the mixture should not be too low to avoid unnecessarily long periods of dry matter content adjustment in the hot solution. Preferably, the mixture contains at least 60% by weight of sucrose.

The size of the seed crystals should not exceed 30 microns, and in particular be 18 microns or smaller.
As mentioned above in the discussion of the prior art, for the crystallization of sugar from a sucrose solution, the number of seed crystals, but not their size, is crucial. The larger the seed crystals are, the higher the mass that must be added to the sucrose solution for sugar crystallization to obtain a corresponding number of seed crystals. However, this larger mass is disadvantageous from an economic point of view.

The size of the resulting seed crystals and their number can be controlled by the selected conditions of cooling, such as time and final temperature.
Seed crystals of an appropriate size and number can be obtained by cooling the aforementioned solution to 50 ° C or less within 2 hours or less, preferably within 1 hour or less, and more preferably within 15 to 40 minutes. Preferably, the cooling is carried out at 50 ° C to 30 ° C.

The process according to the invention gives a slurry, ie suspension, in which the seed crystals are dispersed in a sucrose-containing aqueous solution.

In order to avoid premature sedimentation of the seed crystals, which would be detrimental to their further use as inoculum for a sucrose solution for sugar production, suitable emulsifiers may be added, as they are generally known in the sugar industry for these purposes. For example, invert sugar may be added for stabilization. In principle, any commercially available invert sugar can be used.

According to another embodiment, a viscosity-increasing agent may be added. Examples of viscosity enhancing agents are oligomeric or polymeric carbohydrates such as glucose syrup, polydextrose, thickening agents such as xanthan, locust bean gum or other viscosifying agents known and suitable for crystallization.

The addition of the viscosity-increasing agent or of invert sugar can already take place during the preparation of the mixture of sucrose and water. Good effects are obtained with a content of viscosity-increasing agent or invert sugar of 5 to 25% by weight (based on the dry matter content), in particular 8 to 12% by weight, based on the mixture of water and sucrose (before heating the mixture).
The upper limit is not critical here, but a higher level of viscosity-increasing agent or invert sugar would not show a significantly improved effect, but on the other hand reduce the sucrose content and thus the content of seed crystals in the finished suspension.

The inventive method of producing seed crystals for the production of sucrose by means of cooling crystallization by spontaneous nucleation is similar to the fondant production, so that existing fondant plants can be used for the inventive method. Commercially available fondant plants include a digester for producing the sucrose solution and a screw conveyor surrounded by a cooling jacket for cooling the heated sucrose solution.

Hereinafter, the present invention will be explained in more detail by way of example, wherein for this example, the existing fondant plant was used in a plant of Nordzucker AG.

Crystalline sucrose is dissolved in water in a ratio of 2: 1 and then 10% by weight of glucose syrup with the product name GS3980H from Syral S.A. added with a dry matter content of 80%. Subsequently, the resulting mixture is thickened in a digester at a temperature of about 113 ° C to a dry matter content of 83.5%. Once the desired dry matter content has been obtained, the hot solution is introduced into a screw conveyor surrounded by a cooling jacket. Through this cooling jacket flows cold water to cool the solution. As a result of the cooling, supersaturation builds up in the solution, which triggers spontaneous nucleation. The cooling takes place within 20 min at 40 ° C. As a result, sugar crystals having an average size of 11 μm ± 2 μm are obtained. The amount of seed crystals at the end of the cooling crystallization is usually 40 to 60% by weight.

Therefore, in order to obtain cooling water with the lowest possible temperature, or to recirculate after re-use through the screw conveyor for reuse, a chiller can be interposed in the cooling circuit.
Of course, any other suitable coolant can be used instead of water.

According to the present invention, since the crystals spontaneously emerge from the solution, as a result of the cooling crystallization, a crystal suspension consisting of whole crystals rather than crystal fragments is obtained. Whole crystals in the seed lead to significantly lower levels of unwanted crystal aggregates in the subsequent sugar production.

As a result of the cooling crystallization, a suspension of small sucrose crystals in a saturated sucrose solution is obtained. As is known, the phase boundary between crystal surface and solution is subject to very dynamic processes. Sucrose molecules permanently go from the crystal surface into the solution and vice versa. These processes are further enhanced when the crystal suspension is agitated, pumped, or otherwise agitated, or even exposed to temperature fluctuations for a long time. This leads to Oswald ripening, with the small crystals dissolving and the big crystals continue to grow. In the end, only a few large crystals remain, which are unsuitable as seed crystals.

To prevent Oswald ripening, replace the sucrose solution in which the seed crystals are dispersed with another non-sucrose solution. However, separation of the solution from the crystals by mechanical means such as centrifugation is not possible due to the small size of the crystals in the amount of tonnes required for industrial use.

According to the invention, this problem is solved by chemically converting at least part of the sucrose molecules present in solution, and thus removing them from the process described above.

The chemical transformation of a part of the dissolved sucrose causes a small part of the seed crystals to dissolve again, so that the content of seed crystals is reduced. However, Ostwald ripening is prevented in the resulting seed crystal suspension, which far outweighs the disadvantage of reducing the seed crystal content.

In principle, any chemical conversion is suitable, which converts the sucrose into compounds or conversion products that do not interfere with the technical sugar crystallization or influence and are preferably suitable for food.

According to a preferred embodiment, for this purpose, a part of the dissolved sucrose molecules is inverted, that is, the sucrose in solution is cleaved into its constituents, glucose and fructose (also referred to as invert sugar). Since invert sugar can not be incorporated into the sucrose crystals, the process of Oswald ripening is fully or at least greatly suppressed, depending on the extent of the conversion. An exchange of the solution is therefore no longer necessary according to the invention, only a transformation takes place.

The inventively preferred inversion of the sucrose in solution can basically be done in two different ways. The inversion can be carried out by special enzymes, the so-called invertases, or by acid-catalyzed hydrolysis. For the acid-catalyzed hydrolysis, the solution is lowered to an appropriate pH by addition of an acid.

However, the enzymatic inversion has the disadvantage that the enzymes remain in the solution. This means that they are introduced into the sugar process together with the seed crystals and can continue to work there if necessary.
The acid-catalyzed hydrolysis is therefore preferred according to the invention.

After the sucrose content in the solution has been reduced so much that the Oswald ripening is reduced to a desired level, the hydrolysis is stopped by increasing the pH. The interruption of the hydrolysis or inversion, is required because the sucrose concentration in solution must not be lowered so far that due to the phase equilibrium, the seed crystals go back into solution.
In general, it has proven sufficient to reduce the sucrose content of the suspension by about 15 to 25% by weight.

It has been found that until the end of the conversion, the sugar crystals in the suspension can still grow somewhat so that the final seed crystals have a slightly larger average size than the sugar crystals obtained in the crystallization.

The following is an example of an acid-catalyzed inversion of the seed crystal suspension obtained in the above Example to better illustrate the present invention.

For the acid-catalyzed hydrolysis, the pH of the crystal suspension, which is about pH 7, is lowered to a pH of from 2 to 3 by stirring in weak sulfuric acid (2.0%). Subsequently, the acidified seed crystal suspension is stored over a period of several hours, until an invert sugar content of 20% has been reached. The increase in invert sugar content can be detected by a process refractometer since the invert sugar content is manifested by an increase in the dry matter content of the solution. Then, for neutralization, 25% sodium hydroxide solution is added until a pH of about 9 has been obtained.

• 25 Gew.% Saatkristalle, 16 Gew.% Wasser, 29 Gew.% gelöste Saccharose,
• 20 Gew.% Invertzucker als chemisches Umwandlungsprodukt und 10 Gew.% Glukosesirup

Die mittlere Größe der Saatkristalle beträgt 16 µm ±2 µm.The resulting seed crystal suspension has the following composition:

• 25% by weight of seed crystals, 16% by weight of water, 29% by weight of dissolved sucrose,
• 20% by weight of invert sugar as a chemical conversion product and 10% by weight of glucose syrup

The mean size of the seed crystals is 16 μm ± 2 μm.

The finished seed crystal suspension can be filled for transport in a sugar factory and for storage in containers of a suitable size. It can be stored and distributed in these containers and is always ready for use in addition to a sucrose solution for sugar production.
It has been shown that the sedimentation of the seed crystals over several months is only small.

The handling in the sugar factories is very simple. For example, the seed crystals can be fed via a ring line to the designated crystallizers.

According to the invention, a method is thus provided with which a seed crystal suspension can be obtained in a controllable manner, which contains whole sucrose crystals, and which can advantageously be added as seed to sucrose solutions for sugar production. According to the invention, it is also not necessary to exchange the dispersing medium in the seed crystal suspension or to remove the seed crystals in a mechanical manner. The seed of the invention contains no alcohol or dispersant such as glycerin. Thus, no additives are introduced into the sugar crystallization process, which could possibly cause problems.

Bibliography

• Buchholz, K .; Schliephake, D. Sugar Industry 113 (1988) 361,379
• Qiu Tai-quin Int. Sugar J. 95 (1993) 513-519
• Grabka, J. Zucker Industrie 114 (1989) 467-468

Claims (15)

1. Method for producing a seed product for manufacturing sugar, wherein the seed product contains whole sucrose seed crystals and wherein a mixture of sucrose and water is produced, the mixture obtained is heated to boiling point with the sucrose dissolving in the water, where applicable the dry substance content of the solution is adjusted by keeping the solution at boiling point with evaporation of the water, the heated solution is cooled to 50°C or less with crystallisation of the seed crystals, and wherein, because of the cooling, a supersaturation builds up in the solution and induces the crystallisation of the seed crystals.
2. Method according to claim 1, wherein the seed product is a seed crystal suspension.
3. Method according to claim 1 or 2, wherein the sucrose content of the hot solution is 70% by weight or more, where applicable after adjustment of the dry substance content.
4. Method according to any one of claims 1 to 3, wherein a viscosity-increasing agent is added to the mixture in a quantity of at least 5% by weight, based on the mixture of water and sucrose.
5. Method according to any one of claims 1 to 4, wherein the cooling to 50°C or less takes place within 1 hour or less.
6. Method according to any one of claims 1 to 5, wherein the content of sucrose in the seed crystal suspension is reduced by chemical conversion of the dissolved sucrose.
7. Method according to claim 6, wherein the chemical conversion is an inversion of the dissolved sucrose to form invert sugar.
8. Method according to claim 7, wherein the inversion takes place enzymatically or by acid catalysis.
9. Method according to claim 8, wherein for the acid-catalysed inversion, the pH of the seed crystal suspension is adjusted by adding acid in the acid range, the seed crystal suspension is kept in the acid range for the duration of the inversion and the inversion is stopped by neutralising the solution with the addition of a base.
10. Method according to claim 9, wherein the inversion is carried out until the content of sucrose has been reduced by 15 to 25% by weight.
11. Seed crystal suspension, containing sucrose seed crystals in an aqueous sucrose solution and a chemical conversion product of sucrose.
12. Seed crystal suspension according to claim 11, wherein the chemical conversion product is invert sugar.
13. Seed crystal suspension according to claim 11 or 12, wherein the sucrose seed crystals have a mean size of 30 µm or less.
14. Seed crystal suspension according to any one of claims 11 to 13, wherein the suspension additionally contains a viscosity-increasing agent.
15. Use of a seed crystal suspension, obtainable according to any one of claims 1 to 10 or according to any one of claims 11 to 14 as a seed product for seeding sucrose solutions in sugar manufacturing.