CZ281653B6 - Process for preparing lactulose - Google Patents

Abstract

Lactulose is mfd. by heating, at over 80 deg.C an aq. soln. of lactose and borax contg. no additional alkali (Process A). Pref. the lactulose is sepd. from the soln. of reaction prods. after removal of Na ions, by passing the soln. through a weakly basic ion-exchange chromatography column (claimed). The Na ions are removed by either electrodialysis (a) or by ion-exchange (b) the removed ions in each case being returned to the prodn. cycle.

Description

Technical field

The invention relates to a process for the manufacture of lactulose, wherein an alkaline aqueous solution of lactose and borax is prepared and heated to a temperature above 80 ° C and the lactulose is separated from the obtained conversion products.

BACKGROUND OF THE INVENTION

This method is known, for example, from Chemical Abstracts 86: 173382h. Since the conversion requires an alkaline medium, sodium hydroxide solution is additionally added. The yield of the process is relatively high. Boric acid forms a complex with lactulose that shifts the balance towards lactose. In addition, lactose is converted into galactose, tagatose, other sugars, organic acids and dyes as conversion products.

SUMMARY OF THE INVENTION

SUMMARY OF THE INVENTION It is an object of the present invention to provide a process for the production of lactulose which is similarly economical but ecologically more advantageous.

According to the invention, this object is achieved by virtue of the fact that, in the above process, essentially no alkali is added to the solution, apart from borax.

Thus, the burden of wastewater with alkali salts, which are formed after the removal of alkali ions by ion exchangers during ion exchange regeneration, is substantially reduced.

As a further fulfillment of the above requirement, the sodium ion recycling method according to two modified embodiments of the method of the invention allows:

One embodiment is based on the fact that borax is formed in an aqueous boric acid solution, preferably at the same time as lactose, wherein the sodium ions are transferred from the solution of the conversion products to the boric acid solution by electrodialysis. In this process, the complete recycling of sodium ions is possible.

Only two chambers separated by a catheter membrane are required for this purpose. One chamber is a cathode compartment and a boric acid solution, preferably a boric acid-lactose solution, flows through it. The conversion product solution flows through the second chamber, which is the anode compartment. Under the applied voltage, the sodium ions move into the first chamber so that a borax solution is formed in the chamber.

A second embodiment of the method according to the invention is based on removing sodium ions from the solution of the conversion products substantially as perfectly as possible by means of a weakly acidic ion exchanger and only thereafter with a strongly acidic ion exchanger. and the borax thus formed is at least partially reused

-1GB 281653 B6

In other words: If the concentration of sodium ion in the solution of the conversion products is so high that a weakly acidic ion exchanger also binds sodium ions, such an ion exchanger is used. The stronger acid ion exchanger is then used only to complete the separation of sodium ions from solution. As a result of the advantageous regeneration of the weak acid ion exchanger with boric acid, the sodium ions bound by the boric acid remain in the production cycle. Only the remainder reaches the waste water. However, even if the weak acid ion exchanger is not regenerated with boric acid, its use is preferred. In any case, it can be regenerated with a weak acid, which is ecologically more advantageous. For example, carbonic acid is environmentally safe.

As a further embodiment of the process according to the invention, it is recommended to separate the solution of reaction products after separation of the sodium ions, before or after separation of the borate ions, preferably after evaporation to a dry matter content of 15 to 20% by weight, through a long vessel filled with a weakly basic ion exchanger. an organic column, preferably at a temperature of 30 to 60 ° C, using water as the eluent. As used throughout the specification, the percentages are percentages by weight.

This new use of the ion exchanger results in excellent separated lactulose but also galactose from the reaction product mixture. Lactulose can be obtained at a purity level above 99%, which has hitherto been possible on an industrial scale only at immense costs.

As a final step of the process according to the invention and the modified process according to the invention, it is finally recommended for the production of powdered lactulose to add, preferably spray, a concentrated lactulose solution having at least 90% lactulose purity on dry weight basis to the lactulose powder to be moved, preferably mix, slowly to rapidly distribute the feed in the lactulose powder; the spray is fine so that the lactulose solution always forms only a thin film on the surface of a portion of the powder, thereby increasing the solid material on the powdered particles.

It is known that it is not possible to simply crystallize lactulose by concentration from an aqueous solution.

Methanol and other organic solvents are added in the manufacture of lactulose powder because lactulose has less solubility in these solvents and precipitates. The mechanically separated and dried powder is then always contaminated with solvent residues.

The process according to the invention, on the other hand, allows the production of free-flowing, only slightly hygroscopic lactulose powder of high purity.

In the process of the invention, the slow addition and immediate distribution and distribution of the lactulose syrup on the powder grains to form a thin film is critical. Only local buildup of syrup should be avoided. Moreover, the crystalline material no longer needs to be dissolved again into the syrup. For example, spray drying, paddle dryer and other hot air dryers having agitation mechanisms are suitable for this purpose.

-2GB 281653 B6

The above recommendations for the preparation of the borax solution by electrodialysis, for the removal of sodium ions from the solution of the products of weak acid ion exchange, for the separation of lactulose by the weakly basic ion exchanger as a chromatographic column and for the production of powdered lactulose are preferred. Used alone, it also brings some advantages.

The method according to the invention is illustrated by the following non-limiting example.

Examples

Example

It is heated to 95 DEG C. and 175 kg of lactose monohydrate, 46.3 kg of borax and 800 kg of demineralized water are maintained at this temperature for three hours. A mixture of reaction products is formed comprising essentially 74.2 kg of lactulose, 75.3 kg of lactose, 8.0 kg of galactose and 0.8 kg of tagatose. The resulting sugar mixture solution is passed through a weakly acidic ion exchanger and then stronger with an acidic ion exchanger so as to remove the sodium ions originating from the borax. The solution is then evaporated to a 15 wt. dry matter.

The solution having this concentration is passed through a chromatography column containing a weak basic ion exchange resin.

The column consists of a hollow cylinder having a diameter of approximately 90 cm and a height of 2 m, filled with 1000 liters of a weakly basic ion exchange resin. 1000 L of a solution of 40 to 60 ° C is introduced into a column which is pre-filled with water and subsequently filled with water at a flow rate of 1 to 2 bed volumes / hour.

Figure 1 shows the achieved distribution of the components of the solution (distribution of the mixture of sugars). It can be seen that it is possible to achieve with little loss of almost pure lactulose fraction free of other sugars. The sharp distribution of lactose and lactulose is particularly surprising. In Figure 1, c represents the concentration in g / 100 ml, f represents the fraction, L represents the lactulose fraction free of other sugars.

The obtained lactulose solution is freed from boric acid in a boron-specific ion exchanger and then evaporated to a content of 65% by weight. lactulose, for example under vacuum at 40,000 Pa. A marketable syrup is then obtained. However, the syrup may be converted into a powder.

For this purpose, for example, a steam heated paddle dryer (De Dietrich SP 200) with a total capacity of 200 liters, with a useful capacity of 130 liters, is used, the speed of the agitator being given by a speed of 10 rpm. 20 kg of powdered lactulose are introduced into the container and a total of 100 kg of syrup is heated to 60 ° C and introduced at a rate of 2 L / hour. The whole is then dried for 30 minutes. 20 kg of the obtained powder is then left as a sample for the next batch.

Instead of adding borax as described above, the following method may be used:

-3GB 281653 B6

Dissolve with stirring at approximately 45 ° C 175 kg of lactose monohydrate, 30 kg of boric acid and 600 kg of demineralized water and pass through the described weak acid ion exchanger, which is saturated with sodium ions. Elution is performed with demineralized water. The resulting solution, which regenerated the ion exchanger at least partially with boric acid and received sodium ions, is then adjusted to a pH of 8.3, i.e. the pH of the lactose-borax solution described above, with a sodium hydroxide solution.

The conversion then proceeds as with said solution.

PATENT CLAIMS

Claims (6)

The conversion then proceeds as with said solution. PATENT CLAIMS A process for the preparation of lactulose, comprising preparing an alkaline aqueous solution of lactose and borax, which is heated to a temperature above 80 ° C, and separating the resulting lactulose from the obtained conversion product, characterized in that the reaction is carried out at a natural pH of the solution borax under the conditions of the manufacturing process. Method according to claim 1, characterized in that the borax is formed in an aqueous boric acid solution, preferably already with lactose, wherein the sodium ions are transferred from the solution of the conversion products to the boric acid solution by electrodialysis. Method according to claim 1, characterized in that the sodium ions are removed from the solution of the conversion products first with a weakly acidic ion exchanger and then with a more acidic ion exchanger. The method of claim 3, wherein the weakly acidic ion exchanger is at least partially regenerated with boric acid, wherein the borax formed in said regeneration is at least partially used in the production of lactulose by the method of claim 1. Process according to any one of Claims 1 to 4, characterized in that, for the removal of lactulose, the solution of the reaction products after removal of the sodium ions, before removal of the borate ions, preferably after evaporation to a dry matter content of 15 to 20 wt. filled with a weakly basic ion exchange resin, preferably at a temperature of 30 to 60 ° C, using water as the eluent. Method according to any one of claims 1 to 5, characterized in that a concentrated lactulose solution having a lactulose content of at least 90% by weight, based on at least 90% by weight, is slowly added, preferably by spraying, to the production of powdered lactulose. to the dry matter, and disperses in the lactulose powder so quickly and gently that the lactulose solution forms at all times only a thin layer on the surface of the lactulose powder particles, thereby increasing the solid material on their surface.