FI92490C - Method for the preparation of lactulose - Google Patents

Description

92490

Method for the preparation of lactulose

The invention relates to a process for the preparation of lactulose, which process comprises (a) preparing an aqueous solution containing lactose 5 and borax, (b) reacting said various components in a lamp room above 80 ° C and (c) separating lactulose from unreacted lactose and by-products.

The TSmS method is known: see, for example, Che-10 mical Abstracts 86: 173382h. Since an alkaline medium is required for the conversion, sodium hydroxide is added to the process. The yield of the process is relatively high: boric acid forms a complex with lactulose which shifts the equilibrium away from lactose. In addition, lactose forms galactose, tagatose, other sugars, organic acids and dyes as conversion products.

The invention relates to a new process for the production of lactulose which has a similar economy but is more ecologically advantageous.

According to the invention, this object is achieved by following the aforementioned method, so that in step (a), with the exception of borax, substantially no alkalizing agent is added to the solution.

The effluent load of alkali salts, which. Alkali salts are formed during the removal of alkali ions from ion exchangers during their regeneration, thus being significantly reduced.

A further step in the same direction is the process variants of the invention in which sodium ions are recycled according to two different embodiments.

In the first embodiment, boron is prepared in an aqueous solution of boric acid, preferably already at the same time as the lactose, by transferring sodium ions from the solution of the conversion product to the solution of the boron-35 acid by electrodialysis. In this way, complete recycling of sodium ions is possible.

2 92490 For this purpose, only two compartments separated by a cation exchange membrane are required. The second compartment is a cathode compartment and a boric acid solution, preferably a boric acid-lactulose solution, flows through it. A solution of conversion products flows through the second 5 compartments, the anode compartment. In the voltage used, the sodium ions move to the first compartment and form a borax solution there.

In another embodiment, the sodium ions are removed from the solution of the conversion products as completely as possible by a weakly acidic ion exchanger and only then using a more strongly acidic ion exchanger, whereby the weakly acidic ion exchanger is preferably at least partially regenerated by boronic acid and thus formed by boron.

That is, when the sodium ion concentration in the solution of the conversion products is so high that the weakly acidic ion exchanger binds myGs sodium ions, such an ion exchanger is used. The strongly acidic ion-20 exchanger is used only for complete separation of sodium ions from solution. When the weakly acidic ion exchanger is then preferably regenerated with boric acid, the sodium ions bound to the ion exchanger remain in the process cycle. Only the rest goes into the wastewater. However, myGs. In the case that the weakly acidic ion exchanger is not regenerated with boric acid, its use is preferred. In any case, it can be regenerated with a weaker acid, the use of which is more ecologically advantageous. For example, carbonic acid is suitable from an ecological point of view.

In one embodiment of the process according to the invention, it is further proposed to separate lactulose from the solution of reaction products after separation of sodium ions before or after separation of borate ions, preferably after evaporation of the solution after evaporation of the solution to 15-35 20% solids. the vessel was passed through, for example through a chromatography column, preferably at 30 to 60 ° C and using water as eluent.

With the new ion exchanger, TS-lactose, but still galactose, is very well separated from the mixture of reaction products. In this way, lactulose with a purity of more than 99% can be produced, which has hitherto been possible on an industrial scale only at a much higher cost.

Finally, as a final step in the process according to the invention and its extracts 10, it is proposed to prepare lactulose powder by preferably adding a concentrated lactulose solution containing at least 90% lactulose (calculated as dry matter) to a mobile, preferably mixed lactose. the lactulose solution and is distributed to the powder particles so rapidly and finely that the substance forms only a thin film on the surface of the powder particles, which increases the solids of the powder particles.

It is known that lactulose cannot be crystallized simply by concentrating the aqueous solution.

Up to the preparation of lactulose powder, the addition of methanol or another organic solvent in which lactulose is less soluble than in water and which precipitates lactulose has been used. Mechanically separated and dried. The 25 watt powder then always contains the solvent as an impurity.

Instead, the proposed new process can produce a free-flowing, only weakly hygroscopic lactulose powder of high purity.

Crucial in carrying out this method is that the lactulose syrup is added slowly and in such a way that it is distributed to the particles, forming a thin film. Local accumulation of myds syrup should be avoided. Above all, the redissolution of the already crystalline material in the syrup must be prevented. Suitable devices for this purpose are, for example, spray dryers, wing dryers and other hot air dryers with a mixing mechanism.

The above proposals for the preparation of a borax solution by electrodialysis, for the removal of sodium ions from a solution of conversion products by a weakly acidic ion exchanger, for the chromatographic separation of lactulose from a process containing Mybs can be used separately to achieve certain benefits.

Example 175 kg of lactose monohydrate, 46.3 kg of borax and 15,800 kg of deionized water are heated to 95 ° C and kept at this temperature for 3 hours. This gives a reaction product mixture which contains 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 to a weakly acidic ion exchanger and then to a strongly acidic ion exchanger to remove sodium ions from the borax. The solution is then evaporated to a dry matter content of 15%.

The concentrated solution is then passed weakly to a chromatography column containing 25 basic ion exchangers.

As such a column, a hollow cylinder having a diameter of about 90 cm and a height of 2 m and loaded with 1000 liters of weakly basic ion exchanger-30 resin is used. To the water-filled column of the front cover is added 1000 l of solution at 40-60 ° C, and then water is introduced into the column at a flow rate of 1-2 filling volumes / hour.

Figure 1 shows the separation of the solution component-35 pathway achieved. This shows that a nearly pure, sugar-free lactulose fraction is obtained only from the lactulose acid. The precise separation of lactose and lactulose is particularly surprising.

II

92490 5

The resulting lactulose solution is stripped of boric acid with a boron-specific ion exchanger and the solution is then evaporated to a lactulose content of 65%, for example under a vacuum of 40 mba. NS gives a marketable sii-5 rapeseed.

However, the syrup can be myds converted to a powder.

For the purpose of TShS, for example, a rotary vane dryer (De Dietrich SP 200) with a total capacity of 200 l, a working volume of 130 l and a mixing speed of 10 rpm is used. 20 kg of lactulose powder are placed in the sieve and a total of 100 kg of syrup heated to 60 [deg.] C. is passed through the sieve at a flow rate of 2 liters per hour. The whole mixture is then dried for 30 minutes. A 20 kg portion of the resulting powder is left in the next batch.

Instead of adding borax as described above, the following procedure can be used: 175 kg of lactose monohydrate, 30 kg of boric acid and 600 kg of deionized water are dissolved with stirring at about 45 ° C and the solution is passed to the weakly acidic sodium ion described above. ion exchange resin.

Elution is performed with deionized liquid. The resulting solution, which has at least partially regenerated the ion exchanger with boric acid and into which the sodium ions have been transferred, is brought to pH 8.3 with sodium hydroxide solution, i.e.

. 25 to the pH of the lactose-borax solution described above. The conversion is then carried out in the same way as with the solution described above.

Claims (7)

9249U A process for preparing lactulose, which process comprises (a) preparing an aqueous solution containing lactose and borax, (b) allowing said components to react at a temperature above 80 ° C, and (c) separating your lactulose from unreacted lactose and by-products, known in the art. that substantially no alkalizing agent other than borax is added to the aqueous solution in step (a). Process according to Claim 1, characterized in that the borax is prepared in an aqueous solution of boric acid, preferably already at the same time as the lactose, and the sodium ions are transferred by electrodialysis from a solution of the conversion products to the boric acid solution. Process according to Claim 1, characterized in that the sodium ions are removed from the solution of the conversion products substantially as completely as possible by means of a weakly acidic ion exchanger and only in the form of a strongly acidic ion exchanger. Process according to Claim 3, characterized in that the weakly acidic ion exchanger is regenerated at least in part with boric acid and that the tar is regenerated. The borax formed during the generation is used at least in part in the process according to claim 1. Process according to one of Claims 1 to 4, characterized in that, in order to separate lactulose, the solution of the reaction products is passed to a sodium ion separation fraction before borate ion separation, preferably to a solution containing 15 to 20% of dry matter, from weakly basic ionizers. through a long chromatography column, preferably at 30-60 ° C, using water as eluent. 92490 Process according to one of Claims 1 to 5, characterized in that a concentrated lactulose solution with a purity of 90%, calculated as dry matter, is added slowly, preferably by spraying, to the circulating solution of lactulose powder. preferably to a mixed lactulose powder, whereby it is applied to the powder so rapidly and finely that it always forms only a thin film on the surface of the powder particles from which the solid grows into the powder particles. Lactulose prepared by the methods of claims 1-6. 92490