A composition comprising xylan and a method for making a
Composition comprising xylan

Technical area

The invention relates to a method for producing a xylan-containing composition, in which an aqueous alkaline solution containing hemicelluloses, acid is added and a xylan-containing precipitate is precipitated from the resulting precipitation suspension.

State of the art

It is known that both in the production of pulp and in the alkalization of pulp in a viscose process, aqueous alkaline solutions arise as streams which are enriched with hemicelluloses.

Hemicelluloses are generally understood to mean polyoses made from pentoses and / or hexoses, such as xylose, arabinose, glucose, mannose or galactose. Hemicelluloses refer in particular to all polysaccharides except cellulose, which occur as a component of plant cell walls, the matrix of which consists of fibrillary, partially crystalline cellulose, as well as low molecular weight degradation products of cellulose, e.g. hydroxycarboxylic acids, which can be formed in the course of digestion processes. In contrast to cellulose, which is a non-branched homopolymer made from glucose, hemicelluloses are generally branched heteropolymers made from the above-mentioned pentoses and hexoses. Most of these have a homopolymer as the main chain to which branches from other sugars are bound and thus form an irregular macromolecule. Hemicelluloses also have significantly lower degrees of polymerization or chain lengths than cellulose. Such hemicelluloses can be, for example, xylans, mannans, galactans, or other pentosans or hexosans. Plant heteropolysaccharides with a D-xylose as the main repeating unit (monomer unit) are referred to as xylans.

A distinction between celluloses (α-fraction) and hemicelluloses (β- and g-fraction) is defined in the prior art by the solubility in 17.5% sodium hydroxide solution (WÜSTENBERG, Tanja. Cellulose and cellulose derivatives: Basics, Effects and applications. Hamburg: Behr's Verlag, 2013.). While ß- and g-hemicelluloses can be dissolved in 17.5% sodium hydroxide solution, α-cellulose is insoluble. During the subsequent neutralization, the ß-hemicelluloses then precipitate, while the g-hemicelluloses remain in solution.

From WO 2007/128025 A1 a method for producing a xylan-containing composition is known, in which an aqueous alkaline solution containing hemicelluloses is mixed with a dilute sulfuric acid, a pH value between 4 and 5 sets. The precipitate obtained after 6-8 h is then centrifuged, washed and dried. However, such processes suffer from a low chain length and size selectivity in the precipitation of the hemicelluloses, which leads to a reduced yield. In addition, the lengthy precipitation process results in reduced throughput and higher production costs.

Disclosure of the invention

It is therefore an object of the invention to improve a method of the type mentioned at the outset in such a way that a higher yield can be achieved with lower production costs.

The invention solves the problem in that acid is continuously added to the aqueous alkaline solution until the pH falls below 4 in the precipitation suspension and the temperature of the precipitation suspension does not fall below 40 ° C. during precipitation.

If acid is continuously added to the precipitation suspension until the pH value drops below 4 in the precipitation suspension, the yield and quality of the precipitate produced can be significantly improved. At pH values ​​below 4, very advantageous conditions can be created for complete precipitation of the hemicelluloses. In addition, if the temperature of the precipitation suspension during the precipitation does not fall below a precipitation temperature of at least 40 ° C., an optimal particle size distribution can also be ensured during the precipitation. In particular, by holding the

Precipitation suspension at an increased precipitation temperature, the average particle size can be enlarged, which enables better filterability of the precipitate. A production method of the type mentioned at the beginning with a higher yield and higher cost efficiency can thus be created.

In general, it is stated that the method according to the invention is independent of the composition of the pulp from which the aqueous alkaline solution was produced. If aqueous alkaline solutions from the production of beech wood pulp or the alkalization of beech wood pulp are used, a composition comprising xylan with high quality and purity can be created.

If the aqueous alkaline solution has a pH of at least 8, in particular of at least 11, it can be ensured that all hemicelluloses are present in dissolved form in the aqueous alkaline solution. This makes the solution easier to process, since undesired formation of precipitates in the aqueous solution can be reliably prevented. A particularly reliable process with an improved yield can thus be created.

The yield of the process can be further improved if the aqueous alkaline solution has between 5 g / l and 150 g / l, in particular between 30 g / l and 70 g / l, hemicelluloses. If the aqueous alkaline solution has such a hemicellulose content, a precipitate of higher quality can be created. In particular, the xylan content in the precipitate can be increased further by concentrating the hemicelluloses in the aqueous alkaline solution.

The process according to the invention can be further improved if the acid is continuously added to the aqueous alkaline solution with constant stirring. By slowly adding the acid, large jumps in the pH value can be avoided. Too great a local decrease in the pH value can lead to an undesired premature precipitation of the hemicelluloses, whereby the quality of the precipitate and in particular its particle size and molar mass distribution are negatively influenced. The slow addition with constant stirring can therefore enable a pH value that is homogeneous over the entire precipitation suspension and thus ensure a high quality of the precipitate. The acid added as a precipitant can preferably be a water-miscible organic or inorganic acid, for example sulfuric acid or acetic acid. Advantageously, acid is added to the aqueous alkaline solution until a precipitation suspension with a pH of less than 3 is obtained. In a particularly advantageous embodiment variant, acid is added to the aqueous alkaline solution until the pH value in the precipitation suspension falls below 2.5. The pH value of the precipitation suspension is decisive for the yield and quality of the precipitate produced, since complete precipitation of the desired ß-hemicelluloses, in particular the xylan, can only be guaranteed when the pH value falls below a certain level.

If the temperature of the precipitation suspension falls below the

If the precipitation does not reach a precipitation temperature of at least 50 ° C., the particle size distribution in the precipitate can be further optimized. It can be particularly advantageous if the precipitation temperature is at least 60.degree. C. and, in addition, the precipitation suspension does not exceed a temperature of 95.degree. C. during the precipitation. Because of the thixotropy of the precipitation suspension, the particle size and molar mass distribution of the precipitate are strongly influenced by the temperature during the precipitation. At low precipitation temperatures, very small hemicellulose particles with a low DP value (degree of polymerization) preferably precipitate, while at high precipitation temperatures it is predominantly hemicelluloses with a high DP value that precipitate. The desired properties of the precipitate in terms of particle size and molar mass can thus be controlled by a suitable choice of the precipitation temperature. In particular, a precipitate can be created that is particularly easy to filter from the supernatant, as a result of which the yield of the process can be further improved.

The method can be made more reliable if the aqueous alkaline solution is heated to at least the precipitation temperature before adding the acid. Alternatively, an aqueous alkaline solution which is already at a temperature higher than the precipitation temperature can also be fed in directly.

By heating the aqueous alkaline solution before adding the acid and thus before precipitation, temperature fluctuations can namely be avoided during precipitation and thus a particularly stable and reliable process can be created.

If the aqueous alkaline solution is also with a maximum heating rate of

50 ° C / h heated, large temperature jumps in the aqueous solution can be avoided during heating, which is further beneficial to the quality of the precipitate during precipitation. The reliability of the method can thus be further improved.

The method according to the invention can be particularly characterized in that at least 90% of the xylan-containing precipitate has a particle size greater than 5 μm after precipitation. If the particle size of the precipitate is more than 5 μm, a precipitate which can be separated particularly easily from the supernatant can be produced, whereby the yield of the process can be increased further.

If the xylan-containing precipitate is separated from the supernatant after precipitation, in particular by filtering, a particularly simple method for producing a xylan-containing composition can be provided. If the supernatant is also washed and / or dried, the quality of the process product can be further improved.

The inventive method is particularly suitable when the hemicellulosic aqueous alkaline solution is a waste liquor from a pulp or viscose production. In particular, the aqueous alkaline solution can be a press liquor which is obtained or obtained in a viscose process, for example in the alkalization of cellulose with sodium hydroxide solution to alkali cellulose and subsequent pressing of the alkalized cellulose. Such a press liquor typically contains 100-300 g / l sodium hydroxide solution and has a hemicelluloses content of between 5-150 g / l, based in each case on the total volume of the press liquor. Such a press liquor advantageously has from 150 to 250 g / l sodium hydroxide solution. In addition, the hemicelluloses content is advantageously between 30 and 70 g / l.

Another object of the invention is to provide a xylan-containing composition which is characterized by low contamination and high xylan content and thus, in particular, by a high level of tolerance in the human or animal body.

The invention solves the problem posed by a composition which, based on its dry substance, has at least 85% by weight of polysaccharides from ß-hemicelluloses containing xylan and the remainder contains ash, water and unavoidable impurities.

The composition according to the invention can also be distinguished if it has at least 80% by weight of xylan, based on its dry substance. If the composition, based on its dry substance, has at least 84% by weight of xylan or, in further advantageous embodiments of the invention, at least 88% by weight or 90% by weight of xylan, a particularly high-quality product with high compatibility and more versatile Application possibility can be created.

The composition can be further improved if, based on its dry substance, it has less than 10% by weight, in particular at most 8% by weight, of glucan and less than 1% by weight of other polysaccharides. Because of the particularly low glucan content, the composition can be particularly suitable for medical applications and can be highly tolerated in the human and / or animal body.

The composition according to the invention according to any one of claims 1 1 to 13 can be particularly suitable for use as a tablet excipient in medicaments. Because of their special swelling properties, xylans can be used as tablet disintegrants and the need for synthetic ones

Make pill disintegrants unnecessary. The production of pharmaceuticals can thus be further simplified, since the composition according to the invention can be pressed directly with the pharmacologically active substance to form tablets. In addition, xylans can cause a delayed release of pharmacologically effective compositions and thus enable the simple production of sustained-release preparations (for example for delayed release of active ingredients).

The composition according to the invention according to any one of claims 1 1 to 13 can also advantageously be used for the production of xylan sulfate. Sulphated xylans can be used as antivirals, anticancer agents, or anticoagulants, for example.

Brief description of the drawings

The embodiments of the invention are described below with reference to the drawings. Show it:

1 shows a schematic representation of an embodiment of the method according to the invention in a first method step,

FIG. 2 shows a schematic representation of the method from FIG. 1 in a further method step, and FIG

3 shows a schematic representation of the method from FIGS. 1 and 2 in a third method step.

Ways of Carrying Out the Invention

1 to 3, a method 100 for producing a is schematically

Composition 1 comprising xylan shown in various stages of the process. An aqueous alkaline solution 2, which contains hemicelluloses 3 and is obtained, for example, as waste liquor 201 in a cellulose or viscose production 200, serves as the starting material for method 100. Corresponding to the exemplary embodiment of the method shown in FIG. 1, the aqueous alkaline solution 2 is a waste liquor 201, which is obtained in an alkalization stage 203 during the alkalization of cellulose 204 with liquor 205 as part of a viscose process 200. For this purpose, the alkalized cellulose 206 is pressed out in a press 207 and the waste liquor 202 is obtained as press liquor 201, which is fed to the method 100 according to the invention as an aqueous alkaline solution 2.

As shown in FIG. 1, the aqueous alkaline solution 2 is fed to a container 10 via a first inlet 11 in a first process step from the viscose process. The container 10 also has a second inlet 12, via which acid 4 can be supplied. Before adding the acid 4, the aqueous alkaline solution 2 is heated to at least the precipitation temperature - which is at least 40 ° C in one embodiment variant, at least 50 ° C in another embodiment variant and at least 60 ° C in a further embodiment variant - heated during the Heating, a maximum heating rate of 50 ° C / h is not exceeded. In one embodiment, as shown in FIG. 1, the heating can take place via a heater 13 integrated in the container. In a further embodiment variant, the heater 13 can be connected upstream of the first inlet 11 and heat the aqueous alkaline solution 2 as it passes through. In a further exemplary embodiment, the aqueous alkaline solution 2 is supplied directly as an aqueous alkaline solution 2 from the viscose process 200 that has already been heated above the precipitation temperature. There is therefore no need for additional heating.

In a first exemplary embodiment, the aqueous alkaline solution 2 has a pH of at least 8, such as at least 9, such as at least 10, such as at least 11. In addition, in a first variant, the aqueous alkaline solution has between 5 and 150 g / l, such as between 10 and 120 g / l, such as between 20 and 100 g / l, such as between 30 and 70 g / l hemicelluloses.

The hemicelluloses 3 contained in the aqueous alkaline solution 2 can essentially be divided into β-hemicelluloses 31 and g-hemicelluloses 32, as described in the introductory part of the description. Before the acid 4 is added in the first process step, both ß- and g-hemicelluloses 31, 32 are present in dissolved form in the aqueous alkaline solution 2.

FIG. 2 shows the method 100 according to the invention in a second method step after the aqueous alkaline solution 2 has been fed to the container 10 and heated above the precipitation temperature. In this step, acid 4 is added to the aqueous alkaline solution 2 through the second inlet 12 to the container 10 until the pH value in the precipitation suspension 5 obtained therein falls below 4. In another embodiment variant, acid 4 is added to the alkaline solution 2 until a pH value of below 3, such as below 2.5, is reached in the resulting precipitation suspension 5. The acid 4 is continuously added to the aqueous alkaline solution 2 in the container 10 through the second inlet 12 with constant stirring in order to ensure a homogeneous distribution of the pH value in the precipitation suspension 5

to ensure. According to the embodiment shown in FIG.

Such an acid 4 can be, for example, acetic acid, sulfuric acid, silica or another water-soluble organic or inorganic acid. The acid 4 is added to the alkaline solution 2, as shown in FIGS. 1 to 3, in the container 10 in batches or in a discontinuous process. Alternatively, however, is in a further

Embodiment possible that the addition of acid 4 to the alkaline solution 2 takes place in a continuous process, but this was not shown in the figures.

During the entire precipitation and in particular also during the addition of the acid 4, the temperature of the precipitation suspension 5 is kept above a precipitation temperature of at least 40 ° C. in order to achieve an advantageous particle distribution in the precipitate 6 (see FIG. 3). In another embodiment, the precipitation temperature is at least 50 ° C, such as at least 60 ° C. However, the temperature of the precipitation suspension 5 should not exceed 95 ° C. in order to ensure the best possible yield. The acid 4 should therefore be fed in slowly and continuously in order to avoid excessive temperature increases which can be caused by the exothermic neutralization reaction between the aqueous alkaline solution 2 and the acid 4.

In Fig. 3, the inventive method 100 is in a third

Process step shown, wherein the xylan-containing precipitate 6 was precipitated from the precipitation suspension 5. The precipitation suspension 5 is separated into a supernatant 7, which is essentially free from β-hemicelluloses 31, and a precipitate 6, which essentially consists of β-hemicelluloses 31. The supernatant 7 also contains the g-hemicelluloses 32, which are not precipitated. In a first exemplary embodiment, at least 90% of the particles 8 in the precipitate 6 comprising xylan have a precipitate after precipitation

Particle size greater than 5 pm. In a further exemplary embodiment, at least 95% of the particles 8 have a particle size greater than 5 μm.

After precipitation, the precipitate 6 and the supernatant 7 can be fed to a filter 16 through an outlet 15 of the container 10 in order to separate the precipitate 6 from the supernatant 7. The membrane of the filter 16 is selected in such a way that the supernatant 7 and the g-hemicelluloses 32 contained therein can pass unhindered, while the precipitate 6 with the β-hemicelluloses 31 is reliably retained. In one embodiment variant, for example, a microfilter membrane with a pore size between 0.1 μm and 1 μm can be used.

The supernatant 7 passes through the filter as permeate 18 and can be used for further use as recovered alkalizing liquor 208 in a viscose or cellulose process 200. The recovered alkalizing liquor 208 can be used at least partially as liquor 205 for alkalizing pulp 204 in the alkalizing stage 203, thereby creating an extremely efficient and cost-effective viscose or cellulose process 200, which comprises the process 100 according to the invention.

The precipitate 6 leaves the filter 16 as retentate 17 and is then washed and dried as a filtered precipitate 8 via a conveying unit 19 and a washing and drying unit 20. In one embodiment, the filtered precipitate 8 is dried using a dryer 20 with indirect heating in order to avoid damage to the temperature-sensitive β-hemicelluloses 31. The washed and dried precipitate 9 can optionally also be comminuted, for example ground, in order to obtain a xylan-containing composition 1 with uniform properties. The entire batch 21 of the xylan-containing composition 1 is then subjected to an analytical quality control and a specification for the batch 21 is drawn up.

Examples

In the following Table 2, the specifications and analysis results of various batches of the xylan-containing composition according to the invention are shown as Examples B1 to B4. All of the compositions of Examples B1 to B4 were each produced in accordance with a method according to one of Claims 1 to 10. The aqueous alkaline solutions were the press liquors after the alkalization of beech wood pulp in a viscose process. The aqueous alkaline solutions were mixed with sulfuric acid or acetic acid to form the precipitation suspension, the precipitation taking place at a temperature between 60 ° C. and 80 ° C. and the pH of the precipitation suspension being below 3. The resulting precipitate was filtered off from the supernatant, and washed and dried.

To determine the specification (determination of the polyose content in the xylan-containing composition), anion exchange chromatography combined with pulsed amperometry was used. The method parameters used are listed in Table 1.

Table 1: Parameters for anion exchange chromatography

Guard column: Dionex CarboPac SA10 4 * 50 mm

Separation column: Dionex CarboPac SA10 4 * 250 mm

Eluent A: Deionized water

Eluent B: 350 mM sodium hydroxide solution (NaOH)

Pump seal wash: Deionized water

Flow rate: 1 ml / min

Injection volume: 10 ml

Post-column reagent: 350 mM sodium hydroxide solution (NaOH) - 0.8 ml / min

Detection: pulsed amperometry

The anion exchange chromatography is regularly calibrated using sample standards (for example glucose, xylose, mannose) in order to ensure a consistently high level of accuracy.

The contents given in Tables 2 and 3 relate to percentages by weight (% by weight) of the dry matter of the composition

(abbreviated:% TM). The dry matter content is given in percent by weight (% by weight) based on the total weight of the composition. In addition to the listed ß-hemicelluloses xylan, glucan, mannan, arabinan, rhamnan and galactan, further polyoses that are not explicitly mentioned can be contained, the sum of which does not exceed 0.1% DM.

Table 2: Specifications of Examples B1 to B4 according to the invention.

Xylan Glucan Mannan Arabinan Rhamnan Galactan Ash drym.

example

[% DM] [% DM] [% DM] [% DM] [% DM] [% DM] [% DM] [% by weight]

B1 86.3 3.1 0.0 0.0 0.0 0.0 10.6 95.1

B2 86.7 7.3 0.4 0.0 0.0 0.0 5.6 94.9

B3 86.2 7.3 0.4 0.0 0.0 0.0 6.1 94.8

B4 83.6 7.5 0.7 0.0 0.0 0.0 8.2 95.0

The compositions according to Examples B1 to B4 all show a xylan content of greater than 80% by weight based on the dry matter. In addition, the glucan content in all examples is below 10% by weight or below 8% by weight, based on the dry matter. In Examples B1 to B3 the xylan content is over 84% by weight of DM, or even over 86% by weight of DM. In example B1 the glucan content is below 6% by weight of DM or even below 4% by weight of DM. All examples B1 to B4 have a content of β-hemicelluloses of more than 85% by weight based on the dry matter.

Table 3 shows the specifications and analysis results of comparative examples C1 to C3 available on the market:

C1 is a beechwood composition comprising xylan available from Symrise Bioactives AG, acquired in July 2011.

C2 is also a composition comprising xylan made from beech wood available from RCMDT GmbH, Germany, acquired in October 2017.

C3 is another xylanic composition made from beech wood from Megazyme uc, Ireland, acquired in March 2018.

Table 3: Specifications of the comparative examples C1 to C3.

Xylan Glucan Mannan Arabinan Rhamnan Galactan Ash drym.

example

[% DM] [% DM] [% DM] [% DM] [% DM] [% DM] [% DM] [% by weight]

C1 72.3 2.3 0.0 0.4 0.6 0.8 23.6 90.3

C2 74.7 2.2 0.0 0.4 0.7 1.2 20.7 89.8

C3 79.8 1.4 0.1 0.4 0.5 1, 2 16.4 91, 1

The comparative examples C1 to C3 all show a xylan content of less than 80% by weight based on the dry matter. In addition, the total content of β-hemicelluloses in all comparative examples C1 to C3 is below 85% by weight of DM.

The xylan-containing compositions according to the invention of Examples B1 to B4 accordingly show, compared with the xylan-containing compositions available on the market, a greatly improved, high degree of purity, which can be particularly advantageous for medical applications.

Expectations

1. A method for producing a composition (1) containing xylan, in which acid (4) is added to an aqueous alkaline solution (2) containing hemicelluloses (3) and a precipitate containing xylan (5) is thereby obtained from the resulting precipitation suspension (5). 6) is precipitated, characterized in that acid (4) is continuously added to the aqueous alkaline solution (2) until the pH value drops below 4 in the precipitation suspension (5) and the temperature of the precipitation suspension (5) during the precipitation does not fall below a precipitation temperature, the precipitation temperature being at least 40.degree.

2. The method according to claim 1, characterized in that the aqueous alkaline solution (2) has a pH of at least 8, in particular of at least 11, before adding the acid (4).

3. The method according to any one of claims 1 or 2, characterized in that the aqueous alkaline solution (2) so long continuously with constant stirring

Acid (4), in particular an acid (4) selected from the group comprising water-miscible organic or inorganic acids, is added until the pH falls below 3, particularly preferably a pH of 2.5.

4. The method according to any one of claims 1 to 3, characterized in that the precipitation temperature is at least 50 ° C, in particular at least 60 ° C, and the

Temperature of the precipitation suspension (5) does not exceed 95 ° C during the precipitation.

5. The method according to any one of claims 1 to 4, characterized in that the aqueous alkaline solution (2) is heated to at least the precipitation temperature before adding the acid (4).

6. The method according to claim 5, characterized in that the aqueous alkaline solution (2) is heated at a maximum heating rate of 50 ° C / h.

7. The method according to any one of claims 1 to 6, characterized in that at least 90% of the xylan-containing precipitate (6) has a particle size of greater than 5 pm after precipitation.

8. The method according to any one of claims 1 to 7, characterized in that the xylan-containing precipitate (6) is separated from the supernatant (7) after precipitation, in particular by filtering, and in particular is washed and / or dried.

9. The method according to any one of claims 1 to 8, characterized in that the aqueous alkaline solution (2) is a press liquor (201), which in a viscose process (200), in particular in an alkalization stage (203) in the alkalization of pulp ( 204), is obtained.

10. Composition, in particular produced by a method (100) according to one of claims 1 to 9, which, based on its dry substance, has at least 85% by weight of polysaccharides from ß-hemicelluloses, containing xylan, and the remainder ashes, water and unavoidable impurities contains.

11. Composition according to claim 10, wherein the composition (1), based on its dry substance, has at least 80% by weight of xylan, in particular at least 84% by weight of xylan.

12. Composition according to claim 11, wherein the composition (1) based on its dry substance is less than 10 wt .-%, in particular at most 8

% By weight, glucan and less than 1% by weight of other polysaccharides.

13. Composition according to one of claims 10 to 12 for use as a tablet excipient, in particular for the delayed release of pharmacologically active compositions.

14. Use of a composition (1) according to any one of claims 10 to 12 for the production of xylan sulfate.

15. Pulp or viscose process, in which the pulp (204) in a

Alkalization stage (203) is alkalized with sodium hydroxide solution (205) and a press liquor (201) is separated from the alkalized cellulose (206) by pressing (207), which has hemicelluloses (3) in an aqueous alkaline solution (2), and from the Press liquor (201) in a method (100) according to one of claims 1 to 9, a xylan-containing composition (1) is produced, wherein the supernatant (7) after precipitation to the alkalization stage (203) for further alkalization of pulp (206) is returned.