A METHOD FOR MANUFACTURING MICROFIBRILLATED POLYSACCHARIDE

Abstract

The present invention relates to a method for manufacturing microfibrillated polysaccharide, preferably microfibrillated cellulose. The invention also relates to microfibrillated cellulose obtainable by the method and use of the microfibrillated cellulose. The method of manufacturing microfibrillated cellulose comprises the following steps: a) Providing a hemicellulose containing pulp, b) Providing wood degrading enzymes c) Mixing pulp and enzymes d) Keeping the mixture in a continuous, flowing system of essentially cylindrical geometry (for example in a plug-flow reactor), e) Conveying the mixture to one or more mixing zones for recirculating and homogenizing the mixture, and f) Harvesting microfibrillated cellulose with a relatively narrow size distribution during the recirculation.

Claims

1. Method for manufacturing a microfibrillated polysaccharide, comprising the following steps: a) providing a hemicellulose containing pulp, b) providing one or more wood degrading enzymes, c) mixing said pulp with one or more wood degrading enzymes, d) keeping said mixture in a continuous, flowing system of essentially cylindrical geometry, e) conveying said mixture to one or more mixing zones for recirculating and homogenizing said mixture, and f) harvesting during the recirculation of said step e) microfibrillated polysaccharide.

2. A method according to claim 1 wherein the microfibrillated polysaccharide obtained in step f) has a relatively narrow size distribution, wherein the distribution resembles a Gaussian curve.

3. A method according to claim 2 wherein the Gaussian curve has its endpoints of the size classes at about 8 to about 100-200 μm at a volume density of about 0.5%, or has its endpoints of the size classes at about from 9 to about from 150-175 μm at a volume density of about 1.0%, or has its endpoints of the size classes at about from 15-20 to 100 μm at a volume density of about 4.0%, or a combination of two of said features or all three, wherein preferably size classes at about 30-40 μm provides a peak for the volume density.

4. A method according to claim 1 wherein the homogenization pressure is about 500 bars or higher.

5. A method according to claim 1 wherein the pressure in one or more of steps d), e) or f) is kept from about 2 to about 6 bars.

6. A method according to claim 1 wherein the continuous, flowing system of essentially cylindrical geometry is a plug flow reactor.

7. A method according to claim 1 wherein the re-circulation of the mixture in step e) is performed at least 5 times before harvesting the microfibrillated polysaccharide.

8. A method according to claim 1 wherein the re-circulation of the mixture in step e) is performed using at least two conveying means.

9. A method according to claim 1 wherein the mixture in the plug flow reactor is kept during from 1 to 5 hours.

10. A method according to claim 1 wherein said enzyme is used at a concentration of from 0.1 to 500 ECU/g fibres.

11. A method according to claim 1 wherein said enzyme is a hemicellulase or a cellulase or a mixture thereof.

12. A method according to claim 1 wherein said enzyme is a cellulase.

13. A method according to claim 1 wherein said pulp is a sulphite pulp.

14. A microfibrillated polysaccharide, obtainable by a method according to claim 1.

15. (canceled)

16. A method according to claim 1, wherein said microfibrillated polysaccharide is a microfibrillated cellulose.

17. A method according to claim 1, wherein the pulp is a chemical pulp.

18. A method according to claim 2, wherein said curve has its endpoints of the size classes at about from 1 to 5 to about from 100 to 300 μm, respectively, whereas at the same time the volume density is from about 9.0 to about 10% at the top of said curve.

19. A method according to claim 2, wherein the Gaussian curve has its endpoints of the size classes at about from 3 to 5 to about from 200 to 300 μm.

20. A method according to claim 1, wherein the homogenization pressure is about 700 to about 1000 bars.

21. A method according to claim 1, wherein the pressure in one or more of steps d), e) or f) is kept from about 3 to about 5 bars

22. A method according to claim 21, wherein the pressure in said range is applied during step d).

23. A method according to claim 1, wherein the mixture in the plug flow reactor is kept during 2 to 4 hours, at a temperature from about 50° C. to about 70° C.

24. A method according to claim 1, wherein said enzyme is used at a concentration of from 0.5 to 250 ECU/g fibres.

25. A method according to claim 1, wherein said enzyme is used at a concentration of from 5 to 150 ECU/g fibres.

26. A method according to claim 1, wherein said enzyme is used at a concentration of from 50 to 150 ECU/g fibres.

27. A method according to claim 1, wherein said enzyme is a cellulase of endoglucanase type.

28. A method according to claim 1, wherein said enzyme is a mono-component endoglucanase.

29. A method according to claim 1, wherein said pulp is a pulp from softwood.

30. A microfibrillated cellulose, obtainable by the process of claim 1.

Description

FIGURES

[0033] FIG. 1 discloses a set-up for using the method according to the first aspect whereby a plug flow reactor has been introduced combining the separate batch wise enzyme treatment with the recirculation vessel into a continuous process. FIG. 1. gives an overview of the process setup according to the first aspect. By introduction of a plug flow reactor the separate vessel for batch wise enzyme treatment can be omitted and the enzyme treatment can be run in a continuous mode (e−treated=enzyme treated).

[0034] FIG. 2 discloses a further setup for the method according to the first aspect. FIG. 2. shows a further preferred embodiment of the general process schematic of the refinerless MFC process setup according to the first aspect.

[0035] FIG. 3 discloses MFC made using the method according to the first aspect.

[0036] FIG. 4 discloses the size distribution of MFC made using the method according to the first aspect. The black curve (red curve) shows the size distribution by laser diffraction of the MFC produced with the refinerless process according to the first aspect of the present invention whereas the grey curve (green curve) shows MFC produced at a plant batch as comparison.

EXAMPLE

[0037] The method according to the first aspect had only two steps; pulp at 5% or higher solids is mixed with enzyme (ECOPULP® 892—4816, AB Enzymes—previously known as ECOPULP®—R) diluted in water so the final solids of pulp is 4%. Both the pulp and the enzyme solution were kept at 60° C. before mixing. This temperature was then kept for 3 hours without further mixing. The pre-treated material was then homogenized at 700 bars in recirculation mode which increases the temperature to 90° C. thus killing the enzyme and potential microbes. If the temperature reached over 90° C. the material was cooled to avoid boiling. The recirculation vessel would be pressurized and the temperature further increased so steam can be flashed off for energy recovery.

[0038] Viscous MFC, (see FIG. 3), was produced which indicates a high aspect ratio material and the particle size analysis by laser diffractometry indicated a particle size distribution comparable with refiner based pre-treatment process, see FIG. 4. The simplified process solution, thus the process according to the first aspect of the present invention, is easier to clean and to start up and it is also easier to maintain sterilization temperatures in the homogenization stage.

[0039] Compared to refiner based pre-treatment the time for evaluation of MFC starting materials and enzymes is greatly reduced. This is also due to the reduced recirculation volume in this design that reduces the start-up sequence time essentially.

[0040] To summarize a simplified process for the manufacture of MFC was developed and implemented in large lab scale as well as in industrial scale. The simplified solution has beside the homogenizer only two vessels one for the enzyme treatment and one for feeding, recirculation and mixing. The refining section is completely omitted. Enzyme is denatured (inactivated) by the temperature increase to 90° C. during the homogenization step. High or low pH is also possible to use.

[0041] The process equipment is easy to clean and the temperature increase ensures microbial purity of the product.

[0042] Scalability is judged to be improved compared with the current process solution due the simplification and so is the ability to keep the process at high hygienic standard.

[0043] In view of the above detailed description of the present invention, other modifications and variations will become apparent to those skilled in the art. However, it should be apparent that such other modifications and variations may be effected without departing from the spirit and scope of the invention.