CA2078345A1

CA2078345A1 - Process for enzymatic bleaching of celluloses

Info

Publication number: CA2078345A1
Application number: CA002078345A
Authority: CA
Inventors: Hans-Peter Call
Original assignee: Individual
Current assignee: Individual
Priority date: 1990-03-20
Filing date: 1991-03-19
Publication date: 1991-09-21
Also published as: FI924169A; HUT64119A; BR9106411A; NO180388B; FI924169A0; DE4008893C2; JPH05505857A; DE4008893A1; AU7543291A; DK0447673T3; AU641494B2; EP0447673B1; DE59008655D1; EP0447673A1; NO923601L; NO923601D0; ATE119593T1; NO180388C; ES2072965T3; HU9202982D0

Abstract

ABSTRACT

The present invention concerns a process for the enzy-matical bleaching of celluloses wherein a) a redox potential in the range between 200 and 500 mV is adjusted while metered addition of oxidants and reductives and addition of salts and complexing agents to an aqueous solution containing cellulose takes place simultaneously, b) a bleaching reaction is started by addition of lig-nolytical enzymes and c) the reaction is maintained for a period of 15 mi-nutes up to 12 hours during which time it is con-stantly stirred.

Description

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March 18, 1991 _ Dr. Hans-Peter Call Heinsberger Strasse 14a D-5132 Uebach-Palenberg A process ~or Enzymatic Bleaching of Celluloses The present invention concerns a process for enzymatic bleaching o celluloses.

The biological ~roc~sses for cellulose production known so far work with micro-organisms, especially fungi. From DE-PS 31 10 117, for example, there is known a process for ohtaining cellulose from wood or other plant fibre materials where the lignocellulose is decomposed with the aid of pocket rot fungi. However, the processes working with micro-organisms have considerable disadvan-tages. For example, it is still not possible to achieve decomposition and separation of the lignine from its accompanying polymers (cellulose) without simultaneous growth of the micro-organisms and without loss of cellu-lose. The simultaneous growth of the fungus causes long decomposition periods which can last up to several weeks.

Owing to the akove-described difficulties of using micro-organisms, the possibilities of using isolated enzyme systems have been examined during the last few years. Especially, the enzymes of the pocket rot fungus 20783~

Phanerochaete chrysosporium were researched and clarifi-cation obta ned in many details. For example, it is ~nown from "Biotechnology in the Pulp and Paper In-dustry, ~rd International Conference, Stockholm, 1986"
that the e~uilibrium of the reaction is on the polymeri-sate side during the decomposition o~ lignine, i.e. non-cell systems do not decompose lignine, but contribute to its polymerisation Since the discovery of the lignolytical enzymes of the pocket rot fungus Phanerochaete chrysosporium, a number of enzymatical processes for bleaching cellulose by means of living ~ungus systems or non-cell systems, too, have become known in literature. Also, a number of expe-riments were carried out to blea~h by means of haeme systems. All these systems re~uire reaction times of more than 12 hours. This means that all these systems require considerable time and are costly. The latter applies es~ecially to the pure heame systems.

Tod~y, bleaching is still carried out purely chemically in several stages by adding chlorine. However, chlorine bleaching causes considerable environmental problems. In the general bleaching processes, the kappa number, i.e.
the lîgnine content, is reduced by removing the chromo-phore residual lignine conden,ation products that occur during the koiling process fcr lignine removal, and the cellulose is thus lightened.

The Present invention now has the object of providing a process for the enzymatical bleaching of celluloses which no longer has the disadvantages of the biological and chemica] bleaching processes described above.

This object is solved by a~ adjusting a redox potential in the range between 200 and 500 mV while metered addi-207834~

tion of oxidants and reductives and the addition ofsalts and complexing agents to an aqueous solution con-taining cellulose takes 21ace simultaneously, b) start-ing a bleaching reaction by adding lignolytical enzymes, and c) maintaini~g the reaction for a period of 15 minu~es up to 12 hours during which time it is con-stantly stirred. This type of process prevents repoly-merisation of the lignine and makes possible depolyme--risation in the first place.
.

The redox potential is preferably in the range between 250 and 450 mV. In the process according to the inven-tion, it can be determined with the aid of a redox electrode and, by means of a control unit and an actua-tor, can be kept constant during the entire reaction time by adding o~idants and reductives, salts and pheno-lic compounds.

Hydrogen peroxide, oxygen and ozone are preferably used as oxidants. Suitab]e reductives are ascorbic acid, dithionite and sodium bisulphite.

The salt added to the aqueous solution containing cellu-lose is cupric sulphate. Mn(II)sulphate, Mn(III)acetate, Fe(II)sulphate, Ti(III)chloride, Ce(III)nitrate and Ce(IV)ammonium nitrate can addi-tionally be used as salts. Salts containing the elements of zinc, antimon and lead are also suitable.

Possibly, phenolic compounds can be added to the aqueous solution containing cellulose. Especially proven com-pounds of this type are veratryl alcohols.

Further, fatty acids such as oleic acids, haeme com-pounds such as haemoglobin and bleaching reagents such as sodium perborate can be added to the aqueous solution 207834~

containing cellulose. Moreover, an after-bleach can be ca~ried out wi-th conventional bleachirlg agents such as sodium hypochlorite, 2~ chlorine dioxide, ozone, H202 and sodium dithionite.

Further, it is pointed out that the addition of complex-ing agents ic very important for the success of the pro-cess according to the invention. Preferably, ethylene diamine tetraacetic acid (EDTA) or dieth~lene triamine pentaacetic acid (DTP~) are used as such complexing agents. As soon as the required redox potentiaI has been adjusted, the bleaching process sets in comparatively quickly. This process can already be completed after a few minutes, but in that case the kappa figure which, depending on the cellulose content, can be decreased up to 90 % after several hours is hardly reduced.

In addition to the above-mentioned substances, further substances can be added to the aqueous solution con-taining cellulose. These can be sodium hypochlorite, sodium perkorate, detergents, surface-active agents and polysaccharides such as glucanes and xanthane.

LignolyticaI enzymes are preferably used as enzymes in the process according to the invention. Among others, these are phenol oxidases, laccases and peroxidases~ The effectiveness of the process can be further increased by using pectinases and/or hemicullases. Especially sui~-able lignolytical enzymes are those obtained from the pocket rot fungus Phanerochaete chrysosporium. However, the use o~ such enzymes is already known from U.S.-PS 4 692 413, 4 69~ 895 and 4 687 741. However~ enzymes obtained from special mutants of Phanerochaete chryso-sporium are used Lor bleaching according to these print-ed patent spec~fications. This is not necessary in the process according to the invention. Rather, all lignoly-2V7~34~

tical enzymes known today can be used if the above-described prerequisites are complied with. The main difference can ke found in the function of the reduc-tives or oxidants added by metered addition as well as the mediators which capture the radicals. This is be-cause these substances prevent repolymerisation and therefore make possible the decomposition of lignine in the akove-described manner and quantity within the sti-pulated short period of time in the first place.

The p~ value is gerlerally between 2 and 5 in the process according to the inv~ntion. A pH value of 3 is prefer-red. The temperature is 20 to 60C, preferably 40C. If these conditions are complied with, a redox potential of 200 to 500 mV is adjusted when the above-mentioned sukstances are added. It is determined by the ratio of ~he different substances added to the reaction vessel.
It can be maintained during the entire reaction period, if the addition of oxidants and reductives, salts and pos$ibly phenolic compounds is monitored and controlled accordingly.

~ith the aid of the bleaching process described above, it was possible or the first time to bleach celluloses within a very short period of time (15 minutes to 2 hours), ak physiological temperatures (40C), without pressure and with a minimum of chemical sukstances added in a manner which is inexpensive and, especially impor-tant, does not affect the environment. Another advantage of the process according to the invention is the possi-bility of operating the process continuously.

The process according to the invention is illustrated by the following e~amples.

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50 a abs dry (atro) cellulose (sulphate cellulose) are stirred in a stirring vessel at 1 % consistency, approx.
500 rpm and 40C. The pH value is adjusted to pH 3 by means of 1 n HCL. 0.1 -1.5 % H2O2 based on abs.dry sub-stance, aoprox 2 ~ 10-5 % to 2 x 10-3 % veratryl alco-hol (VA), Q.l % EDTA or DTPA and 0.001 - 0.01 % cupric sulphate based on abs.dry substance are added. After 500 - 5,000 IU lignolytical en~ymes (1 IU = turnover of 1 nmol VA/min. to veratryl aldehyde) have been added, the bleaching process is started by simultaneous metered addition of H2O2 and sodium bisulphite solution. The redox potential of approx. 400 mV is maintained. Once the process has keen initiated, it is continued for 2 hours. Process control and adjustment is carried out by means of a redox electrode and a pump control.

Claims

1. A process for encymatical bleaching of celluloses characterised in that a) a redox potential in the range between 200 and 500 mV is adjusted while metered addition of oxidants and reductives and the addition of salts and com-plexing agents to an aqueous solution containing cellulose takes place simultaneously, b) a bleaching reaction is started by adding ligno-lytical enzymes and c) the reaction is maintained for a period of 15 minutes up to 12 hours during which time it is constantly stirred.

2. A process according to claim 1, characterised in that the redox potential is between 250 and 450 mV.

3. A process according to claim 1 or 2, characterised in thak H2O2,O2 or ozone are used as oxidant.

4. A process according to any of the claims 1 to 3, characterised in that ascorbic acid, dithionite or sodium bisulphite are used as reductive.

5. A process according to any of the claims 1 to 4, charac erised in that lignine peroxidases and lacca-ses are used as lignolytical enzymes.

6. A process according to any of the claims 1 to 5, characterised in that cupric sulphate is used as salt.

7. A process according to any of the claims 1 to 6, characterised in that Mn(II)sulphate, Mn(III)acetate, Fe(II)sulphate, Ti(III)chloride, Ce(III)nitrate and/
or Ce(IV)ammonium nitrate are used as salt in addition to cupric sulphate.

8. A process according to any of the claims 1 to 7, characterised in that phenolic compounds are additio-nally added to the aqueous solution containing cellu-lose for the purpose of adjusting the redox poten-tial.

9. A process according to claim 8, characterised in that veratryl alcohol is used as the phenolic compound.

10. A process according to any of the claims 1 to 9, characterised in that pectinases and/or hemicellu-lases are used in addition to the lignolytical en-zymes.

11. A process according to any of the claims 1 to 10, characterised in that the pH value is between 2 and 5.

12. A process according to any of the claims 1 to 11, characterised in that the pH value is 3.

13. A process according to any of the claims 1 to 12, characterised in that the temperature is between 20 and 60°C.

14. A process according to any of the claims 1 to 13, characterised in that the temperature is 40°C.

15. A process accordiny to any of the claims 1 to 14, characterised in that sodium hypochlorite is added to the reacting solution.

16. A process according to any of the claims 1 to 15, characterised in that ethylene diamine tetraacetic acid (EDTA) or diethylene triamine pentaacetic acid (DTPA) is used as complexing agent.

17. A process according to any of the claims 1 to 16, eharacterised in that polysaccharides are added to the aqueous solution eontaining cellulose.

18. A process aceording to claim 17, characterised in that the polysaccharides are glucanes and/or xanthane.

19. A process according to any of the claims 1 to 18, characterised in that detergents are added to the aqueous solution containing cellulose.

20. A process according to any of the claims 1 to l9, eharacterised in that surface-active agents are added to the aqueous solution containing cellulose.

21. A process according to any of the claims 1 to 20, characterised in that fatty acids are added to the aqueous solution containing cellulose.

22. A process according to any of the claims 1 to 21, characterised in that haeme compounds are added to the aqueous solution containing cellulose.

23. A process according to any of the claims 1 to 22, characterised in that bleaching reagents are additio-nally added to the aqueous solution containing cellu-lose.

24. A process according to claim 23, characterised in that sodium perborate is used as bleaching reagent.

25. A process according to any of the claims 1 to 24, characterised in that an extraction is carried out by means of NaOH and/or H2SO4 after the reaction is com-pleted.

26. A process according to any of the claims 1 to 25, characterised in that an after-bleach by means of usual bleaching agents is carried out.

27. A process according to claim 26, characterised in that sodium hypochlorite, chlorine, chlorine dioxide, O2, ozone, H2O2 and sodium dithionite are used for the after-bleach.