CA2076679A1

CA2076679A1 - Method of pulp bleaching

Info

Publication number: CA2076679A1
Application number: CA002076679A
Authority: CA
Inventors: Tomoaki Nishida; Yoshinori Kashino; Yoshimasa Takahara; Kokki Sakai; Ryuichiro Kondo
Original assignee: Individual
Current assignee: Kobe Steel Ltd
Priority date: 1991-01-21
Filing date: 1992-01-16
Publication date: 1992-07-22
Also published as: WO1992013131A1; JPH04240287A; AU647891B2; SE9202592D0; FI923798A; AU1168892A; FI923798A0; SE9202592L

Abstract

ABSTRACT
Disclosed is a method of pulp bleaching by combination of microbial treatment and chlorine-free chemical treatment.
Where no chlorine-based chemical is used in the method of the present invention, pulp can be bleached with a high efficiency, completely preventing generation of dioxin or the like.

Description

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SPECIFICATION
Title of the Invention METHOD OF PU~P BLEACHING
Field of the Invention The present invention relates to bleachimg of pulp of wood resources. More precisely, it relates to a method of pulp bleaching, which comprises combination of treatment with microorganism having a high lignin-degrading activity and a low fiber-degrading activity, with the culture of such microorganism or with the processed product -thereof to degrade lignin in -the pulp and -treatment with chlorine-free chemical.
In accordance with the present invention, since pulp may be bleached in the ab~ence of chlorine-based chemicals and/or in the presence of a noticeably reduced amount oE
them, generation of environment polluting substances such as dioxin and chlorinated phenols from chlorine-based chemicals can completely be prevented and/or can noticeably be reduced. Thus, the present invention is important in the point that it can bleach pulp without environmental pollution.
Prior Arts and Problems Unbleached chemical and semi-chemical pulps to be obtained after digestion of a raw material wood chip s-till con-tain a strongly colored-lignin. Therefore, for use of them in preparing high quality paper or the like needing a high-brightness, bleaching is necessary for removing the remaining lignin from them so as to impart the brightening thereto.

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The mainstream of the current bleaching technology in this technical field is a multi-stage chlorine-based bleaching process comprising -treatment with chlorine (C) - alkali (El) -sodium hypochlorite (H) - alkali (E2) - chlorine dioxide (D). In accordance with the process, however, since the bleachin~
waste liquor from the process contains much chlorine to cause corrosion of metals, concentration and combustion in the chemical recovering step for digestion and re-cycle and re-use in the bleaching step are difficult. Because of the reasons, the bleaching waste liquor is, after having been treated by an activated sludge process or coagulation and sedimen-tation process, taken out from the system. However, since the processedwaste liquor contains carcinogenic dioxin and chlorina-ted phenols, prevention of environmental pollution by chlorine-based chemicals is now an important theme ~C. Rappe, S.
Swan~on, B. Glas, K.P. Kringstad, F. De Sousa, L. Johansson and Z. Age; Pulp and Paper Canada, 90, T273 ~1989)~.
From the viewpoint, a bleaching method with chlorine-free chemical~ has become marked, and bleaching by treatment with oxygen and alkali ~oxygen bleaching) is now being put to practical use. Oxygen bleaching is such that sodium hydroxide is added to an unbleached pulp and the pulp is treated with oxygen under the condition of an oxygen pres~ure of from 5 to 10 kg/cm2 and a temperature of from 110 to 140C
for delignification. Using this, substitution of a part of the chlorine tC) treating stage in the multi-stage chlorine-based bleaching process by oxygen bleaching is possible, whereby pollution with chlorine-based chemicals, can be ~' - 3 - 7~6~7,~

reduced in the process (I. Cxoon and D. H. .Andrews; TaPPl, 54, 1983 (1971)).
Problems to be Solved bY the Invention ~ owever, since it is impossible to obtain a full-bleached pulp having a brigh-tness of about 85 % by only oxygen bleaching, it is the current ~itual:ion that the stages after the oxygen bleaching stage are obliged to u~e a large amount of chlorine-based chemicals still in the same manner as in the conventional means. As a matter of course, the bleaching waste liquors after oxygen bleaching stage contain environmental polluting substances such as dioxin. Therefore, if chlorine-free chemical3 are not used .in the stages after oxygen bleaching and/or if use of chlorine- based chemicals in them is not reduced drastically, it would be impossible to completely prevent and/or noticeably reduce generation of environmental polluting substances in the process of pulp bleaching.
From the points, the present inventors have already tried to use hydrogen peroxide, which is a chlorine-free chemical, in the stages a~ter oxygen bleaching to bleach pulp so as to completely prevent generation of environmental polluting substances. However, where a ~ull-bleached pulp having a brigntness of about % is desired to be obtained by the process of using hydrogen peroxide, the yield of the bleached pulp and the viscosity of it noticeably lower due to degradation of cellulose. ~ Therefore, the process has not been put to practical use (T. Nishida, K. Sakai ~ T. Kondo; Japan TAPPI Journal, 28, 564 (1974)).

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~ 4 ~ ~ ~& ~7 Means for Solvinq the Problems The present invention has been made in ~onsidexation of the current technical level that production of a full-bleached pulp by selective degrada-tion and removal of lignin with repressing degradation of cellulose in an un-bleached pulp is impossible by oxygen/alkali treatment and by combination of oxygen/alkali treatment and hydrogen peroxide treatment. After investigation from variou~ physical, chemical and biological aspects, the present inventors knew that the conventional physical and chemical treatments are limited so that they have noted biological treatment, especially with microorganisms, in pulp bleaching.
However, even after various trials of treatment with microorganisms in pulp bleaching, they could not attain the intended object and they were obliged to drastically convert their ideas. Under the situation, they tried to combine other treatments along with screening of microorganisms capable of being used in them and, as a result, they have noted combination of microorganisms haviny excellent selective li~nin-degrading activity and chlorine-free chemicals for delignification of an unbleached pulp. Af-ter all, they have attained the intended object due to such combination.
As microorganisms for use in the present invention, all microorganisms having a high lignin- degrading activity and having a low fiber-degrading activity, or that is, those capable of selectively and highly degrade lignin can be used singly or in combination of plural kinds of them.

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As examples of such microorganisms, those belonging to the following genera are referred to: Coriolus ~e.g., Coriolus versicolor IFO 30340), Phanerochaete (e.g., Phanerochaete chrYsosporium ATCC 34541), Trametes (e.g., Trametes dickin~ii IFO 648B), Polyporus te.g. r Polyporus mikadoi IFO 6517), Stereum (e.g. r Stereum frustulosu IFO 4932), Ganoderma (e.g., Ganoderma applanatum IFO 6499), Len~ites (e.g., Lenzites betulina IFO 8714), Fomes ~e79,. Fome~ fomentarius IFO
30371), Lentinus (e.g., Lentinus edodes IFO 31336), strePtomyces te.g., StrePtomvces vir_dosPorus IFO 13353, S.
badiu~ IFO 12745, S. etonii IFO 13085), etc.
In the present inven~ion, the above-mentioned microorganisms may be used suitably. Above all, as microorganism having an e~pecially excellent and selective lignin-degrading activity, which is especially preferably used in -the present inven-tion, NK-1148 strain is referred to.

NK-1148 strain has the following microbial properties.

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~1) State of Growth in Various ~edia:
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Culture Medium Sta-te of Grow-th _~_ Malt Extract ~gar Medium ~++

Potato-Glucose Agar Medium ~+

Czapek'~ Agar Medium +

Sabouraud's Agar Medium Synthesized Mucor Agar Medium +~

YpSs Agar Medium +++

Glucose-Dried Yeast Agar Medium +++ ;.
~_, Note-l, Culture Medium pH: ~.0 (before autoclave s-terilization) Note-2, Culture Condition~ 28C x 7 days Note-3, State of Growth:
Weak: ~
Medium: ~t Abundant: ~++
(2) Physiological and Morphological Properties:
~ pH range for growth (cultivation in potato-glucose agar medium, 28C, 4 days):
Grows at a p~ of abou-t 3-9, and not grow a-t pH 2 and 10. 11he op-timum pH range for the growth is approximately from 4 to 6.
~ emperature range for growth (cultivation in potato-glucose agar medium, pH 5, 4 days):

Grows at a temperature of abou-t 10-45C, and not grow at 50C. The optimum temperature range for the growth i5 approximately from 28 to 37C.

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Phenol oxidase reaction (cultivation at 28C, 4 days):
Shows weak or nega-tive.
@3 Morphology of colony (cultivation in potato-glucose agar medium, pH 5, 28C, 4 day~):
White and fel-t-like.
NK-1148 strain was identified not only -to be superior in lignin-degrading activity than fungi of the genera Coriolu~ and Phanerochaete, which have heretofore been espe-cially well-known as lignin-degrading fungi, but also to have an especially excellent selectivity of the lignin degradation. The pre~ent inventors admitted that the strain is novel and named it NK-1148. The ~train was deposited in Fermentation Research Institute, Agency of Indus-trial Science and Technology (Japan) as FERM BP-1859.
For degradation of lignin with microorganism, lignin-degrading microorganism, -the culture of the microorganism, or the processed product thereof is added to a medium con-taining pulp and -treated at a temperature of 20 to 40OC for a determined period of time. ~here lignin-degrading microorganism is used, water and a suspension of the microorganism are added to pulp and aerobical incubation is carried out for a determined period of time under the condition of a pulp consistency of approximately from 0.5 to 30 %. In place of water, a liquid medium containing glucose and other nutrient sources may also be used with no problem.
The culture of lignin-degrading fungus widely means a mix-ture comprising the mycelia of the fungus and mediuml obtained by culturing. Further, in the present invention, the ~ 8 - 2~7~7~

mycelia separa-ted from the cul-ture and the residue obtained by said separa-tion, as well as the cul-ture broth from which all solids have been removed, may be used. The processed produc-t means any produc-t obtained by concentrating, drying or diluting each material above~mentioned.
In the present invention, the microbial -treatment and the treatment with chlorine-free chemical may be suitably combined, and the order and the frequency of these treatments are not specifically de~ined. If desired, the process of the present invention may further be combined with light chlorine-based chemical treatment.
The treatment with chlorine-free chemical to be e~fected in the present invention includes all treatment3 with chlorine-free chemical~s) which are known in the current paper pulp industrial field. A3 unlimited example~ of them, there are mentioned oxygen/alkali treatment, treatment with peroxide type chemicals (e.g., hydrogen peroxide, sodium peroxide, sodium percarbonate), treatment with peracid type chemicals ~e.g., peracetic acid, performic acid, perbenzoic acid, permanganates, persulfates), ozone treatment and/or alkali treatment. As the conditions for such treatments, various conditions which are employed in the curren~ paper pulp industry may well be used.
The treatment with chlorine-based chemical which may optionally be combined with the process of the present invention includes all treatments with chlorine- based chemical(s) which are known in the current paper pulp industrial field. For example, there are mentioned chlorine , , ~ .
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treatment, chlorine dioxide treatment and/or hypochlorite treatment. As the conditions for such treatments, various conditions which are employed in the current paper pulp industry may well be used.
As the unbleached pulp to be bleached by the method of the present invention, usable are unbleached chemical pulps and/or semi-chemical pulps of broadlea~ trees and/or coniferous trees as prepared by conventional di~estion-method, such as kraft, soda or sulfite pulp.
Next, examples of the present invention are mentioned below.
EXAMPLE 1:
An unbleached kraft pulp made of beech was subjected to oxygen/alkali treatment (NaOH amount added: 2 %
to pulp, pulp consis-tency~ 20 %~ oxygen pressure: 5 kg/cm3, treating temperature: 100Cr treating time: 30 minutes, MgCO3 amou1lt added: 0.5 % to pulp) and then washed with water.
250 ml of water was added to 100 9 (as absolute dry weight) of the oxygen/alkali treated pulp ( brightness: 47.8 %, Kappa number: 11.4) and was sterilized at 120C for 15 minutes. Then, a mycelial suspension of NK-1148 strain (FERM
BP-1859) was added thereto and the pulp consistency in the resulting blend was made to be 20 ~. Under t~le cond;tion, incubation was carried out at 28C for 3 days and the cul-ture was then washed with water.
Next, the NK-1148 strain treated pulp ( brightnesso 70.0 ~, Kappa number: 5.4) was treated with hydrogen peroxide (H2O2 amount added: 2 to 4 % to pulp, NaOH amount added: 0.5 to 4 % to pulp, pulp consistency: 10 %, -trea-ting :`

lo- 2~7~679 temperature: 60C, treating time: 2 hours) and then washed with water. The brigntness (JIS P8123-1961) of the thus treated pulp and the bleachad pulp yield were measured.
As control, the oxygen/alkali treated pulp was directly treated with hydrogen peroxide (H2O2 amount added: 2 to 6 % to pulp, NaOH amount added: 0.5 to 3 % to pulp, pulp consis-tency : 10 %, treating temperature: 60~C, treating time: 2 hours), without treatment with NK-1148 strain.

The results obtained are ~hown in Table 1 below.

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Table 1 - Bleaching Sequence and Pulp Properties . . _ . . . . . ... . . ~- _ Amou:nts of Chemicals added in P stage (%, to pu1p ) - Bleaching ~equence H202 NaOH
.. . , , ~ ~__ Embodiment O-F-P 2.0 0.~
of the . 2.0 2.0 Invention 4.0 2.0 4.0 4.0 Control O-P 2.0 0.~

3.0 1.0 4.Q 2.0 6.0 3.0 ~ .,,.,. ~

Table 1 - continued Brigh-tness (%) Bleached Pulp Yield (%, to . . afterheatunbleached pulp) after alr drledtreated 33mbodiment 84.3 80.6 94O3 of the 84.5 81.7 94.1 invention 85.7 81.2 94.0 86.5 81.7 93.7 Control 72.4 - 93.4 73.3 91.8 : 74.4 - 90.3 7~ 7.4 _ ~ Note~:
;;( O : Oxygen/alkali treatment, F : NK-1148 strain treatment P : Hydrogen peroxide treatment .
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As is obvious from the results a~ mentioned above, the following matters were confirmed. Precisely, in accordance with the process of the present invlention comprising combination of the microbial treatment ancl the chlorine-free chemical treatment, a ~ull-bleached pulp can be obtained easily with a high yield. As opposed to this, however, by only the chlorine-free chemical treatment in the control case, it was difficult to obtain a full-bleached pulp having a brightness of about 85 ~ eventhough a large amount of hydrogen peroxide was used. In addition, decrease of -the bleached pulp yield due to brightening of pulp was noticeable in the control case, as opposed -to the embodimen-t of the presen-t invention.
EXAMPLE 2:
A washed NK-1148 Ytrain treated pulp was prepared in the same manner as in Example 1. Thi~ was further treated with NaOH ~NaOH amount added: 1.5 % to pulp, pulp consistency:
10 %~ treating temperature: 70C, treating time: 40 minutes).
After washed with waterl it was treated with hydrogen peroxide (H~O2 amount added: 1, 2 or 4 % to pulp, NaOH amount added: 0.3, 0.5 or 2.0 % to pulp, pulp consis-tency: lO ~, treating temperature: 60C, treating time: 2 hour~). The ~amples thus treated were compared with those of Example 1 which were not treated with NaOH after the NK-1148 strain treatment, with respect to the brightness of the bleached pulp and the bleached pulp yield.
The results obtained are shown in Table 2 below.

~~ - 13 - 2~7~679 Table 2 - Comparison of Bleaching Sequence~
':
___ Amount of Chemicals Added ('ro, to pulp) Bleaching P stag~
Sequence E stage NaOH H202 NaOH

O-F-E-P 1.6 1.0 0.3 1.5 2.0 0.5 1.~ 'L.0 2.0 O-F-P 0 2.0 0.5 0 2.0 2.0 0 4.0 2.0 0 4.0 4.0 ~

Table 2 -continued __ _ _ _. ~
Brightness (~0) Bleached Pulp Yield (%, to unb~eached after air driedafter heat treated pulp ) . . .
84.2 80.7 94.3 85.8 ~1.6 33.9 872 ~3.1 93.7 __ 84.3 80.6 94.3 84.S ~1.7 94.1 8~.7 81.~ 94.0 86.5 81.7 93.7 ~ _~

Notes:
O : Oxygen/alkali treatment, F : NK-1148 strain treatment E : Sodium hydroxide treatment, P ; Hydrogen peroxide treatment ~ - 14 ~ ~7~7~

As is obvious from the results as men-tioned above, the following ma-tters were confirmed. Precisely, by effec-ting -the sodium hydroxide treatment, lignin decomposed to low-molecule or modified lignin was removed from the NK-1148 strain treated pulp so that the lignin content as remained in the treated pulp decreased. Therefore, in the case as combined with the NaOH
treatment, the amount of hydrogen peroxide necessary for obtaining the brightness of the same level was smaller than that in the case not combined with the NaOH treatment.
EXAMPLE 3:
A washed NK-1148 strain treated pulp was prepared in the same manner as in Example 1. This was further treated with NaOH (NaOH amount added: 1.5 % to pulp, pulp consis-tency:
10 %, treating temperature: 70C, treating time: 40 minutes).
After washed with water, it was treated with chlorine dioxide (amount added: 0.3 ~ to pulp~ pulp consis-tency: 10 %~
treating temperature: 70C, treating time: 2 hours) and then again washed with water. The brightness of the thus bleached pulp and the bleached pulp yield were measured.
As control, the oxygen/alkali treated pulp was directly treated by treating sequence of chlorine-NaOH-chlorine dioxide (for chlorine treatment, amount added: 2~1 ~ to pulp, pulp consis-tency: 4 ~0, treating temperature: room temperature, treating time: 40 minutes; for NaOH treatment~
amount added: 1.2 % to pulp, pulp consistency: 10 %~
treating temperature 70C, treating times 40 minutes; for chlorine dioxide treatment, amount added: 0.6 % to pulp, pulp consis-tency: 10 %, treating temperature: 70C, treating time: 2 hours), without being treated with NK-1148 strain.

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The results obtained are shown in Table 3 below.

Table 3 - Comparison of Bleaching Sequences , Total Ef~ective Chlon~e A~unt Bleachlng Sequence (%, to pulp) .. . .~
O-F-E-D (embodiment of the 0.79 invention 3 5~ _ Table 3 ~ continued Brightness (%) Bleached Pulp Yield (%, to . . af~er hea~ unbleached pulp) after alr drled treated 8~.9 81.5 94.
_ , __ _ Notes:
O : Oxygen/alkali treatment F t NK-1148 strain treatment E : Sodium hydroxidé treatment C : Chlorine treatment D : Chlorine dioxide treatment As is obvious from the results as mentioned above, the following matters were confirmed. Precisely, in the control case of not having the microbial treatment, large amounts of chlorine- based chemicals must be used for obtaining a ~ull~bleached pulp. AB opposed to thi~, in accordance . . .

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with the embodiment of the present invention comprising combination o~ the microbial treatment, the chlorine-free chemical treatment and additionally the chlorine-based chemical treatment, a full-bleached pulp could be obtained easily even when a remarkably small amount of ~he chlorine-based chemical was used. In the case of the present invention, 78.5 %
reduction o~ the e~ective chlorine amount was possible, as compared with the control case.
Advantaqe of the Invention:
In accordance with the present invention, ~ince pulp can be bleached without use of chlorine- based chemicals and/or with use of a noticeably reduced amount of chlorine-based chemicals, generation of substances causing environmental pollution, such as dioxin, can completely be prevented and/or can noticeably be reduced. Therefore, effective bleaching of pulp is possible by the present invention without causing environmental pollution.

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Reference to Microorganism as Deposited under Rule 13.2:
1. NK-1148 a. Name and address of the organization in which the microorganism was deposited.

Name~ Fermentation Research Institute, Agency of Industrial Science and Technology, Ministry of In-ternational Trade and Industry Address: 1-3, Higashi l~chome, Tsukuba-shi, Ibaraki-ken 30~, Japan b. Date of deposition of the microorganism in the organization of a.
May 23, 1987 c. Deposit number of the microorganism as rendered by the organization of a.

Claims

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1. A method of pulp bleaching, wherein pulp is treated and bleached by combination of microbial treatment and chlorine-free chemical treatment.

2. The method of pulp bleaching as claimed in claim 1, wherein the microbial treatment is effected with microorganism having a high lignin-degrading activity and a low fiber-degrading activity.

3. The method of pulp bleaching as claimed in claim 2, wherein the microbial treatment is effected with microorganism NK-1148 strain.

4. The method of pulp bleaching as claimed in claim 1, which is further combined with light chlorine-based chemical treatment.