CA2278188C - Oxygen delignification process of pulp - Google Patents
Oxygen delignification process of pulp Download PDFInfo
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- CA2278188C CA2278188C CA002278188A CA2278188A CA2278188C CA 2278188 C CA2278188 C CA 2278188C CA 002278188 A CA002278188 A CA 002278188A CA 2278188 A CA2278188 A CA 2278188A CA 2278188 C CA2278188 C CA 2278188C
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- pulp
- sulphite
- oxygen
- alkali source
- reducing agent
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- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
- D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
- D21C9/10—Bleaching ; Apparatus therefor
- D21C9/147—Bleaching ; Apparatus therefor with oxygen or its allotropic modifications
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
- D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
- D21C9/10—Bleaching ; Apparatus therefor
- D21C9/1026—Other features in bleaching processes
- D21C9/1036—Use of compounds accelerating or improving the efficiency of the processes
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
- D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
- D21C9/10—Bleaching ; Apparatus therefor
- D21C9/1084—Bleaching ; Apparatus therefor with reducing compounds
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- Wood Science & Technology (AREA)
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Abstract
The present invention is concerned with a single stage method delignification process for pulps, preferably sulphite pulps. The improvement to conventional oxygen delignification process comprises in situ addition of a reducing agent substantially non-reactive with oxygen. The end result is a pulp having enhanced strength properties and higher viscosity. Sodium borohydride is the preferred reducing agent, and MgO is the preferred alkali source. Similar results can be obtained with a two-stage oxygen delignification wherein the pulp is treated with the reducing agent in the first stage, and then washed and pressed conventionally before proceeding with the oxygen delignification in a second stage.
Description
. WO 98/31t3'f2 PCT/CA981~0020 Oxygen delignification process of pulp FIELD O~ THE INVENTION
S The present invention is concerned with a single stage process for decreasing carbohydrate degradation of sulphite pulps during the O~ process by the addition of a catalytic amount of sodium borohydride in situ to provide a pulp with enhanced strength properties and increased viscosity.
BACKGROUND OF THE INVENTItaN
Because of increasing environmental concerns worldwide) pulp and paper mills discharge effluents are constantly under scrutiny to ensure that environmental regulations are followed. Because of the high costs involved in the treatment of effluents before their release in the environment, a great deal of research is directed to the modification of current pulp and paper production processes. The research concentrates its efforts in replacing toxic reagents with more environmentally friendly products. A further benefit sought with such changes is that effluents will hopefully require fewer costly conditioning treatments before their release in the environment.
In the various processes proposed in the literature) the oxygen deligniFcation technology is one of the available options towards this direction.
Conventionally, oxygen delignification technology uses sodium hydroxide as the alkaline source and the resulting effluent produced can therefore he incorporated into the chemical recovery system of the process for preparing kraft pulps hecause the same reagent, namely sodium hydroxide) is used, and therefore) there is no rca~~cnt interference. On the other hand, the eff7ucnt from . WO 98!31872 PCT/CA98/00020 the sodium hydroxide-based oxygen deligniflcation process (referred to as the O,~aOII
technology herein) cannot be sent to the recovery system of the magnesium-based sulphite process because, obviously, the sodium salts are not compatible with the magnesium-based sulphite recovery process. Several publications have therefore concluded that magnesium oxide-based oxygen deligniflcation technology, referred to as OMB herein) is preferred for magnesium-based sulphite pulping processes. {see for example Bokstrom et al., Pulp and Paper Canada, 1992, 92 (11)) 38; and Luo et al., Tappi Journal, 19~, 75 (6), 183).
Sodium hydroxide has been replaced lately as a base with magnesium oxide (Mg0) or magnesium hydroxide {Mg(OH)~ for the oxygen delignification of sulphite pulps.
However, because of the low alkalinity of Mg0 or Mg(OH)2, the temperature of delignifieation with Mg0 or Mg(OH)Z must be about 30°C higher than for the same process using NaOH as the delignification agent (see Luo et al., supra).
Alternatively) the deligniftcation rate can be increased in the OMB process by the addition of a very limited amount of NaOH) since small concentrations of sodium salts can be tolerated in the recovery system of magnesium-based sulphite process. However, the risk of contamination in the long run is such that this alternative does not represent a desirable selection.
Changing the alkali source in the oxygen delignification process from sodium hydroxide to magnesium oxide or magnesium hydroxide) as taught by Bokstrom et al.
supra, decreases the selectivity of lignin to carbohydrate degradation.
Moreover, the strength properties also decrease, as illustrated in the relationship between tear index versus tensile index of Fig. 6, by Luo et al. supra. For a given type of wood chips used as starting material, it is well known that sulphite pulps usually have strength prupcnies inferior to that of kraft pulp) and a further decrease in strength properties durin~~ the CVO 98J318'12 PCT/CA9881~100p20 delignification process is therefore unacceptable for commercial operations.
It is known that a post treatment stage with sodium borohydride on an oxidized pulp, such as ozone deligni>ied pulp, leads to increased pulp viscosity. For example) it was S reported by Chirat et al. in Holzforschung, X94, 48 Suppl. 133) that a reduction treatment stage with 0.1 % sodium borohydride increases the viscosity of ozone bleached pulp from DP" of 710 to 920. The chemistry of sodium borohydride reduction is well understood:
carbonyl groups present in carbohydrates are reduced to alcohol funetionalities (B.
Browning, Methods of Wood Chemistry, Vol. 2, P. 685, Interscience Publishers).
In addition) it is proposed by S. Beharic in Papir 20) December 1992, 3(4) pp.
11-15 to add sodium borohydride either before ozone bleaching or after peroxide bleaching to limit the reduction in pulp viscosity. Again, two stages are involved for this pulp treatment.
Accordingly) there is therefore a great need to develop an oxygen delignifieation process providing pulps with enhanced strength properties and increased viscosity. Preferably, a single stage bleaching process should be considered, wherein a reducing agent would be added in situ. This would represent a significant advance in pulp bleaching) and bring significant benefits to the industry) because the elimination of one treatment stage of pulp represents a significant capital cost reduction.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is now provided an improvement to oxygen delignitiration process of pulps. More specifically, the preacnt . WO 98131872 PGT/CA98ro00Z0 invention comprises the conventional steps of oxygen deligniflcation of pulp) namely treating a pulp slurry in a reactor under oxygen overpressure in the presence of an alkali source, over a period of time sufficient to complete deligniflcation of the pulp, with the improvement comprising adding in situ an effective amount of a reducing agent substantially non-reactive with the oxygen, to provide delignifled pulps with enhanced strength properties and increased viscosity.
The present oxygen deligniflcation process is particularly advantageous for sulphite pulps when Mg0 or Mg(OH)Z are used as the alkali source. Other possible alkali sources include Ca(OH)Z, NH40H, NaOH and the like. Reducing agents include sodium borohydride) sodium hydrosulphite and the like, with sodium borohydride being the most preferred.
In another aspect of the present invention, the process comprises a first stage wherein the pulp is treated with the reducing agent, and then washed and pressed if necessary, and a second conventional oxygen delignification stage. Although good results are obtained with the two-stage process) the single stage process is much preferred because of the elimination of washing and pressing operations required after treatment with the reducing agent in the two-stage process.
IN THE DRAWINGS
Figure 1 illustrates the strength properties of 0~,,,go + RDoEop(DP) bleached pulp and those of OM~DoE~ (DP) bleached pulp.
DETA ED DESCRIPTION OF THE INVENTION
. ;wo msn rczicao It is an object of the present invention to provide a single or two-stage oxygen delignification process of pulp which can minimize the carbohydrate degradation and thus enhance the strength properties of the pulp, as well as the viscosity. The present single stage process is most advantageous for Mg0 delignification of sulphite pulps.
It is .also an object of the present invention to provide a two-stage oxygen delignification process of pulps which can minimize the carbohydrate degradation and thus enhance the strength properties of the pulp, as well as the viscosity. As for the single stage process, the two-stage process is also most advantageous for Mg0 delignification of sulphia; pulps.
The present invention comprises the use of a small amount of a reducing agent, most preferably sodium borohydride, either before or during the oxygen delignification prcx;css. Preferred alkali source, as mentioned above) are MgO) Mg((?H)2 and the like.
The key feature of the unexpected results obtained with the present single stage process is that the activity of the reducing agent is substantially not affected by the ovcrprcssure of oxygen in the reaction media. The reducing agent and the alkali source may be added simultaneously) or the reducing agent is added to the pulp shortly before the alkali source.
The reverse order of addition of reagents is also possible. Preferred experimental conditions for carrying the present single stage process are as follows: pH
from H t~ 13;
temperature of from 80 to 140°C; an oxygen overpressure of from 30 to 20U psi; a pulp consistency of from 1°k to 50%; an addition of tom 0.01% to 10°%
of sodium borohydride, an addition of Mg0 of from 0.2 to 10%; and a reaction time of from 0.1 to 4 hours. !vlost preferred conditions are: 127 ° C; 1 tlU psi Oz pressure; 10~ pulp consistency; an addition of 0.1 °k of sodium borohydridc. an addition of 2% Mg0 and a reaction time of 2 hours.
. WO 98131872 PCT/CA98I00020 It has been unexpectedly found that the addition of sodium borohydride in conventional magnesium oxide-based oxygen delignification process of sulphite pulp results in the production of pulps having an increased viscosity and improved strength properties when compared to -pulp prepared in the same manner but without the addition of sodium borohydride.
In the case of a two-stage process) the experimental conditions for the oxygen delignification stage are the same as those above. With respect to the first stage, preferred conditions are as follows: 0.1% to 10~k (by weight on pulp) of reducing agent is mixed with a pulp suspension at a pH of from 5 to 13 and maintained at a temperature of 20 to 100°C
for a period of time of a few seconds up to 2 hours. The pulp is then washed conventionnally, for example with water, and pressed if necessary) to collect the pulp fibers which will be treated under the above oxygen delignificativn stage. It has been unexpectedly found that the treatment of sulphite pulp with sodium borohydride before treating the pulp with a conventional magnesium oxide-based oxygen delignification process results in the production of pulps having an increased viscosity and improved strength properties when compared to pulp prepared in the same manner but without the addition of sodium borohydride. Results hereinbelow will also show that if the pulp is Lust treated under oxygen deligniflcation conditions and then with a reducing agent, the properties of the pulp are not as good as the single stage treated pulp) or two stage treated pulp wherein the treatment with reducing agent occurred before oxygen deligniflcation.
The expression "enhanced stength properties" should be interpmted as meaning that the strength properties of the pulp are at least comparable, and generally better than those of pulp obtained from a hk:aching ~quence using chlorine or chlorine dioxide without wo sn pc~riGzo _7_ oxygen deligniflcation. Further) "increased viscosity" means that the viscosity is at least equivalent to that of eastern Canadian softwood sulphite pulp after conventional O~~
delignification) i.e., typically about 25 mPa.s to about 45 mPa.s.
The following examp~s are provided for illustrating the present invention and should not be construed as limiting its scope.
Example 1 40 g of eastern softwood sulphite pulp (kappa no. 26.0, pulp viscosity 40.1 mPa~s determined on the chlorite delignified pulp) in a pulp consistency of 28.5% is weighed into a beaker containing about 360 ml of water, resulting in a pulp consistency of about 10% and then disintegrated in a conventional manner) for example by a blender to be free from fiber bundles. 0.5 % sodium borohydride (by weight on pulp) is rapidly mixed with the pulp slurry prepared above (-- 400 ml). The slurry has a pulp consistency of 10%
and contains about 2% Mg0 (by weight on pulp) and 0.2% MgS04 (by weight on pulp).
The pulp slurry is subsequently transferred to a Parr pressure reactor preheated at a temperature of about 100°C. The O~,go rR Press, that is, conventional OMB, technology with the addition of sodium borohydride in situ) is performed at about 127°C and 100 psi for 2 hours in a single stage. The resulting pulp with a kappa number of 14.(.) is then bleached to full brightness (90% ISO) in accordance with the conventional D~,E~~ (DP) wherein - Do stands for a chlorine dioxide stage;
- E~ represents a peroxide reinforced oxidative stage; and - (DP) means that no washing is performed between chlorine dioxide treatment and peroxide treatment sequence.
i' . wo mars rcTic~srooo2o _g_ The detailed conditions of each stage in the DoEoP(DP) sequence is provided in Table 1 below. The tear-tensile beating curve of the OMB+e DoEoP (DP) bleached pulp is shown in Figure 1.
Table 1 Detailed Conditions of Each Stage in the DoE°p(DP) Stage (DP) Da EW
D P
Consistency (~o)3.5 10 11.5 10 Time (min) 12 30 145 70 Temperature ( 60 70 72 80 'C) O~ pressure (psi)- 40 for - -4 min.
Chemicals (96 Kappa: HiOz: 0.8 CIOz: 0.4 HzO:: 0.5 oa pulp) 0.14 NaOH:l.8 NaOH:0.7 C10,:0.75 Example 2 This experiment is provided to illustrate the properties of a pulp obtained in experimental conditions similar to those of Example 1 without adding sodium borohydride during the conventional O",~ process. As it will be seen, the strength properties of the OMB DoE°P{DP) bleached pulp are inferior to those of the OMgo+R Do EoP(DP) bleached pulp.
The eastern softwood sulphite pulp (kappa no. 26.0) pulp viscosity 40.1 mPa.s determined on the chlorite delignil3ed pulp) used in Example 1 is also used in the present example. 2 % Mg0 (by weight on pulp) and 0.2% MgS04 are mixed with a pulp suspension containing 40 g pulp. The pulp slurry is then transferred to a Parr pressure reactor preheated at a temperature of about 100°C. The OMBO
deligniftcadon process is wo ~m pcric~srooozo perfornied at a temperature of 127°C with an oxygen overpressure of about 100 psi for 2 hrs. At the end of these 2 hours, the resulting pulp with a kappa number of 13.8 is then ' further bleached to a full brightness in accordance with the D°E°P(DP) sequence described above. The -tear-tensile beating curve of the O~ D° E~ (DP) bleached pulp is also illustrated in Figure 1, which shows that the strength properties of 0,,,~0 +
RDoE°P(DP) bleached pulp are significantly improved over those of OM~DoE~ (DP) bleached pulp.
Example 3 This example is provided to show the effect of sodium borohydride concentration on the pulp viscosity after the OMB, R delignification process.
An Eastern softwood sulphite pulp with a kappa no. of 25.2 and viscosity of 43.1 mPa~s determined on the chlorite delignified pulp is used. The sodium borohydride concentration varies from 0 to 0.05 to 0.1 to 0.2°k (by weight on pulp)) The required amount of NaBH, is rapidly mixed with a pulp slurry having a pulp consistency of 10% and containing about 2% Mg0 and about 0.2 % MgSO,. The subsequent procedures are identical to those described in Example 1. The kappa number) viscosity and brightness of the OMBO+R ~ligniGed pulps at various NaBH, concentrations are given in Table 2.
. WO 98131872 PCTICA98N0020 Table 2 Effect of the sodium borohydride concentration on pulp viscosity during the O,r,~ process Sodium borohydride concentrationKappa ~lp Brightness (% on pulp) number viscosity(% ISO) (mPa.s) 0 12.8 27.8 57.7 0.05 13.9 39.1 59.6 0.1 12.4 43.0 62.5 IO 0.2 14.6 43.0 60.9 ~
The above results clearly show that the pulp viscosity is significantly improved when sodium borohydride is present during the OMB delignification stage. In addition, the brightness of the OMgO+R delignified is always higher than that of the OMgp treated pulp under otherwise the same condition. Furthermore, the data show that a sodium borohydride concentration as low as 0.05% is sufficient to achieve the desired benet7cial effect.
Example 4 This example is provided to show that a two-stage ROMgo, i.e., treatment with sodium borohydride in a first stage followed by water washing and then conventional 0~,~
in a second stage) can produce acceptable delignified pulp with properties inferior to those of the OMB+R treated pulp.
The same Eastern softwood sulphite pulp as that used in Example 3 is uu;d in this example. 0.1% NaBH, (by wci~,ht on pulp) is mixed with a pulp suspension of pI-i 9.5 and containing 20 g pulp in a polyethylene bag. Sodium hydroxide is used to increase the pH. The polyethylene bag is then thernu~stated at 50°C. At the completion of 30 minutes) r . WO 98I31t8?2 PCT/CA98IOOOZO
the pulp slurry is thoroughly washed with purified water and the pulp fibres are collected for the subsequent O~ treatment under tl~ conditions of 10% pulp consistency, 2%a MgO, 0.2% MgSO,, 100 psi, 127°C, 2 h and without the addition of sodium borohydride. The kappa number, viscosity and pulp brightness of the resulting pulp are compared to those of OMB treated and OMB+R treated pulps in Table 3.
Table 3 Kappa number, viscosity and brightness obtained for pulp treated under different processes Technique Kappa no. ~'i~osityBrightness (mPa.s) ~' (~ ISO) OMao 12.8 27.8 57.7 ~MgO+R (0.1% NaBH4) 12.4 43.0 62.5 RO (0.1% NaBH ) 13.8 39.5 59.9 Table 3 shows that the results obtained for a pulp treated under the ROu~
process are better than that treated under the OMB process. However) the best results are obtained with a single stage OMB,, R Process.
Example 5 This example is provided to show that a reduction with sodium borohydride in a second stage after the OMB treatment of the pulp in a first stage, i.e., a OM~R sequence, . also increases the pulp viscosity) but rather moderately. However) the viscosity of the O,",~R treated pulp is substantially lower than that of the single stage OM~+
a treated pulp according to the present invention.
The same Eastern sot'twcu~d sulphite pulp as in Example 3 is used. 20 g oC
pulp i . WO 98/31872 PCT/CA98/00020 is subjected to a first stage OMB process under the conditions of 10% pulp consistency, 2%
MgO, 0.2% MgS04, 100 psi, 127°C, 2h) without adding sodium borohydride.
Subsequently) the O~ delignified pulp is treated in a second stage with 0.1 %
sodium borohydride at pH 9.5, 10% pulp consistency and 50°C for 30 minutes.
The kappa number, the viscosity and the pulp brightness of the resulting pulp are compared to those of OMB, treated and OMB+R treated pulps in Table 4.
Table 4 Kappa number, viscosity and brightness obtained for pulp treated under different processes Technique Kappa no. Vi~Sih' Brightness (mPa.s) (% ISO) 12.8 27.8 57.7 OMB ~ R (U. l 6 NaBH4) 12.4 43.0 62.5 O ,R (0.1% NaBH ) 12.0 32.9 63.3 The above results show that the viscosity of the OM~R treated pulp is about 5 units higher than that of the OMB treated pulp) however about 10 units lower than that of the OMB+R treated pulps.
In view of the above results, it is apparent that the addition of a reducing agent in situ during the oxygen delignification process provides pulps with a high«r viscosity and increased strength properties than that obtained during two-stage processes wherein the reducing agent is added either prior to or after the oxygen delignification process. The combination of a two-stage operation into a single stage one is beneficial not only hc:cause one stage has been removed) but also because the physical properties of the resulting pulp are significantly better. Nevertheless) good results are also obtained with a two stage . WO 981318?2 PCTICA98IOOOZO
process wherein the treatment with the reducing agent is carried out before the oxygen delignification stage. For obvious reasons, as mentioned above, a single stage process is most preferred.
While the invention has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modifications and this application is intended to cover any variations) uses or adaptations of the invention following) in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice within the art to which the invention pertains, and as may be applied to the essential features hereinbefore set forth, and as follows in the scope of the appended claims.
S The present invention is concerned with a single stage process for decreasing carbohydrate degradation of sulphite pulps during the O~ process by the addition of a catalytic amount of sodium borohydride in situ to provide a pulp with enhanced strength properties and increased viscosity.
BACKGROUND OF THE INVENTItaN
Because of increasing environmental concerns worldwide) pulp and paper mills discharge effluents are constantly under scrutiny to ensure that environmental regulations are followed. Because of the high costs involved in the treatment of effluents before their release in the environment, a great deal of research is directed to the modification of current pulp and paper production processes. The research concentrates its efforts in replacing toxic reagents with more environmentally friendly products. A further benefit sought with such changes is that effluents will hopefully require fewer costly conditioning treatments before their release in the environment.
In the various processes proposed in the literature) the oxygen deligniFcation technology is one of the available options towards this direction.
Conventionally, oxygen delignification technology uses sodium hydroxide as the alkaline source and the resulting effluent produced can therefore he incorporated into the chemical recovery system of the process for preparing kraft pulps hecause the same reagent, namely sodium hydroxide) is used, and therefore) there is no rca~~cnt interference. On the other hand, the eff7ucnt from . WO 98!31872 PCT/CA98/00020 the sodium hydroxide-based oxygen deligniflcation process (referred to as the O,~aOII
technology herein) cannot be sent to the recovery system of the magnesium-based sulphite process because, obviously, the sodium salts are not compatible with the magnesium-based sulphite recovery process. Several publications have therefore concluded that magnesium oxide-based oxygen deligniflcation technology, referred to as OMB herein) is preferred for magnesium-based sulphite pulping processes. {see for example Bokstrom et al., Pulp and Paper Canada, 1992, 92 (11)) 38; and Luo et al., Tappi Journal, 19~, 75 (6), 183).
Sodium hydroxide has been replaced lately as a base with magnesium oxide (Mg0) or magnesium hydroxide {Mg(OH)~ for the oxygen delignification of sulphite pulps.
However, because of the low alkalinity of Mg0 or Mg(OH)2, the temperature of delignifieation with Mg0 or Mg(OH)Z must be about 30°C higher than for the same process using NaOH as the delignification agent (see Luo et al., supra).
Alternatively) the deligniftcation rate can be increased in the OMB process by the addition of a very limited amount of NaOH) since small concentrations of sodium salts can be tolerated in the recovery system of magnesium-based sulphite process. However, the risk of contamination in the long run is such that this alternative does not represent a desirable selection.
Changing the alkali source in the oxygen delignification process from sodium hydroxide to magnesium oxide or magnesium hydroxide) as taught by Bokstrom et al.
supra, decreases the selectivity of lignin to carbohydrate degradation.
Moreover, the strength properties also decrease, as illustrated in the relationship between tear index versus tensile index of Fig. 6, by Luo et al. supra. For a given type of wood chips used as starting material, it is well known that sulphite pulps usually have strength prupcnies inferior to that of kraft pulp) and a further decrease in strength properties durin~~ the CVO 98J318'12 PCT/CA9881~100p20 delignification process is therefore unacceptable for commercial operations.
It is known that a post treatment stage with sodium borohydride on an oxidized pulp, such as ozone deligni>ied pulp, leads to increased pulp viscosity. For example) it was S reported by Chirat et al. in Holzforschung, X94, 48 Suppl. 133) that a reduction treatment stage with 0.1 % sodium borohydride increases the viscosity of ozone bleached pulp from DP" of 710 to 920. The chemistry of sodium borohydride reduction is well understood:
carbonyl groups present in carbohydrates are reduced to alcohol funetionalities (B.
Browning, Methods of Wood Chemistry, Vol. 2, P. 685, Interscience Publishers).
In addition) it is proposed by S. Beharic in Papir 20) December 1992, 3(4) pp.
11-15 to add sodium borohydride either before ozone bleaching or after peroxide bleaching to limit the reduction in pulp viscosity. Again, two stages are involved for this pulp treatment.
Accordingly) there is therefore a great need to develop an oxygen delignifieation process providing pulps with enhanced strength properties and increased viscosity. Preferably, a single stage bleaching process should be considered, wherein a reducing agent would be added in situ. This would represent a significant advance in pulp bleaching) and bring significant benefits to the industry) because the elimination of one treatment stage of pulp represents a significant capital cost reduction.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is now provided an improvement to oxygen delignitiration process of pulps. More specifically, the preacnt . WO 98131872 PGT/CA98ro00Z0 invention comprises the conventional steps of oxygen deligniflcation of pulp) namely treating a pulp slurry in a reactor under oxygen overpressure in the presence of an alkali source, over a period of time sufficient to complete deligniflcation of the pulp, with the improvement comprising adding in situ an effective amount of a reducing agent substantially non-reactive with the oxygen, to provide delignifled pulps with enhanced strength properties and increased viscosity.
The present oxygen deligniflcation process is particularly advantageous for sulphite pulps when Mg0 or Mg(OH)Z are used as the alkali source. Other possible alkali sources include Ca(OH)Z, NH40H, NaOH and the like. Reducing agents include sodium borohydride) sodium hydrosulphite and the like, with sodium borohydride being the most preferred.
In another aspect of the present invention, the process comprises a first stage wherein the pulp is treated with the reducing agent, and then washed and pressed if necessary, and a second conventional oxygen delignification stage. Although good results are obtained with the two-stage process) the single stage process is much preferred because of the elimination of washing and pressing operations required after treatment with the reducing agent in the two-stage process.
IN THE DRAWINGS
Figure 1 illustrates the strength properties of 0~,,,go + RDoEop(DP) bleached pulp and those of OM~DoE~ (DP) bleached pulp.
DETA ED DESCRIPTION OF THE INVENTION
. ;wo msn rczicao It is an object of the present invention to provide a single or two-stage oxygen delignification process of pulp which can minimize the carbohydrate degradation and thus enhance the strength properties of the pulp, as well as the viscosity. The present single stage process is most advantageous for Mg0 delignification of sulphite pulps.
It is .also an object of the present invention to provide a two-stage oxygen delignification process of pulps which can minimize the carbohydrate degradation and thus enhance the strength properties of the pulp, as well as the viscosity. As for the single stage process, the two-stage process is also most advantageous for Mg0 delignification of sulphia; pulps.
The present invention comprises the use of a small amount of a reducing agent, most preferably sodium borohydride, either before or during the oxygen delignification prcx;css. Preferred alkali source, as mentioned above) are MgO) Mg((?H)2 and the like.
The key feature of the unexpected results obtained with the present single stage process is that the activity of the reducing agent is substantially not affected by the ovcrprcssure of oxygen in the reaction media. The reducing agent and the alkali source may be added simultaneously) or the reducing agent is added to the pulp shortly before the alkali source.
The reverse order of addition of reagents is also possible. Preferred experimental conditions for carrying the present single stage process are as follows: pH
from H t~ 13;
temperature of from 80 to 140°C; an oxygen overpressure of from 30 to 20U psi; a pulp consistency of from 1°k to 50%; an addition of tom 0.01% to 10°%
of sodium borohydride, an addition of Mg0 of from 0.2 to 10%; and a reaction time of from 0.1 to 4 hours. !vlost preferred conditions are: 127 ° C; 1 tlU psi Oz pressure; 10~ pulp consistency; an addition of 0.1 °k of sodium borohydridc. an addition of 2% Mg0 and a reaction time of 2 hours.
. WO 98131872 PCT/CA98I00020 It has been unexpectedly found that the addition of sodium borohydride in conventional magnesium oxide-based oxygen delignification process of sulphite pulp results in the production of pulps having an increased viscosity and improved strength properties when compared to -pulp prepared in the same manner but without the addition of sodium borohydride.
In the case of a two-stage process) the experimental conditions for the oxygen delignification stage are the same as those above. With respect to the first stage, preferred conditions are as follows: 0.1% to 10~k (by weight on pulp) of reducing agent is mixed with a pulp suspension at a pH of from 5 to 13 and maintained at a temperature of 20 to 100°C
for a period of time of a few seconds up to 2 hours. The pulp is then washed conventionnally, for example with water, and pressed if necessary) to collect the pulp fibers which will be treated under the above oxygen delignificativn stage. It has been unexpectedly found that the treatment of sulphite pulp with sodium borohydride before treating the pulp with a conventional magnesium oxide-based oxygen delignification process results in the production of pulps having an increased viscosity and improved strength properties when compared to pulp prepared in the same manner but without the addition of sodium borohydride. Results hereinbelow will also show that if the pulp is Lust treated under oxygen deligniflcation conditions and then with a reducing agent, the properties of the pulp are not as good as the single stage treated pulp) or two stage treated pulp wherein the treatment with reducing agent occurred before oxygen deligniflcation.
The expression "enhanced stength properties" should be interpmted as meaning that the strength properties of the pulp are at least comparable, and generally better than those of pulp obtained from a hk:aching ~quence using chlorine or chlorine dioxide without wo sn pc~riGzo _7_ oxygen deligniflcation. Further) "increased viscosity" means that the viscosity is at least equivalent to that of eastern Canadian softwood sulphite pulp after conventional O~~
delignification) i.e., typically about 25 mPa.s to about 45 mPa.s.
The following examp~s are provided for illustrating the present invention and should not be construed as limiting its scope.
Example 1 40 g of eastern softwood sulphite pulp (kappa no. 26.0, pulp viscosity 40.1 mPa~s determined on the chlorite delignified pulp) in a pulp consistency of 28.5% is weighed into a beaker containing about 360 ml of water, resulting in a pulp consistency of about 10% and then disintegrated in a conventional manner) for example by a blender to be free from fiber bundles. 0.5 % sodium borohydride (by weight on pulp) is rapidly mixed with the pulp slurry prepared above (-- 400 ml). The slurry has a pulp consistency of 10%
and contains about 2% Mg0 (by weight on pulp) and 0.2% MgS04 (by weight on pulp).
The pulp slurry is subsequently transferred to a Parr pressure reactor preheated at a temperature of about 100°C. The O~,go rR Press, that is, conventional OMB, technology with the addition of sodium borohydride in situ) is performed at about 127°C and 100 psi for 2 hours in a single stage. The resulting pulp with a kappa number of 14.(.) is then bleached to full brightness (90% ISO) in accordance with the conventional D~,E~~ (DP) wherein - Do stands for a chlorine dioxide stage;
- E~ represents a peroxide reinforced oxidative stage; and - (DP) means that no washing is performed between chlorine dioxide treatment and peroxide treatment sequence.
i' . wo mars rcTic~srooo2o _g_ The detailed conditions of each stage in the DoEoP(DP) sequence is provided in Table 1 below. The tear-tensile beating curve of the OMB+e DoEoP (DP) bleached pulp is shown in Figure 1.
Table 1 Detailed Conditions of Each Stage in the DoE°p(DP) Stage (DP) Da EW
D P
Consistency (~o)3.5 10 11.5 10 Time (min) 12 30 145 70 Temperature ( 60 70 72 80 'C) O~ pressure (psi)- 40 for - -4 min.
Chemicals (96 Kappa: HiOz: 0.8 CIOz: 0.4 HzO:: 0.5 oa pulp) 0.14 NaOH:l.8 NaOH:0.7 C10,:0.75 Example 2 This experiment is provided to illustrate the properties of a pulp obtained in experimental conditions similar to those of Example 1 without adding sodium borohydride during the conventional O",~ process. As it will be seen, the strength properties of the OMB DoE°P{DP) bleached pulp are inferior to those of the OMgo+R Do EoP(DP) bleached pulp.
The eastern softwood sulphite pulp (kappa no. 26.0) pulp viscosity 40.1 mPa.s determined on the chlorite delignil3ed pulp) used in Example 1 is also used in the present example. 2 % Mg0 (by weight on pulp) and 0.2% MgS04 are mixed with a pulp suspension containing 40 g pulp. The pulp slurry is then transferred to a Parr pressure reactor preheated at a temperature of about 100°C. The OMBO
deligniftcadon process is wo ~m pcric~srooozo perfornied at a temperature of 127°C with an oxygen overpressure of about 100 psi for 2 hrs. At the end of these 2 hours, the resulting pulp with a kappa number of 13.8 is then ' further bleached to a full brightness in accordance with the D°E°P(DP) sequence described above. The -tear-tensile beating curve of the O~ D° E~ (DP) bleached pulp is also illustrated in Figure 1, which shows that the strength properties of 0,,,~0 +
RDoE°P(DP) bleached pulp are significantly improved over those of OM~DoE~ (DP) bleached pulp.
Example 3 This example is provided to show the effect of sodium borohydride concentration on the pulp viscosity after the OMB, R delignification process.
An Eastern softwood sulphite pulp with a kappa no. of 25.2 and viscosity of 43.1 mPa~s determined on the chlorite delignified pulp is used. The sodium borohydride concentration varies from 0 to 0.05 to 0.1 to 0.2°k (by weight on pulp)) The required amount of NaBH, is rapidly mixed with a pulp slurry having a pulp consistency of 10% and containing about 2% Mg0 and about 0.2 % MgSO,. The subsequent procedures are identical to those described in Example 1. The kappa number) viscosity and brightness of the OMBO+R ~ligniGed pulps at various NaBH, concentrations are given in Table 2.
. WO 98131872 PCTICA98N0020 Table 2 Effect of the sodium borohydride concentration on pulp viscosity during the O,r,~ process Sodium borohydride concentrationKappa ~lp Brightness (% on pulp) number viscosity(% ISO) (mPa.s) 0 12.8 27.8 57.7 0.05 13.9 39.1 59.6 0.1 12.4 43.0 62.5 IO 0.2 14.6 43.0 60.9 ~
The above results clearly show that the pulp viscosity is significantly improved when sodium borohydride is present during the OMB delignification stage. In addition, the brightness of the OMgO+R delignified is always higher than that of the OMgp treated pulp under otherwise the same condition. Furthermore, the data show that a sodium borohydride concentration as low as 0.05% is sufficient to achieve the desired benet7cial effect.
Example 4 This example is provided to show that a two-stage ROMgo, i.e., treatment with sodium borohydride in a first stage followed by water washing and then conventional 0~,~
in a second stage) can produce acceptable delignified pulp with properties inferior to those of the OMB+R treated pulp.
The same Eastern softwood sulphite pulp as that used in Example 3 is uu;d in this example. 0.1% NaBH, (by wci~,ht on pulp) is mixed with a pulp suspension of pI-i 9.5 and containing 20 g pulp in a polyethylene bag. Sodium hydroxide is used to increase the pH. The polyethylene bag is then thernu~stated at 50°C. At the completion of 30 minutes) r . WO 98I31t8?2 PCT/CA98IOOOZO
the pulp slurry is thoroughly washed with purified water and the pulp fibres are collected for the subsequent O~ treatment under tl~ conditions of 10% pulp consistency, 2%a MgO, 0.2% MgSO,, 100 psi, 127°C, 2 h and without the addition of sodium borohydride. The kappa number, viscosity and pulp brightness of the resulting pulp are compared to those of OMB treated and OMB+R treated pulps in Table 3.
Table 3 Kappa number, viscosity and brightness obtained for pulp treated under different processes Technique Kappa no. ~'i~osityBrightness (mPa.s) ~' (~ ISO) OMao 12.8 27.8 57.7 ~MgO+R (0.1% NaBH4) 12.4 43.0 62.5 RO (0.1% NaBH ) 13.8 39.5 59.9 Table 3 shows that the results obtained for a pulp treated under the ROu~
process are better than that treated under the OMB process. However) the best results are obtained with a single stage OMB,, R Process.
Example 5 This example is provided to show that a reduction with sodium borohydride in a second stage after the OMB treatment of the pulp in a first stage, i.e., a OM~R sequence, . also increases the pulp viscosity) but rather moderately. However) the viscosity of the O,",~R treated pulp is substantially lower than that of the single stage OM~+
a treated pulp according to the present invention.
The same Eastern sot'twcu~d sulphite pulp as in Example 3 is used. 20 g oC
pulp i . WO 98/31872 PCT/CA98/00020 is subjected to a first stage OMB process under the conditions of 10% pulp consistency, 2%
MgO, 0.2% MgS04, 100 psi, 127°C, 2h) without adding sodium borohydride.
Subsequently) the O~ delignified pulp is treated in a second stage with 0.1 %
sodium borohydride at pH 9.5, 10% pulp consistency and 50°C for 30 minutes.
The kappa number, the viscosity and the pulp brightness of the resulting pulp are compared to those of OMB, treated and OMB+R treated pulps in Table 4.
Table 4 Kappa number, viscosity and brightness obtained for pulp treated under different processes Technique Kappa no. Vi~Sih' Brightness (mPa.s) (% ISO) 12.8 27.8 57.7 OMB ~ R (U. l 6 NaBH4) 12.4 43.0 62.5 O ,R (0.1% NaBH ) 12.0 32.9 63.3 The above results show that the viscosity of the OM~R treated pulp is about 5 units higher than that of the OMB treated pulp) however about 10 units lower than that of the OMB+R treated pulps.
In view of the above results, it is apparent that the addition of a reducing agent in situ during the oxygen delignification process provides pulps with a high«r viscosity and increased strength properties than that obtained during two-stage processes wherein the reducing agent is added either prior to or after the oxygen delignification process. The combination of a two-stage operation into a single stage one is beneficial not only hc:cause one stage has been removed) but also because the physical properties of the resulting pulp are significantly better. Nevertheless) good results are also obtained with a two stage . WO 981318?2 PCTICA98IOOOZO
process wherein the treatment with the reducing agent is carried out before the oxygen delignification stage. For obvious reasons, as mentioned above, a single stage process is most preferred.
While the invention has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modifications and this application is intended to cover any variations) uses or adaptations of the invention following) in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice within the art to which the invention pertains, and as may be applied to the essential features hereinbefore set forth, and as follows in the scope of the appended claims.
Claims (25)
1. A method for the oxygen delignification of sulphite pulp, the method comprising treating a sulphite pulp slurry in a reactor under oxygen overpressure at a pH of from 8 to 13 with an effective amount of an alkali source over a period of time sufficient to complete delignification of the sulphite pulp; and adding in situ an effective amount of a reducing agent substantially non-reactive with the oxygen to provide a sulphite pulp with enhanced strength properties and increased viscosity.
2. A method according to claim 1 wherein the alkali source comprises MgO, Mg(OH)2, Ca(OH)2, NH4OH, NaOH or mixtures thereof, and the reducing agent comprises sodium borohydride or sodium hydrosulphite.
3. A method according to claim 1 wherein the alkali source and the reducing agent are added simultaneously in the reactor.
4. A method according to claim 1 wherein the reducing agent is added in the reactor before the alkali source.
5. A method according to claim 1 wherein the temperature of the reactor is maintained between 80 and 140°C with the oxygen overpressure being from [2,07 to 13,79]x10 5 Pa(30 to 200 psi), a pulp consistency of from 1 to 50%, and the period of time is from 0.1 to 4 hours.
6. A method according to claim 1 wherein 0.01% to 10% by weight of pulp of reducing agent is added, and 0.5 to 10% by weight of pulp of alkali source is added.
7. A method for the oxygen delignification of sulphite pulp, the method comprising treating a pulp slurry in a reactor at a temperature of from 80 to 140°C
under an oxygen overpressure and at a pH of from 9 to 12 with from 0.5 to 10%
by weight of pulp of an alkali source over a period of time sufficient to complete delignification of the pulp; and adding in the reactor simultaneously with the alkali source from 0.01 to 10% by weight of pulp of a reducing agent substantially non-reactive with the oxygen, improve the strength properties and increased the viscosity of the pulp.
under an oxygen overpressure and at a pH of from 9 to 12 with from 0.5 to 10%
by weight of pulp of an alkali source over a period of time sufficient to complete delignification of the pulp; and adding in the reactor simultaneously with the alkali source from 0.01 to 10% by weight of pulp of a reducing agent substantially non-reactive with the oxygen, improve the strength properties and increased the viscosity of the pulp.
8. A method according to claim 7 wherein the alkali source comprises MgO and the reducing agent comprises sodium borohydride.
9. A method according to claim 7 wherein the oxygen overpressure is from [2,07 to 13,79]x10 5Pa (30 to 200 psi) and the pulp consistency is from 1 to 50%.
10. A method for the oxygen delignification of sulphite pulp, the method comprising a first stage wherein a sulphite pulp suspension is treated with an effective amount of a reducing agent, and then washing and pressing the sulphite pulp in a conventional manner, and collecting the sulphite pulp; and a second stage wherein a sulphite pulp slurry is treated in a reactor under oxygen overpressure at a pH
of from 8 to 13 with an effective amount of an alkali source over a period of time sufficient to complete delignification of the sulphite pulp, to provide a sulphite pulp with enhanced strength properties and increased viscosity.
of from 8 to 13 with an effective amount of an alkali source over a period of time sufficient to complete delignification of the sulphite pulp, to provide a sulphite pulp with enhanced strength properties and increased viscosity.
11. A method according to claim 10 wherein the amount of reducing agent added in the first stage is from 0.01 to 10% by weight of pulp at a pH of from 5 to 13, and wherein the temperature in the first stage is maintained between 20 to 100°C for a period of time of a few seconds up to 2 hours.
12. A method according to claim 10 wherein the alkali source comprises MgO, Mg(OH)2, Ca(OH)2, NH4OH, NaOH or mixtures thereof, and the reducing agent comprises sodium borohydride or sodium hydrosulphite.
13. A method according to claim 10 wherein the temperature of the reactor is maintained between 80 and 140°C with the oxygen overpressure being from [2,07 to 13,79]x10 5 Pa (30 to 200 psi), a pulp consistency of from 1 to 50%.
14. A method for the oxygen delignification of sulphite pulp, the method comprising a first stage wherein a sulphite pulp suspension is treated with 0.01 to 10%
by weight of pulp of a reducing agent, and then washing and pressing the sulphite pulp in a conventional manner, and collecting the sulphite pulp; and a second stage wherein a sulphite pulp slurry is treated at a temperature of from 80 to 140°C
in a reactor under oxygen overpressure at a pH of from 9 to 12 with 0.5 to 10% by weight of pulp of an alkali source over a period of time sufficient to complete delignification of the sulphite pulp, to provide a sulphite pulp with enhanced strength properties and increased viscosity.
by weight of pulp of a reducing agent, and then washing and pressing the sulphite pulp in a conventional manner, and collecting the sulphite pulp; and a second stage wherein a sulphite pulp slurry is treated at a temperature of from 80 to 140°C
in a reactor under oxygen overpressure at a pH of from 9 to 12 with 0.5 to 10% by weight of pulp of an alkali source over a period of time sufficient to complete delignification of the sulphite pulp, to provide a sulphite pulp with enhanced strength properties and increased viscosity.
15. A method according to claim 14 wherein the alkali source comprises MgO and the reducing agent comprises sodium borohydride.
16. A method according to claim 14 wherein the oxygen overpressure is from [2,07 to 13,79]x105 Pa (30 to 200 psi) and the pulp consistency is from 1 to 50%.
17. A method for the oxygen delignification of sulphite pulp comprising the steps of:
- treating a sulphite pulp slurry in a reactor under oxygen overpressure at a pH of from 8 to 13 with an effective amount of an alkali source over a period of time sufficient to complete delignification of the sulphite pulp wherein the alkali source is selected from the group consisting of MgO, Mg(OH)2, Ca(OH)2, NH4OH, NaOH and mixtures thereof; and - adding an effective amount of reducing agent which is substantially non-reactive with the oxygen to provide a sulphite pulp with enhanced strength properties and increased viscosity, with the proviso that reducing agent addition is carried out i) in a separate stage before adding the alkali source in the reactor; or ii) simultaneously with the alkali source in the reactor.
- treating a sulphite pulp slurry in a reactor under oxygen overpressure at a pH of from 8 to 13 with an effective amount of an alkali source over a period of time sufficient to complete delignification of the sulphite pulp wherein the alkali source is selected from the group consisting of MgO, Mg(OH)2, Ca(OH)2, NH4OH, NaOH and mixtures thereof; and - adding an effective amount of reducing agent which is substantially non-reactive with the oxygen to provide a sulphite pulp with enhanced strength properties and increased viscosity, with the proviso that reducing agent addition is carried out i) in a separate stage before adding the alkali source in the reactor; or ii) simultaneously with the alkali source in the reactor.
18. A method according to claim 17 wherein the temperature of the reactor is maintained between 80 and 140°C with the oxygen overpressure being from [2,07 to 13,79]x10 5 Pa (30 to 200 psi) a pulp consistency of from 1 to 50%, and the period of time is from 0.1 to 4 hours.
19. A method according to claim 17 wherein 0.01 % to 10% by weight of pulp of reducing agent is added, and 0.5 to 10% by weight of pulp of alkali source is added.
20. A method according to claim 17 wherein the reducing agent comprises sodium borohydride or sodium hydrosulphite.
21. A method for the oxygen delignification of sulphite pulp comprising the steps of:
- treating a sulphite pulp slurry in a reactor at a temperature of from 80 to 140°C under oxygen overpressure at a pH of from 9 to 12 with from 0.5 to 10% by weight of pulp of an alkali source over a period of time sufficient to complete delignification of the sulphite pulp, wherein the alkali source is selected from the group consisting of MgO, Mg(OH)2, Ca(OH)2, NH4OH, NaOH and mixtures thereof;
and - adding in the reactor simultaneously with the alkali source from 0.01 to 10% by weight of pulp of sodium borohydride to improve strength properties and increase the viscosity of the sulphite pulp.
- treating a sulphite pulp slurry in a reactor at a temperature of from 80 to 140°C under oxygen overpressure at a pH of from 9 to 12 with from 0.5 to 10% by weight of pulp of an alkali source over a period of time sufficient to complete delignification of the sulphite pulp, wherein the alkali source is selected from the group consisting of MgO, Mg(OH)2, Ca(OH)2, NH4OH, NaOH and mixtures thereof;
and - adding in the reactor simultaneously with the alkali source from 0.01 to 10% by weight of pulp of sodium borohydride to improve strength properties and increase the viscosity of the sulphite pulp.
22. A method according to claim 21 wherein the oxygen overpressure is from [2,07 to 13,79) x 105 Pa (30 to 200 psi) and the pulp consistency is from 1 to 50%.
23. A method for the oxygen delignification of sulphite pulp, the method comprising a first stage wherein a sulphite pulp suspension is treated with an effective amount of sodium borohydride, and then washing and pressing the sulphite pulp in a conventional manner, and collecting the sulphite pulp; and a second stage wherein a sulphite pulp slurry is in a reactor under oxygen overpressure at a pH of from 8 to 13 with an effective amount of an alkali source selected from the group consisting of MgO, Mg(OH)2, Ca(OH)2, NH4OH, NaOH and mixtures thereof, over a period of time sufficient to complete delignification of the sulphite pulp, to provide a sulphite pulp with enhanced strength properties and increased viscosity.
24. A method according to claim 23 wherein the amount of sodium borohydride added in the first stage is from 0.01 % to 10% by weight of pulp at a pH
of from 8 to 13, and wherein temperature in the first stage is maintained between 20 and 100°C for a period of time of a few seconds up to 2 hours.
of from 8 to 13, and wherein temperature in the first stage is maintained between 20 and 100°C for a period of time of a few seconds up to 2 hours.
25. A method according to claim 19 wherein the oxygen overpressure is from [2,07 to 13,79]x10 5 Pa (30 to 200 psi), and the pulp consistency is from 1 to 50%.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US78621697A | 1997-01-21 | 1997-01-21 | |
| US08/786,216 | 1997-01-21 | ||
| PCT/CA1998/000020 WO1998031872A1 (en) | 1997-01-21 | 1998-01-19 | Oxygen delignification process of pulp |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2278188A1 CA2278188A1 (en) | 1998-07-23 |
| CA2278188C true CA2278188C (en) | 2003-11-25 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002278188A Expired - Fee Related CA2278188C (en) | 1997-01-21 | 1998-01-19 | Oxygen delignification process of pulp |
Country Status (6)
| Country | Link |
|---|---|
| EP (1) | EP0960235B1 (en) |
| AT (1) | ATE216741T1 (en) |
| AU (1) | AU5546498A (en) |
| CA (1) | CA2278188C (en) |
| DE (1) | DE69805056T2 (en) |
| WO (1) | WO1998031872A1 (en) |
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| US9932709B2 (en) | 2013-03-15 | 2018-04-03 | Ecolab Usa Inc. | Processes and compositions for brightness improvement in paper production |
| BR102014027199B1 (en) * | 2014-07-14 | 2022-10-04 | Nalco Company | METHOD TO IMPROVE THE MANUFACTURING OF SODA OR KRAFT PULP |
| US20180030651A1 (en) * | 2016-07-27 | 2018-02-01 | Ecolab USA, Inc. | Method and compositions for oxygen delignification of chemical pulp |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3809332A1 (en) * | 1988-03-19 | 1989-10-05 | Degussa | Multi-stage process for bleaching wood pulps |
| FR2692917A1 (en) * | 1992-06-30 | 1993-12-31 | Air Liquide | Chemical pulp bleaching - using ozone followed by borohydride treatment, to avoid degradation during complementary bleaching step |
| SE9402726L (en) * | 1994-08-16 | 1995-08-28 | Kvaerner Pulping Tech | Chemical pulp bleaching sequence comprising a sulfonating bleaching step |
| CA2157154A1 (en) * | 1994-08-29 | 1996-03-01 | Gordon Leary | Bleaching of high-yield pulps with oxygen |
-
1998
- 1998-01-19 CA CA002278188A patent/CA2278188C/en not_active Expired - Fee Related
- 1998-01-19 EP EP98900506A patent/EP0960235B1/en not_active Expired - Lifetime
- 1998-01-19 AT AT98900506T patent/ATE216741T1/en not_active IP Right Cessation
- 1998-01-19 AU AU55464/98A patent/AU5546498A/en not_active Abandoned
- 1998-01-19 WO PCT/CA1998/000020 patent/WO1998031872A1/en active IP Right Grant
- 1998-01-19 DE DE69805056T patent/DE69805056T2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| ATE216741T1 (en) | 2002-05-15 |
| DE69805056T2 (en) | 2002-11-14 |
| AU5546498A (en) | 1998-08-07 |
| CA2278188A1 (en) | 1998-07-23 |
| EP0960235B1 (en) | 2002-04-24 |
| DE69805056D1 (en) | 2002-05-29 |
| WO1998031872A1 (en) | 1998-07-23 |
| EP0960235A1 (en) | 1999-12-01 |
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