CA1268906A - Procedure for delignification of sulphate pulp - Google Patents
Procedure for delignification of sulphate pulpInfo
- Publication number
- CA1268906A CA1268906A CA000500799A CA500799A CA1268906A CA 1268906 A CA1268906 A CA 1268906A CA 000500799 A CA000500799 A CA 000500799A CA 500799 A CA500799 A CA 500799A CA 1268906 A CA1268906 A CA 1268906A
- Authority
- CA
- Canada
- Prior art keywords
- pulp
- procedure according
- polysulphide
- treatment
- weight
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
Classifications
-
- 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
- D21C9/001—Modification of pulp properties
- D21C9/002—Modification of pulp properties by chemical means; preparation of dewatered pulp, e.g. in sheet or bulk form, containing special additives
-
- 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
- D21C9/001—Modification of pulp properties
- D21C9/002—Modification of pulp properties by chemical means; preparation of dewatered pulp, e.g. in sheet or bulk form, containing special additives
- D21C9/004—Modification of pulp properties by chemical means; preparation of dewatered pulp, e.g. in sheet or bulk form, containing special additives inorganic compounds
Landscapes
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- General Chemical & Material Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
- Wood Science & Technology (AREA)
- Inorganic Chemistry (AREA)
- Paper (AREA)
Abstract
ABSTRACT
In the manufacture of bleached sulphate pulp a chemical cellulose pulp is delignified with an alkaline polysulphide solution after cooking but before any bleaching. According to the invention the pulp is treated after digestion at a temperature of 100-160 °C with a solution containing 0.2-0.6 mol/l effective alkali, 0.5-5 per cent by weight sulphur of the weight of the pulp in the form of polysulphide, i.e.
Na2Sx, where x is 2 or higher, and in the presence of a stabilizer for polysulphide.
In the manufacture of bleached sulphate pulp a chemical cellulose pulp is delignified with an alkaline polysulphide solution after cooking but before any bleaching. According to the invention the pulp is treated after digestion at a temperature of 100-160 °C with a solution containing 0.2-0.6 mol/l effective alkali, 0.5-5 per cent by weight sulphur of the weight of the pulp in the form of polysulphide, i.e.
Na2Sx, where x is 2 or higher, and in the presence of a stabilizer for polysulphide.
Description
9o~
3332 ~28 PROCEDURE FOR DELIGNIFICATION OF SULPHATE PULP
The present invention relates to a procedure for the manufacture of unbleached or bleached sulphat:e pulp, whereby a chemical cellulose pulp after digestion but hefore any subsequent bleaching is delignified with an alkaline polysulphide solution.
Delignification of pulp with an alkaline polysulphide solution can take place in milder conditions than prevail in a normal sulphate digestion and imply that the carbohydrate yield and pulp viscosity at a certain lignin content will be higher than if a corresponcling delignification had been achieved through Eur ther cooking. To att~in thi~ eE~ect it is necessar~ either Eor the pulp to have been treated prior to delignification with polysul-phide in order to remove metal ions (e.g. washing with acid) or for the polysulphide solution to contain a stabilizer for polysul-phide.
In the manufacture of bleached sulphate pulp it is desirable for reasons of environmental conservation to perform the delignification in the closed part of the plant as ar as possible so as to limit emissions from the plant. The closed part of the ~ 20 plant comprises digestion and, where provided, oxygen bleaching.
;~ The waste liquors from these stages containing consumed chemicals and liberated wood substance are returned via the washing stages to evaporation and chemical recovery.
The quality requirements imposed on the pulp set a limit, however, to how far the delignification can be taken in - cooking and oxygen bleaching. The final delignification in the .
~ manufacture of bleached pulp i5 normally perEormed with the aid of .~; J
~`, ' ,, .,~ ' ' chlorine chemicals and results in emission of liberated wood sub-stance and residual chemicals with the effluentO
Increased delignification through so-called modified digestion implying a controlled variation of the contents of chem-icals during the digestion process is a recently introduced method for reduction of environmental impact in the manufacture of bleached sulphate pulp. According to the invention the polysul-phide treatment is carried out after sulphate digestion regardless of how this is elaborated and at lower temperatures than used for digestion. Moreover, in accordance with the proceclure according to the invention actions are taken to stabilize polysulphide.
S. Rydholm, Pulping Processes, Interscience Publishers, New York, 1967, p. 642 and G.C. Smith, S.E. Knowles, R.D. Green, Paper Trade Journal 38 (1975), p. 13, 159, indicates that the addition of polysulphide to sulphate cooking liquid ~white liquor) results in a higher pulp yield in sulphate digestion, thanks to stabiliYation of the carbohydrates. If polysulphide is added during cooking, the carbohydrate stabilizing reactions take place during the initial phase or impregnation phase of the cook, i.e.
before the maximum cooking temperature has been reached. In conse-quence of the instability of the polysulphides, the sulphide in the cooking liquid will no longer appear in the form of polysul-phide at the end of the cook but as monosulphide, i.e. sulphide and hydrogen sulphide ions.
According to the present invention polysulphide is used to accomplish further delignification of sulphate-cooked pulp and in a manner that counteracts reversion of polysulphide to monosul-. .
, ,, .~ .
" " . ~ .
~2~0~
phide. The object of using polysulphide in this way is in fact to achieve an increased carbohydrate yield.
U.S. Patent 3,716,448 discloses that polysulphide can be used as an additive in the actual oxygen reactor in oxygen bleach~
ing in order to reduce depolymerization of the cellulose. This, however, has proved not to function satisfactorily in practice.
Normally, white liquor is used as the source of alkali in oxygen bleaching. According to standard procedure, the white liquor is oxidized before being added to the pulp in oxygen bleaching so as to transform sulphide into thiosulphate. It is well known that the presence oE sulphide ions during oxygen bleaching affects the ratio between lignin and carbohydrate di~solution negativel~. This i9 expressed in a lowered viscosity of the pulp.
It has also been proposed by A.G. Kirkman, E.K. Andrews, H.M. Chang, AIChE Annual Meeting, Los Angeles, ~ovember 1982, to render the oxygen bleaching more efficient through pretreatment of the sulphate pulp with green liquor. The principal ingredients of green liquor are sodium sulphide and sodium carbonate and the content of polysulphide is negligible.
The procedure according to the present invention seeks to attain a lower lignin content than normal, with retained high pulp ~iscosity, prior to bleaching with chlorine chemicals. In .
this procedure, after boiling at a temperature between lOO~C and;
160C the pulp is treated with a solution containing 0.2-0.6 mol/l ` effective alkali, 0.5-5 per cent by weight sulphur of the weight .,;
, r~
~, . .
391(1 ~JI
of the pulp in the form of polysulphide, i.e. ~ia2Sx, where x is
3332 ~28 PROCEDURE FOR DELIGNIFICATION OF SULPHATE PULP
The present invention relates to a procedure for the manufacture of unbleached or bleached sulphat:e pulp, whereby a chemical cellulose pulp after digestion but hefore any subsequent bleaching is delignified with an alkaline polysulphide solution.
Delignification of pulp with an alkaline polysulphide solution can take place in milder conditions than prevail in a normal sulphate digestion and imply that the carbohydrate yield and pulp viscosity at a certain lignin content will be higher than if a corresponcling delignification had been achieved through Eur ther cooking. To att~in thi~ eE~ect it is necessar~ either Eor the pulp to have been treated prior to delignification with polysul-phide in order to remove metal ions (e.g. washing with acid) or for the polysulphide solution to contain a stabilizer for polysul-phide.
In the manufacture of bleached sulphate pulp it is desirable for reasons of environmental conservation to perform the delignification in the closed part of the plant as ar as possible so as to limit emissions from the plant. The closed part of the ~ 20 plant comprises digestion and, where provided, oxygen bleaching.
;~ The waste liquors from these stages containing consumed chemicals and liberated wood substance are returned via the washing stages to evaporation and chemical recovery.
The quality requirements imposed on the pulp set a limit, however, to how far the delignification can be taken in - cooking and oxygen bleaching. The final delignification in the .
~ manufacture of bleached pulp i5 normally perEormed with the aid of .~; J
~`, ' ,, .,~ ' ' chlorine chemicals and results in emission of liberated wood sub-stance and residual chemicals with the effluentO
Increased delignification through so-called modified digestion implying a controlled variation of the contents of chem-icals during the digestion process is a recently introduced method for reduction of environmental impact in the manufacture of bleached sulphate pulp. According to the invention the polysul-phide treatment is carried out after sulphate digestion regardless of how this is elaborated and at lower temperatures than used for digestion. Moreover, in accordance with the proceclure according to the invention actions are taken to stabilize polysulphide.
S. Rydholm, Pulping Processes, Interscience Publishers, New York, 1967, p. 642 and G.C. Smith, S.E. Knowles, R.D. Green, Paper Trade Journal 38 (1975), p. 13, 159, indicates that the addition of polysulphide to sulphate cooking liquid ~white liquor) results in a higher pulp yield in sulphate digestion, thanks to stabiliYation of the carbohydrates. If polysulphide is added during cooking, the carbohydrate stabilizing reactions take place during the initial phase or impregnation phase of the cook, i.e.
before the maximum cooking temperature has been reached. In conse-quence of the instability of the polysulphides, the sulphide in the cooking liquid will no longer appear in the form of polysul-phide at the end of the cook but as monosulphide, i.e. sulphide and hydrogen sulphide ions.
According to the present invention polysulphide is used to accomplish further delignification of sulphate-cooked pulp and in a manner that counteracts reversion of polysulphide to monosul-. .
, ,, .~ .
" " . ~ .
~2~0~
phide. The object of using polysulphide in this way is in fact to achieve an increased carbohydrate yield.
U.S. Patent 3,716,448 discloses that polysulphide can be used as an additive in the actual oxygen reactor in oxygen bleach~
ing in order to reduce depolymerization of the cellulose. This, however, has proved not to function satisfactorily in practice.
Normally, white liquor is used as the source of alkali in oxygen bleaching. According to standard procedure, the white liquor is oxidized before being added to the pulp in oxygen bleaching so as to transform sulphide into thiosulphate. It is well known that the presence oE sulphide ions during oxygen bleaching affects the ratio between lignin and carbohydrate di~solution negativel~. This i9 expressed in a lowered viscosity of the pulp.
It has also been proposed by A.G. Kirkman, E.K. Andrews, H.M. Chang, AIChE Annual Meeting, Los Angeles, ~ovember 1982, to render the oxygen bleaching more efficient through pretreatment of the sulphate pulp with green liquor. The principal ingredients of green liquor are sodium sulphide and sodium carbonate and the content of polysulphide is negligible.
The procedure according to the present invention seeks to attain a lower lignin content than normal, with retained high pulp ~iscosity, prior to bleaching with chlorine chemicals. In .
this procedure, after boiling at a temperature between lOO~C and;
160C the pulp is treated with a solution containing 0.2-0.6 mol/l ` effective alkali, 0.5-5 per cent by weight sulphur of the weight .,;
, r~
~, . .
391(1 ~JI
of the pulp in the form of polysulphide, i.e. ~ia2Sx, where x is
2 or higher, and in the presence of a stabilizer for polysul-phide.
The treatment can be combined advantageously with oxygen bleachin~, resul-ting in a beneficially low lignin content before chlorine bleaching. The process of this invention makes it possi~
ble when manufacturing bleached pulp, to lower the lignin content of the pulp before bleaching with chlorine chemicals to a lower level than is possible with the traditional sulphate digestion technique without the viscosity becoming too low. Treatment of sulphate pulp with alkaline polysulphide according to the process of the invention before oxygen bleaching makes it possible to attain a lower lignin content after oxygen bleaching than normal, with retained pulp quality. The polysulphide treatment results in a lowering of the lignin content of the pulp by about 25 per cent.
In subsequent oxygen bleaching, the lignin content can be further lowered by around 50 per cent.
By carrying out the polysulphide treatment in accordance with the invention in a new stage of the manufacturing process for sulphate pulp, namely after digestion but before oxygen bleaching, and through addition of a stabilizer for the polysulphide, it has ; proved possible to attain a selective delignification, i.e. a good dissolution of lignin with a significantly reduced dissolution and degradation of carbohydrates.
Magnesium salts, e.g. magnesium sulphate, or complexers, e.g. ethylenediamine tetraacitic acid (EDTA) are used as stabil-izing substances.
:' .
iB~
- 4a -In the manufacture of sulphate pulp in a continuous digester it is possibLe to introduce the polysulphide treatment without having to install a separate reactor. In a continuous digester with a washing zone the conditions with regard to temper-ature, dwell time and liquid module prevailing in the washing zone are such as are favourable for the polysulphide treatment. In such a digester, the treatment can be performed by adding alkali, poly-sulphide and stabilizer to the washing liquid which is conducted into the washing zone.
In the manufacture of sulphate pulp in a batch digester, the polysulphide treatment according to the process of this inven-tion can be performed in conjunction with pulp wrashing. In this case, the process equipment must be supplemented with a reaction vessel for the polysulphide treatment.
Another possibility is to displace the black liquor at the end of the cook from the batch digester with polysulphide solution, and then to use the digester to carry out the polysul~
phide treatment.
The polysulphide treatment can also be utilized to increase the capacity of an existing digester house. The cook is then interrupted at a higher kappa number than normal, i.e. after a shorter cooking time than normally, and , ', '' : , ,. :, :
5 ~ 9~
continued delignification is done with polysulphide solution. This can be utilized regardless of whether the pulp is to be bleached or not.
For maximum utilization of the chemicals added for the polysulphide treatment these can be returned to the ordinary chemical recovery system via the cookinq, whereby the load on this system is reduced. This means that the filtrate from washing of the pulp after the polysulphide treatment is charged together with white liquor at the start of the cook.
In polysulphide treatment in the washing zone in a continuous digester it is necessary for the removal of poly-sulphide solution from the digester to be separated from the removal of black liquor.
In order to further clarify the invention, a number of embodiment examples performed on a laboratory scale are described below. In all the examples, the kappa number and viscosity determinations have been performed in accordance with SCAN test.
Example 1 The treatment was performed in an autoclave containing 8 g of dry pine sulphate pulp with a kappa number of 45.3 and 100 ml of an aqueous solution which contained 1.6 g NaO~, 3.2 g Na2S x 9 ~2~ 39.5 mg MgSO4 and 0.24 g sulphur.
The autoclave was rotated for one hour at a temperature of 135 C. The pulp treated in this manner had a kappa number of 28.2 and a viscosity of 1208 dm3/kg.
Example 2 A pine sulphate pulp with a kappa number of 32 and a viscosity of 1177 dm3/kg was treated as follows.
a) Washing with acid followed by polysulphide treatment:
8 g of pulp according to the above was suspended in - 1.5 1 of water. 40 ml of acetic acid was added while stirring. After five minutes, the pulp was washed on a filter with water to a filtrate pH of 5.5. The pulp was then charged in an autoclave together with 100 ml aqueous ~, , ' , .
. .
:
6 ~L2~90~
solution containing 20 g NaOH, 4.0 g Na2S x 9H20 and 0.5 g sulphur. The autoclave was rotated for 30 minutes at a temperature of 120 C. The obtained pulp had a kappa number of 22.7 and a viscosity of 1075 dm3/kg.
b) Polysulphide treatment without prior washing with acid:
8 g of the pulp with a kappa number of 32 as per the above was charged in an autoclave together with 100 ml aqueous solution containing 2.0 g NaOH, 4.0 g Na2S x 9H20 and 0.5 g sulphur. The autoclave was rotated for 30 minutes at a temperature of 120 C. The obtained pulp had a kappa number of 26.7 and a viscosity of 1067 dm3/kg.
Example 3 Polysulphide extraction of pine sulphate pulp with a kappa number of 32 and a viscosity of 1177 dm3/kg.
~ n autoclave containing 8 g of pulp and 100 ml of an aqueous solution containing 2.~ g NaOH, 4.8 Na2S x 9 H20, 0.4 g sulphur of and 24 mg of ethylenediamine tetraacetic acid (EDTA) was rotated for one hour at a temperature of 120 C. The obtained pulp had a kappa number fo 23.2 and a viscosity of 1001 dm3/kg.
Example 4 -Polysulphide extraction of birch sulphate pulp with a kappa number of 14.5 and a viscosity of 1333 dm3/kg.
An autoclave containing 8 g of pulp and 100 ml of an aqueous solution containing 2.0 g NaOH, 4.0 g Na2S x 9 H20, 0.32 g sulphur and 39.5 mg MgS04 was rotated for 20 minutes at a temperature of 120 C. The treated pulp had a kappa number of 10.9 and a viscosity of 1298 dm3/kg.
Example 5 A pine sulphate pulp with a kappa number of 30.9 and a viscosity of 1130 dm3/kg was treated as follows:
a) Polysulphide treatment:
50 g of pulp as above was charged in an autoclave together with 625 ml of an a~ueous solution containing 10.0 g NaOH, 20 g Na2s x 9 H20, 0.25 g MgS04 and 2.0 g sulphur. The autoclave was rotated for one hour at a , ' : : '. . , ' :
~ ' ~ ' ~ ' ' ' :
.
7 ~2~390~
temperature of 120 C. After the treatment, the kappa number of the pulp was 23.9 and its viscosity 1124 dm3/kg.
b) Oxygen bleaching:
50 g of pulp treated according to a) above was charged in an indirectly heated autoclave fitted with an agitator together with 150 ml of an aqueous solution containing 0.8 g NaOH and 0~25 g MgSO4. The pulp was treated in the autoclave for one hour at a temperature of 90 C under an axygen pressure of 8 bar. The thus treated pulp had a kappa number of 11.9 and a viscosity of 915 dm3/kg.
, . - ~ .. . . .
The treatment can be combined advantageously with oxygen bleachin~, resul-ting in a beneficially low lignin content before chlorine bleaching. The process of this invention makes it possi~
ble when manufacturing bleached pulp, to lower the lignin content of the pulp before bleaching with chlorine chemicals to a lower level than is possible with the traditional sulphate digestion technique without the viscosity becoming too low. Treatment of sulphate pulp with alkaline polysulphide according to the process of the invention before oxygen bleaching makes it possible to attain a lower lignin content after oxygen bleaching than normal, with retained pulp quality. The polysulphide treatment results in a lowering of the lignin content of the pulp by about 25 per cent.
In subsequent oxygen bleaching, the lignin content can be further lowered by around 50 per cent.
By carrying out the polysulphide treatment in accordance with the invention in a new stage of the manufacturing process for sulphate pulp, namely after digestion but before oxygen bleaching, and through addition of a stabilizer for the polysulphide, it has ; proved possible to attain a selective delignification, i.e. a good dissolution of lignin with a significantly reduced dissolution and degradation of carbohydrates.
Magnesium salts, e.g. magnesium sulphate, or complexers, e.g. ethylenediamine tetraacitic acid (EDTA) are used as stabil-izing substances.
:' .
iB~
- 4a -In the manufacture of sulphate pulp in a continuous digester it is possibLe to introduce the polysulphide treatment without having to install a separate reactor. In a continuous digester with a washing zone the conditions with regard to temper-ature, dwell time and liquid module prevailing in the washing zone are such as are favourable for the polysulphide treatment. In such a digester, the treatment can be performed by adding alkali, poly-sulphide and stabilizer to the washing liquid which is conducted into the washing zone.
In the manufacture of sulphate pulp in a batch digester, the polysulphide treatment according to the process of this inven-tion can be performed in conjunction with pulp wrashing. In this case, the process equipment must be supplemented with a reaction vessel for the polysulphide treatment.
Another possibility is to displace the black liquor at the end of the cook from the batch digester with polysulphide solution, and then to use the digester to carry out the polysul~
phide treatment.
The polysulphide treatment can also be utilized to increase the capacity of an existing digester house. The cook is then interrupted at a higher kappa number than normal, i.e. after a shorter cooking time than normally, and , ', '' : , ,. :, :
5 ~ 9~
continued delignification is done with polysulphide solution. This can be utilized regardless of whether the pulp is to be bleached or not.
For maximum utilization of the chemicals added for the polysulphide treatment these can be returned to the ordinary chemical recovery system via the cookinq, whereby the load on this system is reduced. This means that the filtrate from washing of the pulp after the polysulphide treatment is charged together with white liquor at the start of the cook.
In polysulphide treatment in the washing zone in a continuous digester it is necessary for the removal of poly-sulphide solution from the digester to be separated from the removal of black liquor.
In order to further clarify the invention, a number of embodiment examples performed on a laboratory scale are described below. In all the examples, the kappa number and viscosity determinations have been performed in accordance with SCAN test.
Example 1 The treatment was performed in an autoclave containing 8 g of dry pine sulphate pulp with a kappa number of 45.3 and 100 ml of an aqueous solution which contained 1.6 g NaO~, 3.2 g Na2S x 9 ~2~ 39.5 mg MgSO4 and 0.24 g sulphur.
The autoclave was rotated for one hour at a temperature of 135 C. The pulp treated in this manner had a kappa number of 28.2 and a viscosity of 1208 dm3/kg.
Example 2 A pine sulphate pulp with a kappa number of 32 and a viscosity of 1177 dm3/kg was treated as follows.
a) Washing with acid followed by polysulphide treatment:
8 g of pulp according to the above was suspended in - 1.5 1 of water. 40 ml of acetic acid was added while stirring. After five minutes, the pulp was washed on a filter with water to a filtrate pH of 5.5. The pulp was then charged in an autoclave together with 100 ml aqueous ~, , ' , .
. .
:
6 ~L2~90~
solution containing 20 g NaOH, 4.0 g Na2S x 9H20 and 0.5 g sulphur. The autoclave was rotated for 30 minutes at a temperature of 120 C. The obtained pulp had a kappa number of 22.7 and a viscosity of 1075 dm3/kg.
b) Polysulphide treatment without prior washing with acid:
8 g of the pulp with a kappa number of 32 as per the above was charged in an autoclave together with 100 ml aqueous solution containing 2.0 g NaOH, 4.0 g Na2S x 9H20 and 0.5 g sulphur. The autoclave was rotated for 30 minutes at a temperature of 120 C. The obtained pulp had a kappa number of 26.7 and a viscosity of 1067 dm3/kg.
Example 3 Polysulphide extraction of pine sulphate pulp with a kappa number of 32 and a viscosity of 1177 dm3/kg.
~ n autoclave containing 8 g of pulp and 100 ml of an aqueous solution containing 2.~ g NaOH, 4.8 Na2S x 9 H20, 0.4 g sulphur of and 24 mg of ethylenediamine tetraacetic acid (EDTA) was rotated for one hour at a temperature of 120 C. The obtained pulp had a kappa number fo 23.2 and a viscosity of 1001 dm3/kg.
Example 4 -Polysulphide extraction of birch sulphate pulp with a kappa number of 14.5 and a viscosity of 1333 dm3/kg.
An autoclave containing 8 g of pulp and 100 ml of an aqueous solution containing 2.0 g NaOH, 4.0 g Na2S x 9 H20, 0.32 g sulphur and 39.5 mg MgS04 was rotated for 20 minutes at a temperature of 120 C. The treated pulp had a kappa number of 10.9 and a viscosity of 1298 dm3/kg.
Example 5 A pine sulphate pulp with a kappa number of 30.9 and a viscosity of 1130 dm3/kg was treated as follows:
a) Polysulphide treatment:
50 g of pulp as above was charged in an autoclave together with 625 ml of an a~ueous solution containing 10.0 g NaOH, 20 g Na2s x 9 H20, 0.25 g MgS04 and 2.0 g sulphur. The autoclave was rotated for one hour at a , ' : : '. . , ' :
~ ' ~ ' ~ ' ' ' :
.
7 ~2~390~
temperature of 120 C. After the treatment, the kappa number of the pulp was 23.9 and its viscosity 1124 dm3/kg.
b) Oxygen bleaching:
50 g of pulp treated according to a) above was charged in an indirectly heated autoclave fitted with an agitator together with 150 ml of an aqueous solution containing 0.8 g NaOH and 0~25 g MgSO4. The pulp was treated in the autoclave for one hour at a temperature of 90 C under an axygen pressure of 8 bar. The thus treated pulp had a kappa number of 11.9 and a viscosity of 915 dm3/kg.
, . - ~ .. . . .
Claims (14)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A procedure for the manufacture of unbleached or bleached sulphate pulp, whereby a chemical cellulose pulp after digestion but before possible subsequent bleaching is delignified with an alkaline polysulphide solution, wherein the pulp is treated after digestion at a temperature of between 100°C and 160°C with a solution containing 0.2-0.6 mol/l effective alkali, 0.5-5 per cent by weight sulphur of the weight of the pulp in the form of polysulphide, i.e. Na2Sx where x is 2 or higher, and in the presence of a stabilizer for polysulphide.
2. A procedure according to Claim 1, wherein magnesium salts, are used as stabilizer for polysulphide.
3. A procedure according to Claim 1, wherein complex-forming substances are used as stabilizer for polysulphide.
4. A procedure according to Claim 1, wherein the treatment is performed at a pulp concentration of about 3-40 per cent by weight.
5. A procedure according to Claim 1, wherein the treatment time is 10 minutes - 4 hours.
6. A procedure according to Claim 1, wherein the polysul-phide treatment is preceded by a washing with acid.
7. A procedure according to Claim 1, wherein the treatment is performed in conjunction with washing of the pulp in the washing zone in a continuous digester.
8. A procedure according to Claim 1, wherein the treatment is performed in a batch digester in direct association with the cook, through displacement of the utilized cooking liquor prior to the treatment with polysulphide solution.
9. A procedure according to Claim 1, wherein the polysul-phide solution is returned to the cook after the polysulphide treatment.
10. A procedure according to Claim 1, wherein hydrogen dioxide, ozone, oxygen, chlorine, chlorine dioxide, hypochloride or sodium hydroxide is used in subsequent bleaching.
11. A procedure according to claim 2 wherein the magnesium salt is magnesium sulphate.
12. A procedure according to claim 3 wherein the complex forming substance is ethylenediamine tetraacetic acid (EDTA).
13. A procedure according to claim 4 wherein the pulp con-centration is 8-15 per cent by weight.
14. A procedure according to claim 5 wherein the treatment time is 20-60 minutes.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| SE8500472A SE452483B (en) | 1985-02-01 | 1985-02-01 | PROCEDURE FOR DELIGNIFICATION OF SULPHATE MASS |
| SE8500472-9 | 1985-02-01 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1268906A true CA1268906A (en) | 1990-05-15 |
Family
ID=20358977
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000500799A Expired - Fee Related CA1268906A (en) | 1985-02-01 | 1986-01-31 | Procedure for delignification of sulphate pulp |
Country Status (3)
| Country | Link |
|---|---|
| CA (1) | CA1268906A (en) |
| FI (1) | FI81135C (en) |
| SE (1) | SE452483B (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| SE8704041L (en) * | 1987-10-16 | 1989-04-17 | Sca Development Ab | SEATED WHITE CELLULOSAMASSA WHITE |
-
1985
- 1985-02-01 SE SE8500472A patent/SE452483B/en not_active IP Right Cessation
-
1986
- 1986-01-29 FI FI860421A patent/FI81135C/en not_active IP Right Cessation
- 1986-01-31 CA CA000500799A patent/CA1268906A/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| FI860421A (en) | 1986-08-02 |
| FI860421A0 (en) | 1986-01-29 |
| FI81135B (en) | 1990-05-31 |
| SE8500472D0 (en) | 1985-02-01 |
| SE452483B (en) | 1987-11-30 |
| FI81135C (en) | 1990-09-10 |
| SE8500472L (en) | 1986-08-02 |
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