CA2036173C - Process for the chlorine-free bleaching and delignification of cellulose - Google Patents
Process for the chlorine-free bleaching and delignification of celluloseInfo
- Publication number
- CA2036173C CA2036173C CA002036173A CA2036173A CA2036173C CA 2036173 C CA2036173 C CA 2036173C CA 002036173 A CA002036173 A CA 002036173A CA 2036173 A CA2036173 A CA 2036173A CA 2036173 C CA2036173 C CA 2036173C
- Authority
- CA
- Canada
- Prior art keywords
- cellulose
- cyanamide
- process according
- weight
- peroxide
- 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
- 229920002678 cellulose Polymers 0.000 title claims abstract description 49
- 239000001913 cellulose Substances 0.000 title claims abstract description 43
- 238000004061 bleaching Methods 0.000 title claims abstract description 37
- 238000000034 method Methods 0.000 title claims abstract description 26
- 150000002978 peroxides Chemical class 0.000 claims abstract description 26
- XZMCDFZZKTWFGF-UHFFFAOYSA-N Cyanamide Chemical compound NC#N XZMCDFZZKTWFGF-UHFFFAOYSA-N 0.000 claims abstract description 18
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims abstract description 17
- 239000001301 oxygen Substances 0.000 claims abstract description 17
- 229910052760 oxygen Inorganic materials 0.000 claims abstract description 17
- 150000001912 cyanamides Chemical class 0.000 claims abstract description 12
- CBENFWSGALASAD-UHFFFAOYSA-N Ozone Chemical compound [O-][O+]=O CBENFWSGALASAD-UHFFFAOYSA-N 0.000 claims abstract description 6
- 239000000463 material Substances 0.000 claims description 8
- 239000007787 solid Substances 0.000 claims description 4
- 235000010980 cellulose Nutrition 0.000 description 36
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 33
- MHAJPDPJQMAIIY-UHFFFAOYSA-N Hydrogen peroxide Chemical compound OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 description 22
- WQYVRQLZKVEZGA-UHFFFAOYSA-N hypochlorite Chemical compound Cl[O-] WQYVRQLZKVEZGA-UHFFFAOYSA-N 0.000 description 12
- ZAMOUSCENKQFHK-UHFFFAOYSA-N Chlorine atom Chemical compound [Cl] ZAMOUSCENKQFHK-UHFFFAOYSA-N 0.000 description 10
- 239000000460 chlorine Substances 0.000 description 10
- 239000000243 solution Substances 0.000 description 10
- 229910052801 chlorine Inorganic materials 0.000 description 9
- 238000000605 extraction Methods 0.000 description 8
- OSVXSBDYLRYLIG-UHFFFAOYSA-N dioxidochlorine(.) Chemical compound O=Cl=O OSVXSBDYLRYLIG-UHFFFAOYSA-N 0.000 description 6
- 239000007864 aqueous solution Substances 0.000 description 4
- 239000004155 Chlorine dioxide Substances 0.000 description 3
- 235000019398 chlorine dioxide Nutrition 0.000 description 3
- 238000002203 pretreatment Methods 0.000 description 3
- 239000000725 suspension Substances 0.000 description 3
- 239000012190 activator Substances 0.000 description 2
- 239000003795 chemical substances by application Substances 0.000 description 2
- 238000001914 filtration Methods 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 230000035484 reaction time Effects 0.000 description 2
- 239000007858 starting material Substances 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- LSNNMFCWUKXFEE-UHFFFAOYSA-L sulfite Chemical compound [O-]S([O-])=O LSNNMFCWUKXFEE-UHFFFAOYSA-L 0.000 description 2
- 239000008399 tap water Substances 0.000 description 2
- 235000020679 tap water Nutrition 0.000 description 2
- 238000005406 washing Methods 0.000 description 2
- MVXMNHYVCLMLDD-UHFFFAOYSA-N 4-methoxynaphthalene-1-carbaldehyde Chemical compound C1=CC=C2C(OC)=CC=C(C=O)C2=C1 MVXMNHYVCLMLDD-UHFFFAOYSA-N 0.000 description 1
- 241000609240 Ambelania acida Species 0.000 description 1
- 239000004698 Polyethylene Substances 0.000 description 1
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 description 1
- 230000004913 activation Effects 0.000 description 1
- 239000010905 bagasse Substances 0.000 description 1
- 238000004182 chemical digestion Methods 0.000 description 1
- JFBJUMZWZDHTIF-UHFFFAOYSA-N chlorine chlorite Inorganic materials ClOCl=O JFBJUMZWZDHTIF-UHFFFAOYSA-N 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 230000029087 digestion Effects 0.000 description 1
- 238000011835 investigation Methods 0.000 description 1
- 238000002386 leaching Methods 0.000 description 1
- 229920005610 lignin Polymers 0.000 description 1
- GOKQBRXJUKTYSC-UHFFFAOYSA-N magnesium;azanidylidenemethylideneazanide Chemical compound [Mg+2].[N-]=C=[N-] GOKQBRXJUKTYSC-UHFFFAOYSA-N 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 125000000864 peroxy group Chemical group O(O*)* 0.000 description 1
- -1 polyethylene Polymers 0.000 description 1
- 229920000573 polyethylene Polymers 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 150000003839 salts Chemical class 0.000 description 1
- 239000002002 slurry Substances 0.000 description 1
- PFUVRDFDKPNGAV-UHFFFAOYSA-N sodium peroxide Chemical compound [Na+].[Na+].[O-][O-] PFUVRDFDKPNGAV-UHFFFAOYSA-N 0.000 description 1
- MBEGFNBBAVRKLK-UHFFFAOYSA-N sodium;iminomethylideneazanide Chemical compound [Na+].[NH-]C#N MBEGFNBBAVRKLK-UHFFFAOYSA-N 0.000 description 1
- 239000010902 straw Substances 0.000 description 1
- 229910021653 sulphate ion Inorganic materials 0.000 description 1
- 235000013311 vegetables Nutrition 0.000 description 1
- 239000002351 wastewater Substances 0.000 description 1
- 239000002023 wood Substances 0.000 description 1
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
- D21C9/10—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
- D21C9/147—Bleaching ; Apparatus therefor with oxygen or its allotropic modifications
- D21C9/153—Bleaching ; Apparatus therefor with oxygen or its allotropic modifications with ozone
-
- 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
- D21C9/16—Bleaching ; Apparatus therefor with per compounds
- D21C9/163—Bleaching ; Apparatus therefor with per compounds with peroxides
Landscapes
- Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
- Wood Science & Technology (AREA)
- Paper (AREA)
- Polysaccharides And Polysaccharide Derivatives (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
- Cereal-Derived Products (AREA)
- Eye Examination Apparatus (AREA)
- Ultra Sonic Daignosis Equipment (AREA)
- Gyroscopes (AREA)
Abstract
The present invention provides a process for the chlorine-free bleaching and delignification of cellulose pre-bleached with oxygen and peroxide or oxygen and or ozone, wherein the pre-bleached cellulose is treated twice with peroxide activated by cyanamide and/or a cyanamide salt.
Description
_ 2 The present invention is concerned with a process for the chlorine-free bleaching and delignification of cellulose which has already been pre-bleached with oxygen and peroxide or oxygen and or ozone.
For the production of white-stabilised and/or high strength paper products, substantially lignin-free cellulose is needed. For this purpose, cellulose which is obtained from vegetable raw materials, for example wood, cane, straw, bagasse and the like, by a chemical digestion (sulphate or sulphite digestion) is subjected to a delignifying bleaching.
In the case of this usually multi-step bleaching process, there were previously essentially employed elementary chlorine (C) and hypochlorite (H) as treating agents, in which case, for example, for sulphite cellulose the following bleaching sequence was conventional:
(C) - (E) - (H) - (H) in which (C) = chlorine bleaching, (E) = extraction of the chlorolignins with an aqueous solution of sodium hydroxide and (H) = hypochlorite treatment.
For the reduction of the environmentally stressing use of elementary chlorine, the extraction step was increasingly carried out with peroxide, in which case a distinct reduction of the use of chlorine could be achieved.
In order to be able completely to avoid the use of elementary chlorine, in recent years the chlorine step has been replaced by an oxygen step (EO) or by an extraction step (EOP) `- 2036173 assisted with oxygen and peroxide. However, with the help of these bleaching steps, only semi-bleached celluloses are obtainable which have a degree of whiteness of 75 to 80~.
Three quarter-bleached celluloses with a degree of whiteness of 80 to 87~ are admittedly possible without the use of elementary chlorine but, instead thereof, it is necessary to make use of a treatment step with hypochlorite (H) or chlorine dioxide (D), in which case the following sequences are then usual:
EOP - D - EP
EOP - H - EP
EOP = extraction with oxygen/peroxide EP = extraction with peroxide D = treatment with chlorine dioxide H = treatment with hypochlorite.
The same also applies in the case of fully bleached celluloses with degrees of whiteness of 88 to 90 ~ which are obtainable, for example, with the following bleaching sequence:
EOP - D - EP - D - EP
However, as before, not only the use of hypochlorite but also of chlorine dioxide represents a loading of the waste water and of the exhaust air.
Therefore, it is an object of the present disclosure to develop a process for the chlorine-free bleaching and delignification of cellulose which has been pre-bleached with oxygen and peroxide or oxygen and or ozone, which process does not suffer from the disadvantages of the prior art but rather, without the help of chlorine-containing treatment agents and i ~r .~-_ 4 with a small technical expense, makes possible the production of celluloses with a high degree of whiteness.
Thus, according to the present invention, there is provided a process for the chlorine-free bleaching and delignification of cellulose which has been pre-bleached with oxygen and peroxide or oxygen and or ozone, wherein the pre-bleached cellulose is treated twice with peroxide activated by cyanamide and/or a cyanamide salt.
The activation of peroxide by means of cyanamide derivatives is admittedly known, for example, from published Federal Republic of Germany Patent Application No. 35 44 398 but, according to this process, essentially unbleached cellulose is used as starting material.
Furthermore, from our own investigations, it is known that the action of these activators decreases very quickly in the case of celluloses pre-bleached with chlorine or hypochlorite, as well as in the case of relatively high temperatures and long reaction times. Therefore, it was completely surprising that, in the case of cellulose pre-bleached with oxygen and peroxide, the action of the cyanamide derivatives was also so good in the case of comparatively high temperatures that, in this way, a very good degree of whiteness could be achieved.
In this case of the new process here described, as starting material there is used pre-bleached cellulose which has been pre-treated by a conventional extraction step with oxygen and peroxide or oxygen and or ozone and which, according to the nature of the cellulose, displays greatly differing degrees of whiteness. Whereas, for example, pinewood cellulose .
.,p .~
_ 5 pre-bleached in this way has a degree of whiteness of 65 to 75~, the corresponding degree of whiteness for beechwood cellulose is already, in some cases, above 80~. The kappa values for the degree of delignification are normally from 2 to 10 and especially from 3 to 8.
The two treatment steps include the bleaching and delignification of cellulose with peroxide and cyanamide or cyanamide salts, which are preferably used in the form of alkaline-reacting salts, for example sodium hydrogen cyanamide, calcium cyanamide or magnesium cyanamide. The amounts of peroxide or of cyanamide derivatives differ only slightly in the two treatment steps. As peroxide, there can be used all water-soluble, bleach-active peroxy compounds, the use of hydrogen peroxide or sodium peroxide being preferred.
Whereas in the first step, the cyanamide content is preferably 0.05 to 1.0~ by weight and especially 0.07 to 0.33 by weight, in the second step it is preferable to work with a cyanamide content of 0.01 to 0.7~ by weight and especially of 0.03 to 0.23~ by weight, in each case referred to the dry weight of the cellulose.
During the first treatment step, the peroxide content can be varied from 0.1 to 3.0 by weight and during the second treatment step from 0.1 to 2.0~ by weight, referred to the dry weight of the cellulose.
The other process conditions for the two treatment steps are substantially identical. The pH value is, as is usual in the case of peroxide bleachings, in each case adjusted alkaline and, as a rule, is from 9 to 12. The adjustment of the pH value ' ~
.~ 6 takes place with known alkaline-reacting substances, in which case sodium hydroxide is preferred for reasons of better solubility. For this purpose, 0.3 to 1.5% by weight of sodium hydroxide normally suffice in order, in each case, to adjust the desired pH value.
In both treatment steps, the solids densities can be varied within wide limits, in which case solids densities of 5 to 30% by weight, especially those of 7 to 20% by weight are especially preferred.
Depending upon the nature of the cellulose and the desired degree of whiteness, the treatment steps here described are preferably carried out at a temperature of from 30 to 95C. and especially preferably of from 55 to 80C., treatment times of from 1 to 8 hours thereby usually being necessary in order to achieve the desired degree of whiteness. However, by means of the addition of cyanamide and/or of cyanamide salts, it is, in general, possible to shorten the reaction time and/or to lower the temperature in comparison with the peroxide treatment without this activator if, for any reason, this is desired.
Thus, with the help of the new process herein, three-quarter to completely bleached cellulose can be produced in a technically simple manner and without the help of chlorine-containing chemicals, said celluloses having a degree of whiteness of >80%.
The following Examples are given for the purpose of illustrating the present invention:
Examples.
,~
All the bleaching steps were carried out in polyethylene bags.
Determinations Degree of whiteness: from washed cellulose were formed standardised white sheets on a sheet-making apparatus (according to Rapid Kothen) and the degree of whiteness determined in percentages according to the iso-standard 2470 with a measurement apparatus of the type Elrepho 2000*
(Datacolor).
Kappa number: the determination of this parameter, which is a measure for the lignin content in cellulose, takes place according to iso-standard 302.
Bleaching sequences: these are abbreviated as follows:
EOP =extraction assisted with oxygen and hydrogen peroxide EP =extraction assisted with hydrogen peroxide (peroxide bleaching steps).
Exam~le 1 (comparison).
1st treatment step.
Into 175.82 g. of pinewood-magnesium bisulphite cellulose (40 g. otro), after EOP pre-treatment, with 73.6~ whiteness and kappa 4.8, were intensively kneaded 224.18 g. of an aqueous solution which contained 3.60 g. of sodium hydroxide (10~) and 0.69 g. hydrogen peroxide (35~). For the complete reaction, the 10~ cellulose slurry was introduced into a water-bath with a temperature of about 74C. After a * Trademark X
8 2o36l73 bleaching period of 120 minutes, the suspension was diluted with tap water and the pH adjusted to 6.0, followed by filtering off with suction and subsequent washing. The cellulose obtained had a degree of whiteness of 79.4.
2nd treatment step.
The cellulose so pre-treated was subjected to a further peroxide treatment.
amount of material: 140.85 g.
bleaching solution: 259.12 g. with 2.00 g. sodium hydroxide (10~) and 0.34 g. hydrogen peroxide (35~) bleaching temperature: 74C.
bleaching period: 120 minutes degree of whiteness: 81.1 Example 2.
1st treatment step.
Into 175.82 g. pinewood-magnesium bisulphite cellulose (40 g. otro), after EOP pre-treatment, with 73.6~ whiteness and kappa 4.8, were incorporated 88.44 g. of an aqueous solution which contained 0.80 g. of the 10~ cyanamide solution. After 2 to 5 minutes, a further 134.74 g. of an aqueous solution, which contained 3.60 g. sodium hydroxide (10~) and 0.69 g. hydrogen peroxide (35~), were added thereto and also intensively kneaded in. For the complete reaction, the 10~ cellulose suspension was introduced into a water-bath with a temperature of about 74C.
After a bleaching period of 120 minutes, the suspension was diluted with tap water, adjusted to pH 6.0, followed by ~r g filtering off with suction and subsequent washing. The degree of whiteness of the cellulose obtained was 82.2.
2nd treatment step.
The cellulose so pre-treated was subjected to a further peroxide treatment.
amount of material: 140.85 g.
aqueous cyanamide solution: 102.96 g. with 0.40 g.
cyanamide (10~) bleaching solution: 156.19 g. with 2.00 g. sodium hydroxide (10%) and 0.34 g. hydrogen peroxide (35%) bleaching temperatures: 74C.
bleaching period: 120 minutes degree of whiteness: 85.5~.
Example 3 (comparison).
Beechwood-magnesium bisulphite cellulose was, after an EOP
pre-treatment, with a degree of whiteness of 82.6~, further treated analogously to Example 1 under the following conditions:
1st treatment step.
amount of material: 357.14 g. (100 g. otro) bleaching solution: 642.86 g. with 5.00 g. sodium hydroxide (10~)and 1.00 g. hydrogen peroxide (35%) bleaching temperature: 55C.
bleaching period: 120 minutes degree of whiteness: 86.0%.
2nd treatment ste~.
amount of material: 178.59 g. (50 g. otro) 2036173 leaching solution: 321.43 with 2.50 g. sodium hydroxide (10%)and 0.50 g. hydrogen peroxide (35%) bleaching temperature: 55C.
bleaching period: 120 minutes degree of whiteness: 86.7%.
Example 4.
Beechwood-magnesium bisulphite cellulose corresponding to Example 2 with a degree of whiteness of 82.6~ was post-treated under the following conditions:
1st treatment step.
amount of material: 357.14 g. (100 g. otro) aqueous cyanamide solution: 255.46 g. with 1.20 g.
cyanamide (10%) bleaching solution: 387.39 g. with 5.00 g. sodium hydroxide (10%) and 1.00 g. hydrogen peroxide (35%) bleaching temperature: 55C.
bleaching period: 120 minutes degree of whiteness: 88.3%
2nd treatment step.
amount of material: 178.57 g. (100 g. otro) aqueous cyanamide solution: 127.73 g. with 0.60 g.
cyanamide (10%) bleaching solution: 193.70 g. with 2.50 g. sodium hydroxide (10%) and 0.50 g. hydrogen peroxide (35%) bleaching temperature: 55C.
bleaching period: 120 minutes degree of whiteness: 89.5%.
, .
For the production of white-stabilised and/or high strength paper products, substantially lignin-free cellulose is needed. For this purpose, cellulose which is obtained from vegetable raw materials, for example wood, cane, straw, bagasse and the like, by a chemical digestion (sulphate or sulphite digestion) is subjected to a delignifying bleaching.
In the case of this usually multi-step bleaching process, there were previously essentially employed elementary chlorine (C) and hypochlorite (H) as treating agents, in which case, for example, for sulphite cellulose the following bleaching sequence was conventional:
(C) - (E) - (H) - (H) in which (C) = chlorine bleaching, (E) = extraction of the chlorolignins with an aqueous solution of sodium hydroxide and (H) = hypochlorite treatment.
For the reduction of the environmentally stressing use of elementary chlorine, the extraction step was increasingly carried out with peroxide, in which case a distinct reduction of the use of chlorine could be achieved.
In order to be able completely to avoid the use of elementary chlorine, in recent years the chlorine step has been replaced by an oxygen step (EO) or by an extraction step (EOP) `- 2036173 assisted with oxygen and peroxide. However, with the help of these bleaching steps, only semi-bleached celluloses are obtainable which have a degree of whiteness of 75 to 80~.
Three quarter-bleached celluloses with a degree of whiteness of 80 to 87~ are admittedly possible without the use of elementary chlorine but, instead thereof, it is necessary to make use of a treatment step with hypochlorite (H) or chlorine dioxide (D), in which case the following sequences are then usual:
EOP - D - EP
EOP - H - EP
EOP = extraction with oxygen/peroxide EP = extraction with peroxide D = treatment with chlorine dioxide H = treatment with hypochlorite.
The same also applies in the case of fully bleached celluloses with degrees of whiteness of 88 to 90 ~ which are obtainable, for example, with the following bleaching sequence:
EOP - D - EP - D - EP
However, as before, not only the use of hypochlorite but also of chlorine dioxide represents a loading of the waste water and of the exhaust air.
Therefore, it is an object of the present disclosure to develop a process for the chlorine-free bleaching and delignification of cellulose which has been pre-bleached with oxygen and peroxide or oxygen and or ozone, which process does not suffer from the disadvantages of the prior art but rather, without the help of chlorine-containing treatment agents and i ~r .~-_ 4 with a small technical expense, makes possible the production of celluloses with a high degree of whiteness.
Thus, according to the present invention, there is provided a process for the chlorine-free bleaching and delignification of cellulose which has been pre-bleached with oxygen and peroxide or oxygen and or ozone, wherein the pre-bleached cellulose is treated twice with peroxide activated by cyanamide and/or a cyanamide salt.
The activation of peroxide by means of cyanamide derivatives is admittedly known, for example, from published Federal Republic of Germany Patent Application No. 35 44 398 but, according to this process, essentially unbleached cellulose is used as starting material.
Furthermore, from our own investigations, it is known that the action of these activators decreases very quickly in the case of celluloses pre-bleached with chlorine or hypochlorite, as well as in the case of relatively high temperatures and long reaction times. Therefore, it was completely surprising that, in the case of cellulose pre-bleached with oxygen and peroxide, the action of the cyanamide derivatives was also so good in the case of comparatively high temperatures that, in this way, a very good degree of whiteness could be achieved.
In this case of the new process here described, as starting material there is used pre-bleached cellulose which has been pre-treated by a conventional extraction step with oxygen and peroxide or oxygen and or ozone and which, according to the nature of the cellulose, displays greatly differing degrees of whiteness. Whereas, for example, pinewood cellulose .
.,p .~
_ 5 pre-bleached in this way has a degree of whiteness of 65 to 75~, the corresponding degree of whiteness for beechwood cellulose is already, in some cases, above 80~. The kappa values for the degree of delignification are normally from 2 to 10 and especially from 3 to 8.
The two treatment steps include the bleaching and delignification of cellulose with peroxide and cyanamide or cyanamide salts, which are preferably used in the form of alkaline-reacting salts, for example sodium hydrogen cyanamide, calcium cyanamide or magnesium cyanamide. The amounts of peroxide or of cyanamide derivatives differ only slightly in the two treatment steps. As peroxide, there can be used all water-soluble, bleach-active peroxy compounds, the use of hydrogen peroxide or sodium peroxide being preferred.
Whereas in the first step, the cyanamide content is preferably 0.05 to 1.0~ by weight and especially 0.07 to 0.33 by weight, in the second step it is preferable to work with a cyanamide content of 0.01 to 0.7~ by weight and especially of 0.03 to 0.23~ by weight, in each case referred to the dry weight of the cellulose.
During the first treatment step, the peroxide content can be varied from 0.1 to 3.0 by weight and during the second treatment step from 0.1 to 2.0~ by weight, referred to the dry weight of the cellulose.
The other process conditions for the two treatment steps are substantially identical. The pH value is, as is usual in the case of peroxide bleachings, in each case adjusted alkaline and, as a rule, is from 9 to 12. The adjustment of the pH value ' ~
.~ 6 takes place with known alkaline-reacting substances, in which case sodium hydroxide is preferred for reasons of better solubility. For this purpose, 0.3 to 1.5% by weight of sodium hydroxide normally suffice in order, in each case, to adjust the desired pH value.
In both treatment steps, the solids densities can be varied within wide limits, in which case solids densities of 5 to 30% by weight, especially those of 7 to 20% by weight are especially preferred.
Depending upon the nature of the cellulose and the desired degree of whiteness, the treatment steps here described are preferably carried out at a temperature of from 30 to 95C. and especially preferably of from 55 to 80C., treatment times of from 1 to 8 hours thereby usually being necessary in order to achieve the desired degree of whiteness. However, by means of the addition of cyanamide and/or of cyanamide salts, it is, in general, possible to shorten the reaction time and/or to lower the temperature in comparison with the peroxide treatment without this activator if, for any reason, this is desired.
Thus, with the help of the new process herein, three-quarter to completely bleached cellulose can be produced in a technically simple manner and without the help of chlorine-containing chemicals, said celluloses having a degree of whiteness of >80%.
The following Examples are given for the purpose of illustrating the present invention:
Examples.
,~
All the bleaching steps were carried out in polyethylene bags.
Determinations Degree of whiteness: from washed cellulose were formed standardised white sheets on a sheet-making apparatus (according to Rapid Kothen) and the degree of whiteness determined in percentages according to the iso-standard 2470 with a measurement apparatus of the type Elrepho 2000*
(Datacolor).
Kappa number: the determination of this parameter, which is a measure for the lignin content in cellulose, takes place according to iso-standard 302.
Bleaching sequences: these are abbreviated as follows:
EOP =extraction assisted with oxygen and hydrogen peroxide EP =extraction assisted with hydrogen peroxide (peroxide bleaching steps).
Exam~le 1 (comparison).
1st treatment step.
Into 175.82 g. of pinewood-magnesium bisulphite cellulose (40 g. otro), after EOP pre-treatment, with 73.6~ whiteness and kappa 4.8, were intensively kneaded 224.18 g. of an aqueous solution which contained 3.60 g. of sodium hydroxide (10~) and 0.69 g. hydrogen peroxide (35~). For the complete reaction, the 10~ cellulose slurry was introduced into a water-bath with a temperature of about 74C. After a * Trademark X
8 2o36l73 bleaching period of 120 minutes, the suspension was diluted with tap water and the pH adjusted to 6.0, followed by filtering off with suction and subsequent washing. The cellulose obtained had a degree of whiteness of 79.4.
2nd treatment step.
The cellulose so pre-treated was subjected to a further peroxide treatment.
amount of material: 140.85 g.
bleaching solution: 259.12 g. with 2.00 g. sodium hydroxide (10~) and 0.34 g. hydrogen peroxide (35~) bleaching temperature: 74C.
bleaching period: 120 minutes degree of whiteness: 81.1 Example 2.
1st treatment step.
Into 175.82 g. pinewood-magnesium bisulphite cellulose (40 g. otro), after EOP pre-treatment, with 73.6~ whiteness and kappa 4.8, were incorporated 88.44 g. of an aqueous solution which contained 0.80 g. of the 10~ cyanamide solution. After 2 to 5 minutes, a further 134.74 g. of an aqueous solution, which contained 3.60 g. sodium hydroxide (10~) and 0.69 g. hydrogen peroxide (35~), were added thereto and also intensively kneaded in. For the complete reaction, the 10~ cellulose suspension was introduced into a water-bath with a temperature of about 74C.
After a bleaching period of 120 minutes, the suspension was diluted with tap water, adjusted to pH 6.0, followed by ~r g filtering off with suction and subsequent washing. The degree of whiteness of the cellulose obtained was 82.2.
2nd treatment step.
The cellulose so pre-treated was subjected to a further peroxide treatment.
amount of material: 140.85 g.
aqueous cyanamide solution: 102.96 g. with 0.40 g.
cyanamide (10~) bleaching solution: 156.19 g. with 2.00 g. sodium hydroxide (10%) and 0.34 g. hydrogen peroxide (35%) bleaching temperatures: 74C.
bleaching period: 120 minutes degree of whiteness: 85.5~.
Example 3 (comparison).
Beechwood-magnesium bisulphite cellulose was, after an EOP
pre-treatment, with a degree of whiteness of 82.6~, further treated analogously to Example 1 under the following conditions:
1st treatment step.
amount of material: 357.14 g. (100 g. otro) bleaching solution: 642.86 g. with 5.00 g. sodium hydroxide (10~)and 1.00 g. hydrogen peroxide (35%) bleaching temperature: 55C.
bleaching period: 120 minutes degree of whiteness: 86.0%.
2nd treatment ste~.
amount of material: 178.59 g. (50 g. otro) 2036173 leaching solution: 321.43 with 2.50 g. sodium hydroxide (10%)and 0.50 g. hydrogen peroxide (35%) bleaching temperature: 55C.
bleaching period: 120 minutes degree of whiteness: 86.7%.
Example 4.
Beechwood-magnesium bisulphite cellulose corresponding to Example 2 with a degree of whiteness of 82.6~ was post-treated under the following conditions:
1st treatment step.
amount of material: 357.14 g. (100 g. otro) aqueous cyanamide solution: 255.46 g. with 1.20 g.
cyanamide (10%) bleaching solution: 387.39 g. with 5.00 g. sodium hydroxide (10%) and 1.00 g. hydrogen peroxide (35%) bleaching temperature: 55C.
bleaching period: 120 minutes degree of whiteness: 88.3%
2nd treatment step.
amount of material: 178.57 g. (100 g. otro) aqueous cyanamide solution: 127.73 g. with 0.60 g.
cyanamide (10%) bleaching solution: 193.70 g. with 2.50 g. sodium hydroxide (10%) and 0.50 g. hydrogen peroxide (35%) bleaching temperature: 55C.
bleaching period: 120 minutes degree of whiteness: 89.5%.
, .
Claims (15)
1. Process for the chlorine-free bleaching and delignification of cellulose pre-bleached with oxygen and peroxide or oxygen and/or ozone, wherein the pre-bleached cellulose is treated twice with peroxide activated by cyanamide and/or a cyanamide salt.
2. Process according to claim 1, wherein, in the first treatment step, 0.05 to 1.0% by weight of cyanamide and/or cyanamide salt, referred to the dry weight of the cellulose, is added.
3. Process according to claim 2, wherein, in the first treatment step, 0.07 to 0.33% by weight of cyanamide and/or cyanamide salt, referred to the dry weight of the cellulose, is added.
4. Process according to claims 1, 2 or 3, wherein, in the first treatment step, the peroxide content is adjusted to 0.1 to 3.0% by weight, referred to the dry weight of the cellulose.
5. Process according to claims 1, 2 or 3, wherein, in the second treatment step, there are added 0.01 to 0.7% by weight, referred to the dry weight of the cellulose, of cyanamide and/or cyanamide salt.
6. Process according to claim 5, wherein, in the second treatment step, there are added 0.03 to 0.23% by weight, referred to the dry weight of the cellulose, of cyanamide and/or cyanamide salt.
7. Process according to claim 5, wherein, in the second treatment step, the peroxide content is adjusted to 0.1 to 2.0% by weight, referred to the dry weight of the cellulose.
8. Process according to claims 1, 2, 3, 6 or 7, wherein, the pH
value in both treatment steps is adjusted to 9 to 12.
value in both treatment steps is adjusted to 9 to 12.
9. Process according to claims 1, 2, 3, 6 or 7, wherein, in both treatment steps, the solids material density is adjusted to 5 to 30%
by weight.
by weight.
10. Process according to claim 9, wherein, in both treatment steps, the solids material density is adjusted to 7 to 20% by weight.
11. Process according to claims 1, 2, 3, 6, 7 or 10, wherein both treatment steps are carried out at a temperature of 30 to 95°C.
12. Process according to claim 11, wherein both treatment steps are carried out at a temperature of 55 to 80°C.
13. Process according to claims 1, 2, 3, 6, 7, 10 or 12, wherein the period of treatment per step is 1 to 8 hours.
14. Process according to claim 1 for the chlorine-free bleaching and delignification of cellulose, substantially as hereinbefore described and exemplified.
15. Bleached and delignified cellulose, whenever produced by the process according to claims 1, 2, 3, 6, 7, 10, 12 or 14.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE4004364A DE4004364A1 (en) | 1990-02-13 | 1990-02-13 | Bleaching and delignifying pre-balanced cellulose - in two stages with peroxide activated with cyanamide or cyanamide salt, avoiding agents contg. chlorine |
| DEP4004364.9 | 1990-02-13 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2036173A1 CA2036173A1 (en) | 1991-08-14 |
| CA2036173C true CA2036173C (en) | 1996-01-23 |
Family
ID=6400030
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002036173A Expired - Fee Related CA2036173C (en) | 1990-02-13 | 1991-02-12 | Process for the chlorine-free bleaching and delignification of cellulose |
Country Status (7)
| Country | Link |
|---|---|
| EP (1) | EP0442425B1 (en) |
| AT (1) | ATE103649T1 (en) |
| CA (1) | CA2036173C (en) |
| DE (2) | DE4004364A1 (en) |
| ES (1) | ES2051531T3 (en) |
| FI (1) | FI910703L (en) |
| NO (1) | NO176329C (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE4031597A1 (en) * | 1990-10-05 | 1992-04-09 | Sueddeutsche Kalkstickstoff | METHOD FOR LOW-CHLORINE BLEACHING AND DELIGNIFICATION OF CELLULAR |
| CA2099881A1 (en) * | 1991-01-03 | 1992-07-04 | Omar F. Ali | Chlorine-free process for bleaching lignocellulosic pulp |
| DE4138006A1 (en) * | 1991-11-19 | 1993-05-27 | Degussa | METHOD FOR IMPROVING THE WHITE CONTENT IN THE PEROXIDE BLEACHING OF CELLULAS BY THE ADDITION OF CYANATES |
| US5620563A (en) * | 1994-10-31 | 1997-04-15 | Pulp Paper Res Inst | Process for delignification and bleaching of chemical wood pulps with hydrogen peroxide and a dicyandiamide activator |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4196043A (en) * | 1970-12-21 | 1980-04-01 | Scott Paper Company | Kraft pulp bleaching and recovery process |
| DE3544398A1 (en) * | 1985-12-16 | 1987-06-19 | Sueddeutsche Kalkstickstoff | METHOD FOR THE BLEACHING AND DELIGNIFICATION OF CELLULAR-BASED PRODUCTS |
| DE3714107A1 (en) * | 1987-04-28 | 1988-11-10 | Sueddeutsche Kalkstickstoff | Process for eliminating residual hydrogen peroxide from aqueous solutions |
| DE3802401A1 (en) * | 1988-01-28 | 1989-08-03 | Degussa | METHOD FOR PRODUCING SEMI-BLEACHED FUEL |
-
1990
- 1990-02-13 DE DE4004364A patent/DE4004364A1/en active Granted
-
1991
- 1991-02-06 NO NO910458A patent/NO176329C/en unknown
- 1991-02-11 AT AT91101890T patent/ATE103649T1/en not_active IP Right Cessation
- 1991-02-11 ES ES91101890T patent/ES2051531T3/en not_active Expired - Lifetime
- 1991-02-11 EP EP91101890A patent/EP0442425B1/en not_active Expired - Lifetime
- 1991-02-11 DE DE91101890T patent/DE59101249D1/en not_active Expired - Fee Related
- 1991-02-12 CA CA002036173A patent/CA2036173C/en not_active Expired - Fee Related
- 1991-02-13 FI FI910703A patent/FI910703L/en not_active Application Discontinuation
Also Published As
| Publication number | Publication date |
|---|---|
| ES2051531T3 (en) | 1994-06-16 |
| FI910703A7 (en) | 1991-08-14 |
| DE4004364A1 (en) | 1991-08-14 |
| FI910703L (en) | 1991-08-14 |
| NO910458D0 (en) | 1991-02-06 |
| DE59101249D1 (en) | 1994-05-05 |
| FI910703A0 (en) | 1991-02-13 |
| ATE103649T1 (en) | 1994-04-15 |
| DE4004364C2 (en) | 1992-11-19 |
| NO176329C (en) | 1995-03-15 |
| EP0442425A1 (en) | 1991-08-21 |
| CA2036173A1 (en) | 1991-08-14 |
| NO910458L (en) | 1991-08-14 |
| NO176329B (en) | 1994-12-05 |
| EP0442425B1 (en) | 1994-03-30 |
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| EEER | Examination request | ||
| MKLA | Lapsed |