CA2109179A1 - Process for bleaching of lignocellulose-containing pulp - Google Patents
Process for bleaching of lignocellulose-containing pulpInfo
- Publication number
- CA2109179A1 CA2109179A1 CA002109179A CA2109179A CA2109179A1 CA 2109179 A1 CA2109179 A1 CA 2109179A1 CA 002109179 A CA002109179 A CA 002109179A CA 2109179 A CA2109179 A CA 2109179A CA 2109179 A1 CA2109179 A1 CA 2109179A1
- Authority
- CA
- Canada
- Prior art keywords
- pulp
- bleaching
- compound
- peroxide
- magnesium
- 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.)
- Abandoned
Links
- 238000004061 bleaching Methods 0.000 title claims abstract description 62
- 238000000034 method Methods 0.000 title claims abstract description 39
- 150000001875 compounds Chemical class 0.000 claims abstract description 56
- 150000002978 peroxides Chemical class 0.000 claims abstract description 44
- 150000002681 magnesium compounds Chemical class 0.000 claims abstract description 26
- MHAJPDPJQMAIIY-UHFFFAOYSA-N Hydrogen peroxide Chemical compound OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 claims description 48
- 239000011777 magnesium Substances 0.000 claims description 29
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 claims description 27
- 238000005406 washing Methods 0.000 claims description 27
- 229910052749 magnesium Inorganic materials 0.000 claims description 26
- 238000011282 treatment Methods 0.000 claims description 26
- 229940043430 calcium compound Drugs 0.000 claims description 14
- 150000001674 calcium compounds Chemical class 0.000 claims description 14
- 239000007844 bleaching agent Substances 0.000 claims description 11
- 239000007788 liquid Substances 0.000 claims description 9
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 6
- 239000000203 mixture Substances 0.000 claims description 6
- 239000001301 oxygen Substances 0.000 claims description 6
- 229910052760 oxygen Inorganic materials 0.000 claims description 6
- 238000011221 initial treatment Methods 0.000 abstract description 45
- 230000000694 effects Effects 0.000 abstract description 9
- 229910001425 magnesium ion Inorganic materials 0.000 abstract description 8
- JLVVSXFLKOJNIY-UHFFFAOYSA-N Magnesium ion Chemical compound [Mg+2] JLVVSXFLKOJNIY-UHFFFAOYSA-N 0.000 abstract description 7
- 229910021655 trace metal ion Inorganic materials 0.000 abstract description 7
- 230000008092 positive effect Effects 0.000 abstract description 5
- 230000000717 retained effect Effects 0.000 abstract description 4
- 235000001055 magnesium Nutrition 0.000 description 26
- 229940091250 magnesium supplement Drugs 0.000 description 26
- 229960002163 hydrogen peroxide Drugs 0.000 description 22
- 229910052784 alkaline earth metal Inorganic materials 0.000 description 21
- 150000001342 alkaline earth metals Chemical class 0.000 description 21
- 239000011575 calcium Substances 0.000 description 18
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 description 17
- 229960005069 calcium Drugs 0.000 description 17
- 229910052791 calcium Inorganic materials 0.000 description 17
- 235000001465 calcium Nutrition 0.000 description 17
- 239000002253 acid Substances 0.000 description 11
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 description 10
- 229910021653 sulphate ion Inorganic materials 0.000 description 10
- 239000000725 suspension Substances 0.000 description 10
- 238000009897 hydrogen peroxide bleaching Methods 0.000 description 9
- 229910052751 metal Inorganic materials 0.000 description 8
- 239000002184 metal Substances 0.000 description 8
- 239000011122 softwood Substances 0.000 description 8
- VTYYLEPIZMXCLO-UHFFFAOYSA-L Calcium carbonate Chemical compound [Ca+2].[O-]C([O-])=O VTYYLEPIZMXCLO-UHFFFAOYSA-L 0.000 description 6
- 229920001131 Pulp (paper) Polymers 0.000 description 6
- CBENFWSGALASAD-UHFFFAOYSA-N Ozone Chemical compound [O-][O+]=O CBENFWSGALASAD-UHFFFAOYSA-N 0.000 description 5
- 238000000605 extraction Methods 0.000 description 5
- 150000002500 ions Chemical class 0.000 description 5
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 5
- 229910021645 metal ion Inorganic materials 0.000 description 5
- UXVMQQNJUSDDNG-UHFFFAOYSA-L Calcium chloride Chemical compound [Cl-].[Cl-].[Ca+2] UXVMQQNJUSDDNG-UHFFFAOYSA-L 0.000 description 4
- CSNNHWWHGAXBCP-UHFFFAOYSA-L Magnesium sulfate Chemical compound [Mg+2].[O-][S+2]([O-])([O-])[O-] CSNNHWWHGAXBCP-UHFFFAOYSA-L 0.000 description 4
- KFSLWBXXFJQRDL-UHFFFAOYSA-N Peracetic acid Chemical compound CC(=O)OO KFSLWBXXFJQRDL-UHFFFAOYSA-N 0.000 description 4
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 4
- 239000001110 calcium chloride Substances 0.000 description 4
- 229960002713 calcium chloride Drugs 0.000 description 4
- 235000011148 calcium chloride Nutrition 0.000 description 4
- 229910001628 calcium chloride Inorganic materials 0.000 description 4
- ZCCIPPOKBCJFDN-UHFFFAOYSA-N calcium nitrate Chemical compound [Ca+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O ZCCIPPOKBCJFDN-UHFFFAOYSA-N 0.000 description 4
- OSGAYBCDTDRGGQ-UHFFFAOYSA-L calcium sulfate Chemical compound [Ca+2].[O-]S([O-])(=O)=O OSGAYBCDTDRGGQ-UHFFFAOYSA-L 0.000 description 4
- OSVXSBDYLRYLIG-UHFFFAOYSA-N dioxidochlorine(.) Chemical compound O=Cl=O OSVXSBDYLRYLIG-UHFFFAOYSA-N 0.000 description 4
- 239000001117 sulphuric acid Substances 0.000 description 4
- 235000011149 sulphuric acid Nutrition 0.000 description 4
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 4
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 3
- 229910000019 calcium carbonate Inorganic materials 0.000 description 3
- 230000000052 comparative effect Effects 0.000 description 3
- 229910052802 copper Inorganic materials 0.000 description 3
- 239000010949 copper Substances 0.000 description 3
- 238000010790 dilution Methods 0.000 description 3
- 239000012895 dilution Substances 0.000 description 3
- 229910052742 iron Inorganic materials 0.000 description 3
- 239000007791 liquid phase Substances 0.000 description 3
- 239000000126 substance Substances 0.000 description 3
- BHPQYMZQTOCNFJ-UHFFFAOYSA-N Calcium cation Chemical compound [Ca+2] BHPQYMZQTOCNFJ-UHFFFAOYSA-N 0.000 description 2
- 239000004155 Chlorine dioxide Substances 0.000 description 2
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 2
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 2
- TWRXJAOTZQYOKJ-UHFFFAOYSA-L Magnesium chloride Chemical compound [Mg+2].[Cl-].[Cl-] TWRXJAOTZQYOKJ-UHFFFAOYSA-L 0.000 description 2
- 229910052788 barium Inorganic materials 0.000 description 2
- DSAJWYNOEDNPEQ-UHFFFAOYSA-N barium atom Chemical compound [Ba] DSAJWYNOEDNPEQ-UHFFFAOYSA-N 0.000 description 2
- 229910001424 calcium ion Inorganic materials 0.000 description 2
- 239000001175 calcium sulphate Substances 0.000 description 2
- 235000011132 calcium sulphate Nutrition 0.000 description 2
- 235000019398 chlorine dioxide Nutrition 0.000 description 2
- 239000013505 freshwater Substances 0.000 description 2
- 239000001257 hydrogen Substances 0.000 description 2
- 229910052739 hydrogen Inorganic materials 0.000 description 2
- 229910052500 inorganic mineral Inorganic materials 0.000 description 2
- YIXJRHPUWRPCBB-UHFFFAOYSA-N magnesium nitrate Chemical compound [Mg+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O YIXJRHPUWRPCBB-UHFFFAOYSA-N 0.000 description 2
- 229910052943 magnesium sulfate Inorganic materials 0.000 description 2
- 235000019341 magnesium sulphate Nutrition 0.000 description 2
- 239000011572 manganese Substances 0.000 description 2
- WPBNNNQJVZRUHP-UHFFFAOYSA-L manganese(2+);methyl n-[[2-(methoxycarbonylcarbamothioylamino)phenyl]carbamothioyl]carbamate;n-[2-(sulfidocarbothioylamino)ethyl]carbamodithioate Chemical compound [Mn+2].[S-]C(=S)NCCNC([S-])=S.COC(=O)NC(=S)NC1=CC=CC=C1NC(=S)NC(=O)OC WPBNNNQJVZRUHP-UHFFFAOYSA-L 0.000 description 2
- 150000002739 metals Chemical class 0.000 description 2
- 238000010561 standard procedure Methods 0.000 description 2
- LSNNMFCWUKXFEE-UHFFFAOYSA-L sulfite Chemical compound [O-]S([O-])=O LSNNMFCWUKXFEE-UHFFFAOYSA-L 0.000 description 2
- 239000002351 wastewater Substances 0.000 description 2
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- 235000019738 Limestone Nutrition 0.000 description 1
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 1
- 241000212342 Sium Species 0.000 description 1
- CDBYLPFSWZWCQE-UHFFFAOYSA-L Sodium Carbonate Chemical compound [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 description 1
- 238000010306 acid treatment Methods 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 229920002678 cellulose Polymers 0.000 description 1
- 239000001913 cellulose Substances 0.000 description 1
- 239000004927 clay Substances 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 239000000945 filler Substances 0.000 description 1
- ZZUFCTLCJUWOSV-UHFFFAOYSA-N furosemide Chemical compound C1=C(Cl)C(S(=O)(=O)N)=CC(C(O)=O)=C1NCC1=CC=CO1 ZZUFCTLCJUWOSV-UHFFFAOYSA-N 0.000 description 1
- 239000008233 hard water Substances 0.000 description 1
- 239000011121 hardwood Substances 0.000 description 1
- 150000002431 hydrogen Chemical class 0.000 description 1
- 150000002484 inorganic compounds Chemical class 0.000 description 1
- 229910010272 inorganic material Inorganic materials 0.000 description 1
- 229920005610 lignin Polymers 0.000 description 1
- 239000006028 limestone Substances 0.000 description 1
- ZLNQQNXFFQJAID-UHFFFAOYSA-L magnesium carbonate Chemical compound [Mg+2].[O-]C([O-])=O ZLNQQNXFFQJAID-UHFFFAOYSA-L 0.000 description 1
- 239000001095 magnesium carbonate Substances 0.000 description 1
- 229910000021 magnesium carbonate Inorganic materials 0.000 description 1
- 235000014380 magnesium carbonate Nutrition 0.000 description 1
- 229910001629 magnesium chloride Inorganic materials 0.000 description 1
- 235000011147 magnesium chloride Nutrition 0.000 description 1
- 159000000003 magnesium salts Chemical class 0.000 description 1
- 229910052748 manganese Inorganic materials 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 229910017604 nitric acid Inorganic materials 0.000 description 1
- 150000002894 organic compounds Chemical class 0.000 description 1
- 238000010979 pH adjustment Methods 0.000 description 1
- FHHJDRFHHWUPDG-UHFFFAOYSA-N peroxysulfuric acid Chemical compound OOS(O)(=O)=O FHHJDRFHHWUPDG-UHFFFAOYSA-N 0.000 description 1
- 238000003825 pressing Methods 0.000 description 1
- 238000007670 refining Methods 0.000 description 1
- JVBXVOWTABLYPX-UHFFFAOYSA-L sodium dithionite Chemical compound [Na+].[Na+].[O-]S(=O)S([O-])=O JVBXVOWTABLYPX-UHFFFAOYSA-L 0.000 description 1
- PFUVRDFDKPNGAV-UHFFFAOYSA-N sodium peroxide Chemical compound [Na+].[Na+].[O-][O-] PFUVRDFDKPNGAV-UHFFFAOYSA-N 0.000 description 1
- 230000000930 thermomechanical effect Effects 0.000 description 1
- 238000004448 titration Methods 0.000 description 1
- 229910021654 trace metal Inorganic materials 0.000 description 1
- 239000003643 water by type 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
- D21C9/1005—Pretreatment of the pulp, e.g. degassing the pulp
-
- 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
- D21C9/16—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)
- Diaphragms For Electromechanical Transducers (AREA)
- Agricultural Chemicals And Associated Chemicals (AREA)
- Stringed Musical Instruments (AREA)
- Compositions Of Macromolecular Compounds (AREA)
- Pigments, Carbon Blacks, Or Wood Stains (AREA)
Abstract
Abstract The present invention relates to a process for bleaching of lignocellulose-containing pulp, in which the pulp is treat-ed at a pH between about 1 and about 7 in the presence of a magnesium compound, whereupon the pulp is washed and subse-quently bleached with a peroxide-containing compound. The ini-tial treatment removes from the pulp those trace metal ions that have a negative effect on the subsequent bleaching with a peroxide-containing compound. Owing to the presence of mag-nesium ions in dissolved form during the initial treatment, the magnesium ions are retained in those positions in the pulp where they have a particularly positive effect on the effec-tiveness of the bleaching stage.
Description
~ 1 0 9 1 ~
.
Process for bleachinq of liqnocellulose-containinq pulp The present invention relates to a process for bleaching of lignocellulose-containing pulp, in which the pulp is treat-ed at a pH between about 1 and about 7 in the presence of a magnesium compound, whereupon the pulp is washed and subse-quently bleached with a peroxide-containing compound. The ini~
tial treatment removes from the pulp ~hose trace metal ions that have a negative effect on the subsequent bleaching with i~
a peroxide-containing compound. Owing to the presence o mag-nesium ions in dissolved form during the initial treatment, the magnesium ions are retained in those positions in the pulp where they have a particularly positive effect on the effec-tiveness of the bleaching stage.
Backqround of the Invention 1 In the making of lignocellulose-containing pulp of high brightness, the pulp is bleached in one or more stages. For quite some time, mechanical pulps have been bleached with chlorine-free bleaching agents, the intention in this case being to remove chromophoric groups while preserving the con-tent of lignin. For environmental reasons, it has become in-creasingly common to treat also chemical pulps with chlorine-free bleaching agents, such as hydrogen peroxide, peracetic acid and ozone, already in the first bleaching stages. Unless the pulp is pretreated, however, bleaching with chlorine-free l~
bleaching agents is less effective. Thus, hydrogen peroxide bleaching in alkaline environment is disturbed by the presence ~ `~
in the pulp of ions of certain trace metals, primarily Mn, Cu and Fe. These metal ions cause degradation of hydrogen per- ;
oxide into undesirable products, thereby reducing the effecti-veness of the peroxide bleaching and increasing the consump-tion of peroxide.
The prior art teaches bleaching of chemical as well as mechanical pulps in the presence of magnesium salts. Most of the known bleaching processes do not comprise acid pretreat-35 ment, which preserves the content of undesirab].e trace metals ~ `
in the pulp. E'urthermore, bleaching with chlorine-free bleach-ing agents is normally performed in alkaline environment. As a result, it becomes impossible to retain or reintroduce the especially desirable magnesium ions, since these are precipi- ;;~
~ ~, 2 ~ 1 0 9 1 7 9 ; ~;;
tated at an alkaline pH and thus cannot diffuse into the pulp to such an extent that a pulp of high brightness and strength -can be obtained.
,:: ,:
Description of the Invention The inventio~ provides a process for treating ligno~
cellulose-containing pulp unde.r the conditions disclosed in the claims, whereby the content oE trace metal iOllS ill the pulp i9 selectively altered to render more effective the subsequent bleaching with a peroxide-containing compound.
I'hus, the invention relates to a process for bleaching of lignocellulose-containing pulp, whereby the pulp is treated at a pH within the range of from about 1 up to about 7 in the presence of a magnesium compound, whereupon the pulp is washed and subsequently the pulp is bleached with a peroxide-contain-ing compound.
An initial acid treatment effectively removes metal ions from lignocellulose-containing pulps. However, magnesium ions, especially when in their original positions of the pulp, are known to have a positive influence on the selectivity of the bleaching and the consumption of peroxide-contalning com-pounds. By the present process, undesirable metal ions are removed from the pulp suspension, while the magnesium ions are largely retained in their original positions. The latter is achieved by the presence of a magnesium compound in the treat-ment liquid, at such a pH and temperature that the compound isin dissolved form when contacted with the pulp. The present process further has the advantage of reducing the number of treatment stages compared with prior-art processes.
In the initial treatment, the magnesium compound should be in dissolved form when contacted with the pulp to produce a good effect. This can be achieved in various ways, depend-ing, inter alia, on the type and properties of the pulp. The magnesium compound can be brought to dissolved form by a suitable choice of pH within the range of from about 1 up to about 7, in combination with a suitable temperature and concentration of the magnesium compound.
Besides a magnesium compound, the initial treatment may be carried out in the presence of at least one more compound containing an alkaline earth metal. Thus, a compound contain-2 1 0 9 ~ 7 9 r . 3 - , ~: . ... :
ing calcium or barium may also be present. Preferably, the pulp is treated in the presence of a magnesium compound and calcium compound in optional sequence or mixture.
The magnesium-containing compound used is suitably magnesium sulphate, magnesium chloride, magnesium carbonate or magnesium nitrate, preferably magnesium sulphate. The calcium-containing compound used is suitably calcium chloride, calcium nitrate, calcium sulphate or calcium carbonate, preferably calcium chloride.
In the process according to the invention, the initial treatment is performed at a pH of from about 1 up to about 7, suitably from 1.5 up to 6, and preferably from 2 up to 5. The initial treatment may also be performed at a pH of from 3.1 up to 4.
In the initial treatment in the presence of a magnesium compound, the pH can be adjusted by adding an acid or an acid liquid to the pulp. The acid used may be an inorganic mineral acid or residual acid from a chlorine dioxide reactor, either separately or in optional mixture. Suitably, use is made of an inorganic mineral acid, such as sulphuric acid, nitric acid or hydrochloric acid, preferably sulphuric acid.
The amount of magnesium compound added in the initial treatment may be within the range of from about 100 ppm up to about 4000 ppm, calculated as part by weight of magnesium on part by weight of dry pulp. Suitably, the amount of the magne-sium compound added lies within the range of from 200 ppm up to 3000 ppm, preferably within the range of from 500 ppm up to 2000 ppm.
The amount of an optional compound containing an alkali-ne earth metal added in the initial treatment may be wi.thinthe range of from about 100 ppm up to about 4000 ppm, calcu-lated as part by weight of alkaline earth metal on part by weight of dry pulp. Suitably, the amount of the compound con-taining an alkaline earth metal added lies within the range of from 200 ppm up to 3000 ppm, preferably within the range of from 500 ppm up to 2000 ppm.
The amount of magnesium compound added as well as the other conditions in the initial treatment are so chosen thak the magnesium content of the pulp prior to the bleaching with ..: ~ : ..
r ~ C ~ ~ ~
a peroxide-containing compound amounts to at least about 50%
of the initial content. Suitably, the amount of magnesium compound added as well as the other conditions are so chosen that the magnesium content of the pulp prior to the bleaching with a peroxide-containing compound lies within the range of from 100% up to 300% of the initial content, preferably within the range of from 130i~ up to 200i~
The peroxide-containing eompound ineludes inorganic peroxide eompounds sueh as hydroyen peroxide, sodium peroxide or peroxosulphurie aeid (Caro's aeid), or organie peroxide eompounds, sueh as peraeetie aeid. Preferably, the peroxide~
eontaining eompound is hydrogen peroxide or a mixture oE
hydrogen peroxide and oxygen.
Bleaehing with a peroxide-containing compound is suitab-ly performed at a pH equal to or higher than the pH in theinitial treatment in the presenee of a magnesium eompound. In this way, the trace metal ions having a positive effect on the bleaching are retained also in the bleaching stage itself.
When the peroxide-containing compound is hydrogen peroxide, the pulp can be treated at a pH of from about 7 up to about 13, suitably at a pH of from 8 up to 12, preferably at a pH of from 9.5 up to 11. Bleaehing with the other peroxide-eontain-ing compounds indicated above takes place within the normal pH
ranges for each bleaching agentj which are well-known to the expert.
Suitably, bleaching with a peroxide-containing compound takes plaee in the presenee of yet another compound containing an alkaline earth metal. The compound containing an alkaline earth metal present in the bleaching, may be the same compound that was used in the initial treatment or another compound.
The alkaline earth metal suitably is calcium, magnesium or barium, or a mixture thereof. This further improves the selec-tivity of the bleaching and reduces the consumption of the peroxide-containing compound. It is especially preferred that the bleaching takes plaee in the presence of a calcium com-pound. The caleium eompound ean be added to the pulp suspen-sion outside the bleaching tower, e.g. by introduction into the pipeline leading to the bleaehing tower. Also, the cal-eium eompound can be added to the pulp suspension inside the ': :::...' ~ '"
2 1 ~ 9 1 7 9 bleaching tower, before the bleaching has commenced.
The amount of the compound containing an alkaline earth metal added in the bleaching, may lie withln the range of from about 100 ppm up to about 4000 ppm, calculated as part by weight of alkaline earth metal on part by weight of dry pulp.
Suitably, the a~ount of the compound containing an alkaline earth metal added lies within the range of from 300 ppm up to 3000 ppm, preferably within the range of from 600 ppm up to 2000 ppm.
When a calcium compound is present in the bleaching with a peroxide-containing compound, this compound suitably is cal-cium chloride, calcium nitrate, calcium sulphate or calcium carbonate. Calcium chloride is preferably used. Furthermore, the calcium compound is suitably added at such a combination of pH, temperature and concentration of the calcium compound that said compound is in active form when contacted with the pulp. Thus, suitably the pH lies within the range of from about 7 up to about 11. However, a positive effect is obtained also when the calcium compound is precipitated in the pulp suspension, e.g. as calcium carbonate.
The amount of calcium added as well as the other condi-tions in connection with the addition of calcium are so chosen that the calcium content of the pulp prior to the bleaching with a peroxide-containing compound amounts to at least about 25~ of the calcium content prior to the initial treatment. At this, the pulp may be treated with calcium in the initial treatmént as well as in the bleaching with a peroxide-contain-ing compound. The amount of calcium compound added as well as the other conditions are suitably so chosen that the calcium content of the pulp prior to the bleaching with a peroxide~
containing compound lies within the range of from 40% up to 150% of the original content, preferably within the range of from 50% up to 120% and most preferably within the range of from 50% up to 70%.
It is also within the scope of the invention, that all or a part of the amount of magnesium, and optionally any of the other alkaline earth metals, may be added to the pulp sus-pension by way of the water used for e.g. pH adjustment, wash-ing or dilution. Thus, hard water primarily containing magne-::
~a~l7s . ~
~`` 6 sium or calcium ions, or a combination thereof, is advanta-geously used in the initial treatment, for dilution in the washing stage, or for achieving a suitable pulp concentration in the bleaching stage. In this way, it is possible to reduce the added amount of the corresponding alkaline earth metal, provlded that the combination oE pH, temperature and conce.n-tration of the alkaline earth metal can be so chosen that said allcaline earth metal is in dissolved form when contacted with the pulp. Such hard waters include fresh water from limestone bedrock, white water from papermaking machines using Ch.ina clay or chalk as filler, or process water from production of sulphite pulp based on magnesium or calcium.
The process according to the invention is performed with a washing stage after the initial treatment and before the bleaching with a peroxide-containing compound. Washing effec-tively removes those trace metal ions that have a negative effect on the subsequent bleaching with a peroxide-contalning compound, e.g. ions of manganese, copper and iron. In order to retain the trace metal ions that have a positive effect on the subsequent bleaching with a peroxide-containing compound, pri-marily magnesium and calcium ions, the pH in the washing liquid is preferably equal to or higher than the pH in the initial treatment. However, the pH in the washing liquid should lie within the range of from about 3 up to about 10, suitably within the range of from 5 up to 10. It is especially preferred that the pH in the washing liquid is at least about 2 pH units higher than the pH in the initial treatment.
The washing liquid may be fresh water, optionally con-taining some added pH-adjusting chemical, or wastewater from one or more bleaching stages or extraction stages, giving a suitable pH in the washing stage. Furthermore, the washing liquid may consist of other types of wastewater, optionally purified, provided that it has a low content of undesirable ions of metal, such as manganese, iron and copper.
Washing between the initial treatment and bleaching with a peroxide-containing compound relates to methods -for remov-ing, more or less completely, the liquid phase from the pulp suspension in order to reduce the content of dissolved trace metal ions in said suspension. Washing may involve raising the 7 2~0917~ : :
pulp concentration, e.g. by sucking-off or pressing the sus-pension through a filter, or lowering the pulp concentration, e.g. by dilution with a washing liquid. Washing also relates to combinations and sequences in which the pulp concentration 5 i9 alternatingly raised and lowered, one or more times. In the present process, a washing method should be chosen which effectively removes the trace metal ions released in the ini-tial treatment, aspects of process technique and economy being considered.
The efectiveness of the washing may be indicated as the amount o liquid phase removed, compared with the liquid phase present in the pulp suspension prior to washing. Washing effectiveness can be at least about 80%, and suitably lies within the range of from 90% up to 100%, preferably within the range of from 95% up to 100%.
The initial treatment in the presence of a magnesium compound can also be performed in the presence of a bleaching agent. Bleaching agents that are active within the pH range suitable for the initial treatment include chlorine dioxide, ozone and acid peroxide-containing compounds. Acid peroxide-containing compounds include such organic compounds as per-acetic acid and such inorganic compounds as hydrogen peroxide and peroxosulphuric acid (Caro's acid). Suitably, the initial treatment takes place in the presence of ozone or peroxosul-phuric acid, preferably ozone, since these bleaching agentsaffect but to a minor extent the content of ions of alkaline earth metals in the pulp.
The process according to the invention may also involve an extraction stage before the bleaching with a peroxide-con~
taining compound. This is especially convenient when the ini-tial treatment is performed in the presence of a bleaching agent. Suitably, the extraction is performed at a pH that is equal to or higher than the pH in the initial treatment. Sui-tably, the pH in the extraction stage lies within the range of from about 7 up to about 11, preferably within the range of from 8 up to 10.
Regardless of the number of stages or the type of treat-ment following the initial treatment, the pH in a subsequent stage suitably is equal to or higher than the pH in the prece-~' 8 2 1 0 9 ~ 7 9 .
ding stage, in order to preserve the content of ions of alka-line earth metals in the pulp. In a sequence in which the pulp is first treated at a pH of about 2 in the presence of a mag-nesium compound and then washed and bleached with hydrogen peroxide, the pH in the washing stage should be at least about g, and the pH in the bleachi.ng stage should be at least about 8.
The term lignocellulose-containing pulp relates to pulps containing fibres that have been separated by chemical or mechanical treatment, or recycled fibres. The fibres may be of hardwood or softwood. The term chemical pulp relates to pulps digested according to the sulphate, sulphite, soda or organo-solv process. The term mechanical pulp relates to pulps pro-duced by refining of chips in a disc refiner (refiner mechani-cal pulp) or by grinding of logs in a grinder (groundwoodpulp). The term lignocellulose-containing pulp also relates to pulps produced by modifications or combinations of the above methods or processes. Such pulps include thermomechanical, chemimechanical and chemi-thermomechanical pulp9. Suitably, the lignocellulose-containing pulp consists of chemically digested pulp, preferably sulphate pulp of softwood.
The process according to the invention, can be applied to pulps with a yield of up to about 90%, suitably a yield within the range of from 40% up to 80%, preferably within the range of from 45% up to 65%.
The process according the invention, can be performed at an optional position in the bleaching sequence, e.g. immedia-tely after the making of the pulp. When the process according to the invention is applied to a chemically digested pulp, this is preferably delignified in an oxygen stage before applying the process according to the invention.
The process according to the invention can be applied to chemically digested pulps having an initial kappa number with-in the range of from about 3 up to about 100, suitably from 4 up to 60, preferably from 5 up to 40. The kappa number is established according to the Standard Method SCAN-C 1:77.
In the process according to the invention, the initial treatment can be performed at a temperature of from about 10C
up to about 100C, suitably from 25C up to 90C, preferably --~ 9 ~1~9179 '! ' `
from 40~C up to 80C. The initial treatment can be performed for a period of time of from about 1 s up to about 600 min, sultably from 1 min up to 120 min, preferably from 10 min up to 60 min. The pulp concentration in the initial treatment can be from about 1~ by weight up to about 60% by weight, suitably from 2% by weight up to 40~ by weight, preferably from 3% by weight up to 35% by weight.
When hydrogen peroxide .is used as peroxide-containing compound, the pulp i9 treated at a temperature of from about 30C up to about 100C, preEerably from 60C up to 90C, and for a period oE time of from about 30 min up to about 960 min, suitably from 60 min up to 360 min. Further, when hydrogen peroxide is used as peroxide-containing compound, the pulp concentration can be from about 1% by weight up to about 70%
by weight, suitably from 3% by weight up to 60% by weight, preferably from 10~ by weight up to 50% by weight. Treatment with the other peroxide-containing compounds indicated above takes place within the normal ranges as to temperature, period of time and pulp concentration for each bleaching agent, which are well-known to the expert.
In preferred embodiments involving the use of hydrogen peroxide as peroxide-containing compound, the amount of hydro~
gen peroxide lies within the range of from about 1 kg up to about 60 kg per tonne of dry pulp, calculated as 100% hydrogen peroxide. The upper limit is not critical, but has been set for economic reasons. Suitably, the amount of hydrogen peroxi-de lies within the range of from 2 kg up to 50 kg per tonne of dry pulp, preferably from 5 kg up to 40 kg per tonne of dry pulp, calculated as 100% hydrogen peroxide.
After the initial treatment in the presence of magnesium and subsequent bleaching with a peroxide-containing compound, the pulp can be used as such for making paper of lower bright-ness. Alternatively, the pulp can be finally bleached to the desired higher brightness by treatment in one or more stages.
Suitably, the ~inal bleaching involves chlorine-free bleaching agents such as the peroxide-containing compounds indicated above, ozone, oxygen or sodium dithionite, optionally with intermediate alkaline extraction stages which may be reinforc-ed with peroxide and/or oxygen. In this way, the formation and 2~1q~ ' 1 0 v discharge of AOX is completely eliminated.
The invention and its advantages will be illustrated in more detail by the Examples below which however, are only in-tended to illustrate the invention without limiting the same.
The percentages and parts stated in the description, claims and Examples, reEer to percent by weight and parts by weight, respectively, unless otherwise stated. Furthermore, the pH
values given in the description, claims and Examples refer to the pH at the end of each treatment, unless otherwise stated.
In the following Examples, the kappa number, viscosity and brightness of the pulp were established according to SCAN
Standard Methods, and the consumption of hydrogen peroxide was determined by iodometric titration.
Example 1 Oxygen-delignified sulphate pulp of softwood having a kappa number of 18, a brightness of 34.2% ISO and a viscosity of 1000 dm3/kg was treated at a pH of 2.1 ~/-0.1 in the pre-sence of various alkaline earth metals. After oxygen deligni-fication, the sulphate pulp had a pH of about 11, which was adjusted by an addition of 15 kg sulphuric acid/tonne dry pulp. The amount of alkaline earth metal added was 1000 ppm, calculated as part by weight of each alkaline earth metal on part by weight of dry pulp. In the initial treatment, the temperature was 50C, the treatment time was 30 min and the pulp concentration was 10% by weight. In the initial treat-ment, the general conditions as well as the compound contain-ing an alkaline earth metal were so chosen that the alkaline earth metal present was dissolved in the pulp suspension.
After the initial treatment, the pulp was washed at a pH of 6-7, in order to remove those metal ions that have a negativeeffect on the subsequent chlorine-free bleaching. Subsequent-ly, the pulp was bleached with hydrogen peroxide at a tempera-ture of 90~C, a residence time of 240 min, and a pulp concen-tration of 10% by weight. The addition of hydrogen peroxide was 25 kg/ tonne dry pulp, calculated as 100~ hydrogen peroxide, and the pH was about 10.5. For comparative purposes, the pulp was treated without addition of an alkaline earth metal, and subsequently bleached with hydrogen peroxide under the conditions stated above (Test 4). For further comparison, 2~09~7~ ~
:.. . 11 the pulp was treated with magnesium as in Test 1, but without an intermediate washing stage (Test 5). The results of the ;
tests appear from Table I below.
TABLE I
5Alkaline Pulp properties after peroxide bleaching Test earth Kappa number Viscosity Brightness metal _ ~dm3/kq)(~ ISO) 1 Mg 9.2 830 63.4 ` ;
10 2 Ca 10.5 800 53.0 3 Ba 11.4 880 51.0 4 --- * 12.8 840 45,5 Mg ** 12.2 880 41.0 ~ ~:
* No alkaline earth metal added. ;;
** No washing stage after the magnesium treatment.
As is evident from the Table, pulp treatment according to the invention at a pH of about 2.1 in the presence of a ~ `p magnesium compound, results in a much higher increase in ' ~
brightness and a more substantial reduction of the kappa num- ;
20 ber than does a treatment in the absence of such a compound. `~
Example 2 ~ ;~
The oxygen-delignified sulphate pulp of softwood employ-ed in Example 1 was treated in the presence of a magnesium compound at a pH within the range of from 1.5 up to 11 in order to illustrate the effect of pH in the initial treatment.
The amount of magnesium added was 1000 ppm, calculated as part by weight of magnesium on part by weight of dry pulp. The con-ditions in the initial treatment were identical with those in Example 1, except the pH variation. Likewise, the conditions in the subsequent hydrogen peroxide bleaching were identical with those in Example 1. After the initial treatment, the pulp was washed at a pH that was about 2 pH units higher than that in the initial treatment. The results of the tests appear from Table II below.
- - 12 ~0~79 ~.
TABLE II
pH in the Pulp properties after peroxide bleaching Test initial Kappa number Viscosity Brightness treatment `~
(dm3/kq)(% ISO) 1 1.5 9.1 795 64.0 2 2.0 9.2 835 63.2 3 3.3 9.6 820 61.0 4 ~.4 9.7 815 60.2 6.1 9.9 825 59.3 ~ "
6 6.8 10.2 8~0 57.5 7 10.8 12.1 880 43.6 As is evident from the Table, pulp treatment according to the invention at a pH within the range of from about 1 up 15 to about 7, results in a much higher increase in brightness `~
and a more substantial reduction of the kappa number than does ~ ~ `
treatment at a pH above this range.
Exam~le 3 The oxygen-delignified sulphate pulp of softwood employ-ed in Example 1 was treated in the presence of a magnesiumcompound at a pH of 2.1 +/- 0.1 in order to illustrate the effect of pH in the subsequent washing stage. In the initial l~
treatment, the pH was adjusted by addition of sulphuric acid. !~
The amount of magnesium added was 1000 ppm, calculated as part !~
by weight of magnesium on part by weight of dry pulp. The con~
ditions in the initial treatment as well as in the hydrogen peroxide bleaching were identical with those in Example 1.
After the initial treatment, the pulp was washed at a pH with~
in the range of from 3 up to about 11 where appropriate by de~
ionised water to which sodium hydroxide had been added. The results of the tests appear from Table III below.
, ~ 13 2109~ 79 ~ . . .
TABLE III
pH in the Pulp properties after peroxide bleaching Test washing Kappa number Viscosity Brightness stage `~
_(dm3/kq) (~ ISO) _ 1 3~0 11.9 890 52.9 2 4.3 10.2 830 58.9 3 4.8 10.2 840 59.4 4 6.9 9.0 835 63.4 ~
8.2 9.0 830 64.0 ~ `
6 10.8 9.0 800 59.5 ~` `;``
As is evident from the Table, pulp treatment according ` ;`~
to the invention with an intermediate washing stage at a pH
within the range of from about 3 up to about 10 results in a 15 considerable increase in brightness and a considerable reduc~
tion of the kappa number.
Example 4 ~!;
The oxygen-delignified sulphate pulp of softwood employ-ed in Example 1 was treated in the presence of a magnesium 20 compound at a pH of 2.1 ~/- 0.1 in order to illustrate the effect of pH in the bleaching with hydrogen peroxide within the range of from 7 up to 12. The amount of magnesium added was 1000 ppm, calculated as part by weight of magnesium on part by weight of dry pulp. The conditions in the initial i 25 treatment were identical with those in Example 1, as were the ~ K conditions in the hydrogen peroxide bleaching, except the pH
variation. After the initial treatment, the pulp was washed at a pH of 6-7. The results of the tests appear from Table IV
below.
TABLE IV
pH in the Pulp properties after peroxide bleaching Test bleaching Kappa number Viscosity Brightness stage (dm3/kq)(~ ISO) 1 7.1 12.0 900 50.2 2 8.2 9.9 830 58.0 3 10.3 9.2 825 63.1 4 11.9 9.1 780 62.5 As is evident from the Table, pulp treatment according :~-``'-' .
~- 14 ~109179 to the present invention using hydrogen peroxide as the per-oxide-containing compound, results in a very high increase in brightness and a considerable reduction of the kappa number.
Exam~le 5 The oxygen-delignified sulphate pulp of softwood employ- ~ ` ~
ed in Example 1 was treated in the presence of a magnesium ~`
compound at a pH of 2.1 ~ 0.1 in order to illustrate the effect o a calcium compound on the hydrogen peroxide bleach~
ing (Test 2). The amount of magnesium added was 1000 ppm, cal~
10 culated as part by weight of magnesium on part by weight of ~;
dry pulp. After washing, calcium was added in an amount of 1000 ppm, calculated as part by weight of calcium on part by weight of dry pulp. The conditions in the initial treatment ~ `
were identical with those in Example 1, as were the conditions ` ~
15 in the hydrogen peroxide bleaching, except the presence of a ~ `
calcium compound. After the initial treatment, the pulp was washed at a pH of 6-7. For comparative purposes, the pulp was ; `~
also bleached in the absence of the calcium compound (Test 1). ~` ~ ```
The results of the tests appear from Table V below. `~
TABLE V `
Pulp properties after peroxide bleaching Test Kappa number Viscosity Brightness Remaining (dm3/kq) (~ ISO) (kq/tonne) !`~
25 1 9.2 830 63.1 0 2 8.9 850 68.2 3.1 As is evident from the Table, pulp treatment according `
to the invention using a calcium compound in the hydrogen peroxide bleaching, results in a much higher brightness at a `
lower consumption of hydrogen peroxide than does bleaching in the absence of calcium.
Example 6 The oxygen-delignified sulphate pulp of softwood employ-ed in Example 1 was treated in the presence of a magnesium ~ -compound at a pH of 2.1 +/- 0.1, washed and bleached with hydrogen peroxide, in order to illustrate the effect of a selective metal profile in the pulp prior to bleaching. The amount of magnesium added was 1000 ppm, calculated as part by weight of magnesium on part by weight of dry pulp. After wash- ;
:: ::
~" 15 2109179 ing, calcium was added in an amount of looO ppm, calculated as part by weight of calcium on part by weight of dry pulp (Test 4). The conditions in the initial treatment were identical with those in Example 1, as were the conditions in the hydro-gen peroxide bleaching, except the presence of a calcium com-pound in Test 4. After the initial treatment, the pulp was washed at a pH of about 3 (Test 1) and 6-7 (Tests 2-4), respectively. For comparative purposes, the pulp was treated without any magnesium in the initial treatment and without any calcium in the bleaching stage (Tests 1 and 2). The content of certain metal ions in the sulphate pulp before (test 0) and after the initial treatment, as well as the brightness after the hydrogen peroxide bleaching, appear from Table VI below.
TABLE VI
Test Metal content before bleaching, ppm Brightness after Mg Ca Mn Fe Cu bleaching ~ISO~
0 3001800 68 8.31.5 ----l 30 220 6.5 5.8~ 0.5 45.5 2 lO0 640 20 7.00.9 45.7 3 550 690 18 6.30.7 63.2 4 5501700 18 6.30.7 68.2 As is evident from the Table, the process according to the invention involving treatment in the presence of a magne-sium compound, followed by hydrogen peroxide bleaching, resul-ts in a much higher brightness at a lower consumption of hydrogen peroxide than does bleaching in the absence of calcium.
.
Process for bleachinq of liqnocellulose-containinq pulp The present invention relates to a process for bleaching of lignocellulose-containing pulp, in which the pulp is treat-ed at a pH between about 1 and about 7 in the presence of a magnesium compound, whereupon the pulp is washed and subse-quently bleached with a peroxide-containing compound. The ini~
tial treatment removes from the pulp ~hose trace metal ions that have a negative effect on the subsequent bleaching with i~
a peroxide-containing compound. Owing to the presence o mag-nesium ions in dissolved form during the initial treatment, the magnesium ions are retained in those positions in the pulp where they have a particularly positive effect on the effec-tiveness of the bleaching stage.
Backqround of the Invention 1 In the making of lignocellulose-containing pulp of high brightness, the pulp is bleached in one or more stages. For quite some time, mechanical pulps have been bleached with chlorine-free bleaching agents, the intention in this case being to remove chromophoric groups while preserving the con-tent of lignin. For environmental reasons, it has become in-creasingly common to treat also chemical pulps with chlorine-free bleaching agents, such as hydrogen peroxide, peracetic acid and ozone, already in the first bleaching stages. Unless the pulp is pretreated, however, bleaching with chlorine-free l~
bleaching agents is less effective. Thus, hydrogen peroxide bleaching in alkaline environment is disturbed by the presence ~ `~
in the pulp of ions of certain trace metals, primarily Mn, Cu and Fe. These metal ions cause degradation of hydrogen per- ;
oxide into undesirable products, thereby reducing the effecti-veness of the peroxide bleaching and increasing the consump-tion of peroxide.
The prior art teaches bleaching of chemical as well as mechanical pulps in the presence of magnesium salts. Most of the known bleaching processes do not comprise acid pretreat-35 ment, which preserves the content of undesirab].e trace metals ~ `
in the pulp. E'urthermore, bleaching with chlorine-free bleach-ing agents is normally performed in alkaline environment. As a result, it becomes impossible to retain or reintroduce the especially desirable magnesium ions, since these are precipi- ;;~
~ ~, 2 ~ 1 0 9 1 7 9 ; ~;;
tated at an alkaline pH and thus cannot diffuse into the pulp to such an extent that a pulp of high brightness and strength -can be obtained.
,:: ,:
Description of the Invention The inventio~ provides a process for treating ligno~
cellulose-containing pulp unde.r the conditions disclosed in the claims, whereby the content oE trace metal iOllS ill the pulp i9 selectively altered to render more effective the subsequent bleaching with a peroxide-containing compound.
I'hus, the invention relates to a process for bleaching of lignocellulose-containing pulp, whereby the pulp is treated at a pH within the range of from about 1 up to about 7 in the presence of a magnesium compound, whereupon the pulp is washed and subsequently the pulp is bleached with a peroxide-contain-ing compound.
An initial acid treatment effectively removes metal ions from lignocellulose-containing pulps. However, magnesium ions, especially when in their original positions of the pulp, are known to have a positive influence on the selectivity of the bleaching and the consumption of peroxide-contalning com-pounds. By the present process, undesirable metal ions are removed from the pulp suspension, while the magnesium ions are largely retained in their original positions. The latter is achieved by the presence of a magnesium compound in the treat-ment liquid, at such a pH and temperature that the compound isin dissolved form when contacted with the pulp. The present process further has the advantage of reducing the number of treatment stages compared with prior-art processes.
In the initial treatment, the magnesium compound should be in dissolved form when contacted with the pulp to produce a good effect. This can be achieved in various ways, depend-ing, inter alia, on the type and properties of the pulp. The magnesium compound can be brought to dissolved form by a suitable choice of pH within the range of from about 1 up to about 7, in combination with a suitable temperature and concentration of the magnesium compound.
Besides a magnesium compound, the initial treatment may be carried out in the presence of at least one more compound containing an alkaline earth metal. Thus, a compound contain-2 1 0 9 ~ 7 9 r . 3 - , ~: . ... :
ing calcium or barium may also be present. Preferably, the pulp is treated in the presence of a magnesium compound and calcium compound in optional sequence or mixture.
The magnesium-containing compound used is suitably magnesium sulphate, magnesium chloride, magnesium carbonate or magnesium nitrate, preferably magnesium sulphate. The calcium-containing compound used is suitably calcium chloride, calcium nitrate, calcium sulphate or calcium carbonate, preferably calcium chloride.
In the process according to the invention, the initial treatment is performed at a pH of from about 1 up to about 7, suitably from 1.5 up to 6, and preferably from 2 up to 5. The initial treatment may also be performed at a pH of from 3.1 up to 4.
In the initial treatment in the presence of a magnesium compound, the pH can be adjusted by adding an acid or an acid liquid to the pulp. The acid used may be an inorganic mineral acid or residual acid from a chlorine dioxide reactor, either separately or in optional mixture. Suitably, use is made of an inorganic mineral acid, such as sulphuric acid, nitric acid or hydrochloric acid, preferably sulphuric acid.
The amount of magnesium compound added in the initial treatment may be within the range of from about 100 ppm up to about 4000 ppm, calculated as part by weight of magnesium on part by weight of dry pulp. Suitably, the amount of the magne-sium compound added lies within the range of from 200 ppm up to 3000 ppm, preferably within the range of from 500 ppm up to 2000 ppm.
The amount of an optional compound containing an alkali-ne earth metal added in the initial treatment may be wi.thinthe range of from about 100 ppm up to about 4000 ppm, calcu-lated as part by weight of alkaline earth metal on part by weight of dry pulp. Suitably, the amount of the compound con-taining an alkaline earth metal added lies within the range of from 200 ppm up to 3000 ppm, preferably within the range of from 500 ppm up to 2000 ppm.
The amount of magnesium compound added as well as the other conditions in the initial treatment are so chosen thak the magnesium content of the pulp prior to the bleaching with ..: ~ : ..
r ~ C ~ ~ ~
a peroxide-containing compound amounts to at least about 50%
of the initial content. Suitably, the amount of magnesium compound added as well as the other conditions are so chosen that the magnesium content of the pulp prior to the bleaching with a peroxide-containing compound lies within the range of from 100% up to 300% of the initial content, preferably within the range of from 130i~ up to 200i~
The peroxide-containing eompound ineludes inorganic peroxide eompounds sueh as hydroyen peroxide, sodium peroxide or peroxosulphurie aeid (Caro's aeid), or organie peroxide eompounds, sueh as peraeetie aeid. Preferably, the peroxide~
eontaining eompound is hydrogen peroxide or a mixture oE
hydrogen peroxide and oxygen.
Bleaehing with a peroxide-containing compound is suitab-ly performed at a pH equal to or higher than the pH in theinitial treatment in the presenee of a magnesium eompound. In this way, the trace metal ions having a positive effect on the bleaching are retained also in the bleaching stage itself.
When the peroxide-containing compound is hydrogen peroxide, the pulp can be treated at a pH of from about 7 up to about 13, suitably at a pH of from 8 up to 12, preferably at a pH of from 9.5 up to 11. Bleaehing with the other peroxide-eontain-ing compounds indicated above takes place within the normal pH
ranges for each bleaching agentj which are well-known to the expert.
Suitably, bleaching with a peroxide-containing compound takes plaee in the presenee of yet another compound containing an alkaline earth metal. The compound containing an alkaline earth metal present in the bleaching, may be the same compound that was used in the initial treatment or another compound.
The alkaline earth metal suitably is calcium, magnesium or barium, or a mixture thereof. This further improves the selec-tivity of the bleaching and reduces the consumption of the peroxide-containing compound. It is especially preferred that the bleaching takes plaee in the presence of a calcium com-pound. The caleium eompound ean be added to the pulp suspen-sion outside the bleaching tower, e.g. by introduction into the pipeline leading to the bleaehing tower. Also, the cal-eium eompound can be added to the pulp suspension inside the ': :::...' ~ '"
2 1 ~ 9 1 7 9 bleaching tower, before the bleaching has commenced.
The amount of the compound containing an alkaline earth metal added in the bleaching, may lie withln the range of from about 100 ppm up to about 4000 ppm, calculated as part by weight of alkaline earth metal on part by weight of dry pulp.
Suitably, the a~ount of the compound containing an alkaline earth metal added lies within the range of from 300 ppm up to 3000 ppm, preferably within the range of from 600 ppm up to 2000 ppm.
When a calcium compound is present in the bleaching with a peroxide-containing compound, this compound suitably is cal-cium chloride, calcium nitrate, calcium sulphate or calcium carbonate. Calcium chloride is preferably used. Furthermore, the calcium compound is suitably added at such a combination of pH, temperature and concentration of the calcium compound that said compound is in active form when contacted with the pulp. Thus, suitably the pH lies within the range of from about 7 up to about 11. However, a positive effect is obtained also when the calcium compound is precipitated in the pulp suspension, e.g. as calcium carbonate.
The amount of calcium added as well as the other condi-tions in connection with the addition of calcium are so chosen that the calcium content of the pulp prior to the bleaching with a peroxide-containing compound amounts to at least about 25~ of the calcium content prior to the initial treatment. At this, the pulp may be treated with calcium in the initial treatmént as well as in the bleaching with a peroxide-contain-ing compound. The amount of calcium compound added as well as the other conditions are suitably so chosen that the calcium content of the pulp prior to the bleaching with a peroxide~
containing compound lies within the range of from 40% up to 150% of the original content, preferably within the range of from 50% up to 120% and most preferably within the range of from 50% up to 70%.
It is also within the scope of the invention, that all or a part of the amount of magnesium, and optionally any of the other alkaline earth metals, may be added to the pulp sus-pension by way of the water used for e.g. pH adjustment, wash-ing or dilution. Thus, hard water primarily containing magne-::
~a~l7s . ~
~`` 6 sium or calcium ions, or a combination thereof, is advanta-geously used in the initial treatment, for dilution in the washing stage, or for achieving a suitable pulp concentration in the bleaching stage. In this way, it is possible to reduce the added amount of the corresponding alkaline earth metal, provlded that the combination oE pH, temperature and conce.n-tration of the alkaline earth metal can be so chosen that said allcaline earth metal is in dissolved form when contacted with the pulp. Such hard waters include fresh water from limestone bedrock, white water from papermaking machines using Ch.ina clay or chalk as filler, or process water from production of sulphite pulp based on magnesium or calcium.
The process according to the invention is performed with a washing stage after the initial treatment and before the bleaching with a peroxide-containing compound. Washing effec-tively removes those trace metal ions that have a negative effect on the subsequent bleaching with a peroxide-contalning compound, e.g. ions of manganese, copper and iron. In order to retain the trace metal ions that have a positive effect on the subsequent bleaching with a peroxide-containing compound, pri-marily magnesium and calcium ions, the pH in the washing liquid is preferably equal to or higher than the pH in the initial treatment. However, the pH in the washing liquid should lie within the range of from about 3 up to about 10, suitably within the range of from 5 up to 10. It is especially preferred that the pH in the washing liquid is at least about 2 pH units higher than the pH in the initial treatment.
The washing liquid may be fresh water, optionally con-taining some added pH-adjusting chemical, or wastewater from one or more bleaching stages or extraction stages, giving a suitable pH in the washing stage. Furthermore, the washing liquid may consist of other types of wastewater, optionally purified, provided that it has a low content of undesirable ions of metal, such as manganese, iron and copper.
Washing between the initial treatment and bleaching with a peroxide-containing compound relates to methods -for remov-ing, more or less completely, the liquid phase from the pulp suspension in order to reduce the content of dissolved trace metal ions in said suspension. Washing may involve raising the 7 2~0917~ : :
pulp concentration, e.g. by sucking-off or pressing the sus-pension through a filter, or lowering the pulp concentration, e.g. by dilution with a washing liquid. Washing also relates to combinations and sequences in which the pulp concentration 5 i9 alternatingly raised and lowered, one or more times. In the present process, a washing method should be chosen which effectively removes the trace metal ions released in the ini-tial treatment, aspects of process technique and economy being considered.
The efectiveness of the washing may be indicated as the amount o liquid phase removed, compared with the liquid phase present in the pulp suspension prior to washing. Washing effectiveness can be at least about 80%, and suitably lies within the range of from 90% up to 100%, preferably within the range of from 95% up to 100%.
The initial treatment in the presence of a magnesium compound can also be performed in the presence of a bleaching agent. Bleaching agents that are active within the pH range suitable for the initial treatment include chlorine dioxide, ozone and acid peroxide-containing compounds. Acid peroxide-containing compounds include such organic compounds as per-acetic acid and such inorganic compounds as hydrogen peroxide and peroxosulphuric acid (Caro's acid). Suitably, the initial treatment takes place in the presence of ozone or peroxosul-phuric acid, preferably ozone, since these bleaching agentsaffect but to a minor extent the content of ions of alkaline earth metals in the pulp.
The process according to the invention may also involve an extraction stage before the bleaching with a peroxide-con~
taining compound. This is especially convenient when the ini-tial treatment is performed in the presence of a bleaching agent. Suitably, the extraction is performed at a pH that is equal to or higher than the pH in the initial treatment. Sui-tably, the pH in the extraction stage lies within the range of from about 7 up to about 11, preferably within the range of from 8 up to 10.
Regardless of the number of stages or the type of treat-ment following the initial treatment, the pH in a subsequent stage suitably is equal to or higher than the pH in the prece-~' 8 2 1 0 9 ~ 7 9 .
ding stage, in order to preserve the content of ions of alka-line earth metals in the pulp. In a sequence in which the pulp is first treated at a pH of about 2 in the presence of a mag-nesium compound and then washed and bleached with hydrogen peroxide, the pH in the washing stage should be at least about g, and the pH in the bleachi.ng stage should be at least about 8.
The term lignocellulose-containing pulp relates to pulps containing fibres that have been separated by chemical or mechanical treatment, or recycled fibres. The fibres may be of hardwood or softwood. The term chemical pulp relates to pulps digested according to the sulphate, sulphite, soda or organo-solv process. The term mechanical pulp relates to pulps pro-duced by refining of chips in a disc refiner (refiner mechani-cal pulp) or by grinding of logs in a grinder (groundwoodpulp). The term lignocellulose-containing pulp also relates to pulps produced by modifications or combinations of the above methods or processes. Such pulps include thermomechanical, chemimechanical and chemi-thermomechanical pulp9. Suitably, the lignocellulose-containing pulp consists of chemically digested pulp, preferably sulphate pulp of softwood.
The process according to the invention, can be applied to pulps with a yield of up to about 90%, suitably a yield within the range of from 40% up to 80%, preferably within the range of from 45% up to 65%.
The process according the invention, can be performed at an optional position in the bleaching sequence, e.g. immedia-tely after the making of the pulp. When the process according to the invention is applied to a chemically digested pulp, this is preferably delignified in an oxygen stage before applying the process according to the invention.
The process according to the invention can be applied to chemically digested pulps having an initial kappa number with-in the range of from about 3 up to about 100, suitably from 4 up to 60, preferably from 5 up to 40. The kappa number is established according to the Standard Method SCAN-C 1:77.
In the process according to the invention, the initial treatment can be performed at a temperature of from about 10C
up to about 100C, suitably from 25C up to 90C, preferably --~ 9 ~1~9179 '! ' `
from 40~C up to 80C. The initial treatment can be performed for a period of time of from about 1 s up to about 600 min, sultably from 1 min up to 120 min, preferably from 10 min up to 60 min. The pulp concentration in the initial treatment can be from about 1~ by weight up to about 60% by weight, suitably from 2% by weight up to 40~ by weight, preferably from 3% by weight up to 35% by weight.
When hydrogen peroxide .is used as peroxide-containing compound, the pulp i9 treated at a temperature of from about 30C up to about 100C, preEerably from 60C up to 90C, and for a period oE time of from about 30 min up to about 960 min, suitably from 60 min up to 360 min. Further, when hydrogen peroxide is used as peroxide-containing compound, the pulp concentration can be from about 1% by weight up to about 70%
by weight, suitably from 3% by weight up to 60% by weight, preferably from 10~ by weight up to 50% by weight. Treatment with the other peroxide-containing compounds indicated above takes place within the normal ranges as to temperature, period of time and pulp concentration for each bleaching agent, which are well-known to the expert.
In preferred embodiments involving the use of hydrogen peroxide as peroxide-containing compound, the amount of hydro~
gen peroxide lies within the range of from about 1 kg up to about 60 kg per tonne of dry pulp, calculated as 100% hydrogen peroxide. The upper limit is not critical, but has been set for economic reasons. Suitably, the amount of hydrogen peroxi-de lies within the range of from 2 kg up to 50 kg per tonne of dry pulp, preferably from 5 kg up to 40 kg per tonne of dry pulp, calculated as 100% hydrogen peroxide.
After the initial treatment in the presence of magnesium and subsequent bleaching with a peroxide-containing compound, the pulp can be used as such for making paper of lower bright-ness. Alternatively, the pulp can be finally bleached to the desired higher brightness by treatment in one or more stages.
Suitably, the ~inal bleaching involves chlorine-free bleaching agents such as the peroxide-containing compounds indicated above, ozone, oxygen or sodium dithionite, optionally with intermediate alkaline extraction stages which may be reinforc-ed with peroxide and/or oxygen. In this way, the formation and 2~1q~ ' 1 0 v discharge of AOX is completely eliminated.
The invention and its advantages will be illustrated in more detail by the Examples below which however, are only in-tended to illustrate the invention without limiting the same.
The percentages and parts stated in the description, claims and Examples, reEer to percent by weight and parts by weight, respectively, unless otherwise stated. Furthermore, the pH
values given in the description, claims and Examples refer to the pH at the end of each treatment, unless otherwise stated.
In the following Examples, the kappa number, viscosity and brightness of the pulp were established according to SCAN
Standard Methods, and the consumption of hydrogen peroxide was determined by iodometric titration.
Example 1 Oxygen-delignified sulphate pulp of softwood having a kappa number of 18, a brightness of 34.2% ISO and a viscosity of 1000 dm3/kg was treated at a pH of 2.1 ~/-0.1 in the pre-sence of various alkaline earth metals. After oxygen deligni-fication, the sulphate pulp had a pH of about 11, which was adjusted by an addition of 15 kg sulphuric acid/tonne dry pulp. The amount of alkaline earth metal added was 1000 ppm, calculated as part by weight of each alkaline earth metal on part by weight of dry pulp. In the initial treatment, the temperature was 50C, the treatment time was 30 min and the pulp concentration was 10% by weight. In the initial treat-ment, the general conditions as well as the compound contain-ing an alkaline earth metal were so chosen that the alkaline earth metal present was dissolved in the pulp suspension.
After the initial treatment, the pulp was washed at a pH of 6-7, in order to remove those metal ions that have a negativeeffect on the subsequent chlorine-free bleaching. Subsequent-ly, the pulp was bleached with hydrogen peroxide at a tempera-ture of 90~C, a residence time of 240 min, and a pulp concen-tration of 10% by weight. The addition of hydrogen peroxide was 25 kg/ tonne dry pulp, calculated as 100~ hydrogen peroxide, and the pH was about 10.5. For comparative purposes, the pulp was treated without addition of an alkaline earth metal, and subsequently bleached with hydrogen peroxide under the conditions stated above (Test 4). For further comparison, 2~09~7~ ~
:.. . 11 the pulp was treated with magnesium as in Test 1, but without an intermediate washing stage (Test 5). The results of the ;
tests appear from Table I below.
TABLE I
5Alkaline Pulp properties after peroxide bleaching Test earth Kappa number Viscosity Brightness metal _ ~dm3/kq)(~ ISO) 1 Mg 9.2 830 63.4 ` ;
10 2 Ca 10.5 800 53.0 3 Ba 11.4 880 51.0 4 --- * 12.8 840 45,5 Mg ** 12.2 880 41.0 ~ ~:
* No alkaline earth metal added. ;;
** No washing stage after the magnesium treatment.
As is evident from the Table, pulp treatment according to the invention at a pH of about 2.1 in the presence of a ~ `p magnesium compound, results in a much higher increase in ' ~
brightness and a more substantial reduction of the kappa num- ;
20 ber than does a treatment in the absence of such a compound. `~
Example 2 ~ ;~
The oxygen-delignified sulphate pulp of softwood employ-ed in Example 1 was treated in the presence of a magnesium compound at a pH within the range of from 1.5 up to 11 in order to illustrate the effect of pH in the initial treatment.
The amount of magnesium added was 1000 ppm, calculated as part by weight of magnesium on part by weight of dry pulp. The con-ditions in the initial treatment were identical with those in Example 1, except the pH variation. Likewise, the conditions in the subsequent hydrogen peroxide bleaching were identical with those in Example 1. After the initial treatment, the pulp was washed at a pH that was about 2 pH units higher than that in the initial treatment. The results of the tests appear from Table II below.
- - 12 ~0~79 ~.
TABLE II
pH in the Pulp properties after peroxide bleaching Test initial Kappa number Viscosity Brightness treatment `~
(dm3/kq)(% ISO) 1 1.5 9.1 795 64.0 2 2.0 9.2 835 63.2 3 3.3 9.6 820 61.0 4 ~.4 9.7 815 60.2 6.1 9.9 825 59.3 ~ "
6 6.8 10.2 8~0 57.5 7 10.8 12.1 880 43.6 As is evident from the Table, pulp treatment according to the invention at a pH within the range of from about 1 up 15 to about 7, results in a much higher increase in brightness `~
and a more substantial reduction of the kappa number than does ~ ~ `
treatment at a pH above this range.
Exam~le 3 The oxygen-delignified sulphate pulp of softwood employ-ed in Example 1 was treated in the presence of a magnesiumcompound at a pH of 2.1 +/- 0.1 in order to illustrate the effect of pH in the subsequent washing stage. In the initial l~
treatment, the pH was adjusted by addition of sulphuric acid. !~
The amount of magnesium added was 1000 ppm, calculated as part !~
by weight of magnesium on part by weight of dry pulp. The con~
ditions in the initial treatment as well as in the hydrogen peroxide bleaching were identical with those in Example 1.
After the initial treatment, the pulp was washed at a pH with~
in the range of from 3 up to about 11 where appropriate by de~
ionised water to which sodium hydroxide had been added. The results of the tests appear from Table III below.
, ~ 13 2109~ 79 ~ . . .
TABLE III
pH in the Pulp properties after peroxide bleaching Test washing Kappa number Viscosity Brightness stage `~
_(dm3/kq) (~ ISO) _ 1 3~0 11.9 890 52.9 2 4.3 10.2 830 58.9 3 4.8 10.2 840 59.4 4 6.9 9.0 835 63.4 ~
8.2 9.0 830 64.0 ~ `
6 10.8 9.0 800 59.5 ~` `;``
As is evident from the Table, pulp treatment according ` ;`~
to the invention with an intermediate washing stage at a pH
within the range of from about 3 up to about 10 results in a 15 considerable increase in brightness and a considerable reduc~
tion of the kappa number.
Example 4 ~!;
The oxygen-delignified sulphate pulp of softwood employ-ed in Example 1 was treated in the presence of a magnesium 20 compound at a pH of 2.1 ~/- 0.1 in order to illustrate the effect of pH in the bleaching with hydrogen peroxide within the range of from 7 up to 12. The amount of magnesium added was 1000 ppm, calculated as part by weight of magnesium on part by weight of dry pulp. The conditions in the initial i 25 treatment were identical with those in Example 1, as were the ~ K conditions in the hydrogen peroxide bleaching, except the pH
variation. After the initial treatment, the pulp was washed at a pH of 6-7. The results of the tests appear from Table IV
below.
TABLE IV
pH in the Pulp properties after peroxide bleaching Test bleaching Kappa number Viscosity Brightness stage (dm3/kq)(~ ISO) 1 7.1 12.0 900 50.2 2 8.2 9.9 830 58.0 3 10.3 9.2 825 63.1 4 11.9 9.1 780 62.5 As is evident from the Table, pulp treatment according :~-``'-' .
~- 14 ~109179 to the present invention using hydrogen peroxide as the per-oxide-containing compound, results in a very high increase in brightness and a considerable reduction of the kappa number.
Exam~le 5 The oxygen-delignified sulphate pulp of softwood employ- ~ ` ~
ed in Example 1 was treated in the presence of a magnesium ~`
compound at a pH of 2.1 ~ 0.1 in order to illustrate the effect o a calcium compound on the hydrogen peroxide bleach~
ing (Test 2). The amount of magnesium added was 1000 ppm, cal~
10 culated as part by weight of magnesium on part by weight of ~;
dry pulp. After washing, calcium was added in an amount of 1000 ppm, calculated as part by weight of calcium on part by weight of dry pulp. The conditions in the initial treatment ~ `
were identical with those in Example 1, as were the conditions ` ~
15 in the hydrogen peroxide bleaching, except the presence of a ~ `
calcium compound. After the initial treatment, the pulp was washed at a pH of 6-7. For comparative purposes, the pulp was ; `~
also bleached in the absence of the calcium compound (Test 1). ~` ~ ```
The results of the tests appear from Table V below. `~
TABLE V `
Pulp properties after peroxide bleaching Test Kappa number Viscosity Brightness Remaining (dm3/kq) (~ ISO) (kq/tonne) !`~
25 1 9.2 830 63.1 0 2 8.9 850 68.2 3.1 As is evident from the Table, pulp treatment according `
to the invention using a calcium compound in the hydrogen peroxide bleaching, results in a much higher brightness at a `
lower consumption of hydrogen peroxide than does bleaching in the absence of calcium.
Example 6 The oxygen-delignified sulphate pulp of softwood employ-ed in Example 1 was treated in the presence of a magnesium ~ -compound at a pH of 2.1 +/- 0.1, washed and bleached with hydrogen peroxide, in order to illustrate the effect of a selective metal profile in the pulp prior to bleaching. The amount of magnesium added was 1000 ppm, calculated as part by weight of magnesium on part by weight of dry pulp. After wash- ;
:: ::
~" 15 2109179 ing, calcium was added in an amount of looO ppm, calculated as part by weight of calcium on part by weight of dry pulp (Test 4). The conditions in the initial treatment were identical with those in Example 1, as were the conditions in the hydro-gen peroxide bleaching, except the presence of a calcium com-pound in Test 4. After the initial treatment, the pulp was washed at a pH of about 3 (Test 1) and 6-7 (Tests 2-4), respectively. For comparative purposes, the pulp was treated without any magnesium in the initial treatment and without any calcium in the bleaching stage (Tests 1 and 2). The content of certain metal ions in the sulphate pulp before (test 0) and after the initial treatment, as well as the brightness after the hydrogen peroxide bleaching, appear from Table VI below.
TABLE VI
Test Metal content before bleaching, ppm Brightness after Mg Ca Mn Fe Cu bleaching ~ISO~
0 3001800 68 8.31.5 ----l 30 220 6.5 5.8~ 0.5 45.5 2 lO0 640 20 7.00.9 45.7 3 550 690 18 6.30.7 63.2 4 5501700 18 6.30.7 68.2 As is evident from the Table, the process according to the invention involving treatment in the presence of a magne-sium compound, followed by hydrogen peroxide bleaching, resul-ts in a much higher brightness at a lower consumption of hydrogen peroxide than does bleaching in the absence of calcium.
Claims (10)
1. A process for bleaching of lignocellulose-containing pulp, c h a r a c t e r i s e d in that the pulp is treated at a pH within the range of from about 1 up to about 7 in the presence of a magnesium compound, whereupon the pulp is washed and subsequently the pulp is bleached with a peroxide-contain-ing compound.
2. A process according to claim 1, c h a r a c t e -r i s e d in that the lignocellulose-containing pulp consists of a chemically digested pulp.
3. A process according to claim 1 or 2, c h a r a c -t e r i s e d in that the pulp is treated in the presence of a magnesium compound and calcium compound in optional sequence or mixture.
4. A process according to any of the preceding claims, c h a r a c t e r i s e d in that a bleaching agent is pre-sent in the treatment in the presence of a magnesium compound.
5. A process according to any of the preceding claims, c h a r a c t e r i s e d in that the treatment in the pre-sence of a magnesium compound is carried out at a pH within the range of from 1.5 up to 6.
6. A process according to any of the preceding claims, c h a r a c t e r i s e d in that the pH in the washing liquid is equal to or higher than the pH in the treatment in the presence of a magnesium compound.
7. A process according to any of the preceding claims, c h a r a c t e r i s e d in that the magnesium content of the pulp after treatment in the presence of a magnesium com-pound and subsequent washing, and prior to the bleaching with a peroxide-containing compound lies within the range of from 100% up to 300% of the initial content.
8. A process according to any of the preceding claims, c h a r a c t e r i s e d in that the peroxide-containing compound consists of hydrogen peroxide or a mixture of hydrogen peroxide and oxygen.
9. A process according to any of the preceding claims, c h a r a c t e r i s e d in that the pH in the bleaching with a peroxide-containing compound is equal to or higher than the pH in the preceding stage.
10. A process according to any of the preceding claims, c h a r a c t e r i s e d in that the bleaching with a per-oxide-containing compound is carried out in the presence of a calcium compound.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| SE9203200A SE512137C2 (en) | 1992-10-29 | 1992-10-29 | Process for bleaching lignocellulosic pulp |
| SE9203200-2 | 1992-10-29 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2109179A1 true CA2109179A1 (en) | 1994-04-30 |
Family
ID=20387625
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002109179A Abandoned CA2109179A1 (en) | 1992-10-29 | 1993-10-25 | Process for bleaching of lignocellulose-containing pulp |
Country Status (16)
| Country | Link |
|---|---|
| EP (1) | EP0595386B2 (en) |
| JP (1) | JPH06207392A (en) |
| AT (1) | ATE180523T1 (en) |
| AU (1) | AU659039B2 (en) |
| BR (1) | BR9304438A (en) |
| CA (1) | CA2109179A1 (en) |
| CZ (1) | CZ284366B6 (en) |
| DE (1) | DE69325070D1 (en) |
| FI (1) | FI934705A (en) |
| MX (1) | MX9306618A (en) |
| NO (1) | NO302766B1 (en) |
| NZ (1) | NZ250050A (en) |
| RU (1) | RU2072014C1 (en) |
| SE (1) | SE512137C2 (en) |
| SK (1) | SK117593A3 (en) |
| ZA (1) | ZA937908B (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP3724033B2 (en) * | 1996-01-30 | 2005-12-07 | 住友電気工業株式会社 | High-strength, high-heat-resistant aluminum alloy and its manufacturing method, conductive wire and overhead wire |
| AUPP476398A0 (en) * | 1998-07-21 | 1998-08-13 | Orica Australia Pty Ltd | Bleaching process |
| DE102009050570B4 (en) | 2008-10-23 | 2017-07-06 | Bene_Fit Systems Gmbh & Co. Kg | Production process for bleached organic fiber materials and use of a bleaching agent |
Family Cites Families (15)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US422819A (en) * | 1890-03-04 | Frederick j | ||
| US2687943A (en) * | 1951-06-26 | 1954-08-31 | Du Pont | Bleaching of mechanical wood pulp |
| US3507744A (en) * | 1966-04-01 | 1970-04-21 | Kimberly Clark Co | Wood pulp bleaching process utilizing peroxide pyrophosphate high concentration compositions |
| JPS51102103A (en) * | 1975-03-05 | 1976-09-09 | Nippon Parupu Kogyo Kk | Ryusanenhoparupuno hyohakuhoho |
| JPS583074B2 (en) * | 1975-11-17 | 1983-01-19 | 三菱瓦斯化学株式会社 | Palpuno Kasan Kabutsu Hiyou Hakuhou |
| SE420430B (en) † | 1978-02-17 | 1981-10-05 | Mo Och Domsjoe Ab | PROCEDURE FOR WHEATING AND EXTRACTION OF LIGNOCELLULOSALLY MATERIALS WITH PEROXID CONTAINING BLACKS |
| JPS5927436B2 (en) * | 1979-05-29 | 1984-07-05 | 王子製紙株式会社 | Peroxide bleaching method for wood pulp |
| JPS5721590A (en) * | 1980-07-11 | 1982-02-04 | Mitsubishi Gas Chemical Co | Peroxide bleaching of wood pulp |
| FR2520397A1 (en) * | 1982-01-28 | 1983-07-29 | Centre Tech Ind Papier | PROCESS FOR TREATING CHEMICAL PAPER PASTES |
| AT380496B (en) * | 1984-06-27 | 1986-05-26 | Steyrermuehl Papier | METHOD AND REACTOR FOR DELIGNIFYING CELLULAR WITH OXYGEN |
| JP2827235B2 (en) * | 1988-11-22 | 1998-11-25 | 三菱瓦斯化学株式会社 | High yield pulp bleaching process. |
| JPH0364589A (en) * | 1989-07-28 | 1991-03-19 | Mitsubishi Gas Chem Co Inc | Bleaching of chemical pulp |
| US5091054A (en) † | 1989-08-18 | 1992-02-25 | Degussa Corporation | Process for bleaching and delignification of lignocellulosic |
| CA2053035C (en) † | 1990-10-12 | 1997-09-30 | Repap Enterprises Inc. | Chlorine-free wood pulps and process of making |
| SE470065C (en) * | 1991-04-30 | 1996-01-15 | Eka Nobel Ab | Treatment of chemical pulp with an acid and then a magnesium and calcium compound in chlorine-free bleaching |
-
1992
- 1992-10-29 SE SE9203200A patent/SE512137C2/en not_active IP Right Cessation
-
1993
- 1993-10-04 DE DE69325070T patent/DE69325070D1/en not_active Expired - Lifetime
- 1993-10-04 EP EP93202821A patent/EP0595386B2/en not_active Expired - Lifetime
- 1993-10-04 AT AT93202821T patent/ATE180523T1/en not_active IP Right Cessation
- 1993-10-22 CZ CZ932241A patent/CZ284366B6/en not_active IP Right Cessation
- 1993-10-25 CA CA002109179A patent/CA2109179A1/en not_active Abandoned
- 1993-10-25 FI FI934705A patent/FI934705A/en unknown
- 1993-10-25 AU AU49199/93A patent/AU659039B2/en not_active Ceased
- 1993-10-25 ZA ZA937908A patent/ZA937908B/en unknown
- 1993-10-25 MX MX9306618A patent/MX9306618A/en unknown
- 1993-10-25 SK SK1175-93A patent/SK117593A3/en unknown
- 1993-10-26 NZ NZ250050A patent/NZ250050A/en unknown
- 1993-10-27 NO NO933873A patent/NO302766B1/en unknown
- 1993-10-28 JP JP5291459A patent/JPH06207392A/en active Pending
- 1993-10-29 RU RU9393049739A patent/RU2072014C1/en active
- 1993-10-29 BR BR9304438A patent/BR9304438A/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| BR9304438A (en) | 1994-05-03 |
| FI934705A0 (en) | 1993-10-25 |
| NO933873D0 (en) | 1993-10-27 |
| SE512137C2 (en) | 2000-01-31 |
| SK117593A3 (en) | 1994-05-11 |
| ZA937908B (en) | 1994-05-24 |
| MX9306618A (en) | 1994-04-29 |
| NO302766B1 (en) | 1998-04-20 |
| CZ284366B6 (en) | 1998-11-11 |
| FI934705A (en) | 1994-04-30 |
| ATE180523T1 (en) | 1999-06-15 |
| EP0595386A1 (en) | 1994-05-04 |
| AU4919993A (en) | 1994-05-12 |
| SE9203200D0 (en) | 1992-10-29 |
| JPH06207392A (en) | 1994-07-26 |
| EP0595386B2 (en) | 2002-07-17 |
| EP0595386B1 (en) | 1999-05-26 |
| NZ250050A (en) | 1994-12-22 |
| SE9203200L (en) | 1994-04-30 |
| CZ224193A3 (en) | 1994-05-18 |
| RU2072014C1 (en) | 1997-01-20 |
| AU659039B2 (en) | 1995-05-04 |
| NO933873L (en) | 1994-05-02 |
| DE69325070D1 (en) | 1999-07-01 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| JP2864167B2 (en) | Delignification method of pulp containing lignocellulose. | |
| US5310458A (en) | Process for bleaching lignocellulose-containing pulps | |
| US5658429A (en) | Process for bleaching of lignocellulose-containing pulp using a chelating agent prior to a peroxide-ozone-peroxide sequence | |
| JP2592747B2 (en) | Method for bleaching pulp containing lignocellulose | |
| US6398908B1 (en) | Process for acid bleaching of lignocellulose-containing pulp with a magnesium compound | |
| US6007678A (en) | Process for delignification of lignocellulose-containing pulp with an organic peracid or salts thereof | |
| CA2121387C (en) | Method for bleaching lignocellulose-containing pulp | |
| CA2149649C (en) | Process for bleaching of lignocellulose-containing pulp | |
| CA2109179A1 (en) | Process for bleaching of lignocellulose-containing pulp | |
| CA2490390A1 (en) | Improved process for bleaching kraft pulp |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| FZDE | Discontinued |