EP1161593A1 - Oxygen delignification of pulp in the presence of carbonates as alkali - Google Patents
Oxygen delignification of pulp in the presence of carbonates as alkaliInfo
- Publication number
- EP1161593A1 EP1161593A1 EP00908150A EP00908150A EP1161593A1 EP 1161593 A1 EP1161593 A1 EP 1161593A1 EP 00908150 A EP00908150 A EP 00908150A EP 00908150 A EP00908150 A EP 00908150A EP 1161593 A1 EP1161593 A1 EP 1161593A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- alkali
- oxygen
- pulp
- process according
- deligniflcation
- 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.)
- Withdrawn
Links
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 title claims abstract description 66
- 239000001301 oxygen Substances 0.000 title claims abstract description 66
- 229910052760 oxygen Inorganic materials 0.000 title claims abstract description 66
- 239000003513 alkali Substances 0.000 title claims abstract description 46
- 150000004649 carbonic acid derivatives Chemical class 0.000 title claims abstract description 16
- 238000000034 method Methods 0.000 claims abstract description 131
- 238000011282 treatment Methods 0.000 claims abstract description 27
- 229920001131 Pulp (paper) Polymers 0.000 claims abstract description 23
- 238000004061 bleaching Methods 0.000 claims abstract description 21
- 238000010977 unit operation Methods 0.000 claims abstract description 21
- 239000007864 aqueous solution Substances 0.000 claims abstract description 18
- 239000000243 solution Substances 0.000 claims abstract description 10
- 150000002978 peroxides Chemical class 0.000 claims abstract description 7
- BVKZGUZCCUSVTD-UHFFFAOYSA-M Bicarbonate Chemical compound OC([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-M 0.000 claims abstract description 5
- CDBYLPFSWZWCQE-UHFFFAOYSA-L Sodium Carbonate Chemical compound [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 claims description 26
- 229910000029 sodium carbonate Inorganic materials 0.000 claims description 12
- 238000011084 recovery Methods 0.000 claims description 9
- 238000002309 gasification Methods 0.000 claims description 7
- MYMOFIZGZYHOMD-UHFFFAOYSA-N Dioxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 claims description 6
- 229910001882 dioxygen Inorganic materials 0.000 claims description 6
- BWHMMNNQKKPAPP-UHFFFAOYSA-L potassium carbonate Chemical compound [K+].[K+].[O-]C([O-])=O BWHMMNNQKKPAPP-UHFFFAOYSA-L 0.000 claims description 6
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 claims description 5
- 229910021653 sulphate ion Inorganic materials 0.000 claims description 5
- 238000005516 engineering process Methods 0.000 claims description 4
- 229920001021 polysulfide Polymers 0.000 claims description 4
- 229910052736 halogen Inorganic materials 0.000 claims description 3
- 150000002366 halogen compounds Chemical class 0.000 claims description 3
- 150000002367 halogens Chemical class 0.000 claims description 3
- 229910000027 potassium carbonate Inorganic materials 0.000 claims description 3
- LSNNMFCWUKXFEE-UHFFFAOYSA-L sulfite Chemical compound [O-]S([O-])=O LSNNMFCWUKXFEE-UHFFFAOYSA-L 0.000 claims description 3
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 27
- 238000002474 experimental method Methods 0.000 description 17
- 235000011121 sodium hydroxide Nutrition 0.000 description 10
- 235000017550 sodium carbonate Nutrition 0.000 description 9
- 229940001593 sodium carbonate Drugs 0.000 description 9
- 239000000126 substance Substances 0.000 description 9
- BVKZGUZCCUSVTD-UHFFFAOYSA-L Carbonate Chemical compound [O-]C([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-L 0.000 description 8
- ZAMOUSCENKQFHK-UHFFFAOYSA-N Chlorine atom Chemical compound [Cl] ZAMOUSCENKQFHK-UHFFFAOYSA-N 0.000 description 8
- 239000000460 chlorine Substances 0.000 description 8
- 238000010411 cooking Methods 0.000 description 8
- MHAJPDPJQMAIIY-UHFFFAOYSA-N Hydrogen peroxide Chemical compound OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 description 7
- 229910052801 chlorine Inorganic materials 0.000 description 7
- 238000006243 chemical reaction Methods 0.000 description 5
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 5
- CSNNHWWHGAXBCP-UHFFFAOYSA-L Magnesium sulfate Chemical compound [Mg+2].[O-][S+2]([O-])([O-])[O-] CSNNHWWHGAXBCP-UHFFFAOYSA-L 0.000 description 4
- 230000015556 catabolic process Effects 0.000 description 4
- 238000006731 degradation reaction Methods 0.000 description 4
- OSVXSBDYLRYLIG-UHFFFAOYSA-N dioxidochlorine(.) Chemical compound O=Cl=O OSVXSBDYLRYLIG-UHFFFAOYSA-N 0.000 description 4
- 239000000835 fiber Substances 0.000 description 4
- 229910052708 sodium Inorganic materials 0.000 description 4
- 239000011734 sodium Substances 0.000 description 4
- 150000001720 carbohydrates Chemical class 0.000 description 3
- 235000014633 carbohydrates Nutrition 0.000 description 3
- 239000000706 filtrate Substances 0.000 description 3
- 229920005610 lignin Polymers 0.000 description 3
- -1 perborate Chemical compound 0.000 description 3
- 229910052700 potassium Inorganic materials 0.000 description 3
- 239000000725 suspension Substances 0.000 description 3
- MGWGWNFMUOTEHG-UHFFFAOYSA-N 4-(3,5-dimethylphenyl)-1,3-thiazol-2-amine Chemical compound CC1=CC(C)=CC(C=2N=C(N)SC=2)=C1 MGWGWNFMUOTEHG-UHFFFAOYSA-N 0.000 description 2
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 2
- 239000004155 Chlorine dioxide Substances 0.000 description 2
- LYCAIKOWRPUZTN-UHFFFAOYSA-N Ethylene glycol Chemical compound OCCO LYCAIKOWRPUZTN-UHFFFAOYSA-N 0.000 description 2
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 2
- UIIMBOGNXHQVGW-UHFFFAOYSA-M Sodium bicarbonate Chemical compound [Na+].OC([O-])=O UIIMBOGNXHQVGW-UHFFFAOYSA-M 0.000 description 2
- 229910052792 caesium Inorganic materials 0.000 description 2
- 235000019398 chlorine dioxide Nutrition 0.000 description 2
- 239000004744 fabric Substances 0.000 description 2
- 239000007789 gas Substances 0.000 description 2
- WQYVRQLZKVEZGA-UHFFFAOYSA-N hypochlorite Chemical compound Cl[O-] WQYVRQLZKVEZGA-UHFFFAOYSA-N 0.000 description 2
- 239000007788 liquid Substances 0.000 description 2
- 229910052744 lithium Inorganic materials 0.000 description 2
- 159000000003 magnesium salts Chemical class 0.000 description 2
- 229910052943 magnesium sulfate Inorganic materials 0.000 description 2
- 235000019341 magnesium sulphate Nutrition 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 229910017604 nitric acid Inorganic materials 0.000 description 2
- JCXJVPUVTGWSNB-UHFFFAOYSA-N nitrogen dioxide Inorganic materials O=[N]=O JCXJVPUVTGWSNB-UHFFFAOYSA-N 0.000 description 2
- 238000004537 pulping Methods 0.000 description 2
- 229910052701 rubidium Inorganic materials 0.000 description 2
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 1
- QPCDCPDFJACHGM-UHFFFAOYSA-N N,N-bis{2-[bis(carboxymethyl)amino]ethyl}glycine Chemical compound OC(=O)CN(CC(O)=O)CCN(CC(=O)O)CCN(CC(O)=O)CC(O)=O QPCDCPDFJACHGM-UHFFFAOYSA-N 0.000 description 1
- CBENFWSGALASAD-UHFFFAOYSA-N Ozone Chemical compound [O-][O+]=O CBENFWSGALASAD-UHFFFAOYSA-N 0.000 description 1
- 239000004698 Polyethylene Substances 0.000 description 1
- KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical class [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 description 1
- 229910000831 Steel Inorganic materials 0.000 description 1
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 1
- 239000005864 Sulphur Substances 0.000 description 1
- 239000004809 Teflon Substances 0.000 description 1
- 229920006362 Teflon® Polymers 0.000 description 1
- 239000003570 air Substances 0.000 description 1
- PRKQVKDSMLBJBJ-UHFFFAOYSA-N ammonium carbonate Chemical class N.N.OC(O)=O PRKQVKDSMLBJBJ-UHFFFAOYSA-N 0.000 description 1
- 239000001099 ammonium carbonate Substances 0.000 description 1
- 235000011162 ammonium carbonates Nutrition 0.000 description 1
- PYKYMHQGRFAEBM-UHFFFAOYSA-N anthraquinone Natural products CCC(=O)c1c(O)c2C(=O)C3C(C=CC=C3O)C(=O)c2cc1CC(=O)OC PYKYMHQGRFAEBM-UHFFFAOYSA-N 0.000 description 1
- 150000004056 anthraquinones Chemical class 0.000 description 1
- UORVGPXVDQYIDP-UHFFFAOYSA-N borane Chemical compound B UORVGPXVDQYIDP-UHFFFAOYSA-N 0.000 description 1
- 239000000872 buffer Substances 0.000 description 1
- 239000011575 calcium Substances 0.000 description 1
- 229910052791 calcium Inorganic materials 0.000 description 1
- BRPQOXSCLDDYGP-UHFFFAOYSA-N calcium oxide Chemical compound [O-2].[Ca+2] BRPQOXSCLDDYGP-UHFFFAOYSA-N 0.000 description 1
- 239000000292 calcium oxide Substances 0.000 description 1
- ODINCKMPIJJUCX-UHFFFAOYSA-N calcium oxide Inorganic materials [Ca]=O ODINCKMPIJJUCX-UHFFFAOYSA-N 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 239000001569 carbon dioxide Substances 0.000 description 1
- 229910002092 carbon dioxide Inorganic materials 0.000 description 1
- 238000009993 causticizing Methods 0.000 description 1
- 229920002678 cellulose Polymers 0.000 description 1
- 239000001913 cellulose Substances 0.000 description 1
- 238000005660 chlorination reaction Methods 0.000 description 1
- 150000001805 chlorine compounds Chemical class 0.000 description 1
- 229910001902 chlorine oxide Inorganic materials 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 230000006835 compression Effects 0.000 description 1
- 238000007906 compression Methods 0.000 description 1
- 230000002844 continuous effect Effects 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 239000008367 deionised water Substances 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000004090 dissolution Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000000605 extraction Methods 0.000 description 1
- 239000012065 filter cake Substances 0.000 description 1
- 239000000383 hazardous chemical Substances 0.000 description 1
- 230000007062 hydrolysis Effects 0.000 description 1
- 238000006460 hydrolysis reaction Methods 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-M hydroxide Chemical compound [OH-] XLYOFNOQVPJJNP-UHFFFAOYSA-M 0.000 description 1
- 150000004679 hydroxides Chemical class 0.000 description 1
- WGCNASOHLSPBMP-UHFFFAOYSA-N hydroxyacetaldehyde Natural products OCC=O WGCNASOHLSPBMP-UHFFFAOYSA-N 0.000 description 1
- 239000011777 magnesium Substances 0.000 description 1
- 229910052749 magnesium Inorganic materials 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 229920000573 polyethylene Polymers 0.000 description 1
- 229920001343 polytetrafluoroethylene Polymers 0.000 description 1
- 239000004810 polytetrafluoroethylene Substances 0.000 description 1
- 235000011118 potassium hydroxide Nutrition 0.000 description 1
- 238000002203 pretreatment Methods 0.000 description 1
- 239000000047 product Substances 0.000 description 1
- 239000003223 protective agent Substances 0.000 description 1
- 238000004076 pulp bleaching Methods 0.000 description 1
- 238000000746 purification Methods 0.000 description 1
- 238000010791 quenching Methods 0.000 description 1
- 230000000171 quenching effect Effects 0.000 description 1
- 229920005989 resin Polymers 0.000 description 1
- 239000011347 resin Substances 0.000 description 1
- 239000003352 sequestering agent Substances 0.000 description 1
- 235000017557 sodium bicarbonate Nutrition 0.000 description 1
- 229910000030 sodium bicarbonate Inorganic materials 0.000 description 1
- 239000011122 softwood Substances 0.000 description 1
- 230000003019 stabilising effect Effects 0.000 description 1
- 239000010959 steel Substances 0.000 description 1
- 150000003467 sulfuric acid derivatives Chemical class 0.000 description 1
- 230000001629 suppression Effects 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- BFKJFAAPBSQJPD-UHFFFAOYSA-N tetrafluoroethene Chemical compound FC(F)=C(F)F BFKJFAAPBSQJPD-UHFFFAOYSA-N 0.000 description 1
- 238000003466 welding Methods 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
Definitions
- the present invention relates to a process for pulp deligniflcation and/or pulp bleaching, in which chemical pulp is treated while suspended in an aqueous solution with oxygen in the presence of alkali.
- a prerequisite for successful TCF delignification/bleaching is a lower lignin content in the pulp fed into the bleaching department of the pulp mill, i.e. a lower Kappa number, than previous bleaching processes, as the chlorine free bleaching chemicals are less specific with regard to the removal or modification of the coloured components in chemical pulp than, for instance, chlorine or chlorine dioxide.
- TCF bleaching chemicals have a tendency to affect also the cellulosic fibres.
- these lower Kappa numbers were accomplished in the cooking section of the pulping process. Lately, however, the trend in the art has been to use one or more oxygen deligniflcation stages to achieve the required lower Kappa numbers.
- SE 393 138 discloses an oxygen deligniflcation process in which sodium bicarbonate is used instead of sodium carbonate. This is indicated to give higher viscosity and carbohydrate yield at a given lignin content than when sodium carbonate is used. An important prerequisite for this is, however, that the partial pressure of carbon dioxide during the deligniflcation process is controlled within specified limits, else either the deligniflcation speed or the selectivity will fall outside of acceptable limits.
- FR 2 670 513 relates to an oxygen deligniflcation process in which a mix of sodium hydroxide and sodium carbonate is used as alkali. It is indicated that the sodium carbon- ate charge should be half the charge, at the most, of the sodium hydroxide. By this process any need for protective agents, such as magnesium salts, is said to be eliminated. However, this process has to be run in two different oxygen treatment unit operation stages.
- SE 450 394 discloses an oxygen deligniflcation process aimed at the problem of depolymerisation of carbohydrates. This process consists of a number of unit operation stages, in which the pulp is treated with, apart from oxygen, nitrogen dioxide and optionally nitric acid.
- SE 219 677 discloses a process for pulp purification by oxygen deligniflcation, which is suggested to provide for suppression of fibre degradation.
- the pulp is imbibed by an aqueous 0.5-4.0% solution of sodium carbonate or a 0.1-2.0% solution of sodium hydroxide. It is indicated that when sodium carbonate and sodium hydroxide are used in similar concentrations, the extent of removal of lignin, resins and pentosan from sulphate pulp is similar.
- the pulp is compressed to remove excess liquid to provide wet pulp with a consistency of about 20-66.7%.
- the compressed pulp is dis- integrated to make it porous, after which, fourthly, the disintegrated pulp is treated with oxygen-containing gas under pressure and at an elevated temperature below 100°C.
- US-A-4,115,186 discloses a process for bleaching cellulose pulp with molecular oxygen, which process comprises four treatments, that are carried out one after another.
- SE-B-364,322 discloses a process for bleacing of wood pulp. The process com- prises two treatments, that are carried out one after another.
- SE 9604217-1 discloses a method and apparatus for delignifying chemical pulp. The method comprises at least two separate treatments.
- the problem to be solved is thus to provide a process for oxygen deligniflcation of chemical pulp in the presence of alkali, which is less or, preferably, not at all burdened by the inconveniences associated with prior art.
- the present invention relates to a process for oxygen deligniflcation of chemical pulp, which process comprises an oxygen treatment unit operation stage in which chemical pulp is treated while suspended in an aqueous solution with oxygen in the presence of alkali, whereby the pulp consistency is less than 20%, preferably from about 3 to 15%, in particular from about 10 to 12%; the alkali is preferably used, as added to the solution, in an amount of from about 5 percent by weight, preferably from about 5 to 50 percent by weight, and in particular from about 10 to 30 per by weight, calculated on the weight of said material, whereby more than about 50 percent by weight, preferably from about 90 to 100 percent by weight of said alkali consist of one or more carbonates; and the pH of the aqueous solution is adapted to provide for the essential absence of bicarbonate in said solution during the process.
- unit operation stage indicates an essentially self-contained process, in which basically all, or at least the chemical treatments, that are required to achieve the desired effect, are performed substantially contemporaneously.
- oxygen is intended to comprise elementary oxygen, molecular oxygen, air, hydrogen peroxide, perborate, ozone, and any other oxygen carrying means or oxygen carrying compound conventionally used for the purpose of pulp deligniflcation; elementary oxygen and molecular oxygen, in particular molecular oxygen, is however preferred.
- alkali is intended to comprise hydroxides and carbonates of Li, Na, K, Rb, Cs, Ca, NH , and calcium oxide.
- Oxygen deligniflcation according to present invention to given Kappa numbers provides for better pulp yield than oxygen deligniflcation according to prior art, even when performed at higher temperature.
- the process according to the present invention usually also results in a better final viscosity than obtained with prior art.
- Carbonates are advantageous, in the present context, in that they have a big buffer capacity, providing for a comparably low and even alkali profile during the oxygen deligniflcation process.
- the use of carbonates as alkali is furthermore advantageous in that carbonates are available in large amounts in the pulp mill.
- Conventional green liquor may be used in the present unit operation stage, either as such or after some suitable pre-treatment.
- the sodium carbonate in the green liquor has been converted into sodium hydroxide in a caus- ticizing section.
- the present invention provides for an option to eliminate the need for such conversion, and thus also for such conversion itself.
- Various recovery methods can be used in order to provide the carbonate to be used in the present oxygen deligniflcation process.
- Exemplary of such recovery methods are those according to the so-called black liquor gasification technology, a recent recovery technology in which the recovered chemicals are provided in separate streams, in particular one stream of sulphur-rich liquor and one stream of sulphur- lean liquor, from which sodium carbonate easily can be obtained with greater ease, and in purer form, than from conventional recovery methods, thus making black liquor gasification well suited for the purpose of the present invention.
- Black liquor gasification is described by e.g. Dahlquist, E., Jacobs, R.
- the carbonate(s) may be any suitable alkaline carbonate, but is/are preferably chosen among Li, Na, K, Rb, Cs, Ca, and ammonium carbonates, in particular Na and K carbonates, and combinations thereof.
- essentially all of the alkali consists of one or more carbonates. It is in particular preferred to use carbonates in the absence of sodium and potassium hydroxides, as tests have shown better results regarding final viscosity as well as pulp yield when using only carbonate, than when using carbonate in combination with such a hydroxide.
- the carbonate(s) may be used in combination with one or more additional deligniflcation or stabilising chemicals, such as for instance magnesium salts, which is common in the art.
- additional deligniflcation or stabilising chemicals such as for instance magnesium salts, which is common in the art.
- the oxygen treatment unit operation stage may according to one embodiment be an OP-stage, i.e. basically an oxygen stage supplied with a small charge of hydrogen peroxide, or a PO-stage, i.e. basically a hydrogen peroxide stage supplied with a small charge of oxygen.
- the oxygen deligniflcation process is preferably carried out at a temperature of about 80 - 160°C, in particular 90 - 130°C.
- the pressure is preferably about 0.3 - 2 MPa, suitably 0,5 - 0,8 MPa.
- the pH of the aqueous solution during the process is preferably above about 9, specifically from about above 10.
- the present invention also relates to a process for the bleaching of chemical pulp which comprises the present process for oxygen deligniflcation of chemical pulp, i.e. a process comprising an oxygen treatment unit operation stage in which chemical pulp is treated while suspended in an aqueous solution with oxygen in the presence of alkali, whereby the pulp consistency is less than about 20%, preferably from about 3 to 15%, in particular from about 10 to 12%), whereby more than about 50 percentage by weight, preferably from about 90 to 100 percent by weight of the alkali consist of one or more carbonates; and the pH of the aqueous solution is adapted to provide for the essential absence of bicarbonate in said solution during the process.
- the delignification/bleaching process according to the present invention may comprise a peroxide bleaching unit operation stage, in which the pulp is preferably treated while suspended in an aqueous solution containing alkali, whereby more than 50 percentage by weight of the alkali consist of one or more carbonates.
- Said bleaching process may comprise one or more additional bleach- ing/delignification stages, such as for instance peroxide treatment stages (commonly denoted P-stages), conventional oxygen treatment stages (commonly denoted O-stages), boronhydrid treatment stages (B-stages), sequestering agent treatment stages (commonly denoted Q- stages), further alkali extraction stages (commonly denoted E-stages), even chlorine treatment stages such as hypochlorite treatment stages (commonly denoted H-stages), chlorine dioxide treatment stages (commonly denoted D-stages), and chlorination stages (commonly denoted C-stages), although such chlorine treatment stages are absent in the preferred embodiments of the present invention.
- P-stages peroxide treatment stages
- O-stages conventional oxygen treatment stages
- B-stages boronhydrid treatment stages
- sequestering agent treatment stages commonly denoted Q- stages
- further alkali extraction stages commonly denoted E-stages
- the bleaching/delignification process according the present invention may also comprise a number of oxygen treatment unit operation stages according to the invention, which unit operation stages may be arranged consecutively or in parallel, as well as being positioned separately at various locations in the bleaching/delignification process without any direct connections between said unit operation stages.
- the process may also comprise a combination of a number of consecutive and/or parallel unit operation stages and separate unit operation stages.
- ITC is a modified sulphate cooking process, in which the alkali charge is divided and the alkali profile levelled out; an ITC-process comprises one counter-current and one concurrent zone and is carried out at low cooking temperatures, usu- ally about 160°C, and with long cooking times. ITC-processes are described in US-A-
- ECF Elementary Chlorine Free
- Example I Sulphate pulp from isothermal cooking of softwood was subjected to oxygen deligniflcation according to the present invention, using carbonate and carbonate- containing compositions as alkali, as well as using sodium hydroxide alkali in a reference experiment.
- the pulp had an initial Kappa number of 22.8, a brightness of 27.6%> ISO and an initial viscosity of 1090 ml/g.
- the alkali was added as 1 M solutions of NaOH and Na 2 CO 3 , respec- tively. After having sealed the bag by means of welding, the bag was subjected to shaking for about one minute in a shaker apparatus in order to distribute the alkali, water, and the magnesium sulphate solution all through the pulp. The complete quantity of obtained pulp suspension, having a pulp consistency of 12%, was then brought into a steel autoclave lined with polytetrafluoroethylene (TEFLON*). After having sealed the autoclave, oxygen was introduced from a gas bottle at a positive pressure of 0.7 MPa into the autoclave through a valve in the autoclave lid.
- TEFLON* polytetrafluoroethylene
- the deligniflcation reaction was started by submerging the autoclave into a heated glycol bath, in which the autoclave was rotated for different periods of time according to each individual experiment. Quenching of the deligniflcation reaction was carried out by submerging the autoclave into cold water.
- the lid valve was opened, thus releasing the autoclave from the oxygen pressure, whereupon the lid was removed to unseal the autoclave, and the pulp was washed on a wire cloth screen according to a feedback procedure, in which the pulp is slushed in about 1 1 of deionised water, the pulp is dewatered on a wire, the filtrate recirculated through the dewatered pulp in order to minimise the loss of fines, whereafter 2 doses of 0.5 1 water is passed through the pulp, the filtrate from which is discarded; this feedback procedure is repeated three times. Details and results of experiments # 0-3 are set forth in Table I below.
- oxygen deligniflcation to essentially similar Kappa numbers about 12
- using the process according to the present invention produced better pulp yield than oxygen deligniflcation according to prior art, even when performed at higher temperature.
- the process according to the present invention also resulted in a higher final viscosity than obtained with prior art.
- Example II The experiments in this Example were carried out as described in Example I, except that the pulp had an initial Kappa number of 26, the pulp suspension had a consistency of 10%, and that the O-stage was followed by a Q-stage in which the pulp suspension was treated with 0,27% DTPA at 90°C for 60 minutes, and thereafter in an OP-stage with oxygen at 0.7 MPa, 0.1% Mg, and 1.5% hydrogenperoxid. Details and results of experiments # 4-5 are set forth in Table II below. Table II Experiments
- deligniflcation sequences to essentially similar Kappa numbers, about 6 using the process according to the present invention produced better pulp yield than deligniflcation according to prior art.
- Example III The experiments in this Example were carried out as described in Example I, except that in experiment #8 potassium carbonate was used as alkali. Details and results of experiments # 6-8 are set forth in Table III below.
- oxygen deligniflcation to essentially similar Kappa numbers, about 10 using the process according to the present invention produced better pulp yield than oxygen deligniflcation according to prior art.
- Example IV The experiments in this Example were carried out as described in Example I, except that soda-AQ pulp, having an initial Kappa number of 20, a brightness of 33.8%o ISO and an initial viscosity of 902 ml/g was used in experiments #9-10, and liner pulp, having an initial Kappa number of 97.4 and a brightness of 11.39% ISO was used in experiments #11-12. Details and results of experiments # 9-12 are set forth in Table IV below. Table IV Experiments
- oxygen deligniflcation to essentially similar Kappa numbers using the process according to the present invention produced higher pulp yield than oxygen deligniflcation according to prior art, irrespective of pulp type.
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- Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
- Wood Science & Technology (AREA)
- Paper (AREA)
Abstract
A process for oxygen delignification of chemical pulp comprising an oxygen treatment unit operation stage in which the pulp is treated while suspended in an aqueous solution with oxygen in the presence of alkali, whereby the pulp consistency is less than 20%; more than 50 percentage by weight of the alkali consist of one or more carbonates; and the pH of the aqueous solution during the process is adapted to provide for the essential absence of bicarbonate in said solution during the treatment. Furthermore a process for the bleaching of chemical pulp comprising a peroxide bleaching unit operation stage and an oxygen delignification process of said kind.
Description
OXYGEN DELIGNIFICATION OF PULP IN THE PRESENCE OF CARBONATES AS ALKALI
The present invention relates to a process for pulp deligniflcation and/or pulp bleaching, in which chemical pulp is treated while suspended in an aqueous solution with oxygen in the presence of alkali. Background of the invention
TCF (= Totally Chlorine Free) deligniflcation and bleaching processes have become more common over time. These processes are distinguished by the fact that essentially no chlorine-containing chemicals are added during the bleaching sequences. A prerequisite for successful TCF delignification/bleaching is a lower lignin content in the pulp fed into the bleaching department of the pulp mill, i.e. a lower Kappa number, than previous bleaching processes, as the chlorine free bleaching chemicals are less specific with regard to the removal or modification of the coloured components in chemical pulp than, for instance, chlorine or chlorine dioxide. In other words, TCF bleaching chemicals have a tendency to affect also the cellulosic fibres. Previously, these lower Kappa numbers were accomplished in the cooking section of the pulping process. Lately, however, the trend in the art has been to use one or more oxygen deligniflcation stages to achieve the required lower Kappa numbers.
Conventional oxygen deligniflcation processes are, however, associated with a few problems. As the degree of deligniflcation increases, the relative speed of deligniflcation decreases and the carbohydrate degradation increases. Alkali, usually sodium hydroxide, is used in the oxygen deligniflcation processes in order to dissolve the oxygen treated coloured components in the chemical pulp. Sodium carbonate is also mentioned in prior art documents as a plausible alkali. A higher alkali charge will provide for improved dissolution of the coloured components, i.e. lower Kappa numbers, but unfortunately also to hydrolysis of the fi- bres, causing loss of pulp viscosity. The problem of fibre degradation in oxygen deligniflcation processes has been touched upon in prior art documents.
SE 393 138 discloses an oxygen deligniflcation process in which sodium bicarbonate is used instead of sodium carbonate. This is indicated to give higher viscosity and carbohydrate yield at a given lignin content than when sodium carbonate is used. An important prerequisite for this is, however, that the partial pressure of carbon dioxide during the deligniflcation process is controlled within specified limits, else either the deligniflcation speed or the selectivity will fall outside of acceptable limits.
FR 2 670 513 relates to an oxygen deligniflcation process in which a mix of sodium hydroxide and sodium carbonate is used as alkali. It is indicated that the sodium carbon-
ate charge should be half the charge, at the most, of the sodium hydroxide. By this process any need for protective agents, such as magnesium salts, is said to be eliminated. However, this process has to be run in two different oxygen treatment unit operation stages.
SE 450 394 discloses an oxygen deligniflcation process aimed at the problem of depolymerisation of carbohydrates. This process consists of a number of unit operation stages, in which the pulp is treated with, apart from oxygen, nitrogen dioxide and optionally nitric acid.
SE 219 677 discloses a process for pulp purification by oxygen deligniflcation, which is suggested to provide for suppression of fibre degradation. Firstly, the pulp is imbibed by an aqueous 0.5-4.0% solution of sodium carbonate or a 0.1-2.0% solution of sodium hydroxide. It is indicated that when sodium carbonate and sodium hydroxide are used in similar concentrations, the extent of removal of lignin, resins and pentosan from sulphate pulp is similar. Secondly, i.e. after the imbibment, the pulp is compressed to remove excess liquid to provide wet pulp with a consistency of about 20-66.7%. Thirdly, the compressed pulp is dis- integrated to make it porous, after which, fourthly, the disintegrated pulp is treated with oxygen-containing gas under pressure and at an elevated temperature below 100°C.
US-A-4,115,186 discloses a process for bleaching cellulose pulp with molecular oxygen, which process comprises four treatments, that are carried out one after another.
SE-B-364,322 discloses a process for bleacing of wood pulp. The process com- prises two treatments, that are carried out one after another.
SE 9604217-1 discloses a method and apparatus for delignifying chemical pulp. The method comprises at least two separate treatments.
Thus, all prior art processes to overcome the basic problem of fibre degradation in oxygen deligniflcation processes are either complicated by a multitude of process stages, by critical parameter limits, by the use of hazardous substances such as nitrogen dioxide or nitric acid, or by the use of energy consuming and fibre damaging operations such as compression and disintegration of pulp.
Accordingly, the problem to be solved is thus to provide a process for oxygen deligniflcation of chemical pulp in the presence of alkali, which is less or, preferably, not at all burdened by the inconveniences associated with prior art.
This problem has been solved by means of the present invention, which involves a process for pulp deligniflcation as defined by the appended claims. More particularly, the present invention relates to a process for oxygen deligniflcation of chemical pulp, which process comprises an oxygen treatment unit operation stage in which chemical pulp is treated
while suspended in an aqueous solution with oxygen in the presence of alkali, whereby the pulp consistency is less than 20%, preferably from about 3 to 15%, in particular from about 10 to 12%; the alkali is preferably used, as added to the solution, in an amount of from about 5 percent by weight, preferably from about 5 to 50 percent by weight, and in particular from about 10 to 30 per by weight, calculated on the weight of said material, whereby more than about 50 percent by weight, preferably from about 90 to 100 percent by weight of said alkali consist of one or more carbonates; and the pH of the aqueous solution is adapted to provide for the essential absence of bicarbonate in said solution during the process. Depending upon various product and/or process properties, such as the type of pulp under treatment, desired Kappa number, acceptable treatment period etc., the artisan may chose a suitable set of parameter values within the ranges indicated above, if desired (or even required) based on some trial-and-error experimentation.
In this context the term "unit operation stage" indicates an essentially self-contained process, in which basically all, or at least the chemical treatments, that are required to achieve the desired effect, are performed substantially contemporaneously. The term
"oxygen" is intended to comprise elementary oxygen, molecular oxygen, air, hydrogen peroxide, perborate, ozone, and any other oxygen carrying means or oxygen carrying compound conventionally used for the purpose of pulp deligniflcation; elementary oxygen and molecular oxygen, in particular molecular oxygen, is however preferred. The term "alkali" is intended to comprise hydroxides and carbonates of Li, Na, K, Rb, Cs, Ca, NH , and calcium oxide.
Oxygen deligniflcation according to present invention to given Kappa numbers provides for better pulp yield than oxygen deligniflcation according to prior art, even when performed at higher temperature.
When performed at similar deligniflcation temperatures, the process according to the present invention usually also results in a better final viscosity than obtained with prior art.
Apart from solving the problems indicated above, it has also surprisingly been found that it is possible to run the present oxygen deligniflcation process at comparatively high temperatures, and thereby achieve higher deligniflcation speed or rate, with essentially no corresponding diminution of the pulp yield or the pulp viscosity.
Carbonates are advantageous, in the present context, in that they have a big buffer capacity, providing for a comparably low and even alkali profile during the oxygen deligniflcation process.
The use of carbonates as alkali is furthermore advantageous in that carbonates are available in large amounts in the pulp mill. Conventional green liquor may be used in the present unit operation stage, either as such or after some suitable pre-treatment. Previously, the sodium carbonate in the green liquor has been converted into sodium hydroxide in a caus- ticizing section. The present invention provides for an option to eliminate the need for such conversion, and thus also for such conversion itself. Various recovery methods can be used in order to provide the carbonate to be used in the present oxygen deligniflcation process. Exemplary of such recovery methods are those according to the so-called black liquor gasification technology, a recent recovery technology in which the recovered chemicals are provided in separate streams, in particular one stream of sulphur-rich liquor and one stream of sulphur- lean liquor, from which sodium carbonate easily can be obtained with greater ease, and in purer form, than from conventional recovery methods, thus making black liquor gasification well suited for the purpose of the present invention. Black liquor gasification is described by e.g. Dahlquist, E., Jacobs, R. in "Development of a Dry Black Liquor Gasification Process", 1992 International Chemical Recovery Conference Proceedings, CPPA and TAPPI, June 7- 11, Seattle, WA, USA, p.457, and by Stigsson, L.L., Hesseborn, B., in "Gasification of Black Liquor" 1995 International Chemical Recovery Conference Proceedings, CPPA and TAPPI, April 24-27, Toronto, Ontario, Canada, p.B 277
The carbonate(s) may be any suitable alkaline carbonate, but is/are preferably chosen among Li, Na, K, Rb, Cs, Ca, and ammonium carbonates, in particular Na and K carbonates, and combinations thereof. In a preferred embodiment essentially all of the alkali consists of one or more carbonates. It is in particular preferred to use carbonates in the absence of sodium and potassium hydroxides, as tests have shown better results regarding final viscosity as well as pulp yield when using only carbonate, than when using carbonate in combination with such a hydroxide.
Apart from other alkali, the carbonate(s) may be used in combination with one or more additional deligniflcation or stabilising chemicals, such as for instance magnesium salts, which is common in the art.
The oxygen treatment unit operation stage may according to one embodiment be an OP-stage, i.e. basically an oxygen stage supplied with a small charge of hydrogen peroxide, or a PO-stage, i.e. basically a hydrogen peroxide stage supplied with a small charge of oxygen.
The oxygen deligniflcation process is preferably carried out at a temperature of about 80 - 160°C, in particular 90 - 130°C. During the process, the pressure is preferably
about 0.3 - 2 MPa, suitably 0,5 - 0,8 MPa. The pH of the aqueous solution during the process is preferably above about 9, specifically from about above 10.
The present invention also relates to a process for the bleaching of chemical pulp which comprises the present process for oxygen deligniflcation of chemical pulp, i.e. a process comprising an oxygen treatment unit operation stage in which chemical pulp is treated while suspended in an aqueous solution with oxygen in the presence of alkali, whereby the pulp consistency is less than about 20%, preferably from about 3 to 15%, in particular from about 10 to 12%), whereby more than about 50 percentage by weight, preferably from about 90 to 100 percent by weight of the alkali consist of one or more carbonates; and the pH of the aqueous solution is adapted to provide for the essential absence of bicarbonate in said solution during the process.
The delignification/bleaching process according to the present invention may comprise a peroxide bleaching unit operation stage, in which the pulp is preferably treated while suspended in an aqueous solution containing alkali, whereby more than 50 percentage by weight of the alkali consist of one or more carbonates.
Said bleaching process may comprise one or more additional bleach- ing/delignification stages, such as for instance peroxide treatment stages (commonly denoted P-stages), conventional oxygen treatment stages (commonly denoted O-stages), boronhydrid treatment stages (B-stages), sequestering agent treatment stages (commonly denoted Q- stages), further alkali extraction stages (commonly denoted E-stages), even chlorine treatment stages such as hypochlorite treatment stages (commonly denoted H-stages), chlorine dioxide treatment stages (commonly denoted D-stages), and chlorination stages (commonly denoted C-stages), although such chlorine treatment stages are absent in the preferred embodiments of the present invention. It should be noted that the bleaching/delignification process according the present invention may also comprise a number of oxygen treatment unit operation stages according to the invention, which unit operation stages may be arranged consecutively or in parallel, as well as being positioned separately at various locations in the bleaching/delignification process without any direct connections between said unit operation stages. The process may also comprise a combination of a number of consecutive and/or parallel unit operation stages and separate unit operation stages.
Oxygen deligniflcation according to the present invention may be applied in combination with various, per se known, pulp mill processes, e.g. sulphate processes, such as ITC or EMCC processes (ITC = Isothermal Cooking; EMCC = Extended Modified Continu-
ous Cooking) and polysulphide processes, and sulphur-free processes, such as soda-AQ processes, as well as sulphite processes. ITC is a modified sulphate cooking process, in which the alkali charge is divided and the alkali profile levelled out; an ITC-process comprises one counter-current and one concurrent zone and is carried out at low cooking temperatures, usu- ally about 160°C, and with long cooking times. ITC-processes are described in US-A-
5,470,437 and US-A-5, 567,280. Polysulphide processes are described in, for instance, US-A- 3,874,991 (Kleppe). Soda-AQ processes are essentially sulphur- free cooking processes carried out at about 160-170°C with charges of NaOH and anthraquinone (= AQ); this type of process is advantageous in that it is odourless. Soda-AQ processes are described by e.g. Gratzl, J. S. "The reaction mechanisms of AQ in alkaline pulping", Eucepa Symp. June 1980 Helsinki paper 12, 27pp.
In a preferred embodiment of the present invention no elementary halogen or gaseous halogen compound is added during the pulp mill process. In a specific embodiment, the process is an ECF (ECF = Elementary Chlorine Free) process, in which essentially no elementary chlorine is added during the process, and in another embodiment the process is a TCF process, in which no or essentially no chlorine compound is added during the process. The present invention will be further described below with reference to a few examples, the purpose of which are merely to illustrate the invention, and which should not be regarded as limiting the scope of the present invention; this scope is defined solely by the ap- pended claims.
Examples Example I: Sulphate pulp from isothermal cooking of softwood was subjected to oxygen deligniflcation according to the present invention, using carbonate and carbonate- containing compositions as alkali, as well as using sodium hydroxide alkali in a reference experiment. The pulp had an initial Kappa number of 22.8, a brightness of 27.6%> ISO and an initial viscosity of 1090 ml/g.
All experiments followed the following, general procedure: Moist or wet pulp corresponding to 25 g dry substance was slushed in about 2 1 of water in a pulper at 3000 rpm. The pulp was dewatered on a wire cloth screen, and the filtrate was brought through the filter cake a second time in order to minimise the loss of fines. Then the pulp was weighed in order to calculate the contents of liquid, after which the pulp was shredded by hand. The shredded pulp was transferred to a polyethylene bag, and alkali, water, and an amount of an aqueous solution magnesium sulphate corresponding to 0.1 % Mg2+, based on dry pulp, were added to the pulp in the bag. The alkali was added as 1 M solutions of NaOH and Na2CO3, respec-
tively. After having sealed the bag by means of welding, the bag was subjected to shaking for about one minute in a shaker apparatus in order to distribute the alkali, water, and the magnesium sulphate solution all through the pulp. The complete quantity of obtained pulp suspension, having a pulp consistency of 12%, was then brought into a steel autoclave lined with polytetrafluoroethylene (TEFLON*). After having sealed the autoclave, oxygen was introduced from a gas bottle at a positive pressure of 0.7 MPa into the autoclave through a valve in the autoclave lid. The deligniflcation reaction was started by submerging the autoclave into a heated glycol bath, in which the autoclave was rotated for different periods of time according to each individual experiment. Quenching of the deligniflcation reaction was carried out by submerging the autoclave into cold water. The lid valve was opened, thus releasing the autoclave from the oxygen pressure, whereupon the lid was removed to unseal the autoclave, and the pulp was washed on a wire cloth screen according to a feedback procedure, in which the pulp is slushed in about 1 1 of deionised water, the pulp is dewatered on a wire, the filtrate recirculated through the dewatered pulp in order to minimise the loss of fines, whereafter 2 doses of 0.5 1 water is passed through the pulp, the filtrate from which is discarded; this feedback procedure is repeated three times. Details and results of experiments # 0-3 are set forth in Table I below.
Table I Experiments
Accordingly, oxygen deligniflcation to essentially similar Kappa numbers, about 12, using the process according to the present invention produced better pulp yield than oxygen deligniflcation according to prior art, even when performed at higher temperature. When performed at similar deligniflcation temperatures, the process according to the present invention also resulted in a higher final viscosity than obtained with prior art.
Example II: The experiments in this Example were carried out as described in Example I, except that the pulp had an initial Kappa number of 26, the pulp suspension had a consistency of 10%, and that the O-stage was followed by a Q-stage in which the pulp suspension was treated with 0,27% DTPA at 90°C for 60 minutes, and thereafter in an OP-stage with oxygen at 0.7 MPa, 0.1% Mg, and 1.5% hydrogenperoxid. Details and results of experiments # 4-5 are set forth in Table II below.
Table II Experiments
Accordingly, deligniflcation sequences to essentially similar Kappa numbers, about 6, using the process according to the present invention produced better pulp yield than deligniflcation according to prior art.
Example III: The experiments in this Example were carried out as described in Example I, except that in experiment #8 potassium carbonate was used as alkali. Details and results of experiments # 6-8 are set forth in Table III below.
Table III Experiments
Accordingly, oxygen deligniflcation to essentially similar Kappa numbers, about 10, using the process according to the present invention produced better pulp yield than oxygen deligniflcation according to prior art.
Example IV: The experiments in this Example were carried out as described in Example I, except that soda-AQ pulp, having an initial Kappa number of 20, a brightness of 33.8%o ISO and an initial viscosity of 902 ml/g was used in experiments #9-10, and liner pulp, having an initial Kappa number of 97.4 and a brightness of 11.39% ISO was used in experiments #11-12. Details and results of experiments # 9-12 are set forth in Table IV below.
Table IV Experiments
Accordingly, oxygen deligniflcation to essentially similar Kappa numbers using the process according to the present invention produced higher pulp yield than oxygen deligniflcation according to prior art, irrespective of pulp type.
Claims
1. A process for oxygen deligniflcation of chemical pulp, which process comprises an oxygen treatment unit operation stage in which chemical pulp is treated while suspended in an aqueous solution with oxygen, preferably molecular oxygen, in the presence of alkali, characterised in that the pulp consistency is less than 20%; more than 50 percentage by weight of the alkali consist of one or more carbonates; and the pH of the aqueous solution during the process is adapted to provide for the essential absence of bicarbonate in said solution during the treatment.
2. A process according to claim 1 , characterised in that essentially all of the alkali consists sodium carbonate, potassium carbonate, or a combination thereof.
3. A process according to claim 1, characterised in that essentially no elementary halogen or gaseous halogen compound is added to the chemical pulp during the process.
4. A process according to claim 1, characterised in that the chemical pulp is treated with oxygen at a temperature of about 90-130°C.
5. A process according to claim 1, characterised in that the pressure during the oxygen treatment is from about 0.5 to about 0.8 MPa.
6. A process according to claim 1, characterised in that the pH of the aqueous solution during the process is above about 10. 7. A process according to claim 1 , characterised in that the treated pulp originates from a soda process, such as a soda-AQ process, or a sulphate process, such as an ITC-process or a polysulphide process, or a sulphite process.
8. A process according to claim 1, characterised in that at least part of the alkali originates from green liquor and/or black liquor, preferably from an alkali recovery process, such as an alkali recovery process based on black liquor gasification technology.
9. A process for the bleaching of chemical pulp, which process comprises a peroxide bleaching unit operation stage, characterised in that it comprises an oxygen deligniflcation process according to any preceding claim.
10. A process according to claim 9, characterised in that the pulp is treated in the peroxide deligniflcation unit operation stage while suspended in an aqueous solution containing alkali, whereby more than 50 percentage by weight of the alkali consist of one or more carbonates.
AMENDED CLAIMS
[received by the International Bureau on 04 July 2000 (04.07.00); original claim 5 replaced by new claim and remaining claims unchanged (1 page)]
1. A process for oxygen deligniflcation of chemical pulp, which process comprises an oxygen treatment unit operation stage in which chemical pulp is treated while suspended in an aqueous solution with oxygen, preferabh' molecular oxygen, in the presence of alkali, characterised in that the pulp consistency is less than 20° o: more than 50 percentage by weight of the alkali consist of one or more carbonates: and the pH of the aqueous solution during the process is adapted to provide for the essential absence of bicarbonate in said solution during the treatment.
2. A process according to claim 1. characterised in that essentially all of the alkali consists sodium carbonate, potassium carbonate, or a combination thereof.
3. A process according to claim 1. characterised in that essentially no elementary halogen or gaseous halogen compound is added to the chemical pulp during the process.
4. A process according to claim 1. characterised in that the chemical pulp is treated with oxygen at a temperature of about 90 - 130°C.
5. A process according to claim 1, characterised in that the pressure during the oxygen treatment is from about 0.3 to about 2 MPa.
6. A process according to claim 1 , characterised in that the pH of the aqueous solution during the process is above about 10.
7. A process according to claim 1, characterised in that the treated pulp originates from a soda process, such as a soda-AQ process, or a sulphate process, such as an ITC-process or a polysulphide process, or a sulphite process.
8. A process according to claim 1 , characterised in that at least part of the alkali originates from green liquor and/or black liquor, preferably from an alkali recovery process, such as an alkali recover}' process based on black liquor gasification technology.
9. A process for the bleaching of chemical pulp, which process comprises a peroxide bleaching unit operation stage, characterised in that it comprises an oxygen deligniflcation process according to any preceding claim.
10. A process according to claim 9, characterised in that the pulp is treated in the peroxide deligniflcation unit operation stage while suspended in an aqueous solution containing alkali, whereby more than 50 percentage by weight of the alkali consist of one or more carbonates.
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
SE9900425 | 1999-02-09 | ||
SE9900425A SE9900425L (en) | 1999-02-09 | 1999-02-09 | Pulp Delignification Procedure |
PCT/SE2000/000172 WO2000047813A1 (en) | 1999-02-09 | 2000-01-28 | Oxygen delignification of pulp in the presence of carbonates as alkali |
Publications (1)
Publication Number | Publication Date |
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EP1161593A1 true EP1161593A1 (en) | 2001-12-12 |
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Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
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EP00908150A Withdrawn EP1161593A1 (en) | 1999-02-09 | 2000-01-28 | Oxygen delignification of pulp in the presence of carbonates as alkali |
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EP (1) | EP1161593A1 (en) |
AU (1) | AU2952400A (en) |
SE (1) | SE9900425L (en) |
WO (1) | WO2000047813A1 (en) |
Families Citing this family (3)
Publication number | Priority date | Publication date | Assignee | Title |
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US7182836B2 (en) * | 2001-06-29 | 2007-02-27 | Voith Paper Fiber Systems Gmbh Kg | Method for delignifying lignocellulosic raw materials |
DE10323376A1 (en) * | 2003-05-21 | 2004-12-16 | Voith Paper Fiber Systems Gmbh & Co. Kg | Delignification procedure |
FI20070126A0 (en) | 2006-09-08 | 2007-02-13 | Linde Ag | Process for de-pulping and using carbon dioxide or (bi) carbonate for this |
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SE219677C1 (en) * | ||||
GB1262655A (en) * | 1968-09-20 | 1972-02-02 | Canadian Ind | Bleaching of wood pulp |
FI48764C (en) * | 1973-05-30 | 1977-07-26 | Ahlstroem Oy | Method and apparatus for bleaching cellulose pulp with molecular weight. |
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1999
- 1999-02-09 SE SE9900425A patent/SE9900425L/en not_active Application Discontinuation
-
2000
- 2000-01-28 WO PCT/SE2000/000172 patent/WO2000047813A1/en active Application Filing
- 2000-01-28 EP EP00908150A patent/EP1161593A1/en not_active Withdrawn
- 2000-01-28 AU AU29524/00A patent/AU2952400A/en not_active Abandoned
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SE9900425D0 (en) | 1999-02-09 |
AU2952400A (en) | 2000-08-29 |
SE9900425L (en) | 2000-09-04 |
WO2000047813A1 (en) | 2000-08-17 |
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