EP0513140B1 - A process for the bleaching of chemical pulp - Google Patents
A process for the bleaching of chemical pulp Download PDFInfo
- Publication number
- EP0513140B1 EP0513140B1 EP91903684A EP91903684A EP0513140B1 EP 0513140 B1 EP0513140 B1 EP 0513140B1 EP 91903684 A EP91903684 A EP 91903684A EP 91903684 A EP91903684 A EP 91903684A EP 0513140 B1 EP0513140 B1 EP 0513140B1
- Authority
- EP
- European Patent Office
- Prior art keywords
- pulp
- enzyme
- steps
- bleaching
- treatment
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
- 238000000034 method Methods 0.000 title claims abstract description 39
- 238000004061 bleaching Methods 0.000 title claims abstract description 28
- 229920001131 Pulp (paper) Polymers 0.000 title claims abstract description 6
- 238000011282 treatment Methods 0.000 claims abstract description 50
- 108090000790 Enzymes Proteins 0.000 claims abstract description 49
- 102000004190 Enzymes Human genes 0.000 claims abstract description 49
- 239000000126 substance Substances 0.000 claims abstract description 23
- 239000003513 alkali Substances 0.000 claims abstract description 18
- OSVXSBDYLRYLIG-UHFFFAOYSA-N dioxidochlorine(.) Chemical compound O=Cl=O OSVXSBDYLRYLIG-UHFFFAOYSA-N 0.000 claims abstract description 16
- 230000003647 oxidation Effects 0.000 claims abstract description 13
- 238000007254 oxidation reaction Methods 0.000 claims abstract description 13
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims abstract description 11
- 239000001301 oxygen Substances 0.000 claims abstract description 11
- 229910052760 oxygen Inorganic materials 0.000 claims abstract description 11
- 230000001590 oxidative effect Effects 0.000 claims abstract description 9
- 239000004155 Chlorine dioxide Substances 0.000 claims abstract description 8
- 235000019398 chlorine dioxide Nutrition 0.000 claims abstract description 8
- 150000002978 peroxides Chemical class 0.000 claims abstract description 4
- 229940088598 enzyme Drugs 0.000 claims description 42
- 108010002430 hemicellulase Proteins 0.000 claims description 7
- 229940059442 hemicellulase Drugs 0.000 claims description 6
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 claims description 3
- 102000003425 Tyrosinase Human genes 0.000 claims description 3
- 108060008724 Tyrosinase Proteins 0.000 claims description 3
- 108010059892 Cellulase Proteins 0.000 claims description 2
- 108090000371 Esterases Proteins 0.000 claims description 2
- 235000008331 Pinus X rigitaeda Nutrition 0.000 claims description 2
- 235000011613 Pinus brutia Nutrition 0.000 claims description 2
- 241000018646 Pinus brutia Species 0.000 claims description 2
- 108010059820 Polygalacturonase Proteins 0.000 claims description 2
- 229940106157 cellulase Drugs 0.000 claims description 2
- 108010093305 exopolygalacturonase Proteins 0.000 claims description 2
- 108010062085 ligninase Proteins 0.000 claims description 2
- 239000011122 softwood Substances 0.000 claims description 2
- ZAMOUSCENKQFHK-UHFFFAOYSA-N Chlorine atom Chemical compound [Cl] ZAMOUSCENKQFHK-UHFFFAOYSA-N 0.000 abstract description 6
- 239000000460 chlorine Substances 0.000 abstract description 6
- 230000003247 decreasing effect Effects 0.000 abstract description 6
- 230000036284 oxygen consumption Effects 0.000 abstract description 4
- 231100000331 toxic Toxicity 0.000 abstract description 2
- 230000002588 toxic effect Effects 0.000 abstract description 2
- 229910001902 chlorine oxide Inorganic materials 0.000 abstract 1
- 150000002894 organic compounds Chemical class 0.000 abstract 1
- 238000002474 experimental method Methods 0.000 description 9
- 229920005610 lignin Polymers 0.000 description 6
- 239000000203 mixture Substances 0.000 description 6
- 229910052801 chlorine Inorganic materials 0.000 description 5
- 230000007423 decrease Effects 0.000 description 5
- 150000004045 organic chlorine compounds Chemical class 0.000 description 4
- QTBSBXVTEAMEQO-UHFFFAOYSA-N Acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 description 3
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 3
- 239000000470 constituent Substances 0.000 description 3
- 239000007787 solid Substances 0.000 description 3
- 238000005406 washing Methods 0.000 description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 3
- KZBUYRJDOAKODT-UHFFFAOYSA-N Chlorine Chemical compound ClCl KZBUYRJDOAKODT-UHFFFAOYSA-N 0.000 description 2
- 229920002488 Hemicellulose Polymers 0.000 description 2
- MHAJPDPJQMAIIY-UHFFFAOYSA-N Hydrogen peroxide Chemical compound OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 description 2
- 108010029541 Laccase Proteins 0.000 description 2
- 238000010411 cooking Methods 0.000 description 2
- 238000000354 decomposition reaction Methods 0.000 description 2
- 238000000746 purification Methods 0.000 description 2
- VGVRPFIJEJYOFN-UHFFFAOYSA-N 2,3,4,6-tetrachlorophenol Chemical class OC1=C(Cl)C=C(Cl)C(Cl)=C1Cl VGVRPFIJEJYOFN-UHFFFAOYSA-N 0.000 description 1
- 101710121765 Endo-1,4-beta-xylanase Proteins 0.000 description 1
- 239000007844 bleaching agent Substances 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
- 230000000694 effects Effects 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 238000011835 investigation Methods 0.000 description 1
- 238000009533 lab test Methods 0.000 description 1
- 238000009896 oxidative bleaching Methods 0.000 description 1
- 231100000683 possible toxicity Toxicity 0.000 description 1
- 238000004076 pulp bleaching Methods 0.000 description 1
- 238000004537 pulping Methods 0.000 description 1
- 231100000419 toxicity Toxicity 0.000 description 1
- 230000001988 toxicity Effects 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
- D21C5/00—Other processes for obtaining cellulose, e.g. cooking cotton linters ; Processes characterised by the choice of cellulose-containing starting materials
- D21C5/005—Treatment of cellulose-containing material with microorganisms or enzymes
-
- 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
- D21C9/1057—Multistage, with compounds cited in more than one sub-group D21C9/10, D21C9/12, D21C9/16
-
- 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
- D21C9/12—Bleaching ; Apparatus therefor with halogens or halogen-containing compounds
- D21C9/14—Bleaching ; Apparatus therefor with halogens or halogen-containing compounds with ClO2 or chlorites
- D21C9/142—Bleaching ; Apparatus therefor with halogens or halogen-containing compounds with ClO2 or chlorites with ClO2/Cl2 in a multistage process involving ClO2/Cl2 exclusively
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
- D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
- D21C9/10—Bleaching ; Apparatus therefor
- D21C9/147—Bleaching ; Apparatus therefor with oxygen or its allotropic modifications
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
- D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
- D21C9/10—Bleaching ; Apparatus therefor
- D21C9/16—Bleaching ; Apparatus therefor with per compounds
- D21C9/163—Bleaching ; Apparatus therefor with per compounds with peroxides
Definitions
- the chemical pulp obtained by sulfate cooking is brown in color, which is mainly due to lignin remaining in the pulp.
- Lignin is removed by bleaching, which is usually a multiple-step process in which the pulp is treated alternately with oxidizing chemicals which decompose lignin and with chemicals which dissolve the substances produced as products of the decomposition.
- oxidizing chemicals have been chorine-containing substances and oxygen, whereas alkali solutions have been used as chemicals removing the decomposition products.
- the object of the present invention is to provide a new method, based on enzyme treatment of pulp, by which pulp can be bleached in such a manner that the need for bleaching chemicals decreases and at the same time the chemical oxygen consumption and toxicity of the bleaching effluent decrease so that the need for water purification will be smaller. It is characteristic of the invention that the pulp is treated with an enzyme in two or more steps of the bleaching process, wherein the pulp subsequent to each enzyme treatment step is treated in an oxidation step.
- the pulp was subjected to an oxidizing bleaching treatment by using a mixture which contained 50 % chlorine dioxide and 50 % chlorine gas.
- the mixture was proportioned at 2.0 x the kappa number after the pulping.
- the treatment temperature was 40 ° C and the treatment time 45 min and the consistency of the pulp 3.5 %.
Landscapes
- Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
- Wood Science & Technology (AREA)
- Chemical & Material Sciences (AREA)
- Biochemistry (AREA)
- Microbiology (AREA)
- Paper (AREA)
- Investigating Or Analysing Biological Materials (AREA)
- Hard Magnetic Materials (AREA)
- Agricultural Chemicals And Associated Chemicals (AREA)
Abstract
Description
- The present invention relates to a process for the bleaching of chemical pulp as set forth in the preamble of claim 1.
- Especially the chemical pulp obtained by sulfate cooking is brown in color, which is mainly due to lignin remaining in the pulp. Lignin is removed by bleaching, which is usually a multiple-step process in which the pulp is treated alternately with oxidizing chemicals which decompose lignin and with chemicals which dissolve the substances produced as products of the decomposition. The most commonly used oxidizing chemicals have been chorine-containing substances and oxygen, whereas alkali solutions have been used as chemicals removing the decomposition products.
- When reacting, the chlorine-containing bleaching chemicals convert the lignin present in the pulp into organic chlorine compounds, which will pass into the bleaching effluents removed from the pulp. The bleaching effluents constitute an environmental problem owing to the potential toxicity of the organic chlorine compounds passing into the effluents, and also the values of chemical oxygen consumption in the bleaching effluents are detrimentally high.
- The bleaching effluents which load the environment the worst are produced in the washing steps following the first chlorination and the first alkali step of the bleaching. Efforts have been made to decrease the load by various methods, for example by replacing the chlorine gas with chlorine dioxide or by using oxygen as the oxidizing chemical in the first step. However, fully satisfactory results have not been achieved by these methods. Efforts to decrease the quantities of chlorophenols and other toxic chlorine compounds in the effluents have indeed been successful, but the values of chemical oxygen consumption of the effluents have not decreased. Therefore, effective biological purification has been needed to back up the said methods.
- In recent investigations it has been observed that by using enzymes as an aid in bleaching it is possible to separate lignin and/or hemicellulose from cellulose and to make the pulp in this manner easier to bleach in the subsequent bleaching steps. According to WO-A-89/08738, the residual chlorine content of a pulp bleached by using chlorine chemicals can also be decreased by an enzyme treatment. It is proposed that the enzyme treatment should in this case be carried out either before the oxidation and alkali steps of the bleaching or after them.
- The object of the present invention is to provide a new method, based on enzyme treatment of pulp, by which pulp can be bleached in such a manner that the need for bleaching chemicals decreases and at the same time the chemical oxygen consumption and toxicity of the bleaching effluent decrease so that the need for water purification will be smaller. It is characteristic of the invention that the pulp is treated with an enzyme in two or more steps of the bleaching process, wherein the pulp subsequent to each enzyme treatment step is treated in an oxidation step.
- According to the invention it has thus been observed that the action of enzymes is enhanced when they are used in several different steps. It has been noted that an enzyme treatment carried out at the beginning of the bleaching step enables the amount of chlorine chemicals used to be decreased by approx. 25 %, and thus the repeated enzyme treatments according to the invention will result in considerably higher savings in bleaching chemicals.
- The expedient number of enzyme treatment steps in the bleaching process according to the invention is from two to four.
- In order to minimize the amount of organic chlorine compounds in effluents and in the obtained bleached chemical pulp, it is advantageous to use oxygen and/or hydrogen peroxide and/or chlorine dioxide in the oxidation steps of the process. By this procedure the amount of organic chlorine compounds in the effluents can be decreased by more than 90 % also in the bleaching of softwood pulp, which has not been possible by using the prior-art methods.
- According to one preferred embodiment of the invention, at least one enzyme treatment step is followed in the process by a treatment with alkali, in which an oxidizing chemical, such as oxygen or peroxide, is used besides the alkali. It has been observed that such an oxidizing alkali treatment decreases especially effectively the need for chlorine chemicals in bleaching.
- In the bleaching process according to the invention, the enzyme treatments break down the hemicellulose and/or lignin present in the pulp and make the pulp more porous, thus increasing the action of the chemicals in subsequent pulp treatment steps. The enzyme treatment may be followed by a washing of the pulp, removing constituents broken down from the pulp; these constituents can be led to a burning so that they will cause no effluent load but the energy contained in them can be exploited in the energy supply of the mill.
- With the exception of the enzyme treatment steps, the pulp bleaching according to the invention can be carried out in the conventional manner so that the oxidation and alkali steps alternate. After the various steps the pulp can be washed in order to remove the bleaching chemicals and the broken-down constituents.
- According to the invention, the enzyme treatment is preferably carried out within a temperature range of 10-90 °C, preferably within 40-80 °C, and at a pH of 3.3-11.0, preferably 4.0-10.0. The enzyme used may be hemicellulase, cellulase, pectinase, esterase, ligninase, phenol oxidase, or a mixture of the same. Hemicellulases and laccase, which belongs to phenol oxidases, are particularly preferred.
- It is possible to use one and the same enzyme, such as hemicellulase, in the enzyme treatments belonging to the process according to the invention. It is also possible that the process includes at least two separate enzyme treatment steps, in which at least two different enzymes are used. The process may thus begin, for example, with a hemicellulase treatment, which is followed by a laccase treatment after the oxidation step, and by another hemicellulase treatment after the subsequent alkali step. When different enzymes are used, the enzyme treatments can also take place successively in the process.
- The invention is described below in greater detail with the help of an embodiment example based on laboratory experiments.
- To 300 g of pulp solids obtained from pine sulfate cooking (solids content of pulp 30 %) was added a diluted enzyme mixture Pulpzyme@(Novo, hemicellulase) so as to make the consistency of the pulp 10 % and its xylanase activity 5 U/g of pulp solids. Before this the pH of the pulp had been adjusted by means of acetic acid to a level of 5.5-6.0. The temperature of the enzyme treatment was 55 ° C and the treatment time 2 h.
- After the enzyme treatment the pulp was washed with water.
- Next, the pulp was subjected to an oxidizing bleaching treatment by using a mixture which contained 50 % chlorine dioxide and 50 % chlorine gas. The mixture was proportioned at 2.0 x the kappa number after the pulping. The treatment temperature was 40 ° C and the treatment time 45 min and the consistency of the pulp 3.5 %.
- Next, the pulp was subjected to an alkali treatment by using a 2-% sodium hydroxide solution the proportion of which was 0.9 x kappa. The consistency of the mixture was 10 %, and the treatment temperature was 60 ° C and the treatment time 90 min. After the alkali treatment the pulp was washed with a 20-fold amount of water.
- Thereafter the bleaching was continued by repeating the enzyme step by using the same enzyme mixture as in the first step and the oxidation step by using chlorine dioxide and by washing the pulp between the steps as described above. In this case the amount of enzyme in the second enzyme treatment was 2.5 U/g of pulp. The amount of chlorine dioxide in the second oxidizing step was 1.5 % of the amount of the pulp being bleached.
- The bleached pulp was analyzed. The results are shown in the following Table 1.
- In addition to the experiment (Experiment 2) described above and illustrating the invention, a reference experiment (Experiment 1) was carried out, the results of which are also shown in the following Table 1.
- The experiments were carried out as follows:
- Experiment 1 (reference experiment): the pulp was not subjected to a second enzyme treatment. In other respects the experiment corresponded to that described above (Experiment 2).
Claims (9)
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FI900549A FI89814C (en) | 1990-02-02 | 1990-02-02 | FOERFARANDE FOER BLEKNING AV CELLULOSAMASSA |
| FI900549 | 1990-02-02 | ||
| PCT/FI1991/000033 WO1991011553A1 (en) | 1990-02-02 | 1991-02-01 | A process for the bleaching of chemical pulp |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| EP0513140A1 EP0513140A1 (en) | 1992-11-19 |
| EP0513140B1 true EP0513140B1 (en) | 1995-09-27 |
| EP0513140B2 EP0513140B2 (en) | 1998-03-18 |
Family
ID=8529828
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| EP91903684A Expired - Lifetime EP0513140B2 (en) | 1990-02-02 | 1991-02-01 | A process for the bleaching of chemical pulp |
Country Status (8)
| Country | Link |
|---|---|
| EP (1) | EP0513140B2 (en) |
| JP (1) | JPH05509362A (en) |
| AT (1) | ATE128498T1 (en) |
| CA (1) | CA2075187A1 (en) |
| DE (1) | DE69113444D1 (en) |
| ES (1) | ES2079062T5 (en) |
| FI (1) | FI89814C (en) |
| WO (1) | WO1991011553A1 (en) |
Families Citing this family (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FI90670C (en) * | 1991-05-02 | 1994-03-10 | Metsae Serla Oy | Treatment of alkali-treated pulp for use in papermaking |
| US7816129B2 (en) | 1994-07-29 | 2010-10-19 | Ab Enzymes Gmbh | Production and secretion of proteins of bacterial origin in filamentous fungi |
| EP0905306A1 (en) | 1997-09-26 | 1999-03-31 | Consortium für elektrochemische Industrie GmbH | Multicomponent system for modifying, decomposing or bleaching lignin or lignin-containing materials and method of using this system |
| WO2000014243A1 (en) | 1998-09-04 | 2000-03-16 | University Of Georgia Research Foundation, Inc. | Phenolic acid esterases, coding sequences and methods |
| US6602700B1 (en) | 1998-09-04 | 2003-08-05 | University Of Georgia Research Foundation, Inc. | Phenolic acid esterases, coding sequences and methods |
| US7541175B1 (en) | 2000-12-22 | 2009-06-02 | Iogen Energy Corporation | Alkaline extraction stages comprising xylanase |
| US7320741B2 (en) | 2001-01-18 | 2008-01-22 | Iogen Bio-Products Corporation | Method of xylanase treatment in a chlorine dioxide bleaching sequence |
| WO2003074780A1 (en) * | 2002-03-06 | 2003-09-12 | Iogen Bio-Products Corporation | Xylanase treatment of chemical pulp |
| BRPI0312121B1 (en) | 2002-06-14 | 2019-10-01 | Verenium Corporation | PREPARATION OF PROTEIN, PROPERTY POLYPEPTIDE AND METHODS FOR PREPARING AND USING THEM |
| BRPI0707784B1 (en) | 2006-02-14 | 2018-05-22 | Verenium Corporation | ISOLATED, SYNTHETIC OR RECOMBINANT NUCLEIC ACID, EXPRESSION CASSETTE, CLONING VECTOR OR VEHICLE, TRANSFORMED ISOLATED HOST CELL, AND METHOD FOR PRODUCTION OF A RECOMBINANT POLYPEPTIDE |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FI90888B (en) * | 1989-02-14 | 1993-12-31 | Enso Gutzeit Oy | Method for bleaching cellulose pulp |
| ZA904441B (en) * | 1989-06-22 | 1991-03-27 | Int Paper Co | Enzymatic delignification of lignocellulosic material |
-
1990
- 1990-02-02 FI FI900549A patent/FI89814C/en not_active IP Right Cessation
-
1991
- 1991-02-01 WO PCT/FI1991/000033 patent/WO1991011553A1/en active IP Right Grant
- 1991-02-01 JP JP3503752A patent/JPH05509362A/en active Pending
- 1991-02-01 CA CA002075187A patent/CA2075187A1/en not_active Abandoned
- 1991-02-01 EP EP91903684A patent/EP0513140B2/en not_active Expired - Lifetime
- 1991-02-01 AT AT91903684T patent/ATE128498T1/en not_active IP Right Cessation
- 1991-02-01 DE DE69113444T patent/DE69113444D1/en not_active Expired - Lifetime
- 1991-02-01 ES ES91903684T patent/ES2079062T5/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| ATE128498T1 (en) | 1995-10-15 |
| FI900549A (en) | 1991-08-03 |
| CA2075187A1 (en) | 1991-08-03 |
| FI89814B (en) | 1993-08-13 |
| JPH05509362A (en) | 1993-12-22 |
| FI900549A0 (en) | 1990-02-02 |
| EP0513140B2 (en) | 1998-03-18 |
| WO1991011553A1 (en) | 1991-08-08 |
| FI89814C (en) | 1993-11-25 |
| EP0513140A1 (en) | 1992-11-19 |
| ES2079062T5 (en) | 1998-07-16 |
| DE69113444D1 (en) | 1995-11-02 |
| ES2079062T3 (en) | 1996-01-01 |
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