Method for bleaching fibrous materials

Abstract

The invention relates to a method for bleaching fibrous materials, in particular lignin-containing materials for producing paper consisting in adding at least a first additive and at least one type of bleaching liquid to a fibrous solution which contains at list one bleaching agent. After mixing said bleaching solution with the fibrous suspension and at the end of determined bleaching time, the bleaching process is ended by adding at least a second additive. Said invention is characterised in that the pH of the fibrous suspension is obtained by adding lime.

1 . Method for bleaching fibre materials, in particular lignin-containing fibre materials for the production of paper, including the steps of 
 adding at least one first additive into a suspension of fibre material;    adding at least one bleaching lye into the suspension of fibre material, the bleaching lye having at least one bleaching agent;    mixing the bleaching lye with the suspension of fibre material;    completing the bleaching process with the addition of at least one second additive,    characterized in that    lime is used at least for adjusting the pH value of the suspension of fibre material before the bleaching.    
     
     
         2 . The method according to  claim 1 , 
 characterized in that    the lime is dispersed at least partially in water.    
     
     
         3 . The method according to  claim 1 , 
 characterized in that    the lime has at least one component selected from a group consisting of calcium hydroxide, calcium oxide, carbonates, natural and fired natural minerals such as, for example, orthoclase, albite, anorthite, kaolinite, mullite, muscovite, calcite, magnesite, artinite, periclase, brucite, dolomite, wollastonite, talc, clinochlore and accompanying substances such as, for example, magnesium oxide, aluminium oxide, iron oxide, sodium oxide, potassium oxide, silicon oxide, sulfur oxide, as well as bound gaseous components and suchlike.    
     
     
         4 . The method according  claim 1 , 
 characterized in that    the fibre material is selected from a group of fibre materials containing natural fibre materials such as cellulose, waste paper, mechanical wood pulp, in particular stone groundwood (SGW) with and without chemical pretreatment, refiner mechanical pulp with and without chemical pretreatment, thermo-mechanical pulp (TMP), reground stone groundwood pulp (RSGW), pressurized stone groundwood (PGW), refiner mechanical pulp (RMP), pressurized refiner mechanical pulp (PRMP), chemi-groundwood (CGW), chemi-refiner mechanical pulp (CRMP), chemi-thermo-mechanical pulp (CTMP) and suchlike.    
     
     
         5 . The method according to  claim 1 , 
 characterized in that    the material density of the suspension of fibre material is between 5% and 55% preferably between 10% and 50%, particularly preferably between 15% and 46% and particularly between 5% und 20% for low consistency, between 20% and 28% for medium consistency and between 28% and 46% for high consistency.    
     
     
         6 . The method according to  claim 1 , 
 characterized in that    the bleaching lye contains at least one bleaching agent from a group of bleaching agents which cause oxidative or reductive bleaching, in particular from the group of hydrogen peroxide, hypochloride, ozone, oxygen, sodium sulfite, formamidine sulfonic acid, sodium dithionite, hydrosulfite and suchlike.    
     
     
         7 . The method according to  claim 1 , 
 characterized in that    the first additive is selected from a group of auxiliary means containing water glass, in particular alkaline and/or alkaline earth silicates, complexing agents such as, for example, DTPA, EDTA and phosphates, stabilizers, catalysts, inhibitors and suchlike.    
     
     
         8 . The method according to  claim 1 , 
 characterized in that    the second additive is a complementary agent to the bleaching lye.    
     
     
         9 . The method according to  claim 1 , 
 characterized in that    the second additive is selected from a group containing reductive and oxidative agents such as, for example, hydrosulfite, sodium bisulfite, sodium hydrosulfite, sodium borohydride and suchlike.    
     
     
         10 . The method according to  claim 1 , 
 characterized in that    the lime is taken out as a solid essentially continuously from a container.    
     
     
         11 . The method according to  claim 10 , 
 characterized in that    the lime with a solids content of between 92% and 100%, preferably between 95% and 99.9% and particularly preferably between 98% and 99.5% is stored.    
     
     
         12 . The method according to  claim 2 , 
 characterized in that    the aqueous dissolved and/or dispersed lime has a solids content of between 5% and 30%, preferably of between 7% and 25%, particularly preferably of between 15% and 20% and particularly of approximately 17% odri.    
     
     
         13 . The method according to  claim 1 , 
 characterized in that    the lime is dosed into the suspension of fibre material before the addition of the first additive and the bleaching lye.    
     
     
         14 . The method according to  claim 1 , 
 characterized in that    the lime is dosed into the suspension of fibre material after the first additive and before the addition of the bleaching lye.    
     
     
         15 . The method according to  claim 1 , 
 characterized in that    the lime is dosed into the suspension of fibre material essentially simultaneously with at least the first additive.    
     
     
         16 . The method according to  claim 1 , 
 characterized in that    the pH value of the suspension of fibre material after the addition of the dissolved and/or dispersed lime is between 8 and 12, preferably between 9 and 11 and particularly preferable between 10.3 and 10.8.    
     
     
         17 . The method according to  claim 1 , 
 characterized in that    the amount of lime added is between 0.01% and 5%, preferably between 0.1% and 2%, and particularly preferably between 0.3% and 1% in relation to the odri (oven dried) amount of fibre material.    
     
     
         18 . The method according to  claim 1 , 
 characterized in that    the fibre material is heated by means of steam addition, in particular of low pressure steam and/or by means of mechanical energy during the mixing, to a temperature between 50° C. and 100° C., preferably between 55° C. and 90° C. and particularly preferably between 60° C. and 70° C.    
     
     
         19 . The method according to  claim 1 , 
 characterized in that    the fibre material is diluted before the addition of the second additive.    
     
     
         20 . The method according to  claim 1 , 
 characterized in that    before the bleaching process the catalytic effect of available metals, in particular available metal ions, on the decomposition of at least one bleaching agent is reduced at least partially by means of the addition of at least one complexing agent such as, for example, diethylenetriaminepentaacetic acid (DTPA), ethylenediaminetetraacetic acid (EDTA), phosphates, polycarboxylic acids and suchlike.    
     
     
         21 . A device for bleaching fibre materials with at least one mixer and one reaction space in which an aqueous suspension of fibre material is subjected to at least one bleaching, in particular one bleaching stage, 
 characterized in that    a dosing device, which regulates and/or controls the addition of lime, in particular a lime at least partially dispersed in water, into the aqueous suspension of fibre material in the bleaching process as a function of predefined process parameters is provided.    
     
     
         22 . The device according to  claim 21 , 
 characterized in that    the process parameters are selected from a group of parameters containing the pH value, the amount of bleaching agent, the amount of bleaching lye, the brightening, the degree of whiteness, the chromaticity coordinate, the reaction time, the material density, the pressure, the mixing, the temperature, the content of residual bleaching means and suchlike.    
     
     
         23 . The device according to  claim 21 , 
 characterized in that    the lime is taken out as a solid essentially continuously from a storage container and diluted with water to a predefined solids content before being added into the suspension of fibre material.    
     
     
         24 . A device for bleaching fibre materials with at least a first container for storing lime having a predefined particle size distribution and purity, an extracting device and a transport and mixing device in which the lime is dissolved and/or dispersed and transported to at least a second container, and in which the at least partially dispersed lime is mixed with a suspension of fibre material according to predefined process parameters.