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Method for bleaching fibrous materialsRelated Patent Categories: Paper Making And Fiber Liberation, Processes Of Chemical Liberation, Recovery Or Purification Of Natural Cellulose Or Fibrous Material, Treatment With Particular ChemicalMethod for bleaching fibrous materials description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060130984, Method for bleaching fibrous materials. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] The present invention relates to a method and a device for bleaching fibre materials, in particular lignin-containing fibre materials for the production of paper. BACKGROUND OF THE INVENTION [0002] Methods for bleaching fibre materials are known in the state of the art, wherein, in addition to oxidative bleaching means, reductive bleaching means are also used in the paper industry for bleaching fibre materials. [0003] In industry, bleaching of lignin-containing fibre materials is carried out in particular using lignin-preserving bleaching sequences, which are presently, particularly for reasons of environmental protection, halogen-free bleaching sequences using for example hydrogen peroxide, oxygen or ozone as bleaching means. [0004] For attaining an optimal bleaching result, besides the application of a specific bleaching means, the process control, in particular the process conditions, is also of decisive significance. [0005] Thus, for example, sodium hydroxide is used in conjunction with the application of hydrogen peroxide, which is admixed to the fibre material in form of caustic soda lye (aqueous sodium hydroxide solution) together with the hydrogen peroxide, or before the hydrogen peroxide is added. [0006] The disadvantages of using caustic soda lye are its relatively high cost and the problems associated with its dosage. Thus, in particular a large deviation of the pH value as a result of using caustic soda lye will lead again to a reduction of the initial degree of whiteness of the fibre material to be bleached. SUMMARY OF THE INVENTION [0007] It is the object of the present invention to overcome the known disadvantages of the prior art at least partially and, in particular, to provide a cost effective method featuring the use of a cheap lye for bleaching fibre materials for the paper industry. [0008] This object is solved by a method according to claim 1. This object is also solved by a device according to claim 21, preferred embodiments of the invention being the objects of the sub-claims. [0009] According to the present invention, the method for bleaching fibre materials, in particular of lignin-containing materials for the production of paper, includes a plurality of steps, where in at least one of those steps at least one first additive is dosed into a suspension of fibre material. [0010] According to the present invention, a suspension of fibre material is understood to be an aqueous suspension of fibre material containing in particular natural fibres such as cellulose, waste paper, mechanical wood pulp and suchlike. Besides the fibre materials, the suspension can however also include mineral or other types of components, as is the case particularly when waste paper is used as heterogeneous raw material. [0011] Besides the addition of the first additive, at least a bleaching lye is dosed to the fibre material, in particular into the suspension of fibre material, the bleaching lye including at least one bleaching agent. According to the invention, both the first additive and the bleaching lye are mixed with the suspension of fibre material, the bleaching process then finalizing, according to the invention, with the addition of at least one second additive. [0012] According to the present invention, the pH value of the suspension of fibre material is adjusted using lime that is, according to a particularly preferred embodiment of the invention, dispersed at least partially in water. [0013] According to the present invention, the pH value adjustment is carried out by means of the dosed addition of lime in such a manner that either the amount of lime is dosed as a function of a pH value determined in the suspension of fibre material and/or, according to a particularly preferred embodiment, the dosage is conducted as a function of the amount of bleaching lye used. However, other dosage forms are also imaginable, such as, for example, dosing as a function of the amount of fibre material and/or suchlike, which are also understood to be dosing methods according to the present invention. [0014] According to the present invention, lime is understood to be a substance including at least one component being selected from a group including calcium hydroxide, calcium oxide, (calcium) carbonate, fired natural and/or synthetic minerals, such as, for example, orthoclase, albite, anorthite, kaolinite, mullite, muscovite, calcite, magnesite, artinite, periclase, brucite, dolomite, wollastonite, talc and clinochlore. Furthermore, this group can include further substances, which are preferably but not exclusively added as impurities and which are, for example, magnesium (oxide), aluminium silicates/oxides and/or transition metal components, in particular iron and manganese oxides/hydroxides, sodium oxide, potassium oxide, silicon oxide, sulfur oxide, as well as bound gaseous components and suchlike. [0015] According to the present invention, mechanical wood pulp is understood to be, in particular, stone groundwood with and without chemical pretreatment, refiner mechanical pulp with and without chemical pretreatment, thermo-mechanical pulp, reground stone groundwood pulp, pressurized stone groundwood, refiner mechanical pulp, pressurized refiner mechanical pulp, chemi-groundwood, chemi-refiner mechanical pulp, chemi-thermo-mechanical pulp and suchlike. [0016] According to a particularly preferred embodiment, the method according to the present invention is used for bleaching fibre materials having a material density between 5% and 55%, preferably between 10% and 50%, particularly preferably between 15% and 46%. In this context, the material density can be between 5% and 20% for so-called low consistency, between 20% and 28% for a medium consistency, and between 28% and 46% for a so-called high consistency. [0017] According to a further preferred embodiment, the material density is reduced by adding process water and/or fresh water. [0018] According to a further particularly preferred method, the material density of the fibre material is increased mechanically and/or thermally and/or chemically, that is to say that liquid is removed from the dispersion. In particular, the mechanical increase of the material density is carried out, for example, through the removal of water from the suspension of fibre material by means of a twin wire press, a disc filter or suchlike, as they are known in the state of the art. [0019] According to the present invention, the chemical increase of the material density is understood to be the addition of dry components, such as lime, which has not been dispersed in water at least partially in a preceding dispersion step, but is, instead, dosed into the suspension of fibre material as a solid, thereby increasing the material density of the suspension of fibre material, that is to say, the solid content in relation to a predefined volume. [0020] According to a preferred embodiment, the bleaching lye being dosed into the suspension of fibre material contains at least one substance with oxidative or reductive effects, causing at least partial bleaching of the fibre material, in particular the at least partial destruction of chromophoric groups, as known in the state of the art. According to a particularly preferred embodiment, these agents are selected from within a group containing hydrogen peroxide, hypochloride, ozone, oxygen, sodium sulfite, formamidine sulfonic acid, sodium dithionite, sodium borohydride, peracetic acid, perchloric acid, hydrosulfite, and suchlike. [0021] It should be noted, however, that in the case of fibres, which are in particular loaded with impurities with only very weak or no catalytic effect, the addition of substances such as complexing agents can be dispensed with. The same applies to the use of water glass, such as alkaline silicates and alkaline earth silicates. [0022] According to a particularly preferred embodiment of the present invention, the first additive is understood to be an auxiliary means selected from a group containing water glass, in particular alkaline and/or alkaline earth silicates, complexing agents such as DTPA, EDTA and phosphates and phosphonates, polyhydroxycarboxylic acids, sugar derivates, stabilizers, catalysts, inhibitors and suchlike. Continue reading about Method for bleaching fibrous materials... Full patent description for Method for bleaching fibrous materials Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Method for bleaching fibrous materials patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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