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.

Description

[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 c...

AI Technical Summary

Benefits of technology

[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.

[0017] According to a further preferred embodiment, the material density is reduced by adding process water and / or fresh water.

[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.

[0024] According to a preferred executive example, they are used, amongst other things, to reduce residues of the bleaching agent previously added by means of the bleaching lye as much as possible at the end of the bleaching process, so that its effectiveness for a further subsequent treatment may not adversely affect the use of further bleaching agents, for example in a second step. According to a particularly preferred embodiment, these can be different bleaching agents, although it is also possible to achieve the desired effect in a single step by means of a selective agent.

[0036] According to another particularly preferred embodiment of the method for bleaching fibre materials, a complexing agent is dosed to the fibre material, in particular into the suspension of fibre material, the complexing agent particularly reducing the catalytic effect of metals such as transition metals, in particular metal ions, on the decomposition of at least one bleaching agent. Diethylenetriaminepentaacetic acid (DTPA), ethylenediaminetetraacetic acid (EDTA), phosphates, phosphonates, polycarboxylic acids, sugar derivates, polyhydroxycarboxylic acids and suchlike can for example be used as complexing agents.

Problems solved by technology

The disadvantages of using caustic soda lye are its relatively high cost and the problems associated with its dosage.

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