CN1154729A

CN1154729A - Method for bleaching wood pulp using hydrogen peroxide

Info

Publication number: CN1154729A
Application number: CN 95194049
Authority: CN
Inventors: 古斯塔沃·L·波坦
Original assignee: Beloit Technologies Inc
Current assignee: Beloit Technologies Inc
Priority date: 1994-07-11
Filing date: 1995-06-28
Publication date: 1997-07-16

Abstract

A method for bleaching wood pulp using a hydrogen peroxide solution as a bleaching agent, utilizes a two phase reaction, viz. a short high temperature phase followed by a longer second phase to consume virtually all the hydrogen peroxide remaining after the short phase. The method includes the steps of introducing pulp (10), at a consistency of 10-18 %, to a mixer (100) in which the pulp is heated to a temperature between 80 and 100 DEG C; adding sufficient sodium hydroxide (15) to bring the pulp to a pH of 9.5-11.5; adding sufficient hydrogen peroxide (35) to provide a peroxide residual after the first reactor column; passing the pulp through a reactor column (400) at a rate providing a reaction time on the column of between 5 to 60 minutes; introducing the pulp to a mixer (500) and reactivating residual hydrogen peroxide by bringing the pulp to a pH of at least 9; and depositing the pulp in a reaction tower (600) and allowing the reaction to proceed for 1-4 hours until a substantial portion of the residual hydrogen peroxide has been consumed.

Description

Method with the hydrogen peroxide bleaching wood pulp

The present invention generally relates to the pulp bleaching method, and more specifically relates to the paper pulp that uses hydrogenperoxide steam generator bleaching medium consistency at two one-Step bleach in the stage.

Hydrogen peroxide is widely used in brightening of mechanical pulp, semi-mechanical pulp, semi-chemical pulp and recycle slurry.The bleaching that nearest hydrogen peroxide has been used for chemical pulp helps its delignification.Also adopt the oxidation-extraction stage of hydrogen peroxide to reduce needed amount of chlorine of association with pulp bleaching phase I outside the current deoxygenation.Hydrogen peroxide also is used for the association with pulp bleaching final stage to obtain high whiteness, stable bleached pulp.

For mechanical pulp, semi-mechanical pulp and semi-chemical pulp, hydrogen peroxide is mainly used in the high-consistency system, and wherein dewatering of pulp is concentrated into about 30% denseness and fluffer or high-consistency blender by having added hydrogenperoxide steam generator therein.This paper pulp is because gravity is fallen in the reaction tower then, and this tower is typically designed to the retention time of several hrs.As above-mentioned stage or bleach in two stages continuously.At latter event, wherein one section can medium consistency be carried out.

In chemical pulp, hydrogen peroxide is mainly used in the medium consistency system, and wherein the paper pulp that comes out from initial segment dewaters thickener or wash engine to about 10-14% denseness.In pulper (repulper) (discharging) from thickener or wash engine or before the medium consistency tower medium consistency pump or blender, hydrogen peroxide and alkali are added together, use with other oxides (as oxygen) usually.

There is several method to come bleach chemical pulp.Wherein, hot peroxide systems is valuable, because its same whiteness of having improved with conventional high-consistency system, but carry out in medium consistency (10-14%).It is by rising to the paper pulp temperature 85 ℃ and reduce pH and realize that this is different from the high-consistency peroxide systems of routine to about 9.5-10.5.Because fast reaction, retention time is reduced to some minutes (15-30 branch) from a few hours does not need silicate to stablize this peroxide solutions.The peroxidating material is about the same with conventional system still.

Proposed the reactivation of residual peroxide is used for the bleaching of mechanical pulp.This improvement makes peroxide (behind the first stage of reaction tower) reactivation that does not consume by the basicity that improves this pulp suspension.Its objective is and save expensive dehydration equipment that this equipment is used for will getting back to the peroxide that the fresh peroxide of adding (blender before bleaching tower usually) reclaims remnants from the filtrate cycle that dehydration equipment comes out behind the bleaching tower.Compare with the two sections peroxide bleaching systems of routine at the expensive dehydration equipment of two intersegmental needs, this suggestion has important commercial significance.

The exploitation of being known as of high-consistency system has the optimal path of high whiteness under minimum peroxide consumption.Its shortcoming is because the expense and the expensive high-consistency tower discharging equipment of expensive dehydration equipment (to 30% denseness), expensive blender-fluffer, long retention time tower need a large amount of costs of investment.In addition, any circulation residual peroxide all need be carried out the dehydration equipment second time with the trial that reduces chemical cost behind this tower, and this is similar to the equipment that it uses previously.

Medium consistency body yarn can not increase enough whiteness, and thinks that it has consumed more peroxide and has needed extremely long retention time in order to consume this peroxide.In order to obtain more significant delignification and whiteness effect, peroxide must be used for several towers, promptly uses in first extraction section and oxygen chemical bleaching together, uses separately separately or before the high density tower that other chemicals use in second extraction section, bleaching.Remaining peroxide does not reclaim in these systems.

Above-mentionedly known some limitations that in current pulp bleaching process, exist have been introduced.It will be favourable that the alternative method that overcomes one or more these limitations is provided.Therefore, this paper provides a suitable alternative method, and this method has hereinafter abundant more disclosed performance.

In one aspect of the invention, with the method for hydrogenperoxide steam generator, may further comprise the steps: paper pulp is added in the blender with 10%-18% (absolutely dry base, oven dried basis) as the bleaching agent bleached wood pulp; Heat this paper pulp to 80-100 ℃; Adding enough NaOH, to make the pH of this paper pulp be 9.5-11.5; Add enough hydrogen peroxide to guarantee behind first reaction tower a large amount of remaining peroxide being arranged; With the reaction time in reaction column be 5-60 minute speed, allow this paper pulp pass through reaction column; This paper pulp is added blender and passes through the enough NaOH of adding, so that the pH of this paper pulp is at least the remaining hydrogen peroxide of 9 reactivations; This paper pulp of deposition and allow this reaction carry out all consuming up to nearly all residual hydrogen peroxide in 1-4 hour in reaction tower.

From following detailed introduction and simultaneously with reference to the accompanying drawing, will more clearly understand above-mentioned viewpoint of the present invention and other viewpoints.

Fig. 1 is a method flow schematic diagram of introducing the inventive method preferred embodiment.

With reference to this figure, from conventional wash engine or thickener paper pulp is drawn off, enter blender 100 by managing 10, add the alkali that is used to heat the steam of this paper pulp and adjusts this paper pulp pH by managing 16 and 15 respectively at this.But this alkali NaOH, white liquid or other alkali sources.This paper pulp is heated to above conventional 60 ℃, is preferably 85-95 ℃ and regulate pH greater than 8.5, preferred 9.5-10.5.That this has heated and paper pulp of crossing of pH regulator is added to conventional medium consistency pump 200 by managing 20 from blender 100 dischargings, and this pump is sent this pulp pump into blender 300 by managing 30.Guarantee that by managing 35 hydrogen peroxide that add q.s to blender 300 sufficient residue peroxide is arranged at the end of this reaction first step.As in the peroxide bleaching system of routine, in order to the magnesium compound of protection cellulose viscosity and sequestering agent [as SiO ₂And/or chelating agent (as EDTA or DTPA)] also can be by managing 15 with alkali lye, adding with peroxide solutions or add by pipe 16 and 36 separately by managing 35.

The setting reaction temperature is also adjusted to pump into upper reaches reaction column 400 to the paper pulp of setting pH by managing 40 being heated to, and this column dimension is designed to have the needed retention time of this reaction first step.According to the present invention, the size design of upper reaches pipe guarantees that the retention time of paper pulp is 5-55 minute, and preferred 10-20 minute, after this retention time, this paper pulp kept a large amount of residue peroxide.This paper pulp wherein adds the pH to 9.5-11.5 that other alkali improves this paper pulp by managing 55, preferred 10.5-11.0 by in the suitable blender 500 of pipe 50 dischargings to.The adding of this alkali (NaOH) has activated remaining hydrogen peroxide once again, makes that when passing through pipe 60 dischargings to reactor 600, this paper pulp is owing to the peroxide reactions between the retention period of reactor 600 continues bleaching.The time of staying that typical reactor is designed to paper pulp is 1-4 hour.

Claims

1, use the method for hydrogen peroxide, may further comprise the steps as the bleaching agent bleached wood pulp:

With 10%-18% (over dry base) denseness paper pulp is added blender;

Heat said paper pulp to 80-100 ℃ temperature;

Adding enough alkali makes the pH of said paper pulp greater than 8.5;

Add enough hydrogen peroxide to guarantee that abundant remaining peroxide is arranged behind first reaction column;

With in reaction time of reaction column less than 60 minutes speed said paper pulp by said post;

Said paper pulp added in the mixing device and make the pH of this paper pulp be at least 9 to come the remaining hydrogen peroxide of reactivation by adding enough alkali; With

In a reaction tower, deposit said paper pulp and allow this reaction carry out 1-4 hour up to consuming most remaining hydrogen peroxide.

2, the process of claim 1 wherein that it is 9.5-10.5 that the enough alkali of adding makes the PH of said paper pulp.

3, the process of claim 1 wherein with the reaction time that in reaction column, provides be 10-15 minute speed said paper pulp by said reaction column.