CA1335687C - Method for increasing the degree of whiteness of waste paper with neutral water circulation - Google Patents
Method for increasing the degree of whiteness of waste paper with neutral water circulationInfo
- Publication number
- CA1335687C CA1335687C CA 609695 CA609695A CA1335687C CA 1335687 C CA1335687 C CA 1335687C CA 609695 CA609695 CA 609695 CA 609695 A CA609695 A CA 609695A CA 1335687 C CA1335687 C CA 1335687C
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- Prior art keywords
- bleaching
- stage
- deinking
- peroxide
- consistency
- 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.)
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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
- D21C5/02—Working-up waste paper
- D21C5/025—De-inking
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
- Y02W30/00—Technologies for solid waste management
- Y02W30/50—Reuse, recycling or recovery technologies
- Y02W30/64—Paper recycling
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Abstract
According to the method of deinking and bleaching waste paper, operation in a stock pulper is carried out without chemicals or with only minimum quantities of chemicals, particularly alkali. Subsequent to a first or initial printing ink removal, for instance, in a washing process, a two-stage bleaching process is effected, preferably by adding peroxide and then formamidine sulfinic acid. Subsequent to the first bleaching stage using peroxide as the bleaching agent, the pH value is in the alkaline range of approximately pH 8.5 to 9.5. In the case of approximately stoichiometric ratios of alkali and formamidine sulfinic acid there exists, subsequent to the second bleaching stage, a medium in the neutral range of pH 6.5 to 7.5, without the need for additional acidification. In this manner, purification of circulating or recycle water in closed circuits, for instance, by means of flotation by expansion, is essentially facilitated. Two-stage bleaching is accomplished, for example, in the combination of a disperser bleaching process and a bleaching process carried out at a medium pulp consistency. Subsequent to the disperser treatment or subsequent to the bleaching process, a further removal of ink and dirt is effected, for example, by flotation or washing, whereby also non-ionic frothing or collecting agents have proven useful. Residual peroxide from the first bleaching stage, which peroxide would decompose formamidine sulfinic acid used in the second bleaching stage, can be not only rendered harmless by the addition of thiourea, but also advantageously converted into additional formamidine sulfinic acid.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a new and improved method of increasing the degree of whiteness of waste paper with neutral water circulation.
Generally speaking, the present invention specifically relates to a new and improved method of increasing the degree of whiteness of raw pulp prepared from waste paper and used for manufacturing paper. This new and improved method may encompass bringing such waste paper into the form of an aqueous stock suspension and subsequently deinking as well as ~leaching the latter.
Methods of this type combine the bleaching process for the prepared fiber stock suspension with the so-called deinking process. The latter serves to remove interfering small particles, particularly printing ink particles or paint color particles as well as very small, yet visible dirt particles or contraries. The method principles or systems of flotation and washing are advantageously employed for the deinking process, and this applies not only for single-stage but also for multi-stage deinking. These two systems used for the deinking of secondary fibers have the advantage of a multitude of combinatorial variants, for example, washing or flotation, washing plus flotation, flotation plus washing, washing plus washing, or flotation plus flotation.
The object of every deinking method is the removal of printing ink particles as well as, if any, paint color particles from the fibers. This is accomplished primarily in the course of the first method step during the more or less complete or entire defiberization of the waste paper into individual fibers. Depending on the deinking method, different stock or pulp consistencies and temperatures can be set in so-called stock pulpers. It is known that now and then also defiberizing or breaker drums are used.
Decomposition into individual fibers also can be effected by means of dispersers.
1 3~5687 In order to augment the process of removing printing ink and paint lines from the fibers, it is often advantageous to add chemicals during the defiberizing process, above all alkalies and wetting agents, but also bleaching agents, such as peroxide, as well as bleaching auxiliaries or bleaching aids, such as water glass and complexing agents. Already in the pulper, it is quite customary to also add flotation auxiliaries consisting of frothing or collecting agents such as, for example, soap.
A method of deinking secondary fibers, according to which alkaline chemicals are added to the pulp in a stock pulper and the subsequent deinking processes of washing and flotation are performed, is described, for example, in a reprint in the journal TAPPI, Volume 63, No. 9, September 1980, based on a paper written by Lothar Pfalzer of J.M.
Voith GmbH, Heidenheim, West Germany, entitled "DEINKING OF
SECONDARY FIBERS - A COMPARISON OF WASHING AND FLOTATION" and published in the 1979 Pulping Conference Proceedings, a TAPPI
press publication.
However, it is known that the use of alkali has various disadvantages, some of which are hereinafter listed:
a) Due to the normally used purification or classification process of flotation by expansion, alkaline water circuits are more difficult to purify or clarify than at a neutral pH level.
b) As a function of the alkali concentration, there is an increased extraction or elimination from the waste paper of substances which increase or raise the chemical oxygen demand ~COD) in the water circulation circuit as well as in waste water.
c) Residual alkali in the fiber stock is unwanted in any case. It causes, for example, yellowing in groundwood-containing waste paper, and this must be counteracted by the addition of peroxide.
d) At the end of the deinking process the deinked fiber stock often has to be acidified for sedimentation and flocculation.
e) The capability of dehydration of the fiber stock is substantially decreased.
These disadvantages of the addition of alkali in the stock pulper are often accepted or taken into account, in order to obtain a sufficiently bright and clean fiber stock.
In view of such disadvantages, already a number of deinking systems for secondary fibers, particularly systems including the ink-separation stage in the washing process and the process of purifying circulating water, are applied such that the addition of alkali or other chemicals in the stock pulper is entirely excluded or eliminated. This total exclusion of alkali has heen the case so far in papermaking plants in which practically without exception wood-free waste paper is processed. Nevertheless, alkali is used now as before for the deinking of quantitatively more predominant wood-contained waste paper, such waste paper containing printing colors which are more difficult to remove or separate.
During the ink-separation process operating without any alkali or only with a minimum amount of alkali it is possi~le that the removal of printing color particles from the fibers or fiber network is quite incomplete and thus insufficient. In such installations it is therefore often the case that a disperser is installed upstream of or between the individual deinking stages, for example, between the washing process and the flotation process. This disperser not only serves for dispersing fine "stickies" or "tackies"
and other contaminants and impurities, but often also for effectively removing remaining or residual printing ink and paint colors.
The shortening or reduction of the bleaching time by means of a high-speed disperser is disclosed, for example, in the German Published Patent Application No. 3,610,940, published September 10, 1987. However, in order to remain in the neutral range of approximately pH 6.5 to 7.5, generally only a subsequent single-stage reductive bleaching process using sodium dithionite as a bleaching agent is carried out, so that the achievable whiteness-level gain is substantially limited. A single-stage oxidative bleaching, namely peroxide bleaching, or a double-stage oxidative and reductive bleaching, using the combination of peroxide and hydrosulfite (dithionite), can be in principle likewise carried out.
However, since an alkaline pH value is required in the peroxide bleaching process, acidification or acid treatment would have to be carried out subsequent to such oxidative bleaching, in order to remain in the neutral range. Such acid treatment is complicated and the expenditure resulting therefrom is relatively high.
SUMMARY OF THE INVENTION
Therefore with the foregoing in mind, it is a primary object of the present invention to provide a new and improved method of increasing the degree of whiteness of raw pulp used for manufacturing paper and which method is not afflicted with the drawbacks and limitations of prior art methods heretofore discussed.
Another significant object of the present invention is directed to providing a new and improved method of increasing the degree of whiteness of raw pulp used for manufacturing paper and which method renders possible that, although a considerable use or application of chemicals is required for the hleaching process, such chemicals can infiltrate at no location into the water circuit or circulation or be entrained in detrimental manner with the finished fiber stock.
It is a further important object of the present invention to provide a new and improved method of increasing the degree of whiteness of raw pulp used for manufacturing paper and which method effectively precludes the use of further chemicals which may reduce or counteract the damaging effect of the chemicals already present but which, on the other hand, could produce other interfering agents or constituents.
These o~jects of the present invention are particularly predominant in the case of modern bleaching methods in conjunction with water treatment and water conditioning as well as water reuse or recycling.
Yet a further significant object of the present invention aims at providing a new and improved method of increasing the degree of whiteness of raw pulp used for manufacturing paper and which method ensures that the whiteness level is substantially increased or raised in a bleaching process which requires neither complicated means nor extra expense for various chemicals.
Now in order to implement these and still further objects of the present invention, which will become more readily apparent as the description proceeds, the pulp processing method of the present development is manifested, among other things, by the features that the acqueous stock suspension is produced without any addition of alkaline chemicals or only with a bare minimum of alkaline chemicals, and that the bleaching process is carried out in at least two stages, the bleaching chemicals being selected such that subsequent to the final bleaching stage a medium of approximately pH 6.5 to 7.5 prevails in the waste paper without the addition of further substances, particularly acids or bases which change the pH value. In this manner, water to be diverted or branched off during the bleaching treatment, particularly washing filtrate or thickened filtrate, is likewise substantially within this medium.
1 335~7 Subsequent to the bleaching treatment the deinking process is advantageously carried out in a substantially chemically neutral medium.
The deinking process is carried out in several partial steps, whereby a partial step subsequent to the bleaching treatment is preferably effected in a substantially chemically neutral medium.
The deinking process also can be accomplished in several stages, whereby the two process systems, namely washing and flotation, as well as combinations of these two process systems can be applied.
A mechanical dispersion process can be carried out prior to, between or subsequent to the method steps for deinking, such mechanical dispersion being effected in a stock or pulp consistency range of 10% to 50% by weight and in a temperature range of 40C to 125C. In this manner, printing ink particles and paint color particles rem~;n;ng subsequent to the essentially neutral decomposition thereof are separated or detached from the fibers, and interfering substances are substantially reduced in size.
The preselected bleaching agent is advantageously formamidine sulfinic acid.
~ 1 335687 The at least two-stage bleaching process of the inventive method operates, for instance, in two stages with oxidative and reductive bleaching agents. Preferably, a high temperature high-consistency bleaching process, i.e.
disperser bleaching, is carried out for the first or initial bleaching stage, while the su~sequent second bleaching stage is effected as a so-called medium-consistency bleaching process with formamidine sulfinic acid as the bleaching agent.
The disperser bleaching process is carried out by means of peroxide at a stock or pulp consistency of approximately ~5% by weight and at a temperature of about 90C, while the medium-consistency bleaching process is effected at a stock or pulp consistency of approximately 15%
by weight and at the temperature resulting in the course of dilution required to obtain medium stock or pulp consistency.
In some cases it is advantageous to also carry out the second bleaching stage as a high temperature high-consistency bleaching process (disperser bleaching), preferably at 95C and 30% stock or pulp consistency and by using formamidine sulfinic acid as the bleaching agent.
Surplus oxidative bleaching means at the end of the first or initial ~leaching stage can be converted into a new reductive bleaching agent by adding other chemical compounds.
~uch new reductive bleaching agent can be applied, for example, in the second bleaching stage.
The first or initial bleaching agent contains peroxide and the chemical compound added at the end of the first or initial bleaching stage, namely thiourea.
Formamidine sulfinic acid originates as the new bleaching agent resulting from the thiourea together with the residual bleaching agent from the first or initial bleaching stage, preferably in the range of pH greater than 7. The aforesaid thiourea-containing chemical compound can be added separately prior to or together with the second bleaching agent, which is likewise formamidine sulfinic acid.
In certain cases, an excessive quantity of peroxide is added in the oxidative bleaching process such that a defined peroxide surplus or excess remains. Addition of thiourea produces a corresponding amount of formamidine sulfinic acid. Therefore, in the second bleaching stage, i.e. for inductive bleaching, either no formamidine sulfinic acid or only a substantially reduced amount of additional formamidine sulfinic acid must be added.
Surplus or excess thiourea at the end of the second or inductive bleaching stage is oxidatively decomposed, preferably by means of peroxide.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be better understood and objects other than those set forth above will become apparent when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings wherein throughout the various figures of the drawings, there have been generally used the same reference characters to denote the same or analogous components and wherein:
Figure 1 diagrammatically shows an exemplary embodiment of an installation or plant for carrying out the inventive method;
Figure 2 shows the reaction mechanism of the bleaching process or stage using formamidine sulfinic acid as the bleaching agent; and Figures 3 shows the reaction mechanism of the production of formamidine sulfinic acid from peroxide.
1 ~35687 DETAILED DE~CRIPTION OF THE PREFERRED EMBODIMENTS
Describing now the drawings, it is to be understood that to simplify the showing thereof, only enough of the construction of an exemplary embodiment of an installation or plant for carrying out the inventive method has been illustrated therein as is needed to enable one skilled in the art to readily understand the underlying principles and concepts of this invention. Turning attention now specifically to Figure 1 of the drawings, the installation diagrammatically illustrated therein by way of example and not limitation will be seen to depict the inventive method of operation of a deinking process containing water circuits in the neutral pH range.
The deinking process includes in fact a two-stage bleaching process which is conceived:
- in the first or initial bleaching stage, with peroxide as the bleaching agent in the alkaline medium, as a high temperature high-consistency bleaching process (disperser bleaching) operating, for example, at a stock or pulp consistency of 25% by weight and a temperature of 90C;
and - in the second bleaching stage in the existing or newly set alkaline medium, commencing with formamidine sulfinic acid, as a medium-consistency bleaching process operating, for example, at a stock or pulp consistency of 15%
by weight and a temperature of 65C.
The schematic and diagrammatic representation of the processing steps will be seen to contain a stock pulper 1 in which an aqueous stock suspension is produced from waste paper A and water Wl which are brought substantially from above into the stock pulper 1. The waste paper A is rid of the coarsest impurities and contaminations in the stock pulper 1 as well as in a precleaner ~. A subsequent defiberizing stage 3 effects a further defiberization of the waste paper or pulp into individual fibers and, furthermore, causes to some extent a removal of dirt and color particles from the fibers.
With the addition of water W2 the raw pulp or stock suspension is then diluted. In a subsequent washer 4, for example, a washer of the Variosplit type, the first deinking process is carried out. This means that a part of the ink or color particles as well as dirt particles, if any, are removed and discharged with the used washing water Fl, provided such ink and dirt particles do not exceed a certain particle size.
The washed fiber stock is passed onto a strainer or wire press 5 in which it is thickened such that the first or initial bleaching stage can be carried out in the form of a high temperature high-consistency disperser bleaching process. The thus obtained fiber stock is heated in a screw worm system 6 by means of directly in~ected superheated steam D. Directly upstream of a disperser 7, bleaching chemicals CHl, peroxide, alkali, complexing agents such as DTPA, and water glass as a stabilizer are added. The chemical medium is thus raised to approximately pH 8.5 to 10. The high-consistency stock or raw pulp is then fed into a bleaching reactor 8 which ensures a dwell time of about 15 to 30 minutes. After termination of this first or initial bleaching stage, intermediary dilution to a medium stock or pulp consistency of about 15% by weight is effected by adding dilute water W3, thus also reducing the temperature of the bleached stock or pulp.
It is now advantageous to use thiourea as a further chemical CH2 for converting residual peroxide into formamidine sulfinic acid. Subsequently, a second bleaching agent CH3, namely formamidine sulfinic acid, is added. The fiber stock or pulp is then fed, via a further bleaching reactor 9 in which again a dwell time of about 15 to 30 minutes is set, into a bleaching chest or vat 10, from which ~ 335687 the fi~er stock suspension is drawn off in bleached quality in a practically neutral medium.
The next following process is the second deinking stage in a flotation cell 11. The task of this flotation cell 11 is to blend air in the form of bubbles with the fiber stock suspension. ~uch air bubbles, loaded with ink particles and dirt, rise to the surface of the flotation cell 11, where they are skimmed off as a layer of froth. For this purpose, known collecting agents have to be added.
The fine cleaning following flotation is advantageously carried out in a fine sorting or separation unit 12 which is followed by a cleaner system 13. For processing reasons the stock or pulp consistency, which is now close to 1% by weight~ is again substantially increased, for example, in a thickener 14. By virtue of the advantageous embodiment of the inventive method a resulting filtrate F2 is chemically neutral and therefore can be readily reused or recycled. The thickened or concentrated fiber stock is now passed on to the papermaking machine.
Figure 2 shows by means of the customary chemical symbols the reaction mechanism of the bleaching process using formamidine sulfinic acid as the kleaching agent. By means of the reaction of formamidine sulfinic acid, water and sodium hydroxide, there results bleaching-active hydrogen as well as sodium hydrogen sulfate and thiourea. At the end of the bleaching process and in the case of suitable stoichiometric ratios, it is thus possible to obtain a pH
value or level in the neutral range, for example, by using during the second bleaching stage the residual alkali from the first bleaching stage. Due to the higher consistency of the fiber stock or pulp in the disperser bleaching process of the first or initial ~leaching stage, there is no alkaline thickening filtrate which would negatively affect the closed water circuit.
The second or reductive bleaching stage by means of formamidine sulfinic acid could be carried out in very much the same manner as the first or initial bleaching stage, namely likewise as a high temperature high-consistency disperser bleaching process, in that dilution is excluded subsequent to the first disperser 7 and the pulp or stock transfer to the second disperser is accomplished by means of a screw or worm system or similar structure. In such a case the inlet stock consistency in the second bleaching stage is nearly the same as the discharge stock consistency subsequent to the first disperser 7. Also the temperature can be maintained at approximately the same level.
1 335~87 Figure 3 shows by means of the customary chemical symbols the reaction mechanism of the conversion of peroxide into formamidine sulfinic acid by means of thiourea, which reacts with hydrogen peroxide to produce formamidine sulfinic acid and water.
A further positive effect of the inventive method is seen in the fact that the normally negative effect of residual peroxide in the alkaline medium after the first or initial bleaching stage, namely the decomposition of the following reductive bleaching agent, is advantageously converted into a positive effect. This can be accomplished by producing a new bleaching agent by means of suitable reaction partners or compounds. Such new bleaching agent would then be additionally available in the second bleaching stage. This problem is most advantageously solved when the residual bleaching agent from the first or initial bleaching stage is converted into the very same bleaching agent which is used in the second or reductive bleaching stage.
~ uch a positive conversion of the residual bleaching agent from the first or initial bleaching stage is readily possible in the above-described bleaching arrangement. It is known that the reductive bleaching agent of the second bleaching stage, namely formamidine sulfinic acid, is produced ~y admixing peroxide with thiourea. In ~ 335687 other words, in order to produce formamidine sulfinic acid a reaction partner or compound is used, namely peroxide, which exists as residual peroxide at the end of the first or initial bleaching stage. Therefore, there is the possibility, with the addition of the aforenoted reaction partner, namely thiourea, of rendering harmless residual peroxide as well as of producing additional formamidine sulfinic acid.
Addition of thiourea should be effected prior to adding the reductive bleaching agent of the second ~leaching stage, i.e. between the first and the second bleaching stages. In this manner, residual peroxide can timely react.
However, it is also conceiva~le that the addition of thiourea and the addition of formamidine sulfinic acid can be mutually carried out prior to the second or reductive bleaching stage.
In such a case it would depend on whether residual peroxide is admixed rapidly enough with thiourea to preclude the other possible reaction with the second bleaching agent, namely with formamidine sulfinic acid.
The present invention relates to a new and improved method of increasing the degree of whiteness of waste paper with neutral water circulation.
Generally speaking, the present invention specifically relates to a new and improved method of increasing the degree of whiteness of raw pulp prepared from waste paper and used for manufacturing paper. This new and improved method may encompass bringing such waste paper into the form of an aqueous stock suspension and subsequently deinking as well as ~leaching the latter.
Methods of this type combine the bleaching process for the prepared fiber stock suspension with the so-called deinking process. The latter serves to remove interfering small particles, particularly printing ink particles or paint color particles as well as very small, yet visible dirt particles or contraries. The method principles or systems of flotation and washing are advantageously employed for the deinking process, and this applies not only for single-stage but also for multi-stage deinking. These two systems used for the deinking of secondary fibers have the advantage of a multitude of combinatorial variants, for example, washing or flotation, washing plus flotation, flotation plus washing, washing plus washing, or flotation plus flotation.
The object of every deinking method is the removal of printing ink particles as well as, if any, paint color particles from the fibers. This is accomplished primarily in the course of the first method step during the more or less complete or entire defiberization of the waste paper into individual fibers. Depending on the deinking method, different stock or pulp consistencies and temperatures can be set in so-called stock pulpers. It is known that now and then also defiberizing or breaker drums are used.
Decomposition into individual fibers also can be effected by means of dispersers.
1 3~5687 In order to augment the process of removing printing ink and paint lines from the fibers, it is often advantageous to add chemicals during the defiberizing process, above all alkalies and wetting agents, but also bleaching agents, such as peroxide, as well as bleaching auxiliaries or bleaching aids, such as water glass and complexing agents. Already in the pulper, it is quite customary to also add flotation auxiliaries consisting of frothing or collecting agents such as, for example, soap.
A method of deinking secondary fibers, according to which alkaline chemicals are added to the pulp in a stock pulper and the subsequent deinking processes of washing and flotation are performed, is described, for example, in a reprint in the journal TAPPI, Volume 63, No. 9, September 1980, based on a paper written by Lothar Pfalzer of J.M.
Voith GmbH, Heidenheim, West Germany, entitled "DEINKING OF
SECONDARY FIBERS - A COMPARISON OF WASHING AND FLOTATION" and published in the 1979 Pulping Conference Proceedings, a TAPPI
press publication.
However, it is known that the use of alkali has various disadvantages, some of which are hereinafter listed:
a) Due to the normally used purification or classification process of flotation by expansion, alkaline water circuits are more difficult to purify or clarify than at a neutral pH level.
b) As a function of the alkali concentration, there is an increased extraction or elimination from the waste paper of substances which increase or raise the chemical oxygen demand ~COD) in the water circulation circuit as well as in waste water.
c) Residual alkali in the fiber stock is unwanted in any case. It causes, for example, yellowing in groundwood-containing waste paper, and this must be counteracted by the addition of peroxide.
d) At the end of the deinking process the deinked fiber stock often has to be acidified for sedimentation and flocculation.
e) The capability of dehydration of the fiber stock is substantially decreased.
These disadvantages of the addition of alkali in the stock pulper are often accepted or taken into account, in order to obtain a sufficiently bright and clean fiber stock.
In view of such disadvantages, already a number of deinking systems for secondary fibers, particularly systems including the ink-separation stage in the washing process and the process of purifying circulating water, are applied such that the addition of alkali or other chemicals in the stock pulper is entirely excluded or eliminated. This total exclusion of alkali has heen the case so far in papermaking plants in which practically without exception wood-free waste paper is processed. Nevertheless, alkali is used now as before for the deinking of quantitatively more predominant wood-contained waste paper, such waste paper containing printing colors which are more difficult to remove or separate.
During the ink-separation process operating without any alkali or only with a minimum amount of alkali it is possi~le that the removal of printing color particles from the fibers or fiber network is quite incomplete and thus insufficient. In such installations it is therefore often the case that a disperser is installed upstream of or between the individual deinking stages, for example, between the washing process and the flotation process. This disperser not only serves for dispersing fine "stickies" or "tackies"
and other contaminants and impurities, but often also for effectively removing remaining or residual printing ink and paint colors.
The shortening or reduction of the bleaching time by means of a high-speed disperser is disclosed, for example, in the German Published Patent Application No. 3,610,940, published September 10, 1987. However, in order to remain in the neutral range of approximately pH 6.5 to 7.5, generally only a subsequent single-stage reductive bleaching process using sodium dithionite as a bleaching agent is carried out, so that the achievable whiteness-level gain is substantially limited. A single-stage oxidative bleaching, namely peroxide bleaching, or a double-stage oxidative and reductive bleaching, using the combination of peroxide and hydrosulfite (dithionite), can be in principle likewise carried out.
However, since an alkaline pH value is required in the peroxide bleaching process, acidification or acid treatment would have to be carried out subsequent to such oxidative bleaching, in order to remain in the neutral range. Such acid treatment is complicated and the expenditure resulting therefrom is relatively high.
SUMMARY OF THE INVENTION
Therefore with the foregoing in mind, it is a primary object of the present invention to provide a new and improved method of increasing the degree of whiteness of raw pulp used for manufacturing paper and which method is not afflicted with the drawbacks and limitations of prior art methods heretofore discussed.
Another significant object of the present invention is directed to providing a new and improved method of increasing the degree of whiteness of raw pulp used for manufacturing paper and which method renders possible that, although a considerable use or application of chemicals is required for the hleaching process, such chemicals can infiltrate at no location into the water circuit or circulation or be entrained in detrimental manner with the finished fiber stock.
It is a further important object of the present invention to provide a new and improved method of increasing the degree of whiteness of raw pulp used for manufacturing paper and which method effectively precludes the use of further chemicals which may reduce or counteract the damaging effect of the chemicals already present but which, on the other hand, could produce other interfering agents or constituents.
These o~jects of the present invention are particularly predominant in the case of modern bleaching methods in conjunction with water treatment and water conditioning as well as water reuse or recycling.
Yet a further significant object of the present invention aims at providing a new and improved method of increasing the degree of whiteness of raw pulp used for manufacturing paper and which method ensures that the whiteness level is substantially increased or raised in a bleaching process which requires neither complicated means nor extra expense for various chemicals.
Now in order to implement these and still further objects of the present invention, which will become more readily apparent as the description proceeds, the pulp processing method of the present development is manifested, among other things, by the features that the acqueous stock suspension is produced without any addition of alkaline chemicals or only with a bare minimum of alkaline chemicals, and that the bleaching process is carried out in at least two stages, the bleaching chemicals being selected such that subsequent to the final bleaching stage a medium of approximately pH 6.5 to 7.5 prevails in the waste paper without the addition of further substances, particularly acids or bases which change the pH value. In this manner, water to be diverted or branched off during the bleaching treatment, particularly washing filtrate or thickened filtrate, is likewise substantially within this medium.
1 335~7 Subsequent to the bleaching treatment the deinking process is advantageously carried out in a substantially chemically neutral medium.
The deinking process is carried out in several partial steps, whereby a partial step subsequent to the bleaching treatment is preferably effected in a substantially chemically neutral medium.
The deinking process also can be accomplished in several stages, whereby the two process systems, namely washing and flotation, as well as combinations of these two process systems can be applied.
A mechanical dispersion process can be carried out prior to, between or subsequent to the method steps for deinking, such mechanical dispersion being effected in a stock or pulp consistency range of 10% to 50% by weight and in a temperature range of 40C to 125C. In this manner, printing ink particles and paint color particles rem~;n;ng subsequent to the essentially neutral decomposition thereof are separated or detached from the fibers, and interfering substances are substantially reduced in size.
The preselected bleaching agent is advantageously formamidine sulfinic acid.
~ 1 335687 The at least two-stage bleaching process of the inventive method operates, for instance, in two stages with oxidative and reductive bleaching agents. Preferably, a high temperature high-consistency bleaching process, i.e.
disperser bleaching, is carried out for the first or initial bleaching stage, while the su~sequent second bleaching stage is effected as a so-called medium-consistency bleaching process with formamidine sulfinic acid as the bleaching agent.
The disperser bleaching process is carried out by means of peroxide at a stock or pulp consistency of approximately ~5% by weight and at a temperature of about 90C, while the medium-consistency bleaching process is effected at a stock or pulp consistency of approximately 15%
by weight and at the temperature resulting in the course of dilution required to obtain medium stock or pulp consistency.
In some cases it is advantageous to also carry out the second bleaching stage as a high temperature high-consistency bleaching process (disperser bleaching), preferably at 95C and 30% stock or pulp consistency and by using formamidine sulfinic acid as the bleaching agent.
Surplus oxidative bleaching means at the end of the first or initial ~leaching stage can be converted into a new reductive bleaching agent by adding other chemical compounds.
~uch new reductive bleaching agent can be applied, for example, in the second bleaching stage.
The first or initial bleaching agent contains peroxide and the chemical compound added at the end of the first or initial bleaching stage, namely thiourea.
Formamidine sulfinic acid originates as the new bleaching agent resulting from the thiourea together with the residual bleaching agent from the first or initial bleaching stage, preferably in the range of pH greater than 7. The aforesaid thiourea-containing chemical compound can be added separately prior to or together with the second bleaching agent, which is likewise formamidine sulfinic acid.
In certain cases, an excessive quantity of peroxide is added in the oxidative bleaching process such that a defined peroxide surplus or excess remains. Addition of thiourea produces a corresponding amount of formamidine sulfinic acid. Therefore, in the second bleaching stage, i.e. for inductive bleaching, either no formamidine sulfinic acid or only a substantially reduced amount of additional formamidine sulfinic acid must be added.
Surplus or excess thiourea at the end of the second or inductive bleaching stage is oxidatively decomposed, preferably by means of peroxide.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be better understood and objects other than those set forth above will become apparent when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings wherein throughout the various figures of the drawings, there have been generally used the same reference characters to denote the same or analogous components and wherein:
Figure 1 diagrammatically shows an exemplary embodiment of an installation or plant for carrying out the inventive method;
Figure 2 shows the reaction mechanism of the bleaching process or stage using formamidine sulfinic acid as the bleaching agent; and Figures 3 shows the reaction mechanism of the production of formamidine sulfinic acid from peroxide.
1 ~35687 DETAILED DE~CRIPTION OF THE PREFERRED EMBODIMENTS
Describing now the drawings, it is to be understood that to simplify the showing thereof, only enough of the construction of an exemplary embodiment of an installation or plant for carrying out the inventive method has been illustrated therein as is needed to enable one skilled in the art to readily understand the underlying principles and concepts of this invention. Turning attention now specifically to Figure 1 of the drawings, the installation diagrammatically illustrated therein by way of example and not limitation will be seen to depict the inventive method of operation of a deinking process containing water circuits in the neutral pH range.
The deinking process includes in fact a two-stage bleaching process which is conceived:
- in the first or initial bleaching stage, with peroxide as the bleaching agent in the alkaline medium, as a high temperature high-consistency bleaching process (disperser bleaching) operating, for example, at a stock or pulp consistency of 25% by weight and a temperature of 90C;
and - in the second bleaching stage in the existing or newly set alkaline medium, commencing with formamidine sulfinic acid, as a medium-consistency bleaching process operating, for example, at a stock or pulp consistency of 15%
by weight and a temperature of 65C.
The schematic and diagrammatic representation of the processing steps will be seen to contain a stock pulper 1 in which an aqueous stock suspension is produced from waste paper A and water Wl which are brought substantially from above into the stock pulper 1. The waste paper A is rid of the coarsest impurities and contaminations in the stock pulper 1 as well as in a precleaner ~. A subsequent defiberizing stage 3 effects a further defiberization of the waste paper or pulp into individual fibers and, furthermore, causes to some extent a removal of dirt and color particles from the fibers.
With the addition of water W2 the raw pulp or stock suspension is then diluted. In a subsequent washer 4, for example, a washer of the Variosplit type, the first deinking process is carried out. This means that a part of the ink or color particles as well as dirt particles, if any, are removed and discharged with the used washing water Fl, provided such ink and dirt particles do not exceed a certain particle size.
The washed fiber stock is passed onto a strainer or wire press 5 in which it is thickened such that the first or initial bleaching stage can be carried out in the form of a high temperature high-consistency disperser bleaching process. The thus obtained fiber stock is heated in a screw worm system 6 by means of directly in~ected superheated steam D. Directly upstream of a disperser 7, bleaching chemicals CHl, peroxide, alkali, complexing agents such as DTPA, and water glass as a stabilizer are added. The chemical medium is thus raised to approximately pH 8.5 to 10. The high-consistency stock or raw pulp is then fed into a bleaching reactor 8 which ensures a dwell time of about 15 to 30 minutes. After termination of this first or initial bleaching stage, intermediary dilution to a medium stock or pulp consistency of about 15% by weight is effected by adding dilute water W3, thus also reducing the temperature of the bleached stock or pulp.
It is now advantageous to use thiourea as a further chemical CH2 for converting residual peroxide into formamidine sulfinic acid. Subsequently, a second bleaching agent CH3, namely formamidine sulfinic acid, is added. The fiber stock or pulp is then fed, via a further bleaching reactor 9 in which again a dwell time of about 15 to 30 minutes is set, into a bleaching chest or vat 10, from which ~ 335687 the fi~er stock suspension is drawn off in bleached quality in a practically neutral medium.
The next following process is the second deinking stage in a flotation cell 11. The task of this flotation cell 11 is to blend air in the form of bubbles with the fiber stock suspension. ~uch air bubbles, loaded with ink particles and dirt, rise to the surface of the flotation cell 11, where they are skimmed off as a layer of froth. For this purpose, known collecting agents have to be added.
The fine cleaning following flotation is advantageously carried out in a fine sorting or separation unit 12 which is followed by a cleaner system 13. For processing reasons the stock or pulp consistency, which is now close to 1% by weight~ is again substantially increased, for example, in a thickener 14. By virtue of the advantageous embodiment of the inventive method a resulting filtrate F2 is chemically neutral and therefore can be readily reused or recycled. The thickened or concentrated fiber stock is now passed on to the papermaking machine.
Figure 2 shows by means of the customary chemical symbols the reaction mechanism of the bleaching process using formamidine sulfinic acid as the kleaching agent. By means of the reaction of formamidine sulfinic acid, water and sodium hydroxide, there results bleaching-active hydrogen as well as sodium hydrogen sulfate and thiourea. At the end of the bleaching process and in the case of suitable stoichiometric ratios, it is thus possible to obtain a pH
value or level in the neutral range, for example, by using during the second bleaching stage the residual alkali from the first bleaching stage. Due to the higher consistency of the fiber stock or pulp in the disperser bleaching process of the first or initial ~leaching stage, there is no alkaline thickening filtrate which would negatively affect the closed water circuit.
The second or reductive bleaching stage by means of formamidine sulfinic acid could be carried out in very much the same manner as the first or initial bleaching stage, namely likewise as a high temperature high-consistency disperser bleaching process, in that dilution is excluded subsequent to the first disperser 7 and the pulp or stock transfer to the second disperser is accomplished by means of a screw or worm system or similar structure. In such a case the inlet stock consistency in the second bleaching stage is nearly the same as the discharge stock consistency subsequent to the first disperser 7. Also the temperature can be maintained at approximately the same level.
1 335~87 Figure 3 shows by means of the customary chemical symbols the reaction mechanism of the conversion of peroxide into formamidine sulfinic acid by means of thiourea, which reacts with hydrogen peroxide to produce formamidine sulfinic acid and water.
A further positive effect of the inventive method is seen in the fact that the normally negative effect of residual peroxide in the alkaline medium after the first or initial bleaching stage, namely the decomposition of the following reductive bleaching agent, is advantageously converted into a positive effect. This can be accomplished by producing a new bleaching agent by means of suitable reaction partners or compounds. Such new bleaching agent would then be additionally available in the second bleaching stage. This problem is most advantageously solved when the residual bleaching agent from the first or initial bleaching stage is converted into the very same bleaching agent which is used in the second or reductive bleaching stage.
~ uch a positive conversion of the residual bleaching agent from the first or initial bleaching stage is readily possible in the above-described bleaching arrangement. It is known that the reductive bleaching agent of the second bleaching stage, namely formamidine sulfinic acid, is produced ~y admixing peroxide with thiourea. In ~ 335687 other words, in order to produce formamidine sulfinic acid a reaction partner or compound is used, namely peroxide, which exists as residual peroxide at the end of the first or initial bleaching stage. Therefore, there is the possibility, with the addition of the aforenoted reaction partner, namely thiourea, of rendering harmless residual peroxide as well as of producing additional formamidine sulfinic acid.
Addition of thiourea should be effected prior to adding the reductive bleaching agent of the second ~leaching stage, i.e. between the first and the second bleaching stages. In this manner, residual peroxide can timely react.
However, it is also conceiva~le that the addition of thiourea and the addition of formamidine sulfinic acid can be mutually carried out prior to the second or reductive bleaching stage.
In such a case it would depend on whether residual peroxide is admixed rapidly enough with thiourea to preclude the other possible reaction with the second bleaching agent, namely with formamidine sulfinic acid.
Claims (26)
1. A method of increasing the degree of whiteness of waste paper, comprising the steps of:
preparing an aqueous fiber stock suspension from waste paper;
deinking said aqueous fiber stock suspension;
bleaching said aqueous fiber stock suspension;
said step of bleaching including at least two bleaching stages; and during said at least two bleaching stages, adding preselected bleaching agents such that, subsequent to the last bleaching stage of said at least two bleaching stages, a medium of approximately pH 6.5 to 7.5 prevails in the fiber stock suspension without admixing further substances which affect the pH value, so that any water and filtrates to be discharged during said at least two bleaching stages are likewise in said medium.
preparing an aqueous fiber stock suspension from waste paper;
deinking said aqueous fiber stock suspension;
bleaching said aqueous fiber stock suspension;
said step of bleaching including at least two bleaching stages; and during said at least two bleaching stages, adding preselected bleaching agents such that, subsequent to the last bleaching stage of said at least two bleaching stages, a medium of approximately pH 6.5 to 7.5 prevails in the fiber stock suspension without admixing further substances which affect the pH value, so that any water and filtrates to be discharged during said at least two bleaching stages are likewise in said medium.
2. The method as defined in claim 1, wherein:
said step of preparing an aqueous fiber stock suspension from waste paper is carried out without adding alkaline chemicals.
said step of preparing an aqueous fiber stock suspension from waste paper is carried out without adding alkaline chemicals.
3. The method as defined in claim 1, wherein:
said step of preparing an aqueous fiber stock suspension from waste paper includes adding a minimum of alkaline chemicals.
said step of preparing an aqueous fiber stock suspension from waste paper includes adding a minimum of alkaline chemicals.
4. The method as defined in claim 1, wherein:
said step of deinking said aqueous fiber stock suspension is carried out subsequent to said step of bleaching and in a substantially chemically neutral medium.
said step of deinking said aqueous fiber stock suspension is carried out subsequent to said step of bleaching and in a substantially chemically neutral medium.
5. The method as defined in claim 1, wherein:
said step of deinking includes at least two partial steps.
said step of deinking includes at least two partial steps.
6. The method as defined in claim 5, wherein:
one of said at least two partial steps is carried out subsequent to said step of bleaching and in a substantially chemically neutral medium.
one of said at least two partial steps is carried out subsequent to said step of bleaching and in a substantially chemically neutral medium.
7. The method as defined in claim 1, wherein:
said step of deinking includes at least two deinking stages.
said step of deinking includes at least two deinking stages.
8. The method as defined in claim 7, wherein:
during said at least two deinking stages of said step of deinking, said aqueous fiber stock suspension is subjected to a washing process.
during said at least two deinking stages of said step of deinking, said aqueous fiber stock suspension is subjected to a washing process.
9. The method as defined in claim 7, wherein:
during said at least two deinking stages of said step of deinking, said aqueous fiber stock suspension is subjected to a flotation process.
during said at least two deinking stages of said step of deinking, said aqueous fiber stock suspension is subjected to a flotation process.
10. The method as defined in claim 7, wherein:
during said at least two deinking stages of said step of deinking, said aqueous fiber stock suspension is subjected to a combination of washing and flotation processes.
during said at least two deinking stages of said step of deinking, said aqueous fiber stock suspension is subjected to a combination of washing and flotation processes.
11. The method as defined in claim 10, further including the step of:
prior to said at least two deinking stages of said step of deinking, mechanically dispersing said aqueous fiber stock suspension at stock consistencies between 10% and 50%
by weight and at temperatures between 40°C and 125°C, and thereby separating from the fibers ink and paint particles still remaining subsequent to the essentially neutral decomposition thereof and thereby also substantially reducing in size interfering substances.
prior to said at least two deinking stages of said step of deinking, mechanically dispersing said aqueous fiber stock suspension at stock consistencies between 10% and 50%
by weight and at temperatures between 40°C and 125°C, and thereby separating from the fibers ink and paint particles still remaining subsequent to the essentially neutral decomposition thereof and thereby also substantially reducing in size interfering substances.
12. The method as defined in claim 10, further including the step of:
between said at least two deinking stages of said step of deinking, mechanically dispersing said aqueous fiber stock suspension at stock consistencies between 10% and 50%
by weight and at temperatures between 40°C and 125°C, and thereby separating from the fibers ink and paint particles still remaining subsequent to the essentially neutral decomposition thereof and thereby also substantially reducing in size interfering substances.
between said at least two deinking stages of said step of deinking, mechanically dispersing said aqueous fiber stock suspension at stock consistencies between 10% and 50%
by weight and at temperatures between 40°C and 125°C, and thereby separating from the fibers ink and paint particles still remaining subsequent to the essentially neutral decomposition thereof and thereby also substantially reducing in size interfering substances.
13. The method as defined in claim 10, further including the step of:
subsequent to said at least two deinking stages of said step of deinking, mechanically dispersing said aqueous fiber stock suspension at stock consistencies between 10% and 50% by weight and at temperatures between 40°C and 125°C, and thereby separating from the fibers ink and paint particles still remaining subsequent to the essentially neutral decomposition and thereby also substantially reducing in size interfering substances.
subsequent to said at least two deinking stages of said step of deinking, mechanically dispersing said aqueous fiber stock suspension at stock consistencies between 10% and 50% by weight and at temperatures between 40°C and 125°C, and thereby separating from the fibers ink and paint particles still remaining subsequent to the essentially neutral decomposition and thereby also substantially reducing in size interfering substances.
14. The method as defined in claim 1, wherein:
said step of adding preselected bleaching agents includes adding formamidine sulfinic acid as a bleaching agent.
said step of adding preselected bleaching agents includes adding formamidine sulfinic acid as a bleaching agent.
15. The method as defined in claim 1, wherein:
said step of adding preselected bleaching agents during said at least two bleaching stages entails working with oxidative and reductive bleaching agents in a first bleaching stage and a second bleaching stage;
during said first bleaching stage, a high temperature high-consistency dispersing bleaching process is carried out;
during said second bleaching stage, a medium-consistency bleaching process is carried out; and said step of working with oxidative and reductive bleaching agents includes adding formamidine sulfinic acid as the bleaching agent for said second bleaching stage.
said step of adding preselected bleaching agents during said at least two bleaching stages entails working with oxidative and reductive bleaching agents in a first bleaching stage and a second bleaching stage;
during said first bleaching stage, a high temperature high-consistency dispersing bleaching process is carried out;
during said second bleaching stage, a medium-consistency bleaching process is carried out; and said step of working with oxidative and reductive bleaching agents includes adding formamidine sulfinic acid as the bleaching agent for said second bleaching stage.
16. The method as defined in claim 15, wherein:
said high temperature high-consistency dispersing bleaching process of said first bleaching stage entails bleaching by means of peroxide at a stock consistency of approximately 25% by weight and at a temperature of approximately 90°C; and said medium-consistency bleaching process includes diluting said aqueous fiber stock suspension to a stock consistency of approximately 15% by weight and bleaching the thus diluted fiber stock suspension at the temperature resulting subsequent to said step of diluting.
said high temperature high-consistency dispersing bleaching process of said first bleaching stage entails bleaching by means of peroxide at a stock consistency of approximately 25% by weight and at a temperature of approximately 90°C; and said medium-consistency bleaching process includes diluting said aqueous fiber stock suspension to a stock consistency of approximately 15% by weight and bleaching the thus diluted fiber stock suspension at the temperature resulting subsequent to said step of diluting.
17. The method as defined in claim 1, wherein:
said step of adding preselected bleaching agents during said at least two bleaching stages entails working with oxidative and reductive bleaching agents in a first bleaching stage and a second bleaching stage;
during said first bleaching stage, a first high temperature high-consistency dispersing bleaching process is carried out; and during said second bleaching stage, a second high temperature high-consistency dispersing bleaching process is carried out.
said step of adding preselected bleaching agents during said at least two bleaching stages entails working with oxidative and reductive bleaching agents in a first bleaching stage and a second bleaching stage;
during said first bleaching stage, a first high temperature high-consistency dispersing bleaching process is carried out; and during said second bleaching stage, a second high temperature high-consistency dispersing bleaching process is carried out.
18. The method as defined in claim 17, wherein:
said first high temperature high-consistency dispersing bleaching process of said first bleaching stage entails bleaching by means of peroxide at a stock consistency of approximately 30% by weight and at a temperature of approximately 95°C; and said second high temperature high-consistency dispersing bleaching process of said second bleaching stage entails bleaching by means of formamidine sulfinic acid at a stock consistency of approximately 30% by weight and at a temperature of approximately 95°C.
said first high temperature high-consistency dispersing bleaching process of said first bleaching stage entails bleaching by means of peroxide at a stock consistency of approximately 30% by weight and at a temperature of approximately 95°C; and said second high temperature high-consistency dispersing bleaching process of said second bleaching stage entails bleaching by means of formamidine sulfinic acid at a stock consistency of approximately 30% by weight and at a temperature of approximately 95°C.
19. The method as defined in claim 16, further including the step of:
adding further chemical compounds at the end of said first bleaching stage and thereby converting surplus peroxide into a new reductive bleaching agent which can be used in said second bleaching stage.
adding further chemical compounds at the end of said first bleaching stage and thereby converting surplus peroxide into a new reductive bleaching agent which can be used in said second bleaching stage.
20. The method as defined in claim 18, further including the steps of:
at the end of said first bleaching stage, adding the preselected chemical compound thiourea to said bleaching agent peroxide;
mixing excess peroxide and the added preselected chemical compound thiourea and thereby producing formamidine sulfinic acid as a new bleaching agent in the range of pH
greater than 7; and said step of adding the preselected chemical compound thiourea entails separately adding the latter prior to adding the second bleaching agent which is likewise formamidine sulfinic acid.
at the end of said first bleaching stage, adding the preselected chemical compound thiourea to said bleaching agent peroxide;
mixing excess peroxide and the added preselected chemical compound thiourea and thereby producing formamidine sulfinic acid as a new bleaching agent in the range of pH
greater than 7; and said step of adding the preselected chemical compound thiourea entails separately adding the latter prior to adding the second bleaching agent which is likewise formamidine sulfinic acid.
21. The method as defined in claim 18, further including the steps of:
at the end of said first bleaching stage, adding the preselected chemical compound thiourea to said bleaching agent peroxide;
mixing excess peroxide and the added preselected chemical compound thiourea and thereby producing formamidine sulfinic acid as a new bleaching agent in the range of pH
greater than 7; and said step of adding the preselected chemical compound thiourea entails adding the latter together with the second bleaching agent which is likewise formamidine sulfinic acid.
at the end of said first bleaching stage, adding the preselected chemical compound thiourea to said bleaching agent peroxide;
mixing excess peroxide and the added preselected chemical compound thiourea and thereby producing formamidine sulfinic acid as a new bleaching agent in the range of pH
greater than 7; and said step of adding the preselected chemical compound thiourea entails adding the latter together with the second bleaching agent which is likewise formamidine sulfinic acid.
22. The method as defined in claim 20, further including the steps of:
during said first high temperature high-consistency dispersing bleaching process of said first oxidative bleaching stage, adding an excessive quantity of the oxidative bleaching agent peroxide and thereby providing a predetermined quantity of surplus peroxide; and said step of adding the preselected chemical compound thiourea entails producing a predetermined quantity of formamidine sulfinic acid, so that in the reductive second bleaching stage no additional formamidine sulfinic acid must be added.
during said first high temperature high-consistency dispersing bleaching process of said first oxidative bleaching stage, adding an excessive quantity of the oxidative bleaching agent peroxide and thereby providing a predetermined quantity of surplus peroxide; and said step of adding the preselected chemical compound thiourea entails producing a predetermined quantity of formamidine sulfinic acid, so that in the reductive second bleaching stage no additional formamidine sulfinic acid must be added.
23. The method as defined in claim 20, further including the steps of:
during said first high temperature high-consistency dispersing bleaching process of said first oxidative bleaching stage, adding an excessive quantity of the oxidative bleaching agent peroxide and thereby providing a predetermined quantity of surplus peroxide; and said step of adding the preselected chemical compound thiourea entails producing a predetermined quantity of formamidine sulfinic acid, so that in the reductive second bleaching stage only a reduced quantity of additional formamidine sulfinic acid must be added.
during said first high temperature high-consistency dispersing bleaching process of said first oxidative bleaching stage, adding an excessive quantity of the oxidative bleaching agent peroxide and thereby providing a predetermined quantity of surplus peroxide; and said step of adding the preselected chemical compound thiourea entails producing a predetermined quantity of formamidine sulfinic acid, so that in the reductive second bleaching stage only a reduced quantity of additional formamidine sulfinic acid must be added.
24. The method as defined in claim 19, further including the step of:
oxidatively destroying surplus thiourea by adding peroxide at the end of said second bleaching stage.
oxidatively destroying surplus thiourea by adding peroxide at the end of said second bleaching stage.
25. The method as defined in claim 20, further including the step of:
oxidatively destroying surplus thiourea by adding peroxide at the end of said second bleaching stage.
oxidatively destroying surplus thiourea by adding peroxide at the end of said second bleaching stage.
26. The method as defined in claim 21, further including the step of:
oxidatively destroying surplus thiourea by adding peroxide at the end of said second bleaching stage.
oxidatively destroying surplus thiourea by adding peroxide at the end of said second bleaching stage.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19883831668 DE3831668A1 (en) | 1988-09-17 | 1988-09-17 | METHOD FOR INCREASING WHITE GRADE OF WASTE PAPER WITH NEUTRAL WATER CIRCUIT |
| DEP3,831,668.4 | 1988-09-17 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1335687C true CA1335687C (en) | 1995-05-30 |
Family
ID=6363166
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 609695 Expired - Fee Related CA1335687C (en) | 1988-09-17 | 1989-08-29 | Method for increasing the degree of whiteness of waste paper with neutral water circulation |
Country Status (3)
| Country | Link |
|---|---|
| EP (1) | EP0360993A3 (en) |
| CA (1) | CA1335687C (en) |
| DE (1) | DE3831668A1 (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE102020111675A1 (en) * | 2020-04-29 | 2021-11-04 | Kübler & Niethammer Papierfabrik Kriebstein AG | Process for producing a label paper from detached wet labels |
Family Cites Families (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2311674C3 (en) * | 1973-03-09 | 1978-01-19 | Degussa | PROCESS FOR REGENERATING WASTE PAPER |
| DE2813448B1 (en) * | 1978-03-29 | 1978-09-21 | Voith Gmbh J M | Process and plant for recycling waste paper |
| DE2816148B1 (en) * | 1978-04-14 | 1978-10-12 | Voith Gmbh J M | Procedures for recycling paper |
| DE3305131A1 (en) * | 1983-02-15 | 1984-08-16 | Degussa Ag, 6000 Frankfurt | METHOD FOR REMOVING WASTE PAPER |
| DE3309956C1 (en) * | 1983-03-19 | 1984-07-12 | Degussa Ag, 6000 Frankfurt | Process for bleaching paper raw materials |
| CA1249402A (en) * | 1984-12-21 | 1989-01-31 | Pulp And Paper Research Institute Of Canada | Multistage brightening of high yield and ultra high- yield wood pulps |
| DE3610940A1 (en) * | 1986-03-04 | 1987-09-10 | Escher Wyss Gmbh | HIGH TEMPERATURE HIGH CONSISTENCY FAST WHITE |
| DE3616816A1 (en) * | 1986-05-17 | 1987-11-19 | Degussa | METHOD FOR REMOVING BULK COLORED PAPER AND SELF-COPYING PAPER |
| US4675076A (en) * | 1986-10-01 | 1987-06-23 | Ppg Industries, Inc. | Method for brightening pulp |
-
1988
- 1988-09-17 DE DE19883831668 patent/DE3831668A1/en active Granted
-
1989
- 1989-07-13 EP EP19890112810 patent/EP0360993A3/en not_active Withdrawn
- 1989-08-29 CA CA 609695 patent/CA1335687C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| EP0360993A2 (en) | 1990-04-04 |
| EP0360993A3 (en) | 1991-11-06 |
| DE3831668C2 (en) | 1992-10-15 |
| DE3831668A1 (en) | 1990-03-22 |
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