EP0652321A1 - Blanchiment de pâte à papier chimique - Google Patents

Blanchiment de pâte à papier chimique Download PDF

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Publication number
EP0652321A1
EP0652321A1 EP94307702A EP94307702A EP0652321A1 EP 0652321 A1 EP0652321 A1 EP 0652321A1 EP 94307702 A EP94307702 A EP 94307702A EP 94307702 A EP94307702 A EP 94307702A EP 0652321 A1 EP0652321 A1 EP 0652321A1
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Prior art keywords
pulp
brightness
solution
bleaching
sodium
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EP94307702A
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German (de)
English (en)
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EP0652321B1 (fr
Inventor
Lawrence J. Guilbault
Maurice Hache
David C. Munroe
David L.K. Wang
Graziella Teodorescu
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Morton International LLC
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Morton International LLC
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    • 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
    • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
    • D21C9/10—Bleaching ; Apparatus therefor
    • D21C9/1057—Multistage, with compounds cited in more than one sub-group D21C9/10, D21C9/12, D21C9/16
    • 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
    • D21C5/005—Treatment of cellulose-containing material with microorganisms or enzymes
    • 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
    • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
    • D21C9/10—Bleaching ; Apparatus therefor
    • D21C9/1084—Bleaching ; Apparatus therefor with reducing compounds

Definitions

  • This invention relates to a process for bleaching wood pulp to enhance its brightness, to improve brightness stability and generally to improve the physical properties of the pulp.
  • Wood pulp can be produced by numerous different processes which can be classified under the broad headings of mechanical, chemical and hybrid processes.
  • chemical processes are the kraft process wherein the wood chips or the like are treated at elevated temperature and alkaline pH with sodium sulfide, sodium hydroxide and sodium carbonate, and the sulfite process wherein the wood chips are treated at acid pH, again at elevated temperature, with sodium and magnesium bisulfites.
  • the process of the present invention has been found to be particularly advantageous in relation to pulps produced by these chemical processes, but is not limited to any particular type of wood pulp.
  • Kassepi et al Pulping Conf, (Toronto) Proc, 327-340 (Oct 1992) disclose the effect of ozonisation on kraft-oxygen (K-O) and kraft oxygen-peroxide (K-OP) pulps.
  • K-O kraft-oxygen
  • K-OP kraft oxygen-peroxide
  • the K-OP pulps generally responded better to ozone bleaching than K-O pulps. It was found that too high an ozone concentration gave rise to carbohydrate degradation and decreased viscosity of the pulp.
  • ozone can be used effectively in both pre-bleaching and final bleaching but both lignins and carbohydrates tend to be attacked.
  • Carbohydrate degradation has to be suppressed by preacidification of the pulp, low-temperature bleaching, slow addition of ozone to the pulp and proper mixing. Under these conditions, an ozone concentration of 0.1% can reduce the pulp kappa number by one unit.
  • This object is achieved according to the present invention in that there is provided a process for bleaching wood pulp which comprises treating the pulp, first with one or more oxidising agents and then with a reducing agent. A further oxidising treatment may optionally be carried out after the treatment with the reducing agent.
  • One preferred reducing agent is sodium borohydride.
  • Preferred oxidising agents for the initial treatment of the pulp are oxygen, ozone and hydrogen peroxide.
  • the various bleaching stages are preferably carried out at alkaline pH, for which purpose an alkaline metal hydroxide such as sodium hydroxide may be added.
  • a final oxidising step is carried out, this is preferably done with hydrogen peroxide and sodium hydroxide.
  • Brightness may be further enhanced by the use of enzymes such as xylanase and chelants such as ethylene diamine tetraacetic acid (EDTA) or, more preferably, diethylene triamine pentaacetic acid (DTPA).
  • enzymes such as xylanase and chelants such as ethylene diamine tetraacetic acid (EDTA) or, more preferably, diethylene triamine pentaacetic acid (DTPA).
  • EDTA ethylene diamine tetraacetic acid
  • DTPA diethylene triamine pentaacetic acid
  • the sodium borohydride is preferably used in alkaline solution, and a particularly advantageous form is an aqueous solution of 10 to 25 wt.% of sodium borohydride and 15 to 45 wt.% of sodium hydroxide.
  • a particularly advantageous form is an aqueous solution of 10 to 25 wt.% of sodium borohydride and 15 to 45 wt.% of sodium hydroxide.
  • One commercially available solution of this type comprises 12% of sodium borohydride and 40% of sodium hydroxide, and is supplied by Morton International, Inc under the trade mark Borol.
  • Another such solution developed more recently comprises 20% of sodium hydroxide and 20% of sodium borohydride.
  • concentrations are based on ODP (oven-dried pulp) unless otherwise stated.
  • the oxidative bleaching sequence was as follows:
  • the pulp was taken out after SO2 addition after the last peroxide stage and had a pH value of 4.5 and a consistency of 31.8%.
  • the initial ISO brightness was 73.9% but was not stable and varied between 70.9 and 71.8% several days later.
  • the pulp was diluted down to 10% consistency with distilled water and a series of reductive bleaching trials was carried out at 70°C, for a retention time of 60 minutes in each case.
  • the trials were conducted using sodium borohydride, alone and in combination with sodium bisulfite and with hydrogen peroxide.
  • Aqueous solutions of 11.5% H2O2 and 10% NaOH were used for the peroxide bleaching.
  • a 32% DTPA solution considered as 100% was diluted with distilled water to a 1% solution to be used for the peroxide stage.
  • handsheets were prepared.
  • the trials were performed with 20g samples in sealed polyethylene bags plunged into an agitating water bath.
  • the first series of the trials was conducted with different amounts of alkaline borohydride solution (NaBH4 12%, NaOH 40%, water 48%).
  • the bleaching conditions and the results are listed in Table 1 below and the brightness response versus the NaBH4 solution addition rate is illustrated in Figure 1, which also illustrates the brightness after aging.
  • Figure 1 shows that the brightness response is increased very fast by adding the borohydride solution to 0.6%.
  • a further increasing of chemical charge to 1% can achieve 0.5% brightness extra.
  • a maximum brightness gain of 2.6% ISO points can be achieved by adding 1% of the borohydride solution.
  • the brightness reversion of the untreated kraft pulp was 1.1 points.
  • the reductive treatment with sodium borohydride solution can offer a relatively stable brightness gain, if one compares the brightness gain before and after aging.
  • the second series of the trials was performed with 1% of the borohydride solution and subsequently with 1% hydrogen peroxide with and without washing between these two stages.
  • the pulp was also bleached with 1% hydrogen peroxide alone.
  • the bleaching conditions and the results are compiled in Table 2.
  • the combined treatment was carried out for 180 min. and the peroxide-only treatment for 240 min.
  • a treatment with 1% hydrogen peroxide can increase the final brightness by 3.6 points.
  • a reductive treatment with 1% of the borohydride solution increases the brightness by 3 points.
  • a subsequent peroxide bleaching can increase the brightness by 2.8 points more.
  • the brightness response is slightly reduced (0.2 points) if the pulp is not washed between the borohydride solution stage and the peroxide stage.
  • this combination is very interesting, because the mill can not only save the investment cost for the washer, but also use residual NaOH of the borohydride solution.
  • the third series of the bleach trials was carried out with sodium bisulfite and a combination of sodium bisulfite and the sodium borohydride solution.
  • the addition rate of NaHSO3 was kept constant by 1.5%/o.d. pulp, while the NaBH4 addition rate was varied between 0.1% and 0.5%.
  • the treatment rates and brightness gains are given in Table 3.
  • Sodium bisulfite is a weak reductant.
  • a reductive treatment of the TCF bleached kraft pulp with 1.5% NaHSO3 can increase the final brightness by 0.3 points.
  • a combination of sodium bisulfite and alkaline borohydride solution can improve the bleaching efficiency to gain 1.9 brightness points.
  • little synergistic bleaching effect is obtained by adding two reductants serially. This has already been established in the case of mechanical pulp and deinked pulp. The reason might be due to the lower residual lignin content of the bleached chemical pulp.
  • the brightness gains before and after aging are illustrated in Figure 2 which shows that the brightness stability of the treated only with 1.5 NaHSO3 pulp is inferior to that of the combination of NaHSO3 and borohydride solution.
  • Example 1 100g oven dry pulp as used in Example 1 were treated with 1% of an alkaline NaBH4 solution having the composition of the Borol solution described above. The reaction time was prolonged to 90 min. to compensate for the difficult mixing of the pulp at the medium consistency of 10% in the laboratory.
  • the treatment temperature was 70°C as in Example 1, with an initial pH of 11.8 and a final pH of 11.6
  • the yield of the borohydride treated pulp was 99.7% and the final brightness before and after aging was 74.6% and 73.3% ISO respectively.
  • the physical properties of the untreated and treated pulps are set out in Tables 4 and 5 respectively.
  • the beating energy as well as the strength properties, especially tensile strength and burst index of the borohydride treated pulp were positively influenced, whereas the tear index of the treated and untreated pulps remained at the same level, as can be seen from Figures 3 and 4.
  • the optical properties, i.e. opacity, absorption coefficient and light-scattering coefficient of the borohydride-treated pulp were reduced slightly due to the higher final brightness of the treated pulp (2.8 points higher).
  • the viscosity of the borohydride treated pulp was increased from 748 dm3/kg to 762 dm3/kg. This can explain the improvement of the strength properties after the borohydride treatment.
  • Kappa number and all strength properties were determined according to ZELLCHEMING standards. Brightness, viscosity and light-scattering,were tested according to SCAN-C 11:75, SCAN-CM : 88 AND SCAN-C 27:76, respectively.
  • the treatment conditions were the same as those of Example 1.
  • the pH value of the pulp was adjusted to 5.5 with 0.1% H2SO4 before handsheets were prepared for brightness determination.
  • the initial ISO brightness of the untreated pulp was 75.6% before aging and 74.2% after aging for 4 hours at 105°C.
  • the first series of the trials was performed by adding the alkaline borohydride solution only.
  • the addition rate of this solution was varied between 0.2% to 1%.
  • the maximum achieved brightness response was 3.6% ISO points by adding 0.6% of the NaBH4 solution.
  • a further increase of the amount of NaBH4 solution reduced the bleaching efficiency of this solution, most probably because the high alkalinity of the solution causes a negative alkaline darkening effect.
  • the aging test was conducted for 4 hours at 105°C, according to the TAPPI-method.
  • the brightness of the untreated and reductively treated pulps decreased after the aging.
  • Fig 5 and 6 show the brightness reversion varies between 1.4 and 2.5 points.
  • the brightness reversion of the OP bleached pulp was 1.4 points.
  • the brightness reversion of the reductively treated pulps varied between 1.4 and 2.5% ISO. However the final brightness of reductively treated pulps (after aging) was still 2.8 - 3.1 points higher than the final brightness of untreated pulp.
  • Example 2 100g o.d. pulp as used in Example 3 were treated with 1% of the Borol NaBH4 solution described above. The results before treatment are listed in Table 7 and those after are listed in Table 8. The conditions were the same as in Example 2 and the pH was 11.7 before and after treatment. The physical properties were measured as in Example 2.
  • the yield of the borohydride-treated pulp was 99.8% and the final brightness was 78.5% ISO before aging and 77.8% after.
  • the beating energy as well as the strength properties of the borohydride-treated pulp were not influenced significantly.
  • Reductive bleaching trials using sequences OQPR and OQPRP were carried out on samples of kraft hardwood (birch) pulp, the oxidative sequence being carried out as in Example 3.
  • the pulp samples came from Sweden.
  • the kappa number after the cooking process was 15 and 10 after the O-stage.
  • the residual kappa number of the OQP bleached pulp was determined as 5.4 in the laboratory.
  • the trials were conducted by using the Borol NaBH4 solution described above, directly or in combination with hydrogen peroxide.
  • Two pulps, namely wet pulp (ledge) and pulp sheet, with an initial brightness of 79.7% ISO and 81.6% ISO were used for the laboratory bleach trials.
  • a first series of the trials was performed by adding the NaBH4 solution to both pulp samples.
  • the addition rate was varied between 0.2% and 1.2% (the solution contains 12% wt NaBH4, 40% wt NaOH and 48% wt H2O).
  • the second series of the bleach trials was done by adding 1% peroxide or 0.5-1% NaBH4 solution and 1% peroxide with and without washing between these two stages.
  • the bleach trials were performed in sealed PE-bags plunged into an agitating water bath.
  • 1% H2O2 can increase the brightness of 2.6 points. Reductive treatments with 0.5 and 1% of the NaBH4 solution increased the brightness response of 2.1 and 2.8 points respectively. Subsequently the pulps were bleached with 1% H2O2. The final brightness was 85.1% ISO and 85.4% ISO respectively. If the pulp was not washed between the R-stage and the P-stage, the brightness response was reduced by 0.2 and 0.4 points.
  • the initial pulp had a viscosity of 770 dm3/kg.
  • the viscosity of the pulp was increased to 800 dm3/kg. But the viscosity of the pulp dropped again to 756 dm3/kg after the P-stage. In comparison with peroxide bleaching the viscosity difference was not significant.
  • the yield of the peroxide treated and with the combination of NaBH4 solution and peroxide treated pulp ranged between 99.8-99.7%.
  • optical properties i.e. opacity, absorption coefficient and light-scattering coefficient of the P and RP treated pulps were reduced slightly due to the higher final brightness of the treated pulps.
  • Bleaching sequences with and without a borohydride treatment stage were carried out to compare the brightness level and viscosity of the resulting pulp.
  • One pulp sample was subjected to the bleaching sequence (OP) (OP N ) ZRP with the results shown in Table 14. TABLE 14 Stage No. Treatment Step Residual kappa No.
  • the bisulfite is washed into a 500 ml Erlenmeyer flask with the 370 ml distilled water.
  • a magnetic stirrer is used to mix the solution in the flask, and it is cooled continuously in an ice bath.
  • the reaction will be vigorous during the addition of the borohydride solution.
  • the reaction vessel cannot be closed because of the escaping hydrogen.
  • the colour of the solution will change from orange to clear again, because of the pH change during the Borol solution addition.
  • the pH of the solution is adjusted between 9 and 10 with 25% NaOH and a pH meter.
  • the concentration of this solution is measured according to TAPPI standard method T622 CH-84.
  • Fig. 7 illustrates that the brightness response is increased with an increasing BGH addition rate to a maximum of 4.4 brightness points, then is reduced again if the BGH addition rate is beyond 1%.
  • the high amount of hydrosulfite decomposes more quickly before it can be used for the bleaching. In practice, a high amount of hydrosulfite is not only uneconomical but also can bring the corrosion problem due to the high sodium thiosulfate concentration.
  • the aging test shows that the brightness reversion of the BGH treated pulp is higher than that of the borohydride-treated pulp.
  • the brightness reduction is kept lower than 1 point.
  • a maximum brightness achievement of 3.6 points can be gained by adding 1% Na2S2O4 after aging.
  • Example 3 Bleaching trials were carried out on the pulp of Example 3, using an OQPY bleaching sequence, with varying amounts of borohydride-generated hydrosulfite and a procedure similar to that of Example 3.
  • the BGH was produced by the procedure described in Example 7.
  • the bleaching conditions and results are shown in Table 16 and the brightness response, before and after aging, is illustrated in Figure 8, which shows the results for a wet pulp sample, and Figure 9 which shows the results for a pulp sheet.
  • Figure 8 illustrates that the brightness response of the wet pulp sample is increased with an increasing BGH addition rate to a maximum of 2.4 brightness points, then is reduced again if the BGH addition rate is beyond 0.5%.
  • the maximum brightness response of 2.6 points is achieved by adding 0.75% BGH (see Figure 9).
  • the aging test shows that all reductive treatments have a lightly better brightness stability than that of the untreated pulp, but that the brightness reversion of the BGH treated sheet pulp is higher than that of the borohydride-treated sheet pulp. But for the wet pulp sample, the brightness response with BGH is lower than that with borohydride solution. Therefore the brightness reversion of the BGH treated pulp is also less than that of the borohydride-treated pulp.

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  • Life Sciences & Earth Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Wood Science & Technology (AREA)
  • Chemical & Material Sciences (AREA)
  • Biochemistry (AREA)
  • Microbiology (AREA)
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EP19940307702 1993-11-04 1994-10-20 Blanchiment de pâte à papier chimique Expired - Lifetime EP0652321B1 (fr)

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US14811893A 1993-11-04 1993-11-04
US148118 1993-11-04

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EP0652321A1 true EP0652321A1 (fr) 1995-05-10
EP0652321B1 EP0652321B1 (fr) 1998-01-21

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2014149302A1 (fr) 2013-03-15 2014-09-25 Ecolab Usa Inc. Procédés et compositions pour amélioration du degré de blancheur dans la production de papier
AU2012291873B2 (en) * 2011-07-29 2016-03-10 Cambridge Epigenetix Limited Methods for detection of nucleotide modification
EP3169843A4 (fr) * 2014-07-14 2018-01-24 Nalco Company Procédé et compositions chimiques d'amélioration de l'efficacité de réduction en pâte chimique
US10563248B2 (en) 2012-11-30 2020-02-18 Cambridge Epigenetix Limited Oxidizing agent for modified nucleotides

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1991014823A1 (fr) * 1990-03-20 1991-10-03 Call Hans Peter Procede de blanchiment enzymatique de celluloses
WO1992007139A1 (fr) * 1990-10-17 1992-04-30 Interox International S.A. Procede pour la preservation des caracteristiques de resistance mecanique des pates a papier chimiques
FR2692917A1 (fr) * 1992-06-30 1993-12-31 Air Liquide Procédé de blanchiment d'une pâte papetière chimique.

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1991014823A1 (fr) * 1990-03-20 1991-10-03 Call Hans Peter Procede de blanchiment enzymatique de celluloses
WO1992007139A1 (fr) * 1990-10-17 1992-04-30 Interox International S.A. Procede pour la preservation des caracteristiques de resistance mecanique des pates a papier chimiques
FR2692917A1 (fr) * 1992-06-30 1993-12-31 Air Liquide Procédé de blanchiment d'une pâte papetière chimique.

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AU2012291873B2 (en) * 2011-07-29 2016-03-10 Cambridge Epigenetix Limited Methods for detection of nucleotide modification
US9290807B2 (en) 2011-07-29 2016-03-22 Cambridge Epigenetix Limited Methods for detection of nucleotide modification
EP2737085B1 (fr) * 2011-07-29 2016-10-12 Cambridge Epigenetix Limited Procédés de détection d'une modification nucléotidique
US10428381B2 (en) 2011-07-29 2019-10-01 Cambridge Epigenetix Limited Methods for detection of nucleotide modification
US10563248B2 (en) 2012-11-30 2020-02-18 Cambridge Epigenetix Limited Oxidizing agent for modified nucleotides
WO2014149302A1 (fr) 2013-03-15 2014-09-25 Ecolab Usa Inc. Procédés et compositions pour amélioration du degré de blancheur dans la production de papier
EP2971350A4 (fr) * 2013-03-15 2016-12-14 Ecolab Usa Inc Procédés et compositions pour amélioration du degré de blancheur dans la production de papier
US9932709B2 (en) 2013-03-15 2018-04-03 Ecolab Usa Inc. Processes and compositions for brightness improvement in paper production
EP3169843A4 (fr) * 2014-07-14 2018-01-24 Nalco Company Procédé et compositions chimiques d'amélioration de l'efficacité de réduction en pâte chimique

Also Published As

Publication number Publication date
FI945202A0 (fi) 1994-11-04
EP0652321B1 (fr) 1998-01-21
FI945202A (fi) 1995-05-05

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