EP0652321B1 - Bleichen von chemischem Zellstoff - Google Patents

Bleichen von chemischem Zellstoff Download PDF

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Publication number
EP0652321B1
EP0652321B1 EP94307702A EP94307702A EP0652321B1 EP 0652321 B1 EP0652321 B1 EP 0652321B1 EP 94307702 A EP94307702 A EP 94307702A EP 94307702 A EP94307702 A EP 94307702A EP 0652321 B1 EP0652321 B1 EP 0652321B1
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EP
European Patent Office
Prior art keywords
pulp
brightness
solution
iso
bleaching
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EP94307702A
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English (en)
French (fr)
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EP0652321A1 (de
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 kraft or sulfite 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.
  • WO-A-92/07139 describes a method for preserving the mechanical strength properties of chemical paper pulp comprising two steps using a peroxygenated reagent, the first of which is carried out in an acidic medium while the second is carried out in an alkaline one treatment with a reducing compound being inserted therebetween.
  • the present invention consists in a process for bleaching kraft or sulfite wood pulp which comprises treating the pulp first with at least one oxidising agent and then with a reducing agent, characterised in that the oxidising agent comprises alkaline hydrogen peroxide or ozone and the reducing agent comprises sodium borohydride.
  • a pulp bleaching process preferably totally chlorine free, which gives a pulp of high and stable brightness without adversely affecting the physical properties of the pulp and in particular without degrading the polysaccharides or reducing the viscosity of the pulp.
  • a further oxidising treatment may optionally be carried out after the treatment with the reducing agent. This is preferably done with hydrogen peroxide and sodium hydroxide.
  • the various bleaching stages are preferably all carried out at alkaline pH, for which purpose an alkaline metal hydroxide such as sodium hydroxide may be added.
  • 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.
  • D C10 2 Not used in the most preferred embodiments which are totally chlorine-free.
  • EOP Alkaline extraction enhanced with peroxide and oxygen.
  • ER Alkaline extraction enhanced with sodium borohydride.
  • O Oxygen O 2 Preferred concentration 2-5% based on oven-dried pulp (ODP). Typically about 3% may be used with NaOH, at a preferred concentration of 2.0-3.0%.
  • P Hydrogen Peroxide H 2 O 2 Preferred concentration 2.0-3.0% on ODP. Generally used with NaOH at a preferred concentration of 2.0-3.0%.
  • Preferred temperature about 70°C.
  • concentrations are based on ODP (oven-dried pulp) unless otherwise stated.
  • the oxidative bleaching sequence was as follows:
  • the pulp was taken out after SO 2 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% H 2 O 2 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 (NaBH 4 12%, NaOH 40%, water 48%).
  • the bleaching conditions and the results are listed in Table 1 below and the brightness response versus the NaBH 4 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.
  • RUN N° STAGE CHEMICALS (% / o.d. pulp) pH BRIGHTNESS (% ISO) ⁇ -BRIGHTNESS (% ISO) NaBH 4 /NaOH solut.
  • the third series of the bleach trials was carried out with sodium bisulfite as a reference and a combination of sodium bisulfite and the sodium borohydride solution.
  • the addition rate of NaHSO 3 was kept constant by 1.5%/o.d. pulp, while the NaBH 4 addition rate was varied between 0.1% and 0.5%.
  • the treatment rates and brightness gains are given in Table 3.
  • RUN N° CHEMICAL % / o.d.
  • Sodium bisulfite is a weak reductant.
  • a reductive treatment of the TCF bleached kraft pulp with 1.5% NaHSO 3 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 NaHSO 3 pulp is inferior to that of the combination of NaHSO 3 and borohydride solution.
  • Example 1 100g oven dry pulp as used in Example 1 were treated with 1% of an alkaline NaBH 4 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 dm 3 /kg to 762 dm 3 /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% H 2 SO 4 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 NaBH 4 solution.
  • a further increase of the amount of NaBH 4 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 NaBH 4 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 NaBH 4 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 NaBH 4 solution to both pulp samples.
  • the addition rate was varied between 0.2% and 1.2% (the solution contains 12% wt NaBH 4 , 40% wt NaOH and 48% wt H 2 O).
  • the second series of the bleach trials was done by adding 1% peroxide or 0.5-1% NaBH 4 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% H 2 O 2 can increase the brightness of 2.6 points. Reductive treatments with 0.5 and 1% of the NaBH 4 solution increased the brightness response of 2.1 and 2.8 points respectively. Subsequently the pulps were bleached with 1% H 2 O 2 . 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 dm 3 /kg.
  • the viscosity of the pulp was increased to 800 dm 3 /kg. But the viscosity of the pulp dropped again to 756 dm 3 /kg after the P-stage. In comparison with peroxide bleaching the viscosity difference was not significant.
  • 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.

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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)
  • Paper (AREA)

Claims (11)

  1. Verfahren zum Bleichen von Kraft- oder Sulfitholzstoff, bei dem man den Holzstoff zunächst mit wenigstens einem Oxidationsmittel und dann mit einem Reduktionsmittel behandelt, dadurch gekennzeichnet, daß das Oxidationsmittel alkalisches Wasserstoffperoxid oder Ozon und das Reduktionsmittel Natriumborhydrid umfassen.
  2. Verfahren nach Anspruch 1, bei dem das Natriumborhydrid in einer wäßrigen alkalischen Lösung verwendet wird.
  3. Verfahren nach Anspruch 2, bei dem die wäßrige Lösung 10 bis 25 Gew.% Natriumborhydrid und 15 bis 45 Gew.% Natriumhydroxid umfaßt.
  4. Verfahren nach Anspruch 3, bei dem die wäßrige Lösung etwa 12 % Natriumborhydrid und etwa 40 % Natriumhydroxid umfaßt und in einer Menge von 0,5 bis 2,0 %, bezogen auf ofentrockenen Holzstoff (ODP), verwendet wird.
  5. Verfahren nach einem der vorausgehenden Ansprüche, bei dem eine weitere Oxidationsbehandlung nach der Behandlung mit dem Reduktionsmittel durchgeführt wird.
  6. Verfahren nach Anspruch 5, bei dem die weitere Oxidationsbehandlung unter Verwendung von Wasserstoffperoxid durchgeführt wird.
  7. Verfahren nach einem der vorausgehenden Ansprüche, bei dem die Behandlungen mit Oxidations- und Reduktionsmitteln bei alkalischem pH-Wert durchgeführt werden.
  8. Verfahren nach einem der vorausgehenden Ansprüche, bei dem der Holzstoff mit einem Enzym behandelt wird, um die Helligkeit zu verbessern.
  9. Verfahren nach Anspruch 8, bei dem das Enzym Xylanase ist.
  10. Verfahren nach einem der vorausgehenden Ansprüche, bei dem der Holzstoff mit einem chelatbildenden Mittel behandelt wird, um die Helligkeit zu verbessern.
  11. Verfahren nach Anspruch 10, bei dem das chelatbildende Mittel Diethylentriaminpentaessigsäure (DTPA) ist.
EP94307702A 1993-11-04 1994-10-20 Bleichen von chemischem Zellstoff Expired - Lifetime EP0652321B1 (de)

Applications Claiming Priority (2)

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

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EP0652321B1 true EP0652321B1 (de) 1998-01-21

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9932709B2 (en) 2013-03-15 2018-04-03 Ecolab Usa Inc. Processes and compositions for brightness improvement in paper production
HK1198547A1 (en) * 2011-07-29 2015-05-15 剑桥表现遗传学有限公司 Methods for detection of nucleotide modification
ES2786984T3 (es) 2012-11-30 2020-10-14 Cambridge Epigenetix Ltd Agente oxidante para nucleótidos modificados
BR102014027199B1 (pt) * 2014-07-14 2022-10-04 Nalco Company Método para aprimorar a fabricação de polpa de soda ou kraft

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE4008893A1 (de) * 1990-03-20 1991-09-26 Call Hans Peter Verfahren zum enzymatischen bleichen von zellstoffen
BE1004630A3 (fr) * 1990-10-17 1992-12-22 Interox Internat Sa 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.

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EP0652321A1 (de) 1995-05-10
FI945202A0 (fi) 1994-11-04
FI945202L (fi) 1995-05-05
FI945202A7 (fi) 1995-05-05

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