EP0348411A1 - An improved peroxide bleaching method. - Google Patents

An improved peroxide bleaching method.

Info

Publication number
EP0348411A1
EP0348411A1 EP88901957A EP88901957A EP0348411A1 EP 0348411 A1 EP0348411 A1 EP 0348411A1 EP 88901957 A EP88901957 A EP 88901957A EP 88901957 A EP88901957 A EP 88901957A EP 0348411 A1 EP0348411 A1 EP 0348411A1
Authority
EP
European Patent Office
Prior art keywords
acid
pulp
bleaching
suspension
peroxide
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.)
Granted
Application number
EP88901957A
Other languages
German (de)
French (fr)
Other versions
EP0348411B1 (en
Inventor
Josef Kubat
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Kemira Kemi AB
Original Assignee
Individual
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Individual filed Critical Individual
Priority to AT88901957T priority Critical patent/ATE83016T1/en
Publication of EP0348411A1 publication Critical patent/EP0348411A1/en
Application granted granted Critical
Publication of EP0348411B1 publication Critical patent/EP0348411B1/en
Expired legal-status Critical Current

Links

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
    • 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
    • D21C9/16—Bleaching ; Apparatus therefor with per compounds
    • D21C9/163—Bleaching ; Apparatus therefor with per compounds with peroxides

Definitions

  • Combinations of hydrogen peroxide with certain organic acids stand out as an especially efficient form of the peroxide bleaching technique.
  • the treatment is carried out within the acid range of the pH-scale, facilitating the formation of peroxyacid ⁇ which are the active chemical species in the bleaching process.
  • the common way, of bleaching with peroxides is carried out using slightly alkaline conditions enhancing the formation of peroxide anions HC which are the active ionic species. Higher alkalinities are to be avoided since hydrogen peroxide then decomposes to oxygen.
  • the purpose of the present disclosure is to describe a simple method to enhance the bleaching efficiency of hydrogen peroxide by adding certain inexpensive organic acids to the bleaching solution.
  • the acids in question are formic, acetic, lactic, maleic acid and phtalic acid; they can be used separately or in various combinations. Contrary to similar mixtures of hydrogen peroxide with such acids which have been proposed to increase the efficiency of the bleaching process, cf. for instance Austrian Patent 203.454, the mixtures of the present disclosure are being used within the alkaline range of the pH-scale and not on its acid side.
  • This alkalinity of the treating solution is the main characteristic feature of the present invention relating to peroxide bleaching process in the presence of the organic acids enumerated above, i.e. formic, acetic, lactic, maleic acid and phtalic acid or mixtures thereof.
  • the bleaching efficiency of peroxides can be improved if the bleaching process is carried out in the presence of low concentrations of one or more of the enumerated acids while maintaining the pH-value within the alkaline range 8-13, which pH-range is provided by the addition of an alkali metal hydroxide, such as sodium hydroxide or potassium hydroxide.
  • an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide.
  • potassium hydroxide gives a significantly higher brightness of the bleached material than does sodium hydroxide. The difference amounted to 2-8 SCAN brightness units.
  • Example 1 The invention is illustrated by means of the following examples.
  • Example 1 The invention is illustrated by means of the following examples.
  • a bleaching mixture containing 4% H ? 0 2 , 1% acetic acid, and 1% formic acid (based on the weight of the quantity of pulp present in the system) gave after bleaching carried out as described above a brightness of 78%, the brightness gain being 18 units.

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  • Life Sciences & Earth Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Wood Science & Technology (AREA)
  • Paper (AREA)
  • Detergent Compositions (AREA)

Abstract

A method for bleaching wood pulp without the use of peroxy acids by means of from 0.1 to 10 %, based on the dry weight of the pulp, of hydrogen peroxide characterized in that an organic acid selected from the group formic acid, acetic acid, lactic acid, maleic acid and phtalic acid or any mixture thereof is added together with such an amount of an alkali hydroxide to the pulp suspension to be bleached as to give a pH-value of the suspension within the alkaline range of from 8.0 to 13.

Description

An improved peroxide bleaching method
The bleaching of wood pulp with peroxides is an established technique in the manufacture of bleached pulp grades, hydrogen peroxides being the by far the most common reagent used for such purposes. In a large number of patents and reports various details of this technique and its- numerous ramifications are described .
Combinations of hydrogen peroxide with certain organic acids stand out as an especially efficient form of the peroxide bleaching technique. The treatment is carried out within the acid range of the pH-scale, facilitating the formation of peroxyacidε which are the active chemical species in the bleaching process. Contrary to this, the common way, of bleaching with peroxides is carried out using slightly alkaline conditions enhancing the formation of peroxide anions HC which are the active ionic species. Higher alkalinities are to be avoided since hydrogen peroxide then decomposes to oxygen.
The purpose of the present disclosure is to describe a simple method to enhance the bleaching efficiency of hydrogen peroxide by adding certain inexpensive organic acids to the bleaching solution. The acids in question are formic, acetic, lactic, maleic acid and phtalic acid; they can be used separately or in various combinations. Contrary to similar mixtures of hydrogen peroxide with such acids which have been proposed to increase the efficiency of the bleaching process, cf. for instance Austrian Patent 203.454, the mixtures of the present disclosure are being used within the alkaline range of the pH-scale and not on its acid side. This alkalinity of the treating solution is the main characteristic feature of the present invention relating to peroxide bleaching process in the presence of the organic acids enumerated above, i.e. formic, acetic, lactic, maleic acid and phtalic acid or mixtures thereof.
Disclosures similar to those of the Austrian Patent 203.454, relating to the use of hydrogen peroxide containing certain organic acids at acidic conditions, can also be found in a number of other patents, cf. for instance US 2.720.441, FR 1:565.397, Japan 77.120.104. It is therefore even more surprising that a significant enhancement of the bleaching efficiency of hydrogen peroxide can be attained in the alkaline range of the pH-scale, where such an enhancement normally would not be expected. The increased bleaching efficiency of hydrogen peroxide in the presence of certain organic acids under acidic conditions can be related to the formation of peroxy acids. However, under the conditions specified in the present invention peroxy acids cannot be of any importance since the alkaline environment does not favor recations leading to such peroxy acids.
It has according to the present invention been found that the bleaching efficiency of peroxides can be improved if the bleaching process is carried out in the presence of low concentrations of one or more of the enumerated acids while maintaining the pH-value within the alkaline range 8-13, which pH-range is provided by the addition of an alkali metal hydroxide, such as sodium hydroxide or potassium hydroxide.
When using peroxide and alkali metal hydroxide for bleaching of pulp with the addition of low concentrations of the enumerated acids a considerably improved bleaching is attained as compared to bleaching carried out with peroxide and the alkali metal hydroxide without the use of said acids. The method according to the present invention allows bleaching with lower acid and peroxide concentrat ons than when using common peroxy acid methods while still obtaining the same bleaching effect .
Furthermore by using the method according to the present invention problems associated with the use of common peroxide stabilizers are avoided. Among these primarily silicates may be mentioned which when utilizing bleaching processes based on such methods in a technical scale may give rise to undesirable deposits (scaling).
Another surprising finding according to the present invention is the fact that potassium hydroxide gives a significantly higher brightness of the bleached material than does sodium hydroxide. The difference amounted to 2-8 SCAN brightness units.
The enhancement of the bleaching efficiency of hydrogen peroxide by the acids listed above, using KOH to adjust the pH-value, will now be illustrated by some examples. The experiments were carried out with unbleached mechanical pulp (pine). The chemicals (peroxide and acid) were added simul¬ taneously to a 2% suspension of the pulp in water, whereafter the pH-value was immediately adjusted to 9-10 by KOH at 60°C, 1 h stirring. After completing the treatment, the pulp was formed into laboratory sheets using standardized procedures (SCAN Cll:75). The measurement of brightness was carried out accord¬ ing to SCAN Cll:75, the brightness being expressed in ISO-units. The brightness value of the unbleached pulp was 57-60.
The invention is illustrated by means of the following examples. Example 1
A bleaching mixture containing 4% H?02, 1% acetic acid, and 1% formic acid (based on the weight of the quantity of pulp present in the system) gave after bleaching carried out as described above a brightness of 78%, the brightness gain being 18 units.
Example 2
When carrying out the bleaching operation at lower peroxide and acid concentrations, namely 1.5% H?0?, 0.75% acetic acid, and 0.75% formic acid a brightness of 72% (gain 15 units) was recorded. Again, the concentration figures are percentages of the amount of pulp used in the reaction. In all other respects, the conditions were similar to those used in Example 1.
Example 3
With a reaction mixture of 4% H_02 and 4% lactic acid a brightness value of 78% was obtained. This value was increased to 81.4 when adding a magnesium compound (0.4% Mg = 4% MgS04x7H.?0) . Reducing the peroxide and lactic acid concentra¬ tions to 1.5% resulted in a brightness reading of 72% which could be increased to 75 in the presence of 0.4% Mg (= 4% MgS04x7H20) .
With H20?/maleic acid mixtures similar results were obtained. With H^C /pntalic acid mixtures similar results were obtained.
The above results have been optimized with regard to the pH- -value of the reaction mixture, the pH-value being adjusted using KOH. As already mentioned, the use of NaOH at the same pH resulted in lower brightness values. No optimization was, how¬ ever, carried out with regard to the pulp concentrations. Using higher pulp concentrations, the brightness gain can be expected to increase by at least 6 units (cf. "The Bleaching of Pulp", L.A. Beeman and J.S. Reichert, Tappi Monograph No. 10, 210 (1953)). The efficiency of the present method thus appears to have been demonstrated with sufficient clarity. It may be mentioned that experiments where the acid was added to the pulp suspension after the addition of alkali and peroxide produced similar results.

Claims

1. A method for bleaching wood pulp without the use of peroxy acids by means of from 0.1 to 10%, based on the dry weight of the pulp, of hydrogen peroxide characterized in that an organic acid selected from the group formic acid, acetic acid, lactic acid, maleic acid and phtalic acid or any mixture thereof is added together with such an amount of an alkali hydroxide to the pulp suspension to be bleached as to give a pH-value of the suspension within the alkaline range of from 8.0 to 13.
2. A method according to claim 1, characterized in that the acid is used in an amount of from 0.25 to 10 % based on the dry weight of the pulp.
3. A method according to claim 1 or 2, characterized in that the alkali metal hydroxide used is potassium hydroxide.
4. A method according to any of the preceding claims, characterized in that the alkaline pH-range used is 9-10.
EP88901957A 1987-02-12 1988-02-12 An improved peroxide bleaching method Expired EP0348411B1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AT88901957T ATE83016T1 (en) 1987-02-12 1988-02-12 PEROXIDE BLEACHING PROCESS.

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
SE8700569A SE8700569D0 (en) 1987-02-12 1987-02-12 AN IMPROVED PEROXIDE BLEACHING METHOD
SE8700569 1987-02-12
CA000612006A CA1333650C (en) 1987-02-12 1989-09-19 Peroxide bleaching method

Publications (2)

Publication Number Publication Date
EP0348411A1 true EP0348411A1 (en) 1990-01-03
EP0348411B1 EP0348411B1 (en) 1992-12-02

Family

ID=25673050

Family Applications (1)

Application Number Title Priority Date Filing Date
EP88901957A Expired EP0348411B1 (en) 1987-02-12 1988-02-12 An improved peroxide bleaching method

Country Status (7)

Country Link
EP (1) EP0348411B1 (en)
AT (1) ATE83016T1 (en)
CA (1) CA1333650C (en)
DE (1) DE3876429T2 (en)
FI (1) FI91545C (en)
SE (1) SE8700569D0 (en)
WO (1) WO1988006202A1 (en)

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
SE505980C2 (en) * 1993-12-23 1997-10-27 Bim Kemi Ab Ways to prevent peroxide-degrading enzymes by bleaching with hydrogen peroxide
DE19516151A1 (en) * 1995-05-03 1996-11-07 Sven Siegle Process for the production of a pulp from cellulosic material, the pulp itself and its use
FI115470B (en) * 1996-02-19 2005-05-13 Kemira Oyj Process for the treatment of chemical cellulose material
FI115641B (en) * 1996-02-19 2005-06-15 Kemira Oyj Bleaching process for high yields

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
BE633420A (en) * 1962-07-16
DE2219505C3 (en) * 1972-04-21 1974-10-17 Deutsche Gold- Und Silber-Scheideanstalt Vormals Roessler, 6000 Frankfurt Chlorine-free multi-stage bleaching of cellulose

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO8806202A1 *

Also Published As

Publication number Publication date
DE3876429D1 (en) 1993-01-14
FI91545B (en) 1994-03-31
EP0348411B1 (en) 1992-12-02
SE8700569D0 (en) 1987-02-12
ATE83016T1 (en) 1992-12-15
FI893742A0 (en) 1989-08-08
WO1988006202A1 (en) 1988-08-25
DE3876429T2 (en) 1993-07-01
CA1333650C (en) 1994-12-27
FI91545C (en) 1994-07-11

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