EP0214982A1 - Verfahren zum bleichen von faserpulpe zur herstellung von papier und karton - Google Patents

Verfahren zum bleichen von faserpulpe zur herstellung von papier und karton

Info

Publication number
EP0214982A1
EP0214982A1 EP19850902705 EP85902705A EP0214982A1 EP 0214982 A1 EP0214982 A1 EP 0214982A1 EP 19850902705 EP19850902705 EP 19850902705 EP 85902705 A EP85902705 A EP 85902705A EP 0214982 A1 EP0214982 A1 EP 0214982A1
Authority
EP
European Patent Office
Prior art keywords
pulp
suspension
base
bleaching
water
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.)
Withdrawn
Application number
EP19850902705
Other languages
English (en)
French (fr)
Inventor
Karl-Evert Flinck
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.)
FLINCK KARL EVERT
Original Assignee
FLINCK KARL EVERT
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 FLINCK KARL EVERT filed Critical FLINCK KARL EVERT
Publication of EP0214982A1 publication Critical patent/EP0214982A1/de
Withdrawn legal-status Critical Current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

  • This invention relates to a method of bleaching fibre pulps, which are obtained mechanically, chemi-mechanic ⁇ ally, che i-thermomechanically or semi-chemically from wood, especially hardwood, and are used for the making of paper or paperboard.
  • the aforementioned types of pulps are bleach ⁇ ed in most cases by using hydrogen peroxide as bleaching agent.
  • the bleaching is carried out normally as follows: The pulp resulting from one of the said defibering or digesting methods preferably first is washed more or less completely, in order to remove as completely as possible soluble substances originating from the raw material or pulp or obtained at the defibration.
  • the pulp then is mixed with bleaching agents, especially hydrogen peroxide, alkali and sodium silicate, whereby the bleaching is initiated, which normally is carried out at pH 8 to 9 and at appr. 6 ⁇ °C.
  • bleaching agents especially hydrogen peroxide, alkali and sodium silicate
  • the processed susp ⁇ ension of the pulp in water then has a concentration of about 10 to 30$ by weight.
  • the bleaching requires a reaction time of some hours.
  • the pulp shall not contain large amounts of water- -soluble substances, which arose or were released at the pre-treatment.
  • the bleaching shall be carried out at a high concen ⁇ tration of the pulp in water.
  • the bleaching shall be carried out with a high per ⁇ oxide concentration.
  • the bleaching shall be carried out in two steps. First a normal bleaching operation is carried out where- after the residual chemicals and the soluble substances resulting at the bleaching are removed by a washing. In a second step bleaching is then carried out with new chemicals.
  • the present invention proposes a new bleaching method, which renders it possible to entirely eliminate the afore ⁇ said disadvantages.
  • a suspens ⁇ ion of hydrogen peroxide is produced in air or water vapour, i.e. a suspension of a liquid as disperse phase in a gas as continuous phase, which means in principle it is a mist.
  • air is preferred as continuous phase, because it is thereby possible to keep the temperature of the suspension very low until immediately before its mixing with the pulp suspension.
  • hydrogen peroxide can be brought into direct contact with the pulp, without causing the per ⁇ oxide in the first place to meet too high a base concen ⁇ tration (too high a pH value) and to be decomposed there ⁇ by. A greater proportion of the hydrogen peroxide is then available for bleaching the pulp.
  • the hydrogen peroxide can be combined in very high concentration with dry pulps and, consequently, this bleaching results in high, improved brightness degrees.
  • the base is added in the form of a suspension to the dried pulp.
  • the suspension of the base preferably is produced separately, so that peroxide and base do not meet unnecessarily early.
  • a pref ⁇ erable step further is, not to mix the suspensions of peroxide and bases with each other in air or water vapour, before they are added to the pulp suspension.
  • An improved contact and a more uniform absorption of the hydrogen peroxide by the pulp can be obtained by electro ⁇ statically charging the hydrogen peroxide suspension prior to i.ts admixture to the pulp.
  • the charge must be suitable with respect to attraction to the particles of the pulp.
  • the same step can be taken for admixing the base suspension, the particles of which are to be charged so that they have a charge opposed to the pulp particles containing hydrogen peroxide.
  • an alkali hydroxide is used as base, in order to obtain the pH most favourable for the bleaching.
  • a strong base at the high necessary concentrat ⁇ ions would cause a rapid premature decomposition of the hydrogen peroxide.
  • a carbonate, or still better a bicarb ⁇ onate, of an alkali metal, especially sodium or ammonium is used. This step can be improved still more by using a difficultly soluble or a slowly soluble substance.
  • difficultly soluble basic substances such are to be used which have a solubility lower than 0,015 g/100 g water at 20°C.
  • Such difficultly soluble substances can be regarded to be especially magnesium hydroxide, magnesium oxide or basic magnesium carbonate.
  • Magnesium carbonates and calcium-magnesium carbonates.- (dolomites) also can be used, but then the type to be used must be selected accurately, because the natural minerals in this combination often dissolve too slowly even in finest ground state.
  • the natural calcium carbonates normally are too slowly soluble for being usable at this method.
  • some qualities of chalk can be used which have a relatively very rapid dissolving rate.
  • other bases can be used which have a higher solub ⁇ ility, for example up to 0,1 g/100 g water at 20°C. These bases, however, should dissolve relatively slowly, as a matter of fact so slowly, that when 1 g of the subst ⁇ ance is intensely stirred in 100 g of water at 8 ⁇ °C during two minutes the pH value of the suspension does not exceed the value of 9,5, especially 9,0.
  • magnesium hydroxide basic magnesiu carbonates, magnesium oxide, magnesium carbonates or chalk with quick-soluble properties are suitable bases.
  • two or more of the aforementioned bases can be combined with each other.
  • a pH value of between 7,5 and 9,0, preferably a pH value between 7,8 and 8,5 is achieved.
  • the present invention is based on the supply ' of hydrogen peroxide as suspension in air or water vapour to the suspension of the pulp dried and suspended in air or water vapour. This does not imply that also the base must be added entirely or partially after the drying of the pulp.
  • the base on the contrary, can be added entire ⁇ ly or partially to the aqueous suspension of the pulp prior to its final dewatering and drying.
  • the base in order to facilitate the redefibration at the papermaking it is advantageous to add part of the base necessary for bleaching prior to the drying of the pulp.
  • basic substance enters also into the inner zones of the subsequently forming fibre aggregates.
  • the pH is increased, the re- redefibration is facilitated, and the hydrogen peroxide, which subsequently by diffusion as liquid or gas enters into the interior of the aggregates, can even there have a bleaching effect due to the higher pH value.
  • the suspensions of the reagents especially those of the hydrogen peroxide, after the drying of the pulp are added to its suspension in air or water vapour, whereby a rapid and uniform mixing with the pulp takes place.
  • the pulp suspension in the place where other substances are added flows with high turbulence. This is achieved in that the pulp suspension is passed at high speed through a pipe. During the flow through this pipe, at least the peroxide suspension is admixed.
  • the flow rate in the pipe should be at least 50 m/sec, preferably at least 150 m/sec.
  • the suspension of the base can be introduced in the same pipe, or it can be added lateron to the pulp suspension, for example together with the cooling and transport air for the pulp suspension.
  • the concentration of the pulp in suspension in the place where the peroxide suspension is added requires to be taken into regard. In a pulp suspension too concentrated, fibre flocculations or loose aggregates will form, which render a homogenous admixing of the peroxide difficult. According to the invention, it is advantageous when the pulp suspension contains at maximum 15 kg of dry pulp per cubic meter, preferably at maximum 8 kg/m and especially advantageously at maximum 5 kg/m .
  • the invention can be applied with special advantage to pulps, which were obtained with a high yield of 80 to 95% from wood, calculated on dry matter. These pulp types normally often can be redefibred only with difficulty, after they have been dried, pressed and stored.
  • the method according to the invention can also be the last step in a multi-step bleaching process.
  • the steps preceding the bleaching according to the invention can be conventional bleaching processes in aqueous phase. By means of such bleaching methods comprising two or more steps a much stronger bleaching can be obtained,
  • the wood chips was heated to 90°C, pressed and introd ⁇ uced into an alkaline sodium sulphite solution.
  • the impregnation solution had a temperature of about 50°C.
  • the chips was cooked for about 30 minutes with steam at atmospheric pressure. Thereafter it was defibred in two steps. The resulting pulp was washed in order to remove solved constituents. The pulp was then conventionally bleached, with 2% hydrog ⁇ en peroxide, 0,1$ complexing agent (DDPA), 3% sodium silicate and about 1% sodium hydroxide. The pulp was then at low concentration (about 1% ) cleaned of splint ⁇ ers and dewatered to a concentration of 5% » After a partial washing the pulp was dewatered to about 9% con ⁇ centration. At this point the method according to the invention commences. The 9% pulp suspension was intens ⁇ ively mixed with 1% finely ground chalk, calculated on the dry weight of the pulp.
  • DDPA complexing agent
  • the pulp suspension was thereafter transferred to cooling and drying air, the amount of which was about four times the weight of the pulp. In this cooling air about 0,8% by weight of magnesium oxide was suspended. This cooling and transporting air was then separated from the pulp in a cyclone. The pulp was pressed to bales and wrapped up.
  • the pulp bleached according to the invention could after storage also be redefibrated more easily, compared with normally bleached pulp.

Landscapes

  • Life Sciences & Earth Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Wood Science & Technology (AREA)
  • Paper (AREA)
EP19850902705 1984-05-15 1985-05-15 Verfahren zum bleichen von faserpulpe zur herstellung von papier und karton Withdrawn EP0214982A1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
CH2384/84 1984-05-15
CH238484 1984-05-15

Publications (1)

Publication Number Publication Date
EP0214982A1 true EP0214982A1 (de) 1987-03-25

Family

ID=4232515

Family Applications (1)

Application Number Title Priority Date Filing Date
EP19850902705 Withdrawn EP0214982A1 (de) 1984-05-15 1985-05-15 Verfahren zum bleichen von faserpulpe zur herstellung von papier und karton

Country Status (3)

Country Link
EP (1) EP0214982A1 (de)
AU (1) AU4404285A (de)
WO (1) WO1985005386A1 (de)

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE4400954B4 (de) * 1994-01-14 2007-03-01 Stefan Kürzeder Verfahren zur Helligkeitssteigerung bei der Bleiche von Holzstoffen mit Wasserstoffperoxid
DE10211292A1 (de) 2002-03-14 2003-09-25 Basf Ag Verfahren zur Herstellung von gefälltem Calciumcarbonat mit hohem Weißgrad
ES2806475T3 (es) * 2016-04-15 2021-02-17 Marinko MIKULIC Un proceso continuo para la producción de pulpa de celulosa

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2492047A (en) * 1946-03-30 1949-12-20 Du Pont Bleaching wood pulp
DE1546282A1 (de) * 1965-10-16 1969-10-02 Agricola Ind Per La Cellulosa Verfahren und Anlage zum Bleichen von Zellulose
BE681488A (de) * 1965-10-25 1966-10-31
SE333498B (de) * 1967-11-09 1971-03-15 Sunds Ab
SE324285B (de) * 1968-11-22 1970-05-25 T Norin
SE362910B (de) * 1972-06-13 1973-12-27 Defibrator Ab

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO8505386A1 *

Also Published As

Publication number Publication date
AU4404285A (en) 1985-12-13
WO1985005386A1 (en) 1985-12-05

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