AU603556B2

AU603556B2 - Process for bleaching chemical paper pulps

Info

Publication number: AU603556B2
Application number: AU64492/86A
Authority: AU
Inventors: Lucien Bourson
Original assignee: Atochem SA
Current assignee: Arkema France SA
Priority date: 1985-10-30
Filing date: 1986-10-29
Publication date: 1990-11-22
Anticipated expiration: 2006-10-29
Also published as: AU6449286A; NO864319L; JPS62141188A; PT83649A; DE3667184D1; FR2589494B1; FI864411A0; JPH0116958B2; EP0222674A1; FI864411A; EP0222674B1; FR2589494A1; DE222674T1; ES2000019A4; FI85294B; NO864319D0; PT83649B; ES2000019B3; ZA868275B; ATE48291T1

Abstract

1. Process for bleaching chemical papermaking pulps in a bleaching sequence including, in succession, a treatment of the pulp by means of chlorine and chlorine dioxide acting in a single bath, a first alkaline extraction by means of sodium hydroxide, a treatment of the pulp by means of chlorine dioxide, a second alkaline extraction by means of sodium hydroxide and again a treatment of the pulp by means of chlorine dioxide, characterized in that the pulp is subjected at the same time to the action of oxygen during the first alkaline extraction and to the action of hydrogen peroxide during the second alkaline extraction.

Description

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11 FORM 10 SPRUSON FERGUSON COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952 COMPLETE SPECIFICATION (ORIGINAL) FOR OFFICE USE:

VP

6 4"12 0 Class Int. Class Complete Specification Lodged: Accepted: Published: 00 4 o a 0 0 t 0 00 ooo 00 0000 0 0 ai 0 r a Priority: Related Art: Name of Applicant: Address of Applicant: Actual Inventor: Address for Service:

ATOCHEM

La Defense 10, 4 8 Cours Michelet, 92800 Puteaux, France LUCIEN BOURSON Spruson Ferguson, Pa gnt Attorneys, Level 33 St Martins Tower, 31 Market Street, Sydney, New South Wales, 2000, Australia for the invention entitled: Complete Specification 0l 0~ I "PROCESS FOR BLEACHING CHEMICAL PAPER PULPS" The following statement is a full description of this invention, including the best method of performing it known to us SBR/JS/0080W Abstract A process for bleaching chemical paper pulp which comprises the following successive steps: a treatment of the pulp with a solution of chlorine and a solution of chlorine dioxide; a first alkaline extraction with a solution of sodium hydroxide in the presence of oxygen; a treatment of the pulp with a solution of chlorine dioxide; a second alkaline extraction with a solution of sodium hydroxide, said solution containing 0.5 to 2% by weight relative to the oi weight of the dry pulp, in the presence of 0.1 to 0.5% by weight of t hydrogen peroxide relative to the weight of the dry pulp; and 000 t 000 a further treatment of the pulp with chlorine dioxide, the total amount of chlorine dioxide ,lsed in steps and being at most 1% by 0 0 0 o c15 weight relative to the weight of the dry pulp.

n eo oct00 o a o e0 o a o at

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-LId-~ .I U la "PROCESS FOR BLEACHING CHEMICAL PAPER PULP" The present invention relates to a process for bleaching chemical paper pulp.

The bleaching of chemical paper pulp, that is, unbleached cellulose pulp produced by cooking lignocellulose substances according to the so-called sulphite, sulphate or Kraft, sodium hydroxide or carbonate processes, is generally carried out in the industry by using chlorine or a chlorine derivative, which, like chlorine, is oxidizing in nature. Examples of such derivatives are chlorine G -i0 dioxide (C10 2 or sodium hypochlorite (NaOCI).

o 0o° However, none of these oxidizing agents on its own is capable of ensuring a satisfactory bleaching in a single 0o0 operation. It is essential to operate the bleaching process ooo0 0 0 in several distinct stages and to carry out intermediate 0 15 operations such as alkaline bath extraction.

Ott The use of non-chlorinated oxidizing agents in bleaching sequences normally using chlorinated agents has been proposed in order to reduce the quantity of chlorinated agents usually employed and the diFadvantages of their use, such as the production of polluting, corrosive Sand very strongly coloured effluents.

Thus, for example, in a bleaching sequence which typically comprises the following steps: a treatment with a solution of chlorine and chlorine dioxide; L I- r~ p i -2 a first alkaline extraction with a solution of sodium hydroxide; a treatment with a solution of chlorine dioxide; a second alkaline extraction of the same type as the first; and a second treatment with a solution of chlorine dioxide; it has been proposed to use a reaction with oxygen during the first alkaline extraction or the reaction with hydrogen peroxide during the second alkaline extraction.

The use of oxygen or the use of hydrogen peroxide in a mutually exclusive manner, makes it possible, in either €9 case, to reduce, in a practically similar way, the amount 00 of chlorinated bleaching agents usually required in order 00 15 to produce a given bleaching effect. The process is still 000 oar inadequate, however, from the cost effectiveness point of view. Additionally there is not much reduction of the disadvantages mentioned above.

The process of the present invention substantially overcomes the above difficulties without substantially causing any deterioration of the quality of the bleached pulp finally obtained.

Accordingly the present invention provides a chemical paper pulp bleaching sequence which successively includes a treatment of the pulp with chlorine and chlorine dioxide in solution acting in a single bath, a first alkaline -e i I C -3extraction with sodium hydroxide in solution, a treatment of the pulp with chlorine dioxide in solution, a second alkaline extraction with a sodium hydroxide solution, said solution containing 0.5 to 2% by weight relative to the weight of the dry pulp, and a further treatment with chlorine dioxide in solution, the pulp being subjected to the action of oxygen during the first alkaline extraction and to the action of hydrogen peroxide in an amount of 0.1 to 0.5% by weight relative to the weight of the dry pulp during the second alkaline extraction, the total amount of chlorine dioxide used being at most 1% by weight relative to the weight of the dry 0 JO0 pulp.

0 00C S"0 The process of the present invention is particularly well suited for 0 0 o the bleaching of softwood chemical paper pulps.

0000oooo 0o The amount of oxygen used during the first alkaline extraction is oo generally from 0.2% to 1% by weight relative to the weight of the dry pulp.

The treatment of the pulp with a solution of chlorine and chlorine 00-0 dioxide can be carried out in a known way, preferably in a single bath, using a quantity of total active chlorine in the form of chlorine and chlorine dioxide which is generally from 3% to 10% by weight relative to the weight of the dry pulp. The quantity of chlorine dioxide 000 0 soo 20 advantageously represents from about 10% to 70%, preferably 10% to 50%, of 0 0 9 the total active chlorine. The treatment may preferably be carried out at 000 a temperature of from 20 0 C to 50 0 C, and preferably for a period of from minutes to 60 minutes, the action of chlorine dioxide taking place simultaneously or, preferably, prior to that of 'I RA4 152 52u lo~"la'3 I I 4 chlorine and the pulp having a consistency which is most commonly from approximately 3% to The first alkaline extraction is carried out in the presence of oxygen under conditions usually employed when the extraction is carried out in the absence of oxygen, at a temperature of from approximately 50 0 C to 80 0 C, for a period which is generally from 1 hour to 2 hours, with a quantity of sodium hydroxide which is generally from to 5% by weight relative to the weight of the dry pulp, and the consistency of the pulp preferably being from 10% to The treatment of the pulp with chlorine dioxide, which follows the first alkaline extraction, involves a °o pulp having a consistency of from approximately 10% to The treatment is generally carried out for from 1 to 4 o° 15 hours at a temperature which is generally from 60 0 C to 4 The second alkaline extraction, carried out in the presence of hydrogen peroxide, is generally performed at a temperature of from approximately 70 0 C to 90 0 preferably for from 0.5 to 2 hours, using a quantity of sodium hydroxide which g-ne-ally- represents from 0.5°o to 2% by weight relative to the weight of the dry pulp. The consistency of the pulp is generally from 10% to ij 1 The treatment of the pulp with chlorine dioxide, which follows the second alkaline extraction, is usually carried out under conditions analogous to those described for the treatment with the same reagent which follows the first alkaline extraction.

I 5 The total quantity of chlorine dioxide used in the two treatments of the pulp with this reagent depends on the conditions chosen for the combined use of oxygen and of hydrogen peroxide. The quantity is generally much lower than the 1% to by weight relative to the weight of the dry pulp, which is usually required, in the absence of the combined use of oxygen and hydrogen peroxide according to the invention, to achieve the same bleaching effect as that obtained when operating according to the invention.

In the present invention, the total quantity of 04s o chlorine dioxide used preferably -does--e-s-e-e-x-d-- o0' m-e--ore prefer2bly is less than by weight relative to the o0 0 weight of the dry pulp.

S 15 The Examples below either illustrate the invention or 0 o0 are given by way of comparison.

The following symbols have been used for denoting o a4 the different successive stages in the bleaching sequence: C/D: treatment of the pulp with chlorine dioxide alo: 20 and with chlorine in a single bath, the action of chlorine dioxide preceding that of chlorine.

oa" o E alkaline extraction with a solution of sodium 00 0 Co hydroxide.

E

1

E

1 alkaline extraction with a solution of sodium hydroxide in the presence of oxygen.

DI: treatment of the pulp with chlorine dioxide,

_~I

6 which follows either E or E /0.

E2: same meaning as E 1 4-

E

2

E

2 alkaline extraction with a solution of sodium hydroxide in the presence of hydrogen peroxide.

D

2 same meaning as D1, D 2 being carried out after either E 2 or E,/P.

In all Examples, the quantities of reagents are expressed in percent by weight relative to the weight of dry pulp, except where indicated otherwise.

The condition of the pulp is defined by its degree of polymerization (dp) and by its whiteness expressed in 0 4 o degrees ELREPHO (OER) as can commonly be determined by a 0 o person skilled in the art by means of an ELREPHO spectrophometer made by CARL ZEISS.

EXAMPLE 1 An unbleached softwood KRAFT pulp having a KAPPA index, which is a measure of the lignin content of the o pulp, of 30 and a whiteness of 26.6 0 ER, is subjected to C/D under the following conditions: total active chlorine: 5.7% 4 t t e.

active chlorine from C102: 14% of the total active o chlorine.

O action of C102: temperature 250C period 0.25 hour action of C12 temperature 40 0

C

period 0.5 hour A" 7 pulp, consistency: 3.2% The alkaline extraction E 1 /0 which follows is carried out under the following conditions? NaOH: 3.9% 02: temperature: 60°C, (the pressure being 2 bar (2 x 105 Pa) period: 1.5 hours pulp, consistency:

D

1 is then carried out as follows: ClO2: 0.3% o" temperature: 70 0

C

Speriod: 2.5 hours pulp, consistency:

E

2 /P as follows: NaOH 0.75% H202: 0.20% temperature: BO°C period 1.5 hours pulp, consistency: and finally, D 2 in the following way: C102:0.2% temperature: 80 0

C

period: 2.5 hours pulp, consistency: I-'i L

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^r -8- The bleached pulp which finally results from this bleaching sequence has a whiteness of 90.10 ER.

For the purpose of comparison, the same sequence is carried out omitting the use of oxygen and hydrogen peroxide.

A whiteness of 88.40 ER is obtained only when, in comparison with the process according to the invention, a quantity of C10 2 \hich is 4 times greater during D 1 and 3 times greater during D02 is employed.

Again Tr the purpose of comparison, when, compared with the process of the invention, the use of either oxygen o" or hydrogen peroxide is omitted, a whiteness of 890 ER is obtained when at least twice as much ClO 2 is used during o D and D 2 than is required when operating according to the invention.

Finally, the use of the same quantities of C10 2 in D

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and in D 2 as is used in the process of the present invention L leads to a much lower whiteness of the pulp obtained when the oxygen and hydrogen peroxide treatments are omitted.

S,,4 1 Thus, if the quantities of C10 2 mentioned in the S" 20 process of the invention described at the beginning of aD04 this Example are used in D 1 and D2, but the use of hydrogen 00 4 a peroxide is omitted, the whiteness of the pulp finally 0 00 obtained is only 84.90 ER.

The process carried out according to the invention gives a bleached pulp the characteristics of which, especially the dp, are at least equal to those of bleached pulps obtained by known processes, in spite of the fact I 1- I- d

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9 that the opposite could perhaps have been expected.

EXAMPLE 2 The process of Example 1 is carried out until D1, but, from D 1 onwards, in a way which differs from that of Example 1 in that the quantities of C10 2 employed in D

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and D 2 are and 0.4'1 respectively and in that the quantity of hydrogen peroxiue in E /P is only 0.1%o. The whiteness of the pulp thereby bleached is nearly 88.50 ER.

This Example illustrates the fact that even when only a very small quantity of hydrogen peroxide is employed, the enhancing effect of the combined actions of Oat o oxygen and hydrogen peroxide according to the invention is retained.

a a t t t t 0

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Claims

1. A process for bleaching chemical paper pulp which comprises the following successive steps: a treatment of the pulp with a solution of chlorine and a solution of chlorine dioxide; a first alkaline extraction with a solution of sodium hydroxide in the presence of oxygen; a treatment of the pulp with a solution of chlorine dioxide; a second alkaline extraction with a solution of sodium 0o d hydroxide, said solution containing 0.5 to 2% by weight relative to the weight of the dry pulp, in the presence of 0.1 to 0.5% by weight of 0 hydrogen peroxide relative to the weight of the dry pulp; and 00oooo oo0 a further treatment of the pulp with chlorine dioxide, the total amount of chlorine dioxide used in steps and being at most 1% by weight relative to the weight of the dry pulp.

2. A process according to claim 1, wherein the pulp is a softwood pulp.

3. A process according to claim 1 or 2, wherein the quantity of 0 oxygen employed in step is from 0.2% to 1% by weight relative to the 000 oa weight of the dry pulp.

4. A process according to any one of claims 1 to 3, wherein step is carried out at a temperature of from 50°C to 80°C using from 2% to sodium hydroxide by weight relative to the weight of the dry pulp. A process according to any one of claims 1 to 4, wherein the o consistency of the pulp in step is from 10% to <t 6. A process according to any one of claims 1 to 5 wherein step (d) is carried out at a temperature of from 70°C to 90 0 C using from 0.5% to 2% sodium hydroxide by weight relative to the weight of the dry pulp.

7. A process according to any one of claims 1 to 6, wherein the consistency of the pulp during step is from 10% to

8. A process according to any one of claims 1 to 7, wherein the treatment of the pulp In step is carried out at a temperature of from 0 C to 50°C, the quantity of total active chlorine in the form of chlorine and of chlorine dioxide being from 3% to 10% by weight relative to the weight of the dry pulp.

9. A process according to claim 8, wherein the chlorine dioxide represents 10% to 70% of the total active chlorine. TM 152u I 11 A process according to claim 9 wherein the chlorine dioxide represents 10% to 50% of the total active chlorine.

11. A process according to any one of claims 1 to 10 wherein the consistency of the pulp in step is from 3% to

12. A process according to any one of claims 1 to 11 wherein in step the pulp is first treated with chlorine dioxide and subsequently treated with chlorine.

13. A process according to any one of claims I to 12 wherein steps and are each carried out at a temperature of from 60°C to oo o 14. A process according to any one of claims 1 to 13 wherein the treatment with chlorine dioxide in steps and involves a pulp having 00 a consistency of from 10% to A process according to any one of claims 1 to 14 wherein the 3 o° total amount of chlorine dioxide used in steps and totals at most Soo 0.5% by weight relative to the weight of the dry pulp.

16. A process according to claim 1 substantially as hereinbefore described with reference to any one of the Examples.

17. A bleached chemical paper pulp when produced by a process o"0, according to any one of the preceding claims. ooo cooo DATED this TNENTY-SECOND day of AUGUST 1990 o°o00. Atochem 00° t Patent Attorneys for the Applicant SPRUSON FERGUSON t T TMS CT1N 52u