AU641640B2 - Bleaching of lignocellulosic material with dioxiranes - Google Patents

Description

OPI DATE 03/09/91 AOJP DATE 10/10/91 APPLN. ID 51686 PCT NUMBER PCT/CA90/00052 )N TREATY (PCT) INTER (51) International Patent Classification 5 (11) International Publication Number: WO 91/12369 D21C 9/16, 9/14 Al (43) Internatiroal Publication Date: 22 August 1991 (22.08.91) (21) International Application Number: PCT/CA90/00052 Published (22) International Filing Date: 16 February 1990 (16.02.90) With international search report.

(71) Applicant (for all designated States except US): PULP AND PAPER RESEARCH INSTITUTE OF CANADA [CA/ CA]; 570 St. Johns Boulevard, Pointe Claire, Quebec H9R 3J9 641640 (72) Inventor; and Inventor/Applicant (for US only) LEE, Chung-Li 3333 E. 43rd Avenue, Vancouver, British Columbia 3A2 (CA).

(74)Agent: FETHERSTONHAUGH CO.; Suite 456, 409 Granville Street, Vancouver, British Columbia V6C

(CA).

(81) Designated States: AT, AT (European patent), AU, BB, BE (European patent), BF (OAPI patent), BG, BJ (OAPI patent), BR, CA, CF (OAPI patent), CG (OAPI patent), CH, CH (European patent), CM (OAPI patent), DE*, DE (European patent)*, DK, DK (European patult), ES, ES (European patent), Fl, FR (European patent), GA (OAPI patent), GB, GB (European patent), HU, IT (European patent), JP, KP, KR, LK, LU, LU (European patent), MC, MG, ML (OAPI patent), MR (OAPI patent), MW, NL, NL (European patent), NO, RO, SD, SE, SE (European patent), SN (OAPI patent), SU, TD (OAPI patent), TG (OAPI patent), US.

(54)Title: BLEACHING OF LIGNOCELLULOSIC MATERIAL WITH DIOXIRANES (57) Abstract A process of bleaching a chemical pulp with a dioxirane produces a pulp of good quality and reduces environmental concerns in so doing. A chemical pulp is contacted with a dioxirane, and either with or without known bleaching agc:ts, in combination or sequence.

See back of page WO 91/12369 PCT/CA90/00052

I

BLEACHING OF LIGNOCELLULOSIC MATERIAL WITH DIOXIRANES This invention relates to a process for bleaching a chemical pulp.

In the manufacture of paper, wood is converted into a pulp, usually by chemical means, and then spread on a wire to be dewatered to form the paper.

Kraft pulping is the most widely practiced form of chemical pulping in North America. The pulp is relatively dark in colour and to produce a commercially acceptable paper, it is generally bleached before being formed into paper.

A variety of bleaching agents is used. They include chlorine, chlorine dioxide, hypochlorites, hydrogen peroxide and oxygen. Typically, more than one of these chemicals is required and they are used singly or in admixture in sequence. In the art the various bleaching compounds, are designated by letter; chlorine is C, chlorine dioxide is D, caustic extraction is E, hypochlorite is H, hydrogen peroxide is P and oxygen is 0.

The above compounds include chlorine and certain chlorine containing compounds and there are concerns about the use of chlorine and chlorine compounds in bleaching pulp. Chlorine and chlorine containing compounds react with pulp constituents mainly lignin, fatty acids and resin acids to produce chlorinated organic compounds.

Some of these chlorinated organic compounds are of concern environmentally and some major pulp producing countries have restricted the amount that can be discharged from the bleaching process into waterways. It is reasonable to assume that most countries will introduce legislation restricting the discharge of such compounds.

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WO 91/X12369 PCTCA90/0005 2 2 The elimination of elemental chlorine and its related compounds in the bleaching process would eliminate the production of chlorinated organic compounds in the effluent but efforts along this line have not been wholly effective.

The use of elemental chlorine and its related compounds in bleaching may lead to the formation of tetrachlorinated dioxins (TCDD) and furans (TCDF) which are contained in the pulp and in the pulp mill effluent.

However, the formation of these two toxins can be eliminated by reducing the amount of chlorine applied.

Unfortunately, this is difficult to do with existing technology without sacrificing some pulp quality or introducing further problems into the pulping process.

Oxygen delignification is a process of treating pulp under oxygen pressure, about 100 psig, at elevated temperature, about C0' to 120'C, and for extended periods of time, about 30 to 90 minutes. This oxygen delignification process tends to produce weak pulp if delignification is extended too far i.e. down to about Kappa number. In this regard the Kappa number of a pulp is a measure of the bleachability of the pulp. It is a number indicating the number of milliliters of 0.1 Normal potassium permanganate solution that can be consumed under standard conditions by one gram of pulp (oven dried basis) corrected to 50% consumption of permanganate.

United States Patent 4,439,271 to 0. Samuelson discloses a process using nitrogen dioxide pretreatment before oxygen delignification. The process retards the depolymerization of cellulose during oxygen bleaching.

However, the emission of nitrogen-containing compounds from the bleaching effluent may pose another problem and these nitrogen compounds cannot be recovered by existing kraft pulping chemical recovery systems.

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WO 91/12369 PCT/CA90/00052 3 U.S. Patent 4,404,061 to J.J. Cael discloses that pulps produced from a standard alkaline pulping process can be bleached with monoperoxysulphate to produce papermaking pulps and bleached pulps. Also, U.S. Patent 4,756,800 to E.L. Springer discloses a method of producing salts of monoperoxysulphuric acid and simultaneously bleaching pulp. Neither patent describes the strength properties of the fully bleached pulps.

There is a need for a bleaching process that produces pulp of good quality and which reduces environmental concerns in so doing.

The dioxiranes are known compounds of the general structural formula: 0---0 RI R2 in which R 1 and R 2 may be aliphatic or aromatic groups and may be linked to form cyclic compounds. The dioxirane compounds and their preparation are described, for example, in the Journal of Organic :hemistry, 50 20847- 20853 (1985) by R.W. Murray and R. Jeyaraman.

The present invention is a process for the bleaching of chemical pulps without use of elemental chlorine or by using elemental chlorine at a lower level than in the prior art, thus avoiding the production of the toxins TCDD and TCDF.

Accordingly, in its broadest aspect, the present invention is a process of bleaching a chemical pulp that comprises contacting the chemical pulp with a dioxirane.

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WO 91/12369 PCT/CA90/00052 -4 The dioxirane may be used with known bleaching agents either in combination or in sequence.

The pulp is desirably one having a kappa number in the range of 15 to 60 if derived from a softwood species and 5 to 25 if derived from a hardwood specieso The dioxirane is contacted with the pulp preferably at a temperature in the range of about 5' to/5O'C for a time up to about 90 minutes. Preferably the diox.rane is used in amount sufficient to provide an active oxygen charge, i.e.

one active oxygen atom per dioxirane molecule, of from 0.2 to 1.0% based on the oven-dried pulp. The dioxirane has the structure: 0--0 o o where RI and R 2 which may be the same or different, is each an aliphatic or aromatic group and may be linked together to form a ring. One dioxirane compound that has proved useful is dimethyMioxirane but any dioxirane compound is appropriate, for example, those compounds where R 1 and R 2 are each alkyl groups with 1 to 4 carbon atoms.

If a subsequent bleaching step is used, subsequent that is to the dioxirane treatment then, when the dioxirane-treated pulp has a residual lignin of less than Kappa number, that subsequent bleaching of the pulp may be carried out by chlorine dioxide alone or by the sequence chlorine dioxide, caustic extraction, chlorine dioxide (DED1: When the bleaching is carried out using the DED sequence the sequence may be set out as DIED 2 Chlorine dioxide in the D 1 stage is used in the range SUBSTITUTE SHEET WO 91/12369 PCT/CA9000052 5 to preferably about caustic in the E stage is in the range 0.2 to preferably about and chlorine dioxide in the D 2 stage is in the range 0.2 to 0.7%, preferably about All the percentages are expressed as weight of oven-dried pulp. If chlorine dioxide alone is used, then it is in the range of 0.5 to 1% by weight of the oven-dried pulp, preferably about 0.8% of the ovendried puip.

When the dioxirane-treated pulp has a residual lignin content corresponding to a Kappa number greater than the subsequent bleaching may be carried out using the sequence: chlorine; caustic extraction; chlorine dioxide; caustic extraction; chlorine dioxide (CEDED). In this sequence, expressing the sequence as CE 1

DIE

2

D

2 a substantially reduced amount of chlorine charge is used in stage C, in stage E 1 the caustic charge is 60% of that in the C stage, in stage D 1 0.5 to 1.2% chlorine dioxide charge is used, in stage E 2 the caustic charge is 50% of that used in D 1 stage and in stage D 2 0.25 to 0.6% chlorine dioxide charge is used. The percentages are based on the weight of oven-dried pulp. The chlorine used in the C stage is generally applied in combination with varying amounts of chlorine dioxide.

The invention is illustrated in the examples, which are included for purposes of illustration not limitation.

Example 1 Aspen pulp (50g oven-dried weight), produced by the kraft process to a Kappa number of 16.4, at 39% pulp consistency, was treated with the dimethyldioxirane (DMD) solution in acetone (280mL, 4.59g/L concentration, i.e.

0.55% active oxygen by weight on oven-dried pulp) at for one hour. The dimethyldioxirane-treated pulp was then bleached with chlorine dioxide by weight on ovendried pulp) at 70*C for three hours.

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W 91/12369 PCT/CA90/00052 6 A second sample of the same aspen kraft pulp (100g oven-dried weight) was delignified by molecular oxygen at 10.7% pulp consistency using sodium hydroxide (41 by weight on oven-dried pulp), magnesium sulphate by weight on oven-dried pulp), molecular oxygen (100 psig) at 115°C for one and half hours. This molecular-oxygendelignified pulp was then bleached with elemental chlorine available chlorine by weight on oven-dried pulp) at 20'C for one hour at 3% pulp consistency, extracted with sodium hydroxide by weight on ovendried pulp) at 74'C for two hours at 12% pulp consistency, and further delignified with chlorine dioxide by weight on oven-dried pulp) at 74'C for three hours at 6% pulp consistency. This bleaching sequence will be referred to as OCED.

A third sample of the same aspen kraft pulp oven-dried weight).was also bleached by a conventional process using a CED sequence. Elemental chlorine bleaching was carried out at 3% pulp consistency and for one hour using 3.3% available chlorine charge on oven-dried pulp, extraction at 74*C for two hours using sodium hydroxide by weight on oven-dried pulp) at 12% pulp consistency, and chlorine dioxide by weight on oven-dried pulp) delignification at 74'C for three hours at 6% pulp consistency.

The results, shown in Table 1, illustrate that aspen kraft pulp treated with DMD to a level of delignification has better mechanical properties than that treated with molecular oxygen to a level of 67% delignification. This fully bleached pulp at 86.8% Elrepho, which was DMD-treated, has similar zero-span tensile strength to that of a pulp, at 89.9% Elrepho, bleached by a conventional CED bleaching process.

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WO 91/12369 WO 9112369PCr/CA90/ 00052 -7 TABLE 1 PhiysicalI arnd cptical prcperties of aspen kraft ip blea&-te with dmiethyldioxi-rane or rtolecular oxygen or by a cxoiventicoa1 bleaching prccess.

Palp Kappa DeTgre of Narrber Delig. M% zero Span Tensile (kn) Elrq*0 Brightnes R%) 'Unleaced

EMD-D

Bleahe 0 2 -Delig.

OM)zJ 16.4 16.3 17.0 17.4 10.6 40.6 59.4 86.8 70.7 91.5 89.9 10.0

CED

Be-bd 18.4 SUBSTITUTE

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WO 91/12369 PCT/CA90/00052 8 In these Examples Elrepho Brightness was measured with a Technobrite (trade mark) Micro TB-1C apparatus at 457 nm. The standard test is set out in TAPPI T-452 om- 87 and CPPA E.1.

Zero span tensile strength was measured according to TAPPI T231 cm-85 using Pulmac Instruments' The Troubleshooter (trade mark) zero span tester.

Example 2 A fourth sample of aspen pulp (50g oven-dried weight), produced by the kraft process to a Kappa number 16.4, at 39% pulp consistency, was treated with DMD solution in acetone (170 mL, 4.44g/L concentration, i.e.

0.33% active oxygen by weight on oven-dried pulp) and mL of acetone at 25*C for three hours. This DMD treated pulp was filtered and washed with a large amount of distilled water. The resulting pulp was then further delignified with chlorine dioxide by weight on oven-dried pulp) at 74'C for three hours at 6% pulp consistency, extracted with sodium hydroxide (0.72% by weight on oven-dried pulp) at 10% pulp consistency and 74'C for two hours and bleached by another chlorine dioxide stage by weight on oven-dried pulp) at 6% pulp consistency and 74*C for three hours.

A fifth sample of the same aspen kraft pulp (100g oven-dried weight) was delignified by molecular oxygen at 12% pulp consistency using sodium hydroxide by weight on oven-dried pulp), magnesium sulphate by weight on oven-dried pulp), and molecular oxygen (100 psig) at 110'C for one and a half hours. This molecularoxygen-delignified aspen pulp was further bleached with elemental chlorine available chlorine by weight on oven-dried pulp) at 20'C for one hour at 3% pulp consistency, extracted with sodium hydroxide by SUBSTITUTE SHEET WO 91/12369 PCT/CA90/00052 9 weight on oven-dried pulp) at 12% pulp consistency and 74"C for two hours, and bleached with chlorine dioxide by weight on oven-dried pulp) at 6% pulp consistency and 74'C for three hours.

In this particular example, the aspen kraft pulp was delignified to the same extent by either the DMD bleaching agent or molecular oxygen. Results, shown in Table 2, illustrate that the fully bleached aspen pulp produced from the DMD treatment followed by DED bleaching without elemental chlorine has better zero span tensile strength than that produced by molecular oxygen delignification followed by CED bleaching with 2% available chlorine charge on oven-dried pulp at the elemental chlorine stage. On the other hand the DMDtreated pulp yields a fully bleached pulp with similar zero span tensile strength to that produced by a conventional process involving the use of elemental chlorine for bleaching.

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WO 91/12-169 PCT/CA9O/00052 s- 10 TAE[E 2 Zero spn deligriified strengths Sulps andi and~ viscosities of £t'D-treated, nolecular-oxygenthose produ:xed by a oniventionail procss.

Aspen egree of Pulp Nxber Delig. M% Zero-Span Tensile (kn) Elr~j Brightr~ss M% Unbleached3 16.4 Treated 6.0 Bleached Bleached 16.3 15 0 15.9 12.7 40.6 54.0 91.4 66.7 91.*0 89.9 12.6 18.4 SCUBSrTITUTE

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WO 91/12369 PCT/CA90/00052 11 Example 3 A sixth sample of aspen pulp (50g oven-dried weight), produced by the kraft process to a Kappa number of 16.4, at 35% pulp consistency, was treated with DMD solution in acetone (643 mL, 2.0g/L concentration, i.e.

0.55% active oxygen by weight on oven-dried pulp) at for one hour. The resulting pulp was then washed thoroughly with a large quantity of deionized wat:er.

A seventh sample of the same aspen kraft pulp (100g oven-dried weight) was delignified by molecular oxygen at 12% pulp consistency using sodium hydroxide by t.eight on oven-dried pulp), magnesium sulphate by weight on oven-dried pulp), molecular oxygen (100 psig) at 115*C for one and a half hours. The resulting oxygendelignified pulp was thoroughly washed with a large amount of deionized water.

The results, shown in Table 3, illustrate that the rMD- treated pulp has a better yield than that bleached by molecular oxygen to the same degree of delignification. This illustrates that DMD has better selectivity toward lignin than does molecular oxygen.

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WVO 91/12369 PCT/CA9O/00052 -12 IIBE 3 Pup yields after aM) treatmen-t andi oxye deliT~ification.

Aspet Pulp egree of Delig. Yield Unbleached Pulp UnbeiA-i 16.4 98.0 92.7 02-Deliguf led 5.4 SUB3STITUTE

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WO 91/12369 PCT/CA90/00052 13 Example 4 Spruce pulp (50g oven-dried weight), produced by the kraft process to a Kappa number of 32, at 37% pulp consistency, was treated with a solution of DMD in acetone (330 mL, 4.6g/L concentration, 0.65% active oxygen by weight on oven-dried pulp) at 25'C for half an hour. The DMD-treated pulp was further bleached by a CED sequence.

Elemental chlorine bleaching was carried out at a 3% pulp consistency and 20°C for one hour using 2.8% available chlorine by weight on oven-dried pulp, extraction at 74°C for two hours using sodium hydroxide by weight on oven-dried pulp) at 12% pulp consistency, and chlorine dioxide by weight on oven-dried pulp) delignification at 6% pulp consistency and 74 C for three hours.

A second sample of the same spruce kraft pulp oven-dried weight) was also bleached by a conventional process using CED sequence. Bleaching with elemental chlorine was carried out at a 3% pulp consistency and for one hour using 6.4% available chlorine on oven-dried pulp, extraction at 12% pulp consistency and 74'C for two hours using sodium hydroxide by weight on oven-dried pulp), and chloride dioxide by weight on oven-dried pulp) bleaching at 6% pulp consistency and 74'C for three hours.

Results, shown in Table 4, illustrate that the DMDtreated pulp can be bleached to the same brightness as that bleached by a conventional process. The former uses a si.gnificantly reduced amount of elemental chlorine compared with that required by the conventional process.

The zero span tensile strengths and viscosity of the pulps bleached by both processes are similar.

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WO 91/12369 PCT/CAk9O/OO352 14 TABLE 4 PhYsical and3 optical Properties of sPruce kraft palps bleacF i with DID or by a conventionial process.

Spn- Kappa Degree of Pulp NxLrbe.r Delig. M% zero spn Tensile (kin) Vissmsity Elrpl- Unblead-ke Tieated nMD-CED Blewl-ze Bleached 32.0 19.4 25. 0 32.7 18.8 18.8 18.3 23.*0 18.3 25.*0 40.2 82.5 82.3 19.1 SUBSTITUTE

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WO 91/1369 PCT/CA90/00052 15 Thus, the present invention provides a process for treating pulp that can be subsequently fully bleached to Elrepho, either without or with only small amounts of elemental chlorine. The DMD-treated pulps that have a residual lignin content corresponding to 5 Kappa number or less have pulp strengths equivalent to those of the untreated pulps. The fully-bleached pulps produced by the process of the invention have strength properties similar to those produced by conventional bleaching processes using high elemental chlorine charge.

The bleaching of chemical pulps with the dioxirane compounds can be modified for a range of bleaching conditions, bleaching sequences and combinations with molecular oxygen and other bleaching agents, not specifically exemplified above, for example, hydrogen peroxide, oxygen and monoperoxysulphate. The treatment with dioxirane can also be combined with oxygen delignification, being placed before or after the oxygen treatment. The use of two oxygen containing compounds can have the virtue of eliminating a wash step needed between stages of a sequence when chlorine and compounds of chlorine are used.

The pulps used in this invention can be kraft, sulphite, soda, or other types of chemical pulps from hardwood and softwood species. The invention extends to chemical pulps and this term is intended to extend to pulps produced by the treatment of wood species with organic solvents to separate the wood components.

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Claims (21)

1. A process of bleaching a chemical pulp that comprises contacting the chemical pulp with a dioxirane.

2. A process as claimed in claim 1 in which the chemical pulp has a Kappa number in the range 15 to 60 if derived from a softwood species and 5 to 25 if derived from a hardwood species.

3. A process as clained in claim 1 in which the dioxirane is contacted with the pulp at a temperature in the range about 5' to about 50"C for a time up to about 90 minutes.

4. A process as claimed in claim 1 in which the dioxirane is used in amount sufficient to provide an active oxygen charge of from 0.2 to 1.0% based on the oven-dried pulp.

A process as claimed in claim 1 including, when the dioxirane-treated pulp has a residual lignin corresponding to less than 10 Kappa units, bleaching the pulp by chlorine dioxide or by the sequence chlorine dioxide, caustic extraction, chlorine dioxide (DED).

6. A process as claimed in claim 5 in which the bleaching is carried out using a D 1 E D 2 sequence using chlorine dioxide in the D 1 stage in the range to caustic in the E stage in the range 0.2 to 0.7% and chlorine dioxide in the D 2 stage 0.2 to all percentages being on the weight of the oven-dried pulp. SUBSTITUTE SHEET WO 91/12369 PC/CA90/00052 17

7. A process as claimed in claim 6 in which the chlorine dioxide in stage D 1 is about the caustic in the E stage is about 0.4% and the chlorine dioxide in the D 2 stage is about 0.4%.

8. A process as claimed in claim 5 in which the bleaching is carried out with chlorine dioxide in the range 0.5 to 1% by weight of the oven-dried pulp.

9. A process as claimed in claim 8 in which the chlorine dioxide is about 0.8% of the oven-dried pulp.

10. A process as claimed in claim 1 in which, when the dioxirane-treated pulp has a residual lignin content corresponding to a Kappa number exceeding bleaching is carried out using the sequence chlorine, caustic extraction, chlorine dioxide, caustic extraction, chlorine dioxide (CEDED).

11. A process as claimed in claim 10 in which the sequence is CE 1 DIE 2 D 2 using in stage C an amount of chlorine appropriate for the Kappa number of the pulp after contact with the dioxirane, in stage E 1 the caustic charge is 60% of the charge used in the C stage, in stage D 1 0.5 to 1.2% chlorine dioxide charge is used, in stage E 2 the caustic charge is of that used in the D 1 stage and in stage D 2 0.25 to 0.6% chlorine dioxide charge is used. the percentages being based on the oven-dried pulp.

12. A process as claimed in claim 1 in which the dioxirane has the structure 0-0 SRSTITUTE SHEET WO 91/12369 PCT/CA9O/00052 18 where R1 and R2, which may be the same or different, is each an aliphatic or aromatic group and may be linked together to form a ring.

13. A process as claimed in claim 12 in which R 1 and R 2 are each aromatic groups.

14. A process as claimed in claim 12 in which R 1 and R 2 are each aliphatic groups.

A process as claimed in claim 14 in which the aliphatic groups are alkyl groups with 1 to 4 carbon atoms.

16. A process as claimed in claim 12 in which the dioxirane is dimethyldioxirane.

17. A process for bleaching chemical pulp comprises: contacting the pulp with a dioxirane having the formula in which R 1 and R 2 is each an aliphatic or aromatic group and may be linked together to form a ring at an active oxygen charge of 0.2 to 1% by weight of the oven-dried pulp; bleaching the resulting pulp using the sequence chlorine dioxide or chlorine dioxide, caustic extraction, chlorine divide (DED) when the pulp has SL'STITUTE SHEET -19- extraction, chlorine dioxide (DED) when the pulp has a residual content corresponding to a Kappa number below when the pulp has a residual lignin content corresponding to a Kappa number greater than 10 bleaching the pulp with the sequence chlorine, caustic extraction, chlorine dioxide, caustic extraction, chlorine dioxide (CEDED) using a significantly reduced amount of elemental chlorine charge.

18. A process as claimed in claim 17 in which the dioxirane is dimethyldioxirane.

19. A process as claimed in claim 17 in which the dioxirane is contacted with the pulp at a temperature in the range of about 5 0 to about 50 *C for a time up to about minutes.

20. A process of bleaching a chemical pulp substantially as herein described with reference to the Examples, excluding the comparative Examples. DATED this 27th day of July, 1993. PULP AND PAPER RESEARCH INSTITUTE OF CANADA By its Patent Attorneys DAVIES COLLISON CAVE *e 93O2,q:Noper\bjc,516890.083,19 INTERNATIONAL SEARCH REPORT International Application NO PCT/ CA 90 /00052 L. CLASS7"ICATION OF SUBJECT MATTER (it several eiassificstion symbols apply, Indicate all)I According to international Patent Classification (IPCI or to both National classification and IPC IPC D l C 9/16, D

21 C 9/14 Ii. FIELDS SEARC14ED Minimum Documentation Starched 7 Classification System IClassification IPC 5 I D 21 C, D 06 L Documentation Searched other than Minimum Documnentation to the Extent that such Documevntsa sr e im. the Fields Searched s Ill. DOCUMENTS CONSIDEREDTOMERELEVANT' Category Citation of Document, 11 with Indication, where apcroariate, of the relevant passages It Relevant to Claim No. 13 A Abstracts Bulletin of the Institute of 1,12-18 Paper Chemistry, volume 39, no. April 1969, (Appleton, US), K. Kratzl et "Pulp bleaching experiments with acetone pero~cides", see page 863 Papier 22, no. 10A, pages 686-693 (Oct. 1968) see the abstract A Abstracts Bulletin of the Institute of 2,5-11 Paper Ch~emistry, volume 57, no. 11, May 1987, (Appleton, US), K. Baczynska et al.: "iEffect of oxygen-alkali extraction on the reduction of pollution load on effluents from kraft pulp bleach plant", see page 1557 Przeglad Papier. 42, no. 4, pages 120-124 (April 1986 see the abstract Special categories of cited documenta: 16 IT" ltetr document Published &lter the international filing date A doumet dfinng he eneal eateof he rt hic isnotor priority date and not In conflict with the application but ""dcns ilde in t he gealsae of paticle rlan ar whc sntCited to understand the principle or theory underlying the earlier document but Published on or after the International "X document of particular relevance; the claimed invenition filing date cannot be considered novel or cannot be considered to document which may throw doubts an priority cimir(s) or Involve an inventive step which Is cam to *stabiieh the publication dcile of another document of oarticular relevanc*;' the claimed Invention citation or other special reaaon (as specified) cannot be contitdored to Involve an Inventive step when the document rofoering to an oral disclosure. ties, exhibition or document lis combtied with one, or more other such docu- Othmir meant manta. such combination being obvious to a person skilled document Published prior to the International fI'ling dale ilut In the art. later than the priority date Claimed IV document member oi the same patent family IV. CIER. FICATION Date of the Actual Completion of the International Search Date of Mailing of this International Search Repart October 19901 07, 11i.90 Internatiomal Searching Authority ~Signature fotrthWoaized.Offtcr 4e EUROPEAN PATENT OFFICE Form PRCTIM)A210 (second sheet) (Jarauar 111116)