AU653467B2

AU653467B2 - Bleaching of sulphate pulp

Info

Publication number: AU653467B2
Application number: AU34125/93A
Authority: AU
Inventors: Marten Dahl; Lars-Ake Lindstrom; Solveig Norden; Lars Sjodin
Original assignee: Sunds Defibrator Industries AB
Current assignee: Valmet AB
Priority date: 1992-01-21
Filing date: 1993-01-12
Publication date: 1994-09-29
Anticipated expiration: 2013-01-12
Also published as: DE69309893T2; AU3412593A; FI943431A; SE9200152D0; EP0621915B1; ES2102008T3; BR9305761A; NO942718D0; SE469842C; NO942718L; SE469842B; WO1993014262A1; EP0621915A1; CA2124088A1; ZA93317B; DE69309893D1; SE9200152L; ATE151826T1; JPH07503042A; NZ246713A

Abstract

A method of bleaching sulphate pulp without using chlorine-containing bleaching agents. The sulphate pulp is oxygen delignified and can possibly also be ozone delignified to a kappa number below 9.5. Thereafter a pretreatment with complexing agent is carried out for 1-60 minutes, at which the pulp consistency is 1-15 %, the temperature 70-110 DEG C and pH 5-7. The pulp thus pretreated is washed and dewatered to a consistency of 18-40 %. Thereafter peroxide bleaching in alkaline environment takes place in the presence of silicate or an organic complexing agent of the type phosphonic or carboxylic acid.

Description

ONI DAIL 03/08/93 APPLN. I0 34125/93 111111 iiII111111li AOJP DATE 14/10/93 PCT NUMBER PCT/SE93/0001 21111111li Ili 111li AU9334 125 (51) international Patent Classification D2 IC 9/16 TY (PCIT) (11) International Publication Number: WO 93/14262 At, (43) International PtiblIcatlon Date:. 22 July 1993 (212.07.93) (21) International Application Number: (22) International Filing Date: Priority data: 9200152-8 21lJanua PCT/SE93/00012 2 January 1993 (12.01.93) ry 1992 (21.01.92) SE (71) Applicant (for all designated States except US): SUNDS DE- FIB RATOR INDUSTRIES AKTIEBOLAG [SE/SE]; S-851 94 Sundsvall (SE).

(72) Inventors; and Inventors/Applicants (for US only) LINDSTROM, Lars- Ake [SE/SE]; Skonertvilgen 18, S-860 24 AlnL6 (SE).

SJODIN, Lars [SE/SE]; Sp~invIdgen 5, 5-852 41 Sundsvall NORDEN, Solveig [SE/SE]; Odalvilgen 14, S- 860 20 Njurunda DAHL, MArten [SE/SE]; Ludvigsbergsvflgen 30, S-852 34 Sundsvall (SE).

(74) Agent: SUNDQVIST, Hans;, Sunds Defibrator Industries Aktiebolag, Strand bergsgatan 61, S-112 51 Stockholm

(SE).

(81) Designated States: AU, BR, CA, Fl, JP, NO, NZ, US, European patent (AT, BE, CH, DE, DK, ES, FR, GB, GR, IE, IT, LU, MC, NL, PT, SE).

Published ith international search report.

Before the expiration of the time limnit for amnending the claims andeito be republished in the event of the receipt of amendments.

65346 (54)Title: BLEACHING OF CHEMICAL PULP (57) Abstract A method of bleaching sulphate pulp without using chlorine-containing bleaching agents. The sulphate pulp is oxygen delignified and can possibly also be ozone delignified to a kappa number below 9.5. Thereafter a pretreatment with complexing agent is carried out for 1-60 minutes, at which the pulp consistency is 1-15 the temperature 70-110 'C and pH 5.7. The pulp thus pretreated is washed and dewatered to a consistency of 18-40 Thereafter peroxide bleaching in alkaline environment takes place in the presence of silicate or an organic complexing agent of the type phosphonic or carboxylic acid.

WO 93/1.1262 1101"/S F9310001(112 1 Bleaching of chemical pulp This invention relates to the bleaching of sulphate pulp without using bleaching agents containing chlorine. The technique of bleaching chemical pulps is now developing rapidly, because the bleaching chemicals heretofore mainly used, C12, C102, and hypochl-orite, are feared to give rise to products being a risk for the environment and health.

Until now, the discussions have been concentrated on the emissions of chlorinated organic substance to the recipient.

The majority of the countries in the world have now established limit values for these emissions, which normally are measured as AOX (Adsorbable organic halogens). As a new trend, the customers require to an ever increasing degree paper with a low content of chlorinated organic substance.

Conventional bleaching with C12 disappears now more and more, and C12 is replaced primarily by C102. Bleaching with ClO2 causes substantially lower AOX-emissions to the recipient, but the amount of chlorinated substance in the pulp is affected only insignificantly.

In recent years, the use of hydroperoxide at the bleaching of chemical pulps has increased considerably. Hydrpperoxide can replace part of the chlorine chemicals.

In patent application SE 89 02058-0, a method is described at which the pulp is pretreated with complexing agent under neutral conditions. By this process, coniferous sulphate pulp can be bleached with peroxide-containing bleaching agents to 70-75% ISO at about 10% pulp consistency. In order to achieve fully bleached pulp qualities with higher ISO-brightness (above 83% ISO), this process can be combined with final bleaching with C102. As a result, thris final bleaching then yields emission of AOX from the bleach plant and chlorinated organic susbstance in the bleached pulp.

WO 93/14262 Per/sE93/ 00012 2 Other known methods of reducing emissions of chlorinated organic substance to the recipient are to extend the delignification further in the closed part of the mill, i.e. in the digester house ahd/or oxygen step.

Extended digestion with maintained pulp quality can be achieved by impregnating the chips with black liquor in the initial phase of the cook, as described in Finnish patent application 90 0663. This method renders it possible to digest pulp down to a kappa number of about 10 and obtain strength properties equal to or better than with pulp digested to conventional level, kappa number 25-30.

Combined with oxygen delignification, kappa numbers as low as 5-6 can be obtained for.further bleaching.

By combining conventional digestion, oxygen delignification and ozone bleaching in acid environment, kappa numbers lower than 10 can be obtained.

It has, however, not been possible to produce fully bleached pulp qualities without final bleaching with 0102.

The present invention implies, that fully bleached pulp with a brightness above 83% ISO can be made without the use of chlorine-containing bleaching agents.

At the s.tart of the bleaching, the pulp shall have a kappa number below 9.5. This cAn be achieved by conventional or extended digestion followed by 02-delignification, alternatively by conventional or extended digestion followed by 02- and 03-delignification. The bleaching is initiated by a pretreatment step with pomplexing agent followed by treatment with hydroperoxide in alkaline environment in the presence of silicate or an organic complexing agent of the type phosphonic or carboxylTc acid.

WO 93/14262 [IMS11193/00012 3 The charaotorizing features of the invention are apparont from the attached claims, The pulp digested and delignified with oxygen and possibly ozone according to above shall have a kappa number below This can be achieved by known methods of digestion and delignification. The pulp shall thereafter be pretreated with complexing agent, for example EDTA or DTPA, at a pulp consistency of 1-15% for 1-60 minutes, preferably 5-30 minutes. The temperature shall be 70-100oC, preferably 80-1000C, and the pH-value 5-7.

The pulp thus pretreated is washed and dewatered to a consistency of 18-40%, preferably 20-30%. The pH-value is increased to alkaline level, and hydrpperoxide is added together with silicate, for example sodium silicate, alternatively together with an organic complexing agent of the type phosphonic or carboxylic acid. The dwell time of the pulp in this hydroperoxide step shall be 5 hours, preferably 1-4 hours, and the temperature 70-1000C, preferably 80-1000C. The silicate charge shall be 2-30 kg/ton pulp, preferably 5-15 kg/ton pulp, expressed as Si02.

Alternatively, the chargo of the organic complexing agent shall be 0.5-5 kg/ton pulp.

Fig. 1 is a diagram, in which the brightness of the pulp is plotted as a function of the pulp consistency at the peroxide'bleaching,partly at conventional peroxide bleaching and partly at bleaching according to the invention.

The starting pulp was oxygen-delignified coniferous wood sulphate pulp with kappa number 6.5 (10.5 after digestion).

Curve 1 show, conventional peroxide bleaching, with a consumption of H 2 0 2 of 20 kg/ton pulp. Curve 2 and, respectively, 3 refe-" to bleaching according to the invention with silicate addition and a consumption of H 2 0 2 of 20 and, respectively, 30 kg/ton pulp.

WVO 9)3/14262 I'IMSSE93/00012' 4 It appearo from the diagram how the brightness, after bleaching according to the invention and, respectively, after conventional bleaching, depends on the pulp consistency. At about 12% pulp consistency, the brightness obtained is equal in both cases, but at increased pulp consistency in the peroxide step an increased brightness is obtained according to the invention, while conventional peroxide bleaching results in a deteriorated bright-, ness.

The following examples have the object to additionally elucidate the invention and its advantages.

Example 1 An oxygen-delignified coniferous wood sulphate pulp (Scandinavian fir/pine) with kappa number 6.4 (10.5 after digestion according to above Finnish patent application 90 0663), brightness 43% ISO, intrinsic aiscosity 605 dm 3 /kg, was pretreated with complexing agent and paroxide bleached according to the invention.

Pretreatment Pulp consistency Time mi. Temperature °C EDTA kg/ton 2 Final pH 6.1 Peroxide step Pulp consistency Time min 240 Temperature °C SiO 2 kg/ton H202 consumption kg/ton 13.5 32.0 Final pKI 10.2 10.3 Brightness ISO 79.6 84.2 Intrinsic viscosity dm 3 /kg 520 447 \VO 93/11262 1111/N11193/00012 A coniforoua wood sulphato pulp with kappa numbor 13.3 (digoteod of Scandinavian fir/pino according to Finnish patent application 90 0663), oxygen delignified to kappa number 8.3:and ozone bleached in acid environment to kappa number 3.2, brightness 61% ISO, intrinsic viscosity 582 dm 3 /kg, was bleached according to the invention.

Pretreatment as in Example 1 Peroxide bleaching Pulp consistency Time min 240 Temperature °C Si0 2 kg/ton

H

2 0 2 consumption kg/ton 7.3 14.2 30.1 Final pH 8.9 9.5 10.1 Brightness ISO 85.3 88.4 90.4 Intrinsic viscosity dm 3 /kg 536 498 420 Example 3 An oxygen delignified coniferous wood sulphate pulp (digested of Pinus taeda according to Finnish patent application 90 0663) with kappa number 9.9, ozone bleached to kappa number 4.8, brightness 54.5% ISO, intrinsic viscosity 607 dm 3 /kg was pretreated and bleached according to the invention.

Pretreatment as in Example 1 Peroxide bleaching Pulp consistency Time min 240 Temperature °C SiO 2 kg/ton

H

2 0 2 consumption kg/ton 7.9 14.6 29.6 Final pH 10.2 10.4 10.6 \VWO) 93/1.262 I( WU/PSI'93/0(00 11 6 Brightness ISO 81.3 85.3 87.8 Intrinsic viscosity dm 3 /kg 570 534 459 Example 4 An oxygen delignified birch sulphate pulp with kappa number 9.0, brightness 59.4% ISO and intrinsic viscosity 996 dm 3 /kg was bleached according to the invention.

Pretreatment as in Example 1 Peroxide bleaching Pulp consistency Time min 240 Temperature oC Si02 kg/ton

H

2 0 2 consumption kg/ton 8.5 17.5 Final pH 10.2 10.4 10.5 Brightness ISO 82.2 85.5 86.5 Intrinsic viscosity dm 3 /kg 903 975 822 The invention is not restricted to the embodiments set forth above, but can be varied within the scope of the invention idea.

Claims

1. A imthod of bloanhing aulphato pulp without uong chlorino-containing bleaching agents, comprising oxygen delignification and possibly ozone delignification of the pulp to a kappa number below 9.5 and subsequent peroxide bleaching, c h a r a c t e r i z e d i n that-the pulp directly after the delignification is pretreated with complexing agent for 1-60 minutes, the pulp consistency being 1-15%, the temperature 70-110°C and pH 5-7, and that the pulp thus pretreated is washed and.dewatered to a consistency of 18-40% and thereafter peroxide bleached in alkaline environment in the pres- ence of silicate or an organiccomplexing agent of the type phosphonic or carboxylic acid.

2. A method as defined in claim 1, c h a r a c t e r i z e d i n that the peroxide bleaching is carried out for 1/2-5 hours at the temperature 70-1100C.

3. A method as defined in claim 1 or 2, c h a r a c t- e r i z e d i n that as complexing agent at the pretreatment EDTA or DTPA is used.

4. A method as defined in any one of the preceding claims, c h a r a c t e r i ed i n that at the peroxide bleaching silicate is added in an amount of 2-30 kg/ton pulp, expressed as Si02. A method as defined in any one of the claims 1-3, c h a r a c t e r i z e d i n that at the peroxide bleaching an organic complexing agent of the type phos- phonic acid orcarboxylic- acid is added in an amount of 0.5-5 kg/ton pulp.

6. A method as defined in any one of the preceding claims, c h a r a c t e r i z e d i n that the bleaching is carried out to a brightness exceeding 83% ISO.