AU651462B2 - Bleaching and delignification of pulp - Google Patents

Description

OPI DATE 08/01/93 AOJP DATE 25/02/93 APPLN. ID 18775/92 PCT NUMBER PCT/EP92/01222 AU921 8775 k/to 9.

I S (PCT) (51) Classification internationale des brevets (11) Numno de publication Internationale: WVO 92/21814 D2IC9 6 9/53,917A (43) Date de publication internationale: 10 d~cembre 1992 (10.12.92) (21) Numrnfo de [a demnande internationale: PCT/EP92/01222 (81) Etats disign~s: AT (brevet europ~en), AU, BB, BE (brevet europ~en), BF (brevet OAPI), BG, BJ (brevet OAPI), (22) Date de d~p~t international: I er juin 1992 (01.06.92) BR, CA, CF (brevet QAPI), CG (brevet QAPI), CH (brevet europ~en), CI (brevet OAP1), CM (brevet QAPI), DE (brevet europ~en), DK (brevet europ~en), ES (brevet Donnies relatives i la priorite: europ~en), Fl, FR (brevet europ~en), GA (brevet QAPI), 9100549 6 juin 1991 (06.06.91) BE GB3 (brevet europ~en), GN (brevet OAPI), GR (brevet europ~en), HU, IT (brevet europ~en), JP, KP, KR, LK, LU (brevet europ~en), MC (brevet europ~en), MG, ML (7)Dpsft(oioi~rEa sgi-sifU)-NEO (brevet OAPI), MR (brevet QAPI), MW, NL (brevet 4NER-NF eNA+f-SOEFET-E-A-NON1YME) I BE-/ europ~en), NO, PL, RO, RU, SD, SE (brevet europ~en), -B Ej;2 re +r~nt-AO- uxeles-(BE).- SN (brevet OAPI), TD (brevet OAPI), TG (brevet OAPI), US.

(72) Inventeur; et Inventeur/D~posant (US seilentent) HAMMANN, Maria [DE/DE]; Im Kirchfeld 13, D-6384 Schmitten I Publi~e Aviec rapport de recherche in*'ernation ale.

(74) Mandataires: DECAMPS, Alain etc. SOLVAY CIE (Socikt Anonyme), D~partement de la Propri& Indus- h trielle, 3 10, rue de Ransbeek, B3-I 1120 Bruxelles (BE).

Ae ceK 14eA2/e/ 33 1 5 L~ (54)Title: PROCESS FOR BLEACHING AND DEL IGNIFYING CHEMICAL PAPER PULP (54)Titre: PROCEDE POUR BLANCHIMENT FT LA DELIGNIFICATION DE PATES A PAPIER CHIMIQUES (57) Abstract Process for bleaching and delignifying chemical paper pulp in three stages: a first stage in which the pulp is subjected to gaseous oxygen, followed by two stages in which gaseous ozone and peroxymonosulphuric acid or one of its salts are used in any order.

(57) Abr~gi Proc~d& pour le blanchiment et la d~Iignification d'une pdite d papier chimique consistant soumnettre la pdte un traitement en trois tapes comprenant une premiere tape au moyen dl'oxyg~ne gazeux suivie par deux ktapes avec, respectivement et dans un ordre indifferent, de l'ozone gazeux et de I'acide peroxymonosulfurique ou F'un de ses sels.

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ra i- 1 Process for the bleaching and delignification of chemical paper pulps and application of this process to the bleaching and delignification of kraft pulps and of ASAM pulps

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The invention relates to a process for the bleaching and delignification of cellulose paper pulps belonging to the class of chemical pulps.

It is known to treat unbleached chemical paper pulps obtained by cooking lignocellulosic matter by means of a sequence of stages of delignifying and/or bleaching treatment involving the use of oxidising chemical products.

The aim of the first stage of a conventional sequence of chemical pulp bleaching is to complete the delignification of the unbleached pulp as it is after the cooking operation. This delignifying first stage is conventionally carried out by treating the unbleached pulp with chlorine in an acidic medium or with a combination of chlorine and chlorine dioxide, as a mixture or sequentially. Chlorinecontaining reactants such as chlorine dioxide and sodium or calcium hypochlorite have been conventionally employed for many years in the bleaching stages which follow this delignifying first stage.

In some situations it is found useful, for a variety of reasons, to be able to replace the delignifying first stage and the subsequent stages using chlorine dioxide or hypochlorite by treatments which no longer rely on chlorine-containing reactants.

Patent US-4,372,812 (International Paper Co) discloses a chlorine-free bleaching process wherein a lignocellulosic pulp is treated with a sequence of steps comprising, in sequence, a step with peroxide and at least a step with ozone. An oxygen step may be added before the sequence.

The peroxide is selected from hydrogen peroxide and 3 30 peracetic acid.

4 Ibis European Patent Application EP-A2-0415149 (DEGUSSA discloses a process for the bleaching and delignification of a lignocellulosic paper pulp wherein the pulp is first treated with a source of peroxymonosulfuric acid and then with oxygen and/or hydrogen peroxide.

In Patent US-A-4,080,249 (International Paper Co) it was proposed to bleach cellulose paper pulp, especially kraft pulp, by means of a sequence free from chlorinecontaining reactants, starting with an oxygen first stage followed by an ozone stage in which the consistency of the pulp was between 1 and 10 and by at least one other stage comprising hydrogen peroxide or peracetic acid in an alkaline medium. However, this known process exhibits the disadvantage of giving rise to an excessively high degradation of the cellulose. Furthermore, it is difficult to produce dilute peracetic acid solutions simply and at low cost at the very time of its j use by reacting acetic acid and hydrogen peroxide, given the slowness of the reaction kinetics. Moreover, it is well known that the transport of concentrated peracetic acid solutions can sometimes present safety problems.

The invention overcomes these disadvantages of the known processes by providing a new process for bleaching and/or delignifying chemical paper pulps which makes it possible to attain high brightness values simply and inexpensively without. degrading the cellulose excessively.

To this end, the invention relates to a process for the bleaching and delignification of a chemical paper pulp by means of a sequence of three treatment stages not relying on chlorine-containing reactants, according to which, in a first stage, the unbleached pulp is treated with gaseous oxygen and, in the second and third stages, the pulp originating from the first stage is treated with gaseous ozone and with peroxymonosulphuric acid or one of its salts, respectively and in any order.

According to the invention a chemical paper pulp is intended to denote pulps which have been subjected to a delignifying treatment in the presence of chemical reactants such as sodium sulphide in an alkaline medium (kraft or sulphate cooking), sulphur dioxide or a metal salt of sulphurous acid in an acidic medium (sulphite cooking) or in an alkaline medium, optionally in the presence of anthraquinone and methanol (ASAM pulps such as those described in Das Papier, 40, 10A, 1986, pages Vl to V8, R. Patt and 0. Kordsachia. Herstellung von Zellstoffen unter Verwendung von alkalischen Sulfitlbsungen mit Zusatz von Anthrachinon und Methanol [Manufacture of cellulose pulps with the use of alkaline sulphite solutions with the addition of anthraquinone and methanol]). The chemical pulps obtained by means of one of the known cooking processes which involve the use of an organic solvent can also b used as raw material for the process according to the invention. Examples of such a chemical pulp are the organosolv pulp such as, for 2 i: i.

i example, acetosolv pulp, and pulps using caustic soda and j methanol, also called "MD pulps". Semichemical pulps such as those where the cooking has been carried out with the aid of a sulphurous acid salt in a neutral medium (neutral sulphite cooking, also called NSSC cooking) can also be bleached using the process according to the invention.

The invention is aimed particularly at the pulps which have been subjected to a kraft cooking or an ASAM S! 10 cooking and whose residual lignin content after cooking lies in the range of kappa numbers of between'8 and depending on the type of wood species from which they originate and on the efficiency of the cooking process.

All the types of wood employed for the production of chemical pulps are suitable for use in the process of the invention and, in particular, those employed for the kraft or ASAM pulps, namely resinous woods like, for.

example, various species of pine and fir and leafy tree woods like, for example, eucalyptus, beech, oak and hornbeam.

Chlorine-containing reactants denote the reactants containing chlorine in their molecule, such as molecular chlorine in acidic aqueous solution, chlorine dioxide or an alkali or alkaline-earth metal hypochlorite.

The first stage of the treatment sequence of the process according to the invention consists of a treatment by means of gaseous oxygen. This oxygen treatment is carried' out by bringing the unbleached pulp into contact with gaseous oxygen at a pressure of between 20 and 1000 kPa in the presence of an alkaline compound in such a quantity that the weight of alkaline compound relative to the weight of the dry pulp is between 0.5 and 4.0 The oxygen treatment of the pulp can also be performed in the presence of a protective agent for the cellulose, such as soluble magnesium salts or organic sequestering agents like polycarboxylic or phosphonic acids. The magnesium salts are preferred, in particular magnesium 3, i 1

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sulphate, employed in a proportion of 0.02 to 1 by weight relative to dry pulp.

The temperature of the first stage must be SI adjusted within the range of between 70 and 130*C and preferably between 80 and 120°C. The duration of the oxygen treatment must be sufficient for the reaction of oxygen with the lignin present in the pulp to be complete. However, it must not exceed this reaction time too greatly, or else damage would be induced in the cellulose chain structure of the pulp. In practice, it would be set at a value of between 30 and 180 minutes and, prefer'ably, between 60 and 140 minutes. A combination of the temperature and residence time of 98 0 C and 120 minutes has given good results.

The second and third stages of the process according to the invention consist in subjecting the pulp to a treatment with ozone, followed by a treatment with peroxymonosulphuric acid or one of its salts or, in a reverse order, in first treating with peroxymonosulphuric acid or one of its salts and then with ozone.

According to the invention the ozone treatment consists in subjecting the pulp to a gas stream consisting of a mixture of ozone and oxygen originating from an electrical ozone generator fed with dry gaseous o:;-gen.

In the laboratory, a generator whose throughput is between 50 and 100 I/hour and, preferably, between 70 and I/hour is advantageously employed. The quantity of ozone used may be easily adjusted by varying the time during which the pulp is swept with the stream of ozone/ oxygen mixture. Periods of 20 to 80 minutes are generally sufficient to use a quantity of ozone of between 0.4 and arrangements will be made to control the throughput of the ozone generators and the duration of the treatment to set the quantity of ozone used on the pulp at values which are similar to those obtained in the laboratory.

The duration of the treatment can be reduced substantially in an industrial environment by virtue of a 4i -i continuous operating technique, until it is reduced to durations of the order of 3 minutes.

The ozone treatment is preferably carried out in an acidic medium. pH values of between 0.5 and 5 are suitable and, preferably between 1.5 and 4. A pH of 2 to 3, obtained by subjecting the pulp for 30 minutes to a preliminary conditioning treatment with a solution of SO 2 in a proportion of 0.5 by weight of SO2 relative to the dry pulp and with a consistency of 3 of solid matter has given very good results.

The consistency of the ozone treatment stage will be chosen from the range of between 0.5 and 45 solids content and preferably between 0.5 and 3 (in the case of low-consistency equipment) or between 10 and 15 (in the case of medium-consistency equipment). A consistency of 35 solids content has given excellent results on the laboratory scale.

The temperature of the ozone treatment stage must remain relatively low, or else it may result in considerable deterioration in the mechanical properties of the treated pulp. This temperature is generally between 2 and and preferably between 10 and 35 0 C. In most cases the ozone treatment is carried out simply at room temperature.

An advantageous alternative form of the process according to the invention consists in preceding the ozone treatment with a mechanical treatment for opening the pulp (referred to as "fluffing"), intended to increase the area of contact of the pulp with the ozone.

This operation is particularly useful when the consistency of the pulp during the ozone treatment is higher than 15 solids content.

According to the invention the treatment with peroxymonosulphuric acid or one of its salts consists in treating the pulp with the inorganic acid corresponding to the formula H 2 S0 5 (also called Caro's acid) or one of its alkali, alkaline-earth metal or ammonium salts, or else with a mixture of a number of these salts or of i. peroxymonosulphuric acid with one or several of these salts. In an advantageous alternative form of the process according to the invention the peroxymonosulphuric acid or the salts which are used may have been prepared immediately before their use by reacting a concentrated aqueous solution of sulphuric acid or of its salts with a concentrated aqueous solution of a peroxygen compound, for example hydrogen peroxide. Concentrated solutions are intended to denote solutions of H 2

SO

4 of concentration higher than 10 moles per litre and of H 2 0 2 of concentration higher than 20 by weight.

The peroxymonosulphuric acid stage may also be performed in the presence of a stabilising agent. Known stabilisers for peroxygen compounds are suitable.

Examples of such stabilisers are alkaline-earth metal salts, in particular soluble magnesium salts, soluble inorganic phosphates and polyphosphates such as alkali metal pyrophosphates and metaphosphates, organic polycarboxylates such as tartaric, citric, gluconic, diethylenetriaminepentaacetic and cyclohexanediaminetetraacetic acids and their soluble salts, poly-y-hydroxyacrylic acids and their soluble salts and organic polyphosphonates such as ethylenediaminetetramethylenephosphonic, diethylenetriaminepenta(methylenephosphonic) and cyclohexanediaminetetramethylenephosphonic acids and their soluble salts. It is also possible to combine a number of these stabilising agents as a mixture. As a general rule, organic polycarboxylates or polyphosphonates give good results, in particular when used in combination with a soluble magnesium salt. The combined used of a soluble magnesium salt such as MgSO 4 and of diethylenetriaminepentacetic acid (DTPA) is suitable in concentratibns of 0.02 to 0.2 g MgS04/100 g of dry pulp and of 0.05 to 0.3 g DTPA/100 g of dry pulp, respectively.

The stage of treatment of the paper pulp with peroxymonosulphuric acid takes place equally well under acidic or alkaline pH conditions. Alkaline pHs with a value of between 9 and 12 have given good results. In the case of alkaline pHs, an alkali chosen from alkali or alkaline-earth metal hydroxides and carbonates is added to the pulp. The alkali can also be used in the form of a mixture of a number of alkali or alkaline-earth metal hydroxides and/or carbonates. The mixture of NaOH and of Na 2

CO

3 is-prefered, in molar proportions NaOH/Na 2

CO

3 of between 0.3 and 1.8.

The pressure and temperature conditions of the stage of treatment with peroxymonosulphuric acid are not critical. Atmospheric pressure is generally suitable. The temperature must be simply chosen so that it is sufficient to ensure an efficient usage of peroxymonosulphuric acid and, at the same time, not too high so as not to degrade the cellulose and not to burden the energy cost of the heating means used in the treatment stage. In practice a temperature of between 50 and 100°C is suitable. In the case of an alkaline pH the temperature range of between 60 and 90'C is preferred.

The duration of the stage of treatment with peroxymonosulphuric acid must be sufficient to ensure a complete reaction. Although longer periods have no effect on the degree of delignification of the pulp or on the intrinsic strength properties, it is not advisable to prolong the reaction period beyond that necessary for completion of the reaction, so as to limit the capital costs and the energy costs of heating the pulp. In practice the reaction period is linked to the chosen temperature value, the highest temperatures permitting the shortest periods. Periods of between 30 and 150 minutes and preferably between 40 and 100 minutes are generally sufficient. A period of 60 minutes has given excellent results.

The stage of treatment with peroxymonosulphuric acid is generally performed at a pulp consistency of between 5 and 25 solids content and preferably between 8 and 20 solids content. A consistency of 10 has given good results.

7< In an alternative form of the process according to the invention, if it is desired to obtain high brighti ness levels, the third stage of treatment can be followed by a fourth stage of bleaching by means of a reactant chosen from ozone and hydrogen peroxide.

In the alternative form using ozone the fourth stage is performed under the same operating conditions as the ozone stage which was already performed at the beginning of the sequence. However, it is appropriate to reduce the quantities of ozone used on the pulp to a value of between to 0.8 g of ozone per 100 g ot dry pulp. A quantity of ozone of 0.3 by weight of ozone relative to the dry pulp is highly suitable.

In the alternative form using hydrogen peroxide the fourth stage consists in treating the pulp with an alkaline- aqueous solution of hydrogen peroxide. This stage is performed similarly to a conventional stage of alkaline extraction in which an aqueous solution of hydrogen peroxide is added to the alkaline reactant. The quantities of hydrogen peroxide to be used in this stage depend on the residual lignin content present in the pulp at the outlet of the third stage of treatment and on the nature of the wood and the method and operating conditions of the cooking which was used to manufacture the pulp. As a general rule these quantities will be between 0.3 and 4.0 g H 2 0 2 /100 g of dry pulp and preferably between 0.4 and 2.5 g H 2 0 2 /100 g of dry pulp. The nature of the alkali employed must be such that it exhibits a good effiiency at the same time as a good solubility.

An example of such an alkali is sodium hydroxide in aqueous solution. The alkali content must be adjusted to ensure a peroxide usage at the end of the reaction of between 60 and 95 of the quantity of peroxide introduced. Alkali contents of between 0.5 and 2.5 g of alkali, expressed as NaOH, per 100 g of dry pulp are suitable. Quantities of H 2 0 2 of 2 g H 2 0 2 /100 g of dry pulp and of NaOH of 1 g NaOH/100 g of dry pulp have given excellent results.

Another alternative form of the process according to the invention consists in following the third stage of treatment by two successive stages consisting, in that order, in subjecting the pulp originating from the third stage to an extraction with an alkaline reactant and then to bleaching with hydrogen peroxide in an alkaline medium. These two stages are carried out under operating conditions similar to those commonly used in the conventional and well-known bleaching sequences involving these two reactants.

For example, the fourth stage of alkaline extraction is in most cases carried out by subjecting the pulp to the action of an aqueous solution of NaOH at normal pressure, at a consistency of between 5 and 30 dry solids, a temperature of between 40 and 85°C and for a period of between 40 and 120 minutes, so as to use from to 2.5 g-of NaOH per 100 g of dry pulp (pH of between 10.5 and 13). The conditions of 1.0 of NaOH, 50 0 C, 10 consistency for 90 minutes have given good results.

Similarly, in the fifth stage using alkaline hydrogen peroxide the following conditions will be employed in most cases: 0.5 to 3 g H 2 0 2 per 100 g of dry pulp, 0.5 to 2.5 g NaOH per 100 g of dry pulp, 5 to 30 Iconsistency, 50 to 90 0 C for 30 to 120 minutes. The conditions of 2.0 H 2 0 2 1.0 NaOH, 10 consistency, for 60 minutes have given advantageous results.

Another alternative form of the process according to the invention, which is preferred, consists in introducing into the alkaline extraction stage a reducing compound so as to carry out a sequence of treatment in stages: 0 (oxygen) Z (ozone) CA (Caro's acid).- E (reductive alkaline extraction) P (alkaline hydrogen peroxide) or else O C A Z -ER P. The reducing compound would be chosen from chemical compounds exhibiting reducing properties which are commonly employed in the paper pulp industry. Examples of such reducing compounds are formamidinesulphinic acid and ammonium or alkali or alkaline-earth metal borohydride, hydrosulphite,

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sulphite or bisulphite. The quantity of reducing compound is generally between 0.05 and 1 g per 100 g of dry pulp.

A quantity of 0.12 of NaBH 4 has given good results.

The process according to the invention finds an 5 application for the delignification and bleaching of kraft, ASAM or sulphite chemical pulps or of high-quality semichemical pulps, especially those intended for food packaging. It is equally suitable for pulps originating from resinous woods or from 'leafy tree-woods.

The following examples are given to illustrate the invention without, however, limiting its scope...

Examples 1R and 2R are not in accordance with the invention and have been given by way of reference. Examples 3 to 6 are in accordance with the invention.

Example 1R: (not in accordance with the invention) A sample of kraft pulp from a mixture of pine and spruce (80 by weight of pinus ssp. and 20 by weight of picea ss) originating from Scandinavia and with a kappa number of 26.3 was mixed with 3.0 weight of NaOH and 1.0 by weight of MgSO, relative to dry pulp and was placed in an autoclave fitted with a mechanical stirring system. Demineralised water was then introduced into the autoclave to bring the consistency of the pulp to 10 solids content and gaseous oxygen was introduced at a pressure of 600 kPa. The temperature was raised to 98°C and stirring was continued for 120 minutes.

After reaction the autoclave was opened and the pulp was washed in a volume of demineralised water corresponding to 40 times its dry weight. The pulp was then filtered on a Buchner filter and was then subjected to an acidic pretreatment with a view to its bleaching with ozone. To do this, the pulp was treated' for minutes with 0.5 by weight of SO 2 with a consistency Sof 3 solids content. The pulp was then centrifuged to a consistency of 40 and then diluted with demineralised water so as to lower the consistency to 35 and was placed in a glass round bottomed flask to which a rotary movement of 60 revolutions/minute was imparted and which

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j t i i ir :was immersed in a bath of water thermostated at 200C.

The ozone was produced in an electrical generator S. fed with dry oxygen at a flow rate of 80 1/h and was injected into the glass flask containing the pulp over a period of 25 minutes, so as to use .ozone.at.:the ra-e of 1 g of ozone per 100 g of dry pulp.

The ozone-treated pulp was then washed in a volume cf demineralised water corresponding to 40 times its dry weight. After filtration on a Buchner filter it was placed in a polyethylene bag and then 2 of peracetic acid, 3 of NaOH relative to its dry weight and demineralised water were added to it so as to adjust its consistency to 10 solids content. After mixing of the material present in the bag, the latter was then immersed in a bath of water thermostated at 70'C for 240 minutes.

After reaction, the pulp was washed, dewatered an4 replaced in a polyethylene bag with 1.0 of NaOH and 0.12 of NaBH 4 and demineralised water in order to adjust the consistency to 10 solids content, and was carefully mixed. The polyethylene bag was then immersed in a bath thermostated at 50*C and was left to react for minutes.

The pulp was then washed and dewatered and was subjected to bleaching in a polyethylene bag in the presence of 2.0 of HO0 2 1.0 of NaOH and of demineralised water to adjust the consistency to 10 solids content. The polyethylene bag was immersed in a bath of water thermostated at 60°C and the reaction was allowed to proceed for 60 minutes. At the end of the bleaching sequence the pulp was washed with demineralised water and was dewatered on a Buchner filter.

Between some stages or at the end of the sequence the bleached pulp was subjected to various examinations performed according to well-known standards, namely: S. micro kappa number: TAPPI UM 246 pulp yield: German Zellcheming standard IV/42/62

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brightness: ISO 2470 (Elrepho (registered trademark) 2000 instrument) breaking length: ISO 1924 tearing strength: German Zellcheming standards V/3/62, V/11/57 and V/12/57 The results were as follows: After the O first stage: Kappa number 9.3 Brightness, "ISO 35.7 Pulp yield, 96.9.

Breaking length, km 11.0 Tearing value, cN 100.0 After the stage Z: Kappa number 2.2 Brightness, "ISO 61.7 Pulp yield, 95.8 Breaking length, km 9.9 Tearing value, cN 105.0 After the stage PA (peracetic acid): Kappa number 0.9 Brightness, ISO 61.7 Pulp yield, 95.8 Breaking length, km 8.41 Tearing value, cN 74.6 After the stage _E Brightness, ISO 85.0 Pulp yield, 95.8 Breaking length, km 7.83 Tearing value, cN 65.8 After the stage P: Brightness, "ISO 89.1 Pulp yield, 95.3 Breaking length, km 7.64 Tearing value, cN 68.2 Example 2R: (not in accordance with the invention) A similar treatment was carried out on the same kraft pulp as in Example 1R, except that the second and third stages were permuted to carry out a sequence 12 i i O CA Z ER P. The other operating conditions were the s-.me as in Example 1R. The results obtained were as follows: After the Ist stage 0: Kappa number 9.3 Brightness, ISO 35.7 Pulp yield, 96.9 Breaking length, km 11.0 Tearing value, cN 100.0 After the stage P. (peracetic acid): Kappa number 5.4 Brightness, "ISO 56.9 Pulp yield, 94.5 Breaking length, km 9.88 Tearing value, cN 95.0 After the stage Z: Kappa number Brightness, "ISO 76.2 Pulp yield, 94.5 Breaking length, km 9.69 Tearing value, cN 99.5 After the stage E,: Brightness, "ISO 80.9 Pulp yield, 93.5 Breaking length, km 9.6 Tearing value, cN 87.2 After the stage P: Brightness, "ISO 89.0 Pulp yield, 92.9 Breaking length, km 8.7 Tearing value, cN 79.3 Example 3: (in accordance with the invention) Example 1R was reproduced, the peracetic acid third stage being replaced with a stage with Caro's acid, which was used under the conditions which follow: quantity of H2SO5, g/100 g of dry pulp quantity of NaOH, g/100 g of dry pulp consistency, solids content itl- r ai f 9 tssa-L-^rt-s,.'.

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temperature, OC duration, minutes The results were as follows: After the 1st stage 0: Kappa number 9.3 Brightness, "ISO 35.7 Pulp yield, 96.9 Breaking length, km 11.0 Tearing value, cN 100.0 After the stage Z: Kappa number 2.2 Brightness, ISO 61.7 Pulp yield, 95.8 Breaking length, km 9.9 Tearing value, cN 105.0 After thestage C,: Kappa number Brightness, "ISO 67.4 Pulp yield, 95.0 Breaking length, km 9.85 Tearing value, cN :102.6 After the stage ER: Brightness, "ISO 68.1 Pulp yield, 94.4 Breaking length, km 9.35 Tearing value, cN 100.6 After the stage P: Brightness, ISO 81.1 Pulp yield, 93.8 Breaking length, km 8.62 Tearing value, cN 93.4 Example 4 (in accordance with the invention) Example 2R was reproduced, the peracetic acid stage being replaced with a stage with Caro's acid, performed under the following conditions: quantity of H 2 S0 5 g/100 g of dry pulp quantity of NaOH, g/100 g of dry pulp consistency, solids content temperature, C duration, minutes The results obtained were as follows: After the 1st stage 0: Kappa number. 9.3 Brightness, ISO 35.7 Pulp yield, 96.9 Breaking length, km 11.0 Tearing value, cN :100.0 After the stage C.: Kappa number 6.

Brightness, "ISO 45.6 Pulp yield, 95.8 Breaking length, km 10.42 Tearing value, cN 98.6 After the stage Z: Kappa number 0.9 Brightness, "ISO 70.6 Pulp yield, 94.9 Breaking length, km 9.22 Tearing value, cN 85.5 After the stage E,: Brightness, "ISO 75.6 Pulp yield, 94.9 Breaking length, km 8.75 After the stage P: Brightness, "ISO 83.2 Pulp yield, 94.0 Breaking length, km 9.26 Tearing value, cN 93.2 Example 5: (in accordance with the invention) Example 3 was repeated with a pine (pinusessp.) ASAM pulp with a kappa number of 28.0 and a brightness of 48.6. The fourth stage (alkaline extraction) was carried out without NaBH 4 addition, in contrast to Example 3. The other conditions were identical with those of Example 3.

The results obtained were as follows: L i Cl(l~rrm(L~ After the 1st stage 0: Kappa number 9.6 Pulp yield, 96.7 Breaking length, km 11.54 Tearing value, cN :115.3 After the stage Z: Kappa number 1.9 Brightness, "ISO 78.3 Pulp yield, 95.2 Breaking length, km 11.01 Tearing value, cN 128.8 After the stage CA: Kappa number Brightness, "ISO 84.2 Pulp yield, 94.9 After the stage E: Brightness, "ISO 80.0 Pulp yield, 94.9 Breaking length, km 10.65 Tearing value, cN 120.2 After the stage P: Brightness, ISO 87.0 Pulp yield, 94.6 Breaking length, km 9.64 Tearing value, cN :111.7 Example 6: (in accordance with the invention) A sample of the same pine and spruce kraft pulp as in Examples 1R to 4 was treated according to the sequence 0 Z CA under conditions which were identical with those of Example 3, and was then subjected to a fourth and final bleaching stage using ozone under the following conditions: Quantity of ozone, relative to dry pulp :0.3 Temperature, °C Consistency, solids content Duration, minutes The results obtained were as follows: 16 L I After the stage 0: After the stage 0: j see Example 3 After the stage Z: see Example 3 After the stage CA see Example 3 Pfter the final stage Z: Brightness, "ISO Pulp yield, 86.2 93.9

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Claims (8)

1. Process for the bleaching and delignification of a chemical paper pulp by means of a sequence of three treatment stages not relying on chlorine-containing reactants according to which, in a first stage, the unbleached pulp is treated with gaseous oxygen and charac- terised in that, in the second and third stages, the pulp originating from the first stage is treated with gaseous ozone -nd with peroxymonosulphuric acid or one of its salts, respectively and in any order.

2. Process according to Claim 1, characterised in that, in the second stage of treatment, the pulp is treated with gaseous ozone and in that, in the third stage of treatment, the pulp is treated with peroxymonosulphuric acid or one of its salts.

3. Process according to Claim 1, characterised in that, in the second stage of treatment, the pulp is treated with peroxymonosulphuric acid or one of its salts and in that, in the third stage of treatment, the pulp is treated wich gaseous ozone.

4. Process according to any one of Claims 1 to 3, charac- terised in that the stage of treatment with peroxymonosul- phuric acid or one of its salts is performend in the presence of a sufficient quantity of alkali to raise the pH 25 of the reaction medium to the range between 9 and 12. Process according to any one of Claims 1 to 4, charac- terised in that the third stage of treatment is followed by a fourth stage consisting in treating the pulp originating from the third stage with an oxidising reactant chosen from ozone and hydrogen peroxide in an alkaline medium.

6. Process according to any one of Claims 1 to 4, charac- terised in that the third stage of treatment is followed by two successive stages consisting, in that order, in subjecting the pulp originating from the third stage to an extraction with an alkaline reactant and then to bleaching with hydrogen peroxide in an alkaline f i I medium.

7. Process according to Claim 6, characterised in that the fourth stage of alkaline extraction is performed in the presence of a reducing compound.

8. Process according to Claim 7, characterised in that the reducing compound is chosen from formamidine- sulphinic acid and ammonium, alkali or alkaline-earth metal borQhydride, hydrosulphite, sulphite or bisulphite.

9. Process according to Claim 8, characterised in that the reducing compound is sodium borohydride. Application of the process according to any one of Claims 1 to 9 to the bleaching and delignification of resinous wood kraft pulps and ASAM pulps. 19 I u :Q I~ Abstract Process for the bleaching and delignification of a chemical paper pulp by subjecting the pulp to a three-stage treatment comprising a first stage using gaseous oxygen followed by two stages with gaseous ozone and peroxymonosulphuric acid or one of its salts in any order. INTERNATIONAL SEARCH REPORT International application No. PCT/EP 92/01222 A. CLASSIFICATION OF SUBJECT MATTER Int.Cl 5 D21C 9/16; D21C 9/153; D21C 9/147; D21C 9/10 According to International Patent Classification (IPC) or to both national classification and IPC B. FIELDS SEARCHED Minimum documentation searched (classification system followed by classification symbols) Int.Cl 5 D21C Documentation searched other than minimum documentation to the extent that such documents are included in the fields searched Electronic data base consulted during the international search (name of data base and, where practicable, search terms used) C. DOCUMENTS CONSIDERED TO BE RELEVANT Category* Citation of document, with indication, where appropriate, of the relevant passages Relevant to claim No. A US, A, 4 372 812 (INTERNATIONAL PAPER COMPANY) 8 February 1983 see column 5,line 3 line 46; claims 1,3,5,6,10 A EP, A, 0 415 149 (DEGUSSA AG) 6 March 1991 see page 4,line 21 page 5,line 9 1,5,10 Further documents are listed in the continuation of Box C. O See patent family annex. Special categories of cited documents: later document published after the international filing dateor priority document defining the general state of the art which is not considered date and not in conflict with application but cited to understand to be of particular relevance the principle or theory underlying the invention earlier document but published on or after the international filing date document of particular relevance; the claimed invention cannot be document which may throw doubts on priority claim(s) or which is nsdeed nel r can bcoidered to involve an inventive cited to establish the publication date of another citation or other special reason (as specified) document of particular relevance; the claimed invention cannot be document referring to an oral disclosure, use, exhibition or other considered to involve an inventive step when the document is means combined with oneor more other such documents, such combination being obvious to a person skilled in the art document published prior to the international filing date but later than being ios to a prson skilled in the the priority date claimed document member of the same patent family Date of the actual completion of the international search Date of mailing of the international search report August 1992 (20.08.92) 04 September 1992 (04.09.92) Name and mailing address of the ISA/ Authorized officer EUROPEAN PATENT OFFICE Facsimile No. Telephone No. Form PCT/ISA/210 (second sheet) (July 1992) ANNEX TO THE INTERNATIONAL SEARCH REPORT ON INTERNATIONAL PATENT APPLICATION No. EP SA 9201222 59810 This annex ists the patent family members relating to the patent documients cited in the above-mentioned international search report. The members are as contained in the European Patent Office EDP file on The European Patent Office is in no way liable for these particulars which are mrely given for the purpose of information. 2 0/08/9 2 ij a. w For more details about this annex :see Official Journal of the European Patent Office, No. 12/82 K RAPPORT DE RECHERCI- 1 I. CLASSEMENT DE L'NvENTION (si plusieurs symboles de classific' IE INTERNATIONALE Demande Internationale No PCT/EP 92/01222 nton soot applicables, les lodiquer tous) 7 it I I I Soon [a classification joternationale des brevets (CIO) ou i [a fois selon la classificaion nationale et la CIB CIB 5 021C9/16; 021C9/153; 021C9/147; D21C9/10 U. DOMAINES SUR LESOUELS LA RECH{ERCHE A PORTE Documentation toiniroale consult~es Documentation consultke aute que la documentation minimale dans la mesure oi de tels documents foot partie des domnaines sur lesqoels la recherchme a port# III. DOCUMENTS CONSIDERES COMMTE PERTINENTS' 0 Catftvrie 0 Identification des documents cit~s, avec indication, si n~cessair0 2 No. des revendications des passages pertnentsl1 3 v w1 A USA4 372 812 (INTERNATINAL PAPER COMPANY) 8 1,3,5,6, Fdvrier 1983 voir colonne 5, ligne 3 ligne 46; revendications A EP,A,O 415 149 (D7GUSSA AG) 6 Mars 1991 1,5,10 voir page 4, ligne 21 page 5, ligne 9 Catigories spciales de documents cit~: 11 'T document ulttirieur pubUAk postkrieurement A )a date de dkpot document d~frLnissant I'ttat g~nkral de la technique, nin loteroational ou A la date de prioritt et nappaensmant pas wnsm~xd mmcpaitcullremot prtinnt I'ktat de Ia technique pertinent, malt dtk pour comprentre consdkrkcomm pariculernet petinetIl principe o la thborie constituant la base de l'lnvention 'V document antfirieur, mala publl& i la date de d~pt interna- document pa aailubienat pertinent l'invention revendi- tional ou apris ceste date qu~e no peut fte considkrde cmmc nouvelle ou cmmc IV document pouvant jeter un doute aur une revendication de impliqoant non activitt inventive prlonitt ou citt pour d~terminer la date de publication d'une Onza-ment partiaslikrement pertinent; Ilnvention reven- autre citation ou pour une raison spkdale (Idlle qo'indiqu~e) d iqu"- no pewt tre consid~rke comme impliquant one document so rdifiant A one divolgation orale, i on usage, A activiti inventive lorsque le document est assocA A un o one exposition o tous autres; moyens plosleurs autrs documents de meme nature, cette combl- AOUT 19920A.19 Administration chargit de la recherche intemnationale Signature do foodloonnalre autoiska OFFICE EUROPEEN DES BREVETS BERNARDO NORIEGA F. Fomrhhsk PCT/ISA 12 10 (d~ewd koil WmJier 19M)1 ANNEXE AU RAPPORT DE RECHERCHE INTERNATIONALE RELATIF A LA DEMANDE INTERNATIONALE NO. EP 9201222 SA 59810 La prisente annexe indique Ics membres de la famille de brevets reiatifs znux documents brevets cites dans le rapport de recherche internationale vise ci-dessus. Lesdits membres sont contenus au fichier informatique de l'Ofrace europica des brevets i la date du Les renseignements fournis soot donne~s i tie indicatif et n'engagent pas la respomsbiliti de I'0111ce europien des brevets. 20/08/92 Document brevet cite )c eMmbes eI Date de u rapport de recherche publication famille de brevet(s) T publication US-A-4372812 08-02-83 CA-A- 1132760 05-10-82 EP-A-0415149 06-03-91 US-A- 5091054 25-02-92 CA-A- 2023429 19-02-91 Pour tut rnegnement concernant cette annexe voir Journal Offici de l'Office europeen des brevets, No.12/82 .I INTERNATIONAL SEARCH REPORT International application No. PCT/EP 92/01222 A. CLASSIFICATION OF SUBJECT MATTER D21C 9/16; D21C 9/153; D21C 9/147; D21C 9/10 According to International Patent Classification (IPC) or to both national classification and IPC B. FIELDS SEARCHED Minimum documentation searched (classification system followed by classification symbols) Int.Cl 5 D21C Documentation searched other than minimum documentation to the extent that such documents are included in the fields searched Electronic data base consulted during the international search (name of data base and, where practicable, search terms used) C. DOCUMENTS CONSIDERED TO BE RELEVANT Category* Citation of document, with indication, where appropriate, of the relevant passages Relevant to claim No. A US, A, 4 372 812 (INTERNATIONAL PAPER COMPANY) 8 February 1983 see column 5,line 3 line 46; claims 1,3,5,6,10 A EP, A, 0 415 149 (DEGUSSA AG) 6 March 1991 see page 4,line 21 page 5,line 9 1,5,10 S Further documents are listed in the continuation of Box C. O See patent family annex. Special categories of cited documents: laterdocument publishedafterthe international filingdateorpriority document defining the general state of the art which is not considered date and not in conflict with th- application but cited to understand to be of particular relevance the principle or theory underlying the invention earlier document but published on orafter the international filingdate document of particular relevance; the claimed invention cannot be considered novel or cannot be considered to involve an inventive document which may throw doubts on priority claim(s) or which is sp en the dor caument is taken alonred to involve an inventive cited to establish the publication date of another citation or other special reason (as specified) document of particular relevance; the claimed invention cannot be document referring to an oral disclosure, use, exhibition or other considered to involve an inventive step when the document is means combined with oneor more othersuch documents, such combination being obvious to a person skilled in the art document published prior to the international filing date but later than the priority date claimed document member of the same patent family Date of the actual completion of the international search Date of mailing of the international search report August 1992 (20.08.92) 04 September 1992 (04.09.92) Name and mailing address of the ISA/ Authorized officer EUROPEAN PATENT OFFICE Facsimile No. Telephone No. Form PCT/ISA/210 (second sheet) (July 1992) ANNEX TO THE INTERNATIONAL SEARCH REPORT ,ON INTERNATIONAL PATENT APPLICATION No. EP SA 9201222 59810 This annex ists the patent family members relating to the patent documents cited in the above-mentioned international smarh report. 'Me members are as contained in the European Patent Office EDP file on The European Patent Office is in no way liable for these particulars which are merely given for the purpose of information. 20/08/92- Patent document T Publication Patent family Publication cited in search report date member(s) -Tdate US-A-4372812 08-02-83 C-A- 1132760 05-10-82 EP-A-0415149 06-03-91 US-A- 5091054 25-02-92 CA-A- 2023429 19-02-91 'W For more details about this annex :see Official Journal of the European Patent Office, No. 12/82 ~~2 RAPPORT DE RECH ERCHE INTERNATIONALE Demande Internationale No PCT/EP 92/01222 1. CLASSENIENT DE L/INVEN'TION (si plusieurs symboles de classification sont applicables, les Indiquer tous) I Sedan ia classification intaneationale des brevets (dIB) o i la fois seirin la classification nationale et la CIB CIB 5 021C9/16; D21C9/153; 021C9/147; D21C9/10 UI. DOMAINES SUR LESQUELS LA RECHERCHE A PORTE Documentation minimale consult~e' Systime de classification Symboles de classification CIB 5 D21C Documentation consultde autre que la docamentatioa minimale dans Ia mesure oil do tls domments font partie des domaines sur lesquels la recherchie a portcf A US,A,4 372 812 (INTERNATINAL PAPER COMPANY) 8 1356 Fdvrier 1983 voir colonne 5, ligne 3 11gne 46; revendi cati ons A EP,A,0 415 149 (DEGUSSA AG) 6 Mars 1991 1,5,10 voir page 4, ligne 21 page 5, ligne 9 oCatkgories spidalos do documents citds: 11 'T document ulttriour pubU6k postifieorement A la date do d~p~t international ou i la date do prioritt at n'appoaemeant pas document dbfinissant l'tat gtn~an do la technique, non A lIAtat do la technique pertinent, male dtk pour comprendre considdrk comma particuidement pertinent le principo ou I& tbil constituant la base do linvention E' document antirieur, mais publikd l a date do ddp6t inea documeint partiullfrement pertinent; l'nvestion revendi- tional o apris cetto date 1060 no petut ftre considdiA. commo nouvelle o comma document pouvant jeter on doute sur uno revendication do umpliquant one activit6 inventive priortko citt pour diterminer la date do publication d'une documnt partiaaliremat pertinent; l'invention reven- autre citation o pour 000 rison spkdale (teile qta'indiquke) diue opett fte considit.e comma impllquant 00e document so rim~nt Ak one divuigation crae, A on usage, A aciiiiventive isque le document oct associt A Un 00 one exposition o toot autrec moyens pluslirs auones documents do meme nature, cette combi- .P 0 document publik avant la date do d~p6t international, male naso ktant Avidento pour one parsson du mfiler. posthrlairement A la date do prioritt rovendiqude W& document qul fait partle do la mime famlle do breet Iv. CERTIFICATION____________ Date A laquelle la recherche internatlonale a atC aiectivemett acnevoe AOUT 1992 Administration cliargit do la rechierche internationale OFFICE EUROPEEN DES BREVETS Daa xpdbo o 04 .9aprts. ecece ne92ini Feogwaak pCT/ISAIZI (dwd*= ki&lm) (Javie IM)3 ANNEXE AU RAPPORT DE RECHERCHE INTERNATIONALEE 9212 RELATIF A LA DEMANDE INTERNATIONALE NO. E 212 SA 59810 La prisentc annexe indique les membres de ]a famifle de birevets relatifs aux documents brevets cites dams le rapport de recherche internationale vise ci-desmu. Lesdits membres sont contenus au fichier infonnatique de I'Office europien des brevets i In date du I es renweignements fournis sont donnis i titre indicatif et n'engagent ps In responsabiliti de I'Office eurpen des brevet. 20/08/92 Document brevet cite Date de Membre(s) de In Date de mu rapport de rechercbe T publication famille de brevet(s) F publication US-A-4372812 08-02-83 CA-A- 1132760 05-10-82 EP-A-0415149 06-03-91 US-A- 5091054 25-02-92 CA-A- 2023429 19-02-9 1 Pour tout remseignetnent concernant cette annexe :voir Journal Offloiel dle 1Y01fice elnopien des brevets, No.12/82