FI59432B - FOERFARANDE FOER BLEKNING AV KEMISKA MASSOR - Google Patents

Description

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Patent * och regiiteratyrelaen AnrtkmochHtijkriftwipubiic * ra4 30.Ol.8l (32) (33) (31) «uoikau · —fegifd pHorittt 25.05.70 USA (us) lolol (71) International Paper Company, 220 East l2nd Street, New York, NY 10017, USA (72) Sunanda K. Roymoulik, Suffern, New York, USA (7l) Berggren Oy Ab (5l) Method for bleaching chemical pulps - Förfarande för blekning av kemiska massor

The present invention relates to a novel 2- or 3-stage series for removing lignin from chemical pulps and bleaching them.

Most factory-scale current bleaching series use five or six steps. When bleaching chemical pulps, either sulphate (strength) or sulphite pulp, elemental chlorine is used in one or more stages. Since chlorination is normally carried out at a concentration of J>% in the first stage of a conventional bleaching series, based on the weight of the pulp, very large amounts of water are required in the bleaching system. This results in a large amount of chlorine-containing waste material, i.e. chloride ions which must be discharged into and contaminate water bodies near the bleaching plant.

When elemental chlorine is used in the first stage of most pulp bleaching series, for example CEDED or CEHDED, the purpose is to form alkali-soluble chlorillanine, which can be extracted in the next stage, i. In step E, with sodium hydroxide. However, the use of chlorine in the first stage of bleaching degrades the cellulosic portion of the pulp. This means that in 2,59432 the degree of polymerization decreases, the strength of the pulp and the yield decrease.

It is an object of the present invention to provide a process for the preparation of chemical pulps, while at the same time reducing the exposure of chloride ions to waste materials, reducing water pollution and reducing the degradation of cellulose.

It is an object of the present invention to provide a new two-stage pulp bleaching treatment series to obtain a pulp having a whiteness of about 60% or above.

It is a further object of the present invention to provide a new three-stage pulp bleaching series to obtain a pulp having a whiteness in excess of 80%.

It has been found that bleaching a chemical pulp in the first step with oxygen in the presence of a compound selected from the group consisting of and Na2Sx and optionally sodium hydroxide followed by a second step using Pere-acetic acid gives a pulp with a whiteness of about 60% or above . If the second step, i.e. the peracetic acid bleaching step is followed by a third step in which chlorine dioxide is used, either as a gaseous solution or as a solution, with a whiteness of more than 80%.

The present invention relates to a process for bleaching chemical pulps, wherein the pulp having a% consistency is reacted in a first step with oxygen at a temperature of 70-1 * 10ο0 at an oxygen pressure of 5-10 kp / cm and in a second step with a peroxy compound, alternatively followed by a third bleaching step. , which method is characterized in that the pulp is reacted in a first step with oxygen in the presence of a preservative having a concentration of about 0.2-10% by weight of the oven-dry pulp, using ^ 2820 ^ or Ν & 2 ^ suoja> as the preservative. x is an integer from 2 to about 1/2 to 8 hours, alternatively in the presence of sodium hydroxide in an amount of 0.5 ~ 5%, in the second step the mass is reacted to about 0.5-2%, preferably 1? peracetic acid based on the weight of the oven-dry mass, at a pH of 8-12 at the beginning of the second stage, at a temperature of about 50-90 ° C, preferably 70 ° C for about 50-120 minutes, and if desired n mass in the third step to react with about 0.25-2.0% chlorine dioxide, based on the weight of the oven-dry mass, at about 20-90 ° C, preferably at 70 ° C for about 5-120 minutes. The crude dissolved chemical pulp to be treated in the first step is prepared by either the sulphate or sulphite process and has a concentration of about 3-35% and preferably more than 20% by weight of the oven dry pulp.

In this application, the term "protecting compound" means either an oxidizing or reducing agent capable of preventing the cellulose portion of pulp 3,59432 from decomposing and depolymerizing by reaction with carbonyl end groups, converting them to hydroxyl groups using a reducing agent, and using carboxyl groups using Na 2 S an oxidizing agent. Na 2 S 2 is the most preferred polysulfide.

The concentration of Na 2 S 2 O 2 or Na 2 Sx should be at least about 0.2% and is preferably about 2-10% by weight of the oven dry mass. Using concentrations of more than 10% increases costs and does not provide any additional benefits.

It should be noted that since the preservatives contain only sodium and sulfur ions, both of which are present in sulphate or sulphite cooking systems, the effluent can be fed back to the chemical recovery system, preventing contamination of water bodies which would otherwise occur if waste materials were discharged into waterways in the normal way.

When using pulps with a lignin content of 5% or more, the addition of about 1-5% sodium hydroxide to the reaction mixture can accelerate the reaction. Even if the concentration of Νβ232θ ^: η or Na2Sx is 2% or less, sodium hydroxide can be advantageously used.

After the first step, the pulp, which may have a concentration of about 10-20% and preferably about 10-15%, is washed with water, followed by centrifugation or filtration. The partially bleached pulp of the first stage is then subjected to a bleaching treatment with peracetic acid in the second stage. In the second step, the initial pH should be in the range of about 8.0-12.0, with a range of about 8.0-10.0 being most preferred. The pH can be adjusted by adding Na 2 CO 3 and / or NaOH. The initial pH must be adjusted to about 8.0 or above to obtain the best possible bleaching results.

The whiteness of the pulp after the first and second stages, namely the stage using oxygen (0) and peracetic acid (Pa), is 60% or more, and can be used for the production of newsprint.

In order to improve the whiteness of the pulp to 80% or more so that it can be used as a derivative pulp or in the manufacture of adhesive papers, the pulp is treated in a third step with chlorine dioxide. Either gaseous chlorine dioxide or chlorine dioxide solution can be used.

When an aqueous solution of chlorine dioxide is used, the concentration of the pulp may be about 10-20% and is preferably between 10 and 15% by weight of the kiln-dry pulp. The ClCl 2 concentration can be about 0.5-2.0% by weight of the oven dry mass. The reaction can be carried out at a temperature of about 50 to 90 ° C, preferably 70 ° C, and the starting pH is between 5.0 and 6.0 for about 50 to 120 minutes.

59432 When gaseous chlorine Hi oxide is used, the mass of the machine may be:. 1. i a about id-'1 'k concentration of more than 30% in an object preferred. harm o. a; ka vo: i ia.i is reduced to about 3-10 minutes and the reaction can take place ’. Ήρ'5 ti ia.as n about H-: H ° C with a temperature of 70 ° C being most preferred.

The rake examples illustrate the treatment according to the invention ".

Hi mark 1 laa collar sample hardwood pulp which was made of strong s am e r. e t e 1 m ä 11 ä and then washed with deionized water was bleached as follows. (The first step was performed in an electrically heated pressure reactor).

First stage reaction temperature inn ° c 2 reaction pressure (0 ^) 7.03 k ^ / crn

The reaction time of 3 hours in "Asa concentration 20-22% ka -,.% 0 .: (Hydrosulfite) 2 f uk (oven dry) mass haOK 2% uk mass" was then washed thoroughly with water, centrifuged and further bleached according to step 2 below.

Second phase

Petic acid 1% by mass' cash concentration 10 f, item "-pH (adjusted with MaOH) 8.0

":: e i k c i o 1 ä m p ö t i 1 a 7 00 C

Treatment time 2 hours

The semi - bleached mass was washed thoroughly with water and centrifuged. the whiteness of the cash register was found to be 66% measured *. ui mä 11 «Pin Standard Method T217. third stage

Chlorine dioxide 0.5% uk by mass checkout concentration 10% Starting pH 5.5 - 6.0

Reaction temperature 70 ° C

correctional period. 2 hours The fully bleached pulp was then washed with water, centrifuged and evaluated. The results of this assessment are presented in Table 1 below.

59432

Kr.mark 2 A sample of hardwood pulp prepared by force s s a n e n e t e 11 m and then washed with deionized water was bleached as follows (The first step was performed in an electrically heated pressure reactor).

First phase

Reaction temperature 10n ° c p

Reaction pressure (02) 7.03 kp7om

Reaction time 5 hours

Mass concentration 20-22 7 ”a2ä C Polysulf idi) 2% uk mass

LaOH 2% uk by weight

After thorough washing and centrifugation, the pulp was further bleached using step 2 below.

Second phase

Peracetic acid 1% uk by weight

Mass concentration 10% Starting ρΠ (adjusted with NaOH) 8.0

Reaction temperature 70 ° C

Reaction time 2 hours

The semi-bleached mass was then washed thoroughly with water and centrifuged. The whiteness of the pulp was found to be C> H% as measured by Tappi Standard Method T217.

Ho lm :: oi step

Chlorine dioxide 0,5 to 7 uk mass

Mass concentration 10.0 7 Starting pH 5.5-6.0

Reaction temperature 70 ° C

Reaction time 2 hours The fully bleached mass was then washed with water and centrifuged. the test results are shown in Table 1 below.

The properties shown in Table 1 were determined by Pin Standard Test methods. They are as follows: whiteness T217; 007-7227; resting anise strength - T220 and T *) 03; tear strength - T <? 20 and 7-Ί1 ··; k a t k e a’1 i s p i t u e s - T220 and T * I0H; A SV - T220 and opacity - 7 * 125.

59432

Table 1 7a lk oi - 077 Puncture- Repe'inis- Intermittent- Λ PV Guide1! -mouth mis- strength length tcr-tti strong new 7 i mark 1 33.7 372 99.3 91.0 8036 1.3 ° 7 °, ^ 7 · ', i mark 2 39.1 39 ° 97.7 73 , 9 3275 1.99 75, ° 9DF0-? 33.5 3 ° 3 93.0 39.0 71) 35 1.53, 0 f ^ o y o n -

It can be seen from Table 1 that the ° -Pa -;) -. opacity. The physical characteristics correspond to those obtained by conventional or

Claims (9)

A process for bleaching chemical pulp, wherein a pulp having a concentration of 3-40% is reacted in the first stage with oxygen at a temperature of 70 -14 ° C at an oxygen pressure of 5-10 kp / cm and ι a second stage to react with a peroxy compound, followed by alternatively a third stage, characterized in that the pulp is reacted in the first stage with oxygen in the presence of a protective substance, the concentration of which is about 0.2-10%. the weight of the oven-dried pulp, the protecting substance being Na2S2Oi | or Na 2 S x, where x is an integer 2-4, for about 1 / 2-8 hours, alternatively in the presence of about 0.5-5% sodium hydroxide, that the pulp is reacted at a second stage with 0.5-2% , preferably 1% peracetic acid, based on the weight of oven-dried pulp, wherein the pH at the beginning of the second stage is 8-12, at a temperature of 50-90 ° C, advantageously 70 ° C for 30-120 minutes, and if desired For example, the pulp is reacted in a third stage with about 0.25-2.0¾ chlorine dioxide based on the weight of oven dried pulp, at a temperature of 20-90 ° C, advantageously 70 ° C for about 5-120 minutes. Process according to Claim 1, characterized in that the pH value at the beginning of the second bleaching step with peracetic acid is 8-10. A process according to claim 1 or 2, wherein 0.5 ~ 5% sodium hydroxide based on the weight of the pulp is present at the first stage, characterized in that the concentration of the protective substance is 2% or less based on the weight of oven dried pulp. 4. A process according to claim 1 or 2, characterized in that the protective substance in the first stage consists of Na 2 S 2 and that its concentration is 2% or higher based on the weight of oven dried pulp.