FI58521B - SAETT ATT OEKA CELLULOSAUTBYTET VID SULFITKOKNING AV VED - Google Patents

Description

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IBJ (11) utlAggnINGSSKRIPT 5 8521 C (45) rat.ir ^ i: .. V 'C CC 1931 ^ (51) KrjÄhta1 D 21 C 3/06 FINLAND —FINLAND (21) P «« rttihikwTW ~ r * wciniöknfn | 752508 (22) Hikmihpllv »—AwBIwliiH ^ 05.09.75 '(23) AltcupVvl — GIMxhutsdag 05.09.75 (41) Translators lulkMal - Bllvlt offwttllf 07.03.76

Petent- och registerstyrelaen ^ pubitond 31.10.80 (32) (33) (31) Byyduttjr «TuoHuut-Β ^ priorlm 06.09.lk Sweden-Sweden (SE) 7 ^ 11268-1 (71) Kopparfors Aktiebolag, 8l6 00 Ockelbo, Sweden -Sverige (SE) (72) Sigbjöm Holgersson, Gävle, Sweden-Sverige (SE) (7 * 0 Berggren Oy Ab (5 ^ *) Method for increasing cellulose yield when cooking wood by the sulphite process - Sätt att oka cellulosautbytet vid sulfit-kokning av ved

When cellulose is normally cooked by the sulphite process, in addition to lignin, most of the hemicellulose of the raw material is also soluble and sometimes a smaller amount of alpha-cellulose is also dissolved. A substantially pure alpha-cellulose product may be desirable in cases where the pulp is used to make viscose, but speaking of the pulp, regular removal of hemicellulose only means a loss of yield.

It has now been shown that both the yield of the pulp and the strength of the pulp are increased if small amounts of formic esters (formates) of hexyl alcohol or unsubstituted or methyl-substituted norbornyl alcohols, preferably 2-norbornyl alcohols, are added to the cooking liquid. The formats have the general formula: 0

R-0-C-H

wherein R is thus a hexyl group, an unsubstituted or methyl-substituted norbonyl group.

2,58521

The method according to the invention is thus formed in such a way that at least one of the above-mentioned formates is added to this cooking liquid in an amount of at least 0.02 mol, preferably at least 0.1 mol, per ton of dry wood, before impregnating the wood with the cooking liquid. It is usually sufficient to add one of these substances, but two or more may also be added. The addition preferably takes place immediately before the cooking liquid is added to the kettle, suitably in the form of an aqueous dispersion using a non-ionic dispersant. However, the formate or formates may preferably be dissolved in e.g. turpentine, cymene or diethylbenzene before dispersion. The minimum addition amount of 0.02 moles presented above can be considered as a threshold below which no significant effect can be expected. Of the useful agents of the invention, endophenyl formate and exo-norbornyl formate have proven to be very effective.

This new sulphite cooking method can be used in particular when using spruce as a starting material, but other coniferous species can also be used, e.g. pine, and the method can also be applied to hardwood, e.g. birch, when this is cooked together with softwood.

Examples of suitable formates of the above general formula are the following substances: H 0 ch3- (ch2) 4-c-o-c-h

B

Hexyl formate.

H 3 0-C-H

M

0

Exo-norbornyl formate Endophenyl formate H CH 2

Exo-isophenyl formate 3,58521

The way in which these formates have a beneficial effect in sulphite soup is not yet completely clear, but the observations made so far suggest that these substances resist the condensation of lignin. The purpose of the cooking liquid during cooking is to dissolve the lignin of the wood by sulfonation. This breaks down the carbonic acid bonds of the lignin and forms reactive, rapidly sulfonating intermediates of the benzylium ion type or having a quinonimethide structure. It is known that the sulfonation of these species takes place simultaneously with the lignin condensation reactions, whereby benzyl ions or quinone mimetics react (depending on the conditions) via an aromatic substitution with another phenylpropane unit. This creates a new stable carbon-carbon bond, and the method thus provides an increase in the molecular size of the lignin. This lignin condensation thus counteracts the desired solubilizing effect that cooking oil has due to its sulfonating effect.

Experiments have shown that formates hydrolyze more or less slowly to the corresponding alcohol and formic acid under the conditions prevailing in sulphite soup. The formic acid formed is assumed to inhibit the above-mentioned lignin condensation reaction and this can be thought of as occurring in two different ways. Another way is that formic acid acts directly as a reducing agent and thus reduces some of the above-mentioned benzylium ions or quinone mimetics. (Analogous reactions are known). No condensation can occur in the reduction product formed as described above for benzyl ions or quinonimethides. Another conceivable mechanism of action, which is also due to the reducing effect of formic acid, is that formic acid forms thiosulfate with the cooking liquid. Due to their strong nucleophilicity, the thiosulfate ions then react very rapidly with benzylium ions or quinonimethides, thus preventing the above-mentioned condensation of lignin in them.

Formic acid is normally present in cooking liquor in small but variable amounts. Together with the above-mentioned formates, this formic acid may have a beneficial effect if its concentration is not so great that adverse side effects become predominant. The addition of formic acid together with 4,58521 formate can therefore be highly advantageous in the case where the naturally occurring amount of formic acid in the cooking liquid is very low. However, the additional addition of formic acid should normally be less than 25% of the amount of formate added.

The addition of said substances has been shown to give the best results if the total SO 2 content of the cooking liquid is more than 1.5 times higher than its bound SO 2 content. This means that the invention can be applied not only in conventional cooking using acid sulphite, but also in modern bisulphite soup, e.g. magnesium bisulphite soup.

The method according to the invention is described below by means of implementation examples. All soups using acid sulfite are made on a laboratory scale, but the treatment is directly transferable to the factory scale. Bisulfite cooking examples are taken directly from the factory scale using continuous cooking pots.

In laboratory experiments, an 8-liter laboratory cooking pot was filled with dry spruce chips (dry weight about 1 kg) and 4 liters of preheated cooking acid containing 6.0% total SO 2 and 1.7% CaO-bound SO 2. The starting temperature was 60 ° C. Each soup was preceded by a 2-hour saturation period, during which the temperature was gradually raised to 80 ° C. After the impregnation period, heat conduction was added so that the final cooking temperature, about 130 ° C, was reached 5 hours after the start of cooking. The total cooking time varied in different experiments. At the end of the cooking time, gassing and cooking interruption followed in the usual way. The yield of each individual soup was determined by accurately weighing the chips with a known dry matter content and the amount of pulp produced by washing, defibrating, drying and weighing.

A uniform chip quality was used throughout the test series, but to check that no changes due to variations in the treatment affected the result, zero soup was performed at regular intervals throughout the test period without the addition of yield enhancers. All these zero soups showed very good similarity to each other and gave an average unscreened mass in a yield of 51.4 5 & with a kappa number of 40. The whiteness was 64% 5 58521 SCAN. The average cooking time was 9.0 hours. Using all the experiments shown in the following Table I, 100 parts of formate, 3 parts of formic acid and 30 parts of nonionic dispersant were mixed, and the mixture was mixed in water in a ratio of 1:20. The aqueous dispersion was mixed with the cooking acid immediately before it was added to the kettle.

Table I

Example No. 1 23

Additive Exo-isophenyl- Endophenyl- Exo-norborliformate liformate nylformate

Addition, g per ton of dry wood 24 96 about 10,000

Cooking time, hours 8.5 8.5 9.1

Chapter 38 40 35

Whiteness, SCAN 69.5 70.0 69.5

Yield of unscreened pulp,% 55.5 57.2 56.2

The experiments, using continuous bisulfite cooking on a large scale, were performed using the equipment schematically shown in the accompanying drawing, and the procedure was as follows:

The spruce chips were fed from the chip tank A by means of a chip feeder B (formed as an impeller feeder) and through a low pressure tap C (i.e. a cell feeder) to an evaporation tankD formed by a reclining cylinder with a horizontal feed screw. Fresh steam was passed from below through the chip plug so that a pressure of about 1.5 aty was maintained in the steam tank. The residence time in the steam tank was 2-4 min. The steam mixed with the air removed from the chips was led to the outside air through a chip hopper as it leaked through the low pressure tap and the chip measuring device, but it could also be removed in controlled amounts from the evaporator via a special air conditioning line.

From the steaming vessel, the chips were led down through the chip line E to the high-pressure tap F and here they were packed by means of circulating cooking liquid into the tap chamber, which in this case was vertical. After this chamber had become horizontal due to the rotation of the faucet, more cooking liquid was added, which flushed out the chips and transferred them to the upper 6 58521 separator G. The upper separator is an obliquely lying cylinder with a central screw for transporting chips and acid and a screen at the bottom. to remove the acid circulating through the high pressure tap. Impregnation of the steamed chips took place on the way from the high-pressure tap to the outlet end of the upper separator in about 3 minutes at a temperature of 110 ° C and a pressure of 12 aty. The cooking liquid heated to about 90 ° C by means of alkali vapors was introduced into the system at the upper separator in such an amount that the ratio of wood to cooking liquid was adjusted to 1: 2. The cooking acid contained about 8.5% total SC 2 and 4.2% MgO-bound SC 2.

Chips and acid were dropped from the upper separator into the steam chamber of the boiler H. The boiler was a vertical cylinder with a diameter of 4 m and a height of 48 m, so that its volume was thus 600 m ^ and the daily capacity was e.g. 330 tons of pulp. The upper half of the boiler was used for the actual cooking and the lower part for countercurrent washing at a relatively high temperature.

Direct steam was introduced into the steam space so that the volume of the cooking pot was heated very rapidly to the full cooking temperature, which in this case was 158-160 ° C. At the end of cooking zone J, the liquor was removed via line K and returned to recovery. In the washing zone L below, the pulp was washed with water passed through line M, and the washed mass was removed through outlet line N at the bottom of the boiler.

Of the three implementation examples shown in Table II below, one was performed without additions (comparative experiment) and two experiments with the addition of 50 g of endophenyl formate (EFF) per ton of dry wood. In the same manner as in the above laboratory experiment, the formate (in another case together with 3 .mu.l of formic acid) was dispersed in water with a nonionic active dispersant, and the dispersion was added to the cooking acid immediately before the high-pressure tap. The results of the experiment are shown in Table II below.

58521 7

Table II

Example No. 4 5 6

Addition g per tonne No 50 g pure 50 g pure dry wood addition EFP EFF + 3% other monetary acid

KSC ^ # 8.5 of 8.5

Chapter 45 45 45

Breaking length, 40 ° SR m 8500 8700 9600 'Breaking length, 20 mi after grinding time m 6600 6800 8500

Tear strength with a breaking length of 8000 m g 85 90 101

Whiteness SCAN 69 72 75

Yield of unscreened pulp% 53.0 56.0 57.5

Experiments on a factory scale were also performed by adding hexyl formate (HF) together with 1% formic acid based on the weight of the formate. The results are shown in the following Table III, which shows the same comparative experiments as above.

Table III

Example No. 4 7 8

Addition g per tonne dry- No 50 g HF + 3% 100 g HF + 3% si intended wood addition formic formic acid

KSO2% of cooking acid 8.5 8.5. 8.5 "SSO2% 4.0 4.0 4.0

Chapter 45 45 45

Breaking length, 40 ° SR m 8500 8600 9300

Breaking length, after 20 minutes grinding time m 6600 6800 8300

Tear strength with a breaking length of 8000 m g 85 87 99

Whiteness SCAN 69 71 74

Yield of unscreened pulp% 53.0 55.8 57.3