FI83100C - Process for preparing pulp of lignin-containing cellulose raw material - Google Patents

Description

x 83100

METHOD FOR MAKING PULP FROM LIGIN-CONTAINING CELLULOSE RAW MATERIAL

The present invention relates to a process for producing pulp by an alkaline cooking process as defined in claim 1.

One of the weaknesses of sulfate cooking is the non-selectivity of delignification. To dissolve the lignin 10, harsh cooking conditions have to be used, which, especially in the final stages of cooking, may cause an additional discharge of the carbohydrate part of the pulp and a further reduction in the yield and quality of the pulp. As a result, the aim is to finish the cooking before this final stage, whereby the lignin content of the pulp remains relatively high. On the other hand, a high lignin content of the pulp is disadvantageous in the production of the pulp to be bleached.

The efficiency and selectivity of lignin removal in sulfate cooking can be improved by a variety of additional chemicals. Bringing additional chemicals into the cooking process causes inconvenience in some cases.

The selectivity of sulphate cooking can also be improved to some extent by regulating the time profile during cooking, which requires additional equipment and investments. Among the parameters of normal sulphate cooking, it is mainly possible to improve the selectivity of lignin removal by increasing the sulphidity. In the production of the pulp to be bleached, the trend has recently been the introduction of high sulphidity in cooking, which speeds up the cooking process and allows for further cooking without compromising the strength of the pulp. However, the high sulfur content of the process places demands on the durability of the equipment materials and causes inconveniences to the environment. Increasing the sulfide content increases the amount of volatile sulfur compounds in 35 soups as well as in the treatment and incineration of black liquor. Therefore, the recovery and processing of these compounds into the recoverable form is necessary both for the environment and for the process itself. Even with the current technology, the recovery of volatile sulfur compounds from the various stages of the process for combustion, as well as the scrubbing of flue gases containing sulfur dioxide-5 from the recovery boiler, is then necessary.

The presulfonation of chips with a sulfite solution prior to sulfate cooking has been studied in connection with the preparation of high alpha viscose pulp by prehydrolysis sulfate cooking (Rydholm, S.A .: Pulping Processes 10 Interscience Publishers 1965, p. 658). The aim has been to prevent the condensation of lignin in the prehydrolysis step in order to hydrolyze the hemicellulose as efficiently as possible before the sulphate cooking. The sulfur dioxide-water mixture alone in pretreatment step 15 increases the condensation of lignin because the sulfonic acid groups formed in the sulfonation cause high local acidity in the solid phase. Instead, the sulfonates formed when using bisulfite contain a metal ion as a cation instead of a hydrogen ion, and condensation is prevented, which allows a rather low lignin content to be achieved in the sulfate cooking step.

It is an object of the present invention to obviate the above drawbacks.

In particular, it is an object of the invention to provide a new and more efficient method by which alkaline cooking can be accelerated and pulp bleachability can be improved.

It is a further object of the invention to provide a new method for producing pulp from a lignin-containing cellulosic raw material so that the lignin removal efficiency and selectivity in alkaline cooking, especially sulphate cooking, can be improved to a greater extent.

It is a further object of the invention to provide a new process for producing pulp from a lignin-containing cellulosic raw material by an alkaline cooking process so that too harsh cooking conditions do not have to be used to remove lignin and the cooking does not cause a reduction in pulp yield and quality due to carbohydrate decomposition.

It is a further object of the invention to provide a new process for producing pulp from a lignin-containing cellulosic raw material by an alkaline cooking process so as to achieve the above advantages, but the cooking process does not increase the need for desulfurization and increased environmental damage caused by sulfur.

For aspects of the invention, reference is made to the claims.

According to the invention, the lignin-containing cellulose-15 raw material is treated with a sulphite solution before the actual alkaline cooking. The lignin contained in the pretreated raw material is sulfonated, which promotes the decomposition and dissolution of the lignin in the cooking step following the pretreatment. Due to the increase in lignin removal 20, cooking can be performed under milder conditions than normal, which reduces the degradation of the main ingredients of the pulp, cellulose and hemicelluloses in the cooking, thus giving the pulp better than normal properties for papermaking.

Due to the increased lignin removal caused by the presulfonation, the residual lignin in the pulp after cooking remains more reactive than in the pulp after normal cooking. This makes it easier to remove lignin from the pulp also in bleaching, which reduces the consumption of bleaching chemicals compared to bleaching normal pulp.

The increase in lignin reactivity caused by presulfonation can also be exploited in the so-called in extended cooking, i.e. in the cooking stage, 35 more lignin can be removed than normal without compromising the properties of the pulp. Prolonged cooking, i.e. a lower than normal lignin content in the pulp, reduces the need for bleaching chemicals 4 83100 as well as the amount of bleaching effluent and the need for cleaning.

in general, using the process of the invention, the removal of lignin from the lignocellulosic raw material can be selectively enhanced both in the cooking step and in the subsequent bleaching step. Thus, when the cooking process is carried out to a certain level of lignin, the decomposition of carbohydrates is lower, the quality and yield of the pulp are better, the need for chemicals 10 is lower in cooking and possible bleaching, and the cooking becomes less polluting and less wasteful.

The presulfonation of the cellulosic feedstock according to the invention can be used not only for normal sulphate cooking but also for other alkaline cooking processes, such as sulphate cooking modifications: sulphate-anthraquinone or other additive sulphate cooking, polysulphide soups such as polysulphide-anthraquinone or other in additive sulphide soup, soda soup, such as soda-anthraquinone or other additive-soda soup, in time and semi-alkaline sulphite soups, such as sulphite-anthraquinone or other additive sulphite soup.

The pretreatment of the cellulosic raw material is suitably carried out with a sulphite solution having a total sulfur dioxide content of 0.5 to 15% by weight, preferably 3 to 8% by weight and a pH of 1 to 13.5, preferably on the acid side 1.5-3 or on the basic side 9- 12.

The treatment temperature is suitably 50 to 190 ° C, preferably 100 to 150 ° C.

The treatment time is suitably 1 to 300 minutes, preferably 30 to 120 minutes.

The liquid-wood ratio in the pretreatment is 2 to 15 1 / kg, preferably 3 to 6 1 / kg.

35 The solution used in the pre-treatment can be partially or substantially completely separated from the cellulosic raw material before alkaline cooking.

5 83100

When performing the pretreatment, the cellulosic raw material pretreated with an acidic sulfite solution can be washed neutral or neutralized before alkaline cooking.

5 When pretreating the cellulosic raw material with an alkaline or semi-alkaline sulfite solution, the solution used in the pretreatment can be used in part or in full in the early cooking step. Thus, the sulfite-containing waste solution 10 used in the pretreatment may be added in part or in whole to the beginning of the cooking or to a later stage; e.g., at the end of the alkaline cooking, a portion of the cooking solution may be removed from the digester and at least a portion of the sulfite solution used in the pretreatment may be added to the cooking.

The sulphite solution used in the pretreatment of the cellulosic raw material can also be reused at least in part, e.g. in the pretreatment of another lignin-containing cellulosic raw material. In addition, the solution used in the pretreatment can be used, in part or in whole, to wash the pulp 20 after alkaline cooking.

It should be noted that additives such as anthraquinone or other additives known per se may also be used in the sulphite treatment of the cellulosic raw material according to the invention to enhance the selectivity of lignin removal, to prevent degradation of cellulose and hemicellulose or for other reasons as known in the art.

The invention is described in detail below by means of exemplary embodiments.

30

Example 1

The wood raw material was wood chips made from pine trunks, fractions of more than 32 mm and less than 6 mm were screened out of the wood chips, and the wood chips were air-dried to a dry matter content of about 90% by weight. Experimental soups were performed in a 10 L forced flow digester. Normal sulfate cooking conditions were as follows: 6,838,100

Chip dose 1800 g (a.k.)

Liquid / wood ratio 4 1 / kg

Effective alkali (NaOH + NaaS) 4.5 to 6.5 mol / kg wood

Sulfidity 30 - 50%

5 Temperature increase 20 "C -> 170 * C 2 h Cooking temperature 170 * C

Time at 170 eC 45-210 min

The pre-sulfonation of the chips before the sulphate cooking was carried out under acidic, semi-alkaline or temporal conditions. In the presulfonation, the conditions were:

Acid Semi-Early Early 15 pH 1.7 10 13

Sulphite total SO2 NaaSOa NaaSOa ti 6.4% 4 mol / kg wood 4 mol / kg

NaOH 0.8 mol / kg

Liquid / wood 4 1 / kg 4 1 / kg 4 1 / kg

20 Temperature 120 'C 140 * C 140 * C

Time 1 h 1 h 1 h

After acid pre-sulfonation, the chips were washed with water. After semi-alkaline and alkaline sulfonation, 70% of the sulfonation solution was removed and replaced with an equivalent amount of white liquor. In sulfate cooking 5, the time dose was normal (TA 4.5 mol / kg) or lower than normal (TA 3.15 mol / kg). In the case of semi-alkaline sulfonation, in some cases the solution obtained from the sulfonation was added to the final stage of cooking by first removing 70% of the cooking solution. In some cases, anthraquinone was added to the pre-sulfonoin-10 disulfate soup for either the pre-sulfonation or cooking step, usually 1 g / kg wood. After cooking, the masses were washed and sorted as usual.

The effect of the pre-sulfonation of the chips on the kappa-15 number of the pulp in the sulphate cooking is shown graphically in Figure 1, where the cooking time (h) / 170 ° C on the x-axis and the piece number 7 83100 are shown on the y-axis.

The cooking time at 170 * C could be reduced by 60-70% to achieve the same kappa number compared to normal 5 sulphate soups due to early (pH 13) or semi-alkaline (pH 10) sulphonation of the chips (Figure 1) ·

After acidic presulfonation, the cooking time could be shortened by more than 80% of the cooking time of a normal sulfate soup 10 at the pot level 30 (Figure 1). By adding anthra-quinone to the soup after alkaline or semi-alkaline sulfonation, the rate achieved by almost acid sulfonation in sulfate cooking was achieved. Anthraquinone can also be added to the alkaline presulfonation step. Neutral sulfonation of the chips (pH 8) before acid sulfonation to maintain yield did not slow down sulfate cooking (Figure 1).

Figure 2 shows graphically the effect of wood chip presulfonation on total sulfate mass yield; number of pieces on the x-axis and total yield on the y-axis.

After acidic pre-sulfonation, the yield of sulfate soup was about 3 percentage points lower than without pre-sulfonation at the acid level 30.

25 When anthraquinone was used in cooking 2 g / kg of wood, the yield increased by 2 percentage points, which was sufficient to compensate for the difference in yield compared to normal cooking in advanced cooking with a kappa number of less than 20. In terms of yield, this use of anthraquinone was equivalent to neutralization of 30 chips.

After alkaline sulfonation, the yield of sulfate broth was about one percentage point lower than that of normal sulfate broth (Fig. 2). The use of anthraquinone 35 (1 g / kg) in the cooking step eliminated this difference, and if it was used in addition to the cooking step in the sulfonation step, the yield was higher than in normal β 83100 sulfate soup.

From a yield point of view, semi-alkaline sulfonation of the chips was most preferred; in the subsequent cooking, the yield level of sulfate soup was reached (Fig. 2). If anthraquinone (1 g / kg) was used in cooking 5, the yield was better than that of sulphate cooking.

Figure 3 shows the effect of chip presulfonation on the viscosity value of the pulp after sulphate cooking, the number of pieces on the x-axis and the viscosity on the y-axis.

The viscosity values of the unbleached sulphate pulp were not affected by alkaline or semi-alkaline sulfonation of the chips (Figure 3). In contrast, acid sulfonation had a significant effect: the viscosity-15 value was a quarter higher than that of the corresponding normal sulfate mass.

Example 2. (Semi-alkaline sulfonation-sulphate cooking process) Since semi-alkaline sulphonation with sodium sulphate solution seemed to be the most advantageous for pulp yield, the sulphate cooking rate was of the order of alkaline sulphonation and would be easier to carry out than e.g. acid pre-sulphonation. In these, part (70%) of the sulfonation solution was added back to the soup at the end of the cooking, the alkali dose of the cooking was reduced and in some cases anthraquinone was also used in the sulfonation step. A diagram of the cooking process in which the waste solution from the semi-alkaline (pH 10) pre-sulfonation of the chips is added to the final stage of sulphate cooking at a reduced alkali dose is shown in Figure 4.

The effect of the addition of the chip pre-sulfonation solution on the final stage of cooking and the effect of the addition of anthraquinone 35 on the pulp number in the sulphate cooking are shown in Figure 5, where the cooking time is shown on the x-axis and the number on the y-axis.

9 83100

The results showed that the use of anthraquinone in the sulfonation step increased the cooking rate. Reducing the alkali dose of cooking after sulfonation by 30% from 4.5 ml / kg to 3.15 mol / kg clearly slowed down the cooking-5 process, however, taking a further 25% shorter cooking time to the cup 30 than normal sulphate cooking at 4.5 mol / kg alkali ( Figure 5). When anthraquinone was added to the sulfonation step again, the cooking rate was again in the order of almost 4.5 ml / kg of alkali-boiled sulfonate ti-sulfate cooking.

When using a normal 4.5 mol / kg alkali dose in cooking, the addition of a semi-alkaline sulfonation solution to the final stage of cooking slightly increased the yield, i.e. less than 0.5 percentage points compared to sulfonation-sulfonate cooking without addition of sulfonation solution and 0.5-1 percentage points compared to normal sulphate cooking.

Figure 6 shows the effect of the addition of the pre-sulfonation solution of the chips on the final stage of cooking and the effect of the addition of anthraquinone on the pulp yield in the sulphate cooking; number of pieces on the x-axis and total catch on the y-axis.

Reducing the alkali dose of the soup significantly increased the yield of the sulfonation-sulfate soup. The non-addition of I-25 compared to sulfate soup was 2 to 2.5 percentage points.

Figure 7 shows the effect of the addition of the pre-sulfonation solution of the chips to the final stage of cooking and the effect of the addition of anthraquinone to the pulp viscous after 30 sulphate cooking; piece number on the x-axis and viscosity on the y-axis.

Example 3. (Pre-sulfonation of wood chips in different time soups) 35 The effect of acid pre-sulfonation of wood chips was tested on different time soups. The results are shown in Table 1.

10 831 00

Sulfonation significantly accelerated the cooking process in various sulphate cooking variants (sulphate-AQ-, polysulphide, polysulphide-AQ-) and also in soda-cooking variants (soda, soda-AQ-, soda-5 -NaBH * -). It had the greatest effect on soda NaBH * and soda soups.

The presulfonation significantly accelerated the neutral sulphite AQ (NS-AQ -) cooking of pine.

Table 1.

10 Cooking method Time Normal Pre-sulphonation ** / min * kappa yield /% kappa yield% sulphate 30 59.9 48.8 44.2 46.9 sulphate 60 31.0 44.8 16.5 40.9

Sulphate 120 21.0 42.7 12.9 38.7

15 Sulfate + AQ

(2 g / kg) 30 43.8 47.7 18.7 43.4

Polysulphide (42 g / kg) 30 40.6 52.8 22.3 47.2

Polysulfide (42 20 g / kg) + AQ

(2 g / kg) 30 43.7 53.4 20.5 48.4

Soda 60 93.6 54.3 45.1 44.8

Soda 120 83.7 51.1 27.7 41.6

Soda + AQ

25 (2 g / kg) 60 48.8 49.7 20.1 44.2

Soda + NaBH *) (30 g / kg) 60 10.1 58.1 38.1 50.2 e **) NS-AQ (1.5 g / kg) 180 37.5 56.0 28.4 51.3

30 *> Soup ***> NS-AQ

liquid / wood 3.5 1 / kg 3.5 1 / kg time dose 4.5 mol / kg (effective) 6.25 mol / kg / (NaaSO * + NaaCOs) sulphidity 30% (sulphate) 35 51% (polysulphide) 0% (soda) li 83100

cooking temperature 170 'C 175 * C

raising to cooking temperature 2 h 2 h 5 Presulphonation liquid / wood 5 1 / kg 3.5 1 / kg pH 2 1.8 total SO 7.7% 3.2%

temperature 120 eC 100 * C

10 time up to 120 ° C 60 min 60 min time up to 120 ° C 60 min 60 min

Example 4: (bleaching) In this experiment, the effect of the methods on bleaching was investigated. From different pulp types, pulps with a suitable kappa number were selected for bleaching. Known D / CEDED and D / CED sequences were used for bleaching. The bleaching conditions were:

Step Da 0 / C7 o Ex Dx Ea Da

Consistency,% 3 10 10 10 10 10 Temperature, ° C 35 60 60 60 60

Time, min 1/29 60 180 60 180

The results of the bleaching experiments are shown in Table 2.

15 Pre-sulfonation of the chips, especially acidic, appeared to increase the bleach yield, apparently due to lower than normal carbohydrate losses in the cooking. With respect to the number of pieces at normal chemical dosage, the brightness of the presulfonation-sulfate pulps easily increased above 90 ISO, with a target value of about 89 ISO. The use of sulphite in cooking thus improved the bleachability of the sulphate pulp. Acid presulfonation of the chips had a clear positive effect on the viscosity of the D / CEDED bleached pulp.

25 The tear index slightly decreased the mass number i3 83 1 00

Table 2

Pulp whitening results and properties (OFI grinding)

Kelttomenet. Pulp White- Dosage / Consumption

Teholl.alk. Sulfatoethyl. NaaSO 3 Kappa yield relative to white. kemlkal. mol / kg X raol / kg X distel- X act. Cl I D / C Di Da Kokon.

Sulphate 1. 4.5 30 - 31.5 49.9 D / CEDED 5.6 / 5.5 3.0 / 3.0 1.0 / 0.5 9.6 / 9.0 2. 4.5 30 - 23.3 44.7 D / CEDED 4.7 / 4.5 2.9 / 2.5 1.0 / 0.7 8.6 / 8.0 3. 5.5 40 - 25.3 44.8 D / CEDED 5.1 / 4.8 3.0 / 2.8 1.0 / 0.8 9.1 / 8.4 4. 5.5 40 - 17.8 43.4 D / CEDED 3.7 / 3.7 2.8 / 2.4 1.0 / 0.8 7.5 / 6.9 5. 5.5 40 - 15.6 32.9 D / CEDED 3.3 /3.2 2.7 / 2.3 1.0 / 1.0 7.0 / 6.5

Sulflittleslkäslt.

Sulf on. pH 13 -t- sulphate 6. 4.5 30 - 30.7 45.5 D / CEDED 5.5 / 5.2 3.0 / 2.8 1.0 / 0.9 9.5 / 8.9 7. 4.5 30 - 17.1 42.8 D / CEDED 3.3 / 3.3 2.8 / 2.2 0.8 / 0.6 6.1 / 6.1

Sulfo. pH 10 + sulphate 8. 4.5 30 - 33.3 46.8 D / CEDED 5.8 / 5.8 2.9 / 2.6 0.8 / 0.7 9.5 / 9.1 9. 4.5 '30 - 18.9 44.0 D / CEDED 3.5 / 3.5 2.5 / 2.1 0.8 / 0.6 6.8 / 6.2 10 4.5 30 + si (phl0) K - 44.7 D / CEDED 3.0 / 2.9 2.2 / 2.0 0.7 / 0.5 5.9 / 5.5 11. 18.7 44.7 D / CEDED 2.8 / 2.8 1.9 / 1.8 0.6 / 0.5 5.3 / 5.1 12. D / CEDED 2.6 / 2.5 1.7 / 1.7 0.5 / 0.4 4.8 / 4.7 13. 4.5 30 + si (pH10) x 13.0 41.7 D / CEDED 2.1 / 2.1 2.0 / 1.8 0.6 / 0.5 4.7 / 4.4.

14. 3.15 30 + si (pH10) * c 31.7 48.9 D / CEDED 5.3 / 5.2 2.5 / 2.1 0.7 / 0.6 8.5 / 7.9 15 3.15 30 + si (pH10) x 31.7 48.9 D / CEDED 5.7 / 5.6 2.5 / 2.3 0.8 / 0.6 9.0 / 8.6 16 3.15 30 si (pH10) “33.4 49.2 D / CEDED 5.2 / 5.1 2.2 / 2.1 0.7 / 0.6 8.1 / 7.8. . 17. D / CEDED 4.2 / 4.2 2.2 / 2.2 0.8 / 0.7 7.2 / 7.1 18. 3.15 30 + si (pH10) K 18.5 45.1 D / CEDED 3.0 / 2.9 2.0 / 1.7 0.6 / 0.5 5.6 / 5.2 Γ 19. 4.5 30 + si (pH10) '* 13.0 41.7 D / CED 3.5 / 3.1 2.0 / 1.7 - 5.4 / 5.8

Sulfo. pH 1.7 + sulfate; 20. 4.5 30 - 31.1 42.9 D / CEDED 5.6 / 5.6 30./2.9 1.0 / 0.8 9.6 / 9.3 21 · 4.5 30 - 15.0 40.4 D / CEDED 3.0 / 2.9 2.4 / 1.8 0.7 / 0.5 6.1 / 5.2 22. 4.5 30 + AQ2g / kg 13.4 41.0 D / CED 3.0 / 2.9 1.9 / 1.6 - 4.9 / 4.5 .23. 4.5 30 + AQ2g / kg 14.7 42.1 D / CED 3.7 / 3.3 2.0 / 1.6 - 5.7 / 4.9 h 83100

Table 2 (cont.)

In his own strength. (SR 30)

NaOH Vaal. Viscose PC Yield Flour. Veto- Holiday. Tear-off dose, X X ISO commissioned number X rev. ind. ind. sylnd,

Ex Dx Ea Kokon. dm 3 / kg Nm / g kPa. raN.mVg m2 / g T. 2.1 0.3 0.9 3.3 87.6 1080 1.02 94.1 5636 114.5 8.95 11.2 2. 1.7 0.3 0.9 2.9 88.4 990 0.98 95.5 4750 109.0 8.95 11.0 3. 2.0 0.3 0.9 3.2 90.2 940 0.53 97.6 4500 100.5 8.55 11.9 4. 1.5 0.3 0.9 2.7 89.5 790 0.59 96.8 - - 5. 1.35 0.3 0.9 2.55 90.2 740 - 96.8 5288 102.0 7.50 11.2 6 2.0 0.3 0.9 3.2 91.4 1030 0.56 94.9 6000 107. 8.35 12.1 7. 1.4 0.3 0.9 2.6 91.1 820 0.61 96.9 6400 97.0 7.70 11.6 8. 2.2 0.3 0.9 3.4 91.1 1030 0.61 93.9 5579 103.0 8.80 11.2 9. 1.5 0.3 0.9 2.7 90.1 940 0.58 96.3 ...

10. 1.3 0.3 0.9 2.5 90.2 950 - 97.2 3714 99.0 8.65 11.2 11. 1.2 0.3 0.8 2.3 88.7 980 - 97.3 ...

12. 1.1 0.3 0.7 2.1 88.4 970 - 97.4 ...

13. 1.0 0.2 0.7 1.8 89.4 770 - 98.3 ...

14. 2.0 0.3 0.9 3.2 91.3 1160 0.55 93.6 5000 109.0 8.55 9.60 15. 2.1 0.3 0.9 3.3 91.7 1170 - 93.2 - 16. 1.9 0.3 0.8 3.0 91.0 1190 - 93.2 5269 104.0 8.40 10.6 17. 1.5 0.3 0.7 2.5 87.0 1170 - 93.2 5190 97.0 8.25 11.5 18. 1.3 0.3 0.8 2.4 91.2 1080 96.2 5556 97.5 7.35 11.7 19. 1.4 0.2 - 1.6 87.5 760 - 98.5 5353 104. 8.10 12.1 20. 2.1 0.3 0.9 3.3 91.7 1180 0.48 95.0 7000 87.5 6.70 16.2 21. 1.4 0.3 0.8 2.5 91.4 890 0.28 97.8 ...

22. 1.2 0.2 - 1.4 88.1 920 - 7000 77.5 6.90 15.9 23. 1.40.2 - 1.6 88.8 950 - 97.1 5556 91.5 6.50 14.5 · * 70 X of sulphonation solution added to the final stage of cooking

Claims (11)

A process for preparing pulp of lignin-containing cellulose raw material by an alkaline boiling process, wherein the cellulose raw material is pretreated with sulfite solution prior to the alkaline boiling and to effect the delignification in the kitchen, characterized in that the cellulose raw material is treated in the lignin, and the pH of the sulfite solution is 1.5-3 or 9-13, the treatment temperature is 100-150 ° C and the treatment time in the acid range 1-60 minutes or in the basic range 1-120 minutes. 2. A process according to claim 1, characterized in that the total sulfur dioxide content of the sulfite solution is 0.5 - 15%, advantageously 3 - 8%. 3. A process according to claim 1 or 2, characterized in that the liquid / wood ratio is 2 - 15 l / kg, advantageously 3-6 l / kg. 20 4. A process according to any one of claims 1 to 3, characterized in that the solution used in the pre-treatment phase is separated from the cellulose raw material before the alkaline boiling partially or substantially completely. 25 Process according to any of claims 1 to 4 wherein the pretreatment is carried out with acid sulfite solution, characterized in that the pretreated cellulose raw material is washed so that it becomes neutral or neutralized before alkaline boiling. 30 6. A process according to any one of claims 1 to 4 wherein the pretreatment is carried out with an alkaline or semi-alkaline sulfite solution, characterized in that the solution used in the pretreatment is used partially or completely in the alkaline boiling phase. 35 7. A process according to claim 6, characterized in that in the final stage of the alkaline boiling part of the boiling solution is removed from the boiler ie 83100 and at least part of the solution used in the pre-treatment is added to the boiling. Process according to any of claims 1-7, characterized in that part of the solution used in the pre-treatment is returned in the pre-treatment. 9. A process according to any one of claims 1 to 7, characterized in that the solution used in the pre-treatment is used for washing the pulp after the alkaline boiling. 10. A process according to any one of claims 1-9, characterized in that the alkaline boiling is a sulphate boiling, sulphate anthraquinone or other additive sulphate boiling, polysulphide boiling, polysulphide anthraquinone or other additive sulphide boiling; a soda boiling, soda-anthraquinone or other additive soda boiling, alkaline or semi-alkaline sulphite boiling, sulphite anthraquinone or other additive sulphite boiling. Method according to any of claims 1 to 10, characterized in that anthraquinone or other additive is used in the sulphite pretreatment of the cellulose material.