LT3269B - Process for bleaching of lignocellulose-containing pulps - Google Patents

Abstract

The invention relates to a process, in association with bleaching lignocellulose-containing pulp, for rendering a peroxide-containing bleaching stage more efficient by means of the pulp, prior to such a stage, being treated with a sequestering agent, with the trace metal profile in the pulp being altered by treatment with the sequestering agent, in the absence of sulphite, at a pH within the interval from 3.1 up to 9.0 and at a temperature within the interval from 26 degree C up to 100 degree C, after which the treatment with a peroxide-containing substance is carried out in a second stage, at a pH within the interval from 7 up to 13, with the said two- stage treatment being carried out at an optional position in the bleaching sequence which is used for the pulp.

Description

The present invention relates to a method for bleaching pulp containing lignocellulose to treat the pulp with a complexing agent in a neutral environment and at elevated temperatures in the absence of sulfite before treating the peroxide stage with a compound peroxide containing alkali. .

Pulps containing lignocellulosic are classified as chemical pulps of soft wood and / or hard wood which are delignified by sulphite, sulphate, soda or organosolvent processes or modifications thereof. Before bleaching with chlorine-containing chemical reagents, the pulp may be delignified at the oxygen stage.

Chemical pulp bleaching is performed mainly by bleaching agents which include chlorine such as chlorine, chlorine dioxide and hypochlorite; this results in the bleaching process effluent causing corrosion, which includes chloride, which is difficult to regenerate, resulting in the release of toxic waste into the surrounding environment. At present, the aim is to maximize the use of bleaching agents with little or no chlorine content to reduce waste and possible wastewater regeneration. One example of such a bleaching agent is oxygen, the use of which is increasing recently. The use of an initial oxygen-alkaline stage in a multi-stage bleaching process, such as sulphate pulps, makes it possible to reduce bleaching production waste by more than half as wastewater containing chlorine is susceptible to regeneration. However, after the initial oxygen bleaching stage, the lignin remaining in the pulp accounts for about half of the amount remaining after delignification in the cooking process. This lignin must be extracted from the pulp by further bleaching with chlorine-containing bleaching agents.

Therefore, there is a tendency to reduce the amount of lignin that needs to be removed by bleaching with a chlorine-containing agent at various stages prior to bleaching (i.e., pre-treatment steps).

Other types of bleaching agents are more suitable for regeneration, having peroxides, such as inorganic peroxides, such as hydrogen peroxide and sodium peroxide, and organic peroxides, such as acetic acid. In practice, hydrogen peroxide is not used to a much greater degree for the initial reduction and / or brightening of lignin in the first stage of the multi-stage bleaching process, due to the need to add large amounts of hydrogen peroxide.

Thus, treatment with hydrogen peroxide in an alkaline environment, after reaching a satisfactory degree of lignin dissolution, requires the addition of large amounts of hydrogen peroxide, due to the high degree of hydrogen peroxide decomposition; resulting in a significant increase in the consumption of chemical reagents. When treated with hydrogen peroxide in an acidic environment, the same degree of solubility of lignin as in alkaline treatment can be achieved with significantly lower hydrogen peroxide consumption. However, treatment in an acidic medium leads to a significant decrease in the viscosity of the pulp, i.e. At low pH values, hydrogen peroxide degradation products attack not only lignin but also cellulose, reducing the length of the carbohydrate chain, which results in poor pulp resistance. What's more, the treatment in a very acidic environment is unsatisfactory, because then the already dissolved lignin settles, the resin becomes sticky and difficult to dissolve, and problems arise in the regeneration of acid effluents.

According to Swedish patent application no. A decrease in the viscosity of 420,430 when treated with hydrogen peroxide in an acidic medium can be avoided by treatment with a complexing agent such as DTPA (diethylenetriaminepentaacetic acid) at pH 0.5 to 3.0. This treatment is followed by an alkaline extraction step followed by an alkaline extraction step to remove the dissolved lignin.

Further, metal traces are known to be removed from cellulosic pulps by the action of total sodium sulfite (SO ₂ ) in alkaline solution) and DTPA prior to the peroxide treatment step, cf. Gellertedt et al., Journal of Wood Chemistry and Technology 2 (3), 231-250 (1982). At this point, DTPA complexes with the reconstituted metal ion are formed, these complexes can be removed from the pulp by washing, and then more effectively treated with hydrogen peroxide.

For the incorporation of mechanical pulps into the bleaching process, pretreatment with complexing agents, prior to treatment with hydrogen peroxide in alkaline conditions, is commonplace. e.g. European patent no. 285,530; U.S. Patent No. 3,251,731; and USSR copyright

No. 903.429. However, in this case, the purpose is only to whiten the pulp, but not to delignify it. To this end, the activity of hydrogen is regulated by the addition of silicates, silicate, so that chromophoric groups are reduced. The absence of silicate in the bleaching composition results in the mechanical pulp not getting the best brightness even if it significantly increases the amount of hydrogen peroxide, for example, by 50% compared to the usual amount. Chemical pulp avoids the addition of silicates because it increases the price of chemicals, such as sodium, specifically the price of the reagents without any positive effect, and also makes simple sewage recovery impossible. Moreover, in the case of chemical pulps, the increase in brightness is strongly influenced by the change in pH during the complexing step, whereas it is not observed when treating mechanical pulps with complexing agents.

For delignified pulp containing lignocellulosic pulp, such as softwood pulp, the usual sequence of steps in a multi-stage bleaching process is: D CH / D EDED (D - oxygen stage, CH / D stage using chlorine / chlorine dioxide, E - alkaline extraction stage, D - Stage using chlorine dioxide) Thus, the purpose of the various stages of pretreatment is to reduce the amount of lignin before the first stage with chlorine, which reduces the chlorine demand and reduces the POCH (POCH) in the bleaching process effluent. Because prior art pretreatments include either acid treatment steps or the use of additives that are unsuitable for regeneration during processing, there is a limited possibility of developing a closed system in bleach production. To overcome technical problems arising in this process, expensive equipment needs to be installed.

The possibility of reducing POCH by replacing CH / D in the conventional bleaching sequence by D was discussed, since this latter is characterized by a lower amount of toxic waste compared to CH / D because of the elimination of molecular chlorine. However, high levels of chlorine dioxide must be used at this stage to reduce the lignin content to the required low levels before the subsequent bleaching process steps. It is therefore an object of the present invention to solve the above problem by modifying the existing sequence of steps in the bleaching process to obtain POCH values that are as low as possible and thereby obtain a product of the same or better quality.

The present invention relates to a method of treatment wherein the initial chlorine-free delignification step can be substantially improved without any additional cost or capital ideas. This treatment is carried out in two steps: the first step involves the replacement of the metal trace contents in the pulp by treatment with a complexing agent in an elevated temperature in a neutral environment; The second step involves peroxide treatment in an alkaline environment, and this two step treatment is a bleaching method which is significantly less environmentally harmful due to the substantial reduction in the use of chlorine-containing reagents.

Thus, the invention is a method of treating lignocellulosic pulp according to the formula of the invention. According to the present invention, this bleaching process relates to a method for more efficient peroxide treatment by treating the pulp with a complexing agent prior to this step, thereby changing the amount of metal trace in the pulp by treating with the complexing agent in the absence of sulfite, pH. in the range of 3.1 to 9.0 and at a temperature of 10 ° C to 100 ° C. In the next step, the peroxide treatment is carried out in a pH range of from 7 to 13, and the two-step treatment specified is carried out on a pulp sequence of bleaching steps applied to any step.

The method according to the present invention is most suitable for use in a bleaching treatment pulp which comprises an oxygen stage during the bleaching steps. The treatment according to the claimed invention can be carried out either immediately after the delignification of the pulp, i.e. before a possible oxygen stage, β

or after the oxygen step, according to a sequence of bleaching steps comprising this step.

According to the process of the present invention, the first step may be carried out at a pH in the range of 4 to 8, particularly well at a pH of 5 to 8, most preferably in the range of 5 to 7, particularly in a range of 6 to 7, and

The complexing agents include carbonic acid, polycarbonic acids, nitrogenous polycarbonic acids, most preferably diethylenetriaminepentaacetic acid (DTPA) or ethylenediaminetetraacetic acid (EDTA), or phosphonic acids or polyphosphates. The preferred peroxide reagent is hydrogen peroxide or hydrogen peroxide + oxygen.

The treatment according to the present invention is most suitable where the washing step is between two treatment steps to remove complexly bound metals from the pulp (slurry) prior to the peroxide step. In addition, after this two-step treatment, the pulp can be finally bleached to obtain the required brightness. In known bleaching stages, final bleaching involves the loading of chlorine and chlorine dioxide. Such loading can be completely or partially eliminated from the bleaching process, provided that the pulp is treated after the oxygen step according to the claimed invention, i.e. in a two-step manner.

In the two-step treatment of the present invention, the first step is performed at a temperature of from 10 to 100 ° C, more preferably from 26 to 100 ° C, more preferably from 40 to 90 ° C for 1 to 360 minutes, most preferably from 5 to 60 minutes. and performs the second step at a temperature of from 50 to 130 ° C, more preferably from 50 to 100 ° C, most preferably from 80 to 100 ° C, from 5 to 960 minutes, most preferably from 60 to 360 minutes.

The pulp concentration may be from 1 to 40%, most preferably from 5 to 15%. In preferred embodiments, comprising the first stage treatment with DTPA and the hydrogen peroxide treatment in the second stage, the first stage is carried out by loading the DTPA (100%) from 0.1 to 10 kg / tonne pulp, preferably from 0.5 to 2.5 kg / tonne , and in the second stage by loading hydrogen peroxide from 1 to 10 kg / tonne, preferably from 5 to 40 kg / ton. The treatment conditions for each of the two steps are selected so as to obtain the maximum bleaching effect per kilogram of loaded peroxide agent.

In the first stage of treatment, it reaches the required pH values with sulfuric acid or residual acid from the chlorine dioxide reactor, while at the second stage it reaches the required pH by adding alkali to the slurry or an alkaline liquid such as sodium carbonate, sodium bicarbonate, sodium hydroxide or an acidified white liquid.

The process according to the present invention is preferably carried out without the addition of silicates in the second processing step.

The main difference between the present invention and the prior art, as shown above (Gelerstedt straispnis Journal of Wood Chemistry and Technology), is that it does not add sulfite and thus avoids the additional introduction of chemical reagents. In this way, the process technology can be simplified and the method can be simplified, and the environmental performance of production can be improved. When using SO _{2 in the process} , the possibility of creating a more closed system in bleaching production is eliminated, since such use leads to an increase in the sulfur content of the effluent; at the same time, in the absence of SO _{2, it} can be significantly sealed by reducing the number of security problems. This is because the process of the present invention permits regeneration both after the first step (using a complexing agent) and after the second step (using hydrogen peroxide), that is, at subsequent stages of the multi-step bleaching process as compared to the process using SO ₂ . Moreover, if a more closed system requires the regeneration of O ₂ , the process requires additional equipment to remove O ₂ from the pulp solution, which makes it more complex and expensive. Furthermore, in the most preferred embodiment of the present invention for the surrounding nature, that is, after two steps of post-oxygen treatment, the loading of chlorine dioxide depending on the amount of chlorine-free reagents in the process and the required final brightness can be reduced to a level regeneration after one or more final stages of DED, so that an almost completely closed system can be created for the bleaching process.

system, the surrounding environment

In this embodiment of the invention, when the treatment is carried out after the oxygen step of the multi-step bleaching process, the two-step treatment produces an excellent effect on lignin dissolution because the treated oxygen pulp is more sensitive to hydrogen peroxide treatment which reduces lignin content and / or enhances brightness. In this way, this treatment, when used in combination with the complexing agent and after the oxygen step, produces such good results that, from an environmental point of view, a much better treatment can be realized for a more closed system for the multi-stage bleaching process. In addition, an attempt was made to increase the efficiency of the non-chlorine delignification by using two successive oxygen stages at the beginning of the multi-stage bleaching process. However, it was realized that after the initial oxygen treatment, it was difficult to use oxygen re-treatment to remove such amounts of lignin as to justify the high cost of this step.

By comparing the treatment results of Gellerstein's article with those of the present invention, it has been found that treatment according to the prior art according to the state of the art results in a more complete removal of all traces of metal in the first step. performed only with a complexing agent added in a neutral environment leads to a significant reduction in the amount of metals, such as manganese, which are most negatively affected by hydrogen peroxide degradation. Thus, it has been found that the complete removal of traces of metals by Gellerstein's article is not necessary for the efficient use of the hydrogen peroxide step. In contrast, identified metals, such as magnesium, have, among other factors, a positive effect on the viscosity of the pulp, and the fact that these metals are not removed is therefore mandatory. In this way, the known methods were intended solely to minimize the amount of metals, while, according to the present invention, a change in the distribution of trace amounts of metals by selectively altering their content has a significantly more positive effect on subsequent treatment with hydrogen peroxide. Moreover, by examining the quality of the pulp obtained in a known manner and the pulp obtained by the process according to the present invention, it has been found that a simplified method according to the present invention and carried out by adjusting the pH viscosity and kappa index (a measure of residual lignin content) as well as hydrogen peroxide consumption

Treated with sulfate. The comparative treatment of the oxygen bleached pulp gave equivalent results, whereas the comparative treatment of the unbleached oxygen pulp gave a better result in the method of the present invention. The aim of the bleaching process is to have a low kappa index, which means low insoluble lignin content and high pulp brightness. In addition, the target has a high viscosity, which means that the pulp has long carbon chains which give the product high resistance as well as low hydrogen peroxide yield, which results in lower processing cost.

The invention and its advantages are further illustrated by the following examples, which are provided by way of illustration only and not by way of limitation.

EXAMPLE

This example illustrates the influence of various pH values on the step 1 treatment with hydrogen peroxide in the step 2 unbleached oxygen pulp in the process of the present invention and, for comparison, the treatment with SO ₂ (15 kg per ton of pulp) + DTPA in step 1. Kapp index, brightness and viscosity of the pulps were determined by SCAN standard methods, and the hydrogen peroxide yield was measured by iodometric titration.

The pulp consisted of a softwood pulp which was non-oxygenated and had a kappa index of 27.4 and a viscosity of 1302 dm / kg before treatment.

The processing conditions were as follows:

stage: 2 kg / tonne DTPA; 90 C; 60 min; changing pH.

Stage u: 25 kg / tonne hydrogen peroxide (H ₂ O ₂ );

90 ° C; 60 min; final value pH = 1011.

Table I

PH Kappo indicator Klampu- mas Brightness H ₂ o _{2 is} consumed Stage 1 Stage 2 Stage 2 Stage 2 (% ISO) Stage 2 (kg / tonne) SO ₂ + DTPA 6.9 16.5 1093 54.0 22.1 DTPA 6, 9 16.7 1112 54.2 12.4 SO ₂ + DTPA 7.5 16, 9 1057 48.4 25.0 DTPA 7.8 16.4 1112 52.7 22.4 so ₂ + dtpa 4.8 17.8 1026 49.2 24.3

As follows from the table, the two-step treatment of the unbleached oxygen pulp of the present invention, where the first stage is only treated with DTPA, further treatment with hydrogen peroxide gives better viscosity and hydrogen peroxide yield than the same pulp treatment according to the prior art also uses SO ₂ . It is further clear that the best results are obtained when the pH changes from slightly acidic (4.8 according to prior art) to neutral (6.5-7.0).

EXAMPLE

This example illustrates the effect of various pH values on the efficiency of the hydrogen peroxide treatment in step 1 for the oxygen bleached pulp in the process of the present invention and for comparison without treatment with DTPA in step 1 and with SO ₂ (15 kg / ton pulp) + DTPA in step 1. The Kapp index, the viscosity and the brightness of the pulp were determined by standard SCAN methods, the hydrogen peroxide yield was measured by iodometric titration. The treated pulp consisted of an oxygen bleached sulphate softwood pulp which had a Kapp index of 19.4 and a viscosity of 1006 dm / kg prior to treatment.

The processing conditions were as follows:

stage kg / ton DTPA; changing pH.

90 ° C; 60 min;

stage 1: 15 kg / tonne hydrogen peroxide (H ₂ O ₂ );

kg of NaOH; 90 ° C; 60min .; pH = 10.9-11.7.

Table II

pH Kappo indicator Viscosity Brightness H ₂ O _{2 is} consumed Stage 1 Stage 2 Stage 2 Stage 2 (% ISO) Stage 2 (kg / tonne) 2, 8 14.2 931 44, 6 15.0 4.1 13.8 902 47, 6 14, 9 5, 8 13.4 948 57.5 8.3 6.9 13.5 952 58.0 00 Q. r- 6.9 13.4 938 57.7 7.1 7.7 13.4 938 57.7 9.6 8.3 13.7 933 56.1 10.0 8, 6 13, 7 928 55.5 11.2 6.1 (no DTPA) 15, 3 910 41.7 15.0 6.9 (with SO ₂ + DTPA) 13.4 945 57.5 7.9

As shown in the table, treatment with hydrogen peroxide without pretreatment with DTPA yields worse results than the treatment with the present invention. In the case of a bleached oxygen pulp, treatment with water-20 peroxide, preceded by SO ₂ + DTPA, yields results similar to the process of the present invention. In this case, the advantages of the present invention are not in the quality of the product obtained, but in the safety of the surrounding environment, cost and process technology as stated above.

EXAMPLE

This example illustrates the effect of various pH values in Step 1 on the efficiency of the hydrogen peroxide treatment in the Step 2 bleached oxygen pulp of the present invention. Pulp Kapp index, viscosity, and brightness were determined by standard methods by SCAN; the hydrogen peroxide yield was measured by iodometric titration. The pulp treated consisted of an oxygen-bleached softwood pulp which had a Kapp index of 16.9, a viscosity of 1040 dm / kg sulfate treatment and a brightness of 33.4% ISO.

The processing conditions were as follows:

stage: 2 kg / tonne EDTA; 90 ° C; 60 min;

changing pH.

stage 1: 15 kg / tonne hydrogen peroxide (H ₂ O ₂ );

90 ° C; 240 min .; final value pH = 19.

The results obtained are shown in the table below.

Table III

PH Kappo indicator Viscosity Brightness H ₂ O _{2 is} consumed Stage 1 Stage 2 Stage 2 Stage 2 (% ISO) Stage 2 (kg / tonne) 10.8 11.3 922 45.1 15.0 9.1 9, 80 929 56.4 15.0 7.7 9:00 944 61, 9 13.0 6.7 8.76 948 63.3 11.3 6.5 8.57 950 63.6 11.1 6.1 8.26 944 66.1 OO 00 5, 8 8.53 942 64.0 11.0 4.9 8.52 954 64.0 10.4 3, 8 8, 97 959 61.7 12.2 2.3 10.8 947 46.2 15.0 1.8 10, 6 939 47.0 15.0 1.6 10.4 919 48.2 15.0

As follows from the table, it is important that the 2-stage treatment is carried out at pH values corresponding to the present invention; in which case the maximum is reached

Decrease in Kapp index and hydrogen peroxide yield as well as maximum increase in brightness. Selectivity expressed as viscosity to specific

Kapp index values, above, when using a complexing agent in Step 1. This is true regardless of the pH value, as long as it is within the range of the present invention.

EXAMPLE 4

This example illustrates the influence of the washing step between the first and second processing steps.

The oxygen bleached sulphate pulp with a viscosity of 1068 dm ³ / kg and a Kapp index of 18.1 was treated in two steps according to the present invention under the following conditions:

stage: DTPA 2 kg / tonne; pH 6.9; temperature

90 ° C; time is 1 hour.

stage 1: hydrogen peroxide (H ₂ O ₂ ) - 15 kg / tonne; NaOH - 15 kg / tonne; pH = 1111.9; temperature 90 ° C; time 4 hours.

The results obtained are presented in the table below, which includes treatment without the first step for comparison

Table IV

7> ipdoro j imas Kapp's indicator Viscosity H ₂ O _{2 is} consumed P ° Stage 2 After Stage 2 (kg / tonne) Yes Stage 1 13th 900 15th Yes flushing 13.3 967 15th With washing 10.2 1010 10th

As can be seen from the table, the best results are obtained when washing between the two treatment steps according to the present invention. The shape of the metal trace amounts, whether free or complexed, does not have a significant effect on the Kapp index and hydrogen yield, but the viscosity is higher when complexes are formed. If complexed metals are removed by washing with hydrogen peroxide prior to treatment, the viscosity is further increased and, in addition, the Kapp index and hydrogen peroxide yield are reduced.

EXAMPLE

The metal content in the same pulp as in Example 2 (with a viscosity of 1006 dm / kg and a Kapp index of 19.4) was measured after treatment according to the first step of the claimed process; treated with DTPA at a volume of 2 kg / tonne at 90 ° C for 60 min. at two different pH values, namely 4.3 and 6.2. The results obtained are shown in the table below.

Table V

Metal (m.d.) Without processing After processing at pH 4.3 After processing at pH 6.2 Fe 20th 13th 13th Mn 80 19th 7.5 Cu 0, 6 0.5 0.5 Mg 350 160 300

As can be seen from the table, there is a significant reduction in the amount of manganese when treated with a complexing agent, and it should be noted that manganese is most damaging in the hydrogen peroxide treatment step. In addition, the magnesium content does not change significantly at higher pH values, which works well for the subsequent treatment condition. The presence of manganese has a negative effect and the presence of magnesium has a positive influence on the next stage of hydrogen peroxide treatment.

EXAMPLE

This example illustrates the difference between lignin depletion in the presence of oxygen and hydrogen peroxide in an oxygenated pulp with a Kapp index of 19.4 and a viscosity of 1006 dm ³ / kg, respectively.

Conditions for treatment with hydrogen peroxide:

stage: 2 kg / tonne DTPA (100%); 90 ° C; 60 min

stage: pH about 11; 90 ° C; changing time and changing loading of hydrogen peroxide 5.

Table VI

PH Loading HA Kappo indicator Viscosity Used up HA Time Stage 1 Stage 2 (kg / tonne) Stage 2 Stage 2 Stage 2 (kg / tonne) Stage 2 (hours) 4.0 15th 13, 8 910 14, 8 1 7.0 15th 13.5 952 7.8 1 7.0 15th 10.4 940 10, 3 4 6, 9 25th 8.7 932 15, 2 4

Conditions for oxygen treatment in the laboratory:

stage: as above.

stage: pH = 11, 5-12; 90 ° C; 60 min

Table VII

Kapp's indicator Viscosity Partial pressure O ₂ (MPa) 16, 6 946 0.2 16, 6 953 0.3 16.5 951 0.5 16.4 * 961 0.5

(DTPA pretreatment).

As per the peroxide sequence obtained from Table VI, at the required hydrogen loading level, there may be a delignification rate of 30-46% in the absence of chlorine. At higher loading levels, a higher level of delignification can be achieved (55% at 25 kg H ₂ 0 ₂ / tonne).

Table VII shows that a chlorine-free delignification rate of 15% can be achieved, but this level cannot be increased with large amounts of O ₂ , since an increase in oxygen partial pressure from 0.2 to 0.5 MPa does not lead to a further decrease in the Kapp index. The intermediate DTPA treatment step does not positively influence delignification to further oxygen treatment.

EXAMPLE

This example illustrates the environmental advantages of the process of the present invention, namely the fact that increasing the degree of chlorine-free delignification prior to the use of chlorine / chlorine dioxide can significantly reduce the amount of organohalogen (AOH) adsorbed and the chloride content in sewage bleaching waters. , that is, to improve those parameters which largely affect the possibility of creating a closed system in bleach production. The table below illustrates a comparison between a conventional sequence of steps corresponding to the state of the art, i.e. D CH / D EP ₍₄₎ DEP ₍₁₎ D, and the method of the present invention, i.e., D stage. Stage 2 CH / D EP ₍₄₎ D, where EP ₍₄₎ and EP ₍₁₎ represent the alkaline extraction stages reinforced with 4 kg and 1 kg respectively of hydrogen peroxide per ton of pulp. See page 4 for the remaining abbreviations. The pulp is identical to that used in Example 2 and has a Kapp index of 19.4 after delignification and 10.2 after treatment according to the present invention.

Table VIII

Known Buddha according to the present invention techniques 1 ygis % D X / D 15th 50 100 50 100 100 Chlorine (kg / tonne) 22nd 14th 0 10th 0 0 C1 O ₂ * (kg / tonne) 22nd 33 78 25th 40 35 Final Brightness (% ISO) 90 90 90 90 90 90 Final Viscosity (dm ³ / kg) 880 882 891 950 970 978 Total AOH (kg / tonne) 2.9 2.3 0.95 1.2 0.5 0.35

* Total C1O ₂ content during the bleaching stages (chlorine available).

As can be seen from the table, in the method according to the present invention, the effluent contains substantially lower levels of AOH, which is therefore significantly superior to nature conservation; at the same time, the resulting pulp has a significantly higher viscosity.

EXAMPLE

This example illustrates the effect of different hydrogen peroxide loading in Stage 2 on the final brightness and viscosity of the pulps, which were not subsequently bleached, ie no chlorine-containing reagents are used in the multi-step bleaching process. It is known that there are no AOH emissions. The viscosity and brightness of the columns were determined by the standard method SCAN. The processing pulps were oxygen delignified sulphate pulp and hardwood pulp and sulphite pulp (Mg - base). The softwood pulp was identical to that of Example 3, had a Kapp index of 16.9, a viscosity of 1040 dm ³ / kg, and a brightness of 33.4% ISO prior to treatment. The hardwood pulp before treatment had a Kapp index of 11.3, a viscosity of 1079 dm ³ / kg and a brightness of 48.3% ISO.

The sulfite pulp had a Kapp index of 8.6 and a brightness of 57% ISO before treatment.

Conditions for treatment of soft wood pulp:

stage: 2 kg / tonne EDTA; 60 min, pH = 6.

step: 90 ° C; 240 min .; pH = 11; variable amounts of hydrogen peroxide (H ₂ O ₂ ).

Table IX

Loading H ₂ O ₂ Viscosity Brightness Stage 2 (kg / tonne) Stage 2 (dm ³ / kg) Stage 2 (% ISO) 15th 1006 66, 3 20th 997 69.2 25th 968 71, 6

Conditions for treatment of hardwood pulp:

stage: 2 kg / tonne EDTA; 90 ° C; 60 min; pH = 4.6.

step: 90 ° C; 240 min .; pH = 11; variable amounts of hydrogen peroxide (H ₂ O ₂ ).

Table X

H ₂ O ₂ loading Viscosity Brightness Stage 2 (kg / tonne) Stage 2 (dm ³ / kg) Stage 2 (% ISO) 10th 1040 73.5 15th 1031 77.0 20th 1022 79, 8 25th 1005 80.4

Treatment conditions for sulphite pulp:

stage: 2 kg / tonne EDTA; 50 ° C; 45 min .; pH = 5.0.

step: 80 ° C; 120 min; pH = 10.8; variable amounts of hydrogen peroxide (H ₂ O ₂ ).

Table XI

H ₂ O ₂ loading Brightness Stage 2 (kg / tonne) Stage 2 (% ISO) 2 64 5 74 10th 81 15th 85 22nd 87

As can be seen from the table, the treatment of the present invention can result in a partially bleached pulp of approximately 70, 80 and 85% ISO for soft wood pulp, hard wood pulp and sulphite pulp, respectively, without further bleaching. These results are obtained in the bleaching process, where there is no longer a problem associated with the generation and emission of AOH.

The two-stage treatment of the present invention is favorably replaced by the first treatment step by distributing the amount of trace metals in the slurry (Example 5) so that hydrogen peroxide can be used in the next step, increasing the chlorine-free delignification rate. ). Compared to the prior art, the following are achieved: ecological advantages, technological process improvement, cost reduction and, depending on the location in the multi-stage bleaching process, higher (Example 1) or the same (Example 2) pulp quality. Further, as regards the initial oxygenation of the pulp, the parameters that characterize the effluent from the ecological point of view can be significantly improved to the point where it is possible to create a substantially closed system within the bleaching production frame (Example 7). Reducing the brightness requirements from 90% ISO level 5 to 70-80% ISO allows complete elimination of AOH generation and emissions (Example 8). Comparison of the hydrogen phase of the peroxide with another oxygen stage (Example 8) shows that the pulverized oxygen pulp is more sensitive to treatment with hydrogen peroxide than to subsequent oxygen treatment, both in terms of delignification and increase in brightness.

Claims (11)

DEFINITION OF INVENTION 1. A method of bleaching chemically delignified pulp containing lignocellulose, which increases the activity of the peroxidation treatment by treating the pulp with a complexing agent prior to the peroxidation step, characterized in that it changes the distribution of trace metals by treating the complexing agent in the absence of sulfite, pH 9.0 at a temperature in the range of 40 ° C to 100 ° C, followed by a peroxide treatment step in the pH range of 7 to 13, and the specified two-step treatment in a random sequence of steps in the multi-step bleaching process applied to the pulp. 2. The method of claim 1, wherein the pulp bleaching step sequence used comprises an oxygen step. 3. A process according to claim 2, wherein the two-step treatment is carried out after the oxygen step. 4. A process according to claims 1-3, wherein the first treatment step is carried out in a pH range of 4 to 8. 5. A process according to claim 4, wherein the first treatment step is carried out in a pH range of 6 to 7. 6. A process according to claims 1-3, characterized in that there is an intermediate washing step between the two stages of treatment. 7. The process of claim 1, wherein the complexing agent is a nitrogen-containing polycarboxylic acid, or a phosphonic acid or a polyphosphate. 8. The method of claim 7, wherein the complexing agent is diethylenetriaminopentaacetic acid or ethylenediaminotetraacetic acid. 9. The method of claim 1, wherein the peroxide agent is hydrogen peroxide or hydrogen peroxide + oxygen. 10. A process according to claims 1-3, wherein after two treatment steps, the pulp is finally bleached to obtain the required brightness. 11. The method of claims 1-10, wherein the first of two processing steps is carried out at a temperature of 40 ° C to 100 ° C for 1-360 minutes. and performing the second stage at a temperature of 50 ° C to 130 ° C for 5-960 min. and the pulp to be treated is present in a concentration of 1 to 40% by weight.