FI115469B - Process for the treatment of chemical cellulose material - Google Patents

Abstract

A process for the bleaching or delignification of chemical pulp, wherein, before bleaching or delignification with an oxygen chemical, the pulp is pretreated with a chelating agent in order to eliminate the adverse effects of any heavy metals present in the pulp. The chelating agent used consists of compounds according to Formula (I), where n is 1-3, m is 0-3, p is 1-3, R1, R2, R3 and R4 are H, Na, K, Ca or Mg, R5 and R6 are H, CH2OH, CH2CH2OH or CH2O(CH2CH2O)1-10CH2CH2OH.

Description

115469 j

The present invention relates to a process for bleaching or delignifying a cellulosic material, wherein the pulp is pre-treated prior to oxygen chemical resin or delignification to eliminate the adverse effects of the heavy metals in the pulp.

Chemical pulp, or pulp, is increasingly bleached using bleaching techniques that do not use elemental chlorine or chlorine compounds. Em. bleaching is called ECF (elementary chlorine free) bleaching and totally chlorine-free bleaching is called TCF (total chlorine free) bleaching. Especially TCF bleaching is usually preceded by oxygen delignification. After oxygen delignification, Mas-15 can be bleached with chlorine-free chemicals such as ozone, hydrogen peroxide in acidic and alkaline solutions under non-pressurized or pressurized conditions. Useful bleaching methods include bleaching with peroxy compounds (such as peracetic acid, Ca-20 acid or mixtures of peracids), a peroxide-enhanced oxygen step, and peroxide-enhanced oxygen | ; alkali.

: Typically, such bleaching steps are preceded by heavy metal bonding. Metals can be removed by acid washing. This is · · · often disadvantageous because at least some of the following bleaching steps are performed under alkaline conditions. Jos. ···. heavy metals are removed at low pH, • ·. ··· must be used. first an acid to achieve a low pH and the next 30 steps to neutralize the acid. In addition, Mg and Ca · ... · ions, which are preferred for bleaching, are removed in the acid wash. Acid washing can also reduce the strength of the pulp.

Peroxy compounds such as peracetic acid and hydrogen peroxide are highly sensitive to the catalytic effects of heavy metals. Applicant FI Patent Applications 94 2968, 94 2969 and 94 2970 2 115469 disclose transition metal activated bleaching with peroxy compounds under acidic conditions. For successful bleaching, heavy metals must be bound before and / or during bleaching.

5

Chelating agents for metal ions, for example polyaminocarboxylic acids, are used for the bonding of heavy metals by bleaching with peroxy compounds. These include, in particular, ethylenediaminetetraacetic acid and its salts (EDTA) and diethylene-10-riaminepentaacetic acid and its salts (DTPA).

'[The most harmful ions for bleaching are manganese (Mn), iron (Fe) and copper (Cu). Other heavy metals such as chromium ions (Cr), etc. also adversely affect both the peroxide consumption and often the bleaching result by reducing mm. the viscosity of the bleached pulp. Harmful heavy metals are derived from pulp, treatment waters and pulping equipment.

In chemical pulp bleaching, chelation cannot generally be performed under alkaline conditions, since iron is then purchased in the form of hydroxides, oxides, and oxyhydroxides which strongly catalyze the decomposition of peroxy compounds. Here; Because of this, the chelation prior to peroxygen bleaching is carried out under acidic conditions. In this case, the removal of manganese, in particular, has proved to be important because it does not form as stable complexes as iron and since the chemical pulp, in particular, often contains large amounts of manganese. In, ···. Bryant and L.L.Edwards, Tappi Pulping Conference 1993, ···. pp.43-55, "Manganese removal in closed kraft mill bleach" · "30 plants" states that manganese can best be removed at a pH of 4.5-6.5 before manganese binds too much to the pulp.

____: In modern chemical pulp bleaching processes, bleaching 35 is preceded by oxygen delignification. In this process, magnesium ions have been added to the pulp, the retention of which is important in the pulp when bleached with peroxy compounds such as hydrogen peroxide. According to the article, the best Mg / Mn ratio is achieved at pH 4.5-5.0. Therefore, in practice, chelation must be carried out at well below pH 6, e.g. near pH 5.5. In the examples of the above-referenced publication 5, chelation has been carried out at pH 5.3.

Powerful chelating agents are often poorly degraded in nature, such as DTPA or are completely non-degradable, such as EDTA. The increase in TCF bleaching has use of chelating agents 10. As a result, there has been an interest in replacing biodegradable chelating agents, either wholly or partially, with biodegradable chelating agents. In addition, in order to avoid environmental stress, it would be desirable for the naturally occurring chelating agents to contain as little nitrogen as possible.

Biodegradable complexing agents have been developed as detergent builders. At the same time, they must have a water softening effect, ie they must bind calcium and magnesium ions. One such sequestering agent is ethylenediamine disuccinic acid: EDDS. This compound has three stereoisomers.

• · * · ·

The substance is known per se by F.Pavelcek and J.Majer in Publication: "New Complexanes.XXXIV. Preparation and Properties of Meso and Rac Formations of Ethylenediamine-N, N'-Disuccinic Acid", Chem.Zvesti 32 (1978), pages 37-41. U.S. Patent No. 86554 to Procter & Gamble discloses the use of a substance in detergent compositions. Another application by W0; No. 94/03553 discloses the use of a substance in bleaching solutions as a stabilizer of perox * * * '·' * compounds in pulp bleaching and detergents. In this case the pH of the bleaching solution should be 0.5-6.0. The disclosure states that the compound is biodegradable. According to the patent, the S, S- ... isomer of EDDS is the most biodegradable.

35 4 115469

EP 556 782 discloses the use of EDDS as an iron complexer in photographic chemicals. Example 9 of the publication mentions that Ferri salts of EDTA, DTPA and HEDTAm are not biodegradable. In contrast, the Fe2 + 5 salt of EDDS is biodegradable. The biodegradability of the compounds in the example was tested by a generally accepted test method (301C Amendment MITI Test (I), OECD Chemical Substance Testing Guidelines, May 1981).

Another known biodegradable complexing agent is 2,2'-iminodisuccinic acid (ISA). The use of the compound in alkaline detergents is disclosed in EP-A-509 382. The application mentions the use of 2,2'-iminodimeric succinic acid as a stabilizer for peroxide compounds, in particular in alkaline detergent compositions containing hydrogen peroxide and its derivatives. In the examples of the application, only perborate is used. Because perborate only slowly releases hydrogen peroxide from the examples of the patent, far-reaching conclusions about stabilizing hydrogen peroxide in similar detergent compositions cannot be drawn.

DE · Patent Application 4 216 363 discloses the use of ISA; '·· Stabilization of surfactants. There is no mention of the use of the peroxide compound · ... · '. European Patent Application 513 948 mentions • J. ' 25 for use in hard surface cleaners containing an organic solvent boiling at about 90 ° C. There is no mention of the use of a peroxy di-compound.

. * ··. It is an object of the present invention to eliminate the adverse effects of fatty metals on chemical pulp bleaching and delignification. Another aim is to provide a biodegradable, efficient, chelating agent that provides good bleaching performance.

The features of the invention will be apparent from the appended claims 1-16.

5, 115469

The process of the invention uses compounds of formula I known per se.

5 Formula I

COORi COOR3

I I

(CH 2) n R 5 R 6 (CH 2) p I /

10 HC - N - (CH 2 CH 2 N) m - CH

In part 15, n is 1-3 m is 0-3 p is 1-3

R1, R2, R3 and R4 are H, Na, K, Ca or Mg

R 5 and R 6 are H, CH 2 OH, CH 2 CH 2 OH or CH 2 O (CH 2 CH 2 O) j.

20 "··· 'DTPA, commonly used in cellulose bleaching, best chelates ras-annual metals at about pH 5.

»·

It has now surprisingly been found that the compounds of formula I can advantageously be used as a chelating agent in a pretreatment step prior to bleaching or delignification of cellulose at a higher pH than DTPA. Suitable pHs when using the compounds according to the invention for pulp pre-treatment are pH 4-8, preferably pH 5.0-7.5, most preferably pH 6.5-7.5.

If the compounds are also used in the bleaching or delignification step themselves, suitable pHs are 4-8, respectively, preferably pH 4-6, most preferably 4-5. Since chelation can be performed I · '; at higher pH, the next step does not consume as much alkali as chelating at lower pH. This 35 has a clear advantage over e.g. DTPA.

6, 115469

The process of the invention can be applied to all known chemical pulps. These include alkaline and neutral sulphite pulps, soda pulps, sulphate pulps (kraft pulps), and oxygen delignified (oxygen soap) sulphate-5 pulps. In addition, the method can be used for bleaching so-called. organosolve pulps, in which alcohols or organic acids have been used as a cooking solvent, e.g. Milox soup in formic acid. The chelating method according to the invention can also be used when polysulphides or, for example, anthraquinone are used as adjuvants in the sulphate cooking.

The treatment may be carried out on pulp cooked from a variety of fibrous raw materials, such as softwood, hardwood or strips, straw or other vegetable raw material.

15

Chelation according to the invention with compounds of formula I, e.g. EDDS and ISA, is used as a pretreatment prior to bleaching or delignification with oxygen chemicals. The chelating agents of formula I, such as EDDSra and ISA 20, may also be used as a chelating agent in bleaching or delignification with oxygenates '·· * ·'. * Are for example peracetic acid bleaching, bleaching of peracids

• I

: * ··, bleaching with hydrogen peroxide, bleaching with mixtures of hydrogen peroxide and peracids, transition metal cat-lysed hydrogen peroxide developed by the Applicant, bleaching in acid pH range, alkaline peroxide bleaching and combinations thereof, oxygen delignification, peroxide-enhanced and alkaline coupled with any treatment with enzymes, ozone 30 or chlorine dioxide.

* · ·

The chelating process of the invention can be used as a pretreatment for pulp bleaching or delignification under acidic conditions and possibly also in the bleaching or delignification steps themselves.

7, 115469

Adjustment of the pH of the acid chelating step can be carried out with standard mineral acids such as sulfuric acid, sulfur dioxide or aqueous solution thereof, carbon dioxide or organic acids such as formic and acetic acid.

5

A particularly suitable chelating agent of the formula I in the process of the invention may be ethylenediamine-,? -Dimeric succinic acid, its various isomers or its alkali metal salts such as sodium and potassium salts or its alkaline earth metal salts such as calcium and magnesium salts. It is also possible to use ethylenediamine Ν, Ν'-dimeric succinic acid together with calcium and / or magnesium sulfate. A particularly suitable chelating agent is also 2,2'-iminodimeric succinic acid, its various isomers or its alkali metal salts such as sodium and potassium 15 or its alkaline earth metal salts such as calcium and magnesium. It is also possible to use 2,2'-iminodimeric succinic acid together with calcium and / or magnesium sulfate.

Suitable chelating agents also include N- (1,2-20 dicarboxyethyl) -N- (2-hydroxyethyl) aspartate acid, its various isomers or its alkali metal salts or its alkaline earth metal salts. The acid can also be used in combination with potassium • · * 1 ·· or magnesium sulfate.

The chelating agent may be added in an amount of 0.1 to 5 kg, preferably 0.5 to 2 kg per tonne of dry pulp.

•

It has also been found that EDDS and ISA can be used in combination with hydroxycarboxylic acids without loss of bleaching. Partial Replacement of EDDS and ISA with Non-Nitrogen Active Ingredients such as Hydroxy · · · Carboxylic Acids of the General Formula II ♦ 1 · * »· ♦ 8 115469

R ^ HjOH ^ COOH ^ R, {ID

where n is 1-8 m is 0-2n 5 p is 0 -n q is 0-2 R ·! is COOH and R 2 is H, CH 2 OH or COOH.

10 In this way, the harmful nitrogen load in the waste water from bleaching can be reduced. Substitutes chelating agents in the usual carboxylic acids of formula II, hydroxycarboxylic acid, polyhydroxycarboxylic acids and hydroksipolykarboksyylihappoja, for example, citric 15 acid, tartaric acid, lactic acid, pimelic acid, glutamic acid, glucoheptonic acid, ascorbic acid, glycolic acid, glutaric acid, adipic acid, succinic acid or malonic acid can be used.

20 It is quite surprising that hydroxy acids can be used as a '··· * chelator in bleaching. These substances are very poor binders for heavy metals, but they bind calcium and »·: * ·· magnesium well. In particular, citric acid has been used in the synthesis of phosphates ·, .. · * as substitutes in phosphate-free detergents where calcium and magnesium must be bound. In particular, binding of magnesium should be disadvantageous for bleaching.

»A. ···. The invention is illustrated by the following examples, which, however, do not limit the invention to the * I · '· *' examples set forth herein.

»» ·

Example 1.

* * »« * 35 To determine the chelation of heavy metals and alkaline earth metals, the oxygen-delignified chemical pulp was washed with 9,115,469 aqueous solutions containing EDDS. The metal concentrations of the wash solution were analyzed after washing. The migration of iron (Fe), manganese (Mn), calcium (Ca) and magnesium (Mg) into the wash waters was thus investigated. The transfer of iron and manganese to the wash 5 solutions is advantageous for bleaching. Conversely, the transfer of calcium and magnesium to the washing solutions is disadvantageous for bleaching. In control experiments, the pulp was washed with DTPA or EDTA solutions. Chelating agent concentrations and pH during washing are reported in Table 1.

10

table 1

Coniferous sulphate pulp Chelating conditions

Number of pieces 16.9 Time, min. 60

Viscosity 963 dm3 / kg T, C 70 15 Lightness 39.6% ISO consistency% 12

Chelate Dose, Metal concentrations of filtrate __kg / ts pH Fe, ppm Mn, ppm Mg, ppm Ca, ppm_

Na5DTPA 1 6,71,2 2,9 4 17. Na5DTPA 2 5,72,0 3,3 13 52 ·. ·. · 'Na5DTPA 2 6,52,0 2,8 17 48

Na4EDTA 2 6,51,8 3,3 5 49; ·· 1: H4EDDS 1 5,92,0 2,0 12 45 H4EDDS 1 6,8 1,6 2,6 7 15 H4EDDS (reaction mixture) 1,5 5 , 5 2.0 1.5 15 55 H EDDS (reaction mixture) 1.5 6.5 1.9 2.3 13 37. H4EDDS (S, S) 2 5.0 2.0 1.6 15 35 H4EDDS (S, S) 2 6.8 2.0 3.0 17 36: h4edds (r, r + r, s) 2 5, 5 1.9 1.8 13 50 H4EDDS (R, R + R, S) 2 6.5 1.7 3.3 18 30 t · I,, ··· In Table 1, Na5DTPA represents the pentanedium salt of DTPA,

Na4EDTA represents the tetrasodium salt of EDTA and the H4EDDS EDDSrn: 20 acid form. However, the pH used determines how the chelating agent

the substances are dissociated, that is, in what form they actually occur in processing. H „EDDS mentioned in the table

(reaction mixture) refers to experiments in which the crude reaction product is used directly from the EDDS preparation process.

10 115469

Experiments found that with EDDS at 1.5 kg / tonne, chelation of iron and manganese was almost as complete as with EDTA or DTPA at 2.0 kg / ts under the same experimental conditions. At lower pH, the chelation of manganese-5 was not as complete as that of the reference substances, but at pH 6.5 and more alkaline conditions, the manganese chelated as well or better than with the reference substances. EDDS chelates less calcium and magnesium than the reference substances, which is advantageous for bleaching.

No significant differences in the chelating properties between the S, S isomer, R, R and R, S isomers of EDDS and the chelating agent containing all EDDS isomers were observed in the experiments.

In the examples, the following abbreviations are used: CS denotes 15 densities, PAA peracetic acid treatment, mP molybdate-activated peroxide treatment, O oxygen treatment, P alkaline peroxide treatment and Q chelating step.

Example 2 20 * ·

Table 2 shows the results of * · · washing experiments similar to those described in Example 1 when EDDS was diluted with some hydroxides; sihapoilla.

i i 1 * «! I 1 * «1 I · <1« * '1 * 1 · »<·

»T I

I f f I • 1 1 * I 1 * I »» * I »* i · * i I · *» * »* 1 1

»1 I» »I

i t * 1 11 115469

Table 2

Coniferous sulphate pulp Chelating conditions

Number of pieces 16.9 Time, min. 60 5 Viscosity 963 dm3 / kg T, C 70

Brightness 3 9.6% ISO consistency% 12

Chelate Dose, Metal concentrations of filtrate __kg / ts pH Fe, ppm Mn, ppm Mg, ppm Ca, ppm

Na5DTPA 1 6,71,2 2,9 4 17

Na5DTPA 2 6,52,0 2,8 17 48

Na5DTPA 2 5.72.0 3.3 13 52

Na5DTPA 0.5 6.6 0.8 1.5 5 26

Na4EDTA 2 6,51,8 3,3 5 49

Water wash 6.0 0.3 0.3 6 22

Water wash 7.0 0.3 0.3 14 66

Na3 Citrate 1 6.3 0.0 0.6 9 26 H4EDDS + Na3 Citrate 0.5 + 1 7.5 1.3 2.4 8 18 H4EDDS + Na3 Citrate 0.75 + 1 5.7 2 , 2 1.6 17 58 H4EDDS + Na3 Citrate 1 + 1 7.4 1.4 2.7 10 23 H4EDDS 1.5 7.1 1.9 2.3 13 37 H4EDDS + Na Gluconate 1 + 1 6 , 7 1.8 2.6 9 29 H4EDDS + Na-Gluconate 1 + 1 8.9 0.3 2.2 10 5 DTPA is dosed during the chelating step of softwood pulp, generally at about 2 kg / ts. In a second set of experiments (Table 2), the effect of DTPA dosing on metal chelation was first investigated. Chelation was clearly less when the EDDS dose was reduced from 2.0 kg / ts to 1.0 kg / ts or **. ··· 0.5 kg / ts. In a previous series of experiments (Table 1), it was found that when Na4EDDS at 1.5 kg / ts was used, chelation was? *: As complete as with Na5DTPA at 2.0 kg / ts.

Practical experience and the aforementioned test results show that DTPA must be used in the chelating step at about *: ** at 2.0 kg / ts and EDDS at about 1.5 kg / ts in order to: heavy metals would be • completely stacked for bleaching.

When sodium salts of citric acid or gluconic acid were used as a chelating agent in addition to EDDS, the dosage of EDDS 12125469 could be significantly reduced. Although the dosage of EDDS was reduced to 1.0 kg / ts, the chelation of the metals in these experiments was as complete as 1.5 kg / ts of EDDS. By using the salts of the above hydroxycarboxylic acids 5 with EDDS as the chelating agent, the nitrogen load of the effluent from the chelating step can be significantly reduced and the chelation of the metals was still sufficiently complete for bleaching.

Table 2 shows that water washing is ineffective in chelating metals. Likewise, citric acid alone does not remove heavy metals. Citric acid only chelates alkaline earth metals, which is undesirable for bleaching. This indicates that a good chelating result is obtained as a result of the interaction between EDDS and, for example, citric acid.

It should be noted that washing results such as those described above cannot directly infer from the bleaching result. Therefore, tut-20 was tested for the effect of corresponding chelating agents on alkaline hydrogen peroxide bleaching.

• * ·· Example 3; The oxygen delignified pulp was chelated and bleached with alkaline hydrogen peroxide. The chelating agents used were EDDS or DTPA. The results are summarized in Table 3. · Bleaching Results ···. can be used to estimate peroxide consumption, brightness achieved ··. and the viscosity of the pulp.

115469

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14 115469

In a control experiment, chelation was performed with DTPA before bleaching (Experiment 1). After chelating with EDDS at pH 5.5, the bleaching result was poor (Experiment 5). In contrast, when chelating with EDDS was performed at pH 6.6 (Experiment 6), the val-5 was better than the Comparative Experiment (Experiment 2).

It should be noted that in comparative tests, proper bleaching results were obtained only when DTPA was used for chelating at least 2 kg / tonne (cf. Experiment 3). In contrast, when coil-10 operation was performed using EDDS at only 0.6 kg / ts, a good bleaching result was obtained (Experiment 9). This represents a significant reduction in the consumption of chemicals in bleaching. The use of magnesium sulfate as an additive in chelation with EDDS is also advantageous for bleaching (Experiment 8).

15

Example 4.

In this experiment, the effect of EDDS and salts of hydroxylcarboxylic acids on chelation was investigated. In the experiment, the pretreated softwood pulp described in Example 3 was used. Mass chelation and alkaline peroxide bleaching were performed under the conditions described in Table 4.

»1 * 1 · · et» * ·

* I

»115469

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In comparative experiments, chelation was performed with DTPA and EDDS. When sodium citrate alone was used in the chelation step, the bleaching result was poor (Experiment 9). In contrast, in experiments using chelating with sodium gluconate 5 or Na citrate in combination with EDDS, bleaching results were good.

By using biodegradable auxiliaries that do not contain nitrogen, such as Na-gluconate or Na-10 citrate in combination with EDDS, the dosage of EDDS could be reduced up to 0.25 kg / ts without compromising the bleaching result. This is a significant result, for example in terms of waste water treatment. By using the above-described mixtures of chelating agents, the nitrogen load on the effluent from bleaching can be significantly reduced.

Example 5

For comparison, chelation and alkaline peroxide bleaching were performed on softwood pulp delignified with peracetic acid after oxygen delignification. The conditions for chelation and bleaching are described in Table 5. Comparative experiments; The chelation was carried out with DTPA.

* · · * · · * ♦ · • · · * «* · -« 1 • ♦> · »17 115469

Table S

Coniferous pulp Preliminary treatment: -O-PAA-5 Kappa 5.3

Viscosity 777 dm3 / kg

Brightness 65.7% ISO

Q

n: o ___ 1_2_3_4_5_ t, min 60 60 60 60 | T, C 75 75 75 75 | CS,% 12 12 12 12 j pH 5 6.6 5.1 6.4 j

Na5DTPA, kg / ts 2 2 |

Well, EDDS, kg / ts__1J> _1.5 * _ P 1 i 1 i No __ chelation t, min 180 180 180 180 180 T, C 90 90 90 90 90 CS,% 12 12 12 12 12 pH start 10.4 10.4 10.4 10.4 10.4 pH-end 9.7 9.8 9.8 9.8 9.5 H 2 O 2, kg / t 20 20 20 20 20 Residue -H 2 O 2, kg / t 4.1 4.1 6.1 8.2 8.2 3 Residual H 2 O 2,% 20.5 20.5 30.5 41 15 Residual NaOH, kg / t 2 2.4 2.3 2.8 1.8

Kappa 2.2 2.3 2.2 2.2 2.2. *; ; Viscosity, dm3 / kg 535 553 565 599 465 * Brightness% ISO 85,0 85,0 85,2 85,7 84.6. '···. 10

* I

, In experiment 5, no chelation was performed. This resulted in a * · · poor bleaching result. In particular, the viscosity of the pulp decreased significantly. After chelation at both pH 5 and pH 6.5, better bleaching results were obtained in 15 experiments using EDDS compared to experiments using DTPA. Based on viscosity and brightness estimates, the best bleaching result was obtained after the chelating step was performed using EDDS at pH 6.4. The decomposition of hydrogen peroxide in this experiment was significantly less than in the control experiment with chelation with DTPA.

18 115469

It is noteworthy that in these experiments, the application rate of EDDS (1.5 kg / ts) was significantly lower than that of DTPA (2.0 kg / ts).

Example 6 In this test, oxygen-delignified softwood was bleached with alkaline hydrogen peroxide by adding the chelating agent directly to the bleaching solution. In the comparative experiments, the coil-10 was performed prior to bleaching with DTPA or EDDS.

The pulp used for the comparative tests was also pre-bleached with peretic acid before chelation. The experimental conditions and results are summarized in Table 6.

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20, 115469

It should be noted that the mass used in these experiments was already light in weight after pre-treatment. When the chelating agents were added directly to the bleaching solution, the bleaching result was similar with DTPA 2.0 kg / ts and EDDS 1.5-5 kg / ts. In experiments where chelation was performed before bleaching, a better pulp brightness was achieved. Based on this, it is more advantageous for the bleaching result to perform separate chelation than to add chelating agents to the bleaching solution.

10

When the separate chelation was performed with EDDS, the viscosity decreased less in the bleaching than in the comparative experiment where the separate chelation was performed with DTPA. Hydrogen peroxide consumption was also lower in the bleaching after EDDS chelation.

Example 7 In this experiment, softwood was chelated and delignified under acidic conditions with hydrogen peroxide activated by molybdates (mP step). In the comparative experiment, chelation had: used DTPA. Chelation was carried out at pH 6.0-6.5.

* · · · 21 115469

Table 7 Mass of conifers

Kappa 13.1

Viscosity 878 dm3 / kg

Chelating______ t, min 45 45 45 T, C 60 60 60 CS,% 12 12 12

Chelate No NasDTPA Na4EDDS

kg / ts__2_2__ljj_ mP-delignif joint i__l_i_i_ t, min 180 180 180 T, C 90 90 90 CS,% 12 12 12 H202, kg / ts 15 15 15

Mo, kg / t 0.45 0.45 0.45 pH 5 5 5 Residual H 2 O 2, kg / t 2.6 5.7 6.7 Residual H 2 O 2,% 17.3 38.0 44.7

Kappa 6.4 6.3 6.3

Brightness,% ISO 62.4 63.4 61.4

Viscosity, dm3 / kg 789 825 820 5

From the results (Table 7), it is observed that the peroxide consumption of the mP step without pretreatment was higher than that of the pretreated pulps. Similarly, the viscosity of the pulp after delignification was higher in experiments with direct chelation:. 10 t. The peroxide consumption of EDDS-chelated pulp in the mP step * ♦ · · was lower than that of DTPA-chelated.

• «“ Example 8 • 1 · * · · ♦ t · · 1 · * · · * 1 · • · 22 115469

Table 8 Mass of conifers

Viscosity 798 dm3 / kg

Kappa 55.5

Brightness 9.1% ISO

5 mP_t, min iso 180 T.C 90 90 cs-% 12 12 pH start 5 5 pH end 4.7 4.5 H2 ° 2 »kg / ts 15 15

Mo, kg / ts 0.5 0.5

Na 4 EDDS, kg / ts 2 Residual H 2 O 2, kg / ts 0.08 7.8

Kappa 4.6 4.1

Viscosity, dm3 / kg 756,780

Lightness,% iso 59.3 63.8

Table 8 shows the results of an experiment in which EDDS was added to the actual mP step instead of pretreatment. From Table 10, it can be seen that the addition of chelate provides a significant advantage in reduced peroxide consumption. The viscosity and brightness of the pulp are also better than without EDDS treatment.

• · ·; . ·. 15 Example 9.

»· · ·

To clarify the chelation of heavy metals and alkaline earth metals, the oxygen-delignified chemical pulp was washed with aqueous solutions containing ISA. The metal content of the wash solution was analyzed after washing. The migration of iron (Fe), manganese (Mn), calcium (Ca) and magnesium (Mg) into the wash waters was thus investigated. The transfer of iron and manganese to the washing solutions is advantageous for bleaching. Instead, the transfer of calcium magnesium to the washing solutions is bleaching, ···. 25 disadvantages. In control experiments, the pulp was washed with • DTPA or EDTA solutions. Chelating agent concentrations are: * and pH during washing as shown in Table 9.

23 115469

Table 9

Coniferous sulphate pulp Chelating conditions

Number of pieces 16.9 Time, min. 60 5 Viscosity 963 dm3 / kg T, C 70

Brightness 39.6% ISO consistency% 12

Chelate Dose, Metal concentrations of filtrate __kg / ts_pH Fe, ppm Μη, ρρπι Mg, ppm Ca, ppm

NasDTPA 1 6,71,2 2,9 4 17

Na5DTPA 2 6,52,0 2,8 17 48

Na5DTPA 2 5.72.0 3.3 13 52

Na5DTPA 0.5 6.6 0.8 1.5 5 26

Na4EDTA 2 6.5 1.8 3.3 5 49

Water wash 6.0 0.3 0.3 6 22

Water wash 7.0 0.3 0.3 14 66

Na3 Citrate 1 6.3 0.0 0.6 9 26 ISA 1.5 5.8 1.1 1.9 2 50 ISA 1.5 8.9 0.0 1.3 25 26 ISA + Na Citrate 1 + 1 7.7 0.5 2.2 15 26

In Table 9, Na5DTPA stands for DTPA pentanedium salt, 10 Na4EDTA stands for EDTA tetrasodium salt and ISA for imidodime succinic acid. However, the pH used determines how the chelating agents are dissociated, i.e. in what form they actually occur in the treatment.

It can be seen that in a comparative water wash, iron and manganese are poorly soluble in water at both pH '···' 6.0 and pH 7.0. In a more alkaline solution, magnesium and calcium were more soluble in the washing water. The washing with the sodium salt of citric acid · · · · was also effective in removing iron and manganese. Instead, some alkaline earth metals were removed in this experiment, which is disadvantageous for bleaching.

EDTA and DTPA chelated iron and manganese approximately y equally efficiently at pH 6.5.

'»· 1 1 5469 24 ISA chelated iron and manganese well at pH 5.8. It should be noted that ISA removed very little magnesium from the pulp at pH 5.8. This is advantageous for bleaching. Chelation in an alkaline solution at pH 8.9 was also successful. It should be noted that at this pH iron is precipitated. This explains the low iron content in the filtrate.

The chelation with a mixture of ISA and the sodium salt of citric acid was also successful considering that the chelation was performed at pH 7.7.

It should be noted that washing results such as those described above cannot directly infer from the bleaching result. Therefore, the effect of corresponding chelating agents on alkaline hydrogen-15 peroxide bleaching was investigated.

Example 10

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in 26 115469

When a relatively high dose of 3.0 kg / ton of ISA was used for chelation, the bleaching result was good compared to the bleaching result after DTPA chelation. In contrast, when ISA was used in chelation with citric acid nat-5 rium salt at very low concentrations, up to 0.25 kg / tonne, a good bleaching result was obtained. This is a significant improvement over DTPA chelation. The nitrogen load of bleaching wastewater can be significantly reduced by using this bleaching method.

10

Example 11

In order to find out how ISA works when bleaching is carried out under acidic conditions, chelation was carried out as a pre-treatment for the acidic peroxy bleaching step. The transition metal catalytic bleaching of the applicant's prior invention was used herein.

Table 11 20

Coniferous pulp Kappa 13.1 µ Viscosity 878 dm3 / kg »· U: 25 Chelation ... t, min 45 45 T, C 60 60 60: CS,% 12 12 12

Chelate No DTPA ISA

kg / ts __-_ 2_1,5 mP-delignification__i_1_1_! ”t, min 180 180 180 T, C 90 90 90 es,% 12 12 12 V: H2 ° 2 / kg / ts 15 15 15, ··. Mo, kg / ts 0.45 0.45 0.45 '* pH 5 5 5 Residual H 2 O 2, kg / ts 2.6 5.7 5.2! Residual H 2 O 2,% 17.3 38.0 34.7, ..: Kappa 6.4 6.3 6.4

Brightness,% ISO 62.4 63.4 62

Viscosity, dm3 / kg 789 825 810 27 115469

From the results, it can be seen that without pretreatment, the peroxide consumption of the mP stage is significantly higher if no DTPA or ISA pretreatment has been performed. The viscosity of the pulp was higher if the pretreatment was completed.

5

Example 12 In this experiment, oxygen-delignified softwood was bleached with molybdate-catalyzed hydrogen peroxide by directly adding ISA 10 to the bleaching solution. The chelating wave was not used in the comparative tests. From the results summarized in Table 12, it can be seen that the addition of chelating agent reduced the consumption of hydrogen peroxide in bleaching. The lightness of the pulp was also better than in the control.

15

Table 12

Coniferous sulphate pulp Viscosity 798 dm3 / kg 20 Capacity 55.5

Brightness 9.1% ISO

mP_ • · t, min 180 180: T, C 90 90 CS,% 12 12 • * ·· pH start 5 5. ···. pH end 4.7 4.5 · “* H 2 O 2, kg / ts 15 15: mo, kg / ts 0.5 0.5. !! ISA, kg / ts 2 · 'Residual H 2 O 2, kg / ts 0.08 4.2

Kappa 4.6 4.1

Viscosity, dm3 / kg 756,740

Brightness,% ISO 59.3 63.7 25

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Claims (16)

A process for bleaching or delignifying chemical cellulose material in which the cellulose material process is pre-treated with chelating agent prior to bleaching with oxygen chemicals or delignification to eliminate the deleterious effect of the pulp heavy metals characterized by being used as chelating agent COOR-1 coor3 II (CH2) n R5 R6 (CH2) p \ II / HC - N - (CH2CH2N) m - CH15 / \ C00R2 C00R4 where n is 1-3 m is 0-3 p is 1- 3 / ·; R 2 R 2 / R 3 and R 4 are H, Na, K, Ca, or Mg 3: R 5 and R 5 are H, CH 2 OH, CH 2 CH 2 OH or CH 2 O (CH 2 CH 2 O) C 2 CH 2 OH. Process according to claim 1, characterized in that the chelating agent is ethylenediamine-N-N'-dibaric acid V 1 and / or its alkali and / or alkaline earth metal salt. Process according to Claim 1 or 2, characterized in that, as the chelating agent, ethylene diamine-N-N1-diacetic acid sodium, calcium or; magnesium salt or ethylenediamine-N-N1 diacetic acid and calcium and / or magnesium sulfate. ; 4. A process according to claim 1 characterized in that 2,2'-iminodibarboxylic acid is used as chelating agent and / or its alkali and / or alkaline earth metal salt. Process according to claim 1 or 4, characterized in that as the chelating agent, the 2,2'-iminodibaric acid sodium, calcium or magnesium salt or 2,2'-iminodibaric acid and calcium and / or magnesium sulfate are used. 6. A process according to claim 1, characterized in that the cellulose pulp is pretreated at pH 4-8, preferably at pH 5.0-7.5 and most preferably at pH 6.5-7.5. Process according to Claim 1 or 6, characterized in that the pre-treatment with chelating agent constitutes the stage immediately before bleaching with oxygen chemicals or delignification. Method according to any of claims 1 or 6-7, characterized in that the pretreatment is done one or more times. • 1 ·! 35 · • · 33 115469 Process according to Claim 1 or 9, characterized in that the chelation treatment also occurs at the oxygen-chemical bleaching or delignification stage. 5 Process according to any of claims 1 or 9-10, characterized in that oxygen chemical bleaching or delignification takes place at pH 4-8, advantageously at 4-6 and most advantageously at 4-5. 10 Process according to any one of claims 1 or 9-11, characterized in that the treatment of oxygen chemicals can be done one or more times. A process according to any one of claims 1 or 9 to 12, characterized in that the oxygen chemistry of the cellulose pulp is done simultaneously with peroxide and peracid. Process according to any one of claims 1 or 9-13, characterized in that the peroxide content of the cellulose pulp. , ·. action is taken with hydrogen peroxide, with a mixture of hydrogen peroxide; oxide and oxygen gas or with organic peroxide compounds. 1. I 35 i · Process according to any one of claims 1 or 9 to 14, characterized in that the peracetic acid treatment of the cellulose pulp is made with peracetic, permyric, perpropionic or caonic acid or with transition metals activated peracetic, permyric, perpropionic or caronic acid or combinations of these. , 30: 16. Process according to any of claims 1-15, characterized in that chelating agent is used 0.1-5 kg / ton dry cellulose material.