Method a multi-stage bleaching of pulp

 

(57) Abstract:

Use: production of bleached pulp. The inventive pulp suspension is treated with nitrogen-containing polycarboxylic acid - diethylenetriaminepentaacetic or ethylenediaminetetraacetic at a temperature of 26 to 100C., preferably 40 to 90C, at pH 6 - 7 for 1 to 360 minutes Then treated mass is washed with water and treated with peroxide agent, mainly hydrogen peroxide, at a temperature of 5 to 130C for 5 to 960 minutes These successive stages is carried out after the oxygen-alkali bleaching stage. After the processing stage of the peroxide agent, the pulp suspension is subjected to dobelle. As the initial suspension used for the bleaching of pulp suspension, not the past sulfite treatment. 7 C.p. f-crystals, 15 PL.

The invention relates to the field of pulp and paper production and is intended for use in the production of bleached pulp.

The known method a multi-stage bleaching pulp, comprising the successive stages of processing pulp suspension salpicaduras connection nitrogen-containing polycarboxylic acid in an amount of from 0.1 to 10.0 kg/t a is the n. This method is through the use of stage sulfite treatment leads to complication of the process and environmental pollution.

The objective of the present invention is to simplify the process and improve its environmental performance.

This task is solved in that the method multistage bleaching pulp, comprising the successive stages of processing pulp suspension nitrogen-containing polycarboxylic acid in an amount of 0.1 to 10.0 kg/t pulp at pH 3.1 to 9,0, washing with water and peroxide treatment agent at pH 7-13, according to the invention, the processing nitrogen-containing polycarboxylic acid is carried out at a temperature 26-100oC, preferably 40-90oC, and subjected to bleaching the pulp suspension, not the past sulfite treatment.

These successive stages of processing carried out after the oxygen-alkali bleaching stage. After the processing stage of the peroxide agent, the pulp suspension is subjected to dobelle. Stage of processing peroxide agent is carried out in the presence of oxygen. As the nitrogen-containing polycarboxylic acid is used diethylenetriaminepentaacetic acid (DTPA) or etilendiamintetra agent is conducted at a temperature of 50-130oC for 5-960 minutes as a peroxide agent, preferably using hydrogen peroxide.

The proposed method add the sulfite and thus avoid the introduction of additional chemical reagents. Due to this simplified the process and reduced the price, but also to improve the environmental performance of production. When implementing the method using a SO2the possibility of creating a more closed system within the bleaching production is excluded, as this use leads to an increase in the sulfur content in the wastewater. At the same time, in the absence of SO2you can create a much more closed system that will reduce the number of problems associated with environmental protection. This is due to the fact that the method according to the invention allows to carry out the regeneration after the first stage (using a complexing agent), and after the second stage (using hydrogen peroxide), i.e., at later stages of multi-stage bleaching process in comparison with the method using the SO2. Moreover, if to create a more closed system, you must regenerate ABOUT2< which makes it more difficult and expensive. In addition, when the most preferable from the viewpoint of environmental protection embodiment of the present invention, i.e., when performing the two-stage processing after the initial oxygen stage, the loading of chlorine dioxide can, depending on the number of chlorine reagents in the process and the required end white, be reduced to such a level that it becomes possible to perform regeneration after one or more stages of final sequence DEAD, so for the whitening process, you can create almost completely closed system.

According to this variant embodiment of the invention, when processing is carried out after the oxygen stage multi-stage bleaching process, two-phase treatment has a significant effect in dissolving lignin, as processed by the oxygen mass is more sensitive to treatment with hydrogen peroxide, reducing the lignin content and/or increase the brightness (whiteness). Thus, this processing is applied in combination with a complexing agent and is performed after the oxygen stage, leads to good results from the point of view of environmental protection can be implemented to significantly improve the CLASS="ptx2">

When comparing the results of processing carried out according to a known method, and the results of processing carried out in accordance with this invention, it is necessary that the processing in accordance with the known method, apparently, leads to more completely remove all traces of metals, while processing in accordance with the invention, implemented at the first stage with only a complexing agent is added in a neutral environment, reduces the content of those metals that are most adversely affect the decomposition of hydrogen peroxide, such as manganese. Thus, it was found that more complete removal of traces of metals is not necessary for the effective implementation stage, which uses hydrogen peroxide. On the contrary, certain metals, such as magnesium, even positively influenced, among other factors, on the viscosity of the pulp, and for this reason the fact that these metals are not removed, is an advantage. Thus, known methods were directed only to as much as possible to reduce the metal content, whereas, according to the invention, the distribution of trace metals by selectively.

Moreover, when studying the quality of the pulp obtained in a known manner, and the pulp obtained by the method according to the invention, it was found that the simplified method corresponding to the invention and implemented in terms of regulating the pH, network, depending on the location in the sequence of stages, better or the same results in terms of viscosity and Kappa index (a measure of residual lignin) pulp, as well as in relation to the consumption of hydrogen peroxide. Comparative processing oxygen bleached pulp gave equivalent results, while the comparative processing is oxygen bleached pulp gave the best results according to the method according to the invention. In the bleaching process goal is lowest Kappa, which means a low content of dissolved lignin and high brightness pulp. In addition, the aim is a high viscosity, which means that the pulp contains a long carbohydrate chain, giving the product high strength, and low consumption of hydrogen peroxide, which provides lower cost processing.

The invention and its advantages are further illustrated by the following examples which are given only the from example illustrates the effect of different pH values at stage 1 on the effectiveness of treatment by hydrogen peroxide in stage 2 for non-oxygen bleached pulp of the proposed method and for comparison purposes, in the processing of SO2(15 kg/t of pulp) + DTPA in stage 1. Figure Kappa, brightness and viscosity of the pulp is determined according to SCAN standard methods; the consumption of hydrogen peroxide was measured by iodometric titration. Processed weight consisted of no oxygen bleached sulphate pulp of soft wood, which before treatment had a Kappa index 27,4 and viscosity 1302 DM3/kg.

The processing conditions were as follows: stage 1: 2 kg/t DTPA, 90oC, 60 min, changing the pH value; stage 2: 25 kg/t of hydrogen peroxide (H2O2), 90oC, 60 min, the final pH value of 10-11. The results are shown in table.1.

As follows from the table.1, the two-stage processing is oxygen bleached pulp according to the invention, when the first stage are processed only DTPA, gives the best results with subsequent treatment with hydrogen peroxide in relation to the viscosity and flow rate of hydrogen peroxide than processing the same cellulose according to the method, in which the first stage is also used SO2. Further, it is evident that the best results are obtained when the pH varies from slightly acidic (4,8 according to a known method) to neutral (6,5-7,0).

P R I m m e R 2. This prestatie 2 for oxygen bleached pulp according to the method according to the invention, and, for comparative purposes, the processing without adding DTPA in stage 1 and in the processing of SO2(15 kg/t of pulp) + DTPA in stage 1. The Kappa index, viscosity and brightness of the pulp was determined according to standard methods SCAN, the consumption of hydrogen peroxide was measured by iodometric titration. The treated pulp was bleached with oxygen sulphate pulp of softwood lumber, which before treatment had a Kappa index of 19.4 and viscosity 1006 DM3/kg.

The processing conditions were as follows: stage 1: 2 kg/t DTPA, 90oC, 60 min; changing the pH value; stage 2: 15 kg of hydrogen peroxide (H2O2), 12 kg of NaOH, 90oC, 60 min, pH of 10.9-11,7. The results are shown in table.2.

As follows from the table.2, treatment with hydrogen peroxide without prior processing DTPA gives worse results than the process according to the invention. In the case of oxygen bleached pulp treatment with hydrogen peroxide, which precedes the processing of SO2+ DTPA, it gives the same results as by the method according to the invention. In this case, the advantages of the invention lie not in the quality of the product and safe for the environment, cost and process technology.

P R I m e R Dorada in stage 2 for oxygen bleached pulp according to the method according to the invention. The Kappa index, viscosity and brightness of the pulp was determined according to SCAN standard methods; the consumption of hydrogen peroxide was measured by iodometric titration. The treated pulp was bleached with oxygen sulphate pulp of softwood lumber, which before treatment had a Kappa index of 16.9, viscosity 1040 DM3/kg, and the brightness of 33.4% ISO.

The processing conditions were as follows: stage 1: 2 kg/t of EDTA, 90oC, 60 min, changing the pH value. Stage 2: 15 kg/t of hydrogen peroxide (H2O2), 90oC, 240 min; the final pH value of 11.

The results are shown in table.3.

As follows from the table.3. it is necessary that the processing in stage 2 was carried out at pH values corresponding to the invention. In this case, the maximum decrease in Kappa and consumption of hydrogen peroxide, and the maximum increase in brightness. Selectivity, expressed as the viscosity at a particular value of Kappa, above, when in stage 1 there is a complexing agent. This is true regardless of the pH value, unless it is in the interval corresponding to the invention.

P R I m e R 4. This example illustrates the effect of leaching between PE is UP>/kg and measure Kappa 18,1 was subjected to two-stage processing according to the invention under the following conditions: stage I: DTPA 2 kg/t; pH 6.9, temperature 90oC, 1 h; step 2: hydrogen peroxide (H2O2) 15 kg/t NaOH 15 kg/t, pH 11-11,9, temperature 90oC, time: 4 hours

The results are shown in table.4, in which for comparison included data processing without the first stage.

As follows from the table.4, the best results are obtained when between the two stages of processing according to the invention are washing. Then, in what form are trace amounts of metal - free or complex-bound not have a significant effect on the Kappa index and the consumption of hydrogen peroxide, but the viscosity is higher, if the formation of complexes. If complex-associated metals removed by washing before treated with hydrogen peroxide, the viscosity increases even more, and, in addition, there is a decrease in Kappa and consumption of hydrogen peroxide.

P R I m e R 5. The metal content in the same pulp as in example 2 (with a viscosity of 1006 DM3/kg and a Kappa index of 19.4) was measured after processing according to the first stage predlagaemaya the results are shown in table.5.

As follows from the table.5, when processing the complexing agent is a significant decrease in the content of manganese and manganese has the most damaging effect on the machining stage hydrogen peroxide. In addition, the magnesium content does not undergo major changes at higher pH value, which is favourable for the subsequent processing stages. The presence of manganese has a negative impact on the subsequent stage of processing hydrogen peroxide, the presence of magnesium - positive.

P R I m e R 6. This example illustrates the difference between reducing lignin content by the action of oxygen and hydrogen peroxide, respectively, treated with oxygen pulp with a Kappa index of 19.4 and viscosity 1006 DM3/kg. handling of hydrogen peroxide: stage 1: 2 kg/t DTPA (100%), 90oC, 60 min; stage 2: pH of about 11, 90oC; changing time and changing the loading of hydrogen peroxide (H2O2). Handling of oxygen in laboratory conditions: stage 1: as stated above, stage 2: pH of 11.5-12, 90oC, 60 minutes

The results are shown in table. 6 and 7.

As follows from the table.6, for a given level of loading of hydrogen peroxide in about the high level of delignification (55% at 25 H2O2kg/t).

From table. 7 shows that in the absence of chlorine, you can reach the level of delignification 15%, but this level cannot be increased with the use of large quantities of O2because the increase of oxygen partial pressure of 0.2 to 0.5 MPa does not lead to further decrease in Kappa. Intermediate stage of processing DTPA does not have a positive effect on the delignification during subsequent processing oxygen.

P R I m e R 7. This example illustrates the advantages of the method according to the invention from the point of view of environmental protection, the increase in the degree of chlorine-free delignification before the stage using chlorine/chlorine dioxide can significantly reduce the amount of adsorbed organic halogen (AOG) and the amount of chlorides in wastewater bleaching of production, i.e., to improve those parameters that significantly affect the ability to create a closed system for otbelivayushe production.

Table.8 illustrates a comparison between a regular sequence of stages corresponding to a known method, i.e., KX/DEP(4)DEP(1)D., and method according to the invention, where EP(4)and EP(1)obsn. The pulp is identical to the one that was used in example 2, and has a Kappa index of 19.4 after delignification with oxygen and 10.2 after treatment according to the invention.

As follows from the table.8, the proposed method are significantly smaller levels of AG in the wastewater, resulting in a significant advantage from the point of view of environmental protection; at the same time produces a pulp with a higher viscosity.

P R I m e R 8. This example illustrates the effect of different downloads of hydrogen peroxide in stage 2 on the final brightness and viscosity of the cellulose, which does not undergo any further bleaching, i.e., is the complete absence of chlorine-containing reagents in the multistage bleaching process. This, of course, means no emissions Aug. Viscosity and brightness of the pulps was determined according to the standard method SCAN. The treated pulp was delignification oxygen sulphate pulp of soft and hard wood and sulphite pulp (Mg - base), respectively. Pulp of soft wood, is identical to the cellulose in example 3, had a Kappa index of 16.9, viscosity 1040 DM3/kg and the brightness of 33.4% ISO before rcost 48,3% ISO. Sulphate pulp before treatment had a Kappa index of 8.6 and brightness 57% ISO.

Conditions of treatment for the pulp of soft wood: stage 1: 2 kg/t of EDTA, 90oC, 60 min, pH 6; stage 2: 90oC, 240 min, pH 11; changing the amount of hydrogen peroxide (H2O2).

The results are shown in table.9.

The machining conditions for cellulose solid wood: stage 1: 2 kg/t of EDTA, 90oC, 60 min, pH 4,6; stage 2: 90oC, 240 min, pH 11, changing the amount of hydrogen peroxide (H2O2) (cm.table.10).

The machining conditions for sulfite pulp: stage 1: 2 kg/t EDTA, 50oC, 45 min, pH 5.0; stage 2: 80oC, 120 min, pH 10,8, changing the amount of hydrogen peroxide (H2O2) (cm.table.11).

As follows from the tables, in the processing of cellulose according to the invention without subsequent final bleaching can be obtained partially bleached pulp with a brightness of about 70,80 and 85% ISO for soft wood pulp, hardwood pulp and sulfite pulp, respectively. These results are achieved by way of bleaching, which eliminated the problem associated with the formation and release of Aug.

A two-stage process according to the invention leads, bellunese (example 5), so it is possible to use at the next stage, hydrogen peroxide, increasing the fraction of chlorine-free delignification, especially if between the two stages of processing is carried out stage leaching (example 4). Compared with the known method are achieved environmental benefits, improvement of process technology, cost reduction and, depending on the location in the sequence of stages of multi-stage bleaching process, higher (example 1) or the same (example 2) the quality of the pulp.

Further, as the pre-oxygen bleached pulp, the parameters characterizing the wastewater from the point of view of the environment can be significantly improved to such a level that it becomes possible to create within the bleaching production essentially closed system (example 7). By reducing the requirements to the brightness of 90% ISO to the level of, for example, 70-80% ISO becomes possible to completely eliminate the formation and release of AOG (example 8). Comparison of peroxide-hydrogen stage with other oxygen stage (example 8) shows that the treated oxygen milled pulp more sensitive to treatment with hydrogen peroxide than to further processing oxygen, both from the point swany experiments held at boundary values of parameters when processing nitrogen-containing polycarboxylic acid and a compound containing hydrogen peroxide.

Processing nitrogen-containing polycarboxylic acid in an amount of from 0.1 to 10 kg/ton of pulp; at pH from 3.1 to 9.0, with a temperature of 26 to 100oC; at pH from 7 to 13.

Below in the table. 12-15 presents the effect of boundary numeric values to some essential properties of the pulp after the second stage of processing according to the invention. Determination of permanganate number, viscosity and brightness of the pulp semi-finished product were performed by standard techniques SCAN.

Effect of the number of nitrogen-containing polycarboxylic acid in stage 1.

This experience illustrates the effect of the number of nitrogen-containing polycarboxylic acid in stage 1 on the effectiveness of treatment by hydrogen peroxide in stage 2. As the nitrogen-containing polycarboxylic acid used EDTA, the amount varied from 0.1 to 1.0 kg/t of pulp. The treated pulp was bleached with oxygen sulphate pulp of softwood timber before treatment had a permanganate number of 15.3, the viscosity of 1050 DM3/kg and white 36,7% ISO.

Conditions Dorada (H2O2), 90oC, 240 min, final pH 11, the concentration of cellulose 10 wt.%.

The results obtained are presented in table.12.

This experience illustrates the influence of pH values from 3.1 to 9.0 when processing nitrogen-containing polycarboxylic acid. The treated pulp was bleached with oxygen sulphate pulp of softwood and before treatment had a permanganate number 16,9, the viscosity of 1040 DM3/kg and the whiteness of 33.4% ISO.

The machining conditions are the following: stage 1: 2 kg/t EDTA, 60 min, the concentration of cellulose 10 wt.%, stage 2: 15 kg/t of hydrogen peroxide (H2O2), 90oC, 240 min, final pH 11; the concentration of cellulose 10 wt.%.

The results obtained are presented in table.13.

This experience illustrates the effect of temperature from 26 to 100oC when processing nitrogen-containing polycarboxylic acid. As the cellulose was used that used in the previous example to show the effect of pH on phase 1 (PL.13).

The machining conditions are the following: stage 1: 2 kg/t EDTA, 90oC, 60 min; the concentration of cellulose 10 wt.%, pH 5.5.

Stage 2 : 15 kg/t of hydrogen peroxide (H2O2), 90oC, 240 min, final pH 11, the concentration of cellulose 10 wt.% is in pH from 7 to 13 when processing connection containing hydrogen peroxide. As the pulp used the one that was used in the experiment to show the effect of pH in the first stage (see table.13).

The processing conditions were as follows: stage 1: 2 kg/t of EDTA, 90oC, 60 min, the concentration of cellulose 10 wt.%, pH 5.5; stage 2: 20 kg/t of hydrogen peroxide (H2O2), 90oC, 240 min; the concentration of cellulose 10 wt.%.

The results obtained are presented in table.15.

From table. 12-15 shows that the selected range of values of the parameters of the proposed method provide a bleached pulp with high quality.

1. METHOD a MULTI-stage BLEACHING PULP, comprising the successive stages of processing pulp suspension nitrogen-containing polycarboxylic acid in an amount of 0.1 to 10.0 kg/t pulp at pH 3.1 to 9,0, washing with water and peroxide treatment agent at pH 7 to 13, characterized in that the processing nitrogen-containing polycarboxylic acid is carried out at 26 - 100oWith, preferably 40 to 90oC, and subjected to bleaching the pulp suspension, not the past sulfite treatment.

2. The method according to p. 1, characterized in that the said successive stages of processing carried out after the oxygen the pulp suspension is subjected to dobelle.

4. The method according to p. 1, characterized in that the machining stage peroxide agent is carried out in the presence of oxygen.

5. The method according to p. 1, characterized in that as the nitrogen-containing polycarboxylic acid is used diethylenetriaminepentaacetate or ethylenediaminetetraacetic acid.

6. The method according to PP.1 and 5, characterized in that the processing nitrogen-containing polycarboxylic acid is carried out at pH 6 - 7 for 1 to 360 minutes

7. The method according to PP. 1 and 4, characterized in that the peroxide treatment agent is carried out at 50 - 130oWith over 5 960 minutes

8. The method according to p. 1, characterized in that the peroxide agent use hydrogen peroxide.

 

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