The method of bleaching lignocellulosic wood pulp

 

(57) Abstract:

Usage: the invention relates to a method of bleaching lignocellulosic wood pulp and is intended for use in the pulp and paper industry. The inventive bleaching method includes washing the pulp washing liquid and subsequent bleaching peroxide-based compound. The pulp before leaching process at pH in the range from 1 to 7 in the presence of compounds of magnesium. When processing of the pulp can enter a calcium compound, and the pH of the leaching fluid is equal to or higher pH during processing in the presence of compounds of magnesium. Bleaching is carried out in the presence of calcium. 9 C. p. F.-ly, 6 PL.

The invention relates to a method of bleaching lignocellulosic slurry in which the slurry is treated at a pH from 1 to 7 in the presence of compounds of magnesium, after which the pulp is washed and subsequently bleached peroxide-based compound. Initial treatment is removed from the pulp traces of metal ions, which have a negative impact on subsequent bleaching peroxide-based compound.

Due to the presence of magnesium ions dissolved in the good influence on the performance stage of bleaching.

When cooking lignocellulosic pulp high degree of whiteness, the pulp is bleached in one or more stages. Quite a long time wood pulp bleached bleach, chlorine, having in this case the intention to remove the chromophore group while maintaining the content of lignin. For the protection of the environment is becoming more common to process cellulose by reagents that do not contain chlorine, such as hydrogen peroxide, peracetic acid or ozone already in the early stages of bleaching. However, if the pulp is not to handle pre-whitening chlorine bleach, is less effective. Thus, the bleaching by hydrogen peroxide in alkaline medium is disturbed by the presence in the slurry of traces of certain metal ions, mainly, Mn, Cu and Fe. These metal ions cause the decomposition of hydrogen peroxide on junk foods and, consequently, reduce the efficiency of the whitening hydrogen peroxide and increased consumption of peroxide.

In US-A-4619733 closest analogue reveals the way in which the pulp is bleached various chlorine-free bleach during multiple washing stages.

In the description is in this method of the invention. There does not contain information on prior treatment with acid in the presence of compounds of magnesium. Further, it is not evident that the pulp should be washed after pre-processing, the result would have been the effective removal of liberated during preliminary acid treatment of the ions impacting negatively on subsequent initial stage of bleaching. There is no information that magnesium ions can be retained in the pulp, even if the pulp is washed after adding compounds of magnesium.

The invention provides a method of processing lignocellulosic pulp under the conditions disclosed in the claims, whereby the content of traces of metal ions in the slurry to selectively alter to more effectively carry out the subsequent bleaching peroxide-based compound.

Thus, the invention relates to a method of bleaching lignocellulosic pulp through which the pulp is treated at a pH in the range from 1 to 7 in the presence of compounds of magnesium, after which the pulp is washed, and subsequently peroxide-based bleach connection.

The initial acid treatment effectively removes metal ions and the social provisions in the pulp, have a positive effect on the selectivity of bleaching and consumption of peroxide-based compounds.

This way unwanted metal ions are removed from the pulp suspension, while magnesium ions retain original provisions. The latter is achieved by the presence of compounds of magnesium in the manufacturing of liquid at such a pH and temperature that the compound is in solution in contact with the pulp. The advantage of this method, moreover, is that it decreases the number of processing stages in comparison with the methods known in this field. When the initial processing of the magnesium compound will be dissolved upon contact with the slurry to obtain a good effect. This can be achieved in different ways depending on, among other things, on the type and properties of the pulp.

The magnesium compound can be obtained in solution by appropriate choice of pH in the range from 1 to 7, in combination with a suitable temperature and concentration of magnesium.

In addition to the use of compounds of magnesium, initial processing can be done in the presence of at least more than one compounds containing deliciosamente the pulp is treated in the presence of compounds of magnesium and calcium in random order or in a mixture.

Suitable for use of magnesium-containing compounds are magnesium sulfate, magnesium chloride, magnesium carbonate or nitrate of magnesium, preferably magnesium sulfate. Suitable calcium compounds are calcium chloride, calcium nitrate, calcium sulfate or calcium carbonate, preferably calcium chloride.

In the method according to the invention, the initial processing is carried out at a pH from 1 to 7, from 1.5 to 6.6 and preferably from 2 to 5. Initial processing can also be carried out at a pH from 3.1 to 4.

When the initial processing in the presence of compounds of magnesium pH can be set by adding to the slurry of the acid or acid liquids. Used acid may be an inorganic mineral acid or residual acid from the reactor to obtain chlorine dioxide, or individually or in arbitrary mixtures. Particularly suitable is the use of inorganic mineral acids, such as sulfuric acid, nitric acid or hydrochloric acid, preferably sulfuric acid. The amount of magnesium compound added during the initial processing may be in the range from 100 ppm (part per million) up to 4000 ppm, which is calculated as parts by weight of magnesium STI from 200 ppm to 3000 ppm, preferably in the region from 500 ppm to 2000 ppm.

The number of optional compounds containing alkaline earth metal to be added at the initial stage, and may be in the range from 100 ppm to 4000 ppm, which is calculated as the parts of the mass. A suitable amount of added compounds containing alkaline earth metal is in the range from 200 ppm to 3000 ppm, preferably in the region from 500 ppm to 2000 ppm.

The amount of added metal joining magnesium, and also other terms in the initial processing is chosen so that the magnesium content in the pulp before bleaching peroxide-based compound corresponded to at least 50% original content. A suitable amount of added compounds, as well as other conditions are chosen so that the magnesium content in the pulp before bleaching peroxide-based compound has been in the area from 100% to 300% of the initial content, preferably in the range from 130% to 200%

Peroxide-based compound includes inorganic peroxide compounds such as hydrogen peroxide, sodium peroxide or peroxisomal acid (acid Karo) or organic peroxide compounds, such as, for example, p is ekici hydrogen and oxygen.

Whitening peroxide-based compound, respectively, is carried out at a pH equal to or above the pH at the initial treatment, in the presence of compounds of magnesium. In this way, traces of metal ions having a positive impact on whitening, keep and also on the stage of bleaching. When peroxide-based compound is hydrogen peroxide, the pulp can be processed at a pH of from 7 to 13, it is possible at pH 8 to 12, preferably at a pH of from 9.5 to 11. Whitening other peroxide-based compounds, mentioned above, occurs in conventional pH values for each of the bleach, which is well-known.

Suitable peroxide-based bleaching compound occurs in the presence of another compound containing an alkaline earth metal. A compound containing alkaline earth metal present in the bleaching may be the same connection that is used for initial processing, or other connection. Suitable alkaline earth metal is calcium, magnesium or barium, or a mixture. It also improves the selectivity of bleaching and reduces the consumption of peroxide-based compounds. Particularly preferably, the whitening Pro is the surface bleaching tower, for example, the introduction into the pipeline leading to the bleaching tower. The calcium compound can be added to suspensions also inside bleaching tower before bleaching. The number of compounds containing alkaline earth metal added during the bleaching may be in the range from 100 ppm to 4000 ppm, which is calculated as parts by weight of alkaline earth metal per part by weight of dry pulp. A suitable amount of added compounds containing alkaline earth metal is in the range from 300 ppm to 3000 ppm, preferably in the region from 600 ppm to 2000 ppm.

When a peroxide-based bleaching compound is a calcium compound, they may be calcium chloride, calcium nitrate, calcium sulfate or calcium carbonate. It is preferable to use calcium chloride. Moreover, calcium add this combination of pH, temperature and concentration of calcium that the connection is in the active form in contact with the pulp. Thus, a suitable pH values lie in the range from 7 to 11. However, a positive effect is also obtained when the pulp suspension is precipitated by the calcium compound, for example, in the form of calcium carbonate.


Within the scope of the invention is the fact that all or part of the quantity of magnesium, and optionally any other alkaline earth metal may be added to the pulp suspension through the water that is used, for example, to establish the pH of the washing or dilution. Thus, heavy water, mainly containing magnesium or calcium, or combinations thereof, mainly used in the initial processing, for dilution at the stage of washing or to achieve the appropriate concentration of the pulp at the stage of bleaching. In this way it is possible to reduce the added amount of the relevant school who can be chosen in such a way for the alkaline earth metal was dissolved in contact with the pulp. This heavy water comprises fresh water from the calcareous soil, the clarified water from paper machines using porcelain clay or chalk as filler, or treated water from the production of sulfite pulp-based magnesium or calcium.

The method in accordance with the invention carried out with the stage of washing after the initial treatment and before the bleaching peroxide-based compound. Washing effectively removes traces of metal ions, which have a negative impact on subsequent peroxide-based whitening compounds, for example, ions of manganese, copper and iron. In order to preserve the traces of metal ions that have a positive impact on subsequent bleaching peroxide-based compound, mainly ions of magnesium and calcium, the pH of the wash liquid is preferably equal to or higher than the pH of the initial processing. However, the pH of the washing liquid should be in the range from 3 to 10, preferably in the range from 5 to 10. Particularly preferably, the pH of the wash liquid was at least 2 pH units higher than the pH at nachlesen to establish pH, or waste water with one or more bleaching stages, or stages of extraction, which gives a suitable pH stage of leaching. Moreover, the rinsing water is the liquid may consist of other types of waste water, optionally purified, provided that it has a low content of undesirable metal ions, such as manganese, iron or copper.

Rinsing before between initial processing and peroxide-based whitening connection relates to a method of removal of the liquid phase of the suspension of pulp in order to reduce the content in the above-mentioned suspension dissolved trace metal ions.

Flushing may include increasing the concentration of the pulp, for example, exhaustion or drying of the suspension through the filter, or a decrease in the concentration of the pulp, for example, by diluting the wash liquid. Rinsing also relates to combinations and sequences, in which the concentration of the pulp alternately increase or decrease one or more times. In this way choose a wash that effectively removes traces of metal ions that were selected during the initial processing, aspects of the method of the way and the economy will be considered.

The efficiency of processing ulpi before washing. The washing efficiency may be at least 80% is suitable efficiency in the region from 90 to 100% preferably in the range from 95 to 100%

Initial processing in the presence of magnesium compounds can also be carried out in the presence of bleach. Bleaches that are active within a pH suitable for initial processing includes chlorine dioxide, ozone, and acid peroxide-based compounds. Acid peroxide-based compounds include organic compounds, as peracetic acid, and such inorganic compounds as hydrogen peroxide or paroxetina acid (acid Caro). Appropriate initial treatment is carried out in the presence of ozone or peroxisomal acid, preferably ozone, because the bleach effect, but to a minor extent, on the content of ions of alkaline earth metals in the pulp.

The method in accordance with the invention may also include phase extraction prior to tooth whitening peroxide-based compound. This is especially useful when the initial processing is carried out in the presence of bleach. Accordingly, the extraction is carried out at a pH that is equal to the pH of the initial processing of the sludge is from 8 to 10.

Regardless of the number of stages or treatment following primary treatment, suitable pH at the subsequent stage is equal to the pH at the previous stage or metals in the pulp.

In sequence, when the pulp is first treated at pH 2 in the presence of compounds of magnesium, and then washed and bleached with hydrogen peroxide, pH stage of leaching should be at least about 8.

The term "lignocellulosic pulp" refers to pulp: contains fiber, which is separated by chemical or mechanical treatment, or recycled fiber. Fibers can be made of hard and soft wood. The term "pulp" refers to pulp, boiled in accordance with the sulfate, sulfite, Sadovyi ways or methods that use organic solvents. The term "pulp" refers to pulp obtained by purification of the strands in a disk refiner (refiner wood pulp), or chopping logs in the crusher (shredded wood pulp). The term "lignocellulosic pulp" also refers to the pulps obtained by modifications or combinations of the above methods or processes. Such pulp include thermomechanical from chemically extracted wood pulp, preferably, sulphate pulp of softwood lumber.

The method, in accordance with the invention, can be used for slurries with a cellulose content of up to 90% with appropriate content is a content of from 40 to 80%, preferably in the range from 45 to 65%

The method according to the invention can be carried out at the optimal sequence of bleaching, for example, immediately after preparation of the pulp.

When the method in accordance with the invention is used for chemically extracted wood pulp, it is preferable designerour oxygen stage before use according to the invention.

The method in accordance with the invention can be used to chemically extracted wood mass having an initial Kappa number in the range from 3 to 100, suitably from 4 to 60, preferably from 5 to 40. The Kappa number is set in accordance with the standard method SN 1:77.

In the method in accordance with the invention, the initial processing can be performed at a temperature of from 10 to 100oC, suitably from 25 to 90oC, preferably from 40 to 80oC. Initial processing can be performed during the time from 1 to 600 minutes, suitably from 1 min to 120 min, preferably from 10 min on the SSE to 40% by weight, preferably from 3 mass% to 35 mass%.

When the peroxide-based compounds using hydrogen peroxide, the pulp is treated at a temperature of from 30oC to 100oC, preferably from 60oC to 90oC and over a period of time from 30 min up to 960 min, suitably from 60 minutes to 360 minutes Later, when as a peroxide-based compounds using hydrogen peroxide, the concentration of the slurry can be from 1% by mass to 70% by weight, suitably from 3 mass% to 60 mass%, preferably from 10 mass% to 50% weight. Processing other peroxide-based compounds, described above, occurs in normal conditions, this applies to temperature, time and concentration of pulp for each bleach, which is well known to the expert.

In preferred embodiments, including the use peroxide-based compounds hydrogen peroxide, the amount of hydrogen peroxide is in the range from 1 to 60 kg per tonne of dry matter in terms of 100% peroxide. The upper limit is not normalized and is set taking into account economic considerations. A suitable amount of hydrogen peroxide is in the range from 2 to 50 kg/t of dry mass, before the Ki in the presence of magnesium and subsequent bleaching peroxide-based compound slurry can be used as such to obtain the reduced paper white. Alternatively, the slurry can permanently bleach to the desired high degree of whiteness processing in one or more stages. The final procedure involves a bleach that does not contain chlorine, such as, for example, peroxide-based compounds described above, namely, ozone, oxygen, or dithionite sodium, optionally with intermediate stages of alkaline extraction, which can be strengthened with peroxide and/or oxygen.

The invention and its advantages will be illustrated in more detail by the following examples, which are however only intend to illustrate the invention without limiting it.

The percentages and parts given in the description, claims and examples, refer to percent by weight and parts by weight unless specified otherwise. Moreover, the pH values given in the description, claims and examples, refer to the pH at the end of each treatment, unless specified otherwise.

In the following examples, the Kappa number, viscosity and degree of whiteness of the pulp is installed according to standard methods SCAN and consumption of hydrogen peroxide was determined by iodometric titration.

Example 1.

Sulfate the cellulite, tighten the DNA organization for standardization) and a viscosity of 1000 DM3/kg, were treated at pH 2,1oC-0,1, in the presence of various alkaline earth metals.

After oxygen delignification of Kraft pulp had a pH of about 11, which was set by the addition of 15 kg of sulfuric acid (ton dry matter). The amount of added alkali metal was 1000 ppm, calculated as parts by weight of any alkaline earth metal per part by weight of dry matter.

When the initial processing temperature was 50oC, treatment time 30 min, and the concentration of the slurry of 10% by weight. For initial treatment of common conditions, as well as the compound containing alkaline earth metal selected so that the alkaline earth metal was dissolved in the suspension of the pulp. After the initial processing of the pulp was washed at pH 6-7 in order to remove metal ions that have a negative impact on subsequent bleaching without chlorine. Subsequently, the pulp bleaching without chlorine. Subsequently, the pulp is bleached with hydrogen peroxide at a temperature of 90oC, residence time of 240 min and the concentration of the pulp with 16% by weight. Adding hydrogen peroxide was 25 kg/t of dry mass based on 100% hydrogen peroxide, and pH was 10.5. For comparative zorada under conditions installed above (test 4). For further comparison, the pulp was treated with magnesium, as in test 1, but without the intermediate stage of leaching (test 5). The test results are shown in table 1.

As shown, the processing of the pulp in accordance with the invention at a pH of 2.1 in the presence of compounds of magnesium leads to a higher increase in the degree of whiteness and a more substantial decrease in Kappa number than it does when processing in the absence of such a connection.

Example 2.

Sulphate pulp of softwood lumber delegirovano oxygen used in example 1 was treated in the presence of compounds of magnesium at pH in the range from 1.5 to 11, in order to illustrate the effect of pH during initial processing. The number of added magnesium was 1000 ppm, calculated as parts by weight of magnesium on parts by weight of dry matter. Conditions for initial processing was identical to the conditions of example 1, except for changing the pH. Conditions subsequent bleaching with hydrogen peroxide were also identical to the conditions of example 1. After the initial processing of the pulp was washed with pH, which was 2 units higher than in the initial processing. The results of the experiments sleduet from 1 to 7 leads to a significant increase in the degree of whiteness and a more significant reduction in Kappa number, than that observed at pH above this area.

Example 3.

Sulphate pulp of softwood lumber delegirovano oxygen used in example 1 was treated in the presence of compounds of magnesium at pH 2,1oC-0,1 in order to illustrate the effect of pH on the subsequent stage of leaching. During initial processing, the pH was determined by adding sulfuric acid. The number of added magnesium was 1000 ppm, calculated as parts by weight of magnesium on parts by weight of dry matter. Conditions for initial processing, and when the whitening hydrogen peroxide were the same as in example 1. After the initial processing of the pulp was washed with pH in the range from 3 to 11 with deionized water to which was added sodium hydroxide. The test results shown in table 3.

As follows from table 3, treatment of the pulp in accordance with an intermediate stage of leaching at pH in the range from 3 to 10 leads to a significant increase in the degree of whiteness and a significant reduction in Kappa number.

Example 4.

Sulphate pulp of softwood lumber delegirovano oxygen used in example 1 was treated in the presence of compounds of magnesium at pH 2,1oC-the creation of added magnesium was 1000 ppm, calculated as parts by weight of magnesium on parts by weight of dry matter. Conditions for initial processing were identical to the conditions in example 1, as and when bleaching with hydrogen peroxide, in addition to changes in pH. After the initial processing of the pulp was washed at pH 6-7. The test results follow from table 4.

As follows from table 4, treatment of the pulp in accordance with the invention, when used as a peroxide-based compounds hydrogen peroxide, leads to a significant increase in the degree of whiteness and a marked decrease in the Kappa number.

Example 5.

Sulphate pulp of softwood lumber delegirovano oxygen used in example 1 was treated in the presence of compounds of magnesium at pH 2,1oC-0,1 in order to illustrate the influence of calcium on whitening hydrogen peroxide (test 2). The number of added magnesium was 1000 ppm, calculated as parts by weight of magnesium on parts by weight of dry matter. After washing the calcium was added in the amount of 1000 ppm, calculated as parts by weight of calcium per part by weight of dry matter. Conditions for initial processing were identical to the conditions of example 1 as well as the conditions of the train bleached in the absence of calcium (1). The test results follow from table 5.

As follows from table 5, treatment of the pulp in accordance with the invention, in which use calcium in teeth whitening hydrogen peroxide, leads to a significant increase in the degree of whiteness at a lower consumption of hydrogen peroxide than is observed in the bleaching in the absence of calcium.

Example 6.

Sulphate pulp of softwood lumber delegirovano oxygen used in example 1 was treated in the presence of compounds of magnesium at pH 2,1oC-0,1, washed and bleached with hydrogen peroxide in order to illustrate the effect of the selectivity profile of the metal in the pulp prior to bleaching. The number of added magnesium was 1000 ppm, calculated as parts by weight of magnesium on parts by weight of dry matter. After washing the calcium was added in the amount of 1000 ppm, calculated as parts by weight of calcium per part by weight of dry mass (test 4).

Conditions for initial processing were identical to the conditions in example 1, as and when bleaching with hydrogen peroxide, in addition to the presence of calcium in test 4. After the initial processing of the pulp was washed, accordingly, the C magnesium in the initial processing and without calcium on stage bleaching (tests 1 and 2). The content of ions of a particular metal in a sulphate cellulose before and after initial processing (test 0), and the degree of whiteness after bleaching with hydrogen peroxide is shown in table 6.

As shown, the method in accordance with the invention includes treatment in the presence of compounds of magnesium and subsequent bleaching with hydrogen peroxide, leads to a significant increase in the degree of whiteness at a lower consumption of hydrogen peroxide than is observed in the bleaching in the absence of calcium.

1. The method of bleaching lignocellulosic wood pulp, including leaching pulp washing liquid and subsequent bleaching peroxide-based compound, characterized in that the pulp before washing process at a pH in the range from 1 to 7 in the presence of compounds of magnesium.

2. The method according to p. 1, characterized in that lignocellulosic pulp consists of chemically extracted wood pulp.

3. The method according to PP.1 and 2, characterized in that the treatment of the pulp in the presence of compounds of magnesium administered calcium in random order or in a mixture.

4. The method according to PP. 1 and 2, characterized in that at about the different topics that the processing of the pulp in the presence of magnesium compounds is carried out at a pH of from 1.5 to 6.0.

6. The method according to PP. 1, 2, 4, 5, characterized in that when the pH of the wash liquid is equal to or higher pH during processing in the presence of compounds of magnesium.

7. The method according to PP. 1-6, characterized in that the amount of compounds of magnesium in the processing chosen so that the magnesium content in the pulp after treatment and subsequent washing to the peroxide-based bleaching compound was in the range of from 100 to 300% of the initial content.

8. The method according to PP. 1-7, characterized in that the peroxide-based compound comprises hydrogen peroxide or a mixture of hydrogen peroxide and oxygen.

9. The method according to PP. 1-8, characterized in that the pH during bleaching peroxide-based compound is equal to or higher pH at the previous stage.

10. The method according to PP.1-9, characterized in that the peroxide-based whitening compound is performed in the presence of calcium.

 

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