JP2010116659A - Oxidized white liquor, method for producing the same, and method for producing kraft bleached pulp - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-bleaching oxidized white liquor widely usable as an alkali source in the oxidation bleaching stage (oxygen delignification stage) of the initial stage of pulp bleaching sequence, alkali extraction stage, or the like, recyclingly used as a washing liquid in a pulp washer in the kraft digestion step, the wash filtrate from the bleaching stage(s), and recoverable as white liquor (white water) by reclaiming treatment as a black liquor from the pulp washer, and to provide a method for producing the high-bleaching oxidized white liquor. <P>SOLUTION: The oxidized white liquor is prepared by oxidation treatment with a peroxide of a white liquor or oxidation liquor used in a kraft digestion process. In the oxidized white liquor thus prepared, the molar ratio of the amount of sulfur derived from thiosulfate ions to the total amount of sulfur is 25% or less. The method for producing the objective oxidized white liquor for an alkali source in pulp-bleaching stage is thus provided. In the method, at least one of peroxides to be used is hydrogen peroxide; and the white liquor or oxidized white liquor may be a white liquor reclaimed from the black liquor in the kraft-process digestion step or may be an oxidized white liquor obtained by subjecting the white liquor to oxygen oxidation, respectively. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an oxidized white liquor used as an alkali source in the bleaching stage of a pulp bleaching sequence. More specifically, it can be widely used as an alkali source in an oxygen bleaching stage (oxygen delignification stage) in the first stage of a pulp bleaching sequence, an alkali extraction stage to which oxygen or hydrogen peroxide is added, and washing from the bleaching stage. High bleaching oxidation that can be added as a filtrate to the washing liquid in the pulp washing machine in the Kraft digestion process, taken out as black liquor from the pulp washing machine, recovered and recycled as white liquor The present invention relates to a white liquor and a method for producing the same, and a method for producing a kraft bleached pulp using the oxidized white liquor as an alkali source in a bleaching stage.

  Conventionally, the oxygen bleaching stage (oxygen delignification stage) in the bleaching sequence of the kraft pulp manufacturing process has used an oxidized white liquor produced by air oxidation of the white liquor used in the cooking process as an alkali source. . The oxidized white liquor used in this oxygen bleaching stage is reused as washing water as washing water in the pulp washing machine in the kraft process cooking process, and finally regenerated from the cooking black liquor from the washing machine. It plays the role of keeping the balance of sodium and sulfur constant, but when the regenerated white liquor is added as it is as an alkali source in the oxygen bleaching stage, the sodium sulfide contained in the regenerated white liquor has an adverse effect on oxygen bleaching. (Patent Document 3, Non-Patent Documents 1 and 2).

  Sodium sulfide in the regenerated white liquor as described above becomes sodium thiosulfate when it is oxidized in air, and this sodium thiosulfate is stable in the oxygen bleaching stage and has not been adversely affected by oxygen bleaching. Have reported that oxygen bleaching becomes worse when thiosulfate ions coexist in oxygen bleaching, and that sulfate ions increase with a decrease in thiosulfate ions during oxygen bleaching. (Non-Patent Documents 3 and 4)

  On the other hand, when it is assumed that the wastewater from the alkali extraction stage in the bleaching step is circulated to the cooking black liquor system as well as the wastewater at the time of oxygen bleaching, as an alkali source in the alkali extraction stage, oxidized white liquor for the same reason. Is preferred. However, in the alkaline extraction stage of the bleaching process, hydrogen peroxide is often added. When oxidized white liquor is used as an alkali source, the thiosulfate ions contained in the oxidized white liquor react with hydrogen peroxide, resulting in a bleaching effect. (Non-Patent Document 5).

  As one of the methods for solving these problems, there is a method in which white liquor is oxidized with oxygen at high temperature and high pressure, and hydrosulfide ions are completely oxidized to sulfate ions, and used as a completely oxidized white liquor (Non-patent Document 6, Patent Document 1). However, since this complete oxidation method is performed at a high temperature of about 170 ° C. and under a high pressure, there is a problem that a large cost is required in terms of energy and maintenance of the manufacturing apparatus.

  As another method, a method of selectively removing thiosulfate ions by passing a white oxide liquid through a resin has been proposed (Non-Patent Document 5). However, in this method, since ion exchange with a resin is performed, there are problems that the scale of equipment increases and alkali loss occurs during ion exchange.

  In addition, there is a method of removing ozone by gas-liquid contact with an unreacted ozone-containing gas after being used in the ozone bleaching step, white liquor containing sodium sulfide as the reducing solution, oxidized white liquor, Black liquor and sodium thiosulfate solution are mentioned, and sodium thiosulfate solution is said to be excellent in ozone absorption (Patent Document 2).

JP-A-5-195468 JP-A-9-29064 U.S. Pat. No. 4,053,352

Leader, J. et al. P. , Et al, Appita J. et al. , 39 (6): 451 (1986) Jamison, A .; , Et a1, Tappi J. et al. , 70 (11): 5 (1987) Tigerstrom, A.M. , Et al, International Pulping Bleaching Conference 2005, 112-118. Sankari, M .; , Et al, Nordic Pull and Paper Res. J. et al. , 19 (2): 264 (2004) Jemaa, N .; , Et a1, Pull and PaperCanada, 104 (12): 36 (2003) Hurst, M.M. M.M. , Et al, Pull and Paper Canada, 101 (9): 75 (2000).

  INDUSTRIAL APPLICABILITY The present invention can be widely used as an alkali source in an oxygen bleaching stage (oxygen delignification stage) or an alkali extraction stage in the first stage of a pulp bleaching sequence, and the washing filtrate from the bleaching stage is used as a pulp in a kraft process cooking process. An object of the present invention is to provide a highly bleachable white oxide oxide that can be recycled as a cleaning solution in a washing machine and a method for producing the same. In addition, the present invention circulates and utilizes the oxidized white liquor to integrate a kraft cooking process and a bleaching process having an oxygen bleaching stage (oxygen delignification stage) and further having an alkaline hydrogen peroxide bleaching stage. The object is to provide a process for the production of combined kraft bleached pulp.

  As a result of various studies on the oxidized white liquor obtained by oxidizing the white liquor used in the kraft pulp cooking process, the present inventors oxidized the white liquor using peroxide, and reduced the sulfur content in the white liquor. Oxidation to sulfate ions has been found to provide an oxidized white liquor suitable for use in treatment stages in which alkali and oxidant coexist, such as oxygen bleaching stage (oxygen delignification stage) and alkaline hydrogen peroxide bleaching stage. Furthermore, the effect of oxidation treatment of the sulfur content in the white liquor is achieved when the content in the produced white liquor is below a certain value, using the thiosulfate ion content in the produced white liquor as an index. As a result, the following inventions have been completed.

(1) By oxidizing white liquor or oxidized white liquor used for kraft cooking with peroxide, the amount of sulfur atoms derived from thiosulfate ions is 25% (molar ratio) or less with respect to the total amount of sulfur atoms. A method for producing an oxidized white liquor for an alkali source in a pulp bleaching stage, characterized by preparing an oxidized white liquor.
(2) At least one of the peroxides is hydrogen peroxide, The method for producing a white oxide liquid according to (1),
(3) The white liquor or oxidized white liquor used for the kraft cooking is characterized by comprising white liquor regenerated from black liquor in the kraft method cooking process or oxidized white liquor obtained by oxidizing the white liquor with oxygen. The method for producing an oxidized white liquid according to (1) or (2).

(4) The amount of sulfur atoms derived from thiosulfate ions produced by the method according to any one of items (1) to (3) is 25% (molar ratio) or less based on the total amount of sulfur atoms. Oxidized white liquor for an alkali source in a pulp bleaching stage.

(5) The oxidized white liquor described in the above (4) is used as an alkali source in an oxygen bleaching stage (oxygen delignification stage) and / or an alkaline hydrogen peroxide bleaching stage in the first stage of a pulp bleaching sequence. Pulp bleaching method.
(6) The pulp bleaching method according to (5), wherein the pulp is obtained from a kraft cooking process.

(7) A kraft process cooking step having a black liquor regeneration circulation step for circulating black liquor as a regenerated white liquor, an oxygen bleaching step (oxygen delignification step) at the first stage of the bleaching sequence, and an alkaline hydrogen peroxide bleaching step Connecting the multistage bleaching step of the pulp from the cooking step with
The same white liquor or white liquor used in the Kraft cooking process is oxidized with peroxide, and the amount of sulfur atoms derived from thiosulfate ions is 25% or less (molar ratio) with respect to the total amount of sulfur atoms. A white liquor oxidation treatment step of preparing an oxidized white liquor,
A supply line for supplying the oxidized white liquor obtained from the white liquor oxidation treatment step as an alkali source of an oxygen bleaching stage (oxygen delignification stage) and / or an alkaline hydrogen peroxide bleaching stage in the first stage of a pulp bleaching sequence;
A supply line for supplying the washing filtrate from the oxygen bleaching stage (oxygen delignification stage) and / or the alkaline hydrogen peroxide bleaching stage to the black liquor regeneration circulation step of the Kraft method cooking step;
A method for producing a kraft bleached pulp, comprising: a regenerated white liquor circulation line for supplying a part of the regenerated white liquor from the black liquor recycle cycle to the white liquor oxidation treatment step.
(8) A supply line that supplies the washing filtrate from the oxygen bleaching stage (oxygen delignification stage) and / or the alkaline hydrogen peroxide bleaching stage to the black liquor regeneration circulation step of the kraft method digestion step, Oxygen delignification stage) and / or a washing filtrate from a hydrogen peroxide-added alkali extraction stage is a line connected to a pulp washer for washing the digested pulp in the kraft process cooking step, (7) The manufacturing method of the kraft process bleached pulp of description.

According to the present invention, by using an oxidized white liquor obtained by oxidizing white liquor or oxidized white liquor used in the kraft process cooking step with a peroxide as an alkali source in an alkaline oxidative bleaching stage of a bleaching sequence, oxygen The bleaching efficiency of a bleaching stage where an alkali and an oxidizing agent coexist can be improved, such as a bleaching stage (oxygen delignification stage) or an alkaline hydrogen peroxide bleaching stage.
Further, the oxygen bleaching stage of the present invention used as an alkali source and the multi-stage bleaching process having an alkaline hydrogen peroxide bleaching stage and the kraft process cooking process, and the washing filtrate from the both bleaching stages is kraft process digested. A line for recycling as a washing liquid in a pulp washing machine in the process, and a white liquor (white water) obtained by regenerating the black liquor from the pulp washing machine into a white liquor oxidation treatment process using peroxide By organically connecting and integrating with the supply line, it is possible to configure a continuous production line that enables integrated production of kraft bleached pulp from chips.

The oxidized white liquor used in the present invention is obtained by oxidizing the white liquor or oxidized white liquor used in the kraft pulp cooking process and the oxygen delignification process with a peroxide, and the amount of sulfur atoms derived from thiosulfate ions is total sulfur. It is an oxidized white liquor adjusted to be 25% or less (molar ratio) with respect to the atomic weight.
If the molar ratio of the amount of sulfur atoms derived from thiosulfate ions to the total amount of sulfur atoms is 25% (molar ratio) or less, the bleaching property in the oxygen bleaching stage (oxygen delignification stage) is hardly adversely affected, but preferably 10 % (Molar ratio) or less, more preferably 5% (molar ratio) or less.

  The type of white liquor oxidized with the peroxide is not particularly limited as long as it is a white liquor that can be used for kraft cooking, and is obtained from a black liquor regeneration treatment step in a normal kraft cooking step. And white liquor prepared by adding sodium and sulfur to the white liquor to adjust the composition, white liquor prepared by mixing sodium hydroxide and sodium sulfide, and white liquor containing polysulfide. In addition, a white liquor subjected to air oxidation with respect to a normal white liquor, an oxidized white liquor obtained by oxidation with pure oxygen, and the like can also be treated white peroxide.

  In the present invention, the peroxide used for the oxidation of the white liquor can be either an organic peroxide or an inorganic peroxide, and is not particularly limited. Used. In addition, the oxidizing agent is not limited to peroxide alone, and combined use with other oxidizing agents such as oxygen is allowed.

The peroxide is used in an equimolar to 10-fold mol, preferably 3-fold to 7-fold mol of inorganic sulfur content in the white liquor / oxidized white liquor. If the ratio of the peroxide used is less than an equimolar amount with respect to the inorganic sulfur content, the oxidation will be insufficient, and if it is used more than 10 times the mole, unreacted peroxide will remain and the efficiency will deteriorate.
In addition, the peroxide treatment is usually performed at a temperature in the range of 0 ° C. to 100 ° C. under conditions where the white liquor does not freeze or boil.

Since the oxidized white liquor of the present invention has a low thiosulfate ion content, its use location is not particularly limited as long as it is an alkaline bleaching stage as well as the first oxygen bleaching stage (oxygen delignification stage) in the pulp bleaching sequence. Although not intended, it is preferably used in the oxygen bleaching stage, the alkaline hydrogen peroxide bleaching stage, and the alkaline oxygen hydrogen peroxide bleaching stage.
The oxygen bleaching stage, alkaline hydrogen peroxide bleaching stage, and alkaline oxygen hydrogen peroxide bleaching stage cleaning solution using the oxidized white liquor of the present invention originating from the regenerated white liquor from the cooking process as an alkali source is directly used in the kraft cooking process. Since the alkali balance of the pulp production process is not lost even when used as a cleaning liquid after cooking, the cleaning liquid in the multi-stage bleaching process is recycled as the cleaning liquid after cooking in the cooking process, so that the entire cooking process-bleaching process It is possible to construct a wastewater closed system that does not break the Na / S balance.

  The pulp bleached by the bleaching sequence having the oxygen bleaching stage or the alkaline hydrogen peroxide bleaching stage using the white liquor oxidized with the peroxide of the present invention as an alkali source can be any of chemical pulp, waste paper pulp and mechanical pulp. There is no particular limitation, but kraft pulp is preferred.

The present invention will be specifically described with reference to the following examples and comparative examples. Of course, the present invention is not limited to these examples.
In Examples and Comparative Examples, measurement of pulp kappa number, measurement of pulp whiteness, measurement of composition of white liquor and oxidized white liquor, measurement of each amount of sulfite ion, thiosulfate ion and sulfate ion in the solution are as follows. Went in the way.
The chemical addition rate is a ratio to the absolutely dry pulp.

(1) Measurement of pulp kappa number The kappa number was measured according to JIS P8211.

(2) Measurement of Pulp Whiteness The whiteness was measured according to JIS P 8212.

(3) Measurement of white liquor and _NaOH measurement white liquor and oxidized white liquor in the composition of oxidized white liquor, Na 2 S, the composition of _Na 2 CO ₃ is, SCAN N-30: was carried out according to the 85. Note that performing terms of Na 2 _O for measurement shown below.

(4) Measurement of sulfite ion, thiosulfate ion, and sulfate ion in solution The measurement of sulfite ion, thiosulfate ion, and sulfate ion was performed according to SCAN N-36: 98.

Example 1
NaOH 86.1 g / L, Na ₂ S 36.2 g / L, Na ₂ CO ₃ 19. To 1 L of white liquor containing Og / L, 170 ml of 60% hydrogen peroxide water was added for oxidation treatment to obtain an oxidized white liquor. The total sulfur atom oxidized white liquor obtained, the percentage of those present in the form of thiosulfate ions is 5% (molar _{ratio), NaOH 82.1g / L, Na} 2 S 0g / L, Na 2 CO ₃ 20.0 g / L. To the white kraft pulp with a whiteness of 37.6% and a copper number of 14.4, the oxidized white liquor is added so that the amount of caustic soda is 1.5% by mass, an oxygen pressure of 0.75 MPa, a temperature of 100 ° C., It was subjected to oxygen bleaching in 60 minutes. The whiteness after oxygen bleaching was 47.7%, and the kappa number was 9.6.

Comparative Example 1
NaOH 110 produced by adding 7% by weight of cooking black liquor as a catalyst to the white liquor similar to that of Example 1 and bubbling air to the hardwood unkraft pulp used in Example 1. 0.02 g / L, Na ₂ S 2.7 g / L, Na ₂ CO ₃ 25.5 g / L, and the ratio of those present in the form of thiosulfate ions in the total sulfur atoms in the oxidized white liquor is 78% Oxygen bleaching was performed under the conditions of Example 1 using an oxidized white liquor having a (molar ratio). The whiteness after oxygen bleaching was 46.0, and the kappa number was 10.4.

Example 2
Using the oxidized white liquor obtained in Example 1, the oxidized white liquor was adjusted so that the caustic soda amount was 1.5% by mass relative to the hardwood semi-kraft pulp having a whiteness of 68.5% and a kappa number of 3.2. Then, hydrogen peroxide in an amount of 0.2% by mass was added, and the mixture was subjected to alkaline hydrogen peroxide bleaching at a temperature of 70 ° C. for 60 minutes.
The whiteness after alkaline hydrogen peroxide bleaching was 77.3%, and the kappa number was 2.2.

Comparative Example 2
Using the oxidized white liquor used in Comparative Example 1, the oxidized white liquor was added so that the caustic soda amount was 1.5% by mass with respect to the hardwood semi-kraft pulp having a whiteness of 68.5% and a copper number of 3.2. Furthermore, 0.2% by mass of hydrogen peroxide was added and subjected to alkaline hydrogen peroxide bleaching at a temperature of 70 ° C. for 60 minutes. The whiteness after alkaline hydrogen peroxide bleaching was 73.4%, and the kappa number was 2.6.

Comparative Example 3
Using caustic soda as a reagent product, the aqueous caustic soda solution was added to a hardwood semi-kraft pulp having a whiteness of 68.5% and a kappa number of 3.2 so that the caustic soda amount was 1.5% by mass. Hydrogen peroxide in an amount of 2% by mass was added and subjected to alkaline hydrogen peroxide bleaching at a temperature of 70 ° C. for 60 minutes. The whiteness after alkaline hydrogen peroxide bleaching was 77.4%, and the kappa number was 2.2.

Example 3
To 1 L of white liquor containing 86.1 g / L of NaOH, 36.2 g / L of Na ₂ S, and 19.0 g / L of Na ₂ CO _3, an oxidation treatment is performed by adding 120 ml of 60% hydrogen peroxide water. An oxidized white liquor was obtained. The proportion of those present in the form of thiosulfate ions in the total sulfur atoms in the obtained white oxide liquid is 25% (molar ratio), NaOH 85.3 g / L, Na ₂ S 0.2 g / L, Na ₂ CO ₃ 20.1 g / L.
Oxygen bleaching was performed under the same conditions as in Example 1 except that the oxidized white liquor used was changed to the oxidized white liquor. The whiteness after oxygen bleaching was 47.4%, and the kappa number was 9.8.

Comparative Example 3
To 1 L of white liquor containing 86.1 g / L of NaOH, 36.2 g / L of Na ₂ S, and 19.0 g / L of Na ₂ CO ₃ , oxidation treatment is performed by adding 100 ml of 60% hydrogen peroxide water. An oxidized white liquor was obtained. The ratio of those present in the form of thiosulfate ions in the total sulfur atoms in the obtained oxidized white liquor is 29% (molar ratio), NaOH 90.1 g / L, Na ₂ S 0.4 g / L, Na ₂ CO ₃ 19.9 g / L.
Oxygen bleaching was performed under the same conditions as in Example 1 except that the oxidized white liquor used was changed to the oxidized white liquor. The whiteness after oxygen bleaching was 46.2%, and the copper number was 10.3.

Example 4
To 1 L of white liquor containing 92.2 g / L of NaOH, 2.5 g / L of Na ₂ S, and 12.0 g / L of Na ₂ CO ₃ , oxidation treatment is performed by adding 100 ml of 60% hydrogen peroxide water. An oxidized white liquor was obtained. The ratio of those present in the form of thiosulfate ions in the total sulfur atoms in the obtained white oxide liquor is 7% (molar ratio), NaOH 84.4 g / L, Na ₂ S 0.2 g / L, Na ₂ CO ₃ 10.2 g / L. Oxygen bleaching was performed under the same conditions as in Example 1 except that the oxidized white liquor used was changed to the oxidized white liquor. The whiteness after oxygen bleaching was 47.6%, and the kappa number was 9.8.

  As is clear from the comparison between Example 1 and Comparative Example 1 in Table 1, it is understood that the oxygen bleaching property is improved when an oxidized white liquor oxidized with a peroxide is used. In addition, comparing Example 2 and Comparative Examples 2 and 3 in Table 1, the white oxide oxidized using peroxide is bleaching equivalent to caustic soda when used as an alkali source in an alkaline hydrogen peroxide stage. It turns out that it has sex. When Examples 1 and 3 in Table 1 are compared with Comparative Example 4, it is possible to obtain oxygen bleaching unless the thiosulfate ion ratio in the oxidized white liquor obtained by oxidizing the white liquor with peroxide is 25% or less. It turns out that it has an adverse effect. Further, from Example 1 and Example 4, bleaching using oxidized white liquor obtained by subjecting a conventional oxidized white liquor to oxidation treatment with peroxide is an oxidation produced by subjecting white liquor to peroxide oxidation. It turns out that there exists an effect equivalent to a white liquor.

According to the present invention, by using an oxidized white liquor obtained by oxidizing a white liquor or oxidized white liquor used in a kraft pulp cooking step with a peroxide, oxygen bleachability is improved and / or alkaline. The white liquor can also be used in a bleaching stage where an alkali and an oxidizing agent coexist, such as a hydrogen peroxide stage. In addition, it is possible to configure a continuous production line that can efficiently perform integrated production of kraft bleached pulp from chips.

Claims (6)

  Oxidized white in which the amount of sulfur atoms derived from thiosulfate ions is 25% (molar ratio) or less based on oxidation of white liquor or oxidized white liquor used for kraft cooking with peroxide. A method for producing an oxidized white liquor for an alkali source in a pulp bleaching stage, characterized by preparing a liquid.   The method for producing a white oxide liquid according to claim 1, wherein at least one of the peroxides is hydrogen peroxide.   The white liquor or oxidized white liquor used for the kraft cooking is composed of white liquor regenerated from black liquor in the kraft method cooking process or oxidized white liquor obtained by oxygen oxidation of the white liquor. The manufacturing method of the oxidized white liquid of Claim 1 or Claim 2.   The alkali in the pulp bleaching stage produced by the method according to any one of claims 1 to 3, wherein the amount of sulfur atoms derived from thiosulfate ions is 25% (molar ratio) or less based on the total amount of sulfur atoms. Oxidized white liquor for source.   A method for bleaching a pulp, characterized in that the oxidized white liquor according to claim 4 is used as an alkali source in an oxygen bleaching stage (oxygen delignification stage) and / or an alkaline hydrogen peroxide bleaching stage in the first stage of a pulp bleaching sequence. 6. The method for bleaching pulp according to claim 5, wherein the pulp is obtained from a kraft cooking process.