JPH0987986A - Bleaching method of chemical pulp for papermaking - Google Patents

Abstract

(57) 【Abstract】 PROBLEM TO BE SOLVED: To reduce the amount of chlorine dioxide used in the production of high-whiteness chemical pulp for papermaking, thereby suppressing organic chlorine compound by-products and preventing environmental pollution due to bleaching wastewater. To do. In a method of delignifying and bleaching a chemical pulp, a digested chemical pulp is treated by adding a chelating agent to a chlorine dioxide stage, and then peroxide or peroxide is added in an alkaline medium. A method for bleaching chemical pulp for papermaking, comprising the steps of delignification and bleaching with a product and oxygen.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to the production of chemical pulp for papermaking. More particularly, it relates to improvements in delignification and bleaching of chemical pulp.

[0002]

2. Description of the Related Art Bleaching of chemical pulp for papermaking is carried out by a multistage bleaching process. Conventionally, chlorine-based chemicals have been used as a bleaching agent in this multi-stage bleaching. Specifically, by combining chlorine (C), hypochlorite (H), and chlorine dioxide (D), for example, C-E-H-D,
Bleaching has been performed by a sequence such as C / D-E-H-D (C / D is a combined bleaching stage of chlorine and chlorine dioxide, E is an alkali extraction stage). However, since these chlorine-based bleaching chemicals by-produce an organic chlorine compound that is harmful to the environment during bleaching, environmental pollution of bleaching wastewater containing this organic chlorine compound poses a problem.

The most effective method for reducing or preventing the by-production of organic chlorine compounds is to reduce the amount of chlorine-based chemicals used or not to use them, and especially to avoid using molecular chlorine in the first stage. Is the most effective method. The pulp produced by this method is called ECF (elementary chlorin-free) pulp, and it is most of this pulp in Europe at present.

As a method for producing ECF pulp, Japanese Patent Publication No.
No. 221482, Japanese Patent Publication No. 4-245988, and Japanese Patent Publication No. 6-207390, it is proposed to use an enzyme such as hemicellulase or xylanase as a method for delignification. However, this method includes
There are problems that the viscosity of the pulp is reduced and the yield is decreased due to the use of the enzyme, and the bleaching cost is increased because the enzyme itself is very expensive.

[0005] As another method that has been drawing attention, methods using ozone have been proposed in Japanese Examined Patent Publication No. 3-40888, Japanese Examined Patent Publication No. 5-163691, and Japanese Examined Publication No. 5-302285. When ozone is used, delignification progresses significantly and the whiteness is considerably improved, but this also has problems such as a decrease in pulp viscosity and a decrease in yield. Furthermore, ozone is also a very expensive chemical, and the use of ozone leads to a significant increase in bleaching costs.

As a method for producing ECF pulp in Europe, after cooking or oxygen bleaching, instead of molecular chlorine, a treatment with chlorine dioxide, which produces extremely less organic chlorine compound as a byproduct than molecular chlorine, is carried out. A general method is alkali extraction or peroxide bleaching, which is a non-chlorine bleaching agent under alkaline conditions, and the subsequent transfer.

However, since the effect of peroxide is not sufficiently obtained, in order to replace chlorine used in the first stage with chlorine dioxide, the production capacity of the chlorine dioxide generator is currently 3-5. Doubled, and a huge amount of investment is required for the expansion.

[0008]

DISCLOSURE OF THE INVENTION The object of the present invention is to produce an effect of peroxide when the first stage chlorine dioxide bleaching is carried out and then the peroxide bleaching is carried out in the production of high-whiteness chemical pulp for papermaking. By increasing the amount of chlorine dioxide used, byproducts of organic chlorine compounds are suppressed,
It is to prevent environmental pollution due to bleaching wastewater.

[0009]

[Means for Solving the Problems] The present inventors have been working economically on a method of delignifying and bleaching pulp to obtain pulp with high whiteness and high quality, and the amount of chlorine-based bleaching chemicals used. As a result of diligent study on a method that can significantly reduce the amount of chlorine dioxide, attention has been paid to chlorine dioxide, which is attracting attention as an alternative to molecular chlorine, and when performing peroxide treatment in the bleaching process of chemical pulp using chlorine dioxide, the chlorine dioxide stage It has been found that the addition of a chelating agent to (1) makes it possible to obtain a pulp with delignification and high whiteness extremely effectively after the subsequent peroxide treatment, and completed the present invention.

That is, in the present invention, chlorine dioxide and a chelating agent are added to a chemical pulp that has been subjected to a digestion treatment, and then the pulp is subjected to delignification with a peroxide in an alkaline medium or with a peroxide and oxygen. A bleaching method for chemical pulp for paper making, which is characterized by bleaching. INDUSTRIAL APPLICABILITY The present invention is suitable for bleaching of chemical pulp for papermaking, and particularly suitable for delignification and bleaching of kraft pulp derived from hardwood and softwood.

The feature of the present invention is that this method does not reduce the respective effects of two treatments (chlorine dioxide treatment and chelating agent treatment) which are conventionally performed for completely different purposes, but they are synergistic. It is an economically superior method that can be carried out simultaneously with the improvement of the effective effect, and that the number of bleaching stages is small in addition to the effect.

Further, since the amount of chlorine dioxide used is smaller than that in the general method, when the current process of the first stage chlorine treatment is changed to the ECF process of the first stage chlorine dioxide treatment, the capacity of the chlorine dioxide generator is increased. It can be said to be an economically superior method in that it can be handled with a minimum or no increase, and the investment cost can be kept low.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION In combination with the chelating agent (Q) of the present invention,
The chlorine dioxide treatment (hereinafter, this treatment may be referred to as DQ or DQ stage) depends on the state of the pulp, but for example, the pulp concentration is 1 to 40% by weight, preferably 2 to 30% by weight, more preferably 5%. ~ 20% by weight, temperature is 20 ~ 1
10 ° C, preferably 40-80 ° C, treatment time 15-3
00 minutes, preferably 60-180 minutes, pH 3-9,
It is preferably carried out at 4 to 8.

The amount of chlorine dioxide used varies depending on the amount of lignin contained in the pulp after digestion used, but is 0.05 to 3.0% by weight, preferably 0.1 to 100% by weight of the dry pulp.
1.0% by weight.

The chelating agent used is at least one chelating agent selected from aminocarboxylate type chelating agents and aminoalkylphosphoric acid type chelating agents represented by the general formula (1).

Embedded image (X in the formula represents hydrogen, ammonium, or an alkali metal, m represents an integer of 2 to 3, and n represents an integer of 0 to 3.)

Specifically, ethylenediaminetetraacetic acid (EDT) is used as an aminocarboxylate type chelating agent.
A), diethylenetriaminepentaacetic acid (DTPA), N-
Hydroxyethylethylenediamine-N, N ', N "-
Triacetic acid (HEDTA), nitrilotriacetic acid (NT
A), cyclohexanediaminetetraacetic acid (CyDTA)
And their salts, as aminoalkyl phosphate chelating agents, aminotrimethylene phosphonic acid (ATM
P), ethylenediaminetetramethylenephosphonic acid (E
DTMP), diethylenetriaminepentamethylenephosphonic acid (DTPMP), propylenediaminetetramethylenephosphonic acid (PDTMP), dipropylenetriaminepentamethylenephosphonic acid (DPTPMP), and the like, and salts thereof. The amount used varies depending on the amount of heavy metals contained in the pulp and water, but is 0.01 to 5.0% by weight, and preferably 0.05, per dry pulp.
~ 1.0%.

The pulp after the DQ stage treatment is separated by a dehydrator and then preferably washed. The dehydration / washing step is also included in the DQ treatment of the present invention. The pulp after the DQ stage is later subjected to a peroxide or a delignification / bleaching process using peroxide and oxygen (hereinafter, this peroxide bleaching process is performed in an Ep or Ep stage, and a bleaching process using peroxide and oxygen. The process is sometimes called Eop or Eop stage). In this treatment, the pulp is subjected to delignification / bleaching action by peroxide, or peroxide and oxygen in an alkaline medium. When using peroxide and oxygen together,
Peroxide and oxygen act on the pulp substantially simultaneously.

As the alkaline agent in the Ep stage or the Eop stage, caustic soda, caustic potash, lime, soda ash, etc. can be used. Among them, caustic soda is inexpensive and can be preferably used because it can be recycled to the digestion step to reduce the replenishment of chemicals in the digestion step. The amount of alkaline agent used is 0.1 per absolute dry pulp in terms of NaOH.
˜6.0 wt%, preferably 0.5-3.0 wt%. If the amount of the alkaline agent used is less than this, the delignification / bleaching effect is reduced, and if it is more than this, the viscosity of the pulp is markedly reduced.

As oxygen in the Eop stage, oxygen gas and air can be used, but oxygen gas is preferred. The amount of oxygen used is preferably 0.1 to 1.0% by weight per bone-dry pulp, and the operating pressure of the Eop stage is atmospheric pressure to 3.5 Kg.
f / cm ² (gauge pressure) is preferable.

The Ep stage or Eop stage peroxide includes inorganic and organic substances such as hydrogen peroxide, an adduct of hydrogen peroxide and inorganic salts, sodium peroxide, persulfates, performic acid and peracetic acid. A peroxide can be used, and hydrogen peroxide is generally preferably used. The amount of peroxide used is 0.05 to 8.0% by weight, based on 100% hydrogen peroxide, per absolutely dry pulp.
It is preferably 0.2 to 3.0% by weight. If the amount of the peroxide used is less than this, the delignification / bleaching effect is low, and if it is more than this, the efficiency of the peroxide decreases.

The order of adding the chemicals to the pulp in the Ep stage and Eop stage of the present invention is preferably the order of the alkali agent and oxygen, and the peroxide is added immediately after the addition of the alkali agent and immediately before the addition of the oxygen. Alternatively, it is preferably performed immediately after.

The pulp concentration of the Ep stage and Eop stage of the present invention is 7 to 30% by weight, preferably 10 to 20% by weight.
The temperature is 40 to 120 ° C, preferably 70 to 100 ° C. Treatment time is 15 to 180 minutes, preferably 30 to 12
0 minutes.

Further, it is preferable to use a magnesium compound in combination in the Ep and Eop stages. By using the magnesium compound, the delignification / bleaching action of the peroxide is increased and the decrease in the viscosity of the pulp is reduced. As the magnesium compound, magnesium sulfate, magnesium hydroxide, magnesium oxide, magnesium carbonate, magnesium nitrate or the like can be used, but magnesium sulfate is generally used. The amount of magnesium compound used is 0.005 to 0.7 per absolutely dry pulp as magnesium ion.
It is 5% by weight, preferably 0.01 to 0.3% by weight.
The magnesium compound is preferably added before the addition of the alkaline agent, oxygen and peroxide. That is, it is preferable from the viewpoint of uniform dispersibility of the magnesium compound to add the magnesium compound when the pulp slurry is in the neutral to weakly acidic region.

The bleached pulp obtained by the DQ-Ep (or Eop) of the present invention shows a considerably high whiteness as it is, but it is higher by the full bleaching which is followed by the addition of a single-stage or multi-stage bleaching step. A pulp showing whiteness can be obtained. In that case, since a high degree of delignification has already been performed up to the Ep stage and the Eop stage, and since it is in a high whiteness state at that stage, as a chemical for subsequent bleaching,
Bleaching with little or no chlorine and hypochlorite is possible.

For example, O-DQ-Ep (or Eo
p), chlorine dioxide (D) and then peroxide bleaching (P) are carried out after the step p), and O-DQ-Ep (or Eop) -D-
Full bleaching sequences without chlorine and hypochlorite, such as P, are possible. In these full bleaching sequences, the current representative sequence, OC / D-
High viscosity equal to or higher than Eo (combined with oxygen in E stage) -HD
Pulp products with high whiteness can be obtained. In addition, since chlorine and hypochlorite are not used, bleaching in which the amount of organic chlorine compounds produced as by-products is significantly smaller than in the existing method is possible.

The chlorine dioxide (D) stage condition in the present invention is a normal D stage condition. For example, the pulp concentration is 7 to 30% by weight, the temperature is 40 to 90 ° C, and the time is 1 to 4
The time and the amount of chlorine dioxide used are in the range of 0.1 to 2.0% by weight.

The subsequent peroxide (P) stage is carried out under normal P stage conditions. That is, the pulp concentration is 7 to 30% by weight and the temperature is 40 to 1 in the alkaline medium.
The temperature is 00 ° C. and the time is 1 to 4 hours. Examples of the alkaline agent include caustic soda, caustic potash, lime, soda ash, etc. Generally, caustic soda is used, and the caustic soda is used in an amount of 0.1 to 2.0% by weight. Further, as the peroxide, hydrogen peroxide, an adduct of hydrogen peroxide and inorganic salts, sodium peroxide,
Inorganic and organic peroxides such as performic acid and peracetic acid can be mentioned, but hydrogen peroxide is generally used, and the amount of peroxide used is 100% by weight of hydrogen peroxide in terms of absolute dry pulp. Per 0.1 to 3.0% by weight.

The effect of the method of the present invention is that heavy metals, which are harmful to peroxide bleaching, are used in combination as compared with ordinary chlorine dioxide bleaching or removal by chelating agent treatment.
It can be removed very efficiently, so that wasteful decomposition of the peroxide in the next stage is greatly suppressed, and as a result, the whiteness after peroxide bleaching and delignification are dramatically improved. Is.

[0029]

EXAMPLES The present invention will be described in detail with reference to examples. The% of the amount of each chemical used is shown by weight% per bone dry pulp, and the amount of peroxide used is 100% hydrogen peroxide conversion. The pulp used is L-material pulp which has been subjected to oxygen bleaching after kraft cooking. The analysis method was as follows. -Pulp: Whiteness 45.7%, K value: 7.9, 2
6.2 cP ・ Analytical evaluation: Whiteness ・ ・ ・ ・ JIS-P8123 (Hunter whiteness method) K value ・ ・ TAPPI K value method Viscosity ・ J. TAPPI No. Method 44 Metal content-ICP method AOX-EPA METHOD 9020 method (using Mitsubishi Kasei Co., Ltd. TSX-10 type)

Examples 1 to 3 Regarding L material pulp subjected to oxygen bleaching after kraft cooking,
Delignification bleaching with DQ-Ep was performed according to the following conditions. (DQ-Ep) DQ (chlorine dioxide + chelating agent treatment) 1) ClO ₂ amount: 0.2%, DTPA amount: 0.2%, pulp concentration: 12%, treatment time: 2 hours, treatment temperature: 70
The treatment was carried out under the condition of ° C. However, regarding pH,
6 and 9 (sulfuric acid was used for adjustment). 2) After the treatment, it was diluted with water to a pulp concentration of 2.5% and then dehydrated to a pulp concentration of 22%. Further, the pH was adjusted to 6 to 8 with a dilute NaOH aqueous solution, the pulp concentration was set to 20%, and the process was moved to the next Ep stage. Ep (peroxide bleaching) 1) H ₂ O ₂ amount: 1.0%, NaOH amount: 1.2%, M
The treatment was carried out under the conditions of gSO ₄ amount: 0.25%, pulp concentration: 10%, treatment time: 90 minutes, treatment temperature: 90 ° C. 2) After the reaction, dilute the pulp to 2.5% with water,
Then, the pulp concentration was dehydrated to 20% and the bleaching operation was completed.

Comparative Examples 1 to 3 Bleaching was carried out in the same manner as in Examples 1 to 3 except that the chelating agent in the DQ stage of Examples 1 to 3 was not used. (D-Ep) Comparative Examples 4 to 6 Bleaching was performed in the same manner as in Examples 1 to 3 except that chlorine dioxide in the DQ stage of Examples 1 to 3 was not used. (Q-Ep)

The bleaching results of Examples 1 to 3 and Comparative Examples 1 to 6 are shown in Table 1.

[Table 1] Table 1 DQ stage pH Whiteness (%) K value Viscosity (cP) ────────────────────────────── ─────── Example 1 4 76.7 4.0 24.8 2 6 79.1 3.7 23.5 3 9 76.0 4.6 25.0 (DQ-Ep) Comparative Example 1 4 73.2 4.5 24.5 2 6 73.1 4.7 24.2 3 9 69.4 4.9 23.8 (D-Ep) Comparative Example 4 4 67.0 5.1 25.3 5 6 67.6 5.2 24.8 6 9 62.2 5.8 24.2 (Q-Ep) ──────────────────────── ───────────── As described above, in the present invention, the whiteness and delignification degree, which were not sufficient when only one treatment of D or Q was used, used both at the same time. By processing It is thermocline improved.

Table 2 shows the amounts of heavy metals in the pulp after the DQ, D, and Q treatments in Example 2 and Comparative Examples 2 and 5.

[Table 2] Table 2 Heavy metal content (mg / kg pulp) Treatment Fe Mn Cu ───────────────────────────────── ───── Example 2 DQ 9.2 3.6 1.2 Comparative Example 2 D 36.5 16.2 8.4 Comparative Example 5 Q 28.9 8.8 3.2 ────── ────────────────────────────── Thus, compared to chlorine dioxide and chelating agent alone treatment,
When both are used together, a remarkable metal removing effect is observed.
It is particularly effective in removing Fe, which is difficult to remove.

Example 4 Regarding L material pulp subjected to oxygen bleaching after Kraft cooking,
Delignification bleaching by DQ-Eop was performed according to the following conditions, and then chlorine dioxide bleaching and then peroxide bleaching were performed on the obtained pulp. (DQ-Eop-D
-P) DQ (chlorine dioxide + chelating agent treatment) 1) ClO ₂ amount: 0.3%, DTPA amount: 0.2%, pulp concentration: 12%, treatment time: 2 hours, treatment temperature: 70
The treatment was carried out under the condition of ° C. However, the pH was set to 6 (sulfuric acid was used for adjustment). 2) After the treatment, it was diluted with water to a pulp concentration of 2.5% and then dehydrated to a pulp concentration of 22%. Further, the pH was adjusted to 6 to 8 with a dilute NaOH aqueous solution, the pulp concentration was set to 20%, and the process was moved to the next Eop stage. Eop (peroxide + oxygen bleaching) 1) H ₂ O ₂ amount: 1.0%, NaOH amount: 1.2%, M
gSO ₄ amount: 0.25%, O ₂ amount: 0.5%, reaction pressure:
Initial 2Kgf / cm ² (gauge pressure) → final 0Kgf / c
m ² (gauge pressure), pulp concentration: 10%, treatment time: 9
The treatment was performed for 0 minutes at a treatment temperature of 90 ° C. 2) After the reaction, dilute the pulp to 2.5% with water,
Then, the pulp was dehydrated to a pulp concentration of 20%, and the process was transferred to the next stage, D stage. D (Chlorine dioxide bleaching) 1) Treatment was carried out under the conditions of ClO ₂ amount: 0.2%, pulp concentration: 12%, treatment time: 2 hours, treatment temperature: 70 ° C. 2) After the reaction, dilute the pulp to 2.5% with water,
Then, the pulp was dehydrated to a pulp concentration of 20%, and the process was transferred to the next stage, P stage. P (peroxide bleaching) 1) H ₂ O ₂ amount: 0.2%, NaOH amount: 0.3%, pulp concentration: 15%, treatment time: 120 minutes, treatment temperature: 7
The treatment was carried out under the condition of 0 ° C. 2) After the reaction, dilute the pulp to 2.5% with water,
Then, it was dehydrated to a pulp concentration of 20% and the bleaching operation was completed.

Comparative Example 7 As the current bleaching method, the pulp after oxygen bleaching similar to that in Example 4 was used, and C / D (effective chlorine substitution ratio by D: 10) was used according to the conditions generally practiced. %)-Eo
-HD full bleaching was performed. C / D: 2.0%, Eo: NaOH amount 1.0%, O ₂ amount 0.5%, H: 1.0%, D: 0.15% (C / D-E
o-H-D)

The results of Example 4 and Comparative Example 7 are shown in Table 3. In addition, Table 3 shows the amount of the organohalogen compound (AOX) measured together with all the waste liquids in Example 4 and the amount of AOX in Comparative Example 7.

[0037]

[Table 3] Table 3 Whiteness (%) Viscosity (cP) AOX amount (Kg / Pt) ───────────────────────────── ───────── Example 4 87.6 14.8 0.24 Comparative Example 7 86.4 10.4 3.12 ────────────────── ────────────────────

[0038]

EFFECTS OF THE INVENTION According to the DQ-Ep (Eop) bleaching of the present invention, it is possible to efficiently carry out delignification without a significant decrease in viscosity, and a pulp having a remarkably high whiteness. Can be obtained. As a result, since the amount of chlorine-based chemicals used in the second-stage bleaching can be significantly reduced, it is possible to significantly reduce the by-product of the organic chlorine compound, which contributes to the prevention of environmental pollution due to the bleaching wastewater. Also,
In carrying out the present invention, the high temperature and high pressure oxygen bleaching equipment and the medium and low pressure oxygen bleaching equipment, which are currently popular, can be used as they are, so that a large additional capital investment is not required.

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] April 1, 1996

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claim 2

[Correction method] Change

[Correction contents]

Embedded image (X in the formula represents hydrogen, ammonium, or an alkali metal, m represents an integer of 2 to 3, and n represents an integer of 0 to 3.)

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0015

[Correction method] Change

[Correction contents]

The chelating agent used is at least one chelating agent selected from aminocarboxylate type chelating agents and aminoalkyl phosphoric acid type chelating agents represented by the general formula (1).

Embedded image (X in the formula represents hydrogen, ammonium, or an alkali metal, m represents an integer of 2 to 3, and n represents an integer of 0 to 3.)

Front page continuation (72) Inventor Akiyo Shimada 6-1-1 1-1 Shinjuku, Katsushika-ku, Tokyo Mitsubishi Gas Chemical Co., Ltd. Tokyo Research Laboratory

Claims (4)

[Claims] 1. A method of delignifying and bleaching a chemical pulp, wherein a chelating agent is added to a digested chemical pulp to perform chlorine dioxide treatment, and then peroxide or peroxide is added in an alkaline medium. A method for bleaching chemical pulp for papermaking, characterized in that delignification and bleaching are carried out with substances and oxygen. 2. The chemical pulp for papermaking according to claim 1, wherein the chelating agent is at least one selected from an aminocarboxylate type chelating agent and an aminoalkylphosphoric acid type chelating agent represented by the general formula (1). Bleaching method. Embedded image (X in the formula represents hydrogen, ammonium, or an alkali metal, m represents an integer of 2 to 3, and n represents an integer of 0 to 3.) 3. The method for bleaching chemical pulp for papermaking according to claim 1, wherein the peroxide is hydrogen peroxide. 4. The method for bleaching chemical pulp for papermaking according to claim 1, wherein the chemical pulp subjected to high temperature and high pressure oxygen bleaching treatment after cooking is used.