JPH0593385A - Oxygen delignification method for cellulose pulp - Google Patents

Abstract

(57) [Summary] [Objective] In a method of delignifying cellulosic pulp with oxygen and alkali at a medium concentration of 5 to 18%, the level of Kappa number is significantly reduced without impairing the pulp viscosity. [Structure] When delignifying cellulose pulp with oxygen and alkali, ethylenediaminetetraacetic acid (ED
TA) -sodium salt, EDTA-ammonium salt, nitrilotriacetic acid (NTA) -sodium salt, and NTA-ammonium salt organic chelating agent derivatives selected from the range of 0.01 to 0.01 per weight of the dry pulp. 0.2
Add wt%. These organic chelating agent derivatives can effectively sequester metal ions in alkaline conditions, thereby preventing the depolymerization of cellulose due to the catalytic action of metal ions, thus preventing the viscosity of pulp from decreasing and the degree of delignification. It is thought to improve.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for delignification of cellulose pulp with oxygen. More specifically, the present invention relates to a delignification process which is capable of delignifying cellulosic pulp with oxygen and alkali at a medium concentration of 5-18% to obtain a significant reduction in the level of Kappa number without compromising pulp viscosity.

[0002]

2. Description of the Related Art A method of delignifying medium-digested cellulose pulp (hereinafter referred to as pulp) using oxygen and alkali is well known as an oxygen bleaching method.
Since around 984, it has been the mainstream alternative to the high concentration oxygen bleaching method.

The reason for adopting the enzyme bleaching method is mainly to reduce the cost of bleaching chemicals and the pollution load in the bleaching wastewater, and recently, in addition to the pollution load, the harmful chlorine system which significantly destroys the environment such as TOCL. It is said to be effective in suppressing the amount of chemicals generated.

However, the problem with the method of delignification of pulp by oxygen is that although the reaction between oxygen and lignin proceeds extremely quickly, the solubility of oxygen in water is extremely low, which is the rate-determining step and is delignified. Due to the slow reaction and lack of selectivity of oxygen dissolved in water for lignin, depolymerization of cellulose by oxygen is promoted, resulting in low viscosity of oxygen-treated pulp, resulting in poor pulp strength. It has a serious drawback.

In the high-concentration method, oxygen is dissolved in a thin water film attached to the periphery of pulp fibers by the partial pressure of oxygen, and the reaction between oxygen and lignin is performed, whereas in the medium-concentration method, high-speed shearing is performed by a high-speed shearing machine. It is considered that the oxygen is dissolved in a large amount of water so that the dissolved oxygen and the cellulose are in sufficient contact with each other. On the other hand, in the oxygen delignification reaction, lignin undergoes oxidation by oxygen and is cleaved to produce an organic acid having a carboxyl group at its terminal. Such a reaction suitably proceeds within a certain temperature range. When an alkali such as caustic soda is present, the above-mentioned organic acid produced by the oxidation of lignin is eluted from cellulose to the water side and neutralized, so the presence of alkali in the reaction system causes the delignification reaction. Serve to promote.

The above-mentioned medium-concentration-method oxygen delignification method is a method in which pulp which has been digested and washed is made to have a concentration of 5 to 18% (generally 8 to 12%) by alkali (caustic soda or oxidized kraft white liquor). ) As NaOH 15-30 Kg
/ AD pulp T is added and adjusted, and then pumped into a pressure system (generally less than 10 Kg / cm ² ) and oxygen gas is supplied to the pulp slurry by a high-speed shearing machine while supplying 15 to 30 Kg / AD pulp T of oxygen gas. After fully dissolved, it was introduced into the tower, and the delignification reaction was 5-60.
It is designed to be completed in minutes, typically 15-40 minutes, while being passed through the tower. The steam is added during conditioning of the pulp slurry, or in front of or in the high speed shear, at the desired temperature, typically 7
It is maintained in the range of 0 to 130 ° C.

It has been proposed to provide a high-speed shearing machine in several stages for the purpose of securing sufficient dissolved oxygen and improving the delignification degree (Japanese Patent Laid-Open No. 1-272890). Although the delignification degree is improved by strengthening such oxidizing conditions, if the water or pulp used contains a metal ion, the depolymerization of the cellulose will proceed further, and the viscosity of the pulp will be significantly reduced. There is an unavoidable drawback that the strength of pulp is significantly deteriorated.

Selected from the group consisting of barium carbonate, calcium carbonate, magnesium carbonate, alkali metal borates and titanium dioxide for the purpose of protecting the cellulose during the delignification reaction of the pulp with oxygen and alkali so as not to reduce the viscosity of the pulp. It has been proposed to add 0.5 to about 3% of the catalyst to the pulp (Japanese Patent Publication No. 42-2003). Further, magnesium complex salt obtained by dissolving magnesium compound in complexing agent (Japanese Patent Publication No. 47-9203) or triethanolamine salt (Japanese Patent Publication No. 49-133601)
Has also been shown to be usable for this purpose.

However, the magnesium compound used is insoluble in water and must be sufficiently mixed with the cellulose pulp, and if 1% or more is not added, no substantial effect can be obtained and the cost is high. I have a scale problem. Since triethanolamine salt is completely soluble in water as compared with magnesium, it is convenient to handle and effective as a protective agent for preventing depolymerization of cellulose. However, when iron ions are present in the pulp slurry, triethanolamine Since it forms an ionic complex compound, which on the contrary has a catalytic action to accelerate the depolymerization of cellulose, it has a drawback that the viscosity of pulp is remarkably lowered.

On the other hand, Japanese Patent Publication No. 22601/1975 discloses a method of adding a magnesium compound and a chelating agent such as EDTA and EDTA derivative in combination, but the above-mentioned drawbacks due to the magnesium compound are still unavoidable.

[0011]

SUMMARY OF THE INVENTION In view of the above situation, the inventors of the present invention have earnestly studied a protective agent that produces an effect with a very small amount of addition without generating scale in the method of delignification of cellulose pulp with oxygen. As a result, it was found that a specific compound of the derivative of the organic chelating agent significantly increases the delignification degree while maintaining the pulp viscosity by adding it in the oxygen delignification step, thereby completing the present invention. Came to.

Accordingly, it is an object of the present invention to provide a method for eliminating the above-mentioned drawbacks in a medium-concentration oxygen delignification method and obtaining a marked reduction in the level of Kappa number without impairing the pulp viscosity. ..

[0013]

The present invention provides a method for delignifying cellulosic pulp with oxygen and alkali at a medium concentration of 5 to 18%.
DTA) -sodium salt, EDTA-ammonium salt,
Nitrilotriacetic acid (NTA) -sodium salt and NTA-
One or two or more selected from organic chelating agent derivatives of ammonium salt is used in an amount of 0.0 per 100% by weight of absolutely dry cellulose pulp.
It is a method for delignification of cellulose pulp with oxygen, which is characterized by adding 1 to 0.2% by weight.

Derivatives of the organic chelating agent used in the present invention include ethylenediaminetetraacetic acid (EDTA) -sodium salt, EDTA-ammonium salt, nitrilotriacetic acid (NTA) -sodium salt, and NTA-ammonium salt. One kind or two or more kinds are selected from the above.

The organic chelate derivative used in the present invention can be added at various places in the step of delignifying cellulose pulp with oxygen and alkali at a known medium concentration, but generally sufficient mixing is achieved. As such, it is added in front of the feed pump for injecting the pulp slurry into the oxygen pressure system.

FIG. 1 is a schematic flow diagram for oxygen bleaching pulp at a known medium concentration with two high speed shears and two reaction towers in series. According to this flow,
Pulp slurry 1 with a concentration of 18%, preferably 8-12%
Is heated by adding steam 2, alkali 3 is added, and then organic chelate derivative 4 is added, and then introduced into the pressure system of less than 10 Kg / cm ² by a feed pump 5. After further adding steam 6 to this flow and adjusting it to a desired temperature, it is introduced into the first high-speed shearing machine 8 together with a part of the desired oxygen gas 7, where alkali, oxygen Good mixed contact between the gas and the organic chelate derivative and the pulp is made.

Subsequently, these mixed pulp slurry streams are introduced into the first tower 9 and subjected to initial delignification while passing through the tower, after which the second high speed shear 10 produces the desired lignin. The rest of the oxygen gas 7 (mixed with steam and alkali (not shown) if necessary) is introduced into the second tower 11, where the delignification is completed during the passage and finally It is discharged to the blow tank 12 and the pressure is released to complete the delignification treatment. The organic chelating agent derivative may be added in a divided manner before each high-speed shearing machine, and the method of the present invention can be applied to the case where each high-speed shearing machine and one tower are provided.

The organic chelating agent derivative used in the present invention may be used alone or in combination of two or more kinds, and the addition amount thereof is 0.01 to 0.
It is in the range of 2% by weight, preferably 0.02 to 0.15% by weight. If the addition amount is less than 0.01%, the effect of preventing depolymerization of the pulp is poor, and if it exceeds 0.2%, the effect reaches the ceiling and the cost is unnecessarily increased, which is not suitable.

Surprisingly, the organic chelating agent derivative used in the present invention is Fe, Cu, Mn, Al, Ca, Zn accompanying the pulp or being brought into the system from process water.
It is possible to extremely efficiently block trace amounts of heavy metal ions such as alkali, which can prevent the depolymerization of cellulose and the decomposition of oxidizer due to the catalytic action of metal ions. It is thought that the above can be significantly advanced.

[0020]

The present invention will be described in more detail with reference to the following examples, but of course the present invention is not limited thereto. In the following,% means% by weight
Indicates.

Examples 1 to 4 and Comparative Example 1 Using the medium-concentration oxygen delignification equipment as shown in FIG. 1 equipped with two high-speed shearing machines of 500 AD tons per day and a reaction tower, copper was added under the following conditions. Oxygen bleaching was performed on unbleached softwood kraft pulp having a value of 23 to 25. Organic chelating agent derivatives _{EDTA-2H-2 (NH 4} ), EDTA-
4Na, NTA-H-2 ( NH 4), NTA-H-2N
a in front of the feed pump to 0.
Examples in which 1% was added were Examples 1, 2, 3 and 4, and those in which the organic chelating agent derivative was not added were Comparative Example 1.

Oxygen delignification conditions Pulp treatment amount 500 ADT / day Pulp concentration 10.5% Oxygen addition amount (added before the first high speed shearing machine) 15 Kg / AD pulp T (before the second high speed shearing machine) 10Kg / AD pulp T Amount of oxidized white liquor (added as NaOH before feed pump) 23Kg / AD pulp T Temperature (first tower inlet) 105 ° C (second tower inlet) 110 ° C pressure (Top of the first tower) 6Kg / cm ² (top of the second tower) 4Kg / cm ² retention (first tower) 20 minutes (second tower) 20 minutes

The evaluation of delignification is carried out by the TAPPI test method T-
The Kappa number described in 236 hw-85 is measured and judged by the reduction rate, and the pulp quality is evaluated by JAPANTAP.
The pulp viscosity was measured by the method for measuring the bleached pulp for papermaking described in PI No. 44-84, and the reduction rate was used for the judgment. In addition, these data are shown as an average value of 42 points measured every 4 hours for 7 days, and these results are shown in Table 1.

[0024]

Examples 5 to 6 and Comparative Example 2 Using a hardwood bleached kraft pulp having a kappa number of 19, oxygen bleaching was carried out in the same manner as in Examples 1 to 4 and Comparative Example 1 except for the following conditions. The obtained pulp was evaluated. Organic chelating derivative EDTA-2H-2 (NH
₄ ) and HTA-H-2 (NH ₄ ) were added to the feed pump in an amount of 0.05% based on the weight of the absolutely dried pulp as Examples 5 and 6, respectively, and those without addition of the organic chelating agent derivative were Comparative Examples. It was set to 2.

Oxygen delignification conditions Oxygen addition amount (added before the first high-speed shearing machine) 12 kg / AD pulp T (adding before the second high-speed shearing machine) 8 kg / AD pulp T oxidized white liquor addition Amount (added as NaOH before feed pump) 18 kg / AD pulp T The results obtained are shown in Table 2 in the same manner as in Examples 1 to 4 and Comparative Example 1.

[0027]

As is clear from Tables 1 and 2, in the method of the present invention (Examples 1 to 6), both softwood pulp and hardwood pulp are pulped even if the Kappa number is decreased from the conventional level (Comparative Examples 1 and 2). Viscosity can be maintained in a comparable manner.

[0029]

According to the method of the present invention, by adding an extremely small amount of the above organic chelating agent derivative in the oxygen delignification step, it is possible to increase the delignification degree while maintaining the pulp viscosity. Since the cost can be reduced and the pollution load on the wastewater can be reduced, it is possible to further reduce the wastewater treatment cost and the mixing of chlorine-based harmful substances into the wastewater.

[Brief description of drawings]

1 is a schematic flow diagram for delignification with oxygen and alkali at medium concentration. 5: Supply pump, 8, 10: High-speed shearing machine, 9, 1
1: reaction tower, 12: blow tank.

Claims (1)

[Claims] 1. A method of delignifying cellulosic pulp with oxygen and alkali at a medium concentration of 5-18%,
Ethylenediaminetetraacetic acid (EDTA) -sodium salt,
EDTA-ammonium salt, nitrilotriacetic acid (NTA)
-Oxygen of cellulose pulp, characterized in that 0.01 to 0.2% by weight based on the weight of absolutely dry cellulose pulp is added to one or more selected from derivatives of organic chelating agents of sodium salt and NTA-ammonium salt. Delignification method by.