JPH11107181A - Bleaching of chemical pulp - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a pulp having high whiteness and high viscosity by bleaching with oxygen, treating with an enzyme in acidic state and continuing the treatment at increased temperature. SOLUTION: In a treating stage in the bleaching process of a chemical pulp, the pulp is bleached with oxygen and then with an enzyme in acidic state and the treatment is continued further for 5-20 min (preferably 10-15 min) by raising the temperature to 70-90 deg.C (preferably 60-80 deg.C). The treatment with an enzyme in acidic state is carried out at pH 2.0-4.0 and 40-80 deg.C for 20-60 min and the amount of the enzyme is 0.1-1,000 U/g (based on bone-dry pulp) in the case of xylanase.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for bleaching chemical pulp. More particularly, the present invention relates to a chemical pulp bleaching method for improving the bleaching efficiency in a chemical pulp bleaching process, which comprises performing an acidic enzymatic treatment and subsequently increasing the temperature.

[0002]

2. Description of the Related Art The purpose of pulp bleaching is to increase the whiteness by decomposing, altering or removing lignin and coloring substances adhering to the inside and surface of pulp fibers. Conventionally, chemical pulp bleaching has been carried out by a method of oxygen bleaching followed by stepwise treatment with chlorine, hypochlorite, hydrogen peroxide, chlorine dioxide, or the like. In recent years, a sequence that incorporates ozone after oxygen bleaching has been put into practical use for the purpose of reducing the load on drainage and reducing chlorine-based chemicals.
On the other hand, it has been proposed to provide an acid treatment or an enzyme treatment as a pretreatment of the above-mentioned bleaching stage in order to remove lignin as much as possible.

However, in order to improve the delignification rate by acid treatment, it is necessary to lower the treatment pH or raise the reaction temperature to lengthen the reaction time. Under these conditions, there is a problem that the strength of the pulp is reduced, and an excessively large reactor is required, and the cost is increased.

[0004] In order to improve the delignification rate by enzymatic treatment, it is necessary to increase the enzyme addition rate or prolong the reaction time. Increasing the enzyme addition rate causes a problem of lowering the strength and yield of the pulp and increasing the cost.

[0005]

The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems. As a result, if the temperature is increased after the acid enzyme treatment as the bleaching treatment,
Found that high quality and low cost pulp can be obtained,
Based on this finding, the present invention has been completed. An object of the present invention is to solve the above-mentioned problems in bleaching and to provide a processing method for improving bleaching efficiency.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a chemical pulp bleaching process, wherein the chemical pulp is subjected to an acidic enzymatic treatment after oxygen bleaching, followed by treatment at an increased temperature. For bleaching pretreatment.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Sulfuric acid is mainly used as an acid in the acid treatment of the present invention, but acidic white water such as ozone-stage white water or chlorine-stage white water may be used. May be. Furthermore, an acid may be additionally added in the second stage of the acid treatment.

[0008] The enzyme used in the first acid treatment stage in the present invention is an enzyme called hemicellulase or cellulase, which hydrolyzes particularly hemicellulose.
When hardwood pulp is targeted, it is an enzyme mainly composed of xylanase, and desirably as acid-resistant as possible.

The present invention is generally applied between the oxygen bleaching stage and the chlorine stage, but can be applied to a stage preceding the chlorine stage even in a bleaching sequence without oxygen bleaching. Further, it can be performed in three or more stages.

The treatment conditions in the acid treatment stage affect the pulp quality in the subsequent bleaching stage, and are selected so that the reaction can be carried out efficiently without reducing the quality.

In the acid and enzyme treatment stage, the pulp concentration is 2 to 15% by weight, preferably 5 to 10% by weight, the treatment temperature is 40 to 80 ° C, preferably 50 to 60 ° C, and the treatment time is 20 to 20%. 60 minutes, preferably 30 to 50 minutes.
The amount of the enzyme is 0.1 to 1000 U / g (vs. absolutely dry pulp), preferably 10 to 100 U / g in the case of xylanase. Here, xylanase activity was 1 ml of 1% xylan (about pH 5).
And 1 ml of enzyme at 50 ° C for 30 minutes
The activity of producing reducing sugars corresponding to μmol xylose is expressed as 1 U / g.

In the next high temperature treatment stage, the pulp concentration is 2 to 15% by weight, preferably 5 to 10% by weight, the treatment temperature is 70 to 90 ° C, preferably 60 to 80 ° C, and the treatment time is 5 to 5%.
20 minutes, preferably 10 to 15 minutes, treatment pH 2.0 to
4.0, preferably 2.5 to 3.0.

[0013]

EXAMPLES The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Example 1 Pulp (Kappa number: 10.2, viscosity: 25.2 mPas) obtained by kraft digestion of domestic hardwood and oxygen bleaching was treated with an acid and an enzyme. The treatment conditions were as follows: pulp was put in a polyethylene bag, and pure water was added to adjust the pulp concentration to 5% by weight. Subsequently, sulfuric acid was added until the pH reached 3.0, and xylanase (CARTA manufactured by Sandoz Co.) was further used as an enzyme.
ZYME HS) was added at the same time as 50 U / g (vs. absolutely dry pulp), and the mixture was placed in a 55 ° C. constant temperature water bath and reacted for 30 minutes.
Subsequently, the mixture was placed in a constant temperature water bath at 70 ° C. and reacted for 10 minutes.
Table 1 shows the kappa number which is an index of the lignin content of the obtained pulp and the viscosity which is an index of the pulp strength. The copper value is TAPPI T-236, and the viscosity is TAPPI.
According to T-230.

Comparative Example 1 Pulp after oxygen bleaching of domestic hardwood used in Example 1 was treated with an acid. The treatment conditions were as follows: pulp was put in a polyethylene bag, and pure water was added to adjust the pulp concentration to 5% by weight. Subsequently, sulfuric acid was added until the pH reached 3.0, and the mixture was placed in a constant temperature water bath at 95 ° C. and reacted for 60 minutes. Table 1 shows the kappa number and viscosity of the obtained pulp.

[0016]

[Table 1]

From the comparison between Example 1 and Comparative Example 1 in Table 1, when the treatment with the combination of the acid and the enzyme of the present invention is carried out at two temperatures, the treatment pH is lower than that of the acid treatment alone at the same treatment pH. It can be seen that the kappa number can be reduced by a short reaction and the viscosity can be kept high.

[0018]

According to the processing method for bleaching of the present invention, pulp having high whiteness and high viscosity can be obtained as compared with the conventional acid processing method, and bleaching can be performed at low cost. There are advantages.

Claims (3)

[Claims] 1. A method for bleaching chemical pulp, which is a bleaching step of chemical pulp, wherein the temperature is increased after oxygen bleaching followed by acid enzymatic treatment. 2. The acidic enzyme treatment condition is pH 2.0 to 2.0.
The method for bleaching chemical pulp according to claim 1, wherein the temperature is 4.0, the temperature is 40 to 80 ° C, and the time is 20 to 60 minutes. 3. The treatment condition after the acidic enzyme treatment is at a temperature of 7 ° C.
The method for bleaching chemical pulp according to claim 1, wherein the temperature is 0 to 90 ° C and the time is 5 to 20 minutes.