JPH03130485A - Pulp bleaching method - Google Patents

Abstract

PURPOSE: To bleach pulp by oxidation bleaching with an oxidating/bleaching chemical containing chlorine and treating the pulp with a lignin-modifying oxidation-reduction enzyme at the same time of or before the oxidation bleaching time while reducing the toxic content and the chemical oxygen demand of the spent bleaching liquid. CONSTITUTION: When pulp is bleached in the oxidation phase with the oxidating/ bleaching chemical containing chlorine such as chlorine dioxide and a mixture of chlorine dioxide and chlorine gas, the pulp in the oxidation phase is treated with alkali, at the same time of or before the oxidation time, and treated with the lignin-modifying oxidation-reduction enzyme of lignin-modifying phenol oxidase, for example lactase made from a white-rot germ at pH 3.0-10.0, preferably at pH 4.0-8.0 at 10-90 deg.C, preferably at 40-80 deg.C and at <400 mV redox electrical potential, preferably at <250 mV.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for bleaching valves using chlorine-containing oxidizing bleach chemicals.

In particular, the bulbs obtained from the sulfate bulbing process are brown in color, mainly due to the lignin remaining in the pulp. Lignin is removed from the bulb by bleaching, which is generally a multi-step process. In this process, the pulp is alternately treated with oxidizing, lignin-degrading chemicals and chemicals that dissolve this degradation product. What are the commonly used oxidizing agents? ! Chemicals containing elemental gold and oxygen, whereas alkaline solutions are used to remove the deterioration products.

In the reactions that occur during bleaching using chlorine-containing chemicals, lignin is converted to organochlorine compounds that remain in the used bleach solution. Used bleach solutions are a problem in terms of environmental protection because of the possible toxicity of the organochlorine compounds contained in the solution. Furthermore, the chemical oxygen demand in used bleach solutions reaches harmful levels.

This used bleach solution, which causes the worst environmental pollution load, is produced in the bleaching process during the initial chlorination and subsequent washing steps after the initial alkaline treatment. Various methods have been used to reduce the pollution load, including the use of chlorine dioxide instead of chlorine gas, the use of M bundles as the oxidizing chemical in the first bleaching step, and biological purification of used bleach solutions. has been done. However, these methods have not yielded completely satisfactory results. The concentration of phenol and other toxic chlorine compounds in used bleach solution was significantly reduced by oxygen bleaching using chlorine dioxide, but the chemical oxygen demand of the effluent was significantly reduced. It was not possible to obtain a sufficient reduction in afa. Therefore, this method was said to require the use of dynamic biological purification.

It is an object of the present invention to provide a pulp bleaching process that is capable of reducing the toxic content and chemical oxygen demand of used bleaching liquors so as to reduce the need for liquor purification. The invention is characterized in that, together with or before the oxidation, the pulp is subjected to an enzymatic treatment using oxidoreductases that modify the lignin.

Early studies showed that by using enzymes that degrade hemicells, it was possible to separate lignin and/or hemicells from cellulose, thus making the pulp easier to prepare in the subsequent bleaching step. It has been observed that bleaching is possible. This effect has not been previously observed with the use of lignin-degrading enzymes.

It has been observed in accordance with the present invention that treatment with currently preferred redox enzymes reduces the chlorine chemical base required for bleaching, thereby also reducing the amount of organochlorine compounds left in the used bleach solution. .

According to the present invention, the redox potential of this VI elementary reaction is 40
It should be below 0mV, preferably below 2501VF.

Suitable redox enzymes are, for example, phenol oxidase enzymes, such as lactase produced by the fungus White-Ot.

Other than enzymatic treatment, pulp bleaching according to the present invention is different from conventional pulp bleaching by using alternating oxidation and alkaline stages and washing after each of these stages to remove bleaching chemicals and degradation products. It is done by method.

The enzymatic treatment taught in this invention is preferably carried out at 10-90°C.
The optimum range is 40-80°C, and the p11 value is in the range angle of 3.0-10.0, preferably 4.0-8.0. The enzyme used is a lignin-modifying oxidation-reductase, such as lactase as described above.

The present invention also relates to the use of lignin-modifying enzymes, such as lactase produced by White-Ot bacteria, in the bleaching of pulp using chlorine-containing 16-oxidation bleaching chemicals.

In the following, the invention will be described in more detail with the help of specific examples based on laboratory tests.

Example 1 A diluted enzyme mixture of lactase made by Tralet (33 hinstlta White-rod fungus) was added to pine sulfate pulp ( with a dry matter content of 30%)
220 g of dry material obtained from. The temperature in the enzyme treatment was 55° C., and the treatment continued for 2 hours. After the enzyme treatment, the pulp was filtered through a Puchner funnel and the resulting pulp cake was washed with ion-exchanged water to obtain a wash ratio of 20.

As a control, a corresponding part of the pulp was treated in the other way without adding enzyme.

The enzyme-treated pulp hanging and control sections were then bleached by five successive steps of oxidation and leaching. 1st
In the stage, the chemicals used were chlorine (90%) and chlorine dioxide (10% > -C), in the second stage sodium cum hydroxide, in the third stage metal dioxide, in the fourth stage sodium hydroxide and Step 5 was chlorine dioxide.

The analytical results representing the consumption of super-whitening chemicals and the amount of pulp bleached are shown in Table 1.

Experiments have shown that significant reductions in chlorine emissions can be obtained with a lignin-phagous enzyme, ie, lactase.

Table 1 Enzyme-treated pine sulfate pulp Kappa 21.4 Control part Enzyme-treated pulp Final pH Viscosity Kappa Yield % 8.70 1020 26.4 10G,
848.60 1045 26.5 10
0.63 Continue the experiment with bleaching sequence D/C-E-D-E-D.

Phase D/C10/90 enzyme treatment valve D/C2” Kappa D/C end Consumption % pl+ Temperature ℃ Continuation minutes Phase E E 0.9” Kappa E Dose % 1)H Kappa yield % Mutual relationship Usage% Consumption % pH Consistency% 5.28 5.28 1.65 3.5 5 5 2.38 11.65 9.6 96.13 5.30 5.30 1.55 3.5 5 5 2.39 11.3 8.2 96, 81 Table 1 (continued) Phase D/C10/90 enzyme treatment valve Temperature ℃ Continuation minutes phase [2 ;11f fraud% pH Consistency% Temperature ℃ Continuation power Phase D2 River Bi% Consumption % pH Consistency% Temperature ℃ Continuation minutes Acidification aU yield % Total loss rate % bleaching Sticky punch TCj!　Rg/に9 1) KM pouring % 83.8 1.5 1.42 2.2 0 5 40 98.18 95.65 87.1

Claims (6)

[Claims] (1) A method for bleaching pulp using oxidizing bleaching chemicals containing chlorine, characterized in that, together with or before oxidation, the pulp is treated with an enzyme, in which a lignin-modifying oxidoreductase is used. Pulp bleaching method. (2) The method according to claim 1, wherein the redox potential of the enzymatic reaction is 400 mV or less, preferably 250 mV or less. (3) The method according to claim 1 or 2, wherein the enzyme used is a lignin-modified phenol oxidase, such as lactase produced by White-rod bacteria. 4. A process according to claim 1, wherein the pulp is treated with a phenol oxidase, such as lactase, and washed before the first oxidation phase. (5) The bleaching chemical used in the oxidation phase is chlorine dioxide or a mixture of chlorine dioxide and chlorine gas, and the pulp is treated with an alkali during the oxidation phase. the method of. (6) Enzyme treatment in the range 3.0-10.0, preferably 4
．． 6. Process according to any one of claims 1 to 5, carried out in the temperature range 10-90<0>C, preferably 40-80<0>C, with a pH value within 0-8.0.