JPH0625986A - Method for bleaching pulp with ozone - Google Patents

Abstract

PURPOSE:To enhance the bleaching action of a microbial cell on pulp by treating residual lignin of an unbleached kraft pulp with ozone and then decomposing the lignin with white-rot fungi. CONSTITUTION:The method for bleaching pulp with ozone is to treat residual lignin of unbleached kraft pulp with ozone, then oxidize the aromatic nucleus thereof and subsequently react white-rot fungi such as Phanerochaete.chrysosporium therewith, decompose the lignin and provide the bleached pulp. Thereby, the treating time can be shortened.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ozone bleaching method for pulp, and more particularly to a bleaching method in which lignin is modified by ozone in a bleaching step and then delignified bleaching is carried out by utilizing microorganisms or enzymes. It is about.

[0002]

BACKGROUND OF THE INVENTION Chemical pulp, or kraft pulp cooked by the kraft process, is commonly referred to as UKP or Unbi.
It is called as an Eached Kraht Puip (unbleached pulp), but about 3 to 5% of lignin remains in UKP, and it is gray. To make paper other than corrugated board, a bleaching process is required to further remove the residual lignin and increase the whiteness, but chlorine or chlorine compounds have been usually used for bleaching for many years.

However, in the pulp bleaching method using chlorine and the like, it has been revealed in recent years that a highly toxic dioxin is generated by the reaction of chlorine and lignin, and in order to avoid pollution of the environment by waste water and further to remove residual chlorine in paper. Chlorine-free bleaching has become a global trend to eliminate it. Oxygen, hydrogen peroxide, ozone, etc. are known as bleaching methods to replace chlorine,
Each of these pulp bleaching methods has been tried, and use of microorganisms and enzymes has been proposed.

[0004]

However, the bleaching agent most often used as an alternative to chlorine at present is oxygen, but the removal rate of residual lignin (commonly known as kraft lignin) in kraft pulp can be obtained only by oxygen. It has a problem of only 50%.

Ozone is the strongest oxidant next to fluorine, and is said to be the cleanest bleaching agent in the environment. However, ozone is expensive and the oxidizing power also acts on cellulose to increase the yield. There is a problem that it is decreasing and paper power is decreasing, and it has not been spread in Japan.

Furthermore, recently, bleaching by microorganisms and enzymes
Although delignification has been proposed, it is said that use of these microorganisms and enzymes has a problem that the required treatment time is a long time of several days, and cannot be industrially realized.

Therefore, the present invention has been made in view of the above-mentioned drawbacks, and is a combination of ozone bleaching and bleaching by microorganisms and enzymes, which is economical and the processing time is short in a practically suitable range. It is intended to provide an ozone bleaching method for pulp.

[0008]

In order to solve the above-mentioned problems, in order to solve the above-mentioned problems, the structure of the present invention, which has the above-mentioned object as a gist, solves the above-mentioned problems by using ozone to remove the residual lignin from the unbleached kraft pulp. Then, a technical means characterized by decomposing and removing lignin by a white rot fungus such as Faneroquiete chrysos was taken, and further, a xylanase-based degrading enzyme was used instead of the white rot fungus. Is used to decompose and remove hemicellulose, resulting in lignin separation, which is a technical means.

[0009]

Therefore, the method of the present invention exhibits a pretreatment action with ozone and a bleaching action with a white-rot fungus or a xylanase-type degrading enzyme.

First, regarding the pretreatment effect of ozone,
Unlike the conventional ozone bleaching method, which was intended to utilize the bleaching power of ozone, in the present invention, instead of utilizing the bleaching power of ozone, the contact between the pulp and ozone is kept in a short time and ozone is It only functions to oxidize lignin aromatic nuclei. That is, in the present invention, since the pulp and ozone are in contact with each other, it cannot be said that there is no bleaching action.
Even if it has a bleaching effect, it is so small that it is ignored.

The bleaching action is carried out after the above-mentioned pretreatment action. When the white rot fungus is mixed into the lignin-containing pulp obtained by oxidizing the lignin aromatic nucleus, the lignin structure has already begun to be cleaved. It exhibits the action of proceeding the reaction in a short time including the degrading enzyme reaction secreted from the bacterial cells over the entire lignin. In addition, lignin is said to be a natural inhibitor that blocks the invasion and growth of bacteria, but by oxidizing lignin, it exerts an action that inactivates the inhibitor and permits the growth of bacterial cells. I'm sure.

On the other hand, the xylanase enzyme is originally a hemicellulose-degrading enzyme, but since lignin covers hemicellulose in a net-like manner to prevent the invasion of enemies such as enzymes, in this case as well, the lignin structure is treated by ozone pretreatment. When oxidized and left in a cleaved state, the enzyme can easily enter through the gap, and the enzyme reaction, that is, bleaching, can be performed with high efficiency.

[0013]

EXAMPLES Next, examples of the present invention will be described. First, for bleaching, the present inventors have begun to elucidate the craft lignin to be removed, and usually use a large amount of expensive ozone to bring the craft lignin into a water-soluble compound. He discovered that the partial oxidation of lignin by the ozone reaction over time greatly accelerates the reaction rate by microorganisms and enzymes.

Originally, lignin is a natural barrier that protects cellulose and hemicellulose from external enemies, and it is said that the presence of lignin protects trees and tall plants from animals and microorganisms. Therefore, lignin is a naturally-occurring polymer compound, and its structure is complex and diverse, unlike artificial polymer compounds, and skillfully handles cellulose and hemicellulose to protect them from external enemies. Many scholars have studied lignin since ancient times, but the structure of lignin was only recently revealed, mainly by the knowledge of Japanese and American agrochemists. According to it, although it is slightly different in conifers and broad-leaved trees, they are roughly divided into syringer and guaiaxyl, but they are said to form a complicated mesh. “Chemical formula 1” is the model structural formula.

[0015]

[Chemical 1]

These lignins are water-insoluble, and in order to make them water-soluble compounds, that is, to make them water-soluble compounds that are easily separated from cellulose, the amount of ozone added is set to about 200 mols of lignin. Is usually 0.5 to 1.
It was said that 5 mol of ozone was required, and when a large amount of ozone was added, the cellulose was also slightly damaged, resulting in a decrease in pulp viscosity and paper strength.

Therefore, in the method of the present invention, first, the residual lignin of the unbleached kraft pulp is oxidized with ozone to oxidize its aromatic nuclei.

Oxidation of the aromatic nuclei attacks and cleaves each aroma by ozone, and what it means for delignification and bleaching is from "Chemical formula 1" to "Chemical formula 2" below. The reaction is one example that is easy to understand, but since a carbonyl group is introduced into the aromatic nucleus carbon by attacking ozone on the aromatic nucleus, a chemically stable bond called an arylalkyl ether bond is converted into an ester bond. The ester bond is a bond that is easily cleavable, and many of the esters thus generated appear to be cleaved at the same time.
Since the carboxyl group is introduced into the molecule, it is considered that the lignin oxide in this state has begun to sufficiently improve the solubility in water, and the affinity with microorganisms / enzymes is remarkably improved.

[0019]

[Chemical 2]

Then, when ozone is brought into contact with each other more and more, oxidation and lowering of molecular weight will be in the state of "Chemical formula 3", but if the ozone reaction is continued for a long time, some cellulose / hemylose will be damaged by ozone. As described above, it causes an important decrease in commercial value such as a decrease in yield and a decrease in paper strength. Therefore, the present invention is characterized by limiting the oxidation of lignin up to the state of "Chemical formula 2". In addition, R shown in "Chemical formula 1", "Chemical formula 2", and "Chemical formula 3" indicates a side chain portion after the chain.

[0021]

[Chemical 3]

To oxidize the lignin described above, ozone concentration and contact time may be adjusted. In other words, the amount of ozone input may be adjusted. After injecting ozone or ozone water from the above and stirring with a static mixer, the mixture was allowed to stay in the reaction tank for a certain period of time.

Next, the method of the present invention decomposes and removes lignin by a white-rot fungus such as Faneroquiete chrysos.

[0024] In Japan and other countries as well, research on white-rot fungi such as Faneroquite chrysos, which decomposes only lignin without destroying cellulose, has been advanced, but the biggest drawback is that the treatment time is a general delignification process. It takes an extraordinarily long period of 3 to 10 days as compared with the above, and although it is excellent as a clean delignification method, it has not been put to practical use in terms of economical efficiency. Therefore, when LUKP (beechwood unbleached kraft pulp) that had been subjected to ozone attack in the previous step was treated with a conventionally known funerochete chrysos strain, it was confirmed by an experiment that the treatment time could be shortened to less than 1/10. .

More specifically, the LUKP has a faneroquite
A comparison of the time required to reduce the kappa value from 20 to 10 using Chrysos was found to be 125 hours for ozone-untreated pulp, but only 7.5 hours for pulp that had been subjected to 0.15 mol ozone attack. The same kappa value was obtained. In addition, in the pulp subjected to 1.0 mol ozone attack, the kappa value became 10 in 4.5 hours, but a defect of large viscosity low was recognized.

Therefore, 7.5 in the middle of the pulp conveying path.
A staying reaction tank that can secure a staying time of not less than an hour is provided, and the inside of this staying reaction tank is temperature-controlled (30 to 40 ° C.) and is pre-filled with pulp to which white-rot fungi such as Faneroquiete chrysos are added. As a result, the pulp conveyed thereafter will be bleached continuously, but of course it is necessary to attach a device for supplementing white decay fungi to this staying reaction tank, but from the outlet to the inlet The amount of supplemented strains can be reduced by providing a reflux passage for refluxing a proportion of treated pulp.

Further, as for another method of delignification by a xylanase enzyme known as another bio-delignification method, the amount of enzyme used in the pulp subjected to the ozone attack is greatly reduced as compared with the pulp not subjected to the pretreatment with Ozoon. It was found that it is acceptable, and when comparing the required amount of enzyme using a commercially available xylanase enzyme for 60 minutes, 800 EXU / kg of enzyme is required to reduce the kappa value from 20 to 10 when ozone is not treated. However, when pre-treated with 0.15 mol of ozone, 350EX
Similar Kappa values could be obtained at U / kg.

[0028]

As described above, the method of the present invention uses expensive ozone, but the ozone bleaching method of pulp which can be economically put to practical use because the use thereof is limited to a small amount for pretreatment. Can be provided.

Further, in the present invention, since the pretreatment with ozone can improve the efficiency of the subsequent microorganisms or enzymatic delignification, the treatment time can be shortened to a practical level when using white rot fungi. Further, in the case of using an enzyme, it is possible to provide an ozone bleaching method for pulp, which can greatly reduce the amount of expensive enzyme used.

Claims (2)

[Claims] 1. A pulp bleaching method characterized in that the residual lignin of unbleached kraft pulp is oxidized with ozone to oxidize its aromatic nuclei, and then the lignin is decomposed and removed by a white-rot fungus such as Faneroquiete chrysos. 2. The residual lignin of unbleached kraft pulp is oxidized by ozone to oxidize aromatic nuclei of the lignin, and then hemicellulose is decomposed and removed by a xylanase-based degrading enzyme, resulting in lignin separation. Pulp bleaching method.