JPH08260369A - Method of highly whitening waste paper pulp - Google Patents

Abstract

PURPOSE: To obtain waste paper pulp of high whiteness substantially equal to that of virgin pulp by bleaching the used paper with peroxide after decarbonization, additionally treating with a mixture of hydrogen peroxide/ thiourea, then treating with polysulfide and then with alkali. CONSTITUTION: When pulp is produced from waste paper, the waste paper is decarbonized, bleached with hydrogen peroxide, as a surfactant and a chelating agent such as EDTA are added. Then, the pH is adjusted to <=7, thiourea is added in an amount of at a weight ratio of 1/1-2/1 based on the remaining hydrogen peroxide to effect bleaching, followed by washing and draining. Subsequently, make-up hydrogen peroxide and thiourea are added to the pulp to effect bleaching, polysulfide is added for bleaching, further alkali such as sodium hydroxide is added to continue bleaching. The amounts of the surfactant and the polysulfide range in 0.005-5wt.% based on the absolutely dried weight of the pulp. This process permits the circulation of water through washing, dehydration and drainage in the case that silicate salt is not added.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for enhancing the whiteness of waste paper pulp. More specifically, when recycled waste paper such as newspapers, offsets, and copies is made into recycled pulp, it is deinked and bleached with hydrogen peroxide, and then bleached with hydrogen peroxide and thiourea. The present invention relates to a method for producing waste paper pulp which has whiteness and is capable of collecting and recycling waste water.

[0002]

2. Description of the Related Art Conventionally, waste paper pulp has been used as a raw material for papermaking together with wood pulp. Waste paper pulp was mainly used in newspapers, magazines, toilet paper and other fields where whiteness is not so required. Recently, the waste treatment of waste paper discharged from OA equipment has become a problem, and its recycling is desired. However, the whiteness is low and the color is yellow,
Further, there is a problem of residual ink (black whiskers) and the like, and its use on printing paper, copy paper and the like is restricted.

Therefore, as a method for producing high-whiteness waste paper pulp, JP-A-4-50391 proposes a method of bleaching using formamidinesulfinic acid (hereinafter abbreviated as FAS). However, although high whiteness waste paper pulp can be obtained, there is a problem that the cost of the bleaching chemical increases.
Further, silicate is generally used as a pH buffering agent for suppressing decomposition in bleaching with hydrogen peroxide. However, when the wastewater containing silicate is collected in the system, squeal is generated, which causes a problem. Therefore, it is circulated only at a low recovery rate and most of the waste is discharged to the outside of the system.

[0004]

DISCLOSURE OF THE INVENTION The present inventors have solved the above-mentioned problems and, when converting printed waste paper such as newspapers, offsets and copies into recycled pulp (hereinafter abbreviated as DIP), carry out deinking treatment. After hydrogen peroxide bleaching, further bleaching with hydrogen peroxide and thiourea makes it possible to produce waste paper pulp with high whiteness at low cost, and to provide a method for recovering and reusing wastewater. To do.

[0005]

As a result of intensive studies to solve the above problems, the inventors of the present invention have invented the method for increasing the whiteness of waste paper pulp of the present invention.

That is, in the process of producing waste paper pulp, after disintegrating and deinking the waste paper and then bleaching the waste paper pulp, after bleaching with hydrogen peroxide, bleaching is further performed with hydrogen peroxide and thiourea. It is about the method. In this method, a reducing agent (thiourea dioxide) is synthesized in a pulp slurry to produce waste paper pulp with high whiteness at low cost. Deterioration of hydrogen peroxide is suppressed even without using silicate by pretreatment with surfactant and chelating agent, or addition of surfactant and chelating agent during hydrogen peroxide bleaching, and wastewater washed and dehydrated Sukeru does not occur even when reused, and it can be recycled and reused at a higher rate than before. Furthermore, after thiourea dioxide is synthesized and bleached, polysulfide (hereinafter abbreviated as PS) is added and bleached to obtain a product similar to virgin pulp.

The high whiteness of the waste paper pulp of the present invention will be described in detail. The present invention, when producing waste paper pulp, bleachs hydrogen peroxide after deinking to bring the system to pH 7 or below and react thiourea at a ratio of 1/1 to 2/1 with respect to the residual amount of hydrogen peroxide. After that, alkali is added for further bleaching. Alternatively, deinking, bleaching with hydrogen peroxide, washing and dehydration,
Hydrogen peroxide and thiourea are newly added at a ratio of 1/1 to 2/1 to cause a reaction, and then alkali is added to bleach.

Alternatively, after deinking, a surfactant and a chelating agent are added, and after bleaching with hydrogen peroxide, washing and dehydration are performed, and hydrogen peroxide and thiourea are newly added at a ratio of 1/1 to 2/1 to cause a reaction. After that, add alkali and bleach. Also, at the time of deinking, after adding a surfactant and a chelating agent to bleach hydrogen peroxide, the remaining hydrogen peroxide and thiourea are further added from 1/1 to 2
After reacting at a ratio of / 1, alkali is added to bleach.

[0009]

Embedded image

[0010]

Embedded image

The reaction between hydrogen peroxide and thiourea is
It progresses with heat or a catalyst (such as molybdenum) under the condition of 7 or less. Thiourea dioxide is not synthesized on the alkaline side. Furthermore, the reduction reaction of thiourea dioxide proceeds by applying heat at pH 7 or higher. In addition, hydrogen peroxide /
When the ratio of thiourea is larger than 1/1, thiourea does not completely react and thiourea remains, and when it is less than 2/1, hydrogen peroxide remains excessively and the whiteness increase is not as effective as expected and economic Not at all.

As the surfactant used in the present invention,
Inorganic, organic, polymer, anionic, cationic,
Any amphoteric or nonionic surfactant may be used. For example, as anionic, polyacrylate,
Polycarboxylate, alkyl sulfonate, etc .; cationic as polyacrylamide, alkylammonium bromide, alkylammonium chloride, etc .; amphoteric N-alkylbetaine, N-aluminsulfontine, etc .; nonionic as polyoxyethylene Alkyl ether, polyoxyethylene sorbitan alkyl ester and the like; Among these, anionic polyacrylic acid salts are particularly preferable. Furthermore, one or more of these surfactants can be used in combination. Deinking agents and aggregating agents are also a type of surfactant.

The chelating agent used in the present invention includes
Any of inorganic, organic, and polymeric chelating agents may be used. Of these, EDTA and D are particularly preferable.
Examples thereof include Mg, Na and Ca salts such as TPA and TTHA. Furthermore, one or more of these chelating agents can be used in combination.

The alkali used in the present invention includes commonly used sodium hydroxide, potassium hydroxide, calcium hydroxide and the like.

The disintegration deinking and bleaching conditions for producing waste paper pulp are such that the pulp concentration is 10 to 50% by weight, the reaction temperature is 20 to 100 ° C., and the reaction time is 20 to 120 minutes.

In the production of waste paper pulp, it is known that kneading (stirring and mixing) pulp and chemicals before bleaching and flotation (flotation) after bleaching are known and there is no problem.

The addition ratio of the surfactant and the chelating agent is 0.005 to 5% by weight, and preferably 0.01% to 1.0%, based on the dry pulp. If it is less than 0.005%, almost no effect is exhibited, and if it is added in excess of 5%, no effect appears and it is not economical.

At our company, kraft pulp is cooked using SAQ (tetrahydroanthraquinone 2Na) and PS (Na ₂ S _X ). Therefore, during or after bleaching with hydrogen peroxide and thiourea dioxide, PS is added for further bleaching. That is, the PS obtained by white liquor oxidation is used.

[0019]

Embedded image Main reaction: 4Na ₂ S + 2O ₂ + 2H ₂ O → 2NaS ₂ +
4NaOH side reaction: 2Na ₂ S + H ₂ O → Na ₂ S ₂ O ₃ + 2Na
OH

The PS addition rate is 0.005 to 5% by weight.
(To absolute dry pulp), preferably 0.01% to 1.0%
Is. Less than 0.005% shows almost no effect,
Addition of more than 5% is not economical because the effect does not appear.

By pretreatment with a surfactant and a chelating agent, or by adding a surfactant and a chelating agent during bleaching with hydrogen peroxide, the decomposition of hydrogen peroxide can be suppressed without adding a silicate. This makes it possible to prevent the generation of scale due to silicate, so that the cleaning and dehydrating wastewater can be recycled and reused at a higher ratio than before.

[0022]

The present invention is based on the fact that hydrogen peroxide and thiourea are reacted to bleach in the process of producing waste paper pulp, that is, the oxidation reaction with hydrogen peroxide and the reduction reaction with thiourea dioxide are carried out intermittently. The present invention relates to a method for obtaining a high-whiteness pulp at low cost. Moreover, by using a surfactant and a chelating agent, an excellent bleaching effect can be obtained without adding a silicate. Furthermore, bleaching with PS is no different from virgin pulp.

[0023]

The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.
In the examples, all parts and% are parts by weight and% by weight.
It is due to. The whiteness is JIS-P812.
3 was measured by the Hunter whiteness method, and the color tone was measured by Sigma 80 manufactured by Nippon Denshoku.

DIP Preparation 1 Waste newspaper was deinked in the conventional manner. That is, water is added to waste newspaper and disintegrated with a high-concentration pulper at a concentration of 15%, and NaOH is 1.0% with respect to waste paper pulp (hereinafter, the addition rate is based on the weight of dry pulp), a deinking agent. (DI from Kao Corporation
-800) 0.08% was added, and the mixture was stirred at a temperature of 60 ° C for 30 minutes and then washed and dehydrated to obtain a DIP having a concentration of about 30%.
To this, NaOH 2.0%, NaSiO ₃ 4.0%, H ₂
O ₂ 1.0%, a deinking agent (DI-800) 0.16%, and a coagulant (Kao's DI-260) 0.03% were added and kneaded, and bleaching was performed at a temperature of 80 ° C. for 2 hours. Further, it was subjected to flotation treatment to obtain a DIP having a whiteness of 62.3%.

Comparative Example 1 DIP obtained in DIP preparation 1 was adjusted to a concentration of 15% and NaO was added.
H1.0%, NaSiO ₃ 4.0%, and H ₂ O ₂ 4.0% were added for kneading, and bleaching was performed at a temperature of 80 ° C. for 2 hours. Further, it was subjected to flotation treatment to obtain DIP having a whiteness of 75.6%.

Comparative Example 2 The DIP obtained in Comparative Example 1 was further concentrated to 15% to obtain NaO.
H1.0%, NaSiO ₃ 4.0%, and H ₂ O ₂ 4.0% were added for kneading, and bleaching was performed at a temperature of 80 ° C. for 2 hours. Further, it was subjected to flotation treatment to obtain DIP having a whiteness of 77.1%.

Comparative Example 3 The DIP obtained in Comparative Example 2 was further concentrated to 15% to obtain NaO.
H1.0%, NaSiO ₃ 2.0%, and H ₂ O ₂ 2.0% were added for kneading, and bleaching was performed at a temperature of 80 ° C. for 2 hours. Further, it was subjected to flotation treatment to obtain a DIP having a whiteness of 79.5%.

Comparative Example 4 The DIP obtained in DIP preparation 1 was adjusted to a concentration of 15% and NaO was added.
H1.0%, NaSiO ₃ 5.0%, H ₂ O ₂ 14.0%
Was kneaded and bleached at a temperature of 80 ° C. for 2 hours. Further, it was subjected to flotation treatment to obtain DIP having a whiteness of 78.5%.

Comparative Example 5 The DIP obtained in DIP preparation 1 was made to have a concentration of 15% and FAS
Add 2.0% and NaOH 1.0% and knead,
Bleaching was performed at a temperature of 80 ° C. for 2 hours. Further, it was subjected to flotation treatment to obtain DIP having a whiteness of 73.5%.

Comparative Example 6 The DIP obtained in Comparative Example 1 was further adjusted to a concentration of 15% and FAS was added.
Add 1.0% and 0.5% NaOH and knead,
Bleaching was performed at a temperature of 80 ° C. for 2 hours. Further, it was subjected to flotation treatment to obtain a DIP having a whiteness of 80.8%.

DIP Preparation 2 Waste newspaper was deinked in the conventional manner. That is, water is added to newspaper waste and disintegrated with a high-concentration pulper at a concentration of 15%, and NaOH 1.0% to a waste paper pulp, a deinking agent (D
I-800) 0.08% was added, and the mixture was stirred at a temperature of 60 ° C. for 30 minutes and washed and dehydrated to obtain DIP having a concentration of about 30%. In addition to this, a chelating agent (DTPA-M manufactured by Kirest)
g) 0.2%, NaOH 2.0%, H ₂ O ₂ 1.0%, deinking agent (DI-800) 0.16%, flocculant (DI-26)
0) 0.03% was added and kneading was performed, and bleaching was performed at a temperature of 80 ° C. for 2 hours. Further, it was subjected to flotation treatment to obtain DIP having a whiteness of 63.0%.

Example 1 DIP bleached by DIP preparation 2 was not washed (residual hydrogen peroxide 58%), sulfuric acid was further added to adjust pH to 7, and chelating agent 0.1% and thiourea 0.6% were added. Kneading,
Bleaching was performed at a temperature of 80 ° C. for 2 hours. Further, it was subjected to flotation treatment to obtain a DIP having a whiteness of 80.8%.

Example 2 DIP bleached by DIP preparation 2 was washed and dehydrated, and then chelating agent 0.2%, H ₂ O ₂ 1.0%, and thiourea 1.0%.
% And kneading was performed, and bleaching was performed at a temperature of 80 ° C. for 2 hours. Further, it was subjected to flotation treatment to obtain DIP having a whiteness of 81.8%.

Example 3 DIP bleached by DIP preparation 2 was washed and dehydrated, and then 0.1% of a chelating agent, 0.1% of a nonionic surfactant (NS204.5 manufactured by NOF CORPORATION), and H ₂ O ₂ were added. 2.0%, thiourea 1.0% were added and kneading, and the temperature was 80 ° C for 2
Bleached for hours. Flotation process further whiteness 8
A DIP of 2.3% was obtained.

Example 4 DIP bleached by DIP preparation 2 was washed and dehydrated, and then 0.1% of a chelating agent, 0.1% of an anionic surfactant (primer 850 manufactured by Primal) and H ₂ O ₂ 2.
Kneading was performed by adding 0% and 1.0% of thiourea, and bleaching was performed at a temperature of 80 ° C. for 2 hours. Further, it was subjected to flotation treatment to obtain DIP having a whiteness of 81.4%.

Example 5 DIP bleached in DIP preparation 2 was not washed (residual hydrogen peroxide 58%), and after adjusting the pH to 7 the chelating agent 0.1%,
A nonionic surfactant (0.1%), an anionic surfactant (0.1%) and thiourea (0.6%) were added for kneading, and bleaching was performed at a temperature of 80 ° C. for 2 hours. Further, a flotation process was performed to obtain a DIP having a whiteness of 82.6%.

Example 6 DIP bleached in DIP preparation 2 was not washed (residual hydrogen peroxide 58%), and after adjusting the pH to 7, the chelating agent 0.1 was added.
%, Nonionic surfactant 0.1%, anionic surfactant 0.1%, and thiourea 0.6% were added for kneading, and bleaching was performed at a temperature of 80 ° C. for 2 hours. Further, it was subjected to flotation treatment to obtain a DIP having a whiteness of 81.7%.

Example 7 DIP bleached by DIP preparation 2 was washed and dehydrated, and then chelating agent 0.2%, NaOH 1.0%, H ₂ O ₂ 3.0.
%, Thiourea 1.0% and kneading at a temperature of 8
Bleached at 0 ° C. for 2 hours. Further, it was subjected to flotation treatment to obtain DIP having a whiteness of 81.6%.

Example 8 The bleached DIP prepared in DIP Preparation 2 was washed and dehydrated, and then 0.2% of a chelating agent, 1.0% of NaOH and 2.0 of H ₂ O _{2 were} added.
%, Thiourea 1.0% and kneading at a temperature of 8
Bleached at 0 ° C. for 2 hours. Further, it was subjected to flotation treatment to obtain a DIP having a whiteness of 82.5%.

Example 9 DIP bleached by DIP preparation 2 was washed and dehydrated, and then 0.2% of a chelating agent, 1.0% of NaOH and 0.5% of H ₂ O _{2 were} added.
%, Thiourea 1.0% and kneading at a temperature of 8
Bleached at 0 ° C. for 2 hours. Further, it was subjected to flotation treatment to obtain DIP having a whiteness of 79.6%.

Example 10 DIP of Example 2 was washed and dehydrated, and the waste water was used as dilution water in the deinking step of DIP preparation 2, and after deinking, bleaching was performed to obtain DIP having a whiteness of 62.8%. Chelating agent 0.1
%, Nonionic surfactant 0.1%, NaOH 1.0
%, H ₂ O ₂ 2.0%, and thiourea 1.0% were added for kneading, and bleaching was performed at a temperature of 80 ° C. for 2 hours. Further, a flotation process was performed to obtain a DIP having a whiteness of 80.6%.

Example 11 The bleached DIP prepared in DIP preparation 2 was washed and dehydrated, and then chelating agent 0.2%, NaOH 1.0%, H ₂ O ₂ 2.0
%, Thiourea 1.0% and kneading at a temperature of 8
Bleached at 0 ° C. for 2 hours. PS (homemade by us) 0.1
% And kneading was performed, and bleaching was performed at a temperature of 80 ° C. for 2 hours. DI with a whiteness of 83.8% after flotation
P was obtained.

[0043]

[Table 1]

From Examples 1 to 11 and Comparative Examples 1 to 6 in Table 1, the pulp of the present invention has higher whiteness than the conventional hydrogen peroxide bleaching multistage treatment and the treatment method using FAS.
And the color is bluish. Moreover, the one to which PS is added is almost the same as the virgin pulp. Furthermore, the remaining hydrogen peroxide can be used efficiently, and the amount of bleach used can be greatly reduced. There is no problem even if the bleached waste water is used as dilution water in the deinking process.

[0045]

INDUSTRIAL APPLICABILITY The present invention solves the problems of increasing the cost of bleaching chemicals produced by the method of bleaching waste paper pulp with FAS to a high degree of whiteness and the problem of squeal formation by using silicate for hydrogen peroxide bleaching. Together they provide the means to solve. Compared with the conventional method, this method, which performs pulp bleaching and synthesis of reducing agent (thiourea dioxide) at a time,
It is possible to produce waste paper pulp with high whiteness at low cost. Moreover, pretreatment with a surfactant and a chelating agent is carried out before hydrogen peroxide treatment, or by adding a surfactant and a chelating agent during bleaching with hydrogen peroxide, the use of silicates is eliminated, and the squelch is eliminated. It is possible to prevent the generation of water and to collect and reuse the DIP wastewater at a higher ratio than before. Furthermore, bleaching with PS gives waste paper pulp that is as good as virgin pulp.

Claims (7)

[Claims] 1. When producing waste paper pulp, after deinking, bleaching with hydrogen peroxide to bring the system to pH 7 or lower, and thiourea at a ratio of 1/1 to 2/1 with respect to the residual amount of hydrogen peroxide. A method for increasing the whiteness of used paper pulp, which comprises adding, reacting with, and further bleaching with an alkali. 2. In the production of waste paper pulp, after deinking, hydrogen peroxide bleaching is followed by washing and dehydration, and hydrogen peroxide and thiourea are newly added at a ratio of 1/1 to 2/1 and reacted. After that, an alkali is added to perform bleaching, and the whiteness of the used paper pulp is increased. 3. In the production of waste paper pulp, after deinking, a surfactant and a chelating agent are added, and bleaching with hydrogen peroxide is followed by washing and dehydration to newly add hydrogen peroxide and thiourea from 1/1 to 2
A method for increasing the whiteness of used paper pulp, which comprises adding and reacting in a ratio of / 1 and then bleaching by adding an alkali. 4. In the production of waste paper pulp, after deinking, a surfactant and a chelating agent are added, and bleaching with hydrogen peroxide is performed, and then the pH is adjusted to 7 or less without washing, and residual hydrogen peroxide and thiourea are further added. Is reacted at a ratio of 1/1 to 2/1, and then bleaching is carried out by adding an alkali. 5. A method for increasing whiteness of waste paper pulp, which comprises adding polysulfide during bleaching with hydrogen peroxide and thiourea dioxide according to claim 1, 2, 3 or 4 and further bleaching. . 6. The method for increasing the whiteness of waste paper pulp according to claim 1, 2, 3 or 4, wherein hydrogen peroxide bleaching is performed without adding a silicate, and washing and dehydration drainage is circulated and used. . 7. The addition rate of the surfactant, the chelating agent and the polysulfide is 0.00 per dry pulp.
The method for increasing the whiteness of waste paper pulp according to claim 1, 2, 3 or 4, which is carried out under the condition of 5 to 5% by weight.