JPH04108192A - Method for bleaching pulp - Google Patents

Abstract

PURPOSE:To bleach pulp such as wood pulp at a relatively low bleaching temperature and in an extremely short bleaching time by employing a specific activating agent in a process for bleaching the pulp with a peroxide. CONSTITUTION:When pulp is bleached with a peroxide, an activating agent is employed as an additional component. A compound reacting with the peroxide to release active oxygen is employed as the activating agent. The activating agent is preferably tetraacetylethylenediamine. The bleaching is performed e.g. at 20-60 deg.C at a bleaching start pH of 9-10.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention 1] The present invention relates to a bleaching process that allows the bleaching of pulps, such as wood pulp and waste paper pulp, to be carried out at low bleaching temperatures and short bleaching times.

[Prior art] Ground pulp (GP), refiner ground pulp (RGP), thermomechanical pulp (TMP), chemical ground pulp (CGP), semi-chemical, which belongs to mechanical pulp (high-efficiency pulp), which is wood pulp obtained from wood. Conventionally, peroxides such as hydrogen peroxide, soda percarbonate, etc. have been used to bleach pulp (SCP), kraft pulp (KP), sulfide pulp (SP), and deinked waste paper pulp (DIP), which belong to chemical pulps. Widely used.

The peroxides used in this conventional bleaching process are generally used as a pretreatment for peroxide bleaching to remove trace metals present in nature or metals contained in waste paper. To prevent wasteful decomposition of substances, diethylenetriaminepentaacetic acid soda (DTPA), ethylenediaminetetraacetic acid tetrasodium or m:soda (EDTA), nitrilotriacetic acid (NTA), magnesium sulfate, No. 3 sodium silicate, etc. are added. ing.

It has been found that No. 3 sodium silicate also functions as a buffer to stabilize the pH of the bleaching solution and also exhibits the effect of suppressing the decomposition of peroxide.

Furthermore, it has been confirmed that No. 3 sodium silicate acts to prevent metal corrosion by forming a protective film on the surface of metal.

Also, since peroxide exhibits a bleaching effect in the alkaline region, caustic soda is commonly used as an inexpensive pH adjuster.

It is also known that these agents are generally used prior to the bleaching process or simultaneously with peroxide.

Examples of conventional peroxide bleaching methods using hydrogen peroxide are shown below: In tower bleaching, bleaching conditions include bleaching temperatures of 40-70'C and long bleaching times of 1-4 hours. The pH during bleaching is generally 10-11. High temperature bleaching involves relatively high bleaching temperatures of 75-85°C and bleaching times of 20-30 minutes;
A bleaching time of 3 to 4 hours is required to reach maximum white skin at a temperature of 40 to 60''C at each dosage of peroxide.

OBJECT OF THE INVENTION j It is an object of the present invention to provide a process for bleaching pulp that can be carried out at lower bleaching temperatures and shorter bleaching times compared to the bleaching processes of the prior art described above.

[Structure of the Invention] The present invention provides a method for bleaching pulp using peroxides, in which an activator is used as an additional component, and the activator reacts with the peroxide to release active oxygen. This is a pulp bleaching method characterized by: By this method the highest white skin for each dosage of peroxide is achieved in a very short time of 5 to 60 minutes at relatively low temperatures of 5 to 70 DEG C., preferably 20 to 60 DEG C.

The pulp to be bleached in the method of the present invention is any of the above-mentioned pulps to be bleached.

Peroxides which can be used in the present invention include hydrogen peroxide, inorganic peroxides such as sodium or potassium percarbonate-1-perboric acid, persulfate- or perphosphate.

The activators used in the present invention include di-N-acyl compounds, such as tetraacetylethylenediamine (TABD), tetraacetylmethylmethylenediamine, tetraacetylene glycoluril (uril), which include a variety of known activators, including: ) (TAGU) as well as activated esters such as pentaacetylglucose (PAG
), sodium acetoxybenzenesulfonate, sodium nonanoyloxybenzenesulfonate (NOBS)
, sodium benzyloxybenzenesulfonate (B
OBS) etc.

Among them, tetraacetylethylenediamine (TAED)
is particularly advantageous.

In addition to the peroxide and the activator, the process of the invention also includes additives used in conventional bleaching processes, namely naturally occurring trace metals or metals present in waste paper, which are exposed to the bleaching conditions. Additives to prevent wasteful decomposition of peroxide.
For example, diethylenetriaminepentaacetic acid soda (DTPA)
, ethylenediaminetetraacetic acid tetrasodium or m:soda (
EDTA), nitrilotriacetic acid (NTA), magnesium sulfate, metal chelating agents such as No. 3 sodium silicate, pHtl
J conditioner, metal corrosion inhibitor, etc. can be used.

Examples of the pH adjuster include inorganic alkaline compounds such as caustic soda, No. 3 sodium silicate, and sodium sulfite. In the method of the present invention, the pH value at the start of bleaching is 8 to 12.
is preferable, and exhibits the highest bleaching effect particularly in the pH range of 9 to IO.

The activator is added before the addition of the peroxide, during the step of adding the metal chelating agent and pH adjuster, etc., simultaneously with the addition of the peroxide, or after the addition of the peroxide.

The reaction formula in which the activator used in the present invention reacts with peroxide to release active oxygen is shown below using TAED as an activator and hydrogen peroxide as a peroxide: ( TAED) In the reaction formula, (0) represents active oxygen, which is a substance that exerts a bleaching effect.

Thus, theoretically, the amount required for the reaction of TAED with hydrogen peroxide is 1 mole of TAED per 2 moles of hydrogen peroxide.
It is an AED.

The theoretical value using hydrogen peroxide as an example is that the molecular weight of hydrogen peroxide is 34 and that of TAED is 228, so when bleaching pulp using hydrogen peroxide (Ig),
It takes 3.35g for TAED to react with the entire amount of hydrogen peroxide.
(TAED) required.

Currently, the amount of hydrogen peroxide used in pulp bleaching is 10 hydrogen peroxide per pulp.
It is in the range of 0.63 to 10.chi. in terms of 0%, but in the method of the present invention, this addition amount is expanded to 0.05% at the lower limit. Therefore, the range of use for TAED is from 3.35 times the maximum theoretical value of 0°05χ to 3.35 times the maximum theoretical value of 0°05χ for hydrogen peroxide.
It is specified in the range of 35 times.

However, in reality, it is more rational to use an excess of hydrogen peroxide (which is cheaper than TAED) in order to further increase the reaction rate between TAED and hydrogen peroxide and improve the bleaching effect.

Furthermore, by adding TAED, more hydrogen peroxide is effectively utilized in the bleaching process, so the amount of hydrogen peroxide used can also be reduced.

The above discussion using hydrogen peroxide and TAED also applies to other peroxides and activators.

The method of the invention will be described below for household paper pulp. Pulp for household paper is produced from waste paper such as high-quality paper, medium-quality paper, and imitation paper. There is an earth kettle method for producing this waste paper. In this method, raw material waste paper is heated at high temperature (130-140°C) and under high pressure with a cooking agent and a bleaching agent for 15-25°C.
Treat at χ pulp concentration for 4-5 hours. According to Shizuoka Prefecture Paper Industry Research Station Report No. 36, the combination of sodium percarbonate and No. 3 sodium silicate prevents the ineffective decomposition of sodium percarbonate and has a deinking effect. Advantages such as improved whiteness, reduced COD load, lower cooking temperature, and improved paper quality have been found. TAE
By using D in combination with sodium percarbonate and No. 3 sodium silicate, it is possible to lower the bleaching temperature in the earth pot from 130 to 140°C to about 5 to 70°C, and the bleaching time can be reduced from 5 to 30°C. It can be shortened to minutes. In the earth kettle method, the pulp is cooked by adding other alkaline compounds such as sodium sulfite, and then soda percarbonate is added to bleach the pulp. Compared to the conventional method, the bleaching time can be shortened and the pulp remains clean after cooking. You can save energy and time used for

In the method of the present invention, the activator does not accelerate the decomposition of peroxide, but rather decomposes the available oxygen in peroxide as described above.
It works to generate electricity in a shorter time.

The advantage of the present invention is that effective oxygen can be generated in a short time by the reaction between peroxide and an activator, and bleaching can be performed at low temperatures and in a very short time, reducing energy costs and bleaching. The device can be made more compact and the amount of bleaching per unit time can be increased.

The present invention will be explained in more detail by Examples and Comparative Examples.

2) Perform the bleaching test using the following steps: l) Defibrate the ground pulp (GP), dry it on a hot plate, collect 25g, put it in a polyethylene bag, and let it absorb moisture. Seal it tightly to prevent it from happening.

2) Tetraacetylethylenediamine (TAED)
Dissolve 1g in warm water at 55°C to prepare a 1χ solution,
Keep at 0-55°C.

3) Adjust sodium diethylenetriaminepentaacetate (DTP^) used as a chelating agent to a 4χ solution.

4) Adjust No. 3 sodium silicate to a 1χ solution.

5) Adjust caustic soda to 1χ liquid.

6) Adjust hydrogen peroxide to an active ingredient 3χ solution.

DTPA adjusted in 3) was added to a polyethylene bag containing 25 g of GP collected in 1) so that the ratio to the valve was 0.4χ, and TAED adjusted in 2) was added to the polyethylene bag containing 25 g of GP collected in step 1), and the TAED adjusted in 2) was added to the polyethylene bag containing 25 g of GP collected in step 1).
Then, add hot water so that the final bulb concentration is 20χ. In other words, after adding hydrogen peroxide,
Adjust with warm water so that the final pulp density is 20χ)
, GPSDTPA, and TAED by hand to mix well and leave for 30 minutes.

The sodium silicate prepared in 4) was added to the ratio of 3χ to the valve, and the caustic soda adjusted in 5) was added to the ratio of 1χ to the valve, mixed by hand to mix well with the GP, and the drug-added GP was added. Place the polyethylene bag in a hot bath and raise the temperature to 55"C and maintain this temperature for 15 minutes. Prepare three identical samples (experiment numbers A and C).
and E).

The hydrogen peroxide solution adjusted in step 6) was applied to the three bulbs heated in a hot bath, respectively, for each bulb, 3.35χ and 1.75χ.
, 0.88χ, G in polyethylene
Adjust the pulp density of P to 202 with warm water, put it into the hot bath again, and heat it at 55°C for 5 to 10.15 minutes.
．． 30.60.The whiteness after 120 minutes was measured by Hunter whiteness, and the results are shown in the table below and Figure 1 (whiteness is χ, whiteness of GP before bleaching; 41.6χ).
.

Three samples were prepared and subjected to a bleaching test in the same manner as in the example except that TAED was not used.

The results obtained are shown in the table below and FIG. 1 (experiment numbers B, D, and F).

Table [Effects of the Invention] The method of the present invention has the following points in that it is possible to bleach pulp at a relatively low bleaching temperature and in a very short bleaching time.
The contribution to industry is remarkable.

[Brief explanation of drawings]

FIG. 1 is a graphical representation of the whiteness of treated bulbs versus bleaching time in order to show the bleaching effect of an example of the method of the present invention and a comparative example according to the prior art.

Claims (1)

[Claims] 1) A pulp bleaching method using peroxide, in which an activator is used as an additional component, and the activator reacts with the peroxide to release active oxygen. A pulp bleaching method characterized by using a compound. 2) The method according to claim 1, wherein the activator is tetraacetylethylenediamine.