JPS5917240B2 - Peroxide labeling method for mechanical pulp - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing bleached mechanical pulp such as bleached RGP (refined ground pulp) and bleached TMP (thermomechanical pulp) from wood chips.

More specifically, by refining wood chips in the presence of an organic chelating agent and sulfite, heavy metals in the pulp and white water in the system are efficiently removed, followed by peroxide bleaching, resulting in highly white bleaching. The present invention relates to a method for producing mechanical pulp. Peroxide and hydrosulfide are generally used to bleach mechanical pulps such as RGP, TMP, and GP (groundwood pulp). The advantage of peroxide bleaching, especially hydrogen peroxide bleaching, is that there is no reduction in pulp yield. It is so-called lignin preservation bleaching, and it can bleach to a high degree of whiteness that is impossible with hydrosulfide. On the other hand,
Hydrogen peroxide is unstable in the presence of heavy metals and certain microorganisms, and has the disadvantage of being easily decomposed. Therefore, when bleaching pulp with hydrogen peroxide, stabilizers such as sodium silicate, condensed phosphates, and organic chelating agents are generally used in combination.
Furthermore, a method is known in which heavy metals are dissolved and removed by pretreating the pulp with a mineral acid or a chelating agent prior to bleaching the pulp with hydrogen peroxide. For pretreatment with a chelating agent, use condensed phosphates such as sodium tripolyphosphate, aminopolycarboxylic acids such as DTPA (ethylenediaminetetraacetic acid), EDTX (ethylenediaminetetraacetic acid), NTA (nitrilotriacetic acid), or their alkalis. Metal salts etc. are used. Addition of chelating agent in chelating agent pretreatment is RolfAn.
It is usually carried out between the pulp cleaner and the dewatering thickener before the pulp bleaching tower as proposed by Dersonetal (1979 International
Pulp Bleaching Conference 1 Lecture Proceedings P269). However, the pulp concentration after pulp cleaning is as low as 1% or less, and if the chelating agent is added at that point, the concentration of the chelating agent in water becomes extremely low, making it impossible to sequester metals efficiently. Therefore, after dehydrating the selected cleaner, we installed another Kner, and
A method of treating the pulp with a chelating agent after dehydration to a pulp concentration of about 5% has been used, but this method has the drawback of requiring new expensive thickener equipment. Although it has been acknowledged that chelating agent pretreatment is a theoretically useful method as described above, the reality is that it has hardly been put into practical use due to these drawbacks. In view of the actual state of chelating agent pretreatment in peroxide bleaching, the present inventors conducted intensive research on chelating agent pretreatment methods, and as a result, completed the present invention.

In other words, if wood chips are refined in the presence of sulfite and an organic chelating agent, the efficiency of sequestering heavy metals in the valve will increase, and the amount of free heavy metals in the white water in the system will also decrease. In comparison, we found that the whiteness of unbleached bulbs also increased. The present invention relates to a method for producing bleached mechanical valves from wood chips, which comprises performing defibration in the presence of an organic chelating agent and a sulfite, and then bleaching the unbleached valves with peroxide. This is a material bleaching method. As an organic chelating agent, DTPA. EDTA.
NTA. Aminopolycarboxylic acids or their alkali metal salts such as HEDTA (hydroxyethylenediaminetetraacetic acid), aminoalkyl phosphoric acids such as EDTMP (ethylenediaminetetrakismethylene phosphonic acid), DTPMP (diethylenetriaminepentakismethylenephosphonic acid), or their alkali metal salts; Alkali metal salts, amines such as ethylenediamine and triethanolamine, sugars such as sorbitol and CMC; polycarboxylic acids such as tartaric acid and sodium oxalate, or their alkali metal salts; etc.
and mixtures of these organic chelating agents can be used. The amount of organic chelating agent added depends on the heavy metal content in the valve and white water, but is usually 0.001 to 1.0% by weight, preferably 0.05 to 0.00% by weight, based on the bone dry chips.
It is 5% by weight. Sulfites are NaHSO3, Na2sO
3. Ca(HSO,)2, Mg(HSO3)2 or a mixture thereof can be used, and the amount added is usually 0.01 to 5% by weight, preferably 0.5 to 5% by weight, based on the bone dry chips.
It is 3.0% by weight. With this amount of sulfite,
The reducing action of the residual sulfite does not adversely affect the subsequent hydrogen peroxide bleaching. The pH during refining is usually 4 to 9, preferably 5 to 8, due to the whiteness and physical properties of the unbleached bulb.
A mineral acid or alkali can also be used in combination to adjust the pH. Refining of wood chips is usually carried out in 1 to 3 stages of refining, with a refining pulp concentration of 15 to 40% and a refining temperature of 80 to 130°C.
However, the refining pulp concentration and refining temperature in the method of the present invention are also carried out under these normal conditions.

The organic chelating agent and sulfite are added before the 1-deficiency refiner, at the same time or at separate locations in the 1-3 refiners. The unbleached bulbs obtained by refining by the above-mentioned chip refining method are subjected to selection treatment, dehydration using a thickener, and then peroxide bleaching in a bleaching tower. The peroxides referred to in the method of the present invention are hydrogen peroxide, Na2O
2. Contains sodium percarbonate, sodium perborate, organic peracid, and ozone, but hydrogen peroxide is generally used, and the amount added is usually 0.2 to 8.0% by weight relative to absolute dry valve. . In addition, 0.2 to 4.0% of alkali such as NaOH is used as a bleaching aid.
Sodium silicate 1-8 (Ff) is appropriately added as a H2O2 stabilizer. The bulb concentration of hydrogen peroxide bleach is usually 5-20
%, preferably 8-150t), the bleaching temperature is usually 40-150t)
90℃, preferably 50-70℃, bleaching time is usually 30℃
It is from minutes to 4 hours. In the present invention, a sulfite and an organic chelating agent are used together during refining, and the heavy metal sequestration and deactivation efficiency of the chelating agent is enhanced.

Further, since the addition of the chelating agent in the method of the present invention is carried out using a refiner with a high valve concentration, the concentration of the chelating agent in the water used is high and the temperature is also high, so that the heavy metal sequestering ability in the valve is enhanced. Moreover, compared to the conventional method in which the chelating agent is simply added at a low valve concentration, the refiner acts as a highly efficient mixer, and the mixing and contacting efficiency of the valve and the chelating agent is high. Furthermore, since the chelating agent is added at an earlier stage of the process than in the conventional method, the complex formation reaction time between the chelating agent and the heavy metal is longer, and the heavy metals in the entire white water in the system can be sequestered and inactivated. There are great benefits to be gained by increasing the heavy metal sequestration ability of the chelating agent in this way. One is that the whiteness of unbleached bulbs increases by 1 to 2 points compared to when only sulfite is added, as heavy metals that have a negative effect on bulb color recovery during chip refining and selection processes are inactivated. It is something to do.
Furthermore, compared to the conventional chelating agent pretreatment method, the stability of peroxide in peroxide bleaching is increased, so that bleached mechanical valves with even higher whiteness can be obtained. Furthermore, there is an advantage that new pretreatment equipment required for conventional chelating agent pretreatment is not required. Next, the present invention will be explained with reference to examples.
The present invention is not limited in any way by the following examples.

In the examples, whiteness was measured according to JISP8l23 (hander whiteness). Example 1 Ezo. Todomatsu Chip Absolutely Dry 1009 was soaked in water overnight and then dehydrated.

Experimental refiner (Deflbra-Tor-D type)
After preheating to 10°C, chips were added to it. Add 0.2% by weight of DTPA to the bone dry chip from a chemical injector.
5Nall. O weight percent Na2sO3 and an amount of boiling tap water to give a bulb concentration of 20% were added to the refiner. Refining was performed for 1 minute while maintaining the refiner at 100°C. After the first refining, take out the bulb and add RGP circulating white water (
In-system white water from the RGP factory (preheated to 80°C) was added.

This valve slurry was applied to a preheated ψ12 inch SW type disk cliff eyeer with a clearance of 0.2 m.
Second refining was performed twice at m. After the secondary dilution, the bulb was diluted with the RGP white water (50°C) to a bulb concentration of 101), left at 50°C for 1 hour, and then diluted with the bulb concentration of 1301).
was dehydrated.

The obtained unbleached RGP is designated as A, and the filtrate is designated as white water A. The pH of white water A was 5.6. Next, do Ezo in the same way as above. After first refining of Todomatsu Chip Absolutely Dry 1009, second refining was performed.

After this secondary valve, add white water A (5'C) to 1% valve concentration.
The solution was diluted to 100%, left at 5°C for 1 hour, and then dehydrated to a bulb concentration of 13%. The obtained unbleached RGP is designated as B, and the filtrate is designated as white water B. White water B (7) pH was 5.7. Thereafter, the chips were treated in the same manner three more times, that is, the white water was recycled a total of four times and the unbleached RGPC. D. I got an E. Not exposed at all
H2O2 bleaching was performed on the GPsA. Unbleached RGP. Put 20 g of bone dry above A into a polyethylene bag, add 3.0% by weight of H2O2, 5.0% by weight of No. 3 sodium silicate, 1.8% by weight of bone dry bulb.
NaOH (wt%) and tap water in an amount to give a bulb concentration of 10% were added and bleached at 6'C for 3 hours. Table 1 shows the whiteness of unbleached RGPsA and bleached RGPA. The method of the present invention actually improves the unbleached whiteness even after 4 cycles of white water circulation,
The degree of bleaching after H2O2 bleaching was also 3 to 4 points higher than that of the comparative example. Comparative Example 1 Same as Example 1, Ezo. Todomatsu Chip Absolutely Dry 1009 was subjected to first and second refining to obtain a second valve.

However, in this case, DTPA. 5Na was not added. 2
Next, dilute the bulb with factory RGP white water (50°C) to a bulb concentration of 1%, leave it at 50℃ for 1 hour, and then dilute the bulb to a bulb concentration of 30.
1) Dehydrated.

To this valve slurry, DTPA-5Na was added in an amount of 0.2% by weight based on the bone dry valve, and after being left at 50°C for 30 minutes, it was dehydrated to a valve concentration of 130. The obtained unbleached bulb is called F, and the white water obtained by combining the filtrate from dehydration up to a bulb concentration of 3% and to a bulb concentration of 13% is called white water F. Hakusui F (7) P
H was 5.5. Next, in exactly the same manner as above, the chip was subjected to primary refining without adding DTPA-5Na.
Next, a second refining was performed. This secondary bulb was diluted with white water F (50° C.) to a bulb concentration of 10 f), left at 50° C. for 1 hour, and then dehydrated to a bulb concentration of 301). To this valve slurry, add 0.2% by weight of DT to absolute dry valve.
PA-5Na was added, and after being left at 50°C for 30 minutes, it was dehydrated to a bulb concentration of 13(f). G the obtained unbleached bulb.
．． Let white water be white water G. The pH of Hakusui G was 5.6. The chips were processed three more times in the same manner, i.e., a total of 4
Recycle water and unbleach RGPH. I. I got J. Next, unbleached RGPF-J absolute dry 209 was placed in a polyethylene bag, and the same amounts of H2O2, No. 3 sodium silicate, and NaOH as in Example 1 were added to the absolute dry bulb, and bleached under the same conditions. Unbleached R
Table 1 shows the whiteness of GPF-J and bleached RGPF-J. Practical example 2 Same as practical example 1, Ezo Todomatsuchipu bone dry 100
f! was subjected to l-order refinement treatment.

However, the chemicals added to the primary refiner in this case are DTPA・5Na: 0.1:0.2;0 by weight per bone dry chip.
．． The combination was 5%; Na2SO3:0.5; 1.0:1.5%. The processing after the l-th refining is the same as in the first embodiment. Table 2 shows the results after the 5th chip treatment, ie, 4 times of white water recycling. By comparing the results of Comparative Examples 2 to 4 shown in Table 2, the synergistic effect of the organic chelating agent and sulfite used together during chip refining on unbleached whiteness and whiteness after H2O2 bleaching was confirmed. Is recognized.

Comparative Example 2 Ezo Todomatsuchip Bone Dry 100 was prepared in the same manner as in Example 1.
9 was subjected to primary refining treatment.

However, the chemicals added to the primary refiner in this case are DTPA・5Na: 0.6; 1.2:2 by weight per bone dry tissop.
．． 0 (!l), and no Na2sO3 was added. l
The processing after the next refining is the same as in Practical Example 1.
Table 2 shows the results of the fifth chip treatment. Comparative Example 3 Ezo Todomatsuchipu Absolutely Dry 100
9 was subjected to l-order refining treatment.

However, in this case, the chemical added to the L-order refiner is Na2sO3: 0.6; 1.2; 2 by weight per bone dry tissop.

0 (fl) and no DTPA was added.

The processing after the l-th refining is the same as in the first embodiment. Table 2 shows the results of the fifth chip treatment. Comparative Example 4 In the same manner as in Example 1, Ezo Todomatsuchipu bone dry 10
09 was subjected to primary refining treatment.

However, no chemicals were added in the first refiner. 1
The processing after the next refining was the same as in Practical Example 1, and the results of the fifth chip processing are shown in Table 2.

Claims (1)

[Claims] 1. A method for producing bleached mechanical pulp from wood chips, in which defibration is carried out in the presence of an organic chelating agent and a sulfite. A peroxide bleaching method for mechanical pulp, characterized in that the unbleached pulp is then bleached with peroxide.