JPS583074B2 - Palpuno Kasan Kabutsu Hiyou Hakuhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for bleaching cellulose pulp under the action of peroxides in an alkaline medium.

More specifically, the present invention relates to a peroxide bleaching method for pulp that prevents self-decomposition of peroxide by adding an Mg compound and an alkaline substance, thereby economically obtaining bleached pulp with high brightness.

without any harmful effect on the quality of cellulose pulp.
A number of methods are known intended for bleaching cellulose pulp.

Particularly high-yield pulps, such as ground pulp (GP
), refined ground pulp (RGP), thermomechanical pulp (TMP), chemical ground pulp (C
In bleaching G P ), peroxides, generally H
Oxidative bleaching of pulp in the presence of an alkali with 2O has the advantage that a high degree of whiteness with little fading can be obtained without reducing the yield or the degree of polymerization of cellulose.

However, peroxides are unstable at high temperatures or in the presence of heavy metals and self-decompose during bleaching, which is difficult to predict and control.
It has the serious disadvantage of being easy to occur.

In particular, in H2O bleaching of high-yield pulp, heavy metals such as Mn, Cu, Fe, Ni, and Co present in the pulp and working water act as catalysts to promote the decomposition of H2O, resulting in wasted H2O.
decomposition occurs.

It is said that normal high-yield pulp contains several ppm to several hundred ppm of these heavy metals per bone-dry pulp.
In peroxide bleaching, it is essential to remove or inactivate heavy metals.

Therefore, various H2O2 stabilization methods are being researched or implemented, such as (1) method of adding sodium silicate (water glass), and (2) method of adding sodium silicate (water glass).
Chelating agents, such as aminopolycarboxylic acids such as EDTA, DTPA, NTA or sodium tripolyphosphate (ST
Condensed phosphorus such as PP? Method of adding salt (3) Method of dissolving and removing heavy metals by mineral acid or chelating agent pretreatment before peroxide bleaching.

etc. can be mentioned.

Currently, the sodium silicate method (1) is usually used exclusively from the viewpoint of efficiency and economy, and in some cases, a trace amount of Mg salt is also used in order to enhance the H2O stabilizing effect.

In the sodium silicate method, in order to obtain a sufficient peroxide stabilizing effect, 3 to 15 W/W per bone dry pulp is required.
% of sodium silicate (No. 3 water glass, 40°B
e) must be added.

However, sodium silicate has the disadvantage that it reacts with the Mg salt added together or with metals such as Ca, Mg, and Ba in the pulp or water, forming a metal silicate scale that is sparingly soluble and difficult to remove.

Therefore, the use of large amounts of sodium silicate causes scale not only in the dispensing equipment for peroxide bleaching solutions, but also in the recovery and processing equipment for bleaching waste liquids.

Therefore, in order to reduce the scale as much as possible, Mg++ salt is not used in combination.

Furthermore, wastewater containing sodium silicate also has the disadvantage that coagulation and sedimentation treatment is difficult due to the dispersibility of sodium silicate.

On the other hand, the treatment of pulp bleaching wastewater and the conservation of water are the biggest problems in the current pulp industry, and as a solution to these problems, there is an urgent need to convert bleaching systems into closed systems.

However, if a bleaching system containing sodium silicate is attempted to be closed, there is a serious problem in that scale will form in the wastewater return pipe, wastewater concentration, and combustion furnace system.

Therefore, in the peroxide bleaching of pulp, there is an urgent need to eliminate the disadvantages of the sodium silicate method, that is, non-silicate bleaching (a bleaching method that does not use sodium silicate), and various methods are actively being used. being researched.

As one method, adding a chelating agent according to the above-mentioned method (2) has been proposed, but no chelating agent has been found that sequesters or inactivates all heavy metals. In some cases, the complex may accelerate the decomposition of peroxide, and the pulp contains hundreds of ppm of Ca.
Mg is also chelated, so to completely sequester heavy metals, 0.2-0. A large amount of expensive chelating agent (5 W/W%) is required, which has the drawback of increasing the cost of bleaching chemicals.

In addition, with the above-mentioned method (3) of dissolving and removing heavy metals by pre-treating the pulp with a mineral acid or chelating agent, it is impossible to remove the heavy metals until the influence of the heavy metals disappears. However, there was little effect on stabilizing H2O and increasing whiteness.

Other methods have not yet realized a peroxide-stabilized bleaching method that can replace the sodium silicate method in terms of H2O stabilization, whiteness, and economy in peroxide bleaching of pulp.

Therefore, the present inventors have conducted extensive research on methods to eliminate the influence of heavy metals and stabilize H2O, and as a result, we have determined that only Mg compounds are added as a stabilizer in peroxide bleaching of pulp. It has been found that by selecting an appropriate Mg compound concentration at a suitable pH and an appropriate addition method, a very large peroxide stabilizing effect can be obtained.

In the method of bleaching pulp with peroxide, the present invention uses an Mg compound of 0.1 to 2% per bone dry pulp, calculated as Mg+10.
．． This is a peroxide bleaching method for pulp, which is characterized by adding and mixing the pulp to a pH of 0%, then adding and mixing an alkaline substance, and bleaching with peroxide at a pH of 10.5 to 12.0.

According to the present invention, unlike the sodium silicate method, scale does not occur, and the whiteness of the bleached pulp increases. The bleaching cost is also superior to the current sodium silicate method.

By the way, it is already known that Mg compounds are effective in stabilizing peroxides.

For example, Mg salts are effective in stabilizing H2O aqueous solutions, Mg salts are used as a component of the stabilizer for granular sodium percarbonate, Mg salts are used to stabilize granular sodium perborate, perfucric acid It has been reported that Mg salts are used in combination with various compounds to stabilize aqueous solutions.

Furthermore, in H2O bleaching of pulp or fibers, it is widely known that when a small amount of Mg salt is used in combination with sodium silicate, the H2O stabilizing effect is higher than that of sodium silicate alone, and this is currently being practiced.

However, the amount of Mg salt used in the above examples is extremely small, and the purpose of use or effect is expected to be only as an auxiliary agent for the main stabilizer.Furthermore, the method of addition is different, and the Mg compound alone in the present invention is This is fundamentally different from peroxide stabilization.

It is essential to add and mix the Mg compound to the pulp prior to adding the alkali, and is an important component of the present invention.

In the present invention, the Mg compound is uniformly dispersed in the pulp, and by the addition of alkali, [Mg (OH)2) x
(X-2 or higher) It forms a colloid and at that point induces a heavy metal inactivation effect.

In contrast, in the current Mg salt-sodium silicate method, water, peroxide, NaOH, sodium silicate, and Mg salt are simultaneously mixed to form a bleaching solution, and the bleaching solution is brought into contact with the object to be bleached. there were.

However, the inventors have found that the bleaching method in which a Mg compound and an alkali compound are simultaneously added to the pulp has little H2O2 stabilizing effect.

In addition, in the current method of stabilizing peroxide using the sodium silicate Mg salt method or the combination method of other stabilizing reagents and Mg compounds, the amount of Mg compounds is extremely small, and in the case of pulp H2O2 bleaching, Mg++ Even if Mg++ is added, it has been considered that it is sufficient to add 0.005 W/W% of Mg++ per bone dry pulp.

However, according to the findings of the present inventors, when trying to stabilize peroxide with Mg compound alone, the currently used Mg
The peroxide stabilizing effect was not observed at all because the concentration was completely insufficient.

In the present invention, the peroxide is H2O2, ? a20,
Inorganic or organic peroxides are used, such as peracetic acid, but generally H2O22 is used.

Although the present invention is applicable to all types of pulp in principle, it is applicable to high-yield pulps with high lignin content (e.g. G
It is particularly effective for peroxide bleaching of P, RGP, TMP, CGP, etc.).

Also, chemical pulp with a low degree of refinement (e.g. kraft pulp,
It is also suitable for peroxide bleaching of sulfite pulp, soda pulp, semi-chemical pulp, etc.).

In the present invention, any Mg compound can be used as long as it produces Mg hydroxide in alkaline conditions.

Specific examples include Mgcz2, Mg(NO3)
2,. MgSO+ tMg (OAc)2, Mg
C03, MgO, or their hydrates are used, but Mg(12, MgS04) is recommended from a cost standpoint.

The amount of Mg compound added depends on the amount of heavy metals contained in the pulp and the treated pulp concentration (abbreviated as P.C.), but it is necessary to have an amount that can sufficiently adsorb heavy metals or combine with them to inactivate them. be.

General high-yield pulp is P. C. When bleaching with peroxide at around 10%, the Mg compound is converted to Mg++ in absolute dry pulp (hereinafter, the amount of Mg compound added is in accordance with the above display method). If it is less than 1 W/W%, regardless of the pH, it is insufficient to form a stable colloid of Mg(OH)2:)x, and inactivation of heavy metals cannot be expected.

Furthermore, if the amount of Mg++ added is too large, a stable colloid with good dispersibility cannot be obtained, and the ability to inactivate heavy metals will be weakened.

Therefore, the amount of Mg added is usually 0.1 to 2. 0 W/W%,
Preferably 0.3-0. 8 W/W%.

The Mg compound is added to the pulp in solid or aqueous solution form;
It is preferable to add it as an aqueous solution.

It is important that the added Mg compound is sufficiently mixed with the pulp and uniformly dispersed in the pulp.

A useful method for adding an Mg compound and an alkali is to filter and dehydrate the wood pulp to a pulp concentration for bleaching, then add and mix an aqueous Mg solution, and then add and mix an alkali.

In this case, peroxide may be added at any stage.

This bleach-impregnated pulp is then bleached at a predetermined temperature and time.

In addition, when performing peroxide bleaching of mechanical bulbs, Mg
The compound can also be added with white water in one step in the glider or refiner.

In this case, since the white water is recycled, after the Mg ++ drift in the white water reaches equilibrium, the amount of Mg to be added may be equal to the amount that was removed by adhering to the pulp and added to the white water.

It can also be added between the pulping process and the pre-bleaching dehydration filter, and in this case the amount of Mg added is the same as in the above method.

Examples of alkaline substances used in the present invention include NaOH, KOH, Na2CO3, etc., with NaOH being the most common.

In the present invention, pH is an important factor, and pH is 1.
If it is lower than 0.5, (M g (OH) 2
1x is not produced, but when the pH is higher than 12, the properties of the colloid produced are not favorable for the inactivation of heavy metals.

In addition, at high pH, alkaline coloration of the pulp becomes noticeable, so the initial pH must be carefully selected. In the present invention, the initial pH is selected to be 10.5 to 12.0, preferably pH 11. It is 0 to 11.5.

In peroxide bleaching of pulp, organic acids are produced as the bleaching progresses, so a decrease in pH is unavoidable.

As the pH decreases, the solubility of 1Mg (OH)2 1X increases and the amount of Mg precipitation decreases.

Therefore, it is inappropriate for the pH at the end of bleaching to be too low.
It is desirable to maintain the pH during bleaching so that the pH is 9 or higher at the end of bleaching.

If the pH decreases during bleaching, increasing the hydrolysis of Mg(OH)2 and thus weakening the peroxide stabilization, adding alkali requirements during bleaching can reduce the pH.
It is also possible to maintain and adjust H at a desired level. In the present invention, (Mg(OH)2) x exhibits a pH buffering effect and is effective in maintaining a preferred pH for a long time. .

In the present invention, P. C. (Pulp concentration) is 5 to 20% used in normal peroxide bleaching, preferably 8 to 15%.

As for the bleaching temperature and treatment time, the usual peroxide bleaching treatment conditions can be applied as they are, and the bleaching temperature and treatment time are usually above room temperature, preferably 4.
The treatment is usually carried out at 0 to 80°C for 1 to 4 hours.

The amount of peroxide added varies depending on the pulp type, unbleached whiteness, and desired bleached whiteness, but in the case of general high-yield pulp, it is added in an amount of 1 to 4 W/W% per bone-dry pulp.

However, this amount is not absolute, and a larger or smaller amount can also be used.

In the present invention, Mg compounds and other peroxide stabilizers,
For example, it is possible to use small amounts of sodium silicate, organic chelating agents (e.g. EDTA, DTPA), condensed phosphates, etc., which can further enhance the peroxide stabilizing effect and at the same time provide high whiteness. It is possible to

Further, similar effects can be expected when the present invention is applied to pulp pretreated with an acid or a chelating agent.

Further, it is also possible to increase the whiteness by using a commercially available surfactant with a large detergency or a substance that assists in washing and removing colored substances such as STPP.

In particular, STPP is a useful auxiliary agent because it also has the effect of sequestering metals.

Another feature of the present invention is that since the peroxide is stabilized, the bleaching whiteness increases linearly in proportion to the amount of peroxide added.

According to the present invention, the pulp bleaching wastewater does not contain any silicates unlike the conventional method and does not cause scale damage to the equipment, so the bleaching pulp wastewater, washing wastewater, and papermaking wastewater can be easily recovered and reused. .

Further, since the pulp bleaching wastewater according to the present invention contains a larger amount of residual peroxide than in the conventional method, there is an advantage that the amount of added peroxide can be reduced by reusing the wastewater.

In addition, Mg salt is (Mg (OH)2) in alkaline conditions.
) X precipitates, but under neutral to acidic conditions Mg-
Since the pulp bleaching wastewater according to the present invention is acidified and then recycled as it is before the bleaching process, it is possible to save not only water and peroxide but also added Mg compounds.

Also, if you want to recover Mg salts from acidic wastewater, the pH is 10.
．． If the alkalinity is 5 or higher, it will precipitate as Mg(OH)2, which can be recovered by filtration, and further reductions in chemical costs can be expected.

In a closed system for high-yield pulp production, water is recovered and reused, but it is necessary to extract a portion of the wastewater with a high COD from the system.

In the sodium silicate method, scale becomes a serious hindrance in the concentration and combustion process of the concentrated wastewater extracted, but there is no such concern with the wastewater produced by the method of the present invention.

Moreover, if concentrated wastewater is treated under acidic conditions, scaling can be completely prevented.

Therefore, the bleaching method of the present invention is a very advantageous method when producing high-yield pulp in a closed system.

Further, according to the present invention, there is a great advantage that the chemical cost required for bleaching is less than the current sodium silicate method, and a higher degree of whiteness than the current sodium silicate method can be obtained.

Furthermore, the present invention has the advantage that the COD and chromaticity of bleaching waste liquid are lower than that of the current sodium silicate method.

Examples will be described below, but these examples do not limit the method of the present invention.

Example 1 Comparative Example 1 30g of Siberian spruce RGP (P.C. 1 8%: unbleached whiteness 50.9) was taken in an absolutely dry state, placed in a polyethylene bag, and finally P.C. C. 0 to 1% of absolute dry pulp in terms of Mg++ in tap water in an amount of 10%. Add an aqueous solution of MgS04,7H,20 to 0 W/W% and make sure that Mg++ is uniformly dispersed in the pulp. Mixed thoroughly.

3.0% of H20 was added to the Mg++-impregnated pulp, and one solution of 10% NaOH aqueous solution was added and thoroughly mixed to adjust the initial pH to 11.3.

The polyethylene bag was sealed and kept in a constant temperature water bath at 60°C for 3 hours.

Filter the pulp aqueous solution with cotton cloth, dehydrate it, and check the pH of the bleaching wastewater.
and residual H202 were quantified by the 1-Na2S203 method.

Of the bleached pulp obtained by filtration, 10g was taken out and purified with distilled water. C. Dilute to 1.0% and pH 5.0 with SO2 water.
Adjusted to.

The diluted pulp solution was suctioned, filtered, formed into two sheets, and air-dried overnight to obtain a sheet for whiteness measurement.

The whiteness was determined according to the Hunter whiteness measurement method of JIS-P8123.

(The above method was applied mutatis mutandis to the whiteness measurement below).

The results obtained in Example 1 are shown in Table 1.

Comparing Example 1 with Comparative Example 1 in Table 1, the effects of the present invention are remarkable, and the pH buffering properties of CMg(OH)2)X are also clear.

Comparative Example 2 For comparison, RGP was bleached using the current sodium silicate method.

As in Example 1, 30 g of unbleached RGP was used as the sample pulp.

Finally p. c. Add No. 3 sodium silicate (40°Be') 5-8% to tap water in an amount of 10%, H2 02,3
．． Add 0% aqueous solution to the pulp, then add 10%
% NaOH aqueous solution and mix thoroughly until the initial pH is 1.
．． l. Adjusted to -3.

The subsequent operation method was based on Example 1.

The results are shown in Table 1.

Example 2 In Example 1, the initial pH was adjusted by adjusting the amount of NaOH added.
The procedure was the same as in Example 1, except that the amount of Mg++ was varied between 10.0 and 12.0 and the amount of Mg++ added was constant at 0.50%.

The results are shown in Table 1. Example 3 For comparison, bleaching was performed without sequentially adding M g ++ and Na OH.

As in Example 1, 30 g of unbleached RGP was taken and placed in a polyethylene bag.

Final P. C. Add absolute dry pulp Mg++ 0.5%, NaOH 4.27%, H2 02 to the amount of tap water that makes it 10%.
3. O% was added.

A white precipitate of (Mg(OH)2:]x was suspended. This aqueous solution was added to the pulp and mixed thoroughly.

The following operations were based on Example 1.

The results obtained by this bleaching procedure are shown in Table 2.

In this method, the H2O2 stabilizing effect by the Mg compound is reduced by half compared to Example 1, Exp3, and
In comparison, although the chemical addition rate was the same, the whiteness was 59.1, which was far inferior to the whiteness of Example 1, Exp3, which was 66.0.

Example 3 In Example 1, M g ++0. The procedure and conditions were exactly the same as in Example 1, except that the treatment temperature was changed to 40°C and 50°C when 5% was added, and the results are shown in Table 2.

In the 3-hour treatment at 50° C., a whiteness of 66.0, which is almost the same as that in the 3-hour treatment at 60° C., was obtained.

Example 4 In Example 1, instead of MgS04,7H20, M
As a g++ source, Mg Cl2, ,6 H2O2,
MgCO, ,Mg (NO3)2 t6H2O2
, Mg (OAC) 2 , 4H20 was used, but the same procedure as in Example 1 was carried out.

The results are shown in Table 2. Example 5 In Example 1, M g ++ 0. H with 5% addition
The amount of 2O2 added was varied between 2 and 4%.

Other operating methods and conditions were the same as in Example 1.

As a result, the whiteness was 61, 65.9, and 67.6 when the amount of H2O2 added was 2%, 3%, and 4%, respectively.

Example 6 In Example 1, the amount of Mg++ added was 0.5%, and the ED
TA・4 N a O. The same procedure as in Example 1 was carried out except that 2% was added in combination.

The results are shown in Table 3. A combined effect was observed on whiteness.

Comparative Example 4 Chelating agents for comparison (EDTA・4Na, DTP
A.5Na) addition method was tested.

Without adding Mg++, EDTA・4NaO. 1~0.
2%, DTPA・5NaO. The same procedure as in Example 1 was carried out except that 1 to 0.3 of each was added.

The results are shown in Table 3.

Depending on the EDTA/4Na1DTPA/5Na addition method, no H2O22 stabilizing effect can be obtained, and the bleaching whiteness is 56.
It was as low as ~58.

Example 7 30g of the unbleached RGP of Example 1 was taken and washed with tap water.
C. Diluted to 1.0%.

DTPA・5Na was added at 0.3 W/W% to bone-dry pulp, and the pH was adjusted to 9.0 with NaOH aqueous solution. Adjust to 2 and 1 at room temperature.
I left it for a while.

The aqueous pulp solution was suction filtered, and after washing with 2 liters of tap water, P.I. Dehydrated by suction to 0.20% (DTPA・
Whiteness after 5Na treatment -5 0.9)oDTPA・5
The Na-treated pulp was bleached in the same manner as in Example 1, with the amount of Mg++ added being 0.5%.

The results are shown in Table 3, and a high whiteness of 66.5 was obtained by using both the DTPA pretreatment method and the Mg++ addition method.

Comparative Example 5 For comparison, the same procedure as in Example 7 was carried out without adding Mg++.

The results are shown in Table 3. Poor results were obtained in both H2O2 stabilization and bleaching whiteness.

Example 8 30g of the unbleached RGP of Example 1 was taken and washed with tap water.
C. Diluted to 1.0%.

A few drops of 4N-H2SO were added to adjust the pH to 2.9.

The pulp aqueous solution was suction filtered, and after washing with 2 liters of tap water, P.I. C. It was dehydrated by suction to 20% (whiteness after acid pretreatment 52.3).

The acid-pretreated pulp was bleached in the same manner as in Example 1, with the addition amount of Mg++ being 0.5%.

The results are shown in Table 3, and a high whiteness of 66.8 was obtained by using both the acid pretreatment method and the Mg++ addition method.

Comparative example 6 For comparison, the same procedure as in Example 8 was carried out without adding Mg++.

The results are shown in Table 3. Example 9 in which poor results were obtained in both H2O2 stabilization and bleaching whiteness In Example 1, 5.0% sodium silicate, 1 to 2% sodium tripolyphosphate (STPP), or various surfactants 1 Example 1 was followed except that Mg++ was added at ~2% and Mg++ was kept constant at 0.5%.

The results obtained are shown in Table 4, and in all cases, the effects of combined use were observed.

Comparative example 7 For comparison, it was bleached using the current sodium silicate method.

Exp. of Example 9 except that the amount of Mg++ added was 0.05% and Mg salt, sodium silicate and alkali were added to the pulp at the same time. Same as 1.

The results are also listed in Table 4.

Example 10 Comparative Example 8 Akamatsu GP (P.C.=2 1.3 Unbleached whiteness 5
Take 30g of absolutely dry 5.5) and add H202 according to Example 1.
Bleached.

The results are shown in Table 5. Similar to H202 bleaching of RGP, H202 was stabilized and good whiteness was obtained.

Example 11 Comparative Example 9 Broad-leaved miscellaneous trees such as beech and birch C GP (P.C.-22.
0%, unbleached whiteness 39.8) was taken to an absolutely dry weight and bleached with H2O2 according to the procedure of Example 1.

However, the treatment temperature was 70°C, and the results are shown in Table 6.

M g++ 0. A whiteness of 55.3 was obtained with 30% addition.

Exp. As shown in No. 10, the combined use of a surfactant was effective in increasing whiteness.

Example 12 The unbleached RGP of Example 1 was bleached with peracetic acid.

For peracetic acid, a peracetic acid monoacetic acid-H2O22 equilibrium aqueous solution was used.

The operation method is an example. The procedure of Example 1 was repeated except that H2O2 was replaced with peracetic acid.

As shown in Table 7, good results were also obtained in peracetic acid bleaching of RGP.

Claims (1)

[Claims] 1 In a method of bleaching pulp with peroxide, M
01 to 2.0 g compound per bone dry pulp in terms of Mg + 10
%, then an alkaline substance is added and mixed, and bleaching with peroxide is performed at pH 10.5 to 12.0.