JPS60181391A - Bleaching of chemical pulp for unbleaching papermaking and bleaching agent aqueous solution used therein - Google Patents

Abstract

1. Process for bleaching chemical paper pulps using hydrogen peroxide, characterized in that the operation is carried out in a single stage at a pH of 11 to 11.5, at a temperature of 70 degrees C to 100 degrees C, with the aid of a solution containing, in addition to hydrogen peroxide, at least one alkaline agent chosen from sodium hydroxide and sodium carbonate, at least one alkali metal silicate at a concentration of at least 0.3% by weight, expressed as SiO2 , at least one magnesium salt and at least one calcium salt in such quantity that the weight concentration of each of these alkaline-earth elements is between 0.05% and 1%, these elements being maintained in the dissolved state with the aid of at least one complexing agent for alkaline-earth ions in such quantity that the total concentration of complexant does not exceed 10% by weight.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for bleaching chemical pulp and pulp for paperboard (hereinafter referred to as chemical pulp for papermaking) with hydrogen peroxide, and a bleaching agent used therein.

Bleaching of such chemical pulps, i.e. of unbleached cellulose pulp obtained by cooking lignocellulosic materials according to the so-called sulfide method, sulfate or Kraft method, caustic soda method or carbonate method,
It is widely practiced industrially using chlorine or chlorinated derivatives having an oxidation group, such as chlorine dioxide OTO2 and sodium hypochlorite NaOL.

However, none of these oxidizing agents can give satisfactory bleaching results when used alone and in a single step. It is therefore necessary to carry out the operation in several separate steps and in particular with intermediate treatments such as so-called alkaline bath extraction treatments. The effluent resulting from such continuous processing steps is very highly colored, polluting and corrosive. Moreover, these effluents also pose an explosion risk during the drug regeneration cycle process. especially.

These effluents contain large amounts of chlorinated organic products and large amounts of chloride ions. For this reason, these effluents cannot be disposed of or recycled without complex and expensive treatment.

In order to avoid the above-mentioned disadvantages, it has previously been proposed to use non-chlorinated oxidizing agents, especially oxygen or hydrogen peroxide. However, the use of oxygen requires operation under pressure and is difficult to operate, which is why it is used only to a very limited extent.

Hydrogen peroxide can be used at atmospheric pressure in conventional bleaching equipment. However, as described in 10λ103 and French Patent No. 772 G/3/, which were used directly on unbleached pulps with kappa numbers of the order of 30, supplements for pre-treating the pulp in an acidic medium are necessary. Although the aforementioned results can be improved by carrying out a conventional bleaching process, the effluent after use cannot be disposed of or recycled if it is treated alternately in acid and alkaline baths according to a method similar to all known bleaching methods. Problems caused by circulation cannot be avoided and pulp with a low kappa number cannot be obtained.

According to the method of the present invention, it is possible to obtain cellulose pulp for bleaching paper making having a kappa number of /θ or less, and on the other hand,
At the same time, an effluent can be obtained which can be recycled directly to the bleaching process.

The method of the present invention adjusts the pH to //~/1. a bleaching bath maintained at a pH of 1 to 100 g, and containing hydrogen peroxide in an amount effective to bleach the pulp per 10 parts by weight of the bath liquid, with a pH of 1 to 1;
at least one alkaline agent that can be adjusted during j.
at least 7 alkali metal silicates in an amount equal to at least 0.3% by weight expressed as 5i02, at least /i magnesium salts and at least /i calcium salts of # degree from 0.01 to 7% by weight each; using a bleaching bath capable of keeping the above-mentioned alkaline earth metal ions in solution and containing at least one sequestering agent in a total concentration equal to at most 700% by weight;
It is recalled that the unbleached papermaking chemical pulp is processed in one step at a temperature of 70°C to iooo°C.

The aqueous bleach solution of the present invention is a novel bleach solution as described above.

Regarding the bleach solution of the present invention, the solution must contain hydrogen peroxide, alkaline agents, alkali metal silicates, magnesium and calcium salts and sequestering agents for these alkaline earth metal ions.

The concentration of hydrogen peroxide in the bleach bath is that commonly used and used in this industry. Generally, the concentration will not exceed 7% by weight and is often between 0.0 and 00j% by weight per 100 parts by weight of bath.

The concentration of alkali metal silicates is at least 3% by weight expressed in 5i02, but for economic reasons less than 20% by weight, and in many cases less than 20% by weight.

It is most suitable to use sodium silicate.

The most suitable calcium and magnesium salts are those whose cations are most inert towards hydrogen peroxide under the conditions under which the process of the invention is carried out.

For example, chloride.

The one or more sequestering agents for magnesium and calcium ions are, for example, alkali metal salts of polyphosphoric acid and pyrophosphoric acid; nitrogen-containing acids or salts thereof such as ethylenediaminenatodiacetic acid, diethylenetriaminepetaneacetic acid and nitrilotriacetic acid: Mono- or polyphosphoric acid; selected from polyelectrolytes such as poly-alpha-hydroxyacrylic acid and corresponding lactones.

Although any of the conventional alkaline agents can be used to achieve and/or maintain the desired alkaline pH, sodium hydroxide and sodium carbonate are preferred due to their low cost.

When the method of the present invention is carried out at a temperature below 70°C, bleaching is carried out well, but in order to obtain such an excellent whitening effect, a long treatment time is required, and for this reason, the method of the present invention is difficult to achieve. It suddenly becomes uneconomical.

When the method of the present invention is carried out at temperatures above 100° C., decomposition of peroxide immediately becomes a problem. Therefore, the preferred temperature range is r,t°C to jij°C.

The method of forming the bleach bath is not limited, but may include dissolving calcium and magnesium salts in an aqueous medium in the presence of a sequestrant for these alkaline earth metal ions or a mixture thereof; Sequentially introducing into the solution an alkali metal silicate and hydrogen peroxide in the form of a concentrated aqueous solution and then treating the mixture with an alkaline agent such as sodium hydroxide or sodium carbonate. is preferred.

Contact of the cellulose pulp to be bleached with the bleaching bath (contact time varies, inter alia with respect to temperature, but generally does not exceed about 10 hours) produces a bleaching agent in the solid phase composed of cellulosic material. By passing the solution through, the sieving can be carried out either continuously or batchwise by intimately mixing the bleaching solution with the solid phase consisting of cellulose.

In the first case, namely the leaching technique.

The weight ratio of bleaching solution/solid phase material may be from 10 to 10, preferably from 10 to 10. In the first case, this ratio is t~100. Preferably it is g~λO.

Next, the present invention will be explained in more detail with reference to examples.

Example: Unbleached cellulose pulp with a kappa number of 30 obtained by steaming a resinous material according to the Kraft process - 〇 kf is brought to a pH of ii to //, j by addition of sodium hydroxide.
an aqueous bleach solution 6009, circulating at a flow rate of 3θ Oml/h in a closed loop, with the peroxide concentration kept constant by the addition of hydrogen peroxide, and containing the following components: The leaching treatment was carried out for g hours at 0°C.

Sodium silicate (expressed as Na2O, J, J AS i02)
=7.7% calcium (0aOtz state) = 0.
3% magnesium (MgO12 state) = o, i
5% sodium tripolyphosphate = 0.4% sodium hydroxide - O1 Hirochi 100% hydrogen peroxide = 0.3 The pulp after treatment has a kappa number of approximately The amount of hydrogen peroxide consumed is
The weight was just a little less than the weight of the pulp used.

The example was carried out by operation of a bleach solution and as a bleach solution.
A second unbleached pulp was treated by using the solution used to treat the unbleached pulp of Example 1, followed by a third unbleached pulp. At the end of this third operation, the treated pulp has a kappa number of t, while
The bleaching bath was found to retain its full effectiveness, as consumption of hydrogen peroxide was negligible due to the weight increase of the pulp used.

Example 3 An unbleached cellulose pulp of 109 obtained from the same raw material and having the same kappa number as Example/ was mixed with solution 1001 having the same weight composition as Example/. This mixture was kept at 0°C for 10 hours, and after 15 hours 0.
3419 of hydrogen peroxide was introduced.

The pulp after treatment had a kappa number of t, and the consumption of hydrogen peroxide to achieve this result was only 3% of the weight of the pulp used.

Similar results were obtained at the same temperature as above, but the operation was carried out sequentially. In this continuous process, the pulp to be bleached is introduced and an equal amount of bleached pulp is discharged, during which time it is separated from the extracted pulp and a steady state is maintained in the processing zone and the pulp is removed for g hours. The bleach solution was recirculated to restore the bleach bath pot hydrogen oxide concentration and the concentrations of the other components described above so that contact with the bleach solution could take place.

Claims (1)

[Scope of Claims] f. A one-step bleaching process by contacting an unbleached papermaking chemical pipe with an aqueous bleach solution at a temperature of 70 to 100°C for a time sufficient to bleach to the desired degree. The bleaching agent aqueous solution has a pHt of /l~//,j and is an aqueous solution io. Part by weight, hydrogen peroxide b pH is effective for bleaching pulp //~/ha! at least seven alkali metal silicates in an amount of at least 0.3% by weight expressed as 8i02, each at a concentration of from 0.0j/wt. Sequestration capable of maintaining in solution an amount of at least seven magnesium salts and at least seven calcium salts and the above-mentioned alkaline earth metal ions and in a total concentration equal to at most 70% by weight. 1. A method for bleaching unbleached chemical pulp for papermaking, the method comprising using an aqueous bleaching solution containing at least seven types of bleaching agents. 2. The method according to claim 1, wherein the alkali metal silicate is sodium silicate. 3. The method according to claim 1 or 2, wherein the anion in the magnesium salt and the calcium salt is inert to hydrogen peroxide. ≠ The method according to claim 1 or 2, wherein the magnesium salt is magnesium chloride and the calcium salt is calcium chloride. j. A method of bleaching unbleached papermaking chemical pulp in one step by contacting it with an aqueous solution of bleach at a temperature of 5 to 11° C. for a period sufficient to bleach to the desired degree, the method comprising: As an aqueous solution, l/~//,! Up to 7% by weight of hydrogen peroxide, pH'i//~/l, per 100 parts by weight of an aqueous solution having a pH of ! an alkaline agent selected from sodium hydroxide or sodium carbonate in an amount sufficient to maintain the
Calculated as sodium silicate, calcium ion in an amount of 0.3 to 20% by weight expressed as 0.2. Calcium chloride in an amount of 1% by weight, magnesium chloride in an amount of 0.01 to 7% by weight calculated as magnesium ions, and maintaining the above calcium and magnesium ions in solution. An effective amount of approximately 10% by weight
A method for bleaching unbleached chemical carburetted plastic, characterized in that an aqueous bleach solution containing at least one sequestering agent for calcium and magnesium ions as described above is used in an amount between . t per 100 parts by weight of aqueous solution. Hydrogen peroxide /alkaline agent up to /li amount % Alkaline metal silicates (as Si02) in an amount sufficient to maintain the pH at l/~//, j 0.3-20 quintillion amounts thicalcium salts (as calcium ions) An unbleached chemical pulp for papermaking, characterized in that it contains up to io wt% of a metal ion sequestering agent for calcium and magnesium, O,OS~/wt% magnesium salt (as magnesium ion) 0.0j~/wt% An aqueous bleach solution for bleaching in one step. Z. An aqueous bleach solution according to claim 6, wherein the alkaline agent is selected from sodium hydroxide or sodium carbonate, the alkali metal silicate is sodium silicate, and the salt of calcium and the salt of magnesium are chlorides. The bleach solution according to claim 1 or 7, wherein the amount of hydrogen peroxide is 0.02 to θ,j, and the amount of silicate is 0.3-j%.