JPH0217678B2 - - Google Patents

Abstract

Process for producing a paper pulp comprising a stage of H or P treatment just before the purification of the pulp or its transfer to the papermaking machine, where the neutralisation of the bleached pulp is performed with the aid of carbonic acid instead of sulphur dioxide.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for removing H (hypochlorite) or P immediately before passing through a strainer or paper machine.
The present invention relates to a method for producing paper pulp by bleaching with (peroxide).

In the pulp and paper industry, pulp bleaching is carried out before the production of paper from pulp, whatever its type, i.e. mechanical pulp, chemical pulp, or pulp obtained by reprocessing deinked paper. .

Bleaching processes generally consist of one or more successive stages separated by washing steps. These stages are characterized by the bleaching agent used. For example, for chemical pulp especially kraft, CEHH, CEP, CEDED,
CEDP, CEHDP, and CEDED(P) and
CEHD(P), CEH for sulphite pulp,
HH, H and OH, RP for mechanical pulp,
For PP, RPRP, PRP or P, semi-chemical pulps, a series of stages P, HH, OH is used.

Publications implementing the bleaching process include, for example, U.S. Pat. No. 3,806,404;
There is number 187477.

The end of the bleaching process is usually a treatment of the pulp with SO ₂ before it is strained and/or passed to a paper machine. Generally, treatment with sulfur dioxide in a solution has the following objectives and effects. i.e., destroying the residues or chemical residues of the bleaching stage, whether they are residues of the D treatment (chlorine dioxide), the H treatment (hypochlorite), or the P treatment (peroxide). , removing metal cations (iron, manganese or copper) which reduce whiteness and promote the opposite process of whitening, acidifying the pulp as alkalinity has the detrimental effect of blackening the pulp and paper. That is. This last point is therefore fundamental.

This many " _SO2 effects" are known as "souring."

Destruction of the residue is necessary in the case of D treatment (ClO ₂ ), since ClO ₂ is corrosive and toxic and its presence is incompatible with the rest of the treatment (washer corrosion).

However, on the other hand, it has been found that in case of H or P treatment, the residue is not harmful. Their presence has a favorable effect, since they continue to act as bleaching agents and have a mild biocidal effect.

The inventors have discovered that in the case of bleaching processes employing a final H or P stage or a single H or P stage, the use of SO ₂ is not necessary and the pulp is depleted by CO _{2 rather than by SO 2 .} We have discovered that it is possible to neutralize the

Therefore, according to the present invention, there is provided a method for producing paper pulp, which comprises bleaching the bleached pulp with hypochlorite or peroxide immediately before passing it through a strainer and/or a paper machine, comprising: A method for producing paper pulp is provided, characterized in that the pulp is treated with carbon dioxide essentially immediately after the bleaching treatment.

The process of the present invention is suitable for the bleaching step, whether the pulp is mechanical pulp or chemical pulp or pulp obtained by recycling deinked paper, provided that the last or single stage is H or P type. Either multistage or single type can be used everywhere.

Thus, the invention applies to thermomechanical pulps (TMP) or chemical-thermomechanical pulps (CTMP), which are normally subjected to only bleaching treatment.

After this H or P stage, the pulp is usually washed and processed in suspension form.

According to the invention, carbon dioxide is introduced into the last or single stage cleaning fluid. It may also be introduced into the suspension during development from the last or single bleaching stage.

Carbon dioxide can be introduced in gaseous or liquid form or dissolved in solution, for example in the suspension wash or dilution water.

After the neutralization treatment according to the invention, the pulp is processed in the usual manner. That is, for example, it can be stored or introduced directly into a paper machine or purified.

In addition to the fact that it satisfies the purpose of neutralizing the pulp, the use of carbon dioxide according to the invention avoids harmful alkaline conditions and (as evidenced by the examples) satisfactorily outperforms that with _SO2 . gives bleaching results and has the following advantages:

- Acidification is easy to control and _CO2 is a weak acid, making it less dangerous than with _CO2 .

- There is no corrosion and contamination of cleaning fluids due to the use of acids.

- The P or H stage residues are not destroyed and have mild biocidal properties, thus avoiding the growth of microorganisms which occur, for example, during storage and which darken the pulp.

-The injection operation is easy.

- Indestructible bleaching residue can be reused.

Other features and advantages of the invention will become apparent from the following examples. It should be noted that the following examples demonstrate various non-limiting uses of carbon dioxide to adjust the PH and brightness of pulp.

Example 1 Thermomechanical pulp was treated with a PRP bleaching process.
After the second P treatment, a whiteness of 70.65% ISO was obtained. The second P treatment is based on pulp weight,
% _{H2O2 ,} 1.5%NaOH, 1.0% _Na2SiO3 , _and
It consists of treating the pulp with a solution containing 0.05% _MgSO4 . In this case, the pulp concentration was 10%, the temperature was 65%, and the holding time was 2 hours.

The final PH was 8.3 and the residual peroxide was 1.3% of the dry pulp.

The pulp had a consistency of 27% and was divided into two samples:

1 _SO2 solution was added to the first sample, and the pH
5.5, the concentration was set at 10%.

There was no residual peroxide in the pulp. This sample produced had a whiteness of 80.05% ISO.

2 CO ₂ was dissolved in the second sample and water to obtain a 10% concentration suspension and adjust the PH to 5.7.

Residual peroxide remained unchanged. The brightness was determined and was 81.17% ISO.

This example shows that PH adjustment using CO ₂ after peroxide treatment is improved compared to PH adjustment using SO ₂ .

Example 2 Unbleached thermomechanical pulp (whiteness: 57.43% ISO)
The pulp was treated with a solution containing 2% _H2O2 , 2.0% NaOH, _2.0 % _Na2SiO3 , and 0.05% _{MgSO4 ,} and 0.2% DTPA (sodium diethylenetrimine pentaacetate).

In this case, the pulp concentration was 10%, the temperature was 85%, and the holding time was 30 minutes.

The final PH was 8.1 and the residual peroxide was 0.61% of the dry pulp.

The bleached pulp with a concentration of 10% was divided into two samples:

1. _SO2 solution was added to the first sample, and the pH
It was set as 5.4.

There was no residual peroxide after the SO ₂ injection.
The pulp was discharged and produced by this sample had a brightness of 72.14% ISO.

2 Add CO ₂ to the second sample until the pH is 5.6.
was injected.

Residual peroxide was 0.58%. The brightness was determined and was 74.24% ISO.

Residual peroxide was extracted from the suspension and collected for further bleaching.

The whiteness after adjusting the PH with CO ₂ was improved compared to the whiteness after adjusting the PH with SO ₂ .

Example 3 Chemical kraft pulp with resin base
Bleached with CDEODP process.

After stage P, the PH is 9.9 and the pulp is
It was divided into two samples:

1 The first sample was treated with SO ₂ and the pH was 6.0.
It was said that The suspension was discharged and the product produced had a whiteness of 86.50% ISO. After 1 hour aging at 105℃, whiteness is 83.24%
It was ISO.

2 A second sample was treated with _CO2 until the PH was adjusted to 6.3.

After discharge, the produced had a whiteness of 87.16% ISO.

After aging at 105° C. for 1 hour, the whiteness was 83.24% ISO.

According to this example, the adjustment of PH by _CO2 is
It can be seen that the whiteness is superior to that obtained by adjusting the pH using SO ₂ . Furthermore, the reversal of whiteness is
It was less than when CO ₂ was used.

Claims (1)

[Claims] 1. A method for producing paper pulp in which the bleached pulp is bleached with hypochlorite or peroxide immediately before passing through a strainer and/or a paper machine, wherein the bleached pulp is bleached. A method for producing paper pulp, characterized in that it is essentially treated with carbon dioxide immediately after the treatment. 2. The method for producing paper pulp according to claim 1, wherein the carbon dioxide is introduced into the cleaning liquid in a gaseous or liquid form. 3. A method for producing paper pulp according to claim 1, wherein the carbon dioxide is introduced into the bleached suspension in gaseous or liquid form. 4. The bleached pulp is mechanical pulp, thermomechanical pulp, chemical-thermomechanical pulp, chemical pulp, or pulp obtained by reprocessing deinked paper. The method for producing the paper pulp described.