FR2620144A1 - PROCESS FOR THE MANUFACTURE OF BLEACHED PAPER PULP INCLUDING TREATMENT WITH CARBONIC ACID AFTER BLEACHING - 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

DESCRIPTION

  The present invention relates to a process for manufacturing paper pulp co-carrying a H or P treatment phase before purification.

  pulp or its passage through the paper machine.

  In the pulp industry, whether it is chemical, mechanical or even comes from the reprocessing of de-inked paper, the pulp is generally treated with SO 2 which takes place before refining pulp and / or its passage through the paper machine. The sulfur dioxide treatment, generally in solution, has the purpose and effect of: - destroying the residuals, or chemical residues of the bleaching stages, whether they are residues from treatment D (chlorine dioxide), treatment H (hypochlorte), or treatment P (peroxide); eliminate metal cations (Iron, Manganese or Copper) which reduce whiteness and accelerate the subsequent whiteness reversal process; - neutralize or even acidify the dough, because it is known that alkaline conditions have a harmful effect of blackening of the dough and

  paper. This last aspect is therefore essential.

  This multiple "S02 effect" is known as "souring".

  The destruction of residuals is necessary in the case of treatment D (C102), because C10O2 is corrosive and toxic and its presence

  incompatible with further treatment (corrosion of scrubbers).

  However, in the case of H or P treatment, on the contrary, the

  residues are not harmful, crome has highlighted the plaintiff.

  Their presence has favorable effects because they continue to act camne

  whitening agent and also have a mild biocidal action.

  The applicant therefore demonstrated in the case of whitening treatment using a final step H or P or a single step H or P, that the use of SO 2 is not necessary, and that it is possible to neutralize dough with carbcnic acid, C) 2,

used in place of S02.

  Thus, the present invention relates to a process for manufacturing paper pulp of the type where the bleaching takes place in an H or P phase before the bleached pulp passes through the purifier and / or the paper machine, characterized in that one treats the essentially bleached pulp with carbonic acid and directly after

whitening treatment.

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  The process according to the invention can be implemented whether the pulp is mechanical, chemical or comes from recycling of inked paper, and whatever the bleaching sequence, with multiple or uric steps, provided that the last or only step is type H or P. The invention thus applies to thermal thermal pastes (TIMP) or mechanical chemico-theb (CIMP) which usually only undergo

whitening treatment.

  After this step H or P, the dough is usually washed and

  treated as a suspension.

  According to the invention, the carbonic acid is introduced into the washing waters of the last or only bleaching step. It can also be introduced into the suspension on leaving the last or

single bleaching step.

  Carbonic acid can be introduced in gaseous, liquid form, or in solution, for example in washing or dilution water.

  of the suspension, or in the suspension.

  After the neutralization treatment according to the invention, the pulp is treated in the usual way, that is to say it can be stored or directly introduced into the paper machine, or be purified, by

example.

  The use of carbon dioxide according to the invention, in addition to the fact that it fulfills the purpose of neutralizing the paste, avoids the harmful alkaline conditions and gives satisfactory whiteness results and only with SO2, (cmte this will appear in the examples), has the following advantages: - the acidification is easy to control and, since 2 is a weak acid, the risks of over-acidification are less than with SO2; - there is no corrosion and water pollution due to the use of this acid; - the development of microorganisms which occurs in the dough, during storage for example, and which blackens the dough, is avoided, since the residuals of steps P or H, not destroyed, are exported as soft biocides; - The implementation of the injection is simple; - the bleaching treatment residues, not destroyed, are reusable. Other characteristics and advantages of the invention will appear on reading the examples below, present various uses, without limitation, of carbonic acid for adjusting the

  pH of pasta, and the whiteness results that come with it.

EXAMPLE 1:

  A conventional thenrEm pulp is treated in a PRP bleaching sequence. A whiteness of 70.65% ISO is reached after the second treatment P which consisted in treating the paste with a solution containing: 2% H2O2 compared to the paste 1.5% NaOH 1, O% Na2 0.05% SiO3 "gSO4 when the concentration of the paste was 10%, the temperature 65 ° C. and the retention time 2 h. The final pH is 8.3 and the residual peroxide 1.3% by

compared to dry dough.

  The dough is brought to a concentration of 27% and it is divided into

two samples.

  1. S02 liquor is added to the first sample to

  adjust the pH to 5.5 and reduce the concentration to 10%.

  There is no residual peroxide in the dough. The fozrmettes prepared with this sample have a whiteness of 80.05% ISO. 2. Dissolve 032 in water and the paste from the second sample to obtain a suspension at 10% concentration and adjust

the pH at 5.7.

  The residual peroxide is unchanged. Whiteness is

determines and equals 81.17% ISO.

  By this example, we enter that the adjustment of the pH by 002 after a peroxide treatment improves the whiteness compared to an adjustment of the p by SO2

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EXAMPLE 2

  An unbleached ther = ecanic pulp (whiteness 57.43% ISO) is bleached in a step P, using a solution comprising

2% H202

  2.0% NaOH 2.0% Na2SiO3 0.05% MgSO4 0.2% DTPA (diethylene trimine penta-sodium acetate) The concentration of the dough is 10%, the temperature 85 C

  and the retention time of 30 minutes.

  The final pH is 8.1 and the residual peroxide is equivalent to

  0.61% H202 compared to the dry paste.

  The 10% bleached pulp is divided into two samples.

  1. S02 is added to the first sample, to adjust the pH to

5.4.

  There is no residual peroxide after the SO2 injection. The dough is drained and the whiteness formulas produced according to the

standard procedure.

The whiteness is 72.14% ISO.

  2. O 2 is injected into the dough of the second sample until

obtain a pH of 5.6.

  The residual peroxide is determined and reaches 0.58%.

  The dough is drained and the whiteness is determined on

  foermettes according to the standard procedure. The whiteness is 74.24% ISO.

  By this example, it is shown on the one hand that the residual peroxide can be extracted from the suspension and recovered for subsequent bleaching. On the other hand, the whiteness after adjustment of the pH by C02 is

  superior to whiteness after adjusting the pH with SO2.

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EEMLE 3

  A softwood-based chemical kraft pulp is bleached in

a CDEO DP sequence.

  After stage P, the pH is 9.9 and the dough sample is divided into two parts. 1. The first sample is treated with SO2 to adjust the pH to 6.0. The suspension is drained and the prepared formulas have a whiteness of 86.50% ISO. After one hour of aging at 105 C, the

whiteness is 83.24% ISO.

  LO [0 2. The second pulp sample is treated with CO2 until

adjust the pH to 6.3.

  After draining, the farms have a whiteness of 87.16% ISO. After aging for 1 hour at 105 ° C, the whiteness is 85.30% ISO. This example shows that the adjustment of the pH by CO2 gives a stronger whiteness than the adjustment by S02. In addition, the reversion of

  whiteness is reduced when 00O2 is used.

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REVEDICICNS

  1. A method of manufacturing pulp of the type o the bleaching comprises an H or P phase just before the passage of the bleached pulp through the scrubber and / or the paper machine, characterized in that the pulp is treated bleached mainly with carbonic acid and directly after the bleaching treatment. 2. Method according to claim 1, characterized in that the carbonic acid is introduced in the form of gaseous and / or liquid OC 2

in wash water.

  3. Method according to claim 1, characterized in that the carbonic acid is introduced in the form of gaseous and / or liquid O02

in the bleached suspension.

  4. Method according to one of claims 1 to 3, characterized in

  what the bleached pulp is of mechanical, thermlmechanical, chemothermothermal, chemical type or comes from paper reprocessing

de-inked.