Method for manufacturing papermaking pulp

Abstract

The invention relates to a method for manufacturing papermaking pulp, including: a step of refining wood, including an ozone treatment, so as to obtain a mechanical pulp; a deacidification step including placing the mechanical pulp in contact with a deacidification composition including at least one alkaline agent for more than one hour; and a bleaching step including placing the deacidified pulp in contact with a bleaching composition; wherein the pH varies by less than 0.2 point during the last 30 minutes of the deacidification step, and the pH is 6. to 10 at the end of the deacidification step.

Description

FIELD OF THE INVENTION[0001]The present invention relates to a paper pulp manufacturing process.TECHNICAL BACKGROUND[0002]Paper pulps called “mechanical pulps” or “high-yield pulps” or “wood pulps” are obtained directly from wood by a series of mechanical (defibering and refining) treatments carried out by means of grinders and / or refiners. The pulp may then undergo a bleaching phase in one or more steps.[0003]It is known that an ozone treatment during pulp refining helps to improve the quality of the pulp produced, in particular in terms of physical properties (especially the mechanical strength of the pulp) and to reduce the energy consumption of the process.[0004]However, the ozone treatment raises particular problems, namely a reduction in the whiteness of the pulp, a subsequent bleaching difficulty, a loss of yield relative to the wood and an increase in the chemical oxygen demand of the bleaching effluents.[0005]An ozone treatment as mentioned above is described in document DE...

AI Technical Summary

Benefits of technology

[0046]The present invention makes it possible to overcome the drawbacks of the prior art. More particularly, it provides a more effective paper pulp bleaching process having a better yield and / or using a small amount of chemicals and / or generating less effluent to be treated.

[0048]Specifically, after the ozonation, the acids within the fibers tend to be progressively released. The nature and the duration of the deacidification according to the invention are therefore adapted so as to obtain a stable pH before the bleaching step, thereby making it possible to neutralize all the acid species and obtain better bleaching.

[0050]the invention makes it possible to obtain a paper pulp bleaching efficiency equivalent to or greater than that of the prior art (with a whiteness parameter of the same order or even higher);

[0051]using a mild base (especially magnesium hydroxide, calcium hydroxide, sodium carbonate, magnesium carbonate, sodium silicate or mixtures thereof, and preferably magnesium hydroxide) as the alkaline agent of the deacidification composition, the yield and / or the reduction in the amount of chemicals necessary and the amount of effluent to be treated and / or the whiteness are further improved;

[0052]also using a mild base during the bleaching step, the yield, the reduction of the amount of chemicals necessary and the amount of effluent to be treated, or even the whiteness, are further improved; and

Problems solved by technology

However, the ozone treatment raises particular problems, namely a reduction in the whiteness of the pulp, a subsequent bleaching difficulty, a loss of yield relative to the wood and an increase in the chemical oxygen demand of the bleaching effluents.

None of these approaches is deemed to be satisfactory both as regards the mechanical strength of the pulp, and the optical properties thereof.

That document too does not address the loss of yield observed during bleaching.

However, the methods used in the prior art are not completely satisfactory.

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