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.

1 . A process for manufacturing a paper pulp, comprising:
 refining wood, comprising an ozone treatment, so as to obtain a mechanical pulp;   contacting the mechanical with a deacidification composition comprising at least one alkaline agent for more than 1 hour to form a deacidified pulp; and   contacting the deacidified pulp with a bleaching composition,   wherein the improvement comprises the pH varies by less than 0.2 units during the last 30 minutes of the contacting with the deacidification composition and the pH is between 6 and 10 at the end of the contacting with the deacidification composition.   
     
     
         2 . The process as claimed in  claim 1 , in which the duration of the contacting with the deacidification composition is equal to or greater than 1 hour 30 minutes. 
     
     
         3 . The process as claimed in  claim 1 , in which the pH at the end of the contacting with deacidification composition is between 7 and 8. 
     
     
         4 . The process as claimed in  claim 1 , in which the pH varies by less than 0.1 units during the last 30 minutes of the contacting with the deacidification composition. 
     
     
         5 . The process as claimed in  claim 1 , in which the alkaline agent of the deacidification composition:
 is selected from the group consisting of oxides, hydroxides, silicates and carbonates of alkaline-earth metals and alkali metals, ammonia, aqueous ammonia and mixtures thereof.   
     
     
         6 . The process as claimed in  claim 1 , in which the bleaching composition comprises a bleaching agent and at least one alkaline agent
 selected from the group consisting of oxides, hydroxides, silicates and carbonates of alkaline-earth metals and alkali metals, ammonia, aqueous ammonia and mixtures thereof.   
     
     
         7 . The process as claimed in  claim 1 , which further comprisies contacting the deacidified pulp with a chelation composition comprising a chelating agent. 
     
     
         8 . The process as claimed in  claim 1 , in which 20 kg or less of alkaline agent per tonne of mechanical pulp is used. 
     
     
         9 . The process as claimed in  claim 1 , in which the bleaching composition comprises:
 5 to 100 kg of bleaching agent per tonne of mechanical pulp; and   5 to 100 kg of alkaline agent per tonne of mechanical pulp.   
     
     
         10 . The process as claimed in  claim 1 , in which the loss of wood yield after contacting with the bleaching composition is less than or equal to 20%. 
     
     
         11 . The process as claimed in  claim 1 , in which the whiteness of the pulp after contacting with the bleaching composition is equal to or greater than 65. 
     
     
         12 . The process as claimed in  claim 1 , producing effluents having a chemical oxygen demand less than or equal to 210 kg per tonne of pulp. 
     
     
         13 . The process as claimed in  claim 1 , in which the mechanical pulp is selected from the group consisting of SGW, PGW, RMP, TMP, HTMP and CTMP pulp. 
     
     
         14 . The process as claimed in  claim 1 , in which the wood is selected from the group consisting of resinous wood, deciduous tree wood and a mixture thereof, preferably a resinous wood and more particularly preferably a pinewood or spruce wood. 
     
     
         15 . (canceled) 
     
     
         16 . The process as claimed in  claim 1 , in which the duration of the contacting with the deacidification composition is equal to or greater than 3 hours. 
     
     
         17 . The process as claimed in  claim 1 , in which the pH varies by less than 0.05 units during the last 30 minutes of the contacting with the deacidification composition. 
     
     
         18 . The process as claimed in  claim 1 , in which the alkaline agent of the deacidification composition is selected from the group consisting of potassium hydroxide, sodium hydroxide, magnesium hydroxide, calcium hydroxide, sodium carbonate, magnesium carbonate, sodium silicate and mixtures thereof. 
     
     
         19 . The process as claimed in  claim 1 , in which the bleaching composition comprises a bleaching agent and at least one alkaline agent selected from the group consisting of sodium hydroxide, magnesium hydroxide and mixtures thereof. 
     
     
         20 . The process of  claim 7  wherein said chelating agen is selected from the group consisting of ethylenediaminetetraacetic acid and one of its sodium salts and diethylenetriaminepentaacetic acid and one of its sodium salts. 
     
     
         21 . The process as claimed in  claim 1 , in which the bleaching composition comprises:
 20 to 40 kg of bleaching agent per tonne of mechanical pulp; and   10 to 70 kg, of alkaline agent per tonne of mechanical pulp.   
     
     
         22 . The process as claimed in  claim 1 , in which the loss of wood yield after contacting with the bleaching composition is less than or equal to 10%. 
     
     
         23 . The process as claimed in  claim 1 , in which the whiteness of the pulp after the contacting with the bleaching composition is equal to or greater than 70%. 
     
     
         24 . The process as claimed  claim 1 , producing effluents having a chemical oxygen demand less than or equal to 145 kg per tonne of pulp.