Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
  • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
  • D21C9/10—Bleaching ; Apparatus therefor
  • D21C9/16—Bleaching ; Apparatus therefor with per compounds
  • D21C9/163—Bleaching ; Apparatus therefor with per compounds with peroxides

Definitions

• the present invention relates to bleaching using hydrogen peroxide from mechanical pulps, thermomechanical chemomechanics, or chemothermothermomechanics in the paper industry and related to high degrees of white.
• the dry matter yield of such an operation is always very high and can reach and even often exceed 90%.
• Pasta of mechanical origin also called high-yield pasta obtained in 1 ecru state, must be bleached efficiently and with a minimum loss of material so that the manufacture of the products derived from it can meet the requirements of quality and economy in the industry.
• French Patent No. 2537177 discloses a two-step process at least, wherein a consistency condition is ensured throughout the laundering. He presents the absence of silicate as a possibility, but he does not provide any concrete information as to the impact of this absence on the degree of white achieved.
• DTMPA diethylenetriaminepentamethylenephosphonic acid
• the method of the invention does not appeal to either of them and nevertheless leads, thanks to a particular choice of bleaching conditions, to a paste of white degree of the same level as that authorized by their intervention. .
• the industry thus has, thanks to the process of the invention, a pulp of bleached mechanical origin obtained economically and which does not have any of the drawbacks, such as those mentioned for example in the article by GW KUTNEY cited above, linked to the still substantial presence of sodium silicate.
• the process of the invention is a process for bleaching doughs of mechanical origin to degrees of white high, using hydrogen peroxide in an alkaline medium in two consecutive steps separated by washing and carried out in the absence of sodium silicate or a similarly effective compound, characterized in that the amount of peroxide hydrogen used in the first step is between 0.5% and 3%, the amount of hydrogen peroxide used in the second step is greater than that used in the first step and is between 2% and 5%.
• the alkalinity in the two stages is reached thanks, most frequently, to the use of sodium hydroxide and the quantity of alkaline agent employed in each of the two stages is that necessary to ensure preferably in one as in the other of these steps has an initial pH between about 10.5 and 12.
• the preferred sodium hydroxide / hydrogen peroxide weight ratio in the first step as in the second step is between about 0.6 and 1.2.
• the temperature in the two stages can be the same or different. It is most generally between about 40 ° C and 70 ° C, most often close to 60 ° C-70 ° C.
• the consistency, concentration in weight percent of pulp in the dry state in the bleaching medium is generally between 10% and 30%, often between 10% and 20%.
• the compounds ordinarily associated with sodium silicate which have, however, only an effectiveness in whitening much lower than his, for example diethylenetriaminepentaacetic acid (DTPA) or magnesium presented for example in the form of soluble salt such as sulfate.
• DTPA diethylenetriaminepentaacetic acid
• magnesium presented for example in the form of soluble salt such as sulfate.
• the duration of each of the two stages depends on the choice of the other parameters adopted. When these are within the preferred ranges, the duration of the first stage is generally between 0.5 and 2 hours, that of the second stage between approximately 2 and 4 hours.
• washing between the two stages is meant here the operation which makes it possible to eliminate part of the liquid which is in the dough at the end of the first stage.
• This washing is carried out in a known manner, for example by pressing the dough associated or not with its dilution, generally by water.
• a washing efficiency, or elimination rate of the liquid equal to or greater than about 80% ensures obtaining a paste with a high degree of whiteness at the end of the second step but a lower efficiency, for example equal to About 50% is still sufficient for this purpose.
• the quantities of material are expressed as already indicated, in% by weight relative to the dough in the dry state
• - DTPA is used in the form of the sodium salt in solution at 40% by weight and the quantity indicated is that of this solution
• - by silicate is designated an aqueous sodium silicate solution at 35% by weight and the quantity indicated is that of this solution
• the magnesium is used in the form of a soluble salt, in this case the sulfate, but expressed in Mg
• - H2O2 hydrogen peroxide is counted as 100%
• the washing efficiency which is 80% or more unless otherwise specified, is the same in the case of a comparison as in the illustration of the invention with respect to which the comparison is made.
• the degree of white is measured (457 nm) in% using a CARL ZEISS spectrophotometer of the ELREPHO type.
• a mechanical pulp of a softwood wheel with a white degree equal to 57.2% is subjected in a first step, to a consistency equal to 15%, for 1.5 hours, at a temperature of 60 ° C., at simultaneous action of the following compounds: NaOH: 1.5%, H2O2: 2%, DTPA: 0.5% then washed before being subjected in a second step, for 3 hours, to a consistency and a temperature still equal respectively at 15% and 60 ° C, with the simultaneous action of the following compounds: NaOH: 3%, H2O2: 2.5%, Mg: 0.05%.
• the degree of whiteness of the dough obtained at the end of the second stage is equal to 81.1% while it was only equal to 71.5% at the end of the first stage.
• Example 1 is repeated, using 4% silicate in the first step.
• the degree of white of the paste finally obtained is equal to 81.5%, therefore very close to that obtained when the silicate is omitted, although at the end of the first stage the degree of white was however this time equal to 76%. .
• Example 1 The unbleached pulp of Example 1 is bleached as in Example 1, but using 3.4% H2O2 in the second step instead of 2.5%.
• the degree of whiteness of the paste obtained at the end of the first step is equal to only 72% while that of the paste obtained at the end of the second step rises at 82%.
• the degree of whiteness of the dough at the end of the second step is only 79.3%.
• the washing efficiency between the two stages is equal to 95%.
• the degree of white indicated for the paste at the end of the second stage is preserved by repeating this illustration with a washing efficiency between the two stages equal to both 50% and 80%.
• a mechanical softwood wood pulp with a white degree equal to 53.7% is subjected in a first step, to a consistency of 10%, for 1 hour, at a temperature of 60 ° C, to the simultaneous action of NaOH: 0.7%, H2O2: 0.85%, DTPA: 0.5% before being washed and subjected in a second step, for 4 hours, at a temperature equal to 60 ° C. and at a consistency equal to 20%, to the action of NaOH: 2.7%, H2O2: 3.4%, Mg: 0.03%.
• the degree of whiteness of the dough at the end of the second stage reaches 80.9%.
• a chemothermothermal mechanical pulp of coniferous wood with a white degree equal to 59.6% is treated in a first step using NaOH: 1%, H2O2: 1.2%, DTPA: 0.5%, during 1, 5 hours at a temperature equal to 60 ° C and a consistency equal to 15%, before being washed and being treated in a second step using NaOH: 2.9%, H2O2: 3.4 %, Mg: 0.05% for 3 hours at a temperature equal to 60 ° C and a consistency equal to 15%.
• the paste from the second stage has a degree of whiteness equal to 80.5%.
• the same chemothermal-mechanical paste as above is treated as above but the DTMPA replaces in nature and in quantity the DTPA.
• the amount of DTMPA thus engaged should be equivalent to the presence of around 4 to 5% of silicate and therefore lead to a result greater than that achieved in its absence.
• the degree of whiteness observed in reality at the end of the second stage is only 79.6%.

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• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Wood Science & Technology (AREA)
• Paper (AREA)
• Detergent Compositions (AREA)
• Medicinal Preparation (AREA)
• Pharmaceuticals Containing Other Organic And Inorganic Compounds (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=9356225

Family Applications (1)

Country Status (10)

Cited By (3)

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Citations (3)

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• 1987
  • 1987-10-22 FR FR8714877A patent/FR2622221A1/fr not_active Withdrawn
• 1988
  • 1988-10-06 EP EP19880420339 patent/EP0313478A1/de not_active Withdrawn
  • 1988-10-06 ES ES88420339T patent/ES2008654A4/es active Pending
  • 1988-10-06 DE DE198888420339T patent/DE313478T1/de active Pending
  • 1988-10-20 NO NO884674A patent/NO170348C/no unknown
  • 1988-10-20 NZ NZ226649A patent/NZ226649A/xx unknown
  • 1988-10-20 JP JP63265221A patent/JPH0643674B2/ja not_active Expired - Lifetime
  • 1988-10-21 FI FI884881A patent/FI884881A/fi not_active Application Discontinuation
  • 1988-10-21 PT PT88819A patent/PT88819B/pt active IP Right Grant
  • 1988-10-21 AU AU24130/88A patent/AU615001B2/en not_active Ceased

Patent Citations (3)

Non-Patent Citations (2)

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