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
  • D21C9/1026—Other features in bleaching processes
  • D21C9/1036—Use of compounds accelerating or improving the efficiency of the processes
• • 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
  • D21C9/1026—Other features in bleaching processes
  • D21C9/1042—Use of chelating agents

Definitions

• the invention relates to a method for bleaching wood pulps, cellulose, waste paper and / or their mixtures with hydrogen peroxide or dithionite
• Heavy metals and their salts catalyze the decomposition of bleaching chemicals such as hydrogen peroxide and dithionite.
• bleaching chemicals such as hydrogen peroxide and dithionite.
• chelating agents are used in practice.
• chelating agents must be used which give complexes which are as stable as possible and which are not attacked by the bleaching agent during the bleaching process.
• Organic compounds are usually used, in particular the salts of nitrilo-tri-acetic acid (NTA), ethylenediamine-tetraacetic acid (EDTA) and diethylene-triamine-tpentacetic acid (DTPA) are preferred because of the excellent stability of the complexes in the paper and textile industry.
• NTA nitrilo-tri-acetic acid
• EDTA ethylenediamine-tetraacetic acid
• DTPA diethylene-triamine-tpentacetic acid
• the ions of iron, cobalt and manganese which cause particularly negative effects in bleaching due to catalytic decomposition, are particularly well bound by the multi-toothed DTPA.
• Weaker chelating agents such as citric acid, tartaric acid, sugar acids, polymeric acrylic acid derivatives or even low molecular weight polyoxycarboxylic acids, generally do not form very stable complexes. To obtain adequate protection of the bleaching agent against heavy metal decomposition, they must therefore be added in extremely high amounts. According to the prior art, their use therefore does not constitute an economically acceptable solution, although they can be virtually quantitatively degraded aerobically or anaerobically in conventional waste water treatment plants.
• the compounds EDTA and DTPA described above like their phosphonic acid analogs (for example diethylene-triamine-penta-methylenephosphonate), have the disadvantage of being very difficult to biodegrade. Basically, an accumulation in the environment with the risk of remobilization of precipitated heavy metals, for example from sediments in flowing waters, cannot be ruled out.
• phosphonic acid analogs for example diethylene-triamine-penta-methylenephosphonate
• an alkaline peroxide-containing bleaching agent which contains, as an additive, a silicate ion exchanger modified with an alkali carbonate or alkali bicarbonate. This is intended to achieve the object of achieving bleaching processes using hydrogen peroxide without addition or with only a small addition of alkali metal hydroxide, and without addition or only a small addition of water glass and without addition or only with a small amount of complexing agents.
• the object of the invention is to develop a bleaching process which can be carried out economically using easily degradable complexing agents and leads to good bleaching results.
• the invention relates to a method for bleaching wood pulp, cellulose, waste paper and / or their mixtures with hydrogen peroxide or dithionite in the presence of a chelating agent, which is characterized in that the raw material to be bleached before the bleaching step with a consistency of 1.5 to 25% treated with a natural or synthetic zeolite or a layered silicate.
• the pretreatment process known per se generally runs at weakly acidic to weakly alkaline pH values, in particular pH 6.0 to 8.0, with a consistency of 1.5 to 25%, in particular 2 to 10% dry, at a temperature of 20 to 100 ° C, especially 50 to 80 ° C, from.
• Peroxide bleaching can be followed by other usual washing and bleaching stages with changing conditions.
• the heavy metal content of a bleaching liquor is usually very low in the aqueous phase. This is primarily due to the fact that the heavy metals have only a very low solubility under alkaline conditions. A large part of the heavy metals are bound in a complex manner in the wood pulp fiber. Iron ions, for example, are fixed by the phenolic groups of the lignin.
• the zeolites and / or layered silicates suitable as cation exchangers must therefore have a larger complex formation constant with the heavy metal than the lignin.
• the zeolite component generally has the formula (Na2O) x . (Al2O3) y . (SiO2) .w H2O, where x is 1, y is 0.8 to 1.2, preferably about 1, where z is 1.5 to 3.5, preferably 2 to 3 or about 2 and w is 0 to 8, preferably 2.5 to 6.
• Such zeolites are cation exchangers and have an exchange capacity for calcium ions of about 200 to 400 or more mg equivalent calcium carbonate hardness per g. They are preferably hydrated up to 5 to 30%, especially up to a moisture content of 10 to 25%, e.g. B. about 20% of the same. Zeolite A is preferred, X, Y and P are also suitable.
• Zeolite 4A is particularly preferred, however.
• the particle sizes of the zeolite or zeolites are usually 0.194 to 0.037 mm corresponding to 100 to 400 mesh, preferably 0.105 or 0.074 to 0.044 mm corresponding to 140 or 200 to 325 mesh, but their extreme sizes are in the submicron range.
• the particle size is preferably in a range which is almost an order of magnitude lower than the dimensions of the pulp fibers to be bleached.
• the silicate ion exchangers are not pretreated with a carbonate before they are used and are used in an amount of 0.5 to 2.5, in particular 1.0 to 1.5,% by weight, based on fiber material (atro).
• test results show that the pretreatment according to the invention leads to better bleaching results than are found in conventional bleaching in which DTPA and hydrogen peroxide are used at the same time.
• citric acid tartaric acid, maleic acid, sugar acids, heptagluconate, low molecular weight acrylate or generally known low molecular weight polycarboxylic acids, individually or in a mixture with one another.
• the pulp is generally pretreated within a period of 15 minutes to 24 hours.
• the wood pulp (20% consistency) is pretreated with 1% of a type A zeolite. The subsequent bleaching is carried out without the addition of stabilizers.
• the wood pulp has a whiteness of 66.8 with a residual peroxide content of 0.24%.
• the subsequent bleaching gives a wood pulp with a whiteness of 70.1 with a residual H2O2 content of 0.88%.
• the wood pulp is pretreated with 0.5% Na citrate alone.
• the bleach provides an ISO whiteness of 64.8% with a residual H2O2 content of 0.11%.

Priority Applications (1)

Applications Claiming Priority (2)

Publications (2)

Family

ID=6433502

Family Applications (1)

Country Status (9)

Families Citing this family (35)

Family Cites Families (3)

• 1991
  • 1991-06-08 DE DE4118899A patent/DE4118899C1/de not_active Expired - Lifetime
• 1992
  • 1992-04-25 AT AT92107106T patent/ATE96186T1/de active
  • 1992-04-25 EP EP92107106A patent/EP0518036B1/de not_active Expired - Lifetime
  • 1992-04-25 DE DE92107106T patent/DE59200018D1/de not_active Expired - Fee Related
  • 1992-05-19 US US07/885,688 patent/US5227022A/en not_active Expired - Fee Related
  • 1992-06-05 NO NO922225A patent/NO178831C/no unknown
  • 1992-06-05 CZ CS921709A patent/CZ283368B6/cs unknown
  • 1992-06-05 PL PL92294801A patent/PL168012B1/pl unknown
  • 1992-06-05 CA CA002070556A patent/CA2070556A1/en not_active Abandoned
  • 1992-06-05 FI FI922618A patent/FI922618A/fi not_active Application Discontinuation

Also Published As

Similar Documents

Legal Events