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 invention relates to an addition to an alkaline peroxide-containing bleaching agent for cellulose, wood pulp, waste paper and / or mixtures thereof, and to the use thereof in such a bleaching agent and to a bleaching process.
• JP-A-59/145 300 relates to a bleaching detergent containing a type X zeolite and an H2O2 addition compound, namely sodium percarbonate. So it is not a (peroxide-free) bleach additive. While it is stated that the bleaching detergents are said to have excellent stability; however, this is only valid to a limited extent, since sodium percarbonate loses its active oxygen in a relatively short time.
• JP-A-77 74 605 also relates to bleaching and cleaning agents which are reaction products of zeolites with H2O2. Again, there are no (peroxide-free) bleach additives as precursors to bleaching and cleaning agents.
• the bleaching and cleaning agent should also contain sodium carbonate, but only in a mixture with the H2O2 zeolite reaction product, so that the storage stability is relatively low.
• DE-A-25 35 283 relates to bleaching or oxidizing water-insoluble silicates with cation exchange capacity, which additionally contain hydrogen peroxide. Again, it is not a peroxide-free bleach additive.
• the product is unstable because the hydrogen peroxide in the silicate decomposes during storage.
• the prior binding of H2O2 to the silicate cation exchanger is essential. Strong alkalis are required to activate the hydrogen peroxide, which lead to irreversible alkali yellowing and a high concentration of contaminants (high COD value), especially in the case of wood pulp.
• the bleaching is said to reliably achieve high final whiteness contents with the least possible investment, with a minimum of running costs and, if possible, without any adverse side effects.
• lignin-preserving bleach comes into consideration for the lightening of wood pulp, be it in the form of sanding, pressure sanding, refiner material, thermomechanical or chemical-thermomechanical material and waste paper in contrast to cellulose bleaching.
• H2O2 hydrogen peroxide
• the lignin-removing bleach with oxygen and / or hydrogen peroxide is also used in the production of cellulose.
• the lignins, lignin-like phenols and extract substances and their degradation products, which form chromophore systems as a result of the presence of conjugated double bonds and auxochromic groups, are essentially responsible for the brownish-yellow color of the wood materials.
• Increasing the white content without removing lignin requires specific destruction of the chromophoric systems, if possible without triggering substances, since a content of organic substances in the bleaching medium would increase the chemical oxygen demand (COD).
• Hydrogen peroxide breaks down according to two reaction mechanisms.
• homolytic decay which is given by the equation H2O2 ⁇ 2 HO ⁇ ⁇ H2O + O2 (1) can be represented, the formation of hydroxide radicals takes place, which react in a chain reaction to the decay products water and oxygen.
• This inherently exothermic reaction is normally prevented by the high activation energy for the separation of the oxygen-oxygen bond in H2O2.
• it can be catalyzed in particular by heavy metals and their compounds, which are often contained in bleaching liquids. Homolytic decay can thus become the main reaction.
• this is not desirable since this course of the reaction gives rise to oxidative damage and bleaches only a little in the desired sense.
• the presence of peroxide stabilizers and complexing agents was considered necessary during the bleaching process.
• the desired reaction of the hydrogen peroxide is dissociation in water according to the equation H2O + H2O2 ⁇ HO2 ⁇ + H3O+ (2)
• the equilibrium constant of this reaction is 1.78 x 10 ⁇ 12 at room temperature.
• HO2 ⁇ perhydroxide anion
• a concentration can be increased by increasing the H2O2 concentration or by adding alkali and removing the acid. The latter is carried out generally and one speaks of the activation of the hydrogen peroxide.
• the right ratio between hydrogen peroxide and alkali is very important, this ratio being temperature-dependent.
• the amount of alkali must be matched to the amount of hydrogen peroxide used.
• the pollution of the circulating water also depends on this.
• an initial pH value of 10.5 to 11 is usually set.
• the whiteness maxima are shifted with increasing amounts of hydrogen peroxide to higher alkali inputs (primarily sodium hydroxide). It was previously believed that peroxide bleaching was not sufficiently activated at low alkali hydroxide concentrations.
• the chemistry of the stabilization of hydrogen peroxide by water glass in alkaline solution has not yet been clarified. The reason for this is probably the very difficult colloidal chemical processes.
• the water glass probably also binds heavy metals.
• the stabilization with water glass in connection with magnesium ions important for wood pulp bleaching In addition to its stabilizing effect, the water glass also acts as an alkali dispenser and buffer substance as well as a wetting and dispersing agent. It can also be used inexpensively.
• the attempt to reduce the use of water glass has led to the use of complexing agents.
• compounds complexing heavy metals are used for this.
• the polyphosphates mainly sodium tripolyphosphate
• a high COD load causes an increased consumption of hydrogen peroxide and reduces the strength properties of the fiber materials.
• a high COD load acts as a "disruptive substance" due to unwanted interactions with cationic auxiliaries, the effectiveness of which is impaired. Production disruptions can also occur due to increased deposits.
• the invention has for its object to reduce or even avoid the use of alkalis, water glass and / or complexing agents in the bleaching of pulp, wood pulp, waste paper and / or their mixtures, and even avoid them, and still products with comparable or even higher whiteness to obtain.
• the invention thus relates to an additive to an alkaline, peroxide-containing bleach for cellulose, wood pulp, waste paper and / or mixtures thereof, which may also contain water glass and / or a complexing agent, which is characterized in that it is a water-insoluble material modified with an alkali metal carbonate or alkali metal bicarbonate represents inorganic silicate ion exchanger.
• the silicate ion exchanger is preferably modified by coating it with 1 to 70, in particular with 5 to 50,% by weight, based on the total additive, of alkali carbonate or alkali metal bicarbonate.
• the silicate ion exchanger i.e. the non-carbonate or bicarbonate component
• the silicate ion exchanger has a BET surface area of at least 30 m2 / g and a cation exchange capacity of at least 30 meq / 100 g.
• the silicate ion exchanger is preferably a smectitic clay mineral, an attapulgite or a natural or synthetic zeolite (preferred average diameter 2 to 6 ⁇ m).
• the clay mineral used is preferably a mineral from the montmorillonite-beidellite series, in particular bentonite, hectorite, saponite or Nontronite or an acid activated mineral from the montmorillonite-beidellite range. Acid-activated bentonite is particularly preferably used.
• Acid activation leads to an increase in the specific surface area, which improves the sorption capacity of the silicate ion exchanger.
• the invention also relates to the use of the bleaching agent additive defined above in a bleaching agent for cellulose, wood pulp, waste paper and / or mixtures thereof which contains hydrogen peroxide and optionally water glass, alkali metal hydroxide and / or a complexing agent.
• the bleaching agent preferably contains 20 to 300, in particular 30 to 200 g of additive per mole of hydrogen peroxide.
• the invention further relates to a method for bleaching pulp, wood pulp, waste paper and / or mixtures thereof, the substances to be bleached being treated with a hydrogen peroxide and optionally with a bleaching agent containing alkali hydroxide, water glass and / or a complexing agent; this process is characterized in that the treatment with a bleaching agent as defined above is carried out at a pH of from 7.0 to 12.0, in particular from 7.5 to 9.0.
• the bleaching can therefore be carried out in a weakly alkaline medium, thereby reducing the difficulties which occur when adding a large amount of alkali or water glass.

Landscapes

• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Wood Science & Technology (AREA)
• Paper (AREA)
• Detergent Compositions (AREA)
• Lubricants (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (2)

Family

ID=6341062

Family Applications (1)

Country Status (6)

Families Citing this family (14)

Family Cites Families (9)

• 1987
  • 1987-11-23 DE DE19873739655 patent/DE3739655A1/de not_active Withdrawn
• 1988
  • 1988-11-19 AT AT88119265T patent/ATE80677T1/de active
  • 1988-11-19 DE DE8888119265T patent/DE3874683D1/de not_active Expired - Lifetime
  • 1988-11-19 EP EP88119265A patent/EP0317921B1/de not_active Expired - Lifetime
  • 1988-11-22 JP JP63293740A patent/JPH01162887A/ja active Pending
  • 1988-11-23 FI FI885428A patent/FI91003C/fi not_active IP Right Cessation
• 1990
  • 1990-05-23 US US07/527,532 patent/US5039377A/en not_active Expired - Fee Related

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