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 additive to an alkaline peroxide-containing bleaching agent for cellulose, wood pulp, waste paper and / or mixtures thereof as well as such a bleaching agent and a bleaching process.
• 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.
• a lignin-preserving bleach can be considered for the lightening of wood pulp, be it in the form of sanding, pressure sanding, refining material, thermomechanical or chemical-thermomechanical material and waste paper, in contrast to cellulose bleaching.
• a hydrogen peroxide (H2O2) is used as bleach.
• 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 as well as their degradation products, which form chromophore systems due to 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 a specific destruction of the chromophoric systems, if possible without substance release, 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 "disturbing substance" due to unwanted interactions with cationic aids, 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, Nontronite or a corresponding mineral activated with acid. 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 a bleaching agent for cellulose, wood pulp, waste paper and / or mixtures thereof, containing hydrogen peroxide and optionally water glass, alkali metal hydroxide and / or a complexing agent, which is characterized in that it contains an additive as defined above.
• the bleaching agent according to the invention preferably contains 20 to 300, in particular 30 to 200 g of additive per mole of hydrogen peroxide.
• the invention further relates to a process 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, which reduces the difficulties which arise with a high addition of alkali or water glass.
• the waste paper (daily newspapers or daily newspapers / magazines 50:50) was heat-aged at 60 ° C for 144 hours and then at least 24 hours at 23 ° C and 50% rel. Air-conditioned humidity. After adding the bleaching and flotation chemicals, the waste paper was disintegrated in water brought to a defined hardness with Ca (OH) 2 or CaCl2 at 4% by weight consistency and 40 ° C for 5 minutes at a rotor speed of 3000 min ⁇ 1. After a 90-minute reaction phase at 40 ° C., the mixture was pitched again for 2 minutes at a consistency of 3.5% by weight. The mixture was then diluted to 0.8 wt.
• test sheets were formed on porcelain suction filters, which were dried at about 90 ° C. and air-conditioned.
• the white measurement (R 457) was carried out as above in the Elrepho (R) or Elrephomat (R) .
• the sulfite pulp has a medium purity at whitenesses of 60 to 75. This goal is achieved with one-step peroxide bleaching. In addition to the simple handling, the advantage of the peroxide bleaching process is that the yield remains very high.
• Examples 1 to 32 show the results of the pulp bleaching tests, expressed as R 457 values, which describe the difference in whiteness between the bleached material and the starting material.
• Experiment 1 documents the loss of whiteness compared to the starting material due to alkali yellowing.
• Experiments 2-8 show the results when using water glass, the modified ion exchanger according to the invention and mixtures of both; Combinations such as in Experiment 7 or especially in Experiment 8 were found to be particularly favorable.
• Experiments 1 to 8 were carried out with the addition of 0.5% NaOH, so that the pH was always between 10 and 12. A small addition of NaOH is often advisable if the pulp is acidic.
• Table 2 shows the dependence of the flotation deinking result on the water hardness and the hydrogen peroxide stabilizer. Regardless of the waste paper - only newspapers (Z) or newspapers / magazines 1/1 (Z / I) - the result with the modified ion exchanger according to the invention (acid-activated bentonite, modified with 25% Na2CO3) was always above the result obtained with water glass.
• the pH of the flotation medium was 9 to 12.
• the flotation was carried out as described under 1.2.
• Table 4 shows the results of experiments 23 to 29.
• Experiments 23, 24 and 29 were carried out using newspapers, magazines 1/1 only with water glass, only with modified, acid-activated bentonite or only with the organic complexing agent DTPA.
• Experiments 25 to 28 show an action synergism ion exchanger / DTPA, so that even when 90% DTPA was replaced by the ion exchanger according to the invention (experiment 25) there was no loss of activity.
• test 50 3% water glass, 0.3% DTPA, 2% NaOH
• test 52 3% ion exchanger, no DTPA, no NaOH

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

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ID=6341062

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• 1987
  • 1987-11-23 DE DE19873739655 patent/DE3739655A1/de not_active Withdrawn
• 1988
  • 1988-11-19 DE DE8888119265T patent/DE3874683D1/de not_active Expired - Lifetime
  • 1988-11-19 EP EP88119265A patent/EP0317921B1/fr not_active Expired - Lifetime
  • 1988-11-19 AT AT88119265T patent/ATE80677T1/de active
  • 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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