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
  • D21C9/12—Bleaching ; Apparatus therefor with halogens or halogen-containing compounds
  • D21C9/14—Bleaching ; Apparatus therefor with halogens or halogen-containing compounds with ClO2 or chlorites
  • D21C9/144—Bleaching ; Apparatus therefor with halogens or halogen-containing compounds with ClO2 or chlorites with ClO2/Cl2 and other bleaching agents in a multistage process

Definitions

• the invention relates to a process for the preparation of chemical pulp for bleaching.
• delignification is an operation which consists in removing the maximum of the lignin contained in the fibers. To remove residual lignin and / or degraded by this treatment, the dough must be prepared for the actual bleaching.
• a second type of process consists in treating the dough by means of oxygen in an alkaline medium.
• this process makes it possible to recycle the effluents, on the other hand, in practice, one hardly exceeds a lignin extraction rate close to 50%, in order to avoid oxidation and therefore the degradation of the cellulose by l 'oxygen. (see TAPPl-June 1981 Vol. 64 N ° 6 - pages 91 et seq.).
• US-A-4,402,788 confirms the practice of chlorination using amounts of absorbed chlorine equal to about 4 to 7% and the need to operate at low temperature if one wishes to avoid degradation of the lignocellulosic material that results from hot chlorination, however, carried out at a still relatively low temperature of around 70 ° C before the hydrogen peroxide intervenes.
• the patent FR-A-2 322 235 teaches that a chlorination before action of hydrogen peroxide in a complex sequence for the complete bleaching of cellulose, can only be profitable if it is both partial and of low level by being carried out, even with a reduced amount of chlorine, on a lignocellulosic material having a low consistency, less than 5%, and cold once again.
• the invention overcomes these drawbacks. It relates to an improved process for the preparation for bleaching by means of a compound containing active chlorine then by means of a compound containing oxygen, which is more economical to use, and which makes it possible to achieve improved delignification rate and whiteness.
• chlorine pretreatment inhibits the degradation that normally occurs during peroxide bleaching.
• the method according to the invention makes it possible to achieve an excellent degree of pre-bleaching without, however, degrading the cellulose.
• the chlorine concentration must be between 0.8 and 1.5% by weight of the weight of the pulp.
• the temperature of the chlorine pretreatment were less than 50 ° C., this would pose problems from a practical point of view, in particular for making use of the recycling effluents which are at least at this temperature. Similarly, if this temperature exceeds 100 ° C, it would be necessary to use special devices and a supply of calories, which would make the pretreatment difficult to carry out.
• the temperature of this chlorine pretreatment must be between 70 and 90 ° C. If the temperature exceeds 90 ° C, there is a tendency to degrade the cellulose without appreciably improving the pre-bleaching. If this temperature is below 70 ° C, the treatment loses its effectiveness.
• the method according to the invention essentially resides in a particular selection of the operating conditions of a known method of treatment in several phases, one with chlorine, the other using an oxygenated compound. Thanks to this selection in the operating conditions, this pre-bleaching unexpectedly ensures the protection of the cellulose while allowing the recycling of the effluents after the treatment with the oxygenated compound.
• the chlorination stage being carried out hot, the recycling of these effluents containing very little chlorides in the washing of the unbleached pulp does not in fact pose any problem.
• the method according to the invention has overcome this prejudice because one could not expect that by using a similar but different chlorine concentration on a paste having a particular consistency and at an appropriate temperature, the degradation phenomena are more observed caused by both chlorination and oxidation by the oxygenated compound.
• the levels of reagents indicated will be expressed in percent (%) by weight relative to the weight of the paste counted in dry.
• a witness is produced by operating in the following manner.
• a commercial kraft pulp, of resinous wood of Kappa index 30 (standard NF-T-12018) is treated, the degree of cellulose polymerization (DP) of which is 1600 (TAPPI-T-230 of 76) with oxygen in an alkaline medium under the following conventional and industrial conditions: 0.5% of magnesium sulfate was introduced as a protector for cellulose.
• the Kappa index is reduced to 14.0 and the DP to 1400.
• Example 2 The same kraft pulp is used as in Example 1. The latter is treated, before the oxygen treatment, with 1% of chlorine gas, at 70 ° C., for ten minutes, the pulp concentration being 10%.
• Example 1 After washing, the oxygen treatment is carried out with a 3% sodium hydroxide solution, the other conditions remaining those of Example 1.
• the Kappa index obtained is 9.7 and the DP, instead of falling to 1280 as in Example 1, remains at 1350.
• the degree of polymerization of the cellulose remains at a good level, which allows the mechanical properties of the pulp to be preserved.
• Example 2 is repeated by simply modifying the temperature of the pretreatment with chlorine which is brought to 90 ° C.
• the Kappa index obtained is 8.5 and the DP of 1450.
• Example 2 is repeated, increasing the soda level to 4% during the oxygen treatment.
• the Kappa index obtained is 7.9 and the DP only drops to 1300.
• the Kappa indices obtained in Examples 3 and 4 are of the same level as those obtained by the conventional chlorosodation process (CE) in which approximately 6% chlorine is used.
• Example 2 is repeated while removing the oxygen.
• Example 2 the use of oxygen as a delignification treatment agent has been described. It is also possible to use other oxygenated compounds, such as hydrogen peroxide.
• the method according to the invention requires a low consumption of reagent.
• CE chlorosodation
• the comparison with the conventional treatment of chlorosodation (CE) shows that practically identical performance, the chlorine level used in the process according to the invention represents only a quarter, even a sixth of that of this treatment (CE).
• the oxygen consumption in the process according to the invention (2 to 3% maximum) is significant, but the cost of this consumption is low compared to the savings made on chlorine, so that the economic balance of the process is largely positive.
• the delignification process according to the invention is applicable to any type of chemical pulp regardless of the starting plant (softwood or hardwood, annual plants, etc.).

Landscapes

• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Wood Science & Technology (AREA)
• Paper (AREA)
• Pharmaceuticals Containing Other Organic And Inorganic Compounds (AREA)
• Nitrogen Condensed Heterocyclic Rings (AREA)
• Medicines Containing Antibodies Or Antigens For Use As Internal Diagnostic Agents (AREA)

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Applications Claiming Priority (2)

Publications (3)

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• 1984
  • 1984-10-25 FR FR8416518A patent/FR2572431B1/fr not_active Expired
• 1985
  • 1985-10-22 AT AT85420187T patent/ATE35433T1/de not_active IP Right Cessation
  • 1985-10-22 DE DE8585420187T patent/DE3563548D1/de not_active Expired
  • 1985-10-22 EP EP85420187A patent/EP0180529B2/fr not_active Expired - Lifetime
  • 1985-10-22 DE DE198585420187T patent/DE180529T1/de active Pending
  • 1985-10-23 FI FI854148A patent/FI82726C/fi not_active IP Right Cessation
  • 1985-10-24 ES ES548166A patent/ES8606557A1/es not_active Expired
  • 1985-10-24 CA CA000493708A patent/CA1273755A/fr not_active Expired - Lifetime
  • 1985-10-25 AU AU49108/85A patent/AU576394B2/en not_active Ceased
  • 1985-10-25 JP JP60239261A patent/JPS61102495A/ja active Pending

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