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
  • D21C9/1005—Pretreatment of the pulp, e.g. degassing the pulp
• • 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
  • D21C9/1063—Bleaching ; Apparatus therefor with compounds not otherwise provided for, e.g. activated gases

Definitions

• the present invention relates to a procedure for prebleaching cellulose pulp that has been obtained by a chemical process.
• the chlorine treatment as the first step in the bleaching process for chemical pulps, can be replaced with a phenol treatment.
• the phenol treatment affords numerous advantages over the use of chlorine. Firstly, the phenol can be recovered and reused, whereby there will be no emission of bleaching residues detrimental to the environment.
• the procedure of the invention renders possible also recovery of tine residual lignin that has been detached from the cellulose in the bleaching process, in addition to the phenol.
• phenol in treating substances containing cellulose is not novel in itself.
• cellulose pulp has been made from wood by treating wood chips with a phenol solution containing a strong acid, e.g. hydrochloric acid, acting as a catalyst.
• a strong acid e.g. hydrochloric acid
• said patents relate to solubilizing lignocellulose, such as wood, not to cellulose bleaching.
• phenol in prebleaching cellulose manufactured by chemical methods is not known in the art.
• the procedure of the invention is characterized in that said cellulose pulp is treated with phenol at elevated temperature, whereafter said cellulose pulp, possibly after washing, is bleached by single or multiple-step bleaching known in itself in the art.
• a phenol treatment is applied in the prebleaching of chemical pulp.
• pulp is concerned which has already been defibrated and in which the residual lignin that is present has changed under effect of the digesting chemicals so that condensation with phenol no longer occurs. Therefore a substantially lower catalyst content and lcwer temperature suffice for deteching the lignin frcm the defibrated cellulose.
• the digesting process proper a sulphate process for instance, may be discontinued earlier than conventionally usual without detriment to the quality characfteristics of the ultimate pulp, and hereby the digesting capacity can be substantially increased.
• phenol also dissolves extractible substances contained in the cellulose pulp. This is of significance particularly regarding the quality of hardwood cellulose because extractible substances cause yellow discolouration of the cellulose and impairment of the absortivity, which is importpnt in view of the fluff pulp, and quality inpairment of the soluble cellulose.
• Chemical pulps are here understood to be those pulps which have been obtained by chemical digestion methods. These methods include e.g. the sulphate process various sulphite processes, and the soda process.
• prebleaching as taught by the invention is simply carried cut in that the chemical cellulose pulp from the digesting process is treated with a phenol solution a sufficiently long time and at high enough temperature, whereafter the pulp is conducted, after removal of the treatment liquid, to further bleaching steps.
• the phenol content in the aqueous solution may vary so that the water/phenol proportion is in the range from 3:7 to 1:1.
• the phenol solution preferably also contains a small quantity of an acid, advantageously hydrochloric acid, of which the quantity may vary in the range of 0.1-1.0%, preferably 0.2-0.5%, referred to the water quantity in the solution. Excessive acid quantity causes hydrolysis of the cellulose and hemicelluloses.
• the treatment temperature is not critical from the viewpoint of the invention, but since phenol forms an azeotrope with water, with boiling point about 100°C, it is advantageous to perform the treatment at this temperature.
• the appropriate treatment temperature is thus e.g. 98-102°C.
• the treatment time naturally depends on the chemical concentrations and temperatures employed, but it is normally enough if the temperature is raised to treatment temperature within 30-60 min., and the treatment time at normal temperature may vary from 1 to 60 min.
• the phenol treatment solution is removed from the cellulose pulp after its temperature has been raised to treatment temperature, and it is replaced with fresh solution.
• the prebleaching will then be enhanced because a greater amount of lignin can be removed without substantially affecting the viscosity characteristics.
• the procedure of the invention is applicable both in the case of hardwood and softwood celluloses. Especially in the case of hardwood cellulose, the procedure of the invention has turned out to be advantageous because it eliminates the problems which extractible substances cause regarding the cellulose quality.
• the cellulose is washed in standard manner to be free of phenol compounds, these being returned to the beginning of the process for reuse.
• the cellulose is further conducted, possibly after washing, to further bleaching steps, which thus need not be any chlorine or hypochlorite bleaching processes: they may consist for instance of chlorine dioxide or peroxide bleaching processes.
• the washing is advantageously done with water containing phenol and with hot water.
• Table I is shown a comparison between the characteristics of the cellulose before and after the phenol treatment mentioned above.
• Table I reveals, among other things, that the viscosity of the cellulose is almost unchanged, implying that the low-molecular hemicellulose has not been dissolved and no cellulose chains have been cleaved. The average fibre length is unchanged, indicating that acid hydrolysis has not cleaved any fibres.
• Example 1 was repeated, but the hydrochloric acid content was increased to 1.0%. The quantity of removed lignin rose then to 79%, but the viscosity went down to 480, indicating that there has been substantial cleaving of carbohydrates.
• Example 1 was repeated, changing the water:phenol proportion to be 1:1. Only 32% of the lignin could then be removed from the pulp. This indicates that a greater amount of water impairs the solubilization of lignin and the efficiency of the prebleaching. The viscosity of the cellulose retained the value 1330.
• Example 4
• Example 1 was repeated with the modification that the acid content was 0.12% of the water quantity. A cellulose product was then obtained which has chlorine number 3.27, viscosity 1330. The lignin quantity removed was only 29%.
• Example 5 was repeated, replacing the treatment solution with fresh solvent after the temperature had been raised to treatment tenperature.
• the treatment time was 30 min.
• the chlorine number was 2.46 and viscosity 1030, and removed lignin quantity 52%.
• the chlorine number 1.85 and viscosity 910 were obtained, and removed lignin quantity 65%. The results indicate that it is advantageous to replace the treatment solution.

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• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Wood Science & Technology (AREA)
• Paper (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

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Citations (2)

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• 1986
  • 1986-05-28 FI FI862262A patent/FI75196C/fi not_active IP Right Cessation
• 1987
  • 1987-05-26 FR FR8707401A patent/FR2599398B1/fr not_active Expired
  • 1987-05-27 DE DE19873790278 patent/DE3790278T1/de not_active Withdrawn
  • 1987-05-27 AT AT0901387A patent/AT395027B/de not_active IP Right Cessation
  • 1987-05-27 WO PCT/FI1987/000071 patent/WO1987007314A1/en not_active Ceased
• 1988
  • 1988-01-19 SE SE8800152A patent/SE8800152L/xx not_active Application Discontinuation

Patent Citations (2)

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