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

Definitions

• salts ofhypochlorous acid, H010 and from chlorates, salts of chloric acid, H0103.
• the improved bleaching process of my invention consists essentially of introducing chlorine into an aqueous solution of a chlorite while this solution, the bleaching bath, is in contact with the cellulosic material to be bleached.
• This bleaching operation may be carried out as a single operation, or as a series of repeated operations. It may, with particular advantage, bq used to complete a bleaching opera n initiated by bleaching the cellulosic material to a point short of substantial degradation with orlne or a hypochlorite.
• bq used to complete a bleaching opera n initiated by bleaching the cellulosic material to a point short of substantial degradation with orlne or a hypochlorite.
• the proportion of chlorine used in conjunction with the chlorite in carrying out my invention should with advantage approximate 25%-30% of the amount corresponding to the available chlorine content 01' the chlorite used and should not exceed about 50% of this amount.
• a proportion of 25% of the amount corresponding to the available chlorine content of the chlorite is the proportion indicated by the type reaction cited previously. Frequently, however, a somewhat larger proportion is necessary to efiect complete reaction of the chlorite present, and within the limit indicated the use of such an excess does not seriously impair the results obtained.
• the bleaching operation of my invention may be carried out over a wide range of temperature and a wide range of alkalinity and acidity.
• the bleaching proceeds with suiiicient rapidity at ordinary temperatures or at moderately elevated temperatures to permit substantial savings in heat and in the time required for heating as compared to operations requiring substantially elevated temperatures. Since the acidity or alkalinity of the bleaching bath is not usually critical,
• Example I A kraft pulp with a bleach demand of 12% was chlorinated, in aqueous suspension, with 10% (by weight) of chlorine, this'being the maximum proportion of chlorine which could be used without substantial degradation of the pulp. This partially bleached pulp was then resuspended in water, a 5% suspension, containing in solution a proportion of sodium chlorite corresponding to 1.5% (by weight) available chlorine and 0.45% (by weight) of chlorine was introduced into this solution, the rate of chlorine introduction being adjusted so that the total was introduced over about 30 minutes. The bleaching action was permitted to continue for about 90 minutes after the introduction of chlorine had been completed. The temperature of the bleach bath was maintained at about 20 C. and the pH of the bleaching bath was held at about 4.2 by appropriate additions of sodium acetate-acetic acid as buffers.
• Example 11 A kraft pulp with a bleach demand of 12% was chlorinated, in aqueous suspension, with 10% (by weight) of chlorine, this being the maximum proportion of chlorine which could be used without substantial degradation of the pulp. This partially bleached pulp was then resuspended in water, a 5% suspension, containing in solution a proportion of sodium chlorite corresponding to 1.5%(by weight) available chlorine and a total of 0.36% (by weight) of chlorine was introduced into this solution at intervals while maintaining a temperature of about 40 C. The pH of the bleaching bath, uncontrolled, remained within the range 7.2-8.3.
• Example III A sulfite pulp with a bleached demand of 7% was bleached in successive stages, first in a 3% aqueous suspension containing in solution an amount of sodium chlorite corresponding to a concentration of available chlorine equal to 2.2 g. per liter with introduction of 1.8% of chlorine while maintaining a temperature of 10-15 C. over a period of 4 hours and 45 minutes and, second, a 13% aqueous suspension containing in solution an amount of sodium chlorite corresponding to 2% available chlorine on the weight of the pulp with introduction of 0.6% of chlorine while maintaining a temperature of 15 C, over a period of 1 hour.
• Example IV A sulfite pulp with a bleach demand of 7% was bleached in successive stages, first in a 3% aqueous suspension to which 4.2% of chlorine was added over a period of 2 hours 10 minutes while maintaining a temperature of 20 C. and second, in a 13% aqueous suspension containing in solution an amount of sodium chlorite corresponding to 2% available chlorine with introduction of 0.6% chlorine while maintaining a temperature of 18-23 C. for a period of 4 hours and 45 minutes.
• the pH value of the bleaching bath ranged from 3.8 to 11.5.
• the bleaching process of my invention is also useful in the bleaching of other cellulosic materials, such as cotton linters, cotton textiles and rayon.
• cellulosic materials such as cotton linters, cotton textiles and rayon.
• the following examples will illustrate applications of the present invention to such cellulosic materials:
• Example V g. of cotton linters were placed in a water solution containing 3 g. available chlorine in the form of sodium chlorite and adjusted to pH 4. 0.9 8. of chlorine were added as chlorine water bringing the liquid volume to 1.9 l. The mass was heated to 55C. and maintained at that temperature for 3 hours from the time heating was started. The linters were then washed.
• Example VI 100 g. of cotton linters were placed in a water solution containing 1.5 g. available chlorine in the form of sodium chlorite. 0.45 gof chlorine was added as chlorine water bringing the liquid volume to 1.9 l. The mass was heated to 40 C. and maintained at this temperature for 3% hours. The linters were then washed.
• Example VII 25 g. of viscose rayon were placed for hour at room temperature in a solution containing 1.6 g. available chlorine in the form of sodium chlorite to which was added 0.4 g. chlorine as chlorine water. The final volume was 500 cc. The rayon was then washed.
• Example VIII 25 g, of viscose rayon were placed for /2 hour at 60 C, in a solution containing 1.6 g. available chlorine in the form of sodium chlorite to which was added .4 g. chlorine as chlorine water. The final volume was 500 cc. The rayon was then washed.
• Example IX 1 yard of cotton cloth weighing about g. was immersed in a solution containing 3 g. available chlorine in the form of sodium chlorite to which was added 0.9 g. of chlorine as chlorine water bringing the volume to 1.9 l.
• the mass was heated to 57 C. and maintained at that temperature for 3 hours from the time heating was started.
• the cloth was then washed.
• the breaking strength of the bleached cloth was 44.8 while that of the unbleached was 48.9.
• Example X 1 yard of cotton cloth weighing about 110 g. was immersed in a solution containing 1.5 3. available chlorine in the form of sodium chlorite which had been adjusted to pH 4 before 0.45 g. chlorine were added. The final volume was 1.9 l. The action was allowed to continue for 1% hours at 38-45" C. after which the cloth was washed. The breaking strength of the bleached cloth was 43.5 while that of the unbleached was 44.6.
• Chlorine to be introduced into the aqueous solution of a chlorite in contact with a cellulosic material to be bleached in accordance with my invention, maybe introduced as chlorine gas or as chlorine water, although in the latter case due allowance must be made for the increased volume of the bleaching bath incident to such addition of water with the introduced chlorine.
• the bleaching bath will contain hypochlorite ions, the result of dissociation of hypochlorous acid in the first and the result of dissociation of the hypochlorite in the second.
• hypochlorite ions the result of dissociation of hypochlorous acid in the first and the result of dissociation of the hypochlorite in the second.
• the preliminary bleach is carried only to a point short of that at which substantial degradation of the celluloflc material would be involved, and is then completed, without degradation of the cellulosic material, by introducing chlorine into an aqueous solution 01 a chlorite in contact with the thus partially bleached cellulosic material.
• the improvement which comprises completing the bleaching by introducing free chlorine into an aqueous solution of a chlorite in contact with the material to be bleached and controlling the proportion of chlorine used in conjunction with the chlorite so as not to exceed approximately 50% of the amount corresponding to the available chlorine content or the chlorite used.
• the improvement which comprises bleaching the material to a point short of substantial degradation 3.
• the 10 improvement which comprises completing the bleaching by introducing gaseous chlorine into an aqueous solution of a chlorite in contact with the material to be bleached, and controlling the proportion of chlorine used in conjunction with the chlorite so as not to exceed approximately 50% of the amount corresponding to the available chlorine content of the chlorite used.

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• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Wood Science & Technology (AREA)
• Paper (AREA)
• Chemical Or Physical Treatment Of Fibers (AREA)

Priority Applications (3)

Applications Claiming Priority (1)

Publications (1)

Family

ID=22583603

Family Applications (1)

Country Status (3)

Cited By (5)

Families Citing this family (1)

• 1937
  • 1937-09-01 US US161969A patent/US2235837A/en not_active Expired - Lifetime
• 1938
  • 1938-08-17 GB GB24277/38A patent/GB519522A/en not_active Expired
  • 1938-08-17 FR FR842235D patent/FR842235A/fr not_active Expired

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