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

• This invention relates to an improved method of bleaching cellulosic materials. More particularly, it relates to a method of bleaching woodpulp to high brightness and good color stability without significant loss of strength.
• bleaching has been effected by multi-stage processes which may begin with treatment of the unbleached pulp in water with chlorine. Although subsequent stages of the multi-stage process may carry out bleaching without significant damage to pulp strength (often measured by pulp viscosity) or loss of color stability, the chlorination often decreases pulp strength and makes the pulp susceptible to undesirable yellowing with age.
• a further object is to bleach woodpulp to a brightness greater than that produced by prior methods and to produce a pulp of good color stability and of a strength substantially that of the unbleached fibers.
• unbleached woodpulp is bleached with a mixture of chlorine and chlorine dioxide, followed by subsequent treatments with alkali and chlorine dioxide.
• a mixture of chlorine and chlorine dioxide are realized fully only after the subsequent treatment with chlorine dioxide.
• woodpulp of a consistency between about two and twelve percent is first bleached with a sutficient amount of mixed chlorine and chlorine dioxide to provide the oxidizing power, expressed in terms of available chlorine, for bleaching the color bodies associated with the pulp.
• the quantity of available chlorine used is dependent on the kind of pulp and may be ascertained by known techniques.
• One pound of chlorine is equivalent to one pound of available chlorine and one pound of chlorine dioxide is equivalent to 2.63 pounds of available chlorine.
• chlorine dioxide and chlorine may be employed in such a ratio that each furnishes about half of the available chlorine provided the mixture, it is preferred that from about 20 to about percent (by weight) of the available chlorine provided by the mixture be furnished by the chlorine dioxide, and it is even more preferred that from about 40 to about 95 percent (by weight) of said available chlorine be furnished by the chlorine dioxide.
• the temperature of the first stage bleaching is from 0 to 35 degrees centigrade and the bleaching takes from about 5 to 60 minutes.
• various amounts of available chlorine may be employed to bleach out the color bodies present, at a three percent consistency the available chlorine used may be 3 to 10 percent (3 to 10 pounds of available chlorine per pounds of dry pulp).
• the pulp is treated with chlorine dioxide.
• the pulp is of a consistency of from about five to fifteen percent and the amount of chlorine dioxide employed is from about 0.1 to 2 percent of the pulp.
• the chlorine dioxide treatment is usually undertaken at a temperature from 30 to 90 degrees centigrade and lasts for from 5 to 300 minutes.
• the pulp may be subjected to other bleachings, in addition to the treatments with mixture of chlorine and chlorine dioxide, hot alkali extraction and chlorine dioxide mentioned.
• hot alkali extraction and before chlorine dioxide bleaching the pulp may be treated with hypochlorite or hypochlorite followed by peroxide.
• hypochlorites may be used, those of the alkali and alkaline earth metals, such as sodium and calcium hypochlorites being preferred.
• the woodpulp is of a consistency of five to fifteen percent and the hypochlorite bleaching is carried out at a temperature of about 20 to 70 degrees centigrade for about 5 to minutes, suflicient hypochlorite being utilized to provide from about 0.1 to 4 percent available chlorine based on the weight of the pulp.
• the subsequent treatment with peroxide if employed, utilizes from 0.05 to 4 percent of hydrogen peroxide, based on the weight of the pulp.
• the pulp treated is at a consistency of 5 to 35 percent and is treated for S to 300 minutes at a temperature of about 3 to 90 degrees centigrade.
• the first step is a bleaching of woodpulp with a mixture of chlorine and chlorine dioxide, as described, followed at some suitable point in the overall bleaching process by alkali and chlorine dioxide treatments.
• additional bleachings with chlorine dioxide may be effected and additional extractions with alkali may be advantageous.
• Each sample of pulp was then treated with 2 percent NaOH based on the dry weight of the pulp, at 15 percent consistency, at 60 degrees centigrade for two hours and washed with water.
• each sample was treated with 0.5 percent chlorine dioxide based on dry pulp, at 6 percent consistency, at 70 degrees centigrade for three hours and washed with water.
• the pulp is usually preferably washed with water after the various treatment stages. Such washings are effected to remove substantially all the excess chemicals of the previous treatment.
• the brightness of the samples (expressed in terms of the General Electric Brightness Standard) was determined before and after heating in an oven at 105 degrees centigrade for 18 hours to simulate ageing. The results are shown in Table 'I.
• the second stage of treatment for all samples was with 2 percent NaOH on a dry pulp basis, at 15 percent consistency, and 60 degrees centigrade for two hours.
• chlonne dioxide ageing ageing ccntipoises EXAMPLE 4 An unbleached kraft pulp made from a mixture of softwoods native to central British Columbia was treated in three ways with total weights of chlorine and chlorine dioxide equivalent to 7 percent available chlorine based on the weight of the pulp, percent chlorine, 63.7% chlorine and 36.3% chlorine dioxide by weight of the mixture and 100 percent chloride dioxide being used. In each case, the treatment was carried out at 3 percent consistency at 25 degrees centigrade for one hour. After washing, the bleaching was followed by hot caustic ex traction with 2.5 percent NaOH based on the weight of the pulp, at 15 percent consistency, and 60 degrees centigrade for two hours and another washing.
• H 1 percent available chlorine as hypochlorite based on the weight of pulp, 6 percent consistency, 40 degrees centrigrade, 3 hours, and pH 10;
• P 0.38 percent H based on the weight of pulp, 6 percent consistency, 70 degrees centrigrade, 3 hours, buffered at a pH of 10.5;
• E 2.0 percent NaOH based on the weight of pulp, 15 percent consistency, 60 degrees centrigrade, 3 hours;
• D various percentages of C10 based on the weight of pulp as shown in Table IV as subscripts, 6 percent consistency, 70 degrees centrigrade, 3 hours.
• the present invention produces snlfite woodpulp of 88 to 89 percent brightness, as shown in Example 1 and kraft woodpulp of brightness of 82 to 85 percent as shown in Examples 2, 3 and 4 in only three stages.
• pulp viscosities which are an indication of the amount of degradation of the woodpulp fibers
• the pulp viscosity is higher, the more chlorine dioxide and the less chlorine are used in the chlorination stage of the process of this invention.
• use of chlorine dioxide only in the chlorination stage produces a pulp of lower brightness. Therefore, higher brightness and better color stability of the pulp is obtained with a mixture of chlorine and chlorine dioxide in the chlorination stage of the process of this invention while still retaining more of the inherent pulp strength than is obtained with chlorine alone.
• the method of this invention bleaches different types of wood pulp to higher brightness with better color stability than may be obtained with the methods now in use, with the additional advantage that the amount of degradation of the wood pulp fibers is very low.

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• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Wood Science & Technology (AREA)
• Paper (AREA)
• Polysaccharides And Polysaccharide Derivatives (AREA)

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Citations (3)

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  • NL NL134770D patent/NL134770C/xx active
• 1964
  • 1964-07-08 FR FR981098A patent/FR1407286A/fr not_active Expired
  • 1964-07-08 CH CH894664A patent/CH486596A/de not_active IP Right Cessation
  • 1964-07-10 NL NL6407863A patent/NL6407863A/xx unknown
  • 1964-07-10 DE DE19641546226 patent/DE1546226B1/de active Pending
  • 1964-07-10 SE SE8508/64A patent/SE301583B/xx unknown
  • 1964-07-10 AT AT597864A patent/AT265008B/de active
  • 1964-07-11 FI FI641492A patent/FI43808C/fi active
  • 1964-07-11 ES ES0301960A patent/ES301960A1/es not_active Expired
  • 1964-07-13 JP JP39039203A patent/JPS5235761B1/ja active Pending
  • 1964-07-13 GB GB28752/64A patent/GB1007697A/en not_active Expired
  • 1964-08-18 OA OA50265A patent/OA00199A/xx unknown
• 1968
  • 1968-12-02 US US780593A patent/US3536577A/en not_active Expired - Lifetime

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