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
  • D21C9/142—Bleaching ; Apparatus therefor with halogens or halogen-containing compounds with ClO2 or chlorites with ClO2/Cl2 in a multistage process involving ClO2/Cl2 exclusively
• • 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
  • D21C9/1026—Other features in bleaching processes

Definitions

• I361 Tieferences Cited UNITED STATES PATENTS 1,890,179 12/1932 l-lelder 162/25 2,186,034 1/1940 Murdock 162/89 3,472,731 10/1969 Liebergott et a1. 162/89 OTHER REFERENCES Casey, .l. P Pulp and Paper, 2nd Edition, Volume I, p. 102, lnterscience Pub. 1960.
• the pulp may be fonned from any suitable lignified vegetable matter, examples of which include softwood, hardwood, bagasse, cereal straws and bamboo.
• this invention is directed to the production of partially delignified pulp, partially bleached pulp and fully bleached pulp.
• partially delignified pulp is intended to mean the product obtained by the partial removal of the residual lignin remaining in the pulp after digestion, by means other than by digestion.
• Softwood soda pulping to produce easily bleachable pulp has been found to be no longer practical since to produce softwood soda pulps of acceptably low lignin content, a very long cooking period is required in which the pulps obtained suffer severe degradation and a high yield shrinkage.
• the strength properties of such pulp are substantially inferior to those of kraft pulp.
• Soda pulps of higher lignin content are very resistant to bleaching by conventional liquid phase bleaching techniques, and, in fact, it has been found that the quantity of chemicals required to achieve bleaching is far too great to be commercially attractive.
• kraft pulping suffers the principal disadvantage of the production of malodors which occur due to the formation of hydrogen sulfide and organic sulfur compounds during the kraft cook.
• the necessity for reducing or eliminating such air pollution from kraft mills has now become a serious and costly problem.
• a principal object, therefore, of the present invention is to provide a process for producing partially dilignified pulps, partially bleached pulps, and fully bleached pulps using soda pulping, such pulpsbeing suitable as a replacement for unbleached kraft pulps, semibleached kraft pulps and fully bleached kraft pulps.
• An object of another aspect of this invention is to provide a process for the production of pulp wherein air pollution by malodors is no longer a factor.
• a process for the preparation of pulp which comprises. the steps of: (a) cooking a lignified vegetable material in an alkaline solution containing predominantly sodium hydroxide in a modified cooking step at a temperature, and for a time sufficient to give a yield significantly higher than that normally corresponding to a bleachable pulp for the lignified vegetable material being treated; and (b) at least partially delignifying the cooked pulp in defiberized form by means of a high-density gaseous treating procedure.
• the yield significantly higher than that normally corresponding to a bleachable pulp is at least 48 percent, to give a pulp having a lignin content more than 5 percent.
• the minimum yields for other lignified vegetable material are given in the following table:
• the first essential step of the process of broad aspects of this invention is a modified conventional soda-cooking step.
• the step is carried out under conditions well known to those skilled in the art, with the modification that the cooking conditions are deliberately selected to be such that the yield is significantly higher than that normally corresponding to a bleachable pulp for the lignified vegetable material being treated.
• These modified conditions can be readily chosen by a person skilled in the art.
• Exemplary modifications of the process steps include a reduced cooking time, reduced liquor concentration, reduced maximum cooking temperature, or any combinations thereof.
• the second essential step of the process of broad aspects of this invention is that the pulp produced by the modified sodacooking step is subjected to a high-density gaseous treatment, while it is in defiberized form, in order to delignify the pulp, either partially or completely.
• all or a portion of the cooked material may be subjected to a defiberization treatment.
• the cooked material may be screened and if the quantity of rejects is less than about 2 percent, the rejects may be discarded or be returned to the cooking step, and the accepted material may be directly subjected to the aforementioned high-density gaseous treatment. If the rejects are higher than about 2 percent, they would be defiberized and added to the accepted material.
• This defiberization treatment is most usually effected by mechanical means, such as by the action ofa disc refiner.
• an essential step in the process ofthis invention is that the cooked pulp, in defiberized form, is then delignified, either partially or completely by means of a high-density gaseous treatment.
• a high-density gaseous treatment may be carried out according to a first aspect of this invention by treating the pulp with gaseous chlorine followed by an alkaline extraction according to the following procedure.
• Such process for the high-density gaseous treatment comprises pretreating the cooked pulp by the steps of: (l) continuously passing the cooked pulp which should be in the form of moist fluff through a first zone of an atmosphere containing excess chlorine; (2) limiting the residence time within that first zone (usually for a time of the order of 20 seconds to 5 minutes) to such an extent that less than the potential amount of chlorine is acquired by the flufi (and usually until about 50-85 percent of the potential amount of chlorine is acquired by the fluff); and (3) continuously passing the fluff including the chlorine which has been acquired by the fluff through a second zone of an essentially chlorine-free atmosp'here under such retention time conditions as to permit the amount of said chlorine to react with said fluff (usually for a time of about 1 to 15 minutes); and then carrying out the ad ditional steps of: (4) washing the chlorinated pulp; and (5) further treating the washed pulp with an alkaline reagent.
• a preferred alkaline reagent is gaseous ammonia.
• the alkaline treatment step is preferably carried out as follows: l) washing the pretreated pulp and finely dividing tion time generally of the order of about 1 to about 30 minutes;.and (4) maintaining the temperature during the reaction time within the range, usually, of about 60"-100 C.
• Another high-density gaseous delignification treatment is by treating the soda pulp with gaseous chlorine dioxide followed by an alkaline extraction according to the following procedure.
• Such process for the high-density gaseous treatment comprises pretreating the cooked pulp by the steps of: (1) treating the defiberized pulp which should be in the form of a fluff, generally at a consistency of 20-60 percent with chlorine dioxide, which may contain varying proportions of chlorine gas, diluted to less than 100 mm. mercury partial pressure with air, nitrogen, steam or an inert gas, at a retention time generally of the order of 20 seconds to 60 minutes and at a temperature which usually varies between 15 C. and 100 C.; and then carrying out the additional steps of (2) washing the pretreated pulp; and (3)further treating the washed pulp with an alkaline reagent.
• a preferred alkaline reagent is gaseous ammonia, in which case the alkaline treatment step is preferably carried out as follows: (1) washing the pretreated pulp and finely dividing the washed pulp into fiber aggregates generally at a moisture content of about 40-85 percent; (2) preheating the fiber aggregates to a temperature generally in the range of 60-l00 C.; (3) exposing the preheated fiber aggregates to an atmosphere comprising gaseous ammonia, either undiluted or diluted with steam, air, nitrogen, or other inert gas for a reaction time generally of the order of about 1 to about 30 minutes; and 4) maintaining the temperature during the reaction time within the range, usually, of about 60-100 C.
• the pulp after being partially delignified may be subjected to further delignification
• Such process for the further high-density gaseous treatment comprises the steps of: (1) adjusting the moisture content of the fibers to a level usually within the range of from 60 to 70 percent; (2) exposing the fiber aggregate to chlorine dioxide gas diluted with an inert solvent where the partial pressure of chlorine dioxide is 100 mm. of mercury or less, for a period which usually ranges from about 5 to about 30 minutes at a temperature which usually ranges from about 65 to about 100 C.; and 3) controlling the pH-of the mixture so that final pH is preferably in the range offrom 3.5 to 6.5.
• EXPERIMENT A 42 g./l.).
• the liquor-to-wood ratio was 5:1.
• the digester was brought up to maximum temperature, 170 C., within 90 minutes.
• One cook (Pulp No. l) was terminated after 30 minutes of cooking (temperature 170C. and 100 p.s.i.g. pressure); the other (Pulp No. 11) after 10 minutes of cooking (temperature 170 C. and 100 p.s.i.g. pressure).
• the resultant pulps were fiberized by action of a discrefiner (one pass ata plate separation of 0.01 inch). Cooking and defiberizing produced pulps with the following characteristics:
• EXAMPLE 11 One portion of the chlorinated, extracted and washed pulp produced in example 1 was pressed to 35 percent consistency. The pressed pulp was sprayed with a solution of sodium carbonate equal to 1.25 percent ofthe weight of pulp (B.D. basis) and sufficient water to reduce the consistency to 30 percent. The pulp was then shredded and heated to C. The
• Pulp No. l Another portion of Pulp No. l was shredded. at 30 percent consistency and treated with gaseous chlorine dioxide diluted with nitrogen; 4.3 percent chlorine dioxide on the weight of dry fiber was added to the pulp, maximum temperature was 60 C., retention time 1 minute. After washing, the pulp was shredded at percent consistency and treated with 2.5 percent of ammonia based on dry fiber (in a mixture of ammonia and steam) for 1 minute at 100 C. and washed again. Characteristics of the partially delignified pulp were: Kappa number 4.2, Elrepho brightness 45, visual, efiiciency 58.9 percent, yield on wood 48.6 percent.
• EXAMPLE V One portion ofPulp No. 11 was shredded at 30 percent consistency and treated with gaseous chlorine (158% C1 on pulp o.d. basis), maximum temperature C. for 1 minute,
• Characteristics of the partially delignified pulp were: Kappa number 14.7, brightness 36, visual efficiency 53.7 on the scale of the Elrepho meter, and yield on wood 48.6 percent.
• Pulp No. 11 Another portion of Pulp No. 11 was shredded at 30 percent consistency and treated with gaseous chlorine dioxide diluted with nitrogen; 6.5 percent chlorine dioxide on the weight of dry fiber was added to the pulp, maximum temperature was 97 C., retention time 1 minute. After washing, the pulp was shredded at 20 percent consistency and treated with 4.5 percent of ammonia based on dry fiber (in a mixture of ammonia and steam) for 1 minute at 100 C. and washed again. Characteristics of the partially delignified pulp were: Kappa number 4.8, Elrepho brightness 44, visual efiiciency 57.2 percent, yield on wood 52.7 percent.
• step (B) comprises pretreating the pulp by l. continuously passing the defiberized pulp in the form of moist fluff which is at a moisture content of about 4085 percent through a first zone of an atmosphere containing excess chlorine;
• step (C) comprises the step of pretreating the defiberized pulp in the form of a flufi which is at a moisture content of -40 percent with chlorine dioxide diluted to less than mm. mercury partial pressure with a nonreactive gas, at a retention time of the order of 20 seconds to 60 minutes and at a temperature which varies between 15 C. and 100 C.; and effecting the further steps of (2) washing the pretreated pulp and (3) further treating the washed pulp with an alkaline reagent.
• nonreactive gas is air, nitrogen, steam, or an inert gas.
• ammonia is diluted with steam, air, nitrogen, or other inert gas.
• ammonia is diluted with steam, air, nitrogen, or other inert gas.

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Citations (3)

• 1967
  • 1967-12-15 CA CA849982A patent/CA849982A/en not_active Expired
• 1968
  • 1968-10-15 US US767829A patent/US3617432A/en not_active Expired - Lifetime
  • 1968-11-29 SE SE16324/68A patent/SE358679B/xx unknown
  • 1968-12-13 FI FI3584/68A patent/FI53007B/fi active

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