US3874992A - Press alkaline extraction of cellulosic pulp - Google Patents

Press alkaline extraction of cellulosic pulp Download PDF

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US3874992A
US3874992A US399331A US39933173A US3874992A US 3874992 A US3874992 A US 3874992A US 399331 A US399331 A US 399331A US 39933173 A US39933173 A US 39933173A US 3874992 A US3874992 A US 3874992A
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pulp
consistency
extraction
bleaching
washed
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Norman Liebergott
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FPInnovations
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Pulp Paper Res Inst
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    • 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

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  • cellulosic matter may be bisulfite pulp or kraft chemical pulp. It has unexpectedly been found that when such a pretreated pulp, e.g. a chlorinated and washed pulp, is mixed rapidly with an aqueous solution of an alkali, e.g.
  • sodium hydroxide at a particularly defined concentration correlated to the Kappa number of the pulp and being within the range of about 0.5% by weight, the mixing being conducted at a consistency of up to about 12%, preferably at about 4% to about 12%, at a temperature of from about 40 to about 90C., preferably at a temperature of from about 60C to about 80C., and is substantially immediately thereafter pressed to a pulp consistency of from about 18% to about 40%, preferably to a consistency of from about 20 to about then a single extraction treatment is as effective as conventional alkaline extraction (at to C. for 1 hour), in reducing the Kappa No. of a chlorinated pulp to similar levels.
  • the procedure also is effective in the neutralization step between two or more oxidation stages. Little or no washing with water is necessary following an alkaline extraction by the process according to this invention.
  • Bleaching is a continuation of the cooking process in which the ligneous material and colouring matter which remain in the chemical pulp are removed selectively with as little degradation of the pulp fibre as possible.
  • Bleaching of the pulp has advanced to a high degree of sophistication involving single-stage and multistage procedures.
  • Bleaching of a chemical pulp is accomplished in several stages. As known in the art, a stage constitutes a phase starting with the addition and reaction of a chemical with a pulp and ends with the washing of the pulp.
  • the selection of a proper number of stages, and hence the desired sequence is determined by (a) the nature of the fibre to be bleached (softwood or hardwood), (b) the pulping process which was applied (acid, neutral or alkaline), and (c) whether the pulp is to be used for the manufacture of paper-making grades of pulp, or the manufacture of dissolving pulps.
  • the first step usually consists of treating pulp in aqueous suspension with chlorine solution in the aqueous phase; an aqueous solution of chlorine dioxide may be used either in admixture with the chlorine or in replacement of the chlorine in this first stage. It is also known that, by use of a high consistency, gas phase bleaching technique, pulp at a high consistency (about to about 60%) and in comminuted form, can be reacted with gaseous chlorine, chlorine monoxide, chlorine dioxide, ozone-peroxides and oxides of nitrogen.
  • reaction products resulting from chlorination or delignification by oxidative bleaching are removed as they are formed in those operations by means of an alkaline extraction
  • Caustic soda is a preferred agent, but other alkalis (e.g. ammonia, sodium carbonate, calcium hydroxide, etc.) have been suggested and used.
  • This alkaline treatment on pulp is generally carried out in slurry form at low consistencies ranging from about 8 to about 15% and at times varying from about 60 minutes to about 2 hours, and at temperatures ranging from about 40C to about 70C.
  • FIG. 1 is a schematic flow diagram of a convention such alkaline extraction.
  • a pulp For dissolving purposes a pulp must be of high purity, (e.g. substantially free from ash, resin and hemicelluloses) and have the right reactivity and viscosity, and an alpha cellulose content in excess of about 91%.
  • These objectives can be obtained by intensifying the alkaline extraction, in two modifications, known as hot caustic purification and cold caustic purification.
  • FIG. 2, to be described later, is a schematic flow diagram of a hot caustic purification
  • FIG. 3, to be described later, is a schematic flow diagram of a cold caustic purification.
  • An object of another aspect of this invention is the provision of such an extraction technique which is ecologically attractive in its conservation of water.
  • An object of a further aspect of this invention is the provision of such an extraction technique in which the extracted pulp is delivered at high consistency suitable for fluffing and treating with the gaseous reagent in the next bleaching stage in the manufacture of papermaking grades of pulp.
  • FIG. 1 is a schematic flow diagram of a conventional prior art alkaline extraction in the manufacture of P p P p.
  • FIG. 2 is a schematic flow diagram of a prior art hot caustic purification in the manufacture of dissolving
  • FIG. 3 is a schematic flow diagram of a prior art cold caustic purification in the manufacture of dissolving pulp
  • FIG. 4 is a schematic flow diagram of the alkaline extraction of the present invention in the manufacture of paper pulp.
  • the operating conditions vary all the way from 0.5 to 3.0 NaOH on pulp, 40 to 70C., 60 to 120 min., and 3 to 16% stock consistencies with the higher levels being generally preferred for steam and space economy.
  • the wood pulp is chlorinated in chlorinator l0 and is subjected to a Water wash and thickening in thickener 11. This provides a pulp having a consistency up to 12%.
  • the thickened pulp is mixed in a mixer 12 with steam, water and NaOI-I, in an amount of about 2 to about 5% based on the pulp.
  • the consistency of the mixture is about 10% and the temperataure is generally in the range of 60 C.
  • the mixture is passed to a reaction tower 13, where the residence time is about 1 to 2 hours. After this time the pulp is washed in a washer l4 and discharged at 15 when the NaOl-I is substantially completely used up.
  • the NaOl-I applied to the pulp is generally within the range of 0.5 to 2%, the consistency of the pulp is generally 10 to 22%, the temperature is generally within the range of 50 to 145C., and the time of treatment is generally from one-fourth to 4 hours.
  • the pulp is chlorinated in chlorinator 20 and is subjected to a wash and thickening in thickener 21. This provides a pulp having a consistency of up to 12%.
  • the thickened pulp is mixed in a mixer 22 with water and NaOl-I at a maximum concentration of 16% on the pulp.
  • the consistency during the mixing is 12 to 18% and the temperature is 70 to 120C or even higher.
  • the mixture is passed to a reaction tower 23, where the reaction residence time is 1 or 2 hours or more.
  • the product is then pressed in a press 26 to a consistency of 25 to 35% and is withdrawn at 27.
  • the pressed pulp still contains residual NaOI-I.
  • the operating conditions may be generally based on the use of 6 to 8% caustic soda solution at 3% consistency for 30 to 60 minutes at 30 to 40C.
  • the pulp is chlorinated in chlorinator 30 and is subjected to a wash and thickening in thickener 31. This provides a pulp having a consistency of up to 12%.
  • the thickened pulp is mixed in a mixer 32 with water and NaOI-I at a concentration of 9 to 16% with the pulp at a consistency of 50% at ambient temperature.
  • the mixture is passed to a purifier comprising a plurality of reaction towers 33 and presses 36 so that there are many sequences of the caustic reaction in the reaction tower and the pressing.
  • the total purification time is 1 to 2 hours.
  • the pressed pulp still contains residual NaOI-l.
  • the pulp is chlorinated in chlorinator 40 and is subjected to a water wash and thickening in thickener 41. This provides a pulp having a consistency up to 12%.
  • the thickened pulp is mixed in a mixer 42 with steam and with 0.5 to 5% NaOH based on the pulp, the mixing taking place at a consistency of less than 12%, preferably 4 to 12%.
  • the temperature is within the range of 40 to 90C., preferably 60 to C.
  • the mixing is generally completed within about 5 minutes, and no further reaction time is necessary.
  • the mixture is then substantially immediately rapidly pressed in press 46 to a consistency of about 18 to 40%, preferably 20 to 40%.
  • the pressing is generally completed within about 1 minute.
  • the pulp withdrawn at 45 requires little or no water washing and yet has no residual NaOI-I left thereon.
  • the pulp is preferably pressed to a consistency of about 20% to 40%.
  • the rapid mixing is generally completed within about 5 minutes, although longer times may be used, and the pressing is generally completed within about 1 minute, although longer times may be used.
  • an improved bleaching procedure in the manufacture of paper-making grades of pulp, comprising: (a) subjecting a comminuted pulp to a bleaching treatment; (b) subjecting the bleached pulp to a washing treatment with water; and (c) rapidly mixing the washed prebleached pulp at a consistency up to about 12% with an aqueous solution of an alkali at a concentration of 0.5 to 5% based on the pulp, and, substantially immediately thereafter, subjecting such mixture to a rapid press extraction to a consistency of about 18% to about 40%.
  • the alkali is sodium hydroxide and the concentration of NaOH is interrelated to the Kappa Number of the pulp, according to the following table:
  • the pulp is preferably pressed to a consistency of about 20% to 40%.
  • the rapid mixing is generally completed within about 5 minutes, although longer times may be used, and the pressing is generally completed within about 1 minute, although longer times may be used.
  • the bleaching of the comminuted pulp in step (a) above is carried out: (i) on a pulp pressed to a consistency of about 30% and in fluffed-up form as fibre and fibre aggregates, the bleaching agent being chlorine gas; (ii) on a pulp at a consistency of about 3.5%, the bleaching agent being chlorine in the aqueous phase; or (iii) on a pulp at a consistency of about 12%, the bleaching agent being chloride dioxide.
  • Pretreating Procedures Pretreatin g Procedure (I) Unbleached kraft pulp from coniferous wood, characterized by Roe Chlorine No. 5.6, Kappa No. 38.1, and a 0.5% CED viscosity of 24.2 was pressed to 30% consistency. The pulp was comminuted into fibre and fibre aggregates using the apparatus described in U.S. Pat. No. 3,630,828 issued Dec. 28, 1971. The pulp was then treated with chlorine gas for 1 minute (4.5% chlorine on oven dried pulp); the pH of the chlorinated pulp was 1.0. The pulp was then diluted to 1% consistency with deionized water and then brought to 30% consistency by pressing.
  • One form of apparatus which may be used in the rapid pressing procedure of broad aspects of this invention is a hydraulic press, but other types of equipment such as, for example, screw presses or rolls, are equally suitable.
  • the principal elements of one form of press are an upright cylindrical shell having a perforated removable bottom, a close-fitting inner ram, and means of applying loads to the ram. Pressures of the order of pounds per square inch of crosssection are adequate. Ten gram portion samples of the prepared pulp were treated in the following manner.
  • Pretreating Procedure (II) Unbleached kraft pulp from coniferous wood, characterized by Roe Chlorine No. 4.6, Kappa No.
  • pulp was then brought to 12% consistency by draining on a Buchner funnel fitted with a 100 mesh screen.
  • EXAMPLE 1 EFFECT OF MULTIPLE PRESSINGS ON PRESS EXTRACTION OF CI-ILORINATED PULP
  • Example 1A One portion of the chlorinated washed pulp from the Pretreating Procedure (I) was extracted with dilute sodium hydroxide (3.5% NaOI-l o.d. pulp at consistency for 1 hour at 60C.), and then washed with deionized water at 1% consistency. The washing effluent was I removed from the pulp and the colour, BOD and COD measured by appropriate tests. The pulp was then made into handsheets and the Kappa number and CED viscosity measured.
  • Example 113 One portion of the treated pulp from the Pretreating 'Procedure (I) was mixed rapidly (30 seconds) with an aqueous solution of sodium hydroxide (3.5% on o.d. pulp) at 60C. The consistency of the resulting mixture was 10%. The mixture was immediately pressed to 31% consistency, and this pressing effluent was removed from the pulp and the colour, BOD and COD measured by appropriate tests. The pulp was then washed with deionized water at 1% consistency and made into handsheets and the Kappa number and CED viscosity measured.
  • Example 1C One portion of the treated pulp from the Pretreating Procedure (I) was mixed rapidly with an aqueous solution of sodium hydroxide (3.5% on o.d. pulp) at 60C. The consistency of the mixture was 10%. The mixture was immediately pressed to 30% consistency. The effluent from the pressing was quickly remixed a second time, so that the consistency was again 10%, and the pulp repressed immediately to 29%. The pressing effluent was removed from the pulp, the colour, BOD and COD measured by appropriate tests. The pulp was then washed with deionized water at 1% consistency and made into handsheets and the Kappa number and CED viscosity measured.
  • Example 1D The pressing effluent was removed from the pulp and the colour, BOD and COD measured by appropriate tests. The pulp was then washed with deionized water at 1% consistency, and made into handsheets and the Kappa number and CED viscosity measured. The results obtained are shown in Table I.
  • Example 1E Example 1F One portion of the treated pulp from the Pretreating Procedure (I) was mixed rapidly (30 seconds) with an aqueous solution of sodium hydroxide (3.5% on o.d. pulp) at C. The consistency of the resulting mixture was 10%. The mixture was immediately pressed to 20% consistency and this pressing effluent was removed from the pulp and the colour, BOD and COD measured by appropriate tests. The pulp was then washed with' deionized water at 1% consistency and made into handsheets and the Kappa number and CED viscosity measured.
  • Example 16 One portion of the treated pulp from the Pretreating Procedure (I) was mixed rapidly with an aqueous solution of sodium hydroxide (3.5% on o.d. pulp) at 80C. The consistency of the mixture was 10%. The mixture was immediately pressed to 20% consistency. The effluent from the pressing was quickly remixed a second time, so that the consistency was again 10%, and the pulp repressed immediately to 18%. The pressing effluent was removed from the pulp, the colour, BOD and COD measured by appropriate tests. The pulp was then washed with deionized water at 1% consistency and made into handsheets and the Kappa number and CED viscosity measured.
  • Example 1H One portion of the treated pulp from the Pretreating Procedure (I) was mixed rapidly with an aqueous solution of sodium hydroxide (3.5% on o.d. pulp) at 80C. The consistency of the mixture was 10%. The mixture was then immediately pressed to 20% consistency. The pressing effluent was then mixed with the press cake so that the consistency was 10% and immediately pressed again to 20%. The effluent was again mixed with the press cake so that the consistency of mixing was 10%, and then the mixture was pressed immediately to 22%. The pressing effluent was removed from the pulp, and the colour, BOD and COD measured by appropriate tests. The pulp was then washed with deionized water at 1% consistency, and made into handsheets and the Kappa number and CED viscosity measured.
  • sodium hydroxide 3.5% on o.d. pulp
  • a significant advantage in the press extraction of the chlorinated pulp appears to be that a rapid, preferably single press extraction (i.e. taking a time, generally, of less than 1 minute) can reduce the Kappa number of a chlorinated pulp to a value which is similar to that accomplished by conventional treatment with the same quantity of caustic, at the same tem perature, but for a much shorter time than the conventional time period of 60 minutes.
  • the results in Examples 18, 1C and 1D show that two and three press extractions do not greatly reduce the Kappa number from that obtained after the first press extraction, and this is an unexpected result.
  • EXAMPLE 2 EFFECT OF MIXING CONSISTENCIES ON PRESS EXTRACTION OF CHLORINATED PULP
  • the following examples are intended to show the effect on reduction of Kappa number by mixing chlorinated and washed pulp with dilute solutions of sodium hydroxides at different mixing consistencies and and thereupon immediately pressing the mixture by a single pressing stage to consistencies of from 20 to 40%.
  • Example 2A One portion of the chlorinated washed pressed pulp from the Pretreating Procedure (I) was mixed rapidly (2 minutes) with an aqueous solution of sodium hydroxide (3.5% on o.d. pulp) at 60C. The consistency of the resulting mixture was 5%. The mixture was immediately pressed to 21% consistency in 0.39 minute. and this pressing et'l'luent was removed from the pulp.
  • the pulp was then washed with deionized water at 1% consistency, and made into handsheets, and the Kappa number and CED viscosity measured.
  • Example 28 One portion of the chlorinated washed pressed pulp from the Pretreating Procedure (I) was mixed rapidly (2 minutes) with an aqueous solution of sodium hydroxide (3.5% on o.d. pulp) at 60C. The mixture was pressed to 31% consistency in 0.52 minutes and the pressing effluent was removed from the pulp. The pulp was then washed with deionized water at 1% consistency, and made into handsheets, and the Kappa number and CED viscosity measured.
  • Example 2C Example 2D One portion of the chlorinated washed pressed pulp from the Pretreating Procedure (I) was mixed rapidly (2 minutes) with an aqueous solution of sodium hydroxide (10% on o.d. pulp) at 60C. The mixture was immediately pressed to 22% consistency (pressing time 0.33 minutes), and the pressing effluent was removed from the pulp. The pulp was then washed with deionized water at 1% consistency, and made into handsheets, and the Kappa number and CED viscosity measured.
  • Example 2E One portion of the chlorinated washed pressed pulp from the Pretreating Procedure (I) was mixed rapidly (2 minutes) with an aqueous solution of sodium hydroxide on o.d. pulp) at 60C. The mixture was immediately pressed to 30% consistency (pressing time 0.45 minute), and the pressing effluent was removed from the pulp. The pulp was then washed with deionized water at 1% consistency, and made into handsheets, and the Kappa number and CED viscosity measured.
  • Example 2F TABLE II the procedure of this invention on a pulp which has been chlorinated by conventional aqueous treatment.
  • Example 3A One portion of the chlorinated washed pulp from the Pretreatin g Procedure (II) was extracted with dilute sodium hydroxide (2.0% NaOI-I on o.d. pulp at 10% consistency for one hour at C.), and then washed with deionized water at 1%. The pulp was then made into handsheets and the Kappa number and CED viscosity measured.
  • Example 38 One portion of the treated pulp from the Pretreating Procedure (II) was mixed rapidly (3 minutes) with an aqueous solution of sodium hydroxide (2.0% on o.d. pulp at 60C.). The consistency of the resulting mixture was 10%. The mixture was immediately pressed to 30% consistency, and the effluent removed from the pulp. The pulp was then washed with deionized water at 1% consistency and made into handsheets and the Kappa number and CED viscosity measured.
  • Example 3C One portion of the treated pulp from the Pretreating Procedure (II) was mixed rapidly (2 minutes) with an EFFECT OF MIXING AND PRESSING CONSISTENCY DURING AKALINE PRESS EXTRACTION Softwood Kraft Pulp. Roe Chlorine No. 5.6. Kappa No.. 38.]; 0.5% CED Viscosity, cps. 24.2 Pcntosans 6.771 Alpha-cellulose 89.2%
  • Example 43 press extraction of a commercially-chlorinated pulp appears to be that a single such press extraction can reduce the Kappa number of a chlorinated pulp to a value similar to that which can be accomplished by conventional treatment with the same quantity of caustic, at the same temperature, but for a much shorter time than the conventional time period of 60 minutes.
  • the results in Examples 38 and 3C show that two press extractions did not greatly reduce the Kappa number from that achieved by the first extraction and this is an unexpected result.
  • EXAMPLE 5 EFFECT OF GAS PHASE CI-ILORINATION OF SINGLE PRESS EXTRACTION Example 5A One portion of the chlorinated washed pressed pulp into handsheets and Kappa number and CED viscosity 65 from the Pretreating Procedure (IV) was extracted measured.
  • Example 6A One portion of the semi-bleached pulp from the Pretreating Procedure (V) was extracted with dilute so- The results obtained are shown in Table V. 5 dium hydroxide (10% NaOH on pulp at 10% Example 53 sistency for 1 hour at 60C.), and then washed with deionized water at l% consistency. The pulp was then One portion of the treated pulp fro the pfetreatlflg brought to 12% consistency over a Buchner funnel, and Procedure (IV) W mixed rapldly Q Seconds) then bleached with 0.5% chlorine dioxide (on o.d. pulp an aqueous folutlon of SQdIum hydroxlde 9 10 for 3 hours at 70C.).
  • the consistency of the resulting Examp e mixture was 10%.
  • the mixture was immediately One portion of the treated pulp from the Pretreating pressed to 30% consistency, and the pressing effluent Procedure (IV) was mixed rapidly (30 seconds) with was removed from the pulp. Without any further washan aqueous solution of sodium hydroxide (2.5% on o.d. ing, the pulp was mixed with chlorine dioxide solution pulp) at 60C.
  • the consistency of the mixture was 10%. (0 in x d on p p) at a Consistency
  • the mixture was immediately pressed to 30% consis- 0f 10% for 3 hours at The p p was then Washed! tency.
  • EXAMPLE 6 pulp at 60C.
  • the consistency of the mixture was 10%.
  • the mixture was then immediately pressed to 30% consistency, and the pressing effluent removed from the pulp.
  • the pulp was then washed with deionized water at 1% consistency and then brought to 12% consistency by a-Buchner funnel fitted with a 100 mesh screen.
  • the pulp was then mixed with chlorine dioxide solution (0.5% chlorine dioxide on o.d. pulp at 10% consistency for 3 hours at C. After washing, the pulp was made into handsheets and the brightness measured. The brightness was 91.1 on the Elrepho brightness meter.
  • An improved alkaline extraction procedure in the manufacture of paper-making pulp which comprises:
  • An improved bleaching procedure in the manufacture of paper-making pulp comprising:
  • % NaOH on PULP after chlorination or Oxidative 8 The process of claim 6 wherein the mixing step is substantially completed within about 5 minutes and wherein the rapid press extraction is a single extraction step which is substantially completed Within about 1 minute.
  • steps (a) and (b) are completed within about 6 minutes.
  • steps (c) and (d) are completed within about 6 minutes.

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Cited By (17)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4238281A (en) * 1979-04-30 1980-12-09 Canadian International Paper Company Simplified bleaching process
US4806203A (en) * 1985-02-14 1989-02-21 Elton Edward F Method for alkaline delignification of lignocellulosic fibrous material at a consistency which is raised during reaction
US5011572A (en) * 1989-05-19 1991-04-30 Fmc Corporation Two stage process for the oxygen delignification of lignocellulosic fibers with peroxide reinforcement in the first stage
US5085734A (en) * 1989-02-15 1992-02-04 Union Camp Patent Holding, Inc. Methods of high consistency oxygen delignification using a low consistency alkali pretreatment
US5164044A (en) * 1990-05-17 1992-11-17 Union Camp Patent Holding, Inc. Environmentally improved process for bleaching lignocellulosic materials with ozone
US5164043A (en) * 1990-05-17 1992-11-17 Union Camp Patent Holding, Inc. Environmentally improved process for bleaching lignocellulosic materials with ozone
US5173153A (en) * 1991-01-03 1992-12-22 Union Camp Patent Holding, Inc. Process for enhanced oxygen delignification using high consistency and a split alkali addition
AU634381B2 (en) * 1990-05-04 1993-02-18 Jaakko Poyry Oy Method for treatment and recycling of pulp mill bleach plant effluents
US5188708A (en) * 1989-02-15 1993-02-23 Union Camp Patent Holding, Inc. Process for high consistency oxygen delignification followed by ozone relignification
US5211811A (en) * 1989-02-15 1993-05-18 Union Camp Patent Holding, Inc. Process for high consistency oxygen delignification of alkaline treated pulp followed by ozone delignification
US5217574A (en) * 1989-02-15 1993-06-08 Union Camp Patent Holdings Inc. Process for oxygen delignifying high consistency pulp by removing and recycling pressate from alkaline pulp
US5409570A (en) * 1989-02-15 1995-04-25 Union Camp Patent Holding, Inc. Process for ozone bleaching of oxygen delignified pulp while conveying the pulp through a reaction zone
US5441603A (en) * 1990-05-17 1995-08-15 Union Camp Patent Holding, Inc. Method for chelation of pulp prior to ozone delignification
US5525195A (en) * 1989-02-15 1996-06-11 Union Camp Patent Holding, Inc. Process for high consistency delignification using a low consistency alkali pretreatment
US5554259A (en) * 1993-10-01 1996-09-10 Union Camp Patent Holdings, Inc. Reduction of salt scale precipitation by control of process stream Ph and salt concentration
US5728264A (en) * 1995-10-25 1998-03-17 Union Camp Patent Holding, Inc. Avoidance of salt scaling by acidic pulp washing process
US20050145351A1 (en) * 1999-07-02 2005-07-07 J. Rettenmaier & Soehne Gmbh + Co. Kg Treatment of pulp to produce microcrystalline cellulose

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Publication number Priority date Publication date Assignee Title
SE415581B (sv) * 1977-04-18 1980-10-13 Mo Och Domsjoe Ab Forfarande for perocidblekning av hogutbytesmassa

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US2882965A (en) * 1955-02-23 1959-04-21 Columbia Cellulose Company Ltd High viscosity, high percentage alpha cellulose from sulfite pulp
US3575795A (en) * 1966-09-30 1971-04-20 Int Paper Co Rapid high consistency bleaching with continuous diffusion
US3586599A (en) * 1964-08-07 1971-06-22 Pulp Paper Res Inst Purification of fluffed or shredded pulp with chlorine dioxide
US3632469A (en) * 1969-06-05 1972-01-04 Ethyl Corp Process for the manufacture of dissolving grade pulp

Patent Citations (4)

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Publication number Priority date Publication date Assignee Title
US2882965A (en) * 1955-02-23 1959-04-21 Columbia Cellulose Company Ltd High viscosity, high percentage alpha cellulose from sulfite pulp
US3586599A (en) * 1964-08-07 1971-06-22 Pulp Paper Res Inst Purification of fluffed or shredded pulp with chlorine dioxide
US3575795A (en) * 1966-09-30 1971-04-20 Int Paper Co Rapid high consistency bleaching with continuous diffusion
US3632469A (en) * 1969-06-05 1972-01-04 Ethyl Corp Process for the manufacture of dissolving grade pulp

Cited By (19)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4238281A (en) * 1979-04-30 1980-12-09 Canadian International Paper Company Simplified bleaching process
US4806203A (en) * 1985-02-14 1989-02-21 Elton Edward F Method for alkaline delignification of lignocellulosic fibrous material at a consistency which is raised during reaction
US5409570A (en) * 1989-02-15 1995-04-25 Union Camp Patent Holding, Inc. Process for ozone bleaching of oxygen delignified pulp while conveying the pulp through a reaction zone
US5217574A (en) * 1989-02-15 1993-06-08 Union Camp Patent Holdings Inc. Process for oxygen delignifying high consistency pulp by removing and recycling pressate from alkaline pulp
US5525195A (en) * 1989-02-15 1996-06-11 Union Camp Patent Holding, Inc. Process for high consistency delignification using a low consistency alkali pretreatment
US5085734A (en) * 1989-02-15 1992-02-04 Union Camp Patent Holding, Inc. Methods of high consistency oxygen delignification using a low consistency alkali pretreatment
US5188708A (en) * 1989-02-15 1993-02-23 Union Camp Patent Holding, Inc. Process for high consistency oxygen delignification followed by ozone relignification
US5211811A (en) * 1989-02-15 1993-05-18 Union Camp Patent Holding, Inc. Process for high consistency oxygen delignification of alkaline treated pulp followed by ozone delignification
US5011572A (en) * 1989-05-19 1991-04-30 Fmc Corporation Two stage process for the oxygen delignification of lignocellulosic fibers with peroxide reinforcement in the first stage
AU634381B2 (en) * 1990-05-04 1993-02-18 Jaakko Poyry Oy Method for treatment and recycling of pulp mill bleach plant effluents
US5296099A (en) * 1990-05-17 1994-03-22 Union Camp Holding, Inc. Environmentally improved process for bleaching lignocellulosic materials with oxygen, ozone and chlorine dioxide
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CA973661A (en) 1975-09-02
DE2347398A1 (de) 1974-04-04
FR2201369B1 (index.php) 1977-03-11
NO141617B (no) 1980-01-02
AR201116A1 (es) 1975-02-14
FI63793B (fi) 1983-04-29
FR2201369A1 (index.php) 1974-04-26
BR7307566D0 (pt) 1974-09-05
DE2347398B2 (de) 1977-01-13
JPS5214326B2 (index.php) 1977-04-21
FI63793C (fi) 1983-08-10
NO141617C (no) 1980-04-09
SE405488B (sv) 1978-12-11
JPS4971202A (index.php) 1974-07-10

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